Discussion on the design of wastewater tanks for water-coal slurry

The purpose of this setup is to discharge the coal slurry used for testing during operation as well as for cleaning during start-up and shutdown processes. It should meet the requirements for graded sedimentation and temporary storage. Generally, it is located in the area closest to the coal slurry preparation unit in order to reduce siltation in the drainage channels; alternatively, a recovery tank can be installed at the coal slurry preparation site, with pumps used to transfer the recovered slurry to a waste coal slurry tank.

The waste slurry tank is generally located in the coal slurry preparation section, as the coal slurry is not of satisfactory quality when the mill starts operating; it is then discharged from the mill’s outlet tank or the outlet of the low-pressure coal slurry pump. Only once the coal slurry meets the required standards is it sent to the gasification coal slurry tank. The waste slurry tank is usually located outside the mill building; a wide and deep ditch is installed to channel the waste slurry to this tank. An agitator is provided in the tank, and the slurry is diluted with water before being pumped using an submersible pump to the gasification sedimentation tank for sedimentation, where it can then be removed using a crane grab. As for the size of the slurry waste tank, it should be determined based on how long it generally takes for the mill to produce qualified coal slurry. Generally, the size of the waste slurry tank can be roughly determined based on the mill’s operating load every half hour, after which the required margin factor can be determined.

The Donghua design, located on the first floor of the coal grinding plant, has proven to be not very effective. First, it is difficult to recycle waste coal slurry and wastewater from pipeline flushing for use in the coal grinder, and the operation is complex. Second, the mixer is difficult to operate and often gets clogged. Third, this water needs to be transported to the grinding tank via specialized pipelines, which often get clogged.

Placing it near the mill building also has its advantages, as it allows the coal slurry to travel the shortest distance through the ditch when waste slurry is discharged. Manual cleaning is significantly reduced. Regarding the issues mentioned above, for the first issue, it is not recommended to send the material directly to the grinder for use; instead, it can be sent to a sedimentation tank. As for the second issue, increasing the depth of the stirrer and diluting the waste slurry with water can help avoid the problem ； Thirdly, it is not recommended to send the water from the waste slurry tank directly to the coal grinding water tank. The issue regarding its destination has been discussed earlier; after being treated in a sedimentation tank, the water should be sent back to the coal grinding water tank for reuse using a low-pressure water pump. That being said, problems do tend to arise during the operation of the coal grinding waste slurry tank, but these issues can be addressed through proper management; they are not difficult to solve

I’ve learned it; it seems that the low-pressure ash water pump is quite complex. I heard from my master that our low-pressure ash water pump is also connected to a flushing water network. It is said that the flushing water for the gasification of coal grinding feed has been connected together; when it’s needed, there’s no need to start the coal grinding water pump – just open the valve

If the coal slurry preparation and transportation locations are close to each other, the waste slurry tank should be placed on one side of the transportation facility; this allows for the collection of the waste slurry generated during slurry preparation, as well as the overflow water from the gasification process. Depending on the distance, it can also be used as a slag discharge pipeline in case of failures in the slag skimmer.