A biogas-fired cogeneration (cooling and power) system combined with biomethane facilities: 3E evaluation, sensitivity analyses and optimization

Abstract

AbstractThe increasing demand for power and cooling generation presents a dual challenge: an unavoidable increase in carbon emissions from fossil fuel combustion and the associated difficulties in meeting the escalating investment requirements for power plant generation. As a result, there is an urgent call for the advancement of innovative cycles that not only improve performance, but also play a role in mitigating carbon emissions. This study presents a novel approach to biogas-powered cogeneration with the objective of concurrently producing electricity and cooling while utilizing heat from liquefied natural gas. The primary objective is to achieve a reduction in carbon emissions compared to similar existing work. The innovative system combines an open-loop Brayton cycle (gas turbine cycle) powered by biogas, a closed-loop Brayton cycle, a liquefied natural gas open power generation cycle, and a dual-stage combined cooling and power unit consisting of an organic Rankine cycle integrated with an ejector refrigeration cycle. A thermodynamic and economic analysis was conducted to assess the performance of the current study in comparison to previous models. To achieve optimum conditions, a comprehensive multi-objective optimization has been used, taking into account crucial decision variables, energy and exergy indicators, the carbon emission per energy ratio of the product, and the overall cost of the unit product. The results obtained underscore the environmental superiority of this system over other proposals. In the most optimal state, this system demonstrates a remarkable 48% reduction in carbon emissions. Optimization reveals that the developed unit can generate 1860 kW of net electricity and 427.3 kW of cooling. Achieving an energetic efficiency of 80.79%, an exergetic efficiency of 41.5%, a carbon emission per energy ratio of product of 9.902 kg/kW per day, and a unit cost of products of 9.816 $/GJ. In particular, the energy efficiency of the integrated gas turbine closed-loop Brayton cycle system experiences a remarkable 71.17% improvement under optimal conditions. Among the various components of the developed cogeneration system, the combustion chamber contributes the most to the overall exergy destruction rate, closely followed by the condenser, the first heat exchanger of the liquefied natural gas power system. Proposed CCP system fueled by biogas and LNG. Graphical abstract