WO1997007185A1

WO1997007185A1 - Stabilization of low rank coals after drying

Info

Publication number: WO1997007185A1
Application number: PCT/US1996/013204
Authority: WO
Inventors: Charles E. Spear
Original assignee: Spear Charles E
Priority date: 1995-08-11
Filing date: 1996-08-02
Publication date: 1997-02-27
Also published as: AU6774796A; CA2229130A1

Abstract

A method of increasing the utility of low rank coal of high moisture content by stabilizing essential physical properties of the coal, following its drying by known methods, which without stabilization render it unsuitable for transportation and storage. The method employs controlled partial pyrolysis in a continuous flow configuration, using electromagnetic energy in novel ways. The stabilization an be carried out by this method at the very high rates required for commercial coal operations.

Description

STABILIZATION OF LOW RANK COALS AFTER DRYING

Coal occurs in a multitude of forms in many areas ofthe world as the product of geologic processes well known and amply described in published sources. For purposes of discussion, those forms are often termed peat, brown coal, lignite, subbituminous coal, bituminous coal and anthracite coal in ascending rank of fuel value or heat content. Those from peat upward in rank through subbituminous coal are conventionally regarded as low rank coals.

One important characteristic of most low rank coals is water content, which can range typically from 90% for peat to 40-60% for brown coal to 25-45% for lignite to 15-35% for subbituminous coal. The dominant use for all ranks is as a fuel.

The fuel values of low rank coals rise significantly as water content is reduced. The costs of transporting them decrease accordingly. If they can be dried economically, with other characteristics desirable in the marketplace retained or restored, they can be of interest to a substantially broader market.

Consequently, serious efforts were being made in the 1920s and earlier to devise economical ways to eliminate water from brown coals and lignites. Perhaps the earliest process to reach commercial status was the Fleissner process, described in U.S. Patents No. 1,632,829 and 1,679,078. The Fleissner process employed high pressure steam to remove water from low rank coals. It has been effective on some such coals and has had limited commercial use since 1927. Many other processes with similar objectives have been proposed in the meanwhile.

A publication, "The Science of Victorian Brown Coal: Structure, Properties, and Consequences for Utilization," edited by Dr. R. A. Durie, provides a significant current review of such technology and its application. It contains a comprehensive summary of available knowledge and experience in processing low rank coals and in developing improved methods for their utilization. While the publication is nominally focused on the brown coals of Australia, it incorporates low rank coal technologies and data from worldwide sources and is an authoritative measure ofthe prior art through 1990.

In the fuels marketplace, the as-mined properties of the available low rank coals are generally known and accepted. If such coals are to be dried and sold commercially, it is generally necessary that the dried products be at least comparable in density and in moisture reabsorption, handling, grinding and combustion properties and have no more tendency to self-ignition. Establishing these characteristics in dried coals has been generally referred to as stabilization. While some processes ofthe prior art have demonstrated limited success or allude to being close to more general success in doing so, their cost effectiveness has been limited. Generally, the processes have been applied to a small number of low rank coal drying operations which are old in concept and which, with few exceptions, are carried out where the product is mined and used. In those latter instances, the processes are simple and the only expectation for the product is that it be dry enough for its intended use.

Problems involved in processing low rank coals, and of the prior art directed to their resolution, and ofthe limitations of that prior art are also reviewed in U.S. Patent No. 4,725,337. As that patent points out, batch operations for processing coals have existed on a large scale but have had recognized inadequacies. The difficulties and costs associated with processing coals at high temperatures (450°F to 1250°F) and high pressures (300 psig to 3000 psig) for periods of time varying up to fifteen minutes, even to sixty minutes, are also discussed.

More recently, attention has turned to drying technologies which can be operated at essentially atmospheric pressure and in a continuous flow mode. Those two features, were they to be developed successfully together and yield a product stable enough for transportation and handling, could have the potential for economical operation and very large scale operation, both of which criteria are important measures of usefulness for fuel processing. The status ofthe principal drying technologies under development more recently, some incoφorating stabilization as well, is reported in a publication ofthe United States Department of Energy (USDOE) dated September 1994, entitled "Third Annual Clean Coal Technology Conference: Technical Papers."

