Table Of ContentPower recovery from low- grade heat
by means of screw expanders
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Power recovery from
low- grade heat by
means of screw
expanders
I K. S
AN MITH
N S
IKOLA TOSIC
A K
HMED OVACEVIC
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List of fi gures
1.1 T ypes of positive displacement machines 3
1.2 A ssembled view of a screw expander 4
1.3 E xploded view of a screw expander 4
1.4 P rinciple of operation of a screw expander 5
1.5 I llustration of a blow- hole 7
1.6 O il- fl ooded and oil- free compressors 9
1.7 O il- free compressor/expander lubrication
system 11
1.8 O il- injected expander lubrication system 12
2.1 I nternal combustion engine 14
2.2 P ower plant receiving heat from process
steam 17
2.3 P ower plant receiving heat from a hot fl uid 18
2.4 I nfi nitesimal heat engine 20
2.5 T emperature–entropy diagram for ideal
recovery of power from a hot fl uid stream 20
2.6 I deal cycles between a fi nite heat source
and an infi nite heat sink 21
2.7 P ower plant receiving heat from and rejecting
to external fl uid streams 22
2.8 I deal cycles between a fi nite heat source and
a fi nite heat sink 23
2 .9 C omparison of Carnot cycle with ideal
trilateral cycle 24
2.10 The effect of the fl uid exit temperature
on ideal effi ciency and power output 26
ix
Power recovery using screw expanders
2.11 Pressure–volume diagrams for power plant
cycles based on fl ow and non- fl ow processes 27
2.12 The effect of work ratio on practical cycle
effi ciency 30
2.13 The ideal trilateral cycle using a perfect gas 31
2.14 Comparison of ideal and achievable
trilateral cycle effi ciency using a perfect gas 32
2.15 The ideal quadlateral cycle using a perfect gas 33
2.16 Comparison of ideal and achievable
quadlateral cycle effi ciencies using a
perfect gas 33
2.17 Ideal trilateral and quadlateral cycles
matched to the heat source and sink 35
2.18 Ideal Stirling cycle on p – V and T – s
coordinates 36
2.19 Heat transfer as a function of temperature
for a single- phase heating medium 37
2.20 Temperature–entropy diagram of ideal
Stirling cycle with heat source and sink 38
2.21 Comparison of performance of ideal
quadlateral and Stirling cycles using a
perfect gas 39
2.22 Comparison of performance of practical
quadlateral and Stirling cycles 40
2.23 Simple Rankine cycle system using steam
as the working fl uid 42
2.24 Comparison of ideal steam Rankine and
ideal gas cycles 43
2.25 Comparison of practical steam Rankine
and practical gas cycles 43
2.26 Trilateral fl ash cycle (TFC) system and
components 44
2.27 Comparison of performance of trilateral fl ash
cycles (TFC) and ideal trilateral cycle 45
x
List of fi gures
2.28 TFC temperature matching to a limited
minimum temperature heat source 47
2.29 Improving the Rankine cycle matching to
its heat source 47
2.30 Temperature–entropy diagram for various
working fl uids 49
2.31 Matching the cycle to the heat source
with saturated, superheated and
supercritical cycles 50
2.32 Improving the cycle effi ciency with a
recuperative heat exchanger 52
2.33 The relationship between saturated vapour
pressure and temperature for pure fl uids 55
2.34 Common working fl uids with a saturated
liquid line slope approximately equal to
that of water 56
3.1 S crew rotor profi le 61
3.2 M ost popular screw compressor rotors 65
3.3 C oordinate system of helical gears with
non- parallel and non- intersecting axes 67
3.4 E xample of a gate rotor enveloped by
its main counterpart using direct digital
simulation 72
3.5 S crew expander rotors with parallel
shafts and their coordinate systems 72
3.6 D emonstrator profi le with its details 77
3.7 C ity University ‘N’ profi le details 79
3.8 ‘ N’ rotors compared with Sigma,
SRM ‘D’ and Cyclon rotors 80
3.9 R otor shafts in the expander housing and
