M.Sc Student M.Sc Thesis Cui Rong Control of the Solid Particles Circulation in a Two-chamber Biomass Gasifier Utilizing Horizontal Steam Injectors Department of Mechanical Engineering PROFESSOR EMERITUS Yehoshua Dayan PROFESSOR EMERITUS Arthur Shavit (Deceased)

Abstract

Introducing horizontal gas injection at the bottom of the gasifying compartment will increase the solids circulation flow rate, by forcing the solids into the bottom of the combustor. The velocity profiles of horizontal jet are modeled and the correlation equation of penetration length is chosen according to Merry (1971). Proper parameters of the penetration length are determined to keep the gas injection constant and stable. The solids circulation rate, caused by the gas injection, is calculated. Introducing the steam injection significantly contributes to the control flexibility and stability of the entire system. The influence of several essential parameters on the steady state solution of the new model is discussed. In particular, the steady state solution of carbon concentration c1ss and temperature T1ss decrease as v1 increases. That means as the gasifying reaction processes, both of carbon concentration and temperature in gasification chamber decrease slowly along the vertical length. The system is not carbon concentration controlled but air flow controlled. There should be a minimum value of P to ensure the mathematic model correctly describe the dynamical system. In the above mentioned calculations, the optimal working conditions are chosen similar to those selected by G. Mustafaraj (2003).

In summary, the simulation results show that the new model with the horizontal steam injection is asymptotically stable and quite flexible. The control of the circulation may then be achieved by both the new horizontal gas (steam in this case) flow and the main air flow (main steam to the gasification section may also contribute some flexibility in the control). The steady state solution of the system is sensitive to the changes in biomass feeding rate, but the system’s efficiency can’t be increased by simply feeding more biomass. Investigating the effect of possible pressure surges in the combustion chamber, shows that the system is much safer than the classical one, and effectively suppresses possible accidents caused by such pressure surges in the combustion chamber.