How to recycle methanol waste gas? Condensation of water-soluble solvent and subsequent processing configuration ideas

Methanol is a large amount of water-soluble solvent in fine chemical, pharmaceutical and coating industries. It has high exhaust gas concentration and recovery value, but it is obviously different from other solvents: methanol and water are completely miscible, and there is no layering available. This means that the condensate recovered by condensation is often a methanol aqueous solution, and the direct reuse has to face the problem of water content, and the subsequent treatment links must be designed together. The engineering practice is to reduce the vapor pressure of methanol as much as possible in the condensation section, and then choose to reuse, purify or recover heat according to the concentration of the condensate. The whole configuration revolves around the two goals of "condensation can be collected and condensate can be used.

The characteristics of methanol exhaust gas determine the difficulty of configuration

Methanol is highly volatile at normal temperature, the concentration of gas source is usually high, and a large amount of methanol can be received in the condensation section. The problem is that the gas source often has water vapor. When condensing, water and methanol are liquefied together, and the condensate becomes a mixture. If the workshop has requirements on the moisture content of the recycled methanol, it is necessary to add distillation or membrane dehydration and other purification links after condensation. If the reuse requirements are loose, the condensate can be directly returned to the process that is not sensitive to water content. Whether it is purified and to what extent it is mentioned depends on the actual acceptance of the reuse point.

Configuration points

1. Calculate the condensation load according to the air source temperature, methanol concentration and moisture content, and determine the temperature arrangement of graded condensation;
2. Condenser and condensate pipeline shall be selected according to the requirements of corrosion resistance, and methanol aqueous solution is corrosive to some metal materials;
3. Set condensate intermediate tank and sampling port, and regularly detect methanol content as the judgment basis for reuse or purification;
4. According to the requirements of the reuse point, decide whether to match the distillation or dehydration unit, so as to avoid being useless after receiving it;
5. The exhaust gas at the purification side is provided with a detection port, and the condensed residual gas is further treated according to the emission management requirements.

Three where to go after condensation

There are three common routes for the treatment of condensate: first, condensate with higher concentration is directly returned to the production process for reuse after inspection; Second, condensate with higher water content is sent to the distillation unit for purification to obtain methanol that meets the requirements. Third, condensate with lower concentration and uneconomical purification is sent to waste liquid for treatment or as fuel to recover heat. The choice of the three routes is based on the requirements of concentration, water volume and reuse point, rather than one-size-fits-all. In the design stage, the interfaces of these three routes are reserved and can be flexibly switched according to the working conditions during operation.

Comparison of three routes of condensate treatment

Methanol condensate has high water content, can it be used again?

It depends on the acceptance of the reuse point. Processes that are not sensitive to water content can be directly used; processes with purity requirements need to add purification links after condensation, which are determined according to reuse standards.

Will the water vapor in the gas source zone affect the condensation effect?

The latent heat load of water vapor will occupy a part of the cooling capacity. During design, the load shall be calculated according to the actual moisture content and the allowance shall be reserved. The condensation temperature level and series shall also be adjusted accordingly.

How should materials be selected for the condensation equipment of methanol exhaust gas?

Methanol aqueous solution is corrosive to some metal materials. The heat exchanger and pipeline contacting the condensate shall be made of corrosion resistant materials according to the medium conditions, which shall be determined according to the medium analysis conclusion in the scheme stage.

Operation management suggestions

After the unit is put into operation, three indicators are focused on: condensate outlet temperature, condensate methanol content and recovery trend. Abnormal rise of condensation outlet temperature is usually caused by insufficient refrigeration load or scaling of heat exchange surface. The methanol content of condensate fluctuates with the change of water content of gas source, which needs to be reconciled with the production batch of workshop. If the recovery volume drops suddenly, priority should be given to checking whether the gas source collection is bypassed. The solvent purchase quantity, dosage and recovery quantity are put together to make material balance, and the recovery effect can be explained by figures.

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.