Typical closed loop cooling tower system is shown in figure 7. The thermal capability of a cooling tower used for air condition ing is often expressed in nominal cooling tower tons. The amount of water evaporated from the cooling tower is a function of the recirculation rate and cooling range. Meanwhile, since the cooling water is a very effective air scrubber, dust and debris present in the upflowing air is washed out by downpouring water and collects in the sump.
Water efficiency reporting 12 cooling tower water audit report 12 audit comments 14 1. Cooling towers are used to reject heat through the natural process of evaporation. Using soft water for cooling tower makeup water technology. The coc can be calculated according to the following. Water outputs from a cooling tower include controlled losses such as evaporation, bleed, drift and pump gland leakage and uncontrolled losses including leaks, splash out, overflows and windage. Schematic diagram of a cooling water system calculation. Cooling tower wateris water circulated in an open system, such as the cooling tower and condenser of an airconditioning system or a turbine condenser. Cooling towers save energy but arent they major users of water. Referring to the diagram above the mass flow rate of the makeup water is given by the difference in specific humidity. Nov 25, 20 cooling tower evaporative cooling is achieved by the evaporation of a small fraction, about 1 to 2%, of the recirculating water flow.
Conversely, the formula for calculating blowdown, also known as the. Shown below are two types, modern splash fill and the highest efficiency film fill. Technical reference for water conservation in cooling towers. Cooling tower evaporative cooling system measurement and. The evaporation rate is approximately 2 gpm per 1 million btuhr of heat rejection. Cooling towers how to calculate cycles, blowdown, evaporation, makeup 2 replies here are the governing relationships for the makeup flow rate, the evaporation and windage losses, the drawoff rate, and the concentration cycles in an evaporative cooling tower system. The reduction in cooling system ocean water withdrawals using a seawater cooling tower on unit 1 or unit 2 would be. If you read this book carefully, you can make any cooling tower design programs by yourself.
They reject process heat from the cooling water to atmosphere and keep the water cool. Calculation of effect of cycles of concentration on amount of. Blow down is a term for water that is removed from the recirculated cooling water to reduce contaminant buildup in the tower water. Therefore, the maximum normal water makeup for a cooling tower system is. A correction is needed for factors such as wind, relative humidity, etc. Bleed off is the process of removing a portion of concentrated recirculating water, which is obviously replaced with fresh. Best management practice and guidance manual for cooling towers. Coc ca hardness in cooling water ca hardness in makeup water coc conductivity of cooling water conductivity of makeup water the cycle of concentration normally varies from 3.
Cooling tower blowdown equation by james mcdonald, pe, cwt originally published. Cooling towers and cooling tower parts spx cooling. Chilled water is cold water, circulated in a closed system, that serves as a medium for transferring cold temperatures for air cooling. This water is available from plant wells, municipal supplies, and, increasingly, treated municipal wastewater. Softened and filtered water is then used as cooling tower makeup. While in the cooling tower, the water is naturally degassified to remove dissolved carbon dioxide. Calculation of effect of cycles of concentration on amount of makeup water necessary for seawater cooling towers at diablo canyon power plant. As the water flows through the cooling tower, it is exposed to air, which is being pulled through the tower by the electric motordriven fan. The water balance of a tower or cooling water system involves all of the water inputs and outputs associated with the operation of the system. Understanding the basics of cooling tower heat transfer. Cooling tower makeup water flow calculation rea hvac.
A key component in cooling towers is the fill material, which further helps to maximize air water contact. If we start out with fresh water the tower has one cycle of concentration. Cooling towers may either use the evaporation of water to remove process heat and cool the working fluid to near the wetbulb air temperature or, in the case of closed circuit dry cooling towers, rely solely on air to cool the working fluid to near. Cooling tower must be made up because the water level decrease by the time during operation. When all the fresh water is evaporated solids are still in the tower the tower then refills itself with more fresh water and we have twice the solids in the tower. Cooling tower performance spx cooling technologies, inc. A strict accounting of makeup water impurities is necessary if one is to predict the composition of the recirculating water. Course contents evaporative coolers, often called swamp coolers, are cooling systems that use only water and a blower to circulate air.
