WO2021003231A1

WO2021003231A1 - Simplified chain conveyor for bottom ash conversions

Info

Publication number: WO2021003231A1
Application number: PCT/US2020/040441
Authority: WO
Inventors: Austin T. Little; JR. Billy G. SPRINGER
Original assignee: Babcock and Wilcox Co
Current assignee: Babcock and Wilcox Co
Priority date: 2019-07-02
Filing date: 2020-07-01
Publication date: 2021-01-07
Anticipated expiration: 2022-01-02
Also published as: KR102835393B1; KR20220025013A; CN114072342A

Abstract

An ash removal conveyor system comprises a hopper and a chain conveyor with an elongated enclosed duct separate from the hopper, a receiving section positioned for receiving ash from the hopper, and an internal chain inside the elongated enclosed duct. The chain conveyor has a bottom section and a top section with flights in the top section and flights in the bottom section moving in opposite directions inside the elongated enclosed duct, and with one of the top or bottom sections moving the ash from the receiving section to the distal end. The conveyor system may not include a bottom gate interposed in an ash flow path from the hopper to the chain conveyor; or may not include a grinder interposed in this ash flow path; or may not include either a bottom gate or a grinder interposed in this ash flow path.

Description

SIMPLIFIED CHAIN CONVEYOR FOR BOTTOM ASH CONVERSIONS

[0001] This application claims the benefit of U.S. Provisional Application No.

62/869,738 filed July 2, 2019 and titled “SIMPLIFIED CHAIN CONVEYOR FOR BOTTOM ASH CONVERSIONS”. U.S. Provisional Application No. 62/869,738 filed

July 2, 2019 is incorporated herein by reference in its entirety.

FIELD OF THE INVENTION

[0002] This invention relates to a system for handling ash, and particularly to a simplified chain-conveyor system for removing bottom ash from large-scale coal fired boilers. The disclosed ash handling systems may be more generally employed for removal of ash produced by other types of combustion processes.

BACKGROUND OF THE INVENTION

[0003] U.S. Pat. No. 10,124,968 issued November 13, 2018 is incorporated herein by reference for its teaching of certain chain conveyor systems.

[0004] U.S. Pat. No. 5,775,237 issued July 7, 1998 is incorporated herein by reference for its teaching of a dry bottom ash handling system.

[0005] The following description of general background of the present invention makes reference to the appended drawing Figures 1 through 4 which show prior art systems. The combustion process of coal in power utility fired boilers produces two types of waste products; 1) ash particles that are small enough to be entrained in the flue gas referred to as fly ash, and 2) relatively large ash particles that overcome drag in the combustion gases and drop to the bottom of the boiler referred to as bottom ash. Typically, bottom ash is either collected in a water impoundment or in a dry bottom. Water impounded ash, referred to as wet bottom ash, is typically collected in individual water filled hoppers, as shown in Figure 1 which illustrates a typical bottom ash-to- pond system 10, or in a closed loop recirculation system 26 shown in Figure 2, or in a water filled trough with a submerged drag chain system 12 as shown in Figure 3. In the system of Figure 1 , ash is discharged each shift in a batch process from hoppers 14 through bottom gate 16 on the side of the hoppers 14. Ash grinders 18 are provided to reduce ash particle size to less than about 3 in. (typically) to allow conveyance in a pipe as an ash/water slurry. The slurry is discharged into a storage pond 20 where the ash settles out over time. Surge tank 30 is provided to handle transient surges in the slurry flow. Numerous pumps 22 and valves 24 are provided for moving the slurry through system 10 (these elements are also shown in Figures 2, 3 and 4).

[0006] Closed loop recirculation system 26 shown in Figure 2 is a modified form of system 10 and provides closed loop dewatering system and uses a settlement unit referred to by applicant as a“Hydrobin®” unit 28 as shown in Figure 2. In the system 26 shown in Figure 2, bottom ash 1 1 is discharged from hoppers 14 into the grinder 18 and is then pumped as an ash-water slurry to remotely located Hydrobin ® dewatering bins 28 which provide a two-stage settling process necessary to clarify the water enough for recycling. Settled ash is drained of water through screens in the dewatering bins 28. Surge tank 30 and settling tank 32 handle the drained water and provide further clarification and separation of coal ash from the water. Clarified water is recycled back to convey the next batch of ash slurry. Dewatered ash slurry is hauled away from the plant site.

[0007] Systems 10 and 26 are so-called wet sluicing systems which operate successfully but have a number of drawbacks, principally requiring large amounts of transport water that requires sophisticated treatment as well as significant capital expenditures.

[0008] The submerged mechanical drag conveyor system 12 (or submerged chain conveyor or“SCC”) is illustrated in Figures 3 and 4, and is typically applied to provide continuous ash removal. Bottom ash continuously falls into the SCC 12 through hopper discharge 42 and settles onto a chain-and-flight conveyor system referred to as a submerged drag chain unit 34. Unit 12 forms an open trough which is filled with water to quench the dry ash as it falls into the unit from the boiler. The chain of unit 34 moves continuously and carries away ash which is dewatered as it moves along an inclined section 36 and is transported via a conveyor 44 and into a bottom ash silo 38, and is later discharged into a truck to transport the material off-site. Makeup water is added to offset water loss with wet ash being removed from the system and due to evaporation. Mill reject hoppers 40 are provided to process such material which is directed onto chain conveyor inclined section 36 for processing along with the bottom ash slurry stream. The submerged drag chain conveyor unit 34 is positioned directly beneath the boiler ash hopper discharge 42. The boiler throat being rectangular shaped requires the orientation of the submerged drag chain conveyor unit 34 and boiler ash hopper discharge 42 to be substantially parallel to the major axis of the boiler throat. Another view of submerged drag chain conveyor unit 12 is shown in Figure 4 which further illustrates the conveyor drive unit 46 and take-up unit 48 which provide proper conveyor chain tensioning. In this prior art system, one of the units 12 shown in Figures 3 and 4 is provided for each boiler ash hopper discharge

42.

