Some Experience of Energy Saving for a Large Scheibel Extraction Column System

Three large Scheibel extraction columns were used for recovery and purification of an intermediate compound in a fine chemical plant. The plant was designed in 1970 when the oil price at that time was relatively low (US$3/barrel). Escalation in the price of oil (US$34/barrel) in mid 1970's caused a great concern on the energy consumption for this process in the plant. It was soon realized that the major energy consumption was in the solvent recovery system. A development program led to a modified process scheme. In the original scheme, the continuous extraction process employed two agitated 1.75 M (5′9″) multistage Scheibel extraction columns which operated in parallel. The extract from these two columns was combined with the extract from a reaction liquor extraction column, which was fed to a first effective evaporator. In the modified process scheme, the continuous extraction process is operated in the same manner as that described above in the original process scheme except the extract from the second Scheibel extraction column was used as solvent feed to the 1st Scheibel extractor. The total cost saving was calculated to be $600,000/yr at 1982 US dollars. The initial cost for modifications of the plant was minimal, and the project was highly cost-effective and well justified.