BioCycle October 2008, Vol. 49, No. 10, p. 38
Operators and facility managers offer recommendations and guidance for moving a composting facility indoors.
AS concerns over emissions and odors mount, an increasing number of composting facilities are moving indoors. This has many obvious advantages, including the ability to more completely control aspects of the composting process, contain odors and protect feedstocks from inclement weather. However, not only is it expensive to construct an industrial building, it must be well equipped to prevent corrosion from the high levels of moisture and gases emitted from the composting process. Options include preengineered steel, concrete, fabric, pressure-treated wood and stainless steel. After-market products include epoxies, foam encapsulation and other corrosion inhibitors. This month’s Operator Insights article examines some of these building and corrosion control options on the market, and offers perspectives and lessons learned from operators in the field.
The Siemens IPS Composting System, an enclosed in-vessel, automated composting process, has dozens of systems installed in various types of buildings. Rich Nicoletti, Technical Sales Manager for Siemens IPS, offers criteria and questions to consider before choosing a building to house a composting operation. “From a corrosion perspective, the main question should be, ‘What are the various corrosive gases that can be generated and what are the potential concentrations?'” This question, he elaborates, should be broken into more specific queries: What is being composted and how much? What blends of materials are being composted, and how does that affect gas formation, pH, expected temperatures, etc.? What type of aeration will be used, and how many air exchanges per hour will the ventilation system be designed for?
Nicoletti cites the example of composting biosolids, which can emit high concentrations of ammonia, inside a steel structure. “Galvanizing or plating with epoxy paint hasn’t held up well over time in those cases,” he says. “Epoxy paint can hold up if good quality control measures are employed during metal preparation, priming and final application,” he says. “From what I’ve seen, however, it is next to impossible to ensure that level of quality control, and if there is the slightest misapplication or abrasion, the surface is compromised. Once corrosion starts, even in a pinhole, it spreads underneath and eventually flakes off.” Two-part foam/epoxy systems appear to hold up the best in steel structures, adds Nicoletti. Because the material is put on relatively thick, at one to two inches (as opposed to epoxy paint at eight millimeters), there is much less chance of pinholes or abrasions, where corrosive gases might enter.
WeCare Organics, based in Jordan, New York, manages several indoor composting facilities around the U.S. “When placing a composting operation indoors, regardless of what you are processing, spend ample time with your engineer or steel manufacturer reviewing corrosion control applications that can be applied prior to start-up,” advises Jeffrey LeBlanc, President of WeCare Organics, LLC. “It will be money well spent.” He recommends focusing on the key processing areas (e.g., mixing, composting and curing), because those have the most potential for severe corrosion, if not properly treated.
Besides those areas, LeBlanc notes that the most important part of a building is the roof. “Spend the time evaluating different roofs because if you have a bad roof (e.g. leaky, weak in structure) you will have a bad building. Do not waste anytime or money on fixing a building without making sure the roof is functioning properly.” WeCare was recently awarded a contract to operate the composting facility at the Burlington County Resource Recovery complex in New Jersey. The facility uses an IPS system to compost biosolids and wood chips, and is permitted to receive food waste. The contract calls for $3.8 million in capital improvements, including corrosion control. “We will be replacing 100 purlins and hundreds of braces, hangers and rods prior to the application of Stayflex foam to prevent future corrosion,” says LeBlanc.
SPRAYED ON PROTECTION
The Stayflex™ system, manufactured by Preferred Solutions, Inc. (PSI), is a two-stage sprayed process that thermally insulates and prevents corrosion, and can be used on any type of building. First, the building is sprayed with Staycell™, a polyurethane foam insulation. For a preengineered steel structure, PSI recommends two-inches thick on the ceiling and one-inch thick on the walls. “By spraying the foam, the building becomes seamless, unlike conventional insulation materials that have joints and seams,” says John Stahl, President and CEO of PSI. The sprayed foam expands to 25 times its original volume, which means it fills small cavities that are formed when corrugated roofs and siding are fastened to the steel supports of a building. Those spots, notes Stahl, are notoriously difficult to clean and paint.
After the insulating foam is applied, Stayflex, a thin hard-shell product made of vinyl ester resin, is sprayed on top at 1/16-inch thickness. Commonly called fiberglass resin, this is the same material used for gasoline and chemical tanks because of its chemical resistance and fireproofing properties. Stayflex creates an impermeable surface that can be pressure-washed.
