Method for improving cyclic utilization efficiency of nitrogen in acrylamide production system
By constructing a nitrogen-efficient utilization system that integrates graded utilization and energy regeneration, the problem of high nitrogen consumption in acrylamide production has been solved, achieving efficient resource recovery and energy regeneration, and reducing production costs and carbon emissions.
Patent Information
- Application Number
- CN202511494786.1
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-10-20
- Publication Date
- 2026-01-23
AI Technical Summary
The production of acrylamide involves high nitrogen consumption and serious resource waste, and the lack of graded utilization and energy regeneration leads to increased production costs and carbon emissions.
A three-in-one nitrogen high-efficiency utilization system integrating graded utilization, intelligent recycling, and energy regeneration is constructed. Nitrogen is recycled in stages through membrane separation and PSA unit, and energy is recovered by turbine expander. High-precision sensors and PLC control are used to achieve dynamic adjustment and establish closed-loop management.
It improves nitrogen recovery rate and energy utilization efficiency, reduces operating costs and carbon emissions, and achieves efficient closed-loop management of nitrogen resources.
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Figure CN121371931A_ABST
Abstract
Description
TECHNICAL FIELD
[0001] The present application belongs to the technical field of chemical production, and particularly relates to a method for improving the nitrogen recycling efficiency in an acrylamide production system, and is particularly suitable for a biological acrylamide continuous production line. BACKGROUND
[0002] Acrylamide production usually adopts biological catalysis, which uses nitrile hydratase to catalyze the hydration reaction of acrylonitrile. The process will accelerate the decline of the strain in the presence of oxygen, so nitrogen needs to be supplied to implement the process in an environment with as low oxygen content as possible to avoid enzyme activity reduction and side reactions. The main applications of nitrogen in the process include: 1. Oxygen content control of the reaction kettle: the oxygen content needs to be maintained below 0.5 ppm to ensure the stability of the catalytic reaction and the purity of the product.
[0003] 2. Material conveying: used for the pneumatic conveying system of acrylonitrile raw materials and acrylamide solution to prevent oxidation deterioration.
[0004] 3. Equipment purging: regular replacement of filters, storage tanks and pipelines to remove residual oxygen and impurities.
[0005] In the traditional process, the nitrogen utilization has the following defects: 1. Nitrogen is mostly used once, with a consumption of 150-200 Nm³ per ton of product, and there is no effective recovery mechanism, resulting in resource waste and rising operating costs. For example, on a 200,000-ton / year production line, the annual nitrogen consumption can exceed 30,000 Nm³.
[0006] 2. Different processes do not achieve graded management of nitrogen purity requirements. For example, the reaction kettle requires 99.999% high-purity nitrogen, while the purging operation only requires 99% purity, but high-purity nitrogen is used uniformly, causing excessive consumption.
[0007] 3. There is no tail gas recovery system in the process design: the residual nitrogen is directly discharged to the atmosphere during production, and the recovery rate is less than 5%.
[0008] 4. The flow control relies on manual valves or simple regulators, which lack precise control and often result in nitrogen overcharging waste (for example, the actual consumption exceeds the demand by 15-20%).
[0009] 5. The pressure energy in the nitrogen supply system is not effectively recovered: when the pressure difference decreases from 0.8 MPa to 0.3 MPa in the operation of the pressure reducing valve, the energy loss is more than 15%, increasing the power consumption of the compressor.
[0010] These defects not only increase the production cost (nitrogen gas procurement accounts for 10-15% of operating costs), but also increase carbon emissions, do not solve the problem of hierarchical utilization and energy regeneration, and are not conducive to sustainable development. SUMMARY
[0011] To solve the above technical problems, the purpose of the present application is to provide a method for improving the nitrogen recycling efficiency in an acrylamide production system, to build a three-in-one nitrogen efficient utilization system of hierarchical utilization-intelligent recycling-energy regeneration, and to realize closed-loop management of nitrogen resources.
