Refrig Course

5/27/2018 Refrig Course

1/112

Gas Plant Refrigeration

Nev Hircock

Process Consulting Ltd.

Mollier

P- H Charts


2/112

MollierPH

Charts

Gas Plant

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2

Gas Chiller

Gas In

Gas Out

Glycol Injection

Propane In Deoiler


3/112

MollierPH

Charts

Gas Plant

Refrigeratio

l

3

Compressor Scrubber

Note temperaturedifferential


4/112

MollierPH

Charts

Gas Plant

Refrigeratio

l

4

Compressor

Oil separator Inlet Discharge


5/112

MollierPH

Charts

Gas Plant

Refrigeratio

l

5

Compressor Panel

Suction, Discharge and

Oil pressures

Status on two

Parallel machines


6/112

MollierPH

Charts

Gas Plant

Refrigeratio

l

6

Condenser

Two x 7 diameter fans Manual top louvres


7/112

MollierPH

Charts

Gas Plant

Refrigeratio

l

7

Gas/Gas Exchanger

Inlet

Outlet

Glycol

injection

Cold

insulation


8/112

MollierPH

Charts

Gas Plant

Refrigeratio

l

8

Simple Refrigeration Circuit

CompressorCondenser

Acc.Chiller

F.V.

Gas In

Gas Out

LiquidOut


9/112

MollierPH

Charts

Gas Plant

Refrigeratio

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9

The Mollier or P H Chart

Pressure-

psia

Enthalpy - BTU/lb

-1000 -900 -800 -700 -600 -500

1000

500

100

50

10

Gas

Two Phase

Liquid

10060

20-20

-40Critical Point

Dense Phase


10/112

MollierPH

Charts

Gas Plant

Refrigeratio

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10

The Mollier Chart Density Lines

Pressure-

psia

Enthalpy - BTU/lb

-1000 -900 -800 -700 -600 -500

1000

500

100

50

10

Gas

Two Phase

Liquid

10060

20-20

-400.2

1.0

3.0

6.0

0.1

0.03


11/112

MollierPH

Charts

Gas Plant

Refrigeratio

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11

The Mollier Chart Entropy Lines

Pressure-

psia

Enthalpy - BTU/lb

-1000 -900 -800 -700 -600 -500

1000

500

100

50

10

10060

20-20

-400.2

1.0

3.0

6.0

0.03

0.1


12/112

MollierPH

Charts

Gas Plant

Refrigeratio

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12

The Mollier Chart Processes

Heat Loss at Constant Pressure

Pressure-

psia

Enthalpy - BTU/lb

-1000 -900 -800 -700 -600 -500

1000

500200

100

50

20

10

10060

20-20

-40

120

Gas

Two Phase

Liquid

Diff.= 160

Condenser


13/112

MollierPH

Charts

Gas Plant

Refrigeratio

l

13

Propane Condenser

CompressorCondenser

Acc.Chiller

F.V.


14/112

MollierPH

Charts

Gas Plant

Refrigeratio

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14


Heat Gain at Constant Pressure

Pressure-

psia

Enthalpy - BTU/lb

-1000 -900 -800 -700 -600 -500

1000

500200

100

50

20

10

10060

20-20

-40

120

Gas

Two Phase

Liquid

Diff.= 130

Chiller


15/112

MollierPH

Charts

Gas Plant

Refrigeratio

l

15

Gas Chiller

CompressorCondenser

Acc.Chiller

F.V.

Gas In

Gas Out

LiquidOut


16/112

MollierPH

Charts

Gas Plant

Refrigeratio

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16

The Mollier Chart Heat Loss & Gain

at Constant Volume

Pressure-

psia

Enthalpy - BTU/lb

-1000 -900 -800 -700 -600 -500

1000

500

100

50

10

Gas

Two Phase

Liquid

10060

20-20

-400.2

1.0

3.0

6.0

0.1

0.03


17/112

Mollier

PH

Charts

Gas Plant

Refrigeratio

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17

Accumulator

CompressorCondenser

Acc.Chiller

F.V.

