CO2Recovery unit
CO2Recycling deviceIt is an environmentally friendly product that caters to the requirements of the era's development.
Currently, nuclear energy, hydropower, and renewable energy sources including solar, wind, tidal, and geothermal energy, all of which produce relatively low levels of CO₂ emissions, remain in the initial stages of development. By 2030, fossil fuels such as petroleum, coal, and natural gas will still be the dominant sources in global primary energy consumption. This situation will inevitably result in an increase in CO₂ emissions. With the growing pressure on emission reduction and energy supply across different regions or countries, the development of cleaner energy has become an urgent necessity. Nevertheless, for clean energy to achieve substantial progress, it largely relies on technological and economic driving forces. For instance, efforts should be made to make clean energy more efficient, cost - effective, and less expensive compared to fossil fuels. Consequently, at the present stage, it is essential to implement certain measures to maintain the atmospheric CO₂ concentration at a level that does not pose a threat to human survival due to climate change. These measures may include reducing CO₂ emissions, carbon dioxide sequestration, and carbon dioxide utilization。
In alignment with the developmental requirements of the era, since 2016, Kaifeng SEPAIR Group Co., LTD has successively fabricated nearly 20 units of CO₂ recycling devices. The scale of these devices varies from 30,000 tons per annum to 300,000 tons per annum. Regarding the quality of the liquid CO₂ products, customers can opt for the industrial - grade standard（GB/T 6052-2011 Industrial liquid carbon dioxide and food - grade carbon dioxide（GB 10621-2006 Food additive - liquid carbon dioxide. It is also possible to obtain products of both grades concurrently. This is an environmentally friendly product that combines social and economic benefits.
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CO2Classification of Feedstock Gas Sources
The capture and purification technologies of carbon dioxide (CO₂) are associated with the sources of CO₂ and can be categorized into three major groups.：
1、Raw gases with low CO₂ concentrations, such as lime kiln gas and boiler flue gas
Sources of feedstock gas: Gases emitted from lime kilns and boiler chimneys。
Main characteristics: The CO₂ concentration is approximately 30%, and there are few organic impurities. Typically, the solution absorption method or pressure - swing adsorption method is employed for the pre - treatment and concentration of the raw gas, raising the CO₂ concentration of the raw gas to 98%. Each of the solution absorption method and the pressure - swing adsorption method has its own advantages and limitations. The raw gas obtained by the solution absorption method features high CO₂ purity. However, it may contain organic impurities that are toxic and harmful to humans, which are attributed to the characteristics of the solution itself. Although the pressure - swing adsorption method circumvents the presence of toxic and harmful organic impurities, due to the influence of its process, the CO₂ purity of the resulting raw gas is relatively low. A low CO₂ purity implies higher liquefaction energy consumption.
2、The decarburization desorption gas in ammonia synthesis is utilized as the feedstock gas for carbon dioxide (CO₂).
The source of raw gas: In the production process of synthetic ammonia, the decarbonization desorption gas from the purification section is sent to the urea workshop. Part of it is used for urea production, and the remaining surplus gas is directly discharged into the atmosphere. If the existing water, electricity, steam and other public utilities are utilized to purify and liquefy this part of CO2 for recovery, it can not only solve environmental problems but also generate certain economic benefits.
Main characteristics: The CO₂ concentration is approximately 90%. The gas contains trace amounts of impurities such as CH₄, N₂, O₂, CO, H₂, H₂S, and hydrocarbons. In particular, toxic and harmful impurities to humans, such as hydrocarbons, benzene, and COS, far exceed the standard limits. For this type of decarbonization desorption gas, desulfurization and removal of high - carbon hydrocarbons are required initially. Subsequently, CO₂ purification is achieved by leveraging the differences in boiling points between CO₂ and other gaseous impurities.
