Device and method for extracting ethanol from fermentation tail gas

Abstract

The present invention relates to a device and method for extracting ethanol from fermentation tail gas, and belongs to the technical field of renewable energy preparation. The device of the present invention is designed with multiple membrane modules, and the number of modules connected in series can be selected according to demand. In the process of producing ethanol by biomass fermentation, the fermentation tail gas generated is controlled by a gas booster pump to control its pressure, enters the device, is processed by the membrane module, and the gas on the interception side of the membrane module is processed to meet the discharge standard or directly used by downstream processes or users. On the permeation side, the condensable gas is condensed into liquid for collection by a condenser, and the non-condensable gas is pressurized by the gas booster pump and continues to circulate in the permeation side pipeline or is discharged in proportion, so as to reduce the permeation of the non-condensable gas through the membrane, and make the gas that permeates the membrane module quickly leave the outlet of the membrane module, and increase the separation driving force of the condensable components on both sides of the membrane.

Description

Technical Field

[0001] The present invention relates to a device and method for extracting ethanol from fermentation tail gas, belonging to the technical field of renewable energy preparation. Background Art

[0002] With the development of the economy and the continuous growth of the population, the demand for energy increases. Although traditional fossil fuels (coal, oil, natural gas) are the main energy sources globally, their sustainability is low and they cannot meet the needs of social development. Renewable energy can not only achieve energy self-sufficiency but also reduce greenhouse gas emissions, thereby slowing down the progress of climate change.

[0003] Bioethanol, as a renewable clean energy, is an important way to reduce carbon emissions and has been widely used in many aspects. During the process of biomass fermentation to produce ethanol, the generated fermentation tail gas contains a large amount of carbon dioxide and organic gases mainly composed of trace ethanol (0.1 - 2 vol%). Efficient recovery and utilization of a small amount of ethanol in the fermentation tail gas. This research work will provide an important basis for the development and application of VOCs treatment technologies.

[0004] According to whether VOCs treatment has recycling value, we divide it into two major treatment methods: recycling technology and destruction technology. Among them, recycling treatment mainly utilizes the physical properties of VOCs (such as differences in boiling point, solubility, diffusion rate), and through physical processes such as absorption, adsorption, condensation, or membrane separation technology, operations of separating and recycling volatile organic compounds are carried out; destruction treatment mainly utilizes processes such as incineration, biodegradation, catalysis, and plasma technology to decompose volatile organic compounds into harmless or non-volatile small molecule substances through chemical processes.

[0005] Membrane separation has the following advantages: (1) high selectivity and low separation efficiency; (2) simple operation process; (3) does not require complex chemical reactions and can directly obtain condensable VOCs gas; (4) low requirements for operating temperature and pressure, low requirements for equipment, and does not introduce a third organic component; (5) more importantly, it is extremely easy to couple with other technologies.

[0006] Vapor permeation separation, as a new type of membrane separation technology, is based on the principle of solution-diffusion and uses the differences in solubility and diffusion rate of the VOCs and non-condensable gas mixture in the membrane to achieve the separation process. It has been applied to the recovery of high-value solvents, liquefied petroleum gas, methane enrichment (CO 2 removal), removal of volatile organic compounds, etc. And it has the advantages of good separation performance, clean feed, low energy consumption, and large operation flexibility. Combining vapor permeation membrane separation with condensation technology has a broader application prospect in the field of fuel ethanol production and VOCs separation and recovery. Summary of the Invention

[0007] The technical problem to be solved by the present invention is to overcome the deficiencies of the prior art and propose a device and method for extracting ethanol from fermentation tail gas.

[0008] The technical solution of the present invention is as follows:

[0009] A method for extracting ethanol from fermentation tail gas, the steps of which include:

[0010] In the first step, during the process of producing ethanol by biomass fermentation, the generated fermentation tail gas is transported into a membrane module. The gas permeating through the membrane is the permeate gas, and the retained retentate gas is treated to meet the standards and directly discharged or supplied to downstream processes or users.

[0011] In the second step, the permeate gas in the first step is condensed through a condenser tube, and the condensate is recovered. At the same time, the non-condensable gas is circulated through the pipeline on the permeate side or discharged in proportion, completing the operation of extracting ethanol from the fermentation tail gas.

