How to prevent self-ignition of pellet factory

From small spaces heating to 600 megawatts of power plants, wood pellets are widely used as fuels for home and industrial applications at all sizes. If the wood comes from a sustainably managed forest, the pellets are considered renewable fuels. Using them instead of fossil fuels such as coal can help reduce carbon dioxide emissions and mitigate climate change.

Wood pellets are inherently flammable and can be ignited from a variety of sources. Large amounts of stored wood pellets may oxidize, which results in self-heating and may result in spontaneous combustion. In addition, the dust of the pellets will cause dust explosion under certain sealing conditions when dispersed and ignited.

Fortunately, there are techniques to detect the early stages of spontaneous heating and combustion, providing operators the opportunity to prevent problems and avoid costly losses.

Gas Detection

◢  Carbon monoxide (CO) monitoring is the most efficient way to detect spontaneous heating or combustion in an enclosed space such as a silo or shredder. CO detection can quickly and clearly indicate that spontaneous combustion is occurring.

◢  The concentration of CO in the ambient air is very low, and as the spontaneous combustion begins to produce a large amount of this gas, the rapid increase in CO concentration is a clear signal that action is required. The measurement of CO in the pulverizer is particularly important. In addition to the risk of introducing a burning material, the machine can perform a large amount of mechanical work to break up fuel that could cause a fire or explosion.

◢  The risk is small when the mill is running because the pellet concentration is above the upper explosion limit. However, whenever the grinding starts or stops, the concentration inevitably goes through the explosion range, and if there is a burning material, a potentially serious accident is highly likely to occur.

Temperature Measurement

◢  The action of bacteria and fungi causes the temperature of the storage pile to rise, whether open or closed. Temperature measurement is the most effective option for outdoor locations.

◢  The easiest way to scan a storage heap is to use a handheld thermal imager. Such devices are relatively inexpensive, but intermittent measurements mean that spontaneous heating cannot be detected. A fixed imaging system is preferred because it allows the operator to store and compare images over time. In addition, the image processing software measures the temperature on different areas of the storage stack and can also exclude short-term fluctuations, such as vehicles passing through the field of view.

◢  Temperature measurements can be made on a conveyor belt using a line scan-infrared pyrometer that uses a single detector with a high speed scanning mirror to produce up to 1,000 discrete readings across the width of the conveyor. The movement of the conveyor allows the scanner software to create a two-dimensional image of the material on the belt and display any hot spots associated with the burning material.

◢  Natural heating and spontaneous combustion pose risks anywhere in the processing and use of woody biomass. Choosing the right test method can significantly improve site safety by reducing fire risk.