Bioenergy Plant Precautions
No matter the depth of familiarity an employee may have with power, pellet or biogas plants, safety should remain a major priority. Steam, pressure, heat, dust, electricity and lots of moving parts can equal the perfect recipe for disaster under certain conditions. While on the exterior some accidents seem impossible to foresee, almost all are preventable.
That’s the perspective of Beth Hurley, vice president of health and safety at Covanta Energy. Hurley, who describes her career path as “growing up with Covanta,” has been in her position since 1990. In her years there, she has seen significant changes in not only health and safety regulations, but also innovation in employee safety gear, hazard combat equipment and the adaption of rigorous required and voluntary safety programs and policies, which combined allow the company to boast an accident rate much lower than average in its National Bureau of Labor Statistics category.
Covanta Energy owns and operates both biomass power and energy-from-waste (EfW) plants and, while both possess many of the same hazards, and Hurley says EfW are somewhat unique due to the nature of their fuel. “Municipal solid waste (MSW) is delivered to us from a variety of haulers all over the U.S., and occasionally a load that we dub as a ‘hot load’ will come in, which means there is some thermal activity going on.”
If employees aren’t careful and the hot load is disposed of into the EfW facility fuel pit, a fire could result. “That’s a big area we’re focused on—safe delivery of MSW,” Hurley says. Sometimes the vehicle operators will know about a hot load, but not always, so there are procedures to address such instances. One includes tipping fuel loads onto the floor and having the load operator cut the waste by spreading it into a thinner bed for closer inspection. Most times hot loads will be detected in that fashion, according to Hurley, but other times it may end up in the pit and result in a visual indicator—smoke.
Though a rare occurrence, pit fires can be extinguished by fire cannons, stationary but rotatable devices that project high-pressure water into the desired area.
While pit fires caused by hot loads are one of the hazards best prevented before the fuel enters the plant, normal operating conditions inside a plant pose their own set of risks each day.
Potential Hazard Preparation
Hurley notes that plant evacuation plans are essential to ensure employees are able to exit in a safe and efficient manner if needed. An evacuation could be prompted by a variety of forces, including the plant being knocked offline, which can happen if it is struck by lightning. “We do have fire rods that protect us from lightning strikes, but occasionally lightening might get through and we have an event called a black plant,” Hurley says. “A fire and evacuation route would be used in an event like that.”
Catwalks, especially if elevated, access routes and moving equipment are potentially hazardous when employees are working on or near them. “Employees are trained to always be sure they’re on a suitable walking/working surface, which means it has the proper set of handrails,” Hurley says. “If in the event work takes them to an area which isn’t suited for that type of design, they may need to wear a harness and fall protection.”
Occasional cleaning activities are another potential hazard that could result in the release of particulate. “In that case, we’re always measuring and monitoring with various industrial hygiene methods to determine whether the particulate is a concern, and if it is, it’s usually known well in advance and they’re prepared by using a respirator,” Hurley explains. “They are trained for this situation, and have medical clearances to being able to protect themselves from inhalation hazards as needed.”
Gear such as respirators and protective wear are an essential component of safety, including hardhats, ear protection from noise, side-shielded safety glasses designed to resist impact breakage, long-sleeved shirts and pants for protection against heat and steam, composite-toe or steel-toed boots for protection against potential falling objects, and reflective vests for wear in dark areas. Additional gear may be required for different job functions, Hurley adds. For example, electricians who get involved in work with energized medium- and high-voltage electrical equipment wear some additional gear for protection against the release of electrical energy that could burn through garments. “This kind of new safety gear has been on the market since about 1999, and it falls in compliance with NFPA 70E Standard for Electrical Safety in the Workplace that requires identification of electrical hazards and equipping employees in a safe manner,” Hurley says. “Years ago electricians didn’t have that gear when doing a job, so they had greater hazard exposure. Today the garments we provide are much better.”
New employees at Covanta Energy are required to go through safety training, some of which is minimum regulatory training, but also beyond that; topic-specific training that is done upon employment, as well as on a monthly basis. “We also have turnover meetings, a continued communication of the conditions of the facility,” Hurley says. “It prepares employees going off work to convey status and transfer knowledge to the oncoming work team.”
So who’s responsible for overseeing normal/safety operations at a single plant day to day? “On the most basic level, the answer to that is everyone,” Hurley says. “Every employee has a critical responsibility to foresee and identify hazards, so we have a program that allows us to trickle up recognition of conditions and document them. If it’s not measured, it’s not well-known. We look for trends, ways to convey improvements that can be made, and hopefully, reduce occurrences of concerns. All of this plays into everyone’s participation.”