[0009] The handling of ash from large-scale coal burning boilers is subject to ever increasingly stringent governmental regulations, including the US EPA’S federal ELG (Effluent Limitations Guidelines) rules. These rules treat different forms of water streams found in bottom ash handling systems in different ways. For example, these rules preclude the discharge into the environment of ash transport water such as used in the pond system 10 shown in Figure 1 and in the closed loop hydraulic system 26 shown in Figure 2, and ash basins. Water streams not subject to these ELG requirements (presently) include quench water used in submerged chain conveyor systems 12 and other minor discharges. Retrofitting existing coal-fired boilers to modem ash handling system frequently involves a considerable capital expense. Operators of these systems will often decommission boilers in view of the significant expenses associated with retrofits.

[0010] With the above considerations in mind, boiler operators are often faced with difficult decisions regarding continuing the lifetime of existing installations. Installation of a conventional submerged drag chain system 12 as illustrated in Figure 3 ordinarily requires removal of existing bottom ash hoppers 14 and replaced with a rectangular shape trough hopper 42 that can accept a continuous flow of ash. As mentioned previously, make-up water must be added to offset water loss. The water temperature is relatively high in these systems and therefore a cooling system is provided, such as through recirculation to a pond or installation of heat exchangers. Existing SCC systems 12 provide the benefits of not requiring transport water and the equipment cost is relatively low. In addition, maintenance and operating costs are relatively low as compared with wet sluicing systems. However, significant disadvantages are associated with the major reworking of the boiler mentioned above and the significant space requirements of such systems including orientation constraints. Since the system 12 is situated directly beneath the boiler without any isolation valves, a break in the SCC chain or other maintenance issue may require boiler shutdown in order to repair the fault.

[0011] This invention is related to embodiments of simplified chain-conveyor systems (SCS) which are adaptable for retrofit applications which avoid the disadvantages mentioned previously. Several embodiments of the invention are illustrated and described herein.

BRIEF SUMMARY

[0012] In some illustrative embodiments disclosed herein, a conveyor system for removing ash is disclosed. The conveyor system comprises a hopper for collecting the ash, and a chain conveyor. The chain conveyor includes an elongated enclosed duct that is separate from the hopper, with a receiving section positioned for receiving the ash from the hopper. The chain conveyor further includes an internal chain disposed inside the elongated enclosed duct for transporting the ash from the hopper to a distal end of the chain conveyor for discharge from the chain conveyor. The chain conveyor has a bottom section and a top section with flights in the top section and flights in the bottom section moving in opposite directions inside the elongated enclosed duct, and with one of the top or bottom sections moving the ash from the receiving section to the distal end. In some embodiments, the conveyor system does not include a bottom gate interposed in an ash flow path from the hopper to the chain conveyor. In some embodiments, the conveyor system does not include a grinder interposed in an ash flow path from the hopper to the chain conveyor. In some embodiments, the conveyor system does not include a bottom gate interposed in an ash flow path from the hopper to the chain conveyor and also does not include a grinder interposed in an ash flow path from the hopper to the chain conveyor. The conveyor system may be a wet ash conveyor system in which at least a lower portion of the elongated enclosed duct is flooded with water, or may be a dry ash conveyor system in which the elongated enclosed duct is not flooded with water. The conveyor system may optionally further include a chain support configured to support the internal chain, and a cooling apparatus in the chain support. In some embodiments, the chain conveyor includes at least a first chain conveyor with a water-cooled housing. In some embodiments, the conveyor system further comprises an electronic controller configured to receive sensor readings indicative of a temperature of the chain conveyor and to control temperature of the chain conveyor based on the received sensor readings by controlling at least one of (i) flow of ash from the hopper to the chain conveyor by controlling a flow control device configured to control the flow of ash from the hopper to the receiving section of the chain conveyor and/or (ii) a speed of the chain conveyor.

[0013] In some illustrative embodiments disclosed herein, in a conveyor system as set forth in the immediately preceding paragraph, the chain conveyor comprises a top carry chain conveyor including a floor beneath the flights moving in the top section and above the flights moving in the bottom section, in which the top section moves the ash from the receiving section to the distal end. Such a top carry chain conveyor system may be a wet ash conveyor system in which the elongated enclosed duct is flooded to immerse both the flights in the top section and the flights in the bottom section. In some illustrative embodiments disclosed herein, in a conveyor system as set forth in the immediately preceding paragraph, the chain conveyor comprises a bottom carry chain conveyor in which the bottom section moves the ash from the receiving section to the distal end. In some such bottom carry chain conveyors in which the conveyor system also does not include a grinder interposed in an ash flow path from the hopper to the chain conveyor, a spacing between adjacent flights is large enough to allow ash without grinding to fall between the flights moving in the top section to reach the bottom of the elongated enclosed duct, and/or a spacing between the flights moving in the top section and the flights moving in the bottom section is effective for the flights moving in the top section to contact and break apart ash moved by the bottom section.

[0014] In some illustrative conveyor systems as set forth in either of the two immediately preceding paragraphs, the chain conveyor is loaded from a single point input from the hopper allowing the conveyor system to be rotated in any of 360° directions in plan relative to the hopper. The conveyor system optionally may further comprise a lateral cooling section interposed between an ash discharge of the hopper and the receiving section of the chain conveyor, wherein an ash movement apparatus is disposed in the lateral cooling section. The ash movement apparatus may in some embodiments comprise a mechanical screw disposed in the lateral cooling section, optionally with a water-cooled shaft. In some embodiments the lateral cooling section comprises a water-cooled jacket.

BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 illustrates a typical bottom ash-to-pond ash handling system in accordance with the prior art.

[0016] Figure 2 illustrates a typical closed loop recirculation system for ash slurry handling in accordance with the prior art.

[0017] Figures 3 and 4 illustrate a typical bottom ash submerged drag chain conveyor system in accordance with the prior art.

[0018] Figure 5 illustrates a SCS in accordance with the present invention.

[0019] Figure 6 illustrates an embodiment of the SCS illustrated in Figure 5 operated in a dry ash hopper and gaseous spray configuration.

