US20080223267A1 - Direct sorbent preparation/feed apparatus and method for circulating fluidized bed boiler systems - Google Patents
Direct sorbent preparation/feed apparatus and method for circulating fluidized bed boiler systems Download PDFInfo
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- US20080223267A1 US20080223267A1 US11/685,447 US68544707A US2008223267A1 US 20080223267 A1 US20080223267 A1 US 20080223267A1 US 68544707 A US68544707 A US 68544707A US 2008223267 A1 US2008223267 A1 US 2008223267A1
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- 238000000034 method Methods 0.000 title claims description 18
- 238000002360 preparation method Methods 0.000 title description 14
- 239000002245 particle Substances 0.000 claims abstract description 24
- 238000002485 combustion reaction Methods 0.000 claims abstract description 23
- 238000003860 storage Methods 0.000 claims abstract description 10
- 230000003750 conditioning effect Effects 0.000 claims abstract description 8
- 235000019738 Limestone Nutrition 0.000 claims description 53
- 239000006028 limestone Substances 0.000 claims description 53
- 239000000463 material Substances 0.000 claims description 9
- 239000003570 air Substances 0.000 description 89
- NINIDFKCEFEMDL-UHFFFAOYSA-N Sulfur Chemical compound [S] NINIDFKCEFEMDL-UHFFFAOYSA-N 0.000 description 9
- 229910052717 sulfur Inorganic materials 0.000 description 9
- 239000011593 sulfur Substances 0.000 description 9
- 238000005496 tempering Methods 0.000 description 9
- UGFAIRIUMAVXCW-UHFFFAOYSA-N Carbon monoxide Chemical compound [O+]#[C-] UGFAIRIUMAVXCW-UHFFFAOYSA-N 0.000 description 7
- 238000001035 drying Methods 0.000 description 7
- 239000003546 flue gas Substances 0.000 description 7
- 238000011084 recovery Methods 0.000 description 7
- 238000010586 diagram Methods 0.000 description 6
- 239000003245 coal Substances 0.000 description 5
- 230000001143 conditioned effect Effects 0.000 description 5
- 238000006477 desulfuration reaction Methods 0.000 description 4
- 230000023556 desulfurization Effects 0.000 description 4
- 238000009826 distribution Methods 0.000 description 4
- 239000000446 fuel Substances 0.000 description 4
- 230000008569 process Effects 0.000 description 4
- 230000009467 reduction Effects 0.000 description 4
- 238000005549 size reduction Methods 0.000 description 3
- VTYYLEPIZMXCLO-UHFFFAOYSA-L Calcium carbonate Chemical compound [Ca+2].[O-]C([O-])=O VTYYLEPIZMXCLO-UHFFFAOYSA-L 0.000 description 2
- 230000005587 bubbling Effects 0.000 description 2
- 238000006243 chemical reaction Methods 0.000 description 2
- 239000007789 gas Substances 0.000 description 2
- 230000007774 longterm Effects 0.000 description 2
- 238000000926 separation method Methods 0.000 description 2
- 239000004449 solid propellant Substances 0.000 description 2
- 239000002028 Biomass Substances 0.000 description 1
- 230000009471 action Effects 0.000 description 1
- 239000012080 ambient air Substances 0.000 description 1
- 230000008901 benefit Effects 0.000 description 1
- 238000007664 blowing Methods 0.000 description 1
- 229910000019 calcium carbonate Inorganic materials 0.000 description 1
- 239000000428 dust Substances 0.000 description 1
- 230000008030 elimination Effects 0.000 description 1
- 238000003379 elimination reaction Methods 0.000 description 1
- 238000005516 engineering process Methods 0.000 description 1
- 239000003344 environmental pollutant Substances 0.000 description 1
- 239000010419 fine particle Substances 0.000 description 1
- 239000012530 fluid Substances 0.000 description 1
- 238000005243 fluidization Methods 0.000 description 1
- 238000009434 installation Methods 0.000 description 1
- 238000004519 manufacturing process Methods 0.000 description 1
- 238000002156 mixing Methods 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
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- 231100000719 pollutant Toxicity 0.000 description 1
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- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 1
Images
Classifications
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
- F23J—REMOVAL OR TREATMENT OF COMBUSTION PRODUCTS OR COMBUSTION RESIDUES; FLUES
- F23J7/00—Arrangement of devices for supplying chemicals to fire
Definitions
- the present disclosure relates generally to circulating fluidized bed (CFB) combustion systems and, more particularly, to an improved direct sorbent preparation/feed apparatus and method for a CFB boiler system.
