CN105091957A - A thermal power generating unit feedwater flow measuring method - Google Patents

Abstract

The invention provides a thermal power generating unit feedwater flow measuring method. The method comprises the steps of: determining the design working condition feedwater flow of a unit, the design working condition unit power, the feedwater pipe inner diameter, the to-be-measured working condition feedwater pressure, the feedwater temperature, the feedwater dynamic viscosity, the measuring point positions and the feedwater dynamic pressure of measuring points measured by a Pitot tube; calculating the feedwater flow rate at each measuring point; calculating the feedwater flow estimated value, the feedwater average flow rate, and the feedwater pipe interior flow Reynolds number; determining the feedwater flow rate distribution along the cross section of a pipe; by means of the feedwater flow rate distribution along the cross section of the pipe, calculating the relationship between the feedwater flow rates at the measuring points and the average feedwater flow rate and determining the flow rate weight of each measuring point; calculating the average feedwater flow rate and the feedwater flow by means of the measured feedwater flow rate at each measuring point and the flow rate weight of each measuring point; comparing the feedwater flow with the water flow initial value; if the deviation does not meet the requirement of precision, performing iterative computations until the deviation meets the requirement of precision; determining the feedwater flow.

Description

A kind of fired power generating unit feedwater flow assay method

Technical field

The present invention relates to a kind of assay method of fired power generating unit feedwater flow.

Background technology

Feedwater flow is the important parameter needing in fired power generating unit automatic control system to detect, its measuring accuracy is directly connected to the quality of feedwater regulation quality, meanwhile, feedwater flow is also the important influence factor of fired power generating unit economic target, is related to the accuracy of performance Index Calculation result.Therefore, the Measurement accuracy of unit feedwater flow the on-line performance of unit is monitored, process control, running optimizatin, economic analysis and carry out and energy-saving and cost-reducing etc. have vital meaning.

At present, measure fired power generating unit feedwater flow method and mainly contain two large classes: the direct method of measurement and the indirect method of measurement.The direct method of measurement, namely adopting standard knot fluid element as flow nozzle or orifice plate, by measuring the pressure reduction before and after restricting element, and through temperature pressure compensation correction, just can record the feedwater flow by restricting element.The method under certain condition, there is simply and intuitively advantage, but the method has the following disadvantages: one is can cause larger restriction loss when measuring feedwater flow, the wasted work of feed pump is increased, affect the heat-economy of unit, two is when unit variable load operation, and measuring accuracy declines.The indirect method of measurement is exactly based on condensing water flow, utilizes the variable condition calculation of the through-flow characteristic of Steam Turbine and well heater at different levels, carrys out the feedwater flow of indirect calculation unit.The method carrys out indirect calculation feedwater flow by measuring condensing water flow, advantage is that condensate water parameter is lower than feedwater, measuring accuracy is higher and restriction loss is less, but the method relate to lowly to add, thermodynamic computing that oxygen-eliminating device, height add, more parameter and link bring larger uncertainty, make the computational accuracy of feedwater flow lower.

Summary of the invention

Goal of the invention: for above-mentioned prior art, proposes a kind of fired power generating unit feedwater flow assay method, can realize the accurate hard measurement of fired power generating unit feedwater flow.

The present invention realizes by following technical solution:

(1) point layout and point velocity are calculated:

Be measuring point along four positions of radial direction selected distance cross section circle centre position length r=0, r=0.4R, r=0.8R, r=0.95R in the arbitrary cross section of feedwater piping, utilize Pitot tube to measure the dynamic pressure Δ p of feedwater _i, then each measuring point place feedwater flow rate measurements v _mifor:

$v_{\mathrm{mi}}=\sqrt{\frac{2\mathrm{\Δ}{p}_i}{\mathrm{\ρ}}}---\left(1\right)$

In formula: v _mi---i gets 1 ~ 4, respectively the feedwater flow rate measurements that records of corresponding r=0, r=0.4R, r=0.8R, r=0.95R measuring point place; Δ p _i---i gets 1 ~ 4, respectively the feedwater dynamic pressure measurement value that records of corresponding r=0, r=0.4R, r=0.8R, r=0.95R measuring point place; ρ---to water-mass density; R is feedwater piping radius;

(2) estimate feedwater flow, obtain feedwater flow initial value:

$D_{w1}\≈D_{w0}\frac{P_{\mathrm{el}}}{P_{\mathrm{el}0}}---\left(2\right)$

In formula: D _w1---feedwater flow initial value; P _el---the operating mode power of the assembling unit to be measured; D _w0---the design conditions feedwater flow of taking; P _el0---the design conditions power of the assembling unit of taking;

(3) each point velocity flexible strategy are calculated:

31), described feedwater flow initial value D is utilized _w1, feedwater piping internal diameter and give water-mass density, estimate feedwater mean flow rate initial value v _a':

${v_a}^{,}=\frac{4D_{w1}}{\mathrm{\ρ\π}{d}^2}---\left(3\right)$

In formula: v _a'---feedwater mean flow rate initial value; D---feedwater piping internal diameter;

32), according to feedwater mean flow rate initial value, the reynolds number Re of flowing in feedwater piping is calculated:

$\mathrm{Re}=\frac{\mathrm{\ρ}{v_a}^{,}d}{\mathrm{\η}}---\left(4\right)$

In formula: η---feedwater kinetic viscosity;

33), in turbulent situation, namely during Re > 2000, the velocity distribution v calculating feedwater piping cross-section radial is:

$v=v_{\max }{(1-\frac{r}{R})}^{\frac{1}{n}}---\left(6\right)$

V in formula _maxfor feedwater piping axle center place is to water flow velocity, turbulent velocity distributed constant n calculates such as formula shown in (7):

$n=10-3e^{{-10}^{-6}\mathrm{Re}}---\left(7\right)$

34), according to velocity distribution v and the pipeline section area of described feedwater piping cross-section radial, set up along feedwater piping cross section average velocity v according to formula (8) _amodel:

$v_a=\frac{{\∫}_0^{R}2\mathrm{\πrvdr}}{\mathrm{\π}{R}^2}=2(\frac{n}{n+1}-\frac{n}{2n+1})v_{\max }---\left(8\right)$

35), when the velocity distribution v of feedwater piping cross-section radial, the mean flow rate that each measuring point is corresponding is estimated:

Each measuring point distance cross section circle centre position length r is substituted into formula (6), obtains each measuring point place predicted velocity v ₁, v ₂, v ₃, v ₄:

$\left\{\begin{array}{c}{v}_1=v_{\max }\\ v_2={0.6}^{\frac{1}{n}}{v}_{\max }\\ v_3={0.2}^{\frac{1}{n}}{v}_{\max }\\ v_4={0.05}^{\frac{1}{n}}{v}_{\max }\end{array}\right.---\left(9\right)$

Simultaneous (8) and formula (9), cancellation v _max, obtain the mean flow rate predicted value v that each measuring point is corresponding _a1, v _a2, v _a3, v _a4:

$\left\{\begin{array}{c}{v}_{a1}=2(\frac{n}{n+1}-\frac{n}{2n+1})v_1\\ v_{a2}=\frac{2(\frac{n}{n+1}-\frac{n}{2n+1})}{{0.6}^{\frac{1}{n}}}{v}_2\\ v_{a3}=\frac{2(\frac{n}{n+1}-\frac{n}{2n+1})}{{0.2}^{\frac{1}{n}}}{v}_3\\ v_{a4}=\frac{2(\frac{n}{n+1}-\frac{n}{2n+1})}{{0.05}^{\frac{1}{n}}}{v}_4\end{array}\right.---\left(10\right)$

36), corresponding according to each measuring point mean flow rate predicted value v _a1, v _a2, v _a3, v _a4, calculate along feedwater piping cross section average speed value, shown in (11):

$v_a=\frac{{\mathrm{\Σ}}_{i=1}^4{v}_{\mathrm{ai}}}{4}---\left(11\right)$

Formula (10) is substituted into (11),

$v_a=0.5(\frac{n}{n+1}-\frac{n}{2n+1})v_1+\frac{0.5(\frac{n}{n+1}-\frac{n}{2n+1})}{{0.6}^{\frac{1}{n}}}{v}_2+\frac{0.5(\frac{n}{n+1}-\frac{n}{2n+1})}{{0.2}^{\frac{1}{n}}}{v}_3+\frac{0.5(\frac{n}{n+1}-\frac{n}{2n+1})}{{0.05}^{\frac{1}{n}}}{v}_4---\left(12\right)$