[0020] Figure 7 illustrates a bottom carry arrangement of a SCS.

[0021] Figure 8 illustrates a SCS including a lateral cooling section with a cooled mechanical screw.

[0022] Figure 9 illustrates an SCS with multiple conveyors in series, in which the first conveyor includes a fluid-cooled housing.

[0023] Figure 10 illustrates a cross-sectional view of the first conveyor with the fluid-cooled housing of the SCS of Figure 9.

[0024] Figure 11 illustrates a top carry arrangement of an SCS.

[0025] Figure 12 illustrates a simplified SCS in which the bottom gate and grinder are omitted.

[0026] Figure 13 illustrates a maintenance shutdown process suitably performed using the simplified SCS of Figure 12.

[0027] Figure 14 illustrates a temperature control process for an SCS.

DETAILED DESCRIPTION OF THE INVENTION

[0028] Now with reference to Figures 5 through 14, embodiments of the present invention will be described. Figure 5 represents the basic configuration of the SCS in accordance with the present invention, generally designated by reference number 50. In describing SCS 50 certain components are common with the prior art systems described previously, and the same reference numbers are used to designate them. SCS 50 includes receiving section 52 directly connected with the existing ash hopper 14. Bottom gate 16 disposed in gate housing 17 can be opened or closed to connect or isolate ash hopper 14 from receiving section 52. An optional grinder 18 is provided to control flow of ash out of the hopper 14. The grinder 18 has the additional benefit of reducing particle size to less than about 2 inch (typically) to fit in a smaller conveyor cross-section (although the grinder is contemplated to provide larger or smaller particle grind sizes in specific implementations). SCS 50 forms an elongated closed duct 54 which extends from receiving section 52. Duct 54 has a generally horizontal section 56 and may include inclined or declined portions. Horizontal section 56 is primarily provided to adapt the system to existing plant installation space constraints. Inclined or declined portions enable ash transport to subsequent ash handling equipment. Closed duct 54 is fully enclosed hydraulically on all sides for some embodiments of operating configurations. Duct 54 preferably has a generally rectangular cross-section, may be water proof, has removal covers at appropriate places with special seals and a double strand drag chain conveyor 60 moving inside the duct in an endless manner between sprocket 62 near receiving section 52 and drive sprocket (not shown) at the terminal end of duct. A mechanism is provided for adjusting tension in conveyor 60 which may operate at either of sprocket 62 or a drive sprocket. Drag chain conveyor 60 forms a lower carrying section 66 which moves accumulated ash from receiving section 52 along horizontal section 56, with an upper retur section 68 completing the endless chain loop. Optional inclined section 58 typically extends at an angle of around 30 to 40° which is intended to provide optimized ash dewatering (in wet applications) while providing efficiency of ash transport. SCS 50 can be easily installed with existing boilers since the existing hoppers 14 may be utilized and only a sluice line is replaced (when replacing a hydraulic transport system). In some embodiment the existing hopper 14 is modified by altering the cross-section geometry and/or modifying the wall angle of at least one wall of the hopper and/or changing the location from which ash leaves the hopper. A benefit of this may be, for example, that a steeper wall can improve efficiency of gravity feed (or gravity-assisted feed) of ash into the grinder 18. Similarly, the bottom ash gate 16 and grinder 18 normally provided may be left in place. Maintaining bottom ash gate 16 provides maintenance isolation between the boiler and SCS 50 allowing maintenance operations without requiring the associated boiler to be taken off line. On the other hand, the alternative options of not leaving the bottom gate in place (but retaining the grinder), or not leaving the grinder in place (but retaining the bottom gate), or not leaving the bottom gate in place and not leaving the grinder in place provide benefits such as reducing the number of mechanical components, avoiding the potential for the gate 16 being blocked open or grinder 18 becoming clogged or otherwise malfunctioning, and providing more space for retrofitting in the case of a boiler that is retrofitted to incorporate SCS 50. Another benefit of the disclosed embodiments is that since ash is loaded into the conveyor at a single, approximately square or round point location 53 in receiving section 52 rather than along a long, rectangular shaped opening below the boiler throat, the orientation of the SCS 50 can be rotated 360° in any direction from a plan view. One option is to use a single conveyor arranged in the same manner as a conventional SCC to pick up multiple single loading points. Alternatively, multiple smaller conveyors can be used for each single loading point if pre-existing structures occlude a conventional arrangement. This provides great flexibility for space-congested retrofit applications. Another advantage of the point loading configuration is that secondary isolation valves can be installed between the grinder 18 and the conveyor 60 for an additional level of personnel safety when performing conveyor maintenance while the boiler remains operational.

[0029] Under certain conditions it may be necessary to limit the feed of ash into the SCS 50 to prevent over-filling. The present invention accomplishes this by monitoring the conveyor drive torque during operation. Torque monitoring can be achieved in several ways, including but not limited to an output of electric motor current or hydraulic pressure. At a pre-determined high set point for the output, simple logic can be used to close an upstream feed valve or stop a preceding conveyor, thereby stopping the feed of additional ash. The conveyor whose drive has reached the high set point can continue to run until sufficiently emptied of ash, as represented by a low set point for the drive output parameter. At this point the signal would then initiate the re-opening of a valve or re-starting of an upstream conveyor to begin feeding ash again. Torque control in this manner also provides benefits for chain size selection and wear life. Because the amount of ash accumulated in the conveyor can be controlled, much smaller chain sizes can be used compared to a conventional SCC in which large masses of ash could pile on top of the chain and flight mechanism. Indeed, the chain size of conventional SCCs is dictated by the amount of ash that could accumulate on top of the chain and flight mechanism rather than the conveying capacity of the machine. Despite the large pile of ash accumulated on the chain in a conventional SCC, the removal rate remains constant based on the dimensions of the flight bars. Therefore, a SCS 50 as described in the present invention can provide an equivalent conveying capacity to a conventional SCC with a given flight bar size while using smaller chain. The use of smaller chain provides considerable cost savings. Additionally, chain wear life is prolonged by lower link-to-link stresses realized by reduced ash loading.