A process concept common to numerous coal drying and stabilizing technologies ofthe prior art is heating to pyrolysis temperature first the surface, then eventually much or even all ofthe coal substance in each coal particle in process. This has been done by hot oil, hot gases, hot water, heated coal or other heated solids, by radiant energy or by indirect heat transfer. The stated reasons for the necessity of utilizing that concept are numerous. They have included not only drying the coal, but also reduction of its moisture-reabsorption characteristic; simultaneous shrinkage to preserve coal density for economy in transport; minimization of loss of product by volatilization and by dust; and, very importantly, ensuring commercially acceptable handling, shipping and self-ignition characteristics.

The establishment of those qualities is termed "stabilization" of the low rank coals. The economic standard to be met by a stabilized product, much more difficult to accomplish with such a low-priced commodity as coal, is to process the coal at a cost less than the gain in value. The great majority of processes for drying and, for some, also stabilizing low rank coals rely upon external heating of each coal particle for the energy to drive out the water and also to cause pyrolysis ofthe coal to start at the surface and work its way inward. Except for applications where product stability is not required, such as mine-mouth Fleissner or Perry operations, or where unique cost-price circumstances prevail, these have not produced commercially attractive products. The problems responsible for that lack of success include high temperatures and long processing times necessary to transfer heat from the surface to the interior of the coal particles, the losses of combustible components from the raw coal and the complex equipment and operations required. Capital contributions and tax advantages made available from public entities in the United States of America have enabled certain processes for drying and stabilization to be demonstrated on a minor commercial scale. However, the costs of such complex processes, exemplified by those described in considerable detail in the previously cited USDOE publication entitled, "Third Annual Clean Coal Technology Conference: Technical Papers," are clearly very high and their commercial application in an unsubsidized market has not occurred.

Drying of low rank coal by radio frequency or microwave energy has been demonstrated technically by several investigators who described the absorption ofthe energy by the water in the coal and reported the energy requirements. All of them contemplated evaporation of all ofthe water, with resultant investment levels and electrical energy demands which were clearly uneconomic. Significantly, all used relatively low microwave field intensities. Some have also mentioned in passing that a side effect existed of a deterioration of physical properties comparable to the results of most other drying processes, rendering the products similarly prone to crumbling, dusting, self- ignition, moisture reabsorption and bulk density problems. Moreover, none of their published reports proposed solutions to these problems.

Other investigators have employed microwaves as a way to pyrolyze coal for the purposes of char production, to generate gas and liquid products or to otherwise pyrolyze coal extensively.

So far as is known, the need for stable, economical dry low rank coal has not been satisfied by processes ofthe prior art

Briefly, with the present invention, it has been found that low rank coals can be subjected to electromagnetic energy in a manner to effectively stabilize them and form a resultant stabilized coal substance as an end product. The present invention employs electromagnetic energy of one or more electromagnetic field characteristics to generate heat within particles of low rank coal. Preferably, most of the original water content of the low rank coal has been removed by some suitable conventional technique which does not irreversibly degrade the physical structure of the coal. The low rank coal substances after drying are then partially altered by the electromagnetic energy in a novel way, preferably in a continuous flow of such particles, to effect the desired stabilization. This stabilization occurs as a result of controlled heating by electromagnetic wave energy fields.

The present invention can be used to advantage to convert a low rank coal, whose water content limits its value, to a more marketable form. It has been found that the present invention serves to stabilize such a coal for use as a fuel, when such a coal after merely being dried would not be commercially acceptable as a fuel. So far as is known, there are no processes other than the present invention which can stabilize previously dried coal at comparable cost and yield. Application of electromagnetic energy to stabilize low rank coal particle according to the present invention occurs virtually instantaneously within a coal particle when it is exposed to electromagnetic fields. That result is obtained in contrast to slow heating from the surface inward obtained in the past with attendant problems, such resultant high surface temperature, steep thermal gradient and excessive pyrolysis ofthe first-heated coal substances.

