阅读说明：本技术 正压连续自补偿吹扫式防堵风速风量测量方法 (Positive-pressure continuous self-compensation blowing type anti-blocking wind speed and wind volume measuring method ) 是由 田必勇 霍蕾 苗赛赛 于 2019-10-10 设计创作，主要内容包括：本发明提供正压连续自补偿吹扫式防堵风速风量测量方法,包括步骤1：首先在大管径管道上设置测量装置,所述测量装置包括依次设置的压缩干空气源、气体发生器、质量流量自动控制器、流速调节电磁阀、靠背取压管和差压变送器；其所述靠背取压管插入大管径管道内；所述靠背取压管内嵌套设置正压补偿管；步骤2：其中所述压缩干空气源中的压缩空气,由气体发生器分两路统一输出,并分别通过质量流量自动控制器和流速调节电磁阀来自动调节正压吹扫气体的流速；正压补偿管用于往靠背取压管取压口连续输出正压吹扫气体；步骤3：当大管径管道内有气流流动时,背取压管用于取得大管径管道内气流的总压值和静压值。(The invention provides a positive pressure continuous self-compensation blowing type anti-blocking wind speed and wind volume measuring method, which comprises the following steps of 1: firstly, arranging a measuring device on a large-diameter pipeline, wherein the measuring device comprises a compressed dry air source, a gas generator, a mass flow automatic controller, a flow velocity regulating electromagnetic valve, a backrest pressure sampling pipe and a differential pressure transmitter which are arranged in sequence; the backrest pressure tapping pipe is inserted into a large-diameter pipeline; a positive pressure compensation pipe is nested in the backrest pressure tapping pipe; step 2: the compressed air in the compressed dry air source is uniformly output by the gas generator in two paths, and the flow rate of the positive pressure blowing gas is automatically adjusted through the automatic mass flow controller and the flow rate adjusting electromagnetic valve respectively; the positive pressure compensating pipe is used for continuously outputting positive pressure sweeping gas to a pressure taking port of the backrest pressure taking pipe; and step 3: when airflow flows in the large-diameter pipeline, the back pressure taking pipe is used for obtaining the total pressure value and the static pressure value of the airflow in the large-diameter pipeline.)

1. The positive pressure continuous self-compensation blowing type anti-blocking wind speed and wind volume measuring method is characterized by comprising the following steps of: comprises the following steps

Step 1: firstly, arranging a measuring device on a large-diameter pipeline, wherein the measuring device comprises a compressed dry air source (7), a gas generator (6), a mass flow automatic controller (5), a flow rate regulating electromagnetic valve (4), a backrest pressure tapping pipe (1) and a differential pressure transmitter (2) which are arranged in sequence; the backrest pressure tapping pipe (1) is inserted into a large-diameter pipeline; a positive pressure compensating pipe (3) is nested in the backrest pressure tapping pipe (1);

step 2: clean compressed air in the compressed dry air source (7) is uniformly output by the gas generator (6) in two paths, and the flow rate of positive pressure purging gas is automatically adjusted through the automatic mass flow controller (5) and the flow rate adjusting electromagnetic valve (4) respectively; the positive pressure compensating pipe (3) is used for continuously outputting positive pressure purging gas to a pressure taking port of the backrest pressure taking pipe (1);

and step 3: when airflow flows in the large-diameter pipeline, the windward side of the backrest pressure tapping pipe (1) is impacted by the airflow, the kinetic energy of the airflow is converted into pressure energy, and therefore the pressure in the windward backrest pressure tapping pipe is higher and is called as total pressure; the leeward side is not stamped by airflow, the pressure in the pressure taking pipe of the backrest is the static pressure in the air pipe, the pressure is called static pressure, the difference between the total pressure and the static pressure is called differential pressure, and the magnitude of the differential pressure value is related to the wind speed in the air pipe: the larger the wind speed is, the larger the differential pressure value is, and the smaller the wind speed is, the smaller the differential pressure value is; therefore, the wind speed in the large-diameter pipeline can be accurately measured only by using the differential pressure transmitter to measure the value of the differential pressure and according to the corresponding relation between the dynamic pressure and the wind speed; therefore, the back pressure sampling pipe (1) is used for obtaining the total pressure value and the static pressure value of the airflow in the large-diameter pipeline, and the nested positive pressure compensation pipe (3) is used for continuously outputting positive pressure purging gas to the pressure sampling port of the back pressure sampling pipe (1) to prevent dust in the airflow from entering the back pressure sampling pipe (1) to influence pressure measurement.

