Bio-solid materials as alternate fuels in cement kiln, riser duct and calciner

Abstract

Alternate fuels and method of using the alternate fuels for replacing all or part of conventional fuels used to heat a riser duct, calciner or kiln in a cement making process.

Description

CROSS REFERENCE TO RELATED APPLICATIONS

This Application is a Continuation-in-Part of U.S. patent application Ser. No. 10/866,999 filed Jun. 14, 2004.

BACKGROUND OF THE INVENTION

The present invention pertains to use of bio-solid materials as a fuel or fuel additive in a cement making process. In particular, the present invention pertains to bio-solid materials as an alternate fuel in a cement kiln, riser duct and calciner. Bio-solids can be mixed with mineral by-products and introduced into the riser duct or calciner in the cement making process.

Bio-solids are defined as a residual by-product from biological activity or the residual by-products from processing of biological materials. Materials that are of interest for use in the method and apparatus of the present invention include sewage sludge, paper pulp residue, industrial sludge, food processing sludge and agricultural waste sludge.

Mineral or industrial by-products are defined as having some heat value and ash compositions that are compatible with mineral requirements of Portland cement manufacturing.

Conventional cement making processes e.g. the manufacturing processes and apparatus for the manufacture of Portland Cement, are based upon the processing of limestone (CaCO₂) by heating to achieve a cement clinker which is basically calcium oxide (CaO) chemically bound with other materials such as alumina, silica and iron.

In a conventional Portland Cement manufacturing process the main raw ingredient limestone is prepared with or without smaller amounts of materials containing alumina, silica and iron and ground to produce what is called a raw meal. The meal is then conducted to a pyro-processing area, which may include preheaters and calciners to condition the raw meal for introduction into a rotary kiln where the intermediate product clinker is produced. The main kiln and the preheaters and calciners are conventionally heated with a burner using coal, oil or gas as the fuel component. The coal, oil or gas is generally mixed with preheated combustion air and ignited to provide the heat necessary to decarbonate and melt the raw meal to produce clinker. At the discharge end of the conventional rotary kiln, the hot clinker is introduced into a clinker cooler wherein large amounts of air are blown through the hot clinker to cool it to a temperature of about 200° F. After sufficient cooling the clinker can be ground into a final product. In the grinding operation of the cooled clinker a small amount of gypsum may be added to produce the finished Portland Cement.

One of the largest cost items in the manufacture of cement is the cost of fuel. With ever increasing prices for coal, oil and gas alternate fuel sources are constantly be sought for use in the process.

Among the materials which have been considered for use as alternate fuels are bio-solid materials, which have been processed prior to delivery to the cement manufacturing plant to remove moisture so that the dried bio-solid materials are of a moisture content and size to be introduced into the combustion processes for the cement manufacturing process.

U.S. Pat. No. 4,627,877 discloses a method and apparatus for continuously producing cement clinker. Patentees disclose use of waste material as fuel in a cement manufacturing process. The method and apparatus of the '877 Patent provide for a cooling of cement clinker and the use of recovered energy to promote heat decomposition of combustible material.

U.S. Pat. No. 5,336,317 granted Aug. 9, 1994, is directed to a process for making cement using low-grade fuels. The use of low-grade fuels in production of cement provides for an exhaust gas that is substantially reduced in nitrogen oxides and other pollutants. The low-grade fuels replace only a portion of the fuel used in the cement making process and are materials such as bio-mass, wood waste, chemical industry waste material as well as old tires and paper. The alternate fuel materials are gasified in a fluidized bed reactor and burned in the main burner of the rotary kiln. A portion of the gasified stream is mixed with the exhaust gas from the rotary kiln and another portion of the gas stream is fed to the calciner and replaces high grade fuel that is normally used in the calciner. Gasification residues may also be used as a raw material in the production of cement since they contain less than 2% by weight carbon. According to Patentees, 50 to 70% of the high grade fuels are replaced by low grade fuels. It should be noted that the combustion air which is fed to the rotary kiln and the gasifying air which is fed to the fluidized bed are preheated in the clinker cooler. Patentees also allude to the fact that because of the circulation of solids, the gasification residue which is withdrawn from the gasifier has a low carbon content and in some cases, depending upon the quality requirements specified for the cement, can be mixed with the raw material introduced into the calciner or the kiln for production of the cement.

