BioCycle March 2008, Vol. 49, No. 3, p. 44
Nuts & Bolts
Deciding what type of screen meets an operation’s needs can be guided by end markets to be tapped. Recent buyers and vendors offer insights and evaluation tips.
Rhodes Yepsen and Nora Goldstein
WHEN it comes to selling compost, the markets can drive equipment purchase decisions. This was the case for the Lehigh County, Pennsylvania yard trimmings composting operation, which produced 14,000 cubic yards of compost in 2007. “We are doing a lot of work with a soil amendment company that makes products for golf courses,” says Tim Bollinger, Composting Operations Manager for the Lehigh County Office of Solid Waste. “We couldn’t get the product they needed out of a trommel and they are looking for a 3/8-inch minus particle size. Also, our site is on compacted subsoil, which is 100 percent shale. We can’t have flakes of shale in a product for golf clubs.”
The operation, which already owns a Rawson trommel and an Erin star screen, purchased a CEC deck screen to tap this high-end market. The screen provides a three way product split, which is beneficial for another market the county services – erosion and sediment control and storm water management. “Erosion control is a very important market for the middle fraction,” adds Bollinger. “This is material that is less than 2-inch minus but greater than 3/8-inch. It is a real benefit in erosion and sediment control because it allows water to pass through, but holds back the sediment.”
For its mulch operation, the county finds that its star screen works well, especially when the material is high in moisture. “The trommel can be a workhorse in terms of screening a lot of compost and mulch, but when we have a lot of rainy weather, as we’ve had this winter, we can’t put the material through our trommel,” he says. “We originally purchased our star screen to deal with higher moisture products.”
The county has a 1/4-inch minus screen plate for the bottom deck for customers who want a very fine compost product. “Screening to that size is when you have to be concerned about moisture with a deck screen,” notes Bollinger. “The material has to be extremely dried out for a long period of time, and you still have way too much material in the overs fraction. We charge a lot and the customer has to want a lot to make it economical for us to produce a 1/4-inch minus product.”
This second installment of BioCycle’s 2008 Nuts & Bolts series looks at screens for both upfront materials preprocessing as well as back-end product finishing. Editors interviewed compost and mulch facility operators as well as vendors of screening equipment. Screen options for preprocessing and end product finishing that are discussed fall into several categories – trommels, stars, deck and bucket. Other types of screens include disc and oscillating, which are primarily used in upfront materials sorting.
The primary factors organics processors consider for a screening plant are: ability to make a variety of particle sizes; ability to handle materials of varying moisture content; parts and service availability; ease of changing screen sizes; ease of maintenance. Notes François Brodeur, Process Equipment & Recycling Director with Premier Tech Systems, which sells the Erin star screens: “Whether private or municipal, we see compost producers consistently driven to maximize production, in spite of weather or material conditions. Their customers don’t care about their processing challenges. They want finished product when they want finished product! And of course this starts at the beginning of spring, when producers are commonly facing their highest moisture conditions!”
For preprocessing applications, in the interviews conducted for this article, the key factor is separating contaminants and fines out of yard trimmings, brush and C&D materials prior to size reduction to minimize damage to the grinder and optimize throughput. Screens utilized to separate mixed materials, such as construction and demolition debris prior to hand sorting or processing, were not covered in this article.
Product loyalty also plays a role in equipment selection. Alan Boehm of Chesterfield Farms in Crofton, Maryland, has been in the soil products industry for a number of years. He has always used the Powerscreen brand of screens for his operation. “I just purchased the 2100 trommel, which is a replacement for an older Powerscreen trommel we had,” says Boehm. “We were able to do this because the 2100 is so efficient, and the old trommel had good resale value. We also use a 1400 Chiefton Flat Deck. For us, convenience of service and parts is very important when buying equipment. Aggregate Screens and Crushers is a nearby dealer and is very reliable. We can get same day service on repairs and parts. That means we have less down time, and no extra cost for shipping parts.”
For Greg Ovenall of Ovenall Farms, Inc. in eastern Washington State, the ability to meet product demands of different customers was key to determining the type of screen he would purchase. Ovenall Farms is a heifer replacement feedlot that raises 70,000 dairy heifers a year. The operation generates 30,000 tons of manure and straw bedding annually. “We were giving the material away and/or broadcast spreading it,” says Ovenall. “But in the process of doing a nutrient management plan for our conservation district, I began to educate myself about composting.”
