Burnout of residual carbon in coal fly ash using air cyclones

Abstract

This patent application is for the novel utilization of an air cyclone combustion unit (CCU) for burnout of residual carbon from burning of fly ash resulting from coal and/or coke in electric power plants or from natural pozzolans. In some cases, residual carbon and/or moisture is too high in fly ash or pozzolans to meet market conditions for quality or ASTM C 618 Specification for Natural Pozzolans and Coal Fly Ash. Heat treating the coal fly ash or natural pozzolan to remove sufficient amounts of carbon renders the remaining pozzolan capable of meeting specifications and being sufficient in quality to perform as a cementitious material in concrete and mortars. Use of an air cyclone, with suitable mechanical adjustments and heat either from an external source or with the inherent heat value from the residual carbon will be claimed.

Description

REFERENCES CITED FOR THE PRIOR ART: [REFERENCED BY]

• 1. United States Patent Application 20090200156, Whellock; John G., Aug. 13, 2009, Treatment of fly ash from coal combustion to improve its marketability.
• 2. U.S. Pat. No. 4,527,973, Jul. 9, 1985, Precalciner for Cement Raw Meal, Takahiko Kando, Masahiko Kitajima, Yamaguchi, Japan, assigned to UBE Industries, Yamaguchi, Japan.
• 3. U.S. Pat. No. 7,261,047 Ljungdahl, Boo, Aug. 28, 2007, Control of cyclone burner, Assignee: TPS Termiska Processer AB (Nykoping, SE)
• 4. U.S. Pat. No. 5,462,430 Khinkis Oct. 31, 1995, Process and apparatus for cyclonic combustion, Assignee: Institute of Gas Technology (Des Plaines, Ill.).
• 5. U.S. Pat. No. 6,036,475 Matsui, Koichi (Kyoto, JP), Kuwagaki; Isao (Kyoto, JP), Mar. 14, 2000, Cyclonic type combustion apparatus, Assignee: Takuma Co. Ld. (Osaka, JP)
• 6. U.S. Pat. No. 4,934,931, Angelo, II James Jun. 19, 1990, Cyclonic combustion device with sorbent injection Angelo, II; F. (Little Rock, Ark.).
• 7. U.S. Pat. No. 5,220,888, Khinkis; Mark J. (Morton Grove, Ill.), Abbasi; Hamid A. (Darien, Ill.), Jun. 22, 1993, Assignee: Institute of Gas Technology (Chicago, Ill.).
• 8. U.S. Pat. No. 4,920,925, Korenberg; Jacob (York, Pa.), Khinkis; Mark (Morton Grove, Ill.), May 1, 1990, Assignee: Donlee Technologies Inc., (York, Pa.).

OTHER REFERENCES

• 1. A semi-mobile flash dryer/calciner unit to manufacture pozzolana from raw clay soils—application to soil stabilization, S. Salvador, A and O. Ponsb, Ecole des Mines d'Albi Carmaux, Campus Jarlard, 81 013 Albi CT Cedex 09, France Entreprise MALET, 30 Avenue de Larrieu, 31 081 Toulouse Cedex France.
• 2. Fluid Dynamics Applied to a Cement Precalciner, Giddings D. Eastwick C. N; Pickering S. J; Simmons K.1, Proceedings of the I MECH E Part A Journal of Power and Energy, Professional Engineering Publishing, Volume 214, Number 3, 5 Jun. 2000, pp. 269-280.
• 3. Flyash Beneficiation By Air Classification, J. G. Groppo and S. M. Brooks Center For Applied Energy Research University of Kentucky And Clarence Kreiser Buell Division of Fisher-Klosterman, Inc.
• 4. Investigation into the operation of a cement works precalciner vessel, Donald Giddings, Thesis submitted to The University of Nottingham for the Degree of Doctor of Philosophy, Investigation into the operation of a cement works precalciner vessel by Donald Giddings, Thesis submitted to The University of Nottingham for the Degree of Doctor of Philosophy The University of Nottingham School of Mechanical, Materials, Manufacturing Engineering and Management

FEDERALLY SPONSORED RESEARCH/DEVELOPMENT

None at this time.

