China’s pathways of CO2 capture, utilization and storage under carbon neutrality vision 2060

Abstract Carbon dioxide (CO2) Capture, Utilization and Storage (CCUS) is an indispensable part of the carbon removal technologies to achieve carbon neutrality for China. Our study focuses on China’s CCUS pathways, and draws out three key conclusions: (1) in terms of the greenhouse gases emission reductions required to achieve carbon neutrality and based on current technology projections, the CO2 emission reductions to be achieved by CCUS are 0.6 ∼ 1.4 billion tonnes and 1 ∼ 1.8 billion tonnes in 2050 and 2060, respectively; (2) from the perspective of source-sink matching in China, the emission reduction potential provided by CCUS can basically meet the demand of carbon neutrality target (0.6 ∼ 2.1 billion tonnes of CO2); (3) with the development of technologies, the cost of CCUS in China has a great potential to be reduced in the future. It is expected that by 2030, the technical cost of the whole CCUS process (according to 250 kilometers transportation) in China will be 310 ∼ 770 Chinese Yuan per tonne of CO2, and by 2060, it will gradually drop to 140 ∼ 410 Chinese Yuan per tonne of CO2.


Introduction
In September 2020, President Xi Jinping announced that China aims to reach the peak carbon dioxide (CO 2 ) emissions by 2030 and strive to achieve carbon neutrality by 2060 at the general debate of the 75th session of the United Nations General Assembly, which contributes to the global climate governance and the implementation of the Paris Agreement [1]. The announcement of President Xi Jinping opened a new journey for China to tackle climate change. By May 2021, 131 countries, whose greenhouse gas emissions account for more than 65% and gross domestic product (GDP) accounts for more than 75%, have announced the goal of carbon neutrality. With the global carbon neutrality vision becoming clear and mitigation actions being accelerated, the role of CO 2 capture, utilization and storage (CCUS) has become more prominent, and its status is changing significantly [2,3].
CCUS is a large-scale greenhouse gas emissions reduction technology [4][5][6]. In recent years, CCUS policies, research and development in China have been gradually improved under the joint promotion of the Ministry of Ecology and Environment, the Ministry of Science and Technology, and the National Development and Reform Commission [7]. What's more, the scale of pilot demonstration projects continues to grow, and the competitiveness is further enhanced. But overall, China's green and low-carbon technology systems for carbon neutrality has not yet been established [8][9][10]. There is still a big gap between the existing technology system for emission reductions and the actual need for carbon neutrality. The studies have shown that CCUS will become one of the indispensable key technologies for China to achieve the goal of carbon neutrality. Therefore, the strategic positioning of CCUS should be rethought and reassessed according to the new situation, and it should be accelerated and deployed in advance on this basis [11].
This study focuses on China's CCUS pathways, which will play an important role in studying the strategic positioning and development path of CCUS under the carbon-neutral goal in China. This paper introduces the key contents of the CCUS pathways, including the current status, emission reduction needs and potentials, and the cost of CCUS in China. Intelligence gathering and analyzing were the main means to draw the conclusions. Moreover, forty-nine researchers in the CCUS field participated in this research and 12 authoritative experts reviewed the results.
Section "Positioning of CCUS" introduces the position of CCUS in the scenario of carbon neutrality by 2060 and the global theoretical storage capacity; section "Current status of CCUS in China" extracts the current status of CCUS in China from the survey of the CCUS operation enterprises. Section "CCUS needs under the carbon neutrality target" reviewed the CCUS needs of thermal power, steel, cement, petrochemical and chemical industries under the carbon neutrality target, which indicates the role of CCUS in the above industries; section "CCUS potential of China based on source-sink matching" concluded the CCUS potential of China based on source-sink matching, mainly focusing on the utilization and storage technologies; section "CCUS cost assessment in China" forecast the CCUS cost trend to 2060.
The conclusions will support policymakers to carry out CCUS related analyses in strategy, planning, and policy, and help the researchers determine future emissions anchors in different periods based on the current understanding of CCUS. It will further help the public to understand CCUS related knowledge, such as the position and role of CCUS, which will strengthen China's goal of achieving carbon neutrality.

