Pyrolysis Process Analysis in Wood Pellet Silo Fire

Wood pellet silo fires accommodating in addition to endangering also have the potential to cause millions of dollars in losses. The wood pellet container silo is used to temporarily store the wood pellet before it is shipped to the destination country of the buyers or to temporarily accommodate the wood pellet from the seller or producer before being distributed to the users. The typical silo capacity is 15,000 tons and a number of silos are also located close to a wood pellet mill. This makes the wood pellet mill can also burned if there is an uncontrolled fire in the silo that accommodates the wood pellet. At present it seems that there is no silo that accommodates wood pellets in Indonesia because Indonesia is not yet a large producer of wood pellets or users of wood pellets. These silos are usually found in a number of countries that have become large producers of wood pellets such as America, Canada and a number of countries in Europe. The biggest wood producers can be read here.

Charcoal production

The characteristics of wood pellet silo fires in general are unique and unlike the case of fires in general so the handling is also somewhat different. Almost all of these wood pellet silo fires occur due to microbial activity (anaerobic fermentation) which produces heat, thus reaching the ignition point of the wood pellet. And because of the lack of oxygen the thermal process in the wood pellet is a pyrolysis process. So there are two sequential processes in the wood pellet silo fire, namely fermentation and pyrolysis or biological and chemical processes. To overcome the occurrence of anaerobic fermentation and pyrolysis as the cause of the silo fire, the chain of causes must be severed, which is to supply sufficient air to the entire pile of wood pellets in the silo. This can be done by providing adequate air ventilation to the pile of wood pellets in the silo. Besides that, the wood pellet is not stored too long in the silo.

Then what if there is a fire in the silo? In general, silo fire needs to be known for several days because the location of pyrolysis in the middle of the wood pellet pile inside the silo and with a slow processing rate. Indications that can be reflected between the concentration of CO (carbon monoxide) and other O2 (oxygen). The greater the concentration of CO, pyrolysis proves to be a long time. CO gas is also very dangerous because it can eliminate the awareness to death, if exposed to certain concentrations. Exposure to carbon monoxide (CO) can restore the central nervous system and heart. Conclusions from mild poisoning contain headaches and nausea at contributions of less than 100 ppm. Concentrations as low as 667 ppm can cause 50% of the body's hemoglobin to turn into carboxyhemoglobin (HbCO). This causes hemoglobin can no longer bind oxygen so that death can occur. In the United States, the Occupational Health and Safety Administration organization reports at work at 50 ppm. The smaller the concentration of O2 and the greater the concentration of CO means that most of the oxygen in the contribution is used for the pyrolysis process. If the CO concentration is high, but also the O2 concentration also increases, it is feared that there will be a great danger, because an adequate supply of oxygen will change the chemical process from pyrolysis to combustion. Ventilation and all air holes must be closed.

Pyrolysis process in stove

Slow pyrolysis process or carbonization itself is generally used for charcoal production or maximizing the yield of solid. In this process there are three main variables to be controlled namely residence time, temperature and heating rate. Slow pyrolysis process or carbonization with the main product in the form of charcoal operates with a small heating rate. This makes the fire on the silo takes a long time to find out. And if all the pyrolysis process variables in the wood pellet silo can be controlled, a charcoal product with a conversion of around 30% or 5,000 tons will be produced. Under these conditions, the wood pellet silo functions as a carbonization furnace that operates batch direct heating and is expected to take weeks to complete one cycle of the pyrolysis or carbonization so that all wood pellets are converted to charcoal.

The importance of safety instrumentations in wood pellet silos

Control room

The use of gas and heat sensors is important to use in the wood pellet silo. In addition to monitoring the conditions in the silo, information from these sensors should also be connected to safety devices, for example when there is a CO gas concentration of up to 2%, then an alarm sounds, closing all ventilation holes (except the top ) and nitrogen gas is injected from the bottom into the silo so that the conditions become inert. But if the CO gas concentration is above 2% and O2 is above 5% then the nitrogen injection is carried out from above. Wood pellets from the silo can be discharged when the O2 concentration is less than 5% and CO is very low and released in a safe open location. The more complete the sensor is used, the operating conditions in the silo are more comprehensively monitored. But when the entire airway ventilation has been closed but it turns out there is a high concentration of O2 and CO, it is possible that there are leakages in the silo or acceleration of the pyrolysis reaction. A number of safety procedures can also be easily carried out if complete information can be obtained so that the losses incurred can be minimized including the most important safety of human life.

Anticipation and prevention of these accidents is important, so these efforts must be carried out optimally. When there has been a fire at the top of the silo, the use of nitrogen gas is no longer effective. Flames at the top of a silo can occur because pyrolysis gas products (combustible gases) burn. If the conditions are like that then blackouts can only be done with water and with the risk of the silo collapsing. Other things such as the operator's life safety are threatened and tens of thousands of tons of wood pellets are damaged. Each operator is also required to use breathing aids if they are in such a risky location. This further confirms that anticipation and prevention are very important.