Because this system can be used either as a preventative or as a retrofit for corrosion control, the composting industry has become a large growth market for PSI, with over two million square feet installed in new and existing composting facilities. Unlike epoxy coatings and paints, where corrosion must first be removed with an abrasive, only minimal surface preparation (such as air blowing) is needed before application. “Preengineered steel buildings are the lowest-cost option for new construction, but are highly susceptible to corrosion,” says Stahl. “With our system, a low-cost building becomes a viable option for the composting industry.”
Installation is relatively quick: “Four people can spray 400 to 500 square feet/hour,” says Stahl. “The initial installation cost can be higher than painting, but the long-term performance is more cost-effective due to the limited service life of paints and resultant corrosion.” The material can be installed in stages to accommodate a budget, and to allow a facility to continue composting.
RETROFIT IN IOWA
The City of Davenport composting facility in Iowa did just that, installing the Stayflex system over three years to manage its corrosion problems. “We were in full operation during the installation, closing down sections of the composting hall with tarps, about 20,000 square feet at a time,” says Scott Plett, General Manager of Davenport’s composting facility.
The operation is housed in a 134,000-square foot building, and has an annual throughput of 35,000 wet tons of biosolids, 10,000 tons of yard trimmings and 2,000 tons of new wood chips sourced from a local sawmill/lumber company. The building is made of preengineered steel, which was covered with a two-coat epoxy prior to installation in 1995. “The epoxy worked for about 10 years, but then it started peeling off and cracking, and corrosion became a significant problem,” recalls Plett. “At one point, support cables in the composting hall that crisscross beams in the ceiling began to snap due to corrosion.”
After replacing the support cables, Plett looked for alternatives to protect the building’s structural steel. “There weren’t many viable options for corrosion in an existing building,” he says. “So we replaced cables and electrical conduits that had been corroding, took out all of the insulation, and coated the ceiling and structural steel with Stayflex. Although there was no down time in the installation, it was more difficult to operate with 20 percent less space in the production area.”
Corrosion didn’t just damage the walls and roof at the plant, but also the in-floor aeration system. “The original compost trenches were one-meter long sections of precast polymerized concrete, placed end-to-end with a trench cover on top,” explains Plett. “Over time, with negative aeration on the piles, expansion and contraction from changing temperatures fatigued the sidewalls of the trenches. The galvanized metal lip of the trenches corroded quite rapidly, and the concrete cracked after seven or eight years, with the trenches collapsing on themselves.” They cut out the concrete, put in stainless steel trench cover frames and new rebar and poured new concrete into a mold forming the new trenches in place, as one solid piece.
About 60 percent of the trenches have been replaced in that manner, as needed. Also replaced due to corrosion were the blowers for static piles. The originals were five-hp steel fans, with corrosion coating on the inside, but the hot, acidic air pulled through led to rapid corrosion, and in turn, gas leaks. After replacing them with all-aluminum housing and fan blades, there was a dramatic reduction in the amount of odors present in the blower galleries.
COATINGS AND ADDITIVES
Other options for corrosion control on conventional steel and concrete buildings include protective coatings, surface preparations and construction additives. Among the products manufactured by Cortec Integrated Solutions is a permanent protective coating called Corrverter™, which can be applied directly to corroded surfaces. “It converts the rust and then acts like a primer,” says Bob Boyle, Technical Sales Manager for Cortec. “But unlike similar products, it contains active corrosion inhibitors, instead of just tannic acid.” The company’s surface preparation products clean metallic areas without leading to corrosion. “For instance, VpCI 422 can be used as a dip or gel to remove rust from a surface without attacking the good metal underneath,” explains Boyle. “Washing down equipment leaves it wet, thus enabling corrosion.”
One product line of interest to the composting industry is Migratory Corrosion Inhibitors (MCI), which can be blended into concrete for new construction, or used to repair existing structures. “This could be used for repairing mortars and grouts where small batches are made to patch a section,” notes Boyle. “Because it’s common for the alkalinity of concrete to change, a ‘patch’ can actually induce corrosion. MCI stops this.” There also are surface applied inhibitors, which travel through the concrete to the embedded rebar or structural steel, where it forms a protective film.
