RU2008559C1 - Method and device for burning gas - Google Patents

Abstract

FIELD: thermal engineering. SUBSTANCE: method involves feeding gaseous and air flows to a combustion zone and injection of recirculation gases. The recirculation gases are injected into the gas flow before mixing it with the air flow. The device has a gas feed case a gas feed pipe mounted along the case axis. The air feed pipe is mounted in the gas feed case with an annular clearance and has gas nozzles with outlet holes on the side surface, the nozzles are coaxially positioned around the air feed pipe and one nozzle - around the other one. The air feed pipe also has recirculation gas feed nozzles and branch pipes on the side surface of the gas feed nozzle. The branch pipes are brought out into outlet holes. EFFECT: improved efficiency. 2 cl, 1 dwg

Description

 The invention relates to energy and can be used in the combustion of gaseous fuels.

 A known method of burning fuel by mixing it with part of the air and supplying the rest of the air in the form of several air jets with an air flow rate in each subsequent stream exceeding the flow rate in the previous one [1].

 There is a method of burning gaseous fuel by feeding part of the fuel to the combustion zone to form the main flame, and the rest of the fuel in a mixture with air - in separate jets evenly distributed between the jets of the main flame [2].

 The disadvantages of these methods include the low efficiency of suppressing the formation of harmful impurities in the combustion products, the complexity of the technical implementation of the methods.

 A known method of burning gas by supplying a mixture to the combustion zone and recycling hot products of combustion to the root of the flame [3].

 The disadvantage of this method is the instability of the process of recirculation of combustion products, the low efficiency of the suppression of the formation of nitrogen oxides in the combustion products.

 Closest to the invention is adopted as a prototype method of burning gas [4].

 According to this method, counter-gas air flows are fed into the combustion zone in several tiers, secondary air is introduced above them in countercurrent jets, and additionally recirculation gases are introduced into the combustion zone, and one part of the recirculation gases is pre-mixed with the direct-flow jets of secondary air, and the other is fed around all its direct-flow streams .

 The disadvantages of this method are as follows: the complexity of the organization of the process, which consists in the need to create counter swirling jets of air; low efficiency of suppressing the formation of nitrogen oxides due to the long (compared with conventional methods of gas combustion) gas residence time in the high temperature zone (the residence time in the high temperature zone increases due to swirling flows and counter currents); the need for additional atomization of water, the evaporation of which takes part of the heat of combustion of the fuel and therefore reduces the amount of heat used.

 The aim of the invention is to reduce the content of nitrogen oxides in the combustion products.

 The goal is achieved in that, in contrast to the known method, which consists in supplying counter-tidal gas flows by several tiers, introducing secondary air above them with countercurrent jets and additionally introducing recirculation gases into the combustion zone when preliminary mixing part of the recirculation gases with once-through jets of secondary air and supplying another part recirculation gases around all direct-flow streams of secondary air, recirculation gases are introduced into the gas stream before it is mixed with air sweat eye.

 Gas combustion is carried out in a device containing an air supply pipe installed with an annular gap along the axis of the gas supply housing, provided with gas nozzles coaxially arranged around it and one around the other with gas outlets on the side surface, gas recirculation nozzles and nozzles on the side surface of the gas supply nozzle, branch pipes are brought out to openings.

 The drawing shows a General view of a device for implementing the method of burning gas.

 Gas is supplied to a burner containing a gas supply housing 1, gas nozzles 2 and 3 with pipes 4 and openings 5, an air supply pipe 6, gas outlet channels 7 in the gas supply housing, through a pipe 8. At the same time, air is supplied into the air supply pipe and the annular gap. The fuel mixture is ignited and part of the resulting combustion products (recirculation gases) is supplied to the recirculation gas nozzles 2, while supplying gas to the gas nozzles 3.

 The burner works as follows.