BACKGROUND OF THE INVENTION

Of the 72 million tons of Coal Combustion Products (CCPs) generated by the coal-fueled electric power industry, only about 32 million (44%) of CCP production is beneficially used in concrete and cement products, wallboard, highway construction, and other applications. Much fly ash is unusable in concrete as it does not pass the required ASTM C 618 Standard Specification for Coal Fly Ash and Raw or Calcined Natural Pozzolan for Use in Concrete. The unused proportion is increasing as mercury capture and other environmental regulations cause electric power plant boiler techniques that render more fly ash unusable for pozzolans in concrete.

Coal-burning utilities have increasingly turned to low NOx burners to reduce nitrous oxide emissions. It is well documented that changes in the form and quantity of unburned carbon in low NOx fly ash. Small amounts of low-NOx carbon can lead to relatively large and variable increases in air entraining agent (AEA) required for concrete.

Concrete is the most widely used man-made material in the world. In 2007 nearly 3.05 billion tons of portland and hydraulic cement was produced worldwide. The production of cement—the main active ingredient of concrete—accounts for 5 to 10 percent of all anthropogenic carbon dioxide emissions; a leading greenhouse gas involved in global warming. During the portland cement clinker calcining process, CaCO₃ is changed to CaO. Approximately one ton of CO₂ is released in the production of one ton of portland cement. In the United States, portland cement production alone constitutes about 2-3 percent of CO₂ gasses generated annually. Cement production generates carbon-dioxide emissions because it requires fossil fuels to heat the powdered mixture of limestone, clay, ferrous and siliceous materials to temperatures of 2700° F. (1,500° C.). Limestone—Calcium Carbonate (CaCO₃)—is the principle ingredient of cement. During the portland cement clinker calcining process, CaCO₃ is changed to CaO. This conversion releases one mole of CO₂ (carbon dioxide) for every mole of CaCO₃ consumed in the production process. Approximately one ton of CO₂ is released in the production of one ton of portland cement. In the United States, Portland cement production alone constitutes about 2-3 percent of CO₂ gasses generated annually. Chemical reactions with sulfates and other mineral formations occur within the temperature ranges of the unit. Anhydrous calcium sulfate formed from synthetic gypsum is made by heating to a temperature of 325°-450° C. Coal fired electric power plants have already begun capturing mercury to comply with regulations. The Cyclonic Combustion Unit can alleviate the conditions caused by low temperature burning, additions of mercury sequestrants, elevated SOx and Ammonia. It is intended to treat fly ash or pozzolans, no matter how high their moisture or carbon content and reduce the organic content to a target level of Loss On Ignition (LOI) in the product. Capture of mercury metal, in it's gaseous state can be accomplished by extracting the mercury from the gasses in the exhaust duct carrying gasses from the cyclone to the water spray. The mercury vapor can then cooled within a Mercury Capture Unit for recovery of the mercury metal. Activated carbon to sequester Mercury is well known to cause extreme variations in concrete quality. Variations in concrete from using such fly ash can be extreme. Much of this fly ash, now discarded, could be utilized if the quality could be improved.

Sulfates and sulfites in the CCP could be reacted with lime or other materials during the combustion process to render them harmless and become part of the mineralogy of the CCP. Likewise Ammonia (NH₄) could be reacted during combustion to render it harmless.

Finally, it is proposed that combustion fuel for the CCU would be waste oil, predominantly waste engine oil further utilizing recovered materials for improving the environment.

In some cases, residual carbon and/or moisture is too high in fly ash or pozzolans to meet market conditions for quality or ASTM C 618 Specification for Natural Pozzolans and Coal Fly Ash. Heat treating the coal flyash or natural pozzolan to remove sufficient amounts of carbon and/or moisture renders the remaining fly ash or pozzolan capable of meeting specifications and being sufficient in quality to perform as a cementitious material in concrete, mortars or cementitious products. This also reduces the need for utilization of coal in portland cement products and inherent emission of greenhouse gasses. Coal-burning utilities have increasingly turned to low NOx burners to reduce nitrous oxide emissions. It is well documented that changes in the form and quantity of unburned carbon in low Nitrous Oxide (NOx) fly ash, as well as the possible presence of ammonia compounds, have negatively impacted the use of fly ash in concrete. Less well documented are possible changes in Low NOx fly ash that may impact strength activity index values, including particle shape, size and glass content.

