Multitubular Reactor Coolant Flow for Ethane ODH Hot-Spot Control
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Solution Overview
Problem
In oxidative dehydrogenation of ethane to ethylene, fixed-bed reactors face challenges with hot-spot formation due to exothermic reactions, leading to reduced yield and catalyst degradation, and existing solutions like reducing tube diameter or operating at lower productivity increase costs and complexity.
Innovation Solution
A multitubular fixed-bed reactor design with a perforated partition dividing the shell space into upstream and downstream regions, using counter-current coolant flow in the upstream region and co-current flow in the downstream region, allowing for controlled temperature management and minimizing hot-spot formation without reducing tube diameter or increasing length.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If the diameter of the tubes is reduced to increase heat transfer rate per unit volume, then heat transfer efficiency is improved, but the cost of building the reactor and catalyst loading time increase
Solution Approach 1:
The reactor shell space is divided into two distinct regions (upstream and downstream) by a partition, allowing different coolant flow patterns to be applied to different sections. This segmentation enables optimized heat transfer in each region without requiring reduced tube diameters throughout the entire reactor, thus avoiding increased construction costs while maintaining effective temperature control.
2Productivity
If the tube length is significantly increased to maintain productivity, then reaction capacity is improved, but the pressure drop across the reactor increases
Solution Approach 1:
The coolant flow pattern is made dynamic and adaptive to the reaction conditions in different reactor sections. By switching from counter-current flow in the upstream region to co-current flow in the downstream region, the system optimizes heat transfer at different conversion levels, maintaining productivity without requiring excessive tube length that would increase pressure drop.
3Temperature
If the coolant circulation rate is increased to rapidly remove heat and maintain isothermal conditions, then temperature control is improved, but the reactor cost and complexity increase
Solution Approach 1:
Different coolant flow patterns (counter-current in upstream, co-current in downstream) are applied to different regions of the reactor based on local heat transfer requirements. This localized approach achieves effective temperature control and prevents hot-spot formation without requiring uniformly high coolant circulation rates throughout the entire reactor, thereby reducing overall system complexity and cost.
4Reliability
If the reactor operates at lower productivity or lower conversion to avoid hot-spots, then hot-spot formation is reduced, but the cost increases and catalyst recovery becomes more difficult
Solution Approach 1:
The reactor design proactively addresses hot-spot prevention by implementing a partitioned structure with optimized coolant flow patterns before hot-spots can form. The counter-current flow in the upstream region pre-cools the catalyst bed at the point where exothermic reactions are most intense, preventing temperature runaway while maintaining high conversion rates and productivity.
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 maintains isothermal conditions, reduces the risk of reactor runaway, and achieves high productivity while avoiding the formation of hot-spots, thus enhancing the efficiency and safety of the oxidative dehydrogenation process.
Implementation Method 1
a shell in which the tubes are contained through which coolant circulates to facilitate the removal of the reaction heat
Implementation Method 2
circulating a coolant that is in counter-current flow with the flow of the reactants through the tubes at a sufficiently high circulation rate so as to rapidly remove heat
Implementation Method 3
ethane is reacted with oxygen in the presence of an ODH catalyst to produce a product stream comprising predominately ethylene
Implementation Method 4
the undesirable combustion reactions of ethane and ethylene, both of which are highly exothermic and generate carbon dioxide and/or carbon monoxide
Implementation Method 5
both of which are highly exothermic and generate carbon dioxide and/or carbon monoxide
Data Source
Figure 1
AI summary
Processes and associated reaction systems for the oxidative dehydrogenation of ethane are provided. In particular, a process is provided that comprises supplying a feed gas comprising ethane and oxygen to a multitubular fixed-bed reactor, allowing the ethane and oxygen to react in the presence of an oxidative dehydrogenation catalyst to yield a reactor effluent comprising ethylene; supplying a coolant to an upstream region of an interior shell space of the reactor in a flow pattern that is counter-current with the flow of the feed gas; and withdrawing the coolant from the upstream region and supplying at least a portion of the coolant withdrawn from the upstream region to the downstream region in a flow pattern that is co-current with the flow of the feed gas.