For stabilization of the coal, prior drying typically is performed to reduce the moisture content of the coal in process below about 5%, the preferred level being dependent upon the composition and pore structure ofthe coal. An electromagnetic field in either continuous wave or pulsed mode can then be applied to the coal particles to eliminate the remaining free water and to create very high localized temperatures for very short periods of time within the coal. The bulk of the coal substance, of organic origin, is a relatively inefficient absorber of microwave energy. The high localized temperatures occur at sites in the coal where its properties permit selective absorption ofthe radiation, for example, at any site of residual moisture; on mineral components; at the surfaces of voids in the solid coal substances; wherever there is unique coupling of the electromagnetic energy with the substances in process; or in a plasma zone of any degree of ionization.

An effect of the localized heating according to the present invention is to alter the composition of enough coal substance to generate volatile and tarry organic materials, permitting them to move locally in the coal particles. Those materials in turn can react to form polymeric materials, pyrolytic carbon and potentially conductive pregraphitic forms of carbon. The amount of coal substance so altered, typically between about 0.2% and 2%, is small enough that the bulk temperature is normally less than about 150°C. The consequence is a stabilization ofthe mechanical properties ofthe coal through physical bonding, offsetting the weakening and fracturing and dust formation, which have been caused by methods of the prior art, and which in turn render the resultant products uncompetitive in the marketplace. The selection of optimum electromagnetic field characteristics depends to a considerable degree on the characteristics of each particular type or rank of coal to be processed. Those can be determined in part by experience with coals of similar geologic origin and history. A significant objective ofthe optimization process is to minimize the total energy absorbed by the coal particle in order to minimize the bulk temperature rise in the coal, the escape of volatile organic substances and the cost of processing.

An object ofthe present invention is to provide a new and useful process for stabilizing dried low rank coals in terms of moisture reabsorption, self-ignition tendencies and mechanical properties including density, friability and dust formation.

A specific object of this invention is to provide for carrying out all of its process steps in continuous flow modes at essentially atmospheric pressure, permitting large scale operations at minimum cost and with maximum reliability, safety and control.

A further object of this invention is to provide for selectively heating microwave-absorptive sites in low rank coal particles rapidly, while maintaining a low bulk temperature rise with the low energy consumption necessary for economical processing.

The term "low rank coals" is used, according to the present invention, in the same commonly accepted sense it is used in scientific, engineering, mining and commercial communications. Namely, the term is intended to denote the broad range of carbonaceous materials known variously as peat, brown coal, lignite and subbituminous coal. Such materials are found in many areas ofthe world, known by one name or another, with the nomenclature and classification systems often reflecting regional geologic history and regional customs. Peat must be dried to be useful as a fuel; its properties and problems are unique, and its water content must be reduced substantially by other conventional techniques before it can be processed according to the present invention.

The present invention can be used to advantage to convert a low rank coal, whose water content limits its value, to a more marketable form. It has been found that the present invention serves to stabilize such a coal for use as a fuel, when such a coal after merely being dried would not be commercially acceptable as a fuel. In the disclosure which follows, any such raw or processed fuel materials may, for convenience, be designated merely as "coal," or a "coal substance." Due to the wide variability of composition, dielectric properties and other characteristics of these materials from nature, the particular range of operating parameters selected for each such coal to be processed will of course be tailored to that type of coal.

A coal to be fed to the process of this invention is typically sized to pass through a screen with nominal one inch (25 mm) openings. That dimension may, however, be larger or smaller, as preferred, to adapt the process to the frequencies ofthe electromagnetic energy to be employed and the dielectric and other properties ofthe particular coal. Furthermore, engineering considerations may favor separation ofthe feed coal into more than one fraction according to particle size. Each fraction may then be processed similarly but separately, and fine particles too costly to process may of course be eliminated prior to processing. However, the principles of operation of the process described below are in substance the same for any particle size.

