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REFRIGERATION PLANT
INTRODUCTION HISTORY OF REFRIGERATION 1748 - William Coolen of Glasgow University produced refrigeration by cr eating partial vacuum over ethyl ether. But, he could not implemen t his experience in practice. 1834 - The first development took place when Perkins proposed a hand-o perated compressor machine working on ether. 1856 - Linde developed a machine working on ammonia. 1920 - du Pont put in the market a family of new working substances, the fluoro-chloro derivatives of methane, ethane, etc.—popularly kno wn as chloro fluorocarbons or CFCs—under the name of Freons.
INTRODUCTION HISTORY OF REFRIGERATION 1920
- Development was that of the ammonia-water vapour absorption ma chine by Carre. These developments for the major commerci al and industrial applications in the field of refrigeration.
1834 - A phenomenon called Peltier effect was discovered in which is still no t commercialized. 1877 - Advances in cryogenics, a field of very low temperature refrigeration, were ed with the liquefaction of oxygen by Pictet . 1898 - Dewar made the famous Dewar flask to store liquids at cryogenic tem peratures. 1908 - Liquefaction of other permanent gases including helium by Onnes wh ich led to the discovery of the phenomenon of superconductivity.
INTRODUCTION DEFINITION Refrigeration may be defined as the process of achieving and maintaining a temperature below that of the surroundings, the aim being to freeze ice, cool some product, or space to the required temperature. The basis of modern refrigeration is the ability of liquids to absorb enormous quantities of heat as they boil and evaporate.
REFRIGERATORS AND HEAT PUMPS Heat flows in the direction of decreasing temperature, that is, from high-temperature regions to low-temperature ones. This heat-transfer process occurs in nature without requiring any devices. The reverse process, however, cannot occur by itself. The transfer of hea t from a low-temperature region to a high-temperature one requires special devices called refrigerators. Refrigerators are cyclic devices, and the working fluids used in the refrigeration cycles are called refrigerants.
REFRIGERATORS AND HEAT PUMPS Heat flows in the direction of decreasing temperature, that is, from high-temperature regions to low-temperature ones. This heat-transfer process occurs in nature without requiring any devices. The reverse process, however, cannot occur by itself. The transfer of hea t from a low-temperature region to a high-temperature one requires special devices called refrigerators. Refrigerators are cyclic devices, and the working fluids used in the refrigeration cycles are called refrigerants.
REFRIGERATORS AND HEAT PUMPS Another device that transfers heat from a low-temperature medium to a high-temperature one is the heat pump. Refrigerators and heat pumps are essentially the same devices; they differ in their objectives only. The objective of a refrigerator is to maintain the refrigerated space at a low temperature by removing heat from it. The objective of a heat pump, however, is to maintain a heated space at a high temperature.
REFRIGERATORS AND HEAT PUMPS The performance of refrigerators and heat pumps is expressed in of the coefficient of performance (COP), defined as:
COPHP = COPR + 1
REFRIGERATORS AND HEAT PUMPS The performance of refrigerators and heat pumps is expressed in of the coefficient of performance (COP), defined as:
REFRIGERATORS AND HEAT PUMPS The cooling capacity of a refrigeration system—that is, the rate of heat removal from the refrigerated space—is often expressed in of tons of refrigeration. It is equivalent to rate at which heat is removed from 1 ton of w ater at 0 ℃ to freeze it into ice at 0 ℃ in one day.
THE REVERSED CARNOT CYCLE All four processes that comprise the Carnot cycle can be reversed. Reversing the cycle does also reverse the directions of any heat and work interactions. The result is a cycle that operates in the counterclockwise direction on a T-s diagram, which is called the Reversed Carnot cycle. A refrigerator or heat pump that operates on the reversed Carnot cycle is called a Carnot refrigerator or a Carnot heat pump.
REFRIGERATION SYSTEMS A refrigeration system is an assembly of four major components, namely the Compressor, Condenser, Expansion Device and the Evaporator, through which a very low boiling point substance (refrigerant) flow in cycle, and absorbs heat from the immediate surroundings, thereby producing the cooling effect (Refrigerating effect).
TYPES OF REFRIGERATION SYSTEM 1. 2. 3. 4. 5.
Vapor Compression Refrigeration System Absorption Refrigeration System Gas Refrigeration System Cascade Refrigeration Thermoelectric Refrigeration
VAPOR COMPRESSION CYCLE The vapor-compression refrigeration cycle is the most widely used cycle for refrigerators, air-conditioning systems, and heat pumps. It consists of four processes: 1-2 2-3 3-4 4-1
Isentropic compression in a compressor Constant-pressure heat rejection in a condenser Throttling in an expansion device Constant-pressure heat absorption in an evaporator
VAPOR COMPRESSION CYCLE
3
Condenser
High Pressure Side
4 Expansion Device
Compressor
2
1 Evaporator
Low Pressure Side
VAPOR COMPRESSION CYCLE Low pressure liquid refrigerant in evaporator absorbs heat and changes to a gas
3
Condenser
High Pressure Side
4 Expansion Device
Compressor
2
1 Evaporator
Low Pressure Side
IDEAL VAPOR COMPRESSION CYCLE The superheated vapour enters the compressor where its pressure is raised
3
Condenser
High Pressure Side
4 Expansion Device
Compressor
2
1 Evaporator
Low Pressure Side
IDEAL VAPOR COMPRESSION CYCLE The high pressure superheated gas is cooled in several stages in the condenser 3
Condenser
High Pressure Side
4 Expansion Device
Compressor
2
1 Evaporator
Low Pressure Side
IDEAL VAPOR COMPRESSION CYCLE Liquid es through expansion device, which reduces its pressure and controls the flow into the evaporator 3
Condenser
High Pressure Side
4 Expansion Device
Compressor
2
1 Evaporator
Low Pressure Side
ACTUAL VAPOR COMPRESSION CYCLE An actual vapor-compression refrigeration cycle differs from the ideal one in several ways, owing mostly to the irreversibilities that occur in various components. Two common sources of irreversibilities are fluid friction (causes pressure drops) and heat transfer to or from the surroundings.
REFRIGERANT SELECTION When deg a refrigeration system, there are several refrigerants from which to choose, such as chlorofluorocarbons (CFCs), ammonia, Hydrocarbons (propane, ethane, ethylene, etc.), carbon dioxide, air (in the air-conditioning of aircraft), and even water (in applications above the freezing point). The right choice of refrigerant depends on the situation at hand. Two important parameters that need to be considered in the selection of a refrigerant are the temperatures of the two media (the refrigerated space and the environment) with which the refrigerant exchanges heat. To have heat transfer at a reasonable rate, a temperature difference of 5 to 10°C should be maintained between the refrigerant and the medium with which it is exchanging heat.
REFRIGERANT SELECTION AMMONIA Ammonia is predominantly used in food refrigeration facilities such as the cooling of fresh fruits, vegetables, meat, and fish; refrigeration of beverages and dairy products such as beer, wine, milk, and cheese; freezing of ice cream and other foods; ice production; and low-temperature refrigeration in the pharmaceutical and other process industries. The advantages of ammonia over other refrigerants are its low cost, higher COPs (and thus lower energy cost), more favorable thermodynamic and transport properties and thus higher heat transfer coefficients (requires smaller and lower-cost heat exchangers), greater detectability in the event of a leak, and no effect on the ozone layer. The major drawback of ammonia is its toxicity, which makes it unsuitable for domestic use.
REFRIGERANT SELECTION R-11
R-11 is used primarily in large-capacity water chillers serving air conditioning systems in buildings.
R-12
R-12 is used in domestic refrigerators and freezers, as well as automotive air conditioners. R-22 R-22 is used in window air conditioners, heat pumps, air conditioners of commercial buildings, and large industrial refrigeration systems, and offers strong competition to ammonia. R-502 R-502 (a blend of R-115 and R-22) is the dominant refrigerant used in commercial refrigeration systems such as those in supermarkets because it allows low temperatures at evaporators while operating at singlestage compression. R-134a - chlorine-free refrigerant
ICE PLANT One of the important applications of refrigeration is in ice making. The term ice plant is used to mean a complete installation for the production and storage of ice, including the icemaker itself, the unit that converts water into ice, together with the associated refrigeration machinery, harvesting and storage equipment, and the building. Ice plants are usually classified by the type of ice they produce; hence there are block ice plants, flake ice plants, tube, slice or plate ice plants and so on.
TYPES OF ICEMAKER Block Icemaker Tapered rectangular metal cans filled with water are immersed in a tank containing refrigerated sodium chloride brine. The dimensions of the can and the temperature of the brine are usually selected to give a 24 hour production time, and batches of cans are emptied and refilled in sequence during that period. Ice block weight can range from 12 to 150 kg depending on requirements; 150 kg is regarded as the largest size of block one man can conveniently handle. A block ice plant requires continuous attention and is labor intensive. The icemaker and the store require a good deal of floor space and impose heavy loads on the building structure. For these reasons block ice plants are g oing out of use, and more modern automatic plants are replacing them.
TYPES OF ICEMAKER Block Icemaker
A regular schedule of pulling ice cans is maintained and ice is transferred to a storage room that is apart from the ice making plant. Ice plants are rated according to capacity to produce ice in a 24 hour period. Brine tanks located within the building are usually contained in pits lined with concrete and cork or fiberglass insulation
TYPES OF ICEMAKER Block Icemaker
TYPES OF ICEMAKER Block Icemaker
TYPES OF ICEMAKER Rapid Icemaker It is possible to reduce the freezing time for blocks considerably, and thus reduce the space required for the icemaker. This is done by reducing the thickness of ice to be frozen; in one type of rapid icemaker this is achieved by ing refrigerant through tubes around which the ice forms and fuses into a block. The blocks can be released by defrosting and harvested automati cally, thus markedly reducing the labor requirement, but the storage space required is slightly larger than for the same weight of conventional block ice because the blocks have hollow centers after the tubes are removed.
TYPES OF ICEMAKER Flake Icemaker A sheet of ice 2-3 mm thick is formed by spraying water on the surface of a refrigerated drum, and scraping it off to form dry subcooled flakes, usually 100-1000 mm2 in area. No water is sprayed on that part of the drum immediately before the scraper, so that the ice becomes dry and subcooled prior to removal. Refrigerant temperature, drum or scraper speed, and degree of subcooling are all variable within designed limits so that the capacity of the icemaker and the thickness of the ice can be altered. Typical refrigerant temperature in a flake ice machine is 20 to - 25°C, lower than in most other types of icemaker, to give rapid cooling and thus make the machine compact. The low operating temperature requires more power, but this is to some extent compensated for by the absence of a need to defrost.
