06 · Rotary Concentrator & Economic Benefits
It frequently happens that the concentration of VOC is very low and the volume is high — such as in flexible packaging, gravure printing, paint booths, battery and semiconductor manufacturing. Volumes may range from 10,000 m³/hr to 200,000 m³/hr with concentrations of only a few hundred to a few thousand ppm. The equipment shown in Fig. 1 becomes extremely large and the process uneconomic. Recourse is made to a device called a rotary concentrator to increase the concentration to a viable level.
The main equipment is a large, very slowly rotating wheel with a honeycomb structure filled with zeolite or activated carbon. The VOC-laden gas passes through the cooled face of the rotor where VOC is adsorbed and clean air exits to the chimney. A small portion (3–10%) of the air is heated and passed back through the rotor as the desorbing fluid — it emerges with a high concentration of VOC and is then cooled before going to the Genosorb recovery system. The concentration increase can be as high as 30×, limited to about 50–60% of the LEL for safety. A 100,000 Nm³/hr flow is thus reduced to 5,000–7,000 Nm³/hr at the Genosorb plant inlet, cutting equipment cost by 75–85% as well as operating cost — as shown in the table below.
Concentration increase
Up to 30×
~50–60% of LEL · 100,000 Nm³/hr feed → 5,000–7,000 Nm³/hr to Genosorb plant
Economics with vs without concentrator — Table 6
| Parameter | Without | With | Saving |
|---|---|---|---|
| Steam demand | 1,250 kg/hr | 180 kg/hr | ↓ 86% |
| Cooling water | 200 m³/hr | 35 m³/hr | ↓ 83% |
| Refrigeration load | 200 TR | 60 TR | ↓ 70% |
| Genosorb make-up | 80 g/hr | 20 g/hr | ↓ 75% |
Case A — Laminating machine
25,000 Nm³/hr · Ethyl acetate
Recovered
64.5 kg/hr
Annual volume
~419 t/yr
Solvent value
Rs 4,644/hr
Recovery rate
90%
Installed cost
Rs 400–430 lakh (2024)
Case B — Gravure printing
180,000 Nm³/hr · Mixed solvents
Recovered
~159.8 kg/hr
Annual volume
>1,000 t/yr
Solvent value
Rs 14,301/hr
Recovery rate
90%
Gravure printing is required to make flexible packaging ready for retail sale. In this case a combination of multiple solvents is used. The composition may vary considerably from user to user. The solvents are ethyl acetate, ethanol, n-propyl acetate, methyl ethyl ketone, toluene, isopropyl alcohol, etc. These are high-speed machines with air volumetric flows of 100,000 m³/hr or more.
Erected cost
Rs 1,150–1,170 lakh