CN103752160A - Method for realizing ultra-low emission of NOx of circulating fluidized bed boiler - Google Patents

Abstract

The invention relates to a method for realizing ultra-low emission of NOx of a circulating fluidized bed boiler in the technical field of selective non-catalytic reduction. Ammonium hydroxide and hydrogen are sprayed into the circulating fluidized bed boiler and the selective non-catalytic reduction reaction is performed on the sprayed ammonium hydroxide and hydrogen and NOx in circulating fluidized bed flue gas so as to realize ultra-low emission of NOx of the circulating fluidized bed boiler. The method can accord with the limiting value of 100mg/<Nm>3 in the latest emission standard, solves the problem of overhigh reaction temperature of a SNCR denitration technology used in the circulating fluidized bed boiler, and enables the matching degree between the fume temperature of a circulating fluidized bed and a SNCR denitration temperature window to be wide.

Description

Realize the method for CFBB NOx minimum discharge

Technical field

What the present invention relates to is a kind of method of SNCR technical field, specifically a kind ofly realizes the method that denitration efficiency reaches 70% CFBB NOx minimum discharge.

Background technology

The atmosphere pollutants emission standards of latest edition (GB13223-2011) goes into effect on January 1st, 2012, and newly-built fired power generating unit needs strict implement 100mg/Nm ³emission limits of nitrogen oxides, and existing fired power generating unit also will start to carry out on July 1st, 2014 this discharge standard.Recirculating fluidized bed (CFB) boiler, as a kind of efficient, low pollution, clean burning technology, at home and abroad in power industry by extensive concern with fast-developing.What CFB boiler adopted is low-temperature burning technology, relative coal-powder boiler, and CFB boiler is low-temperature burning, the existing low nitrogen burning technology of CFB boiler can make its NOx discharge capacity very low, generally can be controlled in 200-300mg/Nm ³, also well below the NOx discharge capacity of coal-powder boiler.Before 2012, the NOx discharge capacity of the normal operation of CFB boiler can meet original standard (GB13223-2003), has saved installation, the operating cost of equipment for denitrifying flue gas, and this has also shown the environmental protection characteristic of CFB boiler on the one hand.But along with the execution of up-to-date discharge standard (GB13223-2011), the environment-friendly advantage of existing CFB boiler has been cannot meet the discharge to NOx will be controlled at 100mg/Nm ³following strict demand is extremely urgent so seek a kind of method that realizes CFBB NOx minimum discharge.

From aspects such as technique, economy, performance, benefit and practice situations, comprehensively analyze, industry generally believes that it is the final concentration of emission of the NOx in CFB boiler smoke can be controlled to 100mg/Nm that CFB boiler adopts the denitration of SNCR (SNCR) technology ³below, realize the minimum discharge of CFB boiler NOx, meanwhile, technique is simple, and Transformation of Unit is few, invests littlely, meets China's fundamental realities of the country.

SNCR gas denitrifying technology (SNCR) refers in suitable temperature range (850-1100 ℃) do not have under catalyst action, and reducing agent (urea, ammoniacal liquor, liquefied ammonia etc.) is optionally reduced to N by NOx ₂and H ₂o.SNCR course of reaction is very responsive to temperature conditions, and suitable reaction temperature is to guarantee the high key of SNCR denitration efficiency.Because CFB boiler is low-temperature burning, operation bed temperature is 800-950 ℃ of left and right, so the relative coal-powder boiler of CFB boiler furnace outlet smoke temperature is lower, for guaranteeing higher denitrification percent, SNCR conversion zone cigarette temperature must can have good matching degree with SNCR temperature window, therefore need manage temperature window to expand or mobile to low temperature direction, make the flue-gas temperature of boiler hearth of circulating fluidized bed outlet or separator import and export section can be near best denitration temperature.