TYPES OF ICEMAKER Flake Icemaker
TYPES OF ICEMAKER Flake Icemaker
TYPES OF ICEMAKER Tube Icemaker Water is frozen on the inner surface of vertical refrigerated tubes to form hollow cylinders of ice about 50 mm in diameter and with walls 10-12 mm thick. The ice cylinders are released by defrosting the tubes automatically, and are chopped into pieces about 50 mm long by a rotating cutter as they slide out. T he cylindrical pieces can be subcooled by storing them at - 5°C, but they may require further crushing before being suitable for some applications.
TYPES OF ICEMAKER Tube Icemaker
TYPES OF ICEMAKER Tube Icemaker
TYPES OF ICEMAKER Plate Icemaker Water is frozen on one face of a vertical refrigerated plate, and the sheet of ice is released by running warm water on the other face of the plate. The size of ice particle is variable, but the optimum thickness is 10-12 mm. The plates are usually mounted i n banks, often above the refrigeration machinery, to form a self c ontained unit. Water for defrosting has to be heated if its temperature is below 23°C. Like most other icemakers the plate ice machine will operate unattended on an automatic timing cycle.
TYPES OF ICEMAKER Plate Icemaker
TYPES OF ICEMAKER Plate Icemaker
ICE PLANT CONSTRUCTION
ICE PLANT CONSTRUCTION An Ice plant has two additional circuits that help to create ice in huge quantity. 1. Refrigeration Circuit (Primary refrigerant) 2. Cooling Water Circuit (Cooling water) 3. Brine Circuit (Brine solution / Secondary Refrigerant)
Main Components of an Ice Plant
The main components generally used in an ice plant are: Compressor Condenser Expansion Valve Evaporator Chilling Tank
Main Components of an Ice Plant EVAPORATOR The evaporator is an important device used in the low pressure side of the refrigeration system. The liquid refrigerant from the expansion valve enters into the evaporator where its boil and change into vapour. The function of the evaporator is to absorb heat from the surrounding location or medium which is to be cooled, by means of a refrigerant. The temperature of the boiling refrigerant in the evaporator must always be less than that of the surrounding medium so that heat flows to the refrigerant. The evaporator becomes cold and remains cold due to the following two reasons: •
The temperature of the evaporation coil is low due to the low temperature of the refrigerant inside the coil.
• The low temperature of the refrigerant remains unchanged because any heat it absorbs is converted to latent heat as boiling proceeds.
Main Components of an Ice Plant TYPES OF EVAPORATORS 1. Bare-tube Coil Evaporator The bare tube evaporators are made up of copper tubing or steel pipes. The copper tubing is used for small evaporators where the refrigerant other than ammonia is used, while the steel pipes are used with the large evaporators where ammonia is used as the refrigerant. The bare tube evaporator comprises of several turns of the tubing, though most commonly flat zigzag and oval trombone are the most common shapes. The bare tube evaporators are usually used for liquid chilling.
Main Components of an Ice Plant TYPES OF EVAPORATORS 2. Plate Evaporator In the plate type of evaporators the coil usually made up of copper or aluminum is embedded in the plate so as so to form a flat looking surface. Externally the plate type of evaporator looks like a single plate, but inside it there are several turns of the metal tubing through which the refrigerant flows. The advantage of the plate type of evaporators is that they are more rigid as the external plate provides lots of safety. The external plate also helps increasing the heat transfer from the metal tubing to the substance to be chilled. Further, the plate type of evaporators are easy to clean and can be manufactured cheaply.
Main Components of an Ice Plant TYPES OF EVAPORATORS 3. Finned Evaporator The finned evaporators are the bare tube type of evaporators covered with the fins. When the fluid (air or water) to be chilled flows over the bare tube evaporator lots of cooling effect from the refrigerant goes wasted since there is less surface for the transfer of heat from the fluid to the refrigerant. The fluid tends to move between the open spaces of the tubing and does not come in with the surface of the coil, thus the bare tube evaporators are less effective. The fins on the external surface of the bare tube evaporators increases the surface of the of the metallic tubing with the fluid and increase the heat transfer rate, thus the finned evaporators are more effective than the bare tube evaporators.
Main Components of an Ice Plant TYPES OF EVAPORATORS 4. Shell and Tube Evaporator The shell and tube types of evaporators are used in the large refrigeration and central air conditioning systems. The evaporators in these systems are commonly known as the chillers. The chillers comprise of large number of the tubes that are inserted inside the drum or the shell. Depending on the direction of the flow of the refrigerant in the shell and tube type of chillers, they are classified into two types: dry expansion type and flooded type of chillers. In dry expansion chillers the refrigerant flows along the tube side and the fluid to be chilled flows along the shell side. The flow of the refrigerant to these chillers is controlled by the expansion valve. In case of the flooded type of evaporators the refrigerant flows along the shell side and fluid to be chilled flows along the tube. In these chillers the level of the refrigerant is kept constant by the float valve that acts as the expansion valve also.
Main Components of an Ice Plant TYPES OF EVAPORATORS 4. Shell and Tube Evaporator
Main Components of an Ice Plant COMPRESSOR A refrigerating compressor, as the name indicates, is a machine used to compress the vapour refrigerant from the evaporator and to raise its pressure so that the corresponding saturation is higher than that of the cooling medium. It also continually circulates the refrigerant through the refrigerating system. Since the compression of refrigerant requires some work to be done on it, therefore a compressor must be driven by some prime mover. In other words the purpose of the compressor in the vapour compression cycle is to compress the low-pressure dry gas from the evaporator and raise its pressure to that of the condenser. Compressors may be divided into two types, positive displacement and dynamic.
Main Components of an Ice Plant Two Types of Compressors: Positive displacement types compress discrete volumes of low-pressure gas by physically reducing the volumes causing a pressure increase.
Dynamic types raise the velocity of the low-pressure gas and subsequently reduce it in a way which causes a pressure increase.
Main Components of an Ice Plant Three Commonly Used Types of Compressors: Reciprocating - uses piston to compress the refrigerant driven by a crankshaft in a straight line back and forth motion. Vapor from the suction line is moved through the intake valve as the piston move downward. As the piston moves upward, it compresses the vapor refrigerant which is then pushed through the exhaust valve into the condenser. Rotary - A positive displacement machine in which compression of the fluid is effected directly by a rotor and without the usual piston, connecting rod, and crank mechanism of the reciprocating compressor.
Centrifugal - usually used in large capacity refrigerating system. In this compressor, the vapor is moved in a circular motion known as centrifugal force. An impeller which is a disk with radial blades spins rapidly inside this housing causing the gas to gain velocity.
Main Components of an Ice Plant Types of Compressors based on enclosure: Hermetically Sealed Semi-Hermetic Open
The difference between the hermetic and semi-hermetic, is that the hermetic uses a one-piece welded steel casing that cannot be opened for repair; if the hermetic fails it is simply replaced with an entire new unit. A semi-hermetic uses a large cast metal shell with gasket covers that can be opened to replace motor and pump components. The primary advantage of a hermetic and semi-hermetic is that there is no route for the gas to leak out of the system. Open compressors rely on either natural leather or synthetic rubber seals to retain the internal pressure, and these seals require a lubricant such as oil to retain their sealing properties. An open pressurized system such as an automobile air conditioner can leak its operating gases, if it is not operated frequently enough.
Main Components of an Ice Plant
The disadvantage of hermetic compressors is that the motor drive cannot be repaired or maintained, and the entire compressor must be removed if a motor fails. A further disadvantage is that burnt out windings can contaminate whole systems requiring the system to be entirely pumped down and the gas replaced. Typically hermetic compressors are used in lowcost factory-assembled consumer goods where the cost of repair is high compared to the value of the device, and it would be more economical to just purchase a new device. An advantage of open compressors is that they can be driven by non-electric power sources, such as an internal combustion engine or turbine.
Main Components of an Ice Plant
Hermetic
Open Type
Semi-Hermetic
Main Components of an Ice Plant CONDENSER The condenser is an important device used in the high pressure side of a refrigeration system. Its function is to remove heat of hot vapor refrigerant discharge from the compressor. The hot vapour consists of the heat absorbed by the evaporator and the heat of compression added by the mechanical energy of compressor motor. The heat from the hot vapour refrigerant in a condenser is removed first by transferring it to the walls of the condensers tubes and then from the tubes to the condensing or cooling medium. The selection of the condenser depends of the capacity of the refrigerating system, the type of refrigerant used and the type of cooling medium available.
Main Components of an Ice Plant
Main Components of an Ice Plant Types of Condenser: Water-cooled Air-cooled Evaporative .Water-Cooled Condenser It is a heat exchanger that removes heat from refrigerant vapor and transfers it to the running water. Having the refrigerant vapor condensed on the outside of a tube does this. In doing so, the vapor condenses and gives up heat to the water running inside the tube.
Main Components of an Ice Plant Air-Cooled Condenser An air cooled condenser is one in which the removal of heat is done by air. It consists of steel or copper tubing through which the refrigerant flows. The size of tube usually ranges from 6-mm to 18-mm outside diameter, depending upon the size of condenser. Generally copper tubes are used because of its excellent heat transfer ability. The condensers with steel tubes are used in ammonia refrigerating systems. The tubes are usually provided with plate type fins to increase the surface area for heat transfer. The fins are usually made from aluminum because of its light weight. The fin spacing is quite wide to reduce dust clogging. The condensers with single row of tubing provide the most efficient heat transfer. This is because the air temperature rises at it es through each row of tubing. The temperature difference between the air and the vapour refrigerant decrease in each row of tubing and therefore each row becomes less effective. However, single row condensers require more space then multi row condensers.
Main Components of an Ice Plant The single row condensers are usually used in small capacity refrigeration systems such as domestic refrigerators, freezers, water coolers and room air conditioners. The air cooled condensers may have two or more rows of tubing, but the condensers with up to six rows of tubing are common. Some condensers have seven or eight rows. However, more than eight rows of tubing are usually not efficient. This is because the air temperature will be too close to the condenser temperature to absorb any more heat after ing through eight row of tubing.
