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Due to its high demand for energy, pulp and paper industry, along with iron and steel, cement and petrochemical industries, is considered one of the main Energy Intensive Industry (EII).

In UK, these four sectors alone are responsible for almost 60% of the industrial greenhouse gas (GHG) emissions; with the pulp and paper industry contributing with 6% (Griffin et al., 2016). Since their CO₂ emissions are mainly of biomass origin, the pulp and paper industry is in a favourable position to become a carbon-negative industry if carbon capture and storage (CCS) is implemented.

However, the potential of pulp and paper industry to achieve carbon negative emissions has been underestimated. It can be mainly explained by the fact that the carbon-neutral emissions, associated with using biomass as the primary source of energy, are not included in the European Union Emissions Trading System (EU ETS). Therefore, there are currently no incentives to capture CO₂ emissions from carbon-neutral processes, such as the pulp and paper industry.

Therefore, the pulp and paper industry has not been widely considered for implementation of CCS, as opposed to other EIIs for which application of CCS has been thoroughly studied. Among the several CCS technologies that have been considered for decarbonisation of other EIIs, carbonate looping (CaL) has arisen as more energy efficient and less expensive than mature technologies, such as amine scrubbing or oxy-fuel combustion.

CaL is a solid looping technology that uses metal oxides, such as CaO, to remove CO₂ from the flue gas at high temperature (~600–650°C). Yet, its feasibility has not been proven at a commercial scale.

Ca-based sorbents, such as limestone (~95%_wt CaCO₃), are most considered sorbents for CaL. Importantly, CaCO₃is also the main constituent of lime mud, a waste from the Kraft process that was proven to be viable CO₂ sorbent for CaL at a laboratory scale (Sun et al., 2013).

Case Study

Concept Description

We proposed to utilise the inherent CO₂ capture potential of the Kraft process by integration of CaL in the existing lime cycle in the pulp and paper industry, as presented in the Figure 1. The retrofit of the reference pulp and paper plant with CO₂capture can be achieved in the lime production without affecting the rest of the Kraft process.

The flue gas streams from recovery, power and biomass boilers can be merged and directed to the carbonator where the CO₂is captured by lime produced in the lime kiln.

The decomposition of CaCO₃ into CaO and CO₂ occurs in the lime kiln (calciner) at above 900°C. A small fraction (~5%) of the produced CaO is purged from the system to maintain high sorbent conversion in the carbonator, whereas the remaining part is sent back to the existing causticisation process.

Figure 1. Kraft process concept with inherent CO_₂ capture.

Techno-economic assessment

To assess the techno-economic feasibility of the proposed carbon-negative process, we considered the following thermodynamic and economic performance indicators: the net power output, the levelised costs of market products and the cost of CO₂ avoided.

The latter represents the cost of avoiding 1 tonne of CO₂ emissions per unit of a product that is determined considering the performance the plant with CCS (retrofitted plant) and the plant without CCS (reference plant) (Rubin, 2012).

The reference plant is a net electricity importer. However, the main benefit of CaL retrofit is the fact that it is a high temperature process. This implies that the high-grade heat is available at a sufficient temperature (600-900°C) to produce an extra amount of steam that can be used to produce electricity.

Our study showed that regardless of the increased on-site power consumption in the retrofitted plant, the amount of produced electricity exceeded the electricity demand of the entire process.

Therefore, as a result of CaL retrofit, the reference plant was converted from net electricity importer to net electricity exporter. This provides a promising revenue stream for the pulp and paper industry and opportunities to offset CO₂ emissions from sectors that are difficult to decarbonise.

Our economic analysis showed that retrofit of CaL will increase the levelised costs of pulp and newsprint by 13% and 10%, respectively. Namely, we found that for the project to break even, these costs need to be increased from 728.3 and 374.5 €/ADt for the reference plant to 824.4 and 411.1 €/ADt for the retrofitted plant, respectively.

Such a performance corresponds to a cost of CO₂ avoided of 39.0 € per tonne of CO₂. Our figure is 50-65% less than that reported for retrofit of mature amine scrubbing (52-131 €/tCO₂). This confirms that CaL is a viable route for unlocking the potential for carbon negative emissions in the pulp and paper industry.