Gas In

Gas Out

LiquidOut


18/112

Mollier

PH

Charts

Gas Plant

Refrigeratio

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18


Throttling or Flashing

Pressure-

psia

Enthalpy - BTU/lb

-1000 -900 -800 -700 -600 -500

1000

500200

100

50

20

10

10060

20-20

-40

120

Gas

Two Phase

Liquid


19/112

Mollier

PH

Charts

Gas Plant

Refrigeratio

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19

Flash Valve

CompressorCondenser

Acc.Chiller

F.V.

Gas In

Gas Out

LiquidOut


20/112

Mollier

PH

Charts

Gas Plant

Refrigeratio

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20

Ideal Compression Process

Pressure-

psia

Enthalpy - BTU/lb

-1000 -900 -800 -700 -600 -500

1000

500

100

50

10

10060

20-20

-400.2

1.0

3.0

6.0

0.03 0.1

40

180 200


21/112

Mollier

PH

Charts

Gas Plant

Refrigeratio

l

21

Real Compression Process

Pressure-

psia

Enthalpy - BTU/lb

-1000 -900 -800 -700 -600 -500

1000

500

100

50

10

10060

20-20

-400.2

1.0

3.0

6.0

0.03 0.1

60

180 200Effcy=40/60 = 67%


22/112

Mollier

PH

Charts

Gas Plant

Refrigeratio

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22

Compressor

CompressorCondenser

Acc.Chiller

F.V.

Gas In

Gas Out

LiquidOut


23/112

Mollier

PH

Charts

Gas Plant

Refrigeratio

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23

Ideal Expansion Process

Pressure-

psia

Enthalpy - BTU/lb

-1000 -900 -800 -700 -600 -500

1000

500

100

50

10

10060

20-20

-400.2

1.0

3.0

6.0

0.03 0.1

40

180 200


24/112

Mollier

PH

Charts

Gas Plant

Refrigeratio

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24

Simple Refrigeration Circuit

CompressorCondenser

Acc.Chiller

F.V.

Gas In

Gas Out

LiquidOut


25/112

Mollier

PH

Charts

Gas Plant

Refrigeratio

l

25

Simple Refrigeration Process

Pressure-

psia

Enthalpy - BTU/lb

-1000 -900 -800 -700 -600 -500

1000

500

100

50

10

10060

20-20

-40

180 200

Ch

Com

Cond

Fl


26/112

Mollier

PH

Charts

Gas Plant

Refrigeratio

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26

Mixing Process

Pressure-

psia

Enthalpy - BTU/lb

-1000 -900 -800 -700 -600 -500

1000

500

100

50

10

10060

20-20

-40

180 200

A C B

2 lbs at A +

1 lb at B mix

At C in ratio

AC/CB = 1/2


27/112

Mollier

PH

Charts

Gas Plant

Refrigeratio

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27

Compound Refrigeration Circuit

Condenser

Acc.Chiller

F.V.

Gas In

Gas Out

LiquidOut

Compressor

Stg. 2/Stg. 1

F.V.

Econ.

2000

lb/hr

1000

lb/hr

3000

lb/hr


28/112

Mollier

PH

Charts

Gas Plant

Refrigeratio

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28

Compound Refrigeration Process

Pressure-

psia

Enthalpy - BTU/lb

-1000 -900 -800 -700 -600 -500

1000

500

100

50

10

10060

20-20

-40

180 200

Ch

Com 2

Cond

Fl 1

Fl 2 Com 1


29/112

Mollier

PH

Charts

Gas Plant

Refrigeratio

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29

Summary of Processes on Mollier

Review of Processes on Mollier Chart

Heat loss or gain at constant pressure:

Move left or right.

Compression: Move up at const entropy.

Flashing: Move down at constant

enthalpy.


30/112

Mollier

PH

Charts

Gas Plant

Refrigeratio

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30

Refrigeration Circuit Design with P-H

CompressorCondenser

Acc.Chiller

F.V.

