Filter Feed Pumps

Centrifugal pumps are almost universally used for feeding filters because they produce no pulsations to disturb the filter cake. These pumps, however, have two disadvantages (a) their high speed (which tends to break down any large flocculated solids, making them more difficult to filter) and (b) their decrease in delivery as pressure increases. 

To minimize degradation of impurities, low-speed (1800 rpm) pumps with open impellers should be used. Where solids are large and floc-like, it may be advisable to use a recessed impeller centrifugal pump or a multistage piston pump with suitable aircushioning chambers. Reciprocating pumps should have ball valves. Gear or rotary pumps may be used where solids are not abrasive and filter aid is not present. 

All filter feed pumps should operate under a positive head to prevent suction of air into the filter feed liquid. 

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Chlorine has been added to the feedwater upstream of reverse osmosis pretreatment. However, since chlorine will depolymerize the polyurea membrane barrier layer in the spiral wound element, with subsequent loss of desalination properties, the chlorine is removed in the pretreatment system dechlorination basin. This removal is chemically accomplished by the addition of sodium bisulfite. The chlorine level in the influent and effluent to the dechlorination basin is continuously monitored. The feedwater is then transferred from the dechlorination basin to the cartridge filter feed pumping station by gravity flow and it is then pumped to the cartridge filters. 

The initiator assodated with service clarified water is modded by inadvertent serrice clarified water addition to the D E canal or the MB. Service clarified water is supplied to the filter feed pumps in ord r to prime the pumps prior to bdng place on-line. Inadvertent addition to the basin may occur if the service clarified water supply to the filter feed pump remains open following filtration system start-up or if the manual valves supplying s vice clarified water to the punq>s fail... 

The K-, L-, and P-Reactor IKsassembly Basins have 8 ddomzers, each mounted on triers (for easy transportation to the 200 Area fin regeneration) (Ref 8-50). The ddonizers receive water firom the discharge of the VTS filter feed pump (Ref -50). The water flow through each ddonizer is rated at 70 gpm (R 8-50). The piping to the ddonizers has a manifold which allows multiple ddonizers to be hooked up in series or in parallel. 

The original Rhone Poulenc Single Tank system is an exceedingly simple plant. It is air-cooled by passing a flow of air over slurry splashers, and does not have a filter feed tank, the slurry simply overflowing the reactor to a vertical pipe on top of the filter feed pump. 

In the most common production method, the semibatch process, about 10% of the preemulsified monomer is added to the deionised water in the reactor. A shot of initiator is added to the reactor to create the seed. Some manufacturers use master batches of seed to avoid variation in this step. Having set the number of particles in the pot, the remaining monomer and, in some cases, additional initiator are added over time. Typical feed times ate 1—4 h. Lengthening the feeds tempers heat generation and provides for uniform comonomer sequence distributions (67). Sometimes skewed monomer feeds are used to offset differences in monomer reactivity ratios. In some cases a second monomer charge is made to produce core—shell latices. At the end of the process pH adjustments are often made. The product is then pumped to a prefilter tank, filtered, and pumped to a post-filter tank where additional processing can occur. When the feed rate of monomer during semibatch production is very low, the reactor is said to be monomer starved. Under these... 

Another nickel cataly2ed process is described ia a Tolochimie patent (28). Reaction conditions claimed are 1—2.4 MPa (150—350 psi) at 100°C minimum. The combination continuous stirred reactor and gravity decanter uses density-driven circulation between the two vessels to recirculate the catalyst to the reaction 2one without the use of filters or pumps. Yield and catalyst usage can be controlled by varying the feed rates. 

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. 

Feedwater pipework will normally be gravity head suction from the hotwell or feed tanks to the pumps and at a pressure in excess of the boiler working pressure from the pumps to the boiler. Few problems occur on the pipework between pumps and boilers. However, inadequately sized suction lines can give rise to cavitation at the feed pump with subsequent boiler shutdown. The feed tank should always be positioned to suit the temperature of the feed-water and the pipework sized to give free flow at that head, taking account of bends, valves and filters. 

