Methanol Synthesis Loop Purge Gas Stripping
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Solution Overview
Problem
Methanol synthesis processes that use fresh hydrogen streams, particularly from wet hydrogen sources, incur additional capital and operating expenses due to the need for proximity to hydrogen sources and are burdened by increased carbon dioxide requirements, limiting methanol production capacity.
Innovation Solution
The process utilizes a portion of the purge gas to strip dissolved gases from crude methanol, reducing carbon dioxide requirements and enhancing methanol production efficiency without increasing catalyst volume, by contacting crude methanol with a portion of the purge gas in a stripping unit and recycling the enriched gas mixture back into the methanol synthesis loop.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a fresh hydrogen stream is used to strip dissolved gases from crude methanol, then stripping efficiency is improved, but capital and operating expenditure increase and carbon dioxide requirements increase
Solution Approach 1:
The patent recovers dissolved gases (including CO2) from crude methanol by stripping with purge gas, then feeds the enriched gas mixture back to the methanol synthesis loop. This recycles materials that would otherwise be wasted, reducing the need for fresh hydrogen and CO2 while maintaining stripping efficiency.
Solution Approach 2:
The purge gas, which would normally be discarded, is reused to perform the stripping function. This self-service approach uses an available process stream (purge gas) to accomplish the stripping task, eliminating the need for external fresh hydrogen streams and reducing CO2 requirements.
2Measurement precision
If fresh hydrogen stream is used for stripping, then stripping efficiency is improved, but capital and operating expenditure increase
Solution Approach 1:
The process uses the existing purge gas stream to perform the stripping function, making the system self-sufficient. This eliminates the need for external fresh hydrogen streams, reducing both capital expenditure (no need for additional hydrogen infrastructure) and operating expenditure (no need to purchase and transport fresh hydrogen).
Solution Approach 2:
The purge gas serves multiple functions: it maintains the synthesis loop by removing inert gases, and simultaneously performs the stripping function by removing dissolved gases from crude methanol. This multi-functionality reduces the need for separate dedicated stripping streams, lowering overall process costs.
3Productivity
If purge gas is used to strip crude methanol, then carbon dioxide requirements are reduced and methanol production capacity is enhanced, but inert gas buildup may occur
Solution Approach 1:
The process recycles the enriched gas mixture (containing stripped gases including CO2) back to the methanol synthesis loop. This recovery prevents inert gas buildup by continuously cycling useful gases back into the reaction system, while the purge stream maintains loop stability by removing excess inerts.
Solution Approach 2:
The stripped gases are fed back to the synthesis loop, creating a feedback mechanism that maintains gas composition stability. The loop continuously adjusts by recycling useful gases and purging excess inerts, preventing inert gas buildup while maximizing methanol production capacity.
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 stripping efficiency, reduces carbon dioxide consumption, and increases methanol production capacity while minimizing inert gas buildup and operational costs, without the need for additional hydrogen sources or increased catalyst volume.
Implementation Method 1
contacting the crude methanol and a portion of the purge gas in a stripping unit to strip dissolved gases from the crude methanol
Implementation Method 2
cooling the product gas mixture to below the dew point to condense crude methanol
Implementation Method 3
contacting the gaseous feed with a catalyst at a temperature of between 200 and 300° C. and a pressure of between 40 and 200 bar, thereby forming an outlet stream comprising methanol
Data Source
AI summary
A process for synthesising methanol is described comprising the steps of (i) passing a feed gas comprising a make-up gas containing hydrogen and carbon dioxide to a methanol synthesis loop, (ii) recovering a product gas mixture containing methanol from the methanol synthesis loop, (iii) cooling the product gas mixture to below the dew point to condense crude methanol, (iv) separating the crude methanol from an unreacted gas mixture, (v) passing a portion of the unreacted gas mixture to the methanol synthesis loop and (vi) recovering a portion of the unreacted gas mixture as a purge gas stream, characterised by contacting the crude methanol and a portion of the purge gas in a stripping unit to strip dissolved gases from the crude methanol thereby forming a stripped crude methanol and an enriched gas mixture, and feeding at least a portion of the enriched gas mixture to the methanol synthesis loop.