Biomass-coal power BECCS integration emission reduction system and method based on negative carbon emission characteristics

Abstract

The present application relates to the field of low-carbon energy technology, in particular to a biomass-coal power BECCS integrated emission reduction system based on negative carbon emission characteristics, comprising: a biomass pretreatment module for preparing agricultural and forestry waste into biomass fuel; a boiler blending module for mixing and burning biomass fuel and power coal in a coal-fired boiler according to a preset mass blending ratio; a flue gas pretreatment module for purifying the flue gas at the outlet of the boiler to meet the inlet requirements of the carbon capture system; a chemical absorption carbon capture module for capturing CO2 in the purified flue gas using an amine-based absorbent; and a CO2 compression and storage module for transporting the captured CO2 to a geological storage site after pressurization. The present application defines the optimal economic capture rate at around 94.4%, avoiding the sharp increase in marginal energy consumption and cost rebound caused by pursuing the limit capture rate.

Description

Technical Field

[0001] This invention relates to the field of low-carbon energy technology, specifically to a biomass-coal power BECCS integrated emission reduction system and method based on negative carbon emission characteristics. Background Technology

[0002] Coal-fired power generation is one of the main sources of carbon emissions in my country, and its low-carbon transformation is a key link in achieving the "dual carbon" target. Carbon capture, utilization, and storage (CCUS) technology is considered an important technological path for deep emission reduction from fossil fuels. However, post-combustion capture technologies, represented by monoethanolamine (MEA) chemical absorption, suffer from economic bottlenecks such as high regeneration energy consumption, a 20%–30% decrease in net power efficiency, and an increase in power generation costs of about 60%, making it difficult to achieve commercial self-sufficiency under current carbon price levels. The coupling of biomass energy with carbon capture and storage technologies (BECCS) has attracted attention because it can achieve negative carbon emissions throughout its entire life cycle, becoming an important direction for the low-carbon transformation of coal-fired power plants.

[0003] Chinese patent CN115978545A (hereinafter referred to as "Prior Document 1") discloses a biomass carbon capture and coal-fired boiler coupled power generation system and method. This scheme employs a biomass feeding and kiln pyrolysis incineration unit. The flue gas generated from biomass pyrolysis incineration, after waste heat recovery, reacts with hydrogen generated from a water electrolysis hydrogen production unit in a carbon adsorption-catalytic conversion unit to produce methane, thereby achieving CO2 adsorption and resource utilization. This technical route, to a certain extent, integrates biomass energy utilization and carbon capture, and has the potential for energy saving and carbon reduction.

[0004] However, the technical solution disclosed in Prior Art Document 1 still has the following limitations in practical engineering applications: (1) The scheme requires the addition of multiple independent equipment such as biomass pyrolysis incineration unit, water electrolysis hydrogen production unit, and catalytic conversion unit. The process is long and the equipment investment is large. The amount of engineering work required to modify the existing coal-fired units is high. In particular, the water electrolysis hydrogen production unit itself has a large power consumption, which may weaken the net carbon emission reduction benefits of the system after it is included.

[0005] (2) The scheme converts the captured CO2 into synthetic natural gas, which will release CO2 again after being burned as fuel. It is difficult to achieve permanent carbon sequestration throughout the entire life cycle. Its "carbon capture" is essentially carbon conversion, which does not meet the core requirement of BECCS technology for long-term negative carbon emissions.

[0006] (3) Comparative document 1 focuses on independent pyrolysis of biomass, but does not address the matching relationship between the blending ratio and the load, energy consumption, and capture rate of the subsequent MEA capture system when biomass is co-fired in a coal-fired boiler. Practice shows that if the blending ratio and capture operation parameters are not coordinated, the system is prone to operate in the non-economic range, resulting in an "overcapture" phenomenon where marginal energy consumption exceeds marginal emission reduction benefits. This is one of the main reasons for the large economic fluctuations in the current BECCS engineering application.

[0007] (4) Comparative document 1 only focuses on the process integration within the power generation system and does not include the CO2 transportation and storage links in the system boundary. Coal-fired power units are widely distributed in my country, and the distance of carbon storage directly affects pipeline investment and transportation pressure energy loss. When the distance exceeds a certain threshold, the transportation cost increases non-linearly, which may make BECCS retrofitting economically infeasible. Existing technologies lack hierarchical decision-making rules for unit retrofitting based on storage distance.

