Gaseous combustible fuel containing suspended solid fuel particles

Abstract

A gaseous combustible fuel includes a gaseous hydrocarbon fuel feedstock and solid fuel particles suspended in the gaseous hydrocarbon fuel feedstock. The solid fuel particles have a sufficiently small particle size so that they remain suspended during transportation. The hydrocarbon fuel feedstock may include natural gas, ethane, propane, butane, and gaseous derivatives and mixtures thereof. The solid fuel particles may include coal-derived solid carbonaceous matter. Other examples of solid fuel particles include biomass, refined bioproducts, and combustible polymer particles. The gaseous combustible fuel has an energy density at atmospheric pressure which is at least 25% greater than the volumetric energy density of the gaseous hydrocarbon fuel feedstock. Improvements in volumetric energy density of 50%, 100%, and even 500% are disclosed. The gaseous combustible fuel may be pressurized to a pressure in the range from 2 to 100 atmospheres.

Claims

1. A gaseous combustible fuel comprising: a gaseous hydrocarbon fuel; and solid fuel particles suspended in the gaseous hydrocarbon fuel, wherein the solid fuel particles consist of fine coal having a particle size less than 60 μm, wherein the gaseous combustible fuel has a volumetric energy density in the range from 45,000 to 300,000 BTU/m.sup.3 at atmospheric pressure.

2. The gaseous combustible fuel according to claim 1, wherein the gaseous hydrocarbon fuel is selected from natural gas, methane, ethane, propane, butane, and gaseous derivatives and mixtures thereof.

3. The gaseous combustible fuel according to claim 1, wherein the solid fuel particles comprise combustible particles having a heat content greater than 5000 BTU/lb.

4. The gaseous combustible fuel according to claim 1, wherein the solid fuel particles comprise combustible particles having a density greater than 500 kg/m.sup.3.

5. The gaseous combustible fuel according to claim 1, wherein the solid fuel particles comprise combustible particles having a heat content greater than 5000 BTU/lb and a density greater than 500 kg/m.sup.3.

6. The gaseous combustible fuel according to claim 1, further comprising a dispersant associated with the fine coal.

7. The gaseous combustible fuel according to claim 6, wherein the dispersant comprises an organic acid.

8. The gaseous combustible fuel according to claim 7, wherein the dispersant is citric acid.

9. The gaseous combustible fuel according to claim 7, wherein the dispersant is selected from linear, cyclic, saturated, or unsaturated carboxylic acid and polycarboxylic acids.

10. The gaseous combustible fuel according to claim 1, wherein the solid fuel particles have a particle size less than 30 μm.

11. The gaseous combustible fuel according to claim 1, wherein the solid fuel particles have a particle size less than 10 μm.

12. The gaseous combustible fuel according to claim 1, wherein the solid fuel particles have a particle size less than 5 μm.

13. The gaseous combustible fuel according to claim 1, wherein the gaseous hydrocarbon fuel has a volumetric energy density at atmospheric pressure and the gaseous combustible fuel has a volumetric energy density at atmospheric pressure which is at least 25% greater than the volumetric energy density of the gaseous hydrocarbon fuel.

14. The gaseous combustible fuel according to claim 1, wherein the gaseous hydrocarbon fuel has a volumetric energy density at atmospheric pressure and the gaseous combustible fuel has a volumetric energy density at atmospheric pressure which is at least 50% greater than the volumetric energy density of the gaseous hydrocarbon fuel.

15. The gaseous combustible fuel according to claim 1, wherein the gaseous hydrocarbon fuel has a volumetric energy density at atmospheric pressure and the gaseous combustible fuel has a volumetric energy density at atmospheric pressure which is at least 100% greater than the volumetric energy density of the gaseous hydrocarbon fuel.

16. The gaseous combustible fuel according to claim 1, wherein the gaseous hydrocarbon fuel has a volumetric energy density at atmospheric pressure and the gaseous combustible fuel has a volumetric energy density at atmospheric pressure which is at least 500% greater than the volumetric energy density of the gaseous hydrocarbon fuel.

17. The gaseous combustible fuel according to claim 1, wherein the gaseous hydrocarbon fuel is natural gas, wherein the solid fuel particles have a particle size less than 10 μm, wherein the gaseous hydrocarbon fuel has a volumetric energy density at atmospheric pressure, and the gaseous combustible fuel has a volumetric energy density at atmospheric pressure which is at least 25% greater than the volumetric density of the gaseous hydrocarbon fuel.

18. The gaseous combustible fuel according to claim 1, wherein the gaseous hydrocarbon fuel comprises greater than 90 volume % natural gas.

19. The gaseous combustible fuel according to claim 1, wherein the gaseous combustible fuel has a pressure in the range from 2 to 100 atmospheres.

20. The gaseous combustible fuel according to claim 1, wherein the solid fuel particles have a particle size less than 20 μm.

21. The gaseous combustible fuel according to claim 1, wherein the solid fuel particles have a particle size less than 2.5 μm.

22. The gaseous combustible fuel according to claim 1, wherein the solid fuel particles have an average diameter less than 30 μm.

23. The gaseous combustible fuel according to claim 1, wherein the solid fuel particles have an average diameter less than 20 μm.

24. A gaseous combustible fuel comprising: a gaseous hydrocarbon fuel; and solid fuel particles suspended in the gaseous hydrocarbon fuel, wherein the solid fuel particles consist of fine coal having an average diameter less than 10 μm, wherein the gaseous combustible fuel comprises greater that 90 volume % gaseous hydrocarbon fuel.

25. The gaseous combustible fuel according to claim 24, wherein the gaseous hydrocarbon fuel is selected from natural gas, methane, ethane, propane, butane, and gaseous derivatives and mixtures thereof.

26. The gaseous combustible fuel according to claim 24, wherein the solid fuel particles have an average diameter less than 5 μm.

27. The gaseous combustible fuel according to claim 24, wherein the gaseous hydrocarbon fuel has a volumetric energy density at atmospheric pressure and the gaseous combustible fuel has a volumetric energy density at atmospheric pressure which is at least 50% greater than the volumetric energy density of the gaseous hydrocarbon fuel.

28. The gaseous combustible fuel according to claim 24, wherein the gaseous hydrocarbon fuel has a volumetric energy density at atmospheric pressure and the gaseous combustible fuel has a volumetric energy density at atmospheric pressure which is at least 100% greater than the volumetric energy density of the gaseous hydrocarbon fuel.

