CN103521073A - Method for improving denitration rate of SCR (Selective Catalytic Reduction) denitration system of power station boiler - Google Patents

Abstract

The invention discloses a method for improving the denitration rate of an SCR (Selective Catalytic Reduction) denitration system of a power station boiler. The method comprises the following steps: (1) measuring concentration distribution of NOx at the outlet of an SCR denitration reactor; (2) calculating the unevenness Cv of concentration distribution of NOx according to the measuring result in the step (1); (3) when Cv is greater than 20%, adjusting the valve opening in an area corresponding to an ammonia injection grid according to the concentration distribution of NOx at the outlet of the SCR denitration reactor; (4) repeating the steps (1) to (3) until Cv is less than or equal to 20%. Through optimization and adjustment by the invention, the evenness of distribution of NOx at the outlet of the SCR denitration reactor is remarkably improved, and the relative standard deviation of NOx is reduced from 46.4% to 14.8%. On the premise of ensuring that ammonia escape does not exceed standard, the denitration rate is improved from 77% to 83%. The method disclosed by the invention has important guiding meaning and engineering application value to safe, efficient and stable operation of the SCR denitration system of the power station boiler.

Description

Improve the method for station boiler SCR denitrating system denitration rate

Technical field

The present invention relates to coal fired power plant SCR denitrating system, particularly relate to a kind of method that improves station boiler SCR denitrating system denitration rate.

Background technology

The country that coal is main primary energy be take in China, and coal accounts for the more than 60% of total energy consumption, and generating coal consumption accounts for 50% of coal consumption amount, and can within quite long period, keep this trend.National nitrogen oxide emission in 2005 is 19.1 * 106t, the NO in China's atmospheric environment _xconcentration is far away higher than other countries and area, and wherein the contribution rate of power plant is 43%.Visible coal fired power generation is one of main source of China's atmosphere pollution nitrogen oxide." 12 " start, and the Chinese government pays much attention to nitrogen oxide control work, in July, 2011 national environmental protection portion issue Liao《 thermal power plant air pollution emission standard " (GB13223-2011) in, emission limits of nitrogen oxides is from 450mg/m ³be down to 100mg/m ³(new-built unit) and 200mg/m ³(in-service unit), " Chinese national economy and social development 12 planning outlines " have been voted through in four meetings of in March, the 2011 Shi Yijie National People's Congress, clearly propose " 12 " nitrogen oxide and reduce discharging 10% the binding indicator, the control work of visible nitrogen oxide is imperative.

From technology application present situation both domestic and external and discharged nitrous oxides control policy, strict along with discharged nitrous oxides restriction, gas denitrifying technology will generally be applied.In all gas denitrifying technologies, SNCR(SNCR) although technique technical fee is low, equipment is few, because denitration rate is limited, be difficult in fired power generating unit (especially large electric power plant unit) large-scale application; SCR(SCR) technology denitration efficiency is the highest, can meet various strict emission requests, and up to the present, the coal fired power plant that the existing installed capacity in the whole world surpasses 200GW has been applied SCR gas denitrifying technology.Because the current discharged nitrous oxides of China requires to have reached advanced international standard, so SCR gas denitrifying technology will become the main flow of gas denitrifying technology.

The flue gas flow rate field of the SCR catalyst inlet of on-the-spot actual motion is inhomogeneous, can cause catalyst outlet NO like this _xand NH ₃concentration field very inhomogeneous.There is subregion NO _xthe very low and NH of content ₃the very large or subregion NH of escape amount ₃less but NO escapes _xthe situation that content is higher.This can affect the denitration effect of overall system and move and bring very large harm to the economic stability of system.

Summary of the invention

Based on this, the object of this invention is to provide a kind of method that improves station boiler SCR denitrating system denitration rate.