Main Components of an Ice Plant EXPANSION DEVICES The expansion device (also known as metric device or throttling device) is an important device that divides the high pressure side and the low pressure side of a refrigerating system. It is connected the receiver (containing liquid vapour at high pressure) and the evaporator (containing liquid refrigerant at low pressure). The expansion device performs the following functions like to reduce the high pressure liquid refrigerant to low pressure liquid refrigerant before being fed to the evaporator and to maintain the desire pressure difference between the high and low pressure side of the system, so that the liquid refrigerant vaporizes at the designed pressure in the evaporator.
Main Components of an Ice Plant There are many types of expansion devices used like capillary tubes, automatic or constant-pressure expansion valve, low side float valve, high side float valve and thermostatic expansion valve in an ice plant industry depending upon its capacity. In an ice plant the capillary tube type expansion devise is generally used which is discussed in details ahead.
Main Components of an Ice Plant CAPILLARY TUBE The capillary tube is used as an expansion device used in small capacity hermetic sealed refrigeration units such as domestic refrigeration, water cooler, room air conditioner and freezers. It is a cooper tube of small diameter and of varying length depending upon the application. The inside diameter of the tube used in refrigeration work is generally about 0.5 mm to 2.25 mm and the length varies from 0.5 m to 5 m. It is installed in the liquid line between the condenser and evaporator. A small filter drier is used on some system to provide additional freeze-up application. In its operation, the liquid refrigerant from the condenser enter the capillarity tube due to friction resistance offered by small diameter tube, the pressure drops since the frictional resistance is directly proportional to the length and inversely proportional to the diameter, therefore longer the capillary tube and smaller its inside diameter, greater is the pressure drop created in the refrigerant flow. In other words, greater pressure difference between the condenser and the evaporators needed forgiven flow rate of refrigerant.
Main Components of an Ice Plant
CAPILLARY TUBE
Main Components of an Ice Plant CHILLING TANK (BRINE TANK) The main components of chilling tank are : ice tank, insulation of ice tank and ice block. Ice tanks are made of material such as wood, steel or concrete. As wooden tanks do not last long enough and are liable to leak, chilling tanks are usually made of steel or reinforced concrete. The tank contains the direct expansion coils, equally distributed throughout the tank and these coils are submerged in brine. The tank is provided with a suitable frame to the ice cans and a propeller or agitator for keeping the brine in motion: the brine in the tank acts as a medium of only, the refrigerant evaporating in the ice coils extracts the heat from the brine, which again absorbs the heat for the water in the cans. The tank itself should not be much larger than is necessary to hold the cans, the coils, and the agitator. Commercial sizes of Ice cans vary with the weight of ice cakes required. The cans are made to contain about 5% more than their rated capacity to compensate for thawing.
Main Components of an Ice Plant CHILLING TANK
Main Components of an Ice Plant
Ice Plant Auxiliaries
Some of the ice plant auxiliaries are: Receiver Filter Drier Suction Accumulator Oil Separators
Ice Plant Auxiliaries RECEIVER A liquid receiver will be required if it is necessary to temporarily store refrigerant charge within the system, or to accommodate the excess refrigerant arising from changing operating conditions. The total refrigerant charge required in a circuit will vary with different operating loads and ambient, and must be sufficient at all times so that only liquid enters the expansion valve. A receiver requires a minimum operating charge which adds to overall charge and cost, and also increases system complexity. Hence receivers are avoided on many smaller systems.
Ice Plant Auxiliaries FILTER DRYER The function of filter dryer is to remove any physical material from compressor’s wear and tear, and remove any moisture presence within an air conditioning system. The Drier is made up of a metal outer container and inside there is a desiccant (moisture removal material) and strainer. Refrigerant es through the drier and give up any moisture as well as any unwanted matter. The main job of the drier is to protect the metering device from clogging either by Ice (moisture) or blockage by particles.
Ice Plant Auxiliaries
It is not uncommon for driers and filters to block due to their nature of picking up unwanted agents - evidence of this can be seen by frost build up. Filtering process is achieved by mechanical action of partitioning the flow. Particles will be trapped, whilst the refrigerant flow will be maintained. These desiccants can be of two types, viz. absorbent and adsorbent type. In this model adsorbent type filter drier is used which is defined ahead.
Ice Plant Auxiliaries
SUCTION ACCUMULATOR Suction line accumulators are sometimes inserted in halocarbon circuits, to serve the purpose of separating return liquid and prevent it ing over to the compressor. Since this liquid will be carrying oil, and this oil must be returned to the compressor, the outlet pipe within the separator dips to the bottom of this vessel and has a small bleed hole, to suck the oil out.
Ice Plant Auxiliaries OIL SEPARATOR During the compression stroke of a reciprocating machine, the gas becomes hotter and some of the oil on the cylinder wall will out with the discharge gas. Some oil carry-over will occur with all lubricated compressor types, and in small self-contained systems it quickly finds its way back to the compressor. Start up after a long idle period can result in a large amount of oil carryover for a short period due to foaming. With larger more complex systems with remote evaporator oil, it is desirable to fit an oil separator in the discharge line to reduce carry-over to the system.
Ice Plant Auxiliaries AGITATOR The propeller of the agitator is located in the brine tank and the agitator motor extends above the brine tank. Usually the agitator is located at the opposite corner of the brine tank from the accumulator. The function of the agitator is to circulate brine through the brine tank and raceway The agitator consists of a propeller guide vanes a vertically mounted motor and a housing. The agitator motor drives the propeller which circulates brine by drawing it from around the evaporator and discharging it by the ice cans. The agitator must be operated whenever the plant is in operation .
Ice Plant Auxiliaries ICE CANS Ice cans are made of galvanized steel and are tapered from the bottom to facilitate ice removal. Ice cans usually contain from 50 to 300 pound ice blocks. Often two or even four ice cans are fastened together so that two or four ice cans may be removed from the brine tank in one operation
Ice Plant Auxiliaries ICE PLANT WATER FILTERS Clear palatable ice is not produced in an ice plant without proper treatment of the raw water to be frozen. A water filter is installed for this purpose. To assist in filter operation water is treated with alum to coagulate suspended foreign substances in water. The water filter contains quartz sand or gravel through which water is ed for removal of suspended matter. Periodically material accumulated by the filter is flushed from the bed by reversing water flow. Accumulated material is then disposed to a sewer. This operation is called back washing .
Ice Plant Auxiliaries CAN FILLERS Can fillers are used to facilitate filling of ice cans with water. Small plants use a portable can filler that is connected to the water supply by a hose. The can filler is inserted in an ice can and water flows into the can. A float valve which is part of the can filler stops flow of water into the ice can when water reaches the proper level. Large ice plants use wall mounted can fillers. These can fillers are located over a can dump and are used to fill ice cans just after ice has been removed from the cans. A wall mounted can filler consists of one or more tanks depending on the number of ice cans in a group a float valve to regulate the amount of water in the tanks and an operating lever which controls flow of water from the can filler into the ice cans. The lever also acts to shut off the float valve so that the can filler will not begin to fill until the lever is released. Can fillers in large ice plants are automatic
Ice Plant Auxiliaries CAN DUMPS Can dumps are used to facilitate removal of ice from ice cans Ice cans are placed in the can dump while it is in a vertical position. The can dump is then pushed to a horizontal position and ice slides out of the cans and down an ice chute to the storage room. The can dump is so balanced that when ice blocks slide out of the can it returns to a vertical position. In some plants, ice is dipped in a dip tank to loosen it in ice cans. In some installations, a method for loosening ice in ice cans is incorporated directly in the can dump. When the can dump is pushed to a horizontal position, a spray of water is directed on the ice cans until ice loosens in the cans and slides down the ice chute. Water supply stops when the can dump returns to a vertical position
Ice Plant Auxiliaries DIP TANK A dip tank is used to loosen ice in the ice cans when this function is not accomplished by a can dump. The dip tank contains warm water which melts the ice sufficiently to loosen it in the cans. A dip tank water heater keeps the temperature of the water in the dip tank within a range where it will loosen ice in the ice cans effectively. This heater which is of the shell and tube type is installed in the discharge line between compressor and condenser. A dip tank water heater serves to heat water in the dip tank, cool discharge gas before it enters the condenser and separate oil out of ammonia gas.
Ice Plant Auxiliaries ICE CHUTE The ice chute which is located between the ice plant and storage room consists of a reinforced wall frame with a counterweighted swinging door and an inclined ramp. The chute acts as guide to receive ice dumped from ice cans and facilitates movement of ice into the storage room. The swinging door is usually lined with a canvas seal to prevent transfer of heat from ice plant to storage room.
Ice Plant Auxiliaries HOISTS Hoists are used to raise ice cans from the brine tank and to convey filled cans to the can dump. In small ice plants truck hoists are generally used. A truck hoist has wheels and a manual hoisting mechanism. In most large ice plants electric cross mounted joists are used Intermediate size plants may use manually operated cross mounted lifting hoists.
Ice Plant Auxiliaries AIR AGITATION SYSTEM Water produces a better grade of ice when it is kept in constant motion while being frozen. Lack of an air agitation system will cause opaque ice to be produced. To produce clear ice, air is bubbled through water at 1 to 3 pounds pressure from centrifugal or rotary blowers. Air pressure is controlled by means of blast gates or relief valves and air is distributed by a piping system installed directly under ice can covers. From distributing mains or laterals, air is fed to each ice can through a flexible connection and a small diameter tube that extends almost to the bottom of the ice can. This tube has small holes drilled at intervals throughout its length through which air es beneath the water surface. Tubes may be removed from ice just before it is completely frozen or may be loosened from ice with a thawing needle.
Ice Plant Auxiliaries COOLING TOWER Cooling towers are used to cool water from water cooled condensers and water cooled compressors of ice plants. Cooling towers are incorporated in ice plants so that water can be recirculated rather than disposed of. Natural draft cooling towers are usually mounted on the roof of the ice plant where they can make use of prevailing winds. Water is circulated through natural draft cooling towers at a rate of approximately 5 gallons per minute per ton of refrigeration required. Mechanical draft towers are usually installed outdoors but may be installed indoors if a duct system is provided. Water is circulated through mechanical draft cooling towers at a rate of approximately 3 gallons per minute per ton of refrigeration required.
BRINE A brine is any liquid cooled by the refrigerant and used for the transmission of heat without a change in its state, having no flash point above 65 ℃ as determined by the ASTM. Water solutions of calcium chloride and sodium chloride are the most common refrigeration brines.
BRINE Being inexpensive, most common refrigerant brines are based on calcium chloride, sodium chloride and glycols. Brine is used because the addition of salt to water lowers the freezing temperature of the solution and the heat transport efficiency can be greatly enhanced for the comparatively low cost of the material. The lowest freezing point obtainable for NaCl brine is −21.1 °C (−6.0 °F) at 23.3wt% NaCl. This is called the eutectic point.
