December 2001
Success in the Field--Coastal Sand Moves to Modular Wash Plant
Plant Sense--Evaluating Dust Suppression and Collection Systems
Maintenance Matters--For Maximum Bearing Life, Look to the Lubricant
A
sidedump truck unloads material into the main primary plant, which is
mounted on a 4,000-lb. steel structure designed and manufactured by Madden
Steel Inc., in Brighton, Colo. (The retaining wall pictured is made of
Staplestone.)
Recycled Materials Company, teaming with Aggregate Industries, operates the world’s biggest recycling project.
In many ways, recycling Stapleton Airport, with its 4,700 acres of reinforced concrete and asphalt pavements, marks the state-of-the-art in construction debris recycling in the United States.
During bidding, the “big boys” showed up—worldwide contractors that make the impressively sized Recycling Materials Company (RMC) look modest in comparison.
However, size isn’t everything. And city planners were won over by RMC’s track record of the quality and quantity of recycling. Since 1988, RMC has 10 million tons of recycling experience worldwide. The company has also built its market and reputation by focusing on producing quality product rather than simply settling for the production of non-spec road base. That quality focus has been the critical factor in landing the Stapleton redevelopment project.
“‘Never produce anything that we have to apologize for,’ is the motto of Recycled Materials,” said Mark R. Wachal, president of Recycled Materials.
The fact that RMC was there in 1993 at the onset of the project planning may have also improved its bid quality. The company was a member of the task force which investigated the recycling of Stapleton’s runways and continued its involvement with planning agencies. In July 1998, RMC submitted its request for proposal for the removal and recycling of taxi ways, runways and aprons. In August 1998, RMC was selected to be the removal and recycle contractor. After several months of negotiations and permits, Phase One removals began in July 1999.
The “Stapleton Vision” from city planners to politicians to the construction and materials suppliers has taken on monumental ambition.
City planners hired Forest City Stapleton Inc., a developer based in Cleveland, Ohio, to create a multi-use (business, retail and residential) development in the tradition of Denver’s best neighborhoods, which create “a sense of community.”
To view larger image click here
An
early site plan of RMCıs ³Urban Quarry² is illustrated below. Through
its recyling project, RMC produces a vast array of products with very
liittle waste. In general, RMC removes 16-in.-thick, 6,000-7,000 psi concrete
that makes up runways, taxi ways and aprons (material used mainly for
concrete aggregate and BIOTA). The next layer varies from 12-14 in. of
cement-treated base or asphalt pavement. Limited refining of the cement-treated
base yields an aggregate base course with an R-value of 84. Additional
refining of the base enables RMC to produce a No. 67 coarse concrete aggregate.
Fines are used in asphalt and supplement bases and other products. The
third layer consists of a substantial amount of virgin aggregates from
coarse to sand sizes. By washing the virgin material, RMC was able to
increase its value for use in pavement mixes. To make a soil amendment,
³slimes² from RMCıs wash plant are being mixed with shredded wood that
has been collected from a severe winter storm that damaged thousands of
trees, which the city hauled to Stapleton Airport. Dowel bars, steel and
fiber reinforcement pulled out by in-stream magnets go to an on-site recycle
plant. ³In many cases, we say we sell everything but the dust and noise,²
said RMC President Mark Wachal. For the size of the project, in fact,
the amount of waste that ends up in landfills is astonishingly low. Basically,
RMC is pestered by the removal of a pavement fabric that lies between
concrete and asphalt layers. This often requires removal by hand for larger
pieces and the use of a series of blowers at conveyor transfer points,
which blow the fabric off the material into netting. For really tough
fabric removal, material is floated off in a water bath. This fabric,
plus joint and form materials are generally the only waste that is landfilled.
Quality Products
RMC’s Stapleton Vision was to produce the highest end use recycled aggregates possible.
“This means producing concrete and asphalt aggregates, rip rap, drainable rock and pipeline bedding, in other words, ‘a higher value-added aggregate’ as compared to our usual recycled aggregate base course,” said Wachal.