[0012] The technical solution adopted by the present application to solve its technical problems is: a method for improving the nitrogen recycling efficiency in an acrylamide production system, comprising the following steps: (1) Based on the purity requirements of the application scenario, the nitrogen demand is divided into three levels: the first level nitrogen demand application scenario is the reaction kettle and the enzyme protection area; the second level nitrogen demand application scenario is the finished product tank protection; the third level nitrogen demand application scenario is the pipeline purge and pneumatic conveying; (2) According to the application scenario, an integrated recovery system is designed: A, a membrane separation unit is used to recover the exhaust gas of the reaction kettle, separate out high-purity nitrogen gas to meet the first level nitrogen demand, and the oxygen-rich tail gas is treated as waste gas or used for low-level demand; B, a PSA unit is used to recover the exhaust gas of the tank, and medium-purity nitrogen gas is produced to meet the second level nitrogen demand; C, the pipeline purge gas is concentrated into a third level buffer tank, pressurized by a centrifugal compressor and directly stored in the third level buffer tank for meeting the third level nitrogen demand; D, the nitrogen pressure difference energy is recovered by a turbine expander and converted into electrical energy for reuse; (3) The reaction kettle, the tank and the pipeline are respectively provided with high-precision oxygen content sensors for real-time monitoring of O2 concentration, the oxygen content sensor is interlocked with the PLC controller to realize dynamic PID adjustment, and when the O2 concentration of any monitoring point exceeds the set value of 0.3ppm, the system automatically triggers the high-pressure nitrogen emergency supplement unit to realize interlocking protection.
[0013] Further, the first level nitrogen demand requires a purity of ≥99.999%, the second level nitrogen demand requires a purity of ≥99.9%, and the third level nitrogen demand requires a purity of ≥99%.
[0014] Further, in step (2), the membrane separation unit uses a membrane separator, a first level buffer tank and a gas-water separator are sequentially arranged between the reaction kettle and the membrane separator, the reaction kettle exhaust gas enters the gas-water separator after the first level buffer tank, and the gas-water separator is pretreated before entering the membrane separator for treatment, and the separated high-purity nitrogen gas is returned to the first level buffer tank.
[0015] Further, the step (2) adopts a two-bed structure PSA system, the adsorbent is carbon molecular sieve, the adsorption pressure is 0.4-0.8 MPa, the regeneration cycle is less than or equal to 120 seconds, the exhaust of the storage tank is concentrated into a secondary buffer tank, and the medium-purity nitrogen gas is obtained after the pressure swing adsorption treatment of the molecular sieve of the PSA system, and is recovered to the secondary buffer tank, and the low-pressure waste gas is discharged.
[0016] Further, the volume of the buffer tank is designed based on the formula: the first buffer tank V1=0.2Q_{1max}, the second buffer tank V2=0.15Q_{2max}, and the third buffer tank V3=0.1Q_{3max}, wherein Q is the maximum flow of each stage.
[0017] Further, the first buffer tank is made of stainless steel, and the second buffer tank and the third buffer tank are made of carbon steel. The buffer tank is provided with a pressure sensor and an automatic pressure relief valve to ensure that the pressure is stable at 0.3-0.5 MPa, and to avoid overcharging or undercharging.
[0018] Further, the membrane separator selects a hollow fiber membrane module, the operating pressure range is 0.5-1.2 MPa, the oxygen concentration on the permeation side is greater than or equal to 28%, the separation factor aO2 / N2 is greater than or equal to 6.0, and the recovery rate can reach more than 85%.
[0019] Further, the turbine expander in the step (2) is installed in the nitrogen main pipe, the turbine expander drives the generator to generate electricity by using the pressure difference, the turbine expander is coaxially connected with the nitrogen compressor, and the generated electricity is directly used to drive the compressor.
[0020] Further, the high-precision oxygen content sensor in the step (3) can be an infrared sensor or an electrochemical sensor.
[0021] Further, the dynamic PID adjustment in the step (3) adopts a PID control algorithm to dynamically adjust the opening degree of the nitrogen injection valve, and the algorithm is based on the deviation between the set value and the measured value to calculate the output.
[0022] Wherein e(t) is the error (set value-measured value), K p , K i , and K d are tuning parameters.
