Performance analysis of an absorption double-effect cycle for power and cold generation using ammonia/lithium nitrate Articles uri icon

publication date

  • March 2017

start page

  • 256

end page

  • 266

volume

  • 115

international standard serial number (ISSN)

  • 1359-4311

electronic international standard serial number (EISSN)

  • 1873-5606

abstract

  • ABSTRACT: The performance of a two-stage double-effect absorption machine for combined power and cold generation is proposed and studied theoretically, generating innovative schemes. The ammonia/lithium nitrate solution allows this cycle, consuming either solar thermal or residual heat. The machine is represented by means of a thermodynamic steady-state cycle. First, only power generation and only cold production are separately studied as function of the main internal temperatures, introducing the concepts of mixed and unmixed vapour and of virtual temperatures for allowing comparison. The results indicate that for producing power the efficiency of the cycle increases when rising the maximum pressure while for producing cold is the contrary. The maximum efficiency obtained for only power production with no superheating is 19.5% at a high generation temperature of 173 degrees C and at a moderate 20.3 bars of maximum pressure. The solution crystallization avoids a higher efficiency. The combined power and cooling cycle allows adapting the energy production to cold demand or to power demand by splitting the vapour generated. At a generation temperature of 132 degrees C, when splitting the vapour generated into half for power and half for cooling, the cycle obtains an electric efficiency of 6.5% and a COP of 0.52. This cycle is compared to a conventional double-effect cycle configured in parallel flow, obtaining the same electric efficiency but with a 32% higher COP.

keywords

  • ammonia/lithium nitrate solution; double-effect absorption cycle; combined power and cooling; medium temperature solar collectors; organic rankine-cycle; waste heat-recovery; systems; expander; kalina; driven