RMC, for instance, is providing FAA specification aggregate and obtaining excellent flexural strengths in pavement to Denver International Airport from the Stapleton source.
Unlike other bidders, Recycled Materials had the track record to show it could live up to its lofty goals. RMC’s Stapleton Recycle Center now represents the largest of its five metro Denver recycle centers. Six of the seven recycle plants RMC operates are mobile or portable. RMC also performs recycling consulting nationwide and abroad, most notably in Moscow. Key to the success of the project is the strong relationship fostered by RMC with project developers and specifiers to accept all possible uses of recycled aggregates.
It is estimated that the Stapleton project will yield more than 6 million tons of recycled aggregate.
To enable RMC to meet its deadlines for recycled-material utilization, it established a marketing relationship with Aggregate Industries (AI). AI has located ready mix plants and asphalt plants at and near Stapleton. AI expects to use nearly half the recycled material at its plants.
“There has to be blending of recycled material and virgin material,” said Pat Groff, vice president and general manager of AI’s Ready Mix Division. “We’re hoping we will be able to use a higher percentage of recycled material, but that could change as we get into different pockets of material. I would say there would be at least a 50/50 blend of virgin and recycled at the low end for both asphalt and concrete—more virgin if you need it.”
RMC’s Stapleton permit allows on-site processing and storage of recycled materials in a six-year removal period, and a 10-year sales and storage agreement on 100 acres of the property.
Products coming from the project include “Staplestone”—a product name created by RMC to market large concrete blocks for retention walls. The Colorado DOT has already implemented Staplestone in highway projects. RMC participated in studies by the Colorado School of Mines that found that recycled product coming from Stapleton was either equal or higher in quality than virgin mixes.
Mixed Use Development
Demand for the recycled material will certainly be high as an urban development replaces Stapleton. The property was rezoned to create a mixed-use urban development that combines housing, retail, open space and employment centers.
Residential development is intended to mirror traditional Denver neighborhoods with their tree-lined streets and front porches. A total of 12,000 new homes are planned for construction within the next 15 years. Of these, 8,000 will be homes, townhomes and condos, with the remaining 4,000 built as rental apartments. Homes will range in price from the low $100,000s to more than $500,000. The first residential neighborhood is currently being prepared for occupancy. Apartments are expected to first become available in 2002.
Six village-style retail centers are planned, with the first to open by year’s end. These centers, which account for more than 1 million sq. ft., will feature grocery stores and neighborhood shops; while regional retail centers, which will account for 800,000 sq. ft., will feature home improvement and discount retail superstores and other national retailers and restaurants.
Another 10-million sq. ft. will be devoted to office space. When complete, planners estimate that the community’s businesses will employ more than 35,000 workers in a variety of jobs.
Finally, more than 1,100 acres are being reserved for regional parks. In addition, hundreds of acres of neighborhood green spaces will be made available.
An Urban Quarry
Accommodating the numerous activities at the Stapleton site safely and efficiently was no mean task.
“Ken Buesing, chief executive officer and co-founder of RMC, is the equipment mind. His son, Jason, did drafting and engineering on the project, and I was involved in the process thinking,” said Wachal.
To diminish traffic problems, RMC built an oval track surrounding the site where trucks can only travel in a single direction. Trucks that pull off at various stockpiling areas or plants yield back into the track and then circle to the scalehouse.
With the massive amounts of recycled and virgin materials being removed from the site, RMC calls Stapleton its urban quarry. Basically wheel loaders, excavators and special concrete breakers peel the airport surfaces “like an onion,” said Wachal. Two Caterpillar 990 loaders feed rubble into a fleet of side-dump trucks operated by Iron Woman Trucking, a young Native American-owned company RMC provided guidance in its growth.
“On site, we have two primary jaw plants, a secondary plant equipped with two recycle crushers and a wash plant, plus a third track-mounted machine,” said Wachal. “But, generally, day-to-day processing is done by the main primary plant, a secondary plant doing final crushing and a wash plant. We use the other equipment when it is necessary to supplement production or make a special product.”
