Characteristics of circulating fluidized bed:
1.The combustion efficiency and thermal efficiency of the boiler is high.
2.By adding limestone the desulfurization can be done in the furnace. The desulfurization rate can reach above 90%, By low temperature combustion, the amount of harmful gas reduced, it’s conducive to environmental protection.
3.Wide adaptability of coal.
4.It’s conducive to ash utilization, improve economic benefits
5.This boiler adopts a new type of vortex internal separation circulating fluidized bed combustion technology which is developed jointly with Tsinghua University, it also has the following characteristics:
6.Compact structure, neat appearance, the separator and the hearth are connected as a whole.
7.This boiler adopts the double drum horizontal type natural circulation water tube boiler structure, fuel in the hearth is sent by coal feeder, burn with air which is sent by equal pressure bellows, the flue gas produced by burning up into the horizontal cyclone separator, cyclone is composed by two membrane wall, in order to ensure reliable operation of the separator (because of the cooling effect of the membrane water wall).Fly ash in the flue gas is separated due to the inertia force, the material back into the furnace through the feed back path by loosening wind for re-burning, greatly improving combustion efficiency, and significantly reduce the wear of the rear of the heating surface. The flue gas that came out from cyclone separator separated again by the U-shaped flue, and flush superheater from down to up, then transverse flushing the convection bank，and finally into the tail of the heating surface. Both of iron economizer and air preheater are level layout, the flue gas passes through the air preheater, dust, draught fan and discharged from the chimney.
8.Boiler ventilation, balanced ventilation of blast blower and induced draft fan.
Design parameters of cfb boiler”
(1)Rated evaporation 15t/h
(2)Rated steam pressure 1.05MPa
(3)Rated steam temperature 350℃
(4)Feedwater temperature 104℃
(5)Cold air temperature 30℃
(6)Sewage rate 2%
(7)Design thermal efficiency： 85.3%
(8)Boiler excess air ratio： 1.4
(9)Security and stability operating range of the boiler:Heat load: 50%-110%
(10) metal consumption： 90.68 t, in which the structural parts steel consumption is 49.4t.
(11)The design fuel is bituminous coal, the low calorific value is about 4853kcal/kg, and the combustible volatile matter is about 16.3%.
Combustion equipment and features
The combustion equipment is formed by funnel cap, slag off tubes and isobaric bellows, the control air board adopts pattern water cooling structure, there are 466 funnel caps arranged equally on the control air board. The slag came out from the slag off tubes. Use fluidized-bed combustion method which has the wide broad-based in our country currently, and also we use the fly ash cycle combustion technology, to overcome the drawbacks that the combustion efficiency of the old-fashioned boiling furnace is very low, the combustion efficiency of up to 97%. The suspended segment and hearth were designed with lower flue gas velocity, effectively prevent the wear of water wall tube.
Drum and water cooling system
The inner diameter of the upper drum isΦ1200mm, the wall thickness of 16mm, and the inner diameter of the lower drum is Φ900mm, the wall thickness of 14mm, both of them are made of Q245R boiler plate.
The upper drum is put on the two drum bracket freely, and hanging the lower drum by convection bank.
There is three membrane walls in the hearth part of the water cooling system, and its tube pitch is 100mm, tube specifications is Φ51×4, the connection of the membrane wall tube with the header is butt welding, the left side membrane wall has six Φ89×4.5 downcomers, the right side membrane wall has 4 Φ89×3.5 downcomers. The headpiece of furnace connects with upper drum through the twelveΦ89×4.5 gas-guide tube by three headers.
The flow area ratio of the total downcomer and the riser is 0.36, the flow area ratio of the gas-guide tube and the riser is 0.48. To ensure there is good water circulation.
The convection bank of cooling system adopts section-line layout, tube is Φ51 × 3 of high quality 20 (GB3087-2008) seamless pipes. Tubes of convection bank weld with the upper and lower drum.
Superheater and spray type desuperheater
Superheater adopts horizontal suspended structure, ends with a spray type desuperheater to reduce temperature to adjust the outlet temperature of superheated steam. Material of superheater tube is 20 (GB3087-2008). The pressure drop of superheater is 0.12Mpa. Spray type desuperheater barrel is φ273 × 12 of 20 (GB3087-2008) seamless steel pipe, cooling by feedwater.
Boiler feed water enter into inlet header from the feedwater control equipment, then enter into economizer coils for heating into economizer outlet header, and introduced into the upper drum by outlet header. Along the height direction the whole economizer is divided into two sections, there is no examine space among this two sections, economizer tube specifications is φ32 × 4, the inlet and outlet header specifications is φ159, materials are 20 (GB3087-2008) .
In order to reduce the exhaust gas temperature and improve the combustion efficiency, there is a tubular air preheater arranged after the economizer. Air preheater tubes use Φ50×1.5 steel pipe, tube length 2274mm, total of 675 consisted, The flow direction of the air and flue gas is mutually perpendicular, and for the second cross-flow. The flue gas average speed is 8.2m/s, the air speed is 7.4m/s.