CN102125800A - Method for optimized regulation of SCR (Selective Catalyst Reduction) flue gas denitration system in coal-fired power plant - Google Patents

Abstract

At present, a regenerative Junker-type air preheater is used for heating boiler-supplied air in most of large coal-fired power generating sets in China, and ammonium bisulfate results in scaling and corrosion on the surface of heat transfer elements at the medium/low temperature end of the air preheater, thereby threatening the safe and stable operation of the air preheater directly. The invention relates to a method for the optimized regulation of an SCR (Selective Catalyst Reduction) flue gas denitration system in a coal-fired power plant, which comprises the following steps of: (1) jetting ammonia into a denitration reactor; (2) measuring the concentrations, the speeds and the temperature distribution of NO and O2 at an inlet of the denitration reactor; (3) measuring the concentration distribution of NO and O2 at an outlet of the denitration reactor; (4) calculating the unevenness Cv of the concentration distribution of NO at the outlet of the denitration reactor; and (5) comparing the obtained Cv with C%. The method effectively reduces ammonia escape, prevents ammonium bisulfate from scaling and corrosion on the surface of the heat transfer elements of the air preheater, and ensures the safe and stable operation of the air preheater.

Description

A kind of method of optimizing and revising of the SCR of coal-burning power plant flue gas denitrification system

Technical field

The present invention relates to the SCR of coal-burning power plant flue gas denitrification system, specifically a kind of method of optimizing and revising of the SCR of coal-burning power plant flue gas denitrification system.

Background technology

Along with China's development of electric power industry, the discharge capacity of NOx grows with each passing day, and is well-known, and NOx pollutes can form acid rain, photochemical fog, destroys ecological environment, and its influence more and more causes people's attention and attention.Present newly-built coal fired power generation unit requires to install SCR (selective catalytic reduction) equipment for denitrifying flue gas basically and reduces the NOx discharging, along with the raising of China's discharge standard, the operation unit of SCR equipment for denitrifying flue gas is not installed will progressively the SCR equipment for denitrifying flue gas be installed yet by transforming.

The principle of SCR denitrating flue gas is under catalyst action, sprays into ammonia in flue gas, with NO _xBe catalysed and reduced into N ₂And H ₂O, the key reaction formula is 4NO+4NH ₃+ O ₂=4N ₂+ 6H ₂O.Because the ammonia that sprays into and flue gas can not accomplish for 100% even the mixing, in some zone of Benitration reactor, the content of ammonia can be greater than the NO in the flue gas _xContent so just causes ammonia superfluous relatively, thereby forms the escaping of ammonia.Stable operation exerts an influence the escaping of ammonia to unit safety, and its main cause is water vapour, the SO in the flue gas ₃And the escaping of ammonia, can generate ammonium hydrogen sulfate under certain condition, its reaction equation is: NH ₃+ SO ₃+ H ₂O=NH ₄HSO ₄Ammonium hydrogen sulfate is a kind of corrosive substance of very thickness under liquid state, can result in blockage and corrodes Benitration reactor and upstream device.When flue-gas temperature is lower than the initial generation temperature of ammonium hydrogen sulfate, ammonia and SO ₃Will generate ammonium hydrogen sulfate.

The large-scale coal fired power generation unit of China adopts renewable Ljungstrom air heater to come the boiler air feed is heated mostly at present.In air preheater, low-temperature end, because flue-gas temperature is lower than the initial generation temperature of ammonium hydrogen sulfate, ammonium hydrogen sulfate can generate on the heat transfer element surface of the middle low-temperature end of air preheater like this, thereby make on the heat transfer element of air preheater and produce fouling, corrosion, finally cause air preheater phenomenons such as pressure drop rising, heat exchange efficiency reduction to occur, directly threaten the safe and stable operation of air preheater.

The ammonia injection method that is applied to coal-fired power station boiler SCR flue gas denitrification system at present mainly contains three kinds: first eddy current type static mixing gunite, the sheet number that is characterized in spraying the number of ammonia nozzle and static mixer sheet is the same, total amount generally has only several, utilizes flue gas to flow through the eddy current that the blender sheet produced and guarantees that flue gas mixes with the even of spraying into ammonia.It two is that the Linear Control formula is sprayed grid spray ammonia process, is characterized in drawing several pipes respectively along two orthogonal directions of flue, and several nozzles are set again on the every pipe, and the flow of each pipe can be regulated separately, with NO in the coupling flue gas _xContent.It three is that subregion control formula is sprayed grid spray ammonia process, is characterized in the flue cross section is divided into 20～50 zones that size is identical, and there are several nozzles in each zone, and the flow of each subregion is adjustable separately, to mate NO in the flue gas _xDistribution.

The method of optimizing and revising that can be used for the coal-fired SCR flue gas denitrification system of above-mentioned three kinds of typical case's spray ammonia process is not at present appeared in the newspapers as yet.

Summary of the invention

Technical problem to be solved by this invention is to overcome the defective that above-mentioned prior art exists, and provides a kind of method of optimizing and revising that can be used for the coal-fired SCR flue gas denitrification system of above-mentioned three kinds of typical case's spray ammonia process, with effective reduction the escaping of ammonia.

