Summary of the invention
The objective of the invention is to invent a kind of material returning device be difficult for coking, blast cap be difficult for scaling loss and have improve desulfurizing function replace air to carry out the method for hp fluid air with steam.
For realizing above purpose, technical scheme of the present invention provides and a kind ofly replaces air to carry out the method for hp fluid air with steam, it is characterized in that, in servicely carries out hp fluid air with steam in that boiler is normal, and its method comprises:
(1) with jet chimney turbine discharge or other vapour source are connected with material returning device;
(2) when boiler begins to start, open the hp fluid air machine, come recycle stock in the fluidisation material returning device with air;
(3) about the temperature of boiler heating recycle stock in the material returning device is greater than 300 ℃, the fluidization steam vapor of steam turbine or other steam source parameter meet pressure greater than 60Kpa (g), the degree of superheat big sub more than 30 ℃ after, open the stop valve on the steam-turbine lead, use steam to come the interior recycle stock of fluidisation material returning device, and close the stop valve of hp fluid air machine and fluidization air.
(4) in the boiler shutdown process, when material returning device temperature during, open the hp fluid air machine less than 300 ℃, come recycle stock in the fluidisation material returning device with air, and close the stop valve of steam turbine or other steam source.
Use the required system of this method to comprise boiler furnace, cyclone separator, material returning device, blast cap and steam jet, wind and vaporium, afterbody convection pass, hp fluid air machine, stop valve, its characteristics are, connect material returning device and steam turbine or other steam source by jet chimney, on the jet chimney between material returning device and the steam turbine, be equipped with stop valve.
Principle according to Dual-Phrase Distribution of Gas olid, when the gas by fixed bed or gas flow are increased to weight that gas or gas just equal particle to the drag force of particle and deduct buoyancy, particle is in a kind of plan suspended state, particle changes a kind of running status that is similar to fluid into, this moment, fixed-bed conversion was initial fluidized state, and at this moment Zui Xiao wind speed is grain fluidized critical fludization velocity Vlj.It is as follows to calculate and test the empirical equation that draws the critical fluidising air velocity Vlj of calculating according to theory:
Vlj=0.0882Ar
0.528(ν
y/D
dl)m/s
In the formula: Ar=gD
Dl 3/ ν
y 2* (γ
g-γ
y)/γ
y-Archimedes criterion
ν
yThe dynamic viscosity coefficient of-gas (vapour) body, m
2/ s
γ
gThe true specific gravity of-solid particle, kg/m
3
γ
yThe proportion of-bed temperature the therapeutic method to keep the adverse qi flowing downward (vapour) body, kg/m
3
D
DlThe average diameter of-solid particle, m
G-acceleration of gravity is generally got 9.81m/s
2
Influence gas or gas depend on gas or gas to grain fluidized critical speed proportion and dynamic viscosity coefficient as can be seen according to above formula, the proportion of gas or gas is big more, grain fluidized critical fludization velocity is more little, also with regard to the easy more goods fluid that makes, the big more needed critical fludization velocity of dynamic viscosity is more little.According to the physical characteristic of air and steam as can be seen, for steam, when steam pressure is not very big, can be used as perfect gas under the not too low situation of temperature handles, for parts such as boiler hearth of circulating fluidized bed air distribution plate, material returning device, fluidized bed slag cooler and external heat exchangers, steam all can be used as perfect gas and handles.Under uniform pressure and temperature, the proportion of steam is littler than air, and the viscosity ratio air is big, therefore with the effect of steam fluidisation granule materials substantially and air be equal to.Find through computational analysis: under the identical situation of other condition, it is littler than the mass flow of air to reach the required steam mass flow of identical fluidizing velocity.Draw from theory analysis that to use steam to replace air to come the fluidisation material be fully feasible.
Advantage of the present invention is:
1. can prevent the material returning device coking effectively;
Because logical steam replaces air in the material returning device, fuel is disposable can not to burn fully by fire box, a part carbon granules at furnace outlet along with flue gas enters cyclone separator at a high speed, carbonaceous particles is at a high speed rotation and contact the generation after-burning with air in the flue gas in cyclone separator, this after-burning enters material returning device along with material is separated, can avoid further burning, steam heat absorption simultaneously can reduce back grey temperature, prevents coking.