29. A gaseous combustible fuel comprising: a gaseous hydrocarbon fuel; and solid fuel particles suspended in the gaseous hydrocarbon fuel, wherein the solid fuel particles consist of fine coal having a particle size less than 60 μm, wherein the gaseous hydrocarbon fuel comprises greater that 90 volumetric % natural gas and has an energy density greater that 45,000 BTU/m.sup.3.

Description

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

(1) In order that the manner in which the above-recited and other features and advantages of the invention are obtained will be readily understood, a more particular description of the invention briefly described above will be rendered by reference to specific embodiments thereof that are illustrated in the appended drawings. Understanding that these drawings depict only typical embodiments of the invention and are not therefore to be considered to be limiting of its scope, the invention will be described and explained with additional specificity and detail through the use of the accompanying drawings in which:

(2) FIG. 1 shows a schematic representation of a cyclone used in some examples to separate solid fuel particles by particle size.

(3) FIG. 2 is a graph of the differential volume by particle diameter of the fine particles that exited the top of the cyclone shown in FIG. 1 and the larger particles that exited the bottom of the cyclone. FIG. 2 also shows the particle size distribution of the coal particles fed into the cyclone.

(4) FIG. 3 shows a schematic representation of a cyclone used in some examples to separate solid fuel particles by particle size.

(5) FIG. 4 is a graph of the differential volume by particle diameter of the fine particles that exited the top of the cyclone shown in FIG. 3 and the larger particles that exited the bottom of the cyclone.

(6) FIG. 5 is a graph of data for solid fuel particle blended in natural gas at NPT where 50% of the BTU comes from solid fuel particles with density ranging from 1 to 1000 kg/m.sup.3 and heat content ranging from 5,000 to 15,000 BTU/lb.

(7) FIG. 6 is a three dimensional graph of data for solid fuel particle blended in natural gas at NPT where 50% of the BTU comes from solid fuel particles with density ranging from 1 to 1000 kg/m.sup.3 and heat content ranging from 5,000 to 15,000 BTU/lb.

(8) FIG. 7 is a graph of data for the settling velocity of solid fuel particles as a function of average particle size when blended in various gases at normal pressure and temperature. The viscosity of the gases is shown as a reference on the right hand side next to the termination of the data set for each gas.

(9) FIG. 8 is a graph of settling velocity of solid fuel particles ranging in average size up to 60 microns are provided for different pressures ranging from 1 to 100 atm.

DESCRIPTION OF THE INVENTION

(10) This disclosure relates to a modified combustible gaseous fuel, such as natural gas, containing suspended solid fuel particles. The disclosure also relates to a method of increasing the volumetric energy density of a combustible gaseous fuel by suspending small amounts of solid fuel particles within the gaseous fuel. The suspended solid fuel particles greatly enhance the energy density of the base combustible gaseous fuel.

(11) The modified combustible gaseous fuel is a multi-phase fuel composition comprising a blend of combustible gaseous fuel, also referred to herein as gaseous hydrocarbon feedstock, and suspended solid fuel particles. Non-limiting examples of combustible gaseous fuels include natural gas, methane, ethane, propane, butane, etc. These gaseous combustible fuels can also be compressed and transported as a liquid. However, at the end-use, they are almost always transformed into and combusted in the gaseous form.

(12) The solid fuel particles comprise finely-divided particles of an energetic or combustible fuel material. In one non-limiting embodiment the solid fuel particles comprise fine coal particles. More specifically, the fine coal particles comprise coal-derived carbonaceous matter. When milled to a sufficiently small size to be substantially free of inherent mineral matter, coal-derived carbonaceous matter exists as coal-derived solid hydrocarbon. In another non-limiting embodiment the solid fuel particles comprise coal-derived solid hydrocarbon particles.

(13) In another embodiment the solid fuel particles are derived from organic materials, including waste organic materials. In still another embodiment, the solid fuel particles are derived from waste biomass. Non-limiting examples of waste biomass include sawdust, plant cuttings, wood chips, and plant stalks. Further, the solid fuel particles may be a refined bioproduct. Non-limiting examples of a refined bioproduct include sugars, starches, cellulose, flour, etc. Even further, the solid fuel particles may consist of any synthesized solid fuel compound. Non-limiting examples of synthesized solid fuel compounds include which include polymers such as polyethylenes, polypropylenes, polycarbonates, polystyrenes, rubbers, etc. The synthesized solid fuel compounds may be waste organic materials, including waste polymers. Non-limiting examples of waste polymers include used tires, polypropylene grocery bags, and Styrofoam.

(14) The solid fuel particles may be derived from a single source of energetic or combustible fuel materials. Alternatively, the solid fuel particles may be derived from a blend or mixture of different energetic or combustible fuel materials.

(15) The solid fuel particles have a size that enables them to be easily suspended and to remain suspended in the combustible gaseous fuel for a practical period of time during storage, transport, and/or use. Stokes law defines the frictional force or drag force when the Reynold's number is low (e.g. for very small spherical particles) as it passes through a fluid or gas. When the drag force is set equal to the gravitational acceleration force, then a terminal velocity can be calculated for these very small particles. This case assumes no other forces other than the drag of calm air. Thus, Stokes Law can be used to calculate the settling velocity of a sphere of a given density in air or other gasses or liquids if the diameter is less than about 250 microns:

(16) $V=\frac{d^2.Math.g}{18.Math.\eta }.Math.\left(\mathrm{Ws}-\mathrm{Wa}\right)$

(17) Where d=the geometric diameter of the sphere (m)

(18) Ws=the density of the sphere (kg/m.sup.3)

(19) Wa=the density of the air (kg/m.sup.3)

(20) g=acceleration due to gravity (m/s.sup.2)

(21) η=the viscosity of the fluid (kg/(m*s))

(22) Table 2 shows the calculated settling velocity of spherical particles in air at normal temperature and pressure for diameters from 0.5 microns up to 60 microns when Ws=1200 kg/m.sup.3, Wa=1.2 kg/m.sup.3, g=9.8 m/s.sup.2, and η=1.81×10.sup.−5 kg/(m*s) using a model based on Stokes Law.

(23) TABLE-US-00002 TABLE 2 diameter Settling Velocity (μm) (m/s) 0.5 9.01 × 10.sup.−6 1 3.61 × 10.sup.−5 2.5 2.25 × 10.sup.−4 5 9.01 × 10.sup.−4 10 3.61 × 10.sup.−3 20 1.44 × 10.sup.−2 30 3.25 × 10.sup.−2 60 1.19 × 10.sup.−1

(24) A combustible gaseous fuel moving at velocity exceeding the settling velocity of the particles in suspension in the combustible gaseous fuel will keep said particles in suspension.

