Methanol Synthesis Gas Recycling Without a Dedicated Flash Gas Compressor
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Solution Overview
Problem
In carbon dioxide-based methanol synthesis, the expansion gas stream from the low-pressure separator cannot be easily mixed with the synthesis gas feed stream due to pressure differences, requiring separate compression, which is not economically or technically feasible.
Innovation Solution
The expansion gas stream is combined with either the hydrogen-rich or carbon dioxide-rich reactant gas stream before compression to synthesis pressure, or split into partial streams for separate combination with each reactant gas stream, forming mixed gas streams that are then compressed and combined to form a synthesis gas stream suitable for methanol synthesis.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If the expansion gas stream is mixed with the synthesis gas feed stream, then carbon dioxide emissions are reduced, but a dedicated compressor is required due to pressure differences
Solution Approach 1:
The expansion gas stream is merged with the synthesis gas feed stream at a common point after both streams have been compressed to synthesis pressure by their respective compressors. This combining allows the expansion gas to be utilized in the methanol synthesis process without requiring a dedicated compressor for the small-volume expansion gas stream, thereby reducing carbon dioxide emissions while avoiding additional compression equipment
Solution Approach 2:
The synthesis gas compression process is segmented into separate compression streams: one for the main synthesis gas feed and another for the expansion gas. Each stream is compressed independently to synthesis pressure by its own compressor, allowing the expansion gas to be integrated into the synthesis process without requiring a dedicated compressor for the small-volume stream
2Ease of operation
If the expansion gas stream is compressed by a dedicated compressor, then it can be combined with synthesis gas, but the cost and technical feasibility are reduced due to the small quantity and low pressure
Solution Approach 1:
The synthesis gas compressors are designed to handle multiple functions: compressing both the main synthesis gas feed stream and the expansion gas stream to synthesis pressure. This multi-functionality allows the expansion gas to be utilized without requiring a dedicated compressor, improving ease of operation while maintaining economic and technical feasibility
Solution Approach 2:
The expansion gas stream is routed to utilize the compression capacity already provided by the synthesis gas compressors. Instead of requiring a separate dedicated compressor, the expansion gas 'self-services' by being compressed along with or by the same compressors that handle the main synthesis gas feed, thereby avoiding additional equipment costs and technical complexity
3Reliability
If separate compression of reactant gas streams is performed, then pressure requirements are met, but the process complexity increases
Solution Approach 1:
The separately compressed reactant gas streams (main synthesis gas feed and expansion gas) are merged at a common point after both have reached synthesis pressure. This merging strategy maintains reliable pressure fulfillment for each stream while simplifying the overall process by combining the streams into a single synthesized gas stream for the methanol synthesis reactor, thereby reducing process complexity
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 method allows for a more flexible process design, enabling separate or combined compression of reactant gas streams, reduces the need for additional compressors, and optimizes the use of expansion gas, thereby lowering carbon dioxide emissions and energy consumption.
Implementation Method 1
converting the synthesis gas stream at synthesis pressure in a reaction apparatus over a solid methanol synthesis catalyst to form a methanol-containing product gas stream
Implementation Method 2
Introducing the first crude methanol stream into a second separator, wherein the pressure in the second separator is reduced compared to the pressure in the first separator, thereby obtaining in the second separator a second crude methanol stream as a liquid phase and the flash gas stream as a gaseous phase
Implementation Method 3
The following two equilibrium reactions (1) and (2) primarily occur simultaneously on a solid methanol synthesis catalyst: (1) CO2 + 3 H2 → CH3OH + H2O (2) CO + 2 H2 → CH3OH
Data Source
Figure 1
AI summary
A process for producing methanol from a hydrogen-rich and a carbon dioxide-rich reactant gas stream. According to the invention, a flash gas stream containing hydrogen and carbon dioxide, obtained in a low-pressure separator, is returned to one of the two reactant gas streams, or the flash gas stream is split into two partial streams, and the respective partial streams are returned to the respective reactant gas streams. These streams are combined before compression to synthesis pressure and before the formation of the actual synthesis gas stream.