Page 174 - Chemical Process Equipment - Selection and Design

146 FLUID TRANSPORT EQUIPMENT

212
200
180

160
Lz
6
14C
ci
2 120
E
XI00
E
i-"
80
60
40
&-Suction Head-Ft-+-- -- - -- - Suction Lift- Ft -- - --- - ----*
(a)

Capacity. gpm
(b)
Figure 7.15-(continued) TEMPERATURE,'F
(b)
the nature of the gas and the temperature, as indicated on Figure Figure 7.16. Recommended values of net positive suction head
7.26. Maximum compression ratios of 3-4.5 per stage with a (NPSH) at various temperatures or vapor pressures: (a) NPSH of
maximum of 8-12 per machine are commonly used. Discharge several types of pumps for handling water at various temperatures.
pressures as high as 3000-5000 psia can be developed by centrifugal (b) Correction of the cold water NPSH for vapor pressure. The
compressors. maximum recommended correction is one-half of the cold water
A specification form is included in Appendix B and as Table value. The line with arrows shows that for a liquid with 30psia
4.4. Efficiency data are discussed in Section 7.6, Theory and vapor pressure at 100°F, the reduction in NPSH is 2.3ft (data of
Calculations of Gas Compression: Efficiency. Worthington International Inc. ).
AXIAL FLOW COMPRESSORS
specific speeds of axial compressors are in the range of 1000-3000
Figure 7.18(b) shows the axial flow compressor to possess a large or so.
number of blades attached to a rotating drum with stationary but Efficiencies are 8-10% higher than those of comparable cen-
adjustable blades mounted on the case. Typical operating trifugal compressors.
characteristics are shown on Figure 7.22(a). These machines are
suited particularly to large gas flow rates at maximum discharge RECIPROCATING COMPRESSORS
pressures of 80-130 psia. Compression ratios commonly are 1.2-1.5
per stage and 5-6.5 per machine. Other details of range of Reciprocating compressors are relatively low flow rate, high
applications are stated on Figure 7.20. According to Figure 7.21, pressure machines. Pressures as high as 35,000-50,OO0 psi are