5.3 Daya Shankar Pandey – University of Copenhagen

ReUseWaste > Thesis abstracts > 5.3 Daya Shankar Pandey

Optimal combustion and gasification technology for on-farm conversion of animal manures to energy and ash, Daya Shankar Pandey, ULIM

The PhD work focused on the development of Thermodynamic equilibrium-based models of gasification and combustion process for manure based biomass and optimizing syn-gas production while focusing on improving energy and P recovery. He is investigating the effect of temperature in the fluidized bed gasifiers (FBG), moisture content, equivalence ratio, steam to biomass ratio (SBR) on syngas composition and quality of product gas. 

Thermal gasification is one of the promising technologies which utilize the biomass (wood, coal, waste etc.) and low calorific value fuels such as manure to produce energy. The first problem is well explored, the second less so. In particular, manure gasification mechanism is not clear and research on manure based biomass (MBB) is rarely reported till now. Thermodynamic equilibrium-based models of gasification and combustion process are widely used to predict producer gas characteristics in performance studies of energy conversion plants.

To develop a detailed fluidized bed gasifier model, thermodynamic, hydrodynamic and chemical kinetics models are necessary. The main emphasis of the project is related to the consideration of a reliable model for describing the gasification process under conditions relevant for the waste (poultry litter) with focus on improving energy and P recovery. That is why, for consideration of a reliable thermodynamic equilibrium model for the waste, different models available in literature shall be tested, validated and will be utilized for the optimization of the various thermochemical process parameters. The PhD sought to contribute to the knowledge about animal manure gasification for i) optimization of the gasification technology for conversion of animal manure to energy and Ash, ii) to establish and validate equilibrium, kinetic and CFD models for simulation of biomass gasification process using ASPEN Plus and Star CCM+; iii) investigate the importance of model complexity by comparing different models and iv) to evaluate the effects of gasification conditions on performance of gasifier using Aspen Plus.

The first study shows that the predicted outputs of the municipal solid waste gasification process are in good agreement with the experimental dataset and also generalise well to validation (untrained) data. Published experimental datasets are used for model training and validation purposes. The results show the effectiveness of the genetic programming technique for solving complex nonlinear regression problems. The multi-gene genetic programming are also compared with a single-gene genetic programming model to show the relative merits and demerits of the technique. This study demonstrates that the genetic programming based data-driven modelling strategy can be a good candidate for developing models for other types of fuels as well. 

In a second study, fluidised bed air-steam gasification of limestone blended poultry litter is studied in a lab scale bubbling fluidised bed (BFB) gasifier operated at atmospheric pressure using silica sand as a bed material. The effects of air-to-fuel ratio (ER), gasifier temperature and steam-to-biomass ratio (SBR) on product gas yield and conversion efficiencies are discussed. At the optimum condition of ER 0.25 and 800 ºC, poultry litter blended with limestone has yielded a product gas with lower heating value (LHV) of 4.52 MJ/m3 and an average product gas composition (dry basis) of H2: 10.78%, CO: 9.38%, CH4: 2.61 and CO2: 13.13 in an air-blown BFB. Under the optimum condition cold gas efficiency (CGE), carbon conversion efficiency (CCE) and hydrogen conversion efficiency (HCE) are reported over 84, 73 and 42% respectively.

The reported NH3 measurement at ER of 0.28 and 750 ºC is 2.7%whereas 14.7 mg/m3 of HCl content in a dry product gas are observed. Higher temperature and steam injection favour the CO and H2 production however; they do not have positive influence on CH4 formation. Due to high ash content in poultry litter with high K and P, limestone was added to avoid agglomeration and defludisation problem during the gasification.

The experimental results demonstrated that poultry litter can be gasifiedby blending with limestone without affecting significantly the heating value of the product gas. A significant reduction is observed in tar yield while gasifying limestone blended poultry litter. Taking into the consideration of heating value of product gas (4.52 MJ/m3), it can be combusted to generate heat or power.

 

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