COAL UPGRADING UTILIZING NITROGEN

BACKGROUND OF THE INVENTION

Coal, when mined, comes with lot of impurities. The process of coal upgrading at the mine has been practiced for a long time, mainly to remove the moisture and other easily removable impurities. It was found that steam and certain inert gases were used before for this process. This process is not practiced all the time because of unavailability of the ingredients and economical reasons.

BRIEF SUMMARY OF THE INVENTION

The present invention proposes an innovative process to upgrade/clean coal prior to its use. Upgrading the coal refers to reducing various impurities that are present in mined or raw coal to make the coal cleaner, and also to increase the energy content per unit weight of the coal. The proposed process cleans or upgrades the coal using Nitrogen (N2), depending on the impurities targeted and the intended purpose. Combusting upgraded coal results in lower environmental pollutant emissions and increased combustion efficiency. Some coals that cannot be combusted in raw condition can be made possible to combust with the proposed upgrading process.

Purifying the flue gas obtained from combustion of coal is often very expensive. Any effort to purify the coal prior to the combustion can result in significant savings. Also, some lower rank coals that cannot be combusted in typical/traditional combustors can be made possible to combust with the proposed upgrading process.

BRIEF DESCRIPTION OF THE DRAWINGS

For a further understanding of the nature and objects of the present invention, reference should be made to the following detailed description, taken in conjunction with the accompanying drawings, in which like elements are given the same or analogous reference numbers and wherein:

Figure 1 is a schematic of an integrated process for upgrading coal using carbon dioxide and nitrogen;

Figure 2 is a schematic of the process of Figure 1 utilizing a carbon dioxide cleaning unit;

Figure 3 is a schematic of the process of Figure 1 utilizing a nitrogen cleaning unit; Figure 4 is a schematic of the process of Figure 1 utilizing carbon dioxide and nitrogen cleaning units;

Figure 5 is a schematic of the process of Figure 1 utilizing flue gas recycling;

Figure 6 is a schematic of the process of Figure 1 utilizing a carbon dioxide cleaning unit and flue gas recycling;

Figure 7 is a schematic of the process of Figure 1 utilizing a nitrogen cleaning unit and flue gas recycling;

Figure 8 is a schematic of the process of Figure 1 utilizing a carbon dioxide cleaning unit, a nitrogen cleaning unit, and flue gas recycling; Figure 9 is a schematic of a process for upgrading coal using coal carbon dioxide;

Figure 10 is a schematic of the process of Figure 9 utilizing a carbon dioxide cleaning unit;

Figure 11 is a schematic of the process of Figure 9 utilizing combustion with coal to produce the carbon dioxide;

Figure 12 is a schematic of the process of Figure 11 utilizing a carbon dioxide cleaning unit;

Figure 13 is a schematic of the process of Figure 9 utilizing flue gas recycling; Figure 14 is a schematic of the process of Figure 13 utilizing a carbon dioxide cleaning unit;

Figure 15 is a schematic of a process for upgrading coal with nitrogen;

Figure 16 is a schematic of the process of Figure 15 utilizing a nitrogen cleaning unit; Figure 17 is a schematic of the process of Figure 15 utilizing an air separation unit to produce the nitrogen; and

Figure 18 is a schematic of the process of Figure 17 utilizing a nitrogen cleaning unit.

DETAILED DESCRIPTION

The present process and system propose the integrated use of carbon dioxide (CO2) and nitrogen (N2) for the process of upgrading the coal. As CO2 is a better solvent for non-polar compounds, the impurities present in the coal (e.g. Sulfur based) that are non-polar in nature are better removed with CO2 rather than steam. Use of hot N2 mainly to decrease the moisture content in the coal improves the combustion performances of the coal and hence the efficiency of the process. As a result of this upgrading process, a higher heating value coal with lower impurities can be obtained. One aspect of the disclosed processes is directed to an integrated coal upgrading and combustion process including the following steps. Air is separated into streams of oxygen-enriched air and nitrogen-enriched air. The nitrogen-enriched air stream is heated. The heated nitrogen-enriched air stream is introduced into a coal upgrading apparatus containing coal. The heated nitrogen-enriched air is allowed to contact the coal in the coal upgrading apparatus for a selected period of time. The stream of oxygen-enriched air and the coal from the coal upgrading apparatus are introduced to a combustion chamber. The coal and oxygen-enriched air are combusted in the combustion chamber thereby producing flue gas. The flue gas is dried, purified, and compressed to produce a carbon dioxide -rich fluid. The carbon dioxide-rich fluid is introduced to the coal upgrading apparatus. The carbon dioxide- rich fluid is allowed to contact the coal in the coal upgrading apparatus for a selected period of time.

