Concentric Tube Reactor for Lime Recycling Heat Recovery
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Solution Overview
Problem
Existing carbon dioxide capture systems using lime are highly energy intensive, with over 80% of the cost being the energy required to recycle lime, and current methods for heat recovery are inefficient and costly.
Innovation Solution
A chemical processing system with two concentric tubes, where a metal carbonate is decomposed into a metal oxide and carbon dioxide in one tube, and then hydrated into a metal hydroxide in another tube, with excellent thermal coupling allowing heat from the hydration process to flow and provide part of the heat required for decomposition.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If traditional lime kilns are used to recycle limestone, then lime can be produced, but the energy consumption is very high (178 KJ/mole)
Solution Approach 1:
The patent divides the limestone recycling process into two separate stages: (1) thermal decomposition of limestone to produce lime and CO2, and (2) hydration of lime to produce slaked lime. This segmentation allows each stage to be optimized independently, with the hydration stage recovering heat that can be reused in the decomposition stage, thereby reducing overall energy consumption from 178 KJ/mole to 113 KJ/mole.
Solution Approach 2:
The patent recovers and reuses the heat generated during the exothermic hydration reaction (CaO + H2O → Ca(OH)2 + heat) to fuel the endothermic decomposition reaction (CaCO3 → CaO + CO2). This heat recovery mechanism significantly reduces the external energy input required for the recycling process.
2Use of energy by moving object
If steam-generating systems are added to recover heat from hydration, then energy efficiency improves, but capital and maintenance costs increase significantly
Solution Approach 1:
The patent combines the hydration reaction and decomposition reaction into a single integrated system where the heat from hydration directly fuels decomposition. The concentric tube design allows thermal coupling between the two reactions without requiring separate steam-generation equipment, thereby achieving energy efficiency while avoiding additional capital and maintenance costs.
Solution Approach 2:
The concentric tube structure serves as an intermediary that enables thermal energy transfer from the hydration reaction to the decomposition reaction. This thermal coupling mechanism allows heat recovery without requiring complex steam-generation systems, turbines, or condensers, thus simplifying the overall system while maintaining high energy efficiency.
3Temperature
If the hydration reaction temperature is increased to improve heat availability, then more heat can be recovered, but the decomposition temperature requirement must also be met
Solution Approach 1:
The patent optimizes the temperature parameters of both reactions to achieve the best energy balance. By controlling the hydration reaction temperature to be slightly higher than the decomposition reaction temperature, the system maximizes heat availability for the decomposition process while maintaining efficient hydration. This parameter optimization reduces the net energy requirement to 113 KJ/mole.
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 system significantly reduces the total energy required for recycling metal carbonates, lowering the net energy from 178 KJ/mole to 113 KJ/mole, and thereby reducing the total cost of capturing CO2.
Implementation Method 1
a metal carbonate is decomposed into a metal oxide and carbon dioxide
Implementation Method 2
This reaction requires heat
Implementation Method 3
the metal oxide is then injected into the second of the two concentric tubes, and hydrated in an atmosphere of steam to a hydroxide
Implementation Method 4
This reaction produces heat
Implementation Method 5
The wall of the inner concentric tube separates the hydration and decomposition processes, and provides excellent thermal coupling between them
Implementation Method 6
The hydration process, which generates heat, operates at a temperature above the temperature of the decomposition process, which consumes heat. Thus, the heat of hydration can flow down a thermal gradient and provide a significant fraction of the heat required for the decomposition process
Data Source
AI summary
A chemical processing method includes decomposing a metal carbonate in a first tube by exposure to a first quantity of heat, producing a metal oxide and carbon dioxide; and hydrating the metal oxide in a second tube concentric with the first, by exposure to steam, producing a metal hydroxide and a second quantity of heat. The partial pressure of the steam and/or of the carbon dioxide is controlled so that the hydration reaction occurs at a second temperature above a first temperature at which the decomposition reaction occurs. The inner one of the concentric tubes has an inner tube wall. At least some of the second quantity of heat flows from the second tube through the inner tube wall to the first tube, providing at least a part of the first quantity of heat.