DESIGN OF WASTE HEAT BOILERS FOR THE RECOVERY OF ENERGY FROM ARC FURNACE WASTE GASES

Ziel

AT PRESENT THE ELECTRIC ARC FURNACE ACCOUNTS FOR 34 % OF THE STEELMAKING CAPACITY IN BRITAIN AND THERE ARE OVER 250 ELECTRIC ARC FURNACES IN OPERATION WITHIN THE EC. THE COST OF ELECTRICAL ENERGY IN STEELMAKING IS THEREFORE A NOTICEABLE PROPORTION OF THE TOTAL COST.

A LITERATURE SURVEY HAS REVEALED A WIDE AREA OF GENERAL INTEREST IN METHODS OF WASTE HEAT RECOVERY FROM THE ELECTRIC ARC FURNACE BUT NO WASTE HEAT RECOVERY FACILITIES HAVE YET BEEN BUILT.

THIS PROJECT DEALS WITH A FEASIBILITY STUDY FOR A BOILER WHICH WILL BE HEATED WITH FLUE GASES FROM AN ARC FURNACE. THE 180 TONNE ARC FURNACE PRODUCES 350 000 TONNES OF STEEL PER YEAR AND THE WASTE HEAT AVAILABLE FOR RECOVERY IS 15 MW ACCOUNTING FOR 200 KWH PER TONNE OF STEEL. IF THIS WASTE HEAT COULD BE USED TO RAISE STEAM, THUS REPLACING FUEL OIL, THIS WOULD LEAD TO ANNUAL SAVINGS OF UKL 0.5 X 10EXP6 PER FURNACE. THE WASTE HEAT TEMPERATURE VARIES WIDELY DURING THE PROCESS (200 - 500 DEGREES C). A SURVEY OF THE STEAM DEMAND WITHIN BSC SITES WITH ARC FURNACES REVEALED THAT SPECIFIC USES FOR STEAM VARY FROM WORK TO WORK. A LARGE PROPORTION OF THE HEAT DEMAND COMES FROM SPACE HEATING OR HOT WATER PRODUCTION. A STEAM DEMAND EXISTS FOR 5.5 BARS (160 DEGREES C), 15 BARS (200 DEGREES C) AND 45 BARS (425 DEGREES C). THE DISADVANTAGES FOR SPACE HEATING ARE THAT THE DEMAND IS SEASONAL AND FOR THE HIGH PRESSURE STEAM PRODUCTION THAT SPECIAL BOILERS ARE REQUIRED.

THE OPTIONS OF USING STEAM TO SUPPLY PART OF THE INWORKS STEAM DEMAND OR FOR GENERATING ELECTRICITY OR A COMBINATION OF THE TWO HAVE BEEN CONSIDERED.

EXTENSIVE MEASUREMENTS OF THE CONDITIONS EXISTING IN THE WASTE GAS STREAM HAVE BEEN MADE THROUGHOUT THE STEELMAKING CYCLE FOR FURNACE PRACTICES INVOLVING OXYGEN BLOWING, CONTINUOUS CHARGING AND SUPPLEMENTARY FIRING WITH OXYFUEL BURNERS. VARIOUS PRACTICAL IMPLICATIONS OF THE USE OF A WASTE HEAT BOILER HAVE BEEN STUDIED. THESE INCLUDED THE LOCATION OF THE BOILER, THE ACCRETION OF SOLID MATTERS ON TUBES (THE WASTE GASES FROM AN ELECTRIC ARC FURNACE CONTAIN LARGE AMOUNTS OF PARTICULATE MATTER, CONCENTRATIONS OF UP TO 200 G/M3 HAVE BEEN MEASURED), THE EFFECT OF THE PRESENCE OF THE BOILER ON GAS CLEANING AND THE CONTROL OF FURNACE EXTRACTION TO ACHIEVE OPTIMUM PERFORMANCE.