Positioning of CCUS
To achieve the goal of carbon neutrality, China needs to establish a zero-carbon energy system based on non-fossil energy, and decouples economic development from carbon emissions [12,13]. CCUS technology, as an important part of the carbon-neutral technologies in China, is the only technology choice for low-carbon utilization of fossil energy and the main technical means to maintain the flexibility of the power system. Moreover, CCUS is a feasible technical solution for difficult emission reduction industries such as steel and cement. In addition, the negative emission technology coupled with CCUS and new energy is also the base technology guarantee to offset the failure to reduce carbon emissions and achieve carbon neutrality [14,15].
In China, the theoretical storage capacity is about 1.21 $ 4.13 trillion tonnes [21,28,29] (Figure 1). China's oil fields are mainly concentrated in the Songliao Basin, Bohai Bay Basin, Ordos Basin, and Junggar Basin. 5.1 billion tonnes of CO 2 can be sequestered through CO 2 enhanced oil recovery (CO 2 -EOR) technology. China's gas reservoirs, which are mainly distributed in the Ordos, Sichuan, Bohai Bay, and Tarim Basins, can be used to sequester about 15.3 billion tonnes of CO 2 in depleted gas reservoirs, while about 9 billion tonnes of CO 2 can be  [16-26, 30, 31]. Theoretical storage capacity values were taken as the median of the interval. Estimates of cumulative CO 2 emissions to 2060 are calculated based on unchanged emissions from 2019 to 2060, and the emissions data for 2019 are from BP [32]. stored through CO 2 enhanced gas recovery (CO 2 -EGR) technology. The CO 2 storage capacity of the deep saline formations in China is about 2.24 trillion tonnes, and its distribution is basically the same as that of the petroliferous basins. Among them, Songliao Basin (694.5 billion tonnes), Tarim Basin (552.8 billion tonnes), and Bohai Bay Basin (490.6 billion tonnes) are the three largest storage areas, accounting for 55.9% of the total storage. In addition, the Subei Basin (435.7 billion tonnes) and Ordos Basin (335.6 billion tonnes) also have large CO 2 storage potential in the deep saline formations. The CO 2 emissions in 2019 is about 9.8 billion tonnes, the theoretical storage capacity would meet the 120 $ 420 years storage capacity demands based on the 2019 total emissions.

Current status of CCUS in China
In China, about 40 CCUS demonstration and pilot projects have been put into operation and under construction with a capture capacity of 3 million tonnes per year. By 2021, these projects mainly focus on the small-scale EOR demonstration in the petroleum, coal chemical and thermal power industries, lacking large-scale and full-chain industrialization demonstration with various technology combinations ( Figure 2).

Ready to scale up and preparing for CCUS cluster
The engineering capacity in China is ready to capture and store CO 2 on a large scale and is actively preparing for a full-chain CCUS industrial cluster. China Energy Investment Corporation (China Energy) Ordos CCUS Demonstration Project has successfully carried out a full-chain demonstration of CO 2 capture, transportation and storage with a total of 300,000 tonnes of CO 2 injection into deep saline formations. Until 2021, China National Petroleum Corporation (CNPC) Jilin Oilfield EOR project is the only Chinese project among the 21 large-scale CCUS projects currently in operation globally and is presently the largest EOR project in Asia [22,35], with a total of over 2 million tonnes of CO 2 injected. Besides that, the construction of 150,000 tonnes/ year post-combustion CO 2   Corporation (Sinopec Group) officially launched China's first million-tonne CCUS project, i.e. Qilu Petrochemical Corporation-Shengli Oilfield CCUS project.

Diverse types of capture sources and utilization routes
China's CCUS projects are distributed in 19 provinces, and the industries of capture sources and the types of storage and utilization are diversifying. The total scale of China's 13 CO 2 capture demonstration projects involving power plants and cement plants reached 856,500 tonnes/year. The total scale of China's 11 CO 2 geological utilization and storage projects is 1.821 million tonnes/year, among which the scale of CO 2 -EOR is about 1.54 million tonnes/year. China's CO 2 capture sources cover pre-combustion, post-combustion and oxyfuel combustion capture in coal-fired power plants, gas-fired power plants, coal chemical industries, and cement kiln exhaust. CO 2 storage and utilization involve various options such as saline formation storage, EOR, enhanced coalbed methane recovery (ECBM), enhanced uranium leaching, CO 2 mineralization, biodegradable polymers, reforming of methane to syngas, and microalgae immobilization.
Having significant progress in all aspects and commercial potential of some technologies Significant progress has been made in all technical aspects of CCUS in China, and some technologies have the potential for commercial applications ( Figure 3).

