Tandem Reactors for Coal Conversion in Sub- and Supercritical Water
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Solution Overview
Problem
Current methods for converting coal into combustible gases using supercritical water face challenges such as large catalyst particle size, low catalyst activity, and high catalyst amounts, leading to inefficient coal conversion and increased energy and production costs, as well as difficulties in catalyst recovery and recycling.
Innovation Solution
A coal processing method involving a series of tandem reactors with alternating sub-critical and supercritical water states, where coal powder, water, and catalyst are fed through the reactors without separation, allowing for improved catalyst dispersion and activity, reducing catalyst amounts, and enhancing coal conversion efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the amount of catalyst is increased to improve catalysis performance, then the coal conversion efficiency is improved, but the production cost increases and catalyst recovery becomes more difficult
Solution Approach 1:
The patent changes the physical state parameters of water between sub-critical and supercritical conditions to alter catalyst behavior. In sub-critical water, catalyst particles aggregate and settle on coal surfaces; in supercritical water, they disperse uniformly. This parameter cycling allows effective catalysis at lower overall catalyst amounts while maintaining high conversion efficiency.
Solution Approach 2:
The patent employs periodic alternation between sub-critical and supercritical water states in a multi-stage reactor system. This periodic switching creates cyclic aggregation-dispersion behavior of catalyst particles, enabling them to repeatedly contact fresh coal surfaces and maintain high catalytic activity throughout the conversion process without requiring excessive catalyst quantities.
2Quantity of substance
If the particle size of catalyst is large, then the catalyst amount can be reduced, but the specific surface area decreases and catalyst activity is limited
Solution Approach 1:
The patent makes the catalyst particle size dynamic rather than static. Large catalyst particles are introduced but their effective size varies cyclically: they aggregate into larger clusters in sub-critical water stages (reducing effective surface area but facilitating separation), then disperse into smaller effective particles in supercritical water stages (increasing surface area and activity). This dynamic behavior resolves the contradiction between particle size and catalyst activity.
3Quantity of substance
If the concentration of aqueous coal slurry is high, then the energy density increases, but blockage and coking occur in the reactor
Solution Approach 1:
The patent utilizes phase transitions of water between sub-critical and supercritical states to control slurry behavior. In sub-critical water stages, the lower temperature prevents excessive coking despite high coal concentration. In supercritical water stages, the enhanced fluidity and solvating power prevent blockage by keeping the high-concentration slurry flowing smoothly. This phase transition cycling enables high energy density operation without the harmful effects of blockage and coking.
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 method achieves higher yields of methane and hydrogen with reduced catalyst usage, improving catalyst dispersion and activity, and lowering production costs while facilitating easier catalyst recovery and recycling.
Implementation Method 1
beginning from the first reactor, the temperature and pressure of the series of tandem reactors are alternatively arranged in sub-critical water state and supercritical water state
Implementation Method 2
the catalyst particles can not uniformly disperse on the coal particles, which limit the contact of catalyst with coal
Data Source
AI summary
A coal processing method includes adding coal powder, water and catalyst into a series of tandem reactors and processing therein, wherein the coal powder, water and catalyst are added into the first reactor of the series of tandem reactors; and the temperature and pressure of the series reactors is alternatively arranged in sub-critical state and supercritical state of water from the first reactor, the total product from the previous reactor is used as the feed of the next reactor without any further separation.