Frac sand unloading was traditionally done using pneumatic trailers until the Telebelt was introduced in the oil and gas industry in 2010. They have different names depending on the region they’re used in, but are commonly referred to in Alberta as frac sand bulkers, pneumatic trailers, or air slides.
So welcome to part 2 of our series on Telebelting frac sand. This section of the series will focus on how pneumatic trailers operate as opposed to a Telebelt.
Conventional Pneumatic system unloading
Pneumatic systems use PTO driven air pumps for frac sand unloading. Hydraulically operated pumps can also be installed on the truck or trailer but aren’t quite as common as the PTO style. PTO stands for Power Take Off, which is an additional shaft connected to the rear of the transmission similar to a drive shaft.
The shaft spins at a very high velocity and is connected to a pump mounted on the back of the truck. The pump pushes the air needed to build pressure in the tank and lines. The unloading pressure used depends on different things like the product being unloaded, driver preferences, experience, blow off valve settings, etc.., but ideally the tank pressure is around 10 to 14 PSI.
Once the pressure reaches the ideal amount in the tank, an air line valve is opened along with the product purge valve. The tank pressure forces the sand into the main line where the moving air carries the sand through the line and into the vessels. Productivity becomes a “Balance” of air pressure and product. If too much air is used, the product flow will be slower. If too much product is used, there’s a risk of “Plugging off the line”.
It’s difficult to put accurate times on how long it takes to unload load frac sand with so many factors affecting the process, but 1/2 ton per minute is a reasonable average rate.
Telebelt unloading operations
Frac sand unloading using a telebelt is an extendable boom conveyor system that gravity drops the sand into the top of the vessels. (There’s no pressure anywhere in the process.) This system still requires trucks to bring the sand to location, but the trucks only have to gravity feed ( “Bottom drop”) their product onto a drive over belt set up. Bottom drop grain trailers are one of the most preferred methods with large openings (Gates) that can feed the sand at a high rate.
Pneumatic trailers can still be used to gravity drop but there’s been a few growing pains along the way. The dry bulk trailer industry has recently been modifying these trailers to accommodate the needs. Larger valves, quick release valves, and valve handle location on the trailer are some of the issues that are being dealt with.
The drive over belt feeds the hopper on the feeder belt which carries the product up to a pivotal turret where the sand is rolled off the feeder belt onto the main boom belt. The main boom can be extended, retracted, and moved from side to side to quickly drop the sand in the top hatches of the sand vessels.
A typical rate for an experienced operator is 2.5 to 3.5 tons/minute. If you watch this short video, you’ll see a Telebelt in operation. the rate is over 3 tons/minute.
The video puts things into perspective pushing a rate of almost 3 tons a minute faster than a pneumatic trailer at .5 tons/minute.
So there’s an introduction to unloading frac sand with reference to a pneumatic trailer and a telebelt. Next we’ll take a more in-depth look at the advantages and disadvantages. There are 3 main issues with pneumatic systems that have been answered by Telebelts. Pressure, frac sand storage on location, and Speed. The next 3 sections are dedicated to each of these issues.