Biomass Infeed Systems: Cost, Space, and Other Considerations
How much does a biomass infeed system cost? The answer involves a big “it depends.” Systems can be as simple as a wheel loader and a receiving bin or more complex and involve bunkers, metering, and screening equipment. Obviously, the bigger and more complicated the system, the higher the price.
Containers vs. Bunkers
SMART Containers almost always cost less than a concrete bunker due to the price of concrete and the labor involved in pouring it. Containerized storage also has an advantage (in the United States, at least) because it depreciates faster than bunkers, as the containers are not fixed assets. Thus, they pose an advantage on the accounting side of things. Shipping rates further affect the cost difference between bunkers and containers—it may cost less to build a concrete bunker than ship a SMART Container across the world, for example.
In general, smaller storage volumes will favor our container solutions, and larger ones will favor a poured bunker with SMART Floor. Still, of course, one must look at the “system” to really understand the total cost impact of one vs. another.
Otherwise, differences in price between containers and bunkers come down to layout, capacity, and power. A larger bunker costs more, as do additional containers. A denser material and a faster discharge speed also increase the price because more power is required to move the material. Layout and feed considerations affect the price, too. Stacking SMART Containers to increase storage volume costs less than three separate SMART Containers with individual hydraulic systems. Operators cannot dump directly into stacked containers, however. They must instead feed a receiving bin and elevate the materials via a conveyor. The same goes for tall bunkers. Again, it is the “system” cost that must be evaluated.
While operators may feed unstacked SMART Containers and low bunkers with wheel loaders, customers must weigh the disadvantages of this setup. Feeding containers directly via a wheel loader may require a ramp to allow the vehicle space to dump over the retaining wall, and the ramp takes up more ground than a receiving bin and conveyor. Also, unless the customer already owns the necessary components, the ramp can cost more to build than the necessary feed systems, especially if multiple ramps are required.
Increasing the storage volume of direct-feed systems is slightly more complicated with SMART Containers because, unlike bunkers, we cannot simply design the containers wider or longer than they are. Customers must either stack containers or place multiple containers side by side to increase the storage volume. If they wish to feed multiple containers directly, they may need multiple ramps, which will consume more ground space. Though on the other side of that argument, SMART containers are modular and easily expanded when you need more storage, or you need more separations.
SMART containers really shine in applications where you need to store and then accurately blend products, such as in the case of a pellet plant blending various species. A consistent blend allows the pellet mills to be run at maximum output without upsets.
Metering and Blending
Beyond storage, biomass infeed systems often require metering. For this, we offer two options: surge bins and metering bins. The purpose of these two systems is the same—to create a metered flow rate, but their intended use is different (at least in how we differentiate surge and metering equipment). A surge bin collects material surges and discharges the material at a metered rate. The bin thereby protects downstream processes from surges that already exist in a system and against short periods of disruption. A metering bin, on the other hand, is placed at the point where material enters a system. It, too, prevents upstream processes from surging, but its capacity is much smaller; it does not provide much protection against disruptions in the flow of material.
Surge bins are also helpful where a system merges material from multiple sources, as they can mix the material. This use has limits, though, as heterogeneous particles do not always blend properly (the “Brazil nut effect”). The more significant the difference in particle size, density, and shape, the more profound the separation. Surge bins are not blenders, and customers should not think of them as such. Surge bins aren’t always necessary in a biomass feed system, especially when there’s a bin metering material as it enters the system and there isn’t concern with disruption. We can equip SMART Containers with individual metering bins, for example, to prevent surges. These metering bins can discharge materials from multiple containers into a common conveyor and blend material without a mixer (materials stratify in the conveyor but remain in the desired ratio). The advantage of this is that it accurately blends materials in the conveyor stream and costs less than a surge bin, which must be large and powerful enough to handle material from all the discharge points.
Contamination
The ability to remove contaminants from the infeed stream adds additional cost to an infeed system. Still, screening is necessary if the material may include contaminants that may damage upstream equipment and disrupt processes. In applications involving biomass boilers, for example, contaminants affect burn efficiency. They also negatively affect the characteristics of the ash—sand contamination creates clinkers, which can explode when they hit the water in a wet ash system.
In applications where the infeed material must be free of even tiny contaminants like dirt or sand, an oscillating screen or vibratory conveyor is necessary. Disc screens remove oversized particles well in high-volume applications, though they aren’t the best choice as a primary screen for urban waste, which often includes soft plastics that wrap around the discs and shafts. Costs between these systems vary widely, with the type of system, manufacturer, and size playing roles.
Pros and cons are beside the point in most applications, though, as screening is not always optional. The National Fire Protection Agency’s Standard for the Prevention of Fires and Explosions in Wood Processing and Woodworking Facilities (NFPA 664) requires operators to screen wood stock for foreign materials and to prevent materials that could ignite the biomass from entering wood or dust-processing equipment (9.4.11.1-2). Therefore, if a wood processor cannot guarantee their biomass feedstock is free of metal contamination, they must screen it to comply with the NFPA’s fire codes. Similar codes may apply to other industries.
While adding screening to a biomass feed system inevitably increases its upfront cost, it reduces operational costs by preventing downtime and damage to upstream equipment. Thus it is with infeed systems as a whole—how much it costs depends on what you require of the system. A feed system that consists of a receiving bin and front loader will not cost as much as one that removes unwanted particles, includes redundancy, and provides hours of feed capacity between loads. Fortunately, you have the experts at BE&E to help guide you through the decision process. We know biomass, and we know how to design a reliable, high-performing system. Contact us today.
