Method and system for coal pyrolysis coupled with carbon capture

Abstract

The present application relates to the field of energy chemical industry and electric power engineering, and discloses a method and system for coal pyrolysis coupled with carbon capture. The method comprises: pyrolyzing raw coal to generate hydrogen-rich volatile matter and solid semicoke, the carbon-hydrogen mass ratio of the solid semicoke being 30-40; combusting the solid semicoke, and passively enriching carbon dioxide in flue gas generated by the combustion to obtain flue gas enriched with CO2; capturing CO2 from the flue gas enriched with CO2; and dynamically adjusting the temperature of the pyrolysis according to the load demand of the CO2 capture, the method for the dynamic adjustment comprising: adjusting the temperature of the pyrolysis according to the formula T=T0+K×(L-L0). The method disclosed by the present application reduces the introduction of inert nitrogen from the source, passively increases the CO2 concentration in the flue gas, is conducive to reducing the regeneration energy consumption and equipment investment, and simultaneously realizes a higher tar yield.

Description

Technical Field

[0001] This invention relates to the fields of energy, chemical engineering and power engineering, and specifically to a method and system for coal pyrolysis coupled with carbon capture. Background Technology

[0002] Installing carbon capture devices in coal-fired power plants is a key pathway to achieving clean coal utilization. Currently, post-combustion carbon capture mainly employs chemical absorption methods (such as the amine absorption process, MEA) to separate CO2 from the flue gas at the boiler tail end. The basic process is as follows: raw coal is mixed with air and burned in the boiler, and the resulting flue gas, after dust removal and desulfurization, enters the absorption tower for CO2 capture.

[0003] However, existing post-combustion capture technologies face significant energy consumption and cost challenges, with the core limiting factor being the excessively low partial pressure of CO2 in the combustion flue gas. Traditional coal-fired boilers burn raw coal directly in the air. The combustion of carbon in the fuel requires oxygen, and each oxygen consumption in the air produces nitrogen that does not participate in the reaction. This nitrogen remains in the flue gas, resulting in severe dilution of CO2, typically leading to a low volume fraction.

[0004] The dilution effect of flue gas brings the following problems: First, insufficient mass transfer driving force. According to the gas-liquid mass transfer theory, low concentrations of flue gas directly lead to weak mass transfer driving force within the absorber, requiring an increase in absorber volume and gas-liquid ratio to maintain the capture rate, significantly increasing investment. Second, high regeneration heat consumption. The absorbent must form strong chemical bonds with CO2 to capture it at low concentrations, which means that a large amount of high-grade steam heat energy is required during CO2 desorption in the regeneration process (regeneration heat consumption is typically as high as 2.4-3.5 GJ / tCO2).

[0005] In addition, although existing technologies include "oxygen-fuel combustion" solutions, which use pure oxygen instead of air, this solution requires the construction of expensive air separation units (ASU) to produce oxygen, resulting in huge initial investment and operating power consumption, making it difficult to promote on a large scale.

[0006] Therefore, there is an urgent need to develop a technical solution that breaks the inherent coupling relationship between "air combustion and nitrogen dilution" at the source of combustion and increases the CO2 concentration in flue gas at low cost without using expensive pure oxygen combustion. Summary of the Invention

[0007] The purpose of this invention is to overcome the problem of high capture energy consumption due to low CO2 concentration in flue gas from coal-fired power plants, and to provide a method and system for coal pyrolysis coupled with carbon capture. The method described in this invention reduces the introduction of inert nitrogen at the source, passively increasing the CO2 concentration in the flue gas, which helps reduce regeneration energy consumption and equipment investment, while achieving a higher tar yield.

[0008] The concept of this invention originates from a reverse thinking about the stoichiometric equations of combustion. For a long time, to increase the CO2 concentration in flue gas, the technical approaches in this field have mainly focused on oxygen-enriched combustion (relying on expensive air separation) or improving downstream absorbents, always limited by a mindset of "passively responding at the combustion or flue gas end." The inventors of this invention broke away from conventional thinking and, through deconstructive analysis of the combustion process, discovered that the introduction of nitrogen is not solely due to carbon combustion; the nitrogen dilution effect of hydrogen combustion is often overlooked. While carbon combustion produces CO2, introducing N2, this is a necessary cost to CO2 production. Similarly, hydrogen combustion produces H2O, introducing a large amount of N2, but after the product water vapor condenses, the N2 remains in the flue gas, becoming a pure "diluent." Based on this new understanding, this invention proposes an unconventional technical approach: instead of enhancing combustion or purifying flue gas, it actively strips the hydrogen components from the fuel before combustion, thereby cutting off the ineffective N2 entry path brought about by hydrogen combustion. However, simply discarding hydrogen for the purpose of "hydrogen removal" results in energy loss. Therefore, by further integrating the concept of coal fractional utilization, this innovative method extracts hydrogen as high-value tar and coal gas by controlling pyrolysis conditions, obtaining semi-coke with a specific carbon-to-hydrogen ratio. The reduced hydrogen content in this semi-coke, under the same carbon conversion or CO2 generation benchmark, reduces the amount of additional air required for hydrogen combustion and the accompanying nitrogen introduction. Furthermore, by altering the fuel composition without using any air separation oxygen production equipment, the CO2 concentration in the flue gas is increased, thus overcoming the traditional technological bias that increasing flue gas CO2 concentration must rely on pure oxygen.

[0009] To achieve the above objectives, a first aspect of the present invention provides a method for coal pyrolysis coupled with carbon capture, the method comprising the following steps: S1. Pyrolyze the raw coal to produce hydrogen-rich volatiles and solid semi-coke; wherein the carbon-hydrogen mass ratio of the solid semi-coke is 30-40. S2. In an air atmosphere, the solid semi-coke obtained in step S1 is burned, and carbon dioxide is passively enriched in the flue gas produced by combustion to obtain CO2-enriched flue gas. S3. The CO2-enriched flue gas obtained in step S2 is subjected to CO2 capture; the pyrolysis temperature in step S1 is dynamically adjusted according to the CO2 capture load requirement. The dynamic adjustment method includes: During operation, the pyrolysis temperature is adjusted according to the formula T=T0+K×(L-L0); Where T is the pyrolysis temperature, which ranges from 450 to 700℃; T0 is the reference pyrolysis temperature, with a value ranging from 580 to 620℃; L represents the CO2 capture load; L0 is the baseline CO2 capture load, which is 70-80%; K is the adjustment coefficient, which takes a value of 1-3℃ / percentage point.

[0010] A second aspect of the present invention provides a system based on coal pyrolysis coupled with carbon capture, the system comprising: a coal pyrolysis unit, a semi-coke hot conveying unit, a semi-coke combustion unit, a CO2 capture unit, and a cooperative control unit; The coal pyrolysis unit is used to pyrolyze raw coal to produce hydrogen-rich volatiles and solid semi-coke; The semi-coke combustion unit is connected to the solid semi-coke outlet of the coal pyrolysis unit and is used to burn the solid semi-coke from the coal pyrolysis unit to obtain CO2-enriched flue gas. The semi-coke hot conveying unit is located between the coal pyrolysis unit and the combustion unit, and is used to send solid semi-coke from the coal pyrolysis unit into the semi-coke combustion unit. The CO2 capture unit is connected to the semi-coke combustion unit and is used to capture CO2 from the CO2-enriched flue gas from the semi-coke combustion unit. The collaborative control unit is connected to the CO2 capture unit and is used to monitor the load demand of the CO2 capture unit and dynamically adjust the operating temperature of the coal pyrolysis unit accordingly.

