Off-Gas Treatment Unit for Chemical Plant Decarbonisation
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Solution Overview
Problem
Existing chemical plants face challenges in reducing carbon dioxide emissions, particularly due to the combustion of hydrocarbon-containing off-gas streams which are not typically captured, leading to increased carbon intensity and production costs.
Innovation Solution
The installation of an off-gas treatment unit (OTU) that converts hydrocarbon-containing fuel streams into low carbon fuels through hydrogen membrane separation, reforming, water-gas shift, and CO2 removal processes, allowing for the use of hydrogen-rich streams as fuel instead of traditional hydrocarbons.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If hydrocarbon-containing off-gas is combusted as fuel, then energy needs are met, but CO2 emissions increase and carbon intensity increases
Solution Approach 1:
The invention extracts CO2 from the off-gas stream before combustion using a CO2 removal unit. This separates the harmful CO2 component from the fuel stream, allowing the remaining hydrogen-rich gas to be combusted for energy while the CO2 is captured and removed, thus meeting energy needs without the associated CO2 emissions
Solution Approach 2:
The invention changes the composition parameter of the fuel stream by removing CO2 and enriching hydrogen content through the CO2 removal unit and optionally a hydrogen enrichment unit. This parameter change transforms the off-gas from a high-CO2 hydrocarbon stream to a low-CO2 hydrogen-rich stream, reducing carbon intensity while maintaining energy supply capability
2Productivity
If a catalytic reactor is retrofitted into the main steam reforming section to increase hydrogen yield, then hydrogen production increases, but plant downtime occurs and complexity increases
Solution Approach 1:
The invention segments the hydrogen production system by adding a separate off-gas treatment unit that operates independently from the main steam reforming section. This modular approach allows the new functionality (CO2 removal and hydrogen enrichment) to be added without disrupting or complicating the existing reforming section, avoiding plant downtime and reducing integration complexity
Solution Approach 2:
The invention introduces an intermediary off-gas treatment unit that takes the hydrocarbon-containing off-gas from the main process and transforms it into a hydrogen-rich fuel stream. This intermediary unit acts as a bridge, allowing hydrogen production increase without directly modifying the main reforming section, thus avoiding the complexity and downtime associated with integrating a catalytic reactor into the existing section
3Object-generated harmful factors
If CO2 is captured from off-gas at low pressure, then CO2 emissions are reduced, but capture efficiency decreases
Solution Approach 1:
The invention applies preliminary action by removing CO2 from the off-gas stream before it is combusted. By performing CO2 removal upstream at the off-gas conditions (even if low pressure), the process prevents CO2 from being generated in the first place during combustion, thereby achieving effective CO2 emission reduction without requiring high-pressure conditions that would improve capture efficiency
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 solution effectively reduces CO2 emissions by converting hydrocarbon-containing off-gas streams into low carbon fuels, thereby decreasing the carbon intensity of chemical plant products and potentially increasing production capacity without disrupting the main reforming section.
Implementation Method 1
a hydrogen membrane separation unit arranged to accept the hydrocarbon-containing fuel stream and produce a permeate stream and a retentate stream
Implementation Method 2
a reforming section comprising a partial oxidation reactor or an autothermal reformer, arranged to accept the retentate stream and produce a reformed gas stream
Implementation Method 3
a water-gas shift section arranged to accept said reformed gas stream and produce a shifted gas stream
Implementation Method 4
a CO2 removal section comprising one or more CO2 removal units, the CO2 removal section arranged to accept said shifted gas stream and produce a CO2 rich stream and a hydrogen product stream
Implementation Method 5
The permeate stream and/or the hydrogen product stream may be used as a low carbon fuel
Data Source
Figure 1~2
Figure 3~4
AI summary
The specification describes a chemical plant comprising an off-gas treatment unit arranged to accept a hydrocarbon-containing fuel stream comprising hydrocarbons, steam, and hydrogen, the off-gas treatment unit comprising: (i) a hydrogen membrane separation unit arranged to accept the hydrocarbon-containing fuel stream and produce a permeate stream and a retentate stream; (ii) a reforming section comprising a partial oxidation reactor or an autothermal reformer, arranged to accept the retentate stream and produce a reformed gas stream; (iii) a water-gas shift section arranged to accept said reformed gas stream and produce a shifted gas stream; (iv) a CO2 removal section comprising one or more CO2 removal units, the CO2 removal section arranged to accept said shifted gas stream and produce a CO2 rich stream and a hydrogen product stream; wherein at least a portion of the permeate stream and/or the hydrogen product stream is used as a low carbon fuel. Also described is a process for converting a hydrocarbon-containing fuel stream into a low carbon fuel which is carried out in an off-gas treatment unit as described. Also described is a retrofitting method for a chemical plant, in which an off-gas treatment unit as described is installed.