The carbon produced by burning coal in a plant equipped with a low-NOx burner is produced at somewhat cooler and much more reduced conditions, compared with traditional burners. The carbon associated with a low-NOx fly ash is a much more active form than that produced using traditional burners. This highly active low-NOx carbon can adsorb liquid chemical admixtures used in concrete, especially the air-entraining admixtures. This can result in higher and more variable concrete air entraining agent (AEA) dose requirements. Small amounts of low-NOx carbon can lead to relatively large increases in AEA in concrete. Variations in concrete from using such fly ash can be extreme.

SUMMARY OF THE INVENTION

The Cyclonic Combustion Unit (CCU) invention alleviates the coal fired electric power plant conditions caused by low temperature burning, additions of mercury sequestrants, elevated SOx and Ammonia. It is intended to treat resulting non specification or marginal quality fly ash or pozzolans, no matter how high their moisture or carbon content and reduce the organic content to a target level of Loss On Ignition (LOI) in the product. Earlier versions of this technology have been used since the 1970's to flash calcine kiln feed in portland cement kilns. This CCU is novel for numerous reasons including the use of plural heat sources. The CCU will reduce residual carbon and/or moisture is that too high in fly ash to meet market conditions for quality or ASTM C 618 Specification for Natural Pozzolans and Coal Fly Ash. CCU heat treating the coal flyash to remove sufficient amounts of carbon renders the remaining fly ash capable of meeting specifications as a cementitious material in concrete, mortars or cementitious products. This also reduces the need for utilization of coal to produce portland cement products and inherent emission of greenhouse gasses.

Further, capture of Mercury metal, in its gaseous state is accomplished (optional) by extracting the Mercury from the exhaust duct carrying gasses from the cyclone to the water spray. The Mercury vapor can then cooled within the Mercury Capture Unit for recovery of the Mercury metal.

Importantly, utilization of the fly ash, now discarded, will relieve the need for extensive storage of off specification and non-useable fly ash. It would preferentially be used as a supplementary cementitious material, with it's improved quality.

As well, the use of the now discarded fly ash will reduce the amount of carbon dioxide emitted from production of portland cement.

Higher temperatures may be employed to further improve mineralogy of the subject fly ash or materials fed into the unit and heat treated. As well, chemical reactions with sulfates and other mineral formations occur within the temperature ranges under consideration. For instance, anhydrous calcium sulfate form synthetic gypsum by heating to a temperature of 325°-450° C. Illite, anhydrite, quartz, anorthite, microcline, sillimanite and hematite are dominantly influenced up to 700° C., and hercynite, anorthite, albite, pseudobrookite and other iron-titanium oxides were dominant up to 1200° C. in mineralogical formation testing.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The invention is a duel fired counter flow air cyclone utilization for:

• 1. Burnout of residual carbon in fly ash from burning of coal in electric power plants.
• 2. Enhance fly ash and other minerals by enabling control of fly ash residual carbon and/or moisture that is too high to meet market conditions for quality or ASTM C 618 Specification for Natural Pozzolans and Coal Fly Ash.
• 3. CCU heat treating the coal fly ash or natural pozzolan is to remove sufficient amounts of carbon and/or moisture and render the resultant fly ash capable of meeting specifications. It will also be sufficient in quality to competitively perform as a cementitious material in concrete, mortars or cementitious products.
• 4. Reduces the need for utilization of coal in portland cement products and reduction of inherent emission of greenhouse gasses.
• 5. Storage for discarded fly ash from power plants can be reduced by the amount of fly ash treated in the proposed Coal Combustion Unit.

