We have introduced the catalyst management before commissioning of denitrification catalysts, mainly from the aspects of transportation, unloading and storage of catalysts, optimization of reactor design and catalyst installation management, so as to improve the catalyst life and reduce the cost.

There are actually many factors affecting the life of a denitrification catalyst, and this issue will focus on catalyst performance acceptance and operation management.

Performance acceptance of catalysts

01 [Acceptance of catalysts on arrival]

Acceptance on arrival is mainly from the factory data, appearance, shape and nature.

1）Ex-factory data inspection: check whether the parameters meet the requirements of the technical agreement, and whether the test data such as axial extrusion test, transverse extrusion test, anti-wear strength test and material report meet the standard requirements.

2) Visual inspection of appearance: check the catalyst surface to confirm that the catalyst is undamaged.

(3) Shape check: geometry measurement of length, width, height and thickness, and porosity check.

4) Property confirmation: comparison and confirmation of chemical composition, total pore volume, average pore size, specific surface area, density and other parameters.

02 [Performance test acceptance]

By adjusting the relevant parameters of the denitrification system, it was verified that the operating indexes of the denitrification system, such as denitrification efficiency, ammonia escape rate, SO2 oxidation rate, and resistance of the catalyst layer, could meet the performance guarantee made by the supplier for the products they supplied.

The supplier will guarantee the denitrification efficiency during the lifetime of the catalyst based on the catalyst decay characteristics, so the catalyst activity is high in the early stage of operation and the denitrification efficiency is higher than the minimum efficiency guaranteed by the supplier at this time. In order to understand the performance of the catalyst and to manage the catalyst life, it is necessary to increase the amount of ammonia sprayed as much as possible during the performance test to examine the maximum efficiency of the denitrification unit when the ammonia escape rate is close to 3 ppm and to check the quality and use of the catalyst against the supplier's performance curve.

Catalyst operation management

The performance of the catalyst will gradually decrease with the increase of working time. The correct operation method can not only ensure the economic operation of the denitrification unit, but also prolong the service life of the catalyst.

01 [Control of ammonia injection amount]

Within 300-400℃, denitrification rate increases gradually with the increase of reaction temperature. Denitrification reaction rate increases and denitrification rate rises when the temperature rises to 400℃; when the temperature rises to 400℃, denitrification rate decreases with the increase of temperature. When the temperature increases, the NH3 oxidation reaction increases and the denitrification rate decreases. The temperature that the catalyst can withstand for a long time should not be higher than 430℃, otherwise it will lead to sintering and permanent failure of the catalyst. If the temperature in the reactor drops to the minimum operating temperature, ammonia injection must be stopped to prevent sulfate or nitrate deposition on the catalyst surface, which affects the catalyst activity. To extend the catalyst life, the long-term minimum flue gas temperature should be set at 320°C according to the decomposition characteristics of sulfate.

At the same time, during boiler start-up and SCR system commissioning, necessary measures need to be taken in operation adjustment to control the flue gas temperature rise rate at 40℃/min to avoid damage to the catalyst.

02 [Catalyst regular blowing]

To prevent the catalyst from clogging, on-line blowing should be performed in time, and soot blowers are set for each catalyst layer. The pressure difference between the front and rear of the catalyst layer should be monitored during operation, and blowing should be performed when the pressure difference rises above the specified value. For denitrification units using steam blowing, in the daily operation, the pressure of the blowing steam source must be strictly controlled to ensure that the pressure of the blowing steam source reaches the expected blowing effect for different ash coals, but also to control the pressure within the appropriate range to prevent excessive pressure blowing damage to the catalyst; at the same time, to choose the appropriate blowing steam source temperature, if the blowing steam source temperature is too high may cause the local catalyst area to exceed the maximum allowable operating temperature. If the blowing steam source temperature is too high, the local catalyst area will exceed the maximum operating temperature, resulting in permanent failure of the local catalyst; if the blowing steam source temperature is too low, or the blowing steam source is not fully hydrophobic, the water in the blowing steam will cause the catalyst to stick to the ash and damage the catalyst, which will reduce the catalyst activity.