RU2635178C1 - Two-stepted vortex burner - Google Patents

Abstract

FIELD: machine engineering.

SUBSTANCE: burner contains a chamber with tangential nozzles of the oxidant supply and central supply of propane through a gas firing device, a chamber with tangential ducts for supplying a coal dust-air mixture, a nozzle at the outlet of which a swirling flow is realized. The vortex burner includes three axially symmetric chambers in series and coaxially arranged: a first stage chamber, a second stage chamber and a combustion chamber, wherein the chambers of the first and second stages are connected by means of a profile nozzle installed coaxially with the chambers, the diameter of which is determined depending on the power ratio of the first and second stages of vortex burner, taking into account the twist parameter, the tangential nozzles for supplying dust-air coal to the second stage chamber, installed oppositely and mirror-like relative to each other, are arranged mirror-like to the tangential nozzles of the oxidant supply to the first stage chamber.

EFFECT: more efficient and safer burning of coal fuel.

13 Dwg

Description

The invention relates to the field of power engineering and can find application in any industry related to the combustion of coal fuel in vortex furnaces, in particular, in plants for the deep processing of coal into other types of fuel, for example synthesis gas. Vortex burners have occupied a significant and solid place in the power equipment of thermal power plants.

However, due to the complexity of the complex of aerodynamic, chemical and thermal processes that occur during the combustion of coal fuel in vortex burners, the path to their implementation is very time-consuming both in the design process and in the process of their production operation.

Known vortex burner for burning pulverized coal and dust-gas mixtures, as well as gas [RF patent No. 131849, F23C 1/10, F23D 1/02, F23D 17/00, 12/17/2012], in which the mixing of the fuel agent with air is optimized as much as possible, which leads to a more complete combustion of the fuel, and therefore, will increase the economic and environmental effect of the application of the proposed vortex burner. The problem is solved due to the fact that the specified vortex burner containing a housing with a coaxially mounted central pipe and shells forming ring channels for supplying fuel, kindling air, blade swirls, and at the outlet of at least one ring channel located between two other channels , a divider is installed, consisting of alternately directed conical sectors of the diffuser and confuser type, and the conical sectors of the diffuser type are installed on the inner wall channel and cone sector confuser type are mounted on an outer wall of the channel and, in addition, the sectors formed between the conical partition walls, the planes of which are directed through the burner axis.

In the said device, by means of a firing device and a fuel oil nozzle, the kindling fuel is ignited in the furnace, such kindling is a rather long process and takes up to 4 hours, which is economically and technically inefficient. Also, when fuel oil and coal fuel are fed into the furnace together, slagging processes are intensified. In addition, in all channels, with the exception of the channel with the divider installed, swirlers are placed that very significantly affect the processes of occurrence of undesirable pressure pulsations caused by the precessing vortex core.

A known method of burning coal dust in a swirl furnace [RF patent No. 2418237, F23C 5/24, 05/10/2011], including grinding, mechanical activation and combustion, in which coal microfine is used to illuminate the vortex flows of conventional grinding coal, rotating in opposite directions relative to each other friend. At the same time, the zone into which the micro-grinding coal combustion torch is directed is formed due to the tangential supply of the injected air and the change in direction of the tangential component of the vortex flow velocity to the opposite.

The reasons that impede the achievement of the indicated technical result when using the known method include the fact that such illumination is economically viable and effective for maintaining an already burning torch of coal of ordinary grinding, but practically unsuitable for igniting and heating the main stream of coal of ordinary grinding when starting a vortex burner in work.

The closest in combination of features to the claimed device is a coal dust burner [RF patent No. 2294486, F23D 1/00, July 26, 2005], including an ignition chamber with a tangential inlet of the dust-air mixture and an ignition device, a mixing chamber with coaxial channels and tangential inlet of secondary air and coal fuel and a swirl with a flow turbulator made in the form of a cylindrical washer with a hole diameter smaller than the diameters of the channels of the ignition chamber and the mixing chamber.

The specified device uses a multi-chamber scheme for burning coal fuel. With all other things being equal, such a scheme for burning coal fuel is less effective due to the increased resistance to hot flow, and therefore because of greater slagging. Moreover, at high fuel consumption, the combined introduction of secondary air and fuel through a single channel very significantly affects the combustion process and preliminary preparation of coal fuel, and therefore increases the total energy consumption during operation. The effectiveness of the aforementioned burner to a greater extent was confirmed only when the furnace was ignited or illuminated, but all attempts to use it as the main burner have not yet brought the desired result.

