OCR Text |
Show one to result in an average heat flux of 12,240 BTU/HR/SQ.FT when ceramic radiant tube surface temperature was maintained at 2000 degrees F.+. Initially, the flame stability was not satisfactory due to inherent moisture in the mullite material, which needed to be dried before being fired. The temperature profile obtained indicated less than 45 degrees F. temperature gradient along the tube. Maximum flue gas temperature at the exhaust outlet was about 650 degrees F. This resulted in a thermal efficiency of higher than the metallic SER. However, there were some drawbacks observed after firing the system for ten hours. 1) The burner nozzle head was completely disoriented due to intense heat build-up in the surroundings. 2) Ceramic mullite tube failed at the closed end. Thus, it was decided to investigate different ceramic materials and develop a new burner to restrict against such an intense heat build-up. C) Ceramic multi tube plug recuperator - a preliminary test was conducted using a multitube recuperator having an effective heating surface area of 204 squared inches, in a hot flue gas temperature of 1900 degrees F. - 2000 degrees F. The burner was fired in a high and low firing mode for 5 to 6 hours. The maximum heat flux generated on the radiant tube was 55 to 69 BTU/HR/SQ.IN. With the help of the flame control device, flame length was varied to see if there were any effects of flame impingement on the ceramic tubes. Design methods used to hold ceramic tubes with metallic flanges were found satisfactory. However, there could be some design improvements in integrating the different components of the recuperator. Preheat temperature was found to be 600 degrees F. The degree of preheat was minimal because recuperator size was very small. This test was, in essence, conducted to ensure the design methods of using ceramic multitubes in a fashion similar to the metallic one. Extensive tests are underway to use the recuperator for a higher firing rate, i.e., 500 CFH and flue gas temperature of above 2000 degrees F. Different burners are also being considered to be used to observe the impacr of combustion sequence. 73 ACKNOWLEDGEMENT Authors recognize the tireless efforts put forth by Miss Sherri Lepak in typing this manuscript. An appreciation goes to Mr. Dennis Wagen, President of WB Combustion, Incorporated, also. Research work was partially supported by Gas Research Institute. 1. Mike Lukasiewicz "Advance in Natural Gas Combustion Systems for u.S. Industry", paper presented at the Fourth International Symposium on Combustion Processes, June 20, 1985 -- WistaJawornik, Poland. 2. Shyam N. Singh "Recuperative Heat Exchanger Systems for Indirect Fired Furnaces", Industrial Heat Exchangers Conference Proceedings, November 1985. 3. Mike Lukasiewicz "An Integrated High Temperature Regenerative Burner Radiant Tube Application", Industrial Heat Exchangers Conference Proceedings, November 1985. |