Carbon capture and storage (CCS): the way forward
Carbon capture and storage (CCS) is broadly recognised as having the potential to play a key role in meeting climate change targets, delivering low carbon heat and power, decarbonising industry and, more recently, its ability to facilitate the net removal of CO2 from the atmosphere. However, despite this broad consensus and its technical maturity, CCS has not yet been deployed on a scale commensurate with the ambitions articulated a decade ago. Thus, in this paper we review the current state-of-the-art of CO2 capture, transport, utilisation and storage from a multi-scale perspective, moving from the global to molecular scales. In light of the COP21 commitments to limit warming to less than 2 °C, we extend the remit of this study to include the key negative emissions technologies (NETs) of bioenergy with CCS (BECCS), and direct air capture (DAC). Cognisant of the non-technical barriers to deploying CCS, we reflect on recent experience from the UK's CCS commercialisation programme and consider the commercial and political barriers to the large-scale deployment of CCS. In all areas, we focus on identifying and clearly articulating the key research challenges that could usefully be addressed in the coming decade.
Carbon capture and storage (CCS) is recognised as being vital to least cost pathways for climate change mitigation, and in particular the negative emissions technologies (NETs) that are key to limiting warming to “well below” 2C. However, it has not yet been deployed on the scale understood to be required, owing to a variety of technical, economic and commercial challenges. This paper provides a state-of-the-art update of each of these areas, and provides a perspective on how to the discipline forward, highlighting key research challenges that should be addressed over the course of the next decade. Importantly, this perspective balances scientific, policy and commercial priorities.
This paper is the third installment in a series of publications over several years in Energy & Environmental Science.1,2 The first (published in 2010) provided an introduction to CO2 capture technologies, with an overview of solvent-based chemisorption (amines and ionic liquids), carbonate looping, oxy-fuel combustion technologies, CO2 conversion and utilisation (CCU) and multi-scale process engineering of CCS.1 The second installment presented an update on developments in amine scrubbing, ionic liquids, oxy-combustion and calcium looping. New topics added in this second paper include chemical looping combustion, low temperature adsorbents, direct air capture technologies, flexible CCS operation, CO2 transport and storage, and a historical overview of the UK and EU CCS policy and legislation.2
Distinct from the previous installments, this third paper sets out to comprehensively review the state-of-the-art developments in CCS, whilst also providing a holistic perspective on the role of CCS technologies in mitigating anthropogenic climate change. We first discuss the current status of CCS development and highlight key CCS technologies that are near commercialisation phase (Section 2). Then in Section 3 we contextualise CCS technology by considering its representation and utilisation in integrated assessment models (IAMs), challenging the view that it is a “bridging technology”, likely to be relevant for only a few decades. We then go on to quantify and qualify the role and value of CCS at a more granular level by evaluating the way in which CCS interacts with national scale electricity systems. This in turn helps us address the question of what service CCS provides to the electricity system, with whom is CCS competing and what technologies does CCS complement.
We then move on to consider the utility of CCS in decarbonising the industrial sector, with a focus on the key emitters – the production of iron and steel, cement and oil refining and petrochemicals. Throughout, we aim to challenge the perception that industrial CCS is uniquely costly, showing that, for example, the cost of decarbonising the refining sector is essentially “lost in the noise” of market fluctuations of the end use sectors.
Section 4 of the paper considers key post-combustion CCS technologies in detail. The purpose of this paper is not to enumerate the panoply of technologies that are available for capturing CO2. Rather, we focus on solid- and liquid-phase sorbents, and attempt to specify key research questions that need to be address in these areas. We then select three particularly promising alternative technologies for CCS in Section 5: chemical looping combustion, membranes and ionic liquids.
It is well known that the thermophysical and kinetic properties of the sorbents used for CO2 capture dictate both the capital and operating cost of the processes in which they are used. For this reason, there is a concerted effort to rationally design new sorbent materials, with the bulk of the effort in the development of liquid sorbents, where available theories are more readily applied. Thus, we present an assessment of SAFT-based approaches to model and design new materials in Section 6, with a focus on how efforts at the molecular and process scales might be linked.
