A system for producing bio-natural gas by efficient cooperation of biogas and waste incineration

Abstract

This invention discloses a system for the efficient co-incineration of biogas and waste to produce biomethane, comprising an anaerobic digester, a filter, a biogas refrigerated dryer, a compressor, an amine absorption tank, an iron oxide absorption tank, a natural gas refrigerated dryer, an activated carbon desulfurizer, an odorizer, and an external pipeline network connected in sequence for biogas transfer; the amine absorption tank is sequentially and cyclically connected to a heat exchanger, an amine reboiling tank, an amine desorption tank, a heat exchanger, and an amine cooling tank for amine transfer; the amine reboiling tank is sequentially connected to a condensate tank and a power plant regenerative system for steam transfer; the anaerobic digester, biogas refrigerated dryer, and natural gas refrigerated dryer are connected to an external wastewater treatment plant for wastewater transfer. This invention features a small footprint, environmental friendliness, low energy consumption, high methane recovery rate, and high degree of automation.

Description

Technical Field

[0001] This invention relates to the field of biogas treatment, and more particularly to a system for the efficient co-incineration of biogas and waste to produce biogas. Background Technology

[0002] Currently, biogas purification and upgrading technologies in China typically employ a two-stage process of "desulfurization + decarbonization": Desulfurization commonly uses dry methods (iron oxide), wet methods (complexed iron), or biological methods. Decarbonization primarily employs pressure swing adsorption (PSA) and membrane separation.

[0003] However, while the above scheme can produce qualified natural gas, it has the following shortcomings:

[0004] 1) Large footprint: PSA systems occupy a large area, valves are prone to leakage, and regular maintenance is required;

[0005] 2) Poor environmental benefits: The wet desulfurization regeneration workshop has a strong odor and a harsh operating environment;

[0006] 3) High energy consumption: The entire system operates independently and fails to utilize surrounding facilities (such as the steam, electricity, and wastewater treatment systems of the incineration plant), resulting in low overall energy efficiency;

[0007] 4) Low methane recovery rate: The tail gas after PSA separation has a high methane content, which fails to fully utilize biogas resources and is also very likely to cause the project to exceed emission standards.

[0008] Therefore, it is necessary to develop new technologies specifically to overcome the above problems. Summary of the Invention

[0009] Purpose of the invention: To address the shortcomings and defects of existing technologies, this invention provides a system for the efficient co-incineration of biogas and waste to produce biomethane, which features small footprint, environmental friendliness, low energy consumption, high methane recovery rate, and high degree of automation.

[0010] Technical Solution: The present invention provides a system for the efficient co-incineration of biogas and waste to produce biomethane, characterized in that: it includes a gas holder, a filter, a biogas refrigerated dryer, a compressor, an amine absorption tank, an iron oxide absorption tank, a natural gas refrigerated dryer, an activated carbon desulfurizer, an odorizer, and an external pipeline network connected in sequence for biogas transmission; the amine absorption tank is sequentially and cyclically connected to a heat exchanger, an amine reboiling tank, an amine desorption tank, a heat exchanger, and an amine cooling tank for amine transmission; the amine reboiling tank is sequentially connected to a condensate tank and a power plant regenerative system for steam transmission; the anaerobic digester, biogas refrigerated dryer, and natural gas refrigerated dryer are connected to an external wastewater treatment plant for wastewater transmission.

[0011] The biogas mentioned above comes from biogas produced by an external anaerobic digester, which is pressurized by a Roots blower and then sent into a gas holder to stabilize the gas volume and pressure.

[0012] The filter removes dust and particulate impurities from the biogas to prevent clogging of subsequent equipment; the compressor pressurizes the biogas to 0.5MPa-0.6MPa to improve subsequent absorption efficiency.

[0013] The biogas is compressed and cold-dried before entering the amine absorption tank, which is an MDEA amine absorption tank, eliminating the need for pre-dry desulfurization.

[0014] The MDEA amine absorption tank serves as a deep processing unit, enabling integrated treatment that simultaneously removes H2S and CO2.

[0015] The iron oxide absorption tank removes acidic gases without liquid discharge; the acidic gases include H2S.