One aspect of the system is directed to an integrated coal upgrading and combustion system that includes the following: a) an air separation unit having an oxygen-enriched gas stream outlet and a nitrogen-enriched gas stream outlet; b) a heating device operably associated with the nitrogen-enriched air stream outlet; c) a coal upgrading apparatus operatively associated with the heating device via a nitrogen feed line, the apparatus containing coal; d) a combustion chamber fluidly communicating with the oxygen-enriched air stream outlet, the combustion chamber having a flue gas outlet and being configured and adapted to combust coal from the coal upgrading apparatus and oxygen-enriched gas from the air separation unit; e) a flue gas drying, purifying, and compressing device fluidly communicating with the flue gas outlet; and f) a carbon dioxide-rich fluid feed line, wherein:

i) the drying, purifying, and compressing device is configured and adapted to dry, purify, and compress flue gas received from the flue gas outlet to produce a carbon dioxide-rich fluid, and ii) the drying, purifying, and compressing device fluidly communicates with the coal upgrading apparatus via the carbon dioxide-rich fluid feed line.

Another aspect of the disclosed processes is directed to a process of upgrading coal with heated nitrogen that includes the following steps. A nitrogen- containing gas having a nitrogen concentration greater than that of air is heated. The heated nitrogen-containing gas is allowed to contact coal in a coal upgrading apparatus for a selected period of time. The heated nitrogen-containing gas is allowed to be vented from the coal upgrading apparatus thereby removing at least some moisture from the coal and S and N bearing compounds.

Another aspect of the disclosed processes is directed to a process of upgrading coal with carbon dioxide, including the following steps. A carbon dioxide- containing fluid having a carbon dioxide concentration greater than that of air is provided. The carbon dioxide-containing fluid to contact coal in a coal upgrading apparatus for a period of time, wherein the coal is not in a water slurry. The carbon dioxide-containing fluid is allowed to be vented from the coal upgrading apparatus thereby removing at least some non-polar constituents from the coal.

The disclosed processes can also include one or more of the following aspects.

Collecting some of the flue gas from the combustion chamber before said drying, purifying, and compressing step is performed and combining the collected flue gas with the stream oxygen-enriched gas being introduced to the combustion chamber.

Allowing the carbon dioxide-rich fluid to exit the coal upgrading apparatus and into a first cleaning unit, wherein contact between the carbon dioxide-rich fluid and the coal in the coal upgrading apparatus results in solvation of some non-polar constituents of the coal into the carbon dioxide-rich fluid; and separating out some of the carbon dioxide from the combined carbon dioxide-rich fluid and the non-polar constituents at the first cleaning unit; and introducing the separated out carbon dioxide back into the coal upgrading apparatus; and removing at least some of a volatile

component content of the non-polar constituents from non-polar constituents; and introducing the separated volatile content into the combustion chamber.

During the step of allowing the carbon dioxide-rich fluid to contact, the coal upgrading apparatus is sealed and has a pressure greater than ambient. The carbon dioxide-rich fluid is a liquid.

The carbon dioxide-rich fluid is a gas.

The carbon dioxide-rich fluid has a pressure of no less than 1,000 psia.

Allowing the nitrogen-enriched air to exit the coal upgrading apparatus and into a second cleaning unit, wherein contact between the nitrogen-enriched air and the coal in the coal upgrading apparatus results in removal of some of the moisture in the coal; and separating out moisture from the nitrogen-enriched air at the second cleaning unit to produce dried nitrogen-enriched air; and introducing the dried nitrogen-enriched air into the coal upgrading apparatus.

During the step of allowing the heated nitrogen-enriched air to contact, the coal upgrading apparatus is vented.

The stream of nitrogen-enriched air is heated with heat produced by the combusting step.

