International Symposium on Ironmaking for Sustainable Development, 28-29 January. 2010, Osaka, Japan Abstract Large volumes of top gases are generated and often utilized internally as a fuel or in CHP units for producing heat and power at the steel plant. The objective of this study is to analyze the economic potential of using these gases as efficiently as possible to produce methanol in an integrated steelmaking plant, where recycling of the Blast Furnace top gas is an option. The economy of methanol production is investigated by minimizing the cost of liquid steel production in the steel plant, considering the costs of raw materials and fuels, CO 2 emissions and stripping, as well as credits for power, heat and production of methanol. Keywords Process Integration; Optimization; Top Gas Recycling; Methanol Production; CO 2 Emission; Steel Production 1. Introduction Energy saving is an important issue in the steel industry. Improvement of the energy efficiency, to reduce the energy consumption, will increase the economic profitability as well as reducing the environmental impacts. The process industry has experienced increasing expenses related to fulfilling demands of environmental impact and for the assessment and documentation of energy efficiency. It is vital that initiatives within these areas are coordinated and integrated with plans for production. Steelmaking process is well established and has already evolved to mature state 1) and it is therefore difficult to substantially reduce the energy demand and the emissions. Steel plants have a significant contribute to the global CO 2 emission; in the other hand, most of the high value Off- gases from different units such as Coke Oven Gas (COG), Blast Furnace (BF) and Based Oxygen Furnace (BOF) are used in Combined Heat and Power plant which is not the most efficient way to use them. A better way could be integrating steel plant with other chemical plants such as Gas Reforming (GR) and then methanol (MeOH) plant. 2) Methanol is a chemical product which has both Energetic uses, for example: Motor fuels, Gasoline blending, Diesel fuel, Power station, etc., and chemical uses such as Solvents and also raw material for more than ten different chemical plants. 3) In recent years, a growing interest has been observed in the application of methanol as an alternative liquid fuel, which can be used directly for powering Otto engines or fuel cell achieving high thermodynamic efficiency and relatively low environmental impacts, 4) for instance, according to the Exposure Draft of Mid-& Long-Term Development Plans of Coal Chemical Industry, Issued in 2006 by National Development and Reform Commission (NDRC), China’s output of methanol was expected to reach 16 million tons, 25 million tons and 66 million tons by 2010, 2015 and 2020. 5) Raw materials for methanol plant mainly include coal, coke, natural gas, heavy oil, etc. which mostly depend on the geographical region and natural resources. In the other hand, it can be produced as a by-product from acetylene or COG units. Commercial technology to produce MeOH from COG already exists and is in particular in China. According to the China Chemical Reporter (2005), the chemical company Shanxi Tianhao Chemical Company Ltd in the Shanzi province commissioned the first phase of methanol project with the capacity to produce 300000 tons of MeOH per year from COG. 6) The objectives of this research were to identify and predict the potential of using top gases from COG and BF as feed for GR and MeOH plants and show how this integration can effect in costs of steel production, CO 2 emission and methanol production. In this case steel plant has a BF with top gas recycling in order to suppress emission rates. 7,8,9,10) Helle et al. reported the optimal operational condition of steel plant by recycling CO 2 - stripped BF top gases. In this paper, the top gas recycling concept with tuyere injection of the CO 2 -stripped is evaluated by optimizing the performance of the process with respect to oxygen injection, top gas recycling rate and temperature, and oil injection rate using a linearized model of blast furnace and then the optimal states of operation are studied by solving a nonlinear programming problem for different price setting for the energy flows and emissions in an integrated steelmaking plant. 2. Models of the unit processes and emissions The model developed in this work is based on a previous model designed in Thermal and Flow Engineering Laboratory. The models for steelmaking plant are developed on the basis of process data from Finnish integrated steel works. 11) The main processes in the steel production are: sinter plant, coke plant, blast furnace, hot stoves, basic oxygen furnace, combined heat and power plant which integrated with gas reforming and methanol units. For the blast furnace, a thermodynamic first principle model 11,12) was applied to developed a linearized model, Eq. (1), where it was assumed that the part of top gas, β, which is recycled goes to stripping unit and 95% of the CO 2 is removed. The stripped gas is heated in the hot stoves together with the blast (i.e. pure oxygen possibly mixed with air) to the blast temperature (T bl ). The linear process model is expressed as a function of seven input variables, the volume flow rate of recycled top gas (β), the total volume flow rate of blast (pure oxygen Optimization of Steel Production Integrated with Methanol Plant Hannu HELLE, Hamid GHANBARI, Mikko HELLE, Frank PETTERSSON and Henrik SAXEN Thermal and Flow Engineering Laboratory, Åbo Akademi University, Biskopsgatan 8, FI-20500, Åbo, Finland