Our current blow down confirms the above calculation. In ideal case the cold water temperature will be equal to the wet bulb temperature. Utility boilers, operating below 5000 kpa often use sodium zeolite andor hot or cold lime softening, in which case the continuous blowdown will be in constant operation, and the intermittent blowdown will be performed once per day. Jea, as the control authority, is required to regulate cooling tower discharges to the potw. Technical reference for water conservation in cooling towers 1st edition. Thus, over time the level of total dissolved solids tds increases. Drift eliminators are installed to prevent water entrained in the air from leaving the system. The polishing ro concentrate stream is utilized as cooling tower makeup water see figure 1. They reject process heat from the cooling water to atmosphere and keep the water cool. Cooling tower basics calculation formulas cooling tower efficiency. By using a blend of hard water and soft water, the cooling tower may still be able to run at higher cycles requiring less blowdown and makeup water. Applying these values to formula 5, blowdown would be. The historical derivation of this 15,000 btulh cooling tower ton, as compared to the 12,000 btuih evaporator ton, is based. If the calculated load is high, oversize and more costly, equipment.
Seawater cooling tower drift rate the drift rate for a new cooling tower equipped with best available drift eliminators would be 0. Cooling tower blowdown the makeup water cooling tower blowdown water treatment presents several challenges due to the high salt concentrations and chemicals added in the cooling tower. Cooling water treatment manual, national association of corrosion engineers, houston, tx. These maximize the overall recovery and minimize the volume for disposal. Cooling tower evaporative cooling system measurement. Cooling tower water treatment cycles of concentration.
Cooling tower efficiency calculations chemical engineering site. Recirculating water is removed from the system by blowdown in order to control the water quality in the cooling tower system. Blowdown is the difference between the set pressure and the reseating pressure of a safety or relief valve, expressed as a percentage of a set pressure or pounds per square inch. Cooling tower basics calculation formulas cooling tower. Does anyone have a rule of thumb about the amount of blowdown water from a cooling tower. Chilled water is cold water, circulated in a closed system, that serves as a medium for transferring cold temperatures for air cooling in an airconditioning system. Technical reference for water conservation in cooling towers.
To control the level of total dissolved solids tds within the boiler as water is boiled within the boiler and steam is produced, then the solids remain in the water and concentrate. 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 tower calculations cooling water treatment. Further evaporation causes these dissolved solids to come out of so. An additional advantage of cooling blowdown is in helping to comply with local codes regulating the discharge of high temperature liquids into the sewer system. Contact fairfax water at 7036985800 to obtain both the cooling tower submeter and the cooling tower discharge blowdown meter. The blowdown rate will depend on the cycles of concentration required to. Figure 4 illustrates these water system flow locations in generic terms. Any water source has various levels of dissolved and suspended solids. See figure 1 on page 3 for an illustration of the water being recirculated, added to, or lost from a cooling tower. 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.
Noncontact cooling water or condensate and boiler water. 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. Also, a heat balance plus experience shows that evaporation losses are 0. Guides and recommended procedures for water treatment.
Concentration cycles in petroleum refinery cooling towers usually range from 3 to 7. Cooling tower efficiency calculations cooling tower approach. Water efficiency management guide mechanical systems. Best management practice and guidance manual for cooling. Shuichi chino, isamu sugiyama, jeffrey hollooway and deb mukhopadhyay, a new high efficiency r e verse. At these condi tions, the cooling tower rejects 15,000 btuih per nominal cooling tower ton. The water exits the cooling tower and is sent back to the exchangers or to other. Considering the cooling tower blowdown quality, discharge to surface water. Even if the assumed evaporation and drift rates were perfectly accurate, the calculated. Calculation of effect of cycles of concentration on amount. For example, new logic has a fullscale system installed at a gas production plant in the u. The softener regeneration costs salt and water may make using 100% soft makeup uneconomical for a cooling tower. Ides solutions for cooling tower blowdown treatment.