[0008] In summary, existing BECCS-related technical solutions still have shortcomings in terms of system complexity, long-term carbon sequestration, parameter coupling optimization, and distance constraint identification. There is an urgent need for an integrated emission reduction system and method that can integrate biomass co-firing and MEA chemical absorption and capture, dynamically correct emission reduction economics, and integrate carbon sequestration distance determination mechanism in existing supercritical or ultra-supercritical coal-fired units at a lower retrofit cost. Summary of the Invention

[0009] To address the shortcomings of existing technologies, this invention provides a biomass-coal power BECCS integrated emission reduction system and method based on negative carbon emission characteristics.

[0010] To achieve the above objectives, the present invention provides the following technical solution: a biomass-coal power BECCS integrated emission reduction system based on negative carbon emission characteristics, comprising: The biomass pretreatment module is used to convert agricultural and forestry waste into biomass fuel; The boiler co-firing module is used to mix and burn biomass fuel and power coal in a preset mass co-firing ratio in a coal-fired boiler. The co-firing ratio is set so that the proportion of bio-source carbon in the flue gas meets the negative emission requirements and the boiler operates safely. The flue gas pretreatment module is used to purify the flue gas at the boiler outlet to meet the inlet requirements of the carbon capture system. The chemical absorption carbon capture module uses an amine-based absorbent to capture CO2 in the purified flue gas, and sets the absorbent concentration, liquid-to-gas ratio, and regeneration heat consumption parameters to ensure that the overall CO2 removal rate reaches the preset value. The CO2 compression and storage module is used to pressurize the captured CO2 and transport it to the geological storage site.

[0011] Preferably, the higher heating value of the biomass fuel is not less than 18.70 MJ / kg, and the blending ratio is 10% to 15%.

[0012] Preferably, the chemical absorption carbon capture module uses monoethanolamine absorbent at a concentration of 30 wt% and a liquid-to-gas ratio of 3.205 L / Nm³. 3 The overall CO2 removal rate is no less than 90%.

[0013] Preferably, the CO2 compression and storage module pressurizes the captured CO2 to 10-15 MPa and transports it through pipeline in a supercritical state, with a carbon storage distance not exceeding 250 km.

[0014] Preferably, the boiler co-firing module adopts a direct pulverization and co-firing process, which adds a special biomass feeding and pulverizing system to the existing pulverized coal boiler.

[0015] This invention also discloses a biomass-coal power BECCS integrated emission reduction method based on the aforementioned system, comprising the following steps: Steps for building a fuel supply chain: Control the biomass storage radius within an economical range and prepare briquettes; Steps for setting biomass co-firing parameters: Determine the biomass co-firing ratio based on the unit's heat balance and maintain the rated total heat input of the boiler; Carbon capture operation steps: Start the chemical absorption system, set the CO2 removal rate to the initial value, and then adjust it to the economically optimal capture rate based on the principle of minimizing carbon emission costs; Economic evaluation steps: The core indicators are the cost of avoiding carbon emissions and the levelized cost of power generation, combined with carbon market prices to assess the economics of the retrofit. Carbon asset development steps: Apply for certified emission reductions for the negative carbon emissions generated from biomass co-firing.

[0016] Preferably, the biomass co-firing ratio in the co-firing parameter setting step is 10% to 15%, and the total heat input of the boiler is maintained at the rated value.

[0017] Preferably, the initial CO2 removal rate in the carbon capture operation step is 90%, and the economically optimal capture rate is 94.4%. When the CO2 removal rate exceeds 94.4%, the gas-liquid mass transfer driving force of the absorber decreases, and the marginal energy consumption increase exceeds the marginal emission reduction benefit. At this time, the removal rate is maintained in the range of 90% to 94.4%.

[0018] Preferably, when the carbon sequestration distance exceeds 250 km, the pipeline construction cost and pressure energy loss increase non-linearly. Therefore, the installation of CO2 compression and sequestration modules on the unit should be postponed, and only the biomass co-firing step should be performed.

[0019] Preferably, the priority of retrofitting is classified according to the installed capacity of the generating units: units with an installed capacity of 2000 MW are in the first priority tier, units with an installed capacity of 1200-1320 MW are in the second priority tier, and units with an installed capacity of 700 MW are evaluated in conjunction with carbon sequestration conditions.