U.S. Published Patent Application 2002/0148780 A1 is drawn to a method for enhancing biological activated sludge treatment of waste water and production of a fuel product resulting therefrom. According to the publication waste water containing organic compounds is treated biologically using a cellulose-based catalytic media in order to produce a bio-mass fuel product. After treatment with the cellulose-based catalytic media, the product is dried and palletized for shipping to cement kilns or power plants as a bio-mass fuel. As pointed out by applicants the bio-mass fuel provides CO₂ credits by replacing carbon-rich fossil fuels. Another benefit of using the bio-mass fuel is, according to applicants, that the cement kilns are able to utilize the inorganic solids (ash) that are part of the combusted bio-mass fuel.

U.S. Pat. No. 6,176,187 discloses a sludge handling and feeding system. Provision is made for feeding aqueous sludge to a combustor associated with an operation such as cement manufacturing to assist in reducing pollutant emissions associated with the combustion operations. Patentees also address the disposal of biological sludge as produced by a wastewater treatment plant using it in the combustion operation. Patentees specifically provide for the use of aqueous sludge in a cement kiln for production of Portland Cement clinker.

U.S. Pat. No. 4,391,671 discloses a method for producing lime in a rotary kiln using bio-mass residue added to the kiln as a replacement for the normally used fossil fuel.

U.S. Pat. No. 4,984,983 discloses a method of cold firing hazardous waste material in an industrial rotary kiln. Patentees describe destruction of various toxic (stable solid or semi-solid), hazardous waste materials in cement kilns. Along with the destruction of the toxic hazardous waste materials, a benefit is obtained in that they serve as fuel supplements in the cement kiln operation.

U.S. Pat. Nos. 4,913,742; 4,921,538; 5,454,333; and 6,383,283 all disclose production of cement clinker using contaminated materials or other types of materials.

U.S. Pat. Nos. 6,615,751 and 6,692,544 as well as Published Patent Application 2004/0034262 A1 disclose preparation of bio-mass to be used as a fuel product.

None of the references teach or suggest particular combinations of direct firing of dried bio-solids and secondary materials for incorporation into the cement clinker.

U.S. Pat. No. 5,555,823 discloses a method and apparatus for feeding waste material to a rotary cement kiln to be burned therein. According to Patentees hazardous waste materials can be used in a rotary cement kiln. Kiln dust and fly ash as well as other raw materials may be utilized by the continuous introduction of such materials into the calcining zone of the cement kiln. Thus, the waste materials are thermally decomposed with recovery of energy. Solid waste material is used as a secondary fuel and furthermore does not require pre-packaging or such preliminary steps as pre-shredding. The apparatus provides for a constant energy input by providing controlled delivery of the materials into the system. According to Patentees liquid sludge may also be utilized as the waste material used in the process.

Published Patent Application 2003/0061972 A1 is directed to recovery of cement kiln dust through precipitation of calcium sulfate using a sulfuric acid solution. The disclosed method involves treating a raw cement kiln dust to form a gypsum product, which is used to produce a Portland Cement Product.

Published Patent Application 2003/0029364 A1 is drawn to an invention directed to a method for recycling building materials. Building materials are introduced into a cement kiln where a portion of the material is used as the fuel within the kiln. The non-combustible portion of the building material is incorporated into a clinker material in order to reduce emissions. Scrap shingles or a by-product of the manufacturing process for making roofing shingles may be used as the fuel and raw material for the production of cement. Such materials, including asphalt coatings, which are useful as the fuel may also contain materials such as limestone, which is an input material for cement as well. Shingles may also include those having a glass fiber mat which provides a source of silica.

U.S. Pat. No. 4,627,887 is directed to a method and apparatus for continuously producing cement clinker. Combustible waste material is used as a fuel for preheating or calcining a cement material in the production of cement clinker. Combustible waste materials that are used in the process include used tires and other organic materials such as oil waste. The process provides for treatment of combustion gases in order to eliminate or convert the harmful substances produced to harmless substances. Patentees also describe the use of a clinker cooler.

