Surface Condenser and Jet Condenser
Difference between surface condenser and jet condenser The quantity of the cooling water necessary for condensation of vapour is found. Condenser is a heat exchanger used to condense(Cool) the working fluid/ refrigerant after its been heated up (mosty because of compression). difference between condensing temperature and cooling water. No attempt will be made to go through a formal In practice, cooling tower water is first used in the A typical air conditioning surface condenser specification is included.
While this is the ideal method of filtration, for higher flow systems it may be cost-prohibitive. Side-Stream Filtration — Side-stream filtration, although popular and effective, does not provide complete protection. With side-stream filtration, a portion of the water is filtered continuously.
This method works on the principle that continuous particle removal will keep the system clean. Manufacturers typically package side-stream filters on a skid, complete with a pump and controls.
For high flow systems, this method is cost-effective. Properly sizing a side-stream filtration system is critical to obtain satisfactory filter performance, but there is some debate over how to properly size the side-stream system.
Cycle of concentration — Maximum allowed multiplier for the amount of miscellaneous substances in circulating water compared to the amount of those substances in make-up water.
Treated timber — A structural material for cooling towers which was largely abandoned about 10 years ago. The life of treated timber varies a lot, depending on the operating conditions of the tower, such as frequency of shutdowns, treatment of the circulating water, etc. Under proper working conditions, the estimated life of treated timber structural members is about 10 years.
- Surface Condenser | Difference Between Jet Condenser and Surface Condenser
- Surface Condenser and Jet Condenser
Leaching — The loss of wood preservative chemicals by the washing action of the water flowing through a wood structure cooling tower. Pultruded FRP — A common structural material for smaller cooling towers, fibre-reinforced plastic FRP is known for its high corrosion-resistance capabilities. Pultruded FRP is produced using pultrusion technology, and has become the most common structural material for small cooling towers. It offers lower costs and requires less maintenance compared to reinforced concrete, which is still in use for large structures.
Fog clouds produced by Eggborough Power Plant UK Under certain ambient conditions, plumes of water vapor fog can be seen rising out of the discharge from a cooling tower, and can be mistaken as smoke from a fire. If the outdoor air is at or near saturation, and the tower adds more water to the air, saturated air with liquid water droplets can be discharged, which is seen as fog. This phenomenon typically occurs on cool, humid days, but is rare in many climates. Fog and clouds associated with cooling towers can be described as homogenitus, as with other clouds of man-made origin, such as contrails and ship tracks.
For that purpose, in hybrid towers, saturated discharge air is mixed with heated low relative humidity air. Some air enters the tower above drift eliminator level, passing through heat exchangers. The relative humidity of the dry air is even more decreased instantly as being heated while entering the tower.
The discharged mixture has a relatively lower relative humidity and the fog is invisible. The salt deposition problem from such cooling towers aggravates where national pollution control standards are not imposed or not implemented to minimize the drift emissions from wet cooling towers using seawater make-up.
Cooling tower - Wikipedia
Similarly, particles smaller than 2. Though the total particulate emissions from wet cooling towers with fresh water make-up is much less, they contain more PM10 and PM2.
At plants without flue gas purification, problems with corrosion may occur, due to reactions of raw flue gas with water to form acids. Sometimes, natural draft cooling towers are constructed with structural steel in place of concrete RCC when the construction time of natural draft cooling tower is exceeding the construction time of the rest of the plant or the local soil is of poor strength to bear the heavy weight of RCC cooling towers or cement prices are higher at a site to opt for cheaper natural draft cooling towers made of structural steel.
Operation in freezing weather[ edit ] Some cooling towers such as smaller building air conditioning systems are shut down seasonally, drained, and winterized to prevent freeze damage. Down flow surface condenser. Central flow surface condenser. Evaporator condenser Down flow condenser In down flow condenser the steam enters at the top and flow downwards over the tubes due to force of gravity as well as suction of the extraction pump fitted at the bottom.
The condensate is collected at the bottom and then pumped by the extraction pump. The dry air pump suction pipe, which is provided near the bottom, is covered by baffle so as to prevent the condensed steam into it as shown in figure.
As the steam flow perpendicular to the direction of flow of cooling water inside the tubes this is called cross surface condenser.
Central flow surface condenser: In central flow surface condenser, the exhaust steam enters at the top and flow downward. The suction pipe of the air is placed in the center of the tube nest. This causes the steam to flow radically inwards over the tubes towards the suction pipe. The condensate is collected at the bottom and the pumped by extraction pump. The central flow surface condenser is an improvement over the down flow type as the steam is directed radially inwards by a volute casting around the tube nest.
It tubes gives an access to the whole periphery of the tubes. The steam to be condensed enters at the top of a series of pipes outside of which is a film of cold water. A leak into the system low side if operation is at pressures below atmospheric.
