Device for the cleaning of flue gases of a boiler plant of nitrogen oxides from

 

(57) Abstract:

The invention relates to heat engineering, can be used in thermal power stations and other industrial sites associated with the combustion of fuel, and can improve the cleaning efficiency of the combustion products from nitric oxide. According to the invention a device for cleaning the flue gases of a boiler plant NOx containing placed in its pass across the flue gas stream bundle of parallel tubes having feed holes in the flow of the mixture of ammonia with transporting agent (gas or steam), the relative step S/d openings in the pipe meets the condition of

< / BR>
where S is the step holes; d - diameter holes; wc- speed mixture of ammonia transfer agent at the exit of the hole; wr- the speed of the flue gases;cthe density of the mixture at the exit of the hole,gthe density of the flue gas, 1 C. p. F.-ly, 1 Il.

The invention relates to heat engineering and can be used for cleaning flue gases from nitrogen oxides in boiler plants that burn fossil fuels.

Widespread cleaning of flue gases by selective negotitions ammonia with a high consumption of processed flue gas temperature zone 900 - 1100oC, at which most effectively proceed the reaction (1), the ammonia must be submitted in a mixture with transporting agent (gas or steam).

Closest to the invention is a device for cleaning the flue gases of a boiler plant NOx containing placed in its pass across the flue gas stream bundle of parallel tubes having feed holes in the flow of the mixture of ammonia transfer agent (1).

In this device the holes in the pipe is placed with a relative step

S/d 10

where S is the step holes;

d - diameter holes.

It was envisaged that this embodiment of the device will ensure uniform mixing of the ammonia with the flue gases and thus high efficiency purification from nitrogen oxides. Indeed, the choice of the step S in the above condition ensures uniform mixing, however, it requires considerable consumption of carrier agent that causes a significant loss of energy. When applying ammonia gas (air) necessary energy to drive the compressor, and when the supply of steam taken from the turbine, a reduction in its power and necessary costs to fill parushim agent by reducing the consumption of the latter.

For this purpose, the device for cleaning of flue gases of a boiler plant NOx containing placed in its pass across the flue gas stream bundle of parallel tubes having feed holes in the flow of the mixture of ammonia with transporting agent, the relative step S/d openings in the pipe meets the condition of

< / BR>
where Wc- speed mixture of ammonia transfer agent at the exit of the holes;

Wr- the speed of the flue gases;

cthe density of the mixture at the exit orifice;

gthe density of the flue gas.

Parameters Wrandgthe cross section of the flue, where the device is determined from thermal calculation of the boiler in normal mode or test.

Parameters Wcandcdetermined by a preselected pressure and temperature of the transporting medium.

The selection step according to the formula (C) allows, as shown by experiments, to obtain a sufficiently uniform mixing of the ammonia with the flue gases, but reducing several times the flow rate of carrier gas (steam), and thus the corresponding energy loss. If step S to choose less than the left limit in formula (3), unreasonably tion: if the step S is greater than the right limit (3), then, as the experiments showed, rapidly deteriorating the uniformity of mixing of the ammonia gas in the zone of optimum temperature, which reduces the efficiency of nitrogen oxides (the axis of the holes in the pipes should preferably be angled 9045oin relation to the flow velocity of gases).

As shown by measurements on boilers with horizontal flue, temperature profile has a significant irregularity: the average temperature close to the optimum for the chemical reactions (1), in the upper part of the flue gas temperature in the direction of travel of the gases may exceed the lower limit. In this case, in accordance with the invention, the ends of the bundle of parallel tubes in the upper part of the flue can be derived beyond, skipped out of the duct in the direction of the combustion zone to the place of their subsequent entry into the flue gas duct in cross-section, the temperature regime in which the optimal conditions for the reaction of nitrogen oxides with ammonia.

The drawing schematically shows performed in accordance with the invention, the device is placed in the flue of the boiler installation.

The bundle of parallel tubes 1 and collector 2. has 3 holes for filing in the flow of the mixture AMI meets the condition (3).

The beam 1 is placed in the zone temperatures of 900 - 1100oC, at which the effective reaction (1).

If at the top of the flue in the setup of the beam and parallel tubes 3 flue gas temperature is below the lower limit required for the reactions (1), which may be established on the basis of calculations or experiments, the ends 6 of the pipe (shown in the drawing by the dashed line) are displayed through the ceiling duct outside and skipped towards the combustion zone to the place of their subsequent entry into the flue gas duct in cross-section, the temperature regime in which the optimal course of chemical reactions (1).

During operation of the boiler system, the mixture of gas or vapor with ammonia enters the collector 2 and the tube bundle 1, where through holes 3 in the form of streams flows into the flue gas duct 4, where for a small along the flow area of the L are evenly mixed with the flue gas stream, providing the entire area of the flue reactions (1) to reduce the emissions of nitrogen oxides from gases leaving.

Using equation (3) allows the use of relative steps, much greater recommended (1). For example, if the transport agent is water vapor from the flue, where Wr= 10 m/s andg-0,27 kg/m3then (Wc/Wr95, and the valid interval of the selection relative steps, respectively 42,5 - 190. While it is preferable to select a specific value of S/d near the center of the interval, i.e. 80 - 110, however, there is far more variance within it depending on the length of the flue temperature zone corresponding to the optimal conditions of chemical reactions linking nitrogen oxides. At small length of this zone requires organization of the most intensive mixing of the ammonia mixes with the combustion gases, which requires the approximation of S/d to the lower boundary of the interval and correspondingly high energy costs when the length of the specified temperature range, sufficient to complete the chemical reactions (1) for large values of S/d, the relative step can be increased within the limits calculated according to (C) interval until its upper boundary. When you choose a step S/d at the specified interval, you can also increase or decrease its height, thereby changing the distribution of the flow rate of ammonia at the height of the flue, to take into consideration the unevenness of the concentration of nitrogen oxides in flue gases for the conditions of the concrete is carried by the absence of impact erosion and clogging of the holes on the bandwidth.

The device, made in accordance with the invention, was tested on boiler # 7 Toliatinskoe CHP. The resulting reduction in emissions of nitrogen oxides by more than 50% when the boiler to coal dust For the transportation of ammonia with a flow rate of 0.2 t/h was required steam flow rate of 9 t/h, which amounted to 1.5% of the steam capacity of the boiler. If instead of the condition (3) to select the step S hole was made, the condition (2) of the prototype, the steam consumption would exceed 50 t/h

From the above example implementation shows that the proposed device with the simplicity of the design ensures energy savings, as evidenced by the test results.

Literature

Skorik L. D. and other Industrial inspection method of flue gas of thermal power plants from oxides of nitrogen entering the ammonia in the high temperature circuit. Power, 7. 1986, S. 58 - 59.

1. Device for the cleaning of flue gases of a boiler plant NOx containing placed in its pass across the flue gas stream bundle of parallel tubes having feed holes in the flow of the mixture of ammonia with transporting agent, characterized in that the relative pitch holes in the pipe meets the condition of

< / BR>
where S step open is tertia;

Wgthe speed of the flue gases;

cthe density of the mixture at the exit orifice;

gthe density of the flue gas.

2. The device under item 1, characterized in that the ends of a bundle of parallel tubes in the upper part of the flue withdrawn beyond, skipped out of the duct in the direction of the combustion zone to place the entry in the flue section, a temperature which corresponds to the optimal temperature reactions of ammonia and oxides of nitrogen.

 

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