Reduce the method for biomass recirculating fluidized bed boiler discharged nitrous oxides
Technical field
The present invention relates to biomass recirculating fluidized bed boiler, refer to a kind of method reducing biomass recirculating fluidized bed boiler discharged nitrous oxides particularly.
Background technology
At existing boiler, smelting furnace, in the large-scale combustion apparatus such as incinerator, many uses burnout degree system (OFA, OverfireAir) discharge of pollutant is reduced, (coal dust is can be by fuel, fuel oil, natural gas etc.) and Secondary Air (refer to the wind that the some strands of air-flows at a high speed spraying into burner hearth from fire grate top are formed, can be air, oxygen etc.) spray into the combustion zone of burner hearth together and make it burning, and above combustion zone, spray into burnout degree (for reducing the generation of NOx, the hot blast that air stage feeding mode is sent into separately on main burner top is adopted in burner hearth, to make combustible at later stage further after-flame) to form complete combustion zone, thus realize the maximization of burning, the generation of decreasing pollution thing.Even if but have employed burnout degree system, still can contain a certain amount of nitrogen oxide (NOx is mainly NO and NO2) in the burner hearth flue gas that burning generates, and nitrogen oxide can cause the pollution such as acid rain, photochemical fog.In order to reduce the content of the nitrogen oxides in effluent of discharge further, SNCR method (SNCR can be used, SelectiveNon-CatalyticReduction), be about to the reducing agent that can be optionally nitrogen reduction of nitrogen oxide and inject the flue gas that fire box temperature is 850 ~ 1100 DEG C, thus reduce the content of burner hearth nitrogen oxides in effluent, wherein reducing agent sprays into by the spout be located at below furnace arch, furnace nose.
At present, generating power with biomass combustion equipment adopts biomass recirculating fluidized bed boiler mostly, and its nitrogen oxide emission is less than coal-burning boiler, generally at 200mg/m
3left and right, the slightly 100mg/m of superstate standard
3.Because the installed capacity of biomass recirculating fluidized bed boiler is less, if adopt selective catalytic reduction (SCR) to carry out denitrogenation, its investment is large, cost is higher; And use traditional SNCR method (SNCR) to carry out denitrogenation, its reducing agent adopted enters in stove as aqueous solution of urea will carry a large amount of moisture content, carry the deep that urea arrives burner hearth fully to mix with flue gas to enable water droplet, but because the water content of biomass fuel own is just higher, enter a large amount of moisture content by make the heat of flue gas consume by the latent heat of vaporization of water, so the efficiency of biomass recirculating fluidized bed boiler can be caused to decline.
In order to solve the problem, publication number is the reduction nitric oxide system that the Chinese patent of CN201748452U provides a kind of selective non-catalytic reduction system and combustion system and combines, it is provided with fuel nozzle ports on furnace body sidewall, for fuel and Secondary Air are sprayed in burner hearth, position higher than fuel nozzle ports on furnace body sidewall is provided with fire air nozzle, be provided with liquid reducing agent sprayer at fire air nozzle place, make liquid reducing agent form drop and together spray into burner hearth with burnout degree.Because the air quantity of burnout degree is less than Secondary Air, also poor with the mixed effect of flue gas, and it is on the low side to utilize this structure to spray into the reductant solution concentration of burner hearth, still exists and enters the problem that moisture content in stove is too high, denitrification effect is poor, boiler efficiency reduces.
Summary of the invention
Object of the present invention is exactly the defect that will overcome prior art existence, provides a kind of denitrification effect remarkable and the method for the reduction biomass recirculating fluidized bed boiler discharged nitrous oxides that technique is simple, economical and practical.
For achieving the above object, the method for the reduction biomass recirculating fluidized bed boiler discharged nitrous oxides designed by the present invention, comprises the following steps:
1) flue gas that biomass recirculating fluidized bed boiler is discharged is imported in deduster, remove the dust impurities of the wherein overwhelming majority, obtain comparatively clean flue gas;
2) part in flue gas comparatively clean for gained is incorporated into an air compartment from the First air entrance of biomass recirculating fluidized bed boiler circulates, to reduce the oxygen content of First air, and then reduce the combustion temperature in hearth of biomass recirculating fluidized bed boiler;
3) meanwhile, denitrogenation reducing agent is sprayed into wherein from the Secondary Air entrance of biomass recirculating fluidized bed boiler, utilize Secondary Air that the denitrogenation reducing agent of atomization is fully mixed with the flue gas in burner hearth, and then make nitrogen oxide wherein and denitrogenation reducing agent generation chemical reaction and be removed.
