Power Recovery from Low Grade Heat by Means of Screw Expanders (eBook)

Ahmed Kovacevic, Ian K Smith, Nikola Stosic (Autoren)

eBook Download: PDF | EPUB

2014 | 1. Auflage
272 Seiten
Elsevier Science (Verlag)
978-1-78242-190-0 (ISBN)

Infos

Current concerns with climate change have resulted in greatly increased interest in power recovery from low grade heat sources. This includes both hot fluid streams which can be expanded directly to produce mechanical power and those which act as a source of heat to closed cycle power generation systems. Power recovery from low grate heat by means of screw expanders with a generalised overview of how best to recover power from such sources, based on thermodynamic considerations, which differs to the approach used in classical thermodynamics textbooks and which includes an introductory description of the types of working fluid that are used in systems used to recover power from such sources and the criteria that must be taken into account in their selection. This is followed by a description of the mathematical modelling of twin screw machine geometry. The modelling of the thermodynamics and fluid flow through such machines is then given, together with how this is used to predict their performance. Finally a detailed description is given of systems currently used or projected both for direct expansion of the source fluid and by recovery of heat from it, which includes those which are particularly suited to the use of screw expanders in place of turbines. - A novel generalised approach to the thermodynamics of power recovery from low grade heat systems - Gives criteria for working fluid selection - Provides details of, and how to model, screw expander geometry - Details how to estimate screw expander performance - Surveys types of system used for power recovery from low grade heat and where this can be improved by the use of screw expanders.

Ian K Smith is professor of Applied Thermodynamics at City University London, UK, and has been contributing to systems for the recovery of power from low grade heat for more than 40 years.

Textauszug

List of figures

1.1 Types of positive displacement machines  3

1.2 Assembled view of a screw expander  4

1.3 Exploded view of a screw expander  4

1.4 Principle of operation of a screw expander  5

1.5 Illustration of a blow-hole  7

1.6 Oil-flooded and oil-free compressors  9

1.7 Oil-free compressor/expander lubrication system  11

1.8 Oil-injected expander lubrication system  12

2.1 Internal combustion engine  14

2.2 Power plant receiving heat from process steam  17

2.3 Power plant receiving heat from a hot fluid  18

2.4 Infinitesimal heat engine  20

2.5 Temperature–entropy diagram for ideal recovery of power from a hot fluid stream  20

2.6 Ideal cycles between a finite heat source and an infinite heat sink  21

2.7 Power plant receiving heat from and rejecting to external fluid streams  22

2.8 Ideal cycles between a finite heat source and a finite heat sink  23

2.9 Comparison of Carnot cycle with ideal trilateral cycle  24

2.10 The effect of the fluid exit temperature on ideal efficiency and power output  26

2.11 Pressure–volume diagrams for power plant cycles based on flow and non-flow processes  27

2.12 The effect of work ratio on practical cycle efficiency  30

2.13 The ideal trilateral cycle using a perfect gas  31

2.14 Comparison of ideal and achievable trilateral cycle efficiency 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 efficiencies 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 fluid  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 flash cycle (TFC) system and components  44

2.27 Comparison of performance of trilateral flash cycles (TFC) and ideal trilateral cycle  45

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 fluids  49

2.31 Matching the cycle to the heat source with saturated, superheated and supercritical cycles  50

2.32 Improving the cycle efficiency with a recuperative heat exchanger  52

2.33 The relationship between saturated vapour pressure and temperature for pure fluids  55

2.34 Common working fluids with a saturated liquid line slope approximately equal to that of water  56

3.1 Screw rotor profile  61

3.2 Most popular screw compressor rotors  65

3.3 Coordinate system of helical gears with non-parallel and non-intersecting axes  67

3.4 Example of a gate rotor enveloped by its main counterpart using direct digital simulation  72

3.5 Screw expander rotors with parallel shafts and their coordinate systems  72

3.6 Demonstrator profile with its details  77

3.7 City University ‘N’ profile details  79

3.8 ‘N’ rotors compared with Sigma, SRM ‘D’ and Cyclon rotors  80

3.9 Rotor 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

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-pressure side bearings on the right  91

4.1 An 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 Predicted 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 fluid  115

4.4 Predicted 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 fluid  115

4.5 Pressure forces acting on screw machine rotors  117

5.1 General layout of process fluid bearing lubrication for closed-cycle organic fluid power system  130

5.2 General layout of expander-generator within a larger system  131

5.3 A 100 kWe industrial process steam screw expander  134

5.4 Single flash steam system for geothermal power generation  135

5.5 Double flash steam system for geothermal power generation  135

5.6 Single flash steam system with screw expander  136

5.7 Double flash steam system with single screw expander  137

5.8 Basic vapour compression refrigeration system  139

5.9 Vapour 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 profile  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-expander  148

5.21 Carbon dioxide refrigeration system  150

5.22 Estimated performance improvements in an ideal transcritical CO2 cycle system with combined compression and two-phase expansion  150

5.23 Estimated performance improvement in a subcritical CO2 system using a compressor expander  151

5.24 Prototype fuel cell compressor-expander components  152

5.25 Fuel cell compressor-expander revised casing design  152

5.26 Saturated Rankine cycle system with organic working fluid  155

5.27 Wet organic Rankine cycle (WORC)  156

5.28 A 50 kWe screw expander-driven industrial WORC system  157

5.29 Trilateral flash 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...

Produkt-Details

• Erscheint lt. Verlag: 6.5.2014
• Sprache: englisch
• Themenwelt: Naturwissenschaften ► Physik / Astronomie
• Themenwelt: Technik ► Bauwesen
• Themenwelt: Technik ► Maschinenbau
• ISBN-10: 1-78242-190-4 / 1782421904
• ISBN-13: 978-1-78242-190-0 / 9781782421900