CO2 Capture in Cement Calcination via Segmented Oxide Loop
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Solution Overview
Problem
The cement manufacturing process is energy-intensive due to the high endothermic calcining step that converts calcium and magnesium carbonate to calcium and magnesium oxide, resulting in significant carbon dioxide emissions, and existing methods for CO2 capture and separation from cement production are not optimized for efficiency and energy reduction.
Innovation Solution
Separate calcination of limestone and dolomite from other raw materials before calcination, perform low-temperature calcining to release CO2 and form CaO and MgO in a combustion gas-free atmosphere, and use these oxides to capture CO2 from combustion exhaust gases in an open loop system, controlling their addition to enhance belite and alite formation and reduce energy consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If conventional high-temperature calcining is used to convert calcium and magnesium carbonate to calcium and magnesium oxide, then the cement clinker can be produced, but significant energy is consumed and carbon dioxide emissions increase
Solution Approach 1:
The calcining process is divided into two distinct stages: a first calciner operating at lower temperatures (650-1050°C) to convert carbonates to oxides and release CO2, and a second calciner operating at high temperatures (1300-1450°C) to form clinker. This segmentation allows the energy-intensive high-temperature step to be separated from the CO2-releasing low-temperature step, reducing overall energy consumption while maintaining productivity.
Solution Approach 2:
The first calciner performs preliminary conversion of calcium and magnesium carbonates to their oxide forms at lower temperatures before the material enters the second calciner. This preliminary action reduces the energy burden on the second calciner, as the endothermic carbonate decomposition has already occurred, allowing clinker formation at slightly lower temperatures and reduced energy consumption.
2Object-generated harmful factors
If limestone and dolomite are calcined together with other raw materials in a conventional rotary kiln, then cement clinker is produced, but CO2 separation and capture become difficult
Solution Approach 1:
The calcining process is divided into two distinct stages: a first calciner operating at lower temperatures (650-1050°C) to convert carbonates to oxides and release CO2, and a second calciner operating at high temperatures (1300-1450°C) to form clinker. This segmentation allows the energy-intensive high-temperature step to be separated from the CO2-releasing low-temperature step, reducing overall energy consumption while maintaining productivity.
Solution Approach 2:
The first calciner is designed to operate under specific conditions (lower temperature, controlled atmosphere without combustion gases) optimized for carbonate decomposition and CO2 release. This localized optimization allows CO2 to be separated and captured more easily from this specific zone, while the second calciner operates under conditions optimized for clinker formation.
3Productivity
If CaO and MgO are added at standard points in the cement manufacturing process, then clinker is formed, but the yield of hydrating belite and alite is limited
Solution Approach 1:
The process provides multiple dynamic addition points for CaO and MgO throughout the cement manufacturing process, allowing operators to adjust the timing and location of oxide addition based on desired product characteristics. This dynamic control enables optimization of belite and alite formation yields while maintaining ease of operation through flexible process adjustment.
Solution Approach 2:
The process controls the ratio of belite to alite in the final product by adjusting parameters such as addition points, temperature profiles, and residence times in the calciners. These parameter changes allow optimization of hydrating phase yields and control over early and late strength characteristics of the cement.
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 approach reduces energy costs, increases the yield of hydrating belite and alite, minimizes non-hydrating phases, and allows for lower formation temperatures, enhancing early and late hydration strengths while capturing CO2 efficiently, resulting in a more sustainable and cost-effective cement production process.
Implementation Method 1
heating the limestone/dolomite components of the clinker feed in a first calciner at a temperature of between about 650° C. to about 1050° C.
Implementation Method 2
converting calcium and magnesium carbonate to calcium and magnesium oxide (CaO and MgO) with the co-generation of carbon dioxide (CO2)
Implementation Method 3
using the removed CaO/MgO to capture CO2 from fuel combustion flue gas associated with the cement production process, thereby generating a supply of CaCO3/CaMg(CO3)2
Implementation Method 4
exposing the reaction products in a second calciner to a temperature of at least between about 1300° C. to about 1450° C. until clinker is formed
Data Source
AI summary
A process of manufacturing cement clinker is provided in which a clean supply of CO2 gas may be captured. The process also involves using an open loop conversion of CaO/MgO from a calciner to capture CO2 from combustion flue gases thereby forming CaCO3/CaMg(CO3)2. The CaCO3/CaMg(CO3)2 is then returned to the calciner where CO2 gas is evolved. The evolved CO2 gas, along with other evolved CO2 gases from the calciner are removed from the calciner. The reactants (CaO/MgO) are feed to a high temperature calciner for control of the clinker production composition.