Quench Cooling in Fluidized Dehydrogenation Reactors
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Solution Overview
Problem
In fluidized reaction systems for paraffin and alkyl aromatic dehydrogenation, the thermal reaction selectivity is lower than catalytic selectivity due to increased gas residence time caused by product transport and catalyst separation, leading to reduced overall reactor selectivity to the desired olefin product.
Innovation Solution
The implementation of a quench means, such as a quench exchanger, between the fluidized reactor and cyclonic separation system in an up-flow fluidized reactor system, which halts thermal reactions and increases overall molar selectivity to olefin products by reducing gas residence time.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If transport of product gas and solids to catalyst separation system and the separation system itself is implemented, then catalyst separation is achieved, but gas residence time increases resulting in lower overall reactor selectivity
Solution Approach 1:
The system is divided into distinct segments: the fluidized reactor for catalytic dehydrogenation, the quench zone for rapid cooling, and the cyclone separation system for catalyst recovery. This segmentation allows each component to perform its function optimally while minimizing unwanted thermal reactions during transport.
Solution Approach 2:
A quench medium (inert gas or liquid) is introduced as an intermediary between the reactor and separation system. This quench medium rapidly cools the effluent stream, halting thermal reactions that would otherwise continue during transport to the separator, thus preserving selectivity while enabling efficient catalyst separation.
2Productivity
If minimal residence time is used in up-flow fluidized reactors, then dehydrogenation reaction efficiency is improved, but thermal reactions still occur reducing selectivity
Solution Approach 1:
The quenching action is applied immediately after the reactor, before the effluent enters the separation system. This preliminary cooling action stops thermal reactions at their inception, preserving the high selectivity achieved during the brief catalytic reaction period while enabling subsequent catalyst separation.
Solution Approach 2:
The system rushes the hot effluent through the quench zone as quickly as possible, minimizing the time window for thermal reactions to occur. The rapid cooling transitions the stream from reaction conditions to separation conditions in a single swift action, preventing selectivity loss.
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 effectively enhances the overall molar selectivity to olefin products by at least 0.5 mole% compared to processes without cooling means, while maintaining equivalent overall conversion, thereby improving the efficiency of the dehydrogenation process.
Implementation Method 1
rapidly cooling the effluent stream from the reactor with a quench cooling means interposed between the reactor and the cyclone separation system
Implementation Method 2
separating the catalyst from the effluent stream in a cyclone separation system
Data Source
Figure 1
AI summary
An improved catalytic dehydrogenation process which process comprises contacting an alkane or alkyl aromatic feedstream with a dehydrogenation catalyst under catalytic conditions in an up-flow fluidized reactor, wherein the fluidized reactor comprises one or more reactors, which catalytic conditions include a temperature within a range of from 500 to 800 °C, a weight hourly space velocity within a range of from 0.1 to 1000, a gas residence time within a range of from 0.1 to 10 seconds, and, subsequent to the fluidized reactor, effecting separation of entrained catalyst from reactor effluent by use of a cyclonic separation system, wherein the improvement comprises interposing a cooling means between an up-flow fluidized reactor and the cyclonic separation system to substantially halt thermal reactions, thereby effectively increasing overall molar selectivity to alkene product is provided.