[0011] Through the above technical solution, the present invention has the following beneficial effects: (1) The coal pyrolysis coupled carbon capture method provided by the present invention proposes a positive design logic of "fuel side component reconstruction → combustion side hydrogen combustion with additional air reduction → flue gas side concentration increase". Through the coupling process of "pyrolysis hydrogenation-semi-coke carbon-rich combustion" and the dynamic adjustment of pyrolysis temperature according to the load demand of CO2 capture, the introduction of inert nitrogen is reduced from the source. Without the use of expensive air separation equipment, the CO2 concentration of flue gas is passively increased. While maintaining a high tar yield, it is beneficial to reduce the regeneration energy consumption and equipment investment of the downstream carbon capture.

[0012] (2) The coal pyrolysis coupled carbon capture method provided by the present invention utilizes the characteristic of low hydrogen content in the generated solid semi-coke to reduce the additional oxygen consumption caused by hydrogen combustion and the amount of inert nitrogen introduced under the same carbon conversion or CO2 generation benchmark, and obtains a higher flue gas CO2 concentration than that of direct combustion of raw coal under air combustion conditions; no radical modification of the boiler body is required (such as leak prevention, material upgrade, etc.), the combustion characteristics of semi-coke are close to those of anthracite / lean coal, and existing boilers or pulverized coal boilers modified by burners can be directly adapted, which is suitable for the low-carbon upgrading and transformation of existing coal-fired units, and the threshold for promotion and application is low; the internal energy loop of the system is closed and the energy efficiency is high. Attached Figure Description

[0013] Figure 1This is a schematic diagram of a system based on coal pyrolysis coupled carbon capture according to a specific embodiment of the present invention.

[0014] Explanation of reference numerals in the attached figures Detailed Implementation

[0015] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0016] The first aspect of this invention provides a method for coal pyrolysis coupled with carbon capture, the method comprising the following steps: S1. Pyrolyze the raw coal to produce hydrogen-rich volatiles and solid semi-coke; wherein the carbon-hydrogen mass ratio of the solid semi-coke is 30-40. S2. In an air atmosphere, the solid semi-coke obtained in step S1 is burned, and carbon dioxide is passively enriched in the flue gas produced by combustion to obtain CO2-enriched flue gas. S3. The CO2-enriched flue gas obtained in step S2 is subjected to CO2 capture; the pyrolysis temperature in step S1 is dynamically adjusted according to the CO2 capture load requirement. The dynamic adjustment method includes: During operation, the pyrolysis temperature is adjusted according to the formula T=T0+K×(L-L0); Where T is the pyrolysis temperature, which ranges from 450 to 700℃; T0 is the reference pyrolysis temperature, with a value ranging from 580 to 620℃; L represents the CO2 capture load; L0 is the baseline CO2 capture load, which is 70-80%; K is the adjustment coefficient, which takes a value of 1-3℃ / percentage point.

[0017] In this invention, the coal pyrolysis coupled carbon capture method proposes a forward design logic of "fuel-side component reconstruction → combustion-side hydrogen combustion with additional air reduction → flue gas concentration increase". Through the coupling process of "pyrolysis dehydrogenation - semi-coke carbon-rich combustion" and the dynamic adjustment of pyrolysis temperature according to the load demand of CO2 capture, the introduction of inert nitrogen is reduced from the source. Without the use of expensive air separation units, the CO2 concentration in the flue gas is passively increased. While maintaining a high tar yield, it is beneficial to reduce the regeneration energy consumption and equipment investment of downstream carbon capture and realize the tiered and graded utilization of coal resources. No radical modification of the boiler body is required. The combustion characteristics of semi-coke are close to those of anthracite / lean coal. Existing boilers or pulverized coal boilers with burner modifications can be directly adapted. The system has an internal energy closed loop and high energy efficiency.

[0018] According to the present invention, the CO2 capture load L has the conventional interpretation in the art, specifically the percentage of the actual capture amount to the designed capture amount, i.e., L = (actual CO2 capture amount / designed CO2 capture amount) × 100%.

[0019] According to the present invention, the reference CO2 capture load L0 is a reference operating load for determining the dynamic adjustment relationship, and L0 is a predetermined fixed control parameter, rather than a parameter that changes arbitrarily during operation.

[0020] According to the present invention, in the formula, L-L0 represents the percentage point change in CO2 capture load L relative to the baseline CO2 capture load L0.

[0021] According to the present invention, the reference temperature T0 of the pyrolysis is the pyrolysis temperature corresponding to the reference CO2 capture load L0. T0 is a fixed control parameter predetermined for the raw coal to be processed or a predetermined operating cycle, rather than a parameter that changes arbitrarily during operation.

[0022] According to the present invention, the adjustment coefficient K represents the value by which the pyrolysis temperature T needs to be adjusted accordingly for every 1 percentage point change in the CO2 capture load L relative to the baseline CO2 capture load L0, expressed in °C / percentage point. In this invention, the adjustment coefficient K is a fixed control parameter pre-calibrated and determined for the raw coal to be processed or for a predetermined operating cycle, rather than a parameter that changes arbitrarily during operation.

[0023] Before the system is put into operation or when the coal type changes, the baseline CO2 capture load L0 and its corresponding baseline pyrolysis temperature T0 are first determined. L0 is determined comprehensively based on the design capture load of the CO2 capture unit, the long-term stable operating load of the coal-fired unit, or the economic operating load of the system, and remains constant within the same coal type or the same operating cycle. The method for determining T0 is as follows: based on the pyrolysis characteristics of the raw coal to be processed, with the carbon-hydrogen mass ratio of solid semi-coke and the CO2 dry basis volume fraction in the CO2-enriched flue gas reaching the preset requirements as constraints, and comprehensively considering the tar yield and the comprehensive energy consumption per unit of CO2 capture, the pyrolysis temperature with a higher tar yield and a lower comprehensive energy consumption per unit of CO2 capture is selected as the baseline pyrolysis temperature T0.

[0024] After L0 and T0 are determined, at at least one operating point deviating from L0, the pyrolysis temperature that satisfies the constraints of the target semi-coke hydrocarbon mass ratio, the target CO2 dry basis volume fraction, and the tar yield is determined, and the adjustment coefficient K is determined based on the ratio between the change in CO2 capture load and the change in pyrolysis temperature; preferably, calibration or verification is performed at operating points higher and lower than L0, respectively, or the adjustment coefficient K is determined by linear fitting of multiple operating points.

[0025] During operation, the actual CO2 capture load L is adjusted according to the deviation between the actual CO2 capture load L0 and the benchmark CO2 capture load L0 as follows: when L is higher than L0, the pyrolysis temperature is increased to enhance the dehydrogenation degree of raw coal and improve the passive enrichment effect of flue gas CO2; when L is lower than L0, the pyrolysis temperature is reduced to balance tar yield and system operation economy.

[0026] According to a preferred embodiment of the present invention, the baseline CO2 capture load L0 is 75%, and the corresponding baseline pyrolysis temperature T0 is 600°C. When the CO2 capture load L is increased to 100%, based on a pre-established correspondence, the pyrolysis temperature that can increase the dry basis volume fraction of CO2 in the flue gas and meet the tar yield constraint is selected as the target pyrolysis temperature. The target pyrolysis temperature is determined to be 650°C, then K = (650... 600) / (100 75) = 2℃ / percentage point; When the CO2 capture load L decreases to 55%, the pyrolysis temperature that can balance tar yield and passive CO2 enrichment effect in flue gas is selected as the target pyrolysis temperature. The target pyrolysis temperature is determined to be 560℃, then K = (600 560) / (75 55) = 2℃ / percentage point. Therefore, for this type of raw coal and within this operating cycle, the adjustment coefficient K is determined to be 2℃ / percentage point. For other coal types or other operating cycles, K can be determined within the range of 1-3℃ / percentage point using the above method.

