Abstract
A Kalina cycle-based integration concept of municipal air-conditioning, electricity and gas is investigated thermodynamically, economically, and environmentally to reduce the carbon intensity of these supplies, with attention to hot climatic conditions. The proposed poly-generation system is driven by low-grade renewable or surplus heat, and utilizes waste exergy from liquefied natural gas vaporization for refrigeration and power augmentation. At nominal conditions (130 °C driving heat), approximately 561 and 151 kJ of refrigeration and useful power per kg of liquefied natural gas regasified are generated by the proposed system, respectively, at effective first-law and exergetic efficiencies of 33% and 35%, respectively. The Kalina sub-system condenser cryogenic heat rejection condition is found to triple the system useful electrical output compared with high ambient temperature condenser heat sinking conditions. Per million ton per annum of liquefied natural gas vaporization capacity, yearly net power savings of approximately 74 GWhe could be achieved compared to standard air-conditioning, electricity, and gas supply systems, resulting in 11.1 kton of natural gas saved and 30.4 kton of carbon dioxide-equivalent emissions avoided annually. The yearly net monetary savings would range from 0.9 to 4.7 million USD per million ton per annum of liquefied natural gas regasified at local subsidized and international electricity market prices, respectively, with corresponding payback periods of 1.7 and 2.5 years, respectively.
Highlights
The growth in energy demand driven by developing economies, combined with energy security concerns and climate change, have prompted the exploitation of more sustainable energy resources, renewable and excess resources
The thermodynamic performance of the poly-generation system is assessed based on its net power and cooling rates, cooling-to-power and direct-to-indirect cooling ratios, component- and system-level exergy destruction rates, as well as system energetic and exergetic efficiencies that account for the thermodynamic qualities of the system power and cooling outputs
Air-conditioning is produced using vapor compression powered by an LNG open Rankine cycle, as well as using liquefied natural gas as a direct coolant
Summary
The growth in energy demand driven by developing economies, combined with energy security concerns and climate change, have prompted the exploitation of more sustainable energy resources, renewable and excess resources. Less efforts have been invested in LNG cold exergy utilization for cooling provision in municipal air-conditioning and refrigeration systems, or for the enhancement of Kalina cycle (KC)-based energy conversion systems Such systems can offer improved thermal matching with sensible heat sources and sinks (such as vaporized LNG) and operational flexibility, compared with cycles using pure working fluids, and lower irreversibilities, and avoid the use of ozone-depleting or global warming working fluids [11]. Ayou and Eveloy [19,20] proposed LNG-assisted organic Rankine, Brayton, and ammonia-water (NH3 -H2 O) combined APC cycle concepts driven by ultra-low to medium-grade heat (i.e., 70–370 ◦ C). Depending on configuration, these systems could yield a range of cooling-to-power ratios (2.3–7.3) at effective first-law and exergy efficiencies of 24–39%.
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