OCR Text |
Show recuperators in the glass industry must be able to withstand the high temperatures and the corrosive nature of the melter flue gas. In addition, for this process, the material should also have the strength characteristics to handle 150 psia air at elevated temperatures. Internal investigations as well as discussion with equipment vendors suggest that some specialty, high temperature alloys could be successfully used for this application. Ceramics were ruled out because of their lower mechanical strength and vulnerability to corrosive attack, although their ability to withstand much higher temperatures does, of course, make them very desirable for this application. Another important design issue is the choice of the flow pattern within the recuperator: coo-current, counter---current or a little of both. A counter--current flow pattern would provide the highest possible exit temperature for the gas turbine and is desired if not constrained by materials limitations. For the fired gas turbine case, a counter-current flow pattern is used since the air/steam outlet temperature of 981°F gives metal wall temperatures well within the limits of the metals being considered. In the small gas turbine case, complete counter-current flow pattern cannot be used because this would give metal wall temperatures above the limitations of the metals being considered. By using counter-current flow in the cooler section and co-current flow in the hotter section of the heat exchanger, this problem can be avoided. Gas Turbine Gas turbines are commercially available in size ranges from under lMW to over 100MW. For the processes presented here, the gas turbines required fall very much in the low end of this range, especially for the small turbine case. Gas turbine generator sets are usually supplied as single units that include the compressor, combustor and the expander. Generator sets most amenable for use in the indirect fired gas turbine cycles proposed here would be ones with an external combustor. In the small gas turbine case, the combustor would be replaced by a recuperator. For the fired gas turbine case, the recuperator would be added in series between the compressor outlet and the combustor inlet. Discussions during the course of the development project with some of the leading gas turbine suppliers in the U.S. has confirmed the technical viability of these modifications. The recuperator would be supplied by a company specializing in supplying heat exchangers to the glass industry. Overa 11 The technical viability of these processes has been confirmed with companies supplying recuperators to the glass industry and with gas turbine manufacturers. These gas turbine cycle schemes involve the marriage of two well established technologies. Since the equipment needed is either commercially available or can be readily developed, these schemes pose minimal technical risk. - 8 - |