Concrete technical scheme is as follows:

A method that improves station boiler SCR denitrating system denitration rate, comprises the steps:

(1) measure the NO of SCR Benitration reactor outlet _xcONCENTRATION DISTRIBUTION;

(2) according to the measurement result of step (1), calculate NO _xthe unevenness C of CONCENTRATION DISTRIBUTION _v;

(3) work as C _v>20% time, according to the NO of SCR Benitration reactor outlet _xcONCENTRATION DISTRIBUTION adjust the valve opening of ammonia-spraying grid respective regions;

(4) repeating step (1)-(3), until C _v≤ 20%;

Above-mentioned unevenness C _vcomputing formula as follows:

$\mathrm{Cv}=\frac{S}{\stackrel{\‾}{x}}\×100\%,$

$S=\sqrt{\frac{\underset{i=1}{\overset{n}{\mathrm{\Σ}}}(x_i-\stackrel{\‾}{x})}{n-1}},$

$\stackrel{\‾}{x}=\frac{1}{n}\underset{i=1}{\overset{n}{\mathrm{\Σ}}}\mathrm{xi},$

Wherein, xi is the NO of SCR Benitration reactor outlet i measuring point _xconcentration, S is SCR Benitration reactor outlet NO _xthe standard deviation of concentration,

for SCR Benitration reactor outlet NO _xthe mean value of concentration.

Therein in an embodiment, in step (4), C _v≤ 15%.

Principle of the present invention and advantage are as follows:

Although SCR device can be optimized design to the flow field of flue by cold conditions model flow test and in conjunction with three-dimensional two-phase flow numerical simulation calculation conventionally in the design phase.But often, due to the impact of the various factors such as restriction of site space, the flue gas flow rate field of SCR catalyst inlet is inhomogeneous, can cause catalyst outlet NO like this _xand NH ₃concentration field very inhomogeneous.There is subregion NO _xthe very low and NH of content ₃the very large or subregion NH of escape amount ₃less but NO escapes _xthe situation that content is higher.This can affect the denitration effect of overall system and move and bring very large harm to the economic stability of system.Fig. 1 is NO after catalyst in different denitration rate situations _xthe inhomogeneous impact on catalyst life of concentration field, can find out, if concentration deviation increases, can obviously shorten the service life of catalyst.Meanwhile, the increase of the escaping of ammonia can produce more hydrogen sulfate ammonia, causes obstruction and the corrosion of boiler air preheater.Fig. 2 is the impact of the escaping of ammonia on the air preheater cleaning frequency, therefrom can find out, when the escaping of ammonia of SCR system > after 2ppm, the Clean after every of air preheater shortens dramatically.This meeting obviously reduces the availability of generating set, and increases the power consumption (for 600MW grade unit, SR increases 100Pa, and air-introduced machine increases power and has 100kW at least) of air-introduced machine, and the direct and indirect economic loss causing is considerable.In addition NO, _xand NH ₃the inhomogeneous denitration rate that also can obviously affect system of concentration field.

For this reason, the present invention is by being optimized and adjusting to improve catalyst outlet NO spray ammonia system _xand NH ₃cONCENTRATION DISTRIBUTION.The NO of reactor outlet while first measuring SCR operation _xcONCENTRATION DISTRIBUTION, on this basis, adjusts to change the ammonia spraying amount of diverse location to spray ammonia sub valve, thereby obtains uniform NO _xand NH ₃distribution.

By above-mentioned, optimize and revise, the beneficial effect of realization is as follows:

(1) by field optimizing, adjust SCR reactor outlet NO _xthe uniformity distributing is significantly improved, NO _xrelative standard deviation by 46.4%, reduce to 14.8%.NH ₃the deviation of/NOx ratio has also had obvious minimizing, has the NH of 24 measuring points (80%) ₃/ NOx is than in ± 5% scope.

(2), in the situation that guaranteeing that the escaping of ammonia does not exceed standard, denitration rate brings up to 83% by 77%.