- CFB circulating fluidized bed
- Fluidized bed combustion is a combustion technology used in power plants primarily to burn solid fuels. FBC plants are more flexible than conventional plants in that they can be fired on coal, coal waste or biomass, among other fuels.
- the term FBC covers a range of fluidized bed processes which include Circulating Fluidized Bed (CFB) boilers, Bubbling Fluidized Bed (BFB) boilers and other variants. Fluidized beds suspend solid fuels on upward-blowing jets of air during the combustion process, resulting in a turbulent mixing of gas and solids. The tumbling action, much like a bubbling fluid, provides a means for more effective chemical reactions and heat transfer.
- FBC reduces the amount of sulfur emitted in the form of SO 2 by a desulfurization process.
- a suitable sorbent such as limestone containing CaCO 3 , for example, is used to absorb SO 2 from the flue gas during combustion.
- FBC combustion operates at temperatures lower than conventional combustion systems. FBC systems operate in a range typically between about 780° C. and about 1000° C. Since this allows coal to combust at cooler temperatures, NO x production during combustion is lower than other coal combustion processes. Fluidized-bed boilers evolved from efforts to find a combustion process able to control pollutant emissions without external emission controls (such as scrubbers).
- CFB boiler systems are generally associated with limestone feed systems for sulfur capture.
- Processed limestone fed to a boiler is typically conditioned by means of size reduction machines to specific size ranges to allow for the desulfurization process to proceed efficiently. If the particles are too large, the desulfurization process will not be efficient because there is insufficient limestone particle surface area to react with the flue gas. On the other hand, if the particles are too small, the limestone will be carried out of the desulfurization zone with the flue gas before it can react to remove the sulfur.
- limestone is fed to the boiler with a median particle diameter in the range of (as an example, but not limited to) about 100 to about 400 microns.
- raw limestone is reduced in both size and moisture content by size reducing machines.
- machines available for crushing limestone including for example, hammer mills, roll crushers and roller mills. Regardless of the type of equipment used for limestone crushing, the particles are dried either before or during crushing in order to produce a freely flowing material.
- CFB boilers may be equipped with an integrated limestone preparation and feed system that resides in the boiler building. Such a system that dries and prepares limestone as needed is also referred to a Just-In-Time (JIT) limestone system.
- JIT Just-In-Time
- Roller mill systems utilize hot air (mill air) for drying of limestone and transportation to the CFB.
- Mill air is typically obtained from the primary air stream as the mills utilize air at elevated pressures.
- hot primary air in the range of about 400° F. to about 600° F. is typically available.
- the hot air is used to dry the entering limestone, sweep the limestone out of the mill, and convey it to the boiler.
- the operating temperatures thereof are kept relatively low, for example in the range of about 170° F. to about 200° F.
- limestone generally contains low quantities of moisture (e.g., less than 5%).
- the air temperature entering the roller mills is a function of the acceptable mill mechanical operating temperature, the limestone moisture content, and the ratio of air to limestone.
- air temperatures entering the mill will generally be less than about 250° F. Therefore, given the available primary air temperature in the range of about 500° F., the mill air obtained from the primary air stream is therefore tempered in order to produce a mill exit air temperature, typically in the range of about 180° F. to 225° F.
- a sorbent conditioning and feed apparatus for a circulating fluidized bed combustion system includes a dryer apparatus configured to dry unprocessed sorbent material transported thereto from a raw storage container; a sorbent crushing device configured to reduce the particle size of dried sorbent material discharged from the dryer apparatus; and a circulating fluidized bed (CFB) boiler configured to receive processed sorbent material conveyed from the sorbent crushing device; wherein the dryer apparatus utilizes an untempered hot air source diverted directly from a primary air stream input to the circulating fluidized bed boiler.
- CFB circulating fluidized bed
- a direct limestone conditioning and feed apparatus for a circulating fluidized bed combustion system includes a dryer apparatus configured to dry unprocessed limestone material transported thereto from a raw storage container; a roll crushing device configured to reduce the particle size of dried limestone material discharged from the dryer apparatus; and a circulating fluidized bed (CFB) boiler configured to receive processed limestone material conveyed from the roll crushing device; wherein the dryer apparatus utilizes an untempered hot air source diverted directly from a primary air stream input to the circulating fluidized bed boiler.