[0030] The basic system described for SCS 50 can be operated in various configurations, each providing certain features for optimization for a particular plant application. Also, the duct widths, the flight design and the flight distances and the chain speed are flexible and can be adapted to the requirements.

[0031] Now with reference to Figure 6, another configuration for operating SCS

50 is illustrated, referred to as a “dry ash hopper and gaseous media spray” configuration 88. This configuration is essentially a dry system in that the ash is not submerged in water. In this case, some other mechanism(s) for cooling the ash optionally may be employed. For example, a series of gaseous media sprays 90 may be provided. Operation here would typically be continuous with bottom gate 16 open (or omitted entirely) with SCS 50 operated continuously. In one embodiment, ambient or cooled“dry” air is the gaseous media. Gaseous media vents 19 in the housing 17 of bottom gate 16 (as shown) and/or in the hopper 14 (more generally, in fluidic connection to the hopper 14) may also introduce ambient or cooled dry air or another gaseous medium. The gaseous medium introduced by the vents 19 in the hopper and/or gate housing may be the same as, or different from, the gaseous medium introduced by the gaseous media sprays 90 of the SCS 50.

[0032] Alternatively, sprays 90 (and/or vents 19) may be used to inject a wet or dry chemical compound onto the ash for purposes of treating the ash. The wet or dry compound may include a halogen, hydrogen, or metallic material. The treated ash may be reintroduced into the boiler for emissions control or used in a subsequent process. The wet or dry chemical may alternatively be injected into the hopper through vents in fluidic connection with the hopper.

[0033] Under certain conditions it may be necessary to monitor and/or control the temperature of the SCS 50. One such condition is when the SCS 50 is operated in arrangement that do not utilize or otherwise require the use of water (e.g., a dry ash handling system such as that of Figure 6), In these systems, ash may leave the hopper 14 at elevated temperatures, e.g. in some embodiments the dry ash entering the hopper may be at 1500 °F (815 °C) or hotter; whereas, it may be desirable for components of the grinder 18 to be kept to a temperature of around 500 °F (260 °C) or lower, although the precise maximum temperature design parameter will depend on the detailed design of the grinder 18. Gaseous media vents 19 in fluidic connection to the hopper 14 (more specifically in fluidic connection with the gate 16 of hopper 14 in illustrative Figures 5 and 6) may introduce a gaseous media such as ambient air into the system to cool the ash. Slip streams of process gas may also be utilized via the gaseous media vents 19. Cooling may also occur by placing an optional cooling apparatus in the hopper or in fluidic communication with the hopper, e.g. interposed between an ash discharge of the hopper 14 and the point location 53 in receiving section 52 of the SCS 50.

[0034] The optional cooling apparatus may take the form of a flow control device with associated cooling, such a mechanical screw wherein cooling is enabled thru the shaft of the screw and/or the screw housing (e.g. Figure 8). More generally, a flow control device (with or without associated cooling) may also take the form of the gate 16, a valve, a chevron, a plunger, the grinder 18, a hydraulic jaw, various combinations thereof, or so forth; each flow control device is capable of being located partially within, wholly within, or downstream from the hopper. In some arrangements more than one flow control device is used and may further include a rapper system to assist with dislodging ash that may aggregate within the hopper.

[0035] Under certain conditions it may be necessary to provide additional cooling either in addition to that previously discussed or as a stand-alone system.

[0036] Figure 7 illustrates the bottom carry arrangement, for example, taken along the section S1-S1 indicated in Figure 5, in which the chains 65 of the double strand drag chain conveyor 60 (see Figure 5) carry chains flights 66 and 68. The flights 66, 68 are also sometimes referred to as scrapers in the art, as on the lower pass of the double strand drag chain conveyor 60 of the bottom carry arrangement, the flights or scrapers 66 push or“scrape” the ash along a floor 67 of the conveyor 50. The chain flights 66, 68 are directly supported by chains 65. The double strand chains 65 are guided in replaceable wear bars and are guided by “U” channels 69. In other embodiments, some other type of chain supports may be used in place of the“U” channels 69, such as idler wheels. It is also contemplated to omit chain supports entirely, and to rely on the chains 65 being suspended between the flights 66, 68. The SCS 50 is an improvement because all the runs of the chain are contained, and an optional submerged water bath is positioned to clean the return run of chain and deposit ash into the bottom run by gravity. Illustrative Figure 7 is for the wet ash SCS of Figure 5, as indicated by the waterline WL (in some other wet ash handling implementations, the waterline may be above the upper flights 68 so that they are also submerged along with the lower flights 66; it is also noted that in some wet ash handling embodiments the entire duct 54 is flooded, in which case the waterline WL is understood to denote possible air pockets at the ceiling of the flooded duct 54). However, the disclosed cooling approaches are also suitably used in the dry ash SCS of Figure 6. Figure 7 further illustrates the SCS 50 includes a closed vessel having sidewalls 100, bottom plate 102 and upper lid 104. Cooling apparatus 691 may be place in one or more channels 69 to control chain temperature. A cooling apparatus may also be placed within any of the plate 102, upper lid 104 or sidewall to control temperature within conveyor 50. For example, by way of nonlimiting illustrative example the cooling apparatus 691 may comprise a water jacket of the channels 69, water cooled channels bored into plates or other structure forming the channels 69, and/or so forth. In an alternative embodiment in which idler wheels replace the channels 69, the cooling apparatus 691 may be implemented as cooling of the wheel shafts of the idler wheels. Sensors (not shown) may be placed within conveyor 50 to monitor temperature. The sensors may include, by way of nonlimiting illustrative example: temperature sensors immersed in the water (for a wet ash SCS); temperature sensors coupled to the channels 69 (or coupled to shafts of idler wheels if such are used in place of the channels 69) to (approximately) measure temperature of the chains 65; fluid flow rate sensors (for a wet ash SCS); torque sensors (for example, measuring output of electric motor current or hydraulic pressure of the chain drive, as previously mentioned); and/or so forth.