[0016] The biogas, after being pressurized, enters the amine absorption tank from the bottom, while the amine solution is sprayed into the tank from the top. After sufficient contact between the biogas and the amine solution through countercurrent flow, the purified biogas enters the dry purification unit. The amine solution is transformed from lean to rich, and the temperature of the amine absorption tank ranges from 75℃ to 45℃ from bottom to top.

[0017] The rich liquid enters a heat exchanger and is heated through energy recovery. After heating, it enters an amine reboiler and is heated with saturated steam at 0.45 MPa. The hydrophobic portion after heating enters a hydrophobic tank and a power plant reheat system, and is partially used to replenish the water removed during purification in the amine system.

[0018] The rich liquor, heated to 80℃-110℃, enters the amine desorption tank, releasing waste gas which then enters the power plant's primary air main pipe. The released lean liquor enters a heat exchanger to cool to 70℃, and then the amine liquor enters an amine cooling tank to cool to 40℃ via circulating cooling water. The waste gas includes H2S and CO2.

[0019] The heat exchanger is a shell-and-tube heat exchanger; the amine reboiler is also a shell-and-tube heat exchanger.

[0020] Beneficial Effects: Compared with existing technologies, this invention has the following significant advantages: Through integrated design, this invention achieves end-to-end purification of biogas from pretreatment to high-purity methane production, and fully utilizes waste heat resources from power plants, reducing energy consumption and operating costs. This invention has the following advantages: 1) Small footprint: It eliminates the need for numerous valve groups, decarbonization analysis towers, and desulfurization regeneration workshops, occupying only 1 / 4 of the area of ​​a traditional PSA. 2) Environmentally friendly: The entire process is closed-loop, with no odor leakage; the tail gas is decomposed at high temperature in the incinerator, achieving zero odor emissions. 3) Low energy consumption: It utilizes inexpensive steam from the incinerator to regenerate amine liquid, eliminating the need for electric heating or gas-fired boilers, thus reducing operating costs. 4) High methane recovery rate: Minimal methane loss in the tail gas, with a recovery rate ≥98%. 5) High degree of automation: In addition to periodic inspections, it can achieve "one-person monitoring" operation, reducing labor costs. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of the structure of the present invention. Detailed Implementation

[0022] The technical solution of the present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0023] The biogas of this invention is a mixed gas produced by the anaerobic decomposition of organic waste by microorganisms. Its main components are methane (CH4, approximately 50-70%) and carbon dioxide (CO2, approximately 30-50%), with small amounts of impurities such as hydrogen sulfide (H2S) and water vapor. Bio-SNG (Bio-Signal Gas): High-purity methane gas obtained by deeply purifying biogas, meeting or exceeding the national Class I natural gas standard (GB 18047). It can be directly integrated into natural gas pipelines or used as vehicle fuel. MDEA (N-methyldiethanolamine): A commonly used weakly alkaline organic amine solvent with selective absorption capacity for H2S and CO2, widely used in natural gas and biogas desulfurization and decarbonization processes. Waste-to-Energy Plant: A facility that generates heat energy by incinerating municipal solid waste for power generation, typically equipped with waste heat boilers, flue gas purification systems, and utilities (such as steam and electricity). Collaborative processing: refers to the sharing of resources and complementary advantages between the biogas purification system described in this invention and the waste incineration power plant in terms of energy, materials, personnel and environmental protection facilities.

[0024] The present invention discloses a system for the efficient co-firing of biogas and waste incineration to produce biomethane, comprising an anaerobic digester, a filter, a biogas refrigerated dryer, a compressor, an amine absorption tank, an iron oxide absorption tank, a natural gas refrigerated dryer, an activated carbon desulfurizer, an odorizer, and an external pipeline network connected in sequence for biogas transfer; the amine absorption tank is cyclically connected to a heat exchanger, an amine reboiler, an amine desorption tank, a heat exchanger, and an amine cooling tank for amine transfer; the amine reboiler is sequentially connected to a condensate tank and a power plant regenerative system for steam transfer; and the anaerobic digester, biogas refrigerated dryer, and natural gas refrigerated dryer are connected to an external wastewater treatment plant for wastewater transfer.