(25) From Stokes Law and the foregoing discussion, it will also be appreciated that particles having a lower density will also possess a lower settling velocity. It is possible to suspend solid fuel particles in a gaseous hydrocarbon feedstock that have a greater particle size and a lower density compared so smaller and denser solid fuel particles. Thus, different types and sizes of solid fuel particles may be suspended and remain suspended in the combustible gaseous fuel.

(26) As noted above, the solid fuel particles should have a particle size less than 250 μm, and more preferably less than 60 μm. In one non-limiting embodiment, the solid fuel particles have an average diameter less than 30 μm. In another embodiment, the solid fuel particles have an average diameter less than 20 μm. In yet another embodiment, the solid fuel particles have an average diameter less than 10 μm. In a further embodiment, the solid fuel particles have an average diameter less than 5 μm. In one non-limiting embodiment, 99% of the solid fuel particles are all less than 20 μm. In another non-limiting embodiment, 99% of the solid fuel particles are all less than 10 μm. In still another non-limiting embodiment, the solid fuel particles have an average size less than 2.5 μm. In other non-limiting embodiments, larger size and lower density solid fuel particles may be successfully used.

(27) The time period during which the solid fuel particles remain suspended may vary depending upon the intended use of the modified combustible gaseous fuel. For example, if the modified combustible gaseous fuel is prepared on demand for immediate use, then the suspension time period may be short, such as seconds, minutes, or hours. In contrast, if the modified combustible gaseous fuel is stored for a period of time, then the practical suspension time period may be measured in days, weeks, or months. It will be appreciated that finer sized solid fuel particles will naturally remain suspended for a longer time period compared to larger sized solid fuel particles. A particle having a size of about 10 μm may remain suspended for minutes to hours, whereas a particle having a size of about 2.5 μm may remain suspended for days or weeks.

(28) In one disclosed embodiment, the combustible gaseous fuel comprises natural gas and the suspended solid fuel particles comprise fine coal particles which include coal-derived carbonaceous matter. The amount of coal particles blended with natural gas may range from about 5 volume % or less, at atmospheric pressure. The coal particles may have an average particle size less than 30 μm.

(29) A dispersant may be added to the fine coal particles to reduce particle agglomeration. In one non-limiting embodiment, the dispersant is an organic acid. The dispersant may be an organic acid selected from linear, cyclic, saturated, or unsaturated carboxylic acid and polycarboxylic acids. In one currently preferred embodiment, the dispersant is citric acid. In another non-limiting embodiment, the dispersant is a lignosulfonate based surfactant. Another dispersant class that may be used are non-ionic dispersants such as a polyethylene oxide dispersant.

(30) Table 3, below, sets forth the dramatic energy density improvement that is observed with increasing amounts of fine coal particles with an average diameter of 30 μm or less blended with natural gas at normal temperature and pressure where the solid fuel particles have a heat content of 14,500 BTU/lb and a density of 1,200 kg/m.sup.3.

(31) TABLE-US-00003 TABLE 3 % Increase in % of BTU Volume % Volumetric Energy Volumetric Mass % from μCCF μCCF Density (BTU/m.sup.3) Energy Density μCCF  0%   0% 37,038 0% 0.0% 10% 0.01% 41,149 11% 13.9% 20% 0.02% 46,286 25% 26.6% 30% 0.04% 52,889 43% 38.3% 40% 0.06% 61,690 67% 49.1% 50% 0.10% 74,004 100% 59.2% 60% 0.14% 92,460 150% 68.5% 70% 0.22% 123,181 233% 77.2% 80% 0.38% 184,476 398% 85.3% 83.4%   0.48% 222,042 500% 87.9% 90% 0.86% 367,186 891% 92.9% 95% 1.80% 727,410 1864% 96.5%

(32) Solid fuel particles were blended with natural gas at normal temperature and pressure (NPT). NPT=20° C. and 1 atm. Solid fuel particles are blended in with natural gas in way such that 0% to 95% of the BTU of the blend comes from the solid fuel particles. The solid fuel particles have a heat content of 14,500 BTU/lb and a density of 1,200 kg/m.sup.3. The density of natural gas is 0.8 kg/m.sup.3. Because the density of the of the solid particles far exceeds the density of natural gas, the volume % of the solid fuel particle-natural gas blend or enhanced natural gas was less than 2 volume % even when 95% of the BTU of the enhanced natural gas comes from the solid fuel particles. When 83.4% of the BTU comes from the solid fuel particles, there is a 500% increase in BTU of the blend over natural gas alone.

(33) The following non-limiting examples are given to illustrate several embodiments relating to the disclosed gaseous combustible fuel containing suspended solid fuel particles. It is to be understood that these examples are neither comprehensive nor exhaustive of the many types of embodiments which can be practiced in accordance with the presently disclosed invention.

Example 1

(34) An experiment was designed to test whether fine coal particles settle in calm air as predicted by Stokes Law. First, fine coal particles of a defined size were obtained by passing the coal particles through a small cyclone. Cyclones are devices that can be used to classify particles in flowing water or air based on size.

(35) The cyclone used in this experiment is depicted in FIG. 1. It had a bottom opening of about 4.7 mm and a top opening of 14.5 mm and was 105 mm tall. A small vacuum pump operating at a rate of 1.9 liters per minute was connected to the top port of the cyclone. Large particles that fell out of the bottom port were collected in a cap or grit pot. Small particles carried out of the top of the cyclone in the airstream were collected on fine filter paper before entering the vacuum. FIG. 2 shows a particle size analysis graph for the smaller particles that exited the top of the cyclone and the larger particles that exited the bottom of the cyclone. Also shown in FIG. 2 is the particle size distribution of the coal particles that fed into the cyclone. The fine particles exiting the top had an average particles size of 4.4 μm. The large particles exiting the bottom of the cyclone had an average particle size of 18.8 μm.

(36) The cyclone was then set up as shown in FIG. 3. In this configuration, the fine particles exiting the cyclone were passed through a stainless steel cube box with inside wall lengths of 2.25″ with a 1.5″ diameter window on two sides so that one could see through the box and see suspended particles. The volumetric air flow of the vacuum pump was measured at 1.9 liters per minute. The tubing going from the cyclone to the steel box and from the steel box to the vacuum pump had a 6.9 mm inside diameter. Based on the volumetric air flow rate of the vacuum pump, the air velocity in the tube was calculated to be 0.85 m/s. The air velocity in the box slows down due to the larger cross-sectional surface are of the container and was calculated to be 0.0096 m/s.