200810102373.4 disclose a kind of method that promotes selective non-catalytic reduction of nitrogen oxides, are to take microfine coal, natural gas or synthesis gas to promote selective non-catalytic reduction of nitrogen oxides as additive; Chinese patent application 200810209608.X discloses a kind ofly take biomass gasified gas and promotes selective non-catalytic reduction of nitrogen oxides as additive.Two above patents are mainly all for coal-powder boiler, are not to carry out denitrogenation for this distinctive clean burning type of furnace of CFBB, and the technique of interpolation coal dust, gasification gas or natural gas is also comparatively complicated.

Through the retrieval of prior art is found, Chinese patent literature CN101422689, open day 2009.05.06, a kind of method of denitration of storing and reducing nitrogen oxides in circulating fluid bed flue gas is disclosed, comprise the steps: that a. directly sprays into flue gas and take catalyst in the fluid bed depot reaction device of bed material after accelerating or pressurizeing, in mobile with movable bed material, realize the oxidation of NOx and absorb storing; B. by being arranged on the gas-solid separator of depot reaction device afterbody, realizing gas-solid and be separated, gas phase can directly be discharged or enter subordinate's NOx system system and be purified, and solid-phase catalyst enters fluid bed reduction regeneration reactor; C. the catalyst of storing NOx contacts with reducing agent in fluid bed reduction regeneration reactor, and the NOx that reduction is stored, realizes catalyst regeneration; D. the catalyst after regeneration is introduced to fluid bed depot reaction device.But this technology must adopt transition metal composite oxide catalytic agent, and the storage of NOx and reduction need to be carried out respectively in two different fluidized-bed reactors, both operating temperatures, atmosphere, gas flow rate etc. have strict demand, make this technology and are not suitable for being generalized in actual industrial.

Summary of the invention

The present invention is directed to prior art above shortcomings, a kind of method that realizes CFBB NOx minimum discharge of simple and feasible is proposed, without adding any type catalyst, also without regeneration and the renewal of considering catalyst, only that reducing agent (urea, ammoniacal liquor, liquefied ammonia etc.) is directly sprayed in fluidized bed smoke, just can realize the reduction of NOx, in operation, possess flexibility, investment and maintenance cost are also lower.The present invention can meet up-to-date discharge standard 100mg/Nm ³limit value, and solved the too high problem of reaction temperature that SNCR denitration technology exists in CFBB application, make recirculating fluidized bed cigarette temperature and the SNCR denitration temperature window to have broad matching degree.

The present invention is achieved by the following technical solutions, and the present invention comes to react with the NOx generation SNCR in recirculating fluidized bed flue gas by spray into ammoniacal liquor and hydrogen in CFBB, to realize the minimum discharge of CFBB NOx.

Described spraying into specifically refers to: in boiler hearth of circulating fluidized bed exit position section, spray into as the ammonia spirit of reducing agent with as the hydrogen of additive, utilize ammoniacal liquor and H ₂the ultimate density that coordinative role realizes CFBB NOx meets 100mg/Nm ³limit value; Preferably, the reducing agent spraying into and the consumption of additive and temperature match.

Described temperature refers to: reaction temperature is 700-1000 ℃.

Described consumption is specially: the amount of ammoniacal liquor is with the NH in ammoniacal liquor ₃represent with the mol ratio of NOx in flue gas, be preferably 1.5-2; It is 1-3 that the amount of hydrogen be take the mol ratio of NOx in hydrogen and flue gas.

The mist of described flue gas and ammoniacal liquor and hydrogen was determined by flue gas flow rate and flue size in the time of staying of conversion zone:

wherein: τ is the time of staying, s; L is the longitudinal length of the conversion zone counted from eject position, and along flow of flue gas direction, unit is m; U is the flow velocity of flue gas, and unit is m/s.

More than the described time of staying is preferably 0.6s.