2. The positive pressure continuous self-compensation blowing type anti-blocking wind speed and wind volume measuring method according to claim 1, characterized in that: in the step 3, the backrest pressure tapping pipe (1) is used for obtaining a total pressure value and a static pressure value of the airflow in the large-diameter pipeline, and the nested positive pressure compensation pipe (3) is arranged to prevent dust in the airflow from entering the backrest pressure tapping pipe (1) to influence pressure measurement;

suppose A and L are two sections on the compressed air continuous purging channel, wherein L is a pressure taking position section of the backrest pressure taking pipe (1), and A is a position section of an outlet of the positive pressure compensating pipe (3). From bernoulli's equation:

in the formula,. DELTA.p_xIs the loss of resistance between the A-L sections.

Because the flow potential difference and the density difference of the gases at the two sections of A, L can be ignored, therefore:

ρ_AgH_A＝ρ_LgH_L(2)

therefore, the formula (1) can be simplified and rewritten as follows:

as can be seen from the above equation, the following equation is satisfied:

the positive pressure compensation pipe (3) can output positive pressure gas on the section A, and accurate pressure measurement of the backrest pressure measurement pipe (1) on the section L is not affected. Namely:

p_A＝p_L(5)

since it can be approximately considered that:

ρ_A＝ρ_L(6)

so it can be derived from the flow continuity equation:

on the other hand, the hydrodynamic resistance calculation method is known as follows: the resistance loss between the A-L sections is related to the on-way resistance coefficient, the local resistance coefficient, the fluid density and the kinetic energy; then, assuming that Z is the "total equivalent drag coefficient" between the A-L sections, the drag loss Δ p_xCan be expressed by the following formula:

substituting the formulas (6), (7) and (8) into the formula (4) to obtain the compound after preliminary treatment:

further simplification of equation (9) results in effective compensation conditions:

in formulae (1) to (10): pA and pL are respectively A, L section pressures; rho A and rho L are the densities of the A, L section purge gas respectively; VA and VL are respectively the flow velocity of A, L section purge gas; HA. HL, which are respectively the elevation of the section position of A, L; z is the total equivalent resistance coefficient of the purging sections from A to L; SA and SL are respectively the flow area of the section A, L; g is the acceleration of gravity;

from the formula (10): the effective compensation conditions are independent of the purge flow; as long as the compensation condition is satisfied, the wind speed and wind volume measurement effect is not affected by the pressure of the positive pressure gas source and the flow change of the positive pressure gas.

3. The positive pressure continuous self-compensation blowing type anti-blocking wind speed and wind volume measuring method according to claim 1, characterized in that: the positive pressure compensating pipe (3) is welded in the backrest pressure tapping pipe (1) in a nested mode.

Technical Field

The invention relates to a measuring method, in particular to a positive pressure continuous self-compensation blowing type anti-blocking wind speed and wind volume measuring method.

Background

Many large-diameter pipelines in a thermal power plant flow dust-containing gas, and due to the change of measured wind pressure, dust in airflow enters a backrest pressure measuring pipe along with flowing gas and is accumulated continuously, so that the measured backrest pressure measuring pipe pipeline is blocked, and a differential pressure transmitter cannot acquire a differential pressure signal. Although the existing shaking and beating type sampling device is developed, the blockage phenomenon cannot be completely avoided, particularly the shaking and beating mode needs gravity, and the vertical pipeline cannot be installed. Therefore, the research and development of the anti-blocking type wind speed measuring device have practical application value.

The dust in the sampling device is brought along with the air flow because the external pressure is greater than the internal pressure, so that the problem of dust deposition is fundamentally solved, the dust is prevented from entering, the internal pressure is always higher than the external pressure, the air flow always flows from inside to outside, and the measurement is not influenced by the additional flowing gas.

Disclosure of Invention

The invention provides a positive pressure continuous self-compensation blowing type anti-blocking wind speed and wind volume measuring method, which can accurately measure the wind speed in a large-diameter pipeline, uses compressed air to continuously blow, actively prevents blocking, thoroughly avoids the blocking of dust on a pressure measuring pipeline and is reliable in operation.

