1 Overview

During the coking process, coal is not only converted into coke by about 75%, but also generates various chemical products and gas by about 25%. For every 1 ton of coke refined, approximately 430 cubic meters of gas can be produced. After cooling and various recovery systems, the raw gas can be used to extract chemicals such as coal tar, ammonia, naphthalene, hydrogen sulfide, hydrogen cyanide, and crude benzene, and obtain clean coke oven gas.

For an enterprise with an annual output of 900000 tons of coke, about 9500 tons of crude benzene can be recycled each year. If the crude benzene is not recycled and directly used for reheating combustion, it is undoubtedly a serious waste of resources.

Recovering crude benzene, a major chemical product, from coke oven gas is not only in line with the industrial policy of promoting circular economy and comprehensive utilization of resources, but also an important way to improve the economic efficiency of enterprises.

Main process routes and operating parameters for crude benzene recovery

At present, the crude benzene recovery equipment in domestic coking plants mainly includes two parts: benzene washing and benzene removal. Washing benzene involves using tar wash oil to remove most of the benzene from the final cooled coke oven gas, and then sending the gas to various users for use; The benzene removal is to remove the benzene from the rich oil after washing, and the crude benzene obtained is loaded and sold separately. The lean oil after benzene removal is returned to the benzene washing tower for recycling.

The main process flow and parameters are as follows:

After final cooling, the coke oven gas enters the benzene washing tower from the top of the tower. The gas in the benzene washing tower comes into contact with the reverse flowing wash oil, and the benzene in the gas is absorbed by the wash oil, reducing the crude benzene content in the coke oven gas leaving the benzene washing tower to about 2g/Nm. The benzene content is 0.3% to 0. 5% lean oil is pumped from the lean oil tank to the top of the benzene washing tower and discharged from the bottom. Its benzene content increases to 2% to 2.5%, which is called rich oil. Rich oil is converted into lean oil after benzene removal in the benzene removal tower, and then returned to the benzene washing tower for recycling.

The rich oil from the bottom of the benzene washing tower is preheated to 50 ℃ by exchanging heat with the crude benzene steam from the benzene removal tower in the condenser, and then subjected to a rich poor oil heat exchanger to 125 ℃ -135 ℃. It is then heated in a tube furnace to 80 ℃ -190 ℃ before entering the benzene removal tower.

The steam coming out of the top of the benzene removal tower is about 90 ℃. It enters the condenser and first exchanges heat with the rich oil from the bottom of the benzene washing tower. After being cooled by chilled water, it enters the crude benzene separator, and the separated crude benzene enters the crude benzene storage tank. The hot lean oil at the lower part of the benzene removal tower is cooled to 25 ℃ -30 ℃ by the lean rich oil heat exchanger and cooler, and then sent to the benzene washing tower for recycling.

Our company provides engineering design, equipment supply, and installation services for 600000 to 1.2 million tons/year coke ovens (including cold drum section, desulfurization section, sulfur ammonia section, and benzene washing section).