Frac Sand
The Xoptix in-process particle size analyzer is ideally suited to monitor product quality in frac sand production. The allowable particle size distribution limits for frac sand are defined in API RP 56 which refers to using manual sampling and laboratory sieve analysis to test frac sand for particle size. While such methods are useful for quality assurance, they are far too slow and labor intensive to be useful for process control. It can take hours to gather a sample, walk it to the lab, queue it up for analysis, conduct the sieve testing and report the results back to the operators. The labor required and time lag that results from such methods means that samples are taken infrequently, and by the time results are available to operators the data is essentially obsolete.
Consequently it is common for frac sand product quality to vary, and at times vary to the point of going out of spec. This can be the result of screen failures such as tears in the mesh or blinding of the mesh. It can even result from variations in the size of the feed coming from the wet plant. Also, the performance of screening machines is generally a function of the feed rate to them…the higher the feed rate, the lower the product quality coming from the screens. Until now it was impossible for operators to maximize production rates because to do so would risk product quality. If they push the feed rate to the screens too hard they end up overloading the screens which results in fines carryover and excessive screen blinding. And they wouldn’t know it until hours later, after hundreds of tons of off-spec sand was produced.
But now with Xoptix, operators see the product quality being delivered by the screens in real time, with updates as often as once per second. Events like feed PSD changes, screen tears or screen blinding are reflected immediately as a change in the particle size distribution. This enables operators to push the feed to the screens to the optimum rate, without the fear of products going out of spec because the Xoptix constantly monitors product quality.
A typical frac sand plant might have a dozen screening machines. Manual sampling from each product chute of each screening machine and then using sieve analyses to analyze the samples would require an unreasonable amount of labor effort. And the variability inherent in manual sampling and sieve analysis would cast doubt on the accuracy of such measurements. But the Xoptix automatically samples the product streams, and does so in an absolutely consistent manner, thereby eliminating this variable. Also, a single Xoptix sizer can monitor up to four different product flows through the use of valves that automatically sequence sampling from one sample probe to the next. So one Xoptix unit can monitor the output of up to four screening machines.
To see how Xoptix works with frac sand, below is a video demonstration recorded at a recent frac sand trade conference. As can be seen in the video, we first fed the sizer a 40/70 frac sand. The analyzer showed the product was running around 93% between the #40 and #70 test sieves and nothing in the pan (finer than #100 test sieve). Next we bled in some 100 mesh sand to simulate what would happen if the 70 mesh deck in the product screen were to blind. When this happens, 100 mesh sand that should go through that 70 mesh deck ends up carrying over and then contaminates the 40/70 product, causing it to go finer. As seen in the demonstration, the Xoptix detects this anomaly and shows that the product quality drops to around 86%, below the API specified minimum of 90%, while the pan value increases to 4%, well above the 1% maximum allowed by API. Once the 100 mesh bleed is turned off (simulating replacement of the blinded 70 mesh product screen) the system corrects itself and the Xoptix shows the product analysis returning to specified limits.