Capture technology
The maturity of different CO 2 capture technologies varies greatly. At present, the pre-combustion physical absorption technology is already at the commercial application stage. The post-combustion chemical adsorption technology is still at the pilot stage, and most other capture technologies are already at the industrial demonstration stage. The post-combustion capture technology is currently the most mature capture technology, which can be used in the decarbonization transformation of most thermal power plants. For example, the 150,000-tonne-per-year CO 2 capture and storage demonstration project carried out by Guohua Jinjie Power Plant is operating. It is the largest post-combustion CO 2 capture and storage demonstration project in China. The pre-combustion capture system is relatively complicated, and the integrated gasification combined cycle (IGCC) technology is a typical pre-combustion CO 2 capture system. China's IGCC projects include Huaneng Tianjin IGCC project and Lianyungang clean energy power system research facility. Oxyfuel combustion technology is one of the most potential large-scale CO 2 capture technologies for coal-fired power plants, producing higher concentration (about 90% $ 95%) of CO 2 and is easier to capture. The oxyfuel combustion technology has developed rapidly and can be used in new and/or retrofitted coal-fired power plants. At present, the first-generation CO 2 capture technology (postcombustion, pre-combustion, oxyfuel combustion) has gradually matured. The main bottleneck is high cost, high energy consumption and lack of extensive large-scale demonstration project experiences. While, the second-generation technology (such as new membrane separation, new absorption, new adsorption, pressurized oxyfuel combustion, etc.) is still in laboratory research or a smallscale test stage. When the second-generation technology is mature, the energy consumption and cost will be reduced by more than 30% compared with the matured first-generation technology. And it is expected to be widely applied around 2035 [36].

Transportation technology
Among the existing CO 2 transportation technologies, tanker and ship transportation technologies have reached the commercial application stage, while pipeline transportation is still in the pilot stage. CO 2 land vehicle transportation and inland ship transportation technology has matured, and it is mainly applied to CO 2 transportation with a scale of less than 100,000 tonnes/year. The scale of China's existing CCUS demonstration projects is relatively small, and most of them are transported by tankers. Jilin Oilfield and Qilu Petrochemical Corporation use land pipeline transportation. Part of the CO 2 from East China Oil and Gas Field and Lishui Gas Field is transported by ship. The cost of submarine pipeline transportation is 40% to 70% higher than that of land pipelines. At present, the technology of submarine pipeline transportation of CO 2 lacks experience, and it is still at the research stage in China.

Utilization and storage technology
Among CO 2 geological utilization and storage technologies, CO 2 enhanced uranium leaching has reached the commercial implementation stage, CO 2 -EOR has been in the industrial demonstration stage, CO 2 -EWR pilot test has been completed, ECBM has also completed the pilot-scale research and the CO 2 mineralization has also been in the industrial test stage. CO 2 enhanced natural gas and shale gas recovery are still in the primary research stage. China's CO 2 -EOR projects are mainly concentrated in oil fields and offshore areas in eastern, northern, northwestern and western China. The 100,000 tonnes/year CO 2 storage in deep saline formations implemented by China Energy Investment Corporation has completed the injection target of 300,000 tonnes in Ordos Basin in 2015 and stopped further injection. The 150,000 tonnes/year post-combustion CO 2 capture and storage demonstration project, implemented by China Energy Investment Corporation Guohua Jinjie Power Plant, plans to store the captured CO 2 in saline formations. In July 2021, China Petrochemical Corporation (Sinopec Group) officially launched China's first million-tonne CCUS project (Qilu Petrochemical Corporation-Shengli Oilfield CCUS project), which is expected to become the largest demonstration project for the full-chain CCUS technology in China. The Institute of Process Engineering (IPE), Chinese Academy of Sciences, launched a 50,000 tonnes/year steel slag mineralization industrial verification project in Dazhou, Sichuan province. Zhejiang University has carried out a 10,000-tonne industrial test project of CO 2 deep mineralization maintenance for building materials in Henan province. Along with China Petrochemical Corporation (Sinopec Group) and other companies, Sichuan University has made good progress in developing the technology for direct mineralization of phosphogypsum co-production of sulfur-based compound fertilizer from low-concentration CO 2 exhaust gas. In China, significant progress has been made in CO 2 chemical utilization technologies, and many new technologies such as electrocatalysis and photocatalysis have emerged. However, some technical bottlenecks still exist in the post-combustion CO 2 capture system and chemical conversion and utilization device. Biological utilization mainly focused on microalgae fixation and gas fertilizer.

