Ethylene oxide is a highly reactive compound, and the treatment of plant tail gas is more than that of general solvent tail gas. The ethylene oxide in the tail gas cannot be discharged at will, nor should it stay in the equipment for a long time. The mainstream idea of the recovery process is to compress the large end of condensation and collect the residue by membrane separation-the condensation section liquefies most of the ethylene oxide for reuse, and the membrane section enriches the residual components in the uncondensed tail gas for recycling. This article explains how the two levels are divided, how they are connected, and what should be paid attention to in operation.
Ethylene oxide has a low boiling point and is volatile. It has a wide flammable range when mixed with air, and is often associated with carbon dioxide and other components in the exhaust gas of the device. These characteristics determine the two principles of tail gas treatment: first, the process should be continuous and not accumulated, and the collected materials should be returned to the system in time; Second, the retention in the equipment should be small, and open treatment is better than closed pressure suppression. Membrane separation is exactly in line with these two articles-the components are continuously pumped away after permeating the membrane, and there is no place where a large amount of material accumulates in the device.
The tail gas is first pressurized by the compressor and enters the condensing unit to cool down. Most of the ethylene oxide is liquefied at this temperature and the condensate is returned to the system. The recovery rate of condensation depends on the temperature level and the composition of the tail gas: the lower the temperature, the cleaner the collection, but the energy consumption increases, and affected by the non-condensable gas content in the tail gas, it is not economical to lower the temperature level all the way to catch up with the final residual components. The engineering practice is to stop the condensation after receiving a reasonable concentration and hand over the low concentration section to the next level. The load design of the condensing unit should also leave a margin for high ambient temperature in summer, and the temperature level capacity will shrink when the cooling water temperature rises.
After the uncondensed tail gas enters the membrane unit, ethylene oxide molecules preferentially pass through the rubber separation membrane and are enriched at the permeation side, and the enriched gas returns to the compression section or the condensation section for recycling treatment; nitrogen, carbon dioxide and other gases are intercepted and discharged after the concentration reaches the standard. The existence of the membrane section makes it unnecessary for the condensation section to chase the low concentration. The two stages each work in their own concentration range. The overall recovery rate goes up, and the energy consumption curve is flat. This is isomorphic to the division of condensation and film in oil and gas recovery, and the logic is interlinked.
The junction point between the two stages is the concentration: the tail gas concentration at the outlet of the condensation section is the feed concentration of the membrane section. The clearer this value is, the more accurate the membrane area and the configuration of the vacuum system will be. The temperature should also be considered at the junction-the temperature of the condensed tail gas is low, and the working condition of the membrane surface is preferred, but attention should be paid to reheating to prevent the pipeline from condensing and carrying liquid; Therefore, the gas-liquid separation section before entering the membrane cannot be saved, and droplet entrainment is the first killer of the life of the separation layer.
| Stage | Responsible concentration interval | Destination |
|---|---|---|
| Compress | Exhaust gas pressurization | Unified inlet condensation |
| Condensation | High concentration section | Liquefaction return system |
| membrane separation | low concentration section | Post-enrichment cycle |
| Interception side | Standard gas | emission |
| Monitoring | concentration and flow | Account and interlocking |
| Safety | Explosion-proof zone | Type selection matching |
The temperature level is lowered all the way to collect residual components, energy consumption and equipment input rise rapidly, and the economy becomes worse. The combination of condensation and film residue is lower, which is a division of labor that has been repeatedly verified in engineering.
Membrane separation is a continuous process, through the components are immediately pumped away by the vacuum pump, there is no large amount of material accumulation in the device, which is especially important for ethylene oxide such high reactivity media.
The concentration of enriched gas is high, the total amount is small, the upstream circulation treatment is not discharged and the total recovery rate is improved, and the pipeline and control are simpler than that of a separate liquefaction unit.
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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