cfb design description

8/18/2019 CFB Design Description

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CF oiler Design Specification page 1 of 10

Part 1. Summary

This product is a 55t/h CFB boiler with sub-high pressure and sub-high temperature based on the CFB

combustion technology which was developed in recent years. And this product is purified based on the

CFB boiler experience which was developed by the Wuxi Huaguang Boiler Co., Ltd and the famous

Chinese institutions for many years. Besides, the experience of successful operating of the same type

boiler is also for reference here.

The structure of this boiler is simple, compact, and be similar to traditional pulverized coal furnace.

The boiler proper is consisted by the combustion equipments, the coal feeder, the under-bed igniting

equipment, the separation unit and the back feeding device, the water-cooling system, superheater,

economizer, air preheater, steel frame, platform & stairs, furnace walls.

Part 2. Boiler parameter

Rated evaporation 75t/h

Rated steam pressure 6.3MPa

Rated steam temperature 485℃

Feed water temperature 150℃

Smoke-exhausted temperature ~ 150℃

Boiler designed efficiency 88.2%

Sewage rate 2%

Range of boiler safe and stable operating conditions 80~100%(load)

Steel consumption of boiler proper (ton) 510

Steel consumption of steel frame (ton) 145

Part 3. Main technical data of boiler

1.

Boiler external dimension (the max.): height × width × depth = 35000×13200×16600 mm.

2.

Distance between the left column and the right column: 6800mm, distance between the front and the

left column: 13100mm.


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3. Water volume of boiler pressure parts: when the hydrostatic test is done, it is 35 m3. When the boiler

is cooking, it is 28m3.

4. Drum central elevation is 31850mm.

Elevation of the running layer (cement concrete) is 7000mm.

Elevation of the operating layer (cement concrete) is 4200mm.

Part 4. Boiler Structure

1) The combustion device:

The fluidized air distributors adopt the water-cooling air distributor structure, and the effective area is

9.1m2. The air distributor is equipped with 299 bell wind caps, the insulating concrete and the refractory

concrete could be filled on the air plates.

Air is divided into the primary air and the secondary air. PA: SA is about 55: 45. The primary air is sent

from two sides of the water-cooled wind chamber, then it goes into the combustion chamber through the

hood holes on the air distributors. The secondary air is distributed by two layers on height direction of

the air distributor.

Two(Ф 219) slag-discharging tubes are arranged on the air distributor (besides, every

slag-discharging tube is connected with one (Ф 219 ) accident slag-discharging tube), and the slag

cooler can be linked here (supplied by the user).

Suggestion: During the operation process, the slag cooler can discharge slag discontinuously

according to differential pressures.

Bottom of the water-cooling air chamber is equipped with two (Ф 108) slag- discharging tubes, so

that the fouling in the water-cooling air chamber could be removed regularly.

2) Coal-feeding device:


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Three coal-feeding tubes are arranged on boiler front. Coal is sent into the combustion chamber through

coal-feeding tube. Coal-sending air and coal-spreading air are arranged on coal-feeding tube to avoid

clogging. The coal-sending air connects to the primary cool air; the coal-spreading air connects to the

primary hot air. Totally they take 4 percentage of total air volume. Every air-sending tube or

coal-spreading air duct is arranged with one air door (designed by the design institute), so that the

coal-sending air volume could be regulated. The coal inlet is linked with the combustion chamber

1500mm far away form the air caps.

Suggestion: The belt coal feeder with sealed weighing device is adopted by the user, and the installation

position of the coal feeder is designed by the design institute.

3 ) Under-bed ignition device

This technology of “water-cooling air distributors, under-bed oil gun ignition” is adopted in this boiler.

The oil gun would be burnt in the under-bed pre-combustion chamber. And then, by mixing with the

cool air, the high-temperature smoke (


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5) Drum and its internal devices

The drum internal diameter is Ф 1380mm, wall thickness is 60mm. The drum internal device is

composed by the cyclone separator, the top shuffle, the dosing pipe, the sewage tube, the recycle tube

and the emergency water-discharging tube. Besides, the drum is also equipped with the high, low-read

water level meters, the pressure gauge, the safety valve, the steam-discharging valve and the auxiliary

steam valve. 50mm below the drum central line is the normal water level, 75mm far away from the

normal water level is the boundary-beyond alarming line, and 120mm far away from the normal water

level is the limit alarming line.