The present invention is directed to the method that the on-the-spot operation of SCR denitrating system is optimized, to realizing being uniformly distributed of SCR reactor concentration field, raising system denitration rate, avoid obstruction and the corrosion of equipment, to instructing, station boiler SCR denitrating system is safe, efficient, stable operation has important directive significance and engineering using value.

Accompanying drawing explanation

Fig. 1 is NO _xthe inhomogeneous figure that affects on catalyst life of concentration;

Fig. 2 is the affect figure of the escaping of ammonia on the air preheater Clean after every time;

Fig. 3 is automatic measurement system schematic diagram;

Fig. 4 is that ammonia slip is measured sampling system schematic diagram;

Fig. 5 is reactor outlet NO under custom operating mode _xconcentration profile;

Fig. 6 is reactor outlet NO under optimum operating condition _xconcentration profile.

The specific embodiment

By the following examples the present invention is further elaborated.

The 600MW of embodiment of the present invention Dui Mou power plant unit SCR device, has carried out on-the-spot operation Optimum Experiment research.

1, the experimental measurement instrument that on-the-spot operation is optimized

(1) NO _xand O ₂measurement

Field trial NO _xmeasuring instrument be infrared NO _xanalyzer, O ₂measuring instrument be generally paramagnetic oxygen amount meter.Because the area of SCR reactor is very large, conventionally also need to adopt automatic measurement system as shown in Figure 3.

By to NOx and O ₂in time, measures, and by the data reduction of NOx, is 6%O ₂the data of benchmark.

(2) NH ₃measurement

Field trial NH ₃measurement can be according to EPAmethodCTM027 standard, sampling system is as shown in Figure 3.

2, on-the-spot operation Optimization Practice analysis and discussion

For certain 600MW of power plant unit SCR device, carried out on-the-spot operation optimization.This SCR Plant arrangement, after economizer, before air preheater, belongs to high dirt arrangement.Chief component comprises that two are equipped with the reactor of catalyst, two liquefied ammonia storage tanks and a set of ammonia injected system.Two SCR inside reactors are equipped with two-layer catalyst, and every layer of catalyst is 8 * 9 module arrangement.At the gas approach of each SCR reactor, a set of static mixer has been installed, in flue, deflector and fairing have also been installed in corner.Boiler uses refreshing Fu Dong victory coal, SCR import NO _xconcentration is 550mg/Nm ³, design denitration rate is 80%.

(1) measurement result (spray ammonia) of custom operating mode

During spray ammonia, be accustomed to operating mode reactor outlet NO _xmeasurements and calculations result see respectively the data of operating mode 2 in Fig. 5 and table 1.Can find out NO _xdistribution very inhomogeneous.At the middle part of reactor NO _xconcentration is very low, is only 19mg/Nm ³.And the NOx concentration of both sides significantly raises, reach respectively 185mg/Nm ³(enlarging end) and 176mg/Nm ³(stiff end).The relative standard deviation of NOx is up to 46.4%.NH ₃/ NO _xthe deviation of ratio is also very large, only has the NH of 5 points (17%) ₃/ NO _xthan in ± 5% scope.

(2) final result that operation is optimized

By the adjustment to spray ammonia barrier ammonia spraying amount, carried out altogether 6 suboptimization tests, final optimum results is shown in the data of operating mode 8 in Fig. 6 and table 1.Can find out SCR reactor outlet NO _xthe uniformity distributing is significantly improved, NO _xrelative standard deviation by 46.4%, reduce to 14.8%.NH ₃the deviation of/NOx ratio has also had obvious minimizing, has the NH of 24 measuring points (80%) ₃/ NOx is than in ± 5% scope.Accordingly, in the situation that guaranteeing that the escaping of ammonia does not exceed standard, denitration rate brings up to 83% by 77%.

The record of each operating mode ammonia spraying amount, in Table 2, can be found out, due to the skewness of flue gas flow rate, causes required ammonia spraying amount also not identical.In reactor central region, valve is closed substantially.And at the stiff end of reactor, valve is opened completely.

