Carbon capture from reheating furnaces in the Swedish steel industry: evaluation of techno-economic feasibility

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the Swedish steel industry - evaluation of techno-economic feasibility

Anna Haglund

Sustainable Energy Engineering, master's level 2020

Luleå University of Technology

Department of Engineering Sciences and Mathematics

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Luleå University of Technology

Department of Science and Engineering and Mathematics

E7014T

Carbon capture from reheating furnaces in the Swedish steel industry - evaluation of

techno-economic feasibility

Author:

Anna Haglund

Supervisors:

Prof. Ji, Xiaoyan Wetterlund, Elisabeth

June 24, 2020

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I would like to thank the people listed below for the sharing of knowledge and data and for the support I have been given during the work with this project.

Xiaoyan Ji, Examinator LTU

Elisabeth Wetterlund, Supervisor, LTU & TO51 Helena Malmqvist, Supervisor, Jernkontoret TO51 Jonas Engdahl, Superviser, SSAB & TO51

Nan Wang, LTU

Cecilia Lille, Outokumpu Darnis Magalie, Höganäs Anders Lugnet, Ovako

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Abstract

The reduction of greenhouse gas emissions is important to keep climate change under control. One of the largest CO2 emitters of the Swedish industries is the steel industry. This is, among others, due to the need of heat treatments and reheating processes depending on high temperatures and fossil fuels. The business organisation Jernkontoret and their department for energy and furnace technique is working towards reducing the emissions for these processes and one area of research is the carbon capture and storage (CCS) techniques. This report aims to give an overview of existing and emerging CCS techniques applicable for the reheating and heat treating furnaces, along with evaluating one post-combustion carbon capture technique for diﬀerent cases provided by some involved companies. The carbon capture technique investigated in this project can be divided into three main sections; Oxyfuel combustion, pre-combustion and post-combustion capture. Oxyfuel relies on the usage of pure oxygen instead of air for the combustion of the fuel, this gives a high CO2concentration in the flue gas (80-98%).

Concentrations below 95% require further purification before compression and transportation to storage.

Using pre-combustion capture the CO2is removed before the combustion, this can be done by reforming the used fossil fuel to a syngas (a gas with a high H2 and CO concentrations). The CO2 is formed by passing the syngas through a water-gas shift, which also increases the H2 concentration further. The CO2 can then be removed relying on reversible chemical reactions or the aﬃnity between the CO2 and an absorbent. The post-combustion carbon capture also relies on reversible chemical reactions or aﬃnity to an absorption medium, usually an amine solvent. The bond is then broken in the desorption unit, creating a pure CO2stream and a reusable absorbent.

The case studies were done only for a post-combustion capture process with a MEA-water solvent (20%) as the absorption medium. The simulation program Aspen Plus was used both for the technical and economical values, executed by the PhD student Nan Wang at LTU. The values were interpolated / extrapolated nonlinear for each given case. Six diﬀerent cases were given by four companies, four conventional furnaces and two oxyfuel furnaces. Evaluations for the oxyfuel furnaces were excluded, due to big diﬀerences between the model and case values and since the technique evaluated is not implemented at oxyfuel plants. The evaluations done for the conventional furnace cases gave a total cost of between 86 - 126 $/tonne captured CO2. This has to be viewed as a high cost investment even without having a full economic evaluation regarding cost for transportation and storage included.

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1 Introduction 1

1.1 Background . . . 1

1.2 Aim . . . 1

1.3 Scope and limitations . . . 1

2 Carbon Capture Techniques 2 2.1 Background . . . 2

2.2 Oxy-fuel combustion . . . 2

2.3 Pre-combustion capture . . . 3

2.4 Post-combustion capture . . . 4

2.5 Comparison . . . 4

2.6 Transportation and Storage . . . 6

3 Case studies 8 3.1 The capture technique . . . 8

3.2 Aspen Plus . . . 9

4 Methodology 11 4.1 Literature studies . . . 11

4.2 Plant visits and interviews . . . 11

4.3 Simulations . . . 11

5 Results 12 5.1 Capture potential . . . 12

5.2 Economic evaluation . . . 12

5.3 Sensitivity analysis . . . 14

6 Discussion and Conclusions 17 6.1 Source of error . . . 17

6.2 Continued work . . . 17

7 References 18

A Simulated values from Nan Wang 20

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Acronyms

ACapEx annual capital expenditures.