- CFB circulating fluidized bed
- a method of conditioning and feeding sorbent material for a circulating fluidized bed combustion system includes transporting raw, unprocessed sorbent material from a raw storage container to a dryer apparatus; diverting untempered hot air directly from a primary air stream input to the circulating fluidized bed boiler, the untempered hot air used to dry the raw sorbent material; directing dried raw sorbent material from the dryer apparatus to a crushing device configured to reduce the particle size of the dried raw sorbent material discharged from the dryer apparatus; and conveying processed sorbent material from the crushing device to the CFB boiler.
- FIG. 1 is a schematic block diagram of an existing sorbent preparation/feed apparatus, including a roller mill which utilizes tempered air to dry and separate sorbent material;
- FIG. 2 is a schematic block diagram of an improved direct sorbent preparation/feed apparatus and method for a CFB boiler system, utilizing untempered air for sorbent drying, in accordance with an embodiment of the invention.
- FIG. 3 is a schematic diagram of a CFB boiler system incorporating an improved direct sorbent preparation/feed apparatus, utilizing untempered air for sorbent drying, in accordance with a further embodiment of the invention.
- a sorbent preparation/feed apparatus utilizes an alternate crushing device (i.e., one that does not need the use of tempered air) with a separate, high temperature dryer apparatus in order to supply dry, sized limestone on a just-in-time basis to a CFB boiler without reducing boiler efficiency.
- an alternate crushing device i.e., one that does not need the use of tempered air
- a separate, high temperature dryer apparatus in order to supply dry, sized limestone on a just-in-time basis to a CFB boiler without reducing boiler efficiency.
- CFB boilers equipped with roller mill JIT limestone systems employ tempering air in order to control the entering air temperature, which results in reduced heat recovery from the flue gas.
- the reduced heat recovery in turn lowers boiler efficiency (e.g., on the order of about 1%) and thus increases equipment size and operating costs.
- a JIT system incorporating one or more roll crushers and utilizing a separate limestone drying apparatus eliminates the use of tempering air, thus allowing for maximum heat recovery from a boiler air heater.
- Primary Air in the context of FBC boilers, refers to combustion air delivered to the bed fluidization grate at the bottom of the furnace. Primary air is generated at relatively high pressures. In addition, some primary air may be diverted to other equipment, as well as enter the furnace at locations other than the grate. Furthermore, in the context of FBC boilers, “Secondary Air” (SA) refers to combustion air delivered through openings in the furnace walls. Secondary air is generated at pressures lower than primary air, and is used to fluidize the bed and stage combustion for emission control. “Tempered Air” refers to hot air that is cooled (i.e., tempered) with relatively cold air, such as ambient air for example.
- Untempered hot air refers to hot air leaving an air heater of the FBC system. Both primary air and secondary air leaving the air heater are considered untempered hot air streams.
- Unprocessed Sorbent refers to raw sorbent delivered to the FBC boiler conditioning (size reduction & drying) system. Unprocessed sorbent has not been conditioned to the proper size and moisture content required for feeding to the FBC boiler.
- FIG. 1 there is shown a schematic block diagram of an existing sorbent preparation/feed apparatus 100 .
- the apparatus 100 utilizes a roller mill 102 to both dry and separate the raw sorbent material.
- hot primary air (PA) exiting the boiler system air heater 104 is mixed with tempering air (e.g., from cold primary air entering the air heater 104 ) so as to produce tempered primary air for input to the roller mill 102 .
- tempering air e.g., from cold primary air entering the air heater 104
- dampers 106 may be utilized in the hot primary air path and the tempering air path in order to produce the tempered air of a desired temperature and pressure.
- FIG. 1 For purposes of illustration, FIG.
- FIG. 1 further illustrates additional inputs and outputs of the air heater 104 , including cold input secondary air (SA), hot secondary air output to a CFB boiler (not shown), hot gas input to the heater 104 from a boiler backpass heat exchanger 108 , and exiting warm flue gas.
- SA cold input secondary air
- CFB boiler CFB boiler
- One reason for requiring tempered air in a conventional roller mill preparation/feed apparatus 100 relates to the temperature limits of the crushing device (roller mill) itself.
- the velocity of the air conveying the conditioned limestone from the roller mill to the CFB boiler is controlled. If, for example, the velocity of the conveying air is too low, sorbent particles may settle out in the pipe, leading to blockage.