[0027] According to a preferred embodiment of the present invention, the dynamic adjustment method includes: Adjust the pyrolysis temperature according to the formula T=T0+K×(L-75%); Where T0 is 590-610℃ and K is 2-2.5℃ / percentage point.

[0028] According to a particularly preferred embodiment of the present invention, the dynamic adjustment method includes: The pyrolysis temperature is adjusted according to the formula T = 600℃ + 2℃ / percentage point × (L - 75%). Preferably, in this invention, when the calculated pyrolysis temperature is below 540℃, it is controlled at 540℃; when the calculated pyrolysis temperature is above 650℃, it is controlled at 650℃.

[0029] According to a preferred embodiment of the present invention, the pyrolysis temperature T is 450-700℃, for example, it can be 450℃, 460℃, 480℃, 500℃, 520℃, 540℃, 560℃, 580℃, 600℃, 620℃, 640℃, 650℃, 680℃, 700℃, or any value within the range of any two of the above values, preferably 540-650℃; the pyrolysis time is 4-10s, preferably 5-8s. Preferably, the pyrolysis pressure is 0.09-0.12MPa.

[0030] According to the present invention, preferably, the pyrolysis is carried out under hypoxic conditions, wherein the oxygen volume concentration under hypoxic conditions is 0-3 vol%, preferably 0-1 vol.

[0031] In this invention, the hydrogen components in the raw coal, which have high oxygen consumption per unit mass and are prone to generating water vapor, are stripped away through pyrolysis, resulting in solid semi-coke with a specific high carbon-to-hydrogen ratio. Simultaneously, by rapidly extracting and condensing hydrogen-rich volatiles, tar vapors are recovered before secondary pyrolysis. This preferred embodiment is more conducive to simultaneously achieving low capture energy consumption, high tar yield, and combustion flexibility under different operating conditions.

[0032] According to a preferred embodiment of the present invention, when L≥90%, the pyrolysis temperature T is 620-650℃, the pyrolysis time τ is 5-6s, and the carbon-hydrogen mass ratio of the solid semi-coke is 36-40. When 70%≤L<90%, the pyrolysis temperature T is 580-620℃, the pyrolysis time τ is 6-7s, and the carbon-hydrogen mass ratio of the solid semi-coke is 33-36. When L < 70% or the generator set is operating during peak shaving, the pyrolysis temperature T is 540-580℃, the pyrolysis time τ is 7-8s, and the carbon-hydrogen mass ratio of the solid semi-coke is 30-33.

[0033] According to the present invention, the source of the raw coal has a wide range of selection, for example, it can be at least one of low-rank bituminous coal, long-flame coal, and lignite. In the present invention, long-flame coal is preferred, taking into account volatile matter content, pyrolysis oil and gas yield, and semi-coke combustion stability.

[0034] According to a preferred embodiment of the present invention, the carbon-to-hydrogen mass ratio of the raw coal is 15-20, for example, it can be 15, 15.5, 16, 16.5, 17, 17.5, 18, 18.5, 19, 19.5, 20, or any value within the range of any two of the above values, preferably 16-18.5. Using the above preferred embodiment is more conducive to obtaining solid semi-coke with a carbon-to-hydrogen ratio within the optimal control range during subsequent pyrolysis, which, in conjunction with the dynamic adjustment strategy, balances low capture energy consumption and high tar yield.

[0035] According to a preferred embodiment of the present invention, the raw coal contains 62-72 wt% carbon, for example, 62 wt%, 64 wt%, 66 wt%, 68 wt%, 70 wt%, 72 wt%, or any value within the range of any two of the above values, preferably 64-70 wt%; and 3.6-4.8 wt% hydrogen, for example, 3.6 wt%, 3.8 wt%, 4 wt%, 4.2 wt%, 4.4 wt%, 4.6 wt%, 4.8 wt%, or any value within the range of any two of the above values, preferably 3.8-4.4 wt%. In this invention, the remaining components of the raw coal are oxygen, nitrogen, sulfur, ash, and moisture. Using the above preferred embodiment facilitates obtaining solid semi-coke with the desired carbon-to-hydrogen ratio in subsequent pyrolysis, and in conjunction with a dynamic adjustment strategy, achieves low capture energy consumption and high tar yield.

[0036] According to the present invention, preferably, step S1 includes: crushing and grinding the raw coal before pyrolysis. The present invention does not particularly limit the method of crushing and grinding, and methods conventionally used in the art can be employed. Preferably, the particle size of the ground raw coal is 50-300 μm, more preferably 60-150 μm.

[0037] According to a preferred embodiment of the present invention, the carbon-to-hydrogen mass ratio of the solid semi-coke is 30-40, for example, it can be 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, or any value within the range of any two of the above values. Specifically, when the CO2 capture load L ≥ 70%, the carbon-to-hydrogen mass ratio of the solid semi-coke is preferably 33-40; when the CO2 capture load L < 70% or during peak-shaving operation of the generator set, the carbon-to-hydrogen mass ratio of the solid semi-coke is preferably 30-33. Using the above preferred embodiment is more advantageous for adjusting the semi-coke fuel characteristics according to different CO2 capture loads, achieving synergy between the passive enrichment effect of flue gas CO2, tar yield, and capture energy consumption.

[0038] According to a preferred embodiment of the present invention, the carbon content in the solid semi-coke is 82-89 wt%, for example, it can be 82 wt%, 83 wt%, 84 wt%, 85 wt%, 86 wt%, 87 wt%, 88 wt%, 89 wt%, or any value within the range of any two of the above values, preferably 84-88 wt%; the hydrogen content is 2-3.2 wt%, for example, it can be 2 wt%, 2.2 wt%, 2.4 wt%, 2.6 wt%, 2.8 wt%, 3 wt%, 3.2 wt%, or any value within the range of any two of the above values, preferably 2.2-2.8 wt%. In the present invention, the remainder in the solid semi-coke is oxygen, nitrogen, sulfur, ash, and moisture. Using the above preferred embodiment is more conducive to achieving precise control of the hydrogen content on the fuel side, synergizing with dynamic adjustment strategies, and balancing low capture energy consumption and high tar yield.

[0039] In this invention, the carbon and hydrogen contents in the raw coal and solid semi-coke are obtained by elemental analysis; the carbon-hydrogen mass ratio is the ratio of the mass content of carbon to the mass content of hydrogen.

[0040] According to the present invention, preferably, the hydrogen-rich volatiles include tar vapor, light hydrocarbons, hydrogen, carbon monoxide, methane, ethane, ethylene, water vapor, and a small amount of carbon dioxide.

[0041] According to the present invention, preferably, step S1 includes: condensing and separating the hydrogen-rich volatiles to recover coal tar and high-calorific-value coal gas. The present invention does not particularly limit the condensation method and conditions; conventional condensation methods and conditions in the art can be used. Preferably, the hydrogen-rich volatiles are cooled to 20-80°C, more preferably to 30-50°C. More preferably, the hydrogen-rich volatiles are cooled to 20-80°C within 2 seconds after leaving the pyrolysis reactor. Using the above method helps to suppress secondary cracking of tar vapor and improve tar yield.

