Performance evaluation of a gasifier cooling jacket by means of a homogeneous two-phase flow simulation model

Abstract

SASOL II uses a number of coal-fired Gasifiers with water-cooled jackets to produce raw-gas for the purpose of manufacturing petroleum from coal. Excess heat generated by firing of the coal is removed with the aid of a water-cooled jacket. Cooling water circulates through the cooling system by means of natural convection only. During operation of this equipment, excessive deformation, or localised buckling of the Gasifier inner wall is experienced, due to localised overheating. Three Gasifier water jacket concepts were devised to enhance the structural integrity of the Gasifier inner wall, and increase the cooling water mass flow rate. A one dimensional homogenous steady state two-phase flow simulation model was developed to simulate the thermo-hydraulic performance of the Gasifier jacket concepts. Boundary conditions including the heat flux profile, high-pressure boiler feed water inlet temperature and system pressure was specified to calculate (amongst other parameters) the rate of circulation, total pressure drop and heat transfer rate through the wall to the water. The Gasifier cooling system geometry was discretised and numerically solved by programming in a software package called Engineering Equation Solver. Verification of calculated results proved that the model over estimates flow rates with a maximum error of 50 %, with the maximum error made when calculating temperature set at 8 %. The simulation results proved that the Box Belt concept combined with configuration 3a should be employed since it will provide the best performance, which is approximately 15 percent higher than the Base Case. This study was industry driven, with production costs and equipment availability being the main research drivers. The usefulness of the homogenous approach is also proven in this study with the estimation of complex system behaviour.