CCUS needs under the carbon neutrality target
According to the research of various domestic and foreign research institutions, to achieve the carbon neutralization target, China's CO 2 emission reduction is 20 million to 408 million tonnes in 2030, 600 million to 1.45 billion tonnes in 2050, and 1 billion to 1.82 billion tonnes in 2060 ( Table 1). The scenarios mainly consider China's achievement of the 1.5 C and 2 C temperature control targets, sustainable development goals, carbon peaking and carbon-neutral targets, CO 2 emission pathways by industry, development of CCUS technology, and scenarios where CCUS can be used or may be used ( Figure 4).

Thermal power industry
The thermal power industry is the main area of CCUS demonstration in China currently. It is expected that coal-fired power emission reductions will reach 6 million tonnes/year by 2025, peak at 200 million to 500 million tonnes/year in 2040, and then remain unchanged. The CCUS deployment of gas-fired power will be gradually carried out and will remain unchanged after reaching a peak in 2035, with a reduced rate of 20 million to 100 million tonnes/year. Coal-fired power plants equipped with CCUS can capture 90% of CO 2 emissions, turning them into relatively lowcarbon power generation technology. China's current installed capacity of about 900 million kilowatts will still be in operation by 2050. The deployment of CCUS technology helps to make full use of existing coal-fired power generation units, appropriately retain coal-fired power production capacity, and avoid the premature retirement of some coal-fired power assets that may lead to waste. It is an important way to release the emission reduction potential of CCUS by realizing lowcarbon utilization and transformation of existing advanced coal-fired power units combined with CCUS technology. Technical suitability criteria and cost are the main factors affecting the installation of CCUS in active coal-fired power units. Technical suitability criteria determines whether a power Table 1. Potential of CO 2 emission reduction in various industries from 2025 to 2060 (million tonnes/year) [36][37][38][39][40][41][42][43][44][45][46][47][48][49][50][51][52]. Note: DACCS is in the primary research stage, and its technical maturity and economy need to be improved. The emission reduction potential is difficult to release in the short term. It is expected that industrialization demonstration and promotion will be carried out around 2035. Note: Data came from Table 1, and values were taken as the median of the interval.
plant can be a candidate for transformation. At the present stage, technical suitability criteria that need to be considered in retrofitting coal-fired power plants include implementation year of CCUS, unit capacity, remaining service life, unit load rate, capture rate setting, and valley value/ peak value, etc.