U.S. Pat. No. 5,530,176 is directed to a method and apparatus for disposing of hazardous waste material in a cement-producing kiln. Hazardous waste materials which may be either chemical or nuclear are included in the description of the method and apparatus found in this patent. Other hazardous waste material such as discarded plastics, rubber gloves, paper, paint filters, etc. are also deemed suitable for practicing the invention. The hazardous waste materials are introduced into the cement producing kiln and provide supplemental fuel for the process. Patentees provide details of the apparatus used in carrying out the process of the invention.

U.S. Pat. Nos. 4,678,514; 5,224,433; 5,837,052; 5,888,256; 6,391,105; and 6,439,139 all disclose various processes for using alternate materials for fuel and/or for being incorporated into the cement manufacturing process.

U.S. Pat. Nos. 6,168,709; 6,457,425; 6,535,177; and 6,689,925 all disclose processes for converting materials, such as petroleum coke, other low grade hydrocarbon materials, or other refuse material, into fuels.

SUMMARY OF THE INVENTION

The present invention pertains bio-solids having specific characteristics for use as a fuel or fuel additive in a conventional cement making process.

The bio-solids can either be used as a fuel additive or a partial fuel substitute alone or mixed with other mineral waste products such as high carbon fly ash and flue dust.

Therefore, in a first aspect the present invention is a method for supplementing or replacing conventional fuel in a cement making process with waste bio-solid material by selecting a waste bio-solid material having fuel value and other components that would not be deleterious to a finished cement made in the cement making process, providing the waste bio-solid material with a moisture content at or below 10% by weight, the bio-solid material having a maximum particle size of about two (2) inches, and introducing the bio-solid waste material into a combustion apparatus of the cement making process. An additional parameter of concern is the specific gravity of the particle. A large particle size with low specific gravity will allow the particle to float in the gases of the combustion zone until it oxidizes. Conversely, a material with high specific gravity will require a smaller particle size to remain in suspension in the combustion zone until it oxidizes.

In another aspect the present invention is a method for using bio-solids as a fuel including the step of blending non bio-solid industrial waste having fuel and mineral values with the bio-solid waste material prior to introducing the blended material into a combustion apparatus of the cement making process.

A major benefit from the present invention resides in the ability to avoid landfill disposal of bio-solid materials that will decay and generate methane a known and unwanted atmospheric “Greenhouse Gas”.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic representation of a conventional cement making process.

FIG. 2 is a schematic drawing of a method and apparatus for storing fuel substitute waste materials.

FIG. 3a is a schematic representation of one method and apparatus for introducing waste bio-solids into the combustion zone of a cement kiln.

FIG. 3b is an alternate embodiment of another method and apparatus for introducing waste bio-solids into the main burner of a cement kiln.

FIG. 3c is a schematic representation of a method for introducing waste bio-solids directly into a conventional burner of a cement kiln without modification of the main burner.

FIG. 4a is a schematic representation of a method an apparatus for introducing waste bio-solids into a calciner using an auxiliary pipe.

FIG. 4b is a schematic representation of a method and apparatus for introducing waste bio-solids into a calciner using a conventional burner.

FIG. 5 is a schematic representation of a method and apparatus for introduction of waste bio-solids into the loop duct of a preheating apparatus used in a conventional cement making process and apparatus.

DETAILED DESCRIPTION OF THE INVENTION

Waste materials are defined as residual by-products from municipal activities, farming or food processing, wood and paper processing and/or manufacture, and industrial processes.

Table 1 sets forth general categories of waste materials that would be usable in the method and apparatus of the present invention.

TABLE 1
		Fuel %/Ash %		Critical Ash
Material	Solid %/Liquid %	(Dry)	Fuel BTU's/lb (Dry)	Components
Municipal Waste	85/15	70/30	5,000-8,000	P2O5, Cl
Wood Waste	80/20	70/30	5,000-8,000	Na2O, K2O
Industrial Waste	80/20	50/50	5,000-8,000	varies
Food Processing	80/20	50/50	5,000-8,000	varies
Waste
Agricultural Waste	80/20	50/50	5,000-8,000	varies

Example of Municipal waste are refuse derived fuel, waste water treatment sludge, grease, scum and screenings.

Examples of wood waste are bark, hardwoods, railroad ties, saw dust, softwoods, woodex pellets, board plant waste, planer shavings, sander dust, slash, urban wood waste, zinc borate and OSB waste.

