CA2727638A1 - Optimization of combustion process - Google Patents
Optimization of combustion process Download PDFInfo
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- CA2727638A1 CA2727638A1 CA 2727638 CA2727638A CA2727638A1 CA 2727638 A1 CA2727638 A1 CA 2727638A1 CA 2727638 CA2727638 CA 2727638 CA 2727638 A CA2727638 A CA 2727638A CA 2727638 A1 CA2727638 A1 CA 2727638A1
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- fluidized bed
- biomass
- storage tank
- combustion
- fuel
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Classifications
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
- F23G—CREMATION FURNACES; CONSUMING WASTE PRODUCTS BY COMBUSTION
- F23G7/00—Incinerators or other apparatus for consuming industrial waste, e.g. chemicals
- F23G7/10—Incinerators or other apparatus for consuming industrial waste, e.g. chemicals of field or garden waste or biomasses
- F23G7/105—Incinerators or other apparatus for consuming industrial waste, e.g. chemicals of field or garden waste or biomasses of wood waste
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
- F23G—CREMATION FURNACES; CONSUMING WASTE PRODUCTS BY COMBUSTION
- F23G5/00—Incineration of waste; Incinerator constructions; Details, accessories or control therefor
- F23G5/02—Incineration of waste; Incinerator constructions; Details, accessories or control therefor with pretreatment
- F23G5/04—Incineration of waste; Incinerator constructions; Details, accessories or control therefor with pretreatment drying
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
- F23G—CREMATION FURNACES; CONSUMING WASTE PRODUCTS BY COMBUSTION
- F23G5/00—Incineration of waste; Incinerator constructions; Details, accessories or control therefor
- F23G5/30—Incineration of waste; Incinerator constructions; Details, accessories or control therefor having a fluidised bed
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
- F23G—CREMATION FURNACES; CONSUMING WASTE PRODUCTS BY COMBUSTION
- F23G5/00—Incineration of waste; Incinerator constructions; Details, accessories or control therefor
- F23G5/44—Details; Accessories
- F23G5/46—Recuperation of heat
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
- F23G—CREMATION FURNACES; CONSUMING WASTE PRODUCTS BY COMBUSTION
- F23G5/00—Incineration of waste; Incinerator constructions; Details, accessories or control therefor
- F23G5/50—Control or safety arrangements
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F26—DRYING
- F26B—DRYING SOLID MATERIALS OR OBJECTS BY REMOVING LIQUID THEREFROM
- F26B3/00—Drying solid materials or objects by processes involving the application of heat
- F26B3/02—Drying solid materials or objects by processes involving the application of heat by convection, i.e. heat being conveyed from a heat source to the materials or objects to be dried by a gas or vapour, e.g. air
- F26B3/06—Drying solid materials or objects by processes involving the application of heat by convection, i.e. heat being conveyed from a heat source to the materials or objects to be dried by a gas or vapour, e.g. air the gas or vapour flowing through the materials or objects to be dried
- F26B3/08—Drying solid materials or objects by processes involving the application of heat by convection, i.e. heat being conveyed from a heat source to the materials or objects to be dried by a gas or vapour, e.g. air the gas or vapour flowing through the materials or objects to be dried so as to loosen them, e.g. to form a fluidised bed
- F26B3/088—Drying solid materials or objects by processes involving the application of heat by convection, i.e. heat being conveyed from a heat source to the materials or objects to be dried by a gas or vapour, e.g. air the gas or vapour flowing through the materials or objects to be dried so as to loosen them, e.g. to form a fluidised bed using inert thermally-stabilised particles
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
- F23G—CREMATION FURNACES; CONSUMING WASTE PRODUCTS BY COMBUSTION
- F23G2206/00—Waste heat recuperation
- F23G2206/10—Waste heat recuperation reintroducing the heat in the same process, e.g. for predrying
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
- F23G—CREMATION FURNACES; CONSUMING WASTE PRODUCTS BY COMBUSTION
- F23G2206/00—Waste heat recuperation
- F23G2206/20—Waste heat recuperation using the heat in association with another installation
- F23G2206/203—Waste heat recuperation using the heat in association with another installation with a power/heat generating installation
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F26—DRYING
- F26B—DRYING SOLID MATERIALS OR OBJECTS BY REMOVING LIQUID THEREFROM
- F26B2200/00—Drying processes and machines for solid materials characterised by the specific requirements of the drying good
- F26B2200/24—Wood particles, e.g. shavings, cuttings, saw dust
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E20/00—Combustion technologies with mitigation potential
- Y02E20/12—Heat utilisation in combustion or incineration of waste
Landscapes
- Engineering & Computer Science (AREA)
- Mechanical Engineering (AREA)
- General Engineering & Computer Science (AREA)
- Life Sciences & Earth Sciences (AREA)
- Environmental & Geological Engineering (AREA)
- Microbiology (AREA)
- Wood Science & Technology (AREA)
- Sustainable Development (AREA)
- Sustainable Energy (AREA)
- Drying Of Solid Materials (AREA)
Abstract
A process for improving the drying of woody biomass fuel and increasing the efficiency of combustion for the production of energy is provided. The multi-step process comprises of a system that provides biomass to a fluidized bed dryer to dry the approximately 30%
moisture wet fuel, a storage tank used to keep fuel dry until it is required for combustion in a fluidized bed boiler, a control element used to regulate amount of dried fuel fed into fluidized bed boiler and a circulating fluidized bed combustion boiler to circulate with the dried fuel for combustion of said fuel.