6) Water-cooling system

The furnace waterwall adopt the full-suspension membrane wall structure, the furnace room is divided

into the left, right, front, back loops. Tube diameter of the membrane wall isФ60×5 (in water-cooling air

chamber, the front, back waterwall isФ51×5), pitch is 100mm. The rigid beams are arranged on furnace

surroundings, so there would be enough bearing capacity. The downcomer adopt the structure of “first

centralize, and then decentralize”. Two concentrated downcomers with diameter of Ф325×16 would be

introduced from the drum to boiler lower part. Then the dispersed downcomers would be led by the

concentration downcomers, four tubes (Ф108×4.5) for the front wall and two tubes (Ф133×6) for the

two side wall. About the steam-water connecting tube, there are four (Ф108×4.5) on each side wall, the

front- back wall is ofФ133×6, totally there are eight. On the wear and tear parts of waterwall, the fins or

pins could be welded, or the wear-resistant material could be polished.

7) Superheater system

The superheater system is arranged in the tail flue, and it is divided into the high-temperature section and

the low-temperature section. The flue gas flows from the high-temperature section to the low

temperature section. Tube diameter in high-temperature superheater section isФ32 × 4, pitch is 100mm,

and it is of counter-current arrangement, tube material is 12Cr1MoVG. Tube diameter of the upper part

of lower-temperature superheater section isФ32 ×4, pitch is 100mm, and it is also of counter -current


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arrangement. Tube material is of 15CrMoG. Tube diameter of the lower part of lower-temperature

superheater section isФ32 ×4, pitch is 100mm, counter-current arrangement; tube diameter is boiler tube

of 20G.

The high-temperature superheater and the low-temperature superheater would scour the first row of

tube along with the smoke, and the anti-wear cover plate is equipped.

To adjust the overheated steam temperature, the spray desuperheater is arranged between the

high-temperature superheater and the low-temperature superheater. And the maximum sprayed water

capacity is 10 tons.

The steam-collected header of superheater is equipped with many attachments, just like the pressure

gauge, the thermocouple, the safety valve, the steam-exhausted valve, the steam bypass valve and the

water discharge valve.

The high-temperature superheater tubes the low-temperature superheater tubes support each other

in the form of “tube-hanging-tube”. Two rows of high-temperature superheater tube and two rows of

low-temperature superheater tube are lifted by the suspension tube of every row.

8) Economizer

Two groups of economizer (the upper and the lower) are arranged in the superheater system of tail flue.

To protect wear and tear, the two economizer groups adopt the steel-tube economizer structure,

staggered, the horizontal pitch is 80mm and the vertical pitch is 45mm . Tube diameter isФ32 ×4. To

protect wear and tear, the two economizer groups would scour the first, second row of tubes, the

anti-wear cover plate would be installed; besides, the elbows would be installed with the anti-wear

cover.

9) Air preheater

As the air pressure is high, the horizontal air preheater is adopted to avoid air leakage. Smoke is out of

the tube and air is in the tube, using in-line arrangement, tube diameter is Ф40 ×1.5. The first row of

tube which would be scoured by the smoke adopt the tube with thick wall (Ф 42 ×3.5).

Tube box of preheater could be divided into three sections, the top one is the secondary air preheater, the


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horizontal pitch is 69mm, and the vertical pitch is 60mm. The lower two tube boxed are for the primary

air, the horizontal pitch is 68mm and the vertical pitch is 60mm.

10) Beam, columns, platform & stairs

The weight of boiler proper, the furnace walls, the pipeline and the attachments are bore by the steel frame,

it is transferred to the foundation by the steel frame, the steel frame adopt the frame structure. The boiler

room is suspended below the main girder on boiler top, the drum is supported on the main girder on boiler

top. Besides, other load is transferred to the vertical columsn by the relative horizontal beams or the

oblique rods.