Examples of Industrial waste are auto shredding residue, carpet scraps, cellulose acetate, charcoal, oil soaked clay, PET and glycol liquid, petroleum coke, polyolefins, tire derived fuel, cardboard sludge, cellulose absorbent, char, dried paper sludge, paper sludge, petroleum tanker sludge, flue dust, high carbon fly ash and unburned fuel.

Examples of agricultural and food processing waste are alfalfa seed straw; almond shells, apple wood, barley straw, cherry pits, citrus trees, corn cobs, cotton gin wastes, cotton stalks, cubed garlic, fig wood, grape canes, grape scaffolds, nectarine wood, olive pits, paunch manure, peach wood, peat, pistachio shells, plum wood, prune wood, race track straw, rice straw, sunflower hulls, tomato pomace, walnut wood, almond brush, almond wood, apricot wood, bean straw, chicken litter, coffee grounds, corn stalks, cotton see hulls, cow manure, fig culls, garlic and onion skins, grape pomace, manure and wheat straw, oat straw, orange peel and pulp, peach pits, pear wood, pecan shells, pistachio wood, prune pits, race track shavings, rice hulls, safflower stalks, tobacco sludges, walnut shells and wheat straw.

The foregoing materials preferably dried to a residual moisture content of 10% by weight or less and with a maximum particle size about two (2) inches are used in the method and apparatus of the present invention. As set out above the actual required particle size will depend on the specific gravity of the waste material. For example waste paper can have a particle size of two (2) inches but a tire fragment would have to be much smaller to remain suspended in the combustion zone. Materials having moisture content above 10% by weight but less than the moisture content set out in Table 1 can also be used in the process of the present invention.

Of the materials in the foregoing description sewage sludge, a semi-solid residue of sewage treatment processes is available in quantity and may be delivered to the cement making process either pre-dried to a moisture content of 10% by weight or less or dried at the cement plant using the processes described in our co-pending U.S. patent application Ser. No. 10/866,999 filed Jun. 14, 2004.

Paper making waste generally consists of organic based by-products from wood pulping, cardboard, or paper manufacturing. Paper manufacturing uses conventional sources of cellulose such as wood and flax. Together with secondary sources of cellulose such as waste paper and waste cardboard. The manufacturing process requires the grinding, particle size classification, heating, and blending of conventional and secondary sources of cellulose. Wood processing involves, cutting, planning, shaping, sanding, etc., processes that generate large volumes of cellulosic material in dust or larger particle sizes. Such waste may contain mineral by-products such as silica, alumina, etc. from the abrasive material. Such mineral by-products can be incorporated into the finished cement without detriment to the finished cement product. These processes generate by-products that have various concentrations of water and organic components.

Industrial waste for use in the present invention, contain organic based by-products with liquid or solid hydro-carbon components. For example, petroleum tanker sludge, oil soaked clay, oil soaked filter media, sediment from coal washing operations, flue dust, high carbon fly ash, and flexi coke can be used as alternative fuels or fuel components according to the present invention.

Food processing sludges are generated from many operations. At the beginning and end of batch processes, off spec materials are generated and must be disposed. Similarly, when process equipment is periodically cleaned or cleaned between batch runs, materials are generated and must be disposed. These materials generally consist of grain and vegetable based products that are being ground, mixed and dosed to produce various food products. In other processes diatomaceous earth filter media often becomes saturated with the organic residues form mixing, batching, cooking and pasteurizing processes. These saturated filter media materials are suitable bio-solid residues for the processes of the present invention.

Agricultural waste sludges consist of by-products from harvesting and processing crops. Materials such as stalks, seeds, shells, pits, skins, rinds, twigs, leaves, and bark with various concentrations of moisture are suitable for the process of the present invention.

According to the present invention waste materials containing residual water are treated to separate water and organic components from the waste. Organic components can be recovered and burned with ash residue chemically incorporated into the cement manufacturing process. The overall method of the present invention minimizes negative environmental impact and accumulation and/or land-filling of such waste materials. In particular disposal of flue dust and fly ash in land-fills is environmentally undesirable.

