Why is it necessary to first increase the pressure for solvent exhaust gas recovery? Direct answer: Boosting changes the physical property account - the dew point of gas components rises after being pressurized, and most solvents can be condensed at conventional shallow cooling temperatures without having to be plunged into deep cooling; At the same time, pressurization provides osmotic driving force for membrane separation, increasing the flux of membrane units and saving membrane area. The combination of compressed shallow cooling and membrane separation is the mature route to calculate these two accounts together: the compressor first increases the tail gas pressure, the shallow cooling section collects 60-70% of the solvent, the remaining low concentration tail gas enters the membrane unit for enrichment, the permeate gas returns to the compressor inlet for circulation, and the lean gas on the interception side meets the emission standards. Compared with direct cryogenic treatment with the same recovery rate, this route can save a quarter to one-third of the electricity consumption commonly measured. This article clarifies the division of labor and key points of configuration for each paragraph.
Pen one is the condensation account: the dew point of the components rises with the increase of total pressure. For the same exhaust gas, the components that can only condense at minus tens of degrees Celsius under normal pressure can condense more than half after being pressurized, and the specifications and power consumption of the refrigeration unit decrease accordingly. Pen 2 is membrane accounting: the permeation rate of the membrane is driven by the differential pressure on both sides of the membrane, with high intake pressure and strong driving force. Under the same processing capacity, the membrane area and vacuum pump load are both reduced. Both accounts are based on the stable operation of the compressor, and the selection and maintenance of the compressor are the foundation of this route. The maintenance of the oil circuit, gas circuit, and sealing system is carried out on a regular basis, and if the compressor fails, both the front and rear sections will be affected together.
The task of the shallow cooling section is to collect the gas: the pressurized exhaust gas is first cooled by the condenser, and the high boiling point components liquefy first. After gas-liquid separation, the condensed liquid enters the storage tank, and the uncondensed gas continues to move forward. There are several considerations for controlling the condensation temperature: control the temperature of the exhaust gas containing moisture above freezing point to avoid freezing and blockage of the heat exchange surface; Temperature grading setting, gradually cooling down from high to low, with only the components within reach of each level. How much is collected in the shallow cooling section and how much is left in the membrane section depends on the composition and pressure. The division of labor is determined according to the material balance during the design phase, and after being put into operation, the measured data of the outlet concentration at each level is reviewed. Only when the book division of labor is aligned with the actual output, can the entire line be considered smooth.
The membrane section consumes the low concentration exhaust gas left over from the shallow cooling section: organic components preferentially pass through the membrane layer, forming enriched gas on the permeate side, which is then pumped back to the compressor inlet by a vacuum pump for another round; The concentration of lean gas on the interception side has significantly decreased, and it can be controlled by adsorption or directly discharged to meet the standard. The clever feature of this route is the enriched gas recirculation - with each cycle, the concentration is raised by one level, and the recovery rate of the shallow cooling section is taken another bite. The exhaust concentration is controlled by a membrane to be below the emission line. The inlet gas of membrane components still needs to be controlled: droplets, dust, and high humidity are the major enemies of membranes. The front-end foam removal and filtration configuration cannot be omitted, and the filter element pressure difference should be replaced instead of following the calendar.
| Process section | task | key points |
|---|---|---|
| Compressor | Boosting provides dew point for driving force | Maintain according to frequent working conditions |
| Shallow cold section | Take away the high boiling point big head | Temperature classification above freezing point |
| gas-liquid separation | Separate condensate from uncondensed gas | Linkage between liquid level and drainage |
| membrane separation | Low concentration exhaust gas enrichment | Front end foam removal filtration |
| Permeation gas cycle | Return to compressor inlet for recharging | circulating concentration rising step by step |
| Retention side discharge | Standard check | Adsorption Assurance Configuration on Demand |
According to the component dew point and membrane driving force, the higher the better: high pressure compressor investment and power consumption rise, revenue margin decreases.
Organic vapor that can condense and easily pass through the membrane is the applicable main body; The water-containing system is equipped with anti-ice blocking measures. Corrosive components such as chlorine are used to check the compatibility of the materials. Special components shall be tested first and then the route shall be determined. Do not use a process set of all media.
Under the same recovery rate caliber, the common measured interval of compressed shallow cooling film and direct deep cooling, the specific section depends on the composition and concentration, after commissioning, according to the single ton of recovery power consumption and design value comparison verification.
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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