[0042] According to the present invention, preferably, at least a portion of the high-calorific-value gas is used as the heat source for pyrolysis and / or as the fuel for combustion; more preferably, 30-60 vol% of the high-calorific-value gas is used as the heat source for pyrolysis and / or as the fuel for combustion. By adopting the above embodiments, the external heat supply for the pyrolysis stage can be reduced, boiler combustion can be stabilized at low loads, and internal energy self-sufficiency and synergistic optimization of the system can be achieved.

[0043] This invention breaks away from the traditional mindset of passively responding at the combustion or flue gas end, innovatively proposing to remove hydrogen components from raw coal in advance through pyrolysis, resulting in a lower hydrogen content in the solid semi-coke entering the furnace compared to the raw coal. Through "fuel-side directional dehydrogenation," under the same carbon conversion or CO2 generation baseline, it reduces the amount of additional air required for hydrogen combustion during semi-coke combustion and the amount of inert nitrogen introduced, achieving a passive increase in flue gas CO2 concentration without using any air separation oxygen production equipment. Under conventional air combustion conditions, a higher flue gas CO2 concentration than that obtained under direct coal combustion conditions can be achieved, avoiding the high energy consumption and investment of air separation oxygen production in traditional oxygen-enriched combustion routes.

[0044] According to the present invention, preferably, the combustion conditions in step S2 include: an excess air coefficient α of 1.05-1.3; and a flue gas temperature at the boiler furnace outlet of the combustion chamber of 850-1150°C, preferably 900-1050°C.

[0045] According to the present invention, step S2 includes: removing dust and condensing / dehydrating the boiler tail gas generated by the combustion to obtain CO2-enriched flue gas. The present invention does not particularly limit the method and conditions for dust removal; conventional methods and conditions in the art can be used, for example, an electrostatic precipitator or a bag filter can be used to remove fly ash. The present invention also does not particularly limit the method and conditions for condensation / dehydration; conventional methods and conditions in the art can be used. Preferably, the condensation process cools the dust-removed boiler tail gas to 20-45°C.

[0046] According to a preferred embodiment of the present invention, the CO2-enriched flue gas has a dry basis volume fraction of 15-18 vol%, for example, it can be 15 vol%, 15.5 vol%, 16 vol%, 16.5 vol%, 17 vol%, 17.5 vol%, 18 vol%, or any value within the range of any two of the above values, preferably 15.3-17.8 vol%. Using the above embodiment is more conducive to fully utilizing the passive enrichment effect of the flue gas and further reducing the energy consumption per unit of CO2 capture.

[0047] According to a preferred embodiment of the present invention, in step S2, the solid semi-coke is directly burned without cooling. The present invention omits the steps of semi-coke cooling and subsequent reheating, allowing all the sensible heat of the semi-coke to be retained and introduced into the boiler along with the semi-coke, where it is released and utilized during combustion, thus improving the overall thermal energy utilization efficiency of the system.

[0048] During their research, the inventors of this invention discovered that, for the same raw coal to be processed or the same predetermined operating cycle, the pyrolysis temperature T and the hydrogen content H in the solid semi-coke can be established through offline calibration. c and the dry basis volume fraction of CO2 in CO2-enriched flue gas y CO2 The correspondence between them is as follows. Parameters A, B, C, and D in the above relationship are fixed parameters pre-calibrated or fitted for specific coal types, pyrolysis and combustion devices, and corresponding operating conditions, rather than parameters that arbitrarily change during operation. When the coal type or coal quality characteristics, pyrolysis or combustion device type, main pyrolysis or combustion conditions, and flue gas pretreatment or measurement conditions change significantly enough to affect the above correspondence, the corresponding parameters can be recalibrated. In this invention, preferably, multiple pyrolysis temperature points are selected within a predetermined pyrolysis temperature range, and the hydrogen content H in the solid semi-coke corresponding to each temperature point is measured. c A and B are determined through linear fitting, and T and H are established. c Approximate linear relationship between them: H c =AB×T, Among them, H c denoted as wt% (hydrogen content in solid semi-coke); denoted as T (pyrolysis temperature, °C); denoted as A (fit intercept, wt%, A ranges from 5.3 to 6 wt%); denoted as B (fit slope, wt% / °C, B ranges from (5-6) × 10⁻⁶). - 3 wt% / ℃. In this invention, A and B are a set of paired parameters obtained by fitting the same set of data for a specific coal type, pyrolysis reactor and corresponding operating conditions. The values ​​of A and B should correspond to each other and should not be arbitrarily combined within their respective value ranges.

[0049] In this invention, when the coal type or coal quality characteristics, pyrolysis reactor type, and main pyrolysis conditions remain unchanged, or when operating according to a preset pyrolysis control strategy, A and B are predetermined values ​​for the calibration conditions. When the above conditions change significantly enough to affect the correspondence between the pyrolysis temperature T and the hydrogen content Hc in the solid semi-coke, the values ​​of A and B need to be recalibrated.

[0050] In this invention, preferably, materials with different H values ​​are used. c Solid semi-coke was burned under the same or similar combustion conditions, and the CO2 dry basis volume fraction y in the flue gas after dust removal and condensation dehydration was measured. CO2C and D are determined through linear fitting, and y is established. CO2 With H c An approximate negative correlation between them: y CO2 =CD×H c , Among them, y CO2 The dry basis volume fraction of CO2 in the flue gas is expressed as vol%; C is the fitting intercept, also expressed as vol%, with a value ranging from 19.8% to 20.8 vol%; D is the fitting slope, expressed as vol% / wt%, with a value ranging from 1.1% to 1.5 vol% / wt. In this invention, C and D are a set of paired parameters obtained by fitting the same set of data for specific solid semi-coke, combustion device, combustion conditions, and flue gas pretreatment and measurement conditions. The values ​​of C and D should correspond to each other and should not be arbitrarily combined within their respective value ranges.

[0051] In this invention, when the source and composition of the solid semi-coke, the type of combustion device, the main combustion conditions, and the flue gas pretreatment and measurement conditions remain unchanged, or when operating according to a preset combustion control strategy, C and D are predetermined values ​​for the calibration conditions. When the above conditions change significantly, sufficient to affect the hydrogen content H in the solid semi-coke... c The dry basis volume fraction of CO2 in flue gas y CO2 When establishing the correspondence between these parameters, the values ​​of C and D need to be recalibrated. The aforementioned approximate correspondence is used to characterize the changing trends between pyrolysis temperature, semi-coke hydrogen content, and the dry-basis volume fraction of CO2 in flue gas, and to determine the target pyrolysis temperature during the dynamic adjustment process. Based on the above calibration relationship, this invention employs a dynamic adjustment method to control the pyrolysis temperature, making it respond to changes in the CO2 capture load L. By adjusting the hydrogen content and carbon-hydrogen mass ratio in the solid semi-coke, it achieves synergistic optimization among the passive CO2 enrichment effect, tar yield, and CO2 capture energy consumption.

[0052] According to a particularly preferred embodiment of the present invention, segmented control is performed according to different intervals of the CO2 capture load L: When L≥90%, the pyrolysis temperature T is 620-650℃, the pyrolysis time τ is 5-6s, the hydrogen mass content in the solid semi-coke is 2-2.4wt%, the carbon-hydrogen mass ratio of the solid semi-coke is 36-40, the dry basis volume fraction of CO2 in the CO2-enriched flue gas is 16.8-17.8vol%, and the tar yield Yt is not less than 9.6wt%. When 70%≤L<90%, the pyrolysis temperature T is 580-620℃, the pyrolysis time τ is 6-7s, the hydrogen mass content in the solid semi-coke is 2.4-2.6wt%, the carbon-hydrogen mass ratio in the solid semi-coke is 33-36, the dry basis volume fraction of CO2 in the CO2-enriched flue gas is 16.1-17.1 vol%, and the tar yield Yt is 10.2-11.4 wt%. When L < 70% or during peak-shaving operation of the generator set, the pyrolysis temperature T is 540-580℃, the pyrolysis time τ is 7-8s, the hydrogen mass content in the solid semi-coke is 2.6-3.2wt%, the carbon-hydrogen mass ratio of the solid semi-coke is 30-33, the dry basis volume fraction of CO2 in the CO2-enriched flue gas is 15.1-16.3vol%, and the tar yield Yt is not less than 10.8wt%. In this invention, the generator set and the semi-coke combustion unit are coupled and integrated.