The stream of nitrogen-enriched air is heated with heat produced by a flame separate from said combusting step. Stream of nitrogen-enriched air is heated to a temperature of greater than

100 ⁰ C.

The oxygen-enriched gas has an oxygen concentration in a range of from 21% to 99.5%.

The nitrogen-enriched gas has a nitrogen concentration in a range of from 79% to 99.5 %.

The coal is not in a slurry with water.

The combustion chamber is part of a boiler.

The disclosed integrated system can include one or more of the following aspects. The integrated system also includes an oxidant line adapted and configured to facilitate fluid communication between the oxygen-enriched gas stream outlet and the combustion chamber; and a flue gas recycle line fluidly communicating with the drying, purifying, and compressing device and the oxidant line; and a mixing element disposed at a location wherein the flue gas recycle line and the oxidant line fluidly

communicate, the mixing element adapted and configured to mix flue gas received from the flue gas recycle line with oxidant from said oxygen-enriched gas stream outlet.

The integrated system also includes a first cleaning unit fluidly communicating with the coal upgrading apparatus via a carbon dioxide vent line and via the carbon dioxide-rich fluid feed line, said first cleaning unit also fluidly communicating with the combustion chamber via a volatiles line, wherein the first cleaning unit is configured and adapted to: receive carbon dioxide-rich fluid from said coal upgrading apparatus containing a mixture of carbon dioxide and non-polar constituents therefrom; and separate at least some of carbon dioxide from the mixture of carbon dioxide and non-polar constituents; and direct the separated carbon dioxide to said coal upgrading apparatus via said carbon dioxide -rich fluid feed line; and separate out least some of a volatile component content of the non-polar constituents from the non-polar constituents; and direct the separated volatile component content to said combustion chamber via said volatiles line.

The system also includes a second cleaning unit fluidly communicating with the coal upgrading unit via a nitrogen vent line and a nitrogen return line, wherein the first cleaning unit is configured and adapted to: receive a mixture of nitrogen-enriched air and moisture from said coal upgrading apparatus via said nitrogen vent line; separate at least some moisture from the mixture of nitrogen- enriched air and moisture to produce dried nitrogen-enriched air; and direct the dried nitrogen-enriched air into said coal upgrading apparatus.

The system also includes a heat exchanger adapted and configured to heat nitrogen-enriched air from the system also includes a nitrogen-enriched air stream outlet with heat produced from combustion of coal and oxygen-enriched air in the system also includes combustion chamber.

As best illustrated in Figure 1, air feed 5 is separated into oxygen-enriched air and nitrogen-enriched air at air separation unit (ASU) 7. The oxygen-enriched air leaves oxygen-enriched air outlet 8 and is directed by oxidant line 10 to combustion chamber 15. The nitrogen-enriched air leaves nitrogen-enriched air outlet 6 and is directed to heating device 14 and then to coal upgrading apparatus 3. Typical oxygen and nitrogen concentrations are in a range of from 80 % to 99.5 %. Coal from coal supply 1 is also caused to be placed into coal upgrading apparatus 3.

Coal and oxygen-enriched air are combusted in combustion chamber 15 thereby producing flue gas. Optionally, air may also be fed to the combustion chamber. In this case, the total oxygen concentration of the combined oxygen- enriched air and air entering the combustion chamber 15 is 21% by volume or higher. The system and process is particularly applicable to a combustion chamber 15 that is a boiler. The flue gas is directed to optional flue gas cleaning unit 13 to remove impurities in a known way. The non-cleaned flue gas or cleaned flue gas (in the case where unit 13 is selected) is then directed to flue gas drying, purifying, and compressing device 17. Cleaned, dried, purified (as required), and compressed flue gas is then directed to coal upgrading apparatus 3 via carbon dioxide-rich fluid feed line 20. Optionally, cleaned, dried, purified, and compressed flue gas may also be directed out of the drying, purifying, and compressing device to a use or storage device 19.

In operation, coal is alternately upgraded by either the nitrogen-enriched air or the carbon dioxide-rich fluid.

