Description:FIELD OF THE INVENTION
This invention relates to a system for recovery and charging of bed material in Atmospheric Fluidized Boiler (AFB). The said system is consisting of a bed material drain assembly, a sieve shaker assembly for segregation of bed material drained from Atmospheric Fluidized Boiler (AFB), an elevator assembly for lifting of the bed material at elevated height for increasing its gravitational potential energy and a storage and supply assembly for storing of the bed material at elevated height and feeding it at a pressure higher than a furnace pressure of the Atmospheric Fluidized Boiler (AFB).
The said system prevents frequent load reduction during bed material charging while Atmospheric Fluidized Boiler (AFB) is in operation and reduces the shutdown time during fresh charging of bed material during lit up of Atmospheric Fluidized Boiler (AFB). The said invention helps in safe operation and maintains a uniform load by accurate control of combustion in Atmospheric Fluidized Boiler (AFB) which satisfies end requirements. The said system prevents chronic problem of cracking of bed drain pipes of Atmospheric Fluidized Boiler (AFB)
BACKGROUND OF THE INVENTION
Economically operating the Atmospheric Fluidized Boiler (AFB) by burning of fuel in environmentally acceptable conditions is challenging. To achieve this, fuel combustion is carried out in a bed of crushed refractory or sand known as a bed material. In the Atmospheric Fluidized Boiler (AFB) air is blown through a bed of sand and fuel particles at a velocity that is sufficient to suspend the particles on the air stream but not able to lift the particles permanently out of the bed. Advantages of the fluidised bed combustion process along with design and operating characteristics of Atmospheric Fluidized Boiler (AFB) offers number of advantages for industrial steam and power generation.
In the Atmospheric Fluidized Boiler (AFB), combustion temperature is maintained below the fuel ash softening temperature. This limit the formation of nitrogen oxides and low-grade fuels can also be burned without the risk of slagging and fouling in the Atmospheric Fluidized Boiler (AFB). In comparison to the conventional boilers, the Atmospheric Fluidized Boiler (AFB) design is less dependent on type of fuel and fuel ash characteristics due to lower operating temperatures.
In the Atmospheric Fluidized Boiler (AFB), fuel coal is fed to crusher through a conveyor belt taking coal from coal yard. The crushed coal of around 6 mm diameter is then fed to a coal bunker through bucket elevator. From bunker this coal is fed to combustion chamber/furnace through feeder and coal burner with the help of Primary air (PA). In the combustion chamber/furnace this coal is burnt with air and the high temperature flue gas then pass through bed coil, membrane coil, superheater coil and economizer, air preheater (APH) and release its heat to feed water, saturated steam and air before it finally discharge to atmosphere through chimney.
In the furnace of the Atmospheric Fluidized Boiler (AFB), bed material is used to support fluidization of the bed. Bed material is little heavier and rounded spherical shaped particles of 2-3 mm in size and allows uniform primary air distribution for good fluidization. At the same time, it ensures excellent turbulence for combustion with minimum excess air. This helps the combustion with minimum un-burnt and stacks losses. Due to this, bed material fluidized-bed boilers or Atmospheric Fluidized Boiler (AFB) have high heat transfer coefficients, have a uniform temperature distribution, and have a low stable combustion temperature.
Normally bed material is charges when lot of stones and foreign particles are observed inside the bed material and required bed height is not maintained.
Bed material is charged through manholes and during charging it is necessary to reduce the furnace pressure to negative for avoiding back fire from manholes. If furnace pressure remains high during charging of bed material, then flame can come out through manholes and hurt the person charging the bed material. It is a safety hazard and unsafe conditions that can cause injury and illness. Reduction in Forced Draft (FD) fan pressure results into reduction in the load of the boiler.
In addition to above, during boiler start-up, it is necessary to charge fresh and recovered bed material around in a quantity of 15000-20000 kg through manholes which delays the lit-up time of boiler around three to four hours.
DESCRIPTION OF THE RELATED ART
Gutraj et al. provided an overview of the fuel handling requirements, combustion characteristics, emissions control, and project economics of Atmospheric Fluidized Bed Combustion (AFBC) technologies as applied to both new and retrofit boilers along with the discussion on advantages, disadvantages, problems, and solutions. (USACERL TECHNICAL REPORT FE-93/08, November 1992)
Fuller et al. (Energy Studies Review Volume 12, No.2 2004 pp143-l52) presented a performance benchmark study of the Atmospheric Fluidized Bed Combustion (AFBC) plants with three primary purposes (i) to start the process of developing AFBC benchmarks on technical, cost, revenue, and environmental issues, (ii) to inform AFBC owners and operators of contemporary concerns and issues in the industry and, (iii) to improve decision making in the industry with respect to current and future plant start-ups and on-going operations.
Utility model publication no. CZ7066U1 discloses the technical solution refers to a fluid boiler with a stationary atmospheric hearth, where the combustion of solid fuels is solved in a stationary atmospheric fluid layer with enhanced circulation of particles inside the hearth. Patent no. US4228767 discloses a fire tube boilers employing fluidized bed combustion. Patent no. US5255507 discloses a combined cycle power plant incorporating an atmospheric circulating fluidized bed boiler and gasifier.
OBJECT OF THE INVENTION
Principal object of the present invention is to provide a system that; drains bed material from the furnace of the Atmospheric Fluidized Boiler (AFB), segregates the reusable bed material of required size from the drained bed material, convey and store segregated reusable and fresh bed material at elevation and provide controlled charging of the required quantity of bed material to the furnace of the Atmospheric Fluidized Boiler (AFB).
Another object of the present invention is to provide a system for draining of bed material from the furnace of the Atmospheric Fluidized Boiler (AFB) that prevents heat loss and reduces maintenance required.
Another object of the present invention is to provide a system that reduces the overall Atmospheric Fluidized Boiler (AFB) operating cost by segregating and reusing the bed material of required size from the drained bed material.
Another object of the present invention is to provide the system that provides intermediate charging of the bed material in the furnace of the Atmospheric Fluidized Boiler (AFB) at a pressure higher than the furnace pressure of the Atmospheric Fluidized Boiler (AFB) without opening of the man holes.
Another object of the present invention is to provide a system for intermediate charging of the bed material to the furnace of the Atmospheric Fluidized Boiler (AFB) without reducing the Atmospheric Fluidized Boiler (AFB) load and thereby streamlining the Atmospheric Fluidized Boiler (AFB) operation.
Another object of the present invention is to reduce lit up time of the Atmospheric Fluidized Boiler (AFB) by reducing the initial charging time for bed material.
Conventional bed material draining system is consists of drain pipes evenly distributed in the bed of a wind box and a sliding valve provided at bottom of drain pipes outside the wind box. These drain pipes normally remain filled with high temp bed material. Bed material can be drained from the furnace by opening of the sliding valve provided at bottom of the drain pipes. Heat loss is occurred from the high temperature bed material accumulated in the drain pipes. Further, drain pipes are fixed inside the wind box by welding with an upper and a lower plate of the wind box. The drain pipes are heated because of the high temperature bed material accumulated inside it resulting into distortion of the drain pipes and failure of the welded joints. Drain bed material also contains particle of required size along with oversize and undersize particles. If particles with required size is segregated and reuse then it results into considerable reduction in the quantity and cost of bed material.
Present invention prevents failure of the bed material drain pipes, prevents accidents due to backfire, provide intermediate charging of bed material without reducing Atmospheric Fluidized Boiler (AFB) load, reduces the lit up time of the Atmospheric Fluidized Boiler (AFB) and reduces overall operating cost of the Atmospheric Fluidized Boiler (AFB).
SUMMARY OF THE INVENTION
A system for recovery and charging of bed material in Atmospheric Fluidized Boiler (AFB) as per the present invention is consisting of a bed material draining assembly, a sieve shaker assembly, an elevator assembly and a storage and supply assembly.
