MEI Case Study - Cali FBC - Make-Up Bed Sand

Two companies in California decided to install fluid bed combustors to dispose of waste matter harvested with their nut crop in an environmentally acceptable way. The waste comprised of grass, weed, tree branches, waste wood and unacceptable or waste crops.

The iodized bed combustion method was thermally efficient and clean because combustion took place at lower temperatures than conventional combustors to avoid the generation of CO and NOx gasses. California has the highest demands for clean air which are rigidly enforced for new combustion plant. The bed material was a local sand with a start volume of 2.5mT (5500lb).

The sand level was to be maintained to a certain level during combustion to maintain efficiency and to avoid the creation of large clinkers. This was achieved by the SANDPUMP located beneath the sand regeneration storage silo. A 50mm (2") standard steel pipeline re-circulated the spent sand to the top of the storage silo.

The SANDPUMP is a low velocity dense phase pneumatic conveying system in which a special pressure vessel conveys the sand slowly to its destination. In this way very low transfer velocity is achieved to avoid pipewear. Also the power economy is dramatically increased since very low air supply is required. Bed replacement was required to be no less than 680 kg/hr (1500 lb/hr).