moisture wet fuel, a storage tank used to keep fuel dry until it is required for combustion in a fluidized bed boiler, a control element used to regulate amount of dried fuel fed into fluidized bed boiler and a circulating fluidized bed combustion boiler to circulate with the dried fuel for combustion of said fuel.
Description
DESCRIPTION
Field of the invention:
This invention relates to a multi-system process that recycles waste system heat sources, specifically hot flue gases, from a combustion unit to dry wet biomass, which is used as feedstock for said combustion unit process. This invention improves the thermal content of said biomass used in thermal conversion processes by lowering the moisture content. The drying unit consists of a fluidized bed dryer wherein the bed consists of wet biomass, which is fluidized by hot flue gases and dried by the heat of condensation provided by the hot flue gases. The fluidized bed dryer can be incorporated to different power production processes. A storage tank unit which stores the dried biomass to be used for the thermal conversion process is also claimed and is placed after the drying unit.
BACKGROUND OF THE INVENTION
Research and development has been devoted to finding new sources of renewable energy due to the depletion of fossil fuels and environmental issues associated with their use. Combustion of fossil fuels produces high levels of carbon dioxide as well as NOX and SO,, gas emissions which are harmful to the environment (Alauddin, Z. 2010).
Renewable resources are part of our natural environment. Renewable energy is beneficial for the overall global energy consumption. Among renewable energy sources is biomass, which is a broad term that encompasses all solids derived from plant matter and wastes (US2007220805-Al).
Carbonaceous biomass is derived from agricultural residues and industrial wastes (McKendry, P.
2002). Energy can be extracted from biomass through thermal conversion processes such as gasification, pyrolysis and combustion. These processes either convert biomass to another fuel, such as liquid or gas, with a higher calorific value than raw biomass or directly extract heat from biomass for the production of work (Bridgwater, A. V. 1994). The relative energy value of biomass is determined by the chemical and physical properties of the large molecules from which it is made (McKendry, P. 2002.).
One such process to extract energy from carbanaceous biomass includes combustion to produce heat that can be exploited for the production of steam. In order to efficiently extract useful energy from biomass while maintaining low greenhouse gas emissions, thermal conversion processes can be designed to avoid high emissions and result in a high energy yield. (Lundgren, J.
2009).
Field of the invention:
This invention relates to a multi-system process that recycles waste system heat sources, specifically hot flue gases, from a combustion unit to dry wet biomass, which is used as feedstock for said combustion unit process. This invention improves the thermal content of said biomass used in thermal conversion processes by lowering the moisture content. The drying unit consists of a fluidized bed dryer wherein the bed consists of wet biomass, which is fluidized by hot flue gases and dried by the heat of condensation provided by the hot flue gases. The fluidized bed dryer can be incorporated to different power production processes. A storage tank unit which stores the dried biomass to be used for the thermal conversion process is also claimed and is placed after the drying unit.
BACKGROUND OF THE INVENTION
Research and development has been devoted to finding new sources of renewable energy due to the depletion of fossil fuels and environmental issues associated with their use. Combustion of fossil fuels produces high levels of carbon dioxide as well as NOX and SO,, gas emissions which are harmful to the environment (Alauddin, Z. 2010).
Renewable resources are part of our natural environment. Renewable energy is beneficial for the overall global energy consumption. Among renewable energy sources is biomass, which is a broad term that encompasses all solids derived from plant matter and wastes (US2007220805-Al).
Carbonaceous biomass is derived from agricultural residues and industrial wastes (McKendry, P.
2002). Energy can be extracted from biomass through thermal conversion processes such as gasification, pyrolysis and combustion. These processes either convert biomass to another fuel, such as liquid or gas, with a higher calorific value than raw biomass or directly extract heat from biomass for the production of work (Bridgwater, A. V. 1994). The relative energy value of biomass is determined by the chemical and physical properties of the large molecules from which it is made (McKendry, P. 2002.).
One such process to extract energy from carbanaceous biomass includes combustion to produce heat that can be exploited for the production of steam. In order to efficiently extract useful energy from biomass while maintaining low greenhouse gas emissions, thermal conversion processes can be designed to avoid high emissions and result in a high energy yield. (Lundgren, J.
2009).