(37) According to Table 2, the settling velocity for particles suspended in air of a 60 μm diameter particle is 0.12 m/s, the settling velocity of a 30 μm particle is 0.033 m/s, the settling velocity of a 20 μm particle is 0.014 m/s, and the settling velocity of a 10 μm particle is 0.0036 m/s. From FIG. 2, some 30 and 60 μm particles are in the feed particles. The air velocity in the tubing is greater than the settling velocity for particles in this range and thus, they should be able to be transported in the tubing. However, the air velocity inside the box is lower than the settling velocity of these particles. Thus, particles larger than 30 microns are not expected to remain in suspension inside the box with the volumetric air flow rate of this experimental setup.

(38) According to Table 2, the settling velocity of a 10 μm particle is 0.0036 m/s. The air velocity inside the box is 0.0096 m/s which is greater than the settling velocity of 10 μm particles. Thus, particles 10 μm and smaller are expected to be in suspension in the box when air is flowing through it at the volumetric rate of 1.9 liters per minute.

(39) When the experimental setup described herein and shown in FIG. 3 was operating, the particles exiting the top of the cyclone and travelling into the box had an average particle size of 4.4 μm. A light shined through the back window of the box. The particles could be observed traveling in the current of air as it expanded from the volume of the tube entering the box to the volume of the box. As long as the pump was left on and particles were being delivered to the cyclone, particles entered and exited the box without settling to the bottom of the box.

(40) When the pump was turned off, the flow of air stopped. The particles could then be observed to slowly drift to the bottom of the box. The time required for the particles to travel 1 cm was measured to be approximately 10 seconds, corresponding to a settling velocity of 0.001 m/s. This settling velocity matches the calculated settling velocity of 0.0009 m/s for a 5 μm diameter particle.

(41) The cyclone was then removed from the experimental setup so that the suction tube fed the particles into the box. As stated above, any 30 μm and 60 μm particles are expected transport in the tubing but are then expected to settle soon after entering the box, based on the calculated air velocity for the two different cross-sectional areas. Particles in the size range of about 10 μm in the feed are expected to remain suspended in the box because the air velocity in the box exceeds their settling velocity.

(42) When the feed was introduced directly into the box by removing the cyclone from the experimental setup, a higher density of particles was visually observed in the box. When the vacuum pump was shut off and air velocity went to zero, the particles were observed to settle more quickly indicating a population of larger diameter particles. The time required for the particles to travel 1 cm was measured to be approximately 0.8 seconds, corresponding to a settling velocity of 0.012 m/s. The air velocity inside the box calculated from the volumetric flow rate and the cross-sectional area was calculated to be 0.0096 m/s, which is slightly lower than the measured settling rate of 0.012 m/s. The visual method for measuring settling rate may not be accurate enough. However, the fact that the two rates are on the same order and so close to one another validates the assumption that air velocity greater than the settling rate of a particle will keep that particle in suspension in a flowing gas. The settling velocity for a 10 μm diameter particle was calculated to be 0.0036 m/s. Thus, the particles must be larger than 10 μm and smaller than 30 μm on average. In fact, a particle with a diameter of 18.25 μm would have a settling velocity in air at normal pressure and temperature of 0.012 m/s.

Example 2

(43) A larger cyclone was used as part of a powder capture system. The large and small dimensions of the cone were 27.5 cm and 7.3 cm, respectively. The cyclone was 61 cm tall. FIG. 4 shows a graph of the differential volume by particle diameter of the large particles exiting the small opening at the bottom of the cyclone and the small particles carried with the airstream exiting the top of the cyclone. The average particle sizes were 21.4 μm and 6.2 μm respectively. Note that the larger particles were the feedstock used for the experiment with the small cyclone discussed in Example 1, above. The fine particles with an average particle size were transported in metal ducting over 50 feet away without significant sedimentation to the sidewalls of the ducting. Once the ducting was coated with a thin film of fine particles due to static charges, losses were negligible.

Example 3

(44) When a common liquid propane canister is filled with propane, the bulk of the propane is liquid. However, at any typical ambient temperature, a certain amount of the liquid propane will enter the gaseous phase until the pressure of the gas inside the canister equals the vapor pressure of propane at that temperature. For example, the pressure inside a liquid propane tank that contains pure propane will be about 127 pounds per square inch (psi) at 71 degrees Fahrenheit. As propane gas is removed from the canister to power a burner, for example, more liquid propane enters the gaseous phase to maintain the pressure equilibrium inside the canister at the ambient temperature.

(45) A 1 liter liquid propane canister was fabricated such that it could be opened and filled with a small volume fine coal particles. A stirrer was added internal to the system to keep the fine coal particles well distributed in the liquid propane. The canister could then be evacuated with a vacuum to remove air and refilled with liquid propane. The stirrer kept the coal particles in suspension inside of the liquid propane. It was assumed that as propane gas was removed from the canister, some coal particles would also exit. Then as the gaseous propane was burned, the fine coal particles that were transported in the gaseous phase out of the canister with the propane gas would be burned as well.

(46) This canister was first tested with propane only by connecting it to a burner. The color of the flame was blue as expected for propane. Coal is known to burn orange. When coal particles were introduced into the canister, the resulting flame was orange and blue. As the concentration of coal particles increased, the flame became more orange. In this experiment, there was not fine control over the amount of coal blended with the propane gas exiting the canister, but the color of the flame indicated that fine coal particles were introduced into the propane gas stream and burned along with it in the burner.

Example 5

(47) Various other fine particles were also blended with propane as examples of solid fuels that could be blended with a gaseous fuel source inside the modified liquid propane canister: starch, sugar, flour, polycarbonate, chicken manure, and sawdust. All these solid fuels caused the flame to change from blue to orange as the concentration of the fine particles entrained in the gaseous propane increased.

Example 6

(48) A solid fuel particle with an average size of 30 μm was blended with natural gas. The settling velocity was determined at various pressures. A 100× increase in pressure from 1 atm to 100 atm only resulted in a 26% decrease in settling velocity. The reduction in settling velocity was mainly due to the slight increase in natural gas density with increasing pressure as the increase in drag at the elevated pressures was insignificant. As the gas volume decreased with increasing pressure, the gas density and volumetric energy density both increased.

(49) Table 4. Volume Percent and Volumetric Energy Density of natural gas blended with 50% of BTU from solid fuel particles, referred to as micro clean carbon fuel (μCCF), at different pressures. The clean carbon fuel particles were 14,500 BTU/lb and 1200 kg/m.sup.3.

