【Q&A Question 040】May 30, 2016
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This post was last edited by liuquan1100 on 2016-5-30 11:28. [Q&A Question No. 040] 2016.05.30: Why does the temperature rise in two layers of a reactor during a certain shutdown period be higher than that of a single bed layer? The answer key will be available after responding; scoring is based on addressing the key points. 1. Due to the large radial temperature difference across one bed, the catalyst may experience flow bias and channeling, resulting in insufficient reaction; the reaction intensifies only when the feed reaches the second bed. II. Since the temperature in Bed 1 is not high, the reaction has not reached its optimal temperature; it is only when the temperature rises in Bed 2 that a vigorous reaction begins.
The two-layer catalyst has a larger amount than the single-layer one, resulting in more intense heating during the reaction; moreover, the inlet temperature of the two-layer system is higher than that of the single-layer system
Reason: 1. Cold hydrogen interruption； 2. The purity of cold hydrogen is too low. 3. The thermometer is malfunctioning
①Since the hydrogenation reaction is an exothermic reaction, the result of the reaction can increase the temperature of the reactants. The calculation method for the reaction temperature rise is as follows: Temperature rise = Temperature at the highest point of the reactor bed - Reactor inlet temperature. The reaction temperature rise directly reflects the quality of the feedstock and the degree of hydrogenation. Therefore, the temperature rise must be kept within a certain range; an excessive temperature rise can cause sintering of the catalyst bed, damaging the catalyst, and in severe cases, it can damage the equipment as well. The temperature rise can be adjusted by increasing the amount of circulating hydrogen and using cooling hydrogen; if necessary, the reaction temperature can be reduced. ②Factors affecting reaction temperature rise: a. Changes in the properties of the feed oil (bromine value, sulfur and nitrogen content, etc.); b. Water content in the feed (reduces temperature rise); c. Changes in the amount of reactant fed into the reactor; d. Changes in space velocity (an increase in space velocity leads to an increase in temperature rise); e. Fluctuations in the inlet temperature of the reactor; f. Channeling within the reactor or short circuits in the heat exchanger (reduces temperature rise); g. Coking, poisoning, or loss of activity of the catalyst (reduces temperature rise); h. Changes in system pressure (an increase in pressure leads to an increase in temperature rise); i. Changes in the amount or purity of recycled hydrogen (an increase in purity reduces temperature rise; an increase in flow rate also reduces temperature rise); j. Changes in the amount or purity of fresh hydrogen (an increase in purity or flow rate leads to an increase in temperature rise); k. Changes in the amount of quench hydrogen (an increase in quench hydrogen amount reduces temperature rise). ③Treatment methods: a. Contact the tank area to adjust the composition of the reaction feed; if adjustments cannot be made within a reasonable time, switch to a larger circulation mode for the plant; b. Enhance the dehydration of the raw materials; c. Adjust the reactor inlet temperature based on the amount of reaction feed; d. Ensure stable feed supply; e. Improve the operation of the heating furnace to maintain a stable reactor inlet temperature; f. Decide whether to shut down the plant for treatment based on the properties of the produced oil; g. If increasing the reactor inlet temperature does not result in a significant rise in temperature, decide whether to shut down the plant for catalyst regeneration or replacement based on the product properties; h. Stabilize the system pressure; i. Stabilize the flow rate of circulating hydrogen; j. Stabilize the flow rate of fresh hydrogen; k. Stabilize the flow rate of quench hydrogen. ④Use of cold hydrogen: a. Cold hydrogen is an important means for removing the heat generated by reactions and regulating the temperature rise in the bed; its primary purpose is to prevent excessive temperature increases and thus extend the lifespan of the catalyst. b. The amount of cold hydrogen used is determined based on the requirements for cooling. Excessive cold hydrogen not only reduces the amount of circulating hydrogen but also lowers the temperature of the material at the reactor outlet excessively, which hinders heat recovery through heat exchange and increases the energy consumption of the plant.
1. Due to the large radial temperature difference across one bed, the catalyst may experience flow bias and channeling, resulting in insufficient reaction; the reaction intensifies only when the feed reaches the second bed. II. Since the temperature in Bed 1 is not high, the reaction has not reached its optimal temperature; it is only when the temperature rises in Bed 2 that a vigorous reaction begins.
The reaction in one layer is not good, and the inlet temperature in that layer is low
It is related to the catalyst loading in the two-stage reactor