The bed material draining assembly drains bed material from the furnace. The sieve shaker assembly receives the bed material from the bed material draining assembly and segregates it into over size, under size and required size bed material. The elevator assembly lifts the segregated required size bed material from the sieve shaker assembly at elevated height for increasing its gravitational potential energy. The storage and supply assembly receives the required size bed material from the elevator assembly, stores it at elevated height and feed it at a pressure higher than a furnace pressure of the AFB.
Bed material from a furnace is drained by operating a sliding valve provided in drain pipes at top of the wind box just below a wind plate.
The drained bed material from the furnace is segregated into drain bed material, required size bed material and under size bed material using a sieve screen-1 and sieve screen-2 and collected into drain bed material, required size bed material and undersize bed material compartment. Pattern of vibration of the sieve screen-1 and the sieve screen-2 is circular and are positioned at an inclination for discharging segregated bed material in appropriate compartment using gravity. Using the elevator assembly, the required size bed material segregated and collected in the required size bed material compartment is transferred to the storage and supply assembly. The drained bed material is segregated in three groups of grain size above 3 mm, 2-3 mm and below 2 mm respectively. The bed material having grain above 3 mm is collected in the drain bed material compartment, bed material of required grain size of 2-3 mm is collected in the required size bed material compartment and drained bed material having grain size below 2 mm is collected in the under size bed material compartment.
The storage and supply assembly collects and store segregated required size bed material and fresh bed material in hoppers. The hoppers are of inverted frustum shape for generating gravity flow of the bed material. Total volume of the hoppers is kept to charge 15000 – 20000 kg per hour of the bed material during start-up of boiler. Bed material from the hoppers is supplied to the furnace above the required bed material height in the furnace. An angle of the bed material feeding pipe is kept more than the angle of repose of bed material. Sliding valves are provided at bottom of the hopper for isolating the bed material feeding pipe for maintenance purpose. A rotary air valve (RAV) along with driving mechanism is provided in the bed material feeding pipe after the sliding valves to control the flow of bed material to the furnace avoiding heaping of bed material in one place. Flow of the bed material to the furnace is controlled by controlling rpm (revolution per minute) of the rotary air valve (RAV). An auxiliary air supply line is used for supplying an auxiliary air in the bed material feeding pipe for aiding feeding of the bed material into the furnace at a pressure higher than a furnace pressure of the Atmospheric Fluidized Boiler (AFB).
BRIEF DESCRIPTION OF THE DRAWINGS
The features of the invention as per the present patent application are described with reference to the following drawings in which like elements are labeled similarly. The present invention will be more clearly understood from the detailed description and the accompanying drawings, wherein:
FIG. 1 is a schematic diagram showing system for recovery and charging of bed material in Atmospheric Fluidized Boiler (AFB).
FIG. 2 is a schematic diagram showing a bed material draining assembly.
FIG. 3 is a schematic diagram showing a sieve shaker assembly.
FIG. 4 is a schematic diagram showing an elevator assembly.
FIG. 5 is a schematic diagram showing a storage and supply assembly (5).
List of designations/ reference numbers in figure
1. a system for recovery and charging of bed material
2. a bed material draining assembly
3. a sieve shaker assembly
4. an elevator assembly
5. a storage and supply assembly
6. a plurality of drain pipes
7. a bed
8. a wind box
9. drained bed material
10. a furnace
11. a sliding valve
12. a wind plate
13. a means for manual and automatic operating the said sliding valves (10)
14. segregated over size bed material
15. segregated under size bed material
16. segregated required size bed material
17. a frame of the sieve shaker assembly (3)
18. a vibrating mechanism
19. a drain bed material compartment
20. a required size bed material compartment
21. an under size bed material compartment
22. a sieve screen-1
23. a sieve scree-2
24. elevator buckets
25. elevator chains
26. an elevator drum
27. a driving mechanism
28. a head pulley
29. a discharge spout
30. a hopper for collecting and storing segregated required size bed material (16)
31. a hopper for storing fresh bed material (32)
32. fresh bed material
33. sliding valves provided at bottom of the hopper (30, 31)
34. a rotary air valve (RAV)
35. a driving mechanism
36. a bed material feeding pipe
37. an angle of a bed material feeding pipe with horizontal
38. an auxiliary air supply line
DETAILED DESCRIPTION OF THE INVENTION
The following description of the preferred embodiment(s) is merely exemplary in nature and is in no way intended to limit the invention, its application, or uses.
