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 as off-gases are typically combusted without capture, contributing significantly to atmospheric CO2, and retrofitting methods like adding a catalytic reactor disrupt the main reforming section, requiring downtime and are complex and expensive.
Innovation Solution
Install an off-gas treatment unit (OTU) comprising an autothermal reformer, water-gas shift section, and CO2 removal unit to convert hydrocarbons in off-gases to hydrogen and carbon dioxide, allowing the hydrogen to be used as fuel, thereby reducing CO2 emissions without disrupting the main reforming section.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If off-gas is combusted directly as fuel, then the chemical plant operates with simple equipment and continuous operation, but CO2 emissions are released to the atmosphere without capture
Solution Approach 1:
The off-gas treatment system is segmented into three distinct functional units: (i) an autothermal reformer that converts hydrocarbons to synthesis gas, (ii) a water-gas shift section that converts CO to CO2 and produces additional H2, and (iii) a CO2 removal unit that separates and captures CO2. This segmentation allows each unit to be optimized for its specific function while collectively achieving CO2 capture, resolving the contradiction between emission reduction and equipment complexity.
2Object-affected harmful factors
If a catalytic reactor is added to the main reforming section to increase hydrogen production and reduce CO2 emissions, then CO2 capture is improved, but plant downtime is required and the retrofit is complex and expensive
Solution Approach 1:
The off-gas treatment unit is extracted as a separate, independent system from the main reforming section. The off-gas stream is diverted from the main process and routed through the dedicated treatment unit consisting of the autothermal reformer, water-gas shift section, and CO2 removal unit. This extraction allows CO2 capture functionality to be added without disrupting or shutting down the main reforming operations, eliminating plant downtime requirements.
Solution Approach 2:
The off-gas stream itself serves as an intermediary resource that connects the main reforming section to the CO2 capture function. By treating the off-gas stream in a separate unit rather than modifying the main reforming section, the system uses the existing off-gas flow as a mediator to transfer hydrocarbons through the treatment process, enabling CO2 capture without interfering with primary production operations.
3Object-affected harmful factors
If hydrogen yield is increased and used as fuel instead of off-gas, then CO2 emissions are reduced, but the retrofit process is complex and expensive
Solution Approach 1:
The off-gas treatment unit is self-sufficient, using its own internal processes to convert off-gas hydrocarbons into useful products. The autothermal reformer uses controlled combustion of a portion of the off-gas to provide heat for the reforming reactions, and the water-gas shift section naturally produces both CO2 (for capture) and additional H2 (for fuel use). This self-service capability reduces the need for external energy inputs and simplifies the overall retrofit complexity.
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
The OTU effectively converts off-gases into decarbonized fuel, reducing CO2 emissions by capturing and utilizing hydrogen as fuel, offering a cost-effective and efficient solution applicable to various chemical plants without requiring extensive downtime.
Implementation Method 1
an autothermal reformer (ATR), arranged to accept a hydrocarbon-containing fuel stream comprising hydrocarbons and steam and produce a reformed gas stream
Implementation Method 2
a water-gas shift section arranged to accept said reformed gas stream and produce a shifted gas stream
Implementation Method 3
a CO2 removal unit arranged to accept said shifted gas stream and produce a CO2 rich stream and a decarbonised fuel stream
Implementation Method 4
wherein the chemical plant is arranged such that the decarbonised fuel stream, optionally having first undergone further purification, is combusted to provide at least some of the heating duty on the chemical plant
Data Source
AI summary
A chemical plant comprising an off-gas treatment unit arranged to accept a hydrocarbon-containing off-gas stream, the off-gas treatment unit comprising sequentially: (i) an autothermal reformer, arranged to accept a hydrocarbon-containing fuel stream comprising hydrocarbons and steam and produce a reformed gas stream; (ii) a water-gas shift section arranged to accept said reformed gas stream and produce a shifted gas stream; and (iii) a CO2 removal unit arranged to accept said shifted gas stream and produce a CO2 rich stream and a decarbonised fuel stream; wherein said hydrocarbon-containing fuel stream is derived from said hydrocarbon-containing off-gas stream, steam and any supplemental fuel; wherein the chemical plant is arranged such that the decarbonised fuel stream is combusted instead of said hydrocarbon-containing off-gas stream.