AOpEx annual operating expenditures.

CapEx capital expenditures.

CCS carbon capture storage.

CCT carbon capture techniques.

GHG greenhouse gas.

LTU Luleå university of technology.

MEA Monoethanolamine.

OpEx operating expenditures.

PSA pressure swing adsorption.

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1 Introduction

This section intends to give the background and aims for this master thesis project as well as describe the scope and limitation for which this project was restricted by.

1.1 Background

The temperatures on earth are rising due to climate change caused by large emission of greenhouse gas (GHG) created by human activity [1]. Carbon dioxide is the most common GHG, standing for approximatly 80% of all GHG emissions [2].

The steel industry is one of the largest CO2 emitters in Sweden [3]. The industry has multiple points of emission from diﬀerent processes, melting and reduction processes to reheating and heat treatments, which requires a broad research of techniques for reducing these emissions. The heat treatments and reheating processes require high temperatures and are commonly heated by combustion of fossil fuels [4]. The Swedish business organisation for the steel industries Jernkontoret is working towards reducing these emissions and is investigating diﬀerent possibilities, where carbon capture and storage (CCS) is one of them.

TO51 is the technical area for energy and furnace technology at Jernkontoret, and the department for which this thesis works towards.

1.2 Aim

The aim of this master thesis is to provide an overview of the current existing and emerging carbon capture techniques that are relevant for the reheating furnaces in the steel production industry in Sweden.

The aim is also to provide techno-economic analysis for one post-combustion carbon capture technique, based on diﬀerent cases from the Swedish industry.

Provide an overview of diﬀerent carbon capture concepts, commercial as well as emerging, regarding technical performance, cost and technical maturity.

Evaluate the techno-economic feasibility of implementing a post-combustion carbon capture technique, based on diﬀerent cases from the Swedish industry.

1.3 Scope and limitations

This project is limited to evaluate carbon capture techniques (CCT) applicable for the reheating furnaces excluding melting (ore- and scrape-based) and reduction processes, due to the limited time frame.

The economic evaluation is only executed for one post-combustion capture process for diﬀerent cases provided by companies involved.

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2 Carbon Capture Techniques

This section aims to give an overview of the carbon capture techniques available and upcoming, that potentially could be implemented in the steel industry. The most common carbon capture techniques can be separated into three main sections; Oxyfuel combustion, Post-combustion capture and Pre-combustion capture, which are all described separately in the subsections bellow.

2.1 Background

The technique of separating carbon dioxide from gases is not new. It has been in use since the first half of 20th century for the removal of CO2 in natural gas reservoirs, among others. Another usage for this technique has been the enhanced oil recovery, where CO2 is separated from an industry to be used to enhance the oil recovery by pumping it into the reservoirs [5].

To prevent releasing CO2 to the atmosphere the usage of CCT to separate and capture CO2 has gained an increased interest along with the knowledge of greenhouse gases and how it eﬀects the climate change.

Research and implementation have been focusing on industries with large CO2 emission, such as power plants using fossil fuels. The CCS techniques are seen as a potential for reduction of CO2 emission by many big organisations and climate agreements, e.g. the International Energy Agency (IEA) and the Paris agreement, among others [6].

2.2 Oxy-fuel combustion

The oxyfuel combustion technique relies on the usage of pure oxygen instead of air for the combustion of the fuel [7]. Air contains of approximatly 78% nitrogen (N2) and 21% oxygen (O2) [8], hence using air for combustion gives a relatively low concentration of CO2 in the exhaust air, i.e. a high dilution of the carbon dioxide. The nitrogen passes through the combustion needing energy to be heated without contributing to the process. By removing the nitrogen the NOx substances can be reduced (depending on the fuel used), the eﬃciency of the process will go up and the concentration of CO2 in the flue gas will increase to between 80-98% [7] [9]. The aim of this technique is thus to concentrate the CO2in the flue gas giving a easier recovery process using smaller capture units, in comparison with other carbon capture techniques [10].

To sustain the gas volume needed in the chamber and have control over the flame-temperature, some of the flue gas is recycled and put back into the combustion along with the oxygen [9].

The units required for this type of process consume a lot of energy. The air separation unit required for the oxygen separation and the purification of the CO2 stream are energy intense [10].

