How to pretreat dusty and water containing tail gas using membrane method? Key points for filtering, defogging, and temperature control

How to pretreat dusty and water containing tail gas using membrane method? Direct answer: The core of membrane pretreatment is to first solve the two things that membranes are afraid of - solid particles and liquid water. Dust in the intake will stick to the surface of the membrane, and water will damage the separation layer. Therefore, pre-treatment uses wire mesh dehazing and multi-stage precision filtration to remove solvent droplets, material dust, aerosols, and free moisture carried by the airflow. Combined with temperature and humidity control, it protects the rear membrane components. Pre treated exhaust gas has controllable membrane fouling rate and significantly longer lifespan; Cutting corners in pre-processing and quickly deactivating the film core. The judgment criteria should be based on the cleanliness index of the membrane gas, rather than on intuition.

Why do we need to reprocess

Membrane separation relies on the selective permeation of organic vapors through polymer membranes. Once the membrane surface is covered by impurities or the pores are blocked, both flux and selectivity decrease, and some damage is irreversible. The exhaust gas containing dust and water directly enters the membrane, and the dust and droplets adhere to the surface of the membrane element, forming a pollution layer and blocking the pores. In mild cases, it is difficult to clean and restore, and in severe cases, the entire membrane is scrapped. Preprocessing is to intercept these impurities before entering the membrane, which is a prerequisite for the long-term stability of the membrane method. The investment should be included in the overall account, not just the membrane section itself being cheap.

How to allocate graded interception

Pre treatment is carried out step by step according to the particle size of impurities: first, a wire mesh demister is used to remove larger droplets and mist, and then a multi-stage precision filter is used to intercept small dust, colloidal impurities, and aerosols. If necessary, a drying and filtering unit is added to control the moisture content. The advantage of graded interception is that each stage has a section of pipe, and the front-end coarse filter protects the back-end fine filter, resulting in a longer lifespan and more cost-effective replacement of the fine filter. For working conditions where dust and mist droplets are clearly carried, a graded structure can gradually remove impurities according to particle size, effectively protecting the back-end compressor, heat exchanger, and membrane components, and extending the service life of the entire device.

Temperature and humidity control

The membrane is sensitive to both temperature and humidity: a high inlet temperature changes the selectivity and flux of the membrane, while excessive humidity allows moisture to occupy the effective separation interface and also poses a risk of condensation. The preprocessing section should be equipped with temperature monitoring, and if necessary, pre cooling should be added to press the inlet temperature to the stable working range of the membrane; In high humidity areas, a dehumidification or drying filtration unit should be added before the intake enters the membrane to reduce moisture content and prevent water molecules from occupying adsorption and separation active sites. Only by controlling both temperature and humidity can the operation of the membrane section be smooth.

Coordination with membrane segments

The pre-treatment and membrane section are interconnected as a whole: the cleanliness of the pre-treatment outlet directly determines the operating cycle of the membrane, so the pre-treatment status should be included in daily inspections, and the filter material pressure difference should be replaced instead of a fixed cycle to prevent droplets and dust from reaching the membrane surface. Stable feed flow and pressure to avoid sudden pressure changes impacting the separation layer; Calibrate performance quarterly and record trends in flux and pressure difference. The front-end preprocessing and the status of the membrane segment are recorded in the ledger together, as they are pre variables for membrane lifespan.

Comparison of Preprocessing Points

Configuration steps

1. Actual measurement of intake dust, water content, and composition;
2. Equipped with wire mesh to remove foam and large droplets;
3. Equipped with multi-stage precision filtration to fine impurities;
4. High humidity conditions with dry filtration and water control;
5. Add temperature monitoring and pre cool if necessary;
6. Filter material pressure differential change to prevent liquid droplets from falling onto the membrane;
7. Quarterly calibration records the trend of flux pressure difference.

FAQ

Can preprocessing be saved?

Cannot save: tail gas containing dust and water directly enters the film, and dust droplets stick to the film and block the holes. If it is mild, it is difficult to clean, and if it is severe, it will be scrapped; Pre processing input is included in the general ledger, which is much more cost-effective than frequent replacement of membrane cores.

Is the filter material replaced periodically or by differential pressure?

Press the differential switch to make it more stable, observe the trend of resistance; The lifespan of the working condition with dust and water is significantly short, and the front-end state directly determines the frequency of filter replacement. A fixed cycle is prone to early replacement waste or late replacement deactivation.

Do we need to add dehumidification when the humidity is high?

It is recommended to add in high humidity areas, as moisture occupying the effective separation interface of the membrane can also pose a risk of condensation; The selectivity and lifespan of the membrane after air intake dehumidification are more stable, especially for stations along the southern coast.

This article by LuoyangWohong PetrochemicalEquipment Co., Ltd. arranges that the company provides design, manufacturing and operation and maintenance services for condensation recovery, membrane separation recovery and complete solvent recovery devices for chemical and pharmaceutical enterprises. If you need process evaluation or scheme configuration, please contact and exchange.