[0037] Hopper 14 may deliver ash at elevated temperatures to conveyor 50. Controlling temperature within the conveyor 50 enables longer service life. A method of controlling SCS temperature includes one or more of the following steps: establishing an operational temperature range for the conveyor; monitoring and/or measuring one or more of a temperature within conveyor 50, discharge rate of ash from the hopper, a drive torque applied to a chain conveyor, a flowrate of a gaseous media, a temperature of a gaseous media, and a cooling condition of a cooling apparatus; and adjusting one or more of a temperature within conveyor 50, discharge rate from the hopper, a drive torque applied to a chain conveyor, a flowrate of a gaseous media, a temperature of a gaseous media, and a cooling condition of a cooling apparatus to maintain chain conveyor 50 within the operation temperature range. In the following, some further nonlimiting illustrative examples.

[0038] Figure 8 depicts a cooling apparatus comprising a lateral cooling section 110 interposed between an ash discharge of the hopper 14 (for example, the outlet of the grinder 18 discharging ash from the hopper 14) and the point location 53 in receiving section 52 of the SCS 50. As seen in Section S2-S2 of the lateral cooling section 110 of Figure 8, the lateral cooling section 110 comprises a “U"-shaped channel 112 with a hollow interior 114. The top of the“U”-shaped channel 112 may be open or may be covered. The lateral cooling section 110 may be cooled by ambient air contacting the channel 112, or (as shown in Section S2-S2) may be water cooled by designing the channel 112 to have a water jacket 116. In another contemplated embodiment (not shown), the cooling of the“U”-shaped channel 112 may be provided by tubing that is helically wound around the lateral cooling section 110 and that carries water or another coolant. The lateral cooling section 110 provides a defined transport distance for the ash that allows for some cooling of the ash by conduction to ambient air (or by conduction to the water jacket 116 or helical cooling tubing, if provided) before it enters the SCS 50 at the point location 53 in the receiving section 52. The length and cross-sectional area of the“U"-shaped channel 112 is designed based on design constraints such as: (i) providing sufficient cooling (biasing toward a longer length and smaller cross-section, although more cooling can also or alternatively be provided by way of the water jacket 1 16 or helical cooling tubing, or by a cooled mechanical screw 120; (ii) minimizing ash flow resistance introduced by the lateral cooling section 1 10 (biasing toward a shorter length and larger cross section); and (iii) ensuring sufficient ash transport capacity (biasing toward larger cross section).

[0039] The illustrative lateral cooling section 110 is oriented horizontally; however, in other embodiments, the lateral cooling section may have some upward or downward slant. For example, an upward slant may be useful to accommodate vertical space constraints in the case of a retrofit SCS. Conversely, if sufficient vertical space is available, then a downward slant may reduce ash flow resistance, which may allow for a longer length for the lateral cooling section 110. However, especially in retrofit designs but also possibly in new installations, the space available for introducing downward slant to the lateral cooling section 110 may be limited.

[0040] Figure 8 further shows a mechanical screw 120 is disposed inside the hollow interior 114 of the“U”-shaped channel 112. The mechanical screw includes the screw winding 122 and a shaft 124 that is optionally water-cooled to provide further cooling of the ash flowing through the lateral cooling section 110. See also Section S2-S2 of Figure 8. The addition of the mechanical screw 120 provides benefits including: (i) it is rotated to provide motive force for moving the ash through the lateral cooling section 1 10; and (ii) the water-cooled shaft 124 provides cooling for the ash. The screw winding 122 is preferably thermally conductive (e.g. made of steel, aluminum alloy, or some other metal) to effectively act as heat fins for transporting heat from the ash to the water-cooled shaft 124. While the mechanical screw 120 is shown as an illustrative ash movement apparatus disposed in the lateral cooling section 110 shown in Figure 8, other ash movement apparatus embodiments are contemplated, such as an apron conveyor or a pan conveyor. Optionally, the ash movement apparatus disposed in the lateral cooling section 110 is water cooled, e.g. by way of the water-cooled screw shaft 124. An apron or pan conveyor could be water cooled by way of a cooling apparatus similar to the cooling apparatus 691 of Figure 7. As another contemplated variant, if the lateral cooling section 110 is sufficiently short then no ash movement apparatus may be disposed inside the lateral cooling section.

[0041] The embodiment of Figure 8 is shown for a dry ash handling system embodiments. However, the lateral cooling section 110 of Figure 8 or Figure 9 is also suitable for use in conjunction with a wet ash handling system such as that of Figure

5.

[0042] With reference now to Figures 9 and 10, another cooling apparatus is described. Figure 9 shows an SCS with multiple conveyors 50, 50₁ in series, in which the first conveyor 50₁ includes a fluid-cooled housing. Figure 10 depicts a sectional view along Section S3-S3 of the first SCS 50₁ of the dry ash handling system of Figure 9. In this embodiment, the closed duct 54 of the first SCS 50₁ comprises or is surrounded by a water jacket 154. This beneficially provides more efficient cooling of the dry ash flowing through the water jacketed duct 154. In another contemplated embodiment (not shown), the cooling of the duct of the SCS 50 may be provided by tubing that is helically wound around the duct 54 and that carries water or another coolant. In Figure 9, the first and second SCS 50₁, 50 are both oriented horizontally, which then requires (at least) two times the vertical space of a single conveyor. If lateral space constraints, for example in a retrofit design, make such an arrangement impractical, then the first SCS 50₁ could be slanted upward so that the second SCS 50 could be at the same vertical position as the first SCS 50₁ (or at least at a closer vertical position to that of the first SCS 50₁ than the arrangement shown in Figure 9). While this embodiment is particularly useful in the dry ash handling system of Figure 6, it is contemplated to be used in conjunction with a wet ash handling system such as that of Figure 5. In a wet ash handling system, cooling of the duct 54 by forming as a water cooled duct 154 or by tubing that is helically wound around the duct 54 can beneficially increase heat transfer from the water carrying the wet ash inside the duct to the ambient air.

