System and method for preparing liquefied natural gas from septic tank biogas
Through heat exchange network, modified molecular sieve adsorbents, mixed refrigerants and Internet of Things technology, the problems of low energy conversion efficiency and high production costs in biogas utilization are solved, efficient CO2 removal and liquefied natural gas production are achieved, and environmental pollution and production costs are reduced.
Patent Information
- Application Number
- CN202510351391.X
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-03-24
- Publication Date
- 2025-04-25
AI Technical Summary
The prior art has low energy conversion efficiency, poor economy, strong corrosion of impurities to equipment, high energy consumption of purification technology, low cold energy utilization rate in biogas utilization, resulting in high production costs and lack of integrated treatment systems for biogas characteristics.
Energy cascade utilization is achieved through the heat exchange network, and the modified molecular sieve adsorbent and pressure swing adsorption (PSA) process is used to improve the CO2 removal rate, design the mixed refrigerant ratio and combine it with a two-stage expander to reduce liquefaction energy consumption, and conduct real-time monitoring and feedback adjustment based on the Internet of Things (IoT), and dynamically optimize process parameters.
It improves the energy utilization efficiency of organic waste and biogas energy density, improves the CO2 removal rate to ≥99.5%, reduces liquefied energy consumption to ≤0.35 kWh/Nm³ LNG, solves the environmental pollution problem and reduces production costs.
Smart Images
Figure CN119875707A_ABST
Abstract
Description
Technical Field
[0001] The present invention relates to the technical field of renewable energy, and more specifically, to a system and method for preparing liquefied natural gas from biogas in a septic tank. Background Art
[0002] Traditional methods of utilizing biogas (such as power generation and direct combustion) have problems such as low energy conversion efficiency and poor economy. Impurities in biogas (CO2, H2S, water vapor) are highly corrosive to liquefaction process equipment. Existing purification technologies have high energy consumption, and the utilization rate of cold energy in the liquefaction process is low, resulting in high production costs. Conventional membrane separation methods have limited CO2 removal rates, and the liquefaction process mostly relies on a single refrigerant. The cold energy circulation efficiency is insufficient, and there is a lack of integrated processing systems tailored to the characteristics of biogas.
[0003] Therefore, there is an urgent need for a system and method for preparing liquefied natural gas from septic tank biogas to solve the above problems. Summary of the invention
[0004] In order to overcome the above-mentioned defects of the prior art, the embodiments of the present invention provide a system and method for preparing liquefied natural gas from biogas in septic tanks, which solve the environmental problems caused by livestock manure in farms and crop straw of farmers, and at the same time improve the energy utilization efficiency of organic waste, increase the energy density of biogas, realize energy cascade utilization through a heat exchange network, adopt modified molecular sieve adsorbent, and combine with pressure swing adsorption (PSA) process to increase the CO2 removal rate to ≥99.5%, design a mixed refrigerant ratio (such as a mixture of nitrogen, methane, and propane), and combine with a two-stage expander to reduce the liquefaction energy consumption to ≤0.35 kWh / Nm³ LNG, and dynamically optimize process parameters such as pressure, temperature, and flow rate based on real-time monitoring and feedback adjustment of the Internet of Things (IoT) to solve the problems raised in the above-mentioned background technology.
[0005] To achieve the above-mentioned objectives, the present invention provides the following technical solutions: a system for preparing liquefied natural gas from septic tank biogas, comprising a biogas generator, one side of the biogas generator is connected to a buffer tank via a pipeline, one side of the buffer tank is connected to a booster via a pipeline, one side of the booster is connected to a desulfurization tower via a pipeline, one side of the desulfurization tower is connected to a membrane separator via a pipeline, a carbon dioxide exhaust pipe is provided at the top of the membrane separator, a cold box is connected to the bottom of the membrane separator via a pipeline, a refrigerant compressor is provided at one side of the cold box, two pipelines are connected between the cold box and the refrigerant compressor, and one side of the cold box is connected to an LNG storage tank via a pipeline.
[0006] A method for preparing liquefied natural gas from biogas in a septic tank comprises the above-mentioned system for preparing liquefied natural gas from biogas in a septic tank and the following steps: S1: The closed septic tank is equipped with a gas exhaust pipe and a negative pressure extraction system, produces biogas through a biogas generator, and a buffer tank is set up to balance the fluctuation of biogas production; S2: Use dry desulfurization in a desulfurization tower, use iron oxide or activated carbon adsorbent to remove H2S, control the H2S concentration to less than 10ppm, use condensation and molecular sieve adsorption to make the dew point ≤-60℃, and use adsorbents to selectively adsorb CO2 to obtain high-purity CH4 (>95%); S3: Separation of CH4 and CO2 by polymer membrane; S4: Mixed refrigerant liquefaction, using multi-stage compression and throttling expansion refrigeration to cool CH4 to below -162℃ for liquefaction; S5: Use double-layer vacuum insulated storage tanks to store LNG and use tank trucks for transportation.
