Two-Stage Gasification Dual Quench Tar Reduction
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Solution Overview
Problem
Two-stage gasification systems face challenges in reducing costs, maintaining near-zero tar levels, moisturizing syngas without expensive steam, and increasing reliability, while dealing with the fouling and pollution issues associated with high-temperature heat recovery units and residual tars.
Innovation Solution
A two-step quench process is implemented, where a chemical quench in the first stage is followed by thermal cracking of residual tars in a residence vessel, and then a water quench is applied to the near-zero-tar syngas, ensuring it remains above the condensation temperature to prevent fouling and deposition, allowing for efficient particulate removal and steam generation without requiring high-purity boiler feed water.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a complete water quench is implemented in single-stage gasification to eliminate HTHRU, then capital costs are reduced, but in two-stage gasification it creates contaminated black water requiring expensive clean-up and necessitates reheating
Solution Approach 1:
The quenching process is divided into two distinct stages: a chemical quench stage where tars are cracked at high temperature, and a water quench stage applied only after tar removal. This segmentation allows water quenching to be used without creating contaminated black water, eliminating the need for expensive clean-up and reheating processes.
Solution Approach 2:
The chemical quench and tar cracking is performed as a preliminary action before the water quench. By removing tars first through high-temperature cracking, the subsequent water quench produces clean condensate rather than contaminated black water, avoiding energy loss from reheating.
2Device complexity
If residual tars are not removed before water quenching, then the quenching process is simpler, but it creates fouling of downstream equipment and environmental pollution
Solution Approach 1:
The harmful residual tars are converted into beneficial smaller hydrocarbon compounds through high-temperature thermal cracking. This transforms the fouling problem into a benefit where tars are destroyed and converted into useful syngas components, eliminating pollution and equipment fouling.
Solution Approach 2:
The temperature parameter is changed and maintained above 816°C (1500°F) in the chemical quench zone to enable thermal cracking of tars. This parameter change fundamentally alters the chemical behavior of tars, converting them from harmful contaminants into beneficial fuel components.
3Use of energy by moving object
If high-temperature heat recovery units are used to recover sensible heat, then energy efficiency is improved, but they are expensive to build, install, and require regular maintenance
Solution Approach 1:
The troublesome residual tars are extracted and removed from the syngas stream through high-temperature thermal cracking before the water quenching process. This extraction eliminates the fouling problem that would otherwise require expensive HTHRU maintenance, while still allowing for sensible heat recovery.
4Manufacturing precision
If the syngas temperature is reduced below condensation point for particulate removal, then filtration efficiency is improved, but it causes condensation and deposition on filter surfaces
Solution Approach 1:
The temperature parameter is precisely controlled to remain above the condensation point of water vapor while being low enough for effective particulate filtration. This parameter optimization allows simultaneous achievement of high filtration efficiency without condensation-related fouling of filter surfaces.
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 reduces operational expenses, maintains high system reliability, decreases downtime, and achieves near-zero tar levels in the syngas, eliminating the need for costly high-temperature heat recovery units and minimizing environmental contamination.
Implementation Method 1
carbonaceous feedstock and an oxidant are fed and partially combusted to create products comprising synthesis gas and slag
Implementation Method 2
The heat generated in the first stage drives endothermic chemical reactions in the second stage to generate additional syngas
Implementation Method 3
the raw syngas through a residence vessel that allows sufficient high temperature residence time for the tars to thermally 'crack' into smaller hydrocarbon compounds
Implementation Method 4
introducing a water stream via at least one inlet located on the conduit and contacting it with the near-zero-tar syngas, thereby producing steam and a cooled moisturized syngas
Data Source
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AI summary
Improved two-stage entrained-flow gasification systems and processes that reduce the cost and complexity of the design and increase the reliability, while maintaining the efficiency by implementing a first chemical quench followed by a second water quench of the produced syngas. The quenched syngas is maintained above the condensation temperature of at least one condensable component of the syngas, allowing residual particulates to be removed by dry particulate filtration.