Overall Procedure for Process Control of Entrained-
For the initial start up (or with a new feedstock) gasifier flows are set on the basis of values calculated for the coal footprint (van der Burgt 1992) from analyses of coal and blast and of a calculated heat loss from the gasifier. The reaction conditions will in general be set such that there is a surplus of the blast (in most cases is mostly
oxygen). For dry-coal feed entrained-flow gasifiers this means that the reactor operates with a C02 content of, say, 3-4 mol% and a calculated temperature of well above the melting point of the ash components that may already contain fluxing material. The fastest indication for undesirable fluctuations in reactor temperature is reflected in the steam production in the wall of a reactor with a jacket or membrane wall. The next indication is the methane content of the gas. The C02 content can then be decreased to about 1 mol% by decreasing the oxygen/coal ratio and adjusting the steam/coal ratio. During this operation the theoretical coal footprint will be adjusted to the actual values found, for example, for the reactor heat loss and the CH4 content of the gas, which data will then be later used for optimizing the gasification conditions and the control of the reactor. The coal footprint is a very valuable tool. For the C02 content and the percentages of the other major gas components, the theoretical figures and actual figures differ little provided the freezing-in of the CO shift equilibrium is taken into account. Only the actual CH4 data can deviate considerably from the calculated data. Hence, calibrating the theoretical data with actual measurements becomes important.