Spray headers

Vented risers should be provided on most cooling towers to release only light hydrocarbon leakage from the cooling water before the spray header. No ignition or source of spark should be within 30 m of the vented riser. 

The thermocycle system can be operated only when condensing water is available at a temperature lower than the required chilled-water-supply temperature. Modifications for a centrifugal refrigeration unit include the installation of a small liqmd-refrigerant pump, cooler spray header nozzles, and a vapor bypass line between the cooler and the condenser. Without the compressor operating, a thermocycle capacity up to 35 percent of the refrigeration-unit rating can be produced. 

Refrigeration units modified for free cooling do not include the hq-uid-refrigerant pump and cooler spray header nozzles. Without the cooler refrigerant agitation for improved heat transfer, this arrangement allows up to about 20 percent of rated capacity. Expected capacities for both tnermocycle and free cooling are indicated in Fig. 12-21. 

Removal efficiency increased with decreasing droplet size, decreasing spray header elevation (4.87 vs. 2.43 meters), and increasing distance between spray nozzles from 0.30 to 1 meter. 

The differential head of the circulation water pump is relatively small, since dynamic losses are modest (short vertical pipe and a low AP spray nozzle) and the hydrauhc head is small, only about 6 m (20 ft) from the basin to the elevation of the spray header. Combined, the pumping energy demand is about 35 percent that for an equivalent CT application. The capital cost for this complete water system is also relatively small. The pumps and motors are smaller, the piping has a smaller diameter and is much shorter, and the required piping structural support is almost negligible, compared to an equivalent CT application. WSAC fan horsepower is typically about 25 percent less than that for an equivalent CT. 

In spray-header distributors (Fig. 10), a main header with a collection of spray nozzles is used to distribute liquid to the packed bed. Spray header distributors are well suited to liquid distribution at low liquid rates, of moderately fouling fluids, and for... 

Spray nozzle spray angles and droplet size formation are functions of the pressure drop across a spray header. Effective pressure drop range for a spray nozzle distributor varies from 5 to 20psi (from 34 to 138 kPa) for good design practice. Specific designs may operate outside this range. 

Average S02 removal for Run 907-1A was 97.5 percent at 2,350 ppm average inlet SO2 concentration. The SO2 removal stayed within a narrow range of 96 to 99 percent throughout almost the entire run. This was a significant improvement over the 57 percent S02 removal for the base case run, Run 901-1A, at 9.4 ft/sec spray tower gas velocity under similar conditions. On October 19 and on October 27, SO2 removal dropped briefly to less than 90 percent when the pump which supplied the slurry to the top two spray headers was brought offstream for repacking, and the spray tower slurry flow rate was cut in half to 800 gpm. At the reduced slurry recirculation rate, SO2 removal was 82 to 87 percent. 

The pumping energy was calculated for the spray tower assuming that two pumps are used for slurry recirculation one for the two upper spray headers and one for the two lower headers. Equal flows to the upper two headers were assumed for liquid rates up to half the maximum total flow beyond half maximum flow, the bottom two headers were assumed to receive the remaining flow. The venturi, when used, was assumed to be provided with a third pump. The pressure drop across the spray nozzles was assumed constant at 10 psi. 

Figure 4. Sulfur spray header system and spray nozzle details...

The spray header itself is much simpler than the spray header of the pneumatic system. No in-line flow control orifice is needed since each nozzle at these high pressures acts as its own flow control orifice. Furthermore, because no air is used, no pneumatic piping is needed. A high-pressure union allows the header to be rotated so that the angle of spray with reference to the bed can be easily changed. Also, the position of the nozzles with reference to the urea bed can be altered as desired by using externally mounted adjustable hangers. The entire header unit is steam jacketed. 

Flash Tank. The flash tanks will be 22 feet in diameter and 40 feet high with conical tops and bottoms. Two such tanks will be provided, one to serve as a standby and for use when the other tank is being backwashed. In Fig. 36 is shown a diagrammatic cross section of a flash tank. Water from the spray header falls into the tank through a 5-foot spray space, and passes through the filter, located 30 feet below the surface of the water in the tank. The time of residence in the flash tank is about 3.3 min. 

Spray headers are typically used for packed beds in certain process columns. The design of spray headers is not covered in detail in this procedure. However the basic steps are as follows ... 

The CSS consists of two trains which are separate and independent from each other. Each CSS train consists of an identical CSS pump, heat exchanger, mini-flow heat exchanger, spray header, and associated piping, valves and instrumentation as described in CESSAR-DC Section 6.5. The CSS is automatically actuated on a containment spray actuation signal (CSAS) by opening the spray header isolation valves and starting the containment spray pumps. (See CESSAR-DC Section 6.5.2). 

The recirculation mode of the CSS will be initiated manually by the operator. To accomplish this, the sump isolation valves "C" are opened, and the spray pump suction isolation valves "D" are closed. The pumps will then deliver spray from the sump to the spray headers. Spray additive is not injected during this mode. 

A sufficiently large pressure rise (e.g., from a LOCA or steam line break) would trigger the dousing spray system through valves in the dousing spray headers. The purpose of the... 

The process engineer who draws the conclusion from the above data that structured-type packing is superior to trays is correct. However, he should also note that the performance of packing can be no better than the initial liquid distribution provided by the spray headers. 

The demister pad is partially coked. Quite often, the demister spray header (see Fig. 13-1) is designed for too large a wash oil flow. At low flow, the wash oil does not distribute to the ends of the spray header, and the peripheral area of the demister dries up and cokes. The sections of the demister still open are exposed to velocities high enough to promote resid entrainment. A high AP across the demister shows that coke plugging is the problem. An examination c the demister before it is removed from the tower will indicate which areas are not being wetted with wash oil from the spray header. This information should then be used to revamp the spray header. 

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