The present invention is the creation of a two-stage burner with an optimized design, which allows for more efficient and safe burning of coal fuel.

The technical result is a two-stage vortex burner with improved technical and economic indicators. The use of such a vortex burner will make it possible to achieve a more efficient and safe burning of coal fuel and, as a result, reduce the overall costs when introducing this type of vortex burners in thermal power plants.

A two-stage vortex burner, according to the invention, contains three axisymmetric chambers sequentially and coaxially: a first-stage chamber, which is a chamber with tangential oxidant supply pipes located opposite and mirror to each other, and a central propane supply through a gas ignition device, a second-stage chamber, representing a chamber with tangential pulverized coal supply pipes located opposite and mirror relative to the other friend, and the combustion chamber, while the chambers of the first and second stages are connected using a profiled nozzle installed coaxially with the chambers, the diameter of which is determined depending on the power ratio of the first and second stages of the vortex burner taking into account the twist parameter, the tangential nozzles for the supply of pulverized coal into chamber 2 -th steps are located in a mirror to the supply pipes of the oxidizing agent in the chamber of the 1st stage.

In the claimed device, the ignition of the gas is carried out using the ignition device, which works as a protective device in case of the extinction of the torch in the first stage. Under combustion conditions in the first stage, due to the filling of the central recirculation zone with hot combustion products, which act as the arson of the fresh fuel-air mixture, the strong flow instability in the form of a precessing vortex core is substantially suppressed. The determining parameters of such a flow are the twist design parameter, S, and the Reynolds number, Re = D _e U ₀ / ν, where D _e is the diameter of the outlet nozzle of the chamber, U ₀ is the average flow rate at the nozzle exit, and ν is the kinematic viscosity.

In the first stage, sustainable combustion is realized, including in the case of depleted regimes, which are of interest from the point of view of achieving low emissions of nitrogen oxides. The first stage of the vortex burner is used to ignite the coal fuel, which is fed into the second stage.

The swirling flow in the second stage is opposite to the swirling flow in the first stage. The anti-spin helps to more quickly mix the burner jet of the first stage with the flow of the pulverized coal mixture, which is fed to the second stage, and more efficient ignition of the pulverized coal mixture. The advantages of this burner are a more uniform filling of the volume of the working chamber in combination with a pronounced moderate swirl of the flow and flow stability, which allows for more efficient and safe burning of coal fuel.

The essence of the technical solution is illustrated by drawings.

The longitudinal section of the device - Fig. one;

Cross section of the device - FIG. 2;

where 1 is the gas firing device; 2 - the main chamber of the first stage of the vortex burner; 3, 8 - pipe feed oxidizer; 4, 7 - pipe supply of pulverized coal fuel; 5 - the main chamber of the second stage of the vortex burner; 6 - viewing windows; 9 - profiled nozzle; 10 - cylindrical body; 11 - combustion chamber.

The inventive device consists of two steps:

The first step is a vortex gas burner, which is an axisymmetric chamber 2 with two tangential inlet ports 3 and 8 of the oxidizer supply and a central propane supply through the gas ignition device 1 with nozzle 5, at the outlet of which a swirling flow is realized.

The second stage is a vortex dust-coal burner, which is an axisymmetric chamber 5 with two tangential inlet nozzles 4 and 7 for supplying a coal-dust mixture, with a combustion chamber 11, viewing windows 6 and a cylindrical body 10. The flow swirl in the second stage is opposite to the swirl of the flow in the first stage.

The device operates as follows.

First, the oxidant is supplied through the tangential nozzles 3 and 8 into the chamber 2 of the first stage of the vortex burner. After propane is fed to the central part of the first stage through a gas firing device 1, which produces ignition of propane. The torch leaves the profiled nozzle 9 in the second stage of the vortex burner device. The first stage of the vortex burner starts to work.

In the chamber of the first stage, a swirling reactive stream is released, exiting through the nozzle into the second stage. To create a stable responsive flow in the second stage, the nozzle diameter is calculated as a function of the power of the first and second stages and the twist parameter,

,

,

where w1, w2 are the powers of the first and second steps, S is the twist parameter.