Carbonaceous biomass can be combusted in a circulating fluidized bed combustor. It comprises two chambers, a combustion chamber and a cyclone (CA 1261123). The combustion chamber contains a bed of material, sand or limestone. The use of limestone is preferred because it 35 lowers sulfur dioxide emissions of biomass combustion. Biomass is fed into the combustion chamber into which primary and secondary air is injected to fluidize the bed material and combust biomass according to a method described in CA-2148597 to transport the solid particles between chambers. Biomass is combusted in the combustion chamber during this process.
Combustion products are carried to the cyclone separator which expels the cooled flue gases through the top of 40 the cyclone while combustion products and hot bed material are recirculated to the combustion chamber.
A few caveats in the production of energy using biomass as the fuel are:
acquiring a high grade biomass, the time needed for growth and cultivation of biomass, and the limited availability of biomass. The cost for collection and processing of biomass can be very expensive and time 45 consuming. Therefore, when using biomass for the production of energy, a route for maximum efficiency and the ability to capture as much energy as possible, needs to be achieved. To obtain the most efficient route of energy production, the grade and moisture content of the biomass must be accounted for. (Gomez-Barea, A. 2010) The use of high quality biomass will lead to an efficient route for energy production 50 (Pimentel, D. 1981). The moisture content, particle size, and ash melting behaviour play a factor in the quality of fuel. High grade fuel consists of biomass with low moisture content, small particle size and high corrosive ash content (Loo, S. 2008). In combustion systems, the moisture content in the fuel must first be driven off, before combustion can occur efficiently.
The presence of water reduces the combustion temperature below optimal operating conditions;
therefore, the combustion 55 of the fuel may be incomplete and cause unhealthy emissions (Hatfield, J.
2008). The water may also recondense into the combustion system, which may lead to the corrosion of the equipment, causing potential hazards within the system such as fire (Stringer, J. 1996).
To avoid such issues with biomass containing high moisture content, a method to dry biomass prior to its thermal conversion is required.
60 Several methods to dry biomass to an acceptable moisture level have been developed, however there are drawbacks to these methods. Although, in most cases, these methods utilize waste heat sources to render the process more economical, they usually require energy to power the mechanical parts incorporated into these biomass dryers. The general design of these dryers uses concurrent or counter flow of a hot waste source, such as flue gases or steam, with the biomass fed 65 into the dryer to drive off excess moisture.
Some driers are composed of a rotary kiln in which moist biomass is dried through passing hot waste air through the rotating drum, such as that described by JP2010163509-A issued to Kataoka. The design of these driers results in a low residence time and high drying efficiency due to the well-mixing biomass with hot flue gases. However, these driers contain mechanical parts which 70 require high maintenance and increased capital costs. They also lower overall efficiency of the process due to additional external work required for the rotation of the kiln of the dryer.
Other driers contain perforated conveyor belts, which carries the biomass across the dryer, while passing hot air through the belt such as that described by R0109240-B1 issued to Tudose.
Such dryers require high residence times as well as uneven drying of biomass due to poor mixing 75 which results in lower drying efficiency.
A biomass vacuum dryer described by JP200525721 1 -A issued to Doi J. requires lower residence times but requires the use of a vacuum pump which requires higher maintenance costs to operate the pump and a lower overall efficiency of the process.
Drying methods described by DE102007038105-A1 issued to Fudel and 80 U1 issued to Goebler utilize waste hot air injected into a drying vessel, also contain mechanical parts such as a circulating drag chain and stirrer to properly mix biomass and increase the drying surface area. Although these methods recycle waste heat sources, they also require additional maintenance costs and capital costs to operate these additional mechanical parts.
The invention disclosed in this patent addresses these drawbacks by improving the drying of 85 biomass and reducing maintenance and capital costs created by the use of additional mechanical parts in the dryer. The invention consists of a fluidized bed dryer through which hot flue gases from a circulating fluidized bed combustor boiler are injected into the dryer.
Moist biomass is fed into the dryer and fluidized by the flow of hot flue gases that pass through a tube protruding through the distributor plate. Therefore, moist biomass circulates in the dryer which improves the removal of 90 moisture from biomass by the hot flue gases. This drying method, thus, strictly relies on hot flue gases to fluidize and dry biomass without the use of additional mechanical power. The fluidized bed dryer can be incorporated in thermal conversion processes of biomass that produce waste heat sources which can be exploited for drying moist biomass. The efficiency of the thermal conversion process of biomass is increased by the removal of water and recycling of waste heat sources.
Combustion products are carried to the cyclone separator which expels the cooled flue gases through the top of 40 the cyclone while combustion products and hot bed material are recirculated to the combustion chamber.