The description of illustrative embodiments according to principles of the present invention is intended to be read in connection with the accompanying drawings, which are to be considered as a part of the entire written description. In the description of embodiments of the invention disclosed herein, any reference to direction or orientation is merely intended for convenience of description and is not intended in any way to limit the scope of the present invention. Relative terms and directives thereof are for convenience of description only and do not require that the apparatus be constructed or operated in a particular manner unless explicitly indicated as such. Terms such as “attached,” “affixed,” “connected,” “coupled,” “interconnected,” and similar refer to a relationship wherein structures are secured or attached to one another either directly or indirectly through intervening structures, as well as both movable or rigid attachments or relationships, unless expressly described otherwise. Moreover, the features and benefits of the invention are illustrated by reference to the exemplified embodiments. Accordingly, the invention expressly should not be limited to such exemplary embodiments illustrating some possible non-limiting combination of features that may exist alone or in other combinations of features; the scope of the invention being defined by the claims appended hereto.
FIG. 1 shows a schematic diagram of a system for recovery and charging of bed material (1) in Atmospheric Fluidized Boiler (AFB) as per the present invention.
As shown in FIG. 1, a system for recovery and charging of bed material (1) in Atmospheric Fluidized Boiler (AFB) is consisting of a bed material draining assembly (2), a sieve shaker assembly (3), an elevator assembly (4) and a storage and supply assembly (5).
FIG. 2 shows the bed material draining assembly (2) used for draining of bed material (9) from the furnace (10) of the Atmospheric Fluidized Boiler (AFB). The bed material draining assembly (2) is consisting of a plurality of drain pipes (6) evenly distributed in a bed (7) of a wind box (8), a sliding valve (11) for opening and closing of the drain pipe (6) and a means (13) for manual and automatic operating the sliding valves (11). The sliding valve (11) is provided at top of the drain pipe (6) just below a wind plate (12). The drain pipes (6) are in communication with the furnace (10) i.e. one end of the drain pipe is located and kept open in the furnace (10) of the Atmospheric Fluidized Boiler (AFB) for draining of bed material (9) from the furnace (10). As the sliding valve (11) is position on the top side of the drain pipe (6), it remains empty when the sliding valve (11) is in close position. In conventional design, sliding valve is provided at bottom of the drain pipes outside the wind box for ease of operating. In this case, drain pipes remain filled with high temp bed material. This results into heat loss and heating of the drain pipes. As the drain pipe is fixed by welding between top and bottom plates of wind box, frequent failure of the welding joints are observed because of distortion of these drain pipes due to heating. Problem of energy loss and frequent failure of the welding joints associated with the bed material drain pipe is resolved in the bed material draining assembly (2) as per the present invention. The drain pipes (6) are preferably made up of carbon steel pipes of 4 inch diameter.