He began composting three years ago, and purchased a McCloskey trommel screen in 2006. The compost is sold primarily to orchards and vineyards. He also markets an aged manure product (aged over a 6- to 18-month period) that is sold primarily to large-scale agricultural operations. “We can screen different sizes for various customers, creating a nice, fine usable product,” he says. “One of our clients is a company that sells GPS spreaders. We can get a consistent particle size that enables the product to be spread through that equipment.”
West Salem Machinery has a form on its website to guide potential buyers through their screen purchasing process. Information requested includes type of materials to be processed; species of wood, if applicable; moisture content; amount of material to be processed; number of product separations; desired end product size; power availability; and expected amount of machine usage. “We build a range of screening equipment, so our evaluation process is application focused,” says Mark Lyman, President of West Salem. “For example, if a potential buyer has really wet material, it is very common to look at a trommel because of the agitation action. For other people, screening accuracy is very important. They want to make sure they can maintain a certain product size. In that situation, vibrating or oscillating screens are better. The material isn’t being tumbled, so you don’t get stuff diving through the screen holes. It is a more gentle agitation, which provides more accurate particle size.”
RANGE OF OPTIONS
Screen manufacturers (see accompanying directory) were asked about the key features that municipal and private sector buyers are looking for these days. We also inquired about what factors customers want to evaluate when observing an equipment demonstration. The following are the various responses received. Not all manufacturers listed in the directory responded to our questions prior to our editorial deadline.
ALLU Group: This front-end loader bucket – available in a number of models and sizes – has a built in crusher at the base of the bucket. It originally was designed for crushing rock in the mining industry. The SM model replaces the standard bucket on a front-end loader, operating as both a crusher and screener. ALLU introduced a 3/4-inch screen attached in 2007 to process finished compost.
Doppstadt US: For mulch and compost producers that want to prescreen yard trimmings and wood waste ahead of the grinder, one critical issue potential buyers want to avoid is a bottleneck in the feed hopper. “Unprocessed green waste wants to bridge and knit together in a screen hopper, so we have a very large throat opening on our 7-foot trommel,” explains Douglas Sites, when describing the company’s SM720 model. “The machine has about 5.5 to 6 feet worth of hopper. The next critical factor in a preprocessing application is how well the drum rolls the material to get the fines out.”
The Doppstadt trommel models have a horizontal drum with a flight system to move materials along the drum, as compared to an inclined trommel that relies on force of gravity. The drum has metal ridges (flights) designed to reduce spearing. “This rolling of material allows it to be in contact with the screening surface for an extended period of time, leading to increased production capacity and alleviating the potential for speared or elongated material to be discharged in the fines fraction,” adds Joan Ritchie of Doppstadt. The company also has a patented load sensing system that controls the feed to the drum of the trommel in order to optimize screening. “Once the operator is getting either no fines or some fines, e.g., 10 percent, in the overs it locks that feed rate in so the feed has the same weight and amount at all times,” explains Sites.
The screen engine swings out at 90° for accessibility on all sides. Sites adds that the company uses fuel-efficient engines in its screening equipment, burning anywhere from 1.3 to 2.2 gallons/hour. Doppstadt also offers a “wind sifter” unit as an attachment to remove light fraction contaminants, such as film plastic, from the material being screened.
Erin Systems: Erin screens are a product line of Premier Tech Systems. The ability of its Starscreeners to handle wet weather conditions during the highest product demand times of the year has driven sales of Erin Systems, according to François Brodeur. “With consistently ‘moving’ holes (open screen area) vs. rigid holed screens found in trommels and vibratory screens, Starscreeners are able to remain relatively clean and productive when the competing technology screens are plugged and down,” he continues. “The Starscreeners’ ability to easily change sizing of product at the turn of a dial is considered a bonus, more commonly appreciated and used in mulch screening, compared to compost production.”
For demos, Premier Tech analyzes the costumer’s product(s) in terms of size, moisture content and throughput, and then determines the screen length and star spacing needed. The demo therefore mimics the customer’s potential operation. “We also offer a ‘mechanical cleaning system’ for sticky material applications,” says Brodeur. “This option is a series of combs positioned below each shaft and are indexed so as to even out the load on the star deck motors.” The screening equipment can be retrofitted with this mechanical cleaning system, if the customer decides to add it later on. “Star screens are not only used for screening,” he explains. “They are also being used for mixing applications as part of automated mixing lines.” In addition to its Starscreen line, the company offers the Fingertrommel, which incorporates a prescreening fingerscreen, and a fine-screening trommel into one machine.
