Patent EP-2189512-A1 (EP)
Inventor: LEBOUTTE DIDIER
IPC: C10B53/02
Filed: 2008-11-24
Abstract: The process of heat treatment of lignocellulosic biomass at maximum 300[deg] C under controlled atmosphere in the absence of oxygen, comprises mixing the biomass in a reactor through a hot gas flow, primarily drying the resulting biomass, and roasting the dried biomass (5), where biomass undergoes one or more exothermic transformation reactions. The reactor is provided with a unit for conveying and controlling the forwarding speed v of the biomass through the reactor, a heating unit with gas flow, a unit for collecting steam and gas, and a unit for measuring the pressure in the reactor. The process of heat treatment of lignocellulosic biomass at maximum 300[deg] C under controlled atmosphere in the absence of oxygen, comprises mixing the biomass in a reactor through a hot gas flow, primarily drying the resulting biomass, and roasting the dried biomass, where biomass undergoes one or more exothermic transformation reactions. The reactor is provided with a unit for conveying and controlling the forwarding speed v of the biomass through the reactor, a heating unit with gas flow, a unit for collecting steam and gas, a unit for measuring the pressure in the reactor and the pressure of collected steam and gas, and a unit for measuring and controlling the temperature in the reactor. The forwarding speed v and temperature T of heating gas is adjusted according to recorded temperature to ensure: a separation in the time of steam emissions obtained from the drying of gas and pyrolysis gas obtained from the roasting; and a homogeneous and constant roasting at the end of the process. The roasting takes place in an accurate and reproducible interval at a place of the reactor on the forwarding path of the biomass. The reactor is a rotating furnace, a screw furnace or a multiple hearth furnace comprising a series of N 0floors (1) or circular baking plates (2) laid above one another in a steel envelope (3) lined with insulation, a vertical rotating shaft of rotating speed (omega ) laid along the furnace axis bearing arms (4) equipped with back support for mixing the load and moving through holes through each floor. The biomass is loaded at floor top and moving downwards to form a sturdy bed on each hearth and is heated by a hot gas flow to carry the hearth at a temperature for forced drying and roasting the biomass. The speed of rotation of the shaft and the temperature T of heating gas is controlled during complete roasting of the biomass at the floor N. The complete roasting is characterized by a peak of gas pressure peak for roasting almost entirely confined to the level of N floor. Forced drying of the biomass is carried out by one or more previous N' floors, where the localization of gas and steam for forced drying is determined by the position of the pressure peak corresponding to the process. The furnace comprises 6 floors, in which complete drying is entirely carried out in the floors I to III and the roasting is done in floor IV. The steam and gas for forced drying are extracted at the level of floor N-1. The pyrolysis gas for roasting is extracted at the floor N and used as fuel, and oxidized partially in the floor N. The heating gas temperature and the rotation speed of the shaft of the furnace are controlled by analyzing the composition of gas collected from different floors, and pyrometric measurements at different floors. The feeding in biomass of the multiple hearth furnaces is adjusted continuously to maintain the thickness of the constant stocky bed. A sprayer is installed in floor N and used for cooling the heat treated biomass by water vapor at low temperature to prevent its ignition when it is exposed to the air at the furnace outlet. The sprayers are regulated to obtain 3-4% of water in the biomass, which corresponds to the hygroscopic equilibrium of the roasted wood. The extraction of the treated biomass of the furnace is carried out using a cooled screw of sufficient length to bring the temperature of the heat treated biomass below the ignition point.