Transparent carbon capture and storage using blockchain technology

. Carbon capture and storage (CCS) is one of the important initiatives widely used across different industries in reducing atmospheric carbon emissions, which is an essential environmental goal outlined in Sustainable Development Goal 13 (SDG 13) in 2015. In an effort to mitigate carbon-emission problem, CCS extracts (i.e., captures and compresses) and stores CO 2 from industrial by-products as an alternative to releasing it directly into the atmosphere. CCS presents opportunities for the captured CO 2 to immediate utilization or to be stored at adjacent facilities for future utilization in different industrial productions. Despite its potential in reducing carbon emissions, its effectiveness and possible economic incentivization are unknown due to a lack of transparency in tracking the quantitative output concerning carbon reduction at different stages of CCS activities (capture, transportation, and storage) currently deployed in different industrial plants. In this paper, we propose an enhanced CCS for recording and tracking the quantitative output of CCS activities using blockchain (i.e., a distributed-ledger) technology that promotes transparency among stakeholders, e.g., government, regulatory body, technical experts, and general public, and facilitates rewards toward effective carbon-emission reductions. Although blockchain is a promising technology that can increase the efficiency of CCS, we also identify a few future challenges, such as data privacy and scalability, that have to be taken into account toward implementing the proposed architecture.


Introduction
The amount of atmospheric CO2 generated by human activities contributes to more than twothirds of global warming, as outlined by the United Nations' Climate Action, also known as the Sustainable Development Goal 13 (SDG 13) [1].Among different technologies used for reducing carbon emissions, carbon capture and storage (CCS) is one of the widely used and most promising solutions, where it actively separates CO2 contained in the by-products of various large-scale industry facilities, e.g., power plants, natural-gas processing plants, oil refineries, iron and steel industry, and cement factories, instead of directly releasing it into the atmospheric environment [2].According to the International Energy Agency, CCS facilities currently capture more than 45 MtCO2 annually [3].
CCS unit integrated to industrial plants usually entails three major stages: i) carbon capture and compression, ii) transportation, and iii) utilization/storage [4], as illustrated in Figure 1.Carbon capture separates CO2 from the main by-products (such as exhaust gases) generated by industrial plants.For example, in power plants, carbon capture is performed either at post-combustion, precombustion, or oxyfuel combustion stage during power generation.Here, the selection of a suitable capture technology is dependent on the raw materials, CO2 concentration, and pressure in the exhaust gases.However, in some largescale industries concerning oil refineries, cement factories, and ammonia/hydrogen production plants, carbon capture is performed from the main gas stream instead of the factory by-products.The captured CO2 from the by-products or main gas stream is eventually compressed to a denser form in order to reduce its volume for an easier handling during transportation and storage.
Large quantities of captured CO2 are usually transported through pipelines to storage facilities located up to several thousands km away from the industrial plants [5].In North America, an extensive onshore CO2 pipeline network, with a combined length of about 8000 km, currently transports up to 70 Mt CO2 annually [6].When a pipeline network is not available, marine vessels can be used for large quantities of CO2 as an economical means of transportation to storage facilities located at much longer distances from the industrial plants [7].In case of smaller quantities, trucks or rails can also be used to transport captured CO2 when the storage facilities are adjacent to the industrial plants and frequent land transportation is economically feasible [6].
Figure 1 shows that the compressed CO2 is either transported for utilization or storage.The term carbon capture and utilization (CCU) is used when captured CO2 (used with or without conversion) as raw materials in industrial productions [6].Industrial productions at fertilizer factories, oil refineries, food and beverage companies, and greenhouses are examples of CO2 utilization as raw material without conversion.On the other hand, there are also possibilities for producing new items, such as synthetic fuels [8], polymers [9], and building materials [10], from the captured CO2 with conversions due to the recent technological advancements.Alternatively, the compressed CO2 is placed at stor-age facilities in various physical forms based on their storage locations.Super-critical CO2 is an example physical form of compressed CO2 when subsurface storage is used in CCS [7].The effectiveness of CCS in reducing carbon emissions depends on the capture technology at industrial plants and their transportation to the nearest storage facilities [11].It means that when a large-scale carbonemitting industry equipped with a CCS unit is located near possible storage facilities, then the reduction in carbon emissions tends to be significant due to the low energy consumption at the CO2 transportation stage.In other words, technological challenges in reference to the quantity and length of transportation between the industrial plants and storage facilities have a direct impact toward the effectiveness of CCS in reducing annual CO2 emissions.
In short, the effectiveness in reducing atmospheric carbon emissions using CCS integrated with industrial plants is dependent on the choice of capture process, feasibility in transportation, and the locality of the carbon storage facilities.It is also essential to account for the net carbon emissions along the entire CCS process by means of recording quantitative information at all three stages: carbon capture and compression, transportation, and utilization and storage.Because these information on emissions reduction is evaluated during life cycle assessment (LCA) 1 [12], they will contribute to a more accurate and reliable monitoring, reporting, and verification (MRV) [13].A robust MRV will provide transparency in CO2-emission reductions contributed by the employed CCS integrated to various industrial plants.Such transparency can then be used to validate or improve the employed CCS technology.The recorded information can be used to increase public awareness and provide compliance information to the regulatory bodies and policymakers for implementing incentives (e.g., tax credits) to the CCS-integrated indus-trial plants as well.
In this paper, we propose recording both quantitative and related information at each CCS stage in industrial plants using blockchain technology [14].Blockchain is a distributed-ledger technology that stores data in both immutable and traceable manners for transparent record keeping and allows implementations of smart contracts (i.e., executable computing code running on blockchain [15]) for automating incentives.Therefore, it has the potential to enforce transparency in CCS with reliable data toward reducing atmospheric carbon emissions and to facilitate related benefits, e.g., public awareness and compliance-related benefits, as discussed above.To the best of our knowledge, blockchain has not been used to quantitatively evaluate the effectiveness of carbonemission reduction and accountability of industrial plants that use CCS technology.
In the remainder of the paper, Section 2 provides an overview of blockchain technology and its existing applications.Section 3 discusses about the existing work on CCS.Section 4 proposes a solution to the tracking of CCS activities in a transparent and accountable manner using blockchain technology.Section 5 presents our conclusions.

