Pyrolysis, slow product yields with temperature

In pyrolysis the wood material is heated rapidly to about 500 °C at which temperature the wood decomposes to a maximum amount of liquid product. At lower temperatures more char is formed and less liquid and gas, and at higher tenperatures the energy requirements are higher without producing noticeably more liquid. The pyrolysis process is carried out in a fluidised bed where milled material is fed into the bed and the product stream is condensed at temperatures between 30 and 60 °C. The char is usually separated before the condenser and used as fuel - along with the gas -to provide heat to the fluidised bed. The fluidised bed may be bubbling or circulating. In both cases a fast pyrolysis is obtained in contrast to slow pyrolysis which usually yields lower amounts of liquids. 

Due to the wide range of processing conditions (temperature and residence time) available and feedstock options (woody biomass, agricultural biomass, and diverse organic residues) that can be processed in slow pyrolysis units, the yield and properties of biochar can vary widely. This provides an opportunity to optimize the production to yield biochar with properties matching its application. In their research Ronsse et al. (2013) and Zhao et al. (2013) showed that certain biochar properties are primarily affected by processing conditions (eg, surface area, pH, carbon sequestration potential), while others are mainly feedstock-dependent (eg, content of total organic carbon. 

Moreover, polymers 6 and 8 were pyrolyzed in bulk. These pyrolysis experiments were performed in a slow stream of nitrogen and the samples were heated to 1000°C at a rate of 10°C min", remaining at this temperature for 30 minutes Both of the ceramic products were black powders and in X-ray powder diffraction studies they showed only broad peaks of low intensity, indicating the presence of mainly amorphous material To obtain crystalline materials, the ceramic products were heated slowly to 1400°C where they were held for 5 hours. The X-ray powder diffraction showed exclusively sharp peaks, characteristic of P-SiC, respectively. The increased ceramic yield obtained by pyrolysis of the metal modified carbosilane 8, as compared with the polycarbosilane 6, can be explained by an increased concentration of carbon as impurity, which was additionally evidenced by elemental analysis. 

Slow pyrolysis of biomass operates at relatively low heating rates (0. l-2°C/s) and longer solid and vapor residence time (2-30 min) to favor biochar yield (Nanda et al., 2014b). Slow pyrolysis operates at temperature lower than that of fast pyrolysis, t q)ically 400 10°C and has a gas residence time usually > 5 s. Slow pyrolysis is similar to carbonization (for low temperatures and long residence times). During conventional pyrolysis, biomass is slowly devolatilized facilitating the formation of chars and some tars as the main products. This process yields different range of products with their properties dependent on temperature, inert gas flow rate and residence time. 

---