[0020] Compared with existing technologies, this invention has the following advantages: By precisely controlling the biomass co-firing ratio within the engineering safety threshold of 10%~15%, this invention introduces bio-source carbon without large-scale modification of the boiler's main structure, enabling the system to have carbon negative emission potential within the entire life cycle framework. It also quantifies and identifies the nonlinear impact of the overall MEA CO2 removal rate on the cost of avoiding carbon emissions (AOC), defining the optimal economic capture rate at around 94.4%, thus avoiding the surge in marginal energy consumption and cost rebound caused by pursuing the ultimate capture rate. Furthermore, by using 250 km as the economic red line for carbon sequestration distance, a "distance-cost" hierarchical decision-making mechanism is established, effectively mitigating the pressure energy penalty risk of long-distance pipeline transportation. Combined with a retrofit priority classification system based on the dual constraints of unit capacity and carbon sequestration distance, this invention provides an engineering-implementable and economically optimal operating scheme for the coordinated carbon negative retrofit of multi-unit, multi-site coal-fired power plants. Attached Figure Description

[0021] Figure 1 This is a process flow diagram of the biomass-coal power BECCS integrated emission reduction system of the present invention; Figure 2 This is a nonlinear curve showing the impact of the overall CO2 removal rate of the MEA on the cost of avoiding carbon emissions (AOC). Figure 3 A segmented feature map showing the impact of carbon sequestration distance on the AOC of biomass pathways; Figure 4 A four-quadrant bubble diagram for prioritizing the "biomass + CCUS" retrofit of coal-fired power units based on multidimensional constraints. Detailed Implementation

[0022] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0023] like Figure 1 As shown, the biomass-coal power BECCS integrated emission reduction system proposed in this invention is arranged along the process direction as follows: a biomass pretreatment module, a boiler co-firing module, a flue gas pretreatment module, a chemical absorption carbon capture module, and a CO2 compression and storage module. Each module is sequentially connected via conveying equipment, flue gas ducts, and pipelines.

[0024] The biomass pretreatment module uses agricultural and forestry waste (preferably crop straw) as raw material, which is processed through slag removal, screening, crushing, and pelletizing to prepare briquettes. The boiler co-firing module mixes the briquettes with thermal coal in a preset ratio and feeds them into a supercritical or ultra-supercritical coal-fired boiler for combustion. The flue gas pretreatment module includes an electrostatic precipitator and a wet desulfurization tower to reduce the concentration of dust and SO2 in the flue gas. The chemical absorption carbon capture module uses an amine-based absorbent (preferably monoethanolamine solution) to absorb and regenerate CO2 in the purified flue gas. The CO2 compression and storage module pressurizes the separated CO2 to a supercritical state and transports it through pipelines to a geological storage site.

[0025] Example 1 (Ultra-supercritical 2000 MW unit, optimal operating condition for close-range storage) This embodiment uses an ultra-supercritical unit with an installed capacity of 2000 MW and a thermoelectric conversion efficiency of 44.5% as the implementation object. The carbon sequestration distance is 126.88 km, which is within the 250 km threshold, and the unit capacity factor is set to 65%.

[0026] Biomass pretreatment: Straw collection points are set up within a 50 km radius of the collection and storage area. Rice straw and corn straw are used as raw materials, and the straw is crushed and pelletized to prepare briquettes. Batch testing shows that the higher calorific value of the briquettes ranges from 18.70 MJ / kg to 19.20 MJ / kg.

[0027] Blending parameters: Biomass briquettes are mixed with thermal coal at a blending ratio of 15% by weight, ground by the pulverizing system, and then fed into the boiler. The total heat input of the boiler is maintained at the same rated value as under pure coal combustion conditions, and the difference in calorific value of biomass is compensated by adjusting the coal feed rate.

[0028] Flue gas pretreatment. The boiler outlet flue gas sequentially passes through an electrostatic precipitator and a wet desulfurization tower, resulting in a dust concentration below 10 mg / Nm³. 3 The SO2 concentration is below 20 ppm, which meets the inlet requirements of the carbon capture system.

