PURIFICATION OF AIR, WATER AND OFF GAS · SOLVENT RECOVERY

Activated Carbon for Solvent Recovery

K. -D. Henning J. Degel

Paper presented at the Meeting of the European Rotogravure Association Engineers GroupMulhouse/France. 20/21 March 1990

Activated Carbon for Solvent Recovery

Contents

The German engineers Pfefferle and Baurhenne report on the construction of a plant for toluene recovery with integrated waste water purification and heat recovery. In a printing office 160,000 m³/h waste air from a rotogravure printing machine are purified. The toluene concentration amounts to approximately 6 g/m³ and 960 KG toluene per hour are recovered.

The plant consists of three horizontal adsorbers of 3.8 m diameter and 14 m length each. Of the three adsorbers two are always connected to the process gas current whilst the third one is being regenerated by steam. The plant is controlled electronically and fully automatically. The adsorber is automatically switched over from adsorption to regeneration once a specific toluene concentration in the adsorber outlet is exceeded.

The toluene concentration of adsorptively purified exhaust air amounts to approximately 30-80 mg/m³. For improving the purity of exhaust gases the ECB process (Emission Cutback Process), is integrated in the plant. The liquified and cooled toluene-water mixture produced during desorption is separated in a decanter. The separator wastewater is liberated from its dissolved toluene, by air-stripping. The strip air is recycled to the waste air current upstream of the adsorbers. 960 KG toluene per hour are recycled to the printing process. The toluene recovery amounts to 99 %. The toluene recycling principle applied in the printing office can be taken from figure 13

Figure 13: Toluene recycling principle in the printing office

Let me show you by means of some examples what influence the process conditions and the choice of an optimized activated carbon quality may have on the cost effectiveness of the process. The electricity costs for the blower contribute to the operation costs.