Siemens VAI Metals Technologies received an order from the Korean steel producer Posco for the provision of engineering and supervisory services in connection with the installation, operation and maintenance of a selective waste-gas recirculation system for each of two sinter plants located at the company's Pohang Works.
The contract value is a single-digit million-euro figure. Through the recycling of hot offgas containing dust and other pollutants to the sinter strand, a reduction in the specific waste-gas volume and emission level can be achieved, in addition to a lower specific coke consumption. Start-up of the new waste-gas recirculation systems is scheduled for the first quarter of 2010.
At Posco's Pohang Works five sinter plants are in operation, two of which will be retrofitted with a selective waste-gas recirculation system. Sinter Plant No. 3, with a sintering surface area of slightly more than 500 m2, is capable of producing six million tons of sinter per year. A total of 300,000 Nm3/h of offgas (or 15-20% of the total offgas quantity) will be recycled to the sinter strand. Sinter Plant No. 4, with a sintering surface area of 436 m2, produces roughly five million tons of sinter per year. The surface area of this strand will be extended to nearly 520 m2 through an elongation of the sinter-strand length to enable an annual sinter output of approximately 6.7 million tons. Here too, approximately 300,000 Nm3/h of offgas (or 15-20% of the total offgas quantity) will be recirculated to the sinter strand. Installation of the selective waste-gas recirculation system will enable a higher sinter capacity without increasing in the total offgas quantity. The offgas from the sintering process is subsequently treated in an ESP (electrostatic precipitator), DE-SOx plant, DE-NOx plant and bag-filter station to meet municipal environmental regulations.
Contrary to other waste-gas recirculation systems where a portion of the total sinter offgas is extracted for recycling to the sinter strand, only the offgas from selected wind boxes is recycled to the sinter strand with the Siemens VAI solution. This provides a high degree of operational flexibility in that operators can freely select wind boxes for recirculation purposes with, for example, the highest concentrations of CO gas or the highest emission levels. When hot/CO-rich offgas from the sinter strand is selected, the coke consumption required for the ignition of the sinter raw mix can be reduced by up to 10 percent with a corresponding decrease in CO2 emissions. With the recycling of offgas from wind boxes with especially high concentrations of emissions, an increased quantity of dusts and pollutants can be entrapped or chemically bound or neutralized in the sinter bed. This reduces the overall specific load of pollutants contained in the offgas which must be treated prior to being released to the environment. Additionally, the specific quantity of sinter waste-gas is reduced, which not only lowers the electrical energy consumption of the ID (induced draft) fans, but which also considerably lowers the CAPEX (capital expenditures) and OPEX (operational expenditures) for the downstream gas-treatment facilities.
With a crude-steel output of nearly 35 million tons in 2008, Posco (Pohang Iron and Steel Company Ltd.) is the fourth largest steel manufacturer in the world. At its production sites in Korea and elsewhere in Asia, the company produces a wide range of carbon, stainless and electrical-steel grades which are sold as coils, sheets, plates and wire rod that are used for a multitude of industrial applications.
Further information about solutions for steel works, rolling mills and processing lines