Pumping requirements

Friction Coefficient. In the design of a heat exchanger, the pumping requirement is an important consideration. For a fully developed laminar flow, the pressure drop inside a tube is inversely proportional to the fourth power of the inside tube diameter. For a turbulent flow, the pressure drop is inversely proportional to D where n Hes between 4.8 and 5. In general, the internal tube diameter, plays the most important role in the deterrnination of the pumping requirement. It can be calculated using the Darcy friction coefficient,, defined as... 

Correlations for Convective Heat Transfer. In the design or sizing of a heat exchanger, the heat-transfer coefficients on the inner and outer walls of the tube and the friction coefficient in the tube must be calculated. Summaries of the various correlations for convective heat-transfer coefficients for internal and external flows are given in Tables 3 and 4, respectively, in terms of the Nusselt number. In addition, the friction coefficient is given for the deterrnination of the pumping requirement. 

Ideally, a process plant should be examined for its total energy consumption (see Energy management). Other plant energy systems are under consideration (18) and should eventually be included in this type of analysis. This would include not only process thermal energy and shaft energy, but pumping requirements and electrical power as well. 

Example 1 NPSH Calculation Suppose a selected pump requires a minimum NPSH of 16 ft (4.9 m) when pumping cold water What will he the NPSH limitation to pump propane at 55 F (12.8 C) with a vapor pressure of 100 psi Using the chart in Fig. 10-25, NPSH reduction for propane gives 9.5 ft (2.9 m). This is greater than one-half of cold water NPSH of 16 ft (4.9 m). The corrected NPSH is therefore 8 ft (2.2 m) or one-half of cold water NPSH. 

Pnettmatically Actuated Diaphragm Pumps (Fig. 10-53) These pumps require no power source other than plant compressed air. They must have a flooded suction, and the pressure is, of course, limited to the available air pressure. Because of their slow speed and large valves, they are well suited to the gentle handling of liquids for which degradation of suspended solids should be avoided. 

AOC provide the additional advantages of reducing ground-space requirements and piping and pumping requirements and of providing smoother column operation. 

The major difficulty with these reactors is in the outside recycle pump, especially at high temperatures. Reciprocating pumps require seal rings, and these cannot take the high temperature needed for most reactions. If the recycle gas is cooled down before entering the compressor, it must be reheated before it enters the reactor again. This makes them complicated in construction and excessive in cost. 

NPSH is the pressure available at the pump suction nozzle after vapor pressure is subtracted. It is expressed in terms of liquid head. It thus reflects the amount of head loss that the pump can sustain internally before the vapor pressure is reached. The manufacturer will specify the NPSH that his pump requires for the operating range of flows when handling water. This same NPSH is normally used for other liquids. 

Pumps. Specify the type and number of pumps required. Minimum is two full-size pumps. 

Two vacuum systems are used to provide both the high vacuum needed for the mass spectrometer and the differential pumping required for the interface region. Rotary pumps are used for the interface region. The high vacuum is obtained using diffusion pumps, cryogenic pumps, or turbo pumps. 

Table 10.18(c) Direct-indicating Drager diffusion tubes - no pump required... 

For any pump requiring a PR valve for its protection or for protection of downstream equipment, the PR valve set pressure should be higher than the normal pump discharge pressure by 170 kPa or 10% of the set pressure, whichever is greater. Note, however, that in some cases a higher PR valve set pressure may be desirable to assure a sufficient differential when the pump is to... 

These characteristics combine to yield a system that has low heat and pumping requirements, is relatively noncorrosive, and suffers only minimal solvent losses (less than 1 Ib/MMscf). 

More than any other item of equipment, pumps require maintenance while the rest of the plant is on line. Many incidents have occurred because pumps under repair were not properly isolated from the running plant. See Section 1.1. 

There are two major factors that impact the COP temperature difference and system component efficiency. A heat pump requires energy to move heat from a lower temperature to a higher one. As the difference in the two temperatures increases, more energy is required. The COP of a heat pump is high-... 

Figure 11-5. Surface-type condenser, steam jets with three boosters. (Used by permission Ingersoll-Rand Company.) tBased on required N.P.S.H. of pump. May be reduced by pump pit or by pump requiring less N.P.S.H.

These pumps require the maintenance of very close clearances between rubbing surfaces for continual volumetric efficiency. Some of the important pumps are discussed. 

Centrifugal pumps require a rigid foundation that prevents torsional or linear movement of the pump and its baseplate. In most cases, this type of pump is mounted on a concrete pad or pedestal having enough mass to securely support the baseplate, pump and its driver. The following general mles apply to foundation design. 

Birk,J. R. andj. H. Peacock, Pump Requirements for the Chemical Process Industries, Chem. Engineering Feb. 18,1974, p. 117. 

All LC pumps require the use of a non-return valve and so the function of non-retum valves will now be described. 

Initial tests of Brownian pumping required the measurement of Th in colloids separated from seawater samples. " Th proved to be an especially useful tracer of colloidal uptake of metal species because of its constant source and relative abundance. Baskaran et al. (1992) and Moran and Buesseler (1992) used cross-flow filtration to separate the colloidal fraction and both studies reported significant (up to 78% of total) " Th in this fraction. Subsequent work largely supported these observations (Moran and Buesseler 1993 Huh and Prahl 1995) and suggested the importance of colloidal organic matter in scavenging Th (Niven et al. 1995). 

At this point it is worth considering the demands made on the instrumentation for operation with wide bore columns and, in particular, the adaptation of analytical Instruments for this purpose [596,597]. The pump requirements for preparative separations differ from those in analytical HPLC as the ability to generate high flow rates at moderate backpressures is crucial to the efficient operation of wide bore columns. A flow rate maximum of 100 ml/min with a pressure limit of 3000 p.s.i. is considered... 

The chart shown in Figure 5.6 can be used to determine the type of pump required for a particular head and flow rate. This figure is based on one published by Doolin (1977). 

Calculate the line size and specify the pump required for the line shown in Figure 5.15 material ortho-dichlorobenzene (ODCB), flow-rate 10,000 kg/h, temperature 20°C, pipe material carbon steel. 

---