The amount of hydrogen represents with the mol ratio of NOx in hydrogen and flue gas, is specially:

1) the cigarette temperature of reaction zone is in the time of 825-925 ℃, H ₂the preferred ratio of/NOx mol ratio gets 1;

2) the cigarette temperature of reaction zone is in the time of 760-890 ℃, H ₂the preferred ratio of/NOx mol ratio gets 2;

3) the cigarette temperature of reaction zone is in the time of 700-800 ℃, H ₂the preferred ratio of/NOx mol ratio gets 3.

Technique effect

Compared with prior art, the invention has the advantages that:

1. under this overall background of carrying out at environmental protection new national standard, for this clean burning type of furnace of CFBB, proposed a kind of method that realizes its NOx minimum discharge, and technique simply, easily implement, and is beneficial to industry and applies

2. specific embodiments and the preferred operating mode of CFBB SNCR denitrating technique have clearly been provided

3. additive H ₂add, cause that denitration temperature window moves to low temperature direction, solved SNCR denitration technology too high problem of existing reaction temperature in CFBB application, make recirculating fluidized bed cigarette temperature and SNCR denitration temperature window have broad matching degree.

Accompanying drawing explanation

Fig. 1 is the invention process environmental structure schematic diagram;

Fig. 2 is comparative example effect schematic diagram;

Fig. 3 is embodiment 2 effect schematic diagrames;

Fig. 4 is embodiment 3 effect schematic diagrames;

Fig. 5 is embodiment 4 effect schematic diagrames;

In figure: 1 burner hearth, 2 air compartments, 3 upper furnace (containing curtain wall), 4 cyclone inlet flues, 5 cyclone separator cylindrical shells, 6 cyclone separator cone sections, 7 cyclone separator standpipes, 8 material returning devices, 9 refeed lines, 10 central cylinder of separators, 11 separator outlet flues, 12 separator outlet flue reversal chambers, 13 back-end surfaces, 14 back-end ductwork cones, 15 back-end ductwork horizontal segments, 16 additives gas H ₂the eject position of conveyance conduit, 17 reducing agents (ammoniacal liquor) solution line, 18 ammonia water spray gun, 19 reducing agents and additive.

The specific embodiment

Below embodiments of the invention are elaborated, the present embodiment is implemented take technical solution of the present invention under prerequisite, provided detailed embodiment and concrete operating process, but protection scope of the present invention is not limited to following embodiment.

Embodiment 1

As shown in Figure 1, the present embodiment implementation environment comprises: burner hearth, air compartment, cyclone separator, material-returning device and back-end ductwork.CFBB is due to himself characteristic, and its NOx initial concentration generally can be controlled in 200-300mg/Nm ³, higher in up-to-date concentration limit 100mg/Nm ³.The spray gun of reducing agent is arranged in to the internal face of furnace outlet flue, entrance temperature is 700-1000 ℃.Nitrogen reductant adopts solution form, selection be that mass fraction is 10% ammoniacal liquor, additives gas H ₂by ammoniacal liquor, carry through same entrance and be injected in high-temperature flue gas, reduce the NOx concentration in flue gas with ammoniacal liquor coordinative role, and additive H ₂reasonable addition be to determine according to the cigarette temperature of entrance and reaction zone, to guarantee that recirculating fluidized bed cigarette temperature can mate preferably with SNCR denitration temperature window

Fig. 2 is that CFBB does not add any H ₂sNCR denitration characteristic curve.Experiment condition is: the initial NO concentration of flue gas is 268mg/Nm ³, oxygen concentration is 6%, NH ₃/ NOx mol ratio is 1.5, and the time of staying is 0.6s.The experiment value of the best denitration temperature of ammoniacal liquor is 920 ℃ (corresponding simulation value is 930 ℃), and now the best denitration efficiency of gained can reach 70% left and right, guarantees that denitration rate is 910-980 ℃ at more than 50% reaction temperature window, and window width is 70 ℃.