2. steam substitutes hp fluid air, and material returning device regional water vapour concentration is increased, and CaO is activated, and increases the desulfuration efficiency of lime stone;
The desulfurizing agent of desulphurization in circulating fluidized bed boiler generally adopts lime stone CaCO at present
3, dolomite CaCO
3.MgCO
3, under the situation for identical Ca/S mol ratio, Ca (OH)
2Desulfuration efficiency than lime stone CaCO
3, dolomite CaCO
3.MgCO
3Much higher, this is to become Ca (OH) owing to work as the CaO aquation
2The time, its specific area will increase, and void size distributes better, as Ca (OH)
2Being heated to resolve in the process that CaO emits water vapour forms the space again, has increased the specific area of CaO, has strengthened the activity of CaO, and the utilization rate of lime stone is improved.In addition, according to the desulphurization mechanism of CaO, CaCO
3Its molal volume had dwindled 45% when particle was transformed into the CaO particle, thereby made former CaCO
3Interior natural space has enlarged many, and this helps mushy CaO and SO
2React and generate CaSO
4But CaO becomes CaSO
4Its molal volume of course of reaction can increase about 180%, therefore at the beginning, will generate the fine and close CaSO of one deck on the surface of CaO in reaction
4Thin layer has hindered SO
2Further be diffused into the CaO internal granular layer and react, use the steam fluidisation can make CaSO
4Break with the steam generation hydration reaction, expose new CaO surface, improve the desulfurization utilization rate of calcium.
Secondly, substitute the high pressure fluidization air, the vapour content in the flue gas is increased, play the effect of in-furnace calcium spraying back-end ductwork humidification desulfurization, make tiny CaO particle fly out behind the cyclone separator, at afterbody convection pass low-temperature space and H with steam
2The O reaction generates Ca (OH)
2With the SO in the flue gas
2Has very high reaction speed after meeting with SO
2Absorb, improve the utilization rate of calcium and further reduce SO
2Concentration of emission.Under similarity condition, obtain same desulfuration efficiency, the consumption that utilizes vapor stream fossil lime stone is than the low 20-30% of air fluidisation.The experience of boiler actual motion shows that along with reducing of Ca/S mol ratio, the concentration of emission of NOx also decreases.
3. operation maintenance is simple, and steam pressure is easy to regulate;
In Design of CFB Boiler; smooth and prevent burner hearth flue gas anti-channeling for the ease of the material returning device returning charge; the required pressure head of feedback air is more much higher than a blast head; need to be equipped with special fluidisation blower fan; and in order to increase the reliability of system; usually also need be equipped with standby fan, make system layout, safeguard complicatedly, investment increases.If use steam to replace this part fluidization air, the pressure of steam can arbitrarily be adjusted according to the variation in operating condition and the coal, does not also need to be equipped with standby fan, and system equipment is simple and reliable, and is easy to operate.
4. avoid the vibrations and the noise of pipeline and hp fluid air machine, improve power plant's running environment.
The specific embodiment
Because the producing steam of boiler own, to generator for electricity generation, so steam can come from turbine discharge or intermediate extraction to steam by steam turbine, also can be from boiler itself or other source generating means.
Present embodiment is an example with the 150MW of Shanghai Furnace Factory Co., Ltd band resuperheat CFBB, and steam is provided by turbine discharge or intermediate extraction:
As shown in Figure 1, be the circulating fluidized bed boiler systems schematic diagram, by boiler 1, cyclone separator 2, material returning device 3, blast cap and steam jet 4, wind and vaporium 5, afterbody convection pass 6, stop valve 7, steam turbine 8, hp fluid air machine 9, stop valve 10 is formed, cyclone separator 2 connects the upper end of boiler 1, the upper end of cyclone separator 2 connects afterbody convection pass 6, the lower end of cyclone separator 2 connects material returning device 3, material returning device 3 connects the lower end of boiler 1, material returning device is equipped with blast cap and steam jet 4 for 3 li, the lower end of material returning device 3 connects steam turbine 8 with jet chimney, on the jet chimney between material returning device 3 and the steam turbine 8, load onto stop valve 7, connect hp fluid air machine 9 with air duct, on the air duct of material returning device 3 and hp fluid air machine 9, load onto the stop valve 10 of fluidization air.
