What Technologies Can Reduce Pollutant Emissions from Waste Incinerators?
Combustion optimisation technologies
Oxygen-enriched combustion: raising the oxygen concentration makes the waste burn more fully, improves combustion efficiency, reduces the formation of incomplete-combustion products such as carbon monoxide, and at the same time lowers the emission of waste gases such as carbon dioxide; it also effectively reduces slag generation.
Air-staged combustion: the air required for combustion is fed into the furnace in stages, so that combustion takes place in zones with different oxygen concentrations. In the initial combustion stage less air is supplied, so the waste burns under oxygen-deficient conditions and a reducing atmosphere is formed which suppresses the formation of nitrogen oxides; in the subsequent stage enough air is added to ensure complete combustion of the waste and to reduce emissions of carbon monoxide and volatile organic compounds.
Flue-gas recirculation: part of the flue gas after combustion is introduced back into the furnace, lowering the oxygen concentration in the combustion zone and thereby suppressing the formation of nitrogen oxides. At the same time, flue-gas recirculation also increases the residence time of the flue gas in the furnace, so that the waste burns more fully and emissions of unburnt matter are reduced.
Flue-gas cleaning technologies
Dust removal: high-efficiency dust removal equipment such as bag filters and electrostatic precipitators effectively removes particulates from the flue gas, so that the particulate concentration of the emitted flue gas is far below the national standard and pollution of the atmospheric environment is reduced.
Acid-gas removal: wet acid-gas removal (such as the limestone - gypsum process), dry acid-gas removal (such as injecting hydrated lime powder) or semi-dry acid-gas removal is used to remove acid gases such as sulfur dioxide and hydrogen chloride from the flue gas, lowering the risk of acid rain formation and reducing acidic pollution of the environment.
DeNOx: selective catalytic reduction (SCR) and selective non-catalytic reduction (SNCR) are common denitrification methods. By injecting reducing agents such as urea solution and ammonia water into the flue gas, nitrogen oxides are reduced to nitrogen and water under the action of the catalyst, thereby lowering nitrogen oxide emissions.
Activated carbon adsorption: the adsorption performance of activated carbon is used to adsorb harmful substances such as dioxins and heavy metals from the flue gas, effectively removing these persistent organic pollutants that are difficult to degrade and ensuring that the emitted flue gas meets strict environmental standards.
Pyrolysis technologies
Low-temperature pyrolysis: at a relatively low temperature and under oxygen-free or oxygen-deficient conditions, the organic matter in the waste undergoes thermal decomposition and is converted into usable energy and a small amount of residue. This technology can significantly reduce the formation of harmful substances, avoid pollutants such as dioxins that may be produced in high-temperature combustion, and at the same time lower the amount of fly ash generated.
Pyrolysis gasification: the waste is pyrolysed and gasified at high temperature to produce combustible gas and solid residue. The combustible gas can be recovered and used as energy, while the harmful substance content of the solid residue is relatively low and, after further treatment, it can be safely landfilled or utilised as a resource. In the pyrolysis gasification process, because the combustion conditions are relatively mild, the formation and emission of pollutants can be effectively controlled2.
In-furnace treatment technologies
Adding inhibitors: during waste incineration, adding an appropriate amount of inhibitors such as limestone and dolomite can react with the acidic substances in the waste and reduce acid-gas emissions. In addition, some inhibitors can also fix heavy metals, lowering the heavy metal content in the fly ash and thereby reducing the risk of heavy metal pollution of the environment.
Optimising the grate design: advanced grate structures and materials can improve the combustion condition of the waste in the furnace, allow the waste to contact the air fully, raise combustion efficiency and reduce the formation of incomplete-combustion products. For example, double-layer grate or fluidised bed designs allow the waste to be turned over and burnt more fully in the furnace and lower pollutant emissions.
On-line monitoring and automatic control technologies
On-line monitoring system: a continuous emission monitoring system (CEMS) is installed to monitor in real time the various indicators of the flue gas produced during incineration, such as the concentrations of particulates, sulfur dioxide, nitrogen oxides, carbon monoxide and dioxins, as well as parameters such as flue-gas temperature, flow rate and oxygen content. Through the on-line monitoring data, the operating condition of the incinerator and the pollutant emission situation are grasped in good time, providing a basis for adjusting operating parameters and taking control measures.
Automatic control system: with the help of modern sensors, controllers and computer technology, automatic control of the waste incinerator is realised. According to the on-line monitoring data and preset control strategies, operating parameters such as furnace temperature, oxygen content and feed rate are adjusted automatically, ensuring that the incinerator is always in the best operating state, raising combustion efficiency and reducing the formation and emission of pollutants
| 
|—|
70t/d grate of a domestic waste incinerator
