In August 2017, a silo fire broke out in a 350,000 tonne/year particle plant at PacBio in Prince George, British Columbia. The fire was successfully extinguished. The result was the opposite of previous silo and dome fires. They generally result in the complete loss of the warehouse structure, causing significant damage to the surrounding infrastructure, and even the casualties of the personnel.
This successful result was attributed to the Pacific Bioenergy Management and Operations team and the first responders of the Prince George Fire Department, who all followed well-planned control and fire extinguishment plans. Thanks to PacBio CEO Don Steele and vice president of operations. The important guidance and support of President Shawn Bells and his team, as well as the author John Swaan. We can apply industry best practices to their tactical planning. They deliberate before acting and extract information from years of practical experience. They Carefully and carefully, the main goal is to ensure the safety of everyone.
What should not be done
Historically, there are some examples of this industry showing that the extinguishing of silo or dome fires was not very successful. This is due to the lack of knowledge about the characteristics of the wood particles, which are usually incorrect due to the operator of the granulat plant and the first responder. Strategies for self-destruction. The following incorrect strategies are the main causes of the loss of buildings and other assets. In the worst case, people are killed in several accidents.
Although water may help control the flame in an uncontrolled silo fire, spraying water at the top of pellets in silos, domes, or flat storage will not extinguish a smoldering wood pellet. Wood particles at the top of the stack absorb. Moisture swells and forms a layer of material that restricts the penetration of water somewhere in the center of the heap: The smoldering core is in place. The water that comes in contact with the heat of the pyrolysis particles generates carbon monoxide (CO) and hydrogen, which increases The severity of the fire, and is not conducive to extinguish the silo fire. Water may also form a spire or column in the silo, which may become a problem when trying to remove the cargo inside the silo.
If wood chips are removed from the silo, dome or flat storage pile before the pyrolysis activity in the core has extinguished, this can lead to disaster. The gas released by the pyrolysis activity is bad and dangerous, especially It is methane, CO and other life-threatening gases. The ignition of methane released from sawdust is very low, it ignites when it meets the smoldering core, and it gets oxygen from the air. In other words, when the particles are removed, When the smoldering core and pyrolysis gas are exposed to the atmosphere, the possibility of explosion or rapid spread is very high.
Best Practices
The first lesson is: The importance of making plans based on best practices and training local fire departments. Such incidents may cause major casualties and loss of life. Money can replace physical assets, but it cannot replace life. The safety of all on-site personnel and surrounding areas is a top priority. At PacBio, the PacBio team took steps to mitigate the incident. Every conscious step and all support resources are focused on security.
The PacBio operations team also maintains control over the actions taken, including the actions of first responders. The typical response of the fire department is to flood the fire with water. Control actions through the PacBio team avoid some 'do not do' behavior. George The Prince’s fire department trained on site and learned that silo fires are not routine accidents. The response measures need to communicate directly with the fire department, but they need to be controlled by the particle plant's operating team.
Taking the time to research information resources, make plans, and work with local firefighters are the main reasons for the success of the PacBio event. Drawing lessons from the success of other events can help determine the response steps taken during an accident.
The second lesson is: The injection of inert gas can significantly reduce the possibility of negative consequences. Fire scenes are likely to cause gas or dust explosions, which can lead to serious injuries and substantial property losses. Nitrogen is the most effective for minimizing these risks and provides a low-risk way to control the particulate heap while emptying the material. Smolder pyrolysis.
Nitrogen injection is considered a better solution because it is an inert gas that relieves the fire accident in the silo - it is easier to use in large quantities, easier to evaporate, and more economical than carbon dioxide. The use of nitrogen is used to control and extinguish PacBio The key part of the fire strategy.
In PacBio, the recommended nitrogen injection flow in the report was referenced, and taking into account the size of the silo, they quickly sent a call to local gas supplier Praxair. A mobile was mobilized from Edmonton, Alberta. Nitrogen carburetor and tank installations, and other tanker installations that follow. Natural gas and oil industries use this type of equipment on a regular basis. An engineer from Solid Industrial Solutions also came to the scene to assist in setting up the nitrogen distribution system. And control the nitrogen flow injection.
Based on the required nitrogen flow and volume, the PacBio team specified how to set up the spray gun to drive an 80-foot (about 24-meter) diameter silo. Call for mobilization of nitrogen within 24 hours: The vaporization unit was set up on-site, the injection gun was in place, nitrogen was dispensed System connectivity, nitrogen injection begins.
Several attempts were made to foam the top of the silo, but regardless of the foam density, the spray system initially installed for water was not sufficient to evenly distribute the foam on top of the particles to produce an effective seal.
After the oxygen content in the headspace of the silo dropped below 10%, the silo was emptied within 48 hours of nitrogen injection. The PacBio team safely handled and evacuated the removed material. The emergency personnel were equipped with respiratory equipment so that all People are safe. Wood particles and carbonized blocks from the silo are safely transported to a flat area away from the factory. Even when exposed to the atmosphere, there is no problem.
