Sorbent-Enhanced Water Gas Shift Process for Hydrogen Production
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Solution Overview
Problem
Conventional water gas shift (WGS) processes require excessive high-pressure steam, which is costly and inefficient, and struggle to achieve high CO conversion rates with reduced steam feeds.
Innovation Solution
A process involving a WGS reaction stage with a sorbent material that alternates between a reaction stage with a low H2O:CO molar ratio and a regeneration/loading stage at lower pressure, where steam is loaded onto the adsorbent to regenerate it and reduce CO2, allowing for higher hydrogen production efficiency and reduced steam usage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If conventional WGS processes use a high H2O:CO molar feed ratio (typically around 2 or higher), then maximum conversion to hydrogen is achieved, but the cost and energy consumption increase due to excessive high-pressure steam supply
Solution Approach 1:
The sorbent is pre-loaded with water (steam) at low pressure before the high-pressure WGS reaction begins. This preliminary action stores the necessary water on the sorbent, allowing the reaction to proceed with minimal additional steam supply during the actual reaction phase, thereby reducing energy consumption for steam generation while maintaining high hydrogen production rates
Solution Approach 2:
The sorbent acts as an intermediary that temporarily stores and releases water during the WGS process. It absorbs water during the reaction stage and is subsequently regenerated by releasing the stored water, mediating the water supply to the reaction and eliminating the need for continuous high-pressure steam injection
2Loss of energy
If the H2O:CO molar feed ratio is reduced below conventional levels, then energy efficiency improves, but CO conversion rate decreases and CO content in product gas increases
Solution Approach 1:
The sorbent is pre-loaded with water at low pressure before the reaction starts, ensuring sufficient water is available for complete CO conversion even when the feed gas has low water content. This preliminary water loading compensates for the reduced water in feed, maintaining high CO conversion efficiency while improving overall energy efficiency
Solution Approach 2:
The process changes the pressure parameter between stages: water is loaded onto the sorbent at low pressure, then the system switches to high pressure for the WGS reaction. This parameter change allows the sorbent to release stored water precisely when needed during the reaction, ensuring high CO conversion without requiring high water content in the feed gas
3Productivity
If high-pressure steam is supplied continuously to maintain CO conversion, then hydrogen production is sustained, but operational costs increase due to steam generation and compression
Solution Approach 1:
The process operates in periodic cycles: during the reaction stage, the sorbent releases stored water to maintain CO conversion and hydrogen production; during the subsequent regeneration stage, the sorbent is reloaded with water at low pressure. This periodic action ensures continuous hydrogen production while avoiding continuous high-pressure steam supply, reducing operational costs
Solution Approach 2:
The sorbent serves itself by automatically releasing stored water during the reaction stage without external steam supply, and then being regenerated by simple low-pressure water loading. This self-service mechanism maintains hydrogen production continuity while eliminating the need for continuous expensive high-pressure steam generation and compression
4Manufacturing precision
If multiple WGS reactors in series are used with steam addition before each reactor, then CO conversion is improved, but device complexity and steam accumulation requirements increase
Solution Approach 1:
The single reactor is segmented into two functional stages: the reaction stage where the sorbent releases stored water for CO conversion, and the regeneration stage where the sorbent is reloaded with water. This segmentation of functions within a single reactor achieves high CO conversion without requiring multiple physical reactors or complex inter-connected steam supply systems
Solution Approach 2:
The sorbent performs multiple functions: it acts as a water storage medium, a water delivery mechanism during reaction, and a regenerable component. This multi-functionality replaces the need for multiple reactors and continuous steam supply systems, simplifying the overall device while maintaining high CO conversion levels
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 reduces the need for high-pressure steam, enhances sorbent capacity, and achieves higher hydrogen production efficiency while allowing for a hydrogen-rich product gas with lower CO and CO2 content, improving cost-efficiency and conversion rates.
Implementation Method 1
WO 2010/059052 and Van Dijk et al., Intern. J. Greenhouse Gas Control, 5 (2011), 505-511), describe a sorption-enhanced water gas shift (SEWGS) process to produce hydrogen and carbon dioxide as well as hydrogen sulphide, wherein the carbon dioxide and hydrogen sulphide are adsorbed onto an alkali promoted hydrotalcite adsorbent.
Implementation Method 2
The supply of high-pressure steam is relatively expensive and detracts from the total process efficiency. Therefore there is a case for lowering the level of steam in a WGS feed, while retaining high conversion levels of CO to H2.
Implementation Method 3
The water gas shift (WGS) reaction, which can be represented by the equation CO + H 2 O → CO 2 + H 2 , is a powerful tool for efficiently producing hydrogen-containing product gases from carbonaceous sources.
Data Source
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AI summary
High-pressure steam supply in hydrogen production process is made more efficient by water gas shift process which comprises, in alternating sequence: (a) a reaction stage wherein a feed gas comprising CO and H20 is fed into a water gas shift reactor containing a sorbent material capable of adsorbing H20 and C02 and wherein a product gas issuing from the reactor is collected, (b) a regeneration stage wherein C02 is removed from the reactor, (c) a loading stage, wherein H20 is fed into the reactor; wherein said feed gas mixture has a molar ratio of H20 to CO below 1.2, and the loading stage is performed at a lower pressure than the pressure of the reaction stage.