A few caveats in the production of energy using biomass as the fuel are:
acquiring a high grade biomass, the time needed for growth and cultivation of biomass, and the limited availability of biomass. The cost for collection and processing of biomass can be very expensive and time 45 consuming. Therefore, when using biomass for the production of energy, a route for maximum efficiency and the ability to capture as much energy as possible, needs to be achieved. To obtain the most efficient route of energy production, the grade and moisture content of the biomass must be accounted for. (Gomez-Barea, A. 2010) The use of high quality biomass will lead to an efficient route for energy production 50 (Pimentel, D. 1981). The moisture content, particle size, and ash melting behaviour play a factor in the quality of fuel. High grade fuel consists of biomass with low moisture content, small particle size and high corrosive ash content (Loo, S. 2008). In combustion systems, the moisture content in the fuel must first be driven off, before combustion can occur efficiently.
The presence of water reduces the combustion temperature below optimal operating conditions;
therefore, the combustion 55 of the fuel may be incomplete and cause unhealthy emissions (Hatfield, J.
2008). The water may also recondense into the combustion system, which may lead to the corrosion of the equipment, causing potential hazards within the system such as fire (Stringer, J. 1996).
To avoid such issues with biomass containing high moisture content, a method to dry biomass prior to its thermal conversion is required.
60 Several methods to dry biomass to an acceptable moisture level have been developed, however there are drawbacks to these methods. Although, in most cases, these methods utilize waste heat sources to render the process more economical, they usually require energy to power the mechanical parts incorporated into these biomass dryers. The general design of these dryers uses concurrent or counter flow of a hot waste source, such as flue gases or steam, with the biomass fed 65 into the dryer to drive off excess moisture.
Some driers are composed of a rotary kiln in which moist biomass is dried through passing hot waste air through the rotating drum, such as that described by JP2010163509-A issued to Kataoka. The design of these driers results in a low residence time and high drying efficiency due to the well-mixing biomass with hot flue gases. However, these driers contain mechanical parts which 70 require high maintenance and increased capital costs. They also lower overall efficiency of the process due to additional external work required for the rotation of the kiln of the dryer.
Other driers contain perforated conveyor belts, which carries the biomass across the dryer, while passing hot air through the belt such as that described by R0109240-B1 issued to Tudose.
Such dryers require high residence times as well as uneven drying of biomass due to poor mixing 75 which results in lower drying efficiency.
A biomass vacuum dryer described by JP200525721 1 -A issued to Doi J. requires lower residence times but requires the use of a vacuum pump which requires higher maintenance costs to operate the pump and a lower overall efficiency of the process.
Drying methods described by DE102007038105-A1 issued to Fudel and 80 U1 issued to Goebler utilize waste hot air injected into a drying vessel, also contain mechanical parts such as a circulating drag chain and stirrer to properly mix biomass and increase the drying surface area. Although these methods recycle waste heat sources, they also require additional maintenance costs and capital costs to operate these additional mechanical parts.
The invention disclosed in this patent addresses these drawbacks by improving the drying of 85 biomass and reducing maintenance and capital costs created by the use of additional mechanical parts in the dryer. The invention consists of a fluidized bed dryer through which hot flue gases from a circulating fluidized bed combustor boiler are injected into the dryer.
Moist biomass is fed into the dryer and fluidized by the flow of hot flue gases that pass through a tube protruding through the distributor plate. Therefore, moist biomass circulates in the dryer which improves the removal of 90 moisture from biomass by the hot flue gases. This drying method, thus, strictly relies on hot flue gases to fluidize and dry biomass without the use of additional mechanical power. The fluidized bed dryer can be incorporated in thermal conversion processes of biomass that produce waste heat sources which can be exploited for drying moist biomass. The efficiency of the thermal conversion process of biomass is increased by the removal of water and recycling of waste heat sources.
SUMMARY OF THE INVENTION
In the present specification, including the claims, the terms dry biomass' and wet biomass' signify biomass of approximately 30% and 60% moisture content on a wet basis, respectively. The terms `cold flue gas' and `hot flue gas' signify flue gas at a temperature of approximately 120 C and 100 300 C respectively.
The following method of producing high quality biomass for combustion is disclosed.
Specifically, the invention utilizes existing plant waste heat sources, such as hot flue gases, to dry moist biomass to improve their thermal content or processibility. Biomass varies in moisture content and is derived from a variety of sources. Depending on the climate that biomass is extracted from, 105 biomass may contain a high level of moisture. This requires moist biomass to be processed, through pelletizing, briquetting or shredding, to form small and somewhat uniform biomass fragments, which improves handling. These processes not only make biomass more manageable, but also lower the moisture content and increase the thermal content of biomass fuel.
However, these processing methods, while increasing the efficiency of the combustion process, require energy input which 110 lowers the profitability of the process. Disclosed in this patent is a novel dryer and drying process which utilizes recycled waste heat sources from the combustion process, which not only efficiently dries biomass to increase its thermal content but also renders the multi-step process more profitable.
