The biggest difference between methanol and ester and aromatic hydrocarbon solvents is that they are infinitely soluble in water, which makes its recovery side add a dehydration process: the condensate collected by condensation is not pure methanol, but methanol aqueous solution, which should be dehydrated and purified before being recycled. The role of membrane separation in methanol tail gas recovery is consistent with that of other systems-low concentration section checks and enriches. According to the characteristics of methanol tail gas, this paper makes clear the recovery process, dehydration method and key points of back distribution, and can be directly quoted for comparison and selection of alcohol solvent recovery schemes.
Methanol is highly volatile, has a wide explosion range, and requires a high level of tail gas safety; it is infinitely miscible with water, and the condensate is directly dilute methanol aqueous solution, and the concentration varies from tens of percent to close to saturation depending on the working conditions. The economy of recovery depends on two points: the original concentration of tail gas-the higher the concentration, the more cost-effective the recovery; Dehydration energy consumption-dilute solution dehydration and rectification energy consumption, when the concentration is too low, the account is not easy to calculate. The actual measurement of these two sets of numbers before the plan is the premise of decision-making. Nine times out of ten, the plan matched by feeling is stuck in the dehydration process.
Section 4 of the process: the tail gas is collected and pressurized and then condensed, the methanol in the high concentration section is collected, and the condensate is separated from the process wastewater and then enters the distillation; the uncondensed tail gas enters the membrane unit, the rubber separation layer has high solubility for methanol, fast permeation speed, and the enriched gas returns to the compressor inlet for circulation treatment; the interception side meets the discharge standard. In the rectification section, dilute methanol is purified to the concentration of reallocation, qualified products are extracted from the top of the tower, and the waste water at the bottom of the tower is discharged to the sewage system. Four closed-circuit connection, recovery rate and discharge are stable at both ends.
The core of dehydration is rectification: when the concentration of condensate is higher than the requirement of reallocation, it can be simply distilled, and when the concentration is low, it can be configured according to conventional rectification. There are two ways to control energy consumption: one is to preheat the feed-use the sensible heat of the tower kettle wastewater to exchange heat to reduce steam consumption; On the one hand, the enrichment of the membrane section reduces the amount of distillation to a minimum-the concentration is high. The membrane is enriched and recycled. Only the necessary part is distilled, and the load of the tower decreases accordingly. The accounts of both hands must be calculated together so that the specifications of the distillation tower can be pressed to a reasonable range.
One more sentence in the back-to-back link: when recycled methanol is mixed with purchased methanol, the mixing ratio is converted according to the batch detection value, not by volume estimation; Water is sensitive to some downstream reactions. The mixing tank keeps a detection sampling port, and each batch is retested once after mixing. The recovery of solvents should be carried out with confidence, relying on data at every step, not on hand feeling.
| Segment | task | Energy consumption considerations |
|---|---|---|
| Condensation section | Harvend high concentration methanol | Normal temperature or light cold |
| membrane unit | low concentration enrichment cycle | Pressurization and vacuum power consumption |
| rectifying section | condensate dehydration purification | Feed preheating saves steam |
| Waste side | Bottom of tower blowdown system | sensible heat recovery heat exchange |
| Return side | Batch-by-batch inspection sample retention | Index grading use |
| Ledger | Recycled Amount Monthly Reconciliation | Loss traceability |
Yes, but the value is far from good: according to the discount of waste liquid treatment, the solvent value is calculated after recovery and purification. If the concentration reaches the economic line of rectification, the self-recovery account is generally more even and will be determined after calculation.
The rubber separation layer has high solubility in methanol, fast permeation speed and ideal enrichment efficiency in the low concentration section. The high concentration section is handed over to condensation, and the area of the membrane and the load of distillation can be suppressed after the two-stage division of labor.
Two hands: tower kettle wastewater and feed heat exchange recovery sensible heat; Membrane enrichment minimizes the amount of distillation. The combination of the two items can usually reduce the energy consumption of dehydration, and the comparison and selection should be made in the scheme stage.
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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