Inorganic Matter Behavior during Coal Gasification: Effect of Operating Conditions and Particle Trajectory on Ash Deposition and Slag Formation

Abstract

Ash particle deposition and uncontrolled slag flow, which can lead to tap hole blockage, are some of the main issues during coal gasification. In this work, a special collector probe was used to collect ash deposition and analyze slag formation and blockage probability in terms of operating conditions and particle trajectories. Increasing the temperature led to the increase in the total deposition for all of the experiments. However, when the temperature was increased, the weight of produced slag flow increased, but it was observed that increasing the temperature could not guarantee the safe operation by preventing deposition blockage. Using two Canadian coal types proved that the ash composition of coal has a significant effect on the amount and thickness of deposition on the wall. For fuel with low ash viscosity, increasing the temperature increased slag flow and blockage never happened. However, for fuel with high bulk ash viscosity, when the temperature was increased, the blockage probability did not decrease. The reason might be related to the different effects of the temperature on particle stickiness and slag viscosity at a specific range of the temperature. Computer-controlled scanning electron microscopy (CCSEM) analysis showed that excluded iron-bearing minerals of the first coal and included calcium-bearing minerals of the second coal had a substantial effect on the deposition tendency of these fuels. Increasing the velocity of the particles by gas flow rate mostly resulted in reduction of deposition. Fuel with a higher particle size range at a low temperature and high gas flow has the lowest deposition tendency. To evaluate the effect of particle trajectory/aerodynamics, two different types of feeding configurations were used and the results showed that the feeder type has a significant effect on the deposition pattern and growth at different locations. One feeder by injecting the particles in a narrow area led to high inorganic accumulation near the feeding spot, resulting in severe depositions with a thickness of several centimeters. The other feeder caused more uniform deposition by producing a wider sticky surface with a lower deposition thickness on the wall of the furnace.