The starting material or input for the preferred embodiment of the present invention is a continuous flow of a previously dried coal. The coal to be stabilized may be dried by a variety of known processes which retain its basic particle structure. Those processes variously employ direct or indirect heat exchange with fluids, gases or other solids as a source of energy, or radiant energy or electromagnetic energy or a combination of two or more such types of energy. Drying operations built or seriously proposed at present, so far as is known, contemplate coal throughput rates in the range of 100 to 500 tons per hour. Much higher rates would be advantageous from a commercial viewpoint. The capability ofthe process ofthe present invention to stabilize dried coal flows of such magnitude is an important feature.

During the stabilization process ofthe present invention, the dried coal is thereafter subjected to a radio frequency field at a frequency between about five megahertz (MHz) and 500 MHz or to a microwave field at a frequency between about 500 MHz and 30,000 MHz or to a succession of such electromagnetic fields. The choices of such field or fields and the number of successive applications of such energy depend primarily on the composition and dielectric properties ofthe coal and the product specifications which are to be met. The atmosphere surrounding the coal throughout its processing is kept low enough in oxygen content that neither the major coal particle stream nor the inevitable dust oxidizes sufficiently to be a fire or explosion hazard. It will also accordingly not allow significant carbon loss due to oxidation not conventionally identified as combustion. Preferably, the maximum oxygen content ofthe atmosphere is about 1% by volume, with levels as low as 0.2% more desirable.

As stabilization proceeds according to the present invention, the last post-drying traces of pore-bound water and interior-surface-bound water are vaporized, the coal shrinks and the affected interior and exterior surfaces are altered, irreversibly to a considerable extent. Interior heating causes a temperature-dependent degree of decarboxylation of coal substances, evolving carbon dioxide (CO₂). It is to be noted that the loss of CO₂ has no significant effect on the heating value of the product, since that carbon is fully oxidized in the raw coal state. The amount evolved is minor at the coal bulk temperatures of 50° to 150°C experienced in the preferred practice of this invention, rarely over about 0.5% ofthe entering coal. However, the consequent elimination of hydrophilic sites in the coal is sufficient to render its surfaces effectively hydrophobic and to block many pores, restricting the rate of reentry and reabsorption of water and limiting it to an equilibrium moisture level ranging typically from 2% to 14%.

The term "equilibrium moisture" is conventionally accepted to be the moisture content of a dried coal after exposure to an atmosphere of air at 90% relative humidity at 30°C for three days, simulating adverse conditions of transportation and storage. Other test conditions of temperature, humidity or exposure time might be required for technical or commercial purposes. Taking a subbituminous coal with as-mined water content of 30% as an example, equilibrium moisture content of 2% would correspond to 95% water elimination; at 14%, the water elimination would be 62%. While individual fuel markets will have their own criteria for commercially acceptable moisture content of delivered coal, most will prefer the lowest available equilibrium level.

In the preferred embodiment of this invention, the water content of the coal is nearly eliminated before processing to obtain significant stabilization begins. As the coal moves continuously through the process system, it may optionally be preheated by a radio frequency field between 5MHz and 500 Mhz. Then, or initially if no preheating is needed or done, the coal enters a zone provided with one or more electromagnetic fields in succession in the microwave frequency range of about 500 to 30,000 MHz. The electromagnetic energy so applied may be either in continuous wave form or in pulses of five microseconds to 500 milliseconds duration at intervals from one cycle per second to 1000 cycles per second.

The innate variability of low rank coals requires that the wide range of electromagnetic field characteristics outlined above be considered to optimize an individual application of this invention. However, it is already evident from data well known to coal scientists that bulk coal temperatures above 150°C have caused rapid weight loss from the processing of such coals, for example, coals as different as the brown coals of Australia and the subbituminous coals ofthe Powder River Basin in Wyoming, U.S.A.