Conceptual Drawing

(Attached in PDF)

BRIEF DESCRIPTION OF THE DRAWING

Burnout of carbon in fly ash uses fuel at two locations in the cyclone system to reduce carbon to acceptable levels:

The unit is fed with materials metered through a feed inlet (1). Some combustion air is also allowed to enter with the incoming feed. The unit uses ignition of carbon provided by a fuel at the primary combustion zone/controllable high carbon fly ash feed inlet to the primary combustion zone at the lower portion of the riser duct to the cyclone main body (2). The primary combustion zone is preferentially lined with refractory materials. A larger portion of combustion air is inlet and larger agglomerations of feed are dropped from the inlet pipe (3). Materials dropped from the inlet pipe are removed (4) for alternate use by external equipment (5).

A fuel supplied flame (6) that may be fitted with a cone shaped nozzle to better enable oxygen for combustion to the inlet gases is installed in the inlet duct of the cyclone. Heated gases and partially decarbonized material are transported from the primary combustion zone through the cyclone inlet duct. The pipe and flame may be oriented in any fashion desirable, tangential orientation is not necessary or preferred in order to keep heat away from any particular section of the inlet duct.

Gases move through the combustion chamber (7) and with continuing partial and incomplete decarbonation.

Gases and materials swirl inside the cyclone (8). Cooling of this combustion chamber is not desired. It is preferentially lined with refractory materials. Heat from secondary fueled flame(s) (9) consisting of one or more fuel lines and accompanying nozzles that may be outfitted with cone shaped or atomization nozzles below the lower end of the thimble inside the cyclone completes combustion of residual carbon that remained to the level necessary to meet customer requirements.

Material that has become agglomerated in the primary or secondary ignition zones is dropped out through an air lock system for collection (10).

Agglomerated materials and heavier particles of ash dropped from the cyclone are removed (11) for alternate use by external equipment.

A plurality of fuel lances may be employed (12).

Fly ash and remaining carbon and gasses are drawn from the cyclone through thimble into the cyclone outlet (13). The thimble may be adjusted in diameter or length to control the amount of heavier particles rejected through the airlock. Oxygen can be measured to assure safe amounts of exit oxygen (14). A mercury capture unit can be utilized in the general location of (15).

Gases then are cooled with water spray (16) supplied by a water pipe (17). A water outlet (18) fitted to water jacket cooling unit (19) providing a cooling tunnel outfitted with a water inlet valve (20) to reduce gas exit temperature to about 115 degrees C. This same activity also reduces the temperature of the mineral product.

The cooled and reduced carbon fly ash is then delivered to the dust collector inlet (21). Product is collected with a dust collector (22). The dust collector is fitted with electrical or filter media to catch the decarbonated and treated product. A discharge valve (23) is fitted to the duct collector hopper (24) to control storage and outflow of the product.

Product from the dust collector is delivered through a valve or feeder (25) then stored for use as a cementitious material in separate storage. Cleaned air exits the dust collector (26)

An induced draft fan (27) is used to draw ambient air through the cyclone and carry the fly ash from the cyclone in the air stream to the dust collector. Control of airflow through the cyclone allows sufficient residence time to provide oxygen for sufficient combustion of the carbon.

An exhaust stack (28) carries cleaned air from the unit.

DETAILED DESCRIPTION OF THE INVENTION

The proposed Cyclonic Combustion Unit (CCU) unit is a dual fired, temperature controlled, cyclonic, flow adjustable, water spray cooled exhaust gas, dust collected system for reducing carbon or improving mineralogy in fly ash to acceptable levels. Thusly, the need for utilization of coal in portland cement products and inherent emission of greenhouse gasses is reduced. The cyclonic combustion unit utilizes heat from fuel sources employed within the primary feed section of the CCU and within the cyclone for process control of maintaining target amounts of residual carbon or complete combustion of carbon as desired. The carbon-laden pozzolan is fed into an air duct that is fired with fuel to acceptable temperatures. Temperatures will generally need to be in the range of 400 to 1200 degrees centigrade. The cyclone employed will allow circulation of the fly ash and sufficient residence time to ignite and burn the carbon in the feedstock. A secondary flame inside the cyclone will be adjusted as necessary to provide suitable reduction in carbon content or mineralogical improvements to the feedstock fly ash resulting in controlled carbon content and mineralogy in the product. A water spray in the exhaust duct will quench the temperature of the product from the cyclone. The water spray will also cool exhaust gasses to suitable low temperatures to allow safe temperatures for the dust collector and product handling system. A fan for the system will move the gasses and feedstock through the CCU and draw air through the system supplying oxygen for fuel and carbon combustion.

