How to treat ethanol tail gas in pharmaceutical workshops? Collection and recycling configuration for drying and tank washing processes

The pharmaceutical workshop consumes a large amount of ethanol, and its evaporation points are concentrated in two areas: the exhaust from drying ovens and equipment, which has high temperature and stable concentration; and the replacement gas from tank washing and equipment cleaning, which has high concentration but is discharged intermittently. The air volume, concentration, and temperature characteristics of these two types of working conditions are different, so the collection and treatment configurations should be considered separately, which is more economical than the approach of mixing them together for treatment.

Another constraint in pharmaceutical workshops is cleanliness and explosion protection: collection pipelines that pass through clean areas must be sealed and selected for appropriate materials. The explosion-proof grade and installation location of processing equipment should be confirmed during the planning stage. For renovation projects, it is particularly important to first understand the on-site conditions before formulating a plan.

How to collect in the drying process

The exhaust from the drying oven is characterized by both temperature and humidity: the exhaust temperature is in the tens of degrees, and the humidity is close to saturation. Directly entering the condensation section will absorb a large amount of water vapor into the condensate, diluting the solvent content. In terms of configuration, pre-cooling and dehumidification should be carried out first to remove the water vapor before entering the solvent condensation section. This significantly improves both the alcohol concentration in the condensate and the backend load. The exhaust from the drying oven group is converged according to batch time periods, and variable frequency adjustment is used for air volume fluctuations. The condensation unit is matched according to peak and valley loads.

The insulation of the collection pipeline must be kept up to date: when the exhaust temperature is high and the pipeline is exposed, the solvent condenses and accumulates inside the pipeline, and the reflux condensate not only affects the collection efficiency but also poses a burden on pipeline cleaning. The insulation should extend to the inlet of the condensing unit, ensuring no cold spots remain inside the pipeline.

How to handle the gas displaced during tank cleaning

The concentration of replacement gas during tank washing and cleaning is high, and the duration is short. It is uneconomical to use a fixed large device to accommodate instantaneous loads. A collection manifold is equipped to speed up the change of connectors, and a small condensation recovery unit is temporarily connected during the replacement period, which is removed immediately after collection. For workshops with high cleaning frequency, a fixed branch is established, and the unit is started and stopped according to the cleaning schedule. The alcohol-containing condensate from the replacement gas and the condensate from the drying oven are returned to the same dehydration process, with centralized management.

The management of replacement operations should be synchronized: replacement sequence, oxygen and combustible gas detection, work permit system. These safety measures should be implemented in conjunction with recovery and configuration. No matter how good the equipment is, it cannot replace operational management.

The operating periods of the two branches are not synchronized, and the utilization rate of the equipment needs to be clearly accounted for: the drying oven branch operates continuously with production, while the tank washing branch operates intermittently according to the cleaning schedule. Sharing a set of dehydration and storage and transportation processes can spread out costs. When the workshop is renovated or production is adjusted, the load of the branches needs to be recalculated, and 20% of the device's adaptation space should be reserved during configuration. Most fluctuations can be internally absorbed.

Configuration reference

How to implement operation management

1. The two branches, namely the drying oven and the tank washing, are metered separately, and the recovery amounts are accounted for separately;
2. Drain the condensate water from the pre-cooling section every shift, and increase the frequency during seasons with high humidity;
3. The concentration and moisture content of the recovered liquid are tested batch by batch, and it is blended and reused according to its intended purpose;
4. The unit starts and stops according to the cleaning plan, and the valve is closed during the downtime to prevent short circuit;
5. The pipeline sealing points in the clean area are included in the periodic inspection, and any leakage is promptly repaired;
6. Regularly inspect the emission outlets and compare and analyze the data with the factory boundary data.

Frequently Asked Questions

What should be considered when selecting a condensing unit for an oven with high humidity exhaust?

The dehumidification load should be calculated separately: The heat load from water vapor condensation often exceeds that of the solvent itself. The model selection for the precooling section should be based on the water vapor load, while the model selection for the solvent section should be based on the alcohol content. Combining the two calculations can lead to the selection of an oversized unit or a mismatch in temperature range.

Can the ethanol recovery solution be directly reused for tank washing?

Okay. The water used for tank washing has a relaxed requirement for alcohol concentration. After testing, it can be blended in proportion. The high-purity recovered liquid is reserved for the batching process, and its graded reuse can reduce the dehydration load.

What are the constraints on pipeline renovation in the clean zone?

Pipelines passing through clean-grade areas should be sealed and designed for easy cleaning. The location of openings and the method of passage should be confirmed with the user in advance. Most modification windows are scheduled during production downtime for maintenance, so the plan and material preparation should be completed before the window period.

This article is compiled by Luoyang Wohong Petrochemical Equipment Co., Ltd., which provides design, manufacturing, and operation and maintenance services for condensation recovery, membrane separation recovery, and complete solvent recovery equipment to chemical and pharmaceutical enterprises. If you need process evaluation or scheme configuration, please feel free to contact us for discussion.