[0023] The present application has the following beneficial effects: 1. Different types of tail gas are classified and recycled by the integrated recycling system, the membrane-PSA coupling recycling technology is adopted, the membrane separation is used for high-flow and high-purity recovery, the PSA is used for medium and low-purity demand, the overall recycling efficiency is improved, and the energy consumption is reduced.
[0024] 2、The present application adds a turbine expander in the nitrogen main pipe, uses high-pressure nitrogen to drive the generator to generate electricity when reducing pressure, and directly feeds back the motor of the nitrogen compressor to recover energy for reuse, thereby reducing external power consumption.
[0025] 3、The present application constructs a nitrogen efficient utilization system with three-in-one of hierarchical utilization-intelligent recycling-energy regeneration, realizes efficient closed-loop management of nitrogen resources, and can save 2.8 million yuan of annual operating cost. BRIEF DESCRIPTION OF DRAWINGS
[0026] Figure 1 It is a schematic diagram for reaction kettle exhaust nitrogen recycling of the present application.
[0027] Figure 2 It is a schematic diagram for storage tank exhaust nitrogen recycling of the present application.
[0028] Figure 3 It is a schematic diagram for purge gas nitrogen recycling of the present application.
[0029] In the figure, 1 is a primary buffer tank, 2 is a gas-water separator, 3 is a membrane separator, 4 is a primary buffer tank, 5 is a secondary buffer tank, 6 is an adsorption tower, 7 is a secondary buffer tank, 8 is a tertiary buffer tank, 9 is a centrifugal compressor, and 10 is a tertiary buffer tank. DETAILED DESCRIPTION
[0030] The following is a specific embodiment of the present application, which further describes the technical solutions of the present application, but the protection scope of the present application is not limited to these embodiments. Any changes or equivalent replacements without departing from the concept of the present application are included in the protection scope of the present application.
[0031] A method for improving the nitrogen recycling efficiency in an acrylamide production system, comprising the following steps: (1) Based on the purity requirements of application scenarios, the nitrogen demand is divided into three levels: the primary nitrogen demand application scenario is the reaction kettle and the enzyme protection area; the secondary nitrogen demand application scenario is the finished product storage tank protection; and the tertiary nitrogen demand application scenario is the pipeline purge and pneumatic conveying. Specifically, as shown in Table 1.
[0032] Table 1: Nitrogen demand level requirement table based on application scenarios Nitrogen demand level Application scenario Purity requirement Allowed impurities Typical flow range Primary Reaction kettle, enzyme protection zone ≥99.999% O2 < 0.5 ppm 50-100 Nm³ / h Secondary Finished product tank protection ≥99.9% O2 < 100 ppm 30-60 Nm³ / h Tertiary Pipeline purging, pneumatic conveying ≥99% O2 < 1% 20-40 Nm³ / h (2) According to the application scenario, an integrated recycling system is designed: A, adopt a membrane separation unit to recover the reaction kettle exhaust (containing more than 95% nitrogen), separate out high-purity nitrogen (≥99.999%) to meet the primary nitrogen demand, and the oxygen-rich tail gas (oxygen concentration >5%) is treated as waste gas or used for low-level demand.
[0033] For example Figure 1As shown, the membrane separation unit adopts a membrane separator 3, and a first-stage buffer tank 1 and a gas-water separator are sequentially arranged between the reaction kettle and the membrane separator 3; the exhaust gas of the reaction kettle enters the gas-water separator 2 after passing through the first-stage buffer tank 1, is pretreated by the gas-water separator 2, and then is treated by the membrane separator 3, so that high-purity nitrogen gas is separated and returned to the first-stage buffer tank 4.
[0034] The membrane separator 3 selects a hollow fiber membrane assembly, the operating pressure range is 0.5-1.2 MPa, the oxygen concentration on the permeation side is greater than or equal to 28%, the separation factor aO2 / N2 is greater than or equal to 6.0, and the recovery rate can reach more than 85%.
[0035] In the preferred embodiment of the application, the membrane separator 3 adopts PRISM series, and specifically, PRISM PA-1020 type can be selected, the processing capacity is 200 Nm³ / h, the operating pressure is 1.0 MPa, and the membrane area is 20 m².