Steel industry
The emission reduction demand of steel industry is 2 million $ 5 million tonnes/year in 2030 and 90 million $ 110 million tonnes/year in 2060. China's iron and steel production process is dominated by the blast furnace-converter technology with high CO 2 emissions, and the output of electric furnace steel accounts for only about 10%. About 89% of energy input in blast furnace-converter steelmaking comes from coal, leading to high CO 2 emissions per tonne of steel in China. CCUS technology can be applied to many aspects of the steel industry, mainly including hydrogen production and steelmaking processes in hydrogen reduction ironmaking. In addition, the CO 2 -EOR project is also a vital driving force for the development of CO 2 capture technology in China's steel industry. The CO 2 from China's steel plants is mainly of medium concentration, which can be captured by pre-combustion and post-combustion capture technologies. Coking and blast furnace ironmaking processes have the most significant CO 2 emissions in the entire steelmaking process, and these two processes have the largest CO 2 capture potential. The mainstream CO 2 capture technology in China's steel industry is post-combustion capture from coking and blast furnace exhaust gas.
In addition to utilization and storage, CO 2 captured by the iron and steel industry can also be directly used in the steelmaking process. These technologies have been tested successfully by Shougang Group and promoted to Tianjin Pipe International Economic & Trading Corporation and Xining Special Steel Co., Ltd. Full application of these technologies can reduce the total CO 2 emissions by 5% $ 10%. There are four main development directions for CO 2 utilization in the steel industry. (1) It can be used for mixing. CO 2 can replace nitrogen (N 2 ) or argon (Ar) for the top/bottom blowing of the converter or for the mixing of molten steel in the ladle; (2) It acts as a reactant and reduces the volatilization and oxidation loss caused by direct collision of oxygen (O 2 ) and molten iron in CO 2 -O 2 mixed spray steelmaking; (3) It can partially replace N 2 as a protective gas in steelmaking, thereby minimizing the loss of steel, as well as the nitrogen content and porosity in the finished steel; (4) It also can be used to synthesize fuel. The dry reforming reaction of CO 2 and methane can produce synthesis gas (CO and hydrogen), which can then be used in direct reduced iron (DRI) steelmaking or the production of other chemicals.

Cement industry
In the cement industry, the CO 2 emission reduction demand in 2030 will be 10 million $ 152 million tonnes/year, and it will be 190 million $ 210 million tonnes/year in 2060. The CO 2 emissions from the decomposition of limestone account for about 60% of the total emissions in the cement industry. CCUS is a necessary technical means for cement decarbonization.

Petrochemical and chemical industries
The petrochemical and chemical industries are the main areas of CO 2 utilization, through chemical reactions to convert CO 2 into other substances and then for resource reuse. China's petrochemical and chemical industries have many highconcentration (above 70%) CO 2 emission sources. They include natural gas processing plants, coal plants, ammonia/fertilizer production plants, ethylene plants, methanol, ethanol and dimethyl ether production plants, etc. Compared with low-concentration CO 2 emission sources, the capture of high-concentration CO 2 emission sources has lower energy consumption, lower investment costs, and lower operation and maintenance costs, which have significant advantages. Therefore, high-concentration CO 2 emission sources in the petrochemical and coal chemical industries can provide low-cost opportunities for early CCUS demonstrations. Early CCUS demonstration projects in China preferred combining high-concentration CO 2 emission sources and EOR to generate revenue through CO 2 -EOR. When the oil price is high, CO 2 -EOR revenue can fully offset the cost of CCUS and create additional economic profits for the stakeholders of CCUS, that is, it can achieve CO 2 emission reductions at a negative cost. The CCUS demand for CO 2 emission reductions in the petrochemical and chemical industries will be about 50 million tonnes in 2030, and will gradually decrease to zero by 2040.

CCUS potential of China based on sourcesink matching
In the category of CO 2 geological utilization and storage technologies, the CO 2 -EWR technology can achieve large-scale and deep CO 2 emission reductions, with a theoretical storage potential of 2.417 trillion tonnes. Under current technical conditions, both CO 2 -EOR and CO 2 -EWR can be demonstrated on a large scale and can achieve large-scale CO 2 emission reductions under specific economic incentives. Therefore, this research provides source-sink matching of CO 2 -EOR and CO 2 -EWR with major industries in China (Table 2).
China has enormous potential for CO 2 -EOR. From the perspective of basin scale, Bohai Bay Basin and Songliao Basin have great potential for CO 2 -EOR. They are regarded as the priority areas for the implementation of CCUS projects. Combined with the geological characteristics of China's major basins and the distribution of CO 2 emission sources, the key areas for CO 2  The sedimentary basins in the east and north, such as Bohai Bay Basin, Ordos Basin and Songliao Basin, match well with the distribution of carbon sources. The geological conditions in northwest China are relatively good, and the Tarim and Junggar basins have great geological storage potential, however, the distribution of CO 2 emission sources is relatively few. In the southern and coastal areas where CO 2 emission sources are concentrated, the sedimentary basins that can be sequestrated are small in space and scattered in distribution, with relatively poor geological conditions. The potential of onshore storage is very limited in the southern and coastal areas in China, and offshore geological storage is an important alternative.
CCUS source-sink matching mainly considers the geographical location relationship and environmental suitability of emission sources and storage sites. 250 km is the critical distance of the pipeline that does not require a CO 2 relay compressor station, and the pipeline cost is relatively low. Therefore, it is often used as the distance limit in the analysis of source-sink matching in China, and more than 250 km is generally not considered. The Chinese government attaches great importance to the environmental impacts and risks of CCUS. The Ministry of Environmental Protection released the Technical Guideline on Environmental Risk Assessment for carbon dioxide Capture, Utilization and Storage (On Trial) on June 20, 2016. Considering the regulatory requirements of the Chinese government for the environmental impacts and risks of CCUS projects, the environmental impacts and risks of CO 2 geological storage on water resources (i.e. groundwater and surface water), surface vegetation and human health are mainly considered.

