What is CCUS?

Carbon dioxide (CO2) capture, utilization, and storage (CCUS) refers to the process of separating CO2 from industrial processes, energy utilization, or the atmosphere, and directly utilizing or injecting it into geological formations to achieve permanent reduction of CO2 emissions. CCUS has added the concept of “utilization” on the basis of carbon dioxide capture and storage (CCS), which has been widely recognized internationally with the development of CCS technology and the continuous deepening of understanding of CCS technology, under the strong advocacy of China and the United States. CCUS is divided into technical processes such as capture, transportation, utilization, and storage.

CO2 capture refers to the process of separating CO2 from industrial production, energy utilization, or the atmosphere, mainly divided into pre combustion capture, post combustion capture, oxygen enriched combustion, and chemical chain capture.

CO2 transportation refers to the process of transporting captured CO2 to a usable or storage site. According to different modes of transportation, it can be divided into tank truck transportation, ship transportation, and pipeline transportation, among which tank truck transportation includes two modes: automobile transportation and railway transportation.

CO2 utilization refers to the process of utilizing captured CO2 as a resource through engineering techniques. According to different engineering techniques, it can be divided into CO2 geological utilization, CO2 chemical utilization, and CO2 biological utilization. Among them, CO2 geological utilization is the process of injecting CO2 underground to enhance energy production and promote resource extraction, such as improving oil and natural gas recovery rates, and extracting various types of resources such as geothermal, deep saline (brine) water, and uranium mines.

CO2 sequestration refers to the process of injecting captured CO2 into deep geological reservoirs through engineering techniques to achieve long-term isolation of CO2 from the atmosphere. According to different storage locations, it can be divided into land storage and ocean storage; According to different geological storage bodies, they can be divided into saltwater storage, depleted oil and gas storage, etc.

Biomass Energy Carbon Capture and Storage (BECCS) and Direct Air Carbon Capture and Storage (DACCS) have received high attention as negative carbon technologies. BECCS refers to the process of capturing, utilizing, or sequestering CO2 generated during biomass combustion or conversion, while DACCS is the process of directly capturing CO2 from the atmosphere and utilizing or sequestering it.

CCUS Technology and Main Types Diagram

Carbon dioxide capture

The core task of carbon dioxide capture technology is to collect the carbon dioxide produced by major emitters such as liquefied natural gas, hydrogen plants, steel plants, cement plants, power plants, and oil refineries, and store it in various ways to avoid its emission into the atmosphere. How to capture carbon dioxide in the production process is the key to the problem. At present, carbon dioxide capture generally adopts the following methods:

1.Capture after combustion

Post combustion capture is the main method used in China. Capturing carbon dioxide from the flue gas emitted after combustion through methods such as solution absorption, solid absorption, and membrane absorption is more suitable for thermal power generation.

Advantages: Small scale renovation and compact equipment.

Disadvantages: high energy consumption, high cost, low efficiency.

2.Capture before combustion

Introducing oxygen or air into the integrated gasification combined cycle system can enable high-pressure gasification of raw materials such as coal and biomass fuels, followed by water gas conversion to produce carbon dioxide and hydrogen gas. At this time, the pressure and concentration of carbon dioxide are high, making it easy to capture carbon dioxide.

Advantages: Small system size, low energy consumption, and high efficiency.

Disadvantages: High investment cost, reliability needs to be improved.

3.Oxygen enriched combustion

Through oxygen production technology, nitrogen in the air is removed and directly burned with high concentration oxygen and emitted flue gas, thereby improving combustion efficiency (about 17%~35%), increasing carbon dioxide purity, and reducing the production of by-products such as carbon monoxide.

Advantages: Energy saving and environmentally friendly.

Disadvantages: There are requirements for the operating environment, and the oxygen production process is difficult.

4.Solution absorption method

The solution absorption method is also the main method used domestically. Mainly using solvents such as ethanolamine, diethanolamine, triethanolamine, diisopropanolamine, methylpropanol amine, etc.

Advantages: fast absorption speed, high purification degree, and high carbon dioxide recovery rate.

Disadvantages: High energy consumption for solvent regeneration and strong corrosiveness of solvents.

5.Solid absorption method

Mainly using substances such as activated carbon, molecular sieves, hydrotalcite, cage hydrates, silicates, carbonates, etc.

Advantages: Large absorption capacity, low energy consumption, and low corrosiveness.

Disadvantage: Low carbon dioxide recovery rate.

6.Membrane absorption

Membrane absorption method is a combination of membrane and chemical absorption, mainly using microporous membrane technology to isolate the mixed gas and absorption liquid, relying on the selective absorption of the absorption liquid on the other side of the membrane to achieve the separation of carbon dioxide in the mixed gas.

Advantages: Low energy consumption and simple operation.

Disadvantages: High investment and immature industrialization.

