Control of bed height in a fluidized bed gasification system

A method for use in a fluidized bed apparatus comprising a vessel having a bottom, a first substance to be fluidized, a second substance for fluidizing said first substance in a fluidized bed within said vessel, said second substance being a fluid, said fluidized bed having an upper surface and a bed height within said vessel which is the vertical distance from the bottom of the vessel to said upper surface, a controlling means for controlling the flow of at least one of said first or second substance, said controlling means being regulatable by a signal, and a differential pressure detecting system, said system comprising a plurality of differential pressure detectors connected in series, each detector having a high pressure tap connected to said vessel and a low pressure tap connected to said vessel, and adjacent detectors having a common tap to said vessel which serves as said high pressure tap for one detector and said low pressure tap for an adjacent detector, said vessel tap connections for each detector defining a horizontal zone within said vessel corresponding to each said detector, said method for controlling said fluidized bed height comprising the steps of:

• (a) determining the differential pressure sensed by each detector substantially simultaneously;
• (b) repeating step (a), periodically;
• (c) averaging periodically a predetermined number of the latest differential pressures determined for each of said detectors to compute an average differential pressure for each said zone;
• (d) dividing each average differential pressure by the vertical distance in the vessel of each corresponding zone to calculate a fluidized bed density corresponding to each said zone;
• (e) averaging continuously a predetermined number of the most recent fluidized bed densities calculated for each of said zones to obtain an average fluidized bed density for each said zone;
• (f) disregarding any zones for which the most recently calculated average fluidized bed density was non-positive and reserving the zone closest to the bottom of said vessel which was also adjacent to a zone for which the most recently calculated average bed density was non-positive, and for all remaining zones, calculating a weighting factor for each zone by the formula:
• ##EQU6## where zone A is adjacent to and above zone B;
• (g) calculating the height of the bed within the reserved zone by dividing the fluidized bed density of the reserved zone by the fluidized bed density of the zone adjacent to and below the reserved zone, and multiplying by the vertical height of the reserved zone and the last weighting factor calculated for the reserved zone;
• (h) producing said signal representative of said height of said bed within said reserved zone;
• and
• (i) regulating said controlling means with said signal.