3、Feedstock gas with a high CO₂ concentration
Sources of feedstock gas: Fermentation gas from alcohol factories, associated CO₂ gas sources in oil fields, waste gas from ethylene glycol production, tail gas from hydrogen generation, tail gas from natural gas processing, tail gas from oil refining, and tail gas from the cryogenic methanol washing section during urea production, am
Main characteristics: The CO₂ concentration exceeds 98%. There are relatively few impurities, including trace amounts of CH₄, N₂, CO, H₂, H₂S, COS, CS₂, methanol, hydrocarbons, benzene, and other impurities. Oxygen needs to be supplemented during the desulfurization process. The technological process for the purification and liquefaction of this type of gas is relatively straightforward. With low investment requirements, it is particularly suitable for the production of food-grade carbon dioxide that complies with international standards.
For different CO₂ gas sources, there are substantial differences in their liquefaction and purification processes. Moreover, the trace components of impurities in the feedstock gas also lead to significant variations in the purification technology. Consequently, prior to selecting or designing a CO₂ liquefaction and purification process, it is essential to perform detection and analysis at the parts per million (PPM) level on the components of the feedstock gas. Clients can also commission us to engage professional testing institutions for the detection and analysis of sample gases.
Physicochemical absorption method
Chemical absorbents exhibit a high absorption capacity, a relatively rapid absorption rate, and a high level of separation and recovery purity. Nevertheless, since chemical reactions occur during the absorption process, desorbing CO₂ during regeneration requires breaking chemical bonds. This inevitably leads to high energy consumption. In addition, chemical absorbents typically have poor antioxidant capabilities, are susceptible to degradation, possess strong corrosivity, and are prone to issues such as foaming and entrainment. These factors pose numerous challenges to their industrial application. Physical adsorbents, although characterized by relatively poor selectivity and low recovery rates, do not necessitate the disruption of chemical bonds during desorption. As a result, their energy consumption is lower compared to chemical absorbents. Consequently, a logical approach is to utilize physicochemical composite absorbents for CO₂ absorption. This strategy aims to combine the merits of both physical adsorption and chemical absorption.
CO2The skid - mounted cold box leaves the factory.
CO2Introduction to the key recovery processes
Given the differences in various CO₂ gas sources and the trace components of impurities in the raw gas, there are substantial disparities in the process flow. Nevertheless, all processes encompass eight technological units: compression, desulfurization, drying, purification, liquefaction, refinement, storage, and refrigeration. According to the varying concentrations of CO₂, there are primarily three categories of technologies: solution absorption, pressure swing adsorption, and distillation separation.
1、Solution absorption: This method is applicable to gas sources featuring a low CO₂ content. The CO₂ purity achieved can reach approximately 98.5%, resulting in a gaseous product。
In the absorption tower, the solvent absorbs the CO₂ present in the flue gas. The CO₂ - laden solution is then pumped into the regeneration tower. Inside the regeneration tower, CO₂ is released from the solution through heating. After that, the remaining solution is cooled down and repressurized for use in the decarbonization of the next batch of flue gas.
Among the numerous decarbonization methods employed both at home and abroad, the modified hot potassium carbonate process within the realm of chemical absorption, which incorporates various activators, still holds a dominant position. Among these, the Benfield process developed by Union Carbide Corporation is particularly prominent, and new energy - saving processes are continuously being developed. The monoethanolamine (MEA) process has been rejuvenated with new vigor due to the development of the amine protection approach. This has breathed new life into this age - old technique. The activated MDEA process was developed by BASF SE in Germany. Abroad, many large - scale ammonia plants using natural gas as raw material predominantly adopt this method. In the category of physical - chemical absorption methods, the polyethylene glycol dimethyl ether process (NHD) developed by Norton Company and the Rectisol process are widely utilized both at home and abroad. The Rectisol process is primarily applied for desulfurization and CO₂ removal from raw gases obtained through partial oxidation of heavy oil and coal. It is well - coordinated with the liquid nitrogen wash process for removing trace amounts of CO and CH₄. With its extremely low total energy consumption, it is regarded as an ideal method.