For maintenance and operation, some layers of platform is installed on boiler surroundings, the

distance between them is about 3 meters, and platforms are connected by the stairs.

11) Furnace wall

For the furnace wall in dense zone above the air distributors, the high-strength wear-resistant castable

are adopted. The waterwall outside is the wall with tubes, and the outer casing. The high-temperature

cyclone shell, the horizontal flue and the tail flue adopt the structure of “light furnace wall and casing”.

Based on the characteristics of CFB boiler, the high-strength wear-resistant castable or the high-strength

wear-resistant bricks are adopted in boiler parts (like furnace room, high-temperature cyclone shell) to

guarantee boiler ’s safe and reliable operation. User should pay special attention to this point; see details

in the boiler installation instruction.

Thickness of the anti-wear layer in furnace inside: 80mm

Insulating thickness of furnace outside: 200mm

Thickness of furnace wall of cyclone shell: 350mm

Thickness of furnace wall of vertical tube, back-feeding device and back-feeding tube: 244mm

Thickness of the furnace wall which is above the low-temperature superheater area: 380mm

Thickness of the furnace wall which is below the low-temperature superheater area: 310mm

12) Sealing structure


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The flexible non-metallic expansion joint are adopted in furnace outlet and the inlet of high-temperature

cyclone shell to guarantee the sealing effect. The metal expansion joints are used on the back-feeding

tube. Besides, the superheater wall-crossing tube and the economizer wall-crossing tube are all equipped

with the expanding sealing structure.

13) Process of water-steam side of boiler proper

Feedwater ---- Economizer inlet header ----- Economizer pipeline ---- Economizer outlet header ----

Drum --- Downcomer ---- Waterwall lower header ---- Riser ---- Waterwall upper header ----

Steam-water connecting tube --- Drum---- Saturated steam introducing pipe ---- Inlet header of

suspension tube ---- Suspension tube bundles ---- Inlet header of low-temperature superheater ---- Tube

bundles of low-temperature superheater --- Spray desuperheater ---- Tube bundles of high-temperature

superheater ---- Outlet header of high-temperature superheater ---- Connecting tube --- Steam-collected

header

14) Process of smoke-ash side of boiler proper:

Coal feeding→Gas and recycle ash in combustion chamber→Furnace→High-temperature

cyclone separator→Turning room

↓↑ ↓Ash

← Back feeder

Slag-discharging

→High-temperature superheater→Low-temperature superheater→Economizer→Air

preheater for secondary air →Air preheater for primary air→Dust collector

15) Ash-blowing device

As the high-efficiency cyclone separator is adopted in this boiler, the ash which enters into the tail flue is

very tiny and the fouling in superheater might be very serious, the tubes (Ф219 × 6) would be embedded

on two side furnace walls in economizer area. To ensure that the steam parameter would be achieved when

the boiler is of low load, the ash blower must be installed by the user (and it is suggested to use the sonic


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soot blower).

16) Monitor of boiler process

Compared with the pulverized coal boiler, the CFB boiler is similar with it on the controlling method on

steam-water side. But they two own great difference on the combustion controlling. And the biggest

difference is the monitoring, adjusting of recycle material and the interlock protection which is special for

the CFB boiler.

Talking to the CFB boiler, it is of low-temperature combustion, its flame characteristic is greatly worse

than the pulverized coal boiler, So it would not equipped with the furnace flame monitor system (except

for the under-bed ignition device), but it pay great attention to the controlling of furnace bed temperature

and bed pressure, and the monitoring of the rate of air and coal, the adjusting and interlock protection, it

woks hard on the material fluidization, recycle, the monitor of the air volumes, so that a stable recycle

volume could be established and the ash balance, heat balance of boiler combustion could be guaranteed.