According to formula (13), calculate each point velocity flexible strategy K ₁, K ₂, K ₃, K ₄:

$\left\{\begin{array}{c}{K}_1=0.5(\frac{n}{n+1}-\frac{n}{2n+1})\\ K_2=\frac{0.5(\frac{n}{n+1}-\frac{n}{2n+1})}{{0.6}^{\frac{1}{n}}}\\ K_3=\frac{0.5(\frac{n}{n+1}-\frac{n}{2n+1})}{{0.2}^{\frac{1}{n}}}\\ K_4=\frac{0.5(\frac{n}{n+1}-\frac{n}{2n+1})}{{0.5}^{\frac{1}{n}}}\end{array}\right.---\left(13\right)$

(4) iterative logical

By the feedwater flow rate measurements v of described each measuring point _miwith the flow velocity flexible strategy K of each measuring point _i, calculate the mean flow rate in the feedwater piping cross section based on point velocity measured value:

v _ma＝∑K _iv _mi(14)

Then the feedwater flow of surveyed operating mode is:

$D_w=\frac{\mathrm{\ρ}{v}_{\mathrm{ma}}\mathrm{\π}{d}^2}{4}---\left(15\right)$

By the feedwater flow D calculated _wwith initial calculation value D _w1carry out error checking, if relative error is greater than preset value, be then initial flow with calculated flow rate, recalculate, until flow relative error is less than or equal to preset value, the feedwater flow now obtained is the feedwater flow of operating mode to be measured.

Beneficial effect: the invention discloses a kind of fired power generating unit feedwater flow assay method, takes unit design operating mode feedwater flow, the power of the assembling unit, feedwater piping internal diameter, operating mode feed pressure to be measured, feed temperature, feedwater kinetic viscosity; The measuring point place feedwater dynamic pressure that point position, Pitot tube record.Calculate each measuring point place to water flow velocity, calculate feedwater flow estimated value, feedwater mean flow rate, feedwater Bottomhole pressure Reynolds number, determine that feedwater is along pipeline section velocity flow profile.Utilize feedwater along pipeline section velocity flow profile, calculate measuring point place to water flow velocity and on average to the relation of water flow velocity, determine each measuring point place flow velocity flexible strategy.Utilize each measuring point place to record to water flow velocity, in conjunction with each measuring point place flow velocity flexible strategy, calculate average to water flow velocity and feedwater flow, and compare with feedwater flow initial value, if deviation does not meet accuracy requirement, then carry out iterative computation, until deviation meets accuracy requirement, determine feedwater flow.

In traditional direct method of measurement, be adopt standard knot fluid element as flow nozzle or orifice plate, measure feedwater flow by the pressure reduction measured before and after restricting element.The method can cause larger restriction loss when measuring feedwater flow, the wasted work of feed pump is increased, affects the heat-economy of unit.The measuring sensor that the measuring method that the present invention proposes adopts is Pitot tube, decreases the restriction loss in measuring process, is conducive to the economy of unit operation.A kind of flow determining method based on flow field velocity distributed acquisition mean flow rate of the present invention, has and calculates easy, computational accuracy advantages of higher.

Accompanying drawing explanation

Fig. 1 is measuring point distribution schematic diagram of the present invention;

Fig. 2 is calculation flow chart of the present invention.

Embodiment

A kind of fired power generating unit feedwater flow assay method, the measuring sensor used is Pitot tube, on the cross section of feedwater piping to be measured, along radial direction selected distance cross section circle centre position length r=0, r=0.4R, r=0.8R, r=0.95R 4 as measuring point, as shown in Figure 2, Pitot tube output parameter is the dynamic pressure Δ p of each measuring point _i(Pa).

Determination step is as follows:

Step 1: initial parameter is determined

Take design conditions power of the assembling unit P _el0(MW), design conditions feedwater flow D _w0(t/h), feedwater piping internal diameter d (m).

Measure operating mode power of the assembling unit P to be measured _el(MW), feed pressure p _wand feed temperature t (MPa) _w(DEG C), calculates feedwater density p (kg/m ³) and feedwater kinetic viscosity η (Pas).

Step 2: each point velocity measuring and calculating

The dynamic pressure Δ p of each measuring point place feedwater utilizing Pitot tