Composition, biomass products pyrolysis

Woody and Herbaceous Biomass Feeds how can we study their composition and their pyrolysis products ... 

Our methods and experiments (UW) previously addressed composition effects in pyrolysis of RDF (Lai, et al 1993) and wood (Krieger-Brockett, et al 1997). In those papers and this one, even minor components are shown to alter pyrolysis slate when appropriate statistical methods are used. This paper briefly summarizes our work on pyrolysis product slates resulting from large- or macro-particle devolatilization (in which heat transfer is a slow process) of native biomass compositions in under-utilized species. The method has general applicability and owing to the limited scope of this article, the reader is referred to Somasundaram (1990), Lai (1991) and Rodriguez (1996) for details and extensive literature reviews with only a few relevant articles mentioned here,... 

Biomass is composed of various components such as cellulose, hemicellulose, lignin, extractives and mineral water. The composition of biomass plays a definitive role in altering the product distribution and their properties [2-3J. As is shown in earlier publications [4-S] different biomass, on pyrolysis, give different product yield with different product properties. In order to choose a biomass for a particular process (carbonisation, liquefaction, gasification or adsorbent char) knowledge on the product distribution and properties for various biomass are essential. 

The composition of complex liquids (bio-oil) contains oxygenates, nitrogen, and sulfur compounds and when processed, that compounds can produce materials with high added value. The hydrotreatment and, in particular, hydro deoxygenation are used in such cases thus, it becomes necessary to identify the various products contained in the liquid mixture from the pyrolysis. Usually, the bio-oil production via biomass fast pyrolysis produces, approximately, 50% of oxygenated compounds, while the liquids coming from liquefaction contain 25% of oxygenated compounds, approximately. 

Figure 5. Typical composition of products obtained from pyrolysis biomass. Maximal achievable content of different products depends on the speed of pyrolysis.

Yan F, Luo SY, Hu ZQ, Xiao B, Cheng G (2010) Hydrogen-rich gas production by steam gasification of char from biomass fast pyrolysis in a fixed-bed reactor influence of temperature and steam on hydrogen yield and syngas composition. Biores Technol 101 5633-5637... 

The types of biomass, especially ash content, heating rates, and hot vapor residence times, have a major effect on the product composition (Jahirul et al., 2012). The typical product composition for fast pyrolysis of clean dry wood is 75 wt.% liquid, 12 wt.% char (usually consumed in the process for heat), and 13 wt.% gas, compared to slow pyrolysis which is 30 wt.% liquid, 35 wt.% char, and 35 wt.% gas (Bridgwater, 2012a,b). 

As expected, the composition of feedstock can greatly impact the pyrolysis product yields. Table 4.2 reports product yields from pyrolysis of various biomass and fossil feedstocks at 500°C. 

Table 6.4 Compositions of gaseous products from biomass samples by pyrolysis at different temperatures (% by volume)...

Complex pyrolysis chemistry takes place in the conversion system of any conventional solid-fuel combustion system. The pyrolytic properties of biomass are controlled by the chemical composition of its major components, namely cellulose, hemicellulose, and lignin. Pyrolysis of these biopolymers proceeds through a series of complex, concurrent and consecutive reactions and provides a variety of products which can be divided into char, volatile (non-condensible) organic compounds (VOC), condensible organic compounds (tar), and permanent gases (water vapour, nitrogen oxides, carbon dioxide). The pyrolysis products should finally be completely oxidised in the combustion system (Figure 14). Emission problems arise as a consequence of bad control over the combustion system. 

Yields of the different pyrolysis products (i.e. char, bio-oil, and gases) are dependent on the chemical composition of biomass. Biomass with high lignin content produces more char compared to biomass with lower content [20], Furthermore, biomass with high alkali and alkali earth metal concentrations generates less bio-oil and instead more char and gases [14, 15, 21]. Prior to pyrolysis, it is beneficial to dry the biomass to less than 10 wt% moisture in order to minimize the water content in the bio-oil [14],... 

Knowledge of the effects of various independent parameters such as biomass feedstock type and composition, reaction temperature and pressure, residence time, and catalysts on reaction rates, product selectivities, and product yields has led to development of advanced biomass pyrolysis processes. The accumulation of considerable experimental data on these parameters has resulted in advanced pyrolysis methods for the direct thermal conversion of biomass to liquid fuels and various chemicals in higher yields than those obtained by the traditional long-residence-time pyrolysis methods. Thermal conversion processes have also been developed for producing high yields of charcoals from biomass. 

Tars are primary products from pyrolysis of biomass or other carbon-containing materials. Their formation cannot be avoided. However, these primary tars are not stable. After having evolved from the solid matter, they undergo secondary tar reactions, altering both in mass and composition. As shown in fig. /, secondary tar reactions... 

Biomass can be gasified to obtain gas for power generation, hydrogen production or chemical synthesis. The reaction atmosphere can influence very significantly the gas composition and its posterior use. For instance, steam gasification of biomass (1-5) and catalytic steam reforming of liquids from pyrolysis (6,7) produce a rich-hydrogen gas and a CO residual stream. 

Pyrolysis liquid is referred to by many names including pyrolysis oil, bio-oil, bio-crude-oil, bio-fiiel-oil, wood liquids, wood oil, liquid smoke, wood distillates, pyroligneous tar, pyroligneous acid, and liquid wood. The crude pyrolysis liquid is dark brovyn and approximates to biomass in elemental composition. It is conqsosed of a very complex mixture of oxygenated hydrocarbons with an appreciable proportion of water from both the original moisture and reaction product. Solid char and dissolved alkali metals from ash (34) may also be present. 

What are unambiguous ways to study biomass composition and its relationship to pyrolysis rate and products Are traditional, operational definitions of composition such as cellulose, Klason or Kraft lignin, and extractives weight fraction useful What other composition metrics are useful especially as under-utilized or transgenic biomass species are examined ... 

Davis et al (1985) screened 57 dif rent woody and herbaceous biomass feedstocks for their production of liquid hiel constituents from indirect liquefaction of powdered materials in a fluidized b. Composition metrics in Davis studies were ash, proteins, polyphenols, oil, and hydrocarbon content as defined and measured by the USOA (Ibr example, in Adams, et al, 1986 Buchanan, et al, 1980a Roth et al, 1984 Swanson, et al 1979). We will call the USDA-measured compositions traditional" fcr purposes of this article. These feed compositions were correlated with pyrolysis gas production of hydrogen, CO, CjH4, total olefins, paraffins, and H2/CO ratio using direct regression equations of the quadratic type, but tar/char production was not addressed. 

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