Selection of equipment for crude benzene in coke oven gas

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.

Selection of main process equipment for crude benzene recovery

The main equipment of the crude benzene recovery unit includes a benzene washing tower, a benzene removal tower, a tubular furnace, various heat exchangers, and transfer pumps. The benzene washing tower is a packed tower, and the packing is generally made of spherical and perforated corrugated packing with a larger specific surface area.

The application of stainless steel corrugated packing has become increasingly widespread, with advantages such as long service life, high packing efficiency, low adhesion of impurities, and easy cleaning. Although the one-time investment is relatively high, it has gradually replaced other forms of packing such as plastic flower garlands in new construction projects.

At present, there are mainly two types of benzene removal towers: bubble cap tower and float valve tower. Some old benzene washing units use cast iron bubble cap towers for benzene removal, which have a large volume, occupy a large area, have a high overall cost, and have a large pressure drop inside the tower.

In recent years, stainless steel floating valve towers have gradually replaced cast iron bubble cap towers. Stainless steel floating valve towers have higher heat and mass transfer efficiency, and the tower sections are welded. They have the advantages of good corrosion resistance, thin tower walls, light operating weight, and high operating elasticity. Under the same processing capacity, their tower diameter is also much smaller than that of bubble cap towers. Its operating platform can be replaced by a steel platformReplace concrete frame to save engineering costs.

The heat exchangers used in the benzene washing units of various coking plants are mostly spiral plate heat exchangers, which have the advantages of high heat transfer coefficient, no deposition of dirt, easy use, simple operation, and low price. However, due to their small plate wall gaps, they are only suitable for clean materials, and once blocked or flowed, the equipment can only be scrapped, which also has its limitations.

The media involved in the benzene washing device, crude benzene and wash oil, are both flammable and explosive media, and according to the classification of occupational exposure to toxic substances (GB5044), crude benzene belongs to extremely hazardous media. Therefore, the selection of pumps for transporting crude benzene and wash oil and other media is very important.

Generally, for pumps transporting crude benzene, chemical pumps with good sealing performance and reliable quality should be selected. The shaft seal should be reliable and leak free, and shielded pumps are often used.

Crude benzene belongs to the Al class fluid specified in the "Design Specification for Industrial Metal Pipelines", and some pipelines in the benzene washing device belong to GC1 class pressure pipelines. Therefore, it is necessary to comply with the requirements of the "Safety Technical Supervision Regulations for Pressure Pipelines - Industrial Pipelines", and the selection of pipeline standards and materials is particularly important. For example, GC1 type pipelines can be used

Steel pipes that meet the standards of "High pressure Seamless Steel Pipe for Fertilizer" and "Seamless Steel Pipe for High pressure Boiler", if using steel pipes that meet the standards of "Seamless Steel Pipe for Fluid Transport", shall be subjected to ultrasonic testing one by one, and shall not be lower than the requirements of Level 2.5 of "Ultrasonic Testing Method for Seamless Steel Pipes" (GB/T5777-2008).

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).