- FIG. 2 is a schematic block diagram of an improved direct sorbent preparation/feed apparatus 200 for a CFB boiler system, utilizing untempered air for sorbent drying, in accordance with an embodiment of the invention.
- the apparatus 200 utilizes a sorbent dryer 202 and separate roll crusher device 204 .
- the wet, raw sorbent is received into the sorbent dryer 202 , wherein hot, untempered primary air (e.g., on the order of 400° F. or higher is directly input to the dryer 202 to dry the wet, raw sorbent.
- hot, untempered primary air e.g., on the order of 400° F. or higher is directly input to the dryer 202 to dry the wet, raw sorbent.
- the sorbent dryer 202 is configured to discharge warm air, which carries sorbent fines (fine particles) directly to the boiler, thus bypassing the roll crusher device 204 .
- the sorbent dryer 202 has a particle separation capability.
- the remaining dry, raw sorbent that is not already of a fine particulate size is input from the sorbent dryer 202 to the roll crusher 204 .
- the need to temper the air used to dry the particles is eliminated.
- the dry, raw sorbent particles are conditioned (i.e., reduced to the desired size), they are conveyed (e.g., pneumatically or mechanically) to the boiler (not shown in FIG. 2 ) in accordance with a direct (JIT) feed system.
- FIG. 3 is a schematic diagram of a CFB boiler system 300 incorporating an improved direct sorbent preparation/feed apparatus (such as apparatus 200 of FIG. 2 , for example), utilizing untempered air for sorbent drying, in accordance with a further embodiment of the invention.
- the system 300 further includes a CFB boiler 302 , a raw sorbent (e.g., limestone) storage facility/container 304 and cyclone 306 .
- Raw, wet limestone is conveyed from the storage container 304 , is metered and conveyed to the dryer 202 .
- limestone metering may be controlled by sulfur reduction signals received from the associated boiler control system.
- hot, untempered air from the primary air system is directly used as the source of heat to dry the limestone, wherein only enough hot air is diverted from the primary air stream to the dryer 202 as may be needed to dry the limestone.
- the dryer 202 having the capability of operating at high temperatures, is therefore is not subject to tempering.
- the dryer 202 may include a particle separation capability so as to remove sorbent fines with exiting warm air to the boiler, thereby preventing an unnecessary feeding of sorbent fines into the roll crusher 204 .
- One exemplary type of dryer in this regard may be a fluidized bed dryer. However, other types of high-temperature dryers may also be used.
- warm air containing evaporated water and limestone dust (sorbent fines) is conveyed directly to the boiler 302 as part of the combustion air.
- limestone discharged from the dryer 202 is conveyed to one or more roll type crushers 204 arranged in series where it is crushed to a desired size and discharged.
- the dried, sized limestone is conveyed (e.g., pneumatically or mechanically) to the CFB boiler 302 .
- the system 300 may also include surge hoppers and metering systems downstream of the roll crusher 304 to enhance system operation and flexibility.
- the total amount of pressurized primary air in the system may be reduced. Because the elimination of tempering air reduces the amount of primary air needed to dry the sorbent, the total primary air is reduced and replaced by lower pressure secondary air.
- the above exemplary embodiments further improve particle size distribution of the conditioned limestone to the CFB boiler.
- limestone (sorbent) to the boiler requires a specific range of sizes for optimum sulfur capture. If the size distribution becomes coarser, the quantity of unused sorbent rises. Larger particles are not sufficiently broken down in the furnace before removal, thus resulting in a greater amount of unused sorbent. On the other hand, if the size distribution becomes too fine, the quantity of unused sorbent rises due to reduced residence time for the sulfur capture reactions.
- the disclosed embodiments reduce the amount of high pressure air (primary and tempering) in the CFB system. This reduction is obtained primarily by using higher temperature air to dry the sorbent. The reduction lowers total power consumption of the air fans, which in turn improves boiler economics. For example, the use of primary air at a maximum air heater outlet temperature maximizes energy recovery from the flue gas, thus increasing boiler efficiency with respect to a JIT system using tempering air. As the boiler efficiency is significantly increased, a long-term savings in plant operating costs is realized. By way of example, the boiler efficiency may be increased in the range of about 0.5% to about 1.5%.
Abstract
Description
- The present disclosure relates generally to circulating fluidized bed (CFB) combustion systems and, more particularly, to an improved direct sorbent preparation/feed apparatus and method for a CFB boiler system.
