OCR Text |
Show The desired blast air temperatures were obtained in a two step process, as indicated in fig. 6. Firstly, the combustion air was preheated indirectly to about 400°C, and then injected into a special precombustor furnace together with natural gas, where combustion raised the "air" temperature to the correct level. Oxygen was added to the flue gas mixture to restore the oxygen content of the blast air to 21%. On fig. 6 the numbers used in the text to identify the six coal injectors are shown. Standard IFRF techniques were applied for flue gas and detailed flame measurements. Here, only a list of instrumentation employed is outlined, as detailed information on the construction and principle of operation of the instruments are given in various IFRF publications [4J. - Gas temperatures were measured with a suction pyrometer employing a Pt/Rh6, Pt/Rh30 thermocouple. - Gas concentrations were sampled with an IFRF "B" probe. The "B" probe utilizes bronze filters with pore sizes of 5-7 y. The gases were analysed on a water free basis, using a gas chromatograph and also various single specific instruments (CO2, O2, CO, N0X). - Solid samples were also collected with the "B" probe. In-flame gas velocities were approximated by Prandtl probe measurements in the blast air jet and whenever possible solid sampling was done under near isokinetic conditions. The solid samples were analysed for carbon, hydrogen, ash, and volatiles, from which various burnout related quantities can be calculated. RESULTS A list of the input conditions for the measured flames together with the on axis coal burnout at 1.0 and 1.5 m, which are representative of raceway lengths [l] is shown in table 2. The distance is measured from the tuyere exit. The burnout, Tx, has been calculated from an analysis of the solid samples collected in the flames. The results shown here summarize the effectiveness of the various test parameters in controlling the combustion rate within these distances. For a given bituminous coal the parameter exhibiting the strongest influence is stoichiometric ratio. With the Elk Creek coal and a stoichiometric ratio of one, the blast temperature, coal particle size, injector diameter, and oxygen concentration demonstrated very little effect on the burnout at 1.0 and 1.5 m; (for flames F-13, 10-6 |