Applying mass and energy balance calculations enables process engineers to evaluate evaporation loss, blowdown and makeupwater. Closed circuit systems differ in that the return fluid often water, or sometimes water mixed with glycol circulates through the tower structure in a coil, while cooling tower water recirculates only in the tower. If the circulating water has four times the solids concentration than that of the make up water, then the cycles are 4. There are aspect that contribute to calculation of cooling tower makeup water. Calculate the amount of makeup water required for a cooling tower with following conditions. Cooling tower basics calculation formulas cooling tower. Mar 02, 2015 using soft water for cooling tower makeup is less common, however, notwithstanding that this strategy offers significant benefits over the use of hard water. Department of energy assistant secretary for resource. As the water evaporates, the air absorbs heat, which lowers the temperature of the remaining water. The amount of water that is bled off by the water treatment system is usually less than or equal to the amount of water that evaporates. All of the required cooling water was assumed to be makeup water, with the. At these condi tions, the cooling tower rejects 15,000 btuih per nominal cooling tower ton.
The mass balance around a cooling tower as illustrated in the figure to the right is. As with most cooling towers, chlorination would be required to prevent biological growth. Dec 04, 2017 obtain water analyses for the recirculating cooling water and makeup. Tetratech makeup water estimate for diablo canyon units 1 and 2, 95. In the following we show a schematic diagram of a cooling tower in the context of a steam power plant. The evaporation rate is approximately 3 gpm per 100 tons of refrigeration. When dealing with a cooling tower, to cool the incoming water being sprayed over the tower by 10 qf, then 1% of the flowrate over the tower must be evaporated. Obtain water analyses for the recirculating cooling water and makeup. Hot water from heat exchangers is sent to the cooling tower. The technical data has been taken from a mechanical draft cooling tower. Calculations 417 cooling tower blowdown equation by james mcdonald, pe, cwt originally published. A typical example of an openloop system is a recirculating condenser water system with a cooling tower where the water.
Management of cooling tower blow down is necessary to prevent fouling and efficiently use the makeup water resource. A basic understanding of the system water distribution shall be established in order to properly operate and maintain a cooling tower on a water efficient manner. Cooling towers cool water by evaporating a small percentage of the recirculating water. Water efficiency audits 9 cooling tower water audit checklist 10 1. Cstn july 2003 l et s take a look at how to calculate cooling tower blowdown. Guides and recommended procedures for water treatment. Cooling tower plays a major role in chemical process industry. A majority of cooling towers use raw, hard water as makeup. These sources vary in quality depending on the concentration of dissolved and suspended solids.
Cooling tower calculations cooling water treatment. In addition to blow down, most recirculating cooling water system maintenance plans include. These along with flow rates and cycles of concentration are necessary inputs for ones cooling water calculations. Makeup water alkalinity 200 ppm 200 ppm desired recirculating water ph optimal ph determination 2 7. Cooling tower reduces circulation water temperature close to a dry bulb temperature b ambient wet bulb temperature wbt c dew point temperature d none of the above 9. Best management practice and guidance manual for cooling. The water exits the cooling tower and is sent back to the exchangers or to other units for further cooling. Again, this will be a first issue releasing the actual engineering approach of cooling tower with the examples in the world. When warm, dry unsaturated air is pulled through a water soaked pad, water is evaporated and is absorbed as water vapor into the air. Cooling tower efficiency calculations cooling tower approach. Cooling tower evaporative cooling system measurement. For nearly a century, we have provided exceptional quality equipment and service to the hvac, process cooling, industrial, and refrigeration markets. Blowdown from the cooling tower is treated in a reverse osmosis system operating at 90 to.
