Today we share the application of our high temperature plate preheater in the waste heat recovery system of crude oil heating furnace flue gas in petrochemical industry.
The working principle of crude oil heating furnace:
The liquid (gas) fuel is burned in the radiant chamber (furnace) of the heating furnace to produce high-temperature flue gas, which is used as a heat carrier to flow into the convection chamber and discharged from the chimney. The crude oil to be heated first enters the furnace tube of the convection chamber of the heating furnace. The temperature is generally 35 to 50 degrees. The heat of the flue gas is mainly transferred to the outer surface of the furnace tube by convection, and then transferred from the outer surface of the furnace tube to the inner surface of the furnace tube by conduction, and then transferred to the crude oil flowing in the tube by convection.
Then the crude oil enters the furnace tube of the radiant chamber from the convection chamber furnace tube. In the radiant chamber, the flame sprayed by the burner mainly radiates part of the heat to the outer surface of the furnace tube, and the other part radiates to the furnace wall where the furnace tube is laid. The furnace wall radiates heat to the outer surface of the furnace tube on the side of the fire back surface again in a radiant manner. The two parts of radiant heat work together to heat the outer surface of the furnace tube and form a temperature difference with the inner surface of the tube, which is transferred to the inner wall of the tube by heat conduction. The crude oil flowing in the tube continuously obtains heat from the inner wall of the tube in a convection manner, realizing the heating of the crude oil. crafting process.
The crude oil is heated directly through the furnace tube called direct heating; the heat medium is used to increase the temperature through the furnace tube of the heating furnace, and then the heat is transferred to the crude oil through the heat exchanger, which is called indirect heating.
Application of high temperature flue gas preheater :
A large-scale petrochemical company in Zhejiang is a comprehensive petrochemical company with an annual output of 2 million tons of aromatics. It is one of the largest aromatics production companies in China.
The company actively responds to the national carbon peak and carbon neutral requirements and the Zhejiang Province’s guidance on reducing carbon emissions. Based on its own actual situation, after investigation and planning, it has decided to adopt 95+ technology in the flue gas waste heat recovery system of 5 heating furnaces in the aromatics unit. (Ultra-clean and efficient heating furnace waste heat recovery).
After the project was put into operation, the thermal efficiency increased by 1.7%; the nitrogen oxide emission concentration dropped from 100-80 mg/Nm3 to 80-50 mg/Nm3, which was far lower than the national standard. The heating furnace has a thermal efficiency of 95.1% and a near-zero emission of sulfur dioxide and particulate matter. It can save more than 17 million cubic meters of fuel gas and reduce carbon dioxide emissions by 32,000 tons per year compared to before the transformation. The economic and social benefits are very considerable.
The thermal efficiency of the heating furnace is increased to 95%, and the energy consumption index of the petrochemical aromatics heating furnace is further reduced, which is at the leading level of similar devices at home and abroad.
The high-temperature flue gas preheater in the heating furnace flue gas waste heat recovery system is manufactured by Jiema.
Advantage of Jiema’s plate type high temperature flue gas preheater:
1. High efficiency of heat transfer
The plate-type flue gas preheater has compact structure, good heat exchange performance and low resistance, which is one of the development directions of air preheaters.
After testing, the heat transfer coefficient of the plate-type flue gas preheater is 1.2 to 1.5 times that of the tube-bundle air preheater. With the same heat load, the heat exchange area can be saved by 20% to 50%.
2. Compact heat exchange area, high degree of integration
The heat exchange monomer adopts a modular combination. In the design, the heat exchange interval of the flue gas is divided into a high temperature interval and a low temperature interval. The monomers in the high temperature interval do not need to be replaced during use, and the monomers in the low temperature interval It is designed and manufactured to be able to be replaced separately, which can reduce the workload of maintenance.
The total heat exchange area of the high temperature section is 10500 m2. The total heat exchange area in the low temperature section is about 3240 m2. Using thin steel plates, the plate spacing is 24mm, the number of plates per single unit is 320, and the heat exchange area of each plate is 3.65m2.
It can be seen from the above data that the heat exchange area of the plate-type flue gas air preheater for the same volume of heat exchanger is 2 to 2.5 times that of the tube-bundle type, which is much more compact than the tube-bundle type.
The heat exchange core is free to expand when the equipment is running, and the advantage is to prevent the material from cracking due to the excessive temperature difference between the hot and cold sides.
3. Modular production, flexible on-site assembly
This project is produced in three modules: the heat exchange area of each component in the high temperature section is about 3500 m2, and the heat exchange area of each component in the low temperature section is about 3300 m2. The total weight of the equipment is more than 200 tons.
The combination of several monomers ensures the smooth on-site installation of the heating furnace flue gas waste heat recovery system with larger heat load and meets user requirements.
The flue gas of the heating furnace generally flows up and down, and the heat transfer fins of the plate-type flue gas preheater are placed vertically, consistent with the flue gas flow. The flue gas flowing up and down can directly exchange heat with the horizontally flowing air through the vertical heat transfer fins.
Dew point corrosion in the low temperature zone of flue gas has always been a very important issue for petrochemical heating furnaces. The high temperature flue gas plate preheater of Jiema shares is mainly solved from the following three aspects: First, through process calculations, it is ensured that the exhaust gas temperature is slightly higher than the dew point corrosion temperature of the flue gas, so as to avoid dew point corrosion. Secondly, select suitable alloy materials in the low temperature zone to avoid corrosion. Finally, in the flue gas transition section, the bypass opening is designed according to the change of ambient temperature, and the exhaust gas temperature is controlled within a reasonable range, which fundamentally solves the problem of flue gas dew point corrosion.
Post time: Sep-02-2021