[0036] B, the exhaust gas of the storage tank is recovered by the PSA unit to produce medium-purity nitrogen (≥99.9%) for meeting the secondary nitrogen demand.
[0037] As shown in Figure 2 , the PSA unit adopts a two-bed structure PSA system with a double-tower structure, the adsorption tower 6 has a diameter of 0.5 m and a height of 2 m, the adsorbent is carbon molecular sieve, the adsorption pressure is 0.4-0.8 MPa, the regeneration period is less than or equal to 120 seconds, the exhaust gas of the storage tank is concentrated into the second-stage buffer tank 5, and medium-purity nitrogen is obtained after the exhaust gas is treated by the pressure swing adsorption of the molecular sieve of the adsorption tower 6 of the PSA system, and then the medium-purity nitrogen is recovered to the second-stage buffer tank 7, and low-pressure waste gas is discharged.
[0038] C, as shown in Figure 3 , the pipeline purge gas is concentrated into the third-stage buffer tank 8, is pressurized by the centrifugal compressor 9, and then is directly stored in the third-stage buffer tank 10 for meeting the tertiary nitrogen demand.
[0039] The first-stage buffer tank 4 is made of stainless steel, and the second-stage buffer tank 7 and the third-stage buffer tank 10 are made of carbon steel. The buffer tanks are provided with pressure sensors and automatic pressure relief valves to ensure that the pressure is stably kept at 0.3-0.5 MPa, so as to avoid overfilling or underfilling. The maximum flow (Q_max) of each stage is determined through process analysis, and the volume of the buffer tank is designed based on the formula: V1=0.2Q_{1max} for the first-stage buffer tank, V2=0.15Q_{2max} for the second-stage buffer tank, and V3=0.1Q_{3max} for the third-stage buffer tank, wherein Q is the maximum flow of each stage.
[0040] D, the nitrogen pressure difference energy is recovered by a turbine expander to be converted into electric energy for reuse.
[0041] The turbine expander is installed in a nitrogen main pipe, when high pressure nitrogen (0.8 MPa) is decompressed, the turbine expander drives a generator to generate electricity by using pressure difference (decreased to 0.3 MPa), and the power generation efficiency is greater than or equal to 65%. Energy recycling: the generated electricity is directly fed back to the motor of the nitrogen centrifugal compressor for energy recycling, thereby reducing external power consumption, for example, under the pressure difference of 0.8 MPa, the single machine power output can reach 20 kW.
[0042] In the preferred embodiment of the present application, the turbine expander is model TE-100, the input pressure is 0.8 MPa, the output pressure is 0.3 MPa, the power generation power is 18.5 kW, and the turbine expander is coaxially connected with the centrifugal compressor, so that the recovered energy directly drives the centrifugal compressor, thereby reducing external power input.
[0043] (3) The reaction kettle, the storage tank and the pipeline are respectively provided with high-precision oxygen content sensors for real-time monitoring of O2 concentration, the oxygen content sensors are interlocked with a PLC controller to realize dynamic PID adjustment, when the O2 concentration of any monitoring point exceeds the set value of 0.3 ppm, the system automatically triggers a high-pressure nitrogen emergency supplement unit to realize interlocking protection and ensure process safety.
[0044] The high-precision oxygen content sensor can be an infrared sensor or an electrochemical sensor. The PLC controller is selected to be, for example, a Siemens S7-1500 integrated with a PID algorithm module.
[0045] The dynamic PID adjustment adopts a PID control algorithm to dynamically adjust the opening degree of the nitrogen injection valve, and the algorithm calculates the output based on the deviation between the set value and the measured value:
[0046] Wherein e(t) is the error (set value-measured value), K p , K i , K d are tuning parameters.
[0047] After the method of the present application is implemented in a 200,000 tons / year production line, the key indicators are compared as shown in Table 2.
[0048] Table 2 Comparison table of production indicators before and after the method of the present application is modified Index Before transformation After transformation Nitrogen unit consumption 160 Nm³ / t 105 Nm³ / t Recovery rate <5% ≥35% Electricity recovery 0 kWh / year 148,000 kWh / year Oxygen exceeding standard times 3 times / month 0.2 times / month Operating cost savings About 2.8 million yuan / year The present application is not limited to the above-mentioned embodiments, and anyone should know that any structural changes made under the inspiration of the present application, any technical solutions with the same or similar to the present application, all fall within the protection scope of the present application.
