Experimental Studies On Lignite Gasification Process

Abstract

The remote region of India either face a severe shortage of power or are not connected with grid system. Many villages which are connected to grid system the electrical supply is found intermittent and unreliable. For villages/habitations, where grid connectivity is neither feasible nor cost effective, off-grid solution based on stand-alone system may be taken up for supply of electricity so that every house hold gets electricity. Off-grid electrification can provide a more reliable supply and has a great potential to supply power to remote and rural areas. The gas engine coupled with gasifier is a proven technology and can be economically used for decentralized power generation in the remote areas distant from the grid. Various biomass have been used as a fuel for downdraft gasifier. However, their seasonal availability and land requirement for production coupled with other competing use has forced the attention of development of technologies for the use of other comparable gasifier fuels. India has a considerable reserve (6.18 billion tonnes) of lignite. Application of lignite has been limited due to their high moisture and ash content. Lignite has not been exploited to any great extent and its utilization is not properly focused, because it is inferior to higher-rank coals in calorific value, ease of handling, and storage stability. However, lignite seems to be promising material for gasification, as it is highly reactive than other types of coal and high volatile matter content. A little or limited work has been reported on gasification of lignite in downdraft gasifier. In this work, an attempt has been made to use the lignite as a fuel for downdraft gasifier. The main objective of this study is to investigate the feasibility of lignite as a fuel for downdraft gasifier. The first part of the study involves design and development of pilot-scale (10kWe) downdraft gasifier for lignite fuel and to evaluate the effect of the particle size on gasifier performance. Six different particle sizes viz. 13-16 mm, 16-19 mm, 19-22 mm, 22-25 mm, 25- 28 mm, 28-31 mm were selected for experimental work. The performance parameter includes fuel consumption rate, temperature profile in various zone, gas yield, gas composition and cold gas efficiency. With the increase in particle size, the reduction in fuel consumption rate was observed, whereas the producer gas production rate had increased. The heating value of the gas increased as particle size increased from 13-16 mm to 22-25 mm and then same had decreased with increase in particle size. Higher temperature in reduction zone resulted in higher H2 and CO contents in producer gas. Under the experiment conditions, the fuel consumption rate, gas yields, LHV (Lower heating value) of producer gas and cold gas efficiency varied in the range of 9.58-10.67 kg/hr., 2.43-2.63 Nm3/kg, 3.33-4.17 MJ/Nm3 and 51.50%-65.78% respectively. The experimental results showed that the gasification performance was better with lignite particle size of 22-25 mm. In addition, co-gasification of lignite with wood waste have been carried out to address the problems associated with lignite gasification such as clinker formation, ash agglomeration, low heating value of producer gas, etc. Mixture ratios of 0%-100%, 10%-90%, 20%-80% and 30%- 70% (w/w) of wood waste-lignite were investigated. The lignite and wood particle size was 22- 25 mm and 50×50×5 mm respectively. The gasifier performance was evaluated based on the specific gas yield, cold gas efficiency, fuel consumption rate and gas composition. With increase in wood percentage, the clinker formation reduced and almost vanished as wood percentage reached to 30%. The cold gas efficiency, LHV (Lower heating value) of gas and gas yield increased by 8.92%, 6.31% and 9.33%, respectively. A stoichiometric equilibrium model is proposed for the co-gasification of lignite and wood waste. It is validated using experimental work showing good agreement between experimental and predicted data. In addition, this model offers the opportunity to evaluate the influence of various wood-lignite ratio and operating conditions in producer gas quality.