Komptech USA Inc.: Todd Dunderdale, Director of Sales at Komptech USA, says that the key features customers look for are throughput and ease of making different particle sizes. “Komptech introduced its largest star screen, called the Multistar XXL,” notes Dunderdale. “This screen will produce up to 520 cubic yards/hour of very wet material.” During equipment demos, buyers also are looking at output quality and ease of operation and maintenance. “With the Komptech Mulitstar XXL, two loaders can’t keep up with the production, which impresses the customers, while the output can be tailored to the specific product by changing the speed of the stars,” he adds. As far as ease of maintenance, the star screen has automatic lubrication, which activates every seven minutes. Komptech’s “Clean Star” also helps prevent clogging and downtime.
NexGen Composting Ltd.: “Throughput, dust management and, most importantly, local support appear to be the key factors when evaluating screening equipment,” says Steve Kroening of NexGen. “Of course price is always a consideration! The ability to change screen sections is important in cases where the customer does not know what fraction sizes are best suited to the local market.” Customers are generally interested in viewing the particle size distribution of their product during equipment trials, explains Kroening, as well as the quality of each of the separated factions. “We have recently designed larger size feed bins for our trommel screens in response to customer demand,” he continues. “Our standard feed bin has 6.5 cubic yards of capacity.”
Powerscreen/Terex: Stephen Braden, Dealer Manager for Powerscreen, says that production volume is of utmost importance to his customers. Also of interest are service and correct product application, which Powerscreen responds to with its wide range of mobile crushing and screening equipment, including recycling, dry screening and washing plants. Demos are an important part of the selection process. “We offer highly experienced technicians and sales teams to ensure the right product for each demo application,” notes Braden.
REMU USA Inc.: “We find that the key features customers are looking for in their screening equipment is maintaining throughput capacity with difficult moist materials like compost, manure and clay,” says Juha Salmi of REMU USA. “The capacity of one person and one machine, with our screening bucket used for final compost screening with a 3/4-inch particle size, depends on the size of the excavator and bucket attachment. For example, using a 20-ton excavator and a REMU EX 140 screening bucket, capacity is about 200 cubic yards/hour. With a 28-ton excavator and our WL170 bucket, capacity goes over 300 cubic yards/hour. When the capacity of one person and one machine is not enough, our company offers the ST Combi screening plant using the same technology as in the bucket – a line of rotating blades.”
Leif Adler of Pietarsaari, Finland runs a composting site, processing offal from area slaughterhouses, as well as a construction and demolition recycling operation. The compost is mixed with peat, fine sand and lime and sold as fertilizers. “I used trommel screens years ago,” says Adler. “They were great tools for working with sand and crushed stones, especially when multiple particle sizes were needed. The soil in the area where I live has high clay content and my business is working with all kinds of waste products. Horizontal sifter screens did not work with sticky and wet materials. I tested the REMU screening bucket and the performance was much better with topsoil and compost and when separating demolition waste. Because of the rotating blades and its cleaning scrapers, it doesn’t get clogged.” He adds that a big issue on the C&D side is the time needed for transportation and handling. “Loading material into trucks, moving it somewhere to screen, then handling it many times in a yard, simply takes too much effort. By screening on the construction or demolition site, I can add the needed contents and prepare topsoil right there for their specific use.”
Screen Machine Industries Inc.: “The summary phrase that best captures the buying strategies amongst informed municipal and private sector clients is ‘Optimal Life Cycle Value,’ (OLCV),” says Cynda Williams of Screen Machine Industries (SMI). “By definition, OLCV is recognition that the best value is not only a measure of up front costs, but recognition of owning and operating costs in relation to productivity across the life of ownership.” OLCV is a contrast to the low bid mentality. It involves a sum of all considerations, all the way up to resale value.
She adds that the “operational features that are most important to owners are those that directly support the OLCV perspective of ownership. For example, SMI has design-engineered and patented key features such as the integration of shredders into trommel machinery.” Another feature is the dual screen box design, which avoids the detrimental contact of a loader bucket to the screen deck. “Feed-loading bucket contact with the hydraulic vibrating screen decks invariably leads to premature screen and bearing failure,” explains Williams, which in turn negatively affects the OLCV. Equipment demonstrations are viewed as an opportunity to prove a competitive advantage. “SMI’s Shredder Trommels boast integrated free swinging high speed shredders, which will routinely produce 10 to 20 percent more screenable material on the first pass vs. the competition,” says Williams. “Less operator time is needed and there are more cubic yards of saleable material per gallon of fuel consumed.”
