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Natural Gas Refrigeration.
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5/27/2018 Refrig Course
1/112
Gas Plant Refrigeration
Nev Hircock
Process Consulting Ltd.
Mollier
P- H Charts
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MollierPH
Charts
Gas Plant
Refrigeratio
l
2
Gas Chiller
Gas In
Gas Out
Glycol Injection
Propane In Deoiler
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MollierPH
Charts
Gas Plant
Refrigeratio
l
3
Compressor Scrubber
Note temperaturedifferential
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MollierPH
Charts
Gas Plant
Refrigeratio
l
4
Compressor
Oil separator Inlet Discharge
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MollierPH
Charts
Gas Plant
Refrigeratio
l
5
Compressor Panel
Suction, Discharge and
Oil pressures
Status on two
Parallel machines
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MollierPH
Charts
Gas Plant
Refrigeratio
l
6
Condenser
Two x 7 diameter fans Manual top louvres
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MollierPH
Charts
Gas Plant
Refrigeratio
l
7
Gas/Gas Exchanger
Inlet
Outlet
Glycol
injection
Cold
insulation
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MollierPH
Charts
Gas Plant
Refrigeratio
l
8
Simple Refrigeration Circuit
CompressorCondenser
Acc.Chiller
F.V.
Gas In
Gas Out
LiquidOut
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MollierPH
Charts
Gas Plant
Refrigeratio
l
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
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MollierPH
Charts
Gas Plant
Refrigeratio
l
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
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MollierPH
Charts
Gas Plant
Refrigeratio
l
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
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MollierPH
Charts
Gas Plant
Refrigeratio
l
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
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MollierPH
Charts
Gas Plant
Refrigeratio
l
13
Propane Condenser
CompressorCondenser
Acc.Chiller
F.V.
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MollierPH
Charts
Gas Plant
Refrigeratio
l
14
The Mollier Chart Processes
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
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MollierPH
Charts
Gas Plant
Refrigeratio
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15
Gas Chiller
CompressorCondenser
Acc.Chiller
F.V.
Gas In
Gas Out
LiquidOut
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MollierPH
Charts
Gas Plant
Refrigeratio
l
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
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Mollier
PH
Charts
Gas Plant
Refrigeratio
l
17
Accumulator
CompressorCondenser
Acc.Chiller
F.V.
Gas In
Gas Out
LiquidOut
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Mollier
PH
Charts
Gas Plant
Refrigeratio
l
18
The Mollier Chart Processes
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
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Mollier
PH
Charts
Gas Plant
Refrigeratio
l
19
Flash Valve
CompressorCondenser
Acc.Chiller
F.V.
Gas In
Gas Out
LiquidOut
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Mollier
PH
Charts
Gas Plant
Refrigeratio
l
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
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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%
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PH
Charts
Gas Plant
Refrigeratio
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Compressor
CompressorCondenser
Acc.Chiller
F.V.
Gas In
Gas Out
LiquidOut
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Mollier
PH
Charts
Gas Plant
Refrigeratio
l
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
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Mollier
PH
Charts
Gas Plant
Refrigeratio
l
24
Simple Refrigeration Circuit
CompressorCondenser
Acc.Chiller
F.V.
Gas In
Gas Out
LiquidOut
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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
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Mollier
PH
Charts
Gas Plant
Refrigeratio
l
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
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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
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Mollier
PH
Charts
Gas Plant
Refrigeratio
l
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
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PH
Charts
Gas Plant
Refrigeratio
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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.
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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
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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
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PH
Charts
Gas Plant
Refrigeratio
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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
Refrigeratio
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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
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P
H
Charts
Gas Plant
Refrigeratio
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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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P
H
Charts
Gas Plant
Refrigeratio
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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
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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
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Mollier
P
H
Charts
Gas Plant
Refrigeratio
l
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
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Mollier
P
H
Charts
Gas Plant
Refrigeratio
l
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
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Mollier
P
H
Charts
Gas Plant
Refrigeratio
l
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
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P
H
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Gas Plant
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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
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P
H
Charts
Gas Plant
Refrigeratio
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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
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Mollier
P
H
Charts
Gas Plant
Refrigeratio
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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
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P
H
Charts
Gas Plant
Refrigeratio
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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
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Mollier
P
H
Charts
Gas Plant
Refrigeratio
l
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
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Mollier
P
H
Charts
Gas Plant
Refrigeratio
l
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
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P
H
Charts
Gas Plant
Refrigeratio
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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 +
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P
H
Charts
Gas Plant
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Refrigeration Circuit +
Internal Subcooler
CompressorCondenser
Acc.Chiller
F.V.
Gas In
Gas Out
LiquidOut
30F
-20F
120F
70F
Gas Plant
Refrigeration Process +
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P
H
Charts
Gas Plant
Refrigeratio
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Refrigeration Process +
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
Refrigeration Circuit +
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P
H
Charts
Gas Plant
Refrigeratio
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49
Refrigeration Circuit +
External Subcooler
CompressorCondenser
Acc.
Gas In
Chiller
F.V.To G/G Ex.
