How is the flushing time for the demister in the absorption tower determined?

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1. Design phase: Based on the preliminary settings for coverage and water volume, a theoretical flushing procedure is calculated during the design stage to ensure that every area of the demister is effectively covered. Single flushing time: Based on the nozzle’s flow rate, spray angle, and installation distance, the shortest time required for the flushing water to completely cover the surface of the blades is calculated. Typically, this value ranges from 30 to 90 seconds. If it is too short, it won’t clean thoroughly; if it is too long, it will waste water and affect the liquid level in the absorption tower. Rinsing cycle: refers to the total time required for all the rinsing branches to operate sequentially once. To ensure cleanliness, the design typically requires that this cycle last around 1 to 2 hours, meaning that at least one flushing of all the defogger blades takes place per hour. 2. Commissioning and operation: During on-site commissioning and operation of the core control parameters, the pressure difference across the defroster is used as a decisive indicator for adjusting the flushing frequency, based on actual operating conditions. The core of the flushing procedure is to maintain stable pressure difference. A standard procedure is usually established; for example, there are 12 rinsing areas in total, with each area being rinsed for 60 seconds sequentially. One cycle takes 12 minutes in total, after which a pause of 48 minutes is taken before starting the next cycle. Thus, the rinsing interval is 1 hour. The operators will adjust this \"48-minute\" waiting time based on the trends: if the pressure difference increases rapidly, it indicates an increasing tendency to scaling, and it is necessary to shorten the flushing interval (for example, by changing it to 28 minutes with an interval of 40 minutes), or to appropriately extend the duration of each flushing session. Stable or even decreasing pressure difference → indicates excessive flushing; the flushing interval can be increased to save process water and reduce the pressure associated with water balance. 3. Real-time operation: Automatic differential pressure control and water balance constraints. Modern power plants mostly use automated programs, with the flushing time being determined dynamically by two factors: \"differential pressure\" and \"water balance\". Differential pressure trigger mode: The DCS system sets a start value for differential pressure (such as 150 Pa) and a stop value (such as 80 Pa). When the pressure difference rises to the activation value, a complete flushing cycle is automatically executed. This is the most direct way of formulating it. Hard constraint on water balance: Wash water will enter the absorption tower, causing the liquid level to rise. When the liquid level is too high, it is necessary to force a pause or extend the flushing interval; at such times, the priority of pressure difference control is temporarily reduced. The flushing time must be set to match the water supply and drainage capacity of the absorption tower. 4. During adjustments under special operating conditions, when the unit is operating at low load or is shut down: the amount of flue gas is low, and thus less slurry is carried along. To prevent loss of balance in the water level, the interval between flushing operations is extended significantly; however, regular flushing at the minimum frequency is still necessary to avoid scaling in hard-to-reach areas. When the boiler is running on oil or when there is a fault with the dust collector: there is a high amount of dust and oil in the flue gas, which easily causes the demister to become clogged. At this point, the flushing interval must be significantly reduced, or even continuous flushing must be carried out to protect the equipment.