Calculations And Process Optinmization Of Extraction Distillation System

Based on the relevant theories of extraction distillation and chemical engineering, this thesis analyzes the problems of the revamped Butadiene Extraction Plant of Lanzhou Petrochemical Company which adopts the acetonitrile process, and raises the reasonable measures to solve those problems of the revamped plant and to optimize the process. For the revamped First Extraction Column, the cracked C4, after being preheated and vaporized, was fed into the Column so that the plant energy consumption was reduced. However, the negative influence of the gas feed upon the separation should be fully considered in the engineering design and thus the column should be rationally modified, such as optimizing C4 preheating process; correctly engineering the opening rate of trays and the gap of the down-comer in accordance with the calculation of the stripping section of the column; and equipping with a proper distributors for the feed stock to distribute the gas feed evenly for minimizing shock to the adjacent part of the tower tray. In order to keep the total pressure drop of the First Extraction Column within a proper range, the column needs to be equipped with the suitable bubbling propellers and multiple-hem-inclined down comers with adequate passage area of the outlets, which are beneficial for the column under high load to keep normal operation. Furthermore, This thesis raises the optimized process of the Extraction Columns and the following towers to ensure the quality of the product butadiene by means of analyzing the separation actions of the columns and finding the cause of the quality problems of product butadiene ,such as, setting the First Extraction Column feeding nozzle on a correct position and controlling the trans-2-butylene less than 0.1% in the First Extraction Column bottoms; setting the alkyne drawing- outlet on the correct position of the Second Extraction Column to draw out the alkyne as more as possible, reducing the recycle of drawn alkyne and decreasing the alkyne concentration in the Column Bottoms; employing a special process to remove the alkyne to ensure the alkyne less than 5 mg/kg in the product butadiene. In addition, this thesis raises the measures to save energy and to reduce materials consumption, such as, recovering the heat of recycle acetonitrile; preheating the heating mediums of the reboilers by using the heat of the overheads of acetonitrile recovery tower and the heat of the Second Extraction Column side-drawn gas; and preheating the C4 feeding stocks by using the overheads of the First Extraction...