BRINE
BRINE
BRINE
BRINE Brines of low density freeze around evaporator coils and may damage or reduce efficiency of the evaporator. Specific gravity calcium chloride brines should not be less than 1.20 and not more than 1.24 at 60 ˚F. Calcium chloride brines with specific gravities between these two limits have freezing points varying from 7.0 ˚ F to 21.5 ˚ F. The exact specific gravity of brine that should be maintained is dependent on temperature of the refrigerant in evaporator coils. This temperature is the saturation temperature of the refrigerant at suction pressure for which the system was designed to operate. Freezing temperature of the brine must be several degrees below temperature of the refrigerant in evaporator coils. Brine temperature must be read daily as a precautionary measure so that freezing of brine at the evaporator coils can be detected .
ICE PLANT OPERATION
ICE PLANT OPERATION
ICE PLANT INSPECTION AND MAINTENANCE 1.) TESTING FOR AMMONIA LEAKS Ammonia has a disagreeable and pungent odor. A small leak is readily noticed. To locate an ammonia leak the following procedures are recommended: a) Use of reagents. Detector reagents such as sulfur taper sensitive paper caustic soda and Nessler's solution are satisfactory to detect ammonia leaks. The suitability of various reagents to test for ammonia leaks depends on conditions under which the leak may occur. b) Use of soap suds. To prepare soap suds for testing use a soap and water solution of about the consistency of liquid hand soap which will lather freely or work up a lather on a brush by rubbing the wetted brush on a cake of soap. A few drops of glycerine added to the solution will cause lather to remain wet longer. When applying soap suds paint soap lather completely around a t and examine the t thoroughly for bubbles. When the t is located so that a part of it is not visible use a pocket mirror. It will sometimes take a full minute or more for bubbles to appear at a small leak. Questionable spots should be covered with lather and reexamined
ICE PLANT INSPECTION AND MAINTENANCE 2.) SERVICING AMMONIA LEAKS For objectionable leakage at crankshaft stuffing boxes of enclosed compressors, tighten gland bolt nuts gradually and equally to keep gland pressure equal on all sides. For leakage at valve bonnet stuffing boxes, pull up turn clockwise the stuffing box gland gradually. For leakage at cylinder head or flange gaskets, tighten flange bolts gradually and equally all way around. For bad leaks that have filled the space with ammonia fumes, first put a gas mask on then try to get ventilation with fans to blow the fumes to open air. Location of the leak will generally be indicated by a hissing sound from escaping If liquid ammonia has escaped and is on the floor, play a stream of water on it to absorb the escaping ammonia. Close the valve before and after the section where the leak has occurred. Apply a torch for cutting welding or for making other repairs only after the affected section has been thoroughly pumped out.
ICE PLANT INSPECTION AND MAINTENANCE 3.) PUMPING OUT COMPONENTS
Sizable components must be pumped out before they are removed from the system to prevent loss of ammonia or contamination of the area. a) Evaporator. During normal plant operation, the compressor is trying to pump out the evaporator. However, liquid refrigerant is constantly being supplied to the evaporator to replace the gas that is being exhausted from it. To pump out the evaporator, close the valve that its liquid refrigerant to the evaporator and run the compressor as in normal operation until a vacuum of at least 26 inches is obtained. b) Condenser. To pump out the condenser, close the valves that allow liquid refrigerant to from the condenser to the evaporator and allow the evaporator to pump out slightly then stop the compressor. Drain water from the condenser tubes. Close the discharge and suction shutoff valves at the compressor and open the discharge and suction by valves. This allows the compressor to reverse its action and create a suction in the line to the condenser. Start the compressor and pump a 15 inch vacuum in the condenser. Stop the compressor when the compressor comes to rest close the discharge and suction by valves.
ICE PLANT INSPECTION AND MAINTENANCE 4.) NORMAL OPERATION
Observe all components of the ice plant for normal operation Investigate unusual noises vibrations and odors during operation
5.) EQUIPMENT GUARDS
Check protective screens and fan belt guards for damage and security.
6.) FAN ASSEMBLIES
Check fan bearings of the cooling tower fan. Replace bearings if found defective. Observe operation of the fan and check for bent blades and excess vibration. Wipe dirt from shaft bearings and pulley.
7.) FAN DRIVES
Fan drives Check the fan drive for pulley alinement belt tension and condition of belt. Replace frayed or worn belt. Wipe dirt and oil or grease from pulley sheaves and belts.
ICE PLANT INSPECTION AND MAINTENANCE 8.) FAN MOTORS
Check motor bearings for rough running tendencies. Replace defective bearings. Lubricate only when required. Observe the motor when starting for proper speed pickup. Wipe dirt from the motor housing.
9.) EVAPORATOR COILS
Check the outside of evaporator coils for ice formation. Presence of ice around the coils indicates that the brine solution is not at the required specific gravity. Test the brine solution with a hydrometer. Check the coils for excessive corrosion. Check the evaporator s baffles and spacer bars for dirt and rust. Paint when necessary.
10.) EXPANSION VALVE
Check operation of the hand expansion valve in the ammonia float regulator by. Be sure that this valve is used only when the ammonia float regulator does not operate properly. When in use see that the hand expansion valve is properly adjusted to permit correct flow of liquid ammonia to the suction trap.
ICE PLANT INSPECTION AND MAINTENANCE 11.) COMPRESSORS Check the compressor and shaft seals for signs of gasket or seal failures. Replace any defective shaft seal or gasket. Check oil level and observe condition of the oil. Replace contaminated oil with ammonia compressor oil only. Fill the crank case to proper level when necessary. Proper operation of the compressor can best be judged by listening to the sound of the compressor while it is operating. Leaky rings and leaky valves in the compressor cause noticeably and abnormally high discharge temperatures. For example assume that condenser pressure is 185 psi as indicated on the discharge pressure gage. At this pressure temperature of saturated ammonia is 96˚F which also is indicated on the discharge pressure gage.
ICE PLANT INSPECTION AND MAINTENANCE 12.) REFRIGERANT PIPING ASCCESORIES Check to see if the float valve of the oil separator is draining the oil separator properly. If not adjust the float or repair the valve as required. Replace defective parts. Remove clean and replace filter elements located in recesses of the compressor housing. Replace the screen if found defective. Clean or replace the filter element of the ammonia strainer located between the condenser and float regulator. Check the efficiency of compressor suction and discharge valves by recording the maximum vacuum obtainable. Check the operation and setting of the high pressure relief valve located on the condenser and the low pressure relief valve located above the accumulator. Replace defective cartridges.
ICE PLANT INSPECTION AND MAINTENANCE 13.) WATER SUPPLY AND DRAINAGE SYSTEMS Check water supply and drain systems of cooling tower water pump, condenser, compressor, can filler, can dump, and brine tank for leaks tightness of fittings and proper operation of water gate valves. Tighten fittings repair defective valves and replace defective segments of piping.
ICE PLANT INSPECTION AND MAINTENANCE 14.) WATER-COOLED CONDENSER a) Performance Test
An overall check for condenser performance may be used to indicate condition of the condensing. To obtain an overall check for condenser performance proceed as follows. Make preliminary preparations to the system. Read the condensing temperature that corresponds with pressure in the condenser. Read the temperature of the water leaving the condenser. Then subtract the temperature of the water leaving the condenser from the condensing temperature obtained above. Temperature of the water leaving the condenser will be several degrees below the condensing temperature of pure ammonia This temperature difference is affected by the amount of condensing surface per ton of refrigeration by the condition of the condensing surface and by the presence of noncon densable gases Therefore condenser performance should be checked when load conditions are known and when the condenser is known to be clean and free of non condensable gases and results used as a measure of good performance.
ICE PLANT INSPECTION AND MAINTENANCE 14.) WATER-COOLED CONDENSER a) Cleaning Condenser Tubes
To clean condenser tubes, drain the condenser and then remove water connections and heads. When heads are removed be not to damage the rubber between the condenser and heads If the gaskets become detached from the heads use household cement to hold them in while assembling the heads the condenser. To prevent the gaskets from adhering to the shell and being damaged when heads are removed again, coat condenser side of the gasket with mixture of oil and graphite thoroughly clean condenser tubes tube cleaner consisting of a brush attached to the end of a rod should be used. When tubes are dirty, it may be necessary to run stiff wire brush through them and then finish up with tube cleaner. By connecting a water hose to pipe to which the tube cleaner fastened and by drilling a small holes in the pipe at the cleaner end water can be to the tubes during the process cleaning. Water prevents the cleaner from becoming clogged also insures cleaner tubes.
ICE PLANT INSPECTION AND MAINTENANCE 15.) COOLING TOWER Clean the water distribution basin on top of the cooling tower. Make sure that the holes in the splash box are not clogged. Check water distribution over the wooden fill pieces. Check piping and fittings for water leaks. Check float valve operation to see that it opens when water level in the float basin falls below a predetermined level and closes when water level reaches a predetermined level. If the float valve does not open and close properly adjust the valve. If adjustment cannot be made, replace with a new float valve. See that overflow pipes in the steel distribution basin and in the float box are in good condition Replace defective wooden fill pieces. Do not nail. Check for presence of algae formations.
ICE PLANT INSPECTION AND MAINTENANCE 16.) CAN FILLER Check operation of the can filler float valve. Clean the float valve when it becomes clogged. Replace any punctured float ball. Adjust the float valve by trial and error so that the can filler fills ice cans to a level approximately 3 inches from the top. If the float valve cannot be adjusted or is defective, replace the valve . 17.) AGITATOR Check the agitator for noisy operation or vibration. Lubricate motor and shaft bearings as required. Replace defective bearings. Check the agitator coupling for proper alignment. If deposits of calcium chloride appear on any parts, soak the parts in a cleaning solvent such as alcohol until the deposit dissolves. Any deposits left on the impeller will greatly impair its efficiency. Before the agitator is installed in the brine tank, check clearance between the agitator impeller and lower shaft bearing To do this bolt the motor to its base butt motor and agitator shafts together and tighten setscrews in the coupling. Then place a pry bar under the shaft coupling and force the motor rotor to its highest position. The top bearing grease cup must be filled with grease and given a turn every day .
ICE PLANT INSPECTION AND MAINTENANCE 18.) ICE CANS Check ice cans for corrosion. Clean as required. Check ice can covers for loose fits and warped boards. Repair or replace as required.