On the aspect of thermal controlling, the main difference between the CFB boiler and other

pulverized coal boiler are listed in the following:

16.1 The following ones are added in the closed-loop controlling system:

16.1 .1 Bed-temperature adjusting system;

16.1.2 Bed-pressure adjusting system;

16.1.3 SO2 emission system;

16.2 The following functions are added in the interlock protection system:

16.2.1 Under the following circumstance, the main-fuel trip would be caused because of the damage of

material recycle: the added primary air volume caused by main-fuel trip interlock is lower than the min.

data (the fluidization and loss of furnace bed material); the outlet pressure of back-feeding air is lower

than the min. data (the fluidization and loss of material in back-feeding valve); the rate between air and

fuel is 2min (or even worse) than the min. value.

16.2.2 The bed-temperature interlock function for fuel in-and-out is added (be equal to the support

condition of the nozzle ignition energy of pulverized coal boiler).


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16.2.3 The following function is added in furnace blowing logic: “after shutdown, if the bed temperature

is high enough, the MET relay would be returned back directly without furnace blowing”. By this means,

the heat storge function of CFB boiler material could be adopted, and the hot start-up could be carried

out directly without furnace blowing.

16.2.4 When the inlet, outlet smoke temperature of separator is higher than 480℃, the trip is caused

becase the drum water level is too low, the effect of waterwall cooling would not be good as many heat

material are existing in CFB boiler inside. If the superheater flow is less than 10% and the inlet, outlet

steam pressure is reduced to be smaller than 11Kpa, the effect of superheater cooling would not be good.

Both of the two conditions would caused the overheat protection act. It means that the inlet vane of the

primary air fan would point to 0, and the main controlling of air volume would be turned to manual.

16.2.5 As there is so many sets of air fan, the air fan interlock of CFB boiler would be much complex.

16.3 It is very difficult to measure out the following parameters of the monitor system:

16.3.1 The measuring of bed temeprature;

16.3.2 The measuring of bed pressure;

16.3.3 The measuring of the air volumes for fluidization or combustion.

16.4 Basic principle for the adjusting of boiler combustion system are listed:

adjust the coal-feeding volume according to the load requirements; the principle for coal-adjusting is

“ increase coal before the coal is added, decrease air after the coal is reduced; adjust the primary air, the

secondary air, the total air volume according to the load, coal and oxygen. The primary air can garantee

the material fluidization and maintain a certain material recycle volume. The furnace temperature could

be controlled by adjusting the ratio between the primary air and the secondary air. The negative pressure

on furnace outlet could be controlled by the adjusting of the opening degree of the induced draft fan.

16.5 Except for the automatic protection or interlock protection device of normal pulverized coal

boilerm the following requirements are added according to the characteristic of CFB boiler.

16.5.1 Differential pressure of material layer ---- the pressure of air room which is below the air

distributor and the top pressure of dense are should be connected into the differential pressure meter, and

it could be regarded as a parameter of the combustion controlling and the slag discharging.

16.5.2 Differential pressure of the suspension section ---- The top pressure of dense area and the furnace

outlet pressure should be connected into the differential pressure meter, and it could be regarded as a


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parameter of the controlling of boiler recycle material.

16.5.3 The thermocouple with the anti-wear sleeve should be installed in the dense area to monitor the

temperature, the exposed length of the thermocouple is 100~150mm, and the temperature is shown with

numbers in the controlling room.

Part 5. Notes

1. It is suggested that the outlet of the primary air and the outlet of the secondary air should be arranged

according to the drawing of “interfaces of flue, air duct”.

2. The measuring points on the boiler proper should be arranged by the design institute. Except for the

measuring points which are arranged by us, no new ones could be added on furnace part (from air

distributor to furnace outlet).

3. According to the “statistic table of insulating area”, the boiler pipeline, drum, headers, air preheater,

flue and air duct should be designed by the design institute.

4. When the concrete pillars are arranged by the civil engineering professionals of the design institute,

the position of downcomers should be noted.

5. During boiler operation process, the primary air duct, the secondary air duct, the coal-feeding tube,

the coal-spreading air duct, the under-bed ignition burner would expand downwards along with the

furnace. When the air ducts are designed by the design institute, the expanding factor should be

considered.

6. To ensure the normal life of boiler heating surface and the normal life of the wear-resistant material,

long-term overload operation of the boiler is not allowed.

cfb design description

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