MODELLING AND OPTIMIZATION OF A POLYGENERATION HYBRID SOLAR AND BIOMASS SYSTEM FOR POWER, COOLING AND DESALINATION

Abstract

The global warming phenomenon as a significant sustainability issue is gaining worldwide support for development of renewable energy technologies. The term ‘polygeneration’ is referred to as “an energy supply system, which delivers more than one form of energy to the final user”, for example: electricity, cooling and desalination can be delivered from polygeneration process. The polygeneration process in hybrid solar thermal power plant can deliver electricity with lesser impact on environment compared to conventional fossil fuel based power generating system. It is the next generation energy production technique with a potential to overcome intermittence of renewable energy. In this study, the polygeneration process simultaneous production of power, vapor absorption refrigeration (VAR) cooling and multi-effect humidification and dehumidification (MEHD) desalination system from different heat sources in hybrid solar-biomass (HSB) system with higher energy efficiencies (energy and exergy), primary energy savings (PES) and payback period are investigated. There are several aspects associated with hybrid solar-biomass power generation installations such as state wise availability of biomass resources, solar direct normal irradiance (DNI) have been analyzed. Month wise solar and biomass heat utilization also has been analyzed for hybrid system in four regions of India (East: Guwahati, Assam; West: Udaipur, Rajasthan; North: Delhi, South: Madurai, Tamil Nadu). The month wise daily average solar radiation is also considered as 20%, 40%, 60% and 80% and remaining heat is taken from biomass resource in northern region (Delhi) in the proposed hybrid plant. The thermodynamic evaluation (energy and exergy) of HSB power plant has also been investigated. The total input energy of the proposed hybrid system is taken v from the heat transfer fluid through parabolic trough collector (PTC) as per availability of solar resource and remaining from biomass to maintain the steam at superheated state of 5000C and 60 bar and supplied to turbine at steam mass flow rate of 5 kg/sec. The energy and exergy analyses of 5 MW HSB system with series mode was carried out to identify the effects of various operating parameters like DNI, condenser pressure, turbine inlet temperatures, boiler pressure on net power output energy and exergy efficiencies. The VAR cooling system operates using the extracted heat taken from turbine and condenser heat of the VAR cooling system is used in MEHD system for production of drinking water as per demand requirement. Though the production of electricity decreases due to extraction of heat from turbine for VAR cooling and MEHD desalination, the complete system meets the energy requirements & increases the PES. The thermodynamic evaluation (energy and exergy), optimization and payback period of polygeneration process in HSB thermal power plant for combined power, cooling and desalination is investigated to identify the effects of various operating parameters. The system has achieved a maximum energy efficiency of 49.85% and exergy efficiency of 20.94%. The Primary energy savings of polygeneration process (PESPP) in HSB system is achieved at 50.5%. The electricity generation from polygeneration process increased to 78.12% as compared to simple thermal power plant. The payback period of polygeneration process in HSB thermal power plant is 1.5 years, which is less than solar thermal power plant, HSB thermal power plant, Cogeneration in HSB thermal power plant.