[0043] As previously discussed, Figure 7 depicts a bottom carry arrangement for the SCS 50. In this arrangement, the flights 66 on the lower pass of the double strand drag chain conveyor 60 serve as scrapers that push or“scrape” the ash along the floor 67 of the conveyor 50. The top flights 68 serve as the return path of the double strand drag chain conveyor, and the top flights 68 do not contribute to the movement of the ash. Such a bottom carry arrangement has certain advantages. For example, the ash will fall by gravity through the top pass onto the floor 67. Furthermore, the water line WL can be lower, indeed can be below the elevation of the upper flights 68.

[0044] However, it is recognized herein that for some specific applications, the bottom carry arrangement may have some disadvantages. In this arrangement, the grinder 18 is included in order to ensure that the ash is reduced sufficiently in size to pass between the upper flights 68 so as to fall onto the floor 67 of the conveyor 50. The grinder is a mechanical component that is exposed to unprocessed ash, and hence can require relatively frequent maintenance.

[0045] To address such concerns, Figure 11 shows an embodiment in which the SCS 50 employs a top carry arrangement, while still retaining the benefits of the enclosing duct 54. Figure 11 shows the equivalent of cross-section S1-S1 of Figure 5, but for the case of a top carry arrangement. T o enable the top flight to scrape the ash, a floor 160 is added beneath the top flights 68 and above the bottom flights 66. That is, the floor 160 is disposed beneath the flights 68 moving in the top section of the chain conveyor and above the flights 66 moving in the bottom section of the chain conveyor, and the flights 68 moving in the top section move ash over the floor. As entering via the point location 53 in receiving section 52 of the SCS 50 falls onto the floor 160 and is thereby prevented from reaching the floor 67 over which the bottom flights 66 pass. The added floor 160 is suitably a steel plate (or plates) or the like. In the top carry arrangement of Figure 11 , the bottom flights 66 now serve as the return path of the double strand drag chain conveyor, and the bottom flights 66 do not contribute to the movement of the ash. The cross-sectional area through which the ash moves in the top carry arrangement is limited by the added floor 160 - to maximize this cross-sectional area, the top flights 68 (and hence the underlying floor 160) is optionally moved downward closer to the bottom flights 66 as compared with the bottom carry arrangement of Figure 7.

[0046] The illustrative top carry arrangement of Figure 11 is deployed in a wet ash handling system, as indicated by the waterline WL in Figure 11. The waterline WL must be above the added floor 160 (or the duct may be entirely flooded, so that the waterline WL diagrammatically indicates possible occasional air pockets at the ceiling of the duct). In some embodiments, the floor 160 is sealed against the sidewalls 100 of the duct 54 so that water above the floor 160 cannot leak down through the floor 160. In this approach, the space below the added floor 160 would not be flooded with water, and the returning bottom flights 66 would suitably be in ambient air However, if the lower space contains ambient air then the double strand drag chain conveyor would typically be elevated at the point where lower flights 66 transition to upper flights 68, in order for the transitioning flights to move into the flooded upper space through which the upper flights 68 travel. Such an elevation of the SCS may be problematic if there are tight vertical space constraints.

[0047] Contrary to the foregoing, in the illustrated approach of Figure 11 , the lower space through which the lower flights 66 travel is flooded. This is suitably achieved by way of water flow at one or both transitional ends of the conveyor, where lowerflights 66 move up onto the upper track to become upper-flights 68, and/orwhere upper flights 68 move down onto the lower track to become lower flights 66. These transitional ends provide fluidic communication between the upper and lower spaces so that when the upper space is flooded then the lower space is also flooded, which simplifies the design of the chain conveyor with the elongated enclosed duct 54.

[0048] As previously noted, an advantage of the top carry arrangement of Figure 11 is that the ash entering via the point location 53 in receiving section 52 of the SCS 50 does not have to fall through the spaces between the top flights 68 to reach the floor 67. A consequence of this is that the grinder 18 is optionally omitted, as there is no longer a need to ensure that the ash is reduced sufficiently in size to pass between the upper flights 68 so as to fall onto the floor 67 of the conveyor 50.

[0049] With reference to Figure 12, a simplified SCS is shown in diagrammatic side view, which includes the SCS 50 with top carry arrangement as already described with reference to Figure 11 , including the bottom flights 66 scraping the floor 67 of the duct 54, and the top flights 68 scraping the added floor 160. Because there is no need to grind the ash to reduce it sufficiently in size to pass between the upper flights 68, the grinder is omitted in the embodiment of Figure 12, which increases headroom for facilitating a retrofit. Optionally, the bottom gate may also be omitted. The embodiment of Figure 12 in which the grinder and the bottom gate are omitted also eliminates most or all of the mechanical components in the region of the connection from the hopper 14 to the point location 53 in the receiving section 52 of the SCS 50. As hot ash passes through this region, the simplified SCS 50 of Figure 12 has greatly reduced likelihood of mechanical failure at this critical location.

[0050] In another embodiment of the simplified SCS of Figure 12, a bottom carry arrangement is employed. In this case, the floor 160 is omitted and a spacing d between adjacent flights is large enough to allow the ash, without grinding, to pass between the upper flights 68 to reach the bottom of the duct 54 and be transported by the lower flights 66. Additionally for this embodiment, the upper flights 58 should be sufficiently elevated above the tops of the bottom flights 66 to allow for the bottom flights to transport the ash without grinding and without the upper flights 68 moving in the opposite direction to the lower flights 66 impinging on the unground ash. Alternatively, in another contemplated variant, if the ash is sufficiently friable (i.e., crumbly) then the spacing between the upper and lower flights 66, 68 can be intentionally made small enough so that as the upper flights 68 move in the opposite direction to the movement of the lower flights 66 the upper flights 68 contact and break apart the friable ash. In effect, the conveyor thus provides some ash grinding. [0051] It might be thought that removal of the bottom gate would create issues during maintenance, as the bottom gate is conventionally used to isolate the SCS 50 from the hopper 14. However, with reference to Figure 13, an approach for performing maintenance without having a bottom gate is described. In an operation 200, with the chain conveyor of the SCS 50 running, the boiler that transfers ash to the hopper 14 is taken offline. In an operation 202, after the boiler is taken offline the chain conveyor of the SCS 50 is run until all ash is removed. This entails continuing running the chain conveyor to remove ash from the hopper and the chain conveyor. In an operation 204, the SCS 50 is drained of water. In an operation 206, the grinder is de-energized. (If the grinder is omitted, as in the simplified SCS of Figure 12, then this operation 206 is suitably omitted). In an operation 208, downstream equipment including at least stopping the chain conveyor of the SCS 50 is de-energized. In an operation 210, the maintenance is conducted. By following this process, there is less need for the hopper 14 to have a bottom gate.