The intermittent exposure ofthe coal to such microwave fields, timed to control the peak and average temperatures and the heating rate within the coal, can be provided by well established pulse generation technology. The result can also effectively be created by the passage ofthe coal through continuous wave fields at a certain feed rate or can be the resultant product of both technologies in concert. Frequencies officially sanctioned for commercial and industrial use, 915 MHz and 2450 MHz, have been found effective in the practice of this invention. They are advantageous in the practical sense because (1) they pose no problems of interference with communications or other applications of electromagnetic fields and (2) the technology for large scale microwave generation and use is well developed for both frequencies. Higher frequencies, while effective in stabilization, impose practical limitations, including attenuation and depth of penetration in the coal. The particular electromagnetic field characteristics chosen will, of course, vary according to the inherent properties ofthe coal, the response ofthe coal to the electromagnetic fields and the manner in which the coal is moved through these fields.

Microwave heating can generate enough organic liquids, tars and other pyrolysis products within the coal being processed to stabilize the mechanical and other physical properties ofthe coal at a level comparable to those ofthe raw coal, while retaining all but the most volatile substances within the coal particles to conserve its fuel value.

The temperatures required to form tars and various carbon forms cannot be measured directly in the practice of this invention but are well known from gasification, pyrolysis and coking technology to be in the range of 750°C to 1100°C and beyond.

The amount of coal substance so altered, typically between about 0.2% and 2%, is small enough that the bulk temperature is normally less than about 150°C. The consequence is a stabilization of the mechanical properties of the coal through physical bonding, offsetting the weakening and fracturing and dust formation, which have been caused by methods ofthe prior art, and which in turn render the resultant products disadvantageous in the marketplace.

The mechanical properties of primary interest which are stabilized by the process ofthe present invention are its resistance to breakage and resistance to dust formation in subsequent handling, shipping and storage operations. Other properties ofthe product which need also to be controlled include bulk density, resistance to self-ignition, resistance to reabsorption of moisture and resistance to swelling when any moisture is reabsorbed. These other properties are likewise stabilized by the process described above at levels comparable to those ofthe raw coal while the mechanical properties of primary interest are successfully maintained.

With the present invention, the foregoing improvements are achievable over the prior art. The particular methodology used for product comparison purposes may vary to some extent.

Methods of measurement ofthe properties of raw and dried and stabilized coal, developed over many years by coal scientists and fuel technologists, have been described in numerous publications. They provide standardized means of comparing the suitability ofthe products of this invention with other such products and with the raw coals from which they are derived. They are empirical in nature, but they permit an independent observer to evaluate processes and products for the prospective user. A thorough review ofthe art has been published: Anderson, CM., Reducing Moisture in Low Rank Coals: The Stability Issues. Trans. ASME 1994, 375-391.

Set forth below as Examples 1 and 2 below are illustrative results of practice ofthe present invention. By way of contrast, Example 3 below exemplifies undesirable effects of improper application of microwave energy in an attempt to achieve stabilization. Example 1

A subbituminous coal from the Wyodak seam in the Powder River Basin, Campbell County, Wyoming was dried in air at 105°C to constant weight. The compositions before and after drying were approximately:

Raw Coal Dried Coal

Moisture 29% 1%

Ash 5% 7%

Heating Value (HHV) 8500 BTU/lb 11,000 BTU/lb

Volatiles 33% 40%

Particle Size 3/8" x 3/4" 3/8" x 3/4"

The dried coal was then heated in an oven at atmospheric pressure by a microwave field generated at 2450MHz in a series of pulses simulating movement of the coal through a continuous-flow processing system having a succession of continuous-wave fields. Twin magnetrons were energized by single-phase full-wave rectification. The moisture content of the product was essentially zero after 147 switched pulses of 1.67 seconds (100 line cycles) duration and an effective on-time of approximately 50%.

