After the membrane separation device has been running for a period of time, the flux decreases and the recovery rate decreases. The reaction of many operation and maintenance personnel is "the membrane is not working, it should be replaced". In fact, the replacement cost of membrane modules is high, and most of the performance degradation comes from pollution rather than membrane failure-pollutants are blocked on the membrane surface or enter the membrane holes, cleaned in place, and most of the performance can be restored. Judging the type of pollution and choosing the right cleaning method is the key to saving a lot of replacement costs. This article explains the common types of membrane pollution, the judgment method and the steps of cleaning and recovery. When the operation and maintenance personnel encounter performance degradation, they can check according to this.
Membrane pollution is divided into three categories according to pollutants: particle pollution-rust, dust and oil mist droplets are blocked on the membrane surface to form a filter cake layer, which shows that the pressure difference rises rapidly; Organic pollution-heavy hydrocarbons adsorb and condense on the membrane surface to form a viscous layer, which shows a slow decline in flux; Water pollution-water condenses on the membrane surface or interacts with components, and the liquid membrane on the membrane surface hinders mass transfer, showing a step-like decline in flux. Three types of treatment methods are different: particle pollution by back blowing and cleaning, organic pollution by chemical or thermal regeneration, water pollution by dehumidification section repair. If you judge the wrong type, you will do it for nothing if you clean it.
Judging according to the evidence: first look at the operation curve-the sudden rise of pressure difference points to particle pollution, the slow drop of flux points to organic pollution, and the step drop points to water pollution; Then check the pretreatment-filter element pressure difference, drainer state, cold dryer outlet temperature, pretreatment device to make up this section first; When conditions permit, take the membrane surface sample or observe the end surface, and the pollutant form is clear at a glance. The judgment is recorded in the ledger and compared with the cleaning effect-the first judgment may not be accurate. After two or three cycles, the pollution law of the home device will be found out and the plan will be targeted.
Cleaning method according to type: reverse purging with permeate or clean gas for physical cleaning, loosening the filter cake layer on the membrane surface, simple operation, short cycle, and routine maintenance. Chemical cleaning selects cleaning agent according to pollutants, rinses after circulating soaking, and pays attention to the compatibility between cleaning agent and membrane material-the wrong cleaning agent is selected to corrode the separation layer, and the membrane is really broken. Thermal regeneration is suitable for organic pollution, heating desorption within the allowable temperature range, strictly control the upper temperature limit during operation. The criterion of cleaning effect is the magnitude of flux and pressure difference returning to the reference value, which is less than 70% recovered, and whether it enters the replacement window is evaluated in combination with membrane age.
In addition to cleaning, there is also a use discipline: the cleaned device should not be put into operation at full load immediately-the pollutant distribution is not stable after cleaning the membrane surface. First, run at low load for a period of time to make the working condition stable, and then gradually raise the conventional load. It is not uncommon that the residual pollutants on the membrane surface are unevenly redistributed and the flux does not return to the level before cleaning.
| Pollution type | curve feature | Disposal method |
|---|---|---|
| particle pollution | The differential pressure rises quickly | Blow-back and physical cleaning |
| organic pollution | Flux drops slowly | Chemical cleaning or thermal regeneration |
| Water pollution | Flux Step Down | Repair the dehumidification section |
| Judgment sequence | Curve pretreatment end face | Evidence goes without guessing. |
| cleaning criterion | Restoration Range to Benchmark | Less than 70% evaluation of replacement |
| Rhythm of operation | Start at low load after cleaning | Then gradually raise the load. |
Look at the recovery range and membrane age: after cleaning, the recovery to more than 70% of the benchmark and the trend is stable to continue to use.
The agent list and concentration provided by the membrane manufacturer shall be implemented. The compatibility check shall be carried out first, and the risk shall be controllable. Before replacing the agent by oneself, confirm with the manufacturer that the damage of corrosive agent to the separation layer is irreversible.
The dehumidification section in front of the membrane is the key line of defense: dew point index is transcribed daily, and drain and cold dryer are included in monthly maintenance; In high humidity season, the inspection is encrypted, and the water is blocked in front of the membrane, so the liquid membrane problem on the membrane surface will not occur.
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.
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