During treatment by the nitrogen-enriched air, the nitrogen-enriched air is heated at heating device. While the heating device may be external to the combustion chamber 15 and combustion process operated therein, preferably heat is imparted by the combustion process to the nitrogen-enriched air via heating device 15. The system and process are more fully integrated in this manner thereby reducing operating and capital costs. The temperature of the nitrogen is chosen so that a desired level of moisture can be removed with minimal or no release of volatiles from the coal. These volatiles are preferably retained by the coal from a combustion point of view. The nitrogen also may remove some sulfur-containing compounds and nitrogen-containing compounds. Removing the moisture from the coal improves the combustion characteristics as the heating value of the coal (Btu/weight basis) will be increased. In other words, a lower amount of the dried coal will be required to produce the same energy by combustion as the undried coal. One skilled in the art will appreciate that higher temperatures will increase the efficiency by which moisture is removed from the coal. The heated nitrogen-enriched air carries away some of the moisture via vent line 2. While the coal upgrading apparatus 3 may be sealed and optionally pressurized during treatment of the coal by the nitrogen- enriched air, preferably it is at least partially vented during treatment.

During treatment by the carbon dioxide-rich fluid, the coal upgrading apparatus 3 is pressurized with the carbon dioxide-rich fluid from carbon dioxide-rich fluid feed line 20 and then sealed. The pressurized carbon dioxide-rich fluid is then allowed to contact the coal for a desired period of time in order to dissolve non-polar constituents (such as sulfur-containing compounds and nitrogen-containing compounds) in the coal. The pressurized carbon-dioxide can also dissolve heavy metals, non-limiting examples of which include Arsenic and Sodium. At relatively higher pressures, carbon dioxide exhibits excellent solvent properties. The carbon dioxide-rich fluid may be introduced as a gas or a liquid. While the carbon dioxide- rich fluid will often include multiple components, including carbon dioxide, oxygen, nitrogen, and NOx, the carbon dioxide-rich fluid may potentially also be in a supercritical fluid state. One skilled in the art will appreciate that the pressure and temperature of the carbon dioxide -rich fluid may be selected based upon the type of coal and impurities targeted. Preferably, the carbon dioxide-rich fluid has a pressure of no less than 1000 psia. After treatment, the coal upgrading apparatus is vented via a carbon dioxide vent line 4. It should be noted that a single line may be used for vents 2 and 4.

As best shown in Figure 2, carbon dioxide exiting the coal upgrading apparatus 3 may optionally be cleaned and recycled. In this embodiment, carbon dioxide containing non-polar constituents from the coal exits coal upgrading apparatus 3 via carbon dioxide vent line 4 and is introduced to first cleaning unit 11. At least some of the carbon dioxide is then separated from the non-polar constituents in a known manner. The separated carbon dioxide is then directed to carbon dioxide- rich fluid feed line 20 for reentry into coal upgrading apparatus 3. At least some of the volatile content of the non-polar constituents is then separated out and directed to the combustion chamber 15 via volatiles line 18 where they are combusted with the oxygen-enriched air and coal. The remainder of the carbon dioxide-depleted and volatile-depleted content, such as heavy metals, may be vented via vent 22.

As best illustrated in Figure 3, the nitrogen exiting the coal upgrading apparatus 3 may optionally be cleaned and recycled. Nitrogen and moisture exiting the coal upgrading apparatus 3 via nitrogen vent 2 may be dried at second cleaning unit 9 and the dried nitrogen recycled back to the coal upgrading apparatus 3.

As best shown in Figure 4, the nitrogen and carbon dioxide leaving the coal upgrading apparatus 3 may optionally be cleaned and recycled as described above in the embodiments of Figures 2 and 3.

As best illustrated in Figure 5, a portion of flue gas may be recycled to the combustion chamber 15. After the flue gas is cleaned at optional flue gas cleaning unit 13, a portion the cleaned flue gas then may be directed by flue gas recycle line 24 to mixer 12 where it is mixed with oxygen-enriched gas and introduced to combustion chamber 15 via oxidant line 10.

As best shown in Figure 6, the carbon dioxide exiting the coal upgrading apparatus 3 may be cleaned and a portion of the flue gas may be recycled to the combustion chamber 15 as described above in the embodiments of Figures 2 and 5.

