Technical measures to extend the service life of SCR denitrification catalyst
The catalyst and reactor are the main parts of the SCR system. The catalysts contain small amounts of vanadium oxide and titanium oxide because of their high resistance to SO3. The structure and shape of the catalyst varies depending on the environment in which it is used. To avoid clogging by particles, honeycomb and plate catalyst components are commonly used.
To minimize the possibility of clogging by fly ash, the reactor is placed vertically so that the flue gas flows from top to bottom.
To optimize the design of the SCR system, it is necessary to consider the reasonable distribution of flue gas and ammonia at the inlet of the catalytic reactor to prevent the denitrification rate from changing due to the temperature of each part often deviating from the design temperature; the use of inverted flow plates, mixers, ammonia injectors on both sides of the flue are arranged independently, so that the flow of flue gas in each section is basically equal; the design of the catalyst volume should also consider the appropriate amplification of the amount of catalyst; at the same time, it is also necessary to At the same time, the change of effective area in the reactor should be considered.
In the operation of the boiler, we should pay close attention to the flue gas volume and its fluctuation range, the flue gas temperature and its fluctuation range, the flue gas pressure and its fluctuation range, the dust content in the flue gas, the sulfur dioxide content in the flue gas, and other parameters that have a great influence on the denitrification efficiency and catalyst,
Only when the flue gas parameters are in full compliance with the design values, the SCR plant is allowed to be put into operation. If the individual parameters deviate too much from the design value, an analysis should be conducted in time to assess the nature and severity of the hazards, pre-estimate the consequences and consider remedial measures, and finally confirm the SCR unit into or out of operation.
Measures taken during boiler start-up and SCR system operation
During boiler start-up and SCR system commissioning, take necessary measures in operation adjustment to control the rate of flue gas temperature rise to avoid damage to equipment.
In particular, preheating must be performed during cold start-up. In order to reduce the mechanical stress on the catalyst module, the flue gas temperature rise rate should be strictly controlled to not exceed 5 ℃/min when the flue gas temperature is below 70 ℃; the flue gas temperature rise rate should not exceed 10 ℃/min before the flue gas temperature rises to 120 ℃; the rise rate can be increased to 60 ℃/min between the flue gas temperature above 120 ℃ and the catalyst operating temperature.
Make adjustments in the SCR system start-up sequence. First, open the SCR inlet flue gas baffle to start the induced draft fan and the supply fan to clean the SCR flue gas system and the catalyst module with cold air; when the boiler meets the ignition condition, make the flue gas temperature rise and heat the reactor to above 120 ℃; when the boiler has the coal feeding condition, start the primary fan to feed the powder to make the flue gas temperature rise and heat the reactor to above 310 ℃. Next, start the dilution air fan, open the dilution air outlet baffle, make the air flow more than 3200m3 /h, ammonia supply from the evaporator is ready. After that, after meeting the condition of ammonia valve opening, open the ammonia supply
After the ammonia valve is opened, open the ammonia supply valve and switch the ammonia supply to the reactor to the automatic control of ammonia injection by NOx.
Comprehensive review before start-up
Before start-up, the SCR system should be checked in detail to ensure that the equipment and system are good and reliable, and that it is not allowed to run with disease. In particular, make use of the opportunity of each furnace shutdown to strengthen the inspection: ensure that there is no foreign matter on the top of each catalyst basket, no shortage or broken catalyst; ensure the effectiveness of all insulation surfaces to prevent burns to the operator and bake the instrumentation and electrical appliances; carefully confirm the installation quality, functional effectiveness, accuracy level approval, zero point drift adjustment of all instruments and whether they are in line with the design requirements. Before the start-up of the unit, do the adjustment test of important instruments and meters, such as the adjustment of NOx and O2 analyzers, check the control valves and chain valves, check the correctness of all circuits and electrical installations, etc. In normal operation, check whether all inspection holes, manhole doors, equipment access holes have been reliably closed, and whether all utilities (steam, compressed air, water, ammonia, etc.) are correctly in place; at the same time, strengthen the correctness of all expansion support and expansion joint positions to ensure that there is no foreign object blocking along the expansion direction; check whether the main stresses of the steel structure and beam deflection are within the allowable values; check the thermal deformation value of the shell at the preset inspection points after the smoke is passed. Check the value of thermal deformation of the shell; thermal state check
The correctness of the electrical work of the instrument. Ensure normal operation of sootblower and sootblowing effect
Each soot blower is tested by means of a manual button in the local control cabinet, and all control and sequence functions of the soot blower are realized by the DCS. The sootblowers of each reactor are treated in the same way as the sootblowers of the boiler body, and the sootblowers of each reactor run in sequence from top to bottom of the catalyst layer, i.e. the sootblowers of the upper catalyst layer start running in sequence within the set time, and then start running the sootblowers of the next catalyst layer to ensure that only one sootblower of each reactor runs at a time. This prevents the catalyst from blocking and accumulating a lot of soot during operation, which on the one hand reduces the denitrification efficiency and on the other hand damages the service life of the catalyst. For denitrification systems using acoustic sootblowers, the acoustic sootblowers should be put into cycle start.