[0053] Based on the above relationship, the collaborative control unit (dynamic regulation) increases the pyrolysis temperature to reduce CO2 capture energy consumption, with tar yield Y as the key factor. t With a constraint of ≥9.6wt%, secondary pyrolysis of tar is preferentially suppressed by shortening the pyrolysis time and rapidly removing and condensing the volatiles.

[0054] By dynamically adjusting the above-mentioned quantitative relationship, this invention achieves a quantitative response of pyrolysis temperature to CO2 capture requirements. Combined with pyrolysis time control and rapid condensation of volatiles, it ensures a high tar yield and avoids the crude control that relies on experience or fixed temperature zones.

[0055] According to a particularly preferred embodiment of the present invention, S1. Long-flame coal with a carbon content of 62-72 wt% and a hydrogen content of 3.6-4.8 wt% is crushed to 60-150 μm and pyrolyzed in an internally heated fluidized bed pyrolysis reactor at an oxygen volume concentration of 0-3 vol% and a temperature of 450-700℃ for 4-10 s to obtain hydrogen-rich volatiles and solid semi-coke with a carbon-hydrogen mass ratio of 30-40. The hydrogen-rich volatiles are cooled to 20-80℃ within 2 s after leaving the pyrolysis reactor and then separated to recover coal tar and high-calorific-value coal gas, wherein the tar yield is maintained at 9.6-11.4 wt%. 30-60 vol% of the high-calorific-value coal gas is recycled as a pyrolysis heat source. S2. Solid semi-coke at 450-700℃ is directly fed into a pulverized coal boiler through a heat-insulated conveyor and combusted under conditions where the excess air coefficient α is 1.05-1.3 and the flue gas temperature at the furnace outlet is 850-1150℃. The flue gas at the boiler tail end generated by the combustion is dusted and cooled to 20-45℃ to obtain CO2-enriched flue gas. S3. The CO2-enriched flue gas is subjected to CO2 capture; the pyrolysis temperature in step S1 is dynamically adjusted according to the CO2 capture load requirement, wherein the dynamic adjustment method includes: The pyrolysis temperature is adjusted according to the formula T = 600℃ + 2℃ / percentage point × (L - 75%), where T is the pyrolysis temperature, L is the CO2 capture load, and Y is the tar yield. t The constraint condition is that it shall not be less than 9.6 wt%.

[0056] A second aspect of the present invention provides a system based on coal pyrolysis coupled carbon capture, the system comprising a coal pyrolysis unit, a semi-coke hot state conveying unit, a semi-coke combustion unit, a CO2 capture unit, and a cooperative control unit; The coal pyrolysis unit is used to pyrolyze raw coal to produce hydrogen-rich volatiles and solid semi-coke; The semi-coke combustion unit is connected to the solid semi-coke outlet of the coal pyrolysis unit and is used to burn the solid semi-coke from the coal pyrolysis unit to obtain CO2-enriched flue gas. The semi-coke hot conveying unit is located between the coal pyrolysis unit and the combustion unit, and is used to send solid semi-coke from the coal pyrolysis unit into the semi-coke combustion unit. The CO2 capture unit is connected to the semi-coke combustion unit and is used to capture CO2 from the CO2-enriched flue gas from the semi-coke combustion unit. The collaborative control unit is connected to the CO2 capture unit and is used to monitor the load demand of the CO2 capture unit and dynamically adjust the operating temperature of the coal pyrolysis unit accordingly.

[0057] According to the present invention, preferably, the coal pyrolysis unit includes a pyrolysis reactor.

[0058] According to the present invention, preferably, the semi-coke combustion unit includes a semi-coke combustion boiler.

[0059] According to a preferred embodiment of the present invention, the system further includes an oil-gas separation and purification unit, which is connected to the hydrogen-rich volatile matter outlet of the coal pyrolysis unit for condensing and separating the hydrogen-rich volatile matter to recover coal tar and high-calorific-value coal gas.

[0060] According to a preferred embodiment of the present invention, the system further includes a flue gas pretreatment unit disposed between the semi-coke combustion unit and the CO2 capture unit, which is used to remove dust and condense and dehydrate the flue gas generated at the tail end of the boiler generated by combustion, so as to obtain CO2-enriched flue gas which is then sent to the CO2 capture unit.

[0061] The following combination Figure 1The method and system of the present invention will be described below, including preferred embodiments: Raw coal from coal bunker 1 is fed into coal pyrolysis unit 2 for pyrolysis, generating hydrogen-rich volatiles and solid semi-coke. The hydrogen-rich volatiles are sent from the hydrogen-rich volatiles outlet of coal pyrolysis unit 2 to oil-gas separation and purification unit 3, where they are separated after condensation, recovering high-value-added coal tar and high-calorific-value coal gas. The solid semi-coke is discharged from the solid semi-coke outlet of coal pyrolysis unit 2 and directly fed into semi-coke combustion unit 5 via semi-coke hot conveying unit 4. In semi-coke combustion unit 5, the solid semi-coke is mixed with air and burned to generate boiler tail flue gas, in which carbon dioxide is passively enriched. The boiler tail flue gas is sent to flue gas pretreatment unit 6 for dust removal and condensation dehydration to obtain CO2-enriched flue gas, which is then sent to CO2 capture unit for CO2 capture. During the above process, the co-control unit 8 monitors the load demand of CO2 capture unit 7 in real time and dynamically adjusts the pyrolysis temperature of coal pyrolysis unit 2 according to the load demand.

[0062] The present invention will be described in detail below through embodiments.

[0063] In the following examples and comparative examples, Raw coal: long-flame coal, with a hydrogen content of 4.0 wt%, a carbon content of 66 wt%, and a carbon-to-hydrogen mass ratio of 16.5.

[0064] The carbon and hydrogen contents in raw coal and solid semi-coke were determined using an elemental analyzer. Tar yield Y t =m2 / m0×100%, Where m0 is the dry basis mass of raw coal entering the coal pyrolysis unit, in g; and m2 is the mass of coal tar obtained by condensation and separation, in g. CO2 dry basis volume fraction in CO2-enriched flue gas: determined using an online infrared flue gas analyzer. Before measurement, the flue gas was dust-removed and condensed to 25°C for dehydration. The comprehensive energy consumption per unit of CO2 capture refers to the ratio of the sum of the regeneration heat consumption of the CO2 capture unit, the external heat supply of the coal pyrolysis unit, and the equivalent value of the additional energy supply of the system to the amount of CO2 captured, under the condition of using 30wt% monoethanolamine as absorbent and a CO2 capture rate of 90%. The equivalent value of the additional energy supply of the system includes the external energy supply that needs to be supplemented due to semi-coke cooling, heat loss, or other unrecovered energy. CO2 capture load L = (Actual CO2 capture rate / Designed CO2 capture rate) × 100%; Three pyrolysis temperature points (T1=560℃, T2=600℃, and T3=650℃) were selected within the predetermined pyrolysis temperature range. Following the preset temperature-pyrolysis time control relationship, the corresponding pyrolysis times were set to 8s, 6s, and 5s, respectively. The hydrogen content (H) in the solid semi-coke at each operating point was measured. c The H values ​​corresponding to T1, T2, and T3 were measured. c The values ​​were 2.80 wt%, 2.60 wt%, and 2.35 wt%, respectively. Based on these data, a linear fit was performed, yielding A at 5.60 wt% and B at 5 × 10⁻⁶. -3 wt% / ℃, thus establishing the relationship between pyrolysis temperature T and semi-coke hydrogen content H. c Approximate linear relationship between them: H c =5.6wt%-5×10 - ³wt% / ℃×T.