2、Pressure Swing Adsorption (PSA): This technique is applicable for the recovery of CO₂ from synthetic ammonia shift gas. The purity of the recovered CO₂ can reach approximately 98.5%, and the product is in a gaseous state. The synthetic ammonia shift gas mainly consists of components such as H₂, N₂, CH₄, CO, and CO₂. Moreover, it contains certain amounts of impurity components, including H₂O and sulfides. The adsorption affinities of these gas components on adsorbents (such as activated carbon, molecular sieves, and silica gel) follow the order: H₂O and sulfides > CO₂ > CH₄ > CO > N₂ > H₂. The shift gas first undergoes dehydration and desulfurization processes and then enters the PSA unit composed of multiple adsorption towers. Each adsorption tower successively experiences seven steps: adsorption, multiple equalization depressurization steps, forward pressure release, reverse depressurization, evacuation, multiple equalization pressurization steps, and final pressurization. The desorbed CO₂ is extracted from the bottom of the adsorption tower by a vacuum pump and is output as product CO₂, enabling the production of CO₂ with a purity of not less than 98.5%.
3、Distillation Separation: This method is applicable to raw gas with a high CO₂ concentration. Through distillation separation, the purity of CO₂ can reach up to 99.99%, resulting in a liquid product.。
The purity of this kind of raw gas is over 98%, with minimal impurities. The trace impurities to be removed can be categorized into three groups. The first group is sulfides, primarily consisting of H₂S, COS, and CS₂. The second group encompasses substances whose boiling points are close to but slightly higher than that of CO₂, such as methanol, benzene, ethane, propane and other hydrocarbon compounds. The third group contains substances with significantly lower boiling points than CO₂, mainly H₂ and N₂.CH2、CO、Ar。
Fine Desulfurization Technology: Typically, a low - temperature organic sulfur hydrolysis catalyst is employed to convert trace amounts of COS into H₂S. Subsequently, an activated carbon fine desulfurizer is utilized to remove CS₂ and H₂S. The desulfurization precision is such that the H₂S content at the outlet is ≤ 0.03 ppm.
COS+H2O→H2S+CO2 2H2S+O2→2H2O+2S
The desulfurization process necessitates oxygen. In the case where the raw gas lacks oxygen components, a minute quantity of oxygen must be replenished.
Catalytic Oxidation Technology: Building upon the fine desulfurization process, catalytic oxidation incorporates purification steps for catalytic oxidation dehydrogenation and dehydrocarbonation. In the presence of specialized catalysts, all combustible impurities within the raw gas react with oxygen. The products of combustion are CO₂ and H₂O, and no toxic or hazardous substances are generated throughout this process.
2H2+O2→2H2O CnH2n+2+(3n+1)/2O2→nCO2+(n+1)H2O
The occurrence of the combustion reaction ensures the removal of hydrocarbons and oxygenated organic compounds. When the content of combustible components is low, the catalytic oxidation technique leads to an increase in energy consumption. At present, distillation separation is also employed to remove combustible components.
Distillation Purification Technology: Typically, a two - tower configuration is utilized to obtain high - purity liquid CO₂. In Tower T1, components such as methanol and benzene dissolve in the CO₂ liquid at the bottom of the tower and are discharged as residual liquid. The raw gas exiting the top of Tower T1 is partially liquefied after passing through a primary condenser. The resulting liquid enters the upper portion of the tower to partake in the distillation process, while the gas stream proceeds to a secondary condenser for further temperature reduction. The liquid emerging from the secondary condenser is fed into Tower T2 for purification, and the gas is vented as waste gas. At the bottom of Tower T2, a liquid CO₂ product with a purity of not less than 99.99% is obtained. The gas at the top of Tower T2, with a CO₂ concentration of approximately 76%, is likewise discharged as distillation tail gas.
Via the two - tower purification approach, components having boiling points higher than that of CO₂ are eliminated from the bottom of Tower T1, while components with boiling points lower than CO₂ are vented from the top of Tower T2. This enables the acquisition of high - purity CO₂. We employ stainless - steel packed towers and integrated skid - mounted cold boxes. The refrigerants used are either ammonia or environmentally friendly refrigerants. Since the fabrication of the first CO₂ recovery unit in 2016, we have successfully manufactured more than 20 CO₂ recovery units. These units have production scales ranging from 30,000 tons per annum to 300,000 tons per annum, and we offer complete sets of technologies for the production of industrial - grade and food - grade liquid CO₂.