Evaluation of the synergies in cogeneration with steel waste gases based on Life Cycle Assessment: A combined coke oven and steelmaking gas case study

Steel making processes dispose large volumes of waste gases whose potential energy can be transformed into heat and electricity by means of cogeneration. A case study using coke oven and Linz-Donawitz converter gas is presented here. The data is obtained from an existing plant located in Northern Spain. The engines are adapted for its operation with converter gas, and steam is generated in boilers that consume coke gas, converter gas and natural gas in the absence of waste gases. The actual influence on the environmental behaviour of the process is analysed considering the benefits but also the drawbacks derived from the gases low calorific value, toxicity and polluting. The work constitutes the first study in an installation with these characteristics and burning this combination of gases. The functional unit is represented by 1 MWh of thermal energy. The analysis has been developed mainly on the bases of the following sources: site-specific measured or calculated data directly from the process of cogeneration, life-cycle inventory databases and bibliographical information. Operating parameters, as well as production data (thermal and electric energy), emissions of NOx, SO2 and CO2, discharges and wastes associated with this process are exposed. The system boundaries were considered gate to gate, so the results are useful for the integration with other global scenarios. Midpoint and endpoint characterisation factors for humans, ecosystems and resources are given. The main effects are related to Climate change, Ionising radiation, Human toxicity and Fossil and Ozone depletion. The results indicate that the usage of these gases implies an environmental benefit. The operational data belonging to 2014 shows a reduction of more than 100 points in the global impact of the functional unit. In the best scenario, 169.42 Nm(3)/MWh of natural gas may be saved with the consequent reduction in natural resources and ozone depletion. (C) 2019 Elsevier Ltd. All rights reserved.