3.2 on the Efficiencies of Absorption Heat Pumps 37 3.2.1 Thermodynamic Efficiency 38 3.2.2 Exergetic Efficiency 38 3.2.3 Exergy Index 40
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-A- 122- Absorption Heat Cycles An Experimental and Theoretical Study Klas Abrahamsson September 1993 DEPARTMENT LTH CHEMICAL ENGINEERING I LUND INSTITUTE OF TECHNOLOGY LUND-SWEDEN CODEN: LUTKDH/(TKKA-1002)/l-122/(1993) Absorption Heat Cycles An Experimental and Theoretical Study Klas Abrahamsson Department of Chemical Engineering I Lund Institute of Technology Lund • Sweden Dissertation September 1993 To Annika Absorption Heat Cycles An Experimental and Theoretical Study Klas Abrahamsson Avhandling för teknisk doktorsexamen Avhandlingen kommer att försvaras vid en offentlig disputation i sal B, Kemicentrum, Lund, torsdagen den 16 september 1993 kl. 1015. Fakultetsopponent: Prof Pierre Le Goff, Laboratoire des Sciences du Génie Chemique, Nancy, France. Avhandlingen försvaras på engelska. LUND 1993 Organization Document same LUNDUNIVERsnY DOCTORAL DISSERTATION Dept. of Chemical Engineering 1 Dite of issue University of Lund June 1993 P.OBox 124 CODEN: 221 00 LUND LIJTKDH/(TKKA-1002Vl-122/l 1993) Author's) Sponsoring organization Klas Abrahamsson Title and subtitle Absolution Heat Cvcles - An ExDerimental and Theoretical Studv Abstract A flow sheeting programme, SHPUMP, was developed for simulating different absorption heat cycles. The programme consists often different modules which allow the user to construct his own absorption cycle. The ten modules configurate evaporators, absorbers, generators, rectifiers, condensers, solution heat exchangers, pumps, valves, mixers and splitters. Seven basic and well established absorption cycles are available in the configuration data base of the programme. A new Camot model is proposed for absorption heat cycles. Together with exergy analysis, general equations for the Carnot coefficient of performance and equations for thennodynamic efficiency, exergetic efficiency and exergy index, are derived, discussed and compared for both absorption heat pumps and absorption heat transformers. Utilizing SHPUMP, simulation results are presented for different configurations where absorption heat cycles are suggested to be incorporated in three different unit operations within both pulp and paper and oleochemical industries. One of the application studies revealed that an absorption heat transformer incorporated with an evaporation plant in a a major pulp and paper industry, would save 18% of the total prime energy consumption in one of the evaporation plants. It was also concluded that installing an absorption heat pump in a paper drying plant would result in steam savings equivalent to 12 MW. 1- An experimental absorption heat transformer unit operating with self-circulation has been modified and thoroughly tested. A reference heat transformer plant has been designed and installed in a major pulp and paper mill where it is directly incorporated 38 with one of the evaporation plants. Preliminary plant operation data are presented. si Key word» Absorption heat cycles, absorption heat transformers, absorption heat pumps, simulation programme, Carnot efficiency, thennodynamic analysis, industrial application, pulp and paper, evaporation, drying, oleochemical, self-circulation, pilot-plant, reference plant. Classification system and/or index terms (if any) Supplementary bibliographical infomution Language Enp'iah ISBN ^ ^0-2778 Recipient's note* Number of pages j41 Price Security classification Distribution by (name and address) Dept. of Chemical Engineering 1 P.O.Sox 124, S-221 00 LUND, Sweden I, the undersigned, being the copyright owner of the abstract of the above-mentioned diantation. hereby grant to all reference sources permission to publish and disseminate the abstract of the above-mentioned dissertation. Signature Date July 28, 1993 Contents Symbols and abbreviations xvii Acknowledgements xix 1 Introduction i 1.1 Aim 1 1.2 Heat pumps 1 1.3 Outline of the thesis 5 1.4 Papers 5 2 Modelling and simulation of absorption heat cycles 7 2.1 Programme structure 7 2.2 Data base 8 2.3 Component modelling 10 2.4 Cycle modelling and simulation examples 14 2.4.1 Example 1: A single stage absorption heat transformer 15 2.4.2 Example 2: A double lift absorption heat transformer with one working fluid cycle 17 2.4.3 Example 3: A double lift absorption heat transformer with two working fluid cycles 21 2.4.4 Example 4: A double effect absorption heat pump .. 