Wet torrefaction of verge grass - a pretreatment to enable co-firing in a coal power plant

Current energy production is done in a way that cannot be sustained ultimately. Biomass is ideal as a sustainable alternative because it can be used in the existing energy infrastructure. For coal power plants verge grass is one of the products being considered for co-firing. The moisture content and its bioactivity currently prevent direct co-firing on a large scale. A very new and promising pre-treatment technique to counter this is wet torrefaction. Wet torrefaction does not evaporate the moisture, it allows a precise temperature and thus process control, high heat transfer and a combined washing out of unwanted salts. To predict the decomposition of verge grass during wet torrefaction a reaction model was set up. Hemicellulose and cellulose kinetic data was used from previous work on corn cob and pure cellulose. The model was tested with data from research on sugar maple wood meal decomposition. Wet torrefaction experiments showed that verge grass decomposes very rapidly in contrary to the model. Experiments done on xylan showed a very slow decomposition. Bagasse decomposition was very hard to monitor because very little decomposition products were detected. A possible explanation could be that grass is very young and thus has a low degree of polymerization. Xylan and bagasse on the other hand are already treated and therefore the toughest parts of the original material are being torrefied. Overall the biomass species had a very high solid mass loss. Verge grass and bagasse retained around 30% of the original mass and no solid residue was found with xylan. The solid fraction and liquid fraction that could be accounted for is lower than half of the original mass. Although additional tests are needed to accurately predict the decomposition of verge grass a design was made for a pre-treatment plant. This facility was regarded as a stand-alone facility and consists of several parallel CSTR’s and a heat exchanger. The needed calculations are performed to compare wet torrefaction with alternatives.Energy TechnologyProcess & EnergyMechanical, Maritime and Materials Engineerin

Modelling of Biomass Combustor: Final assignment energy from biomass

In this study a 1.1 MW fluidized bed combustor is modeled. A literature study is performed on aspects which determine the characteristics of the combustor. A model is set up and calculations for the design of the Fluidized Bed Combustor (FBC) are performed. Characteristics are calculated for the Fluidized Bed (FB) and Freeboard Zone (FBZ). Matlab is used to perform simulations and generate specific parameters for the design of the FBC. The report starts with an introduction on the FBC, from the sustainable and technological point of view. In Chapter 1 a short overview of the history of biomass is given, from where the link to the FBC design is made. The general aspects of a FBC are stated. Chapter 2 shows the results of the literature study. In particular attention is paid to the formation of greenhouse gasses, which play an important role in power generation and thus in FBC’s. Possibilities to reduce these pollutants are mentioned. It is explained why the formation of thermal NOX is primarily dependent on the temperature and stoichiometry. In the model the formation of thermal NOX is neglected, since the reaction temperature is too low to generate significant amounts of NOX. Fuel NOX seems to contribute in a larger amount to the NOX formation, but the contribution is still unsignificant in the model. The formation of Carbon Monoxide (CO) plays a more important role. This formation is directly related to the mixing of fuel and air at sufficient temperature. To reduce the CO formation, an optimal air to fuel ratio and a greater residence time are suggested. In Chapter 3 the design of the model is presented. This chapter starts with the outcome of the literature study, where the principles of the FBC are described. After that, a list of assumptions is presented. The overview of the assumptions is specified and worked out for the different reactor zones in the FBC: the Fluidized Bed, the Splashing Zone and the Freeboard Zone. Chapter 4 elaborates on the air speed in the FBC. The air speed affects important running characteristics such as the behavior of the sand particles in the bed, the burning efficiency and the formation of greenhouse gasses. It is also an important parameter for the determination of the dimensions of the FB and FBZ. This chapter concludes with a section including numeric values and results of the calculations are presented, which in turn are used for the calculations on the combustor model. The complete model is presented in Chapter 5. Detailed calculations on the model are explained, starting with the combustion reactions. This model description includes molar ratio’s, caloric values and mass flows. Furthermore specific energy balances are shown for each section of the combustor. Finally, the wall losses are defined. A summary of the results can be found in Chapter 6. Results of energy balances and efficiency are presented and a clarification of the temperature profile is given. This document concludes with a discussion on the obtained results and the limitations of the model.Process and EnergyMechanical, Maritime and Materials Engineerin