[0012] The membrane module is a spiral wound membrane module, a hollow fiber module, or a tubular membrane module. The membrane in the membrane module is a polymer membrane with preferential organic matter permeation, a mixed matrix membrane with preferential organic matter permeation, or a polymer-inorganic matrix composite membrane with preferential organic matter permeation.

[0013] The polymer membrane is a polydimethylsiloxane membrane; the preparation method of the mixed matrix membrane is: using inorganic nanomaterials as dispersed particles and filling them into the polymer continuous phase matrix to combine the inorganic filler with the polymer.

[0014] The polymer is polydimethylsiloxane;

[0015] The preparation method of the polymer-inorganic matrix composite membrane is: using an inorganic ultrafiltration membrane as the matrix and coating polydimethylsiloxane or the material for preparing the above-mentioned mixed matrix membrane on the membrane surface.

[0016] The ethanol concentration is tested by installing an ethanol concentration sensor on the pipeline between the membrane module and the condenser tube. At the same time, a gas chromatograph and a flow meter are installed to monitor and calculate the permeability and selectivity in order to test the membrane performance.

[0017] When the retentate gas in the fermentation tail gas is detected to meet the standards, it is directly discharged;

[0018] After the fermentation tail gas is mixed evenly, it enters the membrane module at the required pressure;

[0019] The number of membrane modules is n, and the membrane modules are connected in series; when the tail gas treatment volume is large, the membrane modules can also be connected in parallel.

[0020] When the non-condensable gas passes through the permeate side circulation pipeline and re-enters the condenser, the non-condensable gas is pressurized and circulates in the permeate side circulation pipeline.

[0021] The device includes a fermentation tank, a gas booster pump, a membrane module, a condenser and a recovery tank;

[0022] The fermentation tank is connected to the gas booster pump through a pipeline;

[0023] The gas booster pump is connected to the membrane module through a pipeline;

[0024] The permeate side interface of the membrane module is connected to the inlet of the condenser through a pipeline;

[0025] The condensate outlet of the condenser is connected to the recovery tank through a pipeline;

[0026] The non-condensable gas outlet of the condenser is connected to the inlet of the condenser through a circulation pipeline;

[0027] After the fermentation tail gas is mixed evenly, it is pressurized and transported to the membrane module according to the required pressure. The permeate gas in the fermentation tail gas enters the condenser, the condensate in the condenser enters the recovery tank, and the non-condensable gas re-enters the permeate side pipeline through the circulation pipeline for circulation or is discharged proportionally.

[0028] When the retentate gas in the fermentation tail gas meets the detection standard, it is directly discharged or supplied to downstream processes or users.

[0029] After the fermentation tail gas is mixed evenly, it is pressurized and transported to the membrane module according to the required pressure

[0030] The number of the membrane modules is n, and the membrane modules are connected in series; when the tail gas treatment volume is large, the membrane modules can also be connected in parallel.

[0031] When the non-condensable gas re-enters the condenser through the circulation pipeline, the non-condensable gas is pressurized by the gas booster pump and mixed through the buffer tank and continues to circulate in the permeate side pipeline or is discharged proportionally.

[0032] Beneficial effects

[0033] (1) The device of the present invention is designed with four membrane modules, and the number of series connections can be selected according to requirements. The gas booster pump cooperates with the gas buffer tank to pressurize the fermentation tail gas to control the pressure of the gas entering the membrane module while ensuring the airtightness of the device. The intercepted gas is designed with a circulation pipeline for circulation. The condensable gas is condensed into a liquid and collected by the condenser on the permeate side. The non-condensable gas continues to circulate in the pipeline after being pressurized by the gas booster pump, so that the gas passing through the membrane module quickly leaves the membrane module outlet, increasing the driving force;

[0034] (2) The device of the present invention measures the gas concentrations on both sides of the membrane module and the gas concentration after condensation in real time through gas chromatography and ethanol concentration sensors. By designing the pipeline and using valves to switch the paths, the gas concentration at the outlet of each membrane module can be measured, thereby obtaining the separation performance of each membrane module.

