CN1098455C - Pneumatic measurement method of flow rate and density of two-phase gas and solid flow - Google Patents

Abstract

The present invention relates to a method for measuring the flowrate and the concentration of two-phase gas and solid flow. The method has the scheme that a pneumatic branch pipeline is arranged at the elbow position of a main pipeline; the gas flowrate and the gas pressure of the pneumatic branch pipeline or the electric current value of a power blower fan of the pneumatic branch pipeline are measured to obtain the pressure difference of the inner wall and the outer wall of the elbow position of the main pipeline, and the flowrate of the gas and solid two-phase flow and the solid phase concentration are calculated by utilizing the existing method. The pneumatic branch pipeline can be designed into a closed loop mode, and can also be designed into an open loop mode. The method of the present invention has the advantages of high measure accuracy, safe and reliable operation, and no abrasion or clogging of measuring instrument; the method can be widely used for the on-line measure of the flowrate and the concentration of the gas and solid two-phase flow of a pneumatic coal powder conveying pipeline in a power plant, etc.

Description

The Pneumatic measurement method of Dual-Phrase Distribution of Gas olid flow and concentration

The present invention relates to the measuring method of a kind of Dual-Phrase Distribution of Gas olid flow and concentration.

The pipeline gas fixed double phase flow is a kind of common physical phenomenon in engineering.For example, wind powder feeding pipes of power plant is exactly Dual-Phrase Distribution of Gas olid.The on-line measurement of Dual-Phrase Distribution of Gas olid flow and solid concentration is a difficulty and complicated technology problem, and the scientist of countries in the world and technician have done big quantity research to this.The technology of Cai Yonging has two classes substantially, and a class is the method for contact, and a class is contactless method.Contactless method has advantage of high precision, but this method has relatively high expectations to use occasion, and what have also has Radio Active Hazard, so can not use in more occasion; The contact method mainly is the pressure differential of utilizing between the channel bend place inside and outside wall, measure the flow of Dual-Phrase Distribution of Gas olid, this theoretical method research comparative maturity, still, the general element of settling direct gaging pressure at the channel bend place in actual engineering is as pressure transducer.Because the effect of solid matter in the pipeline, measuring sensor exists serious obstruction and wear problem.Time is long slightly, measures and just can't carry out.

The objective of the invention is to propose a kind of measuring accuracy height, applied range, can avoid stopping up and wear problem, thereby guarantee to measure the Dual-Phrase Distribution of Gas olid flow that carries out smoothly and the measuring method of concentration.

The objective of the invention is to realize: a pneumatic branch is set at center line position, the elbow of Dual-Phrase Distribution of Gas olid main line by following proposal, by measuring the size of current of the driven fan of flow, pressure or the pneumatic branch of gas in the pneumatic branch, the inside and outside wall pressure differential of trunk line elbow can be recorded, thereby flow and the solid concentration that obtains Dual-Phrase Distribution of Gas olid in the pipeline can be calculated.The setting of pneumatic branch as shown in Figure 1.Inside and outside wall A, B place at center line position, channel bend place open an aperture respectively, and A, B place aperture are connected with the branch pipe(tube) of corresponding caliber respectively, feed the air-flow that air pressure is slightly larger than the trunk line internal pressure in the pipeline and get final product.Because the present invention utilizes the mode of pneumatic branch, so title the present invention is a Pneumatic measurement method.

The principle of work that the inventive method is measured Dual-Phrase Distribution of Gas olid is as follows: because action of centrifugal force, when fluid flow through the elbow, internal and external walls produced pressure differential, and has corresponding relation between this pressure differential and the pipeline flow.Therefore, measure the pressure differential of elbow inside and outside wall, can calculate the flow and the solid concentration of pipeline.Specify as follows:

USSR (Union of Soviet Socialist Republics) scientist Kai Suwa (к e с о в а, Л А и д р, И с с д e д о в а н и e Ц e н т р б e ж н Ы х П р e о б р а з а в а т e д e й Р а с х о д а з а п Ы л e н н о г о в о з д у х а, И з в Э н e р г e т и к а, No.3,1978) once with regard to air and solid phase (as coal dust) the flow measurement problem when potpourri flows through elbow study, its result is as follows: $W={\mathrm{<figure-callout\; id="2"\; label="C\; D"\; filenames="C0011953100073.png"\; state="\{\{state\}\}">C</figure-callout>}}_D\sqrt{2\mathrm{\&rho;\&Delta;p}}\frac{R^2-{\mathrm{<figure-callout\; id="2"\; label="r"\; filenames="C0011953100073.png"\; state="\{\{state\}\}">r</figure-callout>}}^2}{\sqrt{\mathrm{Rr}}}\mathrm{\&pi;}(R-\sqrt{R^2-r^2})----\left(1\right)$ In the formula: R---the bending radius on the elbow center line, m;