The technical scheme is as follows: the positive pressure continuous self-compensation blowing type anti-blocking wind speed and wind volume measuring method comprises the following steps:

step 1: firstly, arranging a measuring device on a large-diameter pipeline, wherein the measuring device comprises a compressed dry air source, a gas generator, a mass flow automatic controller, a flow velocity regulating electromagnetic valve, a backrest pressure sampling pipe and a differential pressure transmitter which are arranged in sequence; the backrest pressure tapping pipe is inserted into a large-diameter pipeline; a positive pressure compensation pipe is nested in the backrest pressure tapping pipe;

step 2: clean compressed air in the compressed dry air source is uniformly output by the gas generator in two paths, and the flow rate of the positive pressure blowing gas is automatically adjusted through the automatic mass flow controller and the flow rate adjusting electromagnetic valve respectively; the positive pressure compensating pipe is used for continuously outputting positive pressure sweeping gas to a pressure taking port of the backrest pressure taking pipe;

and step 3: when airflow flows in the large-diameter pipeline, the windward side of the backrest pressure tapping pipe (1) is impacted by the airflow, the kinetic energy of the airflow is converted into pressure energy, and therefore the pressure in the windward backrest pressure tapping pipe is higher and is called as total pressure; the leeward side is not stamped by airflow, the pressure in the pressure taking pipe of the backrest is the static pressure in the air pipe, the pressure is called static pressure, the difference between the total pressure and the static pressure is called differential pressure, and the magnitude of the differential pressure value is related to the wind speed in the air pipe: the larger the wind speed is, the larger the differential pressure value is, and the smaller the wind speed is, the smaller the differential pressure value is; therefore, the wind speed in the large-diameter pipeline can be accurately measured only by using the differential pressure transmitter to measure the value of the differential pressure and according to the corresponding relation between the dynamic pressure and the wind speed; therefore, the back pressure sampling pipe is used for obtaining the total pressure value and the static pressure value of the airflow in the large-diameter pipeline, and the nested positive pressure compensation pipe is used for continuously outputting positive pressure purging gas to the pressure sampling port of the back pressure sampling pipe so as to prevent dust in the airflow from entering the back pressure sampling pipe to influence pressure measurement.

The invention is further improved in that: in the step 3, the backrest pressure tapping pipe (1) is used for obtaining a total pressure value and a static pressure value of the airflow in the large-diameter pipeline, and the nested positive pressure compensation pipe (3) is arranged to prevent dust in the airflow from entering the backrest pressure tapping pipe (1) to influence pressure measurement;

suppose A and L are two sections on the compressed air continuous purging channel, wherein L is a pressure taking position section of the backrest pressure taking pipe (1), and A is a position section of an outlet of the positive pressure compensating pipe (3). From bernoulli's equation:

in the formula,. DELTA.p_xIs the loss of resistance between the A-L sections.

Because the flow potential difference and the density difference of the gases at the two sections of A, L can be ignored, therefore:

ρ_AgH_A＝ρ_LgH_L(2)

therefore, the formula (1) can be simplified and rewritten as follows:

as can be seen from the above equation, the following equation is satisfied:

the positive pressure compensation pipe (3) can output positive pressure gas on the section A, and accurate pressure measurement of the backrest pressure measurement pipe (1) on the section L is not affected. Namely:

p_A＝p_L(5)

since it can be approximately considered that:

ρ_A＝ρ_L(6)

so it can be derived from the flow continuity equation:

on the other hand, the hydrodynamic resistance calculation method is known as follows: the resistance loss between the A-L sections is related to the on-way resistance coefficient, the local resistance coefficient, the fluid density and the kinetic energy; then, assuming that Z is the "total equivalent drag coefficient" between the A-L sections, the drag loss Δ p_xCan be expressed by the following formula:

substituting the formulas (6), (7) and (8) into the formula (4) to obtain the compound after preliminary treatment:

further simplification of equation (9) results in effective compensation conditions:

in formulae (1) to (10): p A and pL are pressures of A, L sections respectively; rho A and rho L are the densities of the A, L section purge gas respectively; VA and VL are respectively the flow velocity of A, L section purge gas; h A, H L, respectively, are elevations of A, L cross-sectional positions; z is the total equivalent resistance coefficient of the purging sections from A to L; s A, SL are the flow areas of section A, L respectively; g is the acceleration of gravity;

from the formula (10): the effective compensation conditions are independent of the purge flow; as long as the compensation condition is satisfied, the wind speed and wind volume measurement effect is not affected by the pressure of the positive pressure gas source and the flow change of the positive pressure gas.