2.2.1 Purification of CO2

The purity of the CO2 stream should reach concentration of at least 95 mol% for transportation and storage. Since some air leakage to the furnace can occur and the production of NOx is still ongoing de-

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pending on the plant and the fuel used, the fuel gas can be in need of purification. One way of achieving this is by using compression and cryogenic separation. To prevent ice formation and corrosion the flue gas is dried and compressed to around 30 bar. The dry and compressed flue gas then enters a cold box, which is a unit utilising flash separation at temperatures of -25°C and -56°C. Here the liquid CO2can be separated from other insoluble gases contained in the flue gas. The pure CO2stream is then compressed further for transportation and storage [9] [10].

Another upcoming method for purification is the usage of membranes which separates and captures the CO2by acting like a filter [11]. This is also researched as a potential alternative to the air separating unit, producing the oxygen needed for combustion [12].

2.3 Pre-combustion capture

The pre-combustion carbon capture technique relies on the separation and capture of CO2 before the combustion. This can be done by a pre-treatment of the used fossil fuel (e.g. natural gas, oil or coal) before combustion, producing a syngas (also known as synthesis gas). This is a gas containing a high content of hydrogen (H2) and carbon monoxide (CO) [9] [13].

The syngas production diﬀers depending on the fuel used. Steam reforming is one technique where the hydrocarbons in the fuel react with high pressure steam. This technique is commonly used when natural gas is used as the fuel. This process is endothermic, hence requires or absorbs energy. Par- tial oxidation is another technique that can be used for the production of syngas. Here the fuel (gas or liquid) is mixed with a limited amount of oxygen and partially combusted. The same process can be applied on solid fuels and is then called gasification. This process is exothermic (releases heat) [13] [14].

To increase the H2 concentration further and convert the CO to CO2 a water-gas shift process can be implemented. This technique lets the carbon monoxide react with water (steam) creating CO2 and H2. This gives a CO2 concentration of 15-50% depending on the fuel and the process. The CO2 is removed from the gas and the H2can be combusted, giving a flue gas free of CO2 [13] [14].

2.3.1 Separation of CO2

The separation of CO2 from the syngas can be executed using diﬀerent technologies, below follows some that are commercialised or under research.

Physical absorption is the most mature pre-combustion carbon capture technique where physical solvents are used as the absorbent, i.e. Selexol or Rectisol among others. The gas mixture and solvent make contact by counter current flow in an absorber where the CO2 gets separated and absorbed by the solvent. The CO2rich solvent is then transported to a desorber where the solvent is stripped of the CO2, using heat, this creates a pure CO2 stream and reusable solvent. Since this absorption does not rely on any chemical reactions, the bonds between the solvent and the CO2 are much weaker than for i.e. a chemical absorption [15].

Adsorption relies on the formation of physical or chemical bond between the surface of an solid-phase (or liquid-phase) adsorbent and the CO2. One technique using adsorption is pressure swing adsorption (PSA) which works by the usage of pressure and an adsorbent, usually activated coal. The CO2 is separated from the gas mixture at high pressure and a low temperature, bonds between the CO2 and the surface of the adsorbent are built until the surface becomes saturated. These bonds are later broken by reducing the pressure, creating a pure CO2 stream and a reusable adsorbent [15] [16].

Membrane is an upcoming alternative that separates and captures the CO2 by passing the gas mixture through a membrane which acts like a filter separating the diﬀerent gaseous components [11] [17].

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2.4 Post-combustion capture

Post-combustion carbon capture technologies rely on the separation and capture of CO2 from the flue gases. The implementation of a post combustion CCS occurs at the end of the combustion process hence no comprehensive change to production line is needed [9].

Since the combustion of the fuel usually occurs in air the CO2 concentration is relatively low, ap- proximately 3-20%, as the gas mixture is diluted significantly with nitrogen [9].

2.4.1 Separation of CO2

The removal of CO2 from the flue gas primary relies on a reversible chemical reaction or the aﬃnity between an absorbent and the carbon dioxide. Some techniques that can be applied for post-combustion capture are described below.

Chemical absorption is currently the most mature technique. This process is a continuous scrubbing technique consisting of an absorber and a desorber (also known as stripper). In the absorber the flue gas and the solvent (usually an amine) meet at a counter flow and the CO2 is absorbed by the solvent by a reversible chemical reaction. In the desorber the chemical bonds are broken creating a pure CO2

stream and a reusable solvent which is transported back to the absorber. The CO2 is then compressed for transportation and storage. This type of process is used for facilities with a low pressure flue gas stream and low concentration of CO2 [9] [18] .

A typical amine solvent used for this process is Monoethanolamine (MEA), but other solvents can be used [15] [19] [20].

Membrane separation and caption of CO2 as a post-combustion technique is an upcoming alternative to the above mentioned techniques. The flue gas is filtered through a membrane system which separates the different molecules creating a pure CO2 stream. This technique has the potential of becoming a more energy efficient and economic alternative since no additional energy is needed for the breaking of bonds or affinity between the CO2 and an absorbent [11] [17] [21].

2.5 Comparison

The three carbon capture techniques described in the sections above diﬀer in a lot of aspects. The subsections below aim to summarise and compare the mentioned techniques from diﬀerent perspectives.

2.5.1 Technical maturity

Oxyfuel-combustion is commercial in use, not primary to capture and store the CO2, but for other purposes such as eﬃcient combustion, high flame temperatures and reduction of NOx emissions [7] [15]

Pre-combustion carbon capture techniques are established at commercial plants, but not to the same extent as post-combustion techniques. The primary focus has been coal fired power plants but research for a broader usage is ongoing [15] [22].

The currently most mature technique is the post-combustion carbon capture using chemical absorption, which is established at a numerous commercial plants [9] [15] [23].

The interest for membrane based technology is increasing as it could oﬀer a more sustainable and potentially more cost eﬃcient method for separating and capturing CO2from all above mentioned techniques [11] [22].

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2.5.2 Technical advantages and disadvantages

Advantages

The usage of oxyfuel combustion has a number of benefits for the process. Some aspects are the increased eﬃciency of the combustion process and the decrease of pollutants such as NOx. The technique is, in relation to other CCS techniques, easily retrofitted into existing plants [7] [15] [24].

Pre-combustion carbon capture is slightly more eﬃcient in comparison with a post-combustion technique, due to the lower volume of gas processed and the lower energy demand for the separation when using pre-combustion techniques [25]. Another advantage is the increased concentration of CO2and the absence of combustion based pollution such as NOx and SOx [15] [26].

The post-combustion technique has advantages in the technical maturity due to all research done, it is also highly compatible for retrofitting at existing plants [15] [23].

Disadvantages

There are some technical uncertainties associated with full-scale oxyfuel plants. Another disadvantage is the need for an air-tight process to avoid air leakage which will dilute the CO2in the flue gas causing need for purification [15] [24].

Pre-combustion technologies require extensive installation and are therefor not as easy to retrofit into existing plants as other CCT [15] [25].

One disadvantage with the post-combustion techniques is the low CO2 concentration and partial pressure in the flue gas. This along with the existence of other air pollutants, such as SO2 and NOx, sets high demands on the absorbent [15] [27] [28].

2.5.3 Economic aspect

The cost of investment needed for an implementation of carbon capture techniques (CCT) diﬀers depending on a number of factors, especially regarding retrofitting to existing plants where a lot of aspects must be taken in consideration [29].

For oxyfuel combustion with an air tight process the air separating unit used for the production of oxygen will have a high cost [15]. If in need of purification the cost will increase further.

For pre-combustion processes the capital expenses are high due to the complex installation needed, especially regarding retrofitting. However the operational expenses for this process can be assumed lower in comparison with post combustion processes, due to the lower amount of gas mixture processed [15] [25].

The post-combustion technologies have a high cost for both capital and operational expenses. This is mainly due to the large equipment size required for the large volume of flue gas that will be processed [15] [25].

In Table 4 cost estimation of each carbon capture technique is shown. The values originate from a compilation of studies done on diﬀerent new fossil fuels power plants and published in the International Journal of Greenhouse Gas Control [29] (cost of transportation and storage is excluded). Hence, the values are not directly applicable for retrofitting of carbon capture techniques at steel production plants.

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Table 1: An cost estimation regarding the implementation of CCS techniques at power plants [29].

CCT Cost per tonne CO2 [$/Tonne CO2]

Oxyfuel 36-73

Pre-comb. 42-87

Post-comb. 36-111

2.6 Transportation and Storage

There are diﬀerent ways to transport and store the captured CO2and this section aims to give an brief overview of the diﬀerent processes for both transportation and storage.

2.6.1 Transportation

There are two main methods to transport the captured CO2, which are described below.

Pipelines are the currently most common method for transportation of CO2. Here the CO2 is transported at high pressure continuously, hence no temporary or additional storage of the captured CO2 is needed. There are two different types of pipeline transportation; onshore and offshore. The onshore pipelines are based on land and therefore limited by length and other restrictions. The offshore pipelines are based under water and can be used for longer distances but are often more costly [30] [31] [32] [33].

Shipping the captured CO2 in tanks could also be an option for transportation. The CO2 needs to be temporary stored since this transportation system in not continuous. Three diﬀerent tanks can be used to transport the liquefied CO2; pressure tanks, low temperature or semi-refrigerated. This transportation method can be used for longer distances of transportation. The liquefied CO2 can be transported by railway or truck as well [33] [34].

In Table 2 below a cost estimation for each technique can be seen. They vary due to the amount of CO2

transported, length of transportation and technical factors. The costs are estimated for a volume of at least 2,5 Mtonne/y [29] [30] [34].

Table 2: Estimated cost for transportation of the captured CO2(>2,5 Mtonne/y) using diﬀerent methods.

Technique cost estimation [€/Tonne CO2]

Onshore 4-6

Oﬀshore 6-50

Shipping [including liquefication] 13-20

The methods are commonly combined, e.g. on shore pipelines can be used for transporting CO2 from the facility and oﬀshore pipelines might then be used if the storage facility is located under sea [33] [34].

Plants or industries with carbon capture processes located in proximity to each other can collabo- rate the usage of transportation creating a network of pipelines. This can increase the amount of CO2

transported and lower the price for the involved companies [29] [30].

2.6.2 Storage

The final storage of the captured CO2 can be found both on land or/and under sea, two methods for storage are described below.

Geological storage includes depleted oil and gas reservoirs, and unmineable coal seams in rock formation is another potential site for storage. The porous structure makes it possible for the CO2to be dissolved

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[35] [36].

Ocean storage refers to methods for containing the captured CO2 in the ocean. This can be done by either dissolving the CO2 in the water, at a great depth, or by creating a lake of CO2 at the ocean floor [36] [37].

In Table 3 an cost estimation for storage can be seen, this is however very dependent on local restrictions [29].

Table 3: Cost estimation for storage of the captured CO2

Technique cost estimation [€/Tonne CO2]

Onshore 1-18

Oﬀshore 2-20

2.6.3 Utilisation

The captured and pure CO2 can instead of being put into storage be utilised in diﬀerent processes.

Below follows a short description of two processes where the CO2 can be used as the feed-stock.

Enhance oil and gas recovery, where the CO2 is injected into the reservoirs to keep the pressure in the rock formation and retrieve otherwise hard to reach oil and gas [38].

Production of fuels and chemicals using CO2 as a feed-stock. Fuels such as methane, methanol and syngas are some examples that can be produced using the captured CO2. The most produced chemical using CO2as the feed-stock is urea, but there is a variety of chemicals that can be produced [38].

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3 Case studies

To provide a techno economic evaluation of one post-combustion carbon capture technique, case studies were done. Data for six diﬀerent cases was given from four companies, four cases regarding conventional furnaces (combustion in air) and two cases for oxyfueld furnaces (combustion in oxygen).

The companies and diﬀerent processes are listed below.

SSAB - provided data for two conventional furnaces using diﬀerent fuels, U301 fueld with PLG (liquefied petroleum gas) combusted in air and U302 natural gas combusted in air.

Höganäs - provided data for the combined flue gas of three tunnel ovens.

Outokumpu - provided data for a conventional tape oven and for an annealing furnace using oxyfuel combustion.

Ovako - provided data for the combined flue gas of eight chamber furnaces.

The dry flue gas in mass flow (tonne/h) and CO2 concentration in wt% were used for the evaluation of CO2 capturing and economic evaluation. In Table 4 the given data for flue gas flow and CO2

concentration for each case are listed.

Table 4: Furnace data provided by the companies, where the flow refers to the flue gas flow and both the concentration and the flow are calculated on a dry basis

CO2 Conc. [wt%] Flow [tonne/h]

SSAB U301 10 58

SSAB U302 16 75

Höganäs 7,5 240

Outokumpu (conv.) 14 46

Outokumpu (oxy.) 90 6,5

Ovako 90 0,9

3.1 The capture technique

The carbon capture technique evaluated for the given cases was a post-combustion technique with a MEA-water solvent (20% MEA) as the absorbent.

The post combustion process consists of absorber, pump, heat exchanger and a desorber. In the absorber the solvent and the flue gas are mixed, and the CO2 is separated and absorbed by the solvent. The CO2 rich solvent is then transported through a pump and a heat exchanger to a desorber (also known as a stripper) where the chemical bond is broken using heated steam. This creates a stream of reusable solvent (transported back to the absorber through the heat exchanger) and a stream of pure CO2 that

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gets compressed in a compressor and be ready for transportation and storage. The parts written in italic are the units included in the simulations, hence the parts included for the economic evaluation.

The chemical reactions considered in the simulations of the MEA-CO2-H2O system were as follows in Equation 1 to Equation 8 below. These reactions are based in the absorption and stripping parts of the process [39] [40] [41].

2 H2O H3O⁺+ OH^– (1)

CO2+ 2 H2O H3O⁺+ HCO3^– (2)

HCO3^–+ H2O CO3^2–+ H3O⁺ (3)

MEAH⁺+ H2O MEA + H3O⁺ (4)

CO2+ OH^– HCO3^– (5)

HCO3^– CO2+ OH^– (6)

MEA + CO2+ H2O MEACOO^–+ H3O⁺ (7)

MEACOO^–H3O⁺ MEA + CO2+ H2O (8)

Where equation 1 to equation 4 are calculated with equilibrium, and the equilibrium constant was calculated from the standard Gibbs free energy change [40]. Equation 5 to equation 8 are kinetic.

3.2 Aspen Plus

Aspen is a simulation software using mathematical calculations to predict the performance of a process in the industry. This program was used to simulate the post-combustion caption process for diﬀerent scenarios. The aspentech Rate-based Model of the CO2 Capture Process by MEA using Aspen Plus was used as a starting template [40].

The simulation for the above described process was done by the PhD student Nan Wang at LTU, see Appendix A for original values. The values were then interpolated / extrapolated for the values given for each case.

3.2.1 Economic evaluation

The capital expenditures (CapEx) and the operating expenditures (OpEx) were simulated for the same process using the program Aspen Process Economic Analyser and a US template.

The variables used for calculation of the operational cost are listed in Table 5 below [42].

CapEx was recalculated as an investment using a lifespan for the plant at 25 years and an interest rate at 10%. Equation 9 was used for this calculation.

ACapEx = CapEx⇤ i⇤ (i + 1)^y

(i + 1)^y 1 (9)

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3 Case studies

Table 5: Cost of the operational variables [42].

Variable Cost Unit

Steam 6 $/GJ

Cooling water 0,35 $/GJ Electricity 0,1 $/kWh Refrigeration 4 $/GJ

MEA 1,3161 $/kg

Where i is the interest rate and y is the expected number of years.

Both ACapEx and OpEx were then calculated to $ per ton captured CO2. This was done by dividing the capital and operational costs with the annual captured CO2 evaluated for each case.

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4 Methodology

In order to reach the set aims for this project a variation of methods were used, which all are described in this section.

4.1 Literature studies

Literature reviews were done to provide an overview of the carbon capture and storage techniques regarding technical properties, maturity, and economic aspects. It was also used to give an economic overview for the techniques, transportation and storage, however not directly applicable for the steel industry.

The literature review also provided knowledge of which methods could be used for the techno economic evaluation.

4.2 Plant visits and interviews

Plant visits were done in the beginning of this project to give a broader perspective of the production lines and the data provided by the companies for the case studies. Interviews with involved people were conducted during these visits.

4.3 Simulations

Since the values for the CO2caption capacity and the economic values were simulated using values for a cement plant, with a flue gas flow and CO2 concentration diﬀerent from the data given for mentioned cases, interpolation and extrapolation had to be done. This was done in Excel using the function Exp- trend which provided nonlinear interpolation / extrapolation for a each case. For these calculations the flue gas flow had to be in mass per hour [tonne/h] and the CO2concentration in wt%, both on a dry basis.

The simulations were done for two different flue gas flows, five different CO2 concentrations and four different recovery rates (65%, 75%, 85% and 95%). The original values used for the simulations, gas flow and concentration, can be seen in Apendix A.