[0029] Carbon capture system operation: A 30 wt% monoethanolamine solution is used as the absorbent, and the liquid-to-gas ratio of the absorber is set to 3.205 L / Nm³. 3 The gas phase pressure drop is 0.01379 MPa. The rich liquid enters the regeneration tower, and the regeneration heat is supplied by steam extracted from the turbine via a heat accumulator. The heat requirement of the heat accumulator is 4494 kJ / kg CO2. Initially, the overall CO2 removal rate is set at 90%. After 72 hours of continuous and stable operation, the operating parameters are gradually adjusted according to the principle of optimizing the avoidance of carbon emission costs (AOC), setting the economically optimal capture rate at 94.4%. At this point, the AOC drops to its lowest value of approximately 92.5%. / tCO2. When the CO2 removal rate exceeds 94.4%, the driving force of gas-liquid mass transfer in the absorption tower decreases significantly, the marginal energy consumption increase exceeds the marginal emission reduction benefit, and AOC increases. Therefore, the removal rate is maintained in the range of 90% to 94.4% during operation.

[0030] CO2 Compression and Storage: The captured CO2 is dried, compressed, and pressurized to 12 MPa, then transported in a supercritical state via pipeline to a saline aquifer storage site 126.88 km away. Since the transport distance does not exceed 250 km, a single-stage pressurization can maintain the supercritical state, eliminating the need for intermediate pumping stations.

[0031] Under the conditions of this embodiment, the levelized cost of electricity (LCOE) is 110.80. / MWh, the lowest among all samples, MEA energy consumption accounts for 27.9% to 32.3% of net electricity output, and the BECCS system achieves negative carbon emissions, meeting the requirements for CCER verification application.

[0032] Example 2 (1200 MW supercritical unit, remote storage) This embodiment focuses on a supercritical unit with an installed capacity of 1200 MW and a carbon sequestration distance of 539.02 km. This distance far exceeds the 250 km threshold.

[0033] (1) Biomass briquettes are blended at a mass ratio of 15%, and the flue gas is directly discharged after dust removal and desulfurization without the addition of carbon capture and storage modules.

[0034] (2) Under the same co-firing ratio and a capture rate of 90%, due to the storage distance of 539.02 km, the pipeline requires two-stage relay pressurization stations, increasing construction investment by approximately US$28 million and operating power consumption by approximately 18%. Simulation results show that the AOC is as high as 119.3. / t CO2, far exceeding the expected price in the carbon market.

[0035] (3) According to the 250 km threshold set by the present invention, when the distance does not exceed 250 km, the transportation cost increases linearly with the distance, which is suitable for installing CCUS; when the distance exceeds 250 km, the pipeline construction and pressure energy loss increase nonlinearly. In this embodiment, the decision to postpone the installation of CO2 compression and storage modules is implemented, and only biomass co-firing is maintained. The connection will be made after the regional CCUS cluster pipeline network is built.

[0036] A comparison of Examples 1 and 2 shows that the system and method of the present invention can output differentiated engineering decision suggestions based on the dual constraints of unit capacity and carbon sequestration distance; large-capacity ultra-supercritical units can achieve optimal emission reduction economy under close-range sequestration conditions, which confirms the scientific nature and engineering guidance value of the parameter setting system of the present invention.

[0037] The priority for retrofitting units is tiered based on their installed capacity: ultra-supercritical units with an installed capacity of 2000 MW are in the first priority tier; units with an installed capacity of 1200–1320 MW are in the second priority tier; and supercritical units with an installed capacity of 700 MW require comprehensive evaluation in conjunction with carbon sequestration conditions. For units with a carbon sequestration distance exceeding 250 km, regardless of capacity, the installation of CCUS modules will be temporarily suspended, and the pure co-firing pathway will be prioritized.

[0038] Parameter selection basis (1) Determination of the co-firing ratio of 10% to 15%: When it is below 10%, the proportion of bio-source carbon is too low and the negative carbon effect is not significant; when it is above 15%, the content of alkali metals in straw increases, which can easily lead to coking and corrosion of the heated surface, and the supply chain cost increases.

[0039] (2) Determination of the optimal economic capture rate of 94.4%: Under the conditions of fixed co-firing ratio and carbon price, the capture rate is scanned with AOC as the objective function. The minimum value of AOC is found at 94.4%. When the value is lower than this, the emission reduction benefits of increasing the capture rate are higher than the cost of additional energy consumption. When the value is higher than this, the regeneration heat consumption increases exponentially, and the economic efficiency deteriorates.