Failure to evacuate completely after part of a system has been open for repair. If permitted to accumulate, non-condensables in the system cause high condensing pressures and, therefore increased power input to the compressors.
Checking the System for Non-Condensables To check the system for non-condensable gases, first close the valve in the liquid line running from the receiver to the evaporator king valvethen pump down the system slightly, enough to assure that if any non-condensables are present they are pumped over to the high side. Immediately after pump-down, close the discharge valve on the compressor.
Operate the evaporative condenser for at least two hours or until the water temperature in the basin or remote sump is the same as the entering wet-bulb temperature. Then the temperature corresponding to the pressure in the evaporative condenser should correspond, or nearly so, to the wet-bulb temperature of the entering air.
Be sure that all gauges are accurate when checking for non-condensables. Purge Connections Purging at the high point of the system can only be effective when the system is down. During normal operation the non-condensables are dispersed throughout the high velocity refrigerant vapor and too much refrigerant would be lost when purging from this high point.
Surface Condenser | Difference Between Jet and Surface Condenser
However, purging at the condenser coil outlet can be effectively accomplished during system operation. The non-condensables will carry through the condensing coil with the refrigerant liquid and vapor and tend to accumulate in the condensing coil outlet header and connection where the temperature and velocity are relatively low. In the BAC condenser coil design, the refrigerant outlet connection is tangent to the top of the coil header so non-condensables cannot trap in the header.
Each connection must be valved so that each coil can be purged separately. Purge Piping All of the purge connections on the condenser coils plus the purge connection in the receiver may be cross connected to a single purge line, which is connected to an automatic purger.
However, only one purge valve should be open at a time. Opening two or more valves tied together equalizes the coil outlet pressures and the effect of the vertical drop legs is lost.
Location In order to obtain specified performance from an evaporative condenser installation, it is essential that the unit or units be located so as to guarantee design airflow to each unit while minimizing recirculation of the discharge air. A single condenser located outdoors will seldom pose any layout problem.
However, multiple units or a single unit with a fan side facing an adjoining building or wall must be located with reference to the wall or to each other to allow ample space for airflow to the fans. Figure 8 illustrates those dimensions which must be taken into consideration when locating evaporative condensers.
Figure 8 - Condenser Spacing Parameters Specific layout recommendations for the various models of BAC evaporative condensers that are available. In Figure 8, the top discharge of the condenser should be at the same or higher level than an adjoining building or wall in order to minimize recirculation caused by down draft between the condenser and wall.
Such a down draft might be created by winds blowing across the condenser discharge towards the wall. If for some reason, it is not possible to raise the condenser to the level of the top of an adjoining building or wall, a discharge hood can be used on centrifugal fan condensers see Figure 9.
Figure 9 - Discharge Hoods to Increase Discharge Air Velocity The hood increases the discharge air velocity and elevates the point of discharge to a height where recirculation is minimized. Elevating the condenser increases the area for airflow from beneath the unit and permits placing the condensers closer together or closer to an adjoining wall. However, there is no spacing advantage to elevations greater than 10 feet in this respect.
Occasionally, the minimum spacing cannot be provided. Some such installations virtually create their own environment and all potential problems of airflow and recirculation are magnified.
In some cases, it may be necessary to increase the design wet-bulb temperature for which the condensers are selected. It is recommended that the layout parameters of any installation other than a single unit on an open roof be reviewed by the local BAC Representative.
Recirculated Water System An evaporative condenser obtains its ability to condense the refrigerant by evaporating a portion of the water recirculated over the condensing coil. As the water evaporates, any impurities present in the supply water remain in the unit. The concentration of impurities increases rapidly, and continues as long as the unit is in operation. In addition, any impurities in the air such as chemical fumes in an industrial area or salt air near the coastline will be absorbed by the recirculated water, resulting in a corrosive solution.
In many localities this constant bleed and replacement with fresh water will keep the concentration of impurities in the system at an acceptable level.Condenser and Cooling tower work in power plant
In addition to any bleed or chemical treatment, all systems must be treated for biological contaminants. An evaporative condenser will evaporate approximately 3 GPM of water per tons of refrigeration. Allowing an equal quantity for bleed, total water consumption is approximately 6 GPM per tons of refrigeration.
Most evaporative condensers that are furnished with a factory-installed recirculating pump or pumps are also furnished with a water bleed line and flow adjusting valve. Units furnished for remote sump application must have a bleed line and valve installed at the remote sump. It is important to keep the bleed lines operative and properly adjusted through periodic inspection.
The water removed through the bleed line will more than pay for itself through increased unit life. A reputable local water treatment company should be consulted to analyze the system water and recommend proper treatment. Most evaporative condensers are constructed of galvanized zinc-coated steel, and any chemical treatment must be compatible with this material.