Preferably, in described step 3), denitrogenation reducing agent adopts the one in aqueous solution of urea, ammonia spirit, amine compound aqueous solution, and the mass percent concentration of each solution is 40 ~ 60%.Like this, the denitrogenation reducing agent of high concentration can make the water yield that enters in biomass recirculating fluidized bed boiler less, avoids a large amount of moisture content to cause heat smoke too much by the latent heat of vaporization consumption of water, ensures the thermal efficiency of biomass recirculating fluidized bed boiler.
Preferably, in described step 3), the average diameter of denitrogenation reducing agent droplet particle is 100 ~ 1000 μm.Because micron-sized droplet particle has great specific area, denitrogenation reducing agent can be made fully to contact mixing with flue gas.
Preferably, in described step 3), temperature when being sprayed into by adjustment Secondary Air, controls the fire box temperature of the Secondary Air porch of biomass recirculating fluidized bed boiler in the scope of 800 ~ 900 DEG C.This temperature, within 850 ~ 1100 DEG C, the optimum temperature interval that denitrogenation reducing agent and nitrogen oxide react, can guarantee that denitrogenation reducing agent and nitrogen oxide fully react.
Preferably, described step 2) in, by adjusting the amount of circulating gas be incorporated in an air compartment, making burner hearth bottom be in oxygen debt fired state, controlling the fuel inlet place fire box temperature of biomass recirculating fluidized bed boiler in the scope of 800 ~ 900 DEG C.Like this, temperature is consistent everywhere to keep burner hearth, local temperature in stove can be avoided too high and the detonation that causes, reduce the generation of fuel bound nitrogen, avoid the slagging scorification of fuel, agglomerate simultaneously, and then improve the efficiency of boiler.
Preferably, in described step 3), the time of staying of denitrogenation reducing agent and reaction of nitrogen oxides in biomass recirculating fluidized bed boiler is controlled in the scope of 0.5 ~ 2s.This time of staying can guarantee that denitrogenation reducing agent and nitrogen oxide fully react.
The invention has the advantages that: the flue gas of biomass recirculating fluidized bed boiler is sent into an air compartment after deduster dust removal process, reduces the oxygen content of First air, reduce the ignition temperature of burner hearth, reduce the generation of nitrogen oxide; Close to the temperature range of the temperature of Secondary Air porch at 800 DEG C ~ 900 DEG C in Boiler Furnace, this temperature range is within the optimum temperature interval of denitrogenation reducing agent denitrification reaction, utilize simultaneously Secondary Air can in stove with the feature of flue gas good mixing, make the atomizing particle carrying denitrogenation reducing agent also can carry out good mixing with flue gas, obtain good denitrification effect.The reducing agent that tradition denitrogenation uses is generally the weak solution of 10%, a large amount of water can be brought into, moisture content in flue gas is increased, reduce boiler efficiency, the present invention sprays into the denitrogenation reducing agent of high concentration in Secondary Air porch, reduce the water content into stove, the basis ensureing denitrification effect improves boiler efficiency.
In sum, the present invention adopts flue gas recirculation and efficiently solves in the method that Secondary Air porch spray high concentration denitrogenation reducing agent combines the problem that flue-gas denitrification and boiler efficiency decline.Meanwhile, present invention process is simple and practical, does not need to carry out large transformation to biomass recirculating fluidized bed boiler, and cost of investment is low, reduces discharged nitrous oxides Be very effective.
Accompanying drawing explanation
Fig. 1 is the syndeton schematic diagram of the biomass recirculating fluidized bed boiler adopting the inventive method.
In figure, each part numbers is as follows: biomass recirculating fluidized bed boiler 1, Secondary Air entrance 1a, First air entrance 1b, cyclone separator 1c, air compartment 1d, fuel inlet 1e, deduster 2, a chimney 3.