[0052] The simplified SCS of Figure 12 is suitably used with a wet ash handling system such as that of Figure 5, and this example is indicated in Figure 12 by diagrammatic inclusion of the water line WL in the hopper 14 of Figure 12. However, the simplified SCS of Figure 12 is also suitably used with a dry ash handling system such as that of Figure 6. In the case of a dry ash handling system, the SCS drain operation 204 is suitably omitted in the process of Figure 13.

[0053] With reference now to Figure 14, a temperature control process for an SCS is described. The temperature control process may be implemented as an electronic controller (not shown, e.g., comprising at least one microprocessor or microcontroller and ancillary electronics such as a flash memory, read-only memory, electronic programmable read-only memory, and/or other non-transitory storage medium, optionally implemented as a computer) programmed to control the flow control device (e.g., the illustrative grinder 18, and/or the mechanical screw 120 of Figure 8, or a valve, a chevron, a plunger, a grinder, a hydraulic jaw, various combinations thereof or so forth) and/or speed of the double strand drag chain conveyor 60 in accordance with the approach diagrammatically shown in Figure 14. In an operation 250, conveyor temperature is measured. In an operation 252, material flow rate from the hopper is measured. In an operation 254, conveyor drive torque is measured. In an operation 256, temperature of the water or other cooling media is measured. In an operation 258, temperature of a cooling apparatus is measured, such as temperature of the cooling apparatus 691 of Figure 7, temperature of the lateral cooling section 110 of Figure 8, temperature of the water-cooled mechanical screw 120 of Figure 9, and/or so forth. It will be appreciated that the order of performing the operations 250, 252, 254, 256, 258 can be varied, and that these operations are repeated at sensor sampling rates (which may be different for the different sensors) to provide (close to) real-time sensor readings. Moreover, in a specific embodiment, more, fewer, and/or different sensors may be employed to monitor the thermal state of the SCS.

[0054] Based on the sensor readings, it is determined whether the ash temperature is too high or too low. The measured conveyor temperature 250 directly measures of whether the conveyor temperature is too high or too low. The measured material flow rate from the hopper 252 allows for indirect inference of whether the ash temperature is too high or too low, since if the material flow rate is high then it may be that the cooling system is unable to handle cooling of the high material flow. (Additionally, high material flow rate by itself can be a problem, since it could overstress the double strand drag chain conveyor 60). Likewise, the measured conveyor torque 254 allows for indirect inference of whether the ash temperature is too high or too low, since if the torque is high then this implies more material is being conveyed, and again the cooling system may be unable to handle the high amount of material. (Additionally, the high conveyor torque by itself can be a problem, since it indicates mechanical stress on the double strand drag chain conveyor 60). The measured temperature of the cooling media 256 and/or the measured temperature of the cooling apparatus 258 are indirect measures of whether the conveyor temperature is too high or too low. If one or more of the sensor readings 250, 252, 254, 256, 258 is too high, then at an operation 260 the flow control device (e.g. grinder 18) is closed (or operated to reduce the flow rate, if the flow control device provides for such adjustment of the flow rate), and/or the speed of the chains of the SCS 50 is decreased. On the other hand, if one or more of the sensor readings 250, 252, 254, 256, 258 is too low, then at an operation 262 the grinder 18 or other flow control device is opened (or operated to increase the flow rate), and/or the speed of the chains of the SCS 50 is increased. While this is a straightforward control approach, more complex flow control is contemplated. For example, if the grinder 18 or otherflow control device allows for continuous or multiple-step adjustment of flow rate (as opposed to just on/off in the case of the bottom gate) then the adjustment operation 260 and/or adjustment operation 262 may employ a more complex adjustment formula, e.g. scaling the amount of flow rate adjustment based on how high (or how low) the sensor reading triggering the adjustment is, and/or whether two or more sensor readings are simultaneously triggering the adjustment.

[0055] The system described herein may also be installed in retrofit application. A method of replacing an existing system comprises on or more of the following steps; removing an existing conveyor, replacing or retaining an existing hopper, installing an SCS, altering the geometry of an existing hopper, altering the wall angle of an existing hopper, adding a gaseous or liquid vent to an existing hopper, and relocating a gate opening to a bottom location of an existing hopper.

[0056] In the described embodiments, the cooling fluid has been described as water. However, in some specific installations, the ash may be reactive with water. In such cases, the cooling fluid may be propylene or some other coolant fluid. Moreover, except as noted herein, the embodiments disclosed herein and the various aspects disclosed herein can be used in any combination, and can be used with either a wet ash handling system or a dry ash handling system.

[0057] While the above description constitutes the preferred embodiment of the present invention, it will be appreciated that the invention is susceptible to modification, variation and change without departing from the proper scope and fair meaning of the accompanying claims.

Claims

1. A conveyor system for removing ash, the conveyor system comprising: a hopper for collecting the ash, and

a chain conveyor including an elongated enclosed duct that is separate from the hopper, with a receiving section positioned for receiving the ash from the hopper, and further including an internal chain disposed inside the elongated enclosed duct for transporting the ash from the hopper to a distal end of the chain conveyor for discharge from the chain conveyor, the chain conveyor having a bottom section and a top section with flights in the top section and flights in the bottom section moving in opposite directions inside the elongated enclosed duct, and with one of the top or bottom sections moving the ash from the receiving section to the distal end;

wherein the conveyor system does not include a bottom gate interposed in an ash flow path from the hopper to the chain conveyor.

2. The conveyor system in accordance with claim 1 wherein the conveyor system does not include a grinder interposed in an ash flow path from the hopper to the chain conveyor.