[0035] (3) The device of the present invention can be applied not only to the ethanol / CO 2 system, but also to the separation and recovery of VOCs / non-condensable gas systems. This method and device can be used in both cases.

[0036] (4) The device of the present invention builds a non-condensable gas circulation pipeline to improve the driving force of condensable gases. On the other hand, due to the circulation of non-condensable gases, the penetration of non-condensable gases can be reduced. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 It is a schematic diagram of the composition of the device of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0038] The present invention will be further described below with reference to the drawings and embodiments.

[0039] A device for extracting ethanol from fermentation tail gas, which includes a fermentation tank, a gas booster pump, four groups of membrane modules, a condenser and a recovery tank;

[0040] The fermentation tail gas tank is connected to the gas booster pump through a pipeline;

[0041] The gas booster pump is connected to the four membrane modules through a pipeline, and the membrane modules are connected in series;

[0042] The permeate side interface of the membrane module is connected to the inlet of the condenser through a pipeline;

[0043] The condensate outlet of the condenser is connected to the recovery tank through a pipeline;

[0044] The non-condensable gas outlet of the condenser is connected to the inlet of the condenser through a circulation pipeline;

[0045] The fermentation tail gas is pressurized and transported to the membrane module according to the required pressure. The permeate gas in the fermentation tail gas enters the condenser, the condensate in the condenser enters the recovery tank, and the non-condensable gas enters the permeate side pipeline again through the circulation pipeline for circulation or is discharged proportionally.

[0046] When the retentate gas in the fermentation tail gas meets the detection standard, it is directly discharged or supplied to downstream processes or users.

[0047] After the fermentation tail gas is mixed evenly, it is pressurized and transported to the membrane module according to the required pressure

[0048] During the process that the non-condensable gas re-enters the condenser through the circulation pipeline, the non-condensable gas is powered by a gas delivery pump and mixed through a buffer tank, and then continues to circulate in the permeate-side pipeline or is discharged proportionally.

[0049] A method for extracting ethanol from fermentation tail gas using the above device, the steps of the method include:

[0050] First step, permeate the fermentation tail gas through four groups of membrane modules, and the membrane modules are connected in series;

[0051] Second step, condense the permeate gas in the first step through a condenser, then recover the condensate, and at the same time, re-condense the non-condensable gas through the permeate-side circulation pipeline and the permeate gas back to the condenser to complete the operation of extracting ethanol from the fermentation tail gas.

[0052] The membrane module described is a spiral-wound membrane module, and the membrane in the membrane module is a mixed matrix membrane;

[0053] Install an ethanol concentration sensor on the pipeline between the membrane module and the condenser to test the ethanol concentration. At the same time, install a gas chromatograph and a flow meter to monitor and calculate the permeability and selectivity in order to test the membrane performance.

[0054] The retentate gas in the fermentation tail gas enters the fermentation tail gas generation tank through the return pipeline or, when the detection meets the standard, is directly discharged or supplied to downstream processes or users.

[0055] The fermentation tail gas is pressurized and transported to the membrane module according to the required pressure; during the process that the non-condensable gas re-enters the condenser through the circulation pipeline, the non-condensable gas is powered by a gas delivery pump and mixed through a buffer tank, and then continues to circulate in the permeate-side pipeline or is discharged proportionally. Select a suitable membrane material, cut it to a length matching the membrane module, and assemble it;

[0056] Check the airtightness of the membrane module. Turn on the instrument power supply and preheat instruments such as the mass flow meter for 15 minutes. After confirming that the set value of the mass flow meter is 0, open the main valve of the raw material gas and perform a pressure reduction operation to reduce damage to the pipeline, close HV-3, HV-5, HV-7; open HV-4, HV-6, HV-8; adjust the three-way valves TWW-3, TWW-4, TWW-5, TWW-6 so that the gas flows to the soap bubble flow meter. Set the raw material gas flow rate to 50 ml / min, suck an appropriate amount of soapy water with a dropper and drop it at the joint of the membrane module. If no soap bubbles are generated, it means the membrane module has good airtightness. After the inspection, set the raw material gas flow rate to zero.