A nominal cooling tower ton is defined as cooling 3 gpm of water from 95f to 85f at a 78f entering air wetbulb temperature. Calculation of effect of cycles of concentration on amount. Multiply the evaporation rate by the appropriate correction factor in the table below to calculate the makeup water. Term that describes the mass flow relationship between the volume of makeup water and the volume of blowdown water. C concentration of cooling water concentration in makeup water so that. The following chart specifies the maximun water make up requirement per model. Technical reference for water conservation in cooling towers 1st edition. Cooling tower evaporation rule of thumb veolia water tech. Energy service company performance contractor hvac. This includes determination of cycle of concentration, evaporation loss, drift or windage loss, blow down water requirement makeup. Cooling towers are a major workhorse at any refinery operation. This water is often discharged to the sanitary sewer system.
At the same time, air is being drawn through the airinlet louvers forcing water to evaporate. Using soft water for cooling tower makeup is less common, however, notwithstanding that this strategy offers. Cooling towers manufacturers typically provide limiting and recommended parameters, like conductivity, total dissolved solids, ph. Department of energy idaho operations office idaho national engineering laboratory this is an informal report intended for use as a preliminaryor working document work supported by the u. Rate of evaporation is approximately 1% of the circulation flow for each 10 f 5. Drift eliminators are installed to prevent water entrained in the air from leaving the system. This is where the rule of thumb for every t of 10 f, 1% of the recirculation rate must be evaporated to achieve this cooling comes from. Effective thermal design of cooling towers a stepbystep approach to cooling tower design, with an example calculation to make it clear jonny goyal air liquide engineering and construction, lurgi india various misconceptions arise when it comes to the thermal design of cooling towers. Cooling tower types cooling towers fall into two main categories. It is advisable to keep the cycle of concentration as high as possible to reduce the makeup water requirement of the. Cooling tower efficiency calculations chemical engineering site. The water then gets distributed by cooling tower nozzles to the wet deck.
The term induced draft denotes that air is drawn by fans through the flow of falling water and up and out of the cooling tower. The makeup water source is used to replenish water lost to evaporation. Cooling tower efficiency calculations cooling tower efficiency calculation is described in this article. Cooling tower calculations water technology report. Cooling towers are a very important part of many process plants. Cooling tower makeup water quantity calculation saubhaya cooling tower makeup water quantity calculation saubhaya cooling towers understanding key components of and pdf cooling towers estimate evaporation losakeup water. Evaporation rate gpm water flow rate gpm x range f x 0. To calculate the makeup water flow rate, determine the evaporation rate using one of the following. Process leaks, windage, and drift are really just forms of uncontrolled blowdown. How to calculate the cooling tower capacity in tr quora. Cooling towers can cycle water numerous times before the water becomes saturated and must be discharged out of the system. In technical terms, cooling towers are engineered and designed based on. Cooling tower makeup water calculation pdf saubhaya makeup. Warm recirculating water is sent to the cooling tower where a portion of the water is evaporated into the air passing through the tower.
Calcium hardness is the primary cause of mineral scale deposits that form on heat transfer surfaces. In this article explained about basic concepts of cooling tower, types of cooling towers, formula for cooling tower efficiency. Xls section 11 cooling towers xlsx sakthikumaran m. Evaporation causes the heat to be removed from the make up water.
Abstract this paper presents detailed methodology of a induced draft cooling tower of counter flow type in which its efficiency, effectiveness, characteristics are calculated. This data helps to illustrate that the primary method of heat transfer in a cooling tower is via evaporation of what is typically a small fraction 2 to 3 percent of the recirculating water. A cooling tower is a heat rejection device that rejects waste heat to the atmosphere through the cooling of a water stream to a lower temperature. Cooling towers cool water by evaporating a small percentage of the recirculating water flow. In summer the ambient air wet bulb temperature raises when compared to winter thus limiting the cooling tower efficiency. Water added to cooling tower basin to replace water loss by evaporation, bleed, drift, splash and overflow. The water exits the cooling tower and is sent back to the exchangers or to other. Observe how much makeup water is required for one cooling tower m qm. Technical reference for water conservation in cooling towers pub. Water treatment of make up water will depend on the source of water and ct manufacturer requirements. Cooling tower makeup water calculation with example. Pressure reduction to d as caused by static height h. Cooling tower makeup water calculation xls saubhaya makeup.
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