- Fluidized bed combustion (FBC) is a combustion technology used in power plants primarily to burn solid fuels. FBC plants are more flexible than conventional plants in that they can be fired on coal, coal waste or biomass, among other fuels. The term FBC covers a range of fluidized bed processes which include Circulating Fluidized Bed (CFB) boilers, Bubbling Fluidized Bed (BFB) boilers and other variants. Fluidized beds suspend solid fuels on upward-blowing jets of air during the combustion process, resulting in a turbulent mixing of gas and solids. The tumbling action, much like a bubbling fluid, provides a means for more effective chemical reactions and heat transfer.
- During the combustion of fuels that have a sulfur containing constitutent, coal for example, sulfur is oxidized to form primarily gasous SO2. In particular, FBC reduces the amount of sulfur emitted in the form of SO2 by a desulfurization process. A suitable sorbent, such as limestone containing CaCO3, for example, is used to absorb SO2 from the flue gas during combustion. In order to promote both combustion of the fuel and the capture of sulfur, FBC combustion operates at temperatures lower than conventional combustion systems. FBC systems operate in a range typically between about 780° C. and about 1000° C. Since this allows coal to combust at cooler temperatures, NOx production during combustion is lower than other coal combustion processes. Fluidized-bed boilers evolved from efforts to find a combustion process able to control pollutant emissions without external emission controls (such as scrubbers).
- CFB boiler systems are generally associated with limestone feed systems for sulfur capture. Processed limestone fed to a boiler is typically conditioned by means of size reduction machines to specific size ranges to allow for the desulfurization process to proceed efficiently. If the particles are too large, the desulfurization process will not be efficient because there is insufficient limestone particle surface area to react with the flue gas. On the other hand, if the particles are too small, the limestone will be carried out of the desulfurization zone with the flue gas before it can react to remove the sulfur. Typically, limestone is fed to the boiler with a median particle diameter in the range of (as an example, but not limited to) about 100 to about 400 microns. In order to achieve this particle size range, unprocessed, raw limestone is reduced in both size and moisture content by size reducing machines. Presently, there are various machines available for crushing limestone, including for example, hammer mills, roll crushers and roller mills. Regardless of the type of equipment used for limestone crushing, the particles are dried either before or during crushing in order to produce a freely flowing material.
- Traditionally, limestone is prepared separately from the boiler system, either on-site or by the limestone supplier. Prepared limestone is conveyed to a storage system in the boiler house from which it is thereafter metered and injected into the boiler. Experience has shown that the cost of prepared limestone using separate on-site systems or supplied from off-site vendors is expensive. In the case of separate, on-site systems a separate building and auxiliary fuel is used to dry the limestone. On the other hand, a limestone preparation and feed system may also be integrated with the boiler system itself, resulting in a significant reduction in capital and operating costs. Specifically, CFB boilers may be equipped with an integrated limestone preparation and feed system that resides in the boiler building. Such a system that dries and prepares limestone as needed is also referred to a Just-In-Time (JIT) limestone system.
- Systems using roller mills have also been designed and installed on CFB boilers. Roller mill systems utilize hot air (mill air) for drying of limestone and transportation to the CFB. Mill air is typically obtained from the primary air stream as the mills utilize air at elevated pressures. For most CFB boilers, hot primary air in the range of about 400° F. to about 600° F. is typically available. The hot air is used to dry the entering limestone, sweep the limestone out of the mill, and convey it to the boiler. However, in order to protect the mechanical components of roller mills, the operating temperatures thereof are kept relatively low, for example in the range of about 170° F. to about 200° F.
- Furthermore, limestone generally contains low quantities of moisture (e.g., less than 5%). For proper system operation, the air temperature entering the roller mills is a function of the acceptable mill mechanical operating temperature, the limestone moisture content, and the ratio of air to limestone. For a JIT system as described above, air temperatures entering the mill will generally be less than about 250° F. Therefore, given the available primary air temperature in the range of about 500° F., the mill air obtained from the primary air stream is therefore tempered in order to produce a mill exit air temperature, typically in the range of about 180° F. to 225° F.
- Experience has shown that the use of tempering air effectively reduces heat recovery from the flue gas. In turn, the reduced heat recovery lowers boiler efficiency, as an example, in the range of about 0.5% to about 1.5%, thereby increasing equipment size and operating costs. Although the installation of a JIT limestone system using roller mills on a CFB boiler provides an initial benefit with respect to reduced capital cost for the CFB boiler, there is a tradeoff with respect to an increase in long term operating costs (e.g., as high as 15% to 30% compared to the cost of the CFB boiler). Accordingly, it would be desirable to be able to improve heat recovery and thus increase boiler efficiency for a CFB boiler equipped with a JIT limestone system.