FIG. 3 shows a sieve shaker assembly (3) for segregation of the drained bed material (9) from the furnace (10) of the Atmospheric Fluidized Boiler (AFB). As shown in FIG. 3, the sieve shaker assembly (3) is consisting of a frame (17), a vibrating mechanism (18), a drain bed material compartment (19), a required size bed material compartment (20), an under size bed material compartment (21), a sieve screen-1 (22) partitioning the drain bed material compartment (19) and the required size bed material compartment (20) and a sieve scree-2 (23) partitioning the required size bed material compartment (20) and the under size bed material compartment (21). The sieve shaker assembly (3) receives the drained bed material (9) from the furnace (10) and segregates it into over size bed material (14), under size bed material (15) and required size bed material (16). For the purpose, the drained bed material (9), drained from the furnace (10) using the drain pipes (6) are discharges into the drain bed material compartment (19). Pattern of vibration of the sieve screen-1 (22) and the sieve screen-2 (23) is circular. The sieve screen-1 (22) and the sieve screen-2 (23) are positioned at an inclination for discharging segregated bed material in appropriate compartment using gravity. The drained bed material (9) is segregated in three groups of grain size above 3 mm, 2-3 mm and below 2 mm respectively. Mesh size of the sieve screen-1 (22) is such that it allows the bed material having grain up to 3 mm to pass through it and retains the bed material having grain size above 3 mm. Mesh size of the sieve screen-2 (23) is such that it allows the bed material having grain size below mm to pass through it and retains the bed material having grain size above 2 mm. Thus, on vibrating the sieve screen-1 (22) and sieve screen-2 (23) using the vibrating mechanism (18), the bed material having grain size above 3 mm retains in the drain bed material compartment (19), the bed material having grain size of 2-3 mm is collected in the required size bed material compartment (20) and drained bed material having grain size below 2 mm is collected in the under size bed material compartment (21). Bed material above 3 mm and below 2 mm grain size collected in the drain bed material compartment (19) and the under size bed material compartment (21) respectively are disposed of and bed material having grain size of 2-3 mm accumulated in the required size bed material compartment (20) is reused. This results into considerable reduction in the operating cost of Atmospheric Fluidized Boiler (AFB).
FIG. 4 shows an elevator assembly (4) for lifting of the segregated required size bed material (16) at elevated height for increasing its gravitational potential energy. As shown in FIG. 4, the elevator assembly (4) is consist of elevator buckets (24) mounted on elevator chains (25), an elevator drum (26) along with a driving mechanism (27) for driving the elevator chains (25), head pulleys (28) supporting the elevator chains (25) and a discharge spout (29) positioned at top of the elevator assembly (4) for collecting the required size bed material (16) flung out of the elevator buckets (24) due to centrifugal force. The sieve shaker assembly (3) and the elevator assembly (4) are connected using appropriate means so that the bed material having grain size of 2-3 mm collected in the required size bed material compartment (20) of the sieve shaker assembly (3) is carried by the elevator buckets (24) of the elevator assembly (4).
FIG. 5 shows the storage and supply assembly (5) for storing of the required size bed material (16) and fresh bed material (32) at elevated height and feeding it at a pressure higher than a furnace pressure of the Atmospheric Fluidized Boiler (AFB).
As shown in FIG. 5, the storage and supply assembly (5) is consisting of a hopper (30) for collecting and storing segregated required size bed material (16) from the discharge spout (29) of the elevator assembly (4), a hopper (31) for storing fresh bed material (32), a bed material feeding pipe (36) connected to the hopper (30, 31) at one end and opened into the furnace (10) above the required bed material height in the furnace (10), sliding valves (33) provided at bottom of the hopper (30, 31) for isolating the bed material feeding pipe (36) for maintenance purpose, a rotary air valve (RAV) (34) provided in the bed material feeding pipe (36) after the sliding valves (33) to control the flow of bed material (16, 32) to the furnace (10) avoiding heaping of bed material in one place, a driving mechanism (35) (not shown in FIG.) for operating the rotary air valves (RAV) (34). An angle (37) of the bed material feeding pipe (36) with horizontal is kept 45 degree. The angle (37) of the bed material feeding pipe (36) with horizontal shall be maintained greater than the angle of repose of bed material. The flow of the bed material is controlled by controlling rpm (revolution per minute) of the rotary air valve (RAV) (34). An auxiliary air supply line (38) is provided for supplying an auxiliary air in the bed material feeding pipe (36) for aiding feeding of the bed material (16, 32) into the furnace (10) at a pressure higher than a furnace pressure of the Atmospheric Fluidized Boiler (AFB).