[0049] The technical, shape and structure parts not described in detail in the present application are all known technologies.
Claims
1. A method for improving the efficiency of nitrogen recycling in an acrylamide production system, characterized by, Comprise the following steps: (1) Based on the purity requirements of the application scene nitrogen demand is divided into three levels: the first level of nitrogen demand application scene for the reaction kettle, enzyme protection area; secondary nitrogen demand application scene for product tank protection; three level nitrogen demand application scene for pipeline purge, pneumatic conveying; (2) According to the application scene design integrated recovery system: A, using membrane separation unit recovery reaction kettle exhaust, separation of high purity nitrogen for meet the first level of nitrogen demand, oxygen rich tail gas as waste gas treatment or for low level demand; B, using PSA unit recovery tank exhaust, output of medium pure nitrogen to meet the secondary nitrogen demand; C, pipeline purge gas into the three level buffer tank, by centrifugal compressor after pressurization is directly stored in three level cache tank, used to meet the three level nitrogen demand; D, through the turbine expander recovery nitrogen pressure difference energy, converted into electrical energy for reuse; (3) Reaction kettle, tank and pipeline are respectively installed with high precision oxygen content sensor, for real time monitoring O2 concentration, oxygen content sensor and PLC controller interlock, realize dynamic PID regulation, when any monitoring point O2 concentration exceeds the set value 0.3ppm, the system automatically trigger high pressure nitrogen emergency supplement unit, realize interlock protection.
2. The method for improving nitrogen recycling efficiency in an acrylamide production system as described in claim 1, characterized in that, The first level of nitrogen demand requires purity ≥ 99.999%, secondary nitrogen demand requires purity ≥ 99.9%, three level nitrogen demand requires purity ≥ 99%.
3. The method of claim 1, wherein the method is characterized by, The membrane separation unit in step (2) uses a membrane separator, a first level buffer tank and a gas-water separator are sequentially arranged between the reaction kettle and the membrane separator, the reaction kettle exhaust enters the gas-water separator after the first level buffer tank, and the high-purity nitrogen separated by the membrane separator is returned to the first level buffer tank after being pretreated by the gas-water separator.
4. The method of claim 3, wherein the acrylamide production system is a system for producing acrylamide by polymerization of an aqueous solution of acrolein and ammonia. The PSA unit in step (2) uses a two-bed structure PSA system, the adsorbent is carbon molecular sieve, the adsorption pressure is 0.4-0.8 MPa, the regeneration period is ≤120 seconds, the tank exhaust is concentrated into a secondary buffer tank, and the medium-purity nitrogen obtained by the PSA system molecular sieve pressure swing adsorption treatment is recovered to the secondary buffer tank, and the low-pressure waste gas is discharged.
5. The method of claim 4, wherein the method is characterized by, The cache tank volume is designed based on the formula: first level cache tank V1=0.2Q_{1max}, second level cache tank V2=0.15Q_{2max}, and third level cache tank V3=0.1Q_{3max}, wherein Q is the maximum flow rate of each level.
6. The method of claim 3, wherein the method is characterized by, The membrane separator selects a hollow fiber membrane module, the operating pressure range is 0.5-1.2 MPa, the oxygen concentration on the permeation side is ≥28%, and the separation factor αO2 / N2 is ≥6.
0.
7. The method of improving nitrogen recycle efficiency in an acrylamide production system of claim 1, wherein, The turbine expander in step (2) is installed in the nitrogen main pipe, the turbine expander drives the generator to generate electricity, the turbine expander is coaxially connected with the nitrogen compressor, and the generated electricity is directly used to drive the compressor.
8. The method of claim 1, wherein the method is characterized by, In step (3), the dynamic PID regulation adopts a PID control algorithm to dynamically adjust the opening degree of the nitrogen injection valve, and the algorithm calculates the output based on the deviation between the set value and the measured value: ； where e(t) is the error (setpoint - measured value), K p , K i , K d is the tuning parameter.