[0057] Specific steps of the experimental operation:

[0058] After determining that the set value of the FM mass flowmeter is 0, turn on the switch of the raw material gas and adjust the corresponding pressure reducing valve to keep the pressure at an appropriate value (<4 MPa), and introduce it into the 15L buffer tank to make the mixture more uniform;

[0059] Open the raw material gas inlet valve TWV-1, open the membrane module rejection side valves HV-3, HV-5, HV-7; open the membrane module inlet valves HV-2, HV-4, HV-6, HV-8; set the raw material gas feed flow value and determine the set value of the FM mass flowmeter;

[0060] Adjust the set values of the feed temperature and pressure as needed. At the same time, according to the requirements of detecting the mixed system, turn on the gas chromatograph and its carrier gas, set the chromatograph parameters, and wait until the temperature and pressure of the membrane module reach the predetermined values and the entire membrane module system is stable;

[0061] ① The gas in the raw material gas generation tank flows through pipeline A, flows to gas booster pump A and the 15L buffer tank, and adjust the readings of pressure gauge PI1 and temperature sensor T1 to meet the experimental requirements. The gas flowing out of the buffer tank (more evenly mixed) flows to three-way ball valve TWV-1, and adjust the direction of three-way ball valve TWV-1 so that the gas flows to the pipeline of the feed gas gas concentration detection and analysis device (ethanol concentration sensor, flowmeter, gas chromatograph) (Use a stopwatch to record the time it takes for the bubbles in the soap film flowmeter to move from the 0 mL scale to the 10 mL scale, and calculate the flow rate (mL / min). Measure the flow rate every 2-3 minutes. If the flow rate values measured three times in a row are the same, it means that the stable state has been reached),

[0062] Thereby judging that the system we need to separate has reached a stable state;

[0063] ② After the raw material gas enters and reaches a stable state, adjust the direction of three-way ball valve TWV-1 again, and it flows to flowmeter FM. Set the required flow rate reading. In order to only evaluate the separation performance of one membrane module, the gas flows through pipeline B to membrane module 1. Close two-way valve HV-4 and open two-way valve HV-3 so that the gas flows along the pipeline to three-way valve TWV-2. In order to measure the upstream rejection side gas concentration and flow rate, adjust the direction of three-way valve TWV-2, and it flows along pipeline K to the gas chromatograph and flowmeter. The test method is the same as ①; conversely, adjust the direction of three-way valve TWV-2 so that the gas passes through three-way valve TWV-10. By adjusting the direction of this valve, the gas can also be discharged or flow back to the raw material gas tank;

[0064] ③ Similarly, if you want to detect the rejection side gas concentration and flow rate after the gas passes through two, three or even four membrane modules, close the two-way valves (HV-6, HV-8) leading to the next pipeline, open the corresponding two-way valves (HV-5, HV-7) on the rejection side, and adjust the direction of three-way valve TWV-2,

[0065] Along pipeline K, direct the trapped gas to flow towards the gas chromatograph and the flowmeter. The testing method is the same as that in ①. ④ When calculating the permeability and selectivity of the gas flowing through a membrane module, adjust the pipe orifice of the three-way ball valve TWV-3 of membrane module 1, and direct it to flow towards the ethanol concentration sensor, the flowmeter, and the gas chromatograph through pipelines L and M to detect its flow rate and concentration. The testing method is the same as that in 1, and calculate the permeability and selectivity.

[0066] ⑤ Similarly, when calculating the permeability and selectivity after flowing through two, three, or even four membrane modules, adjust the pipe orifice of the three-way ball valve of the last membrane module, and direct it to flow towards the ethanol concentration sensor, the flowmeter, and the gas chromatograph through pipelines L and M to detect its flow rate and concentration. The testing method is the same as that in 1, and calculate the permeability and selectivity.

[0067] ⑥ To measure how much ethanol can be condensed by the device after passing through one membrane module, adjust the pipe orifice of the three-way ball valve TWV-3 of membrane module 1, and direct it to flow towards the condenser through pipelines O and P. To determine the components of the mixer after condensation, adjust the direction of the three-way ball valve TWV-7 to flow towards the flowmeter and the gas chromatograph for detection. If it is necessary to recycle the condensed gas, adjust the direction of the three-way ball valve TWV-7 to make the gas circulate through the gas booster pump B and the buffer tank B.

