Liquefaction process

Liquefied gases are in common use for a variety of purposes. For example, liquid propane in cylinders serves as a domestic fuel, liquid oxygen is carried in rockets, natural gas is liquefied for ocean transport, and liquid nitrogen is used for low-temperature refrigeration. In addition, gas mixtures (e.g., air) are liquefied for separation intotheircomponent species by fractionation. 

Liquefaction results when a gas is cooled to a temperature in the two-phase region. This may be accomplished in several ways  

By an expansion process from which work is obtained. 

The first method requires a heat sink at a temperature lower than that to which the gas is cooled, and is most commonly used to precool a gas prior to its liquefaction by the other two methods. An external refrigerator is required for a gas temperature below that of the surroundings. 

The Linde liquefaction process, which depends solely on throttling expansion, is shown in Fig. 9.6. After compression, the gas is precooled to ambient temperature. It may be even further cooled by refrigeration. The lower the temperature of the gas entering the throttle valve, the greater the fraction of gas that is liquefied. For example, a refrigerant evaporating in the cooler at 233.15 K (—40°C) provides a lower temperature at the valve than if water at 294.15 K (21°C) is the cooling medium. 

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Different types of other coal liquefaction processes have been also developed to convert coals to liqnid hydrocarbon fnels. These include high-temperature solvent extraction processes in which no catalyst is added. The solvent is usually a hydroaromatic hydrogen donor, whereas molecnlar hydrogen is added as a secondary source of hydrogen. Similar but catalytic liquefaction processes use zinc chloride and other catalysts, usually under forceful conditions (375-425°C, 100-200 atm). In our own research, superacidic HF-BFo-induced hydroliquefaction of coals, which involves depolymerization-ionic hydrogenation, was found to be highly effective at relatively modest temperatnres (150-170°C). 

W. R. Eppedy and J. W. Taunton, "Exxon Donor Solvent Coal Liquefaction Process Development," paper presented at Coal Dilemma II ACS Meeting, Colorado Spriags, Colo., Feb. 12, 1979. 

W. G. Willson md co-workers, " AppHcation of Liquefaction Process to Low-Rank Coals," paper presented at /0th BiennialEignite Symposium, Grmd Forks, N.D., May 1979. 

Fig. 1. Enzymatic liquefaction processes (9). Alpha-S is the a-amylase from bacillus subtilis alpha-L/ST are a-amylases from B. licheniformis oi B.

Fig. 12. Helium liquefaction process. A represents adsorber E, expander.

Direct-Liquefaction Processes Figure 27-8 presents a simph-fied process flow diagram of a typical direct coal liquefaction plant. Specific processes are described in the following paragraphs. 

TABLE 27-14 Direct Liquefaction Process Conditions and Product Yields... 

Distribution of work used by the liquefaction process (Basis 1 lb of 1,000 psia stream)... 

Accounting of the work in the liquefaction process—effectiveness of various functions... 

In summary, starting with 105°F gas at atmospheric pressure, the theoretical work necessary to liquify one pound of methane is 510.8 Btu or 352 hp/MMcfd. The simplified liquefaction process, as illustrated, uses a turboexpander/compressor and a small propane refrigeration unit. The 41.25% efficiency breaks down as follows one-fourth contributed by the turboexpander/compressor at 35.8% efficiency one-sixteenth contributed by the mechanical propane refrigeration unit at 43% efficiency, at a moderate temperature where its efficiency is high and a large fraction—eleven-sixteenths—contributed at 58.2% efficiency by compression and Joule-Thomson condensation energy. 

During the liquefaction process, usually much of the oxygen, carbon dioxide, sulfur compounds and water are removed so that liquefied natural gas (LNG) IS nearly 100 percent methane. LNG takes up one-six-hundredth the volume of natural gas, with a density less than half that of water. 

Work has also continued on the solvent-refined coal + hydrocracking concept (the NT.SL, or non-integrat-ed, two-stage liquefaction process), and a pilot plant was operated by Amoco, DOE and the Electric Power Research Institute (EPRI) from 1974 to 1992. 