INTRODUCTION HISTORY OF REFRIGERATION 1748 - William Coolen of Glasgow University produced refrigeration by cr eating partial vacuum over ethyl ether. But, he could not implemen t his experience in practice. 1834 - The first development took place when Perkins proposed a hand-o perated compressor machine working on ether. 1856 - Linde developed a machine working on ammonia. 1920 - du Pont put in the market a family of new working substances, the fluoro-chloro derivatives of methane, ethane, etc.—popularly kno wn as chloro fluorocarbons or CFCs—under the name of Freons.
INTRODUCTION HISTORY OF REFRIGERATION 1920
- Development was that of the ammonia-water vapour absorption ma chine by Carre. These developments for the major commerci al and industrial applications in the field of refrigeration.
1834 - A phenomenon called Peltier effect was discovered in which is still no t commercialized. 1877 - Advances in cryogenics, a field of very low temperature refrigeration, were ed with the liquefaction of oxygen by Pictet . 1898 - Dewar made the famous Dewar flask to store liquids at cryogenic tem peratures. 1908 - Liquefaction of other permanent gases including helium by Onnes wh ich led to the discovery of the phenomenon of superconductivity.
INTRODUCTION DEFINITION Refrigeration may be defined as the process of achieving and maintaining a temperature below that of the surroundings, the aim being to freeze ice, cool some product, or space to the required temperature. The basis of modern refrigeration is the ability of liquids to absorb enormous quantities of heat as they boil and evaporate.
REFRIGERATORS AND HEAT PUMPS Heat flows in the direction of decreasing temperature, that is, from high-temperature regions to low-temperature ones. This heat-transfer process occurs in nature without requiring any devices. The reverse process, however, cannot occur by itself. The transfer of hea t from a low-temperature region to a high-temperature one requires special devices called refrigerators. Refrigerators are cyclic devices, and the working fluids used in the refrigeration cycles are called refrigerants.
REFRIGERATORS AND HEAT PUMPS Heat flows in the direction of decreasing temperature, that is, from high-temperature regions to low-temperature ones. This heat-transfer process occurs in nature without requiring any devices. The reverse process, however, cannot occur by itself. The transfer of hea t from a low-temperature region to a high-temperature one requires special devices called refrigerators. Refrigerators are cyclic devices, and the working fluids used in the refrigeration cycles are called refrigerants.
REFRIGERATORS AND HEAT PUMPS Another device that transfers heat from a low-temperature medium to a high-temperature one is the heat pump. Refrigerators and heat pumps are essentially the same devices; they differ in their objectives only. The objective of a refrigerator is to maintain the refrigerated space at a low temperature by removing heat from it. The objective of a heat pump, however, is to maintain a heated space at a high temperature.
REFRIGERATORS AND HEAT PUMPS The performance of refrigerators and heat pumps is expressed in of the coefficient of performance (COP), defined as:
COPHP = COPR + 1
REFRIGERATORS AND HEAT PUMPS The performance of refrigerators and heat pumps is expressed in of the coefficient of performance (COP), defined as:
REFRIGERATORS AND HEAT PUMPS The cooling capacity of a refrigeration system—that is, the rate of heat removal from the refrigerated space—is often expressed in of tons of refrigeration. It is equivalent to rate at which heat is removed from 1 ton of w ater at 0 ℃ to freeze it into ice at 0 ℃ in one day.
THE REVERSED CARNOT CYCLE All four processes that comprise the Carnot cycle can be reversed. Reversing the cycle does also reverse the directions of any heat and work interactions. The result is a cycle that operates in the counterclockwise direction on a T-s diagram, which is called the Reversed Carnot cycle. A refrigerator or heat pump that operates on the reversed Carnot cycle is called a Carnot refrigerator or a Carnot heat pump.
REFRIGERATION SYSTEMS A refrigeration system is an assembly of four major components, namely the Compressor, Condenser, Expansion Device and the Evaporator, through which a very low boiling point substance (refrigerant) flow in cycle, and absorbs heat from the immediate surroundings, thereby producing the cooling effect (Refrigerating effect).
TYPES OF REFRIGERATION SYSTEM 1. 2. 3. 4. 5.
Vapor Compression Refrigeration System Absorption Refrigeration System Gas Refrigeration System Cascade Refrigeration Thermoelectric Refrigeration
VAPOR COMPRESSION CYCLE The vapor-compression refrigeration cycle is the most widely used cycle for refrigerators, air-conditioning systems, and heat pumps. It consists of four processes: 1-2 2-3 3-4 4-1
Isentropic compression in a compressor Constant-pressure heat rejection in a condenser Throttling in an expansion device Constant-pressure heat absorption in an evaporator
VAPOR COMPRESSION CYCLE
3
Condenser
High Pressure Side
4 Expansion Device
Compressor
2
1 Evaporator
Low Pressure Side
VAPOR COMPRESSION CYCLE Low pressure liquid refrigerant in evaporator absorbs heat and changes to a gas
3
Condenser
High Pressure Side
4 Expansion Device
Compressor
2
1 Evaporator
Low Pressure Side
IDEAL VAPOR COMPRESSION CYCLE The superheated vapour enters the compressor where its pressure is raised
3
Condenser
High Pressure Side
4 Expansion Device
Compressor
2
1 Evaporator
Low Pressure Side
IDEAL VAPOR COMPRESSION CYCLE The high pressure superheated gas is cooled in several stages in the condenser 3
Condenser
High Pressure Side
4 Expansion Device
Compressor
2
1 Evaporator
Low Pressure Side
IDEAL VAPOR COMPRESSION CYCLE Liquid es through expansion device, which reduces its pressure and controls the flow into the evaporator 3
Condenser
High Pressure Side
4 Expansion Device
Compressor
2
1 Evaporator
Low Pressure Side
ACTUAL VAPOR COMPRESSION CYCLE An actual vapor-compression refrigeration cycle differs from the ideal one in several ways, owing mostly to the irreversibilities that occur in various components. Two common sources of irreversibilities are fluid friction (causes pressure drops) and heat transfer to or from the surroundings.
REFRIGERANT SELECTION When deg a refrigeration system, there are several refrigerants from which to choose, such as chlorofluorocarbons (CFCs), ammonia, Hydrocarbons (propane, ethane, ethylene, etc.), carbon dioxide, air (in the air-conditioning of aircraft), and even water (in applications above the freezing point). The right choice of refrigerant depends on the situation at hand. Two important parameters that need to be considered in the selection of a refrigerant are the temperatures of the two media (the refrigerated space and the environment) with which the refrigerant exchanges heat. To have heat transfer at a reasonable rate, a temperature difference of 5 to 10°C should be maintained between the refrigerant and the medium with which it is exchanging heat.
REFRIGERANT SELECTION AMMONIA Ammonia is predominantly used in food refrigeration facilities such as the cooling of fresh fruits, vegetables, meat, and fish; refrigeration of beverages and dairy products such as beer, wine, milk, and cheese; freezing of ice cream and other foods; ice production; and low-temperature refrigeration in the pharmaceutical and other process industries. The advantages of ammonia over other refrigerants are its low cost, higher COPs (and thus lower energy cost), more favorable thermodynamic and transport properties and thus higher heat transfer coefficients (requires smaller and lower-cost heat exchangers), greater detectability in the event of a leak, and no effect on the ozone layer. The major drawback of ammonia is its toxicity, which makes it unsuitable for domestic use.
REFRIGERANT SELECTION R-11
R-11 is used primarily in large-capacity water chillers serving air conditioning systems in buildings.
R-12
R-12 is used in domestic refrigerators and freezers, as well as automotive air conditioners. R-22 R-22 is used in window air conditioners, heat pumps, air conditioners of commercial buildings, and large industrial refrigeration systems, and offers strong competition to ammonia. R-502 R-502 (a blend of R-115 and R-22) is the dominant refrigerant used in commercial refrigeration systems such as those in supermarkets because it allows low temperatures at evaporators while operating at singlestage compression. R-134a - chlorine-free refrigerant
ICE PLANT One of the important applications of refrigeration is in ice making. The term ice plant is used to mean a complete installation for the production and storage of ice, including the icemaker itself, the unit that converts water into ice, together with the associated refrigeration machinery, harvesting and storage equipment, and the building. Ice plants are usually classified by the type of ice they produce; hence there are block ice plants, flake ice plants, tube, slice or plate ice plants and so on.
TYPES OF ICEMAKER Block Icemaker Tapered rectangular metal cans filled with water are immersed in a tank containing refrigerated sodium chloride brine. The dimensions of the can and the temperature of the brine are usually selected to give a 24 hour production time, and batches of cans are emptied and refilled in sequence during that period. Ice block weight can range from 12 to 150 kg depending on requirements; 150 kg is regarded as the largest size of block one man can conveniently handle. A block ice plant requires continuous attention and is labor intensive. The icemaker and the store require a good deal of floor space and impose heavy loads on the building structure. For these reasons block ice plants are g oing out of use, and more modern automatic plants are replacing them.
TYPES OF ICEMAKER Block Icemaker
A regular schedule of pulling ice cans is maintained and ice is transferred to a storage room that is apart from the ice making plant. Ice plants are rated according to capacity to produce ice in a 24 hour period. Brine tanks located within the building are usually contained in pits lined with concrete and cork or fiberglass insulation
TYPES OF ICEMAKER Block Icemaker
TYPES OF ICEMAKER Block Icemaker
TYPES OF ICEMAKER Rapid Icemaker It is possible to reduce the freezing time for blocks considerably, and thus reduce the space required for the icemaker. This is done by reducing the thickness of ice to be frozen; in one type of rapid icemaker this is achieved by ing refrigerant through tubes around which the ice forms and fuses into a block. The blocks can be released by defrosting and harvested automati cally, thus markedly reducing the labor requirement, but the storage space required is slightly larger than for the same weight of conventional block ice because the blocks have hollow centers after the tubes are removed.
TYPES OF ICEMAKER Flake Icemaker A sheet of ice 2-3 mm thick is formed by spraying water on the surface of a refrigerated drum, and scraping it off to form dry subcooled flakes, usually 100-1000 mm2 in area. No water is sprayed on that part of the drum immediately before the scraper, so that the ice becomes dry and subcooled prior to removal. Refrigerant temperature, drum or scraper speed, and degree of subcooling are all variable within designed limits so that the capacity of the icemaker and the thickness of the ice can be altered. Typical refrigerant temperature in a flake ice machine is 20 to - 25°C, lower than in most other types of icemaker, to give rapid cooling and thus make the machine compact. The low operating temperature requires more power, but this is to some extent compensated for by the absence of a need to defrost.
