The start-up and shut-down sequence of a fertilizer production line is often dismissed as a simple matter of “pressing a button.” In reality, the equipment is interconnected by the flow of both materials and heat. An incorrect sequence can lead to issues ranging from material blockages to severe damage to thermal processing equipment. A fertilizer production line is not merely a collection of individual machines; its start-up and shut-down sequence must be designed according to the specific process chain.
Cold Start-up: From “Back” to “Front.” The entire line should be started in the direction opposite to the material flow. Begin by activating the dust collection system, followed by the conveying equipment, screening machines, and recycle belts. Once the downstream path is confirmed to be clear, start the main granulation unit, and finally, the mixer and feeder. This ensures that by the time the granulator begins discharging, the screening and conveying systems are already operational, preventing material accumulation on the screens or overloading of the recycle belts. For a roller press granulation line, the closed-loop recycle system must be running before material is fed into the roller press; otherwise, the fine particles (undersize material) will have nowhere to go, quickly causing a blockage in the screening machine.
Thermal Processing Equipment: Rotate the Drum Before Ignition; Shut Down the Heat Source Before the Fan. When starting a dryer, ensure the drum is rotating smoothly, then start the induced-draft fan, and finally ignite the hot-air furnace. Igniting the furnace while the drum is stationary can cause localized overheating and deformation of the drum wall; igniting it without the induced-draft fan running can lead to positive pressure in the combustion chamber, causing a “backfire.” The shut-down sequence is the reverse: turn off the hot-air furnace first, while keeping the induced-draft fan running to exhaust residual heat from the drum and ductwork. Only after the temperature has dropped to a safe range should the fan and the dryer be shut down. This is particularly critical for the drying of bio-organic fertilizers, where a low-temperature, high-airflow process relies on the airflow to remove moisture. Stopping the fan prematurely would cause hot, humid air to remain trapped within the material layer, leading to the re-absorption of moisture by the granules and the potential destruction of microbial cultures.
BB (Bulk Blended) Fertilizer Production Lines: Lacking thermal processing stages, the sequence here focuses on preventing material segregation and blockages. For a BB (bulk blend) fertilizer production line, the startup sequence begins with the dust collection and conveying systems, followed by the BB fertilizer mixer, and finally the multi-silo, single-weigh static batching and feeding system. During shutdown, the batching and feeding systems are stopped first; the mixer should continue running until it is completely empty before being shut down, followed by the conveying and dust collection systems. If the conveying system is stopped prematurely, material discharged from the mixer will accumulate on the conveyor belt, causing an overload during the next startup.
For post-processing equipment—specifically rounding (spheronization) and coating units—the machinery must be set in motion before material is introduced. When starting an organic fertilizer rounding machine or a coating machine, the drum or pan must be rotating before feeding begins. During shutdown, the feed should be stopped first, while the equipment continues to run for a few minutes to clear out any remaining granules; this prevents the particles from sticking together or clumping while stationary. Additionally, the nozzles of the coating machine must be cleaned after shutdown to prevent the coating agent from solidifying and causing blockages.
The fundamental principle behind these startup and shutdown sequences is to ensure that both materials and heat always have a clear path for discharge. In general, start downstream equipment before upstream equipment, and stop upstream equipment before downstream equipment. For thermal processing equipment, the machinery should be set in motion before ignition, and the heat source should be extinguished before the airflow (ventilation) is turned off. Codifying these sequences into formal operating procedures is far more cost-effective than dealing with emergency repairs later.