Screen USA Inc.: The desire for screening equipment that is both portable and affordable has been increasing, says Rick Cohen, President of Screen USA, Inc. “All of our screens are U.S. made. We manufacture a range of portable trommel screens, star screens, box screens and shaker screens.” The wide range of technology offered means that the customer chooses a model that fits the materials being screened, as opposed to a dealer that just sells the equipment that is on hand. Demos are the ideal time to show customers how the screen handles materials given field conditions that exist. “Most of the time, moisture is the issue,” says Cohen. “In these cases, star screens are an excellent choice and can outperform a trommel screen.” Screen USA comes out with new models on a regular basis; the newest is the TROM 406 HMSL. “It’s highly portable, towed behind a 3/4 ton pickup truck, and can be entirely set up in three minutes,” he adds.
Wildcat Mfg.: Moisture content is handled by Wildcat equipment using several methods. “Primarily, it is with the brushes, which have a polystyrene bristle rather than nylon bristle,” says Tim O’Hara of Wildcat Mfg. “These are more efficient, with poking action that keeps holes from clogging, as opposed to nylon brushes, which have more of a sweeping motion across the surface.” O’Hara has seen a shift in popularity from deck to trommel screens, due to the latter’s ability to screen wet material. Also of increasing interest are portable machines. “There’s demand for heavy-duty industrial class machines that can be relocated on site very easily, for on-site screening in several locations,” he adds.
Wildcat has recently been conducting more site surveys, to establish the materials generated and setting of an operation. It then assembles a unit based on the specific needs of that application. This allows for customized equipment that maximizes efficiency, from appropriate sized engines for fuel economy to the size and shape of the screen holes. “We are seeing a lot more customers screening wood for cogeneration, and wanting to load directly into a truck,” notes O’Hara. “So we offer those buyers an extended conveyor to eliminate the need to load twice.” As for the importance of service, Wildcat offers unlimited parts and labor for a year, including phone consultation. With 130 dealer locations in the U.S., same day service is more practical. Besides increased interest in electric screens (generally for indoor/stationary applications), Wildcat has been exploring propane-powered (natural gas) trommels.
West Salem Machinery: “We have several different lines of screening equipment – disc, oscillating, vibrating and trommel screens – ranging from smaller compact units to some of the biggest in the industry,” says Mark Lyman of West Salem. It is therefore important to understand the different screening technologies, and how to size a screen correctly, in order to have the best match possible. “We are also seeing growing interest in two-step screening then grinding, like the system we installed for Norcal Waste Systems at its composting facility,” he continues. “The attempt is to reduce the overall horsepower requirement to process the material, while increasing the system reliability.” Instead of overworking a single machine, which can lead to downtime and more wasted product, two are used in conjunction, such as a grinder and a screen.
For people focused on accuracy, Lyman recommends vibrating or oscillating screens. Disc screens, on the other hand, are ideal for very high volume, low cost and low horsepower screening, but are a rough classifier, and do not deliver a high degree of accuracy. He sees West Salem, and the rest of the screening industry, moving more into contaminant removal, believing that they work well together. Instances that West Salem has been involved with in contaminant removal include reclaiming landfilled wood fiber that has been contaminated with dirt and rock. Other applications include using air separation for cleaning plastic material from processed fiber products, and water bath separation in mulch/landscape products.
700 Huyler St.
Teterboro, NJ 07608
1100 Holland Rd.
Suffolk, VA 23434
Construction Equipment Co. (CEC)
P.O. Box 1271
Lake Grove, OR 97035
Doppstadt US LLC
1030 Jaycox Rd.
Avon, OH 44011
1 Ave. Premier
Canada G5R 6C1
3460 Grant Dr.
Lebanon, OH 45036
Flo-Cait Material Separators
100 Fairbanks, Ste. D
Holland, MI 49423
Komptech USA Inc.
1369 Forest Park Cir. #204
Lafayette, CO 80026
McCloskey International Ltd.
1 McCloskey Rd. RR#7
Canada K9J 6X8
P.O. Box 1330
Rockwell, NC 28138
NexGen Composting Ltd.
P.O. Box 435
11001 Electron Dr.
Louisville, KY 40299
REMU USA Inc.
6080 C Durham Dr.
Lake Worth, FL 33467
561 308 0105
Screen Machine Industries Inc.
10685 Columbus Expressway Park East
Pataskala, OH 43062
Screen USA Inc.
1772 Corn Rd.
Smyrna, GA 30080
West Salem Machinery
665 Murlark Ave. NW
Salem, OR 97304
P.O. Box 1100
Freeman, SD 57029