Cement manufacturing processes use large volumes of raw materials such as limestone and coal to produce Portland Cement. The process consists of three main areas, raw meal preparation, pyro-processing, and finished grinding. Limestone (CaCO₂) is generally the main raw ingredient. Smaller amounts of materials containing alumina, silica and iron are proportioned and ground with limestone to produce a raw meal. A precisely controlled mixture of raw meal is then fed to the pyro-processing area. The pyro-processing area burns large amounts of conventional fuel such as coal, oil and gas to generate the temperatures required to calcine the limestone and allow the new cement components to form. An intermediate product called clinker is produced in the pyro-processing area. Clinker is cooled from high pyro-processing temperatures to ambient temperature. A finished grinding process which incorporates a small percentage of gypsum into the clinker results in a Portland Cement product.

Referring to FIG. 1 a conventional clinkering process is embodied in the apparatus shown as 10. The apparatus 10 includes a preheating section 12 which can include a series of preheater stages 14, 16, 18, 20 and 22, which are interconnected with recovery conduits, e.g. 24, wherein the raw meal represented by arrow 25 introduced by a conduit 26 is gradually preheated for introduction into the main kiln 28 via a conduit 30. Downstream of the preheater section the process apparatus include a calciner 32, which is fired with a conventional burner 34 to begin the conversion of the limestone to clinker. The calciner portion of the process can include a loop system 36 which includes a conduit 38 to introduce additional fuel into the loop system 36 whereby the fines from the calciner are recycled and eventually introduced into the main kiln 28.

Gases and fine particles exiting the preheater section 12 are sent to a cooling tower 32 for cooling of the gases and exhausting via a blower 34. Dust is removed in a dust collector 36.

Main kiln 28 includes a main burner 38 which is fired using a fuel such as coal, oil or natural gas together with an oxygen containing fluid such as air. The preheated or pre-calcined meal enters the kiln at a first or entry end 40. As the meal progresses from the entrance 40 to the exit 42 of the kiln 28 it is converted into a clinker. The clinker exits the kiln 28 and is deposited into a clinker cooler 44 where the clinker is cooled to a temperature of about 200° F. Thereafter, the clinker represented by arrow 45 is conducted via a conduit for other delivery device 46 to the grinding operation. The clinker cooler 44 includes a dust recovery system 48 so that dust can be recycled to the finish grinding area of the cement making process.

Referring to FIG. 2 there is shown an overall system 50 for receipt and storage of pre-dried waste materials suitable for use in the processes of the present invention. System 50 includes a storage silo 52 which receives the waste material from a pneumatic transport vehicle 54. The waste material is transferred to the storage device or silo 52 via a pneumatic line 56. Storage silo 52 includes suitable dust collecting means 58 for recovering dusts that are generated during the loading or off loading of the dried waste material. Dust collecting means 58 is provided with a suitable conduit 59 or other delivery device (not shown) to convey exhaust gases to the inlet of the clinker cooler fans. When dried material is required for use in the cement making process it can be withdrawn from the storage silo 52 through a gate or a metering valve 60 and conveyed to the point of use via conduit 64 which is connected to a blower or other pneumatic transport device 66. For example, the blower 66 can be that is offered for sale by aerzen under the designation VML 33.

Alternatively, the waste material can be received with excess moisture and the waste material dried to the required dryness in a process such as described in our co-pending U.S. Patent Application referred to above.

This material can arrive already classified into a particle size that can be used in the various combustion devices.

It may be possible to accept waste material where the residual moisture content is below 10%. However, as the moisture content is reduced below 10% it is expected that the dried bio-solids will become increasingly dusty (i.e. finer average particle size). Depending on the type of bio-solid material being dried, this may or may not be an advantage in the handling, storage and use of the dried bio-solid material.

As stated above the dried bio-solid material will be pneumatically conveyed to a storage device or silo 52. Depending upon the temperature of the incoming dried waste material, it may be necessary to either cool the dried bio-solid material in a separate cooling (heat exchange) device or use a cooled conveying gas to transport the dried bio-solids to the storage silo 52. Any of these methods or an alternate method of cooling may be employed to ensure that the dried bio-solids are delivered to the storage silo 52 at a temperature of less than 40° C. (less than 104° F.) to, depending upon the composition of the bio-solid material, minimize the opportunity for spontaneous combustion.

