Wood continued pyrolysis

Chemicals have long been manufactured from biomass, especially wood (sHvichemicals), by many different fermentation and thermochemical methods. For example, continuous pyrolysis of wood was used by the Ford Motor Co. in 1929 for the manufacture of various chemicals (Table 20) (47). Wood alcohol (methanol) was manufactured on a large scale by destmctive distillation of wood for many years until the 1930s and early 1940s, when the economics became more favorable for methanol manufacture from fossil fuel-derived synthesis gas. 

To model a packed bed of wood particles pyrolysis and char conversion schemes can be selected from the database. Homogenous reactions within the void space are modelled by describing each volume cell in the numerical grid of the flow model as a continuous stirred reactor. Due to the lack of reliable kinetic data for the conversion of gaseous species under packed bed conditions, only the conversion of hydrogen and carbon monoxide is currently taken into account. For the combustion of hydrogen an infinite rate is assumed whereas the conversion of carbon monoxide is calculated according to [17]. 

A report on the continuous flash pyrolysis of biomass at atmospheric pressure to produce Hquids iadicates that pyrolysis temperatures must be optimized to maximize Hquid yields (36). It has been found that a sharp maximum ia the Hquid yields vs temperature curves exist and that the yields drop off sharply on both sides of this maximum. Pure ceUulose has been found to have an optimum temperature for Hquids at 500°C, while the wheat straw and wood species tested have optimum temperatures at 600°C and 500°C, respectively. Organic Hquid yields were of the order of 65 wt % of the dry biomass fed, but contained relatively large quantities of organic acids. 

Continuing basic research is needed in the pyrolysis, combustion, and fire chemistry of wood leading toward the... 

Except during startup, wood pyrolysis is reported to have been carried out commercially in the 1920s and 1930s without an external heat source. For example, the Ford Motor Company s continuous wood pyrolysis plant was... 

A pyrolysis gas with a high content of "primary" tars (approx. 300 g/Nm ) is produced in the WPU by continuously pyrolyzing wood chips (feed rate 1,6 kg/h) at a mean temperature of 380 C. The evolving gases are swept to the adjacent reactor for homogeneous tar conversion (HOTCR) by means of a N -carrier gas flow (for these... 

Diebold, J. P. (1985) The Cracking Kinetics of Depoiymerized Biomass Vapors in a Continuous, Tubular Reactor. M. S. Thesis, Dept, of Chemical and Petroleum-Refining Engineering, Colorado School of Mines, Golden, Colorado. Liden, A. G. (1985) A Kinetic and Heat Transfer Modelling Study of Wood Pyrolysis in a Fluidized Bed. MASc Thesis, Dept, of Chemical Engineering, University of Waterloo. 

Table 9.1.5. Pyrolysis products at 51CP C of several lignins [6a] (continued). The analyzed materials were milled wood lignin (MLW), steam exploded lignin (StE.), a lignin purified by organosolv procedure (Org.), kraft lignin (Kraft), and bagasse lignin (Bag.).

Biomass thermochemical processes have been studied for at least two reasons (1) a better understanding of the combustion process to control biomass flammability and, (2) research into improved processes for converting biomass into useful energy forms. The late Fred Shafizadeh (see, e.g., 4jt5) laid the groundwork for all recent studies in both arenas. The work on combustion mechanisms continues at the Wood Chemistry Laboratory of the University of Montana in Missoula (see, e.g., 6). Antal has recently (7 ) reviewed all aspects of biomass pyrolysis, and the reader is directed to his reviews for detail study of the processes involved. Chatterjeo has produced an excellent summary (9) of biomass pyrolysis... 

The continuous fast pyrolysis of wood sawdust has been studied in a Lapple type (2.8 x 10" m diameter) cyclone reactor heated between 893 and 1330 K ( ). The wood particles carried away by a flow of steam enter tangentially into the cyclone on the inner hot walls of which they move and undergo decomposition. Mass balances show in all the cases, a very low fraction of char (< 4 %) while the gasification... 

Several processes have been developed [41-43] to overcome the technological drawbacks of plastics incineration cited above. These include continuous rotary-kiln processes a process for glass-reinforced PET a combined system for wood fiber and PET to provide steam to power equipment and a fluidized system for pyrolysis, in combination with silver recovery from photographic film. Incineration of photographic film raises the additional problem of the formation of toxic halogenated compounds due to the presence of silver halides. 

Many variations exist of pyrolysis-based biorefineries, and an early (1920s) example is the production of charcoal and various other products in the continuous wood distillation plant of the Ford Motor Company in Michigan, USA. This plant used 400 tons per day of scrap wood from the automobile body plant.The Ford plant not only produced make acetic acid (among charcoal and other products) but also ethyl acetate (via esterification with bioethanol), which the company required in its lacquer and artificial leather departments. The first T-Fords used bioethanol as their transportation fuel. Figure 8.2 gives a schematic overview of the plant that was completely self-sufficient with regard to its heat demand. 

Corrosivity in complex environments. Experimental design techniques were also used to develop models for understanding the effects of complex environments on materials considered for the operation of different processes such as wood pyrolysis, gas desulfurization, and continuous digestion. In these studies, it was demonstrated that to reduce the complexity of the environments (solution variables, constraints, etc.) to a manageable level, designed experiments are essential. When such studies are properly done, the results can be used to predict the corrosion performance of alloys as a function of solution composition. For the interested reader, reference 54 gives additional details on the actual statistical procedures used for a few typical designs for complex corrosion. 

---