Hydrogen Recovery Membrane Segmentation
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Solution Overview
Problem
Current hydrogen recovery systems are inefficient in removing heavier compounds like nitrogen, carbon oxides, methane, and ethane, leading to increased energy consumption and catalytic poisoning, and often result in hydrogen with a different composition that can impede process efficiency and limit recovery to less than 98%, necessitating the development of improved separation and recovery processes.
Innovation Solution
The process involves sending an effluent from a reaction zone to an adsorption zone, followed by compression and separation using a membrane selective for hydrogen over C1-C6 hydrocarbons, where the permeate stream enriched in hydrogen is recycled back to the adsorption zone, and the residue stream is either used as fuel or returned for further processing, allowing for enhanced hydrogen and hydrocarbon recovery.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If conventional hydrogen recovery systems are used, then hydrogen separation is achieved, but heavier compounds like nitrogen, carbon oxides, methane, and ethane are not sufficiently removed, resulting in increased energy consumption by compressors
Solution Approach 1:
The hydrogen recovery system is divided into multiple stages: a first separation unit (PSA) that removes heavy compounds, and a second separation unit (membrane) that further purifies hydrogen. This segmentation allows each unit to specialize in removing specific contaminants, achieving thorough purification without over-compressing the entire stream, thus reducing overall energy consumption.
Solution Approach 2:
The patent introduces an intermediate processing step where the effluent from the first PSA unit is fed to a membrane separation unit. This intermediate stage acts as a mediator that selectively removes remaining heavy compounds before the final hydrogen product is obtained, reducing the burden on compressors by minimizing the volume of gas requiring high-pressure compression.
2Quantity of substance
If conventional hydrogen recovery systems are used, then hydrogen separation is achieved, but insufficient systems for separating hydrogen gas from contaminants can allow catalytic poisoning if the hydrogen gas is recycled to a reforming zone
Solution Approach 1:
The recovery system uses two distinct separation mechanisms: PSA technology for initial hydrogen concentration and membrane separation for final purification. This segmented approach ensures that contaminants at different stages are removed by appropriate methods, delivering ultra-pure hydrogen suitable for recycling to reforming zones without catalytic poisoning risks.
Solution Approach 2:
The system changes the purity parameter of hydrogen through sequential processing. The first PSA unit concentrates hydrogen to a certain purity level, then the membrane unit further increases purity by selectively permeating hydrogen while retaining heavy compounds. This parameter transformation ensures the final hydrogen product meets the stringent purity requirements for catalytic processes.
3Quantity of substance
If maximum hydrogen recovery is pursued, then hydrogen recovery reaches high levels, but methane builds up in a tail gas recycle loop that limits the amount of PSA tail gas that can be recycled
Solution Approach 1:
The membrane separation unit extracts methane and other heavy compounds from the PSA tail gas stream. By taking out these unwanted substances, the system prevents methane buildup in the recycle loop, enabling higher rates of tail gas recycling while maintaining maximum hydrogen recovery levels.
Solution Approach 2:
The patent converts the harmful effect of methane buildup into a benefit by using the membrane unit to selectively remove methane from the tail gas. This transforms the problematic methane-containing stream into a purified hydrogen stream that can be fully recycled, turning what was previously a limitation into an opportunity for enhanced hydrogen recovery.
4Quantity of substance
If current hydrogen recovery systems are used, then hydrogen separation is achieved, but the recovered hydrogen has a sufficiently different composition that when combined with another hydrogen gas, it may result in process upsets
Solution Approach 1:
The dual separation system systematically changes the composition parameters of the hydrogen stream. The PSA unit adjusts concentration parameters, and the membrane unit refines purity parameters, ensuring the final hydrogen product has consistent and predictable composition. This controlled parameter transformation prevents process upsets when the hydrogen is combined with other hydrogen streams.
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 increases overall hydrogen recovery to 98% or better, reduces energy consumption, and enables the recovery of valuable hydrocarbons like methane, improving process efficiency and product yield by eliminating bottlenecks in hydrogen recovery.
Implementation Method 1
passing at least a portion of the waste hydrocarbon stream as a feed stream across a feed side of a membrane having the feed side and a permeate side, and being selective for hydrogen over one or more C1-C6 hydrocarbons
Implementation Method 2
an effluent from a reaction zone comprising a mixture of hydrocarbons and hydrogen is sent to an adsorption zone
Data Source
AI summary
The process can be used in any hydrocarbon process in which it is desirable to recover hydrogen. The process can include catalytically reforming a hydrocarbon feed, a paraffin dehydrogenation to produce light olefins or a synthesis gas generating process. There is an effluent stream having hydrogen and hydrocarbons that is first sent to an adsorption zone to produce a pure hydrogen stream and a tail gas stream. The tail gas stream is then sent across a feed side of a membrane having the feed side and a permeate side. The membrane that is selected is selective for hydrogen over one or more C1-C6 hydrocarbons and light ends including CO, CO2, N2 and O2, and withdrawing from the permeate side a permeate stream enriched in hydrogen compared with a residue stream withdrawn from the feed side. The permeate stream is then recycled to be sent through the adsorption zone.