Feed pumps

Fig. 38. Caustic purification system a, 50% caustic feed tank b, 50% caustic feed pumps c, caustic feed preheater d, amonia feed pumps e, ammonia feed preheater f, extractor g, trim heater h, ammonia subcooler i, stripper condenser j, anhydrous ammonia storage tank k, primary flash tank 1, evaporator reboiler m, evaporator n, caustic product transfer pumps o, purified caustic product cooler p, purified caustic storage tank q, ammonia stripper r, purified caustic transfer pumps t, overheads condenser u, evaporator v, evaporator vacuum pump w, aqueous storage ammonia tank x, ammonia scmbber y, scmbber condenser 2, ammonia recirculating pump aa, ammonia recycle pump. CW stands for chilled water.

Most cleaners are available for < 2.20/kg either as a dry blend or as aHquid. Liquid cleaners are usually less expensive than the dry blend type. A trend toward Hquid cleaners is evident as of this writing (ca 1994) because of convenience features such as automatic additions of the cleaner by chemical feed pump. Safety features such as minimized heat generation upon blending with water to make the desired concentration are also important. 

P. Cooper and F. Antunes, Proceedings ofEPRI Symposium on Power Plant Feed Pumps, Cherry Hill, N.J., 1982. 

Simplified Cycle. A simplified fossil steam cycle appears in Figure 19. The water accumulates in the bottom of the condenser, called the hotweU. It goes through a feed pump to pressurize it. The pressurized water passes through one or more feedwater heaters, which raise the temperature. The water then enters the boiler where heat from the fuel converts it to steam. The steam expands through the engine, usually a turbine, which extracts work. In the middle of the turbine some of the steam is extracted to supply heat to the feedwater heater. The remainder expands through the turbine and is condensed. The rejected heat is carried away by the condenser coolant, which is usually water, but sometimes air. The condensed steam then returns to the... 

Makeup. Makeup water is the water suppHed to replenish the steam system for any losses. In most systems it is introduced into the condenser or the feed pump suction. In steam systems where the makeup is a small fraction of the total feedwater, its purity may be somewhat lower than the feedwater requirement because it is diluted by condensate. In systems where there is Httie condensate return, such as heating steam suppHes, the makeup purity must be essentially the same as the feedwater. 

Fig. 25. Schematic of large fossil steam turbine system where BFPT = boiler feed pump turbine. To convert MPa to psi, multiply by 145.

Black Liquor Soap Recovery. Black Hquor soap consists of the sodium salts of the resin and fatty acids with small amounts of unsaponifiables. The soap is most easily separated from the black Hquor by skimming at an intermediate stage, when the black Hquor is evaporated to 25% soHds (7). At this soHds level, the soap rises in the skimmer at a rate of 0.76 m/h. At higher soHds concentrations, the tall oil soap is less soluble, but higher viscosity lowers the soap rise rate and increases the necessary residence times in the soap skimmer beyond 3—4 hours. The time required for soap recovery can be reduced by installing baffles, by the use of chemical flocculants (8,9), and by air injection into the suction side of the soap skimmer feed pump. Soap density is controUed by the rate of air injection. Optimum results (70% skimmer efficiency) are obtained at a soap density of 0.84 kg/L (7 lb/gal). This soap has a minimum residual black Hquor content of 15% (10—12). 

Variable-Pressure, Variable-Rate Filtration The pattern of this categoiy comphcates the use of the basic rate equation. The method of Tiller and Crump (loc. cit.) can be used to integrate the equation when the characteristic curve of the feed pump is available. 

The cost of the filter station includes not only the installed cost of the filter itself but also that of all the accessories dedicated to the filtration operation. Examples are feed pumps and storage facihties, precoat tanks, vacuum systems (often a major cost factor for a vacuum filter station), and compressed-air systems. The dehvered cost of the accessories plus the cost of installation of filter and accessories generally is of the same order of magnitude as the dehvered filter cost and commonly is several times as large. Installation costs, of course, must be estimated with reference to local labor costs and site-specific considerations. 

