09 · Flexible Packaging & Gravure Printing
Where the solvent goes
Rotogravure and flexographic inks and solvent-based laminating adhesives carry large amounts of solvent, which evaporates in the drying hoods. To keep the hoods safely below the lower explosive limit, it is exhausted with very large volumes of air — typically 10,000 to 200,000 m³/hr at only a few hundred to a few thousand ppm. Unless it is recovered, solvent bought every month goes straight up the stack.
Typical solvents
Ethyl acetate, ethanol, n-propyl acetate, isopropanol, MEK and toluene, often as a blend that changes from job to job. Genosorb absorbs both the polar and non-polar members of these blends.
Concentrate first, then recover
- 01
Collect the hood exhaust
Exhaust from printing and laminating dryers is ducted to the recovery plant.
- 02
Concentrate it
A slowly rotating rotary concentrator wheel adsorbs the solvent and sends clean air to the stack. A small stream of hot air (3–10% of the flow) desorbs the wheel, carrying the solvent at up to 30× the original concentration.
- 03
Recover it
The concentrated stream goes to the Genosorb absorber and stripper, and the solvent is condensed as liquid.
- 04
Reuse it
The recovered solvent is dehydrated and can be re-blended to the original formulation, used as diluent or wash solvent, or sold.
Concentrating first means a 100,000 Nm³/hr exhaust reaches the recovery plant as 5,000–7,000 Nm³/hr, cutting equipment cost by 75–85% and operating cost with it.
Utilities with and without a concentrator
| Utility | Without concentrator | With concentrator | Saving |
|---|---|---|---|
| Steam | 1,250 kg/hr | 180 kg/hr | 86% |
| Cooling water | 200 m³/hr | 35 m³/hr | 83% |
| Refrigeration | 200 TR | 60 TR | 70% |
| Genosorb make-up | 80 g/hr | 20 g/hr | 75% |
From CCDC’s design comparison on the rotary concentrator page.
Operating cost on a multi-solvent stream
| Technology | Operating cost (₹ per kg recovered) |
|---|---|
| Absorption (Genosorb®) | 7.30 |
| Activated carbon adsorption | 10.6 |
From “VOC recovery from gaseous streams” by Dr D M Mohunta, CCDC (2004). Costs are in 2004 rupees and show how the technologies compare with each other, not today’s prices. Read the original study.
The solvent lost from this stream was valued at about ₹271 lakh a year in the same study.
CCDC installations in printing and packaging
- Gravure printing: a high-speed line exhausting more than 100,000 Nm³/hr with a shifting blend of ethyl acetate, ethanol, n-propyl acetate, MEK, toluene and isopropanol. The recovered mixed solvent is dehydrated and re-blended to the original formulation.
- Flexible packaging: laminating-machine-scale installations recovering single or mixed solvents from high-speed packaging lines.
See all VOC recovery case studies.
Frequently asked questions
Our dryer exhaust is very dilute. Is solvent recovery still worth it?
Usually, yes — that is what the rotary concentrator is for. It raises the solvent concentration up to 30× before recovery, so a large, dilute exhaust can be treated with a much smaller and cheaper Genosorb plant.
Can recovered solvent go back into our inks and adhesives?
Often. On CCDC’s gravure-printing installation the recovered mixed solvent is dehydrated and re-blended to the original formulation. Where that is not practical it can be used as diluent or wash solvent, or sold. CCDC confirms the achievable quality in the feasibility study.
Does recovery work when the solvent blend changes from job to job?
Yes. Genosorb absorbs both polar and non-polar solvents, and recovery systems have kept working as feed flows and concentrations vary widely between sources.
Should a printing plant choose solvent recovery or an RTO?
A regenerative thermal oxidiser destroys the solvent, needs supplemental fuel and adds CO₂. Recovery returns the solvent to use. Which is better depends on the value of your solvent, its mix and your operating hours — the feasibility study compares them for your line.