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

Abstract

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.

Development, testing and evaluation of MHD-materials

“…seeded streams. The marine gas turbine literature concerned with attack by Na 2 S 04 /NaCl mixtures is relatively extensive whereas there is a surprising paucity of data on attack by K^SO^except for the investigations by the U.S. Bureau of Mines at Bruceton, PA (2) and by the Central Electricity Research Laboratories in England (3).…”

“…by means of optical microscopy, SEM techniques, X-ray diffraction, etc. (1) and some results were presented at MHD meetings (2,3). Briefly, K(g) pressures were determined by a weight loss method using our Mettler TGA system and by mass spectrometry using a Bendix Time-of-Flight Mass Spectrometer.…”

“…(1) The mass spectrometer instrument constant is in fact constant; (2) The total weight loss observed is due to vaporization of K 2 O only (3) The only K containing species being~lost is K(g) . A 10 ym beam was used and data were collected at intervals of 30ym from the edge.…”