Derrick Corporation’s Pioneering Technology Incorporated into Unique Frac Sand Processing Plant
Written by Paul Brodzik, Regional Sales Manager at Derrick Corporation
The topic of the use of wet, in-basin sands for use in conventional and unconventional frac sand wells was discussed at the recent North American Frac Sand Conference in Houston, Texas. Some operations in west Texas have begun to use locally produced sands that are delivered with moisture contents ranging from 0 to 5 per cent. This is a break from traditionally supplied sands that were previously processed at facilities as far north as Wisconsin and shipped after being dried to 0 per cent moisture.
The shift to the use of locally produced wet sand has the advantage of lower shipping costs and lower production costs because of the reduction in energy needed to dry the sand prior to processing to make the various in-spec products prior to shipment. The use of wet sands is not without several technical challenges that include the techniques for off-loading wet sand and the potential chemistry of the residual water in the prepared sands. That being said, these issues are not insurmountable and the move to the use of local wet sands seems inevitable.
American Silica, a frac sand producer in Arkansas, was way ahead of this trend when they committed to designing their frac sand production process using Derrick® high-speed vibrating 5-Deck Stack Sizer® screens as the key component to make multiple frac sand products that included 30/50, 40/70, and 100 Mesh frac sand (Figure 1).
In-spec frac sand products are produced using only a wet process. Their process eliminates the traditional high energy-consuming process of drying all the sand, then dry screening to produce the desired in-spec products. The in-spec sand products are staged in open air storage areas and only dried prior to shipment of a customer’s order to meet the current low moisture content requirements for product shipment. American Silica has been producing frac sand products since 2016, thus proving the viability of the state-of-the-art wet process.
The American Silica process includes multiple stages that include blending, coarse scalping, attrition scrubbing, multi-stage wet classification, and dewatering. The Derrick Stack Sizer and SuperStack® wet sizing machines produce the in-spec product fractions, and the Derrick Linear Motion machines are used to dewater the final products in preparation for storage (Figure 2).
High open area, tension-able Derrick Polyweb® urethane screen surfaces are the key to Stack Sizer performance in these applications because the sand is abrasive and prone to blinding traditional wire screen surfaces. The operators have experienced Polyweb screen panel life up to and exceeding eight months depending on the screen panel aperture and mass loading at the various screening stages.
30/50 Frac Sand Stage
The first stage of 30/50 frac sand production required scalp screening to achieve maximum removal of any +30 mesh (600 micron) particles. This was achieved by feeding the sand slurry to four Derrick Model 2SG48-120CP-4 Linear Motion scalping screens fitted with 500 micron Polyweb screen panels. The oversize solids were conveyed to waste piles, while the undersize fraction was collected and utilized as feed slurry for the 50 mesh (600 micron) separation. The 50 mesh (600 micron) separation was accomplished by successive screening stages of the oversize fractions. Each stage utilized 50 mesh (300 micron) screen panels, and screening continued until at least 90 per cent of the final oversize fraction was between 30 and 50 mesh (Figure 3).
A feed slurry density of approximately 25 per cent by weight was necessary for each step because of the increasing percentage of both oversize and near-size particles for each successive screening step. The in-spec 30/50 frac sand was fed to three Derrick Model 2SG48-120W-4 linear motion dewatering machines fitted with 600 micron Polyweb screen panels. The solids produced by the dewatering machines met the 30/50 mesh product quality specification and contained 16 to 20 per cent moisture. The dewatered, in-spec 30/50 product was conveyed directly to the outdoor storage area.
40/70 Frac Sand Stage
The undersize fraction from each 50 mesh (300 micron) screening stage combined to make the feed for the 40/70 mesh product sizing. The multi-step screening process used to produce the 30/50 frac sand was repeated for the 40/70 frac sand; however, the Stack Sizers were fitted with 210 micron Polyweb urethane screen panels. The in-spec 40/70 Frac Sand was fed to two Derrick Model 2SG48-120W-4 linear motion dewatering machines fitted with 210 micron Polyweb screen panels. The solids produced by the dewatering machines met the 40/70 mesh product quality specification and contained approximately 16 to 20 per cent moisture (Figure 4).
The dewatered, in-spec 40/70 product was conveyed directly to the outdoor storage area.
100 Mesh Frac Sand Stage
The overflow fractions from the 30/50 stage, the 40/70 stage, and the undersize fraction from the 40/70 stage Stack Sizers combined to make the feed slurry for the 100 mesh frac sand.
The particle size distribution of the combined 100 mesh stage feed indicated that this slurry could meet the 100 mesh product specification if approximately 3 per cent of the residual -140 mesh (106 microns) material could be removed. Derrick suggested this could be accomplished by using a large diameter hydrocyclone and additional Derrick Model 2SG48-120W-4 linear motion dewatering machines fitted with 500 micron Polyweb urethane screen panels. The underflow fraction from the hydrocylones was fed directly to four dewatering machines. The solids produced by the dewatering machines met the 100 mesh product quality specification and were approximately 16 to 20 per cent moisture. This product was conveyed directly to the outdoor storage area, and the overflow from the hydrocyclone was directed to a settling pond.
Final Preparation and Load Out
Each of the three final frac sand products—30/50, 40/70, and 100 mesh – are conveyed directly from the dewatering screens to an outdoor storage area (Figure 5).
As needed, each product is conveyed from the storage pile to a thermal drying unit. Therefore, only in-spec products are dried minimizing energy expended to dry sand. The final dried product is then conveyed to a second enclosed storage building, where it remains until being conveyed directly to rail cars for delivery to customers.
Process Upgrades
Optimization of the processing plant is ongoing as the facility reacts to the changing demands of the frac sand market. Presently, process changes were incorporated to maximize production of the 40/70 mesh product. In 2019, Derrick’s latest wet screening technology, the SuperStack wet sizing machine was incorporated into the process. This machine is similar to the Stack Sizer machine, but the SuperStack machine includes eight screening decks providing approximately 86-square-feet more screening area, while maintaining almost the same floor space requirement of the 5-Deck Stack Sizer. The SuperStack configuration provides two to three times the capacity of the Stack Sizer machines and helped American Silica reduce the floor space requirements of processing plant. The SuperStack machine also incorporates Derrick’s patented Front-to-Back™ (FTB™) Polyweb screen panel tensioning system that allows for much faster screen panel changes.
A Promising Future for Wet Frac Sand Processing
A shift to the use of wet, in-basin sands, coupled with the success of a proven process for making in-spec frac sand products with a wet-only process, bodes well for the incorporation of Derrick Stack Sizer and SuperStack wet screening technologies into existing or new frac sand production facilities. A transition to processing using high-speed vibrating screens to make in-spec products directly in a wet process can minimize or eliminate processing steps and energy costs associated with drying raw sand or finished sand products. Additionally, the use of a wet-only process minimizes dust generation issues and minimizes operator exposure to respirable silica.