[0068] ⑦ Similarly, to measure how much ethanol can be condensed by the device when the number of membrane modules is greater than or equal to 2, change the gas outlet direction by adjusting the three-way ball valves (TWV-3, TWV-4 / TWV-5 / TWV-6) together, and let the gas on the permeate side flow towards the condenser through pipelines O and P. To determine the components of the mixer after condensation, adjust the direction of the three-way ball valve TWV-7 to flow towards the flowmeter and the gas chromatograph for detection. If it is necessary to recycle the condensed gas, adjust the direction of the three-way ball valve TWV-7 to make the gas circulate through the gas booster pump B and the buffer tank B.

[0069] The experiment is over. Close the main valve of the raw material gas, turn off the heating power supply, reset the mass flowmeter, and observe whether there is any abnormality in the reading of the pressure gauge. If there is no abnormality, then turn off the instrument power supply. After the temperature of the gas chromatograph drops to a certain specified value, turn off the computer, the chromatograph, and the carrier gas.

[0070] This method and device can be applied not only to the ethanol / CO 2 This system can be used as a reference for the recovery of low-concentration organic vapors in other systems.

Claims

1. A method for extracting ethanol from fermentation tail gas, characterized in that The steps of the method include: In the first step, during the biomass fermentation process to produce ethanol, the fermentation tail gas generated is transported into the membrane module. The gas that permeates through the membrane is the permeate gas, and the retained retentate gas is treated to meet the standards and directly discharged or used by downstream processes or users; In the second step, the permeate gas in the first step is condensed through a condenser, the condensate is recovered, and the non-condensable gas is circulated through a pipeline on the permeate side or discharged in proportion, thereby completing the operation of extracting ethanol from the fermentation tail gas; The membrane assembly is a rolled membrane assembly, a hollow fiber assembly and a tubular membrane assembly; The membrane in the membrane assembly is a polymer membrane that allows organic matter to preferentially permeate, a mixed matrix membrane that allows organic matter to preferentially permeate, or a polymer-inorganic matrix composite membrane that allows organic matter to preferentially permeate; The polymer film is a polydimethylsiloxane film; The preparation method of the mixed matrix membrane is as follows: using inorganic nanomaterials as dispersed particles, filling them into a polymer continuous phase matrix, and combining the inorganic filler with the polymer; The polymer is polydimethylsiloxane; The preparation method of the polymer-inorganic matrix composite membrane is as follows: using an inorganic ultrafiltration membrane as a matrix, coating polydimethylsiloxane on the membrane surface; The ethanol concentration is tested by installing an ethanol concentration sensor on the pipeline between the membrane module and the condenser. In order to test the membrane performance, a gas chromatograph and a flow meter are also installed to monitor and calculate the permeability and selectivity. The retentate gas in the fermentation tail gas is directly discharged when the detection meets the standards; The number of the membrane modules is n, and each membrane module is connected in series; The non-condensable gas enters the condenser again through the permeate side circulation pipeline together with the permeate gas, and the non-condensable gas is powered by the gas delivery pump and keeps circulating in the permeate side circulation pipeline; A device for implementing the method of extracting ethanol from fermentation tail gas, comprising a fermentation tank, a gas booster pump, a membrane module, a condenser and a recovery tank; The fermentation tank is connected to the gas booster pump through a pipeline; The gas booster pump is connected to the membrane assembly through a pipeline; The membrane module permeation measurement interface is connected to the inlet of the condenser through a pipeline; The condensate outlet of the condenser is connected to the recovery tank through a pipeline; The non-condensable gas outlet of the condenser is connected to the inlet of the condenser through a circulation pipeline; After the fermentation tail gas is evenly mixed, it is pressurized and transported to the membrane module at the required pressure. The permeate gas in the fermentation tail gas enters the condenser, and the condensate in the condenser enters the recovery tank. The non-condensable gas enters the permeate side pipeline again through the circulation pipeline for circulation or discharge in proportion.

Images