Why is it essential to maintain a stable furnace outlet temperature when adjusting the temperature of the hydrocracking reaction?

The cracking reaction in a hydrocracking unit is primarily achieved by using a heating furnace to raise the temperature to the required level for cracking.

Controlling the outlet temperature of the furnace is done for the safety of the furnace tubes; otherwise, large fluctuations could lead to failures and leaks.

In my opinion, for small adjustments in the amount of reduction, the desired conversion rate can be achieved by adjusting the temperature of the bed layers; moreover, it is important to adjust the temperature of the subsequent bed layers, as this approach has a lesser impact. Adjusting the outlet temperature of the heating furnace at this time involves fuel supply and the adjustment of cold hydrogen in the second bed layer, resulting in a significant impact. When there is a large adjustment in the lift amount, if it becomes difficult to raise the temperature of the subsequent bed layer, it is necessary to adjust the furnace temperature.

We can analyze this from several aspects: 1. Catalysts: To extend the service life of hydrocracking catalysts, it is technically necessary to ensure maximum isothermal operation in each bed. If there are fluctuations in the furnace outlet temperature, this will inevitably cause fluctuations in the temperature of the first bed in the first reactor, which in turn **increases the amount of coke formed and leads to premature deactivation of the catalyst in that first bed. 2. Reaction temperature: Hydrocracking generally involves two reactors. The first reactor is a refining reactor (filled with refining catalysts), while the second reactor is a cracking reactor (filled with cracking catalysts). In hydrocracking reactions, the refining processes (desulfurization, denitration, aromatic saturation, etc.) are exothermic reactions. Although the cracking reaction itself is endothermic, the overall reaction results in a strong exothermic effect. Temperature is a key factor determining the degree of reaction; therefore, fluctuations in the temperature at the outlet of the furnace can lead to significant temperature variations within the reactors. This in turn causes an increase in temperature and a deterioration in the degree of reaction, and in severe cases, it may even result in a runaway reaction. 3. Equipment: The connections of high-pressure equipment are sealed using steel rings (octagonal gaskets). The material of these octagonal gaskets is different from that of the flange surfaces; as a result, their coefficients of thermal expansion differ. When the temperature at the furnace outlet fluctuates, it can lead to increased temperature variations in the subsequent reactors, which may cause leakage at the flange surfaces. Taking all the above points into account, it is easy to see the importance of maintaining stability in the outlet temperature of the reaction furnace for the reaction.

Maintaining a stable furnace temperature prevents the cracking reaction from experiencing excessive temperature rises due to increasing outlet temperatures during heating, and also avoids excessive temperature drops during cooling, which could reduce the extent of the cracking reaction. In short, maintain a stable furnace temperature during normal operation.