It takes about 7 days to evacuate 3,500 tons of over-fired materials. Each truck is safely moved to a safe area away from other fiber debris and is flooded with water when dumped to ensure there are no remaining hot spots.
The third lesson is: Ready to detect and control the silo / dome fire. Monitoring, detection and suppression systems must be installed and maintained in good working condition. The correct installation and operation of the thermal monitoring system will help to discover hot spots in the development of particle silos or domes. When the temperature monitor inside the silo is running When normal, an event warning will be detected and alarmed. The warning before smoke is observed will significantly reduce the loss of the product and the possibility of a more serious accident.
Carbon monoxide and oxygen monitors installed on the top of the silo can provide continuous measurements and can also aid in early event detection. Once nitrogen is injected into the PacBio silo, if there are no sampling devices already installed at the top of the silo to obtain readings, This will make it even more challenging to determine the level of gas required to safely remove material from the silo. Testing and maintaining these systems must be part of a weekly PM (preventive maintenance) program.
It is important to install a permanent, properly sized nitrogen injection system in a silo or dome and install a pipe in a safe location and connect them together. If there is no nitrogen and evaporator supplier nearby Factories should consider using the equipment in the field as much as possible. The fast assembly manifolds used in the PacBio plant are not optimal for controlling the flow to the gun. Managing uniform distribution of the appropriate flow in the silo will be more efficient and may be more Control the pyrolysis core quickly.
When managing silo fires, control of the silo or dome ventilation system is also critical. The system should have the ability to close and enclose the bottom cooling fan, as well as the ability to control the ventilation at the top of the silo. This minimizes exhaust gas flow and improves nitrogen penetration. , It is very advantageous to reduce the total amount of nitrogen required.
The installation of a suitable permanent water rinsing system that can both hold water and dispense the foam correctly at the top of the entire granule stack will be very effective. The unsealable silo or material top makes it easier for the injected nitrogen to escape and thus lowers The ability to control and stop pyrolysis. The PacBio event may be controlled with less nitrogen. If a bubble cap is used, the process may be faster.
The key reason
In most cases, the point of ignition that is suspected of causing pyrolysis activity is due to some foreign thermal debris. This may be due to ball mill roller bearings, conveyor system roller or conveyor belt failure, and possibly molten steel from hot maintenance. All of the above The cause of the accident.
Since wood particles are a biological product, self-heating may also be the cause of silo fire accidents. This may be due to microbial activity, chemical oxidation processes, moisture migration, moisture absorption, or a combination of these. As microorganisms are at higher temperatures It will die, so the process usually occurs in the temperature range of up to 45 to 75 degrees Celsius. Microbial activity produces primarily carbon dioxide and can be detected by measuring the concentration of carbon dioxide in the silo headspace. At higher temperatures, Fever originates from chemical oxidation processes. In wood particles, the cause is usually a chemical oxidation process, because the particles are more or less sterilized during the production process. Practical experience shows that this oxidation process is particularly prone to new production of particles. This is due in part to the oxidation of various resins contained in the wood.
Call for action
From producer to end user, stakeholders in the wood grain industry around the world must actively share knowledge of this event, adopt protocols and technologies to mitigate and hope to eradicate silo fire accidents.
This call for action includes all wood pellet industry associations and agencies, wood pellet factories, shipping terminals and power plant owners. For safety and reliability, these best practices must be managed by the wood pellet plant operations and related personnel Understanding and Adoption, Local and Regional First Responders and Fire Brigade, First Aid Training Institute, Government Workplace Safety Agency, Fire Fighting Equipment Provider, Wood Particle Treatment Supplier (Silo, Dome, Conveyor), Railway and Shipping Companies, as well as wood particle project developers, engineers and EPC contractors all need to be involved.
Any entity in the supply chain with silos or dome storage particles must be encouraged to assess whether their current wood grain storage systems have the capability to detect and control fire events. If there are defects, then the installation of protection technologies and equipment, including ventilation controls, is required. , Foaming equipment and nitrogen injection. The wooden particle plant, wood grain storage and transportation terminal should determine and establish its relationship with the nearest nitrogen supply and gas engineering service. The 10 to 12 hours shipping radius will provide sufficient response time. If the distance is far away, on-site nitrogen production system should be considered.
Any entity with a silo or dome storage in the supply chain must be encouraged to develop a fire accident mitigation and training program. They must ensure that all operators and firefighters who are summoned to the site understand the characteristics of the wood particles in the silo or dome, and How to fight the fire with maximum effectiveness in order to obtain protection only causes minimal danger and damage. All personnel should be familiar with the danger of the gas contained in the released smoke.
It must always be remembered: 'Not if there is going to be a fire, but when it will happen'. At any time, stakeholders should not be allowed to enter a state of complacency. Each stakeholder in the wood pellet industry must work hard to ensure 'if' It is not accepted as usual, and the chance of 'when' is close to zero.
However, if there is a 'when', all stakeholders must fully understand how to handle the incident and are fully prepared to handle the incident safely and effectively.
Author: John Swaan
FutureMetrics Senior Operations Specialist
