Steam Production From Waste Heat Sources of a Steel Plant

Abstract

The objective of the following paper is to confirm, based on a pre-engineering study and a first techno-economic evaluation, the potential of waste heat recovery in the industrial area of Dunkirk. This steam will be used for regeneration of the solvent of the full-scale CO2 capture unit (1,5MtCO2/yr). Results of this study will seriously impact the cost of CO2 capture and, by consequence, the economy of the whole chain. It will be one of the main challenges of 3D project as this kind of study has never been carried in a European steel mill. Innovative solutions will be needed. The need of steam is estimated at 155 MW for a full-scale DMX (200 t/h steam at 180°C). Arcelor Mittal processes generate many sources of lost heat, which could be used for DMX solvent regeneration. Heat recovery potentials have been quantitatively evaluated in terms of annual energy quantity, available power and temperature levels. The waste heat capacity is reaching 1GW through 17 sources. The heat sources are the following: - In the coking plant: extinction of the coke, heat from the coke oven gas, fumes from the coke furnace, - In the sinter plant: heat from the sinter cooler, from wind boxes under the sinter bed, from the air of the dust collector, - In the blast furnace: fumes from cowpers, heat losses from blast furnace slags and gas, - In the steel shop: heat losses from convertors, hot slabs from the continuous caster, mist from continuous casters cooling, slags from the steel shop, - In the hot strip mill: fumes from the reheat furnaces of the hot strip mill, walking beams, laminated steel cooling. However, only few of the previous waste heat can be used for the DMX. Indeed, the level of temperature, the separation distance between each heat source and the CO2 capture unit and the technological maturity have been considered to confirm the feasibility to recover heat from each source. Which quantity of steam can we produce at 10 barA for the DMX? Almost 50% of the target, can be reach by developing the following waste heat recoveries: - Heat recovery in the steel shop (heat losses from convertors): 30t/h of steam at 10barA - Heat recovery in the sinter plant to feed the DMX (sinter cooler and air under sinter bed): 45t/h of steam at 10 barA - Heat recovery on slabs just after oxycutting: 15 t/h of steam at 10 barA However, additional solutions will be necessary to reach a production of 200t/h of steam. It may be on coke extinction or heat recovery on slabs in the slab park. Each heat recovery has its technical constraint. The recovery on BOFG cooling (heat losses from convertors) is a well-known technology, but in Dunkirk, it may be very expensive because of structural cost. The recovery on the sinter cooler will be the most accurate in term of distance with the DMX but the temperature is not high enough (air at 220°C). The recovery on continuous casting after oxycutting is the most accurate in term of economical constraints but there is not a lot of space available. The recovery on coke quenching is the most accurate in term of technology available and quantity of steam but very expensive. As alternate it will be also considered the building of a new boiler fed with steel mill gas in excess. It might seem like the easiest solution as a great volume of gas is flared. The available power from steel-production gases is greatly higher than DMX need, which means that it could serve as backup for heat recovery systems. As alternate it has also been considered the available heat sources in the neighboring of the ArcelorMittal site. However, compared to Arcelor Dunkirk heat potential, the heat recovery on other sites is far less interesting as the heat volume is low and the distance might be greater. This solution has not been retained for the next phases. In a nutshell, the steam production optimum sizing from waste heat will be presented in this paper.