5 Factors to Consider When Building a New Frac Sand Plant.
By Mark S. Kuhar
The very basic function of frac sand is to create and maintain passageways needed for the harvesting of either natural gas or crude oil. There are three basic types of proppants that are being used: natural silica sand resin coated silica sand, and ceramic beads.
The wet processing of frac sand involves taking natural silica sand proppants from the point of a mined stockpile of silica sand to the stockpile that feeds the product for final sizing. The basic function of a wet frac sand processing plant is to provide clean sand that is free of clays in the total range of size classifications required by the end user.
This size range will vary from one producer to another. While there are a variety of configurations you could use to process the frac sand, there are five key factors that all producers should consider when planning and constructing a frac sand plant.
1. Prove Deposit: Size and Uniformity
The ideal frac sand particle needs to be composed almost entirely of silica, be well rounded (weathered), structurally sound (able to withstand high pressure) and be free of clay impurities. API specifications define the required characteristics of frac sand and is used around the world to qualify sand for use in fracking.
This set of standards defines size ranges and tolerances. Tested qualities include mineral composition, compressive strength, acid solubility, conductivity, turbidity, roundness and sphericity. Defining these allows for clear and consistent grading of the vastly different sand produced throughout the world.
It is important to prove reserves for accurate valuation of a frac sand operation. The most accurate ROI calculations are based on comprehensive drill data throughout the breadth of the deposit rather than testing of a single sample. This is common sense to some and overkill to others, but knowledge of the depth, size and mineral the deposit is comprised of gives confidence to investors and insight to your frac sand planning.
The number and location of boreholes required can vary widely among different deposits depending on their size and uniformity, so it is important to consult experts in the field during this process. Once this data is gathered, a knowledgeable equipment manufacturer or a mining engineering firm should be able to provide assistance in calculating the cost of running and maintaining equipment so that your profitability expectations are met or exceeded.
A potential advantage to proper valuation of a deposit is determining potential byproducts in addition to the primary frac sand products. These may be a valuable mineral or simply a size fraction that may otherwise go to waste. Identifying the full range of minerals in a deposit with the help of a geologist is the best way to maximize a mine site’s profitability.
Natural silica sand deposits can exist above or below the water table, therefore the mining methods can range from dredging operations to mining via standard excavators. Some of the deposits above the water table can exist as liberated sand particles or in deposits that require blasting (bumping) and the use of primary crushers, such as jaw crushers.
The crusher can be run in either closed-loop (screens used to close circuit) or open-loop systems depending on the nature of the deposit (ease with which silica particles are liberated) and the efficiency of the silica liberating circuit. It is imperative that methods used to liberate the silica particles do not crush or create fractures in the individual silica particles.
2. Design a Flexible Processing Plant
Final plant designs should be based on run-of-mine feed, but it is important to take into consideration the entire breadth of potential feeds when designing a system.
The borehole data from a proven reserve should be analyzed and (discounting overburden) the best and worst feeds should be considered alongside the run of mine feed. This comparison allows for equipment to be selected that can handle anything you throw at it. It also gives insight into production rate variation from different parts of the pit.
In sand deposits, the feed gradations can be compared in an Excel spreadsheet by analyzing the production rate, fine rejected, how many products are being made, and the oversized material. This will show where bottlenecks may exist in the system and allow some of them to be designed out of the system before the plant is commissioned.
3. Plant Layout
Most frac sand producers push their processing plants to the breaking point and then back off enough to prevent continuous breakdowns. Planning on the front end where the bottlenecks will most likely occur in the system will make future expansion more affordable while keeping initial costs in check.
Site layout is the most critical part of this planning. It is much easier to replace a few pieces of equipment than to rearrange the entire system. Understanding where you are laying out your plant and how your stockpiles can drain can save you money and time in the future.
Stockpiles can produce a good amount of water and if managed correctly can be reused for future processing. Getting bids for a higher feed rate than what is initially required may reveal that some equipment’s capacity is doubled for as little as a 20% increase in price. Upsizing equipment and conveyors during the initial build can amount to significant savings when an expansion is added in the future.
4. Schedule Maintenance Downtime
No one wants to shut down when everything is going right, but that is always the best time to. It is easy to get behind schedule and to put off maintenance until something goes wrong, but experience teaches us that this is always costlier and a less efficient use of time.
An unplanned shutdown can mean hours of digging out conveyors and equipment or replacing parts that were never meant to see wear. Planning equipment runtime based on manufacturer-estimated levels allows for scheduled maintenance so that wear parts are replaced rather than the steel body of equipment or beams from the structure. Analyzing wear patterns also gives insight into what parts will need to be replaced next.
Long lead time items may then be ordered preemptively, reducing downtime and further improving system uptime. Unplanned shutdowns may still happen, but they are much less likely if proper care is taken of the system.
5. Consider All Tailings Management Options
With the decline of water availability and rise of environmental concerns, the days of sending plant tailings to a pond without another thought are coming to a close.
In some regions, we are well past that point. In others, we are only just beginning to consider it. Regardless of where you are, tailings management solutions have come a long way in the past 20 years and can now eliminate settling ponds with high efficiency and reliability.
Many frac sand operations are adding fines recovery systems, thickeners and filter presses (or some combination of the three) to reduce costs and/or to produce a sellable product. It is prudent to consider these options during the initial plant design.
A fines recovery system may significantly reduce the amount of fines sent to the pond. This can cut cleanout costs in half and may provide a sellable product as back fill or a newly popular 200 mesh frac sand, but these results vary based on the deposit, so testing is critical. The next step is to recover the process water and thicken the solids in the tailings to greatly reduce pond size and provide process water at the wash plant, saving horsepower on water pumps.
The last stage is to take the thickened solids and press them into a cake. This allows for the complete elimination of settling ponds, opening up land for mining, eliminating costs of cleaning out those ponds and, sometimes, adding another sellable product.
All Things Considered
At the end of the day there are going to be many equipment options to consider when selecting your plant, but the principles that will ensure you the highest return on investment are going to be the same. These five areas will help to ensure that your plant is successful long-term and will be able to meet changing demands throughout the life of your deposit.
Information for this article courtesy of McLanahan Corp.