In the world of biomass, fuel is collected and produced in a wood yard. There are essentially three broad types of wood yard:
Success in the biomass field from an operations standpoint means, among other things, finding the right type of wood yard for your process. There are a lot of factors that go into finding the right wood yard approach and optimizing the entire system, and each needs to be carefully evaluated before selecting a course of action.
Here, we’ll discuss each type of wood yard in detail and then provide a guide to creating the optimal approach when considering a particular facility for biomass.
Critical Decision-Making Factors
There are several factors that go into choosing the specific type of wood yard you’ll need for your operations. These include:
- Throughput volume
- Storage volume
- Size of the facility
- Upfront capital budget
- Operating budget
- Local regulations
Some of these are specific to the facility itself, while some are specific to the business and to external factors like climate and regulation.
Throughput Volume/Storage Volume
The most compelling metrics for determining whether manual or automated handling should be used for the fuel-feed chain are throughput volume and storage volume.
Size of the Facility
Automation can require significant excavation and construction, and typically has a larger footprint than a manual operation.
Upfront Capital Budget vs. Operating Budget
Fully automated systems require considerably higher capital outlays to implement, but offer lower operating costs than manual systems.
Seasonal extremes can force a facility toward greater automation, which can be easily housed in enclosed systems.
In addition to federal emissions regulations, plants must take into account local requirements governing byproducts such as dust, ash and noise.
It’s important to consider all of these factors, and to avoid moving toward a stock turnkey fuel-feed system, since those systems are created without taking the above factors into consideration for your facility. They could be inefficient or unsuitable for your operation. It’s better to have a custom-designed wood yard engineered to your unique specifications.
Automated Wood Yard Systems
There are many considerations before determining which type of wood yard is ideal. Not all wood yards can be fully automated; those with lower capital budgets, for example, tend to move to semi-automated or manual operation. Those in colder or wetter climates, on the other hand, tend to be automated due to how much manpower a manual operation requires, and harsh climate can result in inefficiencies for those types of operations.
One of our clients – a major Midwestern university – had a limited, half-acre-sized lot for its wood yard. It was subject to harsh northern winters, so it had to be fully enclosed (it also had to abide by dust regulations). Additionally, the university needed to be able to receive up to 60 tons per hour, fed directly into a 11,000 cu.ft. storage unit. Fro there, the feed would be delivered to two boilers at a rate of up to 9 tons per hour.
Based on these considerations, it was determined that a fully automated wood yard design was best. The final design included an A-frame enclosure to house the entire system, which consisted of five belt conveyors, four drag conveyors, a reclaim hopper, a truck dump, a self-cleaning magnet, a dust collection baghouse, a hog and a screen.
This project had a higher initial cost, but a lower operating cost with minimal maintenance and the elimination of certain components, like the need for a front loader.
Manual Wood Yard Systems
On the opposite end of the spectrum is a manual wood yard.
Manual wood yards tend to have lower upfront capital costs. They also tend to require lower throughput and storage volume. One feasibility study for a Kansas City project found that the project required a feed rate of roughly 10 tons per hour, as well as front-end loaders that would periodically transport feed. Based on the yard’s location and large area, the new system wouldn’t require costly feed enclosures or dust control.
Due to these and other factors, the study found that a manual system was the best fit. The final design included an underpile drag chain conveyor, a single belt conveyor, a tire-derived fuel-feed hopper, a disk screen, a live-bottom boiler feed bin and a self-cleaning magnet.
Manual systems have lower initial capital outlay, are best for low-throughput projects, and are most commonly used in warmer climates. Additionally, they incur higher operational costs due to manual labor, yet can get by with less equipment than an automated system.
Semi-Automated Wood Yard Systems
The third type – semi-automated – is somewhere in the middle of the spectrum.
Facilities that choose this approach are looking for a middle-ground solution that doesn’t depend on either low operational costs or a low upfront investment. This approach usually introduces automation into either the setackout or reclaim end of the fuel-feed chain. Combined, these strategies can keep startup capital demands in check and reduce operational costs.
Automating reclaim beyond the kind of underpile reclaimer typically used in manual systems is usually more expensive than automating stackout. Since manually feeding the reclaim end of the chain usually has a lower operational cost than front-loader stackout use anyway, the optimal solution for operational efficiency and low capital costs is often automated stackout combined with manual reclaim.
One Southeast paper mill recently considered the benefits of semi-automation. The mill formerly used a fully manual front-loader process that incurred high labor costs. The facility wanted to reduce long-term operational costs without incurring the high upfront costs associated with full automation.
The plant had a flow rate of 120 tons per hour, fed primarily by front loaders. The wood yard upgrade process first implemented low-cost manual equipment and process upgrades, and added several belt conveyors to prepare for the second phase, which added a new truck dump and receiving belt, as well as a reclaim hopper. The third phase continued these developments and further optimized the entire process.
The result was a highly efficient, semi-automated system constructed with relatively low capital costs that were spread out across multiple years.
Assessing Your Wood Yard Situation
It takes on-site inspection, careful analysis and hard-won experience to develop an optimal wood yard design tailored to a particular facility, whether it’s a conversion or a greenfield project.
While predesigned fuel-feed systems promise to simplify a complex engineering problem, a custom-designed system that takes advantage of component architecture can optimize every stage of the supply chain by using a site-specific combination of conveyors, reclaimers, and front-loaders.
Careful advance planning results in an optimized system matched to capital budgets, operational budgets and production demands.
ProcessBarron specializes in biomass operations, including designing and creating wood yard projects and handling air, fuel, and materials for a wide variety of facilities across the world. Contact the team for more information or to consult on your next project.