Approach the problem of scaling in the black water pipelines for water-coal slurry gasification from a different perspective
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In the water-coal slurry gasification process, scaling and blockage in the black water pipelines and quench water pipelines are long-standing problems, and they are also one of the key factors restricting the long-term operation of water-coal slurry gasification. The methods currently in use involve adding dispersants to the gray water or stopping the system periodically for cleaning. Is it possible to reduce pipe scaling by increasing the flow rate of the black water or cooling water? These past few days, I have calculated the flow velocities and Re numbers for the black water pipes and high-pressure slurry pipes in our process package. It turns out that the flow velocities in the black water and quenching water pipes are not high, generally not exceeding 1.5 m/s, but their Re numbers are quite high. Given that high-pressure coal slurry flows will only cause significant erosion of pipes at flow rates above 1.4 m/s, black water and quenched water, whose viscosity and solid content are much lower than those of water-coal slurry, must reach flow rates far higher than this value in order to cause significant erosion and scouring of the pipes. Then why can’t we increase the flow rate of the black water and chilled water to a level that is about to cause erosion in the pipes but not to an excessive extent? Wouldn’t this significantly reduce scaling in the pipes? What is the reason why the current design doesn’t do this? Please come and discuss this with those of you who are interested.
In addition to being related to water quality, the pipe structure is primarily affected by the decrease in the solubility of scale at high temperatures, which causes it to adhere to the pipe walls. However, the original poster’s idea has indeed broadened our thinking; everyone is welcome to engage in active discussions.
Boss, has your flash vaporization system been affected? Can the system’s water balance be ensured? Can the syngas temperature be maintained?
The original poster’s idea is good, but a laboratory experiment may need to be conducted first as a test before it can be applied in a factory, as the flow rate of the quench water has a significant impact on various aspects and is related to many other parameters as well. One of the tasks of professionals working in water management projects is to determine what the flow rate of river water should be in order to prevent grass from growing on the sides of the waterways, which serves a similar purpose to what the original poster had in mind.
Reply 1# hjy2000: The original poster’s idea is quite innovative. However, to increase the speed, it is necessary to raise the head pressure and reduce the diameter of the pipeline; as a result, if larger amounts of slag get stuck, the water flow is likely to be significantly affected. It can be tried cautiously to see the results. For example, on the existing pipeline, use a smaller pipeline; in case the flow rate decreases, open the main pipeline promptly to ensure safety.
From the perspective of the mechanism of scaling, increasing the flow rate helps to slow down scaling. I think choosing a speed of no more than 1.5 m/s is more of a practical decision. The quench water is pumped in using water pumps, and its flow rate can be well controlled. The black water is discharged from the vaporization furnace and the scrubber tower; there have been cases in some companies where the pipelines for this black water became clogged. To address this issue, it would be necessary to reduce the pipe diameter in order to increase the flow rate, but such an approach poses too many potential risks and is therefore not feasible. Furthermore, as mentioned on the 5th floor, increasing the head pressure and similar factors is a matter of operational economy; different fluids have their own optimal flow velocities, and it’s not clear whether a value above 1.5 m/s is better or worse in this regard.