The activity of SCR denitration catalyst in-service will decrease by being abraded from flue gas, deposited from solid material, poisoned from alkali metal. And then after 2 or 3 years the catalyst would lose activity and end its life. Cleaning the SCR denitration catalyst is becoming very necessary because it costs high, and belongs to consumables. At the same time, the waste catalyst is difficult to handle because of the toxicity which will cause secondary pollution to the environment easily. We push a method for cleaning SCR denitration catalyst on the production process, steps as following:



1. Configure the cleaning solution
Stirring with a machine to mix oxalic acid solution, dispersing agent MF, ammonium metavanadate and ammonium paratungstate for more than 10 minutes for generating cleaning solution. Among them, the mass concentration that MF is 0.1-1wt%, ammonium metavanadate is l-3wt%, and ammonium paratungstate controlled at 5-15wt%. The pH value of the oxalic acid solution supposed to be 5-7;
2. Blowing and cleaning the surface of SCR denitration catalyst by a sonic soot-blower for 15s, and then cleaning the surface and pore of catalyst for 1min in certain circumstances;
3. Washing the SCR denitration catalyst for 5mins, and collect the waste liquid at the same time;
4. Washing the SCR denitration catalyst with cleaning solution for 10-20mins, also the waste liquid should be collected;
5. Dry the catalyst through a hot air drying device for 2-4 hours, thus finish the progress of cleaning SCR denitration catalysts.

Anatase nanometer TiO₂ is mainly used as activity carrier for denitration catalyst. Because of TiO₂ composites with WO₃ in TiO₂-WO₃-SiO₂ powder, the structure and surface properties have been changed. Also it causes WO₃ distributing more uniform, thus improve the processing performance which is advantageous to mixing, extruding, drying process, thus ensure  rate of finished products. We propose a method for preparing composite powder TiO₂-WO₃-SiO₂, and the specific steps as follows:

1. Beating and dispersing the raw material H₂TiO₃, and then adjust the concentration of titanium dioxide slurry;
2. Add ammonium paratungstate and white carbon black into the slurry;
3. Add ammonia to adjust pH to 5.5~8.5 for improving combination with WO3 and the calcination properties of metatitanic acid;
4. Filtrating and dehydrating the slurry to get massive cake, in which mass fraction of TiO₂is controlled in 40%~55%;
5. Crushing massive cake mechanical, then drying it at 200~380℃ for 2.5 hours, and then calcined 380~680℃ for 4.5 hours;
6. Crushing to generate the required composite powder TiO₂-WO₃-SiO₂.

The method descripts above has the following advantages:
1) Low manufacturing cost, simple process;
2) The products obtained are not only with long service life and high surface area, surface chemical activity, good processing performance, but also have the advantages of high mechanical strength and resistance to erosion.

Tungsten carbide ball double V-slot grinding can ensure that the rotation angle of the ball will change with sphericity, but it requires that the grinding tray V-slot up and down has higher properalignment and shape error and assembly error institutions needed to be effectively controlled, otherwise the blank ball can not roll along the groove smoothly. The relevant domestic scholars have done a lot of this research and developed a conical grinding method in which the abrasive disk is tapered, which makes carbide ball blank has a large corner across from the milling process (usually up to 45 ° left and right), to obtain a full rotation, enhanced rotary slide ball blank, improving overall processing efficiency. The following is a schematic view of the three grinding work mode, you can clearly see different from the design of the grinding tray:

Besides these three kinds of conventional grinding methods, Related researchers and academics abroad in order to achieve high-speed grinding ceramic balls have also proposed a flexible and high material removal rate of magnetic fluid polishing. Its basic principle is to use magnetic fluid mixing abrasive particles as an abrasive, when the magnetic fluid is given a certain magnetic field, the magnetic fluid will produce upward thrust, by the corresponding floating disc ceramic balls implement processing load. It remarkably improve the efficiency of precision ceramic ball and its roundness error less than 0.14μm, surface roughness reaches 0.01μm, material removal rate reaches 12μm / min, which is more than 40 times that of conventional grinding method.

However, this method due to the complex structure, inconvenient operation, and the magnetic fluid itself heightening price, after the magnetic fluid and particles worn when machining, material removal will be affected to some extent, it is also the emergence of a non-magnetic fluid polishing (water and glycerol mixture) instead of magnetic fluid and resin bonded diamond grinding wheel instead of embedding the abrasive grinding tray. Although the processing efficiency and processing efficiency and non-abrasive magnetic fluid magnetic fluid grinding pretty, its precision can not be fully guaranteed, both of structure of them are relatively complex, which is not suitable for large-volume production of high-precision machining of tungsten carbide ball.