Gas In =

44.5 MM/d =4868 lbm/hr @

32F

Gas Out

3894 lbm/hr

@ -22F

Liquid Out

974 lbm/hr

St 1 Chill H t L d


31/112

Mollier

PH

Charts

Gas Plant

Refrigeratio

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31

Step 1: Chiller Heat Load

Use GPSA Charts or Hysim to establishthat Chiller Heat Load is: 6.5 mmbtu/hr


32/112

Mollier

PH

Charts

Gas Plant

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32

Step 2: Chiller Temp and Pressure

Chiller Propane (shell side) temperaturemust be LESS than 22F target gas

temperature.

Use arbitrary 9F approach and establish

Propane side temp at

31F.

Using P-H chart, this fixes the C3

pressure at 20 psia.


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PH

Charts

Gas Plant

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33

Refrigeration Circuit Design Chiller

CompressorCondenser

Acc.Chiller

F.V.

Gas In =

44.5 MM/d =4868 lbm/hr @

32F

Gas Out

3894 lbm/hr

@ -22F

Liquid Out

974 lbm/hr

6.5 mmbtu/h

-31F & 20psia


34/112

Mollier

P

H

Charts

Gas Plant

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34

Step 3: Condenser Temp and Pressure

Condenser Propane temperature must beGREATER than 95F ambient temperature.

Use arbitrary 27F approach and establish

Propane side temp at 122F.

Using P-H chart, this fixes the C3

pressure at 240 psia.

R f i ti Ci it D i


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Mollier

P

H

Charts

Gas Plant

Refrigeratio

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35

Refrigeration Circuit Design

Condenser

CompressorCondenser

Acc.Chiller

F.V.

Gas In =

44.5 MM/d =4868 lbm/hr @

32F

Gas Out

3894 lbm/hr

@ -22F

Liquid Out

974 lbm/hr

6.5 mmbtu/h

-31F & 20psia

122F & 240psia

245 psia


36/112

Mollier

P

H

Charts

Gas Plant

Refrigeratio

l

36

Step 4: Compressor Pressures

Compressor must take suction fromChiller pressure of 20 psia less 1.5 DP =

18.5 psia.

Compressor must discharge at condenser

pressure plus 5 DP = 245 psia.

l


37/112

Mollier

P

H

Charts

Gas Plant

Refrigeratio

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37

The Mollier Chart System Design

Pressure

-psia

Enthalpy - BTU/lb

-1000 -900 -800 -700 -600 -500

1000

500

100

50

10

10060

20-20

-40

245

18.5Chill

Cond

G Pl


38/112

Mollier

P

H

Charts

Gas Plant

Refrigeratio

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38

The Mollier Chart Flash Valve

Pressure

-psia

Enthalpy - BTU/lb

-1000 -900 -800 -700 -600 -500

1000

500

100

50

10

10060

20-20

-40

245

18.5Chill

Cond

F.V

G Pl


39/112

Mollier

P

H

Charts

Gas Plant

Refrigeratio

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39

The Mollier Chart Compressor

Pressure

-psia

Enthalpy - BTU/lb

-1000 -900 -800 -700 -600 -500

1000

500

100

50

10

10060

20-20

-40

245

18.5Chill

Cond

F.VComp

781 694640

G Pl


40/112

Mollier

P

H

Charts

Gas Plant

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40

Step 5: Compressor Energies

Compressor must take suction from 18.5psia and energy 694 BTU/lb to 245 psia

and energy 640 BTU/lb for an energy

input of 54 BTU/lb.

G Pl t


41/112

Mollier

P

H

Charts

Gas Plant

Refrigeratio

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41

Step 6: Chiller Energies

Chiller energy increases from

781BTU/lb to energy level 694 BTU/lb for an

energy input of 87 BTU/lb.

Therefore to release the necessary

6,500,000 BTU/hr, Propane flow throughChiller must = 6,500,000/87 = 75000 lb/hr.

