Refractory Lining for Flue Gas and Olivine Sand
The combustor shell is insulated with double-layer refractory lining. The layer exposed to the process flow is designed for erosion resistance, no less than 2” thick. The layer of refractory between the erosion-resistant liner and the shell is insulating to protect the shell from over-temperature. The design temperature of the inner face of all shells is 250°F to avoid carbonic acid corrosion. Acid-resistant coatings on the inside of the shells will be considered during detail design.
The sand and ash from the combustor are discharged to the primary combustor cyclones. The primary combustor cyclones are designed to separate the sand for recirculation to the gasifier while minimizing carryover of sand to the secondary combustor cyclones and minimizing ash in the sand. Ash collected with the sand by the combustor primary cyclones will recirculate with the sand. The secondary combustor cyclones are designed to separate the sand remaining in the offgas and the ash from the combustor primary cyclones to minimize the quantity of solids entering downstream equipment. The solids discharged from the combustor secondary cyclones will be discharged from the plant, so loss of olivine sand is minimized.
The design should include consideration of alternate arrangements, such as multi-clone units, should this reduce the impact of the cyclone height on the “stack-up” and minimize capital costs, O&M costs, exposure of downstream equipment, power requirements and sand losses.
The combustor secondary cyclones minimize the particulate loading in the flue gas entering the dryer and the flue gas treatment system. The ash and sand separated in the combustor secondary cyclones are sent to an ash cooler and then mixed with solids from the gas treatment system for disposal or beneficial use. The sand separated in the combustor primary cyclones falls vertically into Gasifier Seal.
Gasifier Seal Pot
Gasifier Seal Pot is located under the primary combustor cyclones. This seal pot performs the same pressure sealing function as the combustor seal pot, but in the opposite direction. Its function is to prevent gasses from the gasifier running up into the bottom of the combustor cyclones, and allowing flammable gases to mix with flue gas that contains oxygen.
The gasifier seal pot provides a seal by raising the mildly fluidized sand “liquid surface” well up into the dip leg – above the top of the fluidized surface inside the seal pot. Thus, like a liquid sucked up into a straw, the level of the fluidized sand goes up inside the dip leg until it is well above the “liquid level” of fluidized sand inside the seal pot. This fluidized “surface” is level with the overflow line.
The gasifier seal pot provides a negative pressure seal, with the entering sand coming down from the combustor cyclones being at a lower pressure than the gasses entering the gasifier seal pot through its overflow leg. The overflow leg is attached to the gasifier, which operates at a higher pressure than the combustor cyclones.
Fluidization in the gasifier seal pot is provided by low pressure steam, since the fluidizing gases have a direct route to the gasifier. The gasifier seal pot is designed to the following criteria: