WP6: Integration of CCL into Full-scale Industrial Plants (ULster)

Following the experience acquired in the EU projects, the published results of the ULCOS project (Ultra-Low Carbon dioxide Steelmaking) and the Technology Roadmap for carbon capture and storage in industrial applications, published by the International Energy Agency and the United Nations Industrial Development Organization, the research group selected existing cement and steel production plants to be equipped with a CCL plant. In this package the CCL models validated in WP2 were used to define the processes of full scale cement and steel plants. Main objectives of WP6 are:

  1. Evaluation of the process regarding full-scale implementation to cement steel plants;
  2. Techno-economic analysis, identification of dement production cost and cost of CO2 avoided to evaluate CCL technology compared to other CCS solutions;
  3. Assess the environmental impact of CCL system by conducting a life cycle analysis (LCA).

Cement plant definition and integration

In this task an existing cement plant was selected to be equipped with a CCL unit in order to provide the basis of design and the boundary conditions for thermodynamic and economic evaluations to be done in the scope of SCARLET project. The European Benchmarking Task Force definitions are taken into account to guarantee comparability of the results between WPs 4, 5 and 6 as well as comparability with other capture technologies. The selected cement plant is able to produce over  t/day clinker. In order to show the influence of the extraction point of the flue gases, two integration cases, as shown in Figure 1 and Figure 2, are configured.

Figure 1: Simplified schematic of the CCL integration case

Figure 2: Simplified schematic of the CCL integration case II

Integrated steel mill definition and integration

Based on the information provided by our industrial partners and gathered through literature reviews, an integrated steel mill (ISM) is selected. The selected ISM is able to produce 457t/hr of Hot Rolled Coil (HRC). The assessment of the decarbonisation of ISM is rather challenging due to the high complexity of all processes that are interconnected. Taking all factors into account, four major processes for the ISM are selected for an integration of a CCL into the ISM in this study. A simplified process diagram is shown in Figure 3.

Figure 3: Simplified iron and steel plant integrated with a CCL plant

Thermodynamic evaluation of CCL for the selected cement plant

The CO2 absorption efficiency of the carbonator, ECarb and the total CO2 capture rate of the whole system, Etot, are presented in Figure 4. These values are determined depending on the amount of purge material that is fed to the cement making process, and thus strongly influenced by the feeding rate of the make-up stream. It comes apparent, that higher replacement rates are favorable in terms of CO2 capture efficiency, since more limestone is calcined in the oxy-fired calciner of the CCL unit. The specific CO2 emissions, for the two different integration cases (I:flue gas extraction after cyclone pre-heating, II: flue gas extraction between 3rd and 4th pre-heater and fed back in 3rd pre-heater) are compared in Figure 4. Both resulting curves show a similar pattern. Higher raw meal substitution leads to lower specific CO2 emissions. This is due to the increasing share of limestone that is calcined under oxy-fuel combustion conditions in the calciner, and thus all released CO2 is captured directly.

Figure 4: Comparison of carbonator CO2 absorption efficiency and total capture efficiency depending on the raw meal sub-stitution (left) and specific CO2 emissions (right) for integration cases I and II

Thermodynamic evaluation of CCL for an integrated steel mill

In this study, the CO2 absorption rate of 90 % is achieved within the carbonator. The thermal duty of the calciner, and the additional electricity that is generated (Pel,gross, Pel,net) are depicted in Figure 5. Along with a higher sorbent loading, as achieved by longer residence times of the particles within the carbonator, more heat is required in the calciner for calcination of the incoming sorbent. In parallel, the power output of the power cycle as attached to the CCL unit increases as well. The auxiliary demand includes the power consumption of the ID fans within the CCL system, the ASU consumption and the CO2 compression system. The latter represents the greatest share of the total auxiliary consumption of the CCL system (around 53 %).

Figure 5: Thermal input and electricity generation of the CCL integration case

Economic evaluation of CCL for a cement plant

For the base case (without CCL integration) the cement plant has an average of 748 kg CO2/t clinker produced. Integrated with the CCL the cement plant is capable of removing around 90% of the CO2 from flue gases, resulting in CO2 emissions of 82.2 kg CO2/t clinker.

The total capital cost for the reference plant is estimated at €422 millions. If the project design, construction, commissioning time and contingency are included the total capital investment increases to €528 millions. If the load factor for cement production is assumed to be 88%, the levelised cost of €74/t Cement is calculated.

For the integration case, total capital costs increase from €528 millions €946 millions against the base plant due to the additional CCL plant cost and ‘Secondary Steam Cycle’ being introduced. For the plant to have a zero NPV over the lifetime, the levelised cost of €92.5/t cement is required.

Based on the above case study, the cost of CO2 captured and the cost of CO2 avoided relative to the corresponding reference plant are €15.8/t CO2 and €27.6/t CO2, respectively.