Total volume of the hoppers (30, 31) is kept to charge 15000 – 20000 kg per hour of the bed material during start-up of boiler. The hoppers (30, 31) are of inverted frustum shape for generating gravity flow of the bed material. The storage and supply assembly (5) is capable of charging the bed material in the furnace (10) of the Atmospheric Fluidized Boiler (AFB) at a pressure higher than a furnace pressure.
BEST METHOD OF PERFORMING THE INVENTI ON
A system for recovery and charging of bed material (1) in Atmospheric Fluidized Boiler (AFB) as per present invention is implemented in 1×30 TPH 35.00 Kg/cm2g, saturated Coal Fired AFB Boiler with following specifications.
Boiler type: AFB, Single Drum Water tube
Installation: Outdoor
Type of circulation: Natural
Type of support: Bottom Supported
Boiler Design Code: IBR with latest amendments
Boiler capacity, Maximum Continuous Rating (MCR): 30 TPH
Peak capacity of boiler: 110 % of MCR for 30 min in 8 hrs
Steam temperature at Main Steam Stop Valve (MSV) outlet: 320 ± 5 0C
Steam pressure at Main Steam Stop Valve (MSV): 32.00 atm
Fuel: Indian/Imported Coal
Fuel Size: Less than 6 mm
Boiler performance testing: ASME PTC 4.1
Indirect method flue gas
Temperature at air pre heater outlet: 140 - 150 0C
The specified MCR rating is the gross output at main steam stop valve excluding any auxiliary requirement of AFB.
Fuel Specification
The AFB is designed for both Indian as well as imported coal. Specification of the fuel is as below. The AFB is to be operated either using Indian coal or using imported coal or using combination of Indian and imported coal.
Sr. No. Element Content
1 Carbon, As-received Basis (ARB) 37.7 %
2 Hydrogen (ARB) 3.7 %
3 Sulphur (ARB) 0.4 %
4 Oxygen (ARB) 35 %
5 Total Moisture 18.5 %
6 Gross calorific value (GCV), Kcal / Kg 5600 - 5800
7 Size 6 mm

The design, materials and construction of the AFB is in accordance with Indian Boiler Regulations (IBR) 1950, (with the latest amendments) and International Standard Organization (ISO) Code.
TEMPERATURE PROFILE
Flue Gas Temperature
Bed temperature: 850 - 900 0C
Shell inlet temperature: 450 - 475 0C
Shell outlet temperature: 210 - 230 0C
Air Pre-heater Outlet temperature: 140 - 150 0C
Boiler Air Heater
Arrangement: Staggered and multi tubular
Tube size (Outer diameter x Thickness): 60.3 mm x 2.5 mm
Tube material: mild steel
Type of flow: Counter flow
No. of flue gas passes: 2
Inside tubes: Gas
Outside tubes: Air
FLUIDISED BED
No. of compartment: 4
Bed plate material: IS2062
Fuel nozzle material: Mild steel + Stainless steel TIP ON TOP
No of fuel nozzles: 8
Material of air nozzle: Stainless steel
Method of nozzle attachment to bed plate: Tag welded
No. of bed drain pipes per compartment: 3
Ash drain pipe material: Mild steel
Fluidization velocity: 2.5 - 2.7 m/s
TECHNICAL SPECIFICATIONS
Type: Single drum water tube
Atmospheric Fluidized Bed Combustion
Type of circulation: Natural
Type of support: Bottom Supported
No. of boilers: One
Boiler Design Code: IBR1950 with latest amendments
Heat transfer area of boiler: 900 + 350 m²
Twin - BED TUBE ASSEMBLY
Type of tube arrangement: Staggered arrangement, studded
Tube Size (Outer diameter x Thickness) : 63.5 mm x 6.35 mm
Bed tube material: BS – 3059 SEAMLESS.