[0065] The hydrogen content H in solid semi-coke c Solid semi-cokes of 2.80 wt%, 2.60 wt%, and 2.35 wt% were combusted under the same combustion conditions, flue gas pretreatment conditions, and measurement conditions. The CO2 dry basis volume fraction y in the flue gas was measured. CO2 The values ​​were 16.20 vol%, 16.50 vol%, and 16.88 vol%, respectively. Linear fitting was performed based on the above data, yielding C as 20.40 vol% and D as 1.50 vol% / wt, thus establishing the semi-coke hydrogen content H. c Volume fraction of CO2 in flue gas (dry basis, y) CO2 Approximate linear relationship between them: y CO2 =20.4vol%-1.5vol% / wt%×H c .

[0066] In the above formula, A, B, C, and D are a pair of paired parameters, with A and B corresponding to each other, and C and D corresponding to each other. This applies to the long-flame coal, internally heated fluidized bed pyrolysis reactor, corresponding temperature-time synergistic control conditions, and the same combustion, flue gas pretreatment, and measurement conditions used in Examples 1-3. When the above conditions change significantly, it is sufficient to affect T and H. c Between or H c With y CO2 When establishing the correspondence between them, the values ​​of A, B, C, and D need to be recalibrated.

[0067] Example 1 S1. The raw coal is crushed and ground to a particle size of 75μm, and then pyrolyzed at 600℃ for 6s in an internally heated fluidized bed pyrolysis reactor under oxygen-deficient conditions (oxygen volume concentration of 0.5 vol%) to produce hydrogen-rich volatiles and solid semi-coke; wherein the solid semi-coke contains 2.6 wt% hydrogen, 86.0 wt% carbon, and a carbon-hydrogen mass ratio of 33.1. The hydrogen-rich volatiles are separated by condensation (cooling to 40°C) within 2 seconds after leaving the pyrolysis reactor, and high-value coal tar and high-calorific-value coal gas are recovered. The tar yield is 10.8 wt%, and 45 vol% of the high-calorific-value coal gas is returned to the combustion chamber of the pyrolysis reactor as a pyrolysis heat source. S2. Solid semi-coke is directly fed into the boiler at a hot state of about 600°C and mixed with air for combustion to generate flue gas at the tail end of the boiler; the combustion conditions include: excess air coefficient α=1.2, and flue gas temperature at the furnace outlet of 950°C. The flue gas at the tail end of the boiler is subjected to dust removal and condensation (condensed to 25°C) and dehydration to obtain flue gas enriched with CO2; S3. The CO2-enriched flue gas obtained in step S2 is subjected to CO2 capture. During the above process, the load demand for CO2 capture is monitored in real time, and the temperature of pyrolysis in step S1 is dynamically adjusted according to the load demand for CO2 capture using the formula T=T0+K×(L-L0). For the long-flame coal, the baseline CO2 capture load L0 = 75%, the baseline pyrolysis temperature T0 is 600℃, the adjustment coefficient K is 2℃ / percentage point, and T and L satisfy the formula T = 600℃ + 2℃ / percentage point × (L - 75%). When the CO2 capture load L = L0 = 75%, substituting into the formula, we get T = 600℃, i.e., T = T0. This is used to determine and verify the carbon-hydrogen mass ratio of solid semi-coke, the dry volume fraction of CO2 in CO2-enriched flue gas, the tar yield, and the comprehensive energy consumption per unit of CO2 capture at the baseline operating point.

[0068] Tests showed that at a pyrolysis temperature of 600℃, the hydrogen content in the solid semi-coke was 2.6wt%, and the CO2 dry basis volume fraction in the CO2-enriched flue gas was 16.5vol.

[0069] Example 2 S1. The raw coal is crushed and ground to a particle size of 75μm, and then pyrolyzed at 560℃ for 8s in an oxygen-deficient reactor (oxygen volume concentration of 0.5 vol%) to produce hydrogen-rich volatiles and solid semi-coke; the solid semi-coke contains 2.8 wt% hydrogen, 84.0 wt% carbon, and has a carbon-to-hydrogen mass ratio of 30. The hydrogen-rich volatiles are separated by condensation (cooling to 40°C) within 2 seconds after leaving the pyrolysis reactor, and high-value coal tar and high-calorific-value coal gas are recovered. The tar yield is 11.4 wt%, and 45 vol% of the high-calorific-value coal gas is returned to the combustion chamber of the pyrolysis reactor as a pyrolysis heat source. S2. Solid semi-coke is directly fed into the boiler at a hot state of about 560°C and mixed with air for combustion to generate flue gas at the tail end of the boiler; the combustion conditions include: excess air coefficient α=1.2, and flue gas temperature at the furnace outlet of 950°C. The flue gas at the tail end of the boiler is subjected to dust removal and condensation (condensed to 25°C) and dehydration to obtain flue gas enriched with CO2; S3. The CO2-enriched flue gas obtained in step S2 is subjected to CO2 capture. During the above process, the load demand for CO2 capture is monitored in real time, and the temperature of pyrolysis in step S1 is dynamically adjusted according to the load demand for CO2 capture using the formula T=T0+K×(L-L0). For the long-flame coal, the baseline CO2 capture load L0 = 75%, the baseline pyrolysis temperature T0 is 600℃, the adjustment coefficient K is 2℃ / percentage point, and T and L satisfy the formula T = 600℃ + 2℃ / percentage point × (L - 75%). When the CO2 capture load L = 55%, substituting into the formula, we get T = 560℃. Tests showed that at a pyrolysis temperature T of 560℃, the hydrogen content in the solid semi-coke was 2.8wt%, and the CO2 dry basis volume fraction in the CO2-enriched flue gas was 16.2vol.

[0070] Example 3 S1. The raw coal is crushed and ground to a particle size of 75μm, and then pyrolyzed at 650℃ for 5s in an internally heated fluidized bed pyrolysis reactor under oxygen-deficient conditions (oxygen volume concentration of 0.5 vol%) to produce hydrogen-rich volatiles and solid semi-coke; wherein the solid semi-coke contains 2.35 wt% hydrogen, 88.0 wt% carbon, and a carbon-hydrogen mass ratio of 37.4. The hydrogen-rich volatiles are separated by condensation (cooling to 40°C) within 2 seconds after leaving the pyrolysis reactor, and high-value coal tar and high-calorific-value coal gas are recovered. The tar yield is 9.6 wt%, and 50 vol% of the high-calorific-value coal gas is returned to the combustion chamber of the pyrolysis reactor as a pyrolysis heat source. S2. Solid semi-coke is directly fed into the boiler at a hot state of about 650°C and mixed with air for combustion to generate flue gas at the tail end of the boiler; the combustion conditions include: excess air coefficient α=1.2, and flue gas temperature at the furnace outlet of 950°C. The flue gas at the tail end of the boiler is subjected to dust removal and condensation (condensed to 25°C) and dehydration to obtain flue gas enriched with CO2; S3. The CO2-enriched flue gas obtained in step S2 is subjected to CO2 capture. During the above process, the load demand for CO2 capture is monitored in real time, and the temperature of pyrolysis in step S1 is dynamically adjusted according to the load demand for CO2 capture using the formula T=T0+K×(L-L0). For the long-flame coal, the baseline CO2 capture load L0 = 75%, the baseline pyrolysis temperature T0 is 600℃, the adjustment coefficient K is 2℃ / percentage point, and T and L satisfy the formula T = 600℃ + 2℃ / percentage point × (L - 75%). When the CO2 capture load L = 100%, substituting into the formula, we get T = 650℃. Tests showed that at a pyrolysis temperature of 650℃, the hydrogen content in the solid semi-coke was 2.35wt%, and the CO2 dry basis volume fraction in the CO2-enriched flue gas was 16.9vol.

