Multi-Stage Dehydrogenation Reactors with Parallel Heaters
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Solution Overview
Problem
The existing moving-bed dehydrogenation process for producing propylene from propane has limitations due to short catalyst residence time and low conversion rate, leading to inefficient heat supply and hydrogen partial pressure, which affects yield and production efficiency.
Innovation Solution
A method involving multiple stages of dehydrogenation reactors with separate heat supply and steam injection to adjust hydrogen to propane molar ratio, using parallel-connected reaction heaters and a cooling box to quench and purify the product gas, thereby optimizing heat distribution and reducing hydrogen partial pressure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a conventional moving-bed dehydrogenation reactor is used, then continuous catalyst regeneration can be achieved, but the catalyst residence time is short and the conversion rate is low
Solution Approach 1:
The dehydrogenation process is divided into multiple stages with separate reactors, each optimized for specific conversion requirements. This segmentation allows extended catalyst residence time across multiple reaction zones while maintaining continuous regeneration capability, thereby increasing overall conversion rate without sacrificing catalyst utilization efficiency
Solution Approach 2:
The feed gas stream is preheated to 600-700°C before entering the dehydrogenation reactors, and catalyst is pre-regenerated to optimal activity levels before entering the reaction zone. This preliminary preparation ensures maximum reaction efficiency from the start of each catalyst cycle, improving conversion rate while maintaining reasonable residence time
2Productivity
If high temperature is applied to proceed the dehydrogenation reaction at a satisfactory rate, then reaction rate increases, but catalyst deactivation by coking occurs
Solution Approach 1:
The moving-bed system enables continuous catalyst circulation between reaction and regeneration zones. Catalyst undergoes continuous regeneration by burning off coke deposits at high temperature in the regenerator, then returns to the reactor fresh. This continuous cycle maintains catalyst stability and activity over extended periods, allowing sustained high-temperature operation without cumulative deactivation
Solution Approach 2:
Temperature is optimized across different reactor stages rather than using uniform high temperature throughout. The multi-stage configuration allows temperature gradients that balance reaction rate requirements with catalyst protection, while the moving-bed regeneration cycle dynamically adjusts catalyst temperature exposure to prevent excessive coking
3Reliability
If hydrogen partial pressure is high in the feed gas stream, then catalyst coking is reduced, but the basic unit of the process increases and yield decreases
Solution Approach 1:
Steam is introduced as a substitute for high hydrogen partial pressure to suppress catalyst coking. The steam acts as a alternative protective atmosphere that prevents carbon deposition on catalyst surfaces without contributing to the hydrogen partial pressure that would reduce propylene yield. This copying of the protective function using a different substance resolves the contradiction
4Productivity
If multiple stages of dehydrogenation reactors with separate heat supply are used, then total heat supply and propylene production increase, but device complexity increases
Solution Approach 1:
Multiple dehydrogenation reactors are configured in series within an integrated moving-bed system with unified catalyst circulation and continuous regeneration. The separate heat supply to each stage is coordinated through a centralized control system that manages the overall process flow and energy distribution. This merging approach achieves increased propylene production through multi-stage reaction while managing complexity through system integration and standardized reactor modules
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 increases propylene production, improves catalyst longevity by preventing coking, and enhances the overall process efficiency by increasing heat supply and reducing the basic unit operations, resulting in higher yield and selectivity.
Implementation Method 1
two parallel-connected reaction material heaters configured to heat the feed gas stream which is fed into each of the dehydrogenation reactors
Implementation Method 2
cooling and compressing a production gas stream resulting from the previous step, quenching the compressed product gas stream by passage through a cooling box
Implementation Method 3
The dehydrogenation catalyst generally includes a noble metal catalyst on an acidic support, such as an alumina, silica alumina, or zeolite support
Implementation Method 4
the dehydrogenation reaction is a strong endothermic reaction and requires a high temperature for the reaction to proceed at a satisfactory rate
Data Source
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AI summary
The present invention relates to a method for dehydrogenating an alkane, the method including: a step of feeding into dehydrogenation reactors a feed gas stream containing a hydrocarbon to be dehydrogenated, hydrogen, and steam and performing dehydrogenation, wherein the dehydrogenation step is repeated in five or more sets, the dehydrogenation reactors have two parallel-connected reaction material heaters configured to heat the feed gas stream which is fed into each of the dehydrogenation reactors, and the steam is fed separately to the individual reactors for five or more sets of dehydrogenation steps; and a step of cooling and compressing a production gas stream resulting from the previous step, quenching the compressed product gas stream by passage through a cooling box, separating and purifying the product gas stream having passed through the cooling box, and recovering a product.