Analysis of the Causes of Scaling in High-Pressure Heat Exchangers of Hydrogenation Units and Countermeasures
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The last high-pressure heat exchanger in the high-pressure hydrogenation unit is generally used for heat exchange between the produced oil and the feedstock before the furnace; its heat exchange efficiency directly affects the temperature at the inlet of the final reactor, which prevents the catalyst from being utilized to the fullest extent. This, in turn, impacts the unit’s ability to operate over extended periods of time. Generally, severe scaling occurs mainly on the feed oil side; let’s discuss the principles behind scaling.
Scaling can lead to high wall temperatures in the heating furnace tubes, causing the heat exchangers downstream where the reaction products pass through to overheat, which affects the long-term operation of the facility.
Scaling on the crude oil side is also known as carbon deposition or gelation. Studies show that starting from 60°C, for every 10°C increase in oil temperature, the oil’s oxygen absorption rate increases by 1.5 times, while its oxidation rate increases by 2–3 times. This accelerates the formation of carbon deposits and can lead to corrosion beneath the scale, reducing heat transfer efficiency and causing corrosion in the heat exchangers. It also affects subsequent processes, having an impact on both the products and the equipment.
Why does scaling cause the tube wall temperature to rise? Scaling » Increased difficulty in heat exchange » Should the temperature at the furnace outlet be reduced?
As the production cycle lengthens, a layer of scale tends to form on the inner walls of the heat exchanger tubes for crude oil/reactant products; its main components are polycyclic aromatic hydrocarbons, which are insoluble in water, oils, acids, alkalis, and other solutions, thereby affecting operation over long periods of time. To address this issue, a scale inhibitor is injected before the heat exchanger in production; it forms a protective layer on the inner wall of the air-cooled tube bundle. It is usually injected at the inlet of the reaction feed pump to prevent scaling, and practice has shown that by using this scale inhibitor, the heat exchange efficiency can be maintained at a good level.
How can there be oxygen in the system?
It simply refers to oxidation; oxygen is not necessarily required. These are two different concepts, and here it only denotes an increase in the oxidation rate within the system
The heat exchange efficiency of the final-stage high-pressure heat exchanger has decreased, resulting in the inlet temperature of the heating furnace not reaching the designed level; therefore, the heating furnace must burn more gas to generate sufficient heat. This results in high temperatures in the furnace chamber of the heating furnace, as well as high temperatures on the walls of the furnace tubes.
What are the components of scale inhibitors? Will it have an impact on the catalyst?
A good scale inhibitor provides protection for the catalyst, thereby extending its service life
During the petroleum processing process, substances such as polycyclic aromatic hydrocarbons, resins, asphaltenes, and dienes present in crude oil undergo reactions such as dehydrogenation and condensation, as well as free-radical polymerization, at high temperatures to form large molecular compounds. These compounds stick together, causing scaling on the surfaces of equipment; this leads to severe scaling in devices such as distillation columns, heat exchangers, pipelines, and packing in units like vacuum distillation towers and catalytic cracking hydrogenation units； By using the decentralized anti-scaling agent HK series, scale in related towers, heat exchangers, and other equipment can be removed online, thereby effectively improving separation and heat exchange efficiency, reducing processing energy consumption, and extending the operational life of the facility.