R---the inside radius of elbow pipe, m;

The mass rate of W-air and solid phase (coal dust) potpourri, kg/s;

The density of ρ---air and solid phase (coal dust) potpourri, kg/m ³

C _D---coefficient, by test decision, C _DCoal powder density is linear, and relevant with the angle of turn and the R/r of elbow;

Δ p---elbow turning inner and outer pipes wall pressure is poor, N/m ²

From (1) as can be seen, under known mixture density p situation, as long as measure pressure differential deltap p, the mass rate W of flow air coal dust intermixture in both having managed as can be known.Mixture density ρ has many methods to measure, and as calorimetry, also can two same devices be set two elbows, and (1) formula simultaneous solution is obtained.The key of problem is converted into the measurement of the inside and outside wall pressure differential Δ p of channel bend place.Generally be to settle pressure transducer at the elbow turning.But, exist as previously mentioned and stop up and wear problem.

The method that the present invention is provided with pneumatic branch can address the above problem.Because the present invention directly measures is relevant physical quantity in the pneumatic branch, does not exist and stops up and wear problem, can guarantee to measure and carry out smoothly.And, measure safe and reliable, precision height, applied range.For example, the flow of Dual-Phrase Distribution of Gas olid such as power plant's wind-force pulverized coal conveying pipeline and the on-line measurement of solid concentration.

In order effectively to record trunk line elbow inside and outside wall pressure differential by pneumatic branch, the present invention can adopt following two kinds of embodiments to the design of pneumatic branch.

Scheme 1, pneumatic branch are designed to the loop form.Be provided with a source of the gas in the loop, near A, B, one group of gas meter be set at 2 respectively and pressure is taken into account corresponding operation valve, as shown in the figure.Source of the gas produces air pressure to the loop.Bleed pressure requires greater than the hydrodynamic pressure in the trunk line.Find after deliberation, when bleed pressure one regularly, the gas flow of the pipeline (pneumatic branch) by A, B two apertures is directly related with the pressure of 2 of A, B.Therefore, as long as record gas flow in the pneumatic branch, promptly know the pressure of 2 of A, B.And then can obtain the flow and the solid matter concentration of Dual-Phrase Distribution of Gas olid in the trunk line.If on another elbow of trunk line or a segment pipe, a same pneumatic branch loop is set again, then can pass through simultaneous equations (1), try to achieve ducted solid concentration, can realize the flow and the solid concentration while on-line measurement of Dual-Phrase Distribution of Gas olid.In this programme, the gas flow in the pneumatic circuit smaller (the loop caliber is very little) can not exert an influence to the flow of the Dual-Phrase Distribution of Gas olid in the trunk line.In addition, because bleed pressure is greater than the hydrodynamic pressure in the trunk line, the solid phase particles in the trunk line can not enter pneumatic branch.Therefore, its measurement is the flow of single-phase gas, can not produce wearing and tearing and blockage problem.

About pressure, flow (directly measure and obtain) and the A of pneumatic branch, the relation of place, B two ends hydrodynamic pressure, be described below:

According to Bernoulli equation (caliber is identical), following formula is arranged: $\frac{P_1}{\mathrm{\&gamma;}}-\frac{{\mathrm{<figure-callout\; id="2"\; label="P"\; filenames="C0011953100073.png"\; state="\{\{state\}\}">P</figure-callout>}}_2}{\mathrm{\&gamma;}}=\frac{\mathrm{<figure-callout\; id="2"\; label="c\; u"\; filenames="C0011953100073.png"\; state="\{\{state\}\}">c</figure-callout>}{u}^{}{}^2}{2g}----\left(2\right)$

