Physical conversion economics

Fortunately for a poor, would-be chemist like Leblanc, France s aristocratic passion for the physical sciences crossed economic, social, and political borders. Intellectuals such as Rousseau and Diderot cultivated the sciences with enthusiasm and compiled encyclopedias and dictionaries of natural substances. Local academies and institutes in the far-flung provinces sponsored chemical studies. Crowds flocked to hear chemists lecture and to watch their flashy laboratory demonstrations. Even the future revolutionary, Jean-Paul Marat, experimented with fire, electricity, and light and tried—in vain—to become a member of the Royal Academy of Sciences. In America, Benjamin Franklin abandoned his printing and publishing business for physics, and in England his friend Jane Marcet wrote Mrs Marcet s Conversations in Chemistry for women and working-class men. 

Modem catalysts have to be very active and very (100%) selective, that is, they have to catalyze the desired reaction in the temperature window, where the equilibrium conversion is the highest possible and the reaction rate is high enough to permit suitable process economics. To engineer the reaction, one has to obtain first the intrinsic reaction rate, free of heat- and mass-transfer limitations. In many cases this is very difficult, because in the core of the catalytic process there are several physical and chemical steps that must occur and which may preclude the reaction running in the kinetic regime. These steps are as follows ... 

Direct use of coal as a primary fuel is often the most efficient and economic method of utilizing this important energy resource. In many cases, however, certain undesirable properties of coal make direct utilization difficult. Coal is a solid and requires more effort to handle, measure and control than gases or liquids. Coal is usually contaminated with ash and other undesirable components and has widely variable chemical and physical properties. As a result, there is often a need to convert coal into more convenient and cleaner forms of energy and products. Before considering the basic principles of coal conversion, some important characteristics of fossil fuels will be reviewed. 

The physical processes by which natural gas liquids are recovered include phase separation, cooling, compression, absorption, adsorption, refrigeration, and any combination of these. Obviously the definition already stated excludes refinery light volatiles produced by the destructive decomposition of heavy petroleum fractions and it also excludes liquids that may be produced synthetically from natural gas. These distinctions are of economic importance in considering our basic energy reserves. Both the refinery volatiles and the synthetic liquids represent conversion products from other hydrocarbons and the conversion is usually attended by a considerable loss. Thus it has been stated that only about 47% (17) of the energy of natural gas is realized in the liquid hydrocarbon products of the Fischer-Tropsch type of synthesis. 

Lampkin. N. 1994. Estimating the impact of widespread conversion to organic farming on land use and physical output in the United Kingdom. In Lampkin, N. and Padel, S. (eds) The Economics of Organic Farming - An International Perspective. CAB International, Wallingford, pp. 343-359. 

Because every industrial chemical process is designed to economically produce a desired product from a variety of raw materials. The economical extraction and use of exploitable raw materials are the essential prerequisites for a chemical industry. These raw materials usually have to be pretreated. They may undergo a number of steps involving physical treatment, chemical reactions, separation, and purification before their conversion into a desired product. Figure 1.1 shows a typical structure of such a process. 

While all pyrolysis oil production reactor systems produce similar materials, each reactor produces a unique compound slate. The first decision, especially for a potential chemical or fuel producer, rather than a reactor developer, is to determine what products to make and which reactor system to use. The operating parameters of any reactor system designed to produce pyrolysis oil, especially temperature, can be altered to change the pyrolysis oil product composition and yield. Different feedstocks will produce different pyrolysis oil compositions and by-products, e.g. amorphous silica from rice hulls or rice straw, fatty acids from pine. Finally, feedstock pretreatment and/or catalysis, or reactor-bed catalysis can be used to improve specific product yields (7). Reactor system developers need to examine what they can produce and make this information available to chemical manufacturers and suppliers/owners of biomass feedstocks. This assumes that analysis of die entire liquid product from thermal conversion can be made, including quantitative analysis for any compounds that are being considered for recoveiy. Physical characterization - pH, viscosity, solids content, etc.is also needed. However, what can be produced is of no value, if it cannot be recovered or used economically. This involves examining the trade-offs between yield and current commercial value, recovery costs, and potential commercial value,... 

We have in previous chapters frequently had occasion to point out that the commercial success of many operations depends upon the economical utilisation of heat. If we leave out of consideration the power of wind and water, which is at present, and particularly in this country, not much utilised, we find that the results of chemical reactions and of physical processes, as conducted in chemical works, are only due to the conversion of the energy stored up in coal into other kinds of energy. It is therefore of the greatest importance that we should obtain the utmost yield from the latent energy of fuel. In many cases an examination of the products of combustion will enable us to approach that point more closely, and for that reason we should be in a position to analyse the products of combustion quickly and with sufficient accuracy. 

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