CO Shift Unit Heat Recovery for Syngas Hydrogen Yield
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Solution Overview
Problem
Current methods for converting municipal solid waste into syngas, such as incineration and chemical recycling, face inefficiencies in energy conversion and hydrogen yield, leading to low energy efficiency and significant heat loss during cooling of product gases.
Innovation Solution
A method involving the torrefaction of solid recovered fuel pellets to produce syngas, which is then processed through a CO shift unit and a low temperature heat recovery unit, where the heat energy from cooled syngas is used to heat process water streams, optimizing hydrogen content and energy efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If a large excess supply of water steam is used in the CO shift reaction to increase hydrogen output, then the hydrogen content in the product gas increases, but large amounts of water condense during cooling resulting in significant heat loss
Solution Approach 1:
The patent converts the harmful heat loss during cooling into a beneficial resource by using the cooling train to generate process steam. The large amounts of water that would otherwise condense and waste heat are instead utilized to produce steam that can be fed back to the CO shift reactor, thereby converting the waste heat into useful energy for the hydrogen production process.
Solution Approach 2:
The patent changes the temperature parameter along the cooling train to optimize both hydrogen production and heat recovery. By maintaining specific temperature ranges in different sections of the cooling train, the system allows efficient heat transfer for steam generation while preventing excessive condensation losses, thus balancing hydrogen output with energy efficiency.
2Loss of substance
If the product gas is cooled to ambient temperature to condense water, then water removal is achieved, but considerable heat energy is discarded resulting in low energy efficiency
Solution Approach 1:
The patent transforms the waste heat from product gas cooling into a valuable resource by generating process steam in the cooling train. Instead of discarding the heat energy during water condensation, the system captures and utilizes this heat to produce steam that feeds back into the CO shift reaction, thereby converting a harmful waste stream into a beneficial input.
Solution Approach 2:
The cooling train serves multiple functions simultaneously: it cools the product gas to ambient temperature for water removal, generates process steam for the CO shift reactor, and recovers heat energy that would otherwise be wasted. This multi-functionality resolves the contradiction between water removal and energy conservation.
3Use of energy by moving object
If incineration is used to maximize energy content utilization, then energy recovery is improved, but pollutant emissions increase requiring significant technological efforts
Solution Approach 1:
The patent changes the fundamental operating parameters from combustion conditions (high temperature, oxygen-rich) to pyrolysis conditions (controlled temperature, limited oxygen). This parameter change transforms the process from incineration with high pollutant emissions to chemical recycling with minimal emissions, while still achieving effective energy recovery through syngas production.
Solution Approach 2:
The patent employs an inert or controlled atmosphere during the pyrolysis process, preventing complete combustion and the formation of harmful pollutants such as dioxins and furans. By operating in this controlled environment, the system achieves energy recovery without the pollutant emission problems associated with traditional incineration.
4Ease of manufacture
If chemical recycling via pyrolysis is used to recycle waste contents, then molecular-level recycling is achieved, but hydrogen yield and energy efficiency are inappropriate
Solution Approach 1:
The patent introduces a CO shift reactor as an intermediary step between pyrolysis and final product generation. This intermediary unit converts carbon monoxide from the pyrolysis gas into additional hydrogen through the water-gas shift reaction, thereby significantly increasing the hydrogen yield while maintaining the chemical recycling approach.
Solution Approach 2:
The patent implements a continuous process where pyrolysis gas is continuously fed to the CO shift reactor, and the shifted syngas is continuously utilized. This continuous operation maximizes hydrogen production from the chemical recycling process and improves overall energy efficiency by eliminating idle periods and maintaining optimal reaction conditions throughout the system.
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 the hydrogen content in the product gas stream and enhances energy efficiency by utilizing low-temperature heat for heating process water, thereby reducing energy waste and improving overall process yield.
Implementation Method 1
a syngas stream comprising the torrefaction syngas is provided to a CO shift unit for reacting at least a part of the carbon monoxide with water steam to carbon dioxide and hydrogen
Implementation Method 2
the shifted syngas is guided through at least two heat exchangers in which the shifted syngas is in thermal exchange with at least two water streams
Implementation Method 3
The term torrefaction is understood as a substoichiometric oxidization of the solid recovered fuel pellets to generate a raw syngas comprising hydrogen and carbon monoxide
Implementation Method 4
The resulting charred pellets are preferably gasified in a gasification unit creating syngas
Data Source
AI summary
The CO shift unit 500 as part of the plant 1 for conversing solid waste into a product gas stream comprising hydrogen allows an energy efficient use of the low temperature heat energy in the low temperature heat recovery unit 524 to heat process water streams used in the plant 1.