Typically, sidedump trucks circle the track to the primary crushing plant mounted on an impressive 4,000-lb. steel structure which consists of two end-to-end 57-ft. x 24-ft. Simplicity feed hoppers, with 5-ft. grizzly sections. Material feeds into a 42-in. x 54-in. Nordberg Jaw crusher. It is conveyed under a 12 kW Eriez Magnetics Deems Magnetic Separator, then travels through a tunnel conveyor to twin 6-ft. x 20-ft. Simplicity triple-deck screens. On each unit, the top deck consists of a 3-in. opening urethane relief media, the second deck uses a 3/4-in. opening screen used to make base course, and the bottom deck is left blank when the plant is in primary screening mode.
RMC also makes a large amount of BIOTA material (a 12-in. minus aggregate used by the government as cover to keep rodents from digging into landfills). The contract with the government is to make 2 million tons of the material, 1.4 million of which needs to be stored on-site in an 80- to 90-ft.-high stockpile covering 15 acres. When making BIOTA, the second deck is replaced by a 1/2-in. opening mesh and a bottom deck is used to desand 3/8-in. minus material.
RMC uses a series of 36-in. x 60-ft. field conveyors to move the material to stockpile concrete aggregates and BIOTA material (1,500 ft. of overland conveyor was purchased from a Virginia mine. Other conveyors were built by Dakota Fabricating Inc.., Glendale, Ariz.). A Thor 87-ft. to 130-ft. telescopic stacking conveyor is used to stockpile material to cut-down on segregation of higher quality material.
RMC’s secondary plant produces concrete aggregate and other products. It consists of a Hazemag 1515 horizontal impact crusher and SECO feeder. A 10-kW Eriez Magnetics Deems magnet is used to remove tramp metal. Material then feeds to a Simplicity 6-ft. x 16-ft. triple-deck screen. Mounted on that screen trailer is a Nordberg 1315 secondary horizontal impactor which is used to make No. 57 aggregate. For FAA specification and drainable aggregates, material can be transferred to a 6-ft. x 12-ft PEP screen for desanding.
RMC’s wash plant—used to simultaneously make four washed products—uses two feeders, one for virgin base course and the other for crushed coarse concrete. These feed a Simplicity 6-ft. x 16-ft. double-deck wet screen equipped with a 1-in. top deck and 1/2 or 3/8-in. bottom deck, which passes material into a 36-in. single sand screw. Coarse aggregate that picks ups dirt from the base coarse is sent through a log washer. Wash water is run through a Krebs cyclone to capture more 100 mesh material for sand and to minimize waste.
RMC uses a series of four settling ponds and adds powdered flocculant to accelerate the settling process, due to the high cost of water in the area.
RMC also accommodates special order aggregate processing, or bolsters production if necessary, with three Hartl track machines. A large Hartl 405 machine and two Hartl mini-track machines crush material. They are often teamed with a Powerscreen Chieftain mobile screening unit equipped with a 5-ft. x 12-ft. double-deck screen, which makes base course and spec base course. A fleet of Caterpillar 980Gs are used to load plants, and Cat 966s and 950s are used as yard loaders.
In a typical production day, according to Wachal, about 2,000 tons of material leave the gate. This is on top of the ready mixed concrete work and removal process, which is running about 5,000 to 6,000 tons a day. RMC has until Aug. 1 2005 to have all material removed, and until Aug. 1, 2009 to have it all sold.
Bill Welgoss is the senior industry editor for AggMan.
Coastal Sand Moves to Modular Wash Plant
When
Coastal Sand Co., Guyton, Ga., moved its operation to a nearby 98-acre
site (with 52 mineable acres), it acquired a new Eagle Iron Works semi-portable
sand plant built into a modular structure. Timing was important during
the move so as to interrupt as little as possible the supply of material
to its customers in a competitive market. Sandhill Road, where the new
plant is located (about 25 miles west of Savannah), has two other competing
sand plants on it—all serving Savannah and surrounding counties in
about a 35-mile radius.
