SIEMENS

The economic crisis has hit the steel market especially hard. After several very successful years — driven by the boom in emerging markets — demand collapsed dramatically. In the Fall of 2008 the German steel industry, for example, recorded the sharpest decline in orders since the end of World War II. According to the German Federal Statistical Office, raw steel production in Germany in the first half of 2009 alone was down 43.5 % from the level posted in the first half of 2008. In the U.S. during the same period, the World Steel Association reports, production fell by more than 51 %.
In addition, energy-intensive industries in particular are facing increasingly strict environmental regulations. According to the International Energy Agency (IEA), iron and steel mills consume 20 % of the energy required by industry and are responsible for 30 % of industrial CO₂ emissions. Energy consumption alone accounts for about one third of a steel mill’s operating costs. This makes it possible to use energy-efficient technologies to fight both the economic and the climate crisis. "Environmental protection and cost savings are not mutually exclusive," says Olaus Ritamaki, General Manager at Siemens VAI in Oulu, Finland. "In contrast, energy-efficient technologies reduce operating costs and ease the strain on the environment".

Red Hot Results. Among the biggest sources of flue gas emissions in integrated steel mills are coking and sintering plants. While some newer facilities use the Corex or Finex processes developed by Siemens and can thus dispense with coking and sintering, many steelworks still use the traditional blast furnace method, in which pig iron is produced from iron ore using coke and sinter.
To make coke, coal is heated in a coke oven to 1,000 °C in the absence of air. Afterwards, the hot coke must be quenched. For the conventional wet quenching process, water is used. Enormous white clouds of steam are released, dust emissions and wastewater harm the environment, and the energy employed dissipates into the atmosphere. This can be prevented with the help of the coke dry-quenching process (CDQ) offered by Siemens VAI. With CDQ, the heat from the red-hot coke is used to produce steam, which in turn is available for further processes, such as heating, for example, or for generating electricity. A typical CDQ facility from Siemens with a capacity of one million tons of coke per year consists of three cooling chambers — two in full operation and one on "hot stand-by." The latter is only charged with about 10 % of its actual quenching capacity and is ready in case a problem occurs. Quenching is thus possible at all times, including possible maintenance periods.
With CDQ, hot coke is cooled to 180 °C, even as 1,000 °c coke is fed into the cooling chambers from above. A circulating gas flows in at the bottom of the cooling chamber and absorbs the heat. The gas, now at about 800 °C, is channeled with air back into the waste heat water boiler. Here, more than 500 kg of high pressure and high temperature steam can be produced per ton of coke. Connecting a steam turbine yields 15 to 17 MW of generating capacity. That’s equivalent to the power produced by five large wind turbines and adequate for the requirements of about 30,000 four-person households. What’s more, as the coke in the CDQ process is drier than wet-quenched coke, less reducing agent is consumed later in the blast furnace.
Modernization not only saves millions in operating costs — leading to rapid amortization — but environmentally-friendly CDQ also reduces dust and gas emissions to almost zero. With conventional wet quenching, about 500 g of dust are emitted into the atmosphere per ton of coke — frequently much more. Many CDQ systems from Siemens VAI have been operating reliably for years — for example, at an ArcelorMittal plant in Kraków, Poland, since 2000. Siemens is currently taking part in a project run by SAIL, India’s biggest steel producer, which is building a facility that is scheduled to open in 2011.
Sintering plants are another area in which Siemens VAI offers innovative solutions that reduce costs and improve environmental protection. With Selective Waste Gas Recirculation technologies, for example, waste gas produced during sintering can be recirculated. In a sintering plant the ore is baked on a sinter strand, which is similar to a furnace grate. In this way, the fine ore is prepared for the blast furnace. Here, the ore is ignited on the sinter strand, and wind boxes suction off the waste gases from below. "The ore burns from the top down, like in a tobacco pipe," says Andre Fulgencio, Product Manager for sintering plants at Siemens VAI in Linz, Austria.
To allow some of the gas to be recirculated into the process, it is first fed into a chamber. Here it is mixed with waste gases from the sinter cooler, to ensure the oxygen content is at least 16 % and thus high enough for combustion. After that, the waste gas mixture flows into a recirculation hood installed above the sinter strand, from where it is blown back onto the sinter strand — at the most homogeneous possible temperature and pressure. This measure lowers a sintering plant’s CO₂ emissions by up to 10 %; the entire volume of waste gas — which includes sulphur dioxide, various nitrogen oxides and dust — is reduced by 40 %. Taken together, these steps reduce fuel requirements and thus costs. So sinter requires up to 10 % less coke and about 20 % less ignition gas. An investment in CDQ is thus usually amortized in under two years.
To date, this technology has been used at three locations: a plant operated by Austrian steel producer Voestalpine (in operation since 2005); a sinter plant operated by Dragon Steel in Taiwan; and two sinter plants operated by South Korean steel giant Posco.
Siemens VAI has also developed an energy management system that focuses on a steel plant’s total energy use with a view to cutting its energy consumption, costs, and emissions. This involves taking into account the complete production process — from raw materials to final steel products. Organized to be modular, the system can be tailored to the customer’s specific needs, and can even be integrated into existing automation technology at very old facilities. "In the ideal scenario all you need to do is transfer and configure the software," says Franz Hartl, who is responsible for technical marketing of automation solutions at Siemens VAI in Linz.

System-wide Savings. As steel mills use a very large number of processes, it is often also necessary to install additional measurement systems, for example to determine levels in tanks. Key values in terms of energy consumption and distribution can then be recorded every few seconds. Thanks to Siemens’ energy prediction and optimization module, the energy needed for an order can even be predicted on the basis of production planning, enabling operators to purchase fuels at attractive prices. "Steel producers who use the prediction function are superbly equipped for negotiating prices with their energy suppliers," says Hartl.
The high degree of transparency of Siemens’ mill overview processes enables operators to predict and prevent costly load peaks by initiating load shedding — in other words, by reducing energy consumption. This can be achieved by shutting off energy-consuming equipment like furnaces when they are not needed. "Flaring" losses — the burning off of surplus gas, which later must be replaced by energy purchased at a high price — are minimized. In most cases the savings amount to about 3 % of total energy, which is a lot of money and emissions. Given energy savings of only 1 % at an annual production volume of five million tons of steel, CO₂ emissions can be reduced by around 100,000 t per year. Here, an investment in Siemens’ energy-saving solutions can pay for itself very quickly. In fact, depending on the plant, its degree of automation and annual tonnage, the investment can pay off after just a few months.