Studies on Off-Gassing during Storage of Wood Pellets

Abstract

Storage of wood pellets in warehouses results in emission of gases like CO, CO2, and CH4. These gases when they cross the threshold levels will result in serious health problems of pellet warehouse workers. The objective of the present work was to investigate the emission of these gases at ambient storage conditions. Two airtight adiabatic reactors were designed and fabricated for the present studies. Sensors were arranged to measure the temperature along the pellet bed as well as in the headspace also. Commercial wood pellets procured locally with 3.6 % moisture content (w.b) and 10 % fines were used in the experiments. The wood pellet properties measured were pellet density, specific density, porosity, bulk & tapped density and durability. The reactors were filled with wood pellets and were insulated to prevent any loss of heat. The gases were collected for every 15 days of storage using gas sampling bags with help of a vacuum pump. The gases were further analyzed using Gas Chromatography. Results indicated the emission of CO was considerable and reached 800-900 ppm, CO2 around 1800 ppm and CH4 was around 25 ppm. The temperature of the pellets during the complete storage period was around 19± 1 °C. Increasing the moisture content of the wood pellets from 3.6 to 10 % by adding water resulted in an increase in temperature of the wood pellets by 3-4 °C. At the end of 150 days of storage the pellet was very soft and around 70 % dissolved which can be mainly attributed due to change in the moisture content during storage.