Any storage device must be designed in accordance with all applicable local, state and federal codes and regulations to insure safe handling of such material. It is believed that procedures and methods that are used for the storage and handling of pulverized coal will enable a user to comply with such laws and regulations for storage and handling of dried bio-solid materials.

Although any new storage system should have the necessary equipment to withdraw and covey the dried bio-solid material as needed to a point of use, alternate transport methods may be practical in some cement processes. Some cement plans have existing pneumatic transport systems for conveying a primary fuel such as pulverized coal. With such a system it is possible to deposit a controlled flow rate of dried bio-solids directly into an existing pneumatic transport line. In this aspect, the dosing systems would discharge through a rotary air lock directly into the pneumatic transport system.

Referring to FIGS. 3a, 3b and 3c the dried bio-solids transported to the combustion (burning) zone of kiln 28 can be introduced into in several ways. If the dried bio-solids are conveyed to the main burning zone of kiln 28 by an independent pneumatic conveying line, a separate burner pipe, e.g. 112 in FIG. 3a, can be used to introduce the dried bio-solids into the rotary kiln. The nozzle or discharge end 114 of pipe 112 can be placed at any location proximate the discharge end or nozzle end 39 of the main burner 38.

As shown in FIG. 3b the dried bio-solids can be conveyed to the burning (combustion) zone of kiln 28 via an independent pneumatic conveying line 116, which terminates in a conduit 118, which is inside of the burner 120. Burner 120 can be a multi port or a concentric tube burner, such burners being well known in the art.

As shown in FIG. 3c the dried bio-solids can be conveyed directly to the burner 122 in kiln 28 together with the normal fuel, e.g. pulverized coal, as represented by arrow 124 to produce the flame 126 inside the kiln 28.

It should be noted that the particle size of fuels burned in the main combustion zone of the cement kiln is of critical importance. If too many large particles of fuel enter this portion of the kiln there is a possibility that some of them may fall into the reaction zone of the kiln and adversely affect the quality of the clinker produced. For this reason the degree of fineness of the dried bio-solids must be monitored closely. As set forth above the particle size of the dried bio-solids will be a function of the moisture content, which will be adjusted as needed. If adjusting the moisture content does not yield a sufficiently small particle size, it may be necessary to use a mechanical size reduction (i.e. grinding) device to optimize the size of the dried bio-solids to be used in a combustion zone.

As shown in FIG. 4a if the dried bio-solids are conveyed to the calciner 32 via an independent pneumatic conveying line 128 they can be introduced to the calciner 32 combustion zone with a separate burner pipe 130 having a discharge end 132, which is proximate the discharge end 35 of conventional fuel burner 34. Alternatively, as shown in FIG. 4b the dried bio-solids can be conveyed directly to the calciner 32 burner 84 via an existing pneumatic conveying line 134 where they would mix with the primary fuel (e.g. pulverized coal) and introduced into the combustion zone through the existing main burner 34.

As shown in FIG. 5 a calciner includes a loop duct (or riser duct) 136. Dried bio-solids can be introduced into duct 136 via a direct pneumatic transport line 138 as shown in FIG. 5.

Contrary to the requirements of the main kiln burner, particle size is not as critical for dried bio-solids introduced into the calciner and the loop duct combustion zone of the cement plant. Larger particle size dried bio-solids can be accommodated in these areas because of the longer retention time in the combustion zone and the fluidizing effect of high gas flows. Furthermore, any particles or fuel that become mixed with the raw meal (feed) will have ample time to oxidize before they are added to the more critical reaction zone of the kiln.

The combustion zone of a cement kiln is one of the hottest industrial processes. Gas temperatures in the main combustion zone can exceed 3500° F. Additionally, these gases remain above 1800° F. for as long as 5 seconds as they move away from the combustion zone. The combination of preheated high oxygen content air, high combustion temperatures and long residence time above 1800° F. insures complete combustion of all organic compounds. The calciner loop duct combustion zone consists of the main calciner combustion chamber and the loop duct or riser duct. Gas temperatures in the calciner combustion chamber can read 2500° F. These gases can remain above 1500° F. for as long as five (5) seconds as they leave the calciner combustion chamber and pass through the loop duct to the pre-heater cyclone chambers.

