Fischer-Tropsch Tail Gas CO2 Removal for Synthesis Ratio Control
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Solution Overview
Problem
Existing Fischer-Tropsch synthesis processes face challenges in maximizing carbon conversion to liquid hydrocarbon products while maintaining the optimal hydrogen to carbon monoxide ratio in synthesis gas, leading to inefficient equipment sizing and increased operational costs due to varying carbon dioxide concentrations and the need for flaring or inefficient power generation from excess tail gas.
Innovation Solution
A process that includes a carbon dioxide removal unit to adjust the carbon dioxide content in the Fischer-Tropsch tail gas recycle flow, allowing precise control of the hydrogen to carbon monoxide ratio in the synthesis gas generation unit, thereby optimizing carbon conversion and reducing equipment size and operational costs by recycling excess tail gas.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the steam to carbon ratio is increased to adjust the hydrogen to carbon monoxide ratio in synthesis gas, then the hydrogen to carbon monoxide ratio is improved, but the carbon dioxide concentration increases which depresses the conversion rate and requires larger equipment
Solution Approach 1:
The patent removes carbon dioxide from the synthesis gas stream using a carbon dioxide removal unit positioned between the synthesis gas generation unit and the Fischer-Tropsch synthesis unit. This extraction of the harmful inert component resolves the contradiction by allowing high steam to carbon ratios (which produce the desired hydrogen to carbon monoxide ratio) without the penalty of accumulated carbon dioxide that would depress conversion rates.
2Volume of stationary object
If the steam to carbon ratio is decreased to reduce carbon dioxide concentration, then the equipment size is reduced, but the risk for carbon deposit increases which might damage the unit
Solution Approach 1:
By extracting carbon dioxide from the synthesis gas stream, the patent enables operation at lower steam to carbon ratios without accumulating excessive carbon dioxide. This resolves the contradiction by allowing reduced equipment size while maintaining reliability, as the carbon dioxide removal prevents the conditions that would lead to carbon deposit formation.
Solution Approach 2:
The patent changes the operational parameters by removing carbon dioxide, which allows the steam to carbon ratio to be optimized independently of carbon dioxide accumulation. This parameter change enables operation at lower steam to carbon ratios (reducing equipment size) while maintaining conditions that prevent carbon deposit formation.
3Productivity
If tail gas is purged to reduce inert compounds, then the conversion rate is improved, but the loss of hydrogen and carbon monoxide increases which reduces productivity
Solution Approach 1:
The patent selectively extracts only carbon dioxide from the tail gas stream using the carbon dioxide removal unit, while preserving the valuable hydrogen and carbon monoxide. This resolves the contradiction by improving conversion rate through removal of inert compounds without suffering the penalty of losing reactive components, as the removal process is selective for carbon dioxide only.
Solution Approach 2:
The patent applies local quality by selectively removing only the harmful inert component (carbon dioxide) from the tail gas while preserving the valuable reactive components (hydrogen and carbon monoxide). This selective local action resolves the contradiction by addressing the specific problem of inert accumulation without causing the side effect of reactive component loss.
4Productivity
If excess tail gas is flared or used for power generation, then the carbon dioxide concentration is controlled, but the loss of energy increases and operational costs increase
Solution Approach 1:
The patent converts the harmful accumulation of carbon dioxide into a beneficial selective removal process. By using the carbon dioxide removal unit to extract only carbon dioxide from the tail gas, the system transforms what would be a waste stream requiring flaring or inefficient power generation into a valuable recycled stream that maintains proper composition for high conversion rates, thereby eliminating energy loss while controlling carbon dioxide concentration.
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 maximizes carbon conversion to liquid hydrocarbons, reduces equipment size, and minimizes operational costs by maintaining the hydrogen to carbon monoxide ratio and utilizing excess tail gas efficiently, while adhering to environmental regulations.
Implementation Method 1
a carbon dioxide removal unit (22) arranged to adjust a carbon dioxide content in the Fischer-Tropsch tail gas recycle flow (36)
Implementation Method 2
The synthesis gas generation unit generally uses a reforming process which is fed with a mixture of a hydrocarbonaceous feed flow, such as natural gas, an oxidizing flow, such as air and/or oxygen
Implementation Method 3
The Fischer-Tropsch synthesis unit converts the synthesis gas to hydrocarbon chains of various lengths
Implementation Method 4
The chain lengths are controlled by the ratio of hydrogen to carbon monoxide which is fed to the Fischer-Tropsch reactor
Data Source
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AI summary
The process comprises : - introducing the feed flow (14) in a synthesis gas generation unit (16) to form a synthesis gas flow (32) and introducing the synthesis gas flow (32) in a Fischer-Tropsch synthesis unit (18); - at least partially removing carbon dioxide from a first flow (44) formed from a Fischer-Tropsch tail gas flow (38) to form a carbon dioxide depleted flow (50); - forming a tail gas recycle flow (36) from the carbon dioxide depleted flow (50); - introducing the tail gas recycle flow (36) in the synthesis gas generation unit (16) and/or in the synthesis gas flow (32). The process comprises adjusting the carbon dioxide content in the tail gas recycle flow (36) to control the hydrogen to carbon monoxide molar ratio in the synthesis gas flow (32) to a target hydrogen to carbon monoxide molar ratio.