Blockchain technology
Blockchain is a new technology that uses a decentralized network of computers for storing data.It is a distributed ledger technology that represents data in units called blocks, and the storage of these data is performed by sequentially linking the blocks without any central authority.It applies cryptographic hashing on the content (i.e., data) of each block to accomplish sequential linking, which contributes to the data security in the blockchain [16].Since changing the data in a block breaks its link to the sequence, blockchain ensures data immutability.Also, the sequential linking of blocks is done in chronological order; therefore, blockchain enables traceability of stored data for enhanced security.It is important to note that immutability and traceability are the basis of transparent data storage in blockchain technology.
Another important feature of blockchain technology is the implementation of trust in its data storage.There are two different aspects of this implementation.Firstly, blockchain shares a copy of the sequence of blocks with all network nodes (i.e., computers) that prevents single-pointof-failure scenario to increase data owners' confidence.Secondly, it uses a consensus algorithm (e.g., proof-ofwork) to maintain consistency in the stored blocks on all nodes across the entire network.Consensus algorithm ensures a newly created block is added to the blockchain only after the majority (51% or more) of the nodes validate the block.This means creating a block and achieving consensus across the entire network is a computationheavy process; therefore, it is practically difficult for malicious nodes to manipulate the blockchain network.Figure 2 shows a simplified illustration of how blockchain adds a newly created block to the network for clarity.Blockchain networks are often integrated with selfexecutable computer programs called smart contracts [17].Smart contracts allow distributed application development on blockchain networks.They automate the execution of predefined transactional agreements on the stored data when specific transactional conditions are met.Therefore, it enables trusted execution of business transactions using blockchain data without third-party involvement in a transparent, accurate, and instant manner.Smart contracts and distributed application development on blockchain have been popularized by the introduction of Ethereum, a blockchain platform, in 2014 [18].
In general, blockchain networks can be broadly classified into three categories: i) public blockchain, ii) private blockchain, and iii) consortium blockchain.Public blockchain is open to everyone such that anyone can access the network, i.e., join the network, access stored data, and participate in adding new blocks, without restrictions.Private blockchain, on the other hand, is controlled by a single organization such that only users with granted permissions within the organization are allowed to access the network.Finally, consortium blockchain is a compromise between the first two where the blockchain network is controlled by a group of organizations and users selected within these organizations have access to the blockchain network.In terms of using a certain blockchain type, it all depends on the needs (e.g., type of problem being solved, size of the network, and data privacy) for which the blockchain network is implemented.
In recent years, blockchain technology has been implemented in a myriad of use-cases, and it was first successfully adopted in the financial sector for establishing a cryptocurrency in 2009 [19].Example sectors where this technology has seen adoption are healthcare (for secure data access), banking (for trustability), supply chain (for data traceability), and real estate (for enforcing environmental compliance through smart contracts).Environmental sustainability, defined by the United Nations SDGs, is another important and large sector that has started to tap into the potential of blockchain technology for solving dif-ferent problems concerning climate action, energy, water management, circular economy, etc. [20].

