Conventional coal feed systems using gravity flow of solids, such as in a coil feed to coal-fired boilers, allow major fluctuations in the coal suspension density and mass flow rate, which is a product of the density and velocity of the solids.
However, fluctuations of coal suspension density and mass flow rate to burners within a coal gasification reactor, hereinafter referred to as a gasifier, are detrimental to gasifier performance. For example, such fluctuations cause inefficient combustion of fuel within the gasifier and damaging heat fluxes to the burner face within a reaction zone near the burner which result in thermal stresses on the burner face. Since the residence time of the coal within the reaction zone of the reactor is approximately 200 milliseconds or less, preferably 80 milliseconds, the coal suspension density and mass flow rate should preferably be constant over periods of this order and preferably over shorter periods to maintain constant local conditions. The coal suspension densities used in the present invention range from 50-800 kg/m.sup.3, preferably 200-500 kg/m.sup.3.
U.S. Pat. No. 4,049,394 is related to maintaining a predetermined volumetric ratio between fuel and a gasification agent during feeding thereof into a gasification reactor. However, this patent is not directed to controlling the suspension density to yield a uniform, constant mass flow rate of the fuel and gasification agent to the reactor.
The present invention is directed to controlling the suspension density of the coal to provide a uniform, constant mass flow rate to the burners of a gasifier over time periods as short as 0.2 seconds or less.
Applicant is not aware of any prior art which, in his judgment as one skilled in this particular art, would anticipate or render obvious the present invention. However, for the purpose of fully developing the background of the invention, and establishing the state of requisite art, the following are is set forth: U.S. Pat. Nos. 3,339,984; 3,514,217; 4,049,394; 4,482,275; RE 31,676 and 4,490,077.