Supercritical CO2 Coal Pellet Pretreatment for Stable Char Feedstock
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Solution Overview
Problem
Lignite coal, with its low heat content and high moisture content, is inefficient as a feedstock for combustion and gasification, and is prone to self-ignition and crumbling during storage and transportation.
Innovation Solution
Pulverizing and pelletizing coal, followed by pretreatment in a supercritical carbon dioxide environment to produce stable dried coal or char pellets, which are resistant to moisture and improve energy density.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If lignite coal is used as feedstock for gasification, then the process can proceed, but the low heat content and high moisture content make it inefficient and prone to self-ignition
Solution Approach 1:
The patent applies preliminary action by performing drying and pyrolysis treatments on the lignite coal before it is used as feedstock. The coal is first dried to reduce moisture content, then pyrolyzed to convert it into char with higher heat content and improved stability. This preliminary processing eliminates the self-ignition risk and improves energy efficiency before the coal enters gasification operations.
Solution Approach 2:
The patent changes the physical and chemical parameters of the coal through controlled drying and pyrolysis processes. By adjusting temperature, time, and atmospheric conditions during these processes, the coal's moisture content, heat content, and chemical composition are transformed to produce stable char pellets suitable for efficient gasification while eliminating self-ignition hazards.
2Use of energy by moving object
If coal is dried to reduce moisture content, then energy efficiency improves, but the dried coal becomes unstable and prone to self-ignition in outdoor storage
Solution Approach 1:
The patent converts the harmful effect of high energy density in dried coal, which causes self-ignition, into a benefit by controlling the pyrolysis process. The controlled thermal decomposition during pyrolysis transforms the coal structure to create char that maintains energy density while gaining stability through modified chemical composition and reduced oxygen content, thereby eliminating self-ignition risk.
Solution Approach 2:
The patent creates a composite structure by forming pellets from the pyrolyzed coal char. The pelletizing process combines the processed char into dense, stable forms that maintain the benefits of pyrolysis (higher energy density, reduced moisture) while adding structural stability and reduced susceptibility to self-ignition through the pellet matrix and reduced surface area to volume ratio.
3Ease of operation
If coal is pulverized and pelletized, then handling and storage stability improve, but the process complexity increases
Solution Approach 1:
The patent segments the coal processing into distinct sequential steps: pulverizing the coal to fine particles, drying the pulverized coal to reduce moisture, and pelletizing the dried coal to form stable pellets. This segmentation allows each step to be optimized independently and enables the complex processing to be broken down into manageable operations with clear functional purposes.
Solution Approach 2:
The patent uses dried coal as an intermediary material between the raw lignite coal and the final char pellets. The drying step creates an intermediary product that is stable enough for handling but still requires further pyrolysis and pelletizing to achieve the final stable char pellet form. This intermediary approach allows for controlled transformation through each processing stage.
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 pretreated pellets are stable in outdoor environments, reducing self-ignition risk and increasing energy density, making them more efficient for gasification and other processes.
Implementation Method 1
holding the coal pellet in a first supercritical carbon dioxide (sCO2) environment at a first temperature and a first pressure for a first period of time, thereby generating a treated pellet product
Implementation Method 2
pyrolyzing the coal pellet/dried coal pellet to obtain a char pellet
Data Source
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AI summary
This document describes methods for pretreating coal to create either a dried coal or a char product that is stable in the outdoor environment and is more efficient as a feedstock for gasification or other processes than the original coal. Embodiments of the methods include pulverizing and pelletizing the coal, and pretreating the coal pellets to obtain a stable pellet of either dried coal or a stable pellet of chared coal (coal char). The pellets created by the described methods have undergone deoxygenation and carbonization improving their handling and storage properties and, in some cases, energy density. Pore structures within the pellets are stabilized physically and chemically so that the uptake of moisture into dry coal, that leads to internal heat generation, is greatly reduced. Chars are also, therefore, stable against transitions from a dry state to a wet state and less prone to self-ignition.