Multi-Stage Bypass Cooling for Cement Clinker Denitrification
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Solution Overview
Problem
Current denitrification methods for bypass exhaust gases in cement clinker production, such as the SNCR and SCR processes, face challenges due to high temperatures and the need for costly catalysts, especially in plants using secondary fuels and raw materials that introduce pollutants and form adverse material cycles, leading to inefficient nitrogen oxide reduction and increased operational costs.
Innovation Solution
A multi-stage bypass system that cools bypass exhaust gases to a temperature range of 800 °C to 950 °C in a first mixing chamber, followed by injection of ammonia in a pipeline reaction section for selective non-catalytic reduction (SNCR), and further cooling to 150 °C to 250 °C in a second mixing chamber for effective denitrification without the use of SCR catalysts, allowing for efficient pollutant separation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If the bypass exhaust gas is cooled rapidly to low temperatures (below 400°C) in a single stage, then pollutant condensation and separation are improved, but the denitrification efficiency deteriorates due to insufficient temperature for effective SNCR process
Solution Approach 1:
The cooling process is divided into two distinct stages: first cooling to 800-950°C for SNCR denitrification, then second cooling to 150-250°C for pollutant condensation. This segmentation allows each stage to operate at optimal temperature for its specific function, resolving the contradiction between denitrification efficiency and pollutant separation.
Solution Approach 2:
The SNCR denitrification process is performed as a preliminary action before the final cooling and pollutant separation stage. By completing denitrification at 800-950°C before the second cooling stage, the system ensures effective nitrogen oxide reduction while preserving the ability to condense pollutants at lower temperatures afterward.
2Productivity
If SCR catalysts are used for denitrification, then nitrogen oxide reduction efficiency is improved, but operational costs increase due to catalyst investment and maintenance
Solution Approach 1:
The patent replaces expensive SCR catalysts with a cheaper SNCR process that uses ammonia or urea as reducing agents without requiring catalysts. This substitution eliminates catalyst investment and maintenance costs while achieving effective denitrification through the chemical reduction of nitrogen oxides at 800-950°C.
Solution Approach 2:
The catalytic component is extracted and removed from the denitrification process. Instead of using SCR catalysts, the system employs a non-catalytic SNCR process where ammonia or urea directly reduces nitrogen oxides through chemical reactions, eliminating the need for expensive catalyst materials.
3Productivity
If the bypass exhaust gas is cooled to very high temperatures (above 1000°C), then denitrification reaction rate is improved, but the formation of dioxins and furans increases
Solution Approach 1:
The patent optimizes the temperature parameter to a specific range of 800-950°C for the SNCR process. This parameter change from higher temperatures prevents dioxin and furan formation while maintaining effective denitrification reaction rates. The controlled temperature window balances reaction efficiency with harmful substance prevention.
Solution Approach 2:
The patent converts the potential harm of high-temperature processing into a benefit by using the heat from the exhaust gas itself to maintain the 800-950°C temperature window needed for SNCR. The high-temperature environment that could cause dioxin formation is instead harnessed to enable effective denitrification, with the temperature then reduced in a controlled second stage.
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 enables effective denitrification and pollutant separation without the need for costly catalysts, maintaining process control and reducing operational costs while preventing the formation of dioxins and furans, and effectively condensing pollutants for separation in filters.
Implementation Method 1
cooling the bypass exhaust gas to a temperature between 800 °C and 950 °C in a first mixing chamber
Implementation Method 2
ammonia is converted into nitrogen and water by thermolysis with the nitrogen oxides
Implementation Method 3
cooling the bypass exhaust gas to a temperature between 150 °C and 250 °C in a second mixing chamber
Implementation Method 4
these compounds pass through the kiln inlet chamber into the calcination zone and the heat exchanger, where they condense on the raw meal particles
Data Source
Figure 1
AI summary
The invention relates to a method and to a corresponding plant for denitrifying bypass exhaust gases (9) in a plant for producing cement clinker, wherein the plant has a rotary kiln (2) for sintering raw meal (3) and a calciner (7) for deacidifying the raw meal (3), the rotary kiln (2) has a rotary kiln inlet chamber (5), which is connected to the calciner (7) directly or by means of a kiln riser duct (6), and the bypass exhaust gas (9) is drawn off in the region of the rotary kiln inlet chamber (5). According to the invention, the bypass exhaust gas (9) is guided into a first mixing chamber (10), in which the bypass exhaust gas is cooled down to a temperature between 800 °C and 950 °C, then the bypass exhaust gas (9) is guided through a reaction segment (15) arranged in a pipeline (13), wherein the dwell time in the reaction segment (15) is between 0.5 s and 3 s and ammonia, aqueous ammonia solution, or ammonia-releasing substances (14) are injected for denitrification according to the method of selective non-catalytic reduction (SNCR), then the bypass exhaust gas (9) is guided into a second mixing chamber (16), in which the bypass exhaust gas is cooled to a temperature between 150 °C and 250 °C, and then the bypass exhaust gas (9) is guided to at least one filter (17) for dust removal.