Furnace type of tubular cracking furnace

At present, the tubular cracking furnaces widely used in the world include short residence time furnaces, superselective furnaces, Linde-Silas furnaces and ultra-short residence time furnaces.

Short residence time furnace

It is a kind of SRT developed by Rhuems Company in 1960s and 1970s. There are three types: SRT-I, SRT-1II and SRT-III (Figure 2), in which SRT-II can be divided into two types: high selectivity (HS) and high yield (HC). SRT-1 consists of equal-diameter pipes; SRT-Ⅱ and SRT-Ⅲ are variable diameter tubes with thin front and thick back. Four parallel feeds are used to strengthen the early heating, shorten the residence time and reduce the later hydrocarbon partial pressure, thus improving the selectivity and increasing the ethylene yield. Because of the different diameters and arrangements of the three reaction tubes, their technical characteristics are also quite different (see table).

SRT furnace is the most widely used furnace type in large ethylene plants in the world. The cracking furnace was used in 300,000-ton ethylene production units of Yanshan Petrochemical Company, Yangzi Petrochemical Company and Qilu Petrochemical Company in China.

Superselective cracking furnace

Ultra supercritical furnace for short. It is a furnace type developed by Webster Company in Si Tong, USA in 1970s. The basic structure of the furnace is basically the same as that of the SRT furnace, but the reaction tube consists of several groups of W deformed diameter tubes (Figure 3). Each group has four tubes, the first two are made of HK-40 and the last two are made of HP-40. Centrifugal casting, smooth internal processing, pipe diameter from small to large, generally 50 ~ 83 mm, length 60. According to the requirements of production capacity, each furnace can be equipped with 16, 24 or 32 tube groups. After leaving the reaction tubes, the pyrolysis products quickly enter the special quench boiler (USX), and each group of reaction tubes is equipped with a quench boiler.

The main technical features of the ultra-supercritical furnace are as follows: (1) Using multiple groups of small-caliber tubes, double-sided radiation heating, large specific surface area of the furnace tube, uniform heating and high thermal intensity, thus achieving short residence time below 0.3s. (2) Reducing the partial pressure of hydrocarbon in the process by reducing the diameter of pipe. Short residence time and low hydrocarbon partial pressure make the cracking reaction have good selectivity.

The annual ethylene production capacity of a single ultra-supercritical furnace can reach 40kt. China Daqing Petrochemical Complex and many petrochemical plants in the world use it to produce ethylene and its related products.

Linde-Silas cracking furnace

LSCC furnace for short. It was developed by Linde Company and Silas Company in the early 1970s. The basic structure of the furnace is similar to that of SRT furnace. The reactor tube with special structure is suspended in the center of the furnace (Figure 4). Each group of reaction tubes consists of 12 small-diameter tubes (the first 8 tubes form 4 pairs of parallel tubes and the last 4 tubes form 2 pairs of parallel tubes), 4 medium-diameter tubes (4 tubes form 2 pairs of parallel tubes) and 1 large-diameter tubes, with a diameter of 6- 15cm and a total length of 45-60m. Cracking products immediately enter the quenching boiler for quenching after leaving the reaction tube.

The characteristic of LSCC furnace reactor is that the inlet of raw materials is heated by double-row and double-sided radiation with small diameter tubes, which can quickly increase the temperature of raw materials and shorten the residence time. The subsequent reaction tubes are heated by single row and double sides radiation, and the pipe diameter is increased one by one to reduce the partial pressure of hydrocarbons. The residence time of materials in the reaction tube is 0.2 ~ 0.4s s. The short residence time and low hydrocarbon partial pressure make the cracking reaction have high selectivity and high ethylene yield.

LSCC cracking furnace has been applied in industry, and the annual output of ethylene per furnace can reach 70kt.

Ultra-short residence time cracking furnace

USRT furnace for short, or millisecond cracking furnace. It is a new type of tubular cracking furnace jointly developed by Kellogg Company of the United States and Xinwu Petrochemical Company of Japan in the late 1970s. The furnace is composed of more than ten single straight pipes with a diameter of about 2.54cm and a length of about 10m in parallel. The reaction tube is suspended in the center of the radiation chamber and heated by the double-sided radiation of the bottom burner. The material enters the upper part from the lower part, leaves quickly and enters the special USX quench boiler. Every two reaction tubes share a USX, and several USX are connected to a secondary quench boiler. The residence time during pyrolysis can be lower than 100ms, which significantly improves the selectivity of the reaction. Compared with the traditional tubular cracking furnace, the relative yield of ethylene can be increased by about 65438 00%, while the relative yield of methane and fuel oil is decreased.

The annual ethylene production of a single USRT furnace is 50 ~ 60 kt. This furnace was first used in the 300,000-ton/year ethylene production plant of Chiba Chemical Plant under the Japanese Xinwu Petrochemical Company. China Lanzhou Petrochemical Company will also use the cracking furnace to produce ethylene.

In addition to the above-mentioned main furnace types, Japan's Mitsubishi Inverted Ladder Furnace (using elliptical cracking reaction tube), French Petroleum Research Institute (IFP) Ladder Furnace, American Foster-Wheeler Ladder Furnace, multi-zone furnace, etc. It has been used in industry, but these furnaces are rarely used by manufacturers now.