Related Work
In this section, we discuss existing works on tracking the impacts of CCS (a solution related to SDG 13) through monitoring and record keeping of carbon capture using blockchain technology.As of the latest advancements in this category, this discussion presents a brief summary of two existing commercial initiatives: CarbonKerma [21] and CO2NNEX [22] below.
CarbonKerma is a blockchain-based solution that keeps record of the captured CO2 from industrial plants injected into storage facilities.It then converts the record of the captured CO2 as digital tokens for the purpose of establishing a carbon marketplace to interested parties [21].The interested parties constitute individuals and companies who are willing to offset their carbon emissions by purchasing the tokens from the marketplace.Even though this solution claims to transparently track reduction of carbon emissions using CCS technology, the blockchain only tracks the amount of carbon capture possibly at final CCS stage, i.e., during CO2 injection at storage facilities.This is due to the fact that CarbonKerma does not require a comprehensive estimate of carbon emissions along all CCS stages for minting digital tokens since it already allows a way to offset carbon footprints of interested parties.
CO2NNEX is a blockchain solution proposed by Mitshubihi Heavy Industries and IBM Japan that emphasizes on streamlining CO2 supply chain by tracing carbon capture, utilization and storage (CCUS) for providing a unified view of the captured CO2 and its market value on a digital platform [22].This solution also aims to broaden the possibility of offering captured CO2 to a wider range of new industries capable of using CO2 as feedstock.CO2NNEX is capable of recording the amount of CO2 at separate stages, i.e., the amount captured, transported, traded, and stored, using Internet of Things (IoT) devices in the CCS infrastructures.As of 2022, a proof of concept of this solution has been conducted to track the footprint of carbon emissions over the course of production, supply, and usage of synthetic methane gas from captured CO2 [23].
Note that the summary of the above-mentioned initia-tives is a best-effort overview based on available online resources, e.g., the company website or news article, due to the unavailability of related scientific literature.