[0071] Example 4 The method is the same as in Example 1, except that... In step S1, the pyrolysis temperature was reduced from 600℃ to 520℃; the pyrolysis time was increased from 6s to 10s; the hydrogen content in the solid semi-coke was 2.75wt%, the carbon content was 84.0wt%, the carbon-hydrogen mass ratio was 30.5; and the tar yield was 11.8wt%. The remaining steps are the same as in Example 1; During the above process, the load demand for CO2 capture is monitored in real time, and the temperature of pyrolysis in step S1 is dynamically adjusted according to the load demand for CO2 capture using the formula T=T0+K×(L-L0). For the long-flame coal, the baseline CO2 capture load L0 = 75%, the baseline pyrolysis temperature T0 is 600℃, the adjustment coefficient K is 2℃ / percentage point, and T and L satisfy the formula T = 600℃ + 2℃ / percentage point × (L - 75%). When the CO2 capture load L = 35%, substituting into the formula, we get T = 520℃.

[0072] Tests showed that at a pyrolysis temperature T of 520℃, the hydrogen content in the solid semi-coke was 2.75wt%, and the CO2 dry basis volume fraction in the CO2-enriched flue gas was 16.2vol.

[0073] Example 5 The method is the same as in Example 1, except that: In step S1, the pyrolysis time is maintained at 6 seconds, and the pyrolysis temperature is dynamically adjusted according to the CO2 capture load requirement. During the above process, the load demand for CO2 capture is monitored in real time, and the temperature of pyrolysis in step S1 is dynamically adjusted according to the load demand for CO2 capture using the formula T=T0+K×(L-L0). For the long-flame coal, the baseline CO2 capture load L0 = 75% and the baseline pyrolysis temperature T0 is 600℃; when the CO2 capture load L = 100%, the pyrolysis temperature T is 630℃, and thus the adjustment coefficient K = 1.2℃ / percentage point is determined. Tests showed that at a pyrolysis temperature of 630℃ and a pyrolysis time of 6s, the hydrogen content in the obtained solid semi-coke was 2.3wt%, the carbon content was 87.0wt%, and the carbon-hydrogen mass ratio was 37.8; the CO2 dry basis volume fraction in the obtained CO2-enriched flue gas was 16.9vol%, and the tar yield was 9.9wt%.

[0074] Example 6 The method is the same as in Example 1, except that... In step S1, the internally heated fluidized bed pyrolysis reactor is replaced with an externally heated fixed bed pyrolysis reactor; the temperature is increased to 600℃ at a heating rate of 5℃ / min and held for 10s for pyrolysis.

[0075] Tests showed that at a pyrolysis temperature T of 600℃, the obtained solid semi-coke contained 2.6 wt% hydrogen, 85.0 wt% carbon, and a carbon-to-hydrogen mass ratio of 32.7; the obtained CO2-enriched flue gas contained 15.9 vol% CO2 on a dry basis and had a tar yield of 8.8 wt%. Example 7 The method is the same as in Example 1, except that... In step S2, the solid semi-coke is first cooled to room temperature and then fed into the boiler to be mixed with air for combustion, generating flue gas at the tail end of the boiler; the flue gas enriched with CO2 has a dry basis volume fraction of 16.5 vol.

[0076] Comparative Example 1 S1. The raw coal is crushed and ground to a particle size of 75μm, and then fed into the boiler to be mixed with air for combustion, generating flue gas at the tail end of the boiler; the combustion conditions include: excess air coefficient α=1.2, and flue gas temperature at the furnace outlet of 950℃. The boiler tail flue gas is subjected to dust removal and condensation (condensed to 25°C) to dehydrate, resulting in dehydrated boiler tail flue gas, wherein the dry basis volume fraction of CO2 in the boiler tail flue gas is 14.5 vol%. S2. CO2 capture is performed on the flue gas from the boiler tail section obtained in step S1.

[0077] Comparative Example 2 S1. The raw coal is crushed and ground to a particle size of 75μm, and then pyrolyzed at 500℃ for 10s in an internally heated fluidized bed pyrolysis reactor under oxygen-deficient conditions (oxygen volume concentration of 0.5 vol%) to produce hydrogen-rich volatiles and solid semi-coke; the solid semi-coke contains 2.9 wt% hydrogen, 83 wt% carbon, and a carbon-hydrogen mass ratio of 28.6. The hydrogen-rich volatiles are separated by condensation (cooling to 40°C) within 2 seconds after leaving the pyrolysis reactor, and high-value coal tar and high-calorific-value coal gas are recovered. The tar yield is 11.5 wt%, and 50 vol% of the high-calorific-value coal gas is returned to the combustion chamber of the pyrolysis reactor as a pyrolysis heat source. S2. Solid semi-coke is directly fed into the boiler at a hot state of about 500°C and mixed with air for combustion to generate flue gas at the tail end of the boiler. The combustion conditions include: excess air coefficient α=1.2 and flue gas temperature at the furnace outlet of 950°C. The flue gas from the boiler tail end was subjected to dust removal and condensation (to 25°C) to dehydrate, resulting in CO2-enriched flue gas, wherein the dry basis volume fraction of CO2 in the CO2-enriched flue gas was 14.7 vol%. S3. The CO2-enriched flue gas obtained in step S2 is subjected to CO2 capture.

[0078] Table 1

[0079] As can be seen from the results in Table 1, the coal pyrolysis coupled carbon capture method of the present invention can improve the dry volume fraction of CO2 in flue gas and reduce the overall energy consumption per unit of CO2 capture while maintaining a high tar yield.

[0080] Examples 1-3 of this invention correspond to preferred dynamic adjustment conditions under baseline load, low load, and high load, respectively. The CO2 dry volume fraction is 16.2-16.9 vol%, the comprehensive energy consumption per unit CO2 capture is 2.60-2.84 GJ / t CO2, and the tar yield is 9.6-11.4 wt%. This invention can achieve synergistic optimization among CO2 enrichment effect, tar yield, and comprehensive energy consumption per unit CO2 capture.

