Co-grinding Coal and Plastic Pellets for Furnace Injection
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Solution Overview
Problem
Current methods for co-firing secondary fuels like wood pellets or plastic waste in industrial furnaces using powdered coal are limited by milling operations and burning efficiency, often requiring separate milling or injection, which is costly and inefficient, especially when using plastic-containing waste that can melt and cause processing issues.
Innovation Solution
A process that co-grinds coal or cokes with cellulose and plastic pellets larger than 3 mm to a powder with 95% of particles smaller than 2 mm, using roller or ball mills, allowing direct injection into the furnace flame without separate milling or injection, maintaining high throughput and low maintenance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If separate milling or injection is used for co-firing secondary fuels, then burning efficiency is improved, but device complexity and cost increase
Solution Approach 1:
The patent combines the milling of coal and secondary fuels (cellulose and plastic pellets) into a single integrated milling process using roller or ball mills. This eliminates the need for separate milling operations and separate injection systems, reducing device complexity while maintaining effective co-firing. The mixed powder is then injected through a single system into the furnace flame.
2Use of energy by moving object
If plastic-containing waste is used as secondary fuel, then caloric value is improved, but fouling issues occur in milling equipment
Solution Approach 1:
The patent changes the operating parameters of the milling equipment, specifically using roller mills or ball mills that operate at controlled temperatures and with specific mechanical actions that prevent plastic melting and fouling. The milling process is optimized to handle plastic-containing pellets without causing the plastic to melt and adhere to equipment surfaces, thereby maintaining high caloric value utilization while avoiding fouling problems.
3Device complexity
If direct co-firing without separate injection is used, then device complexity is reduced, but manufacturing precision of powder particle size is worsened
Solution Approach 1:
The patent employs roller mills or ball mills that are designed to handle multiple types of materials (coal and plastic-containing pellets) simultaneously while achieving the required particle size distribution. These mills serve multiple functions: grinding coal, grinding pellets, and producing a mixed powder with controlled particle size characteristics suitable for direct injection into the furnace.
4Reliability
If elevated temperatures are used in milling, then burning efficiency is improved, but plastic melting and fouling increase
Solution Approach 1:
The patent optimizes the milling temperature parameter to remain below the melting point of plastic while still achieving effective grinding and preparation of the fuel mixture. The milling process operates at moderate temperatures that prevent plastic softening and fouling, yet the resulting powder maintains good combustion characteristics when injected into the high-temperature furnace environment.
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 enables efficient co-firing of secondary fuels with coal or cokes, achieving higher caloric values and reduced CO2 emissions, with no fouling issues in the milling equipment, even at elevated temperatures, and allows for higher plastic content without compromising burner efficiency.
Implementation Method 1
co-grinded to a powder with a particle size wherein 95 wt% or more of the powder has a particle size smaller than 2 mm using roller or ball mills
Implementation Method 2
The ground fuel powder is blown into the furnace by means of a flow gas, usually air, which generally is heated till at least about 200 °C or higher
Implementation Method 3
the powder is injected in the flame of the furnace
Data Source
AI summary
The invention relates to a process for firing an industrial furnace, in particular for electricity generation, wherein coal or cokes together with a secondary fuel comprising cellulose and plastic, in the form of pellets of a size larger than about 3 mm thickness, and having a caloric value of about 16 GJ/ton or more is ground to a powder wherein about 95 wt% or more has a particle size smaller than 2 mm and wherein the d50 of the particle size distribution is between about 5 and about 100 µm, wherein the powder is injected in the flame of the furnace. In this process the grinding is performed in a roller mill or ball mill, and the amount of pellets used together with the coals preferably is about 3 wt% or more, relative to the coal.