Material balance for the diesel desulfurizer is taken up next. The spreadsheet displays the volume and properties of various diesel streams from the CDU (light diesels), VDU (light-vacuum gas oil, LVGO), and FCCU (light-cycle gas oil, LCGO). Light cycle gas oil must be hydrotreated to send it to diesel pool because of product stability considerations.
The volume of the feedstream to the diesel desulfurizer is manually adjusted to fill the unit. The objective is to give priority to high-sulfur streams. A part of the LCGO from the FCCU is sent to diesel desulfurizer unit. The only other disposition for LCGO in fuel oil is as cutter, so there is every incentive to blend as much LCGO into diesel as possible. The primary purpose is to improve the stability of the LCGO rather than desulfurize it. The remaining capacity is utilized for desulfiirizing straight-run diesel streams, starting with the highest-sulfur streams, until the unit is full.
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