[0025] I. Biogas Feeding and Pretreatment Stage:

[0026] Biogas source: Biogas produced by an external anaerobic digester is pressurized by a Roots blower and sent into an anaerobic tank to stabilize the gas volume and pressure.

[0027] Filter: Removes dust and particulate impurities from biogas to prevent clogging of downstream equipment.

[0028] Biogas cold dryer: It uses cold water to remove most of the moisture, avoiding water vapor from affecting the performance of the adsorbent and the safety of subsequent processes.

[0029] Compressor: Pressurizes biogas to 0.4MPa-0.6MPa to improve subsequent absorption efficiency.

[0030] II. Core Purification Unit - Integrated Desulfurization and Decarbonization Process:

[0031] The key innovation of this invention lies in using an MDEA (N-methyldiethanolamine) amine liquid absorption tank as the first-stage deep purification unit to achieve integrated treatment that simultaneously removes H2S and CO2, greatly simplifying the process and improving efficiency.

[0032] After pretreatment (compression and cold drying), the biogas directly enters the amine absorption tank without the need for pre-dry desulfurization.

[0033] MDEA solution exhibits extremely high reactivity and selectivity for H2S, rapidly absorbing H2S at room temperature. It boasts high single-stage desulfurization efficiency, with the outlet H2S concentration stably controlled at ≤20mg / m³, meeting the requirements for corrosion protection of subsequent equipment and product gas quality.

[0034] MDEA also has a good absorption capacity for CO2, and can achieve large-scale removal of CO2 in the same tower, so that the methane purity in the outlet gas reaches more than 97%.

[0035] It avoids the problems of frequent replacement of dry desulfurization agents such as iron oxide / activated carbon, waste disposal and pressure drop loss in traditional processes, and significantly reduces operation and maintenance costs.

[0036] Iron oxide absorption tank: used as an emergency measure in case of failure of amine liquid absorption tower, used to remove acidic gases such as H2S (hydrogen sulfide), with no liquid discharge, which can ensure the stable operation of the project.

[0037] III. Amine liquid regeneration and heat recovery:

[0038] Adsorption: Pressurized biogas enters the amine absorption tank from the bottom. Amine solution (lean solution) is sprayed into the absorption tank from the top. After sufficient counter-current contact between the biogas and amine solution, the purified biogas enters the dry purification unit. The amine solution is transformed from lean solution to rich solution. The temperature of the amine absorption tank ranges from 75℃ to 45℃ from bottom to top.

[0039] Desorption: The rich liquor enters the lean-rich amine liquor heat exchanger (shell-and-tube heat exchanger), where it is heated through energy recovery. After heating, it enters the amine liquor reboiling tank (shell-and-tube heat exchanger) and is heated with 0.5 MPa saturated steam. The condensate after heating enters the condensate tank and the power plant's regenerative system, and part of it is used to replenish the water removed during purification in the amine liquor system. The heated rich liquor, at a temperature of 80℃-100℃, enters the amine liquor desorption tank, releasing waste gas (H2S and CO2), which enters the power plant's primary air header. The released lean liquor enters the heat exchanger to cool to 70℃, and then the amine liquor enters the amine liquor cooling tank to cool to 40℃ via circulating cooling water.

[0040] The biogas of this invention is pretreated and then directly fed into the MDEA amine absorption tank, where H2S is removed to ≤20mg / m³ and CO2 is removed simultaneously in a single device, producing high-purity methane gas.

[0041] The heat source for amine liquid regeneration comes entirely from the waste heat steam of the waste incineration plant, requiring no additional energy input.

[0042] The system is equipped with a fully automatic emergency switching mechanism. When the purification system fails, it can seamlessly switch to biogas injection or primary air heating mode to ensure safety.

[0043] High-sulfur exhaust gas is sent to the incinerator for incineration through a primary air duct to avoid secondary pollution.

