SU1749618A1 - Method of gas fuel combustion - Google Patents

Abstract

SUBSTANCE: in order to reduce the content of nitrogen oxides in combustion products and prevent resonant burning, equal periods and amplitudes of pulsations superimposed on streams of rich and lean mixtures of fuel and oxidant, and a half-shift in phase are performed. pulsation period, one of the above streams relative to the other, while the cost of enriched and poor mixtures for a time multiple of the pulsation period are equal between by myself. 1 hp f-ly, 2 ill. cl

Description

The invention relates to energy and can be used in the combustion of gaseous fuels and is intended to reduce the toxicity of the products of its combustion discharged into the atmospheric air.

A known method of burning gaseous fuel, which reduces emissions of nitrogen oxide into the atmosphere by increasing the excess air in the furnace or by introducing moisture into the hot air and, accordingly, reducing the temperature in the combustion zone.

However, this is less cost-effective due to an increase in the amount of heat discharged into the atmosphere with flue gases.

There is also known a two-stage combustion method, in the implementation of which the burners are assembled in two or more Rus, and the air flow through the burners rushes varies from flaws to surpluses, and the average excess over the furnace as a whole is equal to the calculated one.

This method is relatively low-cost, but for its implementation it is necessary to place the burners in two or more rus, which is not always justified by capital expenditures and ease of maintenance. In addition, the control of the combustion process is complicated.

There is also known a method for feeding recirculated gases to burners or to different zones of a furnace. This method found quite wide.

N

h about

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For example, because, along with a significant reduction in nitrogen oxide emissions, it is possible to bring the emission characteristics of flares closer together when burning gas and fuel oil and to reduce the heat effect of the screens when burning fuel oil.

However, significant capital expenditures are required to implement this method. In addition, in some abnormal conditions carcinogens can be formed and discharged into the environment.

The closest to the invention in its technical essence is a method of burning gaseous fuel by supplying rich and lean fuel and oxidizer mixtures to the combustion zone, followed by mixing and afterburning, and at least one of the mixtures is oscillated, and rich and lean mixtures are fed in the form of independent swirling threads.

The disadvantage of this method is the possibility of reaching a resonant combustion, as a result of which the destruction of some elements of the furnace and the boiler may occur. The mismatch of frequencies from burner to burner from 0.12 to 0.36 relative to the average frequency is difficult and not always effective for powerful burners, the number of which is relatively small in the boiler, and the torches of each of the burners are slightly mixed with each other.

The purpose of the invention is to reduce the content of nitrogen oxides in combustion products and to prevent resonant combustion.

This goal is ensured by the fact that by supplying rich and lean fuel and oxidizer mixtures with independent swirling flows into the furnace and pulsations on both of these flows, conditions are created for local combustion of the fuel in conditions of insufficient or excess air, followed by mixing and afterburning , the average consumption of enriched and lean mixtures of fuel and oxidant supplied through different burner channels is equal to each other, and pulsations of equal frequency and amplio are applied to each of these mixtures tude but shifted in phase by half a period of the pulsation. At the same time, the expenses of each of these mixtures per unit time multiple of the pulsation period must be equal to the calculated values, and the total expenses of both mixtures at each time point are equal to each other.

Fig 1 shows a graph of pulsating flow rates of enriched (v06) and poor (ve) mixtures of air and combustible gas. Since the pulsations of the enriched and the poor flow rates are shifted by half the period, and the amplitudes and frequencies of the pulsations are equal to each other, then at each moment in time the total consumption of the rich and poor mixtures will be constant and equal to

2) v v06 + V6,

where v06 and ve are the running costs of rich and poor mixtures,

Accordingly, in time intervals 0-1, 2-3, 4-5, ... there will be drawbacks, and in intervals of 1-2, 3-4, 5-6, ... excess air. Since the total flow 2 v from the burner at each time point will be constant in terms of flow rate (Fig. 1) at a given load of the boiler and equal to the calculated value, the total flow pulsations that would cause resonance mishap will not occur.

Example. Initial data:

gas consumption per burner vr 0.2 m3 / s;

the theoretically required amount of air required for burning 1 m3 of gas, v0 10 m3 / m3;

gas consumption in rich and lean vr mixes. about 0.12 m3 / s. vr.e 0.08 m3 / s;

estimated air flow to the burner uv 2m3 / s; air consumption in the enriched mixture ve.o6 1 m3 / s;

the amplitude of the pulsations of the enriched and poor mixtures is 0.1 m3 / s.

Maximum and minimum enrichment mix costs:

Vo6 max (1 + a) (vr, o6 + vB.o6) 1,232 M3 / s;

v06 mim (1 - a) (vr v + vB.o6) 1,008 m3 / s.