[0081] In Example 4 of this invention, the carbon-hydrogen mass ratio of the solid semi-coke falls within the range corresponding to low-load operating conditions, and the dry-basis volume fraction of CO2 in the flue gas is basically the same as in Example 2; however, its pyrolysis temperature and pyrolysis time do not fall within the preferred range for low-load operating conditions, and do not meet the limit control requirement of a pyrolysis temperature not lower than 540℃ in the preferred embodiment, resulting in a higher overall energy consumption per unit of CO2 capture, thus the overall synergistic effect is relatively weak; in Example 5, the adjustment coefficient K does not meet the preferred range defined by this invention, its overall energy consumption per unit of CO2 capture is relatively high, and the overall synergistic effect is relatively weaker; Examples of this invention In Example 6, an externally heated fixed-bed pyrolysis reactor is used, which can achieve passive enrichment of CO2 in flue gas. However, due to the different types of pyrolysis reactors, the secondary cracking of tar is stronger, and the tar yield is slightly lower. This indicates that an internally heated fluidized-bed pyrolysis reactor is more conducive to achieving the synergy of passive enrichment of CO2 in flue gas and high tar yield. In Example 7 of this invention, the semi-coke is cooled before entering the furnace. The sensible heat of the semi-coke is not directly used in the boiler along with the semi-coke, which reduces the sensible heat that can be recovered and utilized by the system. The dry volume fraction of CO2 in the flue gas remains basically unchanged, but the sensible heat of the semi-coke is not directly utilized, and the overall energy consumption per unit of CO2 capture increases.

[0082] In Comparative Example 1 of this invention, the raw coal was not reconstructed through pyrolysis. The hydrogen component in the raw coal directly participated in combustion and introduced additional air, resulting in a strong dilution effect of inert nitrogen in the flue gas, a low CO2 dry basis volume fraction, and a high overall energy consumption per unit of CO2 capture. Comparative Example 2 used a fixed low-temperature pyrolysis at 500℃, without controlling the dynamic adjustment relationship between CO2 capture load, pyrolysis temperature, and tar yield constraints. Due to the low pyrolysis temperature, the degree of primary pyrolysis and dehydrogenation of the raw coal was insufficient, resulting in a high hydrogen content in the obtained solid semi-coke. Therefore, the amount of air and inert nitrogen introduced by hydrogen combustion during the solid semi-coke combustion process was relatively high, and the CO2 dry basis volume fraction in the flue gas was only 14.7 vol%, with the overall energy consumption per unit of CO2 capture increasing to 3.18 GJ / tCO2. The passive enrichment effect and capture energy consumption of flue gas CO2 were poor, indicating that simply using fixed low-temperature pyrolysis cannot achieve synergistic optimization between tar yield, CO2 enrichment effect, and capture energy consumption.

[0083] In summary, the coal pyrolysis coupled carbon capture method provided by this invention can achieve synergistic optimization among passive CO2 enrichment, low-energy capture, and high tar yield by controlling the carbon-hydrogen mass ratio of semi-coke and dynamically adjusting the pyrolysis temperature according to the CO2 capture load.

[0084] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combining the various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A method for coal pyrolysis coupled with carbon capture, characterized in that, The method includes the following steps: S1. Pyrolyze the raw coal to produce hydrogen-rich volatiles and solid semi-coke; wherein the carbon-hydrogen mass ratio of the solid semi-coke is 30-40. S2. In an air atmosphere, the solid semi-coke obtained in step S1 is burned, and carbon dioxide is passively enriched in the flue gas produced by combustion to obtain CO2-enriched flue gas. S3. The CO2-enriched flue gas obtained in step S2 is subjected to CO2 capture; the pyrolysis temperature in step S1 is dynamically adjusted according to the CO2 capture load requirement. The dynamic adjustment method includes: During operation, the pyrolysis temperature is adjusted according to the formula T=T0+K×(L-L0); Where T is the temperature of pyrolysis; T0 is the reference temperature for pyrolysis, with a value ranging from 580 to 620℃; L represents the CO2 capture load; L0 is the baseline CO2 capture load, which is 70-80%; K is the adjustment coefficient, which takes a value of 1-3℃ / percentage point.

2. The method according to claim 1, characterized in that, The dynamic adjustment method includes: Adjust the pyrolysis temperature according to the formula T=T0+K×(L-75%); Where T0 is 590-610℃ and K is 2-2.5℃ / percentage point.

3. The method according to claim 1, characterized in that, The pyrolysis temperature T is 450-700℃; the pyrolysis time is 4-10s; The pyrolysis is carried out under anaerobic conditions, where the oxygen volume concentration is 0-3 vol.

4. The method according to claim 3, characterized in that, The pyrolysis temperature T is 540-650℃; the pyrolysis time is 5-8s.

5. The method according to claim 4, characterized in that, When L≥90%, the pyrolysis temperature T is 620-650℃, the pyrolysis time τ is 5-6s, and the carbon-hydrogen mass ratio of the solid semi-coke is 36-40. When 70%≤L<90%, the pyrolysis temperature T is 580-620℃, the pyrolysis time τ is 6-7s, and the carbon-hydrogen mass ratio of the solid semi-coke is 33-36. When L < 70% or the generator set is operating during peak shaving, the pyrolysis temperature T is 540-580℃, the pyrolysis time τ is 7-8s, and the carbon-hydrogen mass ratio of the solid semi-coke is 30-33.

6. The method according to any one of claims 1-5, characterized in that, The solid semi-coke contains 82-89 wt% carbon and 2-3.2 wt% hydrogen.

7. The method according to any one of claims 1-5, characterized in that, The carbon-to-hydrogen mass ratio of the raw coal is 15-20; And / or, the raw coal contains 62-72 wt% carbon and 3.6-4.8 wt% hydrogen.

8. The method according to any one of claims 1-5, characterized in that, Step S1 includes: condensing and separating the hydrogen-rich volatiles to recover coal tar and high-calorific-value coal gas; At least a portion of the high-calorific-value gas is used as the heat source for the pyrolysis and / or as the fuel for the combustion.

9. The method according to any one of claims 1-5, characterized in that, The combustion conditions described in step S2 include: an excess air coefficient α of 1.05-1.3; and a boiler furnace outlet flue gas temperature of 850-1150℃. Step S2 includes: removing dust and condensing and dehydrating the flue gas generated by the combustion at the tail end of the boiler to obtain flue gas enriched with CO2; The CO2-enriched flue gas contains CO2 with a dry basis volume fraction of 15-18 vol%. In step S2, the solid semi-coke is directly burned without cooling.

10. A system based on coal pyrolysis coupled with carbon capture, characterized in that, The system includes: a coal pyrolysis unit, a semi-coke hot conveying unit, a semi-coke combustion unit, a CO2 capture unit, and a collaborative control unit; The coal pyrolysis unit is used to pyrolyze raw coal to produce hydrogen-rich volatiles and solid semi-coke; The semi-coke combustion unit is connected to the solid semi-coke outlet of the coal pyrolysis unit and is used to burn the solid semi-coke from the coal pyrolysis unit to obtain CO2-enriched flue gas. The semi-coke hot conveying unit is located between the coal pyrolysis unit and the combustion unit, and is used to send solid semi-coke from the coal pyrolysis unit into the semi-coke combustion unit. The CO2 capture unit is connected to the semi-coke combustion unit and is used to capture CO2 from the CO2-enriched flue gas from the semi-coke combustion unit. The collaborative control unit is connected to the CO2 capture unit and is used to monitor the load demand of the CO2 capture unit and dynamically adjust the operating temperature of the coal pyrolysis unit accordingly.

11. The system according to claim 10, characterized in that, The system also includes an oil and gas separation and purification unit, which is connected to the hydrogen-rich volatile matter outlet of the coal pyrolysis unit and is used to separate the hydrogen-rich volatile matter after condensation, and to recover coal tar and high-calorific-value coal gas. The system also includes a flue gas pretreatment unit, which is located between the semi-coke combustion unit and the CO2 capture unit. The flue gas pretreatment unit is used to remove dust and condense and dehydrate the flue gas generated at the tail end of the boiler during combustion, so that the flue gas enriched with CO2 is sent to the CO2 capture unit.

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