If corrosion already has caused significant structural damage, repair and control products may not be cost-effective or feasible. The Lunenburg Regional Community Recycling Facility in Nova Scotia was one of the first to compost residential source separated organics, dating back to 1994. It processes 11,000 to 12,000 tons/year of organics from several municipalities (a 300-mile radius), 80 percent of which is residential.
A 44,000-square foot preengineered steel building houses a sorting line for recyclables, processing equipment for source separated and mixed organics, and an Ebara wide-bed composting system. “Corrosion was noticeable after just two years of operation, but we didn’t know to what extent,” says Kevin Wentzell, Assistant Operations Manager at Lunenburg, who was hired when the facility opened in 1994. “Eventually, part of the roof was torn off because the screws were completely gone. Then sprinkler pipes started to fall from the ceiling, making the state of the building a health and safety issue.”
Although it’s common knowledge now that preengineered steel buildings used for composting should be properly treated to resist corrosion, Wentzell points out that as an early adopter, they didn’t have the opportunity to learn from others. Once the building became a health and safety issue, the choice for Lunenburg was to either put up a new building with a new roof, or shut the facility down. “A new preengineered steel building, properly coated with epoxy would take months to put up, and cost us around $4 million to $5 million ($CAN),” says Mike Fox of Lunenburg. “We were awarded $1 million for upgrades, and went with a fabric structure to fit that budget.”
Lunenburg decided to deconstruct its existing building and put a Cover-All® fabric structure on the existing foundation (modified slightly to fit), all while continuing to compost. Cover-All uses a steel frame made with ViperSteel that is triple-coated with Gatorshield galvanization, and a cover made of DuraWeave, a polyethylene fabric with UV light protection. “The main advantage for Lunenburg seemed to be the two to three week installation time, since they have been continuing to compost while deconstructing the old building, and will only have to put operations on hold for about two weeks,” says John Ray Lawrence of Cover-All. “Due to the quick installation time, and the ability to work with the existing foundation, the cost was much lower than other options.”
Lunenburg’s new building will be a 90 by 252-foot Titan model, but is essentially a custom structure, with a number of side entrance doors, 12-foot leg extensions to clear the compost turner, and adaptations to fit the existing foundation. The deconstruction process has been underway for several months, with the Cover-All installation beginning in early October. The structure will have individual panels of 12-foot fabric installed between each metal truss to allow sections to be replaced when old or damaged. “The design of individual panels is actually more rugged than a continuous cover, with an aluminum extrusion that is screwed into the top side of the truss, and the fabric following the track up and over the building,” says Lawrence. Besides replacing sections, which are expected to last 18 to 22 years, the building could be made longer with additional sections if expansion were required at some point.
An additional liner is available, using the same DuraWeave fabric on the interior to cover the exposed steel and add insulation. “An interior lining would add insulation of about R5,” says Lawrence. “Lunenburg decided against this feature due to budget constraints – the price is calculated by the foot, but it would’ve probably increased the overall price by about 20 percent.” Lunenburg did, however, decide to have all nuts and bolts protected with Sunseal, a relatively inexpensive anticorrosion feature expected to increase the lifetime of the parts.
Several other companies manufacture fabric structures as well, with different designs and materials (e.g., aluminum frames instead of steel). “In the last five years, there’s been a tremendous awareness of the benefits of fabric structures,” says Barry Goldsher, President of ClearSpan. “The fabric lets all natural light in, so little to no daytime lighting is needed, you never have to clean it, painting isn’t necessary, there are no worries about dents, etc. They’re a great fit for the composting industry.” ClearSpan sells over 10,000 fabric structures per year, using Allied GatorShield galvanized steel frames, and a woven poly fabric. About half of its sales are for greenhouses, says Goldsher, but manure storage also has been a core business sector. “In 28 years, we’ve never seen rust in a building storing manure, which is a high-ammonia environment,” he continues. “All of our markets are selecting fabric buildings over conventional ones for the same reasons – less site prep, much lower cost, cheaper to maintain, property tax is lower or nonexistent, and they can be disassembled and relocated or sold.”
Part of the increased interest in fabric structures, says Goldsher, stems from a growing concern about spreading raw manure. “Whether used for manure storage or composting, more farmers are using fabric structures to manage their manure and waste,” he says. “One large project in the works is at Lowell Brook Farms in East Cannon, Connecticut. They plan on using four ClearSpan buildings for composting and anaerobic digestion, processing manure and MSW.” He anticipates that the Lowell Brook project will be completed by early January 2009.