Note: BTU___________

Hr

LB___________

BTU = LB/Hrx

G Pl t


42/112

Mollier

P

H

Charts

Gas Plant

Refrigeratio

l

42

The Mollier Chart C3 Flow Rate

Pressure

-psia

Enthalpy - BTU/lb

-1000 -900 -800 -700 -600 -500

1000

500

100

50

10

10060

20-20

-40

245

18.5Chill

Cond

F.VComp

781 694640

87

54

C3Rate = 6500000/87 = 75000 lb/hr

G Pl t


43/112

Mollier

P

H

Charts

Gas Plant

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43

Step 7: Compressor Power

Compressor energy input of 54 BTU/lb x C3 flow

rate of 75000 lb/hr gives total compressor power

of:

75000 x 54 = 4,050,000 BTU/hr.

Using the equivalent that :

2545 BTU/hr = 1 HP.

Compressor power = 4,050,000/2545 or: 1591 hp.

Using 80% Comp. Eff. = 1591/0.8

= 1990 hp. Required.

G Pl t


44/112

Mollier

P

H

Charts

Gas Plant

Refrigeratio

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44

The Mollier Chart Real Compressor

Pressure

-psia

Enthalpy - BTU/lb

-1000 -900 -800 -700 -600 -500

1000

500

100

50

10

10060

20-20

-40

245

18.5Chill

Cond

F.VComp

781 694640

87

54

C3Rate = 6500000/87 = 75000 lb/hr

626

68

Comp REAL Energy Rise

= 54/0.8 = 68 Btu/lb.Comp REAL exit Energy = 626

Gas Plant


45/112

Mollier

P

H

Charts

Gas Plant

Refrigeratio

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45

The Mollier Chart Real Condenser

Pressure

-psia

Enthalpy - BTU/lb

-1000 -900 -800 -700 -600 -500

1000

500

100

50

10

10060

20-20

-40

245

18.5Chill

Cond

F.VComp

781 694640

87

54

C3Rate = 6500000/87 = 75000 lb/hr

626

68

Cond REAL Energy Drop

= 781 - 626 = 155 Btu/lb.

Gas Plant


46/112

Mollier

P

H

Charts

Gas Plant

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46

Power Reducing Modifications

Subcoolers and Economisers.

Both increase the energy available at the

Chiller.

They can reduce power required by 15 to25% dependent on Chiller temperature

level.

These systems are more effective insummer than winter.

Gas Plant

Refrigeration Circuit +


47/112

Mollier

P

H

Charts

Gas Plant

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47


Internal Subcooler

CompressorCondenser

Acc.Chiller

F.V.

Gas In

Gas Out

LiquidOut

30F

-20F

120F

70F

Gas Plant

Refrigeration Process +


48/112

Mollier

P

H

Charts

Gas Plant

Refrigeratio

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48


Internal Subcool

Pressure

-psia

Enthalpy - BTU/lb

-1000 -900 -800 -700 -600 -500

1000

500

100

50

10

10060

20-20

-40

180200

Ch

Com

Cond

Fl

Extra energy

Gas Plant



49/112

Mollier

P

H

Charts

Gas Plant

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l

49


External Subcooler

CompressorCondenser

Acc.

Gas In

Chiller

F.V.To G/G Ex.

LTS

To DeC2

-10F

70F

120F

40F

Gas Plant



50/112

Mollier

P

H

Charts

Gas Plant

Refrigeratio

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50


External Subcool

Pressure

-psia

Enthalpy - BTU/lb

-1000 -900 -800 -700 -600 -500

1000

500

100

50

10

1006020

-20-40

180200

Ch

Com

Cond

Fl

Extra energy

Gas Plant


51/112

Mollier

P

H

Charts

Gas Plant

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51

Economiser and 2 Stage Refrigeration

Condenser

Acc.Chiller

F.V.

Gas In

Gas Out

LiquidOut

Compressor

Stg. 2/Stg. 1

F.V.

Econ.