 The gas supplied to the gas supply housing 1, the jets exit into the annular gap between the air supply pipe with nozzles and the housing 1, where it is mixed with the air entering the annular gap. The resulting combustible mixture is ignited using a lighter. The combustion products are partially (known ratio of 15-30%) sent to the nozzle 2 for supplying recirculation gases and at the same time supply gas to the nozzle 3. Gas through the nozzles 4 enters the annular gap, recirculation gases also enter through the openings 5. Some of the recirculation gases are mixed with the gas coming from the nozzles 4, and the other part is mixed with the air and gas coming from the gas supply housing 1. A mixture is formed with a lack of air, which burns out some of the gas, since the oxygen contained in the mixture is not enough oxidation of all gas. Since almost all oxygen is consumed for gas oxidation, in this case, the formation of nitrogen oxides is significantly reduced.

 The air supplied to the air supply pipe 6 is shielded by recirculation gases from the mixture burning at the periphery of the burner at the outlet of the burner and passes through the central jet into the zone where it is mixed with gas, combustion products, non-burnt in the first zone, and recirculation gases. A second combustion zone is formed, where the remaining gas is afterburned.

 It is known that for stable ignition and combustion of a gas-air mixture it is necessary that the mixture has certain concentration limits. For example, the concentration limits in air mixtures of natural gas (Saratov) are 5.1-12.1 vol. % Thus, to create a combustible mixture, it is necessary to mix 1 part gas with 8-20 parts air. Uniform mixing of combustible components in such proportions and in a very short time (the flow rate of fuel into the burner chamber is on average 30-50 m / s) is a particular problem. The formation of a combustible mixture usually occurs in two stages: the primary mixing of gas and air in the burner; mixing in the combustion chamber itself.

 The role of primary mixing is decisive, since it should provide the necessary minimum concentration ratio (for Saratov gas 5.1%) of combustible components. Otherwise, the mixture will not ignite. Mixing in the combustion chamber itself is determined by the intensity of the processes of heat and mass transfer in the flare, which can be intensified by increasing turbulence in flows and in other ways. At the same time, high turbulence is necessary only in the core of the torch, and at the mouth of the burners for the possibility of ignition it is necessary to have moderate turbulence, which imposes restrictions on the possibility of mixture formation in the torch. As a result of this, it is necessary to achieve the most complete mixing at the first stage, i.e., in the burner.

It is obvious that the uniform mixing of gas components occurs most quickly when they occupy equal volumes in space. Indeed, if, for example, in a volume of 1 m ^{3 the} air occupies 0.5 m ³ and the gas is 0.5 m ³ and is separated by an impenetrable partition, then after removing the partition each component needs a certain amount of time to spread over the entire volume, i.e. the remaining 0.5 m ³ to create an equal concentration mixture volume. If the gas takes, for example, 0.1 m ² , and the air - 0.9 m ³ , then the gas will require significantly more time to spread to 0.9 m ³ than for 0.5 m ³ , and the time of formation of a homogeneous mixture determined by the maximum mixing time, i.e., the spread of gas over the entire volume.

 The addition of recirculation gases to the combustible gas, and not to the air, makes it possible to reduce the difference (or equalize the volumes) between the volumes of the mixed gas and air flows and thereby improve mixing.

=

exp

-

O₂·N

exp

-

(1) где τ - время, с;
N₂, О₂, NO - концентрация азота, кислорода и закиси азота, г-моль/л.It is known that the rate of formation of nitrous oxide is determined as follows:

=

exp

-

O ₂ · N

exp

-

(1) where τ is the time, s;
N ₂ , O ₂ , NO - the concentration of nitrogen, oxygen and nitrous oxide, g-mol / L.

 From the expression (1) it follows that in order to reduce the formation of nitrogen oxides, it is necessary to lower the temperature in the furnace, reduce the oxygen concentration in the reaction zone, and reduce the residence time of gases in the high temperature zone.

