RU2192928C1 - Method for automatically controlling operation of electric filter of boiler aggregate - Google Patents

Abstract

FIELD: power machine engineering, possibly electric filters for heat and power plants. SUBSTANCE: method comprises steps of using system for removing dust out of discharge hole of hopper when predetermined level of filling discharge hole of hopper is exceeded; determining dust content in flue gases according to its concentration in discharge hole of electric filter; using transporting sectional pipeline for removing dust out of hopper; performing dust fluidizing in each section and then moving dust together with rising flow formed in rising portion of said pipeline; removing part of fluidizing agent out of upper cavity of rising portion of pipeline to upper cavity of hopper and moving dust along inclined portion to next section of pipeline; determining value of predetermined level of filling discharge hole of hopper and effective cross section of inclined portion of transporting pipeline with use of relations given in description of invention for such calculations. EFFECT: enhanced efficiency, improved reliability of electric filter. 3 dwg

Description

 The invention relates to power engineering and can be used in electrostatic precipitators of thermal power plants.

 A known method of automatically controlling the operation of an electrostatic precipitator by changing the frequency of the intervals of shaking the precipitation electrodes depending on the weight of the dust deposited on them, in which the specific electrical resistance of the dust is measured and, depending on the measured value, the frequency of the intervals of shaking the precipitation electrodes is adjusted / 1 /.

 The disadvantage of this method is the complexity of the design of the device that implements the method, which should include weighing devices of each electrode, as well as measuring the electrical resistance of dust on each electrode. The ability of these meters to work on the electrode surface under high supply voltage is quite problematic.

 The closest in technical essence to the proposed one is a method for automatically controlling the electrostatic precipitator of a boiler unit by activating the actuator shaking the electrodes depending on the dust content in the flue gases at the electrode outlet, in which the dust content in the flue gases at the outlet of the electrostatic precipitator is measured by passing microwave pulses through them / 2 /.

 However, the prototype solution has a drawback - the ambiguity of the controlled parameter, since the amount of residual dust (dust content in the flue gases at the output of the electrostatic precipitator) cannot unambiguously characterize the amount of dust deposited on the electrodes, since it mainly depends on the process of deposition of dust particles and gas flow rate.

при S_н/S_в≤1,
где H - установленный уровень заполнения течки бункера;
l_н - длина наклонного участка трубы;
g - ускорение свободного падения;
h - высота секции;
S_н и S_в - соответственно эффективное сечение наклонного и восходящего участков транспортного трубопровода;
t - время транспорта пыли через бункер;
ρ $\genfrac{}{}{0ex}{}{\text{H}}{\text{V}}$ - объемная плотность пыли в наклонном участке трубы;
ΔH_в - длина верхней полости восходящего участка.The subject of the invention is a method for automatically controlling the electrostatic precipitator of a boiler unit by activating an actuator for shaking electrodes depending on the dust content in flue gases, in which the dust content in flue gases is determined by its concentration in the heat of the electrostatic precipitator hopper, and the inclusion of a dust removal system from the hopper estrus is carried out by exceeding the established level of filling the estrus of the hopper, moreover, to remove dust from the hopper, a transport pipeline consisting of sections is used, in each section, after the fluidization of dust, it is moved in an upward flow formed on the upstream section of the transport pipeline, a part of the fluidizing agent is removed from the upper cavity of the upstream section to the upper cavity of the hopper, and dust is moved along the inclined section to the next section of the transport pipeline, while the value of the set level filling the estrus of the hopper and the effective cross section of the inclined section of the transport pipeline is determined according to the expressions:

when S _n / S _in ≤1,
where H is the established level of filling the estrus of the hopper;
l _n - the length of the inclined section of the pipe;
g is the acceleration of gravity;
h is the height of the section;
S _n and S _in - respectively, the effective section of the inclined and ascending sections of the transport pipeline;
t is the time of dust transport through the hopper;
ρ $\genfrac{}{}{0ex}{}{\text{H}}{\text{V}}$ - bulk density of dust in an inclined section of the pipe;
ΔH _in - the length of the upper cavity of the ascending section.