The present invention includes a method for improving the process in drying woody biomass fuel and increasing the efficiency of combustion of said biomass, for power generation, using a 115 multi-step system comprising of.
(a) A fluidized bed dryer to lower the moisture content of moist biomass;
(b) A storage tank used to keep fuel dry until needed for combustion in a fluidized bed boiler;
(c) A control element at the outlet of the storage tank to regulate amount of dried fuel 120 fed into fluidized bed boiler; and (d) A circulating fluidized bed combustion boiler, containing dry solids such as sand or limestone, which circulate with the dried fuel for combustion of said fuel.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1: Overall process diagram.
125 Figure 2: Direction of flow in the circulating fluidized bed combustion boiler.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
The present invention relates to a method and apparatus for drying moist woody biomass, 130 used as a fuel for firing a circulating fluidized-bed combustion (CFBC) boiler.
Embodiments of the claimed process are hereafter described with general reference to Figure 1 and Figure 2.
Turning to figure 1, moist biomass is fed into the bottom portion of the fluidized bed dryer via fuel inlet 20. The fluidized bed dryer 10 has a conical bottom and a roof that is at a 45 angle 135 directed to the storage tank 30. The angled roof facilitates transporting biomass from the fluidized bed dryer 10 to the storage tank 30. Hot flue gas from the CFBC boiler 40 is fed via the flue gas connection pipe 50, either through the conical bottom of the fluidized bed dryer 10 passing through the distributor plate 70, or through a separate pipe 60 extended from the flue gas connection pipe that protrudes through the dryer distributor plate 70. Flow of flue gas is redirected and controlled 140 through either pipe by a controlling valve 80. This setup controls whether the biomass is fluidized in the fluidized bed dryer 10, when the flue gas enters through the flue gas connection pipe 50 which protrudes through the distributor plate 70. Biomass, thus, recirculates in the fluidized bed dryer 10 and is dried through heat transfer between hot flue gases and biomass. The flow of flue gases in fluidized bed dryer 10 is shown in Figure 2. The flue gases provide the required heat to remove the 145 excess moisture from moist biomass, which remains fluidized in the fluidized bed dryer 10 until the moisture content of the biomass reaches approximately 30%. When desired moisture content is attained, the flue gas is redirected by the controlling valve 80 to pass through the conical bottom of the fluidized bed dryer 10 through the dryer distributor plate 70 and the biomass is transported to the storage tank 90 via the top of the fluidized bed dryer 10. This will provide sufficient velocity to 150 transport the biomass via the top of the fluidized bed dryer 10 to the storage tank 30. The flue gas remains directed through the dryer distributor plate 70 until all fluidized dried biomass particles have been transported to the storage tank 30. Particles are transferred to the storage tank 30 via the dryer-storage transfer pipe 90.
Dry fluidized biomass is transferred from the fluidized bed dryer 10 to a cylindrical steel 155 storage tank 30. The storage tank 30 has a conical bottom and a roof. The biomass is transferred to the top of the storage tank 30 from the fluidized bed dryer 10 via dryer-storage transfer pipe 90. The dried biomass is stored in the storage tank 30 which is fixed with a control element 100 which regulates the feed rate into the CFBC boiler 40. Flue gases, cooled from 300 C
to approximately 120 C, exit via exhaust pipe 110 located on the roof of the storage tank 30.
The dried biomass settles 160 to the bottom of the storage tank 30 and accumulates. The bottom of the storage tank 30 is conical so that the accumulated biomass can fall due to gravity directly into the storage-CFBC boiler screw feeder 120. As dried biomass continues to accumulate at the bottom of the storage tank 30, it forms aggregates. The aggregation of biomass at the bottom of the storage tank 30 makes it difficult to extract the biomass fuel to be transported to the CFBC boiler 40. Biomass is transferred, as needed 165 by the CFBC boiler 40, using the storage-CFBC boiler screw feeder which has a sharp blade. As rotation of the storage-CFBC boiler connection screw 120 occurs, biomass aggregates are sheared and then moved through the storage-CFBC boiler screw feeder 120 to the CFBC
boiler 40. This ensures controllable feed into the CFBC boiler 40 via the CFBC boiler inlet 130.
Dried fuel from storage tank 40 is fed to the CFBC boiler 50 via the CFBC
boiler inlet 140, 170 connected to the storage tank 40 by the storage-CFBC connection screw 130.
Through combustion of the fuel, flue gases are produced and expelled though the gas outlet pipe 140 at the top of the cyclone. The flue gases heat steam through a heat exchanger 150. The waste flue gases are then fed to the fluidized bed dryer 10 via the flue gas connection pipe 50.
REFERENCES
175 Alauddin, Z., P. Lahijani, M. Mohammadi. 2010. Gasification of lignocellulosi biomass in fluidized beds for renewable energy development: A review. Renewable & Sustainable energy review. 14:2852-2862.