Thermal power
The Junggar Basin, Turpan-Hami Basin, Ordos Basin, Songliao Basin and Bohai Bay Basin are considered as key areas for the deployment of CCUS technologies including CO 2 -EOR in the thermal power industry, which are suitable for the early integration demonstration projects to promote the large-scale and commercial development of CCUS technologies.
In 2020, China's coal-fired power plants in service will be distributed in 798 grids (one grid with a width of 50 km), covering central and eastern China, most of southern China, and parts of northeast and northwest China ( Figure 5). There are 51 grids with annual CO 2 emissions of more than 20 million tonnes, mainly distributed in central China and the eastern coastal areas. The suitability of storage sites is particularly medium or low. In particular, there are almost no sites suitable for onshore storage along the eastern coast. There are 99 grids with annual CO 2 emissions ranging from 10 million to 20 Note: The upper limit of CO 2 chemical utilization potential is calculated based on the market share of chemical products. In contrast, the upper limit of geological utilization potential and storage potential is calculated based on the matching result of internal source and sink of 250 km.
million tonnes, which have medium and high suitability for geological storage in Turpan-Hami Basin, Ordos Basin, Junggar Basin, Songliao Basin and Qaidam Basin. However, southern inland provinces, such as Guizhou, Jiangxi, Anhui and other regions with significant CO 2 emissions of local thermal power do not have matching storage sites. Hunan and Hubei provinces only have scattered medium and low suitability sites in Dongting and Jianghan Basins. Therefore, source-sink matching is not good within the transportation range of 50 km from the perspective of regional cluster development.

Iron and steel
Iron and steel enterprises are mainly located in provinces with rich iron ore and coal resources, such as Hebei, Liaoning, Shanxi, Inner Mongolia, etc., and the coastal areas with port resources. These regions have developed economies and enormous demand for iron and steel.
In 2020, China's iron and steel enterprises were distributed in 253 grids. There are 26 grids with annual CO 2 emissions more than 20 million tonnes, mainly distributed in Hebei, Liaoning and Shanxi provinces ( Figure 6). 28 grids with annual CO 2 emissions ranging from 10 million to 20 million tonnes, mainly distributed in Hebei, Shanxi, Liaoning, Shandong provinces, etc. In addition, there are 1 grid or 2 grids in Fujian, Hunan, Hubei, Guangdong, Jiangxi, Jiangsu, Xinjiang and other provinces. There are scattered medium and low suitability sites in Bohai Bay Basin, Shandong province, among these high CO 2 emission areas. Shanxi iron and steel plants should increase the transportation distance in the Ordos, Linfen and other basins to find suitable geological storage sites. Under the condition of 250 km matching distance, more than 79% of steel plants can find suitable geological utilization and storage sites.
Steel plant can carry out CO 2 -EOR and CO 2 -EWR joint projects or single CO 2 -EOR projects, and the levelized cost is low, and even some projects can be profitable. Due to the minimal CO 2 storage capacity of oil fields and the competition with CCUS in chemical, thermal power, cement and other industries, it is difficult for the steel industry to obtain enough oil fields to carry out CO 2 -EOR to achieve deep CO 2 reduction. Therefore, the CO 2 -EWR project must be carried out. The higher the net CO 2 capture rate of the steel plant, the lower the levelized cost of large-scale CCUS projects. Under the same net CO 2 capture rate, the larger the matching distance, the more matched CCUS projects, and the more significant the cumulative CO 2 emission reductions. Under the same CO 2 capture rate and matching distance scenarios, the levelized cost of CO 2 -EWR projects is much higher than that of CO 2 -EOR projects. There are many steel plants in Bohai Bay Basin, Junggar Basin, Jianghan Basin, Ordos Basin and nearby regions, large CO 2 emissions, high suitability of storage sites, and good source-sink matching. In contrast, the higher cost of steel plants in southern, coastal and other regions is due to longer transportation distances and the lower estimated CO 2 emissions. The main reason for the project's failure is that the steel plants are far from the onshore basins.