(50) TABLE-US-00004 TABLE 4 Volumetric % Volume Energy Settling % change in change in Pressure % Density Velocity Volumetric settling (atm) μCCF (Btu/m.sup.3) (cm/sec) Energy Density velocity 1 0.09% 71,974 5.34 — — 5 0.47% 358,527 4.83 398% −9.5% 10 0.93% 713,718 4.62 892% −13.4% 20 1.84% 1,414,279 4.29 1865% −19.6% 40 3.62% 2,777,360 3.88 3759% −27.3% 65 5.75% 4,413,356 3.54 6032% −33.7% 100 8.58% 6,585,785 3.20 9050% −40.0%

(51) Table 4 shows a natural gas system where 50% of the BTU of the solid fuel particle enhanced natural gas comes from the solid fuel particles. The solid fuel particles had an energy density of 14,500 BTU/lb and a density of 1200 kg/m.sup.3. The increase in the volume % with increasing pressure is shown. Natural gas is transported at elevated pressures. In the US and China, those transportation pressures often range between 65 and 100 atmospheres for long distance transport.

(52) At 100 atm, the volume percent of solid fuel particles only increased to 8.58%. Settling velocity is shown to decrease as pressure increases. This is due to the increasing density of the pressurized natural gas. In all cases, the velocity of the natural gas in the transportation pipeline must exceed about 3.2 cm/sec in order to maintain the fine 30 micron diameter solid fuel particles in suspension during transportation.

Example 7

(53) Fine solid fuel particles are blended with different gaseous hydrocarbon fuel feed stocks and evaluated in terms of volumetric energy density at different heat contents of 5,000, 10,000, and 15,000 BTU/lb. The results with respect to the different gaseous hydrocarbon fuel feed stocks are reported in Table 5 for natural gas, Table 6 for propane, Table 7 for butane.

(54) TABLE-US-00005 TABLE 5 Natural gas at NPT blended with solid fuel particles, designed μCCF in Table 5, where the density of the particles is 1,200 kg/m.sup.3 for heat contents of 5,000, 10,000, and 15,000 BTU/lb. % of Btu Volume % Volumetric % Increase in from of Energy Density Volumetric Mass % μCCF μCCF (Btu/m.sup.3) Energy Density μCCF 0% 0.00% 37,038  0    0.0% 10%  0.03% 41,140 11% 31.8%  20%  0.07% 46,265 25% 51.2%  30%  0.12% 52,848 43% 64.3%  40%  0.19% 61,614 66% 73.7%  50%  0.28% 73,869 99% 80.8%  60%  0.42% 92,207 149%  86.3%  70%  0.65% 122,658  231%  90.7%  80%  1.11% 183,137  394%  94.4%  90%  2.46% 361,273  875%  97.4%  95%  5.05% 703,336  1799%  98.8%  μCCF Inputs 5,000 Btu/lb μCCF 1,200 kg/m.sup.3 μCCF Specific Gravity Natural Gas Inputs 21,000 Btu/lb Natural Gas 0.80 kg/m.sup.3 Natural Gas % of Btu Volume % Volumetric % Increase in from of Energy Density Volumetric Mass % μCCF μCCF (Btu/m.sup.3) Energy Density μCCF 0% 0.00% 37,038  0    0.0% 10%  0.02% 41,147 11% 18.9%  20%  0.03% 46,281 25% 34.4%  30%  0.06% 52,879 43% 47.4%  40%  0.09% 61,672 67% 58.3%  50%  0.14% 73,972 100%  67.7%  60%  0.21% 92,400 149%  75.9%  70%  0.33% 123,057  232%  83.1%  80%  0.56% 184,157  397%  89.4%  90%  1.24% 365,768  888%  95.0%  95%  2.59% 721,560  1848%  97.6%  μCCF Inputs 10,000 Btu/lb μCCF 1,200 kg/m.sup.3 μCCF Specific Gravity Natural Gas Inputs 21,000 Btu/lb Natural Gas 0.80 kg/m.sup.3 Natural Gas % of Btu Volume % Volumetric % Increase in from of Energy Density Volumetric Mass % μCCF μCCF (Btu/m.sup.3) Energy Density μCCF 0% 0.00% 37,038  0    0.0% 10%  0.01% 41,149 11% 13.5%  20%  0.02% 46,286 25% 25.9%  30%  0.04% 52,890 43% 37.5%  40%  0.06% 61,691 67% 48.3%  50%  0.09% 74,006 100%  58.3%  60%  0.14% 92,465 150%  67.7%  70%  0.22% 123,191  233%  76.6%  80%  0.37% 184,500  398%  84.8%  90%  0.83% 367,292  892%  92.6%  95%  1.74% 727,847  1865%  96.4%  μCCF Inputs 15,000 Btu/lb μCCF 1,200 kg/m.sup.3 μCCF Specific Gravity Natural Gas Inputs 21,000 Btu/lb Natural Gas 0.80 kg/m.sup.3 Natural Gas

(55) Table 5 shows natural gas blended with solid fuel particles at atmospheric pressure and 20° C. where the density of individual particles is 1,200 kg/m.sup.3, meaning one particle has this density and a solid block of this material would also have this density. The solid fuel particles have heat contents of 5,000, 10,000, and 15,000 BTU/lb. Coal derived solid hydrocarbon heat content generally ranges between about 13,500 to 15,000 BTU/lb. The range from 5,000 to 15,000 was chosen to show that the volume % of solid fuel particles (μCCF) changes slightly for natural gas in the three different tables in comparison to the total volume % even though the heat content changed significantly. For a material that is 5,000 BTU/lb and 1,200 kg/m.sup.3, if 95% of the BTU comes from natural gas, only 5.05% of the volume comes from solid fuel particles. The reason for the small volume content is because the solid fuel particles have a large density in comparison to the density of gas at normal temperature and pressure (NPT), wherein NPT is 20° C. and 1 atm.