Embodiment 2

Fig. 3 is that CFBB adds quantitative H ₂(H ₂/ NH ₃mol ratio is taken as 1) SNCR denitration characteristic curve.Experiment condition is: the initial NO concentration of flue gas is 268mg/Nm ³, oxygen concentration is 6%, NH ₃/ NOx mol ratio is 1.5, H ₂/ NH ₃mol ratio is 1, and the time of staying is 0.6s.The experiment value of the best denitration temperature of ammoniacal liquor is 870 ℃ (corresponding simulation value is 820 ℃), best denitration efficiency is 64%, now guarantee that denitration rate is 825-925 ℃ at more than 50% reaction temperature window, window width is 100 ℃, and caused best denitration temperature is 50 ℃ to the side-play amount of low temperature direction.

Embodiment 3

Fig. 4 is that CFBB adds quantitative H ₂(H ₂/ NH ₃mol ratio is taken as 2) SNCR denitration characteristic curve.Experiment condition is: the initial NO concentration of flue gas is 268mg/Nm ³, oxygen concentration is 6%, NH ₃/ NOx mol ratio is 1.5, H ₂/ NH ₃mol ratio is 2, and the time of staying is 0.6s.The experiment value of the best denitration temperature of ammoniacal liquor is 820 ℃ (corresponding simulation value is 785 ℃), best denitration efficiency is 62%, now guarantee that denitration rate is 760-890 ℃ at more than 50% reaction temperature window, window width is 130 ℃, and caused best denitration temperature is 100 ℃ to the side-play amount of low temperature direction.

Embodiment 4

Fig. 5 is that CFBB adds quantitative H ₂(H ₂/ NH ₃mol ratio is taken as 3) SNCR denitration characteristic curve.Experiment condition is: the initial NO concentration of flue gas is 268mg/Nm ³, oxygen concentration is 6%, NH ₃/ NOx mol ratio is 1.5, H ₂/ NH ₃mol ratio is 3, and the time of staying is 0.6s.The experiment value of the best denitration temperature of ammoniacal liquor is 750 ℃ (corresponding simulation value is 760 ℃), best denitration efficiency is 58%, now guarantee that denitration rate is 700-800 ℃ at more than 50% reaction temperature window, window width is 100 ℃, and caused best denitration temperature is 170 ℃ to the side-play amount of low temperature direction.

Claims (5)

1. a method that realizes CFBB NOx minimum discharge, it is characterized in that, by spray into ammoniacal liquor and hydrogen in CFBB, come to react with the NOx generation SNCR in recirculating fluidized bed flue gas, to realize the minimum discharge of CFBB NOx;

Described spraying into specifically refers to: in boiler hearth of circulating fluidized bed exit position section, spray into as the ammonia spirit of reducing agent with as the hydrogen of additive, the reducing agent spraying into and the consumption of additive and temperature match.

2. method according to claim 1, is characterized in that, described temperature refers to: reaction temperature is 700-1000 ℃, and consumption is specially:

The amount of ammoniacal liquor is with the NH in ammoniacal liquor ₃with the mol ratio of NOx in flue gas be 1.5-2;

It is 1-3 that the amount of hydrogen be take the mol ratio of NOx in hydrogen and flue gas.

3. method according to claim 1 and 2, is characterized in that, when the cigarette temperature of reaction zone is during at 825-925 ℃, and H ₂/ NOx mol ratio is 1; When the cigarette temperature of reaction zone is during at 760-890 ℃, H ₂/ NOx mol ratio is 2; When the cigarette temperature of reaction zone is during at 700-800 ℃, H ₂/ NOx mol ratio is 3.

4. method according to claim 1, is characterized in that, the mist of described flue gas and ammoniacal liquor and hydrogen was determined by flue gas flow rate and flue size in the time of staying of conversion zone:

wherein: τ is the time of staying, s; L is the longitudinal length of the conversion zone counted from eject position, and along flow of flue gas direction, unit is m; U is the flow velocity of flue gas, and unit is m/s.

5. according to the method described in claim 1 or 4, it is characterized in that, the described time of staying is more than 0.6s.

Images