Two-Stage Combustion NOx Reduction via Calorific Value Control
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Solution Overview
Problem
Current combustion processes in technical furnaces, such as grate furnaces, face challenges in reducing nitrogen oxide (NOx) formation while avoiding the formation of nitrous oxide (N2O) and ammonia slip (NH3), which are not effectively addressed by existing methods that either lead to incomplete combustion or reduce heat energy utilization.
Innovation Solution
A method involving a two-stage combustion process with a fixed bed burnout zone and a downstream exhaust gas burnout zone, where a gas-water mixture is injected to reduce the calorific value of exhaust gases before the exhaust gas burnout zone, maintaining temperatures above 950°C to prevent N2O formation and ensuring complete breakdown of NH3, while adjusting primary air supply and grate kinematics to optimize combustion stoichiometry and gas mixing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If the calorific value of exhaust gases is reduced before the exhaust gas burnout zone, then NOx emissions are reduced, but the temperature may drop below 950°C causing N2O formation
Solution Approach 1:
The patent applies parameter changes by precisely controlling the calorific value of exhaust gases within a specific range (0.3-1.5 MJ/m³) before the exhaust gas burnout zone. This controlled parameter change reduces NOx formation while maintaining sufficient temperature (>950°C) to prevent N2O formation, resolving the contradiction between reducing harmful emissions and maintaining temperature.
2Productivity
If secondary air is added to complete exhaust gas burnout, then combustion efficiency is improved, but local temperature peaks increase causing NOx formation
Solution Approach 1:
The patent applies local quality by creating different oxygen concentration zones: the primary combustion zone operates with controlled oxygen supply to limit temperature peaks and NOx formation, while the exhaust gas burnout zone receives additional secondary air specifically for completing the burnout of remaining combustible gases. This localized differentiation of combustion conditions achieves both complete combustion efficiency and NOx reduction.
3Object-generated harmful factors
If primary air supply is increased to reduce NOx, then nitrogen oxide formation is reduced, but heat energy utilization decreases
Solution Approach 1:
The patent applies preliminary action by pre-cooling and pre-mixing the exhaust gases before they enter the exhaust gas burnout zone. This preliminary preparation reduces the calorific value to an optimal range, allowing subsequent complete burnout with secondary air to proceed at controlled temperatures that minimize NOx formation while maximizing heat energy recovery from the exhaust gases.
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 significantly reduces NOx emissions without forming N2O or causing ammonia slip, maintains high heat energy utilization, and ensures good slag quality by controlling the calorific value and temperature of exhaust gases, thereby meeting stringent emission limits and operational efficiency.
Implementation Method 1
a gas-water mixture is injected to reduce the calorific value of exhaust gases before the exhaust gas burnout zone
Implementation Method 2
a gas-water mixture is injected to reduce the calorific value of exhaust gases
Implementation Method 3
the primary nitrogen species NH 3 and HCN are completely broken down and N 2 is preferably formed as the end product
Implementation Method 4
the primary nitrogen species NH 3 and HCN are completely broken down and N 2 is preferably formed as the end product at the expense of nitrogen oxide formation
Implementation Method 5
maintaining temperatures above 950°C to prevent N2O formation and ensuring complete breakdown of NH3
Data Source
Figure 1
Figure 2a~2f
Figure 3a
AI summary
Method of reducing the nitrogen oxide formation (NOx) on the primary side and of at the same time avoiding the formation of nitrous oxide (N2O) and ammonia slip (NH3) in the exhaust gas of a two-stage combustion process and of improving the slag balance, comprising a fixed-bed burn-out zone, through which an oxygenous primary gas flows, above a fuel bed and a downstream exhaust-gas burn-out zone into which oxygenous secondary gas is additionally introduced. The object is to propose a simple and reliably controllable method for reducing nitrogen oxide formation on the primary side in combustion plants, for example grate combustion plants, with considerably higher efficiency, wherein no additional pollutants are produced or the utilization of the energy of the heat content of the combustion gases is only marginally impaired. The object is achieved in that the calorific value of the exhaust gas between the fuel bed surface and upstream of the exhaust-gas burn-out zone is reduced in such a way that an average calorific value of less than 1 MJ/m3 occurs, and the temperature of the fuel bed surface is at least 950°C until the exhaust gas leaves the exhaust-gas burn-out zone, and the gas temperature above the fuel bed in the region of the rear grate half is more than 1000°C.