Header material: SA 106 Gr. B
7 WALLS, 2 PASS, TWIN FURNACE WATER WALL ASSEMBLY
Type of construction: Fin welded membrane
Tube size (Outer diameter x thickness): 63.5 mm x 3.66 mm
Tube material: BS – 3059 ERW PT-1 Gr 320
Header material: SA 106 Gr B
Fin material and thickness: IS 2062 and 4 mm
ECONOMIZER
Quantity: 1 Nos.
Type: Horizontal, drainable
Arrangement: Inline
Material of construction: SA 516 Gr 70
Tube Size (Outer diameter x thickness): 50.8 mm x 4.06 mm
Tube Material: BS – 3059 ERW PT - 1 Gr 320
CONVECTIVE SUPER-HEATER
Type of super heater: Bare tube counter flow
Economizer tube material: ASTM A335 P11
Size of super heater tubes (Outer diameter x thickness): 38.1 mm x 3.25 mm
Tube arrangement: Staggered
No. of passes: 1
Heating Surface Area: 65 Square meter
FUEL FEEDING SYSTEM
Type of Feeders: Pocket type rotary Feeder
Location: Below service hopper
Number of feeders: 6
Feeder drive rating: 2 HP
Type of feed control system: Variable Frequency Drive (VFD)
No. of branch feed lines from single feeder: 2
Bunker bottom opening size: 400 x 600 mm
BOILER FEED WATER PUMPS
Model: Standard
Type: Vertical, Multi stage centrifugal
Fluid temperature: 140 0C
Flow: 40 m3/hr
Head: 400 mm Wc
Speed: 2900 rpm
No. of stages: Multi stage
Motor rating: 75 HP
Material of construction: Stainless steel
INDUCED DRAFT (ID) Fan
Qty.: 1
Flow:1200 m³/min
Head: 300 mm WC (i.e. water column)
Medium: Flue Gas
Speed: 1440 rpm
Type of connection: Direct coupled
Motor rating: 125 HP
Type of control system: Damper
FORCED DRAFT (FD) Fan
Qty.: 2
Flow: 525 m³/min - each
Head: 600 mm WC - each
Medium: Ambient air
Speed: 1440 rpm
Type of connection: Direct coupled
Motor rating: 75 HP - each
Type of control system: Damper
PRIMARY AIR (PA) Fan
Qty.: 2
Flow: 100 m³/min - each
Head: 700 mm WC - each
Medium: Air
Speed: 2900 rpm
Type of connection: Direct coupled
Motor rating: 20 HP - each
Type of control system: Damper
All motors are VFD driven
SAFETY VALVES
Location: On Steam drum
Qty.: 2 nos.
Type: Spring loaded mechanical safety valve
REFRACTORY
Type of material used: Cast able refractory
Casing plate thickness: 5 mm
INSULATION
Insulation Material: LRB
Density: 100 Kg/m3
Insulation surface finish: Aluminium cladding 24 SWG , Claims:We claim:
1. A system for recovery and charging of bed material (1) in Atmospheric Fluidized Boiler (AFB) consisting of:
• a bed material draining assembly (2) in communication with a furnace (10) of the Atmospheric Fluidized Boiler (AFB) for draining of bed material (9) from the furnace (10);
• a sieve shaker assembly (3) in communication with the bed material draining assembly (2) for segregation of the drained bed material (9) from the furnace (10) into over size bed material (14), under size bed material (15) and required size bed material (16);
• an elevator assembly (4) in communication with the sieve shaker assembly (3) for lifting of the segregated required size bed material (16) at elevated height for increasing its gravitational potential energy and;
• a storage and supply assembly (5) in communication with the elevator assembly (4) for storing of the required size bed material (16) at elevated height and feeding it at a pressure higher than a furnace pressure of the Atmospheric Fluidized Boiler (AFB)
characterized in that wherein
? the bed material draining assembly (2) is consisting of a plurality of drain pipes (6) evenly distributed in a bed (7) of a wind box (8) to drain bed material (9) from a furnace (10), a sliding valve (11) provided at top of the wind box (8) just below a wind plate (12) along with a means (13) for manual and automatic operating the sliding valves (11),
