Abstract
Gasification is an attractive method for biomass-to-energy conversion and fluidized bed design is one of the best options for large scale operation. A bubbling fluidized bed reactor was used to analyze the effects of biomass type, equivalence ratio (ER) and temperature for product gas compositions. Wood chips, wood pellets and grass pellets were gasified between 650 °C and 800 °C temperature. The ER was varied between 0.08 and 0.16. Gasification of grass pellets was difficult at 800 °C due to agglomeration and the gas composition was poor compared to wood. The reactor performances improved over the temperature and 650 °C was not sufficient to achieve a reasonable carbon conversion. Nitrogen dilution at higher ERs was counter weighted by improved carbon conversion at higher temperatures. The highest carbon conversion was achieved at 800 °C which were 75.8% and 70.6% for wood chips and wood pellets at 0.15 and 0.16 ERs respectively.
Highlights
Bioenergy owns an enduring place in future energy profile, especially due to its dispatchable characteristics and competency in delivering the full spectrum of fossil based fuels and chemicals [1,2]
Precise tuning of biomass flow was difficult and the cold conveyor was operated at 2% capacity, which resulted in 2.3 kg/h, 2.42 kg/h and 2.7 kg/h flowrates for woodchips, wood pellets and grass pellets respectively
Uncertainties related to discontinuous feeding of biomass and ±20 C temperature variation could affect the results comparison
Summary
Bioenergy owns an enduring place in future energy profile, especially due to its dispatchable characteristics and competency in delivering the full spectrum of fossil based fuels and chemicals [1,2]. Heating value of the product gas is possible to upgrade from 5 MJ/Nm3 to 18 MJ/Nm3 if the gasifying agent is shifted from air to oxygen or steam. Using of oxygen involves a high operational cost and air is used as the gasifying agent in general applications. Majority of these reactors are auto-thermal in which, additional amount of air (than the requirement for stoichiometric gasification) is supplied to trigger the oxidation reactions and to keep up the target reactor temperature. Minimization of the excess air supply than what is required for pure gasification This can only be achieved by upgrading the auto-thermal reactor into an allo-thermal or a hybrid reactor.
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