Proposed solution
The use of blockchain in the field of CCS is primarily limited to implementing platforms for carbon market and broadening the utilization of captured CO2, as discussed in Section 3. It suggests that there is a lack of solution for transparent tracing of the technological efficiency for CCS, generating public awareness on CO2, and implementing regulatory/compliance policies among different stakeholders, e.g., industries, government, certification agencies, and general public, within the CCS ecosystem.Therefore, we propose a blockchain-based CCS architecture in Figure 3 in reference to the above-mentioned concerns.
In the proposed architecture, the industrial plants (the left-most circle in Figure 3), one of the stakeholders in the CCS ecosystem, are connected to the blockchain network for the purpose of evaluating the efficiency of their CCS technologies.In fact, the industrial plants facilitate the initial phase of efficiency calculation by recording necessary quantitative measurements and related data about CO2 captures.Figure 4 shows various data that are recorded in blockchain concerning CO2 capture and emissions at all three stages of CCS.In the proposed model, we suggest that the CCS efficiency data (e.g., capture amount, volume, and concentration) are measured using IoT devices (e.g., smart meters) installed in different infrastructural locations of the industrial plants for the accuracy and transparency of LCA reporting.It is to mention that LCA is a widely used method for evaluating technological efficiency; however, there are many factors that affect its accuracy in its reporting [12,24].For example, if consistent data acquisition at each stage of CCS using smart devices is not possible due to low infrastructural maturity and limited capabilities, the missing information is derived using available information through calculation [12].Such gaps in data acquisition during LCA may result in reports that are incomparable for a reliable emissions reduction estimation.In our proposed architecture, storing both the quantitative value and the acquisition method in the blockchain network would provide more reliable and transparent data for CCS efficiency calculation.
The top-most circle in Figure 3 shows another concerned stakeholder, i.e., technical experts, in the proposed architecture.Here, we consider that the technical experts constitute testing agencies or CCS technology manufacturers.This stakeholder will regularly record standards in the blockchain concerning the expected reductions of carbon emissions from using the deployed CCS technologies in the industrial plants.We also propose that the blockchain will use this data against the measured emissions data acquired from the industrial plant to generate LCA reports on net emissions reduction across all CCS stages using a smart contract.LCA reports are usually long and complex that require time and expertise for compilation.Using smart contracts will save time and administrative costs for the involved stakeholders, such as technical experts and industrial plants.Moreover, the technical experts will use the LCA reports stored in the blockchain network to suggest technological improvements and transparently evaluate environmental impacts.The same LCA reports will also be used as references by industrial plants for determining maintenance schedules to maximize the impacts of the deployed CCS technologies.
The bottom-most circle in the proposed architecture represents the third stakeholder, i.e., government or any other regulatory body, in our architecture.The government will access the blockchain and enforce necessary compliance policies on carbon emissions.The suggestion is that this enforcement will be implemented through a smart contract using available emissions data in the blockchain in order to avoid any intermediary.The government will also leverage the smart contract to transparently assign incentives, e.g., tax credits and economic subsidies, to the compliant stakeholder, i.e., industrial plants, for further reducing CO2 emissions.
Finally, the right-most circle represents the remaining stakeholder in the CCS-based emissions reduction efforts, e.g., public and industries, interested in environmental issues.For example, the blockchain will be an accountable source of emissions data for generating awareness in general public, considering climate change is an existential issue in our society.Most importantly, public acceptance is an important aspect of a successful CCS implementation, which can be encouraged through more transparent CCS technology.In addition, new industrial plants will consider integrating CCS technologies based on the evidence-based data that has been made available on the blockchain.
In the proposed architecture, we have so far outlined multiple stakeholders from different fronts and related advantages for adopting blockchain in CCS-based carbon emissions efforts.However, there are two issues regarding the implementation of our architecture that also need careful considerations toward reduction of carbon emissions into the atmosphere: i) data privacy and ii) scalability in the blockchain network.
Even though blockchain is widely deployed nowadays due to its inherent features of establishing trust and transparency, these two characteristics can be counterproductive in the implementation of the proposed architecture for establishing data privacy of the involved stakeholders, e.g., industrial plants.This concern is more compelling if access to the blockchain data is implemented for creating public awareness, as outlined in our proposal.However, such privacy issue has been recently mitigated by dual-chain system for separating sensitive data from public access in a blockchain-based solution concerning plastic recyling [25].
On the other hand, scalability is an inherent impediment toward implementing blockchain solutions because of their high computational/energy cost in adding blocks in the networks [14].For our proposed architecture, consortium blockchain seems to be the suitable blockchain type for its implementation for relatively lower computation/energy cost.
Nevertheless, there will be a considerable amount of CO2 emissions from blockchain network that has the potential to minimize the impact of effective CO2 emissions reduction using blockchain.Therefore, a careful consideration should be taken toward estimating the net CO2 emission while adopting blockchain technology in CCS.This will ensure the most optimized and efficient performance in achieving a transparent CCS technology.

Conclusions
Carbon capture and storage (CCS) is an important technology in the reduction of atmospheric carbon emissions, as outlined in SDG 13.Even though this technology is widely used in various industrial plants, its long-term efficacy in achieving SDG 13 goal requires transparency in the quantitative output annually.In this paper, we proposed incorporating accountability in industrial plants by transparently recording and tracking CO2 capture in blockchain at every stage of their integrated CCS units.We proposed a blockchain-based architecture that defined several stakeholders along with their roles and benefits in optimizing the efficiency of CCS technology in a transparent manner.We argued that the traceability of CO2 captures also has the potential to facilitate regulatory incentives and to generate public awareness of compliant industrial plants by implementing smart contracts.Finally, we outlined challenges concerning the data privacy and scalability issues of blockchain for a more accurate and transparent reduction of carbon emissions while implementing the proposed architecture.

Fig. 1 .
Fig. 1.Three stages of carbon capture and storage (CCS) technology: capture and compression, transportation, and utilization and storage, when integrated as a unit in industrial plants.

Fig. 2 .
Fig. 2. A simplified view of data-storage steps in blockchain through block creation, validation, and blockchain population.

Fig. 3 .
Fig. 3. Proposed blockchain architecture for transparent carbon capture and storage involving various stakeholders, e.g., industrial plants, technical experts, government, and general public.