As best shown in Figure 7, the nitrogen exiting the coal upgrading apparatus 3 may be cleaned and a portion of the flue gas may be recycled to the combustion chamber 15 as described above in the embodiments of Figures 3 and 5. As best shown in Figure 8, the carbon dioxide and nitrogen exiting the coal upgrading apparatus 3 may be cleaned and a portion of the flue gas may be recycled to the combustion chamber 15 as described above in the embodiments of Figures 4 and 5.

The method and system need not be integrated with a combustion process/system nor require treatment by both carbon dioxide-rich fluid and nitrogen- enriched air. Indeed, coal may be upgraded by carbon dioxide-rich fluid alone or by nitrogen-enriched air alone and apart from a combustion process/system.

As best illustrated in Figure 9, coal may be upgraded by carbon dioxide without nitrogen. Carbon dioxide-rich fluid from any source is directed to coal upgrading apparatus 3 via carbon dioxide-rich fluid feed 20. In this case, the carbon dioxide-rich fluid need not be derived from flue gas. During treatment by the carbon dioxide-rich fluid, the coal upgrading apparatus 3 is pressurized with the carbon dioxide-rich fluid from carbon dioxide-rich fluid feed line 20 and then sealed. The pressurized carbon dioxide -rich fluid is then allowed to contact the coal for a desired period of time in order to solvate non-polar constituents in the coal. At relatively higher temperatures and pressures, carbon dioxide exhibits excellent solvent properties. The carbon dioxide-rich fluid may be introduced as a gas or a liquid. While the carbon dioxide-rich fluid will often include multiple components, including carbon dioxide, oxygen, nitrogen, and NOx, the carbon dioxide-rich fluid may

potentially also be in a supercritical fluid state. One skilled in the art will appreciate that the pressure and temperature of the carbon dioxide-rich fluid may be selected based upon the type of coal and impurities targeted. Preferably, the carbon dioxide- rich fluid has a pressure of no less than 1000 psia. After treatment, the coal upgrading apparatus is vented via a carbon dioxide vent line 4.

As best shown in Figure 10, the embodiment of Figure 9 may include carbon dioxide cleaning. In this embodiment, carbon dioxide containing non-polar constituents from the coal exits coal upgrading apparatus 3 via carbon dioxide vent line 4 and is introduced to first cleaning unit 11. At least some of the carbon dioxide is then separated from the non-polar constituents in a known manner. The separated carbon dioxide is then either directed to carbon dioxide-rich fluid feed line 20 for use or to vent 22 for use and/or storage.

As best illustrated in Figure 11, the embodiment of Figure 9 may be integrated with a combustion process/system. The integrated nature of the coal upgrading and combustion of coal and oxygen-enriched air lowers both operating and capital costs. Air feed 5 is separated into oxygen-enriched air and nitrogen-enriched air at air separation unit (ASU) 7. The oxygen-enriched air leaves oxygen-enriched air outlet 8 and is directed by oxidant line 10 to combustion chamber 15. The nitrogen-enriched air leaves nitrogen-enriched air outlet 6 and is directed to heating device 14 and then to coal upgrading apparatus 3. Typical oxygen and nitrogen concentrations are in a range of from 80 % to 99.5 % by volume. Coal from coal supply 1 is also caused to be placed into coal upgrading apparatus 3.

Coal and oxygen-enriched air are combusted in combustion chamber 15 thereby producing flue gas. Optionally, air may also be fed to the combustion chamber. In this case, the total oxygen concentration of the combined oxygen- enriched air and air entering the combustion chamber 15 is 21% or higher. The system and process is particularly applicable to a combustion chamber 15 that is a boiler. The flue gas is directed to optional flue gas cleaning unit 13 to remove impurities in a known way. The non-cleaned flue gas or cleaned flue gas (in the case where unit 13 is selected) is then directed to flue gas drying, purifying, and compressing device 17. Cleaned, dried, purified, and compressed flue gas is then directed to coal upgrading apparatus 3 via carbon dioxide-rich fluid feed line 20. Optionally, cleaned, dried, purified, and compressed flue gas may also be directed out of the drying, purifying, and compressing device to a use or storage device 19.