TYPES OF ICEMAKER Flake Icemaker
TYPES OF ICEMAKER Flake Icemaker
TYPES OF ICEMAKER Tube Icemaker Water is frozen on the inner surface of vertical refrigerated tubes to form hollow cylinders of ice about 50 mm in diameter and with walls 10-12 mm thick. The ice cylinders are released by defrosting the tubes automatically, and are chopped into pieces about 50 mm long by a rotating cutter as they slide out. T he cylindrical pieces can be subcooled by storing them at - 5°C, but they may require further crushing before being suitable for some applications.
TYPES OF ICEMAKER Tube Icemaker
TYPES OF ICEMAKER Tube Icemaker
TYPES OF ICEMAKER Plate Icemaker Water is frozen on one face of a vertical refrigerated plate, and the sheet of ice is released by running warm water on the other face of the plate. The size of ice particle is variable, but the optimum thickness is 10-12 mm. The plates are usually mounted i n banks, often above the refrigeration machinery, to form a self c ontained unit. Water for defrosting has to be heated if its temperature is below 23°C. Like most other icemakers the plate ice machine will operate unattended on an automatic timing cycle.
TYPES OF ICEMAKER Plate Icemaker
TYPES OF ICEMAKER Plate Icemaker
ICE PLANT CONSTRUCTION
ICE PLANT CONSTRUCTION An Ice plant has two additional circuits that help to create ice in huge quantity. 1. Refrigeration Circuit (Primary refrigerant) 2. Cooling Water Circuit (Cooling water) 3. Brine Circuit (Brine solution / Secondary Refrigerant)
Main Components of an Ice Plant
The main components generally used in an ice plant are: Compressor Condenser Expansion Valve Evaporator Chilling Tank
Main Components of an Ice Plant EVAPORATOR The evaporator is an important device used in the low pressure side of the refrigeration system. The liquid refrigerant from the expansion valve enters into the evaporator where its boil and change into vapour. The function of the evaporator is to absorb heat from the surrounding location or medium which is to be cooled, by means of a refrigerant. The temperature of the boiling refrigerant in the evaporator must always be less than that of the surrounding medium so that heat flows to the refrigerant. The evaporator becomes cold and remains cold due to the following two reasons: •
The temperature of the evaporation coil is low due to the low temperature of the refrigerant inside the coil.
• The low temperature of the refrigerant remains unchanged because any heat it absorbs is converted to latent heat as boiling proceeds.
Main Components of an Ice Plant TYPES OF EVAPORATORS 1. Bare-tube Coil Evaporator The bare tube evaporators are made up of copper tubing or steel pipes. The copper tubing is used for small evaporators where the refrigerant other than ammonia is used, while the steel pipes are used with the large evaporators where ammonia is used as the refrigerant. The bare tube evaporator comprises of several turns of the tubing, though most commonly flat zigzag and oval trombone are the most common shapes. The bare tube evaporators are usually used for liquid chilling.
Main Components of an Ice Plant TYPES OF EVAPORATORS 2. Plate Evaporator In the plate type of evaporators the coil usually made up of copper or aluminum is embedded in the plate so as so to form a flat looking surface. Externally the plate type of evaporator looks like a single plate, but inside it there are several turns of the metal tubing through which the refrigerant flows. The advantage of the plate type of evaporators is that they are more rigid as the external plate provides lots of safety. The external plate also helps increasing the heat transfer from the metal tubing to the substance to be chilled. Further, the plate type of evaporators are easy to clean and can be manufactured cheaply.
Main Components of an Ice Plant TYPES OF EVAPORATORS 3. Finned Evaporator The finned evaporators are the bare tube type of evaporators covered with the fins. When the fluid (air or water) to be chilled flows over the bare tube evaporator lots of cooling effect from the refrigerant goes wasted since there is less surface for the transfer of heat from the fluid to the refrigerant. The fluid tends to move between the open spaces of the tubing and does not come in with the surface of the coil, thus the bare tube evaporators are less effective. The fins on the external surface of the bare tube evaporators increases the surface of the of the metallic tubing with the fluid and increase the heat transfer rate, thus the finned evaporators are more effective than the bare tube evaporators.
Main Components of an Ice Plant TYPES OF EVAPORATORS 4. Shell and Tube Evaporator The shell and tube types of evaporators are used in the large refrigeration and central air conditioning systems. The evaporators in these systems are commonly known as the chillers. The chillers comprise of large number of the tubes that are inserted inside the drum or the shell. Depending on the direction of the flow of the refrigerant in the shell and tube type of chillers, they are classified into two types: dry expansion type and flooded type of chillers. In dry expansion chillers the refrigerant flows along the tube side and the fluid to be chilled flows along the shell side. The flow of the refrigerant to these chillers is controlled by the expansion valve. In case of the flooded type of evaporators the refrigerant flows along the shell side and fluid to be chilled flows along the tube. In these chillers the level of the refrigerant is kept constant by the float valve that acts as the expansion valve also.
Main Components of an Ice Plant TYPES OF EVAPORATORS 4. Shell and Tube Evaporator
Main Components of an Ice Plant COMPRESSOR A refrigerating compressor, as the name indicates, is a machine used to compress the vapour refrigerant from the evaporator and to raise its pressure so that the corresponding saturation is higher than that of the cooling medium. It also continually circulates the refrigerant through the refrigerating system. Since the compression of refrigerant requires some work to be done on it, therefore a compressor must be driven by some prime mover. In other words the purpose of the compressor in the vapour compression cycle is to compress the low-pressure dry gas from the evaporator and raise its pressure to that of the condenser. Compressors may be divided into two types, positive displacement and dynamic.
Main Components of an Ice Plant Two Types of Compressors: Positive displacement types compress discrete volumes of low-pressure gas by physically reducing the volumes causing a pressure increase.
Dynamic types raise the velocity of the low-pressure gas and subsequently reduce it in a way which causes a pressure increase.
Main Components of an Ice Plant Three Commonly Used Types of Compressors: Reciprocating - uses piston to compress the refrigerant driven by a crankshaft in a straight line back and forth motion. Vapor from the suction line is moved through the intake valve as the piston move downward. As the piston moves upward, it compresses the vapor refrigerant which is then pushed through the exhaust valve into the condenser. Rotary - A positive displacement machine in which compression of the fluid is effected directly by a rotor and without the usual piston, connecting rod, and crank mechanism of the reciprocating compressor.
Centrifugal - usually used in large capacity refrigerating system. In this compressor, the vapor is moved in a circular motion known as centrifugal force. An impeller which is a disk with radial blades spins rapidly inside this housing causing the gas to gain velocity.
Main Components of an Ice Plant Types of Compressors based on enclosure: Hermetically Sealed Semi-Hermetic Open
The difference between the hermetic and semi-hermetic, is that the hermetic uses a one-piece welded steel casing that cannot be opened for repair; if the hermetic fails it is simply replaced with an entire new unit. A semi-hermetic uses a large cast metal shell with gasket covers that can be opened to replace motor and pump components. The primary advantage of a hermetic and semi-hermetic is that there is no route for the gas to leak out of the system. Open compressors rely on either natural leather or synthetic rubber seals to retain the internal pressure, and these seals require a lubricant such as oil to retain their sealing properties. An open pressurized system such as an automobile air conditioner can leak its operating gases, if it is not operated frequently enough.
Main Components of an Ice Plant
The disadvantage of hermetic compressors is that the motor drive cannot be repaired or maintained, and the entire compressor must be removed if a motor fails. A further disadvantage is that burnt out windings can contaminate whole systems requiring the system to be entirely pumped down and the gas replaced. Typically hermetic compressors are used in lowcost factory-assembled consumer goods where the cost of repair is high compared to the value of the device, and it would be more economical to just purchase a new device. An advantage of open compressors is that they can be driven by non-electric power sources, such as an internal combustion engine or turbine.
Main Components of an Ice Plant
Hermetic
Open Type
Semi-Hermetic
Main Components of an Ice Plant CONDENSER The condenser is an important device used in the high pressure side of a refrigeration system. Its function is to remove heat of hot vapor refrigerant discharge from the compressor. The hot vapour consists of the heat absorbed by the evaporator and the heat of compression added by the mechanical energy of compressor motor. The heat from the hot vapour refrigerant in a condenser is removed first by transferring it to the walls of the condensers tubes and then from the tubes to the condensing or cooling medium. The selection of the condenser depends of the capacity of the refrigerating system, the type of refrigerant used and the type of cooling medium available.
Main Components of an Ice Plant
Main Components of an Ice Plant Types of Condenser: Water-cooled Air-cooled Evaporative .Water-Cooled Condenser It is a heat exchanger that removes heat from refrigerant vapor and transfers it to the running water. Having the refrigerant vapor condensed on the outside of a tube does this. In doing so, the vapor condenses and gives up heat to the water running inside the tube.
Main Components of an Ice Plant Air-Cooled Condenser An air cooled condenser is one in which the removal of heat is done by air. It consists of steel or copper tubing through which the refrigerant flows. The size of tube usually ranges from 6-mm to 18-mm outside diameter, depending upon the size of condenser. Generally copper tubes are used because of its excellent heat transfer ability. The condensers with steel tubes are used in ammonia refrigerating systems. The tubes are usually provided with plate type fins to increase the surface area for heat transfer. The fins are usually made from aluminum because of its light weight. The fin spacing is quite wide to reduce dust clogging. The condensers with single row of tubing provide the most efficient heat transfer. This is because the air temperature rises at it es through each row of tubing. The temperature difference between the air and the vapour refrigerant decrease in each row of tubing and therefore each row becomes less effective. However, single row condensers require more space then multi row condensers.
Main Components of an Ice Plant The single row condensers are usually used in small capacity refrigeration systems such as domestic refrigerators, freezers, water coolers and room air conditioners. The air cooled condensers may have two or more rows of tubing, but the condensers with up to six rows of tubing are common. Some condensers have seven or eight rows. However, more than eight rows of tubing are usually not efficient. This is because the air temperature will be too close to the condenser temperature to absorb any more heat after ing through eight row of tubing.
