Toluene is the main aromatic hydrocarbon solvent in the coating and resin industry. The old problem of tail gas recovery is: condensation alone, the recovery rate at low temperature goes up and the power consumption goes up; With the membrane alone, the load of the high concentration section is fully pressed on the membrane, and the area allocation is too large. The two-stage combination is the answer to most projects-condensation takes away the big head at the appropriate temperature level, and the membrane is enriched in the low concentration section. How to divide the work between the two levels, how to connect the temperature levels, and where to go with the enriched gas, this article makes it clear according to the actual configuration of the toluene system, and can be used in comparison with the selection and operation and maintenance.
The saturated vapor pressure of toluene is moderate, and there is a considerable recovery amount when condensed at normal temperature, which makes the condensation section of toluene system not need to be pressed to the cryogenic temperature level-the range of minus 15 degrees to zero degrees, and most toluene can be liquefied and recovered. The concentration of tail gas fluctuates with the process: the concentration of spraying and leveling section is high, and the concentration of drying section is low due to large air volume. This wide concentration span of the working condition, just two-level combination to play the advantages of division of labor scene: a level of tube a concentration range, who are not hard to carry.
The condensation level is set at about minus 15 degrees: the temperature level is selected according to the balance point of investment and power consumption, the large head of toluene is recovered, and the condensate is directly used in layers. The membrane stage takes over the uncondensed tail gas and enriches the residual toluene under the pressure difference. The solubility of toluene in the rubber separation layer is high, the membrane transmission speed is tens of times that of air, and the enrichment efficiency in the low concentration section is far more cost than lowering of condensation temperature. The enriched gas is returned to the compressor inlet for circulation treatment, and the discharge side meets the standard. The pre-membrane condition between the two stages is the key-dehumidification and filtration to keep the membrane surface, and the buffer tank to stabilize the gas fluctuation.
The control logic of the two-stage combination is also worth saying separately: condensation and the start and stop of the membrane section should be linked and not synchronized-the condensing unit should be graded according to the temperature position, and the membrane section should be switched according to the online concentration signal of uncondensed tail gas; During the drying section with large air volume and low concentration, the membrane section independently carries the emission, and the condensing unit can be reduced to standby. If the control logic is well written, the device will switch smoothly between different working conditions and the power consumption curve will be flat.
The connection of the two-stage temperature level is the key to the design: the temperature of the tail gas at the condensation outlet is low, and it should return to the allowable range before entering the membrane to avoid the influence of low temperature on the membrane layer and the seal; At the same time, the transition section completes secondary liquid removal to prevent fog droplets from entering the membrane. Toluene is swellable to common sealing materials. Pipeline gaskets and pump seals are selected according to medium. These details should be locked in the scheme stage, and it will take a lot of trouble to change the operation and static operation after operation.
| configuration item | Condensation-based scheme | Condensation and film combination |
|---|---|---|
| Condensation temperature level | Press down the ending section | minus 15 degrees |
| Power consumption | Steep rise of low temperature level power consumption | Moderate temperature and stable power consumption |
| low concentration section | Tight recovery rate | Membrane enrichment cycle check |
| Recovery rate | Restricted by temperature level | More than 99% combination |
| investment structure | Refrigeration system is biased | controllable membrane area |
| Adaptability | concentration fluctuation sensitive | Wide concentration span calmly |
Deep cooling puts the recovery rate on the temperature level, and the power consumption and equipment input increase sharply. The combined process makes the condensation stop at the economic temperature level and the membrane makes up the low concentration section. The general ledger is much more flat than that of deep cooling and single drying.
According to the measured gas concentration curve, the residual concentration at the condensation outlet and the target recovery rate determine the membrane area and series, and the first-level check section with high recovery rate is added, and the basis is specified item by item in the configuration list.
After layered dehydration, the purity and moisture shall be tested batch by batch, and those that meet the standards shall be matched according to the process caliber. Refined after not up to the standard, it shall be reused, and the index shall be confirmed with the production line before reuse, and the grading and use shall not cross.
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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