GASIFIERS

Fuel Gasification

Gasification technology is at the forefront in the efforts to develop alternatives for the conventional furnaces. It is of particular interest because it offers an opportunity to use the product fuel gas in integrated gasification combined-cycle electric power generation. The fuel is heated up in the reactor, and then undergoes evaporation and devolatilization. Carbon is gasified by H2O and/or CO2, and the heat for the gasification is provided by partial combustion of released volatile matter and/or gasified combustible gases. The reactor differs when different technologies are adopted. For flow pattern, the reactor can be a circulating fluidized bed, or a bubbling fluidized bed, or an entrained flow reactor. The fuel may be gasified by air, or steam, or combined, or even pure oxygen. The reactor can be pressurized or non-pressurized.

PSL Gasifier Process Model

The three dimensional turbulent reacting flow in the gasifier is simulated by solving the fully three-dimensional Reynolds-averaged transport equations of mass, momentum energy, and chemical species. A two-equation turbulence model is used, in which equations for the turbulent kinetic energy k and its dissipation rate e are solved. A modified k-e two-equation model is also used to account for the effect of curvature under strong swirling conditions. The gas phase combustion of CH4, H2, and CO is modeled by Magnussen model, in which the chemical reaction is controlled by the turbulent diffusion rate. Reactor wall temperatures are calculated based on the balance of heat transfer at the wall. The ray tracing method simulates the radiation heat transfer. Rays are emitted in prescribed directions from points distributed over the domain boundary. Along each ray an energy equation is solved, which accounts the energy emission from gas, the absorption and scattering by fine particulate, H2O and CO2 in gas.

Black Liquor Gasification

PSL has adapted its black liquor combustion model to predict black liquor gasification. In the gasification model, black liquor droplets in the gasifier undergo five stages, namely heating up, evaporation, devolatilization, char gasification, and inorganic reactions. The black liquor gasification model simulates these stages separately.