Main Components of an Ice Plant EXPANSION DEVICES The expansion device (also known as metric device or throttling device) is an important device that divides the high pressure side and the low pressure side of a refrigerating system. It is connected the receiver (containing liquid vapour at high pressure) and the evaporator (containing liquid refrigerant at low pressure). The expansion device performs the following functions like to reduce the high pressure liquid refrigerant to low pressure liquid refrigerant before being fed to the evaporator and to maintain the desire pressure difference between the high and low pressure side of the system, so that the liquid refrigerant vaporizes at the designed pressure in the evaporator.
Main Components of an Ice Plant There are many types of expansion devices used like capillary tubes, automatic or constant-pressure expansion valve, low side float valve, high side float valve and thermostatic expansion valve in an ice plant industry depending upon its capacity. In an ice plant the capillary tube type expansion devise is generally used which is discussed in details ahead.
Main Components of an Ice Plant CAPILLARY TUBE The capillary tube is used as an expansion device used in small capacity hermetic sealed refrigeration units such as domestic refrigeration, water cooler, room air conditioner and freezers. It is a cooper tube of small diameter and of varying length depending upon the application. The inside diameter of the tube used in refrigeration work is generally about 0.5 mm to 2.25 mm and the length varies from 0.5 m to 5 m. It is installed in the liquid line between the condenser and evaporator. A small filter drier is used on some system to provide additional freeze-up application. In its operation, the liquid refrigerant from the condenser enter the capillarity tube due to friction resistance offered by small diameter tube, the pressure drops since the frictional resistance is directly proportional to the length and inversely proportional to the diameter, therefore longer the capillary tube and smaller its inside diameter, greater is the pressure drop created in the refrigerant flow. In other words, greater pressure difference between the condenser and the evaporators needed forgiven flow rate of refrigerant.
Main Components of an Ice Plant
CAPILLARY TUBE
Main Components of an Ice Plant CHILLING TANK (BRINE TANK) The main components of chilling tank are : ice tank, insulation of ice tank and ice block. Ice tanks are made of material such as wood, steel or concrete. As wooden tanks do not last long enough and are liable to leak, chilling tanks are usually made of steel or reinforced concrete. The tank contains the direct expansion coils, equally distributed throughout the tank and these coils are submerged in brine. The tank is provided with a suitable frame to the ice cans and a propeller or agitator for keeping the brine in motion: the brine in the tank acts as a medium of only, the refrigerant evaporating in the ice coils extracts the heat from the brine, which again absorbs the heat for the water in the cans. The tank itself should not be much larger than is necessary to hold the cans, the coils, and the agitator. Commercial sizes of Ice cans vary with the weight of ice cakes required. The cans are made to contain about 5% more than their rated capacity to compensate for thawing.
Main Components of an Ice Plant CHILLING TANK
Main Components of an Ice Plant
Ice Plant Auxiliaries
Some of the ice plant auxiliaries are: Receiver Filter Drier Suction Accumulator Oil Separators
Ice Plant Auxiliaries RECEIVER A liquid receiver will be required if it is necessary to temporarily store refrigerant charge within the system, or to accommodate the excess refrigerant arising from changing operating conditions. The total refrigerant charge required in a circuit will vary with different operating loads and ambient, and must be sufficient at all times so that only liquid enters the expansion valve. A receiver requires a minimum operating charge which adds to overall charge and cost, and also increases system complexity. Hence receivers are avoided on many smaller systems.
Ice Plant Auxiliaries FILTER DRYER The function of filter dryer is to remove any physical material from compressor’s wear and tear, and remove any moisture presence within an air conditioning system. The Drier is made up of a metal outer container and inside there is a desiccant (moisture removal material) and strainer. Refrigerant es through the drier and give up any moisture as well as any unwanted matter. The main job of the drier is to protect the metering device from clogging either by Ice (moisture) or blockage by particles.
Ice Plant Auxiliaries
It is not uncommon for driers and filters to block due to their nature of picking up unwanted agents - evidence of this can be seen by frost build up. Filtering process is achieved by mechanical action of partitioning the flow. Particles will be trapped, whilst the refrigerant flow will be maintained. These desiccants can be of two types, viz. absorbent and adsorbent type. In this model adsorbent type filter drier is used which is defined ahead.
Ice Plant Auxiliaries
SUCTION ACCUMULATOR Suction line accumulators are sometimes inserted in halocarbon circuits, to serve the purpose of separating return liquid and prevent it ing over to the compressor. Since this liquid will be carrying oil, and this oil must be returned to the compressor, the outlet pipe within the separator dips to the bottom of this vessel and has a small bleed hole, to suck the oil out.
Ice Plant Auxiliaries OIL SEPARATOR During the compression stroke of a reciprocating machine, the gas becomes hotter and some of the oil on the cylinder wall will out with the discharge gas. Some oil carry-over will occur with all lubricated compressor types, and in small self-contained systems it quickly finds its way back to the compressor. Start up after a long idle period can result in a large amount of oil carryover for a short period due to foaming. With larger more complex systems with remote evaporator oil, it is desirable to fit an oil separator in the discharge line to reduce carry-over to the system.
Ice Plant Auxiliaries AGITATOR The propeller of the agitator is located in the brine tank and the agitator motor extends above the brine tank. Usually the agitator is located at the opposite corner of the brine tank from the accumulator. The function of the agitator is to circulate brine through the brine tank and raceway The agitator consists of a propeller guide vanes a vertically mounted motor and a housing. The agitator motor drives the propeller which circulates brine by drawing it from around the evaporator and discharging it by the ice cans. The agitator must be operated whenever the plant is in operation .
Ice Plant Auxiliaries ICE CANS Ice cans are made of galvanized steel and are tapered from the bottom to facilitate ice removal. Ice cans usually contain from 50 to 300 pound ice blocks. Often two or even four ice cans are fastened together so that two or four ice cans may be removed from the brine tank in one operation
Ice Plant Auxiliaries ICE PLANT WATER FILTERS Clear palatable ice is not produced in an ice plant without proper treatment of the raw water to be frozen. A water filter is installed for this purpose. To assist in filter operation water is treated with alum to coagulate suspended foreign substances in water. The water filter contains quartz sand or gravel through which water is ed for removal of suspended matter. Periodically material accumulated by the filter is flushed from the bed by reversing water flow. Accumulated material is then disposed to a sewer. This operation is called back washing .
Ice Plant Auxiliaries CAN FILLERS Can fillers are used to facilitate filling of ice cans with water. Small plants use a portable can filler that is connected to the water supply by a hose. The can filler is inserted in an ice can and water flows into the can. A float valve which is part of the can filler stops flow of water into the ice can when water reaches the proper level. Large ice plants use wall mounted can fillers. These can fillers are located over a can dump and are used to fill ice cans just after ice has been removed from the cans. A wall mounted can filler consists of one or more tanks depending on the number of ice cans in a group a float valve to regulate the amount of water in the tanks and an operating lever which controls flow of water from the can filler into the ice cans. The lever also acts to shut off the float valve so that the can filler will not begin to fill until the lever is released. Can fillers in large ice plants are automatic
Ice Plant Auxiliaries CAN DUMPS Can dumps are used to facilitate removal of ice from ice cans Ice cans are placed in the can dump while it is in a vertical position. The can dump is then pushed to a horizontal position and ice slides out of the cans and down an ice chute to the storage room. The can dump is so balanced that when ice blocks slide out of the can it returns to a vertical position. In some plants, ice is dipped in a dip tank to loosen it in ice cans. In some installations, a method for loosening ice in ice cans is incorporated directly in the can dump. When the can dump is pushed to a horizontal position, a spray of water is directed on the ice cans until ice loosens in the cans and slides down the ice chute. Water supply stops when the can dump returns to a vertical position
Ice Plant Auxiliaries DIP TANK A dip tank is used to loosen ice in the ice cans when this function is not accomplished by a can dump. The dip tank contains warm water which melts the ice sufficiently to loosen it in the cans. A dip tank water heater keeps the temperature of the water in the dip tank within a range where it will loosen ice in the ice cans effectively. This heater which is of the shell and tube type is installed in the discharge line between compressor and condenser. A dip tank water heater serves to heat water in the dip tank, cool discharge gas before it enters the condenser and separate oil out of ammonia gas.
Ice Plant Auxiliaries ICE CHUTE The ice chute which is located between the ice plant and storage room consists of a reinforced wall frame with a counterweighted swinging door and an inclined ramp. The chute acts as guide to receive ice dumped from ice cans and facilitates movement of ice into the storage room. The swinging door is usually lined with a canvas seal to prevent transfer of heat from ice plant to storage room.
Ice Plant Auxiliaries HOISTS Hoists are used to raise ice cans from the brine tank and to convey filled cans to the can dump. In small ice plants truck hoists are generally used. A truck hoist has wheels and a manual hoisting mechanism. In most large ice plants electric cross mounted joists are used Intermediate size plants may use manually operated cross mounted lifting hoists.
Ice Plant Auxiliaries AIR AGITATION SYSTEM Water produces a better grade of ice when it is kept in constant motion while being frozen. Lack of an air agitation system will cause opaque ice to be produced. To produce clear ice, air is bubbled through water at 1 to 3 pounds pressure from centrifugal or rotary blowers. Air pressure is controlled by means of blast gates or relief valves and air is distributed by a piping system installed directly under ice can covers. From distributing mains or laterals, air is fed to each ice can through a flexible connection and a small diameter tube that extends almost to the bottom of the ice can. This tube has small holes drilled at intervals throughout its length through which air es beneath the water surface. Tubes may be removed from ice just before it is completely frozen or may be loosened from ice with a thawing needle.
Ice Plant Auxiliaries COOLING TOWER Cooling towers are used to cool water from water cooled condensers and water cooled compressors of ice plants. Cooling towers are incorporated in ice plants so that water can be recirculated rather than disposed of. Natural draft cooling towers are usually mounted on the roof of the ice plant where they can make use of prevailing winds. Water is circulated through natural draft cooling towers at a rate of approximately 5 gallons per minute per ton of refrigeration required. Mechanical draft towers are usually installed outdoors but may be installed indoors if a duct system is provided. Water is circulated through mechanical draft cooling towers at a rate of approximately 3 gallons per minute per ton of refrigeration required.
BRINE A brine is any liquid cooled by the refrigerant and used for the transmission of heat without a change in its state, having no flash point above 65 ℃ as determined by the ASTM. Water solutions of calcium chloride and sodium chloride are the most common refrigeration brines.
BRINE Being inexpensive, most common refrigerant brines are based on calcium chloride, sodium chloride and glycols. Brine is used because the addition of salt to water lowers the freezing temperature of the solution and the heat transport efficiency can be greatly enhanced for the comparatively low cost of the material. The lowest freezing point obtainable for NaCl brine is −21.1 °C (−6.0 °F) at 23.3wt% NaCl. This is called the eutectic point.