- According to aspects illustrated herein, a sorbent conditioning and feed apparatus for a circulating fluidized bed combustion system includes a dryer apparatus configured to dry unprocessed sorbent material transported thereto from a raw storage container; a sorbent crushing device configured to reduce the particle size of dried sorbent material discharged from the dryer apparatus; and a circulating fluidized bed (CFB) boiler configured to receive processed sorbent material conveyed from the sorbent crushing device; wherein the dryer apparatus utilizes an untempered hot air source diverted directly from a primary air stream input to the circulating fluidized bed boiler.
- According to other aspects illustrated herein, a direct limestone conditioning and feed apparatus for a circulating fluidized bed combustion system includes a dryer apparatus configured to dry unprocessed limestone material transported thereto from a raw storage container; a roll crushing device configured to reduce the particle size of dried limestone material discharged from the dryer apparatus; and a circulating fluidized bed (CFB) boiler configured to receive processed limestone material conveyed from the roll crushing device; wherein the dryer apparatus utilizes an untempered hot air source diverted directly from a primary air stream input to the circulating fluidized bed boiler.
- According to other aspects illustrated herein, a method of conditioning and feeding sorbent material for a circulating fluidized bed combustion system includes transporting raw, unprocessed sorbent material from a raw storage container to a dryer apparatus; diverting untempered hot air directly from a primary air stream input to the circulating fluidized bed boiler, the untempered hot air used to dry the raw sorbent material; directing dried raw sorbent material from the dryer apparatus to a crushing device configured to reduce the particle size of the dried raw sorbent material discharged from the dryer apparatus; and conveying processed sorbent material from the crushing device to the CFB boiler.
- The above described and other features are exemplified by the following figures and detailed description.
- Referring now to the figures, which are exemplary embodiments, and wherein the like elements are numbered alike:
-
FIG. 1 is a schematic block diagram of an existing sorbent preparation/feed apparatus, including a roller mill which utilizes tempered air to dry and separate sorbent material; -
FIG. 2 is a schematic block diagram of an improved direct sorbent preparation/feed apparatus and method for a CFB boiler system, utilizing untempered air for sorbent drying, in accordance with an embodiment of the invention; and -
FIG. 3 is a schematic diagram of a CFB boiler system incorporating an improved direct sorbent preparation/feed apparatus, utilizing untempered air for sorbent drying, in accordance with a further embodiment of the invention. - Disclosed herein is an improved direct sorbent preparation/feed apparatus and method for a CFB system. Briefly stated, a sorbent preparation/feed apparatus utilizes an alternate crushing device (i.e., one that does not need the use of tempered air) with a separate, high temperature dryer apparatus in order to supply dry, sized limestone on a just-in-time basis to a CFB boiler without reducing boiler efficiency.
- As indicated above, CFB boilers equipped with roller mill JIT limestone systems employ tempering air in order to control the entering air temperature, which results in reduced heat recovery from the flue gas. The reduced heat recovery in turn lowers boiler efficiency (e.g., on the order of about 1%) and thus increases equipment size and operating costs. As will be illustrated from the embodiments discussed herein, a JIT system incorporating one or more roll crushers and utilizing a separate limestone drying apparatus eliminates the use of tempering air, thus allowing for maximum heat recovery from a boiler air heater.
- As used herein, “Primary Air” (PA), in the context of FBC boilers, refers to combustion air delivered to the bed fluidization grate at the bottom of the furnace. Primary air is generated at relatively high pressures. In addition, some primary air may be diverted to other equipment, as well as enter the furnace at locations other than the grate. Furthermore, in the context of FBC boilers, “Secondary Air” (SA) refers to combustion air delivered through openings in the furnace walls. Secondary air is generated at pressures lower than primary air, and is used to fluidize the bed and stage combustion for emission control. “Tempered Air” refers to hot air that is cooled (i.e., tempered) with relatively cold air, such as ambient air for example. “Untempered hot air” refers to hot air leaving an air heater of the FBC system. Both primary air and secondary air leaving the air heater are considered untempered hot air streams. “Unprocessed Sorbent” refers to raw sorbent delivered to the FBC boiler conditioning (size reduction & drying) system. Unprocessed sorbent has not been conditioned to the proper size and moisture content required for feeding to the FBC boiler.
