Water Requirements for different slurry designs

The following table illustrates the how the water requirement changes with both slurry density and type of additives. Some additives do not have extra water requirement themselves (i.e. hematite, spherelite) whereas others have large water requirements (bentonite, sodium silicate). Thus it is hard to generalize on water requirements. However, the table will give you some idea of ranges. You will see that some slurries in the lighter weight range, would require a ridiculous mixing rate (15.5 bpm) to use the 40 sk/min (approximately 4000 lb/min). It is not advisable to mix above 10 bpm although it is possible. As mixing rate increases, the % of API mixing energy applied to the slurry decreases and thus quality of the mix. Our systems are the highest mixing energy systems available.

You can see in the tables that I forced above design to require approximately 4000 lb/min. Certainly, mixing rates above 10 bpm are not recommended from a slurry quality viewpoint but are possible. Most bulk systems cannot keep up with 40 sk/min delivery rate and thus it makes the density control more difficult. Thus the slurry density tolerance of .1 ppg is less likely to be maintained at the maximum rates. Density tolerance is strongly dependent of the uniformity of the bulk flow. Good uniform bulk results in good density control. Bad bulk delivery can not be fixed with automatic density control. Also, mixing at a high rate increases the problems if something goes wrong (i.e. run out of water - forgot to switch tanks). A car wreck at 20 to 30 mph is usually not a problem with seat belts but 60 to 80 mph it would be a problem. In the one above example of 15.5 bpm, if you ran out of water, it would take about 5 sec to get the slurry too thick to handle (the mixing tank volume is fully changed out every 20 sec. In addition, the mixer cannot meet the 478 gpm mix water requirement (normally limited to 370 to 390 gpm). It is easy for us to increase the mixer capacity to allow over 400 gpm for high water content slurries if necessary. However, an easy option is to open the water bypass line to increase the water rate to over 400 gpm. The water bypass line would discharge into the recirculation suction line just before the recirculation pump. This line is also necessary to get out of trouble if something goes wrong and the density becomes too high (and thick) in the mix tank.