Wherein, P ₁, P ₂Be the pressure of arbitrary section of A end (or B holds) pipeline in the pneumatic branch, N/m ²Here P ₁Get bleed pressure, P ₂Get the pressure that A point (B point) is located, be designated as P _A(P _B), g is an acceleration of gravity, and γ is a gas severe, and γ/g=ρ is a gas density, kg/m ³U is a gas velocity, and c is a coefficient, and ideally, general c gets 1.So relational expression is arranged: ${\mathrm{<figure-callout\; id="2"\; label="P"\; filenames="C0011953100073.png"\; state="\{\{state\}\}">P</figure-callout>}}_2=P_1-\frac{1}{2}\mathrm{c\&rho;}{u}^2---\left(3\right)$

Therefore, record the unit interval flow (u=flow/caliber) in the A end branch road, can by (3) formula conveniently calculate P _AIn like manner, record the flow in the B end branch road, can obtain P _BFurther can get: Δ P=P _A-P _B(3) in the formula, ρ and caliber are known quantity.

Scheme 2, pneumatic branch are designed to the open circuit form, promptly in pneumatic branch, near A, B two holes a blower fan are set respectively, and the motor of blower fan adopts synchronous motor, as shown in Figure 3.Power of fan can adopt less, and the air pressure that blower fan produces requires to be slightly larger than that the pressure of fluid gets final product in the trunk line.Because the rotating speed of synchronous motor is specified, the rotating speed of blower fan is also constant.When pipeline inner pressure changed (not changing too), motor speed was constant, had only the electric current by motor to change.It is big that pressure becomes, and electrorheological is big; Pressure diminishes, and electric current diminishes, the pressure that promptly certain electric current is corresponding certain.This corresponding relation itself is provided by synchronous motor.Therefore, as long as measure the size of current (measurement of electric current is convenient and accurate) of two blower fans on the branch road respectively, can know the pressure of 2 of A, B: P by above-mentioned corresponding relation _AAnd P _BThereby, get Δ P=P _A-P _BSimilar with scheme 1, on another elbow of trunk line or a segment pipe, an open type pneumatic branch is set again, then also can pass through simultaneous equations (1) formula, try to achieve ducted solid concentration, on-line measurement when can realize the flow of Dual-Phrase Distribution of Gas olid and solid concentration.

Description of drawings:

Fig. 1 is the pneumatic branch diagram.

Fig. 2 is closed pneumatic branch diagram.

Fig. 3 is open pneumatic branch diagram.

Number in the figure: 1 is the main line elbow, and A, B are the aperture at elbow center line position, and 2 is pneumatic

The road, 3 is source of the gas, and 4 is pressure gauge, and 5 is flowmeter, and 6 is operation valve, 7 is blower fan.

Claims (5)

1, the Pneumatic measurement method of a kind of Dual-Phrase Distribution of Gas olid flow and concentration, it is characterized in that opening an aperture respectively at the inside and outside wall A and the B place of the elbow of Dual-Phrase Distribution of Gas olid main line centerline feature, A is connected with the bye-pass of corresponding caliber respectively with B place aperture, feed the air-flow that air pressure is slightly larger than the main line hydrodynamic pressure in the bye-pass, constitute pneumatic branch, then by measuring the flow of gas in the pneumatic branch, pressure, or the size of current of pneumatic branch, main line elbow inside and outside wall pressure differential can be recorded, thereby flow and the solid concentration that obtains Dual-Phrase Distribution of Gas olid can be calculated.

2, Pneumatic measurement method according to claim 1, it is characterized in that pneumatic branch is designed to the loop form, a source of the gas is set in the loop, near A, the B one group of gas meter is set at 2 respectively, pressure is taken into account operation valve, so that the gas flow in the measurement branch road, thereby obtain the pressure differential that A, B are ordered in the main line.

3, Pneumatic measurement method according to claim 2.It is characterized in that on another elbow of main line or a segment pipe, being provided with again the pneumatic branch of a same loop form.

4, Pneumatic measurement method according to claim 1, it is characterized in that near the branch road A, the B blower fan being set at 2 respectively, become the open circuit form, the motor of blower fan adopts synchronous motor, the watt level of motor, the air pressure that blower fan is produced are slightly larger than that the pressure of fluid gets final product in the main line; Thus, by the size of measurement blower fan electric current, thus the pressure differential at A, B point place in the acquisition main line.

5, Pneumatic measurement method according to claim 4 is characterized in that being provided with the pneumatic branch of a same open circuit open type again on another elbow of main line or a segment pipe.

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