Favorable market conditions have again brought rise to a boom centered around the quartz sand used in the hydraulic fracturing process; rig counts are up and the amount of sand employed per well is the highest it’s ever been, with one industry expert anticipating 2018 frac sand demand to be 150% higher than 2016 levels.
Just as the frac sand market has undergone many changes in recent years, so too has some of the equipment used in the process, most notably, the sand dryer.
How Sand Dryers are used in Frac Sand Processing
Frac sand undergoes processing upon extraction in order to produce a high quality sand suitable for use as a proppant. This includes washing the sand to rid it of clay impurities.
After washing, the sand is often stockpiled until it is ready for shipment. While stockpiling does allow some of the moisture content in the sand to be reduced, the sand must still be dried to remove the remaining moisture so it can be used as a proppant. For this reason, a drying plant is needed.
The drying plant serves to reduce the moisture content of the sand, as well as to screen the material into the various grades demanded by the market. Depending on the capacity of the plant, one or multiple dryers may be utilized. Material handling equipment such as bucket elevators and conveyors help to move sand through the processing facility.
In addition to preparing the material for use as a proppant, drying the sand has the added value of reducing transportation costs.
Sand Dryer Types
Two main types of industrial drying systems are commonly employed in frac sand drying: rotary dryers and fluid bed dryers. While there has been some disagreement over which type of dryer serves the application best, the industry appears to be settling on rotary dryers, and for good reason; rotary dryers have proven to be the prevailing choice for a number of advantages they offer over their fluid bed counterparts:
Tolerance of Changes in Feedstock
One of the primary reasons why rotary dryers are chosen for frac sand is their tolerance to variance in the feedstock, which is often a given when it comes to frac sand. Frac sand fed to the dryer covers a range of particle sizes and can vary in moisture content.
Rotary dryers provide a uniform drying solution, despite such variance, while fluid bed dryers are highly sensitive to changes in feedstock, requiring a uniform feedstock to maintain efficient operation.
High Capacity
Capable of processing in excess of 200 TPH, rotary dryers are also the preferred choice in frac sand drying because they offer a high throughput. In an industry where production capacity is critical, a high capacity dryer is an obvious choice.
Sand Dryers: Design Considerations
The overall concept of drying in the frac sand industry has changed as well; what was once an industry that favored low costs over design and durability, the frac sand industry has evolved to meet the changing needs of the market.
Frac sand quality is now equally as important as throughput, causing the industry to move away from “commodity dryers” toward more engineered, reliable systems.
Today’s frac sand dryers boast a number of upgrades over commodity dryers when engineered around the unique characteristics of frac sand:
Reduced Carryover & Dust
Frac sand is a fine material that can easily be carried out through the exhaust system. For this reason, minimal carryover is always an objective.
While some manufacturers use a larger diameter drum to accommodate a slower airflow velocity, thereby reducing the amount of carryover, the larger the drum diameter, the higher the cost of the equipment.
FEECO utilizes a smaller drum diameter, allowing us to increase airflow velocity through the drum, which in turn maximizes efficiency. However, with increased airflow comes a risk of entrainment. By utilizing an oversize discharge hood (knockout chamber), FEECO is able to use maximum airflow, while minimizing carryover, resulting in a process that is both high capacity and high efficiency. The use of a smaller diameter drum also substantially reduces the cost of the system.
Along with reduced carryover comes reduced dust and mitigation of its associated issues. The ability to minimize dust on-site is becoming increasingly critical, as regulations around dust control tighten. In addition to minimizing dust from carryover, dust can be further reduced through the selection of a proper seal between the rotating drum and the discharge breeching.
Improved Product Integrity
Combustion chambers have been implemented to maintain product integrity. The use of a combustion chamber prevents the burner flame from coming into direct contact with the product. When working with frac sand, this avoids breakdown of the product, which can occur if critical breakdown temperature were to be reached as a result of direct contact between the material and the flame.
Combustion chambers also promote increased efficiency through more uniform drying, as well as reduced drying costs due to a more complete combustion of the fuel.
Image caption: FEECO combustion chamber model
Built for Longevity
The abrasive characteristics of frac sand, combined with high capacities, require a drying system designed to withstand such aggressive demands. By utilizing higher grade materials in the design of the unit, frac sand dryers can last reliably for years to come.
It’s important to note that this harsh processing environment will also influence the design of frac sand handling equipment. Bucket elevators and conveyor systems will require a heavy-duty design to withstand the demands of handling frac sand.
Customized Flights
While flights have always been used in frac sand dryers, flight design and pattern has become more customized to drying frac sand. Advancing flights are often used at the inlet of the dryer to help move sand into the dryer. Flights can also be bolted in for easy replacement when they become worn out.
Image Caption: Advancing flights help to move sand into the dryer
Conclusion
Throughout the evolution of the frac sand industry, the frac sand dryer has become a cornerstone of processing. This has resulted in the move away from commodity dryers and toward systems engineered around the characteristics of frac sand. As we again approach a boom for the prized sand pumped down hydraulic fracturing wells, producers are looking for high quality dryers that can meet the demanding needs of the industry, while still lasting reliably for years to come.
FEECO provides custom rotary dryers and material handling equipment to the frac sand industry. All of our equipment is designed around the specifications of frac sand to ensure an efficient solution built for longevity. For more information on our custom rotary dryers or material handling equipment, contact us today!