Corrosion of Heat-Exchange Tubes in a Simulated Coal-Fired MHD System

An experimental unit was built to burn 125 lb of coal an hour at 4000 deg F in a cyclone burner with oxygen-enriched air preheated to 1500 deg F to ascertain the fireside corrosion problems that might be encountered in the coal-fired MHD generation of power. Potassium carbonate was added to the coal at seed concentrations that would be expected in an MHD combustor. Tubes having a metal composition used in conventional steam generators, and also having a range of alloy compositions that might have potential use in an MHD system, were maintained at surface temperatures of 800–1500 deg F and exposed to products of combustion at 1800–2500 deg F. The seeded flue gas was generally more corrosive than the unseeded. In tests up to 100-hr duration, Haynes 25 was slightly attacked at a wall temperature of 1500 deg F in combustion gas at 2500 deg F; the stainless steels 310, 316, and 446 were resistant at a metal temperature of 1100 deg F in gas at 2100 deg F; carbon steel was attacked at 800 deg F wall temperature and 1800 deg F flue gas.