A major Chinese refinery
Problem: The existing tray column could not achieve desired flexibility required by the customer. High pressure drop caused high steam consumption and low yield of light side cuts.
History: The ID 4800mm atmospheric column was originally designed with conventional trays with capacity of 3,500,000 tons/year (crude oil base) at the middle of 1990's. Inadequate tray open fraction made its pressure drop increase sharply when the capacity approached designed value. High pressure drop limited the yield of light cuts and more stripping steam was consumed. Before set up this column, Zehua Company had successfully reconstructed an ID 3200mm atmospheric column with structured packings for the customer. Its excellent performance for several years made the customer decide to have the new ID 4800mm tray column also reconstructed with structured packings by Zehua.
Solution: Two PA sections and a stripping section were retrayed with Zehua's proprietary EDV® trays instead of structured packings to minimize the revamping cost. Zehua's SP structured packings were designed for five fractionation beds to improve separation efficiency and reduce pressure drop. More NTS are available from the SP packings for their large specific surface area and special surface features, which are very important for promoting the formation of liquid film inside packing beds. Trough type liquid distributors were used for all the packing beds to attain uniform liquid distribution across the beds. Specially designed chimney trays were used as collector trays with existing tray attachments, which further reduced engineering cost for the customer. For better vapor distribution and lower liquid entrainment at flash zone, Zehua's proprietary streamlined vapor distributor design was adopted at the feed inlet section.
Results: The partially packed atmospheric column obtains higher flexibility and better separation efficiency. The upper limit of capacity increases by over 15%. The yield of light side cuts increase by at least 0.5% (crude oil base). The overlap between adjacent cuts has significantly reduced. ASTM D86 IP of the third side cut has risen by 33¡æ.