Ozone Injection for Nitrogen Oxide Reduction in Waste Incineration
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Solution Overview
Problem
Thermal waste treatment plants face challenges in reducing nitrogen oxides in flue gas due to the inhomogeneous composition and variability of waste fuels, which complicates control and efficiency of existing reduction methods like SNCR and SCR, and ozone has not been previously used in this context.
Innovation Solution
A method combining selective non-catalytic reduction (SNCR) with ozone injection downstream of the secondary treatment unit and upstream of a scrubbing or adsorption unit, allowing for efficient nitrogen oxide reduction at lower temperatures and reducing ozone requirements, thereby lowering operating costs and achieving stringent emission limits.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If selective non-catalytic reduction (SNCR) is used to reduce nitrogen oxides, then the reduction capability is limited and ammonia escape increases at lower nitrogen oxide thresholds, but the method is cost-effective and simple to operate
Solution Approach 1:
The patent combines SNCR (selective non-catalytic reduction) with ozone injection technology to create a hybrid system. The flue gas first passes through the SNCR unit where ammonia reduces nitrogen oxides, then through an ozone injection unit where remaining nitrogen oxides are oxidized to nitrogen dioxide and further converted to soluble nitrate/nitrite compounds. This merging allows the system to achieve low nitrogen oxide emissions (below 20 mg/m³) without the ammonia escape problems of pure SNCR, while maintaining operational simplicity.
2Reliability
If selective catalytic reduction (SCR) is used to reduce nitrogen oxides, then high reduction efficiency is achieved, but very high investment outlays and increased operating costs are required
Solution Approach 1:
The patent replaces the expensive SCR catalyst system with a combination of inexpensive reagents (ammonia for SNCR and ozone generated on-demand). Instead of investing in costly catalytic converters requiring high-temperature operation and regular maintenance, the system uses consumable chemicals that can be easily replenished. The ozone is generated directly in the flue gas stream using electrical discharge, eliminating the need for expensive SCR equipment infrastructure.
3Reliability
If ozone is injected into the flue gas stream upstream of a scrubber unit, then nitrogen oxides are selectively oxidized to water-soluble dinitrogen pentoxide, but high operating costs are incurred due to energy requirements for ozone generation
Solution Approach 1:
The patent applies preliminary action by first conducting SNCR reduction before ozone injection. The ammonia-based SNCR process reduces a significant portion of nitrogen oxides in the high-temperature flue gas, converting them to nitrogen and water. This preliminary reduction decreases the concentration of nitrogen oxides that subsequently require ozone treatment, thereby reducing the total ozone generation energy requirements while still achieving the target emission level of below 20 mg/m³.
4Reliability
If the flue gas temperature is increased to 20-400°C for SCR operation, then nitrogen oxide reduction efficiency is improved, but plant efficiency is reduced and operating costs increase
Solution Approach 1:
The patent changes the temperature parameter from the high-temperature SCR range (20-400°C) to the lower SNCR range (70-900°C), and ultimately to low-temperature operation after ozone injection. The SNCR process operates effectively at lower temperatures than SCR, and the subsequent ozone injection works at ambient or near-ambient temperatures. This parameter change eliminates the need for expensive flue gas heating systems, maintains plant efficiency, and reduces operating costs while achieving the required emission standards.
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 effectively reduces nitrogen oxide emissions to near-zero levels with minimal ammonia escape, offering economic advantages over traditional methods and adapting to fluctuating waste fuel compositions, making it suitable for thermal waste treatment plants.
Implementation Method 1
The nitrogen oxides, nitrogen monoxide and nitrogen dioxide, are selectively oxidized to dinitrogen pentoxide, an extremely water-soluble species, by the following reactions
Implementation Method 2
scrubbing, absorption, or adsorption unit
Implementation Method 3
scrubbing, absorption, or adsorption unit
Data Source
AI summary
A method for reducing the content of nitrogen oxides in a flue gas stream, in which method the flue gas stream is taken from a thermal plant for the treatment of garbage, domestic waste, and/or residual materials similar to domestic waste, and is passed through a secondary treatment unit designed for selective, non-catalytic reduction, and then is subsequently passed through a scrubbing, absorption, or adsorption unit. According to the invention, an ozone injection into the flue gas stream is carried out downstream of the secondary treatment unit and upstream of the washing, absorption, or adsorption unit. The present invention also relates to a corresponding plant.