Purification of blast-furnace gas and energy conservation

Abstract

499 Given the rising prices of natural gas and electric power, Ukrainian metallurgical enterprises need to introduce energy-saving technologies. To reduce energy costs, and hence produce more competitive metal products, the manufacturing technology may be improved, and energy use at the enterprise may be rationalized, with the utilization of waste gases. It is expedient to make full use of the blast-furnace gas produced at the plant. The compressorless waste-gas turbine is intended to generate electrical energy on the basis of the excess pressure of the blast-furnace gas. The turbine power developed depends on the blast-furnace operating conditions and the flow rate and pressure of the gas passing through the turbine. Only the energy of the compressed gas is used; its heat of combustion remains. Radial and axial turbines are made in Russia and Japan and are going into production in Ukraine. They are easily adapted to the technological cycles of new or existing blast-furnace equipment. Such turbines operate effectively at metallurgical enterprises in Europe and Japan and are under design in Russia. In Ukraine, blast-furnace production accounts for most (60%) of the energy consumption in metal production. Currently, Ukraine operates more than 30 blast furnaces of volume 1386 m 3 or more, which may be equipped with waste-gas turbines for power generation. No turbines operate in Ukraine today, although four operated up to 1990. At the Institute of Ferrous Metallurgy (IFM), Ukrainian Academy of Sciences, efforts to improve blast-furnace smelting began in 1953, under the direction of Z. I. Nekrasov; one of the goals was to reduce energy consumption in hot-metal production. On an industrial scale, research focused on the operation of furnaces with an elevated gas pressure at the charge hole, the use of natural gas and complex injection, and the use of higher-grade raw materials. The construction of larger blast furnaces equipped with redesigned (nonconical) charging units was shown to be expedient. These measures proved effective in improving blast-furnace performance and reducing energy consumption. At present, small blast furnaces with outdated equipment, characterized by elevated energy and resource consumption, are being withdrawn from service in Ukraine and Russia, and around the world. The first level of the furnaces is undergoing major overhaul, including modernization of the systems for the preparation and use of blast-furnace gas, with the installation of compressorless waste-gas turbines. Efforts to reduce energy consumption and environmental impact must address blast-furnace technology. Effective operation of waste-gas turbines is hindered by the low quality of the iron ore, by design faults of the conical charging devices, and by furnace operation with a low excess gas pressure at the charge hole (less than 1.5 MPa). The operation of waste-gas turbines is improved by using nonconical charging units capable of stably maintaining an excess gas pressure of 2 MPa at the charge hole. We know that the furnace process is faster when the gas pressure at the charge hole is higher. Experience shows that each 10-kPa increase in gas pressure raises furnace productivity (hot-metal output) by 1.0‐2.0% and reduces coke consumption by 0.1‐0.5%. When furnaces operate at higher gas pressure, charge-hole dust releases are reduced by 35‐50%. The compressorless waste-gas turbine provides an effective means of reducing the energy consumption in hot-metal product and hence the price of the final metal product [1, 2]. Operational experience with such waste-gas turbines within the Commonwealth of Independent States