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By utilizing biomass gasification, the energy contentof the biomass can be utilized to produce gas to be used forcogeneration of heat and power as well as other energy carrierssuch as fuels for vehicles. The concept is suitable forapplication to existing CHP plants as well as for utilizing spentliqour in small scale pulp and paper mills. The introductionwould enable flexible energy utilization, use of problematicfuels as well as protects the environment by e.g. avoiding therelease of toxic substances. In this paper, the possibilities todevelop this concept is discussed. In this paper we comparedifferent gasification processes with respect to what gas qualitywe get, and how the gasification can be modelled usingdifferent modelling approaches, and how these can becombined. Results from simulations are compared toexperimental results from pilot plant operations in differentscales and with different processes like CFB and BFBTechnologies, athmospheric and pressurized, and using steam,air and oxygen as oxidizing media.

To develop a model for biomass gasification in fluidized bed gasifiers with high accuracy and generality that could be used under various operating conditions, the equilibrium model (EM) is chosen as a general and case-independent modeling method. However, EM lacks sufficient accuracy in predicting the content (volume fraction) of four major components (H₂, CO, CO₂ and CH₄) in product gas. In this paper, three approaches—MODEL I, which restricts equilibrium to a specific temperature (QET method); MODEL II, which uses empirical correlations for carbon, CH₄, C₂H₂, C₂H₄, C₂H₆ and NH₃ conversion; and MODEL III, which includes kinetic and hydrodynamic equations—have been studied and compared to map the barriers and complexities involved in developing an accurate and generic model for the gasification of biomass.

This study indicates that existing empirical correlations can be further improved by considering more experimental data. The updated model features better accuracy in the prediction of product gas composition in a larger range of operating conditions. Additionally, combining the QET method with a kinetic and hydrodynamic approach results in a model that features less overall error than the original model based on a kinetic and hydrodynamic approach.

One of the approaches to model fluidized bed gasifiers is to combine the reaction kinetics and bed hydrodynamics. The kinetic part of the model deals with the chemical reactions occurring in different steps of gasification while hydrodynamics of the bed gives more information about the physical phenomena inside the bed. In this paper two major fluidization models; two phase theory (TPT) and counter current back mixing (CCBM) and one kinetic rate model have been developed and compared in terms of accuracy in predicting product gas concentration and the generality of the model to different ranges of input parameters. The results show that including hydrodynamics of the bed as in TPT improves the accuracy of the kinetic rate model. TPT model can be used for air gasification in bubbling fluidized bed gasifiers while for steam gasification it needs further modification.

The mechanism of biomass gasification has been studied for decades. However, for circulating fluidized bed (CFB) gasifiers, the impacts of different parameters on the gas quality and gasifiers performance have still not been fully investigated. In this paper, different CFB gasifiers have been analyzed by multivariate analysis statistical tools to identify the hidden interrelation between operating parameters and product gas quality, the most influencing input parameters and the optimum points for operation. The results show that equivalence ratio (ER), bed material, temperature, particle size and carbon content of the biomass are the input parameters influencing the output of the gasifier the most. Investigating among the input parameters with opposite impact on product gas quality, cases with optimal gas quality can result in high tar yield and low carbon conversion while low tar yield and high carbon conversion can result in product gas with low quality. However using Olivine as the bed material and setting ER value around 0.3, steam to biomass ratio to 0.7 and using biomass with 3 mm particle size and 9 wt% moisture content can result in optimal product gas with low tar yield.

Considering sustainability of energy resources and environmental concerns have led to activities all over the world seeking alternatives for current methods of fuel production. Gasification of biomass to supply bio-methane is one of those options. Bio-methane is carbon neutral and meets the needs of combustion engines in vehicles.Focusing on vehicle fuel production reveals the need for wide research to understand different types of gasifiers in order to find the possibilities for more methane production.In this paper data collected from different experimental setups are summarized and analyzed.Fluidized bed gasifiers show higher methane concentrations in the produced gas while entrained flow and downdraft gasifiers may be the least suitable types for high methane yields.Heating value of the product gas and cold gas efficiency are also studied as the important parameters for evaluating the characteristics of the product gas. This analysis shows that by increasing the equivalence ratio, the heating value of the product gas decreases while the efficiency may not follow the same trend.