Bridgwater, A. V. 1994. Catalysis in thermal biomass conversion. Applied Catalysis A: General 180 116.-5-47.
Gomez-Barea, A., B. Leckner. 2010. Modeling of biomass gasification in fluidized bed. Progress in Energy and Combustion Science, 36 (4): 444-509.
185 Hatfield, J. 2008. Effect of moisture content in biomass material. Crown Royal Corp. Fluid Journal. ]-11.
Loo, S., J. Koppejan. 2008. Biomass Combustion and Co-firing. ISBN 978-1-84407-249-1.
190 Lundgren, J., E. Pettersson. 2009. Combustion of horse manure for heat production Bioresource Technology, 12:3121-3126.
McKendry, P. 2002. Energy production from biomass (part 1): Overview of biomass. Bioresource Technology 83: 37-46.
195 McKendry, P. 2002. Energy production from biomass (part 2): conversion technologies.
Bioresource Technology 83: 47-54.
Pimentel, D., et al. 1981. Biomass Energy from Crop and Forest Residues.
Science, 221:110.
200 Stringer, J., A. J. Minchener. 1996. High temperature corrosion in fluidized bed combustion systems. J. Materials for energy systems, 7:333-334.
In the present specification, including the claims, the terms dry biomass' and wet biomass' signify biomass of approximately 30% and 60% moisture content on a wet basis, respectively. The terms `cold flue gas' and `hot flue gas' signify flue gas at a temperature of approximately 120 C and 100 300 C respectively.
The following method of producing high quality biomass for combustion is disclosed.
Specifically, the invention utilizes existing plant waste heat sources, such as hot flue gases, to dry moist biomass to improve their thermal content or processibility. Biomass varies in moisture content and is derived from a variety of sources. Depending on the climate that biomass is extracted from, 105 biomass may contain a high level of moisture. This requires moist biomass to be processed, through pelletizing, briquetting or shredding, to form small and somewhat uniform biomass fragments, which improves handling. These processes not only make biomass more manageable, but also lower the moisture content and increase the thermal content of biomass fuel.
However, these processing methods, while increasing the efficiency of the combustion process, require energy input which 110 lowers the profitability of the process. Disclosed in this patent is a novel dryer and drying process which utilizes recycled waste heat sources from the combustion process, which not only efficiently dries biomass to increase its thermal content but also renders the multi-step process more profitable.
The present invention includes a method for improving the process in drying woody biomass fuel and increasing the efficiency of combustion of said biomass, for power generation, using a 115 multi-step system comprising of.
(a) A fluidized bed dryer to lower the moisture content of moist biomass;
(b) A storage tank used to keep fuel dry until needed for combustion in a fluidized bed boiler;
(c) A control element at the outlet of the storage tank to regulate amount of dried fuel 120 fed into fluidized bed boiler; and (d) A circulating fluidized bed combustion boiler, containing dry solids such as sand or limestone, which circulate with the dried fuel for combustion of said fuel.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1: Overall process diagram.
125 Figure 2: Direction of flow in the circulating fluidized bed combustion boiler.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
The present invention relates to a method and apparatus for drying moist woody biomass, 130 used as a fuel for firing a circulating fluidized-bed combustion (CFBC) boiler.
Embodiments of the claimed process are hereafter described with general reference to Figure 1 and Figure 2.
Turning to figure 1, moist biomass is fed into the bottom portion of the fluidized bed dryer via fuel inlet 20. The fluidized bed dryer 10 has a conical bottom and a roof that is at a 45 angle 135 directed to the storage tank 30. The angled roof facilitates transporting biomass from the fluidized bed dryer 10 to the storage tank 30. Hot flue gas from the CFBC boiler 40 is fed via the flue gas connection pipe 50, either through the conical bottom of the fluidized bed dryer 10 passing through the distributor plate 70, or through a separate pipe 60 extended from the flue gas connection pipe that protrudes through the dryer distributor plate 70. Flow of flue gas is redirected and controlled 140 through either pipe by a controlling valve 80. This setup controls whether the biomass is fluidized in the fluidized bed dryer 10, when the flue gas enters through the flue gas connection pipe 50 which protrudes through the distributor plate 70. Biomass, thus, recirculates in the fluidized bed dryer 10 and is dried through heat transfer between hot flue gases and biomass. The flow of flue gases in fluidized bed dryer 10 is shown in Figure 2. The flue gases provide the required heat to remove the 145 excess moisture from moist biomass, which remains fluidized in the fluidized bed dryer 10 until the moisture content of the biomass reaches approximately 30%. When desired moisture content is attained, the flue gas is redirected by the controlling valve 80 to pass through the conical bottom of the fluidized bed dryer 10 through the dryer distributor plate 70 and the biomass is transported to the storage tank 90 via the top of the fluidized bed dryer 10. This will provide sufficient velocity to 150 transport the biomass via the top of the fluidized bed dryer 10 to the storage tank 30. The flue gas remains directed through the dryer distributor plate 70 until all fluidized dried biomass particles have been transported to the storage tank 30. Particles are transferred to the storage tank 30 via the dryer-storage transfer pipe 90.