[0040] (3) Determination of the 250 km threshold for carbon sequestration distance: Under the condition of a transport capacity of 2 million tons of CO2 / year, a single-stage pressurization can maintain the supercritical state when the distance does not exceed 250 km; after exceeding 250 km, a relay pumping station needs to be added, and the unit transport cost changes from linear growth to nonlinear jump.

[0041] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A biomass-coal power BECCS integrated emission reduction system based on negative carbon emission characteristics, characterized in that, include: The biomass pretreatment module is used to convert agricultural and forestry waste into biomass fuel; The boiler co-firing module is used to mix and burn biomass fuel and power coal in a preset mass co-firing ratio in a coal-fired boiler. The co-firing ratio is set so that the proportion of bio-source carbon in the flue gas meets the negative emission requirements and the boiler operates safely. The flue gas pretreatment module is used to purify the flue gas at the boiler outlet to meet the inlet requirements of the carbon capture system. The chemical absorption carbon capture module uses an amine-based absorbent to capture CO2 in the purified flue gas, and sets the absorbent concentration, liquid-to-gas ratio, and regeneration heat consumption parameters to ensure that the overall CO2 removal rate reaches the preset value. The CO2 compression and storage module is used to pressurize the captured CO2 and transport it to the geological storage site.

2. The system according to claim 1, characterized in that, The biomass fuel has a higher heating value of not less than 18.70 MJ / kg, and the blending ratio is 10% to 15%.

3. The system according to claim 1, characterized in that, The chemical absorption carbon capture module uses monoethanolamine absorbent at a concentration of 30 wt% and a liquid-to-gas ratio of 3.205 L / Nm³. 3 The overall CO2 removal rate is no less than 90%.

4. The system according to claim 1, characterized in that, The CO2 compression and storage module pressurizes the captured CO2 to 10-15 MPa and transports it through pipelines in a supercritical state, with a carbon storage distance not exceeding 250 km.

5. The system according to claim 1, characterized in that, The boiler co-firing module adopts a direct pulverization and co-firing process, adding a dedicated biomass feeding and pulverizing system to the existing pulverized coal boiler.

6. A biomass-coal power BECCS integrated emission reduction method based on the system described in any one of claims 1 to 5, characterized in that, Includes the following steps: Steps for building a fuel supply chain: Control the biomass storage radius within an economical range and prepare briquettes; Steps for setting biomass co-firing parameters: Determine the biomass co-firing ratio based on the unit's heat balance and maintain the rated total heat input of the boiler; Carbon capture operation steps: Start the chemical absorption system, set the CO2 removal rate to the initial value, and then adjust it to the economically optimal capture rate based on the principle of minimizing carbon emission costs; Economic evaluation steps: The core indicators are the cost of avoiding carbon emissions and the levelized cost of power generation, combined with carbon market prices to assess the economics of the retrofit. Carbon asset development steps: Apply for certified emission reductions for the negative carbon emissions generated from biomass co-firing.

7. The method according to claim 6, characterized in that, In the biomass co-firing parameter setting step, the biomass co-firing ratio is 10% to 15%, and the total heat input of the boiler is maintained at the rated value.

8. The method according to claim 6, characterized in that, In the carbon capture operation steps, the initial CO2 removal rate is 90%, and the economically optimal capture rate is 94.4%. When the CO2 removal rate exceeds 94.4%, the gas-liquid mass transfer driving force of the absorber decreases, and the marginal energy consumption increase exceeds the marginal emission reduction benefit. At this time, the removal rate is maintained in the range of 90% to 94.4%.

9. The method according to claim 6, characterized in that, When the carbon sequestration distance exceeds 250 km, the pipeline construction cost and pressure energy loss increase non-linearly. Therefore, the installation of CO2 compression and sequestration modules will be temporarily suspended for this unit, and only the biomass co-firing step will be performed.

10. The method according to claim 6, characterized in that, The priority of retrofitting is classified according to the installed capacity of the generating units: units with an installed capacity of 2000 MW are in the first priority tier, units with an installed capacity of 1200-1320 MW are in the second priority tier, and units with an installed capacity of 700 MW are evaluated in conjunction with carbon sequestration conditions.

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