Universal Fabric Structures (UFS) recently introduced a new, smaller model of its fabric structures to meet the needs of operations with lower budgets. The company offers seven different models of frame-supported membrane structures. The frames are constructed of either aluminum or galvanized steel, with a heavy-duty PVC coated polyethylene fabric treated with fungicide to resist mold. “Our buildings are capable of holding a negative pressure, which can be an important factor for odor control,” says John Kirsh of UFS. “Also, they can be equipped with inner liners and additional insulation, but this has been more popular with commercial applications than in composting buildings.” Waste Options, a mixed waste composting facility on the Island of Nantucket, Massachusetts, installed a UFS building four years ago to house its active composting windrows.
Commercial pressure-treated wood structures are another option. “High grade wood structures have held up well, as long as the fasteners are properly designed, with stainless steel being the best,” says Rich Nicoletti. Bristol, Rhode Island has been composting biosolids and yard trimmings using a Siemens IPS system since 1993 in a building constructed of concrete blocks and commercial pressure-treated wood, located on top of the town landfill. “The concrete pilings go down about 30 feet and rest on bedrock,” says Matt Calderiso, Superintendent of the Bristol Water Pollution Control Department, who’s worked at the facility since it opened. “The building is stable, although the area around it settles, since the material in the landfill is active. In 16 years, the surrounding area has probably dropped five or six feet, causing us to rebuild the structure’s apron three times.”
Calderiso reports that there haven’t been any major problems with the pressure-treated wood or the roof. “We use moisture sensors on the wood once a year to test levels, but haven’t had any trouble,” he says. “Our ventilation system is set up for 12 air exchanges/hour, and due to moisture-laden dust clogging, some of the ductwork has been replaced. We also replaced some piping in the drainage.” The facility also upgraded its compost agitators. “We increased the horsepower and went with stainless steel drums, but other than that, we haven’t changed much,” he adds.
A last option to consider is a building with stainless steel lining. This can be extremely effective for resisting corrosion, but is quite costly. A recent example of a stainless steel building is the biosolids and yard trimmings composting facility in Fairfield, Connecticut, which started operating in 1989. When the facility opened, it was housed in a standard steel building with industrial type paint. “During construction, a lot of the panels and members were scratched and that led to places where corrosion started,” says Richard White, Director of Public Works for Fairfield. “About five years into operations, we noticed that the building was rusting badly. We hired a consultant to develop a plan to stabilize the building, which involved installation of a false ceiling to reduce the ventilation requirements, rebuilding the ventilation system and sandblasting and repainting the beams and columns.”
In 2005, a structural engineer evaluated Fairfield’s building and stated that it was near the end of its useful life. As it researched replacement options, White notes that their primary goal “was to find a building material that would last and had a guarantee.” Fairfield opted for stainless steel, purchasing the Behlen CORR-SPAN® model. “This design uses deeply corrugated heavy steel panels for the walls, ceiling and roof,” explains Colin Tooth, Vice President of Sales and Marketing for Behlen. The inside of the building does not have any exposed columns or frames, providing a smooth surface that minimizes build up of contaminants and facilitates cleaning, he adds. Five Behlen buildings have been constructed for composting, with the City of Edmonton, Alberta’s being the largest at roughly 240 by 1,000 feet.
Fairfield also replaced its main compost agitator, installed a computerized control system with new temperature probes and replaced the blowers. “A fuel cell was installed that supplies heat to the building from a heat exchanger to reduce fogging,” says White. “The electricity generated is fed into the plant’s grid.” There are also plans to install solar panels to generate electricity.
In short, choosing a building for a new or existing composting operation involves many considerations. With different styles and types of material to choose from, there are several options for composting facilities looking to move indoors, or fix a corroded building. Concludes Rich Nicoletti, “General building rules I have regarding corrosion are: Any insulation material or system that has the potential to absorb or trap moisture is not advisable (e.g., Batt type insulation has failed miserably); Design the ventilation system for 12 air changes per hour, with the ability to reduce via two speed or variable speed fan motors; and, All internal hardware, whether ducting, fasteners, supports, lights, doors/windows etc., needs to be stainless, aluminum or plastic of some sort.”
October 22, 2008 | General
Buildings And Corrosion Control
BioCycle October 2008, Vol. 49, No. 10, p. 38