High-pressure centrifugal pumps

Figure 3-8. Refinery oil and boiler feed high pressure centrifugal pump. Courtesy Delaval Steam Turbine Co., currently Transamerica Delaval, Inc.)...

Fig. 4.1-23. Performance diagram of an eight-stage high-pressure centrifugal pump (adopted from KSB)...

The shaft-seal development for high-pressure centrifugal pumps is quite similar to that explained for compressors. The traditional mechanical seals lubricated by liquids are now being partly replaced, for obvious reasons, by gas-lubricated ones. 

Continuous Starch Hydrolysis. A commercial continuous converter installation for dextrose manufacture employing a continuous, automatically controlled step for the hydrolysis of starch is now in operation. A flow diagram of a modem commercial installation for continuous starch hydrolysis is shown in Fig. 13-4. The starch converter consists of an 8-in. coil, 677 ft long, which is fed by a high-pressure centrifugal pump from a continuous starch make-up tank equipped for automatic control of density (Baumd), level, and acidity. The level controller regulates the addition of 20 B starch suspension, the Baum controller operates the water valve, and a conductivity instrument controls the addition of acid. The head end of the converter coil has an entry chamber to separate non-condensables, and the feed is instantaneously heated with live steam through a jet heater. 

Recycle stream high pressure liquid pump, mainly 3-headed HPLC membrane pumps are used, or high-pressure centrifuge pumps in large industrial systems. 

In principle magnetic drives could be used with high pressure centrifugal pumps, but as the can between the magnet-coupling rotors has to carry the whole pressure differential it needs to be too thick for this technique to be fully effective this solution is not at all promising. 

High-Pressure Centrifugal Pumps and High-Pressure Turhotxmpressors 317... 

Figure 13.4 High-pressure centrifugal pump for a differential pressure of about 2 MPa and a system pressure of about 30 MPa. A inlet B outlet C pressure loading channel...

The urea solution leaving the stripper bottom contains about 12 wt% of NH and is further purified in the 1.8 MPa (18 bar) and 0.2 MPa (2 bar) recovery sections of the plant. The resultant NH and CO2 separated in the decomposers is absorbed and returned to the synthesis section by the high pressure centrifugal carbamate pump. 

Reverse Osmosis. Membranes are used for the separation of smaller components (<500 daltons). They have smaller pore space and are tighter than those used for ultrafiltration. High pressure pumps, usually of the positive piston or multistage centrifugal type, provide pressures up to 4.14 MPa (600 psi). 

From the definition of specific speed (eqs. 9 and 10), it follows that reciprocating pumps operate at high pressures and low flow rates. Conversely, centrifugal pumps are appHed at lower pressures and higher flow rates. Many rotary pumps are selected for viscous Hquids having pressures equal to or less than, and capacities lower than, centrifugal pumps. However, these limits are relative and a gray area exists as some pump types cross boundaries into the domain of other types. 

These pumps are particularly useful when low volumes of low-viscosity liquids must be handled at higher pressures than are normally available with centrifugal pumps. Close clearances limit their use to clean liquids. For veiy high heads, multistage units are available. 

Centrifugal blowers or turbines usually cannot generate enough pressure difference to overcome the added resistance of the recycle pipes. In addition, some components may condense out in the cooler, especially with high-boiling materials or at high pressures. These must be recycled by a liquid pump through an evaporator. This in turn makes them approach a steady-state slowly. ... 

The most reliable recycle reactors are those with a centrifugal pump, a fixed bed of catalyst, and a well-defined and forced flow path through the catalyst bed. Some of those shown on the two bottom rows in Jankowski s papers are of this type. From these, large diameter and/or high speed blowers are needed to generate high pressure increase and only small gaps can be tolerated between catalyst basket and blower, to minimize internal back flow. 

In the left upper corner of Figure 3.4.1, the centrifugal pump performance is shown. As ean be seen, the head generated depends on RPM but is independent of the flow, within a 10 % error, up to a eertain limit. The pressure staits to deeline when that point is reaehed at whieh the flow is high enough that the pump itself limits the flow beeause of its eross-section. 

Volume 1 explains that pumps ean be classified as either positive-displacement or kinetie. The same is true for compressors. In a positive displacement compressor the gas is transported from low pressure to high pressure in a device that reduces its volume and thus inereases its pressure. The most common type of positive displacement eompressors are reeiprocating and rotary (serew or vane) just as was the ease for pumps. Kinetic compressors impart a veloeity head to the gas, which is then converted to a pressure head in accordance with Bernoulli s Law as the gas is slowed down to the velocity in the discharge line. Just as was the case with pumps, centrifugal compressors are the only form of kinetic compressor commonly used. 

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