[0044] The present invention relates to a system for the efficient co-production of biogas from waste incineration. This system deeply couples the biogas purification process with a waste-to-energy plant, and uses an integrated MDEA amine liquid absorption tower to simultaneously remove H2S and CO2, eliminating the need for traditional multi-stage desulfurization. Combined with the waste heat regeneration of the waste incineration plant, it achieves the goal of low energy consumption, small footprint, and high recovery rate in co-purification. It also shares the plant's public and environmental protection facilities such as electricity, flue gas purification, and wastewater treatment, thereby achieving the goal of low energy consumption, small footprint, no odor, high methane recovery rate, and high level of automation in the utilization of biogas resources, significantly improving economic efficiency and environmental friendliness.

Claims

1. A system for efficiently producing biogas through co-incineration of waste, characterized in that: The system includes a filter, a biogas refrigerated dryer, a compressor, an amine absorption tank, an iron oxide absorption tank, a natural gas refrigerated dryer, an activated carbon desulfurizer, an odorizer, and an external pipeline network, all connected in sequence for biogas transfer. The amine absorption tank is cyclically connected to a heat exchanger, an amine reboiler, an amine desorption tank, and an amine cooling tank for amine transfer. The amine reboiler is sequentially connected to a condensate tank and a power plant regenerative system for steam transfer. The anaerobic digester, biogas refrigerated dryer, and natural gas refrigerated dryer are connected to an external wastewater treatment plant for wastewater transfer.

2. The system for producing biogas through efficient co-incineration of waste as described in claim 1, characterized in that: The biogas mentioned comes from biogas produced by an external anaerobic digester, which is pressurized by a Roots blower and then sent into a gas holder to stabilize the gas volume and pressure.

3. The system for producing biogas through efficient co-incineration of waste as described in claim 1, characterized in that: The filter removes dust and particulate impurities from the biogas to prevent clogging of subsequent equipment; the refrigerated dryer removes moisture from the biogas, maintaining the pressure dew point between +5°C and +8°C to prevent the subsequent compressor from producing liquid water due to pressurization, which could lead to oil emulsification and corrosion in a humid environment; the compressor pressurizes the biogas to 0.4MPa-0.6MPa to improve subsequent absorption efficiency.

4. The system for producing biogas through efficient co-incineration of waste as described in claim 1, characterized in that: The biogas is compressed and cold-dried before entering the amine absorption tank, which is an MDEA amine absorption tank, eliminating the need for pre-dry desulfurization.

5. The system for producing biogas through efficient co-incineration of waste as described in claim 4, characterized in that: The MDEA amine absorption tank, as a deep processing unit, achieves integrated treatment for the simultaneous removal of H2S and CO2.

6. The system for producing biogas through efficient co-incineration of waste as described in claim 1, characterized in that: The iron oxide absorption tank is used for deep removal of acidic gases or as an emergency backup, with no liquid discharge; the acidic gases include H2S.

7. The system for producing biogas through efficient co-incineration of waste as described in claim 1, characterized in that: The biogas, after being pressurized, enters the amine absorption tank from the bottom, while the amine solution is sprayed into the tank from the top. After sufficient contact between the biogas and the amine solution through countercurrent flow, the purified biogas enters the dry purification unit. The amine solution is transformed from lean to rich, and the temperature of the amine absorption tank ranges from 75℃ to 45℃ from bottom to top.

8. The system for producing biogas through efficient co-incineration of waste as described in claim 7, characterized in that: The rich liquid enters the heat exchanger and is heated through energy recovery. After heating, it enters the amine liquid reboiler and is heated with saturated steam at 0.5 MPa. The hydrophobic portion after heating enters the hydrophobic tank and the power plant's reheat system, and part of it is used to replenish the water removed during the purification process in the amine liquid system.

9. The system for producing biogas through efficient co-incineration of waste as described in claim 8, characterized in that: The heated rich liquor, with a temperature of 80℃-110℃, enters the amine desorption tank, releasing waste gas which then enters the primary air main pipe of the power plant. The released lean liquor enters a heat exchanger to be cooled to 70℃, and then the amine liquor enters the amine cooling tank to be cooled to 40℃ by circulating cooling water. The waste gas includes H2S and CO2.

10. The system for producing biogas through efficient co-incineration of waste according to claim 8, characterized in that: The heat exchanger is a shell-and-tube heat exchanger; the amine reboiler is also a shell-and-tube heat exchanger.

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