24 -VII - 2.5 Conclusion and improvements 26 3 Thermodynamic analysis of absorption heat cycles 27 3.1 Carnot comparison of multi-temperature levels absorption heat pumps 28 3.1.1 Entropy streams in an ideal cycle 33 3.1.2 Comparison with other Carnot models 35 3.2 On the efficiencies of absorption heat pumps 37 3.2.1 Thermodynamic efficiency 38 3.2.2 Exergetic efficiency 38 3.2.3 Exergy index 40 3.3 Results and discussion for absorption heat pumps 41 3.4 Carnot comparison of multi-temperature levels absorption heat transformers 49 3.4.1 Entropy streams in an ideal cycle 53 3.5 On the efficiencies of absorption heat transformers 54 3.5.1 Thermodynamic efficiency 54 3.5.2 Exergetic efficiency 55 3.5.3 Exergy index 56 3.6 Results and discussion for absorption heat transformers 57 3.7 Conclusion 65 - vni • 4 Industrial applications of absorption heat cycles 67 4.1 Absorption heat transformer systems for evaporation applications in the pulp and paper industry 71 4.1.1 The existing evaporation plant 71 4.1.2 Simulation results 72 4.1.3 Economic evaluation 78 4.2 Heat pump systems for drying application in the pulp and paper industry 79 4.2.1 Existing heat recovery systems 79 4.2.2 Heat sink alternatives and boundary conditions ... 80 4.2.3 Results 81 4.2.4 Economic evaluation 85 4.3 Absorption heat transformer systems for energy conservation in the oleochemical industry 86 4.3.1 Processing of industrial fatty acids 86 4.3.2 Results and discussion 87 4.3.3 Economic evaluation 88 5 Experimental work 91 5.1 Experimental absorption heat transformer operating with self-circulation 92 5.1.1 Design aspects of the pilot-plant absorption heat transformer 92 5.1.2 Pressure profiles 95 5.1.3 Control system 97 5.1.4 Experimental results 98 5.1.5 Simulation results 100 5.2 Reference absorption heat transformer incorporated with an evaporation plant 101 5.2.1 The sulphite-liquor evaporation plant 101 5.2.2 Design aspects of the reference absorption heat transformer plant 103 5.2.3 Preliminary results 106 5.2.4 Future work 110 References ill Appendix 1: List of papers 117 Appendix 2: Cost functions 119 -X- List of Tables Table 2.1 Units and user procedures for WPData 9 Table 2.2 Property procedures available in WPData 10 Table 2.3 Validity ranges for the different fluids in WPData 10 Table 2.4 Input data for a single stage AHT (WP: H20 - NaOH) 16 Table 2.5 Output data for a single stage AHT 17 Table 2.6 Input data for the double lift AHT working with one working fluid cycle (WP: H20 - NaOH) 18 Table 2.7 Output data for the double lift AHT working with one working fluid cycle 20 Table 2.8 Input data for the double lift AHT working with two working fluid cycles (WP: H20 - NaOH) 21 Table 2.9 Output data for the double lift AHT working with two working fluid cycles 23 Table 2.10 Input data for the double effect AHP (WP: CH3OH-LiBr) 24 Table 2.11 Output data for the double effect AHP 24 Table 3.1 Input data to SHPUMP 41 Table 3.2 Calculated efficiencies for both absorption heat pumps (To = 68 °C) 49 Table 3.3 Input data to SHPUMP 58 Table 3.4 Calculated efficiencies for both absorption heat transformers (To = 28 °C ) 64 Table 4.1 Live steam consumption for current (Ai) and modified mode (A2) of operation for Line 2 74 Table 4.2 Simulation results based on mass diffusivity and a turbulent falling film in both components 75 Table 4.3 Basic design data for the liquor evaporation absorption heat transformer system in Configuration A2 75 -xi - Table 4.4 Live steam consumption for modified mode of operation without absorption heat transformer (Bl) and modified mode with absorption heat transformer (B2) 76 Table 4.5 Basic design data for the liquor evaporation absorption heat transformer system in Configuration B2 77 Table 4.6 Data for the existing recovery system 80 Table 4.7 Heat sink alternatives 81 Table 4.8 Temperature boundaries for heat sources and heat sinks 81 Table 4.9 Operation and design data for the compressor heat pump 83 Table 4.10 Simulation results for different working pairs 84 Table 4.11 Design data for the absorption heat pump system with the working pair H2O - NaOH 85 Table 4.12 Energy mapping of the fat hydrolysis unit 87 Table 4.13 Basic design data for the fat hydrolysis absorption heat transformer system 89 Table 5.1 Simulated data for an absorption heat transformer (WP: H20-NaOH) 91 Table 5.2 Simulated data for an absorption heat pump (WP: H20-NaOH) 92 Table 5.3 Samples of solution concentrations at two different times 100 Table 5.4 Input data for the absorption heat transformer pilot-plant simulation 100 Table 5.5 Output data for the absorption heat transformer pilot-plant simulation 101 Table 5.6 Measured data corresponding to the steady-state period in Figure 5.10 108 -xn- List of Figures Figure 1.1 Temperature and pressure levels for an absorption heat pump 3 Figure 1.2 Temperature and pressure levels for an absorption heat transformer 3 Figure 2.1 Schematic structure of SHPUMP 8 Figure 2.2 Schematic structure of WPData 8 Figure 2.3 Ten different modules available in SHPUMP 11 Figure 2.4 A single stage absorption heat transformer 16 Figure 2.5 Operating cycle for the single stage AHT in an enthalpy- concentration chart for H2O - NaOH 17 Figure 2.6 A double