Ultra-low emissions

What are the measures for ultra-low emissions?

It’s been almost 2 years since the implementation of ultra-low emissions standards for coal-fired flue gas. There has been little progress in desulfurization and denitration, but there is a wide variety of approaches to dust removal. Reliable and effective ultra-low dust removal: wet electrostatic precipitator or not

We have modified the original dust collector; now the level is basically below 5. We also plan to start using the ammonia-based desulfurization method, and the ammonia-based denitration process is already in use as well – it’s quite complicated

Particulates: In wet flue gas desulfurization, the type of desulfurizing agent used plays a key role; those that readily dissolve in water present difficulties. Flue gas contains varying amounts of moisture, and the sulfate ions dissolved in this water make it hard to achieve ultra-low levels of particulate emissions through weighing methods. Some organizations have proposed washing the purified flue gas multiple times with water, but it is difficult to maintain a balance of water levels within the desulfurization system, which results in the generation of wastewater. After washing, wet electrostatic demisting is used, and this method can effectively remove heavy metals from the flue gas. However, the gradual accumulation of heavy metals in the waste liquid is also an issue that requires further study. SO2: Keeping SO2 below 35mg is not a major issue ； NOX: The level of NOX should be kept below 50 mg. The investment cost for ozone-based denitration is high, and the operating costs for catalysts and denitration agents are also high. Various studies suggest that ammonia-based desulfurization has a certain denitration capability, but it remains difficult to keep the NOX level under 50 mg; a high effective content of sulfites is required for this purpose. However, dealing with the by-products poses significant challenges. The cost of modifying the crystallization process inside the ammonia-based desulfurization tower is high, while the cost of modifying the crystallization process outside the tower is lower. At present, no company has actually used this method. If a SCNR process is available on the boiler side, it is recommended to use SCNR to remove part of the NOX from the flue gas before sending it to the ammonia-based desulfurization tower, so as to keep the NOX level under 50 mg. This way, ultra-low emissions can be achieved. This method still needs to be tested first.