The product was first exposed to ambient air at 25°C and 60% relative humidity (r.h.), then to a humidity chamber atmosphere at 30°C and 95% r.h. The weight of moisture reabsorbed, effectively an "equilibrium moisture," rose with time and humidity, then fell when the product was placed in a lower-humidity environment: Moisture Content

Initial dry product 0% after 12 hours at 25°C, 60% r.h. 6.0% after 18 hours at 25°C, 60% r.h. 6.2% after 36 hours (18-36 at 30°C, 95% r.h.) 7.6% after 48 hours (36-48 at 20°C, 40% r.h.) 7.2%

The stabilizing effect of the microwave heating was evaluated on an empirical product integrity scale of one to five and found to be four in this example, a level comparable to the raw Wyodak coal which is shipped regularly in its undried state. The product integrity scale, recognizing durability and dusting propensity, is:

5 superior to raw coal in durability and dustiness

4 raw coal quality

3 product with some superficial hardness, but brittle

2 product which crumbles easily and progressively in handling

1 coal merely dried, with no meaningful stabilization

Example 2

The same dried coal was heated in a waveguide applicator at atmospheric pressure by a microwave field in a series of pulses following the same simulation concept of Example 1. A magnetron was energized by a medium-ripple 3 -phase power supply delivering a 2450° MHz field with a peak-to-peak ripple variation of approximately 15%. The moisture content ofthe product was essentially zero after 40 pulses of 50 milliseconds. The bulk product temperature by surface measurement reached 71°C. The product integrity score of 4.5 was matched by companion tests with product surface temperatures of 68°C and 77°C. Example 3

The same dried coal was heated in an oven at atmospheric pressure by a continuous-wave microwave field at 2450 MHz to investigate the nature and the rates ofthe transformations taking place in the coal. Prior observations of suddenly intense coupling of the field with the coal were confirmed, indicating an increasingly energy-absorbtive environment within the coal and extensive devolatilization. A first application lasted 27 seconds before sudden decomposition. A second, immediately after that, lasted two seconds. The product, a char which could not be stabilized and had no apparent value, confirmed the need for close control ofthe microwave fields to contain the transformation reactions within the coal particles.

In the microwave heating step, an electromagnetic field generates localized high temperatures within the coal substances, causing the formation and deposition of organic liquids, tars and other pyrolysis product. The mobilization and deposition of those substances within the coal contributes to the structural stability which is one ofthe main objects ofthe present invention. To minimize the escape of organic substances and consequent reduction ofthe coal's fuel value, it is necessary to minimize the total energy absorbed by the coal and thus the temperature rise ofthe coal. That is accomplished in most coals by generating the localized high temperatures which form the desired substances, employing brief exposure to electromagnetic energy ofhigh intensity. The heat from localized energy absorption is dissipated to adjacent unheated portions ofthe coal substance being processed. Under such conditions essentially all of the mobile substances can be retained effectively within the coal being processed.

The preferred embodiment of this invention thus is to limit the bulk temperature rise by limiting the net electromagnetic energy absorbed by the coal in microwave heating to approximately 60 kilowatt hours (kWh) per ton of dry coal. The control is effected by selection ofthe frequency of the electromagnetic field, of its application in fields of optimum duration and interval, all as outlined above, with the objective of producing the necessary liquids, tars and other pyrolysis products while limiting the bulk product temperature to approximately 150°C. Operation at bulk temperatures up to 3 OOX, which may be required for optimum product stabilization of some coals, is an entirely acceptable option in the practice of this process, with recognition that the evolution of volatile organic materials from the coal particles may reach as much as of 10% ofthe dry coal feed versus a nominal 2% at 150°C and require processing to recover them as byproducts. The consequent energy requirement could then rise to approximately 120 kWh per ton of dry coal.

When the dried and stabilized coal leaves the zone of the final heating step, still in a continuous flow mode, it is cooled to less than 60°C and preferably stored in an atmosphere low enough in oxygen and moisture content to avoid self-ignition and moisture regain, utilizing conventional techniques of coal technology. Should recovery of the heat content of the coal be desired, it can also be realized through conventional engineering practice.