- Referring initially to
FIG. 1 , there is shown a schematic block diagram of an existing sorbent preparation/feed apparatus 100. As is shown, theapparatus 100 utilizes aroller mill 102 to both dry and separate the raw sorbent material. In order to control the temperature of the air utilized by theroller mill 102, hot primary air (PA) exiting the boilersystem air heater 104 is mixed with tempering air (e.g., from cold primary air entering the air heater 104) so as to produce tempered primary air for input to theroller mill 102. As further illustrated inFIG. 1 ,dampers 106 may be utilized in the hot primary air path and the tempering air path in order to produce the tempered air of a desired temperature and pressure. For purposes of illustration,FIG. 1 further illustrates additional inputs and outputs of theair heater 104, including cold input secondary air (SA), hot secondary air output to a CFB boiler (not shown), hot gas input to theheater 104 from a boilerbackpass heat exchanger 108, and exiting warm flue gas. - One reason for requiring tempered air in a conventional roller mill preparation/
feed apparatus 100 relates to the temperature limits of the crushing device (roller mill) itself. In addition, the velocity of the air conveying the conditioned limestone from the roller mill to the CFB boiler is controlled. If, for example, the velocity of the conveying air is too low, sorbent particles may settle out in the pipe, leading to blockage. - Accordingly,
FIG. 2 is a schematic block diagram of an improved direct sorbent preparation/feed apparatus 200 for a CFB boiler system, utilizing untempered air for sorbent drying, in accordance with an embodiment of the invention. In lieu of a roller mill, theapparatus 200 utilizes asorbent dryer 202 and separateroll crusher device 204. The wet, raw sorbent is received into thesorbent dryer 202, wherein hot, untempered primary air (e.g., on the order of 400° F. or higher is directly input to thedryer 202 to dry the wet, raw sorbent. - In an exemplary embodiment, the
sorbent dryer 202 is configured to discharge warm air, which carries sorbent fines (fine particles) directly to the boiler, thus bypassing theroll crusher device 204. In this sense, thesorbent dryer 202 has a particle separation capability. The remaining dry, raw sorbent that is not already of a fine particulate size is input from thesorbent dryer 202 to theroll crusher 204. As such a device does not have the same temperature restrictions as a roller mill, the need to temper the air used to dry the particles is eliminated. Once the dry, raw sorbent particles are conditioned (i.e., reduced to the desired size), they are conveyed (e.g., pneumatically or mechanically) to the boiler (not shown inFIG. 2 ) in accordance with a direct (JIT) feed system. -
FIG. 3 is a schematic diagram of aCFB boiler system 300 incorporating an improved direct sorbent preparation/feed apparatus (such asapparatus 200 ofFIG. 2 , for example), utilizing untempered air for sorbent drying, in accordance with a further embodiment of the invention. As is shown, thesystem 300 further includes aCFB boiler 302, a raw sorbent (e.g., limestone) storage facility/container 304 andcyclone 306. Raw, wet limestone is conveyed from thestorage container 304, is metered and conveyed to thedryer 202. In an exemplary embodiment, limestone metering may be controlled by sulfur reduction signals received from the associated boiler control system. Again, hot, untempered air from the primary air system is directly used as the source of heat to dry the limestone, wherein only enough hot air is diverted from the primary air stream to thedryer 202 as may be needed to dry the limestone. Thedryer 202, having the capability of operating at high temperatures, is therefore is not subject to tempering. - As indicted above, the
dryer 202 may include a particle separation capability so as to remove sorbent fines with exiting warm air to the boiler, thereby preventing an unnecessary feeding of sorbent fines into theroll crusher 204. One exemplary type of dryer in this regard may be a fluidized bed dryer. However, other types of high-temperature dryers may also be used. In any event, warm air containing evaporated water and limestone dust (sorbent fines) is conveyed directly to theboiler 302 as part of the combustion air. On the other hand, limestone discharged from thedryer 202 is conveyed to one or moreroll type crushers 204 arranged in series where it is crushed to a desired size and discharged. Downstream of theroll crushers 204, the dried, sized limestone is conveyed (e.g., pneumatically or mechanically) to theCFB boiler 302. Although not specifically depicted inFIG. 3 , thesystem 300 may also include surge hoppers and metering systems downstream of theroll crusher 304 to enhance system operation and flexibility. - Through the use of the above described CFB boiler system and improved direct sorbent preparation/feed apparatus embodiments, the total amount of pressurized primary air in the system may be reduced. Because the elimination of tempering air reduces the amount of primary air needed to dry the sorbent, the total primary air is reduced and replaced by lower pressure secondary air.