The operation of table 1SCR reactor is optimized each operating mode NOx measurement result and is gathered

Each operating mode ammonia spraying amount record is optimized in the operation of table 2SCR reactor

Note: * valve is standard-sized sheet, and * * valve is closed substantially, and this place's valve of Δ has adjustment.

3, the 600MW of the present embodiment Dui Mou power plant unit SCR device, has carried out on-the-spot operation Optimum Experiment research, and conclusion is as follows:

(1) due to the impact of the various factors such as restriction of site space, the flue gas flow rate field of SCR catalyst inlet is inhomogeneous, can cause catalyst outlet NOx and NH like this ₃concentration field very inhomogeneous;

(2) by spray ammonia system is optimized and is adjusted to improve catalyst outlet NO _xand NH ₃cONCENTRATION DISTRIBUTION.The NO of catalyst outlet while first measuring SCR operation _xdistribute, on this basis, spray ammonia sub valve is adjusted to change the ammonia spraying amount of diverse location, thereby obtain uniform NO _xand NH ₃distribution;

(3) by field optimizing, adjust SCR reactor outlet NO _xthe uniformity distributing is significantly improved, NO _xrelative standard deviation by 46.4%, reduce to 14.8%.NH ₃/ NO _xthe deviation of ratio has also had obvious minimizing, has the NH of 24 measuring points (80%) ₃/ NO _xthan in ± 5% scope.Accordingly, in the situation that guaranteeing that the escaping of ammonia does not exceed standard, denitration rate brings up to 83% by 77%.

The present invention is directed to the method that the on-the-spot operation of SCR denitrating system is optimized, to realizing being uniformly distributed of SCR reactor concentration field, raising system denitration rate, avoid obstruction and the corrosion of equipment, in order to instruct, station boiler SCR denitrating system is safe, efficient, stable operation has important directive significance and engineering using value.

The above embodiment has only expressed several embodiment of the present invention, and it describes comparatively concrete and detailed, but can not therefore be interpreted as the restriction to the scope of the claims of the present invention.It should be pointed out that for the person of ordinary skill of the art, without departing from the inventive concept of the premise, can also make some distortion and improvement, these all belong to protection scope of the present invention.Therefore, the protection domain of patent of the present invention should be as the criterion with claims.

Claims (2)

1. a method that improves station boiler SCR denitrating system denitration rate, is characterized in that, comprises the steps:

(1) measure the NO of SCR Benitration reactor outlet _xcONCENTRATION DISTRIBUTION;

(2) according to the measurement result of step (1), calculate NO _xthe unevenness C of CONCENTRATION DISTRIBUTION _v;

(3) work as C _v>20% time, according to the NO of SCR Benitration reactor outlet _xcONCENTRATION DISTRIBUTION adjust the valve opening of ammonia-spraying grid respective regions;

(4) repeating step (1)-(3), until C _v≤ 20%;

Above-mentioned unevenness C _vcomputing formula as follows:

$\mathrm{Cv}=\frac{S}{\stackrel{\‾}{x}}\×100\%,$

$S=\sqrt{\frac{\underset{i=1}{\overset{n}{\mathrm{\Σ}}}(x_i-\stackrel{\‾}{x})}{n-1}},$

$\stackrel{\‾}{x}=\frac{1}{n}\underset{i=1}{\overset{n}{\mathrm{\Σ}}}\mathrm{xi},$

Wherein, xi is the NO of SCR Benitration reactor outlet i measuring point _xconcentration, S is SCR Benitration reactor outlet NO _xthe standard deviation of concentration,

for SCR Benitration reactor outlet NO _xthe mean value of concentration.

2. the method for raising station boiler SCR denitrating system denitration rate according to claim 1, is characterized in that, in step (4), and C _v≤ 15%.

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