Cooling towers water makeup

Figure 30-lA presents the integrated environmental control potential for maximum control of particulate matter and SO2. Cooling tower water blowdown and treatment by-products may be used to satisfy scrubber makeup requirements. Fly ash and scrubber sludge will be produced separately. If the catalytic NO, process is required, the integration issues will be increased significantly. 

Characteristics of raw makeup and cooling tower waters, temperatures, maximum allowable temperature, flow rates available, and unit costs. 

For example, a cooling tower with water containing four times as much total dissolved solids as its makeup supply would be operating at four cycles of concentration. The cycles of concentration are determined by the cooling tower design, water characteristics, operating conditions and the type of treatment system employed (cooling tower water treatment is discussed in detail in Chapter 8). 

The brominator is installed permanently by the side of the cooling tower, and makeup water (or a sidestream of cooling water) passes through the tank, slowly dissolving the tablets and adding halogen to the water (see Section 6.2.7 on BCDMH for more details and recommendations). 

Refrigeration plants, cooling tower, and makeup water supply... 

Treatment of the spray water is comparable to that of cooling tower water. Chromate treatment is not required polysulfate treatments are adequate. Only a small amount of water is required to maintain the evaporative cooling cycle. The makeup water rate is determined by the amount of water that is lost due to evaporation, blowdown, and entrainment. Higher cycles of concentration can be achieved with evaporative-cooled equipment than with cooling towers. 

Cooling Tower Water. In most large chemical, petrochemical, and refinery plants, cooling water is supplied to process units from a central facility. This facility consists of a cooling tower (or many towers), water makeup, chemical injection, and the cooling water feed punps. A typical cooling water facility is shown in Figure 8.2. 

Chem. Descrip. Syn. and org. polymers and zinc corrosion inhibitors Uses Cooling water treatment, corrosion/scale inhibitor, dispersant for cooling towers cleans existing scale deposits and prevents further scaling Features Rec. for cooling towers utilizing makeup water that is < 10 grains/gal (170 ppm) total alkalinity... 

Precipitation softening processes are used to reduce raw water hardness, alkalinity, siHca, and other constituents. This helps prepare water for direct use as cooling tower makeup or as a first-stage treatment followed by ion exchange for boiler makeup or process use. The water is treated with lime or a combination of lime and soda ash (carbonate ion). These chemicals react with the hardness and natural alkalinity in the water to form insoluble compounds. The compounds precipitate and are removed from the water by sedimentation and, usually, filtration. Waters with moderate to high hardness and alkalinity concentrations (150—500 ppm as CaCO ) are often treated in this fashion. 

Removal of Particulate Matter. The amount of particulate entering a cooling system with the makeup water can be reduced by filtration and/or sedimentation processes. Particulate removal can also be accompHshed by filtration of recirculating cooling water. These methods do not remove all of the suspended matter from the cooling water. The level of fouling experienced is influenced by the effectiveness of the particular removal scheme employed, the water velocities in the process equipment, and the cycles of concentration maintained in the cooling tower. 

Example 6 Cooling Tower Determine water consumption and amount of heat dissipated per 1000 ftVmin of entering air at 90 F drydsulb temperature and 70 F wet-bulb temperature when the air leaves saturated at 110 F and the makeup water is at 75 F. 

Example 13 Calculation of Makeup Water Determine the amount of makeup required for a cooling tower with the following conditions ... 

A comparison unit with identical design used once through water cooling. This is the same high sulfur water that was used as makeup for the above cooling tower. Here the sulfur was not allow ed to concentrate and the unit is working fine after several years. 

Fb = flowrate of cooling tower blowdown Fm = flowrate of makeup water... 

Figure 24.3 Relationship between makeup water and blowdown for cooling towers.

Figure 24.3 shows the relationship between the makeup, blowdown, evaporation and drift versus the cycles of concentration. For a given design of cooling tower, fixed heat duty and fixed conditions, the evaporation and drift will be constant as the cycles of concentration increase. However, as the cycles of concentration increase, the blowdown decreases and hence the makeup water decreases. 

It works on any type of water-using operation (e.g. firewater makeup, cooling tower makeup, and so on). 

Alternative 1 consists of preliminary treatment for heavy metals removal with the primary concern being iron removal (Figure 8.3). The levels of iron observed in the groundwater at this site would be very detrimental to the downstream treatment processes. This pretreated water would then be used for cooling tower makeup water followed by biological treatment. This approach would be the easiest and cheapest alternative. This combined process should provide effective removal of BTEX. 

A key advantage of the PO WW ER system is its ability to treat water contaminated by salts and metals. Also, PO WW ER can reduce high volumes of aqueous waste while producing a high-quality water effluent that can be used as boiler or cooling tower makeup water or discharged to surface water. 

The simplest way to lower the compressor discharge pressure is to reduce the cooling-water temperature to the condenser. One neat trick I have used is to use the cooling-tower makeup water on a once-through basis, to the refrigerant condensers. This supply of water is almost always 10 to 20°F cooler than the cooling-water supply. 

The chemical composition of the cooling water makeup supply used in the plant determines the choice of the cycles of concentration. Some of the important constituents that must be controlled in the tower are calcium, magnesium, silica, carbonate, bicarbonate and sulfate ions. Alkalinity levels are regulated by the addition of acid or alkali to achieve the desired pH. When adding H2S04 (sulfuric acid) for pH control, it should be assured that calcium sulfate solubility limits are not exceeded (see Chapter 8). 

LIC (Level Indicator Control) with low-level alarm on the cooling tower basin and an actuating valve on the water makeup line ... 

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