Taking the post combustion capture chemical absorption method as an example, its carbon dioxide capture process involves decarbonization, absorption regeneration, compression drying, and recycling, involving equipment such as flue gas absorption towers and heat exchangers.

Utilization and storage of carbon dioxide

How do we deal with the captured carbon dioxide? There are generally two methods: utilization and storage.

Carbon dioxide utilization

1.Oil displacement

Principle: When extracting crude oil, it is necessary to press it up from the ground to improve recovery efficiency. Previously, water pressure or other gas operations were usually used, but now captured carbon dioxide can be used for oil displacement.

Disadvantage: This method cannot serve the purpose of sequestration, and the captured carbon dioxide will also escape into the atmosphere.

2.Catalytic reaction

Principle: The captured carbon dioxide and hydrogen are catalytically reduced to methanol.

Disadvantages: High cost, insufficiently clean components for obtaining carbon dioxide, and inefficient catalysts for the reaction.

3.Photosynthesis

Principle: Inject the captured carbon dioxide into the plant greenhouse to increase the concentration of carbon dioxide to several times higher than the atmosphere, enhance plant photosynthesis, accelerate plant growth, and consume carbon dioxide to generate oxygen.

Disadvantage: Extremely low utilization rate.

CO2 sequestration

1.Geological storage

Principle: Capture carbon dioxide in suitable geological structures, such as mature or depleted gas fields, deep saline alkali aquifers, and abandoned coal seams. Pressure will convert carbon dioxide into “supercritical fluid”, making it less likely to leak.

Disadvantages: Limited suitable geological structures and difficult injection methods.

2.Ocean storage

Principle: The captured carbon dioxide is transported by ship or pipeline to the deep seabed for storage in seawater.

Disadvantages: High concentration of carbon dioxide can kill marine organisms and easily lead to seawater acidification.

China has the engineering capability to capture, utilize, and store CO2 on a large scale, and is actively preparing for the full process CCUS industry cluster. Significant progress has been made in all technical aspects of CCUS, and some technologies have the potential for commercial application.

Capture technology: The maturity of CO2 capture technology varies greatly. Currently, the pre combustion physical absorption method is in the commercial application stage, the post combustion chemical adsorption method is still in the pilot stage, and most other capture technologies are in the industrial demonstration stage. Post combustion capture technology is currently the most mature capture technology, which can be used for decarbonization transformation of most thermal power plants. The 150000 ton carbon capture and storage demonstration project carried out by Guohua Jinjie Power Plant is under construction, which is currently the largest demonstration project for the entire process of post combustion carbon capture and storage of coal-fired power plants in China.

The pre combustion carbon capture system is relatively complex, and the Integrated Gasification Combined Cycle (IGCC) technology is a typical system for pre combustion carbon capture. The domestic IGCC projects include the Huaneng Tianjin IGCC project and the Lianyungang Clean Energy Power System Research Facility. Oxygen enriched combustion technology is one of the most promising large-scale carbon capture technologies for coal-fired power plants, producing high concentrations of CO2 (about 90% to 95%) that are easier to capture.

The development of oxygen enriched combustion technology is rapid and can be used for new coal-fired power plants and some renovated thermal power plants. The development of the first generation carbon capture technologies (post combustion capture technology, pre combustion capture technology, oxygen enriched combustion technology) is gradually maturing, and the main bottlenecks are high costs and energy consumption, as well as a lack of extensive experience in large-scale demonstration projects; The second generation technologies, such as new membrane separation technology, new absorption technology, new adsorption technology, and pressurized oxygen enriched combustion technology, are still in the laboratory research and development or small-scale testing stage. After the technology matures, its energy consumption and cost will be reduced by more than 30% compared to the mature first generation technologies, and it is expected to be widely promoted and applied around 2035.

Transportation technology: Among the existing CO2 transportation technologies, tank truck transportation and ship transportation technologies have reached the commercial application stage, mainly used for CO2 transportation with a scale of less than 100000 tons per year.

The existing CCUS demonstration projects in China are relatively small in scale and mostly use tank trucks for transportation. Part of the CO2 from East China Oil and Gas Field and Lishui Gas Field is transported by ships. Pipeline transportation is still in the pilot stage, and Jilin Oilfield and Qilu Petrochemical use road pipelines to transport CO2. The cost of transporting CO2 through submarine pipelines is 40% to 70% higher than that of onshore pipelines. Currently, the technology for transporting CO2 through submarine pipelines lacks experience and is still in the research stage in China.

Utilization and storage technology: In CO2 geological utilization and storage technology, CO2 in-situ leaching uranium technology has reached the commercial application stage, EOR is in the industrial demonstration stage, EWR has completed pilot experimental research, ECBM has completed pilot stage research, mineralization utilization is in the industrial trial stage, and CO2 enhanced natural gas and enhanced shale gas extraction technology is still in the basic research stage.