The concept of cross-flow microfiltration is shown in Figure 16.11, which represents a cross-section through a rectangular or tubular membrane module. The particle-containing fluid to be filtered is pumped at a velocity in the range 1-8 m/s parallel to the face of the membrane and with a pressure difference of 0.1-0.5 MN/m2 (MPa) across the membrane. The liquid penneates through the membrane and the feed emerges in a more concentrated form at the exit of the module.1617 All of the membrane processes are listed in Table 16.2. Membrane processes are operated with such a cross-flow of the process feed. 

Fig. 1. ASPEN-Plus PFD of carbonic acid pretreatment process as analyzed in this study. Bl, pretreatment reactor (Rstoic) B2, screw mixer B3, blowdown tank and screw conveyor B4, slurrying tank and tank agitator B5, cooler B6, reflux drum and condenser B7, feed pump B8, in-line C02 mixer B9, heater BIO, pneumapress filter Bll, heat exchanger B12, loading pump B13, C02 compressor B14, primary filtrate pump.

An RO skid includes the pressure vessels in which the membrane modules are contained (see Chapters 43.3 and 6.3 for detailed discussions about pressure vessels). Skids also commonly include cartridge filters in a housing or housings and an RO feed pump, although combinations exist with just pressure vessels or pressure vessels with cartridge filters. Finally, there are included on the skid instrumentation and controls for the system. Figure 6.1 shows an RO skid with these components. 

Low suction pressure is typically a result of inadequate water supply to the RO feed pump caused by upstream demand starving the RO system. Upstream demands include filter backwash water and water diverted for other applications within the facility. Starving of the RO due to equipment backwashing upstream is a system design flaw. Diversion of feed water usually occurs during installation or... 

EDTA which cloggs filters and, sometimes, even the columns. The feed pump is actuated by the signal of the gamma detector placed near the waste outlet pipe. This allows continuous feed of the active solution without the risk of polluting the waste with americium 241. On the POX. 11 column packed with 9 kg of stationary phase, one cycle served to extract 15.2 g of americium 241 present initially in 685 L of solution. The americium 241 concentration factor was 34, and the americium 241 waste decontamination factor was 250. The americium eluate contained only very small amounts of Fe and Cd. Decontamination factor of Am from Fe and Cd were 130 and 140, respectively. 

Body feed pumps work best if run continuously, recirculating back to body feed tank only when the filter is off-stream for cleaning. Piston pumps should have ceramic pistons, and flush-out connections on packings may be desirable. Outlets on single outlet diaphragm pumps should be at the bottom of the diaphragm chamber to prevent accumulation of filter aid in the chamber. 

Feed-water Heaters.—Types include the open heater (Cochrane, Webster) in which the exhaust steam and water mix, and the closed heater, in which the water circulates in tubes surrounded by exhaust steam. Open heaters give slightly higher feed temperatures at the same back pressure, or slightly less back pressure at the same feed temperature. Filters, separators, etc., are provided to remove oil from the exhaust. The open heater forms a convenient receptacle for various drips, for the automatic introduction of any cold water make-up supply and for certain forms of feed-water treatment and purification. It may be of the thoroughfare type in which all exhaust steam in the pipe passes through the heater, or of the draw in type in which a branch from the auxiliary exhaust leads to the heater as a dead end. Open heaters must be located on the suction side of the feed pump and above (preferably 3 ft. or more above) the level of the feed-pump suction valves. 

FIGURE 23.17 Band vacuum dryer installation (1) feed mixer (2) filter (3) feed pump (4) band (5) heating panels (6) vapor condenser (7) scraper (8) product collector system. 

A sanitary design, positive displacement pump (Model D025. Waukesha Foundry Co., Inc.. Waukesha WI) with 1.5 Hp adjustable drive was used as the feed pump. Flow rate to the filter varied between 10-42 L/min. 

After chemical addition, the feedwater is routed to cartridge filters which serve to mix the chemicals which have been added upstream and to insure that any particles that may have escaped the gravity filters, such as sand or other particulate matter is removed. In general, the cartridge filters do not improve the quality of the reverse osmosis feedwater to a large degree and they are not intended as continuous duty filters. The effluent from the cartridge filters is routed to the primary reverse osmosis feed pump wet well. 

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