- Moreover, the above exemplary embodiments further improve particle size distribution of the conditioned limestone to the CFB boiler. As discussed, limestone (sorbent) to the boiler requires a specific range of sizes for optimum sulfur capture. If the size distribution becomes coarser, the quantity of unused sorbent rises. Larger particles are not sufficiently broken down in the furnace before removal, thus resulting in a greater amount of unused sorbent. On the other hand, if the size distribution becomes too fine, the quantity of unused sorbent rises due to reduced residence time for the sulfur capture reactions.
- Accordingly, improved particle size distribution is achieved when small particles are removed (classified) prior to entering the roll crusher. If allowed to enter the crusher, many initially small particles are made even smaller, thus increasing the amount of unused sorbent. By using a separate sorbent dryer with direct contact of hot air (e.g., a counter flow flash dryer), entrainment of the smaller particles can be achieved thus avoiding additional size reduction in the crusher.
- Further, it will be appreciated that the disclosed embodiments reduce the amount of high pressure air (primary and tempering) in the CFB system. This reduction is obtained primarily by using higher temperature air to dry the sorbent. The reduction lowers total power consumption of the air fans, which in turn improves boiler economics. For example, the use of primary air at a maximum air heater outlet temperature maximizes energy recovery from the flue gas, thus increasing boiler efficiency with respect to a JIT system using tempering air. As the boiler efficiency is significantly increased, a long-term savings in plant operating costs is realized. By way of example, the boiler efficiency may be increased in the range of about 0.5% to about 1.5%.
- While the invention has been described with reference to various exemplary embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the appended claims.
Claims (20)
Priority Applications (4)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
US11/685,447 US20080223267A1 (en) | 2007-03-13 | 2007-03-13 | Direct sorbent preparation/feed apparatus and method for circulating fluidized bed boiler systems |
CN2008800080973A CN101641553B (en) | 2007-03-13 | 2008-01-16 | Improved direct sorbent preparation/feed apparatus and method for circulating fluidized bed boiler systems |
EP08727709A EP2118568A1 (en) | 2007-03-13 | 2008-01-16 | Improved direct sorbent preparation/feed apparatus and method for circulating fluidized bed boiler systems |
PCT/US2008/051114 WO2008112339A1 (en) | 2007-03-13 | 2008-01-16 | Improved direct sorbent preparation/feed apparatus and method for circulating fluidized bed boiler systems |
Applications Claiming Priority (1)
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US11/685,447 US20080223267A1 (en) | 2007-03-13 | 2007-03-13 | Direct sorbent preparation/feed apparatus and method for circulating fluidized bed boiler systems |
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US20080223267A1 true US20080223267A1 (en) | 2008-09-18 |
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US11/685,447 Abandoned US20080223267A1 (en) | 2007-03-13 | 2007-03-13 | Direct sorbent preparation/feed apparatus and method for circulating fluidized bed boiler systems |
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US (1) | US20080223267A1 (en) |
EP (1) | EP2118568A1 (en) |
CN (1) | CN101641553B (en) |
WO (1) | WO2008112339A1 (en) |
Cited By (3)
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CN104338422A (en) * | 2013-07-29 | 2015-02-11 | 碧水蓝天环境工程有限公司 | Desulfurization device and desulphurization method thereof |
CN106168377A (en) * | 2016-08-15 | 2016-11-30 | 南京工程学院 | A kind of boiler hot flue gas igniter |
CN114857577A (en) * | 2022-04-28 | 2022-08-05 | 江苏运能能源科技有限公司 | Automatic pneumatic conveying device and process for realizing hot slag conveying and recycling |
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CN102297439A (en) * | 2011-07-05 | 2011-12-28 | 哈尔滨工业大学 | Ultra-low temperature smoke-exhausting and energy-saving boiler |
CN104548920B (en) * | 2014-12-03 | 2017-02-22 | 河南神马尼龙化工有限责任公司 | Desulfurization device and desulfurization method |
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Also Published As
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WO2008112339A1 (en) | 2008-09-18 |
EP2118568A1 (en) | 2009-11-18 |
CN101641553A (en) | 2010-02-03 |
CN101641553B (en) | 2012-02-15 |
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