The invention is further improved in that: and a positive pressure compensation pipe is welded in the backrest pressure tapping pipe in a nested manner.

The invention does not need to change secondary measurement elements and pipelines and does not need to carry out soft compensation in DCS through a calculation formula. The compensation condition is irrelevant to the continuous blowing flow of the compressed air, so that the measurement effect is basically not influenced by the pressure change of the air source, the flow change of the air source and the distance of the air source, the real pressure difference can be accurately and continuously measured on line, and the measurement error is approximate to 0.

The original measurement form and installation mode are not changed, and the original flow formula is not required to be corrected; the 'gas distribution box' is flexibly arranged and can be arranged near a pressure taking port or a pressure transmitter; does not need manual purging and is easy to maintain.

Reasonable composition, safety and reliability. Even if the purging system fails, the measurement system is recovered to the traditional measurement mode, and the normal work of the system cannot be influenced.

The invention has the beneficial effects that: the device thoroughly solves the main problem that the dust-containing gas flow velocity measuring device is easy to block, can improve the reliability of continuous measurement, improve the dynamic performance, ensure the measurement precision, and further be favorable for improving the adjustment quality of the operation of a power plant, and simultaneously improves the reliability of safety protection through the implementation of the project.

Drawings

FIG. 1 is a schematic view of the structure of the measuring device of the present invention;

Detailed Description

The invention is described in further detail below with reference to the attached drawing figures:

as shown in fig. 1: the positive pressure continuous self-compensation blowing type anti-blocking wind speed and wind volume measuring method comprises the following steps

Step 1: firstly, arranging a measuring device on a large-diameter pipeline, wherein the measuring device comprises a compressed dry air source (7), a gas generator (6), a mass flow automatic controller (5), a flow rate regulating electromagnetic valve (4), a backrest pressure tapping pipe (1) and a differential pressure transmitter (2) which are arranged in sequence; the backrest pressure tapping pipe (1) is inserted into a large-diameter pipeline; a positive pressure compensating pipe (3) is nested in the backrest pressure tapping pipe (1);

step 2: clean compressed air in the compressed dry air source (7) is uniformly output by the gas generator (6) in two paths, and the flow rate of positive pressure purging gas is automatically adjusted through the automatic mass flow controller (5) and the flow rate adjusting electromagnetic valve (4) respectively; the positive pressure compensating pipe (3) is used for continuously outputting positive pressure purging gas to a pressure taking port of the backrest pressure taking pipe (1);

and step 3: when airflow flows in the large-diameter pipeline, the windward side of the backrest pressure tapping pipe (1) is impacted by the airflow, the kinetic energy of the airflow is converted into pressure energy, and therefore the pressure in the windward backrest pressure tapping pipe is higher and is called as total pressure; the leeward side is not stamped by airflow, the pressure in the pressure taking pipe of the backrest is the static pressure in the air pipe, the pressure is called static pressure, the difference between the total pressure and the static pressure is called differential pressure, and the magnitude of the differential pressure value is related to the wind speed in the air pipe: the larger the wind speed is, the larger the differential pressure value is, and the smaller the wind speed is, the smaller the differential pressure value is; therefore, the wind speed in the large-diameter pipeline can be accurately measured only by using the differential pressure transmitter to measure the value of the differential pressure and according to the corresponding relation between the dynamic pressure and the wind speed; therefore, the back pressure sampling pipe (1) is used for obtaining the total pressure value and the static pressure value of the airflow in the large-diameter pipeline, and the nested positive pressure compensation pipe (3) is used for continuously outputting positive pressure purging gas to the pressure sampling port of the back pressure sampling pipe (1) to prevent dust in the airflow from entering the back pressure sampling pipe (1) to influence pressure measurement. In the step 3, the backrest pressure tapping pipe (1) is used for obtaining a total pressure value and a static pressure value of the airflow in the large-diameter pipeline, and the nested positive pressure compensation pipe (3) is arranged to prevent dust in the airflow from entering the backrest pressure tapping pipe (1) to influence pressure measurement;

suppose A and L are two sections on the compressed air continuous purging channel, wherein L is a pressure taking position section of the backrest pressure taking pipe (1), and A is a position section of an outlet of the positive pressure compensating pipe (3). From bernoulli's equation:

in the formula,. DELTA.p_xIs the loss of resistance between the A-L sections.

