Post-combustion capture of CO2 at an integrated steel mill – Part I: Technical concept analysis

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Abstract

In this study different possibilities for applying post-combustion capture at an integrated steel mill in order to reduce carbon dioxide emissions were studied. Implications of different amounts of CO2 captured, different solvents for post-combustion capture and different heat supply options for solvent regeneration to the energy balance and greenhouse gas emissions of the steel mill are compared to that of the base case for the steel mill.

The case study is based on Ruukki Metals Ltd.’s Raahe steel mill that is situated on the coast of the Gulf of Bothnia. It is the largest integrated steel mill in the Nordic countries producing hot rolled steel plates and coils. It is also the largest CO2 point source in Finland emitting approximately 4 Mt/year.

Carbon capture processes were modelled using Aspen Plus process modelling software and results were used to estimate the potential for reducing CO2 emissions at an integrated steel mill from a plant operator's point of view. Different heat integration options and heat utilization scenarios were investigated. The heat available for solvent regeneration varied between these heat utilization scenarios and thus partial capture of CO2 was investigated with the CO2 amount captured depending on the heat available for solvent regeneration in the different case studies.

The results of the study show a significant CO2 reduction potential using CCS. Approximately 50–75% of the emissions from the site could be captured using post-combustion capture. Capturing a larger amount of emissions would be technically less feasible due to the large number of small stacks around the large, integrated steel mill site.

Highlights

► 50–75% CO2 capture potential from a blast furnace process using post-combustion capture at an integrated steel mill. ► Options for integration of post-combustion carbon capture technology to an integrated steel mill. ► Using a solvent that could be regenerated at low temperature enables a higher utilization of the waste heat available and higher capture rate.

Introduction

It has been generally acknowledged that climate change is one of the most serious environmental threats that humankind is facing and that greenhouse gas emissions (GHG's) should be reduced in every field of activities. The iron and steel industry is responsible for about 10% of worldwide CO2 emissions from fossil fuel use (IEA, 2008), which corresponds to about 5% of the overall global GHG emissions. CO2 emissions from iron and steel industry originate mainly from the two most common steel making processes: the Blast Furnace and Basic Oxygen Furnace-based route (BF + BOF route) and the Electric Arc Furnace route (EAF route). Together these processes are responsible for about 99% of the global crude steel production (Worldsteel, 2010). The EAF route results in significantly smaller CO2 emissions per ton of steel produced than the BF + BOF route, but the EAF route is often based on recycled steel and has a smaller unit size. In the previous decade, the growth in global steel production resulted mostly from the growth in production by the BF + BOF route (Worldsteel, 2010). In addition, direct reduction iron production processes (DRI) are already used commercially, but their portion of the global iron production is still minimal.

Because the BF + BOF route utilizes the iron oxide found in iron ore, a powerful reducing agent is needed in the blast furnace. A typical reducing agent is coke, which eventually results in relatively high CO2 emissions (due to subsequent combustion of blast furnace gas). In addition, the production of coke results in coke oven gas and eventually in CO2 emissions. Numerous improvements in the complicated BF + BOF-based steel mills are possible, but the reductions in CO2 emissions are typically small in comparison to the overall CO2 emissions from the mills. By Carbon Capture and Storage (CCS), CO2 emissions could be reduced to a large extent. CCS is generally recognized as one of the key climate change mitigation option and the technology can be utilized in the steel industry as well. Due to large unit sizes, relatively high CO2 concentrations, current utilization of pure oxygen and recoverable heat, CCS may become economically feasible in steel mills considering the likely future costs for CO2, for example in the EU Emission Trading Scheme (EU ETS). In principle, each of the three main CCS technologies, namely post-combustion, pre-combustion and oxyfuel can be utilized in steel mills. Economically feasible options for reducing CO2 emissions are of high interest to European steel producers because of the additional costs due to the EU ETS. While the market for power is typically national or regional, the market for steel is global. The additional production costs due to emission trading can therefore not be transferred to the product price in order for steel to stay competitive in the global market. Therefore, the additional costs due to CCS are even more challenging for the steel industry.

Ruukki Metal Oy's Raahe steel mill is situated on the cost of the Gulf of Bothnia. It is the largest integrated steel mill in the Nordic countries producing hot rolled steel plates and coils. It is also the largest CO2 point source in Finland. In 2008, before the economic down term and blast furnace revisions, the CO2 emissions from the mill were 4.5 Mt/year (EMV, 2011). Replacing sinters by pellets from 2011 onwards reduced the direct CO2 emissions from the site by 0.4 Mt/a.

In this study, different possibilities for reducing carbon dioxide emissions at an integrated steel mill by applying post-combustion capture (PCC) for were studied, using the Raahe steel mill as a base case. Technical implications of different post-combustion capture methods and different amounts of CO2 captured as well as energy balances are presented in this paper. Based on the technical solutions described in this paper, the economics of the solutions and their net effect on the greenhouse gas emissions are assessed in the second part of the study (Tsupari et al., 2012).

Section snippets

General

The CO2 capture processes and the steelmaking processes were modelled using Aspen Plus modelling software and the results were used to estimate the CO2 emission reduction potential using PCC technologies at an integrated steel mill. Only the parts of the steelmaking processes affected by the CO2 capture were modelled with Aspen Plus. Different CO2 capture amounts were investigated with the amount captured depending on solvent properties and heat available for solvent regeneration using two

Conclusion and discussion

As a technical option, it is possible to significantly lower greenhouse gas emissions from the steel industry with the post combustion capture technologies covered in this study. The solutions are technically realisable already in the near future. Nevertheless, no commercial application for such a large scale exists yet. The larger capture amounts studied (2–3 Mt CO2/a) account for approximately 50–75% of the CO2 emissions from the site. If larger amounts of emissions were to be captured it would

Acknowledgements

This paper is published as a part of research in Finnish national technology programmes Climbus and CCSP on carbon abatement options for steel mills covering also oxygen blast furnace. The research was carried out in a project called CCS Finland (2008–2011). The project was coordinated by VTT Technical Research Centre of Finland with participation and financing by Geological Survey of Finland (GTK), Tekes (the Finnish Funding Agency for Technology and Innovation), Fortum, Foster Wheeler Energy,

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