Dry fluidized biomass is transferred from the fluidized bed dryer 10 to a cylindrical steel 155 storage tank 30. The storage tank 30 has a conical bottom and a roof. The biomass is transferred to the top of the storage tank 30 from the fluidized bed dryer 10 via dryer-storage transfer pipe 90. The dried biomass is stored in the storage tank 30 which is fixed with a control element 100 which regulates the feed rate into the CFBC boiler 40. Flue gases, cooled from 300 C
to approximately 120 C, exit via exhaust pipe 110 located on the roof of the storage tank 30.
The dried biomass settles 160 to the bottom of the storage tank 30 and accumulates. The bottom of the storage tank 30 is conical so that the accumulated biomass can fall due to gravity directly into the storage-CFBC boiler screw feeder 120. As dried biomass continues to accumulate at the bottom of the storage tank 30, it forms aggregates. The aggregation of biomass at the bottom of the storage tank 30 makes it difficult to extract the biomass fuel to be transported to the CFBC boiler 40. Biomass is transferred, as needed 165 by the CFBC boiler 40, using the storage-CFBC boiler screw feeder which has a sharp blade. As rotation of the storage-CFBC boiler connection screw 120 occurs, biomass aggregates are sheared and then moved through the storage-CFBC boiler screw feeder 120 to the CFBC
boiler 40. This ensures controllable feed into the CFBC boiler 40 via the CFBC boiler inlet 130.
Dried fuel from storage tank 40 is fed to the CFBC boiler 50 via the CFBC
boiler inlet 140, 170 connected to the storage tank 40 by the storage-CFBC connection screw 130.
Through combustion of the fuel, flue gases are produced and expelled though the gas outlet pipe 140 at the top of the cyclone. The flue gases heat steam through a heat exchanger 150. The waste flue gases are then fed to the fluidized bed dryer 10 via the flue gas connection pipe 50.
REFERENCES
175 Alauddin, Z., P. Lahijani, M. Mohammadi. 2010. Gasification of lignocellulosi biomass in fluidized beds for renewable energy development: A review. Renewable & Sustainable energy review. 14:2852-2862.
Bridgwater, A. V. 1994. Catalysis in thermal biomass conversion. Applied Catalysis A: General 180 116.-5-47.
Gomez-Barea, A., B. Leckner. 2010. Modeling of biomass gasification in fluidized bed. Progress in Energy and Combustion Science, 36 (4): 444-509.
185 Hatfield, J. 2008. Effect of moisture content in biomass material. Crown Royal Corp. Fluid Journal. ]-11.
Loo, S., J. Koppejan. 2008. Biomass Combustion and Co-firing. ISBN 978-1-84407-249-1.
190 Lundgren, J., E. Pettersson. 2009. Combustion of horse manure for heat production Bioresource Technology, 12:3121-3126.
McKendry, P. 2002. Energy production from biomass (part 1): Overview of biomass. Bioresource Technology 83: 37-46.
195 McKendry, P. 2002. Energy production from biomass (part 2): conversion technologies.
Bioresource Technology 83: 47-54.
Pimentel, D., et al. 1981. Biomass Energy from Crop and Forest Residues.
Science, 221:110.
200 Stringer, J., A. J. Minchener. 1996. High temperature corrosion in fluidized bed combustion systems. J. Materials for energy systems, 7:333-334.
Claims (17)
1. A method for improving the process in drying woody biomass fuel and increasing the efficiency of combustion of said biomass, using a multi-step system comprising of.
(a) A fluidized bed dryer to lower the moisture content of moist biomass;
(b) A storage tank used to keep fuel dry until needed for combustion in a fluidized bed boiler;
(c) A control element at the outlet of the storage tank to regulate amount of dried fuel fed into fluidized bed boiler; and (d) A circulating fluidized bed combustion boiler, containing dry solids such as sand or limestone, which circulate with the dried fuel for combustion of said fuel.
(a) A fluidized bed dryer to lower the moisture content of moist biomass;
(b) A storage tank used to keep fuel dry until needed for combustion in a fluidized bed boiler;
(c) A control element at the outlet of the storage tank to regulate amount of dried fuel fed into fluidized bed boiler; and (d) A circulating fluidized bed combustion boiler, containing dry solids such as sand or limestone, which circulate with the dried fuel for combustion of said fuel.
2. A method as defined in claim 1, wherein wet woody biomass is dried to approximately 30%
moisture content on a wet basis in a fluidized bed dryer using waste heat sources, specifically, flue gases, from the combustion of dried biomass in the circulating fluidized bed combustion boiler.
moisture content on a wet basis in a fluidized bed dryer using waste heat sources, specifically, flue gases, from the combustion of dried biomass in the circulating fluidized bed combustion boiler.