Further the CCU can be operated at higher temperatures as needed and/or additional minerals included to form mineralogical changes in the materials fed enhancing the cementing properties of the materials fed into the system. A stoichiometric ratio of combustion oxygen to carbon is not required or suggested.

Since the 1990s and 2000s, power plants have been equipped with additional processes to improve air quality such as scrubbers to reduce SOx emissions, catalytic reduction equipment to reduce NOx emissions, and various systems to reduce mercury emissions. These additional systems have the potential to alter the fly ash with ammonia, sulfite, alkalis, and carbon residues that must be considered in selecting fly ash sources, and specifying additional quality control parameters for acceptance.

Use of a counter flow air cyclone, with suitable mechanical adjustments and heat either from reclaimed oil source incorporated with the inherent heat value from the residual carbon will be used.

Importantly, utilization of the fly ash, now discarded, will relieve the need for extensive storage of off specification and non-useable fly ash. It would preferentially be used as a supplementary cementitious material, with it's improved quality.

As well, the use of the now discarded fly ash will reduce the amount of carbon dioxide emitted from production of portland cement. Much of this fly ash, now discarded, could be utilized if the quality could be improved.

Utilization of every ton of fly ash improved rather than portland cement will reduce approximately one ton of CO2 emitted

If any fraction of the approximately 40 million tons per year of fly ash not being used can be beneficially used instead, there will be several advantages:

• 1. Overall carbon dioxide can be reduced. The amount of reduction is about 1 ton net of CO2 reduced for every additional ton of fly ash processed by a CCU.
• 2. Every amount of fly ash processed by CCU does not have to be impounded or discarded.
• 3. Fly ash previously discarded or ponded could be processed and reused as pozzolan. The amount of fly ash used from this single activity is immense.
• 4. Fly ash from the above activities can be utilized in production of chemically activated hydraulic cements.

These chemically activated cements meet ASTM C 1600, Specification for Rapid Hardening Hydraulic Cements and ASTM C 1157 Specification for Standard Performance Specification for Hydraulic Cements

The utilization of chemically activated fly ash based cements will substitute ton for ton with portland cement. No portland cement is needed in concretes utilizing these cements. As well they are a proven entity.

Fly ash prepared by the CCU will have the following improvements:

• 1. Loss on Ignition (LOI) controlled to predictable and product competitive targets.
• 2. LOI control accomplished by controlling the combustion temperature within the cyclone.
• 3. Temperatures from sensors located in the feed and cyclone combustion areas and the exit duct.
• 4. Fuel is adjusted in the primary and secondary burner in the cyclone to burn out carbon from the fly ash.
• 5. Temperatures can be operated at higher temperatures to affect the mineralogy of the fly ash.
• 6. Fly ash presently failing to meet specifications or competitive requirements of LOI can be controlled to target levels.
• 7. The fly ash so treated in the CCU will not have to be placed in landfill storage or discarded and used instead for beneficial purposes such as replacement of portland cement in concrete. That act further reduces the amount of CO2 produced in the substituted cement.
• 8. Fly ash presently discarded can be used instead to create roadways, structures and other works.

Claims

1. A cyclonic combustion unit consisting of one or more cyclones or combustion chambers outfitted with a feed mechanism to feed one or more materials, two or more sources of fuel combustion utilizing added fuel sources, a means of cooling the resulting exit gasses and materials, a dust collecting system for collecting the product of the unit and a fan for moving gasses through the system.