2000

lb/hr

1000

lb/hr

3000

lb/hr

Gas Plant


52/112

Mollier

P

H

Charts

Gas Plant

Refrigeratio

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52

Compound Refrigeration Process

Pressure

-psia

Enthalpy - BTU/lb

-1000 -900 -800 -700 -600 -500

1000

500

100

50

10

1006020

-20-40

180200

Ch

Com 2

Cond

Fl 1

Fl 2 Com 1

Gas Plant

Troubleshooting: 1 Fouled


53/112

Mollier

P

H

Charts

Gas Plant

Refrigeratio

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53


Condenser

Condenser

170F C3 Vapour

120F C3 Liq.

100F C3 Liq.

90F Air

A clean Condenser may work to a 10F approach to ambient,

i.e a C3 liquid exit temperature of 100F when ambient is 90F.

However fouling may cause the required approach to increase to

30F above ambient. The Condenser now produces C3 liquid at120F to compensate for the fouling. The C3 pressure will increase.

Gas Plant

T bl h i F l d C d



54/112

Mollier

P

H

Charts

Gas Plant

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54

Trouble-shooting: Fouled CondenserTroubleshooting: 1 Fouled

Condenser

Pressure

-psia

Enthalpy - BTU/lb

-1000 -900 -800 -700 -600 -500

1000

500

100

50

10

1006020

-20-40

180200

Ch

Com

OK Cond

Fl

Fouled C.

Reduced Chiller

Energy

Gas Plant

Troubleshooting: 2


55/112

Mollier

P

H

Charts

Gas Plant

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55

Troubleshooting: 2

Air Starved Condenser

Condenser

170F C3 Vapour

120F C3 Liq.

100F C3 Liq.

90F Air

A clean Condenser may work to a 10F approach to ambient,

i.e a C3 liquid exit temperature of 100F when ambient is 90F.

However air starvation may cause the required approach to

increase to 30F above ambient. The Condenser now producesC3 liquid at 120F to compensate for the air shortage. The C3

pressure will increase.

The way to distinguish between a fouled versus an air-starved

condenser, is to measure the air temperature RISE across the

condenser. It will be HIGH in the case of air starvation.

110F Air120F Air

Gas Plant

Trouble-shooting: 2 - Starved


56/112

Mollier

P

H

Charts

Gas Plant

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56

Trouble shooting: 2 Starved

Condenser

Pressure

-psia

Enthalpy - BTU/lb

-1000 -900 -800 -700 -600 -500

1000

500

100

50

10

1006020

-20-40

180200

Ch

Com

OK Cond

Fl

Starved C.

Reduced Chiller

Energy

Gas Plant

Troubleshooting: 3 Compressor


57/112

Mollier

P

H

Charts

Gas Plant

Refrigeratio

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57


Capacity Loss

Chiller

CompressorCondenser

Acc.

F.V.

The compressor

suction pressure

governs the chillershell side pressure

and temperature.

Gas Plant



58/112

Mollier

P

H

Charts

Gas Plant

Refrigeratio

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58

2001006020

-20


Capacity Loss

2001006020

-201000

500

100

50

10

Ps

When the compressor loses capacity, the suction pressure, Ps, rises.

As a result the chiller pressure and temperature also rise.

Gas Plant



59/112

Mollier

P

H

Charts

Gas Plant

Refrigeratio

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59

oub es oot g Co p esso

Valve Leakage

Chiller

CompressorCondenser

Acc.

F.V.

Gas Plant



60/112

Mollier

P

H

Charts

Gas Plant

Refrigeratio

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60

g p

Valve Leakage

2001006020

-20

2001006020

-201000

500

100

50

10

B1

When a compressor valve leaks, point B moves to the right; the compressor

discharge gets hotter and this overloads the condenser thermally.

B

AC

A1

Gas Plant

T bl h ti 5 Chill F li


61/112

Mollier

P

H

Charts

Refrigeratio

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61

Troubleshooting: 5 Chiller Fouling

Chiller

CompressorCondenser

Acc.

F.V.

0

100

30

15

Under design conditions,LMTD = 18.2 deg. Under fouled conditions,LMTD = 21.6 deg.