The main components of the raw materials used to manufacture cement are calcium, silica, alumina and iron. Inorganic ash components of dried bio-solids have high concentrations of calcium and silica that can supplement the conventional minerals. Therefore, the inorganic ash residue of dried bio-solids can be beneficially recovered by incorporation into the cementclinker. The intimate mixing of the combustion gases and the cement raw materials as the gases leave the combustion zone ensure complete integration of inorganic ash residues into the conventional raw materials. In this manner the inorganic ash residues become an integral part of the process chemistry. There are minor constituents in the inorganic ash residue of dried bio-solids that must be monitored to insure the quality of the performance of the cement product. Trace components in the ash such as P₂O₅, Cl, Na₂O, and K₂O must be measured on a regular basis to control any potentially deleterious effect of these components on the cement manufacturing process or the performance of the finished product. Specifically, P₂O₅ from dried bio-solids will increase the concentration of potassium in the finished clinker. Research has indicated that when the level of potassium in a clinker approaches 1.5% the setting time of the resulting concrete will be extended. Additionally, high concentrations of Cl, N₂O and K₂O from dried bio-solids can cause build up in kiln, which, in turn, can cause operational interruptions.

It is within the scope of the present invention to blend various bio-solid residues for use as primary or supplemental fuels in a cement making operation.

It is also within the scope of the present invention to use industrial waste materials, such as a high carbon fly ash or steel mill flue dusts, that contain fuel values as well as mineral values. These wastes can be used alone or blended with the bio-solid materials to recover fuel valves and residual minerals for incorporation into the finished cement product. By careful attention to the composition of the fly ash, flue dust and/or bio-solid materials utilization of the materials can be maximized. It is also possible to create custom fuel/additive mixtures using these materials selectively.

Having thus described our invention what is desired to be secured by Letters Patent of the United States is set forth in the appended claims.

Claims

1. A method for supplementing or partial replacing conventional fuel in a cement making process with waste bio-solid material comprising the steps of:

selecting a waste bio-solid material having fuel value and other components that would not be deleterious to a finished cement made in said cement making process;

providing said waste bio-solid material with a moisture content at or below about 20% by weight said bio-solids having a maximum particle size of about 2 inches; and

introducing said bio-solid waste material into a combustion apparatus of said cement making process.

2. A method according to claim 1 including the step of adjusting said particle size of said waste bio-solid material to that required for the waste particles to remain in suspension in a combustion zone while being oxidized.

3. A method according to claim 1 including selecting said waste bio-solid material from the group consisting of municipal waste, paper making and wood processing wastes, industrial waste, food processing waste, and agricultural waste or mixtures thereof.

4. A method according to claim 3 including using a sludge of said waste material dried to a moisture content of at or below about 10% by weight and having an internal temperature at or below 104° F. (40° C.).

5. A method according to claim 3 including selecting organic dried sewage sludge as said waste.

6. A method according to claim 3 including selecting a waste material with fuel values and mineral values that can be recovered in a cement product by combination of said waste.

7. A method according to claim 1 including inventorying said waste material a storage device.

8. A method according to claim 7 wherein said waste material at a temperature not significantly higher than 104° F. (40° C.).

9. A method according to claim 1 wherein said waste solids are introduced into a main combustion zone of said cement making process.

10. A method according to claim 1 wherein said waste solids are introduced into one of a calciner, loop duct combustion zone or both in said cement making process.

11. A method according to claim 1 including the step of blending non bio-solid industrial waste having fuel and mineral values with said bio-solid waste material prior to introducing said blended material into a combustion apparatus of said cement making process.

12. A fuel or fuel additive resulting from one of municipal waste, paper making and wood processing waste, industrial wastes, food processing waste, agricultural wastes and mixtures thereof dried to a moisture content of at or below 10% by weight and having a maximum particle size of about 2 inches.

13. A fuel or fuel additive according to claim 12 including one of high carbon fly ash, flue dust and mixtures thereof blended with said waste.

14. A fuel or fuel additive resulting from blending one of municipal waste, paper making and wood processing waste, industrial wastes, food processing waste, agricultural wastes and mixtures thereof dried to a moisture content of at or below 10% by weight and having a maximum particle size of about 2 inches; and

one of high carbon fly ash flue dust or mixtures thereof.