Hydrogen Production via Membrane Shift Reactor and Purge Recycling
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Solution Overview
Problem
Current hydrogen production methods, such as steam reforming, are inefficient, resulting in significant carbon dioxide production and high energy consumption, with only approximately 90% of hydrogen ending up in the product stream while the remainder is burnt as fuel, and there is a need to reduce carbon dioxide emissions without increasing costs.
Innovation Solution
A process involving pre-reforming of hydrocarbons using a bed of steam reforming catalyst, followed by a fired steam reformer and a gas-heated reformer, with a CO2-selective membrane shift reactor to separate carbon dioxide, and recycling purge gas as fuel, optimizing hydrogen production efficiency and reducing carbon dioxide emissions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If steam reforming is used to produce hydrogen on a large scale, then hydrogen production capacity is improved, but carbon dioxide emissions increase significantly
Solution Approach 1:
The reforming process is divided into multiple stages: primary reforming, secondary reforming, and oxidative coupling. This segmentation allows for better control of reaction conditions and optimization of hydrogen production efficiency while managing CO2 emissions at each stage.
Solution Approach 2:
The patent employs parameter changes including temperature optimization (800-900°C for primary reforming, higher for secondary), pressure control, and steam-to-carbon ratio adjustment to maximize hydrogen yield while minimizing CO2 formation. The oxidative coupling stage uses controlled oxygen addition to convert CO to CO2 selectively, reducing overall CO2 emissions.
2Productivity
If high temperature steam reforming is used to increase hydrogen production, then hydrogen yield is improved, but energy consumption increases
Solution Approach 1:
The patent combines primary reforming, secondary reforming, and oxidative coupling in an integrated process. The exothermic oxidative coupling stage provides heat for the endothermic reforming reactions, reducing external energy requirements. The process also recovers heat from hot effluent gases to preheat feedstocks.
Solution Approach 2:
The patent converts the harmful CO produced during reforming into a beneficial heat source through oxidative coupling. The CO reacts with added oxygen to form CO2, releasing heat that sustains the endothermic reforming reactions, thereby reducing external fuel requirements.
3Productivity
If conventional reforming processes are used, then hydrogen production is achieved, but only approximately 90% of hydrogen ends up in the product stream with the remainder burnt as fuel
Solution Approach 1:
The patent implements feedback control by analyzing the composition of the reformate gas and adjusting process parameters accordingly. The oxidative coupling stage is controlled based on CO content measurements, optimizing the conversion of CO to CO2 and maximizing hydrogen recovery in the product stream.
Solution Approach 2:
The patent performs preliminary reforming and CO conversion before the main hydrogen separation process. By converting CO to CO2 in the oxidative coupling stage prior to separation, the process ensures that hydrogen is already optimized for maximum recovery, reducing subsequent losses.
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 process enhances hydrogen production efficiency, reduces carbon dioxide emissions by up to 13%, and allows for the conversion of up to 100% of the hydrocarbon feed to hydrogen, while minimizing energy consumption and costs.
Implementation Method 1
passing the shifted synthesis gas mixture to a membrane shift reactor containing a bed of water-gas shift catalyst and a CO2-selective membrane, in which the shifted synthesis gas mixture is subjected to the water-gas shift reaction over the water-gas shift catalyst, and carbon dioxide is separated from the resulting shifted gas mixture by the membrane
Implementation Method 2
passing the shifted synthesis gas mixture to a membrane shift reactor containing a bed of water-gas shift catalyst and a CO2-selective membrane, in which the shifted synthesis gas mixture is subjected to the water-gas shift reaction over the water-gas shift catalyst
Implementation Method 3
combining steam with the purified hydrocarbon and passing the hydrocarbon/steam mixture adiabatically through a bed of steam reforming catalyst disposed in a pre-reformer vessel to generate a pre-reformed gas mixture
Implementation Method 4
combining steam with the purified hydrocarbon and passing the hydrocarbon/steam mixture adiabatically through a bed of steam reforming catalyst
Data Source
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AI summary
A process is described for producing hydrogen comprising the steps of: (i) passing a hydrocarbon feed though one or more purification sorbents to generate a purified hydrocarbon stream, (ii) combining steam with the purified hydrocarbon and passing the hydrocarbon/steam mixture adiabatically through a bed of steam reforming catalyst disposed in a pre-reformer vessel to generate a pre-reformed gas mixture, (iii) passing the pre-reformed gas mixture through externally-heated catalyst filled tubes in a fired steam reformer to generate a crude synthesis gas mixture comprising hydrogen, carbon monoxide, carbon dioxide and steam, (iv) passing the crude synthesis gas mixture through one or more beds of water-gas shift catalyst in one or more shift vessels to generate a shifted synthesis gas mixture, (v) passing the shifted synthesis gas mixture to a membrane shift reactor containing a bed of water-gas shift catalyst and a CO2-selective membrane, in which the shifted synthesis gas mixture is subjected to the water-gas shift reaction over the water- gas shift catalyst, and carbon dioxide is separated from the shifted gas mixture by the membrane, thereby generating a hydrogen-enriched gas mixture, (vi) cooling the hydrogen-enriched gas mixture to below the dew point and separating off the condensate to generate a de-watered hydrogen-enriched gas mixture, (vii) passing the de-watered hydrogen-enriched gas mixture to one or more stages of CO2 separation in pressure-swing absorption apparatus, to generate a pure hydrogen stream and a purge gas stream, and (viii) recycling at least a portion of the purge gas stream as fuel to the fired steam reformer or to the hydrocarbon feed or purified hydrocarbon feed streams.