Gas Plant

Troubleshooting: 6 Refrigerant


62/112

Mollier

P

H

Charts

Refrigeratio

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62

g g

Impurities

Chiller

CompressorCondenser

Acc.

F.V.

0

5

The first indication of refrigerant impurities

may be a temperature rise across the Chiller

although this can also also indicate lowChiller level.

Gas Plant

Troubleshooting: 6 Refrigerant


63/112

Mollier

P

H

Charts

Refrigeratio

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63

2001006020

-20

g g

Impurities

1000

500

100

50

10

A

B

Points A and B will be on the vapour/liquid curve if the refrigerant is pure.

Gas Plant

Troubleshooting: 7 Gas/Gas


64/112

Mollier

P

H

Charts

Refrigeratio

l

64

This typical dewpoint plant comprises a

Gas exchanger of 5 mmbtu/hr which is 2.5x

larger than the chiller. Therefore every 10%thermal deficiency in the gas exchanger needs

a 25% excess performance by the Chiller.

g

Exchanger Faults

120

0

0

30

100

Chiller

CompressorCondenser

Acc.

F.V.

LTS

Gas/Gas

300 hp5 mmbtu/hr

2 mmbtu/hr

Gas Plant

Simple DewPoint Plant: Design


65/112

Mollier

P

H

Charts

Refrigeratio

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65

Simple DewPoint Plant: Design

Chiller

CompressorCondenser

Acc.

F.V.

Gas/Gas

LTS

Design:Legend: Temperatures:

Pressures:

XX

XX

0

25

120

160

0-10

105

-10120

90

225

10

220

Air

Dewpt = 0F

Gas Plant

Simple DewPoint Plant; Fault 1


66/112

Mollier

P

H

Charts

Refrigeratio

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66

Simple DewPoint Plant; Fault 1

Chiller

CompressorCondenser

Acc.

F.V.

Gas/Gas

LTS


Pressures:

XX

XX

10

35

120

175

10-10

105

-10125

90

235

10

230

Air

Dewpt = +10F

Compressor

Valve Leak

Gas Plant

Simple DewPoint Plant: Fault 2


67/112

Mollier

P

H

Charts

Refrigeratio

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67


Chiller

CompressorCondenser

Acc.

F.V.

Gas/Gas

LTS


Pressures:

XX

XX

10

35

120

160

10-10

105

-10125

90

235

10

230

Air

Dewpt = +10F

Condenser

fouled.

Gas Plant



68/112

Mollier

P

H

Charts

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68


Chiller

CompressorCondenser

Acc.

F.V.

Gas/Gas

LTS


Pressures:

XX

XX

10

35

120

160

10-10

95

-10120

90

225

10

220

Air

Dewpt = +10F

Gas exchanger

fouled.

Gas Plant



69/112

Mollier

P

H

Charts

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69


Chiller

CompressorCondenser

Acc.

F.V.

Gas/Gas

LTS


Pressures:

XX

XX

0

25

120

160

0-10

105

-10120

90

225

10

220

Air

Dewpt = +10F

LTS

carryover.

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Chiller

CompressorCondenser

Acc.

F.V.

Gas/Gas

LTS


Pressures:

XX

XX

10

35

120

160

10-2

105

-2120

90

225

20

220

Air

Dewpt = +10F

Compressor

capacity short.

Gas Plant



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Chiller

CompressorCondenser

Acc.

F.V.

Gas/Gas

LTS


Pressures:

XX

XX

10

35

120

160

10-10

105

-10120

90

225

10

220

Air

Dewpt = +10F

Chiller

fouled.

Gas Plant



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Chiller

CompressorCondenser

Acc.

F.V.

Gas/Gas

LTS


Pressures:

XX

XX

10

35

120

160

10-10

105

-2120

90

225

20

220

Air

Dewpt = +10F

Chiller level

Control low.