The calculation of cooling tower efficiency involves the range and approach of the cooling tower. Slug dosed chemicals like nonoxidising biocide calculated based on hold up volume of cooling tower. As pure water is evaporated all of the solids are left behind so they concentrate in the cooling tower water. Cooling tower makeup water calculation with example. Cooling tower evaporative cooling system measurement and verification protocol brian boyd and kate mcmordie stoughton pacific northwest national laboratory. Cooling towers dissipate heat from recirculating water that is run through cool chillers, airconditioning equipment, or other process equipment.
Cooling tower bleedoffblowdown is the flushing of a portion of high mineral concentration cooling tower system water down the drain, while simultaneously replacing it with fresh water. Cooling towers work by evaporating a small portion of water, approximately 1. Handbook of pollution prevention and cleaner production best practices in the petroleum industry, 2009. When all the fresh water is evaporated solids are still in the tower the tower then refills. Cooling tower efficiency is limited by the ambient wet bulb temperature. Cooling tower fundamentals spx cooling technologies. Drift is entrained water in the tower discharge vapors. The mass balance around a cooling tower as illustrated in the figure to the right is. 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. Cooling tower wateris water circulated in an open system, such as the cooling tower and condenser of an airconditioning system or a turbine condenser. If we start out with fresh water the tower has one cycle of concentration. A cooling tower discharge blowdown meter is required to ensure accurate flow measurement for sewer service billing per chapter 67.
As this occurs, a small volume of water is evaporated, reducing the temperature of the water being circulated through the tower. Process description the cooling tower is fed by clarified california aqueduct water. The cooling effect occurs because some of the water evaporates into a stream of air in contact with the water within the cooling tower. Drift eliminators are also known as mist eliminators. Cooling tower efficiency calculation is described in this article. A discharge may be covered under this general permit if the discharge contains a small portion of cooling tower blowdown in addition to the nccw. To calculate the louvers size the following formula is used. Other factors, which we will see, must be stated along with flow rate m3hr. Blowdown discards a portion of the concentrated circulating water due to the evaporation process in.
Cstn july 2003 l et s take a look at how to calculate cooling tower blowdown. Ides endtoend, integrated cooling tower blowdown water treatment solutions include highrecovery reverse osmosis solutions that reduce reject volumes and complete thermal zld solutions. Calculations 417 cooling tower blowdown equation by james mcdonald, pe, cwt originally published. Cooling tower efficiency calculations along with approach, range, cycle of concentration. In some large power plants, the cooling tower concentration cycles may be much higher. Recovery and reuse of water from effluents of cooling tower. Drift loss draw off or blowdown as the cooling water circulates the cooling tower part of water evaporates thereby increasing the total dissolved solids in. Calculate the amount of makeup water required for a cooling tower with following conditions. Heat is removed by the tower primarily as the result of evaporation. Cooling tower blowdown is pumped to a firststage reaction tank. Cooling tower discharges present a potential problem to the treatment of sanitary sewer and sludge quality especially for the biosolids reuse facility. Based on above calculation, one can easily calculate the blow down needed to maintain the tds at any level. Noncontact cooling water nccw nccw includes once through cooling water for processes such as air compressors, welders, etc.
My prime focus is on reducing the water consumption in the cooling tower. However, in a cooling tower circulating seawater, which has a dissolved solid content of about 35,000 ppm, the blowdown rate is typically maintained at about. Cooling tower blowdown equation by james mcdonald, pe, cwt originally published. To control the cycle of concentration blow down or draw off is given. The associated losses caused by blowdown, evaporation, drift, and system leaks must be accounted for by system makeup requirements. Calculate boiler water blowdown flow yamatho supply. Almost 14 th of makeup water water added in a cycle to substitute water losses in a cooling tower is dissipated 25. I know that usually conductivity is the controlling factor but i would like to know if there is any design rule out there that relates the amount of makeup water to the amount of blowdown. They are located in areas that are situated after the fill and water sprays and just before the area where the air exits the cooling tower see figures 6 and 8. Hello, i am working as an intern for a company and i have been given a project for water conservation. Let say we have cooling tower with the following data. Cooling tower efficiency calculations cooling tower efficiency calculation is described in this article. For example, a cooling tower sized to cool 4540 m 3hr through a.
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