 The supply of recirculation gases to the gas stream allows you to organize a two-stage combustion process, resulting in a decrease in temperature, since the combustion zone increases in volume and the amount of heat released as a result of combustion per unit volume is reduced. The oxygen concentration in the reaction zone also decreases, since the zone itself increases in size. All this leads to a decrease in the content of nitrogen oxides in the products of combustion.

It is known that reducing air heating is an effective way to reduce NO _x emissions from gas combustion. In our case, air heating is excluded; instead, gas is heated by heat exchange with recirculation gases, which increases the stability of the combustion process and reduces the formation of NO _x .

 Thus, the proposed method and device for gas combustion during combustion can reduce the content of nitrogen oxides in the combustion products.

G_возд.= 0,0238-0,00952= 0,0143м³/c (4)
Не сгоревший в первой зоне пропан догорает во второй зоне, куда поступает воздух из воздухоподводящей трубы 6. В первой зоне сгорает пропана

_{= 4·10}-4_м3_/c (5)
Продуктов сгорания образуется 25,8м³/м³·4·10^-4м³/c= 0,010м³/c (6)
Таким образом во вторую зону горения поступает следующее количество газов: 0,01м³/c+0,0143м³/c+0,0006м³/c= 0,0249м³/c (7)
Концентрация пропана в смеси составит
0,0006 м³/с : 0,0249 м³/с˙100% =
= 2,41 об. % что входит в концентрационные пределы 2,4-9,5% . Поэтому во второй зоне будет устойчивое горение.PRI me R 1. In a burner containing a gas supply housing 1, gas nozzles 2 and 3 with nozzles 4 and openings 5, an air supply pipe 6, gas outlet channels 7, natural gas containing mainly propane in the amount of 0.001 m ³ / s. As you know, for the complete combustion of 1 m ^{3 of} propane, 23.8 m ^{3 of} air is needed. At the same time, the propane air mixture stably ignites when the propane content in the mixture is in the range of 2.4–9.5 vol. %, i.e., 1 m ^{3 of} propane accounts for 4.6 m ⁴ - 9.52 m ^{3 of} air. Beyond these concentration values, the mixture does not burn. Based on this, air is supplied through the nozzle into the annular gap with a flow rate of:
G _air = 0.001m ³ / s23.8 = 0.00952m ³ / s (2)
Light the fuel mixture. At such air flow rates, propane burns, since for its complete combustion it would be necessary to supply air in the following quantity:
G $\genfrac{}{}{0ex}{}{\text{ps}}{\text{air}}$ _ear = 0.001 m ³ / s · 23.8 = 0.00238 m ³ / s (3) At the same time, air is supplied to the air supply pipe 6 at a rate equal to
G = g

G _air = 0.0238-0.00952 = 0.0143m ³ / s (4)
The propane not burnt in the first zone burns out in the second zone, where air enters from the air supply pipe 6. Propane burns in the first zone

_{= 4 · 10} -4 _m 3 _{/ s} (5)
Combustion products form 25.8 m ³ / m ³ · 4 · 10 ^-4 m ³ / s = 0.010 m ³ / s (6)
Thus, the following amount of gases enters the second combustion zone: 0.01 m ³ / s + 0.0143 m ³ / s + 0.0006 m ³ / s = 0.0249 m ³ / s (7)
The concentration of propane in the mixture will be
0.0006 m ³ / s: 0.0249 m ³ / s˙100% =
= 2.41 about. % which is included in the concentration limits of 2.4-9.5%. Therefore, in the second zone there will be steady combustion.

Next, recycle part of the combustion products, which are fed into nozzles 2 in an amount
G _recycle. = 0.00387m ³ / s (8)
Such an amount of recirculation gases (combustion products) is determined by their optimal amount in terms of reducing emissions of nitrogen oxides (15-30%). At the same time, gas is supplied through nozzles 3 with a flow rate equal to the flow rate of recirculation gases, i.e.

