61- Multi-factor cyclone gas-solid separator for dry desulfurization and denitration of flue gas in fluidized bed boilers

For the inlet gas to dry catalytic denitration and desulfurization reactors, it is required that the amount of dust carried in the flue gas be as low as possible, so as to prevent the dust from entering the reactor with the airflow and gradually accumulating at the top of the catalytic reactor, which would impair the efficiency of the catalytic denitration and desulfurization process as well as increase the operating pressure drop.

For the purification of the inlet air in high-temperature flue gas catalytic desulfurization and denitrification reactors, the conventional arrangement of separation equipment consists of a bag filter + a high-voltage electrostatic precipitator. Fewer companies dare to use standard cyclone separators; it is understood that this is because the actual separation efficiency of such standard cyclone separators designed by many domestic organizations is even less than 70% of the designed value, resulting in a large gap between design efficiency and actual operating efficiency. However, as is well known, high-voltage electrostatic precipitators are unable to handle conditions with large flue gas flow rates and high dust contents, and their electrostatic precipitation efficiency drops rapidly in high-temperature environments ； Therefore, a bag filter must also be installed before the high-voltage electrostatic precipitator to remove most of the dust particles in advance.

However, bag filters require compressed air for pulse backwashing, and some dead corners also need intermittent backwashing with compressed air. High-temperature bag filters are large in size, occupy a lot of space, have numerous program control components, are expensive to manufacture, and are prone to malfunctions at high temperatures. Companies generally design one active unit and one standby unit; some companies even do not provide a backup unit at all. The owner reported that during the few minutes, or even tens of minutes, of backwashing in the bag filter, the dust content in the gas generated surged, resulting in an excessively high dust level in the flue gas entering the high-voltage electrostatic precipitator. The electrostatic precipitator was not capable of handling such conditions, which in turn led to a severely elevated dust level in the gas output by the electrostatic precipitator.

Therefore, an improved process for the traditional dry dust removal system in flue gas from coal-fired boilers using fluidized beds has now emerged, namely: bag filter + multi-factor swirl gas-solid separator + high-voltage electrostatic precipitator. The multi-factor cyclone parent-child separator also belongs to the category of dynamic separators; however, due to the much more uniform velocity distribution of the fluid within its shell compared to traditional large-diameter cyclone separators, as well as higher values for the fluid’s rotational radius and angular velocity, this separator offers significantly improved separation efficiency, operational stability, and flexibility compared to traditional cyclone separators.

The multi-factor cyclone parent-child separator is placed between the bag filter and the electrostatic precipitator for the following main reasons: 1. When the bag filter is in reverse blowing mode, a large amount of dust that rises from below the bag filter can be efficiently removed from the flue gas through the multi-factor cyclone parent-child separator, thereby preventing large quantities of dust from reaching the electrostatic precipitator. 2. After installing a multi-factor cyclone parent-child separator, the bag filters originally planned to operate in one active and one standby configuration no longer require a standby unit. 3. After the vast majority of the dust load is removed using a multi-factor cyclone separator, the extremely small amount of remaining dust enters the electrostatic precipitator, where its efficient capture of such fine particles takes advantage of the electrostatic precipitator’s ability to effectively trap small particles, thereby enabling high-precision removal of dust from flue gases. 4. Although multi-factor cyclone mother-son separators have been widely used internationally for efficient gas-solid separation, given that many domestic enterprises are not well aware of these separators, integrating them between bag filtration and electrostatic dust removal can demonstrate their actual effectiveness to these companies through practical results. The prerequisite is that the multi-factor cyclone parent-child separator must have its system design completed through a system platform designed via precise dynamic calculations.

Regarding the purification of the exhaust gas from the dry catalytic desulfurization and denitrification reactor in fluidized bed boilers, the aim is to recover the catalyst particles that escape with the flue gas during the reaction process and reuse them in the catalytic reactor. On the one hand, it contributes significantly to reducing operating costs; on the other hand, it prevents excessive dust and metal ion emissions in the flue gas. As everyone might expect, for the purification of the exhaust gas from the dry catalytic desulfurization and denitrification reactor used in fluidized bed boilers, the purification process for the inlet gas of such a reactor can also be adopted. In principle, it is possible. However, the cost-performance ratio is too low, and given the limited budget for EPC projects undertaken by environmental protection companies, it is not possible to use all of the components such as bag filters, multi-factor cyclone separators, and electrostatic precipitators. In the combined process of \"bag filter + multi-factor cyclone parent-child separator + electrostatic precipitator\", only the multi-factor cyclone parent-child separator requires neither spare units nor parts for replacement and maintenance, enabling it to operate continuously, efficiently, and stably 24 hours a day. Therefore, the multi-factor cyclone parent-child separator has become the preferred choice in recent years for capturing and recovering catalysts in dry catalytic desulfurization and denitration processes.

Here, a detailed discussion is conducted using the multi-factor cyclone mother-son separator for catalyst recovery, which is involved in a certain dry catalytic desulfurization and denitration process package, as an example. Operating conditions are: 1. Air volume: 130,000 m^3/h; 2. Temperature: 170℃ ； 3. Pressure: 5kPaG ； 4. Flue gas density: 0.83 kg/m^3; 5. Apparent density of catalyst: ~800 kg/m^3; 6. Catalyst content in flue gas: ~500 mg/m^3; Required separation efficiency: not less than 90%.

The following figure is an excerpt from the technical proposal for a multi-factor swirl separator system, developed by a specialized dynamics separation technology company and intended for use with a dry catalytic desulfurization and denitration process supplier:

This post was last edited by luoli519 on 2018-5-16 at 12:43. Here is another summary table showing the multi-factor cyclone mother-son separator technology used for catalyst recovery in the dry catalytic desulfurization and denitrification process packages provided by a company specializing in dynamic separation technologies:

As can be seen from the data table, the main technical specifications of this multi-factor cyclone parent-child separator are as follows: 1. Operating pressure drop: 0.622 psi； 2. Separation efficiency: 100% removal of particles with a size of 8 microns or larger; the particle concentration in the exhaust stream is no more than 30 mg/m^3. 3. The operational flexibility index for this model of multi-factor cyclone parent-child separator is: maximum load/minimum load = 4, indicating a wide range of operational flexibility.