(56) TABLE-US-00006 TABLE 6 Propane blended with solid fuel particles at NPT where the density of the particles is 1,200 kg/m.sup.3 for heat contents of 5,000, 10,000, and 15,000 BTU/lb. % of Btu Volume % % Volumetric % Increase in from of Energy Density Volumetric Mass % μCCF μCCF (Btu/m.sup.3) Energy Density μCCF 0% 0.00% 89,471  0    0.0% 10%  0.08% 99,338 11% 32.4%  20%  0.17% 111,650  25% 51.9%  30%  0.29% 127,447  42% 64.9%  40%  0.45% 148,449  66% 74.2%  50%  0.67% 177,740  99%  81.2%  60%  1.00% 221,432  147%  86.6%  70%  1.55% 293,604  228%  91.0%  80%  2.63% 435,572  387%  94.5%  90%  5.74% 843,372  843%  97.5%  95%  11.39%  1,585,647   1672%  98.8%  μCCF Inputs 5,000 Btu/lb μCCF 1,200 kg/m.sup.3 μCCF Specific Gravity Gas Inputs 21,564 Btu/lb Propane 1.88 kg/m.sup.3 Propane % of Btu Volume % % Volumetric % Increase in from of Energy Density Volumetric Mass % μCCF μCCF (Btu/m.sup.3) Energy Density μCCF 0% 0.00% 89,471  0    0.0% 10%  0.04% 99,375 11% 19.3%  20%  0.08% 111,475  25% 35.0%  30%  0.14% 127,631  43% 48.0%  40%  0.22% 148,783  66% 59.0%  50%  0.34% 178,339  99% 68.3%  60%  0.50% 222,549  149%  76.4%  70%  0.78% 295,903  231%  83.4%  80%  1.33% 441,385  393%  89.6%  90%  2.95% 868,284  870%  95.1%  95%  6.04% 1,681,384   1779%  97.6%  μCCF Inputs 10,000 Btu/lb μCCF 1,200 kg/m.sup.3 μCCF Specific Gravity Gas Inputs 21,564 Btu/lb Propane 1.88 kg/m.sup.3 Propane % of Btu Volume % % Volumetric % Increase in from of Energy Density Volumetric Mass % μCCF μCCF (Btu/m.sup.3) Energy Density μCCF 0% 0.00% 89,471  0    0.0% 10%  0.03% 99,388 11% 13.8%  20%  0.06% 111,776  25% 26.4%  30%  0.10% 127,693  43% 38.1%  40%  0.15% 148,895  66% 48.9%  50%  0.22% 178,540  100%  59.0%  60%  0.34% 222,924  149%  68.3%  70%  0.52% 296,677  232%  77.0%  80%  0.89% 443,358  396%  85.2%  90%  1.99% 876,918  880%  92.8%  95%  4.11% 1,715,919   1818%  96.5%  μCCF Inputs 15,000 Btu/lb μCCF 1,200 kg/m.sup.3 μCCF Specific Gravity Gas Inputs 21,564 Btu/lb Propane 1.88 kg/m.sup.3 Propane

(57) A similar trend for volume % is seen when propane is used as the gaseous hydrocarbon fuel feedstock at atmospheric pressure. However, the volume percentage of the solid fuel particles increased because the density of propane at atmospheric pressure is a little over twice as much as natural gas.

(58) TABLE-US-00007 TABLE 7 Butane blended with solid fuel particles at NPT where the density of the particles is 1,200 kg/m.sup.3 for heat contents of 5,000, 10,000, and 15,000 BTU/lb. % of Btu Volume % % Volumetric % Increase in from of Energy Density Volumetric Mass % μCCF μCCF (Btu/m.sup.3) Energy Density μCCF 0% 0.00% 118,745  0    0.0% 10%  0.10% 131,808 11% 32.5%  20%  0.22% 148,099 25% 52.0%  30%  0.38% 168,986 42% 65.0%  40%  0.59% 196,732 66% 74.3%  50%  0.89% 235,378 98% 81.2%  60%  1.33% 292,919 147%  86.7%  70%  2.05% 387,697 226%  91.0%  80%  3.47% 573,146 383%  94.5%  90%  7.48% 1,098,688   825%  97.5%  95%  14.57%  2,028,860   1609%  98.8%  μCCF Inputs 5,000 Btu/lb μCCF 1,200 kg/m.sup.3 μCCF Specific Gravity Gas Inputs 21,640 Btu/lb Butane 2.49 kg/m.sup.3 Butane % of Btu Volume % % Volumetric % Increase in from of Energy Density Volumetric Mass % μCCF μCCF (Btu/m.sup.3) Energy Density μCCF 0% 0.00% 118,745  0    0.0% 10%  0.05% 131,874 11% 19.4%  20%  0.11% 148,265 25% 35.1%  30%  0.19% 169,311 43% 48.1%  40%  0.30% 197,319 66% 59.1%  50%  0.45% 236,460 99% 68.4%  60%  0.67% 294,878 148%  76.4%  70%  1.04% 391,715 230%  83.5%  80%  1.76% 583,255 391%  89.6%  90%  3.88% 1,141,348   861%  95.1%  95%  7.86% 2,188,288   1743%  97.6%  μCCF Inputs 10,000 Btu/lb μCCF 1,200 kg/m.sup.3 μCCF Specific Gravity Gas Inputs 21,640 Btu/lb Butane 2.49 kg/m.sup.3 Butane % of Btu Volume % % Volumetric % Increase in from of Energy Density Volumetric Mass % μCCF μCCF (Btu/m.sup.3) Energy Density μCCF 0% 0.00% 118,745  0    0.0% 10%  0.03% 131,865 11% 13.8%  20%  0.07% 148,321 25% 26.5%  30%  0.13% 169,419 43% 38.2%  40%  0.20% 197,515 66% 49.0%  50%  0.30% 236,782 99% 59.1%  60%  0.45% 295,537 149%  68.4%  70%  0.69% 393,073 231%  77.1%  80%  1.18% 586,705 394%  85.2%  90%  2.62% 1,156,313   874%  92.8%  95%  5.38% 2,247,148   1792%  96.5%  μCCF Inputs 15,000 Btu/lb μCCF 1,200 kg/m.sup.3 μCCF Specific Gravity Gas Inputs 21,640 Btu/lb Butane 2.49 kg/m.sup.3 Butane

(59) A similar trend for volume % is seen when butane is used as the gaseous hydrocarbon fuel feedstock at atmospheric pressure. However, the volume percentage of the solid fuel particles increased because the density of butane at atmospheric pressure is a little over twice as much as natural gas.

Example 8

(60) Fine solid fuel particles of varying densities of 500, 850, and 1,200 kg/m.sup.3 are blended with natural gas and evaluated in terms of volumetric energy density at different solid fuel heat contents of 10,000, and 14,500 BTU/lb. The results with respect to the different heat contents are reported in Table 8 for the heat content of 10,000 BTU/lb and Table 9 for the heat content of 14,500 BTU/lb.