The CO2-EOR projects in China are mainly concentrated near oil fields in the eastern, northern, northwestern, and western regions, as well as in the offshore areas of China. The 100000 tons/year CO2 saltwater storage project of the National Energy Group in Ordos has achieved its injection target of 300000 tons in 2015 and has stopped injection. The 150000 ton/year post combustion CO2 capture and storage demonstration project of Guohua Jinjie Power Plant of National Energy Group plans to store the captured CO2 in saline layers, which is currently under construction.

Changqing Oilfield Company Yulin Dingbian Jiyuan Oilfield CO2-EOR Experimental Zone Project

In July 2021, Sinopec officially launched the construction of China’s first million ton CCUS project (Qilu Petrochemical Shengli Oilfield CCUS project), which is expected to become the largest CCUS full industry chain demonstration base in China. The Process Engineering Research Institute of the Chinese Academy of Sciences has carried out the industrial verification project of 50000 t/a steel slag mineralization in Dazhou, Sichuan; Zhejiang University and others have carried out a 10000 ton industrial test project for CO2 deep mineralization curing of building materials at Henan Qiangan New Materials Co., Ltd; Sichuan University, in collaboration with Sinopec and other companies, has made good progress in the research and development of low concentration tail gas CO2 direct mineralization phosphogypsum and sulfur based compound fertilizer technology. China’s CO2 chemical utilization technology has made significant progress, with a large number of new technologies emerging such as electrocatalysis and photocatalysis. However, there are still some technical bottlenecks that have not been overcome in the integration of post combustion CO2 capture systems with chemical conversion and utilization devices. Biological utilization mainly focuses on microalgae fixation and gas fertilizer utilization.

Current situation of CCUS in China

There are about 40 CCUS demonstration projects in operation or under construction in China, with a capture capacity of 3 million tons per year. The main focus is on small-scale oil capture and displacement demonstrations in the petroleum, coal chemical, and power industries, lacking large-scale industrial demonstrations of various technology combinations throughout the entire process. Since 2019, the main progress has been as follows:

Capture: National Energy Group Guohua Jinjie Power Plant’s newly built 150000 tons/year post combustion CO2 capture project; The CNOOC Lishui 36-1 gas field is carrying out a CO2 separation, liquefaction, and dry ice production project, with a capture capacity of 50000 tons per year and a production capacity of 250000 tons per year.

Geological utilization and storage: Guohua Jinjie Power Plant plans to store the captured CO2 in saline layers, and expand the scale of some CO2-EOR projects.

Chemical and biological utilization: 200000 tons/year microalgae fixed coal chemical flue gas CO2 biological utilization project; 10000 tons/year CO2 curing concrete mineralization utilization project; 3000 tons/year carbonization method steel slag chemical utilization project.

China has the engineering capability to capture, utilize, and store CO2 on a large scale, and is actively preparing for the full process CCUS industry cluster. The Ordos CCS demonstration project of the National Energy Group has successfully carried out a 100000 ton/year scale CCS full process demonstration. The EOR project of PetroChina Jilin Oilfield is the only Chinese project among the 21 large-scale CCUS projects currently in operation worldwide, and also the largest EOR project in Asia, with a cumulative injection of over 2 million tons of CO2. The 150000 ton/year post combustion CO2 capture and storage demonstration project of Guohua Jinjie Power Plant of National Energy Group has been under construction since 2019, and will become the largest CCUS demonstration project for coal-fired power plants in China upon completion. In July 2021, Sinopec officially launched the construction of China’s first million ton CCUS project (Qilu Petrochemical Shengli Oilfield CCUS project).

The CCUS technology projects in China are spread across 19 provinces, with a diverse distribution of industries for capturing sources and types of storage and utilization. The total CO2 capture scale of 13 pure capture demonstration projects involving power plants and cement plants in China is 856500 tons per year, and the scale of 11 CO2 geological utilization and storage projects is 1.821 million tons per year, of which the CO2 utilization scale of EOR is about 1.54 million tons per year. China’s CO2 capture sources cover various technologies such as pre combustion, post combustion, and oxygen enriched combustion capture in coal-fired power plants, post combustion capture in gas-fired power plants, CO2 capture in coal chemical industry, and post combustion capture of cement kiln exhaust gas. CO2 storage and utilization involve saltwater storage EOR、 There are various methods such as coalbed methane displacement (ECBM), in-situ uranium extraction, CO2 mineralization utilization, CO2 synthesis of degradable polymers, reforming to produce synthetic gas, and microalgae fixation.

Anhui Hailuo Cement Co., Ltd. Baimashan Cement Plant Carbon Dioxide Capture Project

CO2 Tank Truck Wellhead Injection in Xinjiang Oilfield – Initial Stage of the Project

PetroChina Jilin Oilfield Injection and Oil Displacement

Shandong Shanlan Environmental Group Co., Ltd. has incorporated carbon dioxide capture, utilization, and storage into its development core, and has contributed to achieving the “dual carbon” goal through continuous technological maturity.