? the sieve shaker assembly (3) is consisting of a frame (17), a vibrating mechanism (18), a drain bed material compartment (19), a required size bed material compartment (20), an under size bed material compartment (21), a sieve screen-1 (22) partitioning the drain bed material compartment (19) and the required size bed material compartment (20) and a sieve scree-2 (23) partitioning the required size bed material compartment (20) and the under size bed material compartment (21) wherein, the drain bed compartment (19) is in communication with the drain pipes (6) for discharging of the drained bed material (9) from the furnace (10) into the drain bed material compartment (19), pattern of vibration of the sieve screen-1 (22) and the sieve screen-2 (23) are positioned at an inclination for discharging segregated bed material in appropriate compartment using gravity,
? the elevator assembly (4) is consist of elevator buckets (24) mounted on elevator chains (25), an elevator drum (26) along with a driving mechanism (27) for driving the elevator chains (25), a head pulley (28) supporting the elevator chains (25) and a discharge spout (29) positioned at top of the elevator assembly (4) for collecting the required size bed material (16) flung out of the elevator buckets (24) due to centrifugal force and,
? a storage and supply assembly (5) is consisting of a hopper (30) for collecting and storing segregated required size bed material (16) from the discharge spout (29) of the elevator assembly (4), a hopper (31) for storing fresh bed material (32), a bed material feeding pipe (36) connected to the hopper (30, 31) at one end and opened into the furnace (10) above the required bed material height in the furnace (10) wherein an angle (37) of the bed material feeding pipe (36) is kept more than the angle of repose of bed material, sliding valves (33) provided at bottom of the hopper (30, 31) for isolating the bed material feeding pipe (36) for maintenance purpose, a rotary air valve (RAV) (34) provided in the bed material feeding pipe (36) after the sliding valves (33) to control the flow of bed material (16, 32) to the furnace (10) avoiding heaping of bed material in one place, a driving mechanism (35) for operating the rotary air valves (RAV) (34), and an auxiliary air supply line (38) for supplying an auxiliary air in the bed material feeding pipe (36) for aiding feeding of the bed material (16, 32) into the furnace (10) at a pressure higher than a furnace pressure of the Atmospheric Fluidized Boiler (AFB).
2. The system for recovery and charging of bed material (1) in Atmospheric Fluidized Boiler (AFB) as claimed in claim 1, wherein the drained bed material (9) is segregated in three groups of grain size above 3 mm, 2-3 mm and below 2 mm respectively wherein the bed material having grain above 3 mm is collected in the drain bed material compartment (19), bed material of required grain size of 2-3 mm is collected in the required size bed material compartment (20) and drained bed material having grain size below 2 mm is collected in the under size bed material compartment (21).
3. The system for recovery and charging of bed material (1) in Atmospheric Fluidized Boiler (AFB) as claimed in claim 1, wherein the flow of the bed material is controlled by controlling rpm (revolution per minute) of the rotary air valve (RAV) (34).
4. The system for recovery and charging of bed material (1) in Atmospheric Fluidized Boiler (AFB) as claimed in claim 1, wherein total volume of the hoppers (30, 31) is kept to charge 15000 – 20000 kg per hour of the bed material during start-up of boiler.
5. The system for recovery and charging of bed material (1) in Atmospheric Fluidized Boiler (AFB) as claimed in claim 1, wherein the hoppers (30, 31) are of inverted frustum shape for generating gravity flow of the bed material.
6. The system for recovery and charging of bed material (1) in Atmospheric Fluidized Boiler (AFB) as claimed in claim 1, wherein the bed material is charged in the furnace (10) of the Atmospheric Fluidized Boiler (AFB) at a pressure higher than a furnace pressure.