Regardless of the promising economics, we think that the current CO₂ emissions policies are not enough to tackle the climate change. To demonstrate this, we also evaluated the economic indicators under following scenarios:

Scenario 1: No CO₂ emissions taxes and no credits for negative emissions (base line scenario)

Scenario 2: Fossil CO₂ emissions tax and no credits for negative emissions (current situation)

Scenario 3: Fossil CO₂ emissions tax and credits for negative emissions

Figure 2. Effect of different economic scenarios on (a) levelised cost of pulp newsprint and (b) cost of CO_₂ avoided (Ref and Cap correspond to reference pulp and paper plant and retrofitted pulp and paper plant, respectively).

Our analysis (Figure 2) showed that the carbon tax had a minimal impact on CO₂ capture cost, as changed from 39.0 €/tCO₂(Scenario 1) to 38.0 €/tCO₂ (Scenario 2) which can be attributed to more than 95% of the total CO₂ emissions produced by the reference plant were biogenic.

Howver, the introduction of credits for negative emissions (Scenario 3) had a significant effect on the CO₂ avoided cost, reducing it to 16.9 €/tCO₂. That was because there is an additional revenue associated with the negative CO₂ emissions.

In this study we showed that CaL retrofit will become economically viable for the pulp and paper industry if negative CO₂ emissions are recognised in the EU ETS and associated tax credit of at least 41.8 €/tCO₂ is implemented.

In summary

a pulp and paper plant can turn from net electricity importer to net electricity exported on retrofit of calcium looping;
a cost of CO₂ avoided estimated associated with calcium looping retrofit is 39.0 €/tCO₂;
a feasibility of CO₂ capture retrofits to the pulp and paper plants depends strongly on the inclusion of biogenic emissions in the EU ETS and/or on the attribution of tax credits for negative emissions;
considering calcium looping as an emerging technology for CO₂ capture in the pulp and paper industry, its implementation would be viable with the recognition of negative CO₂ emissions and a negative CO₂ emission credit of 41.8 €/tCO₂ applied.

References

Business Insider, 2020. CO₂ European Emission Allowances

Griffin, P.W., Hammond, G.P., Norman, J.B., 2016. Industrial energy use and carbon emissions reduction: a UK perspective. Wiley Interdiscip. Rev. Energy Environ. 5, 684–714

Rubin, E.S., 2012. Understanding the pitfalls of CCS cost estimates. Int. J. Greenh. Gas Control 10, 181–190.

Sun, R., Li, Y., Liu, C., Xie, X., Lu, C., 2013. Utilisation of lime mud from paper mill as CO₂ sorbent in calcium looping process. Chem. Eng. J. 221, 124–132.

Authors

Monica Santos is a PhD researcher at the Centre for Climate and Environmental Protection, Cranfield University. Her research project is focused on the production of clean power, heat, and hydrogen from alternative fuels. She holds a 5-year degree diploma from the Polytechnic of Porto and a Master degree from the University of Porto (Portugal), both in Chemical Engineering with specialisation in Energy and Environmental Technologies. She has been working in Research and Development since 2007, first in academia and recently in a private company.

Dr Hanak is the Senior Lecturer in Energy and Process Engineering. He leads transformational research to develop breakthrough technologies such as direct air capture, carbon capture, hydrogen production, and high-value chemicals and fuels synthesis. His expertise is in process design and development, third-party validation, techno-economic feasibility assessment, environmental impact assessment, and business model development. Dawid works together with businesses and entrepreneurs to demonstrate the feasibility of innovative processes that will enable meeting net-zero emission targets by 2050.

Phil Black - PII Editor 15/12/2020

413 5 minutes read

Can An Energy Intensive Industry Become Carbon Negative?

By Monica P. Santos and Dawid P. Hanak Energy and Power Theme, School of Water, Energy and Environment at Cranfield University, Bedford, Bedfordshire, MK43 0AL, UK