FAQs: Frac Sand Conveying Concerns
Mechanical conveyors have been the most commonly used method to convey frac sand in production facilities across the country. Although these systems have been the historical solution to frac sand conveying, they are limited in how they solve proppant handling issues like plant flexibility, dusting, and downtime due to maintenance. Nol-Tec Systems offers an alternative solution to frac sand conveying that can address these issues: pneumatics. Here are some of the most common concerns about frac sand and proppant conveying and how the established technology of pneumatics can solve these issues for you.
1) How can I quickly and flexibly expand my plant’s capacity to convey frac sand?
Mechanical conveyors typically require additional components (i.e. a motor and a drive) to incorporate turns into the conveying layout. Adding more turns into the mechanical convey system routing leads to both higher capital costs and additional maintenance.
A dense phase pneumatic conveying system consists of motive air carrying a material through a small diameter pipe (typically 2” to 8”) to the end destination. The convey pipe can be routed around existing equipment and offers a smaller footprint compared to typical mechanical conveyors. For new plants, this would equal a smaller building size if all of their mechanical equipment was replaced with pneumatic equipment. For existing plants, changes to the system can be made more quickly, in the space available.
2) Is there a better method for controlling dust when conveying frac sand?
Handling frac sand produces a significant amount of dust. Mechanical conveyor belts are open to the environment. So when frac sand is conveyed and transferred using mechanical systems, the dust produced during transportation is likely to land on any surface near the conveyor belt. This can create a dirty, unsightly working area and put workers in close proximity at risk for long term health effects (i.e. silicosis). Bucket elevators, vibratory feeders, and screw conveyors are also known to have issues with dusting, due to removed or loose access covers. Improper venting at conveyor transfer points are another dust generating source.
In a dense phase pneumatic system, the product and the motive air are completely enclosed in the conveying pipe. The end destination (i.e. a storage bin or receiving hopper) is equipped with dust collection that will filter latent dust particles out of the motive air stream after the product has been conveyed, resulting in a dust free environment. Pneumatic conveying can give you 100% product containment throughout the convey pipeline.
3) Can I be sure that my material’s integrity is maintained?
Yes, dense phase pneumatic conveying works with no detectable product breakage. High pressure, low volume air is used to convey the material at a low velocity. Energy is evenly distributed throughout the system via Air Assist line injectors. In this way, the high pressure/low volume air combination maintains a minimized, controlled product velocity that virtually eliminates product breakage, dusting, and system wear. Frac sand is an ideal material to be conveyed in a dense phase manner, to both maintain product integrity and minimize pipeline component abrasion in the system.
4) How can I minimize the impact that product temperature and moisture, and system capacity have on my conveying process?
Product temperature: Mechanical components are very susceptible to damage (for example, belt breakage) at temperature extremes. Because pneumatic systems limit exposure of components to temperature extremes, pneumatics offers a higher flexibility in temperature range than mechanical systems.
Moisture content: Sand has the unusual property of conveying pneumatically even more easily when wet. From a damp state up to complete saturation, sand conveys very effectively with a dense phase pneumatic system. Additionally, wet sand is less abrasive than dry, which promotes longer system component life.
System capacity: Pneumatic systems have a very broad range of capacity, from very low to high. In very high material convey rates, pneumatic systems can have higher operating costs than mechanical conveyors. Cost comparisons need to be made which consider not only horsepower but other maintenance and health/safety costs as well. A Nol-Tec systems application engineer can walk you through this comparison process to help you determine the best system for your needs.
5) What can be done to keep maintenance costs low on my frac sand conveying system?
Mechanical systems utilize many moving components (such as bearings, seals, drives, motors) which are subjected to a constant exposure to frac sand and dust. The extreme abrasiveness of the product results in frequent maintenance of these items.
Dense phase pneumatic conveying offers a cost-effective alternative to mechanical conveying. There are few moving parts exposed to material in a dense phase pneumatic system. Dense phase conveying minimizes the air velocity in the pipe. This protects the material, but also greatly reduces the stress on various common wear points in the convey line. There is no sand-blasting effect on the system.
6) Is there any way to minimize product loss when conveying frac sand?
Every year, the frac sand industry loses 1 ½% to 3% of product during the handling process. This is primarily due to the unenclosed nature of mechanical conveying systems. In mechanical systems, product can be lost off the belts via directional changes, product orientation on the belts, or other various inconsistencies. These open systems also allow for cross contamination between different sand grades.
Pneumatic systems are completely enclosed from product loading to product discharge. This ensures a higher amount of product accountability and lower amounts of lost profit due to product loss. Additionally, customers demand many different grades of frac sand which need to be separated. Cross contamination of these differing grades can be reduced in a pneumatic system compared to a mechanical one.
This article was authored by Mitch Lund and Michael Thiel of the Technical Services Group, Nol-Tec Systems in Lino Lakes, MN. For more information, please contact Nol-Tec at651-780-8600 or on the web at our frac sand page.