OCR Text |
Show Experimental Procedure Each test was divided into four tasks: observing combustion and operational conditions for (1) matching targeted run conditions, (2) start-up, (3) transition, and (4) steady-state operation. Target run conditions were established before each test, which included several sets of values for bed temperature, excess air, and fuel rates. These target run conditions were derived from assumptions and/or observation of the burning characteristics of char in the shakedown tests. Control parameter (independent variables) were derived from complete theoretical combustion reactions; with bed temperatures to be maintained within the range for efficient sulfur capture. Start-up for each test was achieved basically by combustion of an air/propane mixture fed through the distributor to heat the internals of the combustor. After the combustor's temperature reached about 600°F, limestone (-12 X +28 mesh) was fed to begin bed building. Approximately 6000 grams of limestone was used to bring the bed to its 10-inch static height, the gas mixture continued to supply process heat during bed building. After bed building was completed and the bed temperatures reached the test limits to be maintained by char combustion, the gas mixture was decreased and the char feed was started. The bed temperature, utilizing only char, was stabilized and the transition phase to a target run condition began. The transition phase represents the process of changing from one target run condition to another target run condition, once start-up has been completed. Target run conditions were obtained by slight adjustments to air and fuel feed rates and heat extraction by the in-bed heat exchanger. When conditions stabilized within limits of targeted run conditions, a steady-state period was defined. In order to maintain essentially constant operating conditions, slight adjustments in bed temperature were made by varying the heat extraction rate via the in-bed heat exchanger. Experimental data were obtained during the steady-state periods. Early in the study, steady-state conditions were disrupted by intermittent feed to the combustor. The problem was first observed in shakedown tests; bed temperatures would decrease, followed by fluctuations in flue 22-9 |