## Materials and Methods
### Process Description
#### 2.2.3 Productive Process
The gas fraction is composed of a diverse number of compounds, the so-called condensable gases, which will convert to the liquid fraction, consisting essentially of water, sugars, acids, alcohols, furans, ketones, terpenes, phenols, waxes and tannins. The permanent gases are made up of hydrogen, carbon monoxide, carbon dioxide, methane, other simple hydrocarbons, toluene and benzene. Other compounds may appear, such as furfural, but the amount is usually less, although its presence is often noted by the sweet aroma that denotes the beginning of its formation. These gaseous compounds that form during the biomass torrefraction process are commonly referred to as volatile organic compounds (VOCs). However, as can be seen, not all of them correspond to this designation, but are used in industry for practical reasons and for the uniformity of the gases formed. It is also common to all processes with an industrial dimension that these VOCs are valued energetically, so that the process is more energy-efficient, since it is necessary to provide thermal energy for both drying and torrefraction. In reality, the quantities of these gases can reach a level that can cause difficulties in their management, creating flows that are difficult to eliminate. Figure 7 presents an example of these condensed gases, collected in a container placed before these materials are injected for recovery in the furnace of the drying system. The torrefraction reactor ends in the discharge chamber, which is a section that has two main functions for the process. The first function is the elimination of gases released during the process. This is done by extracting the gases from the upper part of the discharge chamber, and directing them for energy recovery in the drying system furnace. The second function involves the transfer of the solid fraction to the cooling system, composed of a sequence of double-walled augers, where chilled water circulates using a cooling tower placed outside. The cooling system, composed of the augers, will reduce the temperature from approximately 300 \({}^{\circ}\)C to a temperature close to the ambient temperature. This is intended to make the product reach a safe temperature for the following steps, avoiding the ignition of the material when in direct contact with the ambient air. After traveling through the cooling system, the material is poured into a mixing tank, which also functions as intermediate storage, and which controls the admission of material to the conditioning pelletizer auger. It is in the conditioner that the moisture level of the material is corrected, since the moisture content is a determining factor for the pelletization process, working as a lubricant, on the one hand, and in reducing the pellet mill die temperature, on the other. Figure 7: Liquid fraction made up mostly of water. Despite being a product with low calorific value, its valorization allows the reduction of the energy costs of the process, at the same time that it allows the elimination of products that cannot be simply emitted into the atmosphere or dumped in the public domain. The pelletizers available on the market, from numerous manufacturers, are divided into two fundamental types: pelletizers with a horizontal axis with a ring die, and pelletizers with a vertical axis with a flat die. The most representative models of the first type are produced by Andritz (Graz, Austria), Salmatec (Godenstorf, Germany), CPM (Crawfordsville, IN, USA), Buhler (Appenzell, Switzerland) and Prodesa (Zaragoza, Spain), which dominate most of the market, mainly that of the large conventional biomass pellet plants. However, a large number of other manufacturers are disputing the market for small and medium-sized biomass pellet production units. Examples of such companies are La Meccanica (Cittadella, Italy), Muench-Edelstahl (Hilden, Germany) and Mabrik (Barcelona, Spain).