As best shown in Figure 12, the embodiment of Figure 11 may also include carbon dioxide cleaning. In this embodiment, carbon dioxide containing non-polar constituents from the coal exits coal upgrading apparatus 3 via carbon dioxide vent line 4 and is introduced to first cleaning unit 11. At least some of the carbon dioxide is then separated from the non-polar constituents in a known manner. The separated carbon dioxide is then directed to carbon dioxide-rich fluid feed line 20 for reentry into coal upgrading apparatus 3. At least some of the volatile content of the non-polar constituents is then separated out and directed to the combustion chamber 15 via volatiles line 18 where they are combusted with the oxygen-enriched air and coal. The remainder of the carbon dioxide-depleted and volatile-depleted content, such as heavy metals, may be vented via vent 22.

As best shown in Figure 13, the embodiment of Figure 11 may also include flue gas recycling. After the flue gas is cleaned at optional flue gas cleaning unit 13, a portion the cleaned flue gas then may be directed by flue gas recycle line 24 to mixer 12 where it is mixed with oxygen-enriched gas and introduced to combustion chamber 15 via oxidant line 10.

As best illustrated in Figure 14, the embodiment of Figure 12 may also include flue gas recycling. After the flue gas is cleaned at optional flue gas cleaning unit 13, a portion the cleaned flue gas then may be directed by flue gas recycle line 24 to mixer 12 where it is mixed with oxygen-enriched gas and introduced to combustion chamber 15 via oxidant line 10.

As best shown in Figure 15, the coal may be upgraded in coal upgrading apparatus 3 with nitrogen without carbon dioxide. Nitrogen or nitrogen-enriched air from any source is directed to heating device 14 and then to coal upgrading apparatus 3. Typical nitrogen concentrations for use in this embodiment are in a range of from 80 % to 99.5 %. During treatment by the nitrogen-enriched air, the nitrogen-enriched air is heated at heating device. The temperature of the nitrogen is chosen so that a desired level of moisture can be removed with minimal or no release of volatiles from the coal. These volatiles are preferably retained by the coal from a combustion point of view. The heated nitrogen also may remove some sulfur-containing compounds and nitrogen-containing compounds. Removing the moisture from the coal improves the combustion characteristics as the heating value of the coal (Btu/weight basis) will be increased. In other words, a lower amount of the dried coal will be required to produce the same energy by combustion as the undried coal. One skilled in the art

will appreciate that higher temperatures will increase the efficiency by which moisture is removed from the coal. The heated nitrogen-enriched air carries away some of the moisture via vent line 2. While the coal upgrading apparatus 3 may be sealed and optionally pressurized during treatment of the coal by the nitrogen- enriched air, preferably it is at least partially vented during treatment.

As best illustrated in Figure 16, the embodiment of Figure 15 may include nitrogen cleaning and recycling. Nitrogen and moisture exiting the coal upgrading apparatus 3 via nitrogen vent 2 may be dried at second cleaning unit 9 and the dried nitrogen recycled back to the coal upgrading apparatus 3. As best shown in Figure 17, the embodiment of Figure 15 may be integrated with an air separation unit (ASU). Air feed 5 is separated into oxygen- enriched air and nitrogen-enriched air at air separation unit 7. The oxygen-enriched air leaves oxygen-enriched air outlet 8 and is directed by oxidant line 10 to combustion chamber 15. The nitrogen-enriched air leaves nitrogen-enriched air outlet 6 and is directed to heating device 14 and then to coal upgrading apparatus 3. Typical nitrogen concentrations for use in this embodiment are in a range of from 80 % to 99.5 %. Typical nitrogen concentrations in nitrogen-enriched air from an ASU are in a range of from 80 % to 99.5 %.

As best illustrated in Figure 18, the embodiment of Figure 17 may include nitrogen cleaning and recycling. Nitrogen and moisture exiting the coal upgrading apparatus 3 via nitrogen vent 2 may be dried at second cleaning unit 9 and the dried nitrogen recycled back to the coal upgrading apparatus 3.

Preferred processes and apparatus for practicing the present invention have been described. It will be understood and readily apparent to the skilled artisan that many changes and modifications may be made to the above-described embodiments without departing from the spirit and the scope of the present method. The foregoing is illustrative only and that other embodiments of the integrated processes and apparatus may be employed without departing from the true scope of the invention whose aspects are described in the following claims.