3. The conveyor system of any one of claims 1-2 wherein the chain conveyor comprises a top carry chain conveyor including a floor beneath the flights moving in the top section and above the flights moving in the bottom section, and wherein the top section moves the ash from the receiving section to the distal end.

4. The conveyor system of claim 3 wherein the conveyor system is a wet ash conveyor system in which the elongated enclosed duct is flooded to immerse both the flights in the top section and the flights in the bottom section.

5. The conveyor system of any one of claims 1-2 wherein the chain conveyor comprises a bottom carry chain conveyor in which the bottom section moves the ash from the receiving section to the distal end.

6. The conveyor system in accordance with any one of claims 1-5 in which the chain conveyor is loaded from a single point input from the hopper allowing the conveyor system to be rotated in any of 360° directions in plan relative to the hopper.

7. The conveyor system of any one of claims 1 -6 further comprising: a lateral cooling section interposed between an ash discharge of the hopper and the receiving section of the chain conveyor, wherein an ash movement apparatus is disposed in the lateral cooling section.

8. The conveyor system of claim 7 wherein the ash movement apparatus comprises a mechanical screw disposed in the lateral cooling section.

9. The conveyor system of claim 8 wherein the mechanical screw includes a water-cooled shaft.

10. The conveyor system of any one of claims 7-9 wherein the lateral cooling section comprises a water-cooled jacket.

11. The conveyor system of any one of claims 1-10 wherein the conveyor system is one of:

a wet ash conveyor system in which at least a lower portion of the elongated enclosed duct is flooded with water; or

a dry ash conveyor system in which the elongated enclosed duct is not flooded with water.

12. The conveyor system of any one of claims 1 -11 further comprising: a chain support configured to support the internal chain; and

a cooling apparatus in the chain support.

13. The conveyor system of any one of claims 1-12 wherein the chain conveyor includes at least a first chain conveyor with a water-cooled housing.

14. The conveyor system of any one of claims 1 -13 further comprising: an electronic controller configured to receive sensor readings indicative of a temperature of the chain conveyor and to control temperature of the chain conveyor based on the received sensor readings by controlling at least one of (i) flow of ash from the hopper to the chain conveyor by controlling a flow control device configured to control the flow of ash from the hopper to the receiving section of the chain conveyor and/or (ii) a speed of the chain conveyor.

15. A conveyor system for removing ash, the conveyor system comprising: a hopper for collecting the ash, and

wherein the conveyor system does not include a grinder interposed in an ash flow path from the hopper to the chain conveyor.

16. The conveyor system of claim 15 wherein the chain conveyor comprises a top carry chain conveyor including a floor beneath the flights moving in the top section and above the flights moving in the bottom section, and wherein the top section moves the ash from the receiving section to the distal end.

17. The conveyor system of claim 16 wherein the conveyor system is a wet ash conveyor system in which the elongated enclosed duct is flooded to immerse both the flights in the top section and the flights in the bottom section.

18. The conveyor system of claim 15 wherein the chain conveyor comprises a bottom carry chain conveyor in which the bottom section moves the ash from the receiving section to the distal end, and wherein a spacing between adjacent flights is large enough to allow ash without grinding to fall between the flights moving in the top section to reach the bottom of the elongated enclosed duct.

19. The conveyor system of claim 18 wherein a spacing between the flights moving in the top section and the flights moving in the bottom section is effective for the flights moving in the top section to contact and break apart ash moved by the bottom section.

20. A method of maintaining a conveyor system for removing ash from a large-scale coal fired combustion device, the conveyor system comprising a hopper for collecting the ash and a chain conveyor arranged to receive ash from the hopper and transport the received ash, wherein the conveyor system does not include a bottom gate interposed in an ash flow path from the hopper to the chain conveyor, the method comprising:

with the chain conveyor running, taking a boiler that transfers ash to the hopper offline;

after taking the boiler offline, continuing running the chain conveyor to remove ash from the hopper and the chain conveyor and then stopping the chain conveyor.

21. A conveyor system for removing ash from a large-scale coal fired combustion device, the conveyor system comprising:

a hopper for collecting the ash, and

a chain conveyor having a chain conveyor housing that is separate from the hopper, an elongated enclosed duct with a receiving section positioned for receiving the ash from the hopper, and having an internal chain for transporting the ash from the hopper to a distal end of the chain conveyor for discharge from the chain conveyor, the chain conveyor having a bottom section and a top section, flights moving in the top section and flights moving bottom section moving in opposite directions with one of the top or bottom sections moving the ash from the receiving section to the distal end; wherein the hopper and the conveyor system are dry and the conveyor system further includes a cooling apparatus disposed in the hopper and/or in the chain conveyor and/or interposed between an ash discharge of the hopper and the receiving section of the chain conveyor.

22. The conveyor system of claim 21 wherein the cooling apparatus includes:

a lateral cooling section interposed between the ash discharge of the hopper and the receiving section of the chain conveyor, wherein an ash movement apparatus is disposed in the lateral cooling section.

23. The conveyor system of claim 22 wherein the ash movement apparatus comprises a mechanical screw disposed in the lateral cooling section.

24. The conveyor system of claim 23 wherein the mechanical screw includes a water-cooled shaft.

25. The conveyor system of any one of claims 22-24 wherein the lateral cooling section comprises a water-cooled jacket.

26. The conveyor system of any one of claims 21-25 wherein the lateral cooling section comprises a water-cooled jacket of the chain conveyor.

27. The conveyor system of any one of claims 21-26 further comprising: a chain support configured to support the internal chain; and

a cooling apparatus in the chain support.

28. The conveyor system of any one of claims 21-27 further comprising: an electronic controller configured to receive sensor readings indicative of a temperature of the chain conveyor and to control temperature of the chain conveyor based on the received sensor readings by controlling at least one of (i) flow of ash from the hopper to the chain conveyor by controlling a flow control device configured to control the flow of ash from the hopper to the receiving section of the chain conveyor and/or (ii) a speed of the chain conveyor.