What are the characteristics of a cracking furnace

Source：www.cnxinshiji.net Release date： 2024-11-12

Cracking furnace is a key equipment in petrochemical production, with the following characteristics: 1、 Process performance characteristics 1. High temperature cracking characteristics High temperature requirements: The cracking furnace can generate extremely high temperatures, generally between 750-900 ℃. In such a high-temperature environment, the large molecular hydrocarbons in the raw

Cracking furnace is a key equipment in petrochemical production, with the following characteristics:
1、 Process performance characteristics
1. High temperature cracking characteristics
High temperature requirements: The cracking furnace can generate extremely high temperatures, generally between 750-900 ℃. In such a high-temperature environment, the large molecular hydrocarbons in the raw materials (such as naphtha, light hydrocarbons, etc.) undergo cracking reactions, breaking long-chain hydrocarbons into short chain hydrocarbons, which is a key step in the production of basic chemical raw materials such as ethylene and propylene. For example, in the production of ethylene from ethane, high temperature causes the carbon carbon bonds in ethane molecules to break, producing ethylene and hydrogen gas.
Accurate temperature control: Due to the extreme sensitivity of cracking reactions to temperature, excessively high temperatures may lead to excessive cracking, generating too much coke and by-products; If the temperature is too low, the cracking will not be complete, which will affect the product yield. Therefore, the cracking furnace is equipped with an advanced temperature control system that can accurately control the temperature inside the furnace, allowing the reaction to proceed within the ideal temperature range. Real time temperature monitoring is achieved through temperature detection components such as thermocouples, and the fuel supply system and ventilation system are used to adjust the flame size and combustion state, achieving precise temperature control.
2. Characteristics of rapid response
Short residence time: The residence time of the cracking reaction in the cracking furnace is very short, usually between 0.1-0.5 seconds. This is to reduce the occurrence of secondary reactions while ensuring sufficient cracking of raw materials. Because if the cracked product stays in the high-temperature zone for too long, side reactions such as polymerization and condensation may occur, generating coke and other impurities, which can reduce product quality. For example, in the process of ethylene production, short residence time helps to improve the selectivity of ethylene and reduce the generation of by-products.
Efficient reaction kinetics: The design of the cracking furnace enables the raw materials to quickly reach the reaction temperature and complete the cracking reaction in a short period of time. The internal furnace tube structure (such as using small-diameter, high length diameter ratio furnace tubes) can provide a large heat transfer area and good fluid dynamics conditions, accelerate heat and material transfer processes, and promote rapid reaction.
3. Product selectivity characteristics
Flexible adjustment of product distribution: By changing the operating conditions of the cracking furnace, such as temperature, pressure, raw material composition, and residence time, the selectivity of the product can be controlled to a certain extent. For example, appropriately increasing the cracking temperature and reducing the residence time are beneficial for improving the yield of ethylene; Adjusting the composition of raw materials or changing reaction conditions can also increase the production of other olefins such as propylene and butene. This flexibility enables the cracking furnace to produce products such as ethylene and propylene in different proportions according to market demand and the production plan of the enterprise.
Multi product co production capacity: While the cracking furnace produces ethylene and propylene, it also produces various by-products such as hydrogen, methane, ethane, propane, etc. These by-products can be recovered and utilized, such as hydrogen being used for hydrogenation reactions and methane being used as fuel. Some advanced cracking furnace designs can also achieve co production with other chemical processes, such as directly transporting some of the products produced by cracking to downstream polymerization units for polymerization reactions, forming an integrated chemical production process.
2、 Structural characteristics
1. The furnace structure is complex
Multi layer structure: The cracking furnace is generally composed of multiple parts such as radiation chamber, convection chamber, burner, furnace tube, and chimney. The radiation chamber is the main site for cracking reactions, providing heat to the raw materials inside the furnace tube through the high-temperature flame and radiant heat generated by the burner; Convection chamber is mainly used for recovering waste heat from flue gas, preheating raw materials and combustion air, etc; The burner is responsible for the combustion of fuel and provides energy for the reaction. This multi-layer structure design enables the cracking furnace to efficiently utilize energy while achieving different process functions.
Exquisite layout of furnace tubes: The layout of furnace tubes inside the cracking furnace is crucial. Usually, a coil or tube arrangement is used to increase the contact area between the raw materials, flames, and hot flue gas. For example, coil furnace tubes can circulate raw materials multiple times inside the furnace, extending the path in the high-temperature zone and ensuring sufficient heating. And the material of the furnace tube is also specially selected, generally using high-temperature and corrosion-resistant alloy materials, such as nickel based alloys, to withstand high-temperature cracking environments and corrosion of raw materials.
2. Good thermal insulation performance
Application of insulation materials: In order to reduce heat loss and improve energy efficiency, the exterior of the cracking furnace is wrapped with thick insulation materials. These insulation materials can effectively prevent the heat inside the furnace from dissipating outward, keeping the surface temperature of the furnace body at a low level. Common insulation materials include ceramic fibers, rock wool, etc., which have the characteristics of low thermal conductivity and high temperature resistance. For example, ceramic fiber insulation materials have low thermal conductivity and can maintain good insulation performance at high temperatures, reducing heat loss in cracking furnaces.
Reduce thermal bridging effect: In the design of furnace structure, consideration will also be given to reducing thermal bridging effect, which means preventing a large amount of heat from dissipating through conduction paths such as metal components. By adopting special connection structures and insulation measures, such as setting insulation pads between the furnace tube and the furnace body support structure, the insulation effect of the cracking furnace is further improved to prevent heat from being directly conducted from the furnace tube to the outside of the furnace body.
3、 Energy utilization characteristics
1. High energy consumption and energy recovery
High energy input requirements: Cracking furnaces are high-energy consuming equipment that require a large amount of fuel (such as natural gas, fuel oil, etc.) to maintain high-temperature cracking reactions. The fuel burns in the burner to provide the required heat for the cracking reaction. Due to the high cracking temperature and the need for continuous reaction, its energy consumption accounts for a large proportion in petrochemical plants.
Efficient energy recovery system: In order to reduce energy consumption, the cracking furnace is equipped with a comprehensive energy recovery system. In the convection chamber, the waste heat of high-temperature flue gas is utilized through a heat exchanger to preheat the raw materials, combustion air, and steam. For example, preheating the raw materials from room temperature to a higher temperature before entering the radiation chamber for cracking reaction can reduce the fuel consumption of the radiation chamber. At the same time, the recovered steam can also be used for other processes, such as driving steam turbines to generate electricity or providing power for other devices, improving the overall energy utilization efficiency of the entire device.
2. Potential for optimizing energy utilization
Application of Thermal Integration Technology: Cracking furnaces can be thermally integrated with other chemical plants to achieve optimized energy utilization. For example, transporting the high-temperature steam generated by the cracking furnace to adjacent distillation or reaction units to provide a heat source; Alternatively, the low-temperature waste heat from other devices can be utilized to preheat the feed of the cracking furnace, forming an energy recycling system. Through thermal integration technology, the energy consumption of the entire chemical production process can be further reduced, and the economic benefits of energy utilization can be improved.

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