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Conclusion and Implications for Tri-generation Integration

This chapter has presented the evaluation, based on experimental data, of a SDCS. An environmentally friendly potassium formate working fluid has been employed at a solution mass concentration of 0.65-0.7. The SDCS has been developed in response to the shortcomings of the novel IDCS, documented in Chap. 5, and its lack of potential for effective tri-generation system integration. The SDCS experimental set-up, instrumentation and experimental method have all been provided. The thesis has established that during tri-generation system integration it is the operation of the SDCS that will need to be optimised to facilitate successful pairing of the SOFC and liquid desiccant technology. This is due to limited variation in the SOFC CHP system’s operation and thus outputs. This chapter has successfully provided a detailed evaluation of the dehumidifier, regenerator and complete SDCS operational performance so that the central thesis aim of the development of an efficient and effective SOFC liquid desiccant tri-generation system can be accomplished. Furthermore, dehumidifier and regenerator simulation results have been presented to validate the models, presented in Chap. 3, operating with a potassium formate solution. Potential reasons for the discrepancies between experimental and simulations have been previously highlighted in Sect. 3.4.3. Two trigeneration system operating scenarios that use concentrated desiccant solution as a form of thermal energy storage have been introduced. The scenarios demonstrate the significant advantage of the novel SOFC liquid desiccant tri-generation system.

The experimental component evaluation has established that the SDCS demonstrates great potential for the development of an efficient and effective SOFC tri-generation system. This is primarily due to good dehumidification capacity and effective regeneration of a potassium formate solution at a 0.65-0.7 solution mass concentration when using regenerator thermal input values typical of a SOFC CHP WHR circuit.

The SDCS shows potential, compared to the IDCS, with regard to tri-generation system integration for the following reasons:

  • • Effective instantaneous balancing of the dehumidifier and regenerator across a range of environmental and operational values.
  • • The key regenerator variables used to balance dehumidifier and regenerator operation are within an acceptable and realistic operating range, essential for effective tri-generation system integration.
  • • Testing of the complete SDCS within the environmental chamber demonstrates good (non-adjusted) COPth values in the region of 0.4-0.66. System modifications to evaporative cooler could result in a COPth approaching 1.0.
  • • Greater control of individual variables within the desiccant system i.e. dehumidifier and regenerator desiccant solution flow.
  • • No issues with desiccant solution leakage.

Although the SDCS has been developed with the aim of integration alongside a SOFC into a complete tri-generation system, the compact nature and effective use of low grade waste heat means the SDCS shows significant potential for integration with other CHP prime mover technologies such as ICE or SE. As highlighted throughout the thesis, no work has been found detailing a SOFC liquid desiccant tri-generation system. Simulations in Chap. 4 have proved the tri-generation system concept theoretically. Using operational thermal input values based upon those typical of a domestic scale SOFC CHP system, the SDCS evaluation validates the concept of integrating SOFC and liquid desiccant air conditioning technology. The work presented in this chapter provides a contribution to knowledge with the testing of a liquid desiccant air conditioning system based on specific SOFC thermal input values.

Next, Chap. 7 presents tri-generation system integration and evaluation.

References

Elmer, T., M. Worall, S. Wu, and S. Riffat. 2016b. Experimental evaluation of a liquid desiccant air conditioning system for tri-generation/waste-heat-driven applications. International Journal of Low-Carbon Technologies doi: 10.1093/ijlct/ctw012.

James, S. 1998. A new working fluid ‘potassium formate’ for use in absorption heat pumps.

Masters of Philosophy, The University of Nottingham.

Melinder, A. 2007. Thermophysical properties of aqueous solutions used as secondary working fluids. PhD Thesis, KTH Energy and Environmental Technology.

 
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