Gas Movers and Compressors

• Fans

• Centrifugal blowers and compressors

• Rotary blowers and compressors

• Reciprocating compressors

• Ejectors

• Discharge pressure > 2 bara = compressor

Gas Movers and Compressors

• Where are they needed?

Gas Movers and Compressors

• Where are they needed?– utility air, steam– high pressure reactor;– refrigeration– heat pumps– feed to furnaces

• Question: When is redundancy necessary?

Fans

• Low pressure (ca 101 kPa) and low P (1-15 kPa)

• High volume flow to 500 std m3/s

• Efficiencies of 65-80%• Variety of materials• Four types

Centrifugal Fan

Centrifugal Compressors

• Pressure to 700 atm, 1.2-1.4 compression ratio/stage

• Up to 8 stages per casing

• Volume flow to 200 std m3/s

• Efficiencies of 70-80%

• Favored choice for P < 15 atm

What is the compression ratio?

Outlet pressure/inlet pressure

Axial Compressors• Pressures to 14 atm• Compression ratio 1.4

per stage, up to 15 stages/casing

• High volume flow to 300 std m3/s

• Efficiencies of 80-85%• Expensive, inflexible

operation• Base loads, utilities

Rotary Compressors• Medium pressure (to 10

atm) and compression ratio to 4!

• Low volume flow to 20 std m3/s

• Efficiencies of 60-80%• Good for constant volume

delivery• Four types listed in UlrichSliding vane compressor

Reciprocating Compressors

• Pressure to 3000 atm, compression ratio=4/stage

• Up to 8 stages per casing

• Efficiencies of 60-80%

• Expensive, but commonly used for high-pressure applications

All of this information is summarized in one table:consider the first half in detail

Radial Fans Axial Fans CentrifugalCompressors

Summary:Selection of Equipment

• Fans are for low P (101 kPa), low P (1-15 kPa)

• Blowers (centrifugal and rotary) are for moderate pressures, up to 1 MPa

• Compressors operate at 0.01 to 30 MPa depending on type

• Turbo-expanders are like compressors running in reverse for power recovery

Summary: Selection

• Select based on:– range of application– location– cost– service

Costing of Fans and Compressors

• What is the size basis?

For fans, the volumetric flow: P is low

For compressors, power or shaft work: must be considered

Fans

Blo

wer

s an

d C

omp

ress

ors

Mot

ors

Compressor Calculations

/

w m vdp

w w

fp

p

s f i

1

2

Fluid Powerfor costing

Shaft Powerfor driver

Non-ideal fluids:

m

whh

ww

hhmw

sSinTexit

iconstSfs

SinSexitconstSf

in

inin

,,

,

,,,

/

)(

Compressor Calculations (cont)

Ideal Gas:

vp

kk

f

CCk

p

p

kM

kRTmw

/

1)1(

//)1(

1

21

Temperature increases with compression compression ratio p2/p1 < 4 for each stage

Example Compressor

• Hydrogen compressor, from 1 MPa at 25 C to 20 MPa

• Flow rate of 0.123 kg/s

• What is the bare module cost?