Fixed-Bed Reactor Restart Temperature Control
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Solution Overview
Problem
Conventional gas-phase contact oxidation reactions in fixed-bed reactors face instability and catalyst deterioration during restart periods after shutdown, with the maximum temperature in the catalyst layer exceeding desired ranges, leading to concerns about reaction runaway.
Innovation Solution
A method for producing acrolein or acrylic acid involves controlling the heating medium temperature during restarts to be lower than the initial start-up temperature by 1-30°C, maintaining catalyst activity and preventing temperature rises, using a fixed-bed reactor with a specific gas-phase oxidation catalyst and managing load calculations to ensure stable operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the temperature of the heating medium at restart is set the same as the initial start-up temperature, then the reaction can proceed efficiently, but the maximum temperature in the catalyst layer exceeds the desired temperature range causing unstable state and catalyst deterioration
Solution Approach 1:
The patent applies parameter changes by adjusting the heating medium temperature based on the operational history of the reactor. Specifically, when restarting within 90,000 hours after initial startup, the heating medium temperature is controlled to be lower than the initial startup temperature to prevent excessive catalyst layer temperature. This dynamic parameter adjustment resolves the contradiction between maintaining reaction efficiency and preventing catalyst deterioration.
2Ease of operation
If the temperature of the heating medium is increased by 2-3°C after shutdown (conventional method), then the reaction can be restarted, but the maximum temperature in the catalyst layer still exceeds the desired range leading to reaction runaway concerns
Solution Approach 1:
The patent inverts the conventional approach by lowering the heating medium temperature during restart instead of increasing it. This counterintuitive strategy addresses the root cause of the problem: the catalyst's increased activity after shutdown. By reducing the heating temperature, the patent prevents the catalyst layer temperature from exceeding safe limits, thereby eliminating reaction runaway risks while maintaining restart capability.
3Reliability
If the heating medium temperature is lowered by 1-30°C during restart, then catalyst deterioration and reaction runaway are prevented, but the initial start-up temperature advantage is reduced
Solution Approach 1:
The patent applies beforehand cushioning by proactively lowering the heating medium temperature before the catalyst layer temperature can rise to dangerous levels. This preventive measure accounts for the catalyst's heightened activity after shutdown, cushioning against potential temperature excursions that would otherwise lead to catalyst deterioration or reaction runaway, while still maintaining adequate reaction efficiency.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach stabilizes the reaction process, preventing catalyst deterioration and reaction runaway, and maintaining high yields of acrolein and acrylic acid during restarts, ensuring the reaction proceeds in a stable state.
Implementation Method 1
causing a heating medium to contact with or circulate through the fixed-bed reactor and thereby heating the fixed-bed reactor
Implementation Method 2
causing a heating medium to contact with or circulate through the fixed-bed reactor and thereby heating the fixed-bed reactor
Implementation Method 3
filled with a gas-phase oxidation catalyst represented by formula (1) and by subjecting at least one source gas selected from the group consisting of propylene and acrolein to a gas-phase contact oxidation reaction
Implementation Method 4
gas-phase contact oxidation reaction
Data Source
AI summary
A method for producing at least one oxidation product selected from the group consisting of acrolein and acrylic acid is provided. This method can alleviate concerns about deterioration of a gas-phase oxidation catalyst and reaction runaway in a restart period after a shutdown, and can allow the reaction to proceed in a stable state. Using a fixed-bed reactor filled with a gas-phase oxidation catalyst, at least one source gas selected from the group consisting of propylene and acrolein is subjected to a gas-phase contact oxidation reaction while a heating medium is caused to contact with or circulate through the fixed-bed reactor and thereby to heat the fixed-bed reactor. The temperature of the heating medium when the load is maximum in the restart period after the shutdown is controlled to be lower than the temperature of the heating medium when the load is maximum in an initial start-up period.