[0007] Technical effects and advantages of the present invention: The present invention solves the environmental problems caused by livestock manure in farms and crop straw of farmers, while improving the energy utilization efficiency of organic waste, increasing the energy density of biogas, realizing energy cascade utilization through a heat exchange network, using modified molecular sieve adsorbents, combined with a pressure swing adsorption (PSA) process, to increase the CO2 removal rate to ≥99.5%, designing a mixed refrigerant ratio (such as a mixture of nitrogen, methane, and propane), and combining a two-stage expander to reduce the liquefaction energy consumption to ≤0.35 kWh / Nm³ LNG, and dynamically optimizing process parameters such as pressure, temperature, and flow rate through real-time monitoring and feedback adjustment based on the Internet of Things (IoT). BRIEF DESCRIPTION OF THE DRAWINGS
[0008] Figure 1 It is a system schematic diagram of the present invention. DETAILED DESCRIPTION
[0009] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.
[0010] As attached Figure 1As shown, the present invention provides a system for preparing liquefied natural gas from septic tank biogas, including a biogas generator, one side of the biogas generator is connected to a buffer tank through a pipeline, one side of the buffer tank is connected to a booster through a pipeline, one side of the booster is connected to a desulfurization tower through a pipeline, one side of the desulfurization tower is connected to a membrane separator through a pipeline, a carbon dioxide exhaust pipe is provided on the top of the membrane separator, the bottom of the membrane separator is connected to a cold box through a pipeline, one side of the cold box is provided with a refrigerant compressor, two pipelines are connected between the cold box and the refrigerant compressor, and one side of the cold box is connected to an LNG storage tank through a pipeline.
[0011] A method for preparing liquefied natural gas from biogas in a septic tank comprises the above-mentioned system for preparing liquefied natural gas from biogas in a septic tank and the following steps: S1: The closed septic tank is equipped with a gas exhaust pipe and a negative pressure extraction system, produces biogas through a biogas generator, and a buffer tank is set up to balance the fluctuation of biogas production; S2: Use dry desulfurization in a desulfurization tower, use iron oxide or activated carbon adsorbent to remove H2S, control the H2S concentration to less than 10ppm, use condensation and molecular sieve adsorption to make the dew point ≤-60℃, and use adsorbents to selectively adsorb CO2 to obtain high-purity CH4 (>95%); S3: Separation of CH4 and CO2 by polymer membrane; S4: Mixed refrigerant liquefaction, using multi-stage compression and throttling expansion refrigeration to cool CH4 to below -162℃ for liquefaction; S5: Use double-layer vacuum insulated storage tanks to store LNG and use tank trucks for transportation.
[0012] The closed septic tank of the present invention is equipped with a gas exhaust pipeline and a negative pressure exhaust system, produces biogas through a biogas generator, and is provided with a buffer tank to balance the fluctuation of biogas production. A desulfurization tower is used for dry desulfurization, and iron oxide or activated carbon adsorbent is used to remove H2S, and the H2S concentration is controlled to be less than 10ppm. Condensation and molecular sieve adsorption are used to make the dew point ≤-60℃, and the adsorbent is used to selectively adsorb CO2 to obtain high-purity CH4 (>95%). CH4 and CO2 are separated by a polymer membrane, the mixed refrigerant is liquefied, and multi-stage compression and throttling expansion refrigeration are used to cool CH4 to -1 The invention solves the environmental problems caused by livestock manure and farmers' crop straw by liquefying below 62℃, using double-layer vacuum insulated storage tanks to store LNG and using tank trucks for transportation. It also improves the energy utilization efficiency of organic waste and the energy density of biogas, and realizes energy cascade utilization through a heat exchange network. It uses modified molecular sieve adsorbents and combines the pressure swing adsorption (PSA) process to increase the CO2 removal rate to ≥99.5%. It designs a mixed refrigerant ratio (such as a mixture of nitrogen, methane, and propane) and combines it with a two-stage expander to reduce the liquefaction energy consumption to ≤0.35kWh / Nm³ LNG. It dynamically optimizes process parameters such as pressure, temperature, and flow rate by real-time monitoring and feedback adjustment based on the Internet of Things (IoT).
[0013] Finally: The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.
Claims
1. A system for preparing liquefied natural gas from biogas in a septic tank, comprising a biogas generator, characterized in that: One side of the biogas generator is connected to a buffer tank through a pipeline, one side of the buffer tank is connected to a booster through a pipeline, one side of the booster is connected to a desulfurization tower through a pipeline, one side of the desulfurization tower is connected to a membrane separator through a pipeline, a carbon dioxide exhaust pipe is provided on the top of the membrane separator, the bottom of the membrane separator is connected to a cold box through a pipeline, one side of the cold box is provided with a refrigerant compressor, two pipelines are connected between the cold box and the refrigerant compressor, and one side of the cold box is connected to an LNG storage tank through a pipeline.
2. A method for preparing liquefied natural gas from septic tank biogas, characterized in that: The system comprises the system for preparing liquefied natural gas from septic tank biogas as claimed in claim 1 and the following steps: S1: The closed septic tank is equipped with a gas exhaust pipe and a negative pressure extraction system, produces biogas through a biogas generator, and a buffer tank is set up to balance the fluctuation of biogas production; S2: Use dry desulfurization in a desulfurization tower, use iron oxide or activated carbon adsorbent to remove H2S, control the H2S concentration to less than 10ppm, use condensation and molecular sieve adsorption to make the dew point ≤-60℃, and use adsorbents to selectively adsorb CO2 to obtain high-purity CH4 (>95%); S3: Separation of CH4 and CO2 by polymer membrane; S4: Mixed refrigerant liquefaction, using multi-stage compression and throttling expansion refrigeration to cool CH4 to below -162℃ for liquefaction; S5: Use double-layer vacuum insulated storage tanks to store LNG and use tank trucks for transportation.