Poor air consumption:

0

five

0

five

 Max max

1 +3

- Vu, 6

 Wobmin

1-a

- Vr.6

and minimum expenses

VB, 6

.1.04m3 / s. Maximum lean mixture:

Ub.Max. (1 + a) (vr.6 + ov.b) 1.232.

U.min - (1 - a) (vr.6 + vn.e) 1.008.

From the calculation it follows that the cost of enriched and poor mixtures

Vo6 max Ub.max: Wob.min Ub.min

Air consumption per burner vr.e (vB, o6 + ve b) 2.04 m3 / s. This consumption is higher than the calculated

do-lvu.b-0.5uv) -100

v8 / 0

and can be classified as excess air.

Figure 2 schematically shows the development of a flame in a furnace when implementing the proposed method of burning gaseous fuel. In the flame zones limited by cross sections 3 (in these cross sections, excess air is equal to the calculated values), the deficiencies and excess air will periodically alternate so that the adjacent zones will always differ in excess air. If in zones 11, 3,5,.,. there will be air deficiencies at a given time (the amount of the enriched mixture exceeds the amount of the poor mixture), then in zones 2, 41 ,, .. there are surpluses and, conversely, if in zones 1 and З1 there is an excess of air, then in zones 2, 4, - disadvantages (the amount of lean mixture exceeds the amount of enriched mixture).

Unburnt fuel or products of its incomplete combustion will remain in flammable air flaws, and excess air will remain in excess areas. Both one and the other will determine a decrease in the combustion temperature in these zones and a decrease in the intensity of generation of nitrogen oxides. This effect will take place at a seme of the early stage of torch development, which will most likely reduce the intensity of nitrogen oxide formation, since it is in the initial, most high-temperature zone of the torch that intensive oxidation of nitrogen occurs. Outside the initial section of Fzkel, due to intense turbulent pulsations and mass transfer processes, complete combustion of fuel and products of incomplete combustion in the peripheral zone of the plume, in which the generation rate of nitrogen oxides is relatively low, will occur.

The method is implemented as follows.

In accordance with a given program, special devices (for example, butterfly valves) installed as close as possible to burners in boxes for rich and lean mixtures, overlap parts of sections of these boxes with a given frequency, and the periods and amplitudes of the resulting pulsations of both streams should be equal in size and phase shifted by half a period. This creates conditions for the combustion of combustible gas at each time point with deficiencies or excess air, since only two points of the flow schedules of the enriched and the poor flows m 1 and g 2 (Fig. 1) will have a given ratio of these quantities within the pulsation period. media, and within the adjacent half-periods of the pulsations, modes with deficiencies or excess air will alternate. At the same time costs

air and combustible gas and for a time multiple of the pulsation period remain equal to the calculated values for a given performance and operating mode of the boiler. 5

the presence of pulsations in the cost of enriched and lean mixtures will be insignificant, since the devices for the realization of pulsations are located near the burners and, accordingly, at a relatively large distance from the blower fans. Air and combustible gas, or mixtures thereof, are compressible media, therefore the partial overlap of the sections of ducts for enriched and

5 poor mixtures will lead to compression of these media, and when opening sections, the energy expended in compression will be partially released.

In connection with local periodic

0 deficiencies of air (heat of combustion of fuel will be less due to the formation of products of incomplete combustion, as well as heating of excess combustible gas not participating in the combustion) and excess air (heat

5 combustion will be spent on heating the excess air not participating in the combustion) in the root zone of the fzkel, the combustion will occur at a reduced flame temperature, which will determine the reduction in the rate of formation of nitrogen oxides. In subsequent flame development zones due to turbulent pulsations and intense mixture formation - processes will be carried out complete combustion of fuel,

5 but in a larger volume of the furnace and with greater heat transfer to the heating surfaces, which will determine the decrease in the temperature of the flame and, consequently, the decrease in the content of nitrogen oxides in the combustion zone and in the discharged

0 into the atmosphere of flue gases.

Claims (2)

Invention Formula 1, Method of burning gaseous fuel by feeding independent pulsating streams rich and poor 5 mixtures of fuel and oxidant in the combustion zone with their subsequent mixing and afterburning, characterized in that. that, in order to reduce the content of nitrogen oxides in combustion products and prevent resonant combustion, equal periods and amplitudes of pulsations are achieved, as well as a phase shift by half the period of pulsations of the flow of one of the fuel and oxidant mixtures relative to another. five 2. A method according to claim 1, characterized in that the flow rate of the rich and lean mixtures during a time multiple of the pulsation period is equal to each other. W t enriched lliJ mixN P Poor arrogance 2