Coastal stockpiled material at its old site to serve customers as it made the transition to the new location. Critical to the timely move was the delivery and set up of the new Eagle sand section, which Coastal purchased from Norx Equipment Co.
“We poured the foundation,” said Coastal Sand President Brett Herrin, “The sand plant came in on two 18-wheelers. It took a day to set up, and then a day to anchor it to the foundation.”
Capacity of the plant was about equivalent to the plant it replaced. The new plant consists of 40-ft. x 10- ft. water scalping tank, which feeds twin 44-in. screw conveyors. A Seco 4-ft. x 12-ft. high frequency shaker, with a 3/4-in. mesh screen on the top deck and a 3/8-in. mesh screen on bottom deck, feeds the scalping tank.
“The top deck catches larger roots and clay and larger gravel, while the lower deck allows nothing but 3/8-in. minus material to enter the mix,” said Herrin. He estimates only 5 percent waste product is screened off the SECO unit. The operation uses a Cat 225B LC excavator to help bank the pond and make berms from the waste material. The excavator is also used to remove overburden, which is rich topsoil Coastal is able to sell to a few customers, even though it is unscreened.
A Caterpillar 962G loader equipped with a 5-cu. yd. bucket feeds material into a “kill” box, or feed box for the screen. The material is extracted from a pond by a Shark cutterhead dredge, manufactured by Dredging Supply Co. While the dredge pump is rated at 200 tph, due to the hardness of the deposit, production usually averages about 150 tph. The company estimates it will mine about four acres a year.
Choosing an Eagle Iron Works plant to replace an older Eagle plant was an easy decision for Herrin. First, the old plant provided 21 years of low-maintenance performance for his company and for the plant’s previous owners. For the 10 years Coastal owned the plant, the company had invested in $10,000 in wear parts, which it was able to utilize on the new plant design.
The only significant change made to the plant was the switching from 36-in. and 48-in. screw washers on the old plant, to twin 44-in. screw washers on the new one.
“We were moving into a finer deposit than the previous site, so I knew we were going to make more masonry sand and less concrete sand, so the 44-in. screws just fit the deposit better,” said Herrin
Production from the plant averages about 150 tph. The concrete screw feeds to a 36-in. x 120-ft. stacking conveyor, and the mason screw feeds to a 36-in. x 65-ft. stacking conveyor.
With the ease of set-up on the modular Eagle system, Coastal only had to move its dredge and its conveyors to the new site. Herrin said it took only two weeks to get up and running at full production from when it left the old site.
Aside from supplying its main concrete and masonry customers, Coastal also found a small market in its masonry sand for golf course usage. Coarses as prestigious as Savannah Golf Club purchase sand from Coastal, because it is white, rather than yellow. The fine sand mixed with peat is also used as bedding or as top dressing for the greens.
Coastal also supplies one of the largest brick companies in Savannah, which keeps its masonry sand sales up.
So far, according to Herrin, the plant has worked with no major glitches.
“With AR wear liners and reinforcement used throughout the Eagle plant, I don’t plan on doing wear maintenance for a couple years,” said Herrin.
the bottom line...
Coastal Sand purchased a new modular Eagle Iron Works sand section to replace an older plant, partly based on its 21 years of reliable performance. The ability to set up the new plant quickly and supply its customers throughout the site transition was critical to the company.
To submit a suggestion for a Success in the Field or for more information about this story, contact AggMan at (717) 337-0027, fax (717) 337-9337 or e-mail Bill@aggman.com.
Evaluating Dust Suppression and Collection Systems
By Ed Hayes
Editor’s Note:
This is the fifth of a series of articles examining common plant problems
and how they can be fixed.
Every aggregate plant that processes dry raw-feed material has locations
of dust emissions that need to be controlled. This is essential not only
for the resultant pollution, which adversely affects our environment,
but also for the detrimental effects on the health of the plant employees.
These emission locations include truck and loader feed hoppers, feeders,
crushers, screens, chute-work discharge areas, conveyor-to-conveyor transfer
points, as well as conveyor transfer areas at surge piles, surge bins
and stockpiles.
