Fluidized Bed Calcination of Clay and Fly Ash for Cement Clinker
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Solution Overview
Problem
The cement industry faces challenges in reducing CO2 emissions and achieving cost-effective, efficient production of clinker substitutes, particularly due to the limitations of existing methods for calcining clay, which result in red discoloration and require separate storage and mixing of components, leading to inefficiencies and high costs.
Innovation Solution
A method for producing a pozzolanic or latent hydraulic cement clinker substitute by calcining clay with a fuel containing a mineral substance, such as fly ash, at temperatures between 500-1250°C, where the mineral substance contributes at least 20-40% by weight, and using coal as a preferred fuel to control the calcination process, eliminating the need for separate storage and mixing of components.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If clay is calcined using conventional external combustion chambers with cooler outside air, then the calcination process can be controlled, but high excess air causes extensive oxidation of iron compounds leading to red discoloration
Solution Approach 1:
The patent applies the inert atmosphere principle by using a fluidized bed calciner where the clay is calcined in an atmosphere with limited oxygen availability. The fluidized bed system allows for controlled atmosphere conditions that prevent excessive oxidation of iron compounds, thereby avoiding red discoloration while maintaining effective calcination throughput.
2Ease of manufacture
If separate storage and mixing devices are used for calcined clay and fly ash, then component quality can be controlled, but device complexity and costs increase
Solution Approach 1:
The patent merges the calcination of clay with the introduction of fly ash into a single integrated fluidized bed calcination process. Both materials are fed into the same calciner where they are simultaneously calcined and mixed, eliminating the need for separate storage silos and mixing equipment while ensuring homogeneous composition in the final product.
Solution Approach 2:
The fluidized bed calciner serves multiple functions simultaneously: it calcines the clay, introduces and calcines fly ash, provides controlled atmosphere to prevent oxidation, and ensures homogeneous mixing of components. This multi-functionality reduces overall system complexity while maintaining product quality.
3Reliability
If high-purity clays are used as clinker substitutes, then performance requirements are met, but costs increase significantly
Solution Approach 1:
The patent produces a composite material by combining clay with fly ash in the fluidized bed calciner. The fly ash acts as a supplementary component that enhances the pozzolanic properties and hydraulic reactivity of the calcined clay, allowing the use of lower-purity, more economical clay materials while still meeting cement performance requirements.
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 enables faster, more cost-effective production of cement clinker substitutes with improved properties, such as workability and hydraulic reactivity, while minimizing red discoloration and excess air oxidation, thus enhancing the cement's performance and reducing environmental impact.
Implementation Method 1
calcining clay with a fuel containing a mineral substance, such as fly ash, at temperatures between 500-1250°C
Implementation Method 2
During the calcination of clay, which is carried out, for example, in a rotary kiln, a levitation heat exchanger, a fluidized bed or in a multiple-hearth furnace, the clay minerals first release surface water and then lose structural water. A consequence of this release of water is the phase transition of the crystalline clay minerals into X-ray amorphous meta-clay minerals.
Implementation Method 3
the resulting mixture of the mineral substance of the fuel and the calcined clay forms the pozzolanic or latent hydraulic cement clinker substitute
Data Source
Figure 1~2
AI summary
The invention relates to a method for producing a pozzolanic or latent-hydraulic cement clinker substitute in which clay is calcined at temperatures ranging between 500 and 1250°C, preferably between 550 and 1150°C and most preferred between 700 and 900°C, using a fuel that comprises a mineral substance, the resulting mixture of the mineral substance of the fuel and the calcined clay forming said pozzolanic or latent-hydraulic cement clinker substitute, and the proportion of the mineral substance introduced into the hydraulic cement clinker substitute by the fuel being between 1 and 60 % by weight.