(61) TABLE-US-00008 TABLE 8 Natural gas blended with solid fuel particles at NPT where the heat content was 10,000 BTU/lb for solid fuel particles densities of 500, 850, and 1,200 kg/m.sup.3. % of Btu Volume Volumetric % Increase in from % of Energy Density Volumetric Mass % μCCF μCCF (Btu/m.sup.3) Energy Density μCCF 0% 0.00% 37,038  0   0.0% 10%  0.04% 41,138 11% 18.9%  20%  0.08% 46,258 25% 34.4%  30%  0.14% 52,835 43% 47.4%  40%  0.22% 61,592 66% 58.3%  50%  0.33% 73,827 99% 67.7%  60%  0.50% 92,130 149%  75.9%  70%  0.78% 122,499  231%  83.1%  80%  1.33% 182,733  393%  89.4%  90%  2.94% 359,505  871%  95.0%  95%  6.00% 696,302  1780%  97.6%  μCCF Inputs 10,000 Btu/lb μCCF 500 kg/m.sup.3 μCCF Specific Gravity Natural Gas Inputs 21,000 Btu/lb Natural Gas 0.80 kg/m.sup.3 Natural Gas % of Btu Volume Volumetric % Increase in from % of Energy Density Volumetric Mass % μCCF μCCF (Btu/m.sup.3) Energy Density μCCF 0% 0.00% 37,038  0   0.0% 10%  0.02% 41,144 11% 18.9%  20%  0.05% 46,274 25% 34.4%  30%  0.08% 52,866 43% 47.4%  40%  0.13% 61,648 66% 58.3%  50%  0.20% 73,929 100%  67.7%  60%  0.30% 92,321 149%  75.9%  70%  0.46% 122,892  232%  83.1%  80%  0.78% 183,736  396%  89.4%  90%  1.75% 363,904  883%  95.0%  95%  3.62% 713,943  1828%  97.6%  μCCF Inputs 10,000 Btu/lb μCCF 850 kg/m.sup.3 μCCF Specific Gravity Natural Gas Inputs 21,000 Btu/lb Natural Gas 0.80 kg/m.sup.3 Natural Gas % of Btu Volume Volumetric % Increase in from % of Energy Density Volumetric Mass % μCCF μCCF (Btu/m.sup.3) Energy Density μCCF 0% 0.00% 37,038  0    0.0% 10%  0.02% 41,145 11% 18.9%  20%  0.04% 46,278 25% 34.4%  30%  0.07% 52,873 43% 47.4%  40%  0.11% 61,660 66% 58.3%  50%  0.17% 73,951 100% 67.7%  60%  0.25% 92,361 149% 75.9%  70%  0.39% 122,977 232% 83.1%  80%  0.67% 183,952 397% 89.4%  90%  1.49% 364,860 885% 95.0%  95%  3.09% 717,840 1838%  97.6%  μCCF Inputs 10,000 Btu/lb μCCF 1,000 kg/m.sup.3 μCCF Specific Gravity Natural Gas Inputs 21,000 Btu/lb Natural Gas 0.80 kg/m.sup.3 Natural Gas

(62) Table 8 models the blending of solid fuel particles that have a heat content of solid fuel particles of 10,000 BTU/lb with natural gas at NPT. The density of an individual particle is modelled at 500, 850, and 1,200 kg/m.sup.3. For a particle with a medium heat content level of 10,000 BTU/lb and a density of 500 kg/m.sup.3 for each particle, the volume % of the solid fuel particles in the blend with natural gas blend is still only 6.0 volume % solid fuel particles when 95% of the BTU comes from coal because the density of the coal particles is still over 500 times greater than the density of the natural gas.

(63) The large differential between the density of solid fuel particle and the natural gas at atmospheric pressure allows for the small volume % of the fuel particle blended with natural gas. Density drives the low volume % much more than heat content.

(64) TABLE-US-00009 TABLE 9 Natural gas blended with solid fuel particles at NPT where the heat content was 14,500 BTU/lb for solid fuel particles densities of 500, 850, and 1,200 kg/m.sup.3. % of Btu Volume Volumetric % Increase in from % of Energy Density Volumetric Mass % μCCF μCCF (Btu/m.sup.3) Energy Density μCCF 0% 0.00% 37,038  0    0.0% 10%  0.03% 41,142 11% 13.9%  20%  0.06% 46,270 25% 26.6%  30%  0.10% 52,858 43% 38.3%  40%  0.15% 61,634 66% 49.1%  50%  0.23% 73,904 100%  59.2%  60%  0.35% 92,273 149%  68.5%  70%  0.54% 122,795  232%  77.2%  80%  0.92% 183,488  395%  85.3%  90%  2.04% 362,810  880%  92.9%  95%  4.22% 709,516  1816%  96.5%  μCCF Inputs 14,500 Btu/lb μCCF 500 kg/m.sup.3 μCCF Specific Gravity Natural Gas Inputs 21,000 Btu/lb Natural Gas 0.80 kg/m.sup.3 Natural Gas % of Btu Volume Volumetric % Increase in from % of Energy Density Volumetric Mass % μCCF μCCF (Btu/m.sup.3) Energy Density μCCF 0% 0.00% 37,038 0% 0.0% 10%  0.02% 41,147 11%  13.9%  20%  0.03% 46,281 25%  26.6%  30%  0.06% 52,880 43%  38.3%  40%  0.09% 61,673 67%  49.1%  50%  0.14% 73,975 100%  59.2%  60%  0.20% 92,405 149%  68.5%  70%  0.32% 123,068  232%  77.2%  80%  0.54% 184,184  397%  85.3%  90%  1.21% 365,888  888%  92.9%  95%  2.52% 722,054  1850%   96.5%  μCCF Inputs 14,500 Btu/lb μCCF 850 kg/m.sup.3 μCCF Specific Gravity Natural Gas Inputs 21,000 Btu/lb Natural Gas 0.80 kg/m.sup.3 Natural Gas % of Btu Volume Volumetric % Increase in from % of Energy Density Volumetric Mass % μCCF μCCF (Btu/m.sup.3) Energy Density μCCF 0% 0.00% 37,038  0    0.0% 10%  0.01% 41,149 11%  13.9%  20%  0.02% 46,286 25%  26.6%  30%  0.04% 52,889 43%  38.3%  40%  0.06% 61,690 67%  49.1%  50%  0.10% 74,004 100%  59.2%  60%  0.14% 92,460 150%  68.5%  70%  0.22% 123,181  233%  77.2%  80%  0.38% 184,476  398%  85.3%  90%  0.86% 367,186  891%  92.9%  95%  1.80% 727,410  1864%  96.5%  μCCF Inputs 14,500 Btu/lb μCCF 1,200 kg/m.sup.3 μCCF Specific Gravity Natural Gas Inputs 21,000 Btu/lb Natural Gas 0.80 kg/m.sup.3 Natural Gas

(65) Table 9 models the blending of solid fuel particles that have a heat content of solid fuel particles of 14,500 BTU/lb with natural gas at NPT. The density of an individual particle is modelled at 500, 850, and 1,200 kg/m.sup.3. With a heat content level of 14,500 BTU/lb and a density of 500 kg/m.sup.3 for each particle, the volume % of the solid fuel particle-natural gas blend is 4.22 volume % solid fuel particles when 95% of the BTU comes from solid fuel particles because the density of the solid fuel particles is still over 500 times greater than the density of the natural gas.