A sensitivity analysis was done for CapEx and OpEx (in [$/tonne CO2]) where the flue gas flow, CO2

concentration and recovery rate was increased and decreased by 10%, respectively. The recovery rate used as the base for each case was at 85% and the original values for flue gas flow and CO2concentration given for each case.

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5 Results

In this section the results from the evaluation of a post-combustion carbon capture plant, using MEA-water as the solvent, for the case studies are presented.

The two cases provided utilising oxyfuel furnaces were excluded in evaluation. This is due to the high uncertainties regarding the diﬀerence in values for both gas flow and CO2 concentration in comparison to the used data. Post-combustion capture (i.e. MEA scrubbing) is not a technique combined with oxyfuel combustion.

5.1 Capture potential

In Figure 1 below the annual CO2capture capacity in million tonnes for each plant is shown. A recovery rate of 95% was used, all other values used are presented under section 3, Case studies.

Figure 1: The annual capture capacity for each plant using a recovery rate at 95%.

5.2 Economic evaluation

The evaluated annual cost for each case can be viewed in Table 6 below. Here the annual capital expenditures (ACapEx), annual operating expenditures (AOpEx) and the total annual cost can be seen.

All calculated with the evaluated annual captured CO2 can be seen in Figure 1.

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Table 6: Cost for the operational variables.

Variable SSAB U301 SSAB U302 Höganäs Outokumpu

ACapEx [M$/y] 2,5 2,7 4,6 2,4

AOpEx [M$/y] 0,7 1,2 3,5 0,8

Total annual cost [M$/y] 3,2 3,9 8,1 3,2

In Figure 2 to Figure 4 below, the economic evaluation ($/tonne CO2) for the conventional cases studied in this thesis is shown. The results vary depending on the recovery rate.

Figure 2: CapEx for the conventional furnace cases.

Figure 3: OpEx for the conventional furnace cases.

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5 Results

Figure 4: CapEx and OpEx for the convetional furnace cases.

5.3 Sensitivity analysis

Below follows the results of the sensitivity analysis done for the economic calculations.

A sensitivity analysis was done by increasing and decreasing the variables, respectively. In Figure 5 to Figure 8 below the precentual change on CapEx and OpEx combined is shown.

Figure 5: The impact on CapEx and OpEx combined for a change of +/- 10% of each variable, where the blue represents an increase of 10% on each variable, and the orange represents an decrease of 10%

on each variable.

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Figure 6: The impact on CapEx and OpEx combined for a change of +/- 10% of each variable, where the blue represents an increase of 10% on each variable and the orange represents an decrease of 10%

on each variable.

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5 Results

on each variable.

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6 Discussion and Conclusions

The technology field of CCT is in its early stages regarding implementation in steel industry. These technologies are most commonly implemented and researched in the field of fossil fuels based power plants. These types of plants usually have a significantly larger flow of flue gas than that evaluated for in this project.

The economic evaluations show that the implementation of a post combustion capture plant for the prerequisites of the cases studied is a high cost investment. The cost per ton captured CO2is significant, considering that the cost of transport and final storage has not been included, hence further research and development of the CCS techniques for plants with low gas flow is needed to make industrialisation financially viable.

In regards of the steel industry, the aspects of how ash and other compounds in the flue gas will aﬀect the choice of solvent, eﬃciency and total cost of CCT need also to be considered.

Transportation and storage of captured CO2 need to be further analysed. Investment into these technologies at steel plants is with the current values and knowledge hard to motivate.

6.1 Source of error

The technical and economic evaluation of the cases studied is based on values simulated for another case (cement industry). The nonlinear interpolation / extrapolation done for the data regarding each case might therefore be less precise than if simulation would have been done based on data from the same industry as the cases.

In the analysis, only carbon dioxide, nitrogen and oxygen have been considered for the gas mixture.

All substances with low PPM in the flue gas, such as NOx have been disregarded.

6.2 Continued work

Case studies evaluating the technical performance and an economic evaluation for other carbon capture techniques; pre-combustion capture for the conventional cases and purification processes regarding the oxyfuel processes.

Investigation of the market potential and price sensitivity for this sustainable product, "green" steel.

One increasing aspect could be the increasing interest of life cycle analysis including CO2 footprint for all stages of the life cycle, not only use phase, in e.g. the automotive segment. This development could significantly increase the market value of green steel production.

A techno economic evaluation of the transportation and storage options, or potential reuse of CO2

instead of storing.

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A Simulated values from Nan Wang