_{· 100%=3,6%} что находится в концентрационных пределах устойчивого горения.G _gas = 0.00387m ³ / s (9) At the same time, the air flow through the air supply pipe is increased by an amount
0.00387m ³ / s23.8m ³ / m ³ = 0.0921m ³ / s (10) Thus, the total air flow through the air supply pipe will be
0.0921m ³ / s + 0.0143m ³ / s = 0.106m ³ / s (11) The following amount of gases (gas, air, combustion products from the first zone, recirculation gases) enters the second combustion zone: 0.00387m ³ / s + 0,0006m ³ / s + 0,0100m ³ / s + 0,106m ³ / s = 0,124m ³ / s The gas concentration in the second zone will be

_{· 100% = 3.6%} which is in the concentration limits of sustainable combustion.

_{· 100% = 21%} Воздух, подаваемый на сжигание, не подвергается подогреву, а часть продуктов сгорания (газы рециркуляции) возвращается в горелку и проходит через зоны горения, благодаря чему возрастает скорость разложения кислорода, содержащегося в газах рециркуляции.Reducing nitrogen oxide emissions occurs due to the fact that in the first zone with a lack of oxygen gas burns approximately

_{· 100% = 21% The} air supplied to the combustion is not heated, and part of the combustion products (recirculation gases) is returned to the burner and passes through the combustion zones, thereby increasing the rate of decomposition of oxygen contained in the recirculation gases.

_{= 1,19·10}-3_м3_/c В первой зоне образуется следующее количество продуктов сгорания: 10,52м³/м³·1,19·10^-3м³/c= 1,248·10^-2м³/c Во вторую зону горения поступают продукты сгорания из зоны, несгоревший метан и воздух из воздухоподводящей трубы 6 1,248·10^-2м³/c+(0,002-0,00119)м³/c+0,0077м³/c= 0,021м/c Концентрация метана во второй зоне составит величину

_{· 100% = 3,86oб.%}
Для метана нижний концентрационный предел воспламенения составляет 5 об. % . Поэтому для горения во второй зоне необходимо туда подать дополнительно метан. Подачу метана во вторую зону осуществляют через насадок 3 подачи газа. Пусть подают метан через насадок 3 с расходом 0,001 м³/с. Далее производят подачу газов рециркуляции через насадок 2 в количестве 30% от продуктов сгорания в первой зоне, т. е. G_{газ.рецирк.}= 1,248·10^-2м³/c·0,3= 0,0037м³/c
Во вторую зону поступает следующее количество газов: 0,021м³/c+0,0037м³/c+0,001м³/c= 0,0257м³/c Концентрация метана во второй зоне составит величину

_{· 100%=7%} Количество метана, которое должно полностью сгореть во второй зоне, равно 0,00081м³+0,001м³/c= 0,00181м³/c Для сгорания такого количества метана необходимо воздуха 9,52м³/м³·0,00181м³/c= 0,0172м³/c Таким образом, во вторую зону необходимо дополнительно по воздухоподводящей трубе подать воздуха 0,0172м³/c-0,0077м³/c= 0,0095м³/c Следовательно во вторую зону поступит всего газов 0,0257м³/+0,0095м³/c= 0,0352м³/c Концентрация метана в этой зоне будет

100 % = 5,14 об. % т. е. горение будет устойчивым, поскольку 5,14% входит в интервал устойчивого горения метана в воздушной смеси: 5-15% по объему.PRI me R 2. In a burner containing a gas supply housing 1, gas nozzles 2 and 3 with nozzles 4 and openings 5, an air supply pipe 6, gas outlet channels 7, methane gas in the amount of 0.002 m ^{3 is} supplied through the pipe 8 with. Accordingly, air is supplied to the annular channel in an amount of G _air. = 0.002 m ³ / s · 5.67 m ³ / m ³ = 0.0113 m ³ / s where 19-5.67 m ³ / m ³ are the concentration limits of ignition of the methane-air mixture. For the complete combustion of methane, 9.52 m ^{3 of} air per 1 m ^{3 of} methane is needed. Ignition the fuel mixture. Incomplete combustion of methane is carried out since the following amount of air is necessary for its complete combustion: G $\genfrac{}{}{0ex}{}{\text{full sg}}{\text{air.}}$ ^op. = 0.002 m ³ / s · 9.52 m ³ / m ³ = 0.01904 m ³ / s At the same time, air is supplied into the air supply pipe 6 with a flow rate G = 0.01904 m / s ³ = 0.0113 m ³ / s = 0.0077 m ³ / c Unburned methane in the first zone burns out in the second zone, where air enters from the air supply pipe 6. The amount of methane burning in the first zone is