3. A method as defined in claim 1, wherein the storage tank is a cylindrical vessel with a roof and a conical bottom and contains the dried biomass transported from the fluidized bed dryer via the flue gases.
4. A method as defined in claim 1, wherein dried biomass containing approximately 30%
moisture on a wet basis is transported to the circulating fluidized bed combustion boiler from the outlet at the conical bottom of the storage tank.
moisture on a wet basis is transported to the circulating fluidized bed combustion boiler from the outlet at the conical bottom of the storage tank.
5. A method as defined in claim 1, wherein combustion of dried biomass containing approximately 30% moisture on a wet basis is combusted in a circulating fluidized bed combustion boiler.
6. A method as defined in claim 2, wherein waste heat from hot flue gases recycled from the circulating fluidized bed combustion boiler are approximately 300°C and transported to the fluidized bed dryer where they exit at as cold flue gases at a temperature of approximately 120°C.
7. A method as defined in claim 2, wherein the fluidized bed dryer contains a distributor plate at the inlet at the bottom of the fluidized bed dryer.
8. A method as defined in claim 7, wherein flue gases are fed through a pipe at the center of the dryer, at the beginning of the drying process, to allow the wet biomass to recirculate in the fluidized bed dryer providing a sufficient residence time for drying.
9. A method as defined in claim 7, wherein flue gases are distributed throughout the dryer through the distributor plate, at the end of the drying process, to transport the biomass to the storage tank from the outlet at the top of the fluidized bed dryer.
10. A method as defined in claim 2, wherein the hot flue gases contain less than 5% of oxygen.
11. A method as defined in claim 2, wherein flue gas dries the biomass to approximately 30%
moisture on a wet basis.
moisture on a wet basis.
12. A method as defined in claim 2, wherein the dry woody biomass is fluidized by the flue gas and transported to the storage tank.
13. A method as defined in claim 2, wherein the fluidized bed dryer contains a port for flue gas injection.
14. A method as defined in claim 13, wherein the port for the flue gas injection is regulated by a control element by measuring the concentration of oxygen in the hot flue gases in the fluidized bed combustion boiler and regulating accordingly.
15. A method as defined in claim 4, wherein the outlet of the storage tank, found at the conical bottom, is fixed with a control element to regulate the flow of feed at a steady state into the circulating fluidized bed combustion boiler.
16. A method as defined in claim 15, wherein the control element is composed of a screw feeder connecting the storage tank to the circulating fluidized bed combustion boiler.
17. A method as defined in claim 9, wherein the flue gases carrying the dried biomass to the storage tank exit through the top of the storage tank to the stack, while the dried biomass settle to the bottom of the storage tank.
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| Application Number | Priority Date | Filing Date | Title |
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| CA 2727638 CA2727638A1 (en) | 2011-01-05 | 2011-01-05 | Optimization of combustion process |
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| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA 2727638 CA2727638A1 (en) | 2011-01-05 | 2011-01-05 | Optimization of combustion process |
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Cited By (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN103557523A (en) * | 2013-11-21 | 2014-02-05 | 国家电网公司 | Adjustment method for first full charge of circulating fluidized bed boiler burning high-calorific-value bituminous coal |
| WO2014128357A1 (en) * | 2013-02-22 | 2014-08-28 | Endev Oy | Method and apparatus for combustion of sludge |
| CN106152121A (en) * | 2016-08-12 | 2016-11-23 | 淄博弘科电力设备有限公司 | CFBB fly ash reinjection energy-saving equipment |
| CN107189823A (en) * | 2017-07-31 | 2017-09-22 | 陕西延长石油（集团）有限责任公司 | A kind of online sanding device of high circulation multiplying power fluidized-bed gasification furnace and sand adding method |
-
2011
- 2011-01-05 CA CA 2727638 patent/CA2727638A1/en not_active Abandoned
Cited By (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2014128357A1 (en) * | 2013-02-22 | 2014-08-28 | Endev Oy | Method and apparatus for combustion of sludge |
| CN103557523A (en) * | 2013-11-21 | 2014-02-05 | 国家电网公司 | Adjustment method for first full charge of circulating fluidized bed boiler burning high-calorific-value bituminous coal |
| CN103557523B (en) * | 2013-11-21 | 2015-10-28 | 国家电网公司 | Use high heating value bituminous coal CFBB and be with method of adjustment at full capacity first |
| CN106152121A (en) * | 2016-08-12 | 2016-11-23 | 淄博弘科电力设备有限公司 | CFBB fly ash reinjection energy-saving equipment |
| CN107189823A (en) * | 2017-07-31 | 2017-09-22 | 陕西延长石油（集团）有限责任公司 | A kind of online sanding device of high circulation multiplying power fluidized-bed gasification furnace and sand adding method |
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