Economic evaluation of CCL for an integrated steel mill

For the base case (without CCS) the ISM has an average of 1156 kg CO2/t HRC produced. Integrated with the CCL the ISM is capable of removing around 90% of the CO2 from flue gases, resulting in CO2 emissions of 185 kg CO2/t HRC.

Based on the information provided by the reports [1,2] the total capital cost of €2155 millions for the reference ISM is estimated. If the project design, construction, commissioning time and contingency are included the total capital investment increases to €2370 millions. If the load factor for the ISM is assumed to be 100%, the levelised cost of of €434/t HRC is calculated.

For the integration case, total capital costs increase from €2370 millions to €3133 millions against the reference ISM due to the additional CCL plant cost and ‘Secondary Steam Cycle’ being introduced. For the plant to have a zero NPV over the lifetime of the levelised cost of  €459.7/t HRC is required.

Based on the above case study, the cost of CO2 captured and the cost of CO2 avoided relative to the corresponding reference ISM are €12.6/t CO2 and €26.5/t CO2, respectively.

Environmental assessment – Cement Plant

A life cycle analysis (LCA) was completed to evaluate the environmental impact of calcium carbonate looping (CCL) technology integrated with a cement plant. The study is a comparison between a cement with and without the CCL. The function of the process is to produce clinker. In agreement with other similar studies, the functional unit is the production of 1 tonne of clinker [3, 4]. The environmental impacts of the plant technology and its potential hazards to human, wildlife, and bio-systems are considered. The reference flow is 1 tonne of clinker. The LCA was carried out using the ReCiPe methodology and both the midpoint and endpoint were considered. SimaPro 8.3 was used to model the system. The endpoint damage assessment results are shown in Figure 6.

Figure 6: Comparing cement plant with and without CCL

The endpoint analysis indicates that producing clinker has a lower environmental impact with the employment of the CCL as a decarbonisation tool than without the CCL. The damage assessment results indicate a 62% and 69% reduction in potential impact for the human health and ecosystems indicators respectively. This is achieved via a 49% increase in the resource indicator. Some impact categories are lowered by the integration of CCL with the CP and others are higher. This is to be expected as the CCL plant consumes resources to function. One reason for a reduction in impact in the terrestrial acidification, photochemical oxidant formation and particulate matter formation impacts is the further reduction of sulphur dioxide (SO2) by the formation of calcium sulphate (CaSO4) within the CCL process. Other impacts are reduced due to the avoided products; electricity, during the CCL process.  The increase in some impacts is due to the increase in resource extraction and use.

The increase of these impacts has to be balanced against a 78% reduction in the climate change impact.

Environmental assessment – Integrated steel mill (ISM)

A life cycle analysis (LCA) was completed to evaluate the environmental impact of calcium carbonate looping (CCL) technology integrated with the ISM. The study is a comparison between a steel plant with and without the CCL. The endpoint damage assessment results are shown in Figure 7.

Figure 7: Comparing steel plant with and without CCL

The end-point analysis results indicate that producing hot rolled coil has a lower environmental impact with the CCL than without the CCL. The damage assessment indicates a 70% and 132% decrease in the impact scores of human health and ecosystems and an increase in the resource impact of 12%.  The mid-point results show that a number of impacts are low; even in the reference case with no CCL. However, the power plant integrated into the steel plant, nominally powers two steel plants including the downstream processes that are not included in the boundary of this study. Therefore, the power usually consumed by the second power plant and the finishing process stages, is treated as an avoided product.

Conclusion

The evaluation of economics and the comparison to other CCS technologies show the advantages of CCL. The CO2 avoidance costs are significantly lower compared to other technologies (see Figure 8). Especially for the cement industry, the results clearly show the lowest CO2 avoidance costs compared to amine scrubbing and oxy-fuel technology resulting in a main advantage of the CCL technology. This is a result of the synergies using the same feedstock limestone for both processes leading to advantageous economics compared to other technologies.

Figure 8: Comparison of CO2 avoidance costs for cement and steel plants

References

[1] IEA Greenhouse Gas R&D Programme (IEA GHG), Assessing the potential of implementation CO2 Capture in an integrated steel mill, August 2011.

[2] IEA Greenhouse Gas R&D Programme (IEA GHG), Iron and Steel CCS Study (Techno-economics Integrated Steel Mill) 2013/04, July 2013.

[3] D. García-Gusano, D. Garraín, I. Herrera, H. Cabal and Y. Lechón, “Life Cycle Assessment of applying CO2 post-combustion capture to the Spanish cement production,” Journal of Cleaner Production, vol. 104, pp. 328-338, 2015.

[4] F. Stafford, F. Raupp-Pereira, J. Labrincha and D. Hotza, “Life cycle assessment of the production of cement: A Brazilian case study,” Journal of Cleaner Production, vol. 137, pp. 1293-1299, 2016.