displacement in bearings, and coordinate
systems of rotors with intersecting shafts 82
3.10 Rotor manufacturing tools: hobbing tool
and milling/grinding tool 86
xi
Power recovery using screw expanders
3.11 Rotor and tool coordinate systems 88
3.12 Drawing of typical screw rotors and
housing assembled in a screw expander
with low- pressure side bearings on the
left and high-p ressure side bearings on
the right 91
4.1 A n example of volumetric change with
rotation in a screw expander 94
4.2 A typical estimated p – V diagram of a
two- phase expansion process 114
4.3 P redicted and measured pressure change
with rotation in a 163 mm diameter rotor
screw expander operating at 10 m/s tip
speed with R113 as the working fl uid 115
4.4 P redicted and measured pressure change
with rotation in a 163 mm diameter rotor
screw expander operating at 20 m/s tip
speed with R113 as the working fl uid 115
4.5 P ressure forces acting on screw machine
rotors 117
5.1 G eneral layout of process fl uid bearing
lubrication for closed- cycle organic fl uid
power system 130
5.2 G eneral layout of expander- generator
within a larger system 131
5.3 A 100 kWe industrial process steam
screw expander 134
5.4 S ingle fl ash steam system for geothermal
power generation 135
5.5 D ouble fl ash steam system for geothermal
power generation 135
5.6 S ingle fl ash steam system with screw
expander 136
xii
List of fi gures
5.7 D ouble fl ash steam system with single
screw expander 137
5.8 B asic vapour compression refrigeration
system 139
5.9 V apour compression refrigeration system
with economiser 140
5.10 An expressor in a vapour compression system 141
5.11 The effect of the wrap angle on the
trapped volume 142
5.12 Expansion and recompression in one
pair of rotors 143
5.13 The expressor as a single rotor pair unit 144
5.14 Expressor components 144
5.15 Prototype expressor units 145
5.16 Expressor rotor pair for separating the
working chamber into two sections 146
5.17 Expressor rotor profi le 146
5.18 Cross- section of an expressor with
separate expansion and compression
working chambers 147
5.19 Expressor casing with separate expansion
and compression working chambers 147
5.20 Screw compressor-e xpander 148
5.21 Carbon dioxide refrigeration system 150
5.22 Estimated performance improvements
in an ideal transcritical CO cycle system
2
with combined compression and
two- phase expansion 150
5.23 Estimated performance improvement
in a subcritical CO system using a
2
compressor expander 151
5.24 Prototype fuel cell compressor- expander
components 152
xiii
Power recovery using screw expanders
5.25 Fuel cell compressor- expander revised
casing design 152
5.26 Saturated Rankine cycle system with
organic working fl uid 155
5.27 Wet organic Rankine cycle (WORC) 156
5.28 A 50 kWe screw expander- driven
industrial WORC system 157
5.29 Trilateral fl ash cycle (TFC) 157
5.30 Higher temperature two- phase expansion
cycle system 159
5.31 Recuperated higher temperature two- phase
expansion system 160
5.32 Recuperated supercritical ORC system 162
5.33 Superheated ORC system with recuperator 164
5.34 Direct contact regenerative feed heating 166
5.35 Indirect contact regenerative feed heating 167
5.36 (W)ORC system with regenerative feed
heating obtaining heat from a low- grade
heat source 168
5.37 Dual pressure cycle with dry vapour
expansion 170
5.38 Dual pressure cycle system 171
5.39 Binary cycle system with different
working fl uids in the topping and
bottoming cycles 172
5.40 Superheated and saturated steam
evaporative temperatures with maximum
exhaust gas heat recovery 174
5.41 ORC system for exhaust gas heat recovery
with intermediate thermal loop 174
5.42 Wet steam cycle for exhaust gas heat
recovery 176
5.43 Combined wet steam–ORC system 178
5.44 Combined screw–turbine wet steam system 179
xiv
