Overpressure Hazard Assessment of the Mountain Fuels Resources, Inc. Gasifier

摘要

A hazard assessment methodology has been developed to determine the overpressure hazard potential of the Mountain Fuels gasifier. The Mountain Fuels gasifier is the reactor vessel for a high-pressure (20 atm), entrained-flow gasification process that burns a fuel-rich mixture of pulverized coal (80 mu m), oxygen, steam and recycled product gas to yield a medium-BTU product gas. The methodology proceeds in three steps. First, a thermochemical equilibrium code is used to identify hazardous compositions by determining whether the constant volume explosion pressures of plausible mixtures are sufficient to cause overpressure failure of the gasifier. Secondly, process evaluation assesses foreseeable scenarios for arriving at conditions which would create these hazardous compositions. Finally, an explosion code is used to evaluate the effectiveness of venting in reducing the explosion pressure to a safe level. The analysis shows that a fuel blockage resulting in flame quench, followed by fuel feed resumption, can allow hazardous mixtures (with an explosion pressure potential of 5 to 11 times the initial pressure) to form in the gasifier if emergency shutdown or reignition does not occur within 30 seconds. However, calculations show that prompt reignition is most probable due to radiation from the hot walls of the ceramic-lined reactor. If reignition is delayed, pressure relief venting of the explosion will prevent gasifier overpressure provided that the initial burn velocity of the mixture is less than 300 cm/s. However, our crude estimate of initial burn velocity places it in the neighborhood of 500 cm/s; this could produce explosion pressures capable of bursting the gasifier. (ERA citation 08:050516)