There are several types of dust-control equipment used for dust suppression
or collection. Each system has positive and negative capital, installation
and operational features. Here is a list of important points to consider:
1.The bag-house type of collection system can be a cost-effective alternative
if there is a market for or an in-plant use of the collected fine material.
These positive benefits have to be considered in the context of the following
negative system features:
- High capital and installation costs for the total collection equipment
and the supporting electrical system.
- A plant, which is not “compact,” will need several separate
systems.
- The high-horsepower suction fan system will consume considerable electrical
energy.
- The hooded collection areas as well as the necessary collection ductwork
will hinder plant operators and maintenance personnel when performing
plant inspections and repairs.
- The bag house, fan system and the ductwork will require a substantial
investment in supports and foundations.
2Water-spray suppression systems are used considerably more often than bag-house collection systems for several reasons:
- The capital cost of a water-spray suppression system is only a fraction of the cost of a bag-house collection system.
- A plant that is not “compact” needs only one system to reach all the emission areas.
- The horsepower requirements and the resultant energy consumption costs for this type of system are minimal.
- Spray-nozzle assemblies for the dust emission areas require minimal shielding and, therefore, do not extensively hinder maintenance procedures.
- Water supply lines and spray-nozzle assemblies can be quickly and easily attached to existing structures and equipment and, therefore, do not require additional expensive support structures.
However, there are certain negative factors that have to be considered with any conventional water-spray suppression system:
- The spray nozzles need a constant pressure and volume of water to produce the proper atomization of the water droplets to agglomerate the dust particles.
- Some systems need an additional injection system to supply and mix an expensive wetting agent with the water to assist in the agglomeration of the dust particles.
- The water supply system does not “know” when there is a reduced or stopped flow of aggregate at any suppression point and, therefore, continues to supply the same volume of spray water, which excessively wets conveyor belts, chute work and other equipment. This causes excessive “carry-back” with considerable clean up and other problems when the flow of aggregate resumes.
3. In the near future, there will be an advanced water-spray suppression system available with many advanced features. This will take the present technology to a much higher level, at minimal additional cost and with many operational benefits:
- The advanced system will be able to atomize the supply-water to a finer mist than present systems and can achieve the same atomization totally independent of the water volume or pressure. This will allow a special sensing system to regulate the volume of water in direct proportion to the volume of aggregate passing through any dust emission area. This will prevent the wetting of conveyor belts, chute-work, processing equipment and the aggregate itself.
- During freezing weather, the advanced system will not freeze during periods of reduced or stopped water flow.
- During freezing weather, the water-supply piping system to all nozzles will automatically purge itself of all water at plant shutdown.
- The special nozzles and sensors utilized in this new system are relatively inexpensive and almost totally maintenance-free.
The new system will be able to eliminate the operational and maintenance problems that plague the present-technology suppression systems, as well as ensuring improved employee working conditions and a dust-free environment. s
Ed Hayes is the president of H&H Solutions, Inc., in Gettysburg, Pa.
For Maximum Bearing Life, Look to the Lubricant
Editor’s Note: This monthly column is supplied exclusively for AggMan by The Equipment Maintenance Council (EMC).
One
of the factors which contributes to maximum bearing life in screens is
proper lubrication. The incorrect lubricant or improper viscosity grade
can lead to wear and contamination problems that may eventually resonate
throughout the entire system. While the ultimate lubricant choice for
any component should be based on the manufacturer’s recommendations,
some information on the interaction, performance and additive chemistry
of lubricants can be helpful in choosing the final product.
“To better understand the role of additive chemistry in lubricant performance, it is important to review the physics of anti-friction bearing lubrication,” said Drew Nagle, OEM product manager for Castrol Heavy Duty Lubricants Inc., in Baltimore, Md.
Roller bearings in screens are designed to operate in a “hydrodynamic lubrication” environment. Simply defined, hydrodynamic lubrication is a full fluid film, which occurs when the relative motion of the sliding (rolling) surfaces cause the formation of a fluid film sufficient enough to separate surfaces. As speed increases, so does film pressure, thereby lifting and separating opposing surfaces.
