There is a kind of difficult components in solvent recovery: low boiling point solvents-diethyl ether, acetone, dichloromethane, etc., with high saturated vapor pressure, which cannot be condensed at normal temperature, and the power consumption at cryogenic temperature rises sharply. The combination idea of this kind of system is to connect membrane separation with rectification: the membrane is enriched on the gas phase side, and the solvent in the low concentration tail gas is lifted to a condensable concentration; Distillation is purified on the liquid phase side, and the collected condensate is mentioned as a reuse index. Each level is in charge of one section, and no one will carry it hard. In this paper, the division of labor, connection and energy consumption configuration of this two-stage recovery are clearly explained, and the scheme comparison and selection of low boiling point solvent recovery can be referred.
The difficulty of low boiling point components lies in gas-liquid equilibrium: high saturated vapor pressure means high gas phase concentration at the same temperature, and condensation requires very low temperature to recover the amount-the cryogenic temperature of ether system is much lower than that of toluene, and the cost of refrigeration equipment and power consumption is high. Without pressure, the emission concentration cannot come down. Membrane separation has changed the way of thinking: instead of relying on temperature and partial pressure, the osmotic side is vacuumed to create a pressure difference. Solvent molecules are preferentially enriched through the membrane, and the enrichment ratio can reach tens of times. After enrichment, the total amount of air flow is small and the concentration is high, so it is good to enter the condensation account.
The process is divided into two stages: gas phase side, advanced membrane unit after tail gas is collected and pressurized, low boiling point components are enriched through membrane, enriched gas is sent to condensation and liquefaction, and the interception side is discharged up to standard; On the liquid phase side, the condensate enters distillation, the low boiling point components are taken out at the top of the tower, and the tower kettle recombination is disposed of separately. The enrichment ratio of the membrane determines the load of condensation-the enrichment ratio is high, the amount of condensation is small, the concentration is high, and the refrigeration specification decreases accordingly. The feed concentration of distillation determines the energy consumption of the tower-the membrane recovery rate is stable, and the load of the tower is stable. The parameters of the two levels should be adjusted together, and the single-stage optimal is not equal to the overall optimal.
The key to connection lies in three places: dehumidification filtration before the membrane keeps the separation layer, and the swelling of low boiling point solvent to sealing material should be checked during selection; The temperature level of condensation of enriched gas is determined according to the concentration of enrichment, and high concentration can be condensed at room temperature without deep cooling. The feed preheating of the rectification tower uses the waste liquid of the tower kettle to exchange heat, and the steam consumption is reduced by a bit. In terms of energy consumption, the pressurization and vacuum power consumption of the membrane section are stable, and the steam consumption of distillation fluctuates with the feed concentration, stabilizing the membrane recovery rate, and the energy consumption curve of the tower is flat. Two-stage control linkage: the membrane section is cut with the tail gas concentration, and the tower is started and stopped according to the liquid level of the feed tank.
| configuration item | Condensation-based scheme | membrane separation and distillation combination |
|---|---|---|
| Gas phase side | deep cold pressing low concentration | Condensation at room temperature after membrane enrichment |
| Refrigeration input | Cryogenic specifications are heavy | Decreased refrigeration specifications |
| Liquid phase side | Direct back-matching of condensate | Distillation and purification to reuse index |
| Power consumption | Steep rise of low temperature level | Boost vacuum power consumption smooth |
| steam consumption | — | Feed preheating saves a section |
| Adaptability | A single component is more suitable | Wide concentration span calmly |
Cryogenic puts the recovery rate on the temperature level, and the power consumption and refrigeration input increase sharply. Membrane enrichment raises the total amount and concentration of air flow, condensation stops at the economic temperature level, and the two-stage general ledger is flat compared with cryogenic and single-dry.
According to the measured exhaust gas concentration curve: the target recovery rate determines the membrane area and series, the enrichment ratio data out of the configuration list, item by item to write the basis.
Batch by batch detection of purity and moisture, up to the reuse index according to the process caliber back to match.
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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