Gas Plant



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Pressure

-psia

Enthalpy - BTU/lb

-1000 -900 -800 -700 -600 -500

1000

500

100

50

10

1006020

-20-40

180

200

Ch

Com

Cond

Fl

Heat Sink

Heat Source

Refrigeration System is a HEAT PUMP

Gas Plant

Simple Heat Engine Process


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Simple Heat Engine Process

Pressure

-psia

Enthalpy - BTU/lb

-1000 -900 -800 -700 -600 -500

1000

500

100

50

10

Heat Sink

Heat Source

Heat Sink

Heat Source

Feed Pump Turbine

Boiler

Condenser

Gas Plant

Gas Turbine Open Cycle Heat Engine


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75

Gas Turbine Open Cycle Heat Engine

Gas Plant

PH Chart Exercise


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PH Chart Exercise

76

On the attached PH Chart

plot the pressure and

temperatures of :

(a) the propane

at the Compressor suction and

(b) the propane at the

Accumulator.

Use the gauge readings

photographed on slide 78.

What does this tell you about

the condition of the C3 vapour

at the Compressor Suction

and the C3 liquid in the

Accumulator?

Gas Plant

PH Chart Exercise - Answer


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PH Chart Exercise Answer

77

On the attached PH Chart

plot the pressure and

temperatures of :

(a) the propane

at the Compressor suction and

(b) the propane at the

Accumulator.

Use the gauge readingsphotographed on slide 78.

What does this tell you about

the condition of the C3 vapour

at the Compressor Suction

and the C3 liquid in the

Accumulator?

(a) C3 OKplots on DP line

(b) C3 not OKplots above

BP linecontains volatile

impurities

Gas Plant

P & T Gauges at Comp Suction and


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Accumulator

78

Comp SuctionScrubber

Accumulator

Gas Plant

f i i

Section 9 Figure 1


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79

Section 9 Figure 1

Unmeshing rotors at top

induce gas from suction port

Closing rotors at bottom

compress gas toward discharge port

Gas Plant

R f i i

Figure 2


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80

Figure 2

Gas Plant

R f i i

Figure 3


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81

Figure 3

In a recip, when the piston has moved

far enough, the suction valve opens.

In a screw, as the opening rotors unmesh the

gas enters from the suction port.

Gas Plant

R f i i

Figure 4


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Figure 4

In a recip, when the piston has reached

the end of its stroke, suction is complete.

In a screw, when the unmeshing rotors have moved

past the suction port, induction ends and compression starts.

Gas Plant

R f i ti

Figure 5


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Figure 5

In a recip, compression occurs from bottom

dead centre until the discharge valve opens.

In a screw, compression occurs after the lobes pass

the suction port and before they expose discharge port.

Gas Plant

R f i ti

Figure 6


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Figure 6


far enough, the discharge valve opens.

In a screw, when the closing rotors have moved

to expose the discharge port, compression ends.

Gas Plant

R f i ti

Figure 7


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85

gu e


to top dead centre, compression endsThere is always some dead space left.

In a screw, when the meshing rotors have fully

closed, discharge ends. There is NO dead space left.

Gas Plant

R f i ti

Figures 8 & 9


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86

g

Compression ends and the discharge process begins when the meshing

rotors pass the radial port (which may be variable). The axial port relieves

and drains the last drop of oil and gas when the rotors fully close.

Gas Plant

Refrigeratio

Figure 10


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87

g

Gas Plant

Refrigeratio

Figure 11


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88

g

For a given Vs, the position of the radial port determines the Vd,

and therefore determines the ratio Vi.

Gas Plant

Refrigeratio

Table 1


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Table IVi Table

Compression Ratio Ideal Vi Ratio

2.0 1.7

2.5 2.0

3.0 2.3

3.5 2.6

4.0 2.9

4.5 3.2

5.0 3.4

5.5 3.7

6.0 4.0

6.5 4.2

7.0 4.5

7.5 4.78.0 5.0

8.5 5.2

9.0 5.4

9.5 5.7

10.0 5.9

The above values were calculated using a k value of 1.3

Pi = Vik

Gas Plant

Refrigeratio

Figure 12


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90

g

A slide valve may also move a recirculation slot which allows

uncompressed gas to recirculate to suction. This delays the start of

compression and reduces the Vs and therefore the machine capacity.