“In theory, there should be no contact between mating surfaces during operation,” observed Nagle. “In reality, a full fluid film does not always occur and metal-to-metal contact can be anticipated under conditions of heavy and high shock loads.”
Once the fluid film is compromised and bearing surfaces contact with mating raceway surfaces, “boundary lubrication” has occurred. This type of lubrication is common under heavily loaded conditions or during machine start-up or shut down. Over time, the wear generated from boundary lubrication will cause component and possibly system failure. Using a lubricant with the proper viscosity and high quality anti-wear or extreme pressure (EP) additives can minimize the effects of boundary lubrication.
Extreme pressure lubricants utilize additive chemicals that react with metal surfaces to reduce welding and tearing during boundary lubrication. The EP additives in the lubricant coat metal surfaces with a sacrificial film and become more active under high contact pressures or as a result of the higher operating temperatures that accompany friction. These additives are fully activated during extreme high-temperature operation and when heavy loads are present. Their effectiveness is actually limited when operating temperatures are not high enough to fully engage the EP additives. For this reason, the lubricant viscosity is extremely important.
“There is, however, a caution to be placed on lubricants with EP additives,” said Nagle. “EP additives, which can be activated by higher temperatures, pressures and loads, have varying levels of reactivity to metals. Active EP additives, under certain conditions, could cause metallic corrosion and ultimately affect the ability of the oil to withstand and protect components during high operating temperatures.”
Nagle mentioned that although new chemistries are being developed to combat this problem, the more powerful EP additives (specifically sulfur-phosphorous) can have a highly corrosive effect on yellow metals such as brass or bronze, particularly at temperatures of 60°C (140°F) or higher. EP additives will aggressively compete for surface retention to protect metal surfaces; this may corrode softer yellow metals.
Nagle suggested that when selecting lubricants with these additives, it is best to use them only when necessary and to the mildest degree possible. EP lubricants are typically used in high wear, high shock load applications such as spiral bevel, herringbone, helical and hypoid gears. The alternative to an EP lubricant would be an anti-wear or non-EP lubricant.
Anti-wear additives are similar to EP additives in that they coat metal surfaces. But anti-wear additives are activated at lower temperatures. The most common anti-wear additive is a zinc-phosphorous compound, usually zinc dialkyldithiophosphate (ZDDP). These additives are typically used in higher speed, mild boundary lubrication conditions. Although lubricants with EP additives can carry heavier loads, lubricants with anti-wear additives can usually meet or exceed industry test standards for API GL-4 performance.
Additionally, zinc anti-wear compounds have a low level of reactivity with yellow metals and resist oil breakdown or oxidation. When exposed to high temperatures, an oil must have good oxidation stability to avoid the formation of lacquers and residues that can impede the operation of the bearing. Anti-wear additives are typically stable at temperatures up to 100°C (212°F), but equipment should be monitored and caution should be exercised if equipment is operating at temperatures above 82°C (180°F).
The bearing manufacturer typically has data available to make sound lubricant recommendations for their components and may even have performance data on the use of EP versus non-EP gear lubricants. Nagle suggested that to ensure long component life, have an understanding of the loads, bearing speeds and bearing temperatures for a particular application and choose a high performance, field-tested lubricant within the manufacturer’s recommendations.
The Equipment Maintenance Council (EMC) is an individual membership organization comprised of equipment maintenance professionals. Its members are responsible for the purchase, maintenance, employee training, shop facilities and parts management of leading corporations and government entities that utilize heavy, off-road equipment. Its members also represent the major manufacturers and suppliers of the heavy equipment industry. EMC provides end users with cutting-edge education, and it is the only organization to offer a certification program for the industry, the Certified Equipment Manager (CEM). For more information, contact Stan Orr, CAE, EMC executive director, at (970) 384-0510, e-mail at ceo@equipment.org, or visit EMC’s web site at www.equipment.org.