Before CO2 can be safely and reliably sequestered, it must be transported from source to sink. Whilst the majority of studies assume pipeline transport, ship and rail transport are potential alternatives; these other transport options are discussed in Section 7. Similarly, despite the fact that CO2 transport by pipeline is exceptionally mature, the impact of capturing CO2 from a diverse set of power and industrial sources on the quality of CO2 being transported is sufficiently important to warrant careful consideration.
The typical fate of CO2 is to be sequestered, either in a saline aquifer or, potentially, used for enhanced oil recovery (EOR). The various challenges of operation, monitoring and verification of CO2 storage are discussed in Section 8, whereas Section 9 discusses CO2-EOR. A potential alternative to the storage of CO2 is its re-use – the valorisation of CO2 to produce marketable compounds. The argument is sometimes made that this can both contribute to climate change mitigation and provide an attractive revenue stream. Section 10 discusses the potential for CO2 conversion and utilisation (CCU), also its merits and challenges are presented and considered.
In light of the global commitment achieved in Paris in December, 2015,3 we have extended this paper to include key negative emissions technologies (Section 12); bioenergy with CCS (BECCS) and direct air capture of CO2 (DAC). These areas are of particular importance owing to their potential importance and their controversy.
Despite the fact that there are currently 37 CCS projects at various stages in the Americas, Europe, Middle East and Asia-Pacific,4 CCS continues to languish as an “orphan technology”.† With decades of technical experience across the entire value chain, it is clear that it is not a lack of technical expertise that is inhibiting the commercial deployment of CCS technology. Thus, we have devoted a section of this paper to consider “what needs to happen” from a commercial perspective (Section 13), drawing upon experience developed as part of the UK's most recent CCS commercialisation programme.5 Having provided this perspective from the private sector, we then complement this with an international analysis of the political economy of CCS (Section 14). Section 15 then concludes with a proposed approach to evaluate the utility of a “novel technology” and feasibility of particular targets by identifying limitations that might prove to be showstoppers.
2 Current status of CCS development
Carbon capture and storage is expected to play an important role in meeting the global warming targets set by the IPCC6 and at COP21.3 There is a suite of technologies being developed for the capture, transport, storage and utilisation of CO2. Typically, technology development will progress in a series of scale-up steps: (i) bench or laboratory scale, (ii) pilot-scale, (iii) demonstration scale, and lastly (iv) commercial scale.7Fig. 1 summarises the current development progress of different CCS technologies on the TRL scale.‡ As illustrated by Fig. 1, there is congestion of technologies at the TRL 3, TRL 6 and TRL 7 development phases. The progression of a technology beyond TRL 3 requires further research funding, whereas advancing technologies beyond TRL 5 and TRL 7 needs significant financial investment and/or commercial interest (e.g., in the case of polymeric membranes). Further detailed discussion on the technical development of the individual CCS technologies is presented in the following sections of this paper. Here in this section, we highlight the key CCS technologies that have reached (or close to reaching) the commercial phase of development.
Current development progress of carbon capture, storage and utilisation technologies in terms of technology readiness level (TRL). BECCS = bioenergy with CCS, IGCC = integrated gasification combined cycle, EGR = enhanced gas recovery, EOR = enhanced oil recovery, NG = natural gas. Note: CO2 utilisation (non-EOR) reflects a wide range of technologies, most of which have been demonstrated conceptually at the lab scale. The list of technologies is not intended to be exhaustive.
Chemical absorption (e.g., using aqueous amine solutions) has been used to remove CO2 from natural gas for decades,11 thus, it is considered to have a TRL of 9. This technology has been utilised in two commercial-scale post-combustion capture facilities in coal-fired power plants, Boundary Dam12,13 and Petra Nova.14,15 Recent developments in polymeric membranes have enabled the technology to successfully achieve demonstration scale (TRL 7). The Polaris membrane is now available commercially and has been used for CO2 separation from syngas.16 Air Products are licensing a polymeric membrane developed at NTNU, which can be applied to coal-fired power plants and other combustion processes (still under development).17 Thus, The first “commercial-ready” direct air capture (DAC) plant recently opened in Hinwil, Switzerland on May 2017,18 with the support of cost contributions from the Swiss Federal Office of Energy. The plant supplies 900 tonnes of CO2 annually to a nearby greenhouse.19 Capture technologies that have also reached TRL 7 (demonstration) (e.g., oxy-combustion coal power plants, adsorption) could also potentially reached commercial status in the near future. In contrast to post-combustion capture, integrated gasification combined cycle (IGCC) with CCS has been less successful with the Kemper County IGCC Project being suspended recently.20 Southern Company's decision to halt the project came after encountering a series of problems, these include failure to meet the delivery deadline, severe technical issues and being majorly over budget.21,22
The technologies for CO2 transport are well established. There are >6500 km of CO2 pipelines worldwide (both on-shore and off-shore), most of which are associated with EOR operation in the United States.23 The technology for CO2 transport with ships is also relatively mature.24 As these transport technologies are currently being used in commercial applications, all have a TRL of 9.