The continuously stirred mill can be fed by screw feeders from several material bins siiTuiltaneously, thus blending uniform compositions, without incurring problems of transporting imperfectly blended or agglomerated mixtures. A series of mills may be used with decreasing media size and increasing rotary speed to achieve desired fine-particle size. No additional feed pumps are needed. 

FIG. 22-80 Simplified flow schematic for a pervaporation system. Heated feed enters from left through a feed pump. Heaters in a recirculating feed loop may he required (not shown). Stripped liquid exits at the top of the pervaporation membrane. Vapor exits at the bottom to a condenser. Liquid and noncondensibles are removed under vac-imm. Cowiesif Hoechst Celanese. )... 

Provide positive displacement feed pump instead of centrifugal pump or pressurized transfer... 

Thermal power plant auxiliaries such as flow control of primary air fan, ID fan and forced-draught fans, boiler feed pumps circulating water pumps and condensate pumps, coal handling plant (e.g. ball mill, wagon tippler, and stacker reclaimer)... 

These applications have considerably more stringent performance requirements than any other application. Circulating water pumps, boiler feed pumps, forced-draught (FD) and induced-draught (ID) fans, pulverizers (ball mills) and condensate pumps are components in a thermal power station that may require extra safety in a standard motor to make it able to fulfil these requirements and withstand abnormal service conditions and system disturbances. Abnormal operating conditions may be one or more of the following ... 

Power house auxiliaries ID fans, FD fans, primary and secondary air fans, boiler feed pumps and slurry... 

When solution must be pumped, consideration should be given to use of holding tanks between the dry feed system and feed pumps, and the solution water supply should be controlled to prevent excessive dilution. The dry feeders may be started and stopped by tank level probes. Variable-control metering pumps can then transfer the alum stock solution to the point of application without further dilution. Means should be provided for calibration of the chemical feeders. Volumetric feeders may be mounted on platform scales. Belt feeders should include a sample chute and box to catch samples for checking actual delivery with set delivery. Gravimetric feeders are usually furnished with totalizers only. Remote instrumentation is frequently used with gravimetric equipment, but seldom used with volumetric equipment. 

The filtrate flow meter microswitch that stops the slurry feed pump when the chambers are full. 

Corrective Action Check operation of feed pump. Check pump settings. 

As the flow rate and quantity of liquor are the most important controllable variables in developing design data, a feed pump suitable for accurate and continuous flow is required. Depending on the size of the pilot column system, the use of peristaltic, diaphragm, piston-type or centrifugal pumps are recommended. The feed pump should be used in combination with a volumetric or gravimetric flow control... 

Overpressure and tube failure may also result from valve closure on the inlet side of a fomace, or from feed pump failure, etc, if the coil remains pressurized by downstream equipment. In these cases, however, overpressure occurs at or below the normal operating pressure (due to overheating at no-flow conditions), and a PR valve cannot provide the necessary protection. 

An alarm shower can occur when high pressure in the reactor trips the feed by closing a valve and turning off the feed pump. In addition to the high pressure trip alarm, the operator is frequently showered with low feed flow, low-low feed flow, and feed pump off alarms. 

For the steam plant, the condenser pressure, the turbine and pump efficiencies are also specified there is also a single phase of water/steam heating, with no reheating. The feed pump work term for the relatively low pressure steam cycle is ignored, so that /ij, = /i. For the HRSG two temperature differences are prescribed ... 

This is essentially the approach adopted by Ruffi [9] in a comprehensive set of calculations, but he assumed that the economiser entry water temperature 7b is raised above the condenser temperature by feed heating, which was specified for all his calculations. The T,s diagram is shown in Fig. 7.6 the feed pump work terms are neglected so that h.j, = hy and h. = /ib. 

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