Investigation of performance and emission characteristics of a biogas fuelled electric generator integrated with solar concentrated photovoltaic system

Highlights

The performance and the emission analysis of biogas fuelled electric generator is presented.

The comparative analysis of generator using biogas and LPG at different loading conditions are presented.

The effect of pressurizing the biogas container on performance of the generator is analysed at varying load conditions.

The concept of integrating biomass and concentrated photovoltaic energy system is proposed.

Abstract

Integration of renewable energy systems with the appropriate technology plays a pivotal role in resolving the problem of sustainable energy supply. This paper is aimed to describe the concept of integration of biomass and solar concentrated photovoltaic (CPV) energy system. The present study focused particularly on the investigation of performance and emission from a 1.4 kVA Spark Ignition, constant speed generator using raw biogas integrated in hybrid energy system. The experiments are conducted at different fuel flow rates under varying electric loading conditions. Comparing with LPG as fuel, the power deterioration is observed to be 32% on raw biogas, due to its low calorific value. The maximum power output and brake thermal efficiency using biogas is witnessed to be 812 W and 19.50% respectively. The exhaust emission analysis of generator using biogas displays considerably reduced carbon monoxide and hydrocarbons whereas there is no significant difference in nitrogen oxides concentration levels while comparing with LPG, ascertaining it to be an eco-friendly fuel. The biogas fuelled electric generator integration with CPV system can attain sustainable rural energy supply.

Keywords

  • Biogas;
  • Integration of renewable energy systems;
  • Performance analysis;
  • Emission analysis;
  • Electric generator

1. Introduction

With the concerns on fossil fuel depletion and augmenting demand for energy throughout the world, the substantial implementation of decentralised hybrid renewable energy system can be a solution to address this issue. Renewable energy based decentralised energy system is a viable approach to meet the basic energy needs of both rural and urban regions. The principle cause for choosing hybrid technologies is to overcome the inconsistency of power generation in conventional means. The smart integration of different renewable technologies not only balances the annual energy output but also can complement each other to avoid energy storage requirement and improve the overall efficiency of the system. In the recent years, plenty of research on integrating solar and biomass energy system are under the spot light as it helps in self-sufficient and sustainable rural electrification and also boosts the native community to utilize the bio-waste comprehensively.

The concept of hybrid renewable energy technologies has been discussed and developed in a large scale for both urban and rural electrification. A review on various hybrid energy technologies by Subho and Sharma [1] discuss the design parameters and implementation methodology of developing a decentralised hybrid energy technology over a locality. A study by Sebnem and Selim [2] examine the various design techniques of integrated biomass and solar energy systems. Mizanur et al. [3] in their study investigated the technical and economic considerations in hybrid application of biomass and photovoltaic resources using simulation tools. Various researches have been carried out to use biogas as an alternative fuel in IC engines. Studies by Surata et al. [5] have concluded that higher performance of engine using biogas can be attained by completely removing the H2S impurity and H2O content from biogas. An investigation on effect of concentration of CH4 in biogas explains that the performance of engine in terms of thermal efficiency and power output improves by increasing the CH4 concentration but the HC (Hydrocarbons) emissions from the exhaust also increases [6]. Studies on effect of compression ratio (CR) in performance of SI engines suggest that, higher the CR (above 13:1), higher the power output and overall efficiency of the engines [7] and [8]. Chandra et al. [9] executed experiments on performance evaluation of a constant speed IC engine on CNG, methane enriched biogas and raw biogas and concluded that engine experienced similar performance on methane enriched biogas and CNG in terms of brake power output, specific gas consumption and thermal efficiency. An experimental analysis by Bari [10] show that engine combustion performance is lower using biogas compared to diesel because of presence of CO2 in biogas and the engine performance does not depreciate until CO2 concentration increases up to 40%. Jatana et al. [11] presented approaches for high efficiency and stability in biogas fuelled small engines, and confirmed that a combination of technologies such as lean burn, fuel injection, and dual spark plug ignition can provide highly efficient and stable operation in a biogas fuelled small SI engine. The studies on performance and emission characteristics of SI engine fuelled with biogas and LPG blends explains that, at the same conditions of dual fuel operation, the emissions of CO and NO predicted for LPG-biomass blends are higher than those for biogas [12]. The improvement in volumetric efficiency and flame speed of engine can be attained by designing the fuel intake venturi system with low throat diameter that increases the fuel intake pressure as analysed by Arali and Kulkarni [13]. The studies on compatibility of biogas as fuel for vehicle by Lim [14] showed no significant difference with CNG in terms of fuel consumption and NO emissions but CO and HC emissions were higher using Biogas. The experimental analysis of engine using biogas by Huanga and Crookes [15] show that by varying the CO2 levels in simulated biogas, not only improves the NO emissions but also results in higher levels of HC concentration due to poor combustion quality. The combustion and emission investigation on engine using biogas–biodiesel blends by Yoon and Lee [16] shows lower peak pressure and heat release rates and also resulting significant reduction in soot emissions. The performance analysis of SI engine using biogas with varying CO2 levels by Porpatham et al. [17] showed a significant improvement in performance and reduction of HC levels by reducing CO2 levels using lime water scrubber. The combustion and exhaust emission characteristics of a dual fuel CI engine operated with pilot diesel and natural gas by Papagiannakis and Hountalas [18] showed decreased soot and NO formation whereas HC and CO were considerably higher.

This paper mainly deals with the methodology of integrating solar and biomass energy systems and also the performance and emission analysis of biogas fuelled electric generator integrated in this hybrid energy system. This paper is further organised as follows. Section 2 deals with the introduction of biomass hybrid energy systems and the concept of Bio-CPV. Section 3 explains the simple modification of LPG run generator to operate as a biogas run generator by improving the fuel intake at pressure regulator/vaporizer section of engine and the methodology of integrating biomass and solar energy systems with AC grid supply. Section 5 deals the performance of test generator in terms of power output, brake specific fuel consumption (BSFC) and brake thermal efficiency (BTE) under different flow rates, effect of external pressurizing on performance parameters discussed and the comparative performance of the generator using biogas and LPG at various flow rates along with the exhaust emission analysis of generator.

2. Biomass hybrid renewable energy systems

2.1. The biogas energy system

The biogas energy system consists of biogas digester, Iron-chelate chamber, collector and biogas fuelled generator. Biogas originates from bacteria in the process of biodegradation of organic material under anaerobic conditions (absence of oxygen). The design of the digester plays a major role in this system as it determines the biogas composition and its properties. In this investigation the cattle dung is used as the organic material. The cattle dung along with other substrates is constantly heated and stirred to ensure the homogeneity of gas. Floating gas holder type digester is used for biogas production. The gas thus produced is collected in the biogas balloon. Biogas acts as a promising alternative fuel, especially for gaseous fuelled engines. It consists of a varying proportion of CH4 (methane) and CO2 (carbon dioxide) and traces of H2S (hydrogen sulphide), Ammonia (NH3), H2O (water vapour), etc. in which CH4 (around 50%–70% of composition) is the most valuable component under the aspect of using it as a fuel for Internal Combustion (IC) engines.

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