As many commercial-scale CCS projects already use CO2-enhanced oil recovery (EOR), 13 of the 17 operating commercial-scale CCS projects, there is a significant amount of existing experience and knowledge, which has enabled CO2-EOR to reach TRL 9. Similarly, saline formations have been used for CO2 storage at commercial-scale project, including Sleipner CO2 Storage, Snøhvit CO2 Storage and Quest (on-shore and off-shore). In contrast, CO2 storage by enhanced gas recovery (EGR)25 and storage in depleted oil and gas fields have not reached operation at commercial-scale, thus, both are still at the demonstration phase (TRL 7). Ocean storage and mineral storage are still in the early phases of development.
There are a number of facilities that utilise CO2 for various applications. These commercial CO2 utilisation processes are TRL 9 as they are mature technologies. Most are in the food and beverage industry and some in chemical production (e.g., urea, methanol).26 Several projects utilise CO2 for mineral carbonation, for example, Searles Valley plant (US). In Saga City, Japan, CO2 capture from waste incineration is utilised for the cultivation of crops and algae.27 The CO2 for each project is mainly sourced from industrial processes (e.g., fertiliser production, ammonia production, ethylene glycol plants), but some projects capture the CO2 from power plant flue gas.26
Commercial-scale CCS projects
Deployment of large scale CCS projects has been slow. Of the 37 major large scale CCS projects, 17 of these are in operation, 4 in construction and the remainder are in varying stages of development.4 As shown in Fig. 2 and 3, the majority of the commercial large-scale CCS projects are located in the United States. In terms of the project life cycle (i.e., identify, evaluate, define, execute and operate), the US also has the greatest proportion of projects in operation. For all but one of these projects, enhanced oil recovery is the primary storage for the captured CO2. Furthermore, the projects in the US have the largest CO2 capture capacity compared with projects in the rest of the world: Century Plant captures 8.4 MtCO2 per year, whereas Shute Creek Gas Processing Facility capture 7 MtCO2 per year.4
image file: c7ee02342a-f2.tif
Fig. 2 The CO2 capture capacity of commercial-scale CCS projects worldwide. The number labelled on each proportion of capture capacity corresponds to the number of projects. Data from the Global CCS Institute.4
Commercial-scale integrated CCS projects around the world. Circle size is proportional to the CO2 capture capacity of the project and the colour indicates the lifecycle of the project. Data from the Global CCS Institute.4
Although China has the second highest number of projects, only one of these is in the execute phase (Yanchang Integrated CCS Demonstration), and most are in early stages of development (e.g., pre-feasibility, FEED studies). The CO2 capture capacity of the projects in China range between 0.4–2 MtCO2 per year. Europe has the third highest number of large-scale projects, with two operational projects in Norway: the Sleipner CO2 Storage Project captures 1 MtCO2 per year, and Snøhvit CO2 Storage Project 0.7 MtCO2 per year. Of the five projects in Canada, three are in operation: (i) Great Plains Synfuel Plant and Weyburn-Midale Project (3 MtCO2 per year), (ii) Boundary Dam CCS Project (1 MtCO2 per year), and (iii) Quest (∼1 MtCO2 per year). There are also operating CCS projects in Brazil, Saudi Arabia and United Arab Emirates with CO2 capture capacities ranging from 0.8–1 MtCO2 per year. A fundamental requirement for the success of CCS projects in all of these projects is the availability of safe geological storage for the capture CO2. Furthermore, other factors that can help bring CCS projects into operation phase include secure financial funding, as well as supportive policy and legislative frameworks.