How to treat acetone exhaust gas in pharmaceutical workshops? Recycling configuration for crystallization washing and equipment cleaning processes

The uses of acetone in pharmaceutical workshops are mainly focused on crystal washing, equipment cleaning, and material replacement. The air volume at each point is not large, but the points are scattered, and the total volume is considerable. The boiling point of acetone is about 56℃, it is completely miscible with water, and has a low lower explosion limit. The three key words for recovery and configuration are low-temperature collection, strict explosion prevention, and condensate distillation dehydration. By understanding the emission characteristics of each process, the configuration of collection and recovery can be tailored to the site.

The toxicity of acetone ranks among the ketones that require attention. Both the concentration control at the workshop operation surface and at the factory boundary should be closely monitored. The tightness of the collection system takes precedence over the economics of recovery - this is not contradictory to the recovery rate, as a well-sealed system inherently has a higher recovery rate.

The economic benefits of acetone recovery should be calculated together with the purchase price of solvents: acetone has a high unit price and is used in large quantities in workshops. The graded reuse of recovered liquid - low-purity blended liquid for washing and distilled extraction liquid for batching - can reduce both distillation load and operating costs. The investment recovery period for recovery devices is mostly within an acceptable range.

How to collect in each process

The volatilization in the crystallization and washing processes is concentrated in the exhaust from centrifugal, filtration, and washing equipment, with concentrations fluctuating from batch to batch. It is collected through individual equipment nozzles and merged into a main pipe for treatment. Equipment cleaning and replacement involve high-concentration, short-duration operations. Quick-change connectors and collection branches are equipped, allowing for temporary connection during cleaning periods or introduction through fixed branches. The sequence of replacement operations is synchronized with combustible gas detection. The two branches are metered separately, and recovery and emission data are accounted for separately.

Confirm the pipeline constraints in the clean zone in advance: The pipelines that pass through clean zones should be sealed and easily cleanable. The location of openings should be determined jointly with the user. Most modification windows are arranged during production downtime for maintenance. The plan and materials should be in place in advance.

How to determine the recycling configuration

Acetone has a low boiling point, so the condensation temperature needs to be set lower than that of ester aromatic hydrocarbons. For the two-stage condensation, the second stage is calculated based on the dew point of the inlet gas. Under high-concentration conditions, condensation and recovery are the main focus, while under low-concentration conditions, the tail gas from the main pipeline is processed through adsorption or membrane separation in series. The condensate and water are miscible and do not separate into layers, so distillation is used for dehydration. Acetone and water do not form an azeotrope, so ordinary distillation can achieve high-concentration extraction. The ketone-containing wastewater from the tower bottom is metered and then discharged into the sewage system.

Explosion-proofing is a hard constraint in the configuration: acetone has a low lower explosion limit, and pipeline flow rate, electrostatic grounding, and equipment explosion-proofing level are implemented item by item according to standards. Attention should be paid to the heat of adsorption in the adsorption section, and high-concentration gas should be condensed and depressurized before entering the tower. Safety facilities and recovery devices should be designed and inspected together, and regular inspections should be conducted after commissioning without any omissions.

Configuration reference

How to implement operation management

1. Separate metering and billing for the two branches of crystallization washing and cleaning replacement;
2. The condensation temperature level is calculated based on the inlet dew point, and the corresponding relationship is recorded shift by shift;
3. Condensate distillation dehydration, with tower kettle wastewater separately metered into sewage;
4. The purity and moisture content of the recovered liquid are tested batch by batch, and it is blended and reused in different grades;
5. The explosion-proof grounding flow rate is included in the monthly inspection point by point, with a focus on temperature rise in the adsorption section;
6. Regularly detect the concentration on the operation surface and at the factory boundary, and repair the tightness as it is detected.

Frequently Asked Questions

Can the acetone recovery solution be reused for crystal washing?

Yes, the requirements for alcohol and ketone concentration in washing are relatively loose. After testing, they can be blended in proportion. High-purity products can be reserved for the batching process, and graded recycling can significantly reduce the distillation load.

Is the recovery rate higher when the condensation temperature is reduced to below zero?

When the temperature is too low, the marginal return decreases, energy consumption increases rapidly, and it also brings the burden of defrosting. Calculating the economic temperature based on the inlet dew point, retaining the residual in the control section, and the overall cost is more cost-effective than blindly pursuing deep cooling.

What is the biggest constraint in the collection and renovation of the clean area?

It's about the window period: The renovation should be completed during the production downtime for maintenance. The methods for drilling and crossing should be confirmed with the user in advance. The scheme design, material procurement, and prefabrication processing should all be completed before the window period. Only installation and purging should be done on site, so that the construction period can be controlled.

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.