LTS
To DeC2
-10F
70F
120F
40F
Gas Plant
Refrigeration Process +
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P
H
Charts
Gas Plant
Refrigeratio
l
50
Refrigeration Process +
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
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Mollier
P
H
Charts
Gas Plant
Refrigeratio
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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
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Mollier
P
H
Charts
Gas Plant
Refrigeratio
l
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
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Mollier
P
H
Charts
Gas Plant
Refrigeratio
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53
Troubleshooting: 1 Fouled
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
Troubleshooting: 1 Fouled
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P
H
Charts
Gas Plant
Refrigeratio
l
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
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Mollier
P
H
Charts
Gas Plant
Refrigeratio
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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
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Mollier
P
H
Charts
Gas Plant
Refrigeratio
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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
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Mollier
P
H
Charts
Gas Plant
Refrigeratio
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57
Troubleshooting: 3 Compressor
Capacity Loss
Chiller
CompressorCondenser
Acc.
F.V.
The compressor
suction pressure
governs the chillershell side pressure
and temperature.
Gas Plant
Troubleshooting: 3 Compressor
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Mollier
P
H
Charts
Gas Plant
Refrigeratio
l
58
2001006020
-20
Troubleshooting: 3 Compressor
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
Troubleshooting: 4 Compressor
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Mollier
P
H
Charts
Gas Plant
Refrigeratio
l
59
oub es oot g Co p esso
Valve Leakage
Chiller
CompressorCondenser
Acc.
F.V.
Gas Plant
Troubleshooting: 4 Compressor
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Mollier
P
H
Charts
Gas Plant
Refrigeratio
l
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
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Mollier
P
H
Charts
Refrigeratio
l
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
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Mollier
P
H
Charts
Refrigeratio
l
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
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Mollier
P
H
Charts
Refrigeratio
l
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
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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
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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
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Simple DewPoint Plant; Fault 1
Chiller
CompressorCondenser
Acc.
F.V.
Gas/Gas
LTS
Design:Legend: Temperatures:
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
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Simple DewPoint Plant: Fault 2
Chiller
CompressorCondenser
Acc.
F.V.
Gas/Gas
LTS
Design:Legend: Temperatures:
Pressures:
XX
XX
10
35
120
160
10-10
105
-10125
90
235
10
230
Air
Dewpt = +10F
Condenser
fouled.
Gas Plant
Simple DewPoint Plant: Fault 3
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Simple DewPoint Plant: Fault 3
Chiller
CompressorCondenser
Acc.
F.V.
Gas/Gas
LTS
Design:Legend: Temperatures:
Pressures:
XX
XX
10
35
120
160
10-10
95
-10120
90
225
10
220
Air
Dewpt = +10F
Gas exchanger
fouled.
Gas Plant
Simple DewPoint Plant: Fault 4
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Simple DewPoint Plant: Fault 4
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 = +10F
LTS
carryover.
Gas Plant
Simple DewPoint Plant: Fault 5
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Simple DewPoint Plant: Fault 5
Chiller
CompressorCondenser
Acc.
F.V.
Gas/Gas
LTS
Design:Legend: Temperatures:
Pressures:
XX
XX
10
35
120
160
10-2
105
-2120
90
225
20
220
Air
Dewpt = +10F
Compressor
capacity short.
Gas Plant
Simple DewPoint Plant: Fault 6
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Simple DewPoint Plant: Fault 6
Chiller
CompressorCondenser
Acc.
F.V.
Gas/Gas
LTS
Design:Legend: Temperatures:
Pressures:
XX
XX
10
35
120
160
10-10
105
-10120
90
225
10
220
Air
Dewpt = +10F
Chiller
fouled.
Gas Plant
Simple DewPoint Plant: Fault 7
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Simple DewPoint Plant: Fault 7
Chiller
CompressorCondenser
Acc.
F.V.
Gas/Gas
LTS
Design:Legend: Temperatures:
Pressures:
XX
XX
10
35
120
160
10-10
105
-2120
90
225
20
220
Air
Dewpt = +10F
Chiller level
Control low.
Gas Plant
Simple Refrigeration Process
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Simple Refrigeration Process
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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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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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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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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Figure 2
Gas Plant
R f i i
Figure 3
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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
In a recip, when the piston has moved
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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gu e
In a recip, when the piston has moved
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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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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g
Gas Plant
Refrigeratio
Figure 11
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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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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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g
Gas Plant
Refrigeratio
Figure 14
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g
Gas Plant
Refrigeratio
Toromont Screw Package
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g
Suction Scrubber
Oil Separator
Compressor Engine Drive
Gas Plant
Refrigeratio
Screw Compressor Efficiencies
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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.
Gas Plant Refrigeration
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Gas Plant Refrigeration
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
Screw Compressor Lube Oil Cooling
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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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Lube
System
Louvre
System
Winter
Airflow
Summer
Airflow
Gas Plant
Refrigeratio
Screw Compressor Lube Oil Cooling
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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
Screw Compressor Lube Oil Cooling
Option 4 (Refrigeration systems only)
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Option 4 (Refrigeration systems only)
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
Gas Plant Refrigeration
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Gas Plant Refrigeration
Propane Condensers
Aerial; Cooling Tower
and Evaporative
Condenser
Options
Gas Plant
Refrigeratio
Forced Draft Cooler With Stacks
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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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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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Fan
Air
Fill
Water Pump
Louvers
Distributor
Gas Plant
Refrigeratio
Cross-flow Cooling Tower
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Fan
Air
Water
Pump
Louvers
Distributor
FillFill
Gas Plant
Refrigeratio
Cross-flow Cooling Tower
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Gas Plant
Refrigeratio
Cooling Tower Plant P&ID
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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