The pulverized coal mixture is fed into the chamber of the second stage of the vortex burner device 5 through the tangential nozzles 4 and 7, twisting the flow opposite to the swirling flow of the first stage. The pulverized coal mixture is ignited by a torch exiting the profiling nozzle 9. The vortex burner device starts to work.

To substantiate the attainability of the technical result, experimental studies were performed.

In FIG. Figure 3 shows the depleted flame of a reacting stream with an excess air coefficient of φ = 0.5.

According to the photograph, FIG. 3, it can be seen that the lower part of the torch emerging from the nozzle has a clear conical boundary. It was found from an analysis of the average distributions of the axial velocity component under isothermal conditions that the recirculation region penetrates deep into the nozzle, which ensures reliable stabilization of the flame.

The upper part of the torch is an M-shaped front with blurred boundaries due to turbulent mixing with the surrounding air.

Thus, in the first stage of the vortex burner, stable combustion is realized, including in the case of depletion regimes, which are of interest from the point of view of achieving low emissions of nitrogen oxides.

To obtain information on pressure pulsations, signals were used from two acoustic sensors placed in diametrically opposite directions at the nozzle exit of the burner device.

Research results.

In FIG. Figures 4 and 5 show the profiles, respectively, of the average and pulsating velocity components for the isothermal and reacting flow: 1, 2 - axial, 3, 4 - tangential; light symbols - isothermal flow, dark symbols - reactive flow; x / D _e is the ratio of the measuring point at the exit of the nozzle to the total output diameter of the nozzle of the tangential vortex chamber; U is the average axial velocity [m / s]; W / U ₀ - average tangential velocity [m / s].

In FIG. Figures 6 and 7 show the energy spectra of pulsations, respectively, of the pressure and cross-correlation functions of the acoustic signals of the sensors, where 1 is the isothermal condition, 2 is the reactive flow, 3 are the maxima corresponding to the precession vortex core (VWP); vertical axes are given in relative units.

периода пульсаций Т₁, который может быть определен на основе спектра разностного сигнала (фиг. 6), т.е. сигналы изменяются в противофазе, что характерно для неосесимметричной винтовой моды возмущений. Максимум корреляционной функции в реагирующем потоке приходится на нулевой сдвиг фаз, что отражает вклад осесимметричных пульсаций, возможным источником которых является верхняя часть пламени (фиг. 3). Эти пульсации, регистрируемые датчиками в одной фазе, удаляются из разностного сигнала и поэтому не видны в спектре на фиг. 6. Прецессия центра вихря, которая была определена на основе распределения пульсаций тангенциальной скорости, в условиях реагирующего потока дает второй пик в корреляционной функции, сдвинутый примерно на половину периода прецессии Т₂, который также можно определить на основе спектра. Таким образом, можно сказать, что условия реагирующего потока оказывают существенное влияние на параметры ПВЯ, уменьшая амплитуду (отклонение вихря от центра горелки) и увеличивая частоту прецессии. При этом акустические датчики регистрируют снижение уровня пульсаций давления, генерируемых ПВЯ, почти на порядок, на основании чего можно сделать вывод, что условия реагирующего потока приводят к подавлению ПВЯ.From the spectra of the differential signal of the pressure pulsations (Fig. 6), it is seen that in isothermal conditions and in the reacting flow there are isolated frequencies (138 and 177 Hz, respectively) that are associated with the PWR. This conclusion is also confirmed by the cross-correlation functions of the acoustic signals of sensors placed in diametrically opposite directions (Fig. 7). It is seen that the first maximum of the correlation function in the isothermal case falls on

ripple period T ₁ , which can be determined based on the spectrum of the difference signal (Fig. 6), i.e. the signals change in antiphase, which is characteristic of the non-axisymmetric helical mode of perturbations. The maximum correlation function in the reacting flow occurs at a zero phase shift, which reflects the contribution of axisymmetric pulsations, a possible source of which is the upper part of the flame (Fig. 3). These pulsations recorded by the sensors in one phase are removed from the difference signal and therefore are not visible in the spectrum in FIG. 6. The precession of the vortex center, which was determined on the basis of the distribution of the pulsations of the tangential velocity, under the conditions of the reacting flow, gives a second peak in the correlation function, shifted by about half the precession period T ₂ , which can also be determined on the basis of the spectrum. Thus, we can say that the conditions of the reacting flow have a significant effect on the parameters of the PWR, decreasing the amplitude (deviation of the vortex from the center of the burner) and increasing the precession frequency. In this case, acoustic sensors detect a decrease in the level of pressure pulsations generated by the UHF by almost an order of magnitude, on the basis of which it can be concluded that the conditions of the reacting flow lead to the suppression of the UHF.