2. The combustion unit described in claim 1 wherein said material fed into the system consists of coal fly ash, natural pozzolan, cement, cement kiln dust, slag, kaolin, bentonite, salts of metallic carbonates such as calcium, potassium, sodium, etc, hydrated lime, quicklime, clay burned lime, dirt, compost and mineral or feed stocks with compositions to modify the composition of the fed materials either chemically or mineralogically.

3. The combustion unit according to claim 1 which further comprises a chamber connected to a feed system that has been heated with externally supplied fuel.

4. The combustion unit according to claim 1 that is outfitted with a system that conveys the feed from the feed and initial fueled heat system by air into the main body of the cyclone. The configuration of the combustion can be cylindrical, square or other geometric configuration.

5. The combustion unit according to claim 1 that is outfitted with an internal pipe or “thimble” reaching down into the cyclone and attached to the exhaust section of the cyclone.

6. The combustion unit according to claim 5 in which the internal thimble connected to the exhaust section of the cyclone is adjustable in length.

7. The cyclonic combustion unit in claim 3 in which is outfitted with a source of external fueled heat.

8. The combustion unit described in claim 1 in which the fuel may be feed into the cyclone at its periphery or near the adjustable internal pipe.

9. An embodiment of the cyclonic combustion system described in claim 1 in which the primary initial combustion zone fuel is from different points of ignition and/or made up of different fuels, including natural gas, liquefied petroleum gasses such as propane or butane, coal, coke, fuel oil, waste automotive oil or waste cooking grease or oil.

10. An embodiment of the cyclonic combustion system described in claim 1 in which the primary flame(s) at the secondary combustion zone fuel in the cyclone is from different points of ignition and/or made up of different fuels, including natural gas, liquefied petroleum gasses such as propane or butane, coal, coke, fuel oil, waste automotive oil or waste cooking grease or oil.

11. An embodiment of the cyclonic combustion system described in claim 1 in which heat may be from a tertiary source such as waste heat from another system.

12. The cyclonic combustion system described in claim 1 in which the exhaust from the cyclone is outfitted with a duct in which there is a water spray, air, water jacket or product cooling system.

13. An embodiment of the cyclonic combustion system described in claim 1 in which there is a dust collection system consisting of a second cyclone, set of cyclones, baghouse or electrostatic precipitator to collect the product from the cyclone and heat treatment therein.

14. An embodiment of the cyclonic combustion system described in claim 1 in which there is a fan to induce either heated or ambient air, oxygen in part or in total to support combustion of the fuels used for heating the materials.

15. An embodiment of a Cyclonic Combustion Unit capable of heat treating coal fly ash or natural pozzolan to remove sufficient amounts of carbon and/or moisture and render the resultant fly ash capable of exhibiting pozzolanic or cementitious properties. The resulting minerals will be sufficient in quality to competitively perform as a cementitious material in concrete, mortars or cementitious products.

16. A cyclonic combustion unit according to claim 15 in which valves are inserted in the areas at the lower end of the cyclone(s) and primary feed section to remove coarse fractions of minerals that form during combustion and handling.

17. An embodiment of the cyclonic combustion system described in claim 15 in which a device is inserted into the exhaust portion of the cyclone to capture mercury vapors.

18. An embodiment of the cyclonic combustion system described in claim 15 in which the fuel is provided to the heating zones of the CCU are outfitted with pipes to which is attached a means of increasing turbulence within the flame, enabling increased oxygen in contact with heated air for improved combustion of carbon or other organic materials in the feed material.

19. An embodiment of the cyclonic combustion system of the invention in which sulfates and sulfites in the CCP could be reacted with lime containing material added other materials at the feed inlet and minerologically converted during the combustion process to render them harmless and become part of the mineralogy of the CCP materials product.

20. An embodiment of the cyclonic combustion system described in claim 19 in which the heated air in the stream (downstream) coming from the cyclone exhaust duct is fitted with an outer shell in which water inlet and outlet ducts are fitted. The purpose of the outer shell is to provide a water-cooling jacket to cool the exhaust air and to some degree the heated product carried by the exhaust air.