A lot of people think safety is common sense, but it’s really not, Hurley adds. “You’ll hear people say ‘be safe,’ but you can’t train them by just saying that.”
At pellet plants, safety protocol should be of the same caliber as at biomass power or EfW plants, but the majority of hazards stem from potential sources of ignition and fires. It’s important to understand what they are and how to prevent them, according to Nicole Forsberg of Firefly AB, a Swedish spark detection and fire and dust explosion protection system supplier.
Pellet Plant Safety
The most common ignition source generators at pellet plants are places where friction generates overheated material, Forsberg points out. Those places are numerous, and include dryers, dryer cyclones, intermediate storage, mills, presses, coolers, screens, pellet silos, filters, unloading areas and burners. “Glowing embers, sparks, overheated bearings and other hot particles within the manufacturing process can be dangerous and cause fires and/or dust explosions,” Forsberg says.
It’s also common for fires to occur as production stops and starts. “Think of the famous fire triangle—for a fire to take place, three elements are needed: oxygen, heat and fuel,” she explains. “In pellet production we have wood as the fuel and heat within most of the process, but less oxygen. When large amounts of material cover the process flows, only small amounts of oxygen are present. At process stop, all of a sudden there is more room for oxygen, and if the stop is at a hot stage of the process, the risk of a fire is significantly higher.”
Typical stages of the manufacturing process where a fire or explosion can take place within a process stop are in the dryer and in or around the hammer milling function.
Regarding some important steps and precautions to take in preventing fire hazards at a pellet plant, Forsberg says good housekeeping is very important, in order to keep any accumulated dust in or around machinery out of the way. “A solid maintenance schedule is good for many reasons, such as keeping any surfaces clean to prevent hazardous secondary dust explosions, as well as ensuring the machinery is in good shape,” she says. Having a proper dust extraction system is important for avoiding unsafe accumulation of dust.”
Conducting a risk analysis is key, as a plant developer should know where ignition sources are in order to design as safe a process as possible. “If you‘re designing a pellet plant, many risks can be designed out of the process,” Forsberg says. “When conducting a risk analysis, important parameters such as the quantity of material being conveyed, particle size, moisture in various sections of the process, temperatures, conveyor diameters, and the capacity of the fans are important to consider.”
Once a risk analysis is done, risk zones within the manufacturing process can be located and addressed with proper preventive equipment such spark detection. It’s important to design the extinguishing system in such a way that the process is stopped only in extreme emergencies, Forsberg notes, thus avoiding false positives. “Daylight-sensitive detectors can alarm if a ray of sunlight enters the process, which can cause unnecessary production stops and be costly down the road,” she says. “False positives from sparks that are not dangerous can lead personnel to being indifferent to dangerous detections versus serious detections, so this is another reason it is so important to have a system that only detects the true dangerous particulates.”
In terms of meeting hazard regulations, Forsberg says that due diligence is the best path forward. “They should review and understand Occupational Safety and Health Administration requirements and know the National Fire Protection Association guidelines, however, some of the information is over 5 years old, so researching and understanding common and recent industry standards could be the most important factor in determining the level of fire prevention needed or desired.”
Forsberg recommends every facility be aware of and follow the authority having jurisdiction (AHJ) and what standards/requirements are relevant for each case. The AHJ can be anything from a fire marshal to a building inspector from the local OSHA office. “OSHA has several guidelines for factories that one should be aware of, and the NFPA standards as well,” Forsberg says. “For the biomass industry, be aware of the NFPA 664: Standard for the Prevention of Fires and Explosions in Wood Processing and Wood Working Facilities, or the NFPA 654: Standard for the Prevention of Fire and Dust Explosions from the Manufacturing, Processing and Handling of Combustible Particulate Solids.”
Insurance companies may also have requirements for housekeeping, design or routines regarding safety and combustible dust, and some might offer free dust-testing. “To be on the safe side and ensure compliance and safe practices, I’d recommend anyone to contact the local OSHA office,” Forsberg says.
Overall, spending some time and money on safety and prevention up front can save a pellet manufacturer hundreds of thousands of dollars down the road. “Worst case is that you know how to act if an accident should occur, and the best case is you have prevented it from happening,” Forsberg adds. “You must be aware of the risks and dangers you’re exposed to in order to prevent them from being a danger.”
Author: Anna Simet
Managing Editor, Biomass Magazine