Any gas, when compressed, rises in temperature. Conversely, if it is made to do work while expanding, the temperature will drop. Use is made of the sensible heat only (although it is, of course, the basis of the air liquefaction process). 

G. A. White We have looked at a case consisting of a Koppers-Totzek gas, at essentially atmospheric pressure, in combination with the COED liquefaction process. We considered the residue gas that came from gasification at atmospheric pressure, methanated it at atmospheric pressure, and took out C02 at atmospheric pressure before compression. That was the minimum cost for our system. It is obvious that each system will have some difference in economics, depending on what you can achieve by methanation. 

This paper outlines waste plastic liquefaction technology, and discusses its use in the operation of a demonstration plant. The following aspects are considered plastics suitable for liquefaction, basic principals of liquefaction technology, the liquefaction process, examples, results, and conclusions. 4 refs. 

Schols HA, Posthumus MA, Voragen AGJ (1990b) Structural features of hairy regions of pectins isolated from apple juice produced by the liquefaction process. Carbohydr Res 206 117-129... 

If we compare liquefaction to maceration, more activities are needed to liquefy the cell wall. Since 1991, new pectinases activities such as rhamnogalacturonase, pectin acetylesterase and xyloglucanases complex have been found to be important in the apple liquefaction by Henck Schols, Jean-Paul Vincken and Voragen [3]. The cellulose-xyloglucan complex accounts approximatively 57% of the apple cell-wall matrix. In a liquefaction process, an efficient enzymic degradation of this complex is crucial to increase the sugars extraction, to decrease the viscosity of the pulp then to be able to ultra-filtrate the juice without second depectinisation, at last to have negative alcohol tests required by some concentrate customers. 

Even if these liquefaction processes are still not accepted worlwide (for instance in Europe), they should grow within the next few years. We do really believe that they are the processes of the future, and especially the process of pressing / pomace liquefaction because it is an easy process, it allows the production of quality juice combined with high yields within a great flexibility. Such high yields, low production cost and flexibility to process different fruits make that fruit juice producers are more and more choosing the pomace liquefaction. 

NIOSH. 1980a. Control technology assessment for coal gasification and liquefaction processes, General Electric Co., Corporate Research and Development Center, Coal Gasification Section, Schenectady, New York. Cincinnati, OH U.S. Department of Health and Human Services, National Institute for Occupational Safety and Health, Division of Physical Sciences and Engineering. NITS publication no. PB84-181890. 

The second section of this volume describes several potentially new liquefaction processes which may have higher efficiencies than today s developing technologies. The theme of the Storch Award Symposium, featured throughout these six chapters, was new process potentials through the use of short-contact-time thermal processes followed by catalytic upgrading. 

Perhaps the most important components of reactor solids are those that are generated during processing rather than those that are derived from inert minerals (quartz, clays) and macerals (fu-sinites, etc.) in the feed coal (74). The retention of these formed materials is more difficult to predict from the characteristics of the feed and, hence, control in liquefaction processes. 

Epperly, W. R. (Project Director). "EDS Coal Liquefaction Process Development—Phase IV", Annual Tech. Rept. for July 1978-June 1979 from Exxon Research and Engineering Company to U.S. Department of Energy and Electric Power Research Institute under Contract No. EF-77-A-01-2893, September 1979. 

Coal Characteristics and Their Effects in Liquefaction Process... 

The significance of the above-described work is that in all of the presently developing coal liquefaction processes, the initial step in the conversion is thermal fragmentation of the coal structure to produce very fragile molecules which are highly functional, low in solubility, and extremely reactive toward dehydrogenation and char formation. A more detailed discussion of the chemical nature of these initial products has been presented elsewhere (4). ... 

The formation of these thermal fragments is necessary to catalytic liquefaction processes before the catalysts can become effective for hydrogen introduction, cracking and/or heteroatom removal (10). ... 

These observations suggest that new coal liquefaction technology may be possible based on short contact time reactions. The purpose of this and the related papers in this volume by R.H. Heck and W.C. Rovesti is to show some potential advantages for optimized or integrated short contact time liquefaction processes over conventional technology. 

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