| OCR Text |
Show Co-AL mixture respectively, each employed heating to 235°F. Minimum combustion air temperature requirements for stable ignition without support fuel ranged from a low of 500°F for the Pittsburgh No. 8 Co-AL mixture to 700°F for the 50:50 Upper Freeport/Pittsburgh No. 8 Co-AL blend. The low volatile Upper Freeport Co-AL mixture could not be burned with stable ignition using the maximum slurry heating capability of the available test facilities (about 210°F at the time of those tests) even with an 800°F combustion air temperature. This result was not unexpected since B&W's experience with low volatile coals like the Upper Freeport coal indicates that they would require support fuel and special burner and furnace design even when burned as pulverized coal in a large commercial furnace. Burning profiles determined in B&W's laboratories indicate relative combustion characteristics of different fuels and identify relative ease of ignition and residence times for complete combustion. The burning profiles for the Pittsburgh No. 8 and Upper Freeport coals shown in Figure 6 illustrates the expected behavior of these fuels. The curves indicate that Upper Freeport coal, after initial evolution of moisture, requires a higher temperature for the start of oxidation and a higher temperature for completion of combustion than the Pittsburgh No. 8 coal. In a full-scale furnace these laboratory observations translate into the need for support fuel and longer residence time for stable ignition and complete combustion of the Upper Freeport coal. Our experience with the Upper Freeport Co-AL mixture is consistent with the laboratory data. In most of the combustion tests where stable ignition was attained, carbon conversion efficiencies were comparable to those generally experienced for coals of similar volatile content when burned in the facility. Atomizer wear was quite noticeable even during the brief firing periods encountered. Sprayer plates constructed of carbon steel, stainless steel, and hardened tool steel showed significant wear after three to four hours of operation. No attempts were made to utilize other materials or designs due to time constraints. Future development activities include a significant program to address the burner wear problem. PUMPING AND HANDLING A coal-water mixture pumping and handling facility was constructed (Figure7). The same facility, with minor modifications, was used to supply Co-AL mixture to the combustion chamber during that portion of the test program. The equipment consisted of a 600 gallon mixing tank (k ft ID x 6 ft) containing a steam coil 13-7 |