An important result is the fact that under combustion conditions due to the filling of the central recirculation zone with hot combustion products, which perform the function of setting fire to a fresh fuel-air mixture, the strong flow instability in the form of PVY is substantially suppressed.

From the measured energy spectra of the signals of the acoustic sensors, it follows that the suppression of PWR under combustion conditions leads to a significant decrease in the level of pressure pulsations.

Experiments were conducted to evaluate the efficiency of the burner in different modes, with so-twisted and anti-twisted flows of the first and second stages.

In FIG. 8 shows the layout of the measuring sections 1-3.

In FIG. 9, 10, 11, 12 show the velocity profiles for various operating modes of a vortex burner with measuring sections 1-3. Where r / R is the ratio of the position of the measuring point to the full radius of the camera, U _axial / U is the average axial speed, U _tang / U is the average tangential speed.

In FIG. 9, 10 show the axial and tangential components of the velocity, respectively, for the mode with co-twisted flows.

In FIG. 11, 12 show the axial and tangential components, respectively, for the anti-spin flow mode.

You can see a very heterogeneous distribution of the axial velocity for the mode with co-twisting of the flows and a uniform distribution in the axial velocity for the counter-twist.

Thus, in contrast to the co-twist mode, the anti-twist mode showed an effective mixture of swirling flows of the first and second stages. The resulting flow was characterized by a uniform distribution of axial velocity along the cross section in combination with a sufficiently pronounced general rotational movement of the flow in the working section. The difference is also the absence of the formation of large-scale non-stationary structures and, accordingly, intense pulsations of the flow. Based on the results of the conducted isothermal experiments, it can be concluded that the anti-spin option is more preferable for use in a two-stage burner in terms of the possibility of more rapid mixing of the first-stage burner jet with the pulverized-coal mixture flow, which should be supplied to the second stage, by more efficient ignition of the latter.

In FIG. 13 shows graphs of the change in the ignition temperature of the pulverized-coal mixture at different points along the length of the burner (numbering from the swirl to the outlet, where lines 1-8 are the readings of temperature sensors in the combustion chamber located at a distance of 10 cm from each other) during a two-stage combustion.

The graph shows the following stages of the experiments:

I - Turning on the first stage air - 4.49 l / s, gas (propane) - 5 l / min, the second stage of coal fuel supply is off. Stable ignition of the gas flame, flame length 30 mm, temperature increase in the reaction chamber to 700 ° C.

II - Opening of the second stage without coal fuel, air flow 5.17 l / s.

III - Turning on the supply of coal fuel through the second stage of the burner with an initial flow rate of 4 kg / h and a further increase to 14 kg / h. In the process of supplying a dust suspension, an increase in temperature is observed from 550 ° C to 1100 ° C. Effective ignition and steady burning of a coal-dust torch.

VI - Turning off the second and first stage of the burner device.

Fire research showed that in a two-stage burner with an anti-spin flow of the first and second stages, effective ignition of the pulverized-coal mixture and its stable combustion occur. The burnup rate of coal fuel is 98.9%.

Claims (1)

A two-stage vortex burner including a chamber with tangential nozzles for supplying an oxidizer and a central propane feed through a gas igniter, a chamber with tangential nozzles for supplying a coal-dust mixture, a nozzle at the outlet of which a swirl flow is realized, characterized in that the vortex burner includes sequentially and coaxially mounted three axisymmetric chambers: a chamber of the first stage, a chamber of the second stage and a combustion chamber, while the chambers of the first and second stages are connected at the power of the profiled nozzle installed coaxially with the chambers, the diameter of which is determined depending on the power ratio of the first and second stages of the vortex burner, taking into account the twist parameter, the tangential nozzles for the supply of pulverized coal into the chamber of the second stage, which are installed opposite and mirror relative to each other, are located mirrored to the tangential nozzles oxidizing agent in the chamber of the first stage.

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