Detailed description of the invention
Below in conjunction with the drawings and specific embodiments, the present invention is described in further detail.
Biomass recirculating fluidized bed boiler 1 shown in figure, its side wall upper part is provided with Secondary Air entrance 1a, its lower sidewall is provided with fuel inlet 1e, an air compartment 1d is provided with bottom it, one time air compartment 1d is provided with First air entrance 1b, its top exhanst gas outlet is connected by the input of flue with cyclone separator 1c, the bottom of cyclone separator 1c is connected with the adiabatic returning charge pipeline towards biomass recirculating fluidized bed boiler 1, the top exhanst gas outlet of cyclone separator 1c is connected by the import of flue with deduster 2, the outlet of deduster 2 is divided into two-way, communicate with chimney 3 and First air entrance 1b respectively.Meanwhile, the flue that deduster 2 leads to First air entrance 1b is provided with flow control valve.And Secondary Air entrance 1a place is provided with denitrogenation reductant nozzle.
The method that the present invention reduces biomass recirculating fluidized bed boiler discharged nitrous oxides is achieved in that
First, biomass fuel enters biomass recirculating fluidized bed boiler 1 from fuel inlet 1e, burn, the flue gas produced enters cyclone separator 1c from boiler top, unburnt biomass fuel is separated, and turned back in boiler by adiabatic returning charge pipeline and rekindle, import deduster 2 from the isolated flue gas of cyclone separator 1c, remove the dust impurities of the wherein overwhelming majority, obtain comparatively clean flue gas, a part in the flue gas that gained is comparatively clean leads to chimney 3, enters air; Residue flue gas is incorporated into an air compartment 1d from the First air entrance 1b of biomass recirculating fluidized bed boiler 1 and circulates, and to reduce the oxygen content of First air, and then reduces the combustion temperature in hearth of biomass recirculating fluidized bed boiler 1.Introduce an air compartment 1d exhaust gas volumn can by being arranged on deduster 2, the flow control valve led on the flue of First air entrance 1b adjust according to actual condition, burner hearth bottom is made to be in oxygen debt fired state, thus make fuel inlet 1e place fire box temperature control in the scope of 800 ~ 900 DEG C, avoid the generation of local detonation, overtemperature, reduce the generation of fuel bound nitrogen, reduce the slagging scorification of fuel, agglomerate, improve the thermal efficiency of boiler.
Meanwhile, denitrogenation reducing agent is sprayed by the Secondary Air entrance 1a of biomass recirculating fluidized bed boiler 1, burner hearth is imported after mixing with Secondary Air, utilize Secondary Air that the denitrogenation reducing agent of atomization is fully mixed with the flue gas in burner hearth, and then make nitrogen oxide wherein and denitrogenation reducing agent generation chemical reaction and be removed.Denitrogenation reducing agent can select the one in aqueous solution of urea, ammoniacal liquor, amine compound aqueous solution, and the percent concentration of each solution is 40% ~ 60%.In the present embodiment, preferred mass percent concentration is the aqueous solution of urea of 50%.It is 100 ~ 1000 μm of atomized drop particles that this aqueous solution of urea is atomized into average diameter by spray regime, Secondary Air is utilized fully to mix with flue gas, dense due to aqueous solution of urea, water content is little, thus avoiding a large amount of moisture content makes the heat of heat smoke by the too much deficiency of the latent heat of vaporization consumption of water, makes boiler can not lower efficiency because spraying into a large amount of water simultaneously.Temperature when being sprayed into by adjustment Secondary Air, control the fire box temperature at the Secondary Air entrance 1a place of biomass recirculating fluidized bed boiler 1 in the scope of 800 ~ 900 DEG C, and the time of staying of aqueous solution of urea and reaction of nitrogen oxides is controlled in the scope of 0.5 ~ 1s, such aqueous solution of urea fully reacts with the nitrogen oxide in burner hearth, reduce the nitrogen oxide in biomass recirculating fluidized bed boiler 1 emission to greatest extent, thus while free from environmental pollution, ensure the thermal efficiency of biomass recirculating fluidized bed boiler 1.