CCUS cost assessment in China
The overall scale of CCUS demonstration projects in China is small, and the cost is high [33]. The cost of CCUS mainly includes economic costs and environmental costs. Economic costs include fixed and operation costs, while environmental costs include environmental risk and energy consumption emission.
The primary component of economic costs is operation costs, which is the input costs required by each link of CCUS technology in the whole process of actual operation. The operation costs mainly include four segments: capture, transportation, storage and utilization. It is estimated that the capture costs will be 90 $ 390 Chinese Yuan/ tonne in 2030 and 20 $ 130 Chinese Yuan/tonne in 2060. Pipeline transportation is the main transportation mode for future large-scale demonstration projects. It is estimated that the cost of pipeline transportation in 2030 and 2060 will be 0.7 Chinese Yuan and 0.4 Chinese Yuan/(tonneÁkm), respectively. The storage cost in 2030 is 40 $ 50 Chinese Yuan/tonne, and in 2060, it is 20 $ 25 Chinese Yuan/tonne (Table 3, Figure 7).
The extra cost caused by installing a CO 2 capture device is 0.26 $ 0.4 Chinese Yuan/kWh for thermal power. The cost per kilowatt-hour of electricity for power plants with large installed capacity, the increased cost of power generation after the installation of capture devices, and the cost of CO 2 net emission reduction and capture will be lower. In terms of cooling appliances, compared with aircooled power plants, the net CO 2 emission reduction costs and capture costs of wet-cooled power plants are lower. According to the cooling device, wet-cooled power plants have lower net CO 2 emission reduction costs and capture costs compared with air-cooled power plants, but higher water consumption. The total water consumption of the cooling system increases approximately 49.6% after installing a capture device in power plants, which causes more serious water resource pressure to local areas, especially areas with water shortages.
The capture and compression costs are the main sources of CCUS operating costs in the petrochemical Table 3. Economic costs of each segment of CCUS from 2025 to 2060 [33,36,[65][66][67][68][69].  and chemical industries. Higher CO 2 production concentration usually means CO 2 capturing rate is high and compression costs will reduce, so increasing CO 2 production concentration is an effective way to reduce the total cost of CCUS operation. After adopting CCUS processes, the coal gasification costs increase 10% $ 38%. And when the carbon tax is higher than $15/tonne of CO 2 , the production cost of CCUS is more advantageous than that of traditional coal gasification processes. In the CCUS project of Yanchang Petroleum Group, CO 2 is derived from the pre-combustion process of coal-togas (the production of syngas from coal-to-gas). As a result, compared to other CO 2 capture and transport projects, the capture and operation costs of the Yanchang CCUS project decreased by approximately 26.4%, only $26.5/tonne, with capture costs of $17.52/tonne and transport costs of $9.03/tonne.
Another component of the economic cost is the fixed costs, which is the upfront investment of CCUS technology, such as equipment installation, land footprint investment, etc. It costs about $27 million for a steel plant to install a CO 2 capture and storage facility with an annual capacity of 100,000 tonnes. Starting a CCUS project at Baosteel's Zhanjiang plant with an annual capture capacity of 500,000 tonnes (stored in the Beibu Gulf Basin, within 100 km of the plant) will require an investment of $52 million. The economic assessment of Baosteel's Zhanjiang plant shows that combining with fixed and operating costs, the total cost of emission reduction is $65 per tonne of CO 2 , which is similar to the costs in Japan ($54 per tonne of CO 2 ) and Australia ($60 $ $193 per tonne of CO 2 ).
The environmental costs are mainly due to the environmental impacts and risks of CCUS. First, it is the environmental risk of CCUS technology. CO 2 may leak during the process of capture, transportation, utilization and storage, which will have a certain impact on the nearby ecological environment and personal safety. Second, environmental pollution is caused by the additional energy consumption of CCUS technology. Most CCUS technologies have the characteristics of additional energy consumption, and the increase in energy consumption will inevitably bring the emission pollutants. Considering the storage scale, environmental risk and supervision, it is generally required that the safety period of CO 2 geological storage should be no less than 200 years.
The energy consumption is mainly concentrated in the capture stage, wherein the impact of energy consumption on the cost and environment is very significant. For example, alkanolamine absorbent is the most widely used absorbent to capture CO 2 from coal-fired flue gas. However, the chemical absorption technology based on alkanolamine absorbent still has obvious limitations in largescale commercial applications. One of the main reasons is that the energy consumption of operation is too high, reaching 4.0 $ 6.0 MJ/kg CO 2 .

