Fischer-Tropsch Reactor Shutdown Using Coolant Quench and Recycle Gas
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Solution Overview
Problem
Existing methods for shutting down a Fischer-Tropsch reactor are inefficient, requiring extensive purging with inert gas, leading to waste of synthesis gas and extended start-up times, and do not provide sufficient flexibility or protect the catalyst effectively.
Innovation Solution
A method involving depressurization of the coolant to cool the reactant gas mixture, stopping synthesis gas feed, and maintaining recycle gas circulation to quench reactions, minimizing purging and preserving inert gas, thus allowing for a partial shut-down that conserves resources and reduces restart time.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the reactor is shut down using conventional methods with inert gas purging, then the catalyst is protected from overheating, but the synthesis gas is wasted and start-up time is extended
Solution Approach 1:
The patent recovers and reuses the recycle gas that would otherwise be discarded during shutdown. Instead of venting the recycle gas containing unreacted synthesis gas, the system captures it and re-introduces it into the reactor to maintain temperature and prevent catalyst overheating, thereby recovering valuable synthesis gas components
Solution Approach 2:
The patent maintains continuous circulation of recycle gas through the reactor during shutdown to sustain thermal conditions. The recycle gas flow continues uninterrupted, providing both cooling and temperature maintenance functions, which prevents the need for complete gas purging and extends the useful action of the system
2Reliability
If the reactor is shut down using conventional methods with inert gas purging, then the catalyst is protected from overheating, but the start-up time is extended
Solution Approach 1:
The patent prepares the recycle gas system in advance for shutdown operations. By pre-positioning the recycle gas flow path and control mechanisms, the system can rapidly transition to shutdown mode without requiring extensive purging operations, thereby reducing the time loss associated with start-up after shutdown
Solution Approach 2:
The patent implements dynamic control of the recycle gas flow during shutdown transitions. The system can rapidly adjust flow rates and directions of recycle gas to optimize both catalyst protection and shutdown speed, enabling faster transition between operating and shutdown states compared to conventional static purging methods
3Reliability
If the reactor is shut down using conventional methods, then the catalyst is protected, but the process lacks flexibility
Solution Approach 1:
The patent makes the recycle gas system multi-functional by using it for both normal operation and shutdown procedures. The same recycle gas circulation system provides temperature maintenance during operation and catalyst protection during shutdown, eliminating the need for separate inert gas purging systems and enhancing overall process flexibility
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
Minimizes reactant purging, conserves inert gas, and reduces restart time while ensuring catalyst protection, enabling efficient and flexible reactor management.
Implementation Method 1
a fixed bed of Fischer-Tropsch catalyst is cooled in heat exchange with a coolant, such as boiling water under pressure
Implementation Method 2
depressurising the coolant to cool the reactant gas mixture to quench Fischer-Tropsch reactions taking place in the Fischer-Tropsch reactor
Implementation Method 3
maintaining circulation of the recycle gas through the Fischer-Tropsch reactor during steps (a) and (b) to remove heat from the Fischer-Tropsch reactor
Data Source
AI summary
A method is described for shutting down a Fischer-Tropsch reactor fed with a reactant gas mixture comprising a synthesis gas and a recycle gas recovered from the Fischer-Tropsch reactor in a synthesis loop, said Fischer-Tropsch reactor containing a Fischer-Tropsch catalyst cooled indirectly by a coolant under pressure, comprising the steps of: (a) depressurising the coolant to cool the reactant gas mixture to quench Fischer-Tropsch reactions taking place in the Fischer-Tropsch reactor, (b) stopping the synthesis gas feed to the Fischer-Tropsch reactor, and (c) maintaining circulation of the recycle gas through the Fischer-Tropsch reactor during steps (a) and (b) to remove heat from the Fischer-Tropsch reactor. The method safely facilitates a more rapid return to operating conditions than a full shut-down.