In the combustion process of industrial boilers, nitrates, as one of the main components of flue gas, have also prompted Chinese scholars to discuss denitrification technology for flue gas. As early as the 1980s, scholars began to explore the SCR denitrification technology from the perspective of flue gas emissions from industrial boiler combustion. Looking at the current status of existing flue gas denitrification technologies, they include selective non-catalytic reduction, selective catalytic reduction, photo-catalytic reduction, and carbon thermal reduction. With the introduction of various denitrification technologies for flue gas, industrial boilers now have corresponding denitrification treatment methods.

Treating denitrification of flue gas from industrial boilers contributes to achieving the expected denitrification targets more effectively and has a positive impact on further reducing environmental pollution caused by flue gas emissions from industrial boiler combustion. Therefore, studying SCR denitrification technology for industrial boilers is of great significance.

The SNCR process is a method for reducing NOx without a catalyst within the temperature range of 800-1050°C. This method utilizes the furnace as a reactor and can be achieved by modifying the boiler. The optimal reaction temperature is between 800-950°C. Due to the frequent changes in furnace temperature and NOx distribution across the furnace cross-section, a higher ammonia escape rate can occur if too little ammonia is injected at the control point or if ammonia injection across the entire boiler cross-section is uneven. Insufficient reaction of the reductant can lead to leaked NH3 not only causing fly ash in the flue gas to settle on the heat transfer surfaces at the boiler's tail but also reacting with SO3 to form ammonium salts, potentially causing air preheater blockages and corrosion. To ensure the denitrification reaction achieves a good reduction effect with minimal ammonia injection, suitable injectors are selected, arranged in layers, to achieve good mixing of NH3 with the flue gas, thereby achieving the denitrification goal.

The SNCR system's main equipment is designed in a modular manner, primarily including ammonia water or urea solution storage, measurement and transfer of ammonia water and urea solution, compressed air distribution, spray cooling air, and ammonia water jet system. The amount of ammonia water is regulated by adjusting the spray nozzle opening and the speed of the ammonia pump to ensure that the concentration of nitrogen oxides at the outlet remains unchanged during changes in the furnace condition, without the need for a desalinated water system.

Secondly, as reducing agents, ammonia water or urea solutions are accurately metered and distributed to each spray via the metering distribution device.qiangCompressed air is distributed to each nozzle through the distribution module.qiangThen mixed with ammonia water and sprayed...qiangInjected into the furnace, undergo denitrification reaction. Cooling air is distributed to each nozzle via the distribution module.qiangCooling SprayqiangPrevent SprayingqiangHigh temperature burnout.

Three; sprayqiangManufactured from stainless steel and designed for replaceability. Spray often.qiangCool with Air. To make the sprayQiang rarelyExposed to high-temperature flue gas, spray-typeqiangNozzles and some wall-mounted spray nozzles are designed to be adjustable. The injector can be withdrawn from operation when the boiler is started, stopped, operated seasonally, or for other reasons requiring SNCR shutdown. The reagent is sprayed through specially designed nozzles at pressure to achieve droplet size and distribution. This unit employs a two-fluid nozzle with compressed air as the carrier.

SNCR (Selective Non-Catalytic Reduction De-NOx) Technology

SNCR Denitrification Technology Principle

The SNCR process uses the furnace as the reactor and is currently the primary denitrification technology adopted during the retrofitting of old units. It typically achieves a NOx removal rate of 70% to 80%. The commonly used reductants include ammonia, ammonia water, and urea. Due to urea's superior distribution properties within the boiler and its simplicity in transportation, storage, and availability, as opposed to ammonia, which is a hazardous chemical, urea is generally used as the reductant in SNCR. The Selective Non-Catalytic Reduction (SNCR) denitrification technology involves injecting a reductant containing NHx into the furnace, which quickly thermally decomposes into NH3, which then selectively reacts with NOx in the flue gas to produce harmless gases such as N2, CO2, and H2O.

Five: SNCR Denitrification Process: Solid urea granules that meet the requirements are unloaded into the urea storage bin, then metered and fed into the liquid preparation pool. Under heated conditions, the solid urea granules are mixed with process water to form a urea solution, which is then transported to the solution storage tank by the batching pump. The urea solution in the tank is sent to the front of the furnace via a pressure pump and conveying pipelines, and is atomized into the furnace chamber at a temperature range of 900-1100°C by atomizing nozzles arranged around the boiler. The urea solution output from the tank can be mixed with process water to prepare solutions of varying concentrations to meet the different load requirements of the boiler; multiple layers of nozzles can be arranged to cater to different temperature zones. Application Scope: New construction, expansion, reconstruction of units, or existing old units, subject to site limitations.

Six: SNCR Process Features:

The furnace serves as the reactor, eliminating the need for a catalyst, resulting in lower investment and operational costs.