Interpretation! Structural characteristics and types of cracking furnaces in ethylene production plants

"Triene" and "triphenyl" are the foundation of petrochemical industry, and various important organic chemical products must be produced using them as raw materials. So the ethylene plant that produces "triene" and "triphenyl" has also become the leader of the petrochemical industry, and its production scale, output, and technology can reflect the development level of the national petrochemical industry.
Classroom: What are "trienes" and "triphenyls"?
Triene: ethylene, propylene, butadiene
Triphenyl: benzene, toluene, xylene
Do you understand the production methods of ethylene? Do you know about the ethylene production equipment? Today, we will take you through common production methods and provide a detailed introduction to the structural characteristics and types of the most important device in the production process - the cracking furnace.
Production method of ethylene
1 Tube furnace cracking technology
Petroleum hydrocarbons undergo high-temperature cracking reactions in a tubular cracking furnace to produce ethylene, which is the most mature technology for producing ethylene.
2. Catalytic cracking technology
Catalytic cracking, also known as hydrocarbon cracking, occurs in the presence of a catalyst, which can lower the reaction temperature, improve selectivity, and yield. The advantages of catalytic cracking technology make it one of the most promising process technologies for improving the cracking process.
3 Syngas to Ethylene (MTO)
The MTO synthesis route is a route that uses natural gas or coal as the main raw material to produce synthetic gas, which is then converted into methanol, and then used to produce olefins, completely independent of petroleum. In the 21st century, where oil is increasingly scarce, it is expected to become an important route for producing olefins.
At present, almost all ethylene plants in the world use tube furnace steam cracking technology, while other process routes are still at the level of technological development or industrial experiments due to economic or technological "bottlenecks". There are no or very few industrial production plants that operate year-round.
Structure of cracking furnace
The cracking furnace in the ethylene plant consists of three parts: the convection section, the radiation section (including the radiation furnace tube and burner), and the quench boiler system.

The cracking reaction occurs in the radiation section furnace tube to generate products such as ethylene and propylene. The convection section recovers high-temperature flue gas waste heat to gasify and overheat raw materials to the required cross temperature for the reaction, while preheating boiler feedwater and ultra-high pressure steam. The function of the quench boiler system is to terminate the secondary cracking reaction and recover the high-temperature heat of the cracking gas to generate ultra-high pressure steam.

Improving the thermal efficiency of the cracking furnace:
a. During the normal operation of the cracking furnace, strengthen the inspection of the combustion status of the furnace nozzle, and adjust the opening of the air door based on the combustion status of the nozzle. If the fire nozzle is burnt or blocked, it should be replaced and cleaned in a timely manner to prevent the furnace tube from coking and insulation deformation due to local overheating.
b. Control the oxygen content of flue gas.
c. Pay attention to the airtightness of the furnace and reduce heat loss. In daily operations, it is necessary to check whether the observation hole and ignition hole are closed or damaged, and to promptly handle them to reduce cold air leakage.
4. Optimize the coking plan and shorten the coking time
Burning coke in the cracking furnace is a completely energy-efficient working condition. By adjusting the ratio of diluted steam and air, timely analyzing the CO and CO2 content in the coking gas, and switching the side wall nozzle during the pure air coking stage, the furnace can be fully heated, which can effectively reduce the coking time.
In addition, burning for too long or too short is not good. When burning coke, the temperature of the furnace is high, and the temperature of the convection section is higher than normal operation. The radiation section is prone to hot spots exceeding the maximum allowable value of the furnace tube. If the coking time is too long, it will inevitably cause damage to the furnace tube, shorten its service life, and increase maintenance costs. If the coking time is short and the coking is not thorough, it will result in a short cleaning cycle for the next time and affect production.