Regenerative Thermal Post-Combustion for NOx Purification
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Solution Overview
Problem
Industrial processes, particularly in the cement industry, face challenges in reducing emissions of nitrogen oxides (NOx), ammonia (NH3), and carbon monoxide (CO) while minimizing fuel and raw material costs, with existing technologies risking ammonia slip and inefficient pollutant reduction.
Innovation Solution
A regenerative thermal post-combustion system using ceramic heat accumulator bodies and a nitrogen-hydrogen compound, such as ammonia or urea, to thermally reduce NOx and oxidize carbon compounds in multiple zones of a combustion chamber, achieving two-stage NOx reduction without catalysts and minimizing ammonia release.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a regenerative thermal combustion system is used to oxidize carbon compounds and reduce nitrogen oxides, then emission reduction is achieved, but ammonia slip occurs as a harmful by-product
Solution Approach 1:
The combustion chamber is divided into multiple zones with different functions: a first zone for oxidation of carbon compounds and a second zone for reduction of nitrogen oxides. This spatial segmentation allows selective reduction of NOx while preventing ammonia slip by controlling where reduction reactions occur.
Solution Approach 2:
Different local conditions are created in different zones of the combustion chamber. The first zone has conditions favorable for oxidation (excess oxygen), while the second zone has conditions favorable for NOx reduction (controlled reducing atmosphere). This local differentiation enables simultaneous achievement of oxidation and reduction without ammonia slip.
2Loss of energy
If fuel quantity is reduced to lower costs, then operating expenses decrease, but emission reduction effectiveness is compromised
Solution Approach 1:
The system uses the waste gas itself as the fuel source for the regenerative thermal combustion process. The carbon compounds present in the waste gas provide the necessary combustion enthalpy to maintain high temperatures in the combustion chamber, eliminating or reducing the need for additional fuel while simultaneously treating the pollutants.
Solution Approach 2:
The harmful carbon compounds and nitrogen oxides in the waste gas are converted into beneficial effects: carbon compounds serve as fuel for combustion, and nitrogen oxides are reduced to nitrogen. This converts the pollutant load from a liability into a resource that drives the purification process.
3Productivity
If high temperature combustion is used to oxidize carbon compounds, then oxidation efficiency increases, but energy consumption increases
Solution Approach 1:
The system operates in periodic cycles with alternating flow directions through the regenerative heat exchangers. During one half-cycle, waste gas is heated by the hot heat accumulator; during the other half-cycle, the heat accumulator is reheated by combustion. This periodic operation allows efficient heat recovery and reduces the net energy input required.
Solution Approach 2:
The regenerative heat exchangers utilize phase transitions and thermal energy storage in the heat accumulator material to capture and release thermal energy efficiently. The heat accumulator absorbs heat during the combustion phase and releases it during the waste gas heating phase, enabling high oxidation temperatures with reduced net energy consumption.
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
Effectively reduces NOx and ammonia emissions, adheres to strict limit values, and operates autothermally, utilizing the combustion enthalpy of carbon compounds, thus reducing fuel costs and enabling the use of secondary fuels and raw materials.
Implementation Method 1
The waste gas is supplied to at least two regenerators filled with heat accumulator bodies... The waste gas preheated in this way is supplied to the combustion chamber
Implementation Method 2
At this high temperature, the carbon compounds in the combustion chamber are combusted by the atmospheric oxygen in the waste gas
Implementation Method 3
the nitrogen oxides are reduced by means of a nitrogen-hydrogen compound in the combustion chamber at this high temperature
Implementation Method 4
the nitrogen oxides are reduced by means of a nitrogen-hydrogen compound... with formation of nitrogen
Implementation Method 5
at least one catalytically active heat accumulator layer is each provided as a lower part of the regenerators... the catalytically active heat accumulator layer using the additionally formed ammonia in order to improve the reduction of the nitrogen oxides
Implementation Method 6
The combustion enthalpy of the carbon compounds can ensure autothermal operation of the post-combustion system
Data Source
AI summary
For the purification of waste gas containing carbon compounds and nitrogen oxides by means of a regenerative post-combustion system, at least two regenerators (A, B, C) filled with heat accumulator bodies (7a, 7b, 7c) and connected by a combustion chamber (10) are provided, wherein the waste gas is alternately heated in a regenerator (A, B, C), the carbon compounds are oxidised in the combustion chamber (10), and, with the addition of a nitrogen-hydrogen compound, the nitrogen oxides are reduced in the combustion chamber (10) thermally and thus not catalytically. Remaining nitrogen oxides are removed by means of a catalytically active heat accumulator layer (6a, 6b, 6c) and the addition of a further nitrogen-hydrogen compound in the regenerator (A, B, C) from which the clean gas exits.