BRINE
BRINE
BRINE
BRINE Brines of low density freeze around evaporator coils and may damage or reduce efficiency of the evaporator. Specific gravity calcium chloride brines should not be less than 1.20 and not more than 1.24 at 60 ˚F. Calcium chloride brines with specific gravities between these two limits have freezing points varying from 7.0 ˚ F to 21.5 ˚ F. The exact specific gravity of brine that should be maintained is dependent on temperature of the refrigerant in evaporator coils. This temperature is the saturation temperature of the refrigerant at suction pressure for which the system was designed to operate. Freezing temperature of the brine must be several degrees below temperature of the refrigerant in evaporator coils. Brine temperature must be read daily as a precautionary measure so that freezing of brine at the evaporator coils can be detected .
ICE PLANT OPERATION
ICE PLANT OPERATION
ICE PLANT INSPECTION AND MAINTENANCE 1.) TESTING FOR AMMONIA LEAKS Ammonia has a disagreeable and pungent odor. A small leak is readily noticed. To locate an ammonia leak the following procedures are recommended: a) Use of reagents. Detector reagents such as sulfur taper sensitive paper caustic soda and Nessler's solution are satisfactory to detect ammonia leaks. The suitability of various reagents to test for ammonia leaks depends on conditions under which the leak may occur. b) Use of soap suds. To prepare soap suds for testing use a soap and water solution of about the consistency of liquid hand soap which will lather freely or work up a lather on a brush by rubbing the wetted brush on a cake of soap. A few drops of glycerine added to the solution will cause lather to remain wet longer. When applying soap suds paint soap lather completely around a t and examine the t thoroughly for bubbles. When the t is located so that a part of it is not visible use a pocket mirror. It will sometimes take a full minute or more for bubbles to appear at a small leak. Questionable spots should be covered with lather and reexamined
ICE PLANT INSPECTION AND MAINTENANCE 2.) SERVICING AMMONIA LEAKS For objectionable leakage at crankshaft stuffing boxes of enclosed compressors, tighten gland bolt nuts gradually and equally to keep gland pressure equal on all sides. For leakage at valve bonnet stuffing boxes, pull up turn clockwise the stuffing box gland gradually. For leakage at cylinder head or flange gaskets, tighten flange bolts gradually and equally all way around. For bad leaks that have filled the space with ammonia fumes, first put a gas mask on then try to get ventilation with fans to blow the fumes to open air. Location of the leak will generally be indicated by a hissing sound from escaping If liquid ammonia has escaped and is on the floor, play a stream of water on it to absorb the escaping ammonia. Close the valve before and after the section where the leak has occurred. Apply a torch for cutting welding or for making other repairs only after the affected section has been thoroughly pumped out.
ICE PLANT INSPECTION AND MAINTENANCE 3.) PUMPING OUT COMPONENTS
Sizable components must be pumped out before they are removed from the system to prevent loss of ammonia or contamination of the area. a) Evaporator. During normal plant operation, the compressor is trying to pump out the evaporator. However, liquid refrigerant is constantly being supplied to the evaporator to replace the gas that is being exhausted from it. To pump out the evaporator, close the valve that its liquid refrigerant to the evaporator and run the compressor as in normal operation until a vacuum of at least 26 inches is obtained. b) Condenser. To pump out the condenser, close the valves that allow liquid refrigerant to from the condenser to the evaporator and allow the evaporator to pump out slightly then stop the compressor. Drain water from the condenser tubes. Close the discharge and suction shutoff valves at the compressor and open the discharge and suction by valves. This allows the compressor to reverse its action and create a suction in the line to the condenser. Start the compressor and pump a 15 inch vacuum in the condenser. Stop the compressor when the compressor comes to rest close the discharge and suction by valves.
ICE PLANT INSPECTION AND MAINTENANCE 4.) NORMAL OPERATION
Observe all components of the ice plant for normal operation Investigate unusual noises vibrations and odors during operation
5.) EQUIPMENT GUARDS
Check protective screens and fan belt guards for damage and security.
6.) FAN ASSEMBLIES
Check fan bearings of the cooling tower fan. Replace bearings if found defective. Observe operation of the fan and check for bent blades and excess vibration. Wipe dirt from shaft bearings and pulley.
7.) FAN DRIVES
Fan drives Check the fan drive for pulley alinement belt tension and condition of belt. Replace frayed or worn belt. Wipe dirt and oil or grease from pulley sheaves and belts.
ICE PLANT INSPECTION AND MAINTENANCE 8.) FAN MOTORS
Check motor bearings for rough running tendencies. Replace defective bearings. Lubricate only when required. Observe the motor when starting for proper speed pickup. Wipe dirt from the motor housing.
9.) EVAPORATOR COILS
Check the outside of evaporator coils for ice formation. Presence of ice around the coils indicates that the brine solution is not at the required specific gravity. Test the brine solution with a hydrometer. Check the coils for excessive corrosion. Check the evaporator s baffles and spacer bars for dirt and rust. Paint when necessary.
10.) EXPANSION VALVE
Check operation of the hand expansion valve in the ammonia float regulator by. Be sure that this valve is used only when the ammonia float regulator does not operate properly. When in use see that the hand expansion valve is properly adjusted to permit correct flow of liquid ammonia to the suction trap.
ICE PLANT INSPECTION AND MAINTENANCE 11.) COMPRESSORS Check the compressor and shaft seals for signs of gasket or seal failures. Replace any defective shaft seal or gasket. Check oil level and observe condition of the oil. Replace contaminated oil with ammonia compressor oil only. Fill the crank case to proper level when necessary. Proper operation of the compressor can best be judged by listening to the sound of the compressor while it is operating. Leaky rings and leaky valves in the compressor cause noticeably and abnormally high discharge temperatures. For example assume that condenser pressure is 185 psi as indicated on the discharge pressure gage. At this pressure temperature of saturated ammonia is 96˚F which also is indicated on the discharge pressure gage.
ICE PLANT INSPECTION AND MAINTENANCE 12.) REFRIGERANT PIPING ASCCESORIES Check to see if the float valve of the oil separator is draining the oil separator properly. If not adjust the float or repair the valve as required. Replace defective parts. Remove clean and replace filter elements located in recesses of the compressor housing. Replace the screen if found defective. Clean or replace the filter element of the ammonia strainer located between the condenser and float regulator. Check the efficiency of compressor suction and discharge valves by recording the maximum vacuum obtainable. Check the operation and setting of the high pressure relief valve located on the condenser and the low pressure relief valve located above the accumulator. Replace defective cartridges.
ICE PLANT INSPECTION AND MAINTENANCE 13.) WATER SUPPLY AND DRAINAGE SYSTEMS Check water supply and drain systems of cooling tower water pump, condenser, compressor, can filler, can dump, and brine tank for leaks tightness of fittings and proper operation of water gate valves. Tighten fittings repair defective valves and replace defective segments of piping.
ICE PLANT INSPECTION AND MAINTENANCE 14.) WATER-COOLED CONDENSER a) Performance Test
An overall check for condenser performance may be used to indicate condition of the condensing. To obtain an overall check for condenser performance proceed as follows. Make preliminary preparations to the system. Read the condensing temperature that corresponds with pressure in the condenser. Read the temperature of the water leaving the condenser. Then subtract the temperature of the water leaving the condenser from the condensing temperature obtained above. Temperature of the water leaving the condenser will be several degrees below the condensing temperature of pure ammonia This temperature difference is affected by the amount of condensing surface per ton of refrigeration by the condition of the condensing surface and by the presence of noncon densable gases Therefore condenser performance should be checked when load conditions are known and when the condenser is known to be clean and free of non condensable gases and results used as a measure of good performance.
ICE PLANT INSPECTION AND MAINTENANCE 14.) WATER-COOLED CONDENSER a) Cleaning Condenser Tubes
To clean condenser tubes, drain the condenser and then remove water connections and heads. When heads are removed be not to damage the rubber between the condenser and heads If the gaskets become detached from the heads use household cement to hold them in while assembling the heads the condenser. To prevent the gaskets from adhering to the shell and being damaged when heads are removed again, coat condenser side of the gasket with mixture of oil and graphite thoroughly clean condenser tubes tube cleaner consisting of a brush attached to the end of a rod should be used. When tubes are dirty, it may be necessary to run stiff wire brush through them and then finish up with tube cleaner. By connecting a water hose to pipe to which the tube cleaner fastened and by drilling a small holes in the pipe at the cleaner end water can be to the tubes during the process cleaning. Water prevents the cleaner from becoming clogged also insures cleaner tubes.
ICE PLANT INSPECTION AND MAINTENANCE 15.) COOLING TOWER Clean the water distribution basin on top of the cooling tower. Make sure that the holes in the splash box are not clogged. Check water distribution over the wooden fill pieces. Check piping and fittings for water leaks. Check float valve operation to see that it opens when water level in the float basin falls below a predetermined level and closes when water level reaches a predetermined level. If the float valve does not open and close properly adjust the valve. If adjustment cannot be made, replace with a new float valve. See that overflow pipes in the steel distribution basin and in the float box are in good condition Replace defective wooden fill pieces. Do not nail. Check for presence of algae formations.
ICE PLANT INSPECTION AND MAINTENANCE 16.) CAN FILLER Check operation of the can filler float valve. Clean the float valve when it becomes clogged. Replace any punctured float ball. Adjust the float valve by trial and error so that the can filler fills ice cans to a level approximately 3 inches from the top. If the float valve cannot be adjusted or is defective, replace the valve . 17.) AGITATOR Check the agitator for noisy operation or vibration. Lubricate motor and shaft bearings as required. Replace defective bearings. Check the agitator coupling for proper alignment. If deposits of calcium chloride appear on any parts, soak the parts in a cleaning solvent such as alcohol until the deposit dissolves. Any deposits left on the impeller will greatly impair its efficiency. Before the agitator is installed in the brine tank, check clearance between the agitator impeller and lower shaft bearing To do this bolt the motor to its base butt motor and agitator shafts together and tighten setscrews in the coupling. Then place a pry bar under the shaft coupling and force the motor rotor to its highest position. The top bearing grease cup must be filled with grease and given a turn every day .
ICE PLANT INSPECTION AND MAINTENANCE 18.) ICE CANS Check ice cans for corrosion. Clean as required. Check ice can covers for loose fits and warped boards. Repair or replace as required.
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