COAL ASH TILES BY MICROWAVE PROCESSING

THIS PHASE I PROJECT CONSIDERS THE USE OF MICROWAVE HEATING FOR THE PRODUCTION OF TILES AND BRICKS FROM COAL-DERIVED ASH. THE GENERATION OF UNDESIRABLE ASH FROM COAL-FIRED POWER PLANTS HAS BECOME A SERIOUS ENVIRONMENTAL PROBLEM. COAL-FIRED POWER PLANTS ARE RESPONSIBLE FOR THE ANNUAL PRODUCTION OF MORE THAN SIXTY MILLION TONS OF ASH IN THE UNITES STATES. A TYPICAL 800 MEGAWATT STATION CONSUMES 7500 TONS OF COAL AND GENERATES 1000 TONS OF BOTTOM AND FLY ASH DAILY. ASH CONTAINS HEAVY METALS, AND THE DISPOSAL OF THIS MATERIAL IN LANDFILLS IS DRAWING INCREASED ATTENTION. MUCH OF THIS ATTENTION IS WARRANTED BY THE FACT THAT ASH IS A FINELY DIVIDED OXIDE POWDER WITH A LARGE SURFACE AREA. SINCE THE LEACHING OF A CONSTITUENT FROM A POWDER IS PROPORTIONAL TO ITS SURFACE AREA, IT WOULD BE DESIRABLE TO DESIGN A METHOD OF CONSOLIDATION INVOLVING SURFACE AREA REDUCTION. THE INTEREST IN SUCH A TECHNIQUE WOULD BE GREATLY INCREASED IF, IN ADDITION TO VOLUME AND SURFACE AREA REDUCTION, THE PRODUCT HAD USEFULNESS AND COMMERCIAL VALUE. FOR EXAMPLE, TILES OR BRICKS CAN BE FABRICATED, BUT CONVENTIONAL METHODS OF HEATING USED IN TILE MANUFACTURING REQUIRE LARGE FLOWS OF AIR WHICH CAN CAUSE AIR POLLUTION. THEY ARE ALSO TIME AND ENERGY CONSUMING BEACUSE IT IS RELATIVELY DIFFICULT TO HEAT A POWDER. MICROWAVE PROCESSING ALLOWS FOR LOW COST, VOLUMETRIC, ULTRA-RAPID, UNIFORM HEATING WITHOUT AIR POLLUTION. MOST TYPES OF ASH ABSORB MICROWAVES. HOWER, IF SOME DO NOT, SMALL AMOUNTS OF A MICROWAVE COUPLER SUCH AS FERROUS/FERRIC OXIDE MAY BE ADDED TO FORM A MICROWAVE COUPLING MIXTURE. UPON HEATING, THE ASHES WILL SINTER AND UNDERGO A REDUCTION IN SURFACE AREA. UNDER APPROPRIATE PROCESSING CONDITIONS, THIS WOULD RESULT IN (1) THE FORMATION OF A MECHANICALLY STRONG MATERIAL SHAPED AS A TILE OR BRICK, (2) ENCAPSULATION OF HEAVY METALS IN A VERY STABLE GLASSY PHASE, AND (3) ELIMINATION OF THE ENVIRONMENTAL ISSUES ASSOCIATED WITH THE STARTING MATERIAL.