Biomass gasification liquid fuels

Olofsson, I. Nordin, A. Soderlind, U., Initial Review and Evaluation of Process Technologies and Systems Suitable for Cost-Efficient Medium-Scale Gasification for Biomass to Liquid Fuels, ETPC Report 05-02, University of Umea/Mid Sweden University, Umea, 2005, p. 90. 

Neathery JK. Chp 4 Biomass Gasification in Thermochemical Conversion of Biomass to Liquid Fuels and Chemicals (ed. Crocker, M.). Cambridge,UK RSC Publishing 2010, p. 73-4. 

In the United States, where clean and convenient natural gas, propane, and electricity are widely available and affordable, biomass use has limited potential. Nevenheless, U.S. biomass energy production has been increasing because of technological advances for new and improved biomass applications for electricity generation, gasification, and liquid fuels. 

Gasification technologies offer the potential of clean and efficient energy. The technologies enable the production of synthetic gas from low or negative-value carbon-based feedstocks such as coal, petroleum coke, high sulfur fuel oil, materials that would otherwise be disposed as waste, and biomass. The gas can be used in place of natural gas to generate electricity, or as a basic raw material to produce chemicals and liquid fuels. 

Second-generation biofuel technologies make use of a much wider range of biomass feedstock (e.g., forest residues, biomass waste, wood, woodchips, grasses and short rotation crops, etc.) for the production of ethanol biofuels based on the fermentation of lignocellulosic material, while other routes include thermo-chemical processes such as biomass gasification followed by a transformation from gas to liquid (e.g., synthesis) to obtain synthetic fuels similar to diesel. The conversion processes for these routes have been available for decades, but none of them have yet reached a high scale commercial level. 

Liquid fuels have a high energy density, and the widest applicability of all fuel forms, but a low efficiency of conversion from biomass. It is therefore necessary to compare liquefaction with the more efficient processes of direct burning and gasification as alternative modes of use of the biomass. 

Pyrolysis is the degradation of macromolecular materials with heat alone in the absence of oxygen [45]. The development of pyrolysis processes for the production of liquids has gained much attention in the last decade because they offer a convenient way to convert low-value woody residues into liquid fuels and value-added products. Biomass pyrolysis is of growing interest as the liquid product can be stored and easily transported [46]. Pyrolysis processes yield a mixture of gas, liquid, and solid products. If pyrolysis is practiced alone, that is, without a subsequent gasification step (see Section 16.4.3), the process conditions are usually chosen to maximize liquid product yields. 

One can envisage the future production of liquid fuels and commodity chemicals in a biorefinery Biomass is first subjected to extraction to remove waxes and essential oils. Various options are possible for conversion of the remaining biofeedstock, which consists primarily of lignocellulose. It can be converted to synthesis gas (CO + H2) by gasification, for example, and subsequently to methanol. Alternatively, it can be subjected to hydrothermal upgrading (HTU), affording liquid biofuels from which known transport fuels and bulk chemicals can be produced. An appealing option is bioconversion to ethanol by fermentation. The ethanol can be used directly as a liquid fuel and/or converted to ethylene as a base chemical. Such a hiorefinery is depicted in Fig. 8.1. 

A few representative biomass gasification processes that have been commercialized or that are near commercialization are described here to illustrate some of the details of gasifier designs and the operating results. The biomass pyrolysis plants described in Chapter 8 are not discussed here because the major products are liquids and charcoals, and the by-product gases are used for plant fuel. 

Syngas produced from gasification of coal, biomass, petroleum coke, and other types of feedstock can be used to generate electricity or to produce hydrogen and other liquid fuels or chemicals (ammonia, methanol, dimethyl ether, and diesel fuel) by... 

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