A device for implementing the method of automatic control of the electric filter of the boiler is shown in figure 1. Figure 2 shows the dependence of the influence of the length ΔH _{in the} upper cavity of the ascending pipe section on the effective diameter of the inclined pipe section for various ρ $\genfrac{}{}{0ex}{}{\text{H}}{\text{V}}$ and Q. In FIG. Figure 3 shows the dependence of the influence on the dust consumption Q of length ΔH _{in the} upper cavity of the ascending pipe section for various ρ _V and d _n . The device contains electrodes in an electrostatic precipitator located above the hopper 2 at a height from estrus 3, into which a dust concentration meter or level gauge 4 (level indicator) is inserted at a set level H.

 The estrus outlet is aligned with the inlet of the ascending section 5 of the transport pipeline, in the upper cavity of which there is a pipeline for removing a part of the fluidizing agent with the nozzle 6, and a hole for moving dust along the inclined section 7 of the transport pipeline is installed. In the lower part of the ascending section 5 of each section, nodes 8 for fluidization of dust are placed, to which air (fluidizing agent) is supplied through an electro-pneumatic valve 9 from an overpressure source 10. One of the outputs of the dust concentration meter 4 is connected to the drive 11 of the shaking elements of the electrodes 1 of the electrostatic precipitator.

 During the deposition of ash on the electrodes 1 increases the dust capacity of the precipitation electrode (mass of ash per unit surface). An increase in the dust capacity of the electrode to the limiting values causes the self-collapse of ash aggregates into the bunker estrus. When the ash concentration in the estrus exceeds the set value, the meter 4 generates a control signal at the beginning of the shaking cycle of the electrodes 1. After filling the estrus with dust above the level H of the meter 4, the latter generates a signal to turn on the electro-pneumatic valve 9 for air supply for pneumatic dust transportation (removal) from the hopper.

где d_н и d - соответственно эффективный диаметр наклонного трубопровода и средний диаметр частиц пыли;
С - коэффициент расхода (С=0,5).According to experimental data, it was found that the effective cross section of the descending section 7 significantly affects the dust transport process, since air from the subsequent sections fluidizes into the upper cavity of the previous section along its upper cavity. This effect not only increases air consumption for dust transport, but also makes it difficult to transport dust along an inclined section. To select the optimal value of the effective cross section of the inclined section 7, an experimentally determined expression is used for the outflow of fluidized solid particles at d _n / d> 40:

where d _n and d are respectively the effective diameter of the inclined pipeline and the average diameter of the dust particles;
C - flow rate (C = 0.5).

The fulfillment of the calculation conditions according to the above expression is mandatory for the following reasons. It was experimentally established that when the pipe sections of the ascending and inclined sections are equal, a partial discharge of air from the fluidization unit of the subsequent section occurs along the upper cavity of the inclined section. This determines the additional air flow for pneumatic transport and additional resistance to the flow of solid particles, merging along an inclined section only under the influence of gravitational forces. The pneumatic transport process in this case may be uncontrollable. To eliminate the described effect, this expression is used, and the effective section of the pipe of the ascending section is selected by a large S _n .

 Let us consider this process in more detail. To eliminate reverse fluidization of air along the inclined sections, the pressure loss to overcome the static pressure of the column of suspended particles in the ascending section of the pipe should be less than the pressure loss of the flow of particles merging along the inclined section of the pipe.

ρ _V • H _B ≤ρ $\genfrac{}{}{0ex}{}{\text{H}}{\text{V}}$ l _H + ρ $\genfrac{}{}{0ex}{}{\text{H}}{\text{V}}$ ΔH _B. (2)
As a result of transformation (2), taking into account that l _n = H _in -ΔH _in , we get that when determining the ratio of bulk densities of solid particles and effective cross sections in the inclined and ascending sections of the pipes, the following condition must be fulfilled:
S _n / S _at ≤1, (3)
where S _n and S _in - respectively, the effective section of the descending and ascending sections of the pipe.

Here, the pressure loss due to friction against the walls and on the bends of the pipes was not taken into account, for the downward section this loss is much greater (two bends of the pipes). Therefore, even a slight decrease in S _n relative to S _in should eliminate the reverse fluidization of the air.

где P₁, P₀ - соответственно давления узла псевдоожижения у верхней полости бункера;
ρ $\genfrac{}{}{0ex}{}{\text{H}}{\text{V}}$ - объемная плотность пыли в наклонном участке трубы;
H_в, l_н - длина соответственно восходящего и наклонного участков трубы;
m - масса пыли;
h - высота секции.To select the design parameters of the hopper estrus, depending on the dynamic, we write the equations for calculating the pressure loss to overcome the static pressure of a column of particles in the fluidized bed of the estrus and section of the air hill:
P ₁ -P ₀ = ρ _V H (4);
P ₁ -P ₀ = ρ _V H _in (5);

where P ₁ , P ₀ - respectively, the pressure of the fluidization unit at the upper cavity of the hopper;
ρ $\genfrac{}{}{0ex}{}{\text{H}}{\text{V}}$ - bulk density of dust in an inclined section of the pipe;
H _in , l _n - the length of the ascending and inclined sections of the pipe, respectively;
m is the mass of dust;
h is the height of the section.