For this reason, the technical solution used in the present invention is: a kind of method of optimizing and revising of the SCR of coal-burning power plant flue gas denitrification system, and its step is as follows: 1) spray ammonia in Benitration reactor; 2) NO and the O of the import of measurement Benitration reactor ₂Concentration, speed and Temperature Distribution; 3) measure NO and the O that Benitration reactor exports ₂CONCENTRATION DISTRIBUTION; 4) calculate the unevenness C that Benitration reactor exports the NO CONCENTRATION DISTRIBUTION _v5) with the C of gained _vCompare with C%, work as C _vDuring≤C%, optimize and revise and finish; Work as C _vDuring＞C%, export the valve opening that the NO CONCENTRATION DISTRIBUTION is adjusted the ammonia-spraying grid respective regions, then repeat the 3rd according to Benitration reactor)-4) step, until C _v≤ C%;

Above-mentioned unevenness C _vComputing formula as follows:

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

$\mathrm{\σ}=\sqrt{\frac{1}{(n-1)}\underset{i=1}{\overset{n}{\mathrm{\Σ}}}{(x_i-\stackrel{\‾}{x})}^2},$

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

Wherein, x _iFor Benitration reactor exports certain any NO concentration, σ is the standard deviation of Benitration reactor outlet NO concentration,

Measure the mean value of the NO concentration of having a few in the cross section for the Benitration reactor exit, C is a constant, and its ammonia injection method and denitration efficiency with the employing of SCR flue gas denitrification system is relevant, and the span of C is 15～30.

The beneficial effect that the present invention has: effectively reduce the escape amount of ammonia, avoid ammonium hydrogen sulfate on the heat transfer element of air preheater, to produce fouling, corrosion, guaranteed the safe and stable operation of air preheater.

The invention will be further described below in conjunction with specification drawings and specific embodiments.

Description of drawings

Fig. 1 is a schematic flow sheet of the present invention.

The specific embodiment

Technical scheme of the present invention is applied in the concrete power plant:

The spray ammonia technology of power plant, Ninghai, Zhejiang #4 stove denitrating system adopts the Linear Control formula to spray grid spray ammonia process, at 10 sprays of spray ammonia flue lateral arrangement ammonia pipeline, arranged 10 spray ammonia pipelines respectively in both sides longitudinally at spray ammonia flue, but the equal independent regulation of ammonia spraying amount of each spray ammonia pipeline.By technical scheme of the present invention the escaping of ammonia of denitrating system is adjusted to 1.2ppm from 1.8ppm, the escaping of ammonia has reduced by 33%.

Logical sequence power plant, north, Zhejiang #6 unit denitrating system adopts eddy current type static mixing gunite to realize the even mixing of ammonia and flue gas, and A, B Benitration reactor respectively are provided with 5 vortex mixers.The eddy current of this spray ammonia process dependence flue gas is realized the even mixing of ammonia and flue gas, often needs long mixing apart from the even mixing that could realize ammonia and flue gas, and can only carry out the adjustment of ammonia spraying amount in a direction of flue.By technical scheme of the present invention the escaping of ammonia of denitrating system is adjusted to 1.4ppm from 1.7ppm, the escaping of ammonia has reduced by 17.6%.

Ninghai, Zhejiang #6 unit denitrating system adopts the mode of subregion control to arrange spray ammonia valve door (subregion control formula is sprayed grid spray ammonia process), the little subregion of each minute 48 sprays ammonia on the spray ammonia cross section of A, B side, a spray of each spray ammonia valve gate control ammonia subregion can carry out the adjustment of ammonia spraying amount at the horizontal and vertical both direction of spray ammonia flue.By technical scheme of the present invention the escaping of ammonia of denitrating system is adjusted to 0.78ppm from 1.93ppm, the escaping of ammonia has reduced by 59.6%.

Claims (2)

1. the method for optimizing and revising of the SCR of a coal-burning power plant flue gas denitrification system, its step is as follows: 1) spray ammonia in Benitration reactor; 2) NO and the O of the import of measurement Benitration reactor ₂Concentration, speed and Temperature Distribution; 3) measure NO and the O that Benitration reactor exports ₂CONCENTRATION DISTRIBUTION; 4) calculate the unevenness C that Benitration reactor exports the NO CONCENTRATION DISTRIBUTION _v5) with the C of gained _vCompare with C%, work as C _vDuring≤C%, optimize and revise and finish; Work as C _vDuring＞C%, export the valve opening that the NO CONCENTRATION DISTRIBUTION is adjusted the ammonia-spraying grid respective regions, then repeat the 3rd according to Benitration reactor)-4) step, until C _v≤ C%;

Above-mentioned unevenness C _vComputing formula as follows:

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

$\mathrm{\σ}=\sqrt{\frac{1}{(n-1)}\underset{i=1}{\overset{n}{\mathrm{\Σ}}}{(x_i-\stackrel{\‾}{x})}^2},$

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

Wherein, x _iFor Benitration reactor exports certain any NO concentration, σ is the standard deviation of Benitration reactor outlet NO concentration,

Measure the mean value of the NO concentration of having a few in the cross section for the Benitration reactor exit, C is a constant, and its ammonia injection method and denitration efficiency with the employing of SCR flue gas denitrification system is relevant.

2. the method for optimizing and revising of the SCR of coal-burning power plant flue gas denitrification system according to claim 1, the span that it is characterized in that C is 15～30.

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