Because the recirculation is UNCOMPRESSED, the power reduction

is almost linear with speedunlike recirculation around a recip or centrif.

Gas Plant

Refrigeratio

Figure 13


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91

g

Gas Plant

Refrigeratio

Figure 14


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92

g

Gas Plant

Refrigeratio

Toromont Screw Package


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93

g

Suction Scrubber

Oil Separator

Compressor Engine Drive

Gas Plant

Refrigeratio

Screw Compressor Efficiencies


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94

A fixed volume ratio screw

compressor efficiency will

peak at its design volume ratio.

Under-compression occurs

when the required ratio is

LESS than the internal VR.

Over compression occurs when

the required ratio is GREATER

than the internal VR.

In either case the machine

efficiency drops off either side

of ideal VR.



95/112


Screw Refrigeration

Cooling/Condensing

Options

Gas Plant

Refrigeratio

Screw Compressor Lube Oil Cooling


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Option 1

CompressorCondenser

Acc.Chiller

F.V.

20 psia

240 psia

Oil

Cool

-30 F

500,000Btu/hr.

Glycol Rad

Gas Plant

Refrigeratio



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Option 2

CompressorCondenser

Acc.Chiller

F.V.

20 psia

240 psia

-30 F

500,000Btu/hr.

Oil Rad

Gas Plant

Refrigeratio

Air-to-Oil Cooler


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98

Lube

System

Louvre

System

Winter

Airflow

Summer

Airflow

Gas Plant

Refrigeratio



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99

Option 3 (Refrigeration systems only)

CompressorCondenser

Acc.Chiller

F.V.

20 psia

240 psia

-30 F

500,000Btu/hr.

Direct

Injection

Pump

Gas Plant

Refrigeratio




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100


Condenser

The Thermo-siphon Oil Cooler in refrigeration plants offers

maybe the best combination of capital cost and efficiency.

C3 FromCompressor

To Chiller

Hot Oil In

Cold Oil Out

Liquid C3

Vapour C3

C3 Accumulator

Siphon Pot



101/112


Propane Condensers

Aerial; Cooling Tower

and Evaporative

Condenser

Options

Gas Plant

Refrigeratio

Forced Draft Cooler With Stacks


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102

Anti recirc stacks, 15 ft. high

Note fair ground clearance,

but NO bugscreens.

Gas Plant

Refrigeratio

Forced Draft Cooler With Inadequate

Intake Areas


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Intake Areas

Gas Plant

Refrigeratio

Induced Draft Cooler No Stacks


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Induced draft units

have fans over and

motors underthe bundles.

Note fair ground clearance,

including bugscreens.

High fan exit velocity means

no exit stacks needed.

Gas Plant

Refrigeratio

Water Spray Is Damaging


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105

Spraying untreated water directly onto conventional aerial coolers causes:

1 Fin thermal shock and delamination.

2 Corrosion.

3 Salt deposits.

Gas Plant

Refrigeratio

Counter-flow Cooling Tower


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106

Fan

Air

Fill

Water Pump

Louvers

Distributor

Gas Plant

Refrigeratio

Cross-flow Cooling Tower


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107

Fan

Air

Water

Pump

Louvers

Distributor

FillFill

Gas Plant

Refrigeratio

Cross-flow Cooling Tower


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108

Gas Plant

Refrigeratio

Cooling Tower Plant P&ID


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109

CT

Parallel Heat Loads for similar target temperatures

Gas Plant

Refrigeratio

Fan Reversal De-Icing


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Fan

Air

Water

Pump

Louvers

Distributor

FillFill

Gas Plant

Refrigeratio

Evaporative Condenser


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Air In

Water

Process

out

Process In

Air Out

Blower

Gas Plant

Refrigeratio

Evaporative Condenser + AerialCooler In Series


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Aerial Cooler Evaporative Condenser

HighTemp Medium TempLowTemp

Refrig Course

Documents

Transcript of Refrig Course