![]() In general, the larger the tower, the smaller is the approach. ![]() The approach represents the cooling tower capability. The approach is defined as the difference between the water temperature at the tower outlet ( t out) and the wet-bulb temperature of the inlet air ( T w,in). First, the important parameters - approach, range and efficiency - are detailed.Īpproach. This case study is aimed at calculating the unknown variables - that is, evaporation loss, air flow through the tower, blowdown flow, and the required makeup water flow. ![]() ![]() The dry-bulb temperature of the exit air is 41.5☌, and it is assumed to be 100% saturated. The dry-bulb temperature and wet-bulb temperature of the inlet air are measured as 30.3☌ and 29☌, respectively. The total flow 7,500 m 3 /h is measured at the CWR line. The tower has three cells, each operating at 2,500 m 3 /h of water flow. The CWR line from the process unit enters an industrial cooling tower at 45☌ and leaves at 33☌, as shown in Figure 2. A cooling tower is designed to remove the total heat load that is extracted from the plant by reducing the CWR temperature to the CWS temperature. The heat load extracted from the process unit is finally released to the environment in the cooling tower. After extracting heat from the process units, this stream is returned to the cooling tower, as the cooling-water-return (CWR) stream. The cooled water is collected in the sump (or basin) of the cooling tower, and it is typically pumped to the plant as the cooling-water-supply (CWS) stream. Shown here is the typical variation of the water temperature and the wet-bulb temperature of the air stream as the hot water inlet stream flows down from the top of the cooling tower and the air stream flows upward along the height of the cooling tower The temperature profile of the water and the wet-bulb temperature of the air along the height of a typical cooling tower is shown in Figure 1.įIGURE 1. The humidity level of the up-flowing air stream increases, and once it leaves the tower the air stream is almost saturated. As air rises inside the tower, it receives the latent heat of vaporization from the water, and thus the water is cooled.Īs a rule of thumb, for every 10☏ (5.5☌) of water cooling, 1% total mass of water is lost due to evaporation. There are different types of fills - splash, trickle and film - that are aimed at creating more surface area, to maximize contact between the hot water stream and air. In a cooling tower, the hot water stream (typically called the cooling water return) is introduced downward through spray nozzles into fills inside the tower. This is roughly equivalent to 25 barrels of water for every barrel of crude oil processed. A typical large petroleum refinery that processes 40,000 metric tons (m.t.) of crude oil per day requires 80,000 m 3 /h of cooling water. The use of a cooling tower is the most common way of extracting waste heat in CPI operations, and water is the most commonly used coolant to remove waste heat in the majority of such operations. The cooling of process streams and condensation of vapors are important functions in CPI operations.
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