Chemicals should be fed into the recirculated water on a continuous metered basis to avoid localized high concentration which may cause corrosion. Batch feeding of chemicals does not afford adequate control of water quality, and is not recommended. When acid treatment is required, it is essential that the acid be accurately metered into the recirculated water, and the concentration properly controlled.
Acid should not be fed directly into the cold water basin; it must be fed into the recirculated water piping so it will mix thoroughly before reaching the basin. Special Applications Desuperheaters A desuperheater is an air-cooled finned coil usually installed in the discharge airstream of an evaporative condenser. Figure 11 shows a typical arrangement. Figure 11 - Evaporative Condenser With Desuperheater Coil Its primary function is to increase the condenser capacity by removing some of the superheat from the discharge vapor before the vapor enters the wetted condensing coil.
The amount of superheat removed is a function of the desuperheater surface, condenser airflow and the temperature difference between refrigerant temperature and the temperature of the air leaving the condenser. It is economically impractical to provide a desuperheater on an evaporative condenser with enough heat transfer surface to remove all of the superheat in the ammonia refrigerant.
Therefore, complete superheat removal is never attained under design conditions of load and ambient wet-bulb temperature with the standard desuperheater coils furnished by evaporative condenser manufacturers. Occasionally, where condenser space is limited, the addition of a desuperheater may permit a smaller plan area unit. The air-cooled desuperheater is not as efficient as wetted condenser surface, so it is more economical to select a condenser with additional wetted surface to achieve greater capacity.
Desuperheaters have been recommended by some manufacturers to assist in oil removal from the ammonia vapor and also to minimize scaling of the upper tubes of the wetted condensing coil by reducing entering refrigerant gas temperatures to the wetted coil. For oil removal, an oil separator is installed between the desuperheater coil and the wetted condenser coil. The theory is that cooling of the hot discharge refrigerant vapor will promote condensation of the oil vapor from the refrigerant-oil mixture and separation of oil from the refrigerant in the oil separator.
This claim has merit. However, there is normally no control over the amount of heat removed from the refrigerant vapor in the desuperheater coil. At less than design load or wet-bulb temperature, the desuperheater coil often becomes a condensing coil, and when liquid refrigerant mixes with liquid oil, separation becomes quite difficult.
Today there are many oil separators with high efficiencies for removing oil from the hot discharge vapor as it leaves the compressor. The oil separator can be located in the engine room where it can be monitored by the operating engineer and where it is not exposed to the ambient temperatures that would cause refrigerant condensation.
From the scaling standpoint, the presence or absence of a desuperheater is immaterial. The primary factor that determines the tendency to form scale on the wetted coil of an evaporative condenser is the external surface temperature of the coil.
At the inlet of the wetted coil where only hot refrigerant vapor exists, the internal heat transfer coefficient is quite low.
The resulting coil surface temperature at the inlet is not appreciably different from the coil surface temperature in the condensing portion of the coil. Therefore, scaling in an evaporative condenser becomes primarily a function of adequate water distribution over the coil, proper bleed-off to prevent concentration of solids, and proper water treatment where water conditions are particularly bad. The increasing use of screw compressors for industrial refrigeration systems further obsoletes the use of a desuperheater.
The screw compressor is an oil seal, oil cooled unit, with the cooled oil injected into the compressor in contact with the refrigerant vapor. Larger, efficient, de-mister type oil traps furnished as part of the screw compressor package minimize problems of oil carryover. Consequently, any capacity gain of a desuperheater used on a screw compressor installation is negligible. Refrigerant Liquid Subcooling Halocarbon Systems In the case of air conditioning or refrigeration systems, the pressure at the expansion device feeding the evaporator s can be substantially lower than the receiver pressure due to liquid line pressure losses.
If the evaporator is above the receiver, the static head at the evaporator is less than at the receiver, which further reduces the pressure at the expansion device. A refrigerant remains in liquid form only as long as the liquid pressure is at or higher than the saturation pressure corresponding to its temperature.
Any pressure reduction in the liquid line between the receiver and the expansion device causes flashing or vaporization of some of the liquid. The presence of this flash gas will cause erratic operation of the thermal expansion valve and reduce the valve capacity, sometimes to the point of starving the evaporator.
To avoid liquid line flashing where the above conditions exist, it is necessary to subcool the liquid refrigerant after it leaves the receiver. The minimum amount of subcooling required is the temperature difference between the condensing temperature and the saturation temperature corresponding to the pressure at the expansion valve.
To determine the degree of subcooling required, it is necessary to calculate the liquid line pressure drop including valves, ells, tees, strainers, etc. The static head loss due to a vertical rise in the liquid line is a function of the refrigerant density.