_{= 1.19 · 10} -3 _m 3 _{/ c} is formed following number of combustion in the first zone: 10,52m ³ / m ³ · 1.19 · 10 ^-3 m ³ / c = 1.248 x 10 ^-2 m ³ / c The second combustion zone receives combustion products from the zone, unburned methane and air from the air supply pipe 6 1.248 · 10 ^-2 m ³ / s + (0.002-0.00119) m ³ / s + 0.0077 m ³ / s = 0.021 m / s The methane concentration in the second zone will be

_{· 100% = 3,86ob.%}
For methane, the lower concentration limit of ignition is 5 vol. % Therefore, for combustion in the second zone, additional methane must be supplied there. The supply of methane to the second zone is carried out through nozzles 3 of the gas supply. Let methane be fed through nozzles 3 with a flow rate of 0.001 m ³ / s. Then, recirculation gases are supplied through nozzles 2 in the amount of 30% of the combustion products in the first zone, i.e., G _{gas recirc.} = 1.248 · 10 ^-2 m ³ / s · 0.3 = 0.0037 m ³ / s
The following amount of gas enters the second zone: 0.021m ³ / s + 0.0037m ³ / s + 0.001m ³ / s = 0.0257m ³ / s The methane concentration in the second zone will be

_{· 100% = 7%} The amount of methane to be completely burned in the second zone is equal 0,00081m ³⁺ 0,001 m ³ / c = ³ 0,00181m / c For the combustion of methane an amount of air necessary 9,52m ³ / m ³ · 0.00181m ³ / s = 0.0172m ³ / s Therefore, it is necessary to additionally supply air to the second zone through the air supply pipe 0.0172m ³ / s-0.0077m ³ / c = 0.0095m ³ / s Therefore, to the second zone total gas supply 0.0257m ³ / + 0.0095m ³ / s = 0.0352m ³ / c Methane concentration in this zone will be

100% = 5.14 vol. % ie, the combustion will be stable, since 5.14% is included in the interval of sustainable combustion of methane in the air mixture: 5-15% by volume.

 Thus, the use of the proposed method and device for burning gas can reduce emissions of nitrogen oxides in the atmosphere and get an environmental effect. (56) 1. USSR author's certificate N 1456699, cl. F 23 C 5/00, 1989.

 2. USSR author's certificate N 1462063, cl. F 23 C 5/00, 1989.

 3. D. M. Khzmalyan et al. Combustion theory and furnace devices. M.: Energy, 1976, p. 165-166.

 4. Copyright certificate of the USSR N 1477978, cl. F 23 C 11/00, 1989.

 5. I. Ya. Seagal. Protection of the air basin during fuel combustion. M.: Nedra, 1988, p. 243.

Claims (2)

 1. The method of burning gases by feeding gas and air flows into the combustion zone, introducing recirculation gases, characterized in that, in order to reduce the content of nitrogen oxides in the combustion products, recirculation gases are introduced into the gas stream before mixing it with the air stream.  2. A device for burning gas, comprising a gas supply housing and an air supply pipe mounted along the axis of the housing, characterized in that, in order to reduce the content of nitrogen oxides in the combustion products, the air supply pipe is installed in the gas supply housing with an annular gap and is provided with one coaxially arranged around it around another, gas nozzles with exhaust openings on the side surface of the nozzle for supplying recirculation gases and nozzles on the side surface of the gas nozzle, edeny in the outlets.

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