(66) The large differential between the density of solid fuel particle and the natural gas at NPT allows for the small volume % of the fuel particle blended with natural gas. Density drives the low volume % much more than heat content.

Example 9

(67) Fine solid fuel particles of varying densities from 1 to 1000 kg/m.sup.3 are blended with natural gas at NPT wherein 50% of the BTU comes from the solid fuel particles and the heat content of the solid fuel ranges from 5,000 to 15,000 BTU/lb. The results are reported in Table 10.

(68) TABLE-US-00010 TABLE 10 Density 5,000 BTU/lb 10,000 BTU/lb 15,000 BTU/lb kg/m.sup.3 Volume % μCCF Volume % μCCF Volume % μCCF 1 77.06 62.69 52.83 10 25.15 14.38 10.07 50 6.30 3.25 2.19 100 3.25 1.65 1.11 500 0.67 0.33 0.22 1000 0.33 0.17 0.11

(69) FIG. 5 and FIG. 6 are graphical representations of the data represented in Table 10. The density of the solid fuel particles (μCCF) modeled with this data starts at 1 kg/m.sup.3 which is approximately the density of air and slightly more dense than natural gas. If a solid fuel particle had a density of 1 kg/m.sup.3, similar to the density of natural gas, the volume percent of the solid fuel particles dominates the volume % of the blend. As solid fuel particle density exceeds 50 kg/m.sup.3, or in other words is about 62 times greater than the density of natural gas, volume percent of the enhanced combustible gaseous fuel blend is dominated by the volume of the combustible gaseous fuel because the difference in density between the solid particles and the natural gas particles. At particle densities greater than 50 kg/m.sup.3, the volume % of the solid fuel particles was less than 7%. This trend is very evident in the three dimensional surface graph shown in FIG. 6.

(70) FIG. 7 is a graph of data for settling velocity of solid fuel particles as a function of average solid fuel particle size when dispersed in butane, propane, methane, or natural gas at normal temperature and pressure. The data was calculated using a model based on Stokes Law. The solid fuel particles had a density of 1,200 kg/m.sup.3. Density and viscosity of the gases at NPT were used in calculating the data. Table 11 shows the tabulated data.

(71) Table 11 shows settling velocity as a function of average particle size for solid fuel particles suspended in combustible gases at normal temperature and pressure. The density and viscosity of those gases is also shown.

(72) TABLE-US-00011 TABLE 11 Average Settling Velocity (cm/sec) Particle Size Natural (μm) Propane Butane Methane Gas 0.5 0.002 0.002 0.002 0.001 1 0.008 0.008 0.006 0.006 2.5 0.051 0.05 0.04 0.037 5 0.205 0.201 0.158 0.147 10 0.821 0.805 0.634 0.587 20 3.062 3.008 2.536 2.347 30 6.786 6.553 5.597 5.336 60 22.458 21.251 20.351 18.919 Density 1.8820 2.4890 0.6680 0.8000 (kg/m.sup.3) Viscosity 7.95E−06 8.10E−06 1.03E−05 1.11E−05 (kg/m/sec)

(73) At normal temperature and pressure, the density of the gases contributes very little to the settling velocity of a solid particles suspended in the gases. The density of the gas is subtracted from the density of the solid fuel particle (1,200 kg/m.sup.3 in the case of this data) when using Stokes Law to calculate settling velocity. At 1,200 kg/m.sup.3, the result of the above mentioned subtraction is still so close to the 1,200 kg/m.sup.3 of the solid fuel particle that the density of the solid fuel particles dominates the settling velocity result. Viscosity is in the denominator and has a larger influence on settling velocity as can be seen in FIG. 7 where settling velocity goes down as viscosity increases. The dominating factor in this data set for settling velocity of solid fuel particles is the size of the particle. As the size of the particle increases, the mass of the particle increases, and the influence of gravity on the particle increases. The density of the particle is also a major factor in settling velocity because the mass of a particle is a function of both volume and density. In this experiment, the density of the particles was held constant at 1,200 kg/m.sup.3.

(74) Pressurized gas has a higher density than unpressurized gas. In a pressurized system transporting suspended fuel particles, the increased density of the gases would result in decreased settling velocities relative to settling velocity values of gases at normal temperature and pressure. Viscosity of gases is relatively independent of pressure and does not change much in the range of 1 atm to 100 atm. The settling velocities in the various combustible gases at normal temperature and pressure are the maximum settling velocities that are expected to be observed for transportation of solid fuel particles in combustible gases. To further illustrate this point, settling velocity of solid fuel particles ranging in average size up to 60 microns are provided for different pressures in FIG. 8. The viscosity of the gas is relatively unchanged over the pressure range shown. The density of the gas increases 100 times as pressure increases from 1 atm to 100 atm when temperature is held constant at 20° C. As FIG. 8 shows, the largest settling velocities that must be overcome in order to keep solid fuel particles suspended in a flowing natural gas stream, e.g. a natural gas pipeline, occur at normal temperature and pressure. The natural gas must be flowing at a rate greater than about 5.3 cm/sec to at atmospheric pressure and 20° C. for a 30 micron particle to stay suspended; whereas the flow rate falls to 3.2 cm/sec at 100 atm and 20° C. to keep the 30 micron particle suspended. The principle of maximum settling velocities for a system at normal temperature and pressure in comparison to a pressurized system holds true for other combustible gases as well.

(75) The described embodiments and examples are all to be considered in every respect as illustrative only, and not as being restrictive. The scope of the invention is, therefore, indicated by the appended claims, rather than by the foregoing description. All changes that come within the meaning and range of equivalency of the claims are to be embraced within their scope.