OCR Text |
Show Data Acquisition System A computer data acquisition and reduction system has been employed for parametric studies. This system collects, reduces, and analyzes the major data measured for operating control and analysis of overall combustion and heat-transfer characteristics. Flow rates of natural gas, combustion air, and water are metered individually by electronic mass-flow meters and acquired by the computer system. The mass-flow meters for natural gas and combustion air were calibrated by two orifice flow meters. The water mass-flow meter was also calibrated by weighing the mass of water flow at operating conditions. Several flue-gas analyzers, including those for oxygen (O~, carbon monoxide (CO), carbon dioxide (C02), nitric oxide (NO), oxides of nitrogen (NOx), and unburned total hydrocarbons (THC), are installed for combustion monitoring and evaluation of combustion emissions. The gas analyzers were calibrated for measuring ranges using cylinder span gases in every test. A water-cooled probe is used to sample the combustion products. The probe at the cold end is equipped with a section of externally heated stainless steel tubing to maintain a sample temperature of about 1900F so that moisture would not condense. The warm sample is passed through a millipore filter to remove any solid particles and a Permapure dryer to remove moisture. The dried sample is supplied to the analyzers through Teflon tubing. A water-cooled suction pyrometer is used to measure the temperature of the exhaust gas for overall energy balance in the combustor-heater unit. To measure gas temperatures in the porous matrix bed, two thermocouple probes are installed between the grate and the first row of tubes and between the two rows of tubes. All the major data are acquired and reduced by the computer to provide real-time monitoring of operating conditions and combustion/heat-transfer characteristics of the test system. EXPERIMENTAL RESULTS The purpose of the experimental study is to explore effects of major configurations of the combustor-heater and the materials of the porous matrix on the performance of the test surface combustor-heater. The data will be used for the further study on the interactive combustion/heat-transfer as well as to guide and validate the mathematical model for optimization of the combustor-heater design. The experiments were performed for the variable parameters, including air/fuel ratio, firing rate, horizontal spacing (S/D) and vertical spacing (H/D) of the heater tubes, as well as bed materials. The performance of the test combustor-heater was evaluated for combustion stability within the porous matrix, combustion intenSity and turndown operation, heat-transfer rate for each row of tubes, thermal efficiency or energy conversion rate of the unit, combustion emissions (CO, NO/NOx, and THC), and pressure drop across the unit. To ensure accuracy of the experimental results, the natural gas used in the tests was sampled and analyzed. Temperatures on the outer surface of the combustor-heater were measured at a total of 52 pOints by a surface temperature probe to estimate heat loss from the walls. Heat loss from the walls is approximately 3% of the total heat input. Flue-gas temperature was also measured by a suction pyrometer for calculation of exhaust heat. Heat balance for the combustor-heater unit is calculated based on all measured data. The overall discrepancy between heat input and output is around 5% of the total heat input. In each test, 5 |