Pumps, centrifugal positive-displacement

There are no problems with flow, pumping, pipe cleaning, etc. At temperatures between 40 C and 45 C, sulphonic acids can be handled with ordinary pumps (centrifugal, positive displacement) in pipes of normal diameters and lengths. The flow will always be laminar at the velocities applied (0.5 m/s -1.0 m/s) and pressure drops can be calculated from the Poiseuille equation ... 

There are four (4) major types of pumps (I) positive displacement, (2) dynamic (kinetic), (3) lift, and (4) electromagnetic. Piston pumps are positive displacement pumps. The most common centrifugal pumps are of dynamic type ancient bucket-type pumps are lift pumps and electromagnetic pumps use electromagnetic force and are common in modern reactors. Canned pumps are also becoming popular in the petrochemical industiy because of the drive to minimize fugitive emissions. Figure 10-24 shows pump classification ... 

Pump and Downstream Equipment - A PR valve is required for a pump when the shutoff pressure of the pump is greater than the design pressure of the discharge piping, downstream equipment, or pump casing. Positive displacement pumps normally require such protection, while in most cases centrifugal pumps do not. 

In much the same manner as pumps, compressors are classified as one of two general classes positive displacement or dynamic (see Figure 3-68) [23]. These two general classes of compressors are the same as that for pumps. The positive displacement class of compressors is an intermittent flow device, which is usually a reciprocating piston compressor or a rotary compressor (e.g., sliding vane, screws, etc.). The dynamic class of compressor is a continuous flow device, which is usually an axial-flow or centrifugal compressor (or mix of the two). 

There are four (4) major types of pumps (1) positive displacement, (2) dynamic (kinetic), (3) lift, and (4) electromagnetic. Piston pumps are positive displacement pumps. The most common centrifugal... 

The major kinds of pumps used in the chemical and pharmaceutical industries are centrifugal, positive displacement, and turbine pumps. 

Use centrifugal pumps. If positive displacement pumps must be used, these pumps must be fitted with approved pulsation dampening equipment surge tanks may also be required, particularly for very short and very long pipe runs. 

Naphthali-Sandholm method, 404 dgorithm flowsketch, 411 Nitric acid reactor, 576 Nitrogen fixation, 574,578,588 Nitrotoluene isomers separation, 544 Noncatalytic reactions with solids, 595 Non-Newtonian liquids, 100, 103-109 Bineham. 104.105.107-109 dilatant, 103, 104 laminar flow, 108,109 pressure drop in lines, 106, 109 pseudoplaslic, 103, 104 rheopectic, 104,105 slurries, 71 thixotropic, 104-106 viscoelastic, 105, 106 Notation, 672 NPSH, pumps, 133,146 centrifugal pumps, 146 positive displacement pumps, 134, 135 various pumps, 144 NRTL equation, 475... 

UF performance, however, may be influenced by process variables such as pH, nature of ions and ionic strength, temperature and shear. For example, Melling has reported the effect of pH on the specific enzyme activity of E-coli penicillinase in the pH range 5 to 8. Effects of shear inactivation associated with piunping effects are described by O Sullivan et al. Recessed impeller centrifugal pumps or positive displacement pumps may be used to minimize enzyme inactivation due to shear. 

A centrifugal type pump is most commonly used. This should be located so that a positive head is maintained on the suction side of the pump. Many positive displacements are also satisfactory. They allow more flexibility in their location but may need more... 

Process pumps Are many times centrifugal pumps or positive displacement pumps used in process applications. The type of pump and construction details varies depending on the application in which these pumps are used. Slurry pumps A heavy-duty pump that is made to handle thick, abrasive slurries. They are made of durable materials and capable of handling abrasive fluids for long periods of time. 

Basically, pump can be classified into two groups, centrifugal (or rotodynamic) pump and positive displacement pump. Positive displacement pump can be further classified into reciprocating pump and rotary pump. These are rhe pumps, which will be discussed in this chapter. See Figure 1 for the general pump classification. 

Production and Shipment. Estimated adiponitrile production capacities in the U.S. in 1992 were about 625 thousand metric tons and worldwide capacity was in excess of lO metric tons. The DOT/IMO classification for adiponitrile is class 6.1 hazard, UN No. 2205. It requires a POISON label on all containers and is in packing group III. Approved materials of constmction for shipping, storage, and associated transportation equipment are carbon steel and type 316 stainless steel. Either centrifugal or positive displacement pumps may be used. Carbon dioxide or chemical-foam fire extinguishers should be used. There are no specifications for commercial adiponitrile. The typical composition is 99.5 wt % adiponitrile. Impurities that may be present depend on the method of manufacture, and thus, vary depending on the source. 

The ease with which the separated products leave the bowl determines the richness of the fat. Fluid whole milk enters the separator under pressure from a positive displacement pump or centrifugal pump with flow control (Fig. 1). The fat (cream) is separated and moves toward the center of the bowl, while the skimmed milk passes to the outer space. There are two spouts or oudets, one for cream and one for skimmed milk. Cream leaves the center of the bowl with the percentage of fat ( 30 40%) controlled by the adjustment of a valve, called a cream or skim milk screw, that controls the flow of the product leaving the field of centrifugal force and thus affects the separation. 

Positive Pumps. Positive pumps employed by the food industry have a rotating cavity between two lobes, two gears that rotate in opposite directions, or a crescent or stationary cavity and a rotor. Rotary positive pumps operate at relatively low speed. Fluid enters the cavity by gravity flow or from a centrifugal pump. The positive pump also may use a reciprocating cavity, and may be a plunger or piston pump. These pumps are not truly positive with respect to displacement, but are used for metering product flow. 

Positive Displacement Pumps. Positive displacement pumps foUow HI convention (see Fig. 1). As a rule, these pumps work against significantly higher pressures and lower flows than do kinetic, particularly centrifugal, pumps. Positive displacement pumps also operate at lower rotational speeds. There are many types of positive displacement pumps, for which designs are constantly being developed. Some of these are discussed herein. 

Selection of pump for a given appHcation is not a trivial task. Often more than one pump type can accomplish the required job. Thus a final choice on a pump type is often a result of personal experience and usage history. As a rule of thumb, the choice of a kinetic, such as centrifugal, or a positive displacement pump is made on the basis of the specific speed. Whereas specific speed is appHcable primarily for centrifugal but not positive displacement pumps, the US value can be used as a guide. Generally, for calculated values of specific speed, eg, nS > 10 [NS > 500), kinetic-type pumps are usually selected. For nS < 10 [NS < 500), positive displacement pumps are typically appHed. 

For instaUations in which suspended sohds must be handled with a minimum of solids breakage or degradation, such as pumps feeding filter presses, special attention is required either a low-shear positive-displacement pump or a recessed-impeller centrifugal pump may be called for. 

Whereas the total dynamic head developed by a centrifugal, mixed-flow, or axial-flow pump is uniquely determined for any given flow by the speed at whicdi it rotates, positive-displacement pumps and those which approach positive displacement will ideally produce whatever head is impressed upon them by the system restrictions to flow. Actually with slippage neglecTed, the maximum head attainable is determined by the power available in the drive and the strength of the pump parts. An automatic relief valve set to open at a safe pressure... 

In general, overall efficiencies of positive-displacement pumps are higher than those of centrifugal equipment because internal losses are minimized. On the other hand, the flexibihty of each piece of eqmp-ment in handling a wide range of capacities is somewhat limited. 

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