Because the flow potential difference and the density difference of the gases at the two sections of A, L can be ignored, therefore:

ρ_AgH_A＝ρ_LgH_L(2)

therefore, the formula (1) can be simplified and rewritten as follows:

as can be seen from the above equation, the following equation is satisfied:

the positive pressure compensation pipe (3) can output positive pressure gas on the section A, and accurate pressure measurement of the backrest pressure measurement pipe (1) on the section L is not affected. Namely:

p_A＝p_L(5)

since it can be approximately considered that:

ρ_A＝ρ_L(6)

so it can be derived from the flow continuity equation:

on the other hand, the hydrodynamic resistance calculation method is known as follows: the resistance loss between the A-L sections is related to the on-way resistance coefficient, the local resistance coefficient, the fluid density and the kinetic energy; then, assuming that Z is the "total equivalent drag coefficient" between the A-L sections, the drag isLoss of force Δ p_xCan be expressed by the following formula:

substituting the formulas (6), (7) and (8) into the formula (4) to obtain the compound after preliminary treatment:

further simplification of equation (9) results in effective compensation conditions:

in formulae (1) to (10): p A and pL are pressures of A, L sections respectively; rho A and rho L are the densities of the A, L section purge gas respectively; VA and VL are respectively the flow velocity of A, L section purge gas; h A, H L, respectively, are elevations of A, L cross-sectional positions; z is the total equivalent resistance coefficient of the purging sections from A to L; s A, SL are the flow areas of section A, L respectively; g is the acceleration of gravity;

from the formula (10): the effective compensation conditions are independent of the purge flow; as long as the compensation condition is satisfied, the wind speed and wind volume measurement effect is not affected by the pressure of the positive pressure gas source and the flow change of the positive pressure gas.

3. The positive pressure continuous self-compensation blowing type anti-blocking wind speed and wind volume measuring method according to claim 1, characterized in that: the backrest pressure tapping pipe (1) is internally nested with a positive pressure compensation pipe (3).

And (3) measurement verification: the backrest pressure tapping pipe (1) is used for obtaining a total pressure value and a static pressure value of airflow in a large-diameter pipeline, and the nested positive pressure compensation pipe (3) is arranged to prevent dust in the airflow from entering the backrest pressure tapping pipe (1) to influence pressure measurement;

suppose A and L are two sections on the compressed air continuous purging channel, wherein L is a pressure taking position section of the backrest pressure taking pipe (1), and A is a position section of an outlet of the positive pressure compensating pipe (3). From bernoulli's equation:

in the formula,. DELTA.p_xIs the loss of resistance between the A-L sections.

Because the flow potential difference and the density difference of the gases at the two sections of A, L can be ignored, therefore:

ρ_AgH_A＝ρ_LgH_L(2)

therefore, the formula (1) can be simplified and rewritten as follows:

as can be seen from the above equation, the following equation is satisfied:

the positive pressure compensation pipe (3) can output positive pressure gas on the section A, and accurate pressure measurement of the backrest pressure measurement pipe (1) on the section L is not affected. Namely:

p_A＝p_L(5)

since it can be approximately considered that:

ρ_A＝ρ_L(6)

so it can be derived from the flow continuity equation:

on the other hand, the hydrodynamic resistance calculation method is known as follows: the resistance loss between the A-L sections is related to the on-way resistance coefficient, the local resistance coefficient, the fluid density and the kinetic energy; then, assuming that Z is the "total equivalent drag coefficient" between the A-L sections, the drag loss Δ p_xCan be expressed by the following formula:

substituting the formulas (6), (7) and (8) into the formula (4) to obtain the compound after preliminary treatment:

further simplification of equation (9) results in effective compensation conditions:

in formulae (1) to (10): p A and pL are pressures of A, L sections respectively; rho A and rho L are the densities of the A, L section purge gas respectively; VA and VL are respectively the flow velocity of A, L section purge gas; h A, H L, respectively, are elevations of A, L cross-sectional positions; z is the total equivalent resistance coefficient of the purging sections from A to L; s A, SL are the flow areas of section A, L respectively; g is the acceleration of gravity;

from the formula (10): the effective compensation conditions are independent of the purge flow; as long as the compensation condition is satisfied, the wind speed and wind volume measurement effect is not affected by the pressure of the positive pressure gas source and the flow change of the positive pressure gas.

The measurement shows that: when the compensation flow is changed within the range of 0-2 m3/H, the average error is less than 0.8mmH 2O (8 Pa); when the selected compensation flow is 1m3/H, the average error is <0.4mmH 2O (4 Pa).