How to recycle the tail gas from the drying tower? Key points of collection and configuration of spray and fluidization drying discharged solvent
Release time: October 23, 2026
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How to recycle the tail gas from the drying tower? The key points are "reduction first, dust removal first, and condensation later": first, use hot air circulation and sealed transformation to reduce the amount of exhaust gas that needs to be treated, then remove the entrained dust according to the characteristics of the dry material, and finally send the cooled solvent containing exhaust gas to two-stage condensation recovery. The dry exhaust gas has a large air volume, high temperature, and diluted concentration. Directly applying it to the condensing equipment requires high investment and energy consumption. Only by doing enough of the three prerequisites can the recovery economy be established.
What are the characteristics of dry exhaust gas
The first is high air volume and low concentration. Drying relies on a large amount of hot air to bring out solvent vapor, and the concentration of the vapor after dilution is often significantly lower than that of the reaction kettle point. Similarly, the amount of air to be processed for recovery needs to be doubled, and equipment and energy consumption accounts need to be calculated based on the air volume.
The second is high temperature. The tail gas leaving the tower usually carries significant residual temperature, and directly entering condensation will consume cold energy in vain. Cooling down first and then condensing can save cold energy.
The third is the inclusion of dust or mist droplets. The fine powder of the material enters the exhaust gas with the airflow, and without pre-treatment, it will stick to the heat exchange surface, causing the condensation efficiency to quickly decline.
How to reduce the air volume first
The air inlet for spray and fluidization drying is designed to take away water and solvent, but in actual operation, the air volume margin is generally too large: first, calculate and calibrate the air inlet according to the solvent content of the material, and then evaluate the feasibility of hot air circulation - return part of the tail gas to the heating furnace for recycling, and only discharge the part required for balance, the total amount of tail gas can be significantly reduced. Synchronize the inspection of equipment airtightness, and supplement the air leaks at the feeding port, unloading port, and maintenance door to avoid the mixing of ineffective air volume.
How to Pre treat Dust Removal and Cooling
Dust removal should be carried out using cyclone or bag filters based on material characteristics. For exhaust gases with high moisture content, bag filters should be used to prevent condensation; The cooling heat exchanger is used to recover the residual temperature. In the case of hot air circulation, the residual heat is directly reused, and in the case of non circulation, the temperature after cooling is controlled within the design range of the condensation section. The configuration and function of the preprocessing section are shown in the following table:
| pretreatment section | problems solved | Configuration essentials |
|---|---|---|
| dust removal | Dust covers the heat exchange surface | Select cyclone or bag type according to materials to prevent condensation |
| Cooling and heat exchange | Waste of cooling capacity due to residual temperature | Waste heat reuse or preheating of incoming air |
| Hot air circulation | Dilution concentration with high air volume | Determine the circulation ratio based on the solvent content |
| Sealed leak repair | Invalid air volume mixed in | Sealing inspection of feeding and unloading ports |
How should condensation recovery be configured?
The preprocessed exhaust gas is subjected to two-stage condensation: the first stage condenses water vapor and some solvents, and the second stage deeply condenses the remaining solvent vapor, with cold recovery between the two stages; The condensate is divided into layers or refined units according to its composition for processing. In the case of dry batch operation, the condensing unit is configured according to the peak value of the batch, and the buffer tank is flattened and fluctuated; For non condensable gases with high concentration, they should be collected and processed in the main collection pipe of the entire plant. For those with very low concentration, a testing port should also be left before meeting the emission standards, and data should be used to speak for themselves.
How to promote the implementation of transformation
- Measure the actual air volume, temperature, and solvent emissions of the drying tower, and draw a baseline ledger;
- Verify the air volume reduction plan based on the baseline: implement air intake calibration, hot air circulation, and sealed leak repair item by item;
- Select dust removal methods based on material characteristics, confirm anti condensation and dust cleaning arrangements;
- The condensing unit is configured according to the reduced air volume and concentration to avoid exceeding the original air volume design;
- Compare the air volume, recovery amount, and energy consumption before and after the renovation after operation, and verify the renovation account.
Frequently Asked Questions
Is it worth condensing when the concentration of dry exhaust gas is low?
It's not cost-effective to look at the concentration alone, but calculate it after reducing the air volume sufficiently: when the air volume is reduced, the equipment scale and energy consumption are synchronously reduced, and the recycling account can be transferred; Skipping reduction and directly condensing is the most common waste in dry recycling.
What will happen if the dust is not removed?
Fine powder will gradually coat the condensation heat exchange surface, leading to a decrease in condensation efficiency, an increase in cleaning frequency, and in severe cases, blockage of pipelines; Dust removal is the guardrail of the condensing unit and cannot be omitted.
Will hot air circulation affect the quality of drying?
The circulation ratio is determined based on the solvent content and drying index of the material, and is controlled within the equilibrium range without affecting product quality; At the initial stage of operation, encrypt the detection of product residues and use data to determine the cycle ratio.
What supporting services does WoHong offer?
Luoyang Wohong Petrochemical Equipment Co., Ltd. provides design, manufacturing, installation, commissioning, and operation services for drying process exhaust gas reduction and solvent recovery devices. Welcome to contact and exchange ideas.
This article is organized by Luoyang Wohong Petrochemical Equipment Co., Ltd. If you need to evaluate the recovery of dry exhaust gas or conduct on-site inspections, please feel free to contact and exchange ideas.