As has been recounted above, a preferred embodiment of the invention as presently contemplated by applicant has been described. The process is contemplated to differ from the prior art known to applicant in several important ways. First, it employs the virtually instantaneous energy transfer rate mechanisms of electromagnetic fields to make possible integrated multi-step processing, in a continuous flow mode, on the large scale required for cost-effective coal drying and stabilizing. Second, it employs the unique temperature gradient created in a substance heated by electromagnetic fields whereby target sites in the interior ofthe substance can be heated as fast or faster than the surface. Those effects are important features for the practice ofthe present invention.

The stabilization of dried low rank coal by microwave energy according to the present invention also can be seen to include generation of small quantities of volatile and tarry hydrocarbon compounds and other pyrolysis products from the original coal substance without heating the bulk of the coal to a temperature where evolution of volatiles becomes significant. Additionally, the process of the present invention permits mobilization of such compounds to voids and surfaces within the solid coal particle. This accomplishes a reinforcing ofthe coal's structure against physical degradation, such as crumbling and dust formation, typical of other drying processes. The foregoing is achieved in addition to ensuring that other physical properties of the processed coal are at the levels ofthe raw coal or better.

Having described the invention above, various modifications ofthe techniques, procedures, material and equipment will be apparent to those in the art. It is intended that all such variations within the scope and spirit of the inventive concepts and features described above be embraced thereby.

Claims

We claim:

1. A method of stabilizing low rank coals to enhance their physical properties for use as fuel, comprising the steps of: applying electromagnetic energy to dried particles of the low rank coals to cause partial pyrolysis ofthe naturally occurring substances within the coal particles; allowing the products formed by partial pyrolysis to remain within the coal particles and bond the coal particles from within to thereby stabilize the low rank coal.

2. The method of claim 1, further including the step of: initially pre-heating the low-rank coal particles with radio frequency energy.

3. The method of claim 1, wherein the low rank coal is composed of particles sized according to the frequency ofthe electromagnetic energy applied to cause partial pyrolysis ofthe coal particles.

4. The method of claim 1, wherein the low rank coal is composed of particles sized according to dielectric properties ofthe particular low rank coal particles to be processed.

5. The method of claim 1, wherein the products formed by partial pyrolysis during said step of applying electromagnetic energy include organic liquids.

6. The method of claim 1, wherein the products formed by partial pyrolysis during said step of applying electromagnetic energy include tars.

7. The method of claim 1, wherein the products formed by partial pyrolysis during said step of applying electromagnetic energy include polymeric materials.

8. The method of claim 1, wherein the products formed by partial pyrolysis during said step of applying electromagnetic energy include allotropic forms of carbon.

9. The method of claim 1, wherein the physical properties of the low rank coals enhanced during the stabilization thereof include resistance to breakage.

10. The method of claim 1, wherein the physical properties of the low rank coals enhanced during the stabilization thereof include resistance to dust formation.

11. The method of claim 1, wherein the physical properties of the low rank coals enhanced during the stabilization thereof include resistance to self-ignition.

12. The method of claim 1, wherein the physical properties of the low rank coals enhanced during the stabilization thereof include resistance to moisture reabsorption.

13. The method of claim 1, further including the step of: controlling the average bulk temperature of the low rank coal particles while electromagnetic energy is applied.

14. The method of claim 1, further including the step of: controlling the oxygen content of the atmosphere surrounding the low rank coal particles as they are processed.

15. The method of claim 1, wherein the process is performed essentially at atmospheric pressure.

16. The method of claim 1, wherein the electromagnetic energy applied is at radio frequencies from about 5 MHz to about 500 Mhz.

17. The method of claim 1, wherein the electromagnetic energy applied is at microwave frequencies firom about 500 MHz to about 30,000 Mhz.

18. The method of claim 1, wherein the field strength of electromagnetic energy applied is above about 5 watts/cm².

19. The method of claim 1, wherein the electromagnetic energy applied is in continuous wave form.

20. The method of claim 1, wherein the electromagnetic energy applied is in the form of a series of pulses.