Reduction of steam consumption in activated carbon solvent recovery plants

The constant research for the efficiency of the different production processes has allowed Brofind to develop the “Steam back” technology, useful to save up to 30% of the steam used in a solvent recovery plant.

These plants allow solvent to be recovered through an initial adsorption phase on activated carbons, followed by a regeneration phase in which the solvent is stripped by a hot fluid (steam) which is then condensed.

This recovers a water (condensed steam) and solvent mixture which, when cooled, is easy to separate.

Operating principle

Steam consumption can be reduced by exploiting the latent heat still present in the solvent-steam mixture (desorbent) exiting the adsorber during the regeneration phase. In the first few minutes the steam totally condenses as all of the heat is yielded to heat the absorber and the carbon; then the steam (only acting as a carrier medium) is still available under the form of steam exiting the adsorber.

Thanks to the slight degree of vacuum produced by a thermo-compressor (fed with fresh steam at 8-9 bar) and the heat supplied by the desorbate, steam can be produced by re-evaporating the previously stored condensate.

The steam produced, mixed with fresh steam feeding the thermo-compressor, makes up the steam flow rate necessary to regenerate the activated carbon.

This system, supplying about 0.7 kg of fresh steam at 8 bar with traditional boilers, produces approximately 1 kg of the vacuum recovered steam (97°C) for a total of 1.7 kg of steam suited for regeneration (the amount of fresh steam introduced is therefore only 41% compared to that required by a traditional system).

Advantages of the technology

Reduction of steam consumption during normal operation of a solvent recovery plant with steam regeneration.

Intervention and proposal

A regeneration cycle with steam uses about one third of the steam input time only to heat the adsorber and the carbon: during this period, there is no outgoing steam flow from the adsorber and therefore as the evaporator is not fed, it cannot recover steam. Two thirds of the regeneration period are still available for heat recovery, saving about 30% compared to the typical consumption of a traditional system.

FURTHER BENEFITS OF THE SYSTEM

Improvement of Environmental ConditionsLess Cooling Water ConsumptionLess Condensate to Be Treated
The reduction of steam consumption allows boilers which produce it to generate less CO2, due to a reduced consumption of fuel. The consumption of feed water of the boilers and of the relative reagents required for pre-treatment is also reduced.As less steam needs to be condensed and cooled, less cooling water is required thus reducing the operating load of the tower: this entails reduced power consumption of the circulating pumps for the cooling circuit and the fans of the cooling tower.The reduction of steam consumption entails the reduction of the amount of condensate to be treated. This will decrease the consumption linked to the treatment itself (electric energy and steam for the regeneration of the final activated carbon filter, if any).