The method that replaces air to carry out hp fluid air with steam is:
(1) when boiler 1 begins to start, open hp fluid air machine 9, come recycle stock in the fluidisation material returning device 3 with air;
(2) in boiler 1 is warmed up to material returning device 3 temperature of recycle stock greater than about 300 ℃, the fluidization steam vapor vapour source parameter of steam turbine 8 meets pressure greater than 60Kpa (g), the degree of superheat is greater than after more than 30 ℃, open the stop valve 7 on steam turbine 8 jet chimneys, use steam comes the recycle stock in the fluidisation material returning device 3, and closes the stop valve 10 of hp fluid air machine 9 and fluidization air.
(3) in boiler 1 furnace shutting down process, when material returning device 3 temperature during, open hp fluid air machine 9 less than 300 ℃, come recycle stock in the fluidisation material returning device 3 with air, and close the stop valve 7 of the fluidization air on the steam turbine 8.
Fuel burns in the burner hearth of boiler 1, flue gas enters cyclone separator 2 at a high speed, separating the back flue gas is discharged by afterbody convection pass 6, a large amount of materials and a part of unburnt carbonaceous particles high speed rotation and reinforcement in cyclone separator mix with air in the flue gas after-burning take place, this after-burning enters material returning device 3 along with material is separated, the low-pressure steam that is provided by steam turbine enters material returning device 3, by blast cap and steam jet 4 ejections recycle stock is carried out fluidisation.
Shared 2 material returning devices of the 150MW of Shanghai Furnace Factory Co., Ltd band resuperheat CFBB, the bed surface of each material returning device is long-pending to be 4.96m
2, fluidizing velocity is 0.6-0.8m/s during according to design and operation, and the fluidization steam vapor quantity of steam calculates by 1.0m/s, and required fluidization steam vapor is 35712m
3/ h designs back 870 ℃ of grey temperature, pressure 34.0KPa, and absolute pressure is 0.1353MPa, and under this situation, steam is by desirable gas treatment, and the specific volume of steam is: 3.9m
3/ kg, therefore required material returning device fluidization steam vapor amount is 9157kg/h.
According to the vapour source of conveniently choosing in the source of boiler or power plant's steam turbine steam, existing is 150-200 ℃ by the inlet vapor source temperature, and the steam enthalpy is considered by 2800-3000kJ/kg.If the vapour source is from beyond the steam generator system, boiler efficiency will increase.If from boiler self steam, the heat loss due to exhaust gas of boiler will increase.Calculate according to heating power, boiler substitutes under the situation of high pressure fluidization air at steam of no use, the exhaust smoke level of boiler is: 635424kg/h, the weight quota of water vapour is 4.042% in the flue gas, the weight of water vapour is in the flue gas: 25684kg/h, the heat loss of water vapour is 0.97% by high calorific power in the fuel.If boiler utilizes steam to replace the material returning device hp fluid air, the weight quota of water vapour is 5.4% in the boiler smoke at this moment, and the heat loss of water vapour is 1.32% by high calorific power in the fuel, will make the heat loss due to exhaust gas of boiler increase 0.3-0.4%.Calculate by heat loss, boiler per hour thermal losses is about 1620kw, if unit calculates by 35% generating efficiency, then power consumption is 567kw/h, remains basically stable with the power consumption of hp fluid air machine.
From computational analysis as can be seen, the steam fluidisation makes the flue gas water vapour content be increased to 5.4% from 4.04%, therefore as long as the humidity of coal is moderate, the content of tail flue gas steam can obviously not increase, can not cause empty preheater cold end corrosion and to have a strong impact on, simultaneously after the steam fluidisation because the raising of limestone desulfurization efficient, SO
2Discharging reduce, empty preheater cold end corrosion situation is improved greatly.