получим выражение для определения установленного уровня течки H:

Для оценки достоверности полученных выражений были проведены исследования при удалении золы из бункера 1-го поля электрофильтра блока 1 Хабаровской ТЭЦ-3, через секцию аэрогорка со следующими конструктивными параметрами:
H_в=290 см;
ΔH_в=30-60 см;
d_н=76 мм;
d_в=90 мм,
где d_в - гидравлический диаметр восходящего участка трубы.As a result of the joint solution of equations (4) - (6) and for

we get an expression for determining the established level of estrus H:

To assess the reliability of the obtained expressions, studies were carried out when removing ash from the hopper of the 1st field of the electrostatic precipitator of unit 1 of the Khabarovsk CHP-3, through an air hill section with the following design parameters:
H _in = 290 cm;
ΔH _in = 30-60 cm;
d _n = 76 mm;
d _in = 90 mm
where d _in - the hydraulic diameter of the ascending section of the pipe.

 The ash flow through the air hill was regulated from 5 to 20 t / h with shaking of the electrodes by partially overlapping the cross section with a gate installed in the upper part of the hopper estrus. Bulk density was changed by installing nozzles of different diameters through the fluidization units and in the air discharge pipe in the upper part of the ascending section of the pipe; measurements were made by discrete sampling of ash per unit time.

 The coincidence of the research results and calculated dependences proved the correctness of the selected principle of constructing a dust removal system from the hopper.

 An increase in the H level above the set value is limited only by the technical conditions for the operation of the electrostatic precipitator, as well as by the effect of dust caking on the walls of the hopper, which determines the need for mechanical action on the walls of the hopper to collapse the existing dust. The above makes it necessary to automatically maintain the value of the set level H, according to the above expression (4).

 The need to enable the cycle of shaking the electrodes 1 by the concentration of dust in the heat is determined by the fact that at the beginning of the process of dust collapse from the electrode upon reaching its maximum dust absorption, an insignificant amount of dust gets into the heat, the volume of which does not reach the level N. Therefore, to more accurately determine the beginning of the process dust falling from the electrode (when it accumulates on the electrode), it is necessary to start the shaking cycle by the control signal of the dust concentration meter. As the latter, it is advisable to use a capacitive type level switch (СУЗ-01), which generates a signal when the set tank value in the estrus cavity is exceeded, depending on the dust concentration at the location of the signaling electrode.

 Thus, by determining the dust content in flue gases by its concentration in the hopper estrus, turning on the dust removal system from the hopper estrus by exceeding the established level of filling the hopper estrus, and determining the parameters of the dust removal system from the hopper estrus according to the calculated ratios, an increase in reliability and efficiency is achieved the operation of the electrostatic precipitator, due to the reduction of the secondary entrainment of dust with flue gases and pneumatic transport of dust from the electrostatic precipitator hopper.

Sources of information
1. Copyright certificate of the USSR 1002010, B 03 C 3/74, 1981.

 2. USSR author's certificate 1031514, B 03 C 3/76, 1981.

Claims (1)

A method for automatically controlling the electrostatic precipitator of a boiler unit by activating an actuating mechanism for shaking electrodes depending on the dust content in flue gases, characterized in that dust is removed from the hopper estrus by exceeding the established level of filling the hopper estrus, the output of which is aligned with the inlet of the ascending section of the transport pipeline, which after pseudo-fluidization of dust carry out its movement in an upward flow to the upper cavity of the ascending section, where odyat part fluidizing agent into the upper cavity of the hopper and the dust removal is performed through the inclined conduit section, the effective cross section of the pipeline is determined according to the expression

at S _Н / S _В ≤1,
where Q is the dust flow through the hopper;
ρ $\genfrac{}{}{0ex}{}{\text{H}}{\text{V}}$ - bulk density of dust in an inclined section of the pipeline;
g is the acceleration of gravity;
ΔH _B is the length of the upper cavity of the ascending section.

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