Conclusions and suggestion
Conclusions CCUS is one of the indispensable key technologies for China to achieve the goal of carbon neutrality. China attaches great importance to the development of CCUS technology and steadily promotes its research, development and implementation plan. The CCUS in China is on the way to the commercialization with significant emission reduction contribution after 2035.
In terms of the emission reductions required to achieve carbon neutrality and based on current technology projections, the CO 2 emission reductions to be achieved by CCUS are 0.6 $ 1.4 billion tonnes and 1 $ 1.8 billion tonnes in 2050 and 2060, respectively. Among them, BECCS and DACCS need to reduce CO 2 emissions by 0.3 $ 0.6 billion tonnes and 0.2 $ 0.3 billion tonnes in 2060, respectively. From the perspective of source-sink matching in China, the emission reduction potential provided by CCUS can basically meet the demand of carbon neutrality target (0.6 $ 2.1 billion tonnes CO 2 ).
At present, China's CCUS technology is at the industrial demonstration stage, but the scale of the existing demonstration projects is small. The cost of CCUS is an important factor discouraging its large-scale implementation. With the development of technology, the cost of CCUS in China has a great potential to be reduced in the future. It is expected that by 2030, the cost of the whole CCUS process (according to 250 kilometers transportation) in China will be 310 $ 770 Chinese Yuan per tonne of CO 2 , and by 2060, it will gradually drop to 140 $ 410 Chinese Yuan per tonne of CO 2 .

Suggestion
To promote the development of CCUS technologies in China and better support the realization of peak CO 2 emissions and carbon neutrality, the following suggestion can be made: 1. Clarify the development routes of CCUS for the carbon neutrality target. Taking full account of the industrial structure and emission pathway of key industries under the carbon neutrality target, a comprehensive and systematic assessment about the emission reduction demands and potential of CCUS in China from 2021 to 2060 needs to be made. 2. Improve the support and standard system for CCUS policy. It should promote the commercialization of CCUS, including but not limited to include CCUS in the catalog of industrial and technological development, improve and optimize the framework of laws and regulations, and formulate a scientific and reasonable standard system for construction, operation, supervision and termination. 3. Plan and layout of CCUS infrastructure construction. Increase the investment and construction scale of CCUS infrastructure, improve the management level of technical facilities, establish the cooperation and sharing mechanism of related infrastructure, and promote the coupling and integration of CCUS with different CO 2 emission fields and industries. 4. Carry out large-scale CCUS demonstration and industrial cluster construction in an orderly manner. It should improve the compatibility, integration, and optimization of full-chain technology units, accelerate the breakthrough of related bottlenecks of large-scale full-chain CCUS demonstration, and promote the construction of CCUS industrial clusters.
Given the uncertainty of CCUS emission reduction demand and potential assessment in the academic community, it is urgent to carry out indepth analyses under more clear boundary conditions such as technology, capital, and policy in the future to obtain a more reasonable potential assessment and development path.