Ebullated Bed Liquefaction with Hydrocracking for Fuel Quality
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Solution Overview
Problem
The direct coal liquefaction process typically produces fuel bases of poor quality, failing to meet combustion specifications due to high naphtheno-aromatic content, which affects cetane numbers and smoke points, limiting their usability in diesel and kerosene applications.
Innovation Solution
A process involving two successive ebullated bed reactors followed by a fixed bed hydrocracking stage, with intermediate fractionation, to enhance the quality of fuel bases by converting coal into high-quality kerosene and gas oil that complies with European and American specifications.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If direct coal liquefaction is used to produce fuel bases, then the yield of naphtha and diesel is improved, but the quality of the products deteriorates due to high naphtheno-aromatic content
Solution Approach 1:
The process is divided into three distinct stages: first ebullated bed liquefaction stage, second ebullated bed liquefaction stage, and fixed bed hydrocracking stage. Each stage performs a specific function to progressively improve product quality while maintaining high yield.
Solution Approach 2:
The process employs different operating parameters for each stage: first stage operates at 371-427°C and 6.9-27.6 MPa, second stage at 404-460°C and 6.9-27.6 MPa, and hydrocracking at elevated temperatures and pressures. These parameter changes optimize both yield and quality at each stage.
2Speed
If conventional direct liquefaction is used, then the production speed is maintained, but the combustion specifications are not met
Solution Approach 1:
The process maintains continuous operation through three sequential stages that continuously process the fuel base. The effluent from each stage becomes the feed for the next stage, ensuring continuous improvement of product quality without interrupting production.
Solution Approach 2:
The fixed bed hydrocracking stage acts as an intermediary that receives the fuel base from the liquefaction stages and transforms it into specification-compliant product. This intermediary stage resolves the quality issue while maintaining the high production speed established in the liquefaction stages.
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 process significantly improves the cetane number and smoke point of gas oil and kerosene, ensuring they meet commercial specifications, despite a high naphthenes content, by reducing aromatics and increasing paraffins through hydrocracking, resulting in fuels with excellent combustion properties.
Implementation Method 1
The coal is initially ground and mixed with a solvent from the process in order to form a suspension which is then injected into the first ebullated bed reactor in the presence of a hydroconversion catalyst. That first reactor operates at a temperature in the range 371° C. to 427° C. (700° F. to 800° F.), a partial pressure of hydrogen in the range 6.9 to 27.6 MPa (1000 to 4000 psig)
Implementation Method 2
The effluent from the second liquefaction reactor undergoes a gas/liquid separation then a distillation. The heavy fraction is recycled as the solvent to prepare the suspension with the coal. The light fraction is sent to an optional fixed bed hydrotreatment stage using CoMo or NiMo catalysts on alumina to reduce the sulphur and nitrogen contents.
Implementation Method 3
The effluent from the second liquefaction reactor undergoes a gas/liquid separation then a distillation. The heavy fraction is recycled as the solvent to prepare the suspension with the coal.
Data Source
AI summary
A process for the conversion of coal into fuel bases comprises two successive direct liquefaction stages in ebullated bed reactors followed by a fixed bed hydrocracking stage. This process can produce excellent quality fuel bases (kerosene and diesel).