External Water Coolers

A cascade cooler operates in a countercurrent manner in which the cooling air flows in direct contact with the hot material. Lifter flights on the interior wall of the cylinder lift distribute and transport the hot material. 

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In continuously working units cooled hydroxide solution enters at the bottom of the chlorinators which are provided with cooling coils a measured amount of chlorine is simultaneously admitted. The hypochlorite solution leaves the vessels through the overflow, and flows through a stoneware coil, which is externally cooled by water, into a collecting tank with a rubber coated stirrer and a PVC water cooler. The composition of the liquor is here adjusted by the addition of hydroxide or chlorine, and the finished hypochlorite solution is then stored. 

Fig. 8. Installation of external catalyst cooler. 1, riser 2, first-stage regenerator 3, second-stage regenerator 4, catalyst cooler S, distributor I, combustion air II, fluidization air, III, water IV, steam and water.

In atmospheric and some low- to medium-pressure processes, one or more separate oxidation-cooling units are often included prior to gas absorption. These units are built in the form of vertical towers which are cooled with external water curtains, shell-and-tube units, and also drum and cascade coolers. Excess air in the gas promotes initial oxidation, and some of the water vapor also present condenses to form weak nitric acid, which is later concentrated in the absorption section. Additional air for oxidation usually is injected at some point in the process, often in the absorption tower. In some plants, the gas is rapidly cooled to condense the water vapor without forming much weak acid, thereby helping to increase final acid concentration. A special condenseix yclone separator unit designed for this purpose is described by.Graham etal..[10]. 

The required engine horsepower, but not the volumetric capacity, of a two-stage reciprocating compressor is affected by the intercooler outlet temperature. As a rule of thumb, each increment of 12 F increases the engine horsepower load by 1%. Frequently, all that is needed to minimize this problem is an occasional external water wash of the intercooler aerial fin-tube cooler. 

Cascade coolers are a series of standard pipes, usually manifolded in parallel, and connected in series by vertically or horizontally oriented U-bends. Process fluid flows inside the pipe entering at the bottom and water trickles from the top downward over the external pipe surface. The water is collected from a trough under the pipe sections, cooled, and recirculated over the pipe sections. The pipe material can be any of the metallic and also glass, impeiMous graphite, and ceramics. The tubeside coefficient and pressure drop is as in any circular duct. The water coefficient (with Re number less than 2100) is calculated from the following equation by W.H. McAdams, TB. Drew, and G.S. Bays Jr., from the ASME trans. 62, 627-631 (1940). 

Fig. 24.6. Inside an acid cooler. Fig. 9.5 gives an external view. Tubes start through the tube sheet , shown here. They extend almost to the far end of the cooler where there is another tube sheet . Cool water enters at this end and flows through the tubes to the far end. Between the tube sheets , the tubes are surrounded by warm acid moving turbulently around them. Heat transfers from the warm acid to the cool water (through the tube walls). The tube entering from the right contains a thermocouple. The polymer tubes in the foreground surround metal rods. The rods are bare between the tube sheets. An electrical potential applied between them and the water tubes anodically protects the tubes against acid side corrosion.

A fluid flow is said to be natural or forced, depending on how the fluid motion is initiated. In forced flow, a fluid is forced to flow over a surface or in a pipe by external means such as a pump or a fan. In natural flows, any fluid motion is due to natural means such as the buoyancy effect, which manifests itself as tlie rise of the warmer (and thus lighter) fluid and the fall of cooler (and thus denser) fluid (Fig. 6-10). In solar hot-water systems, for example, the tlier-mosiphoning effect is commonly used to replace pumps by placing the water tank sufficiently above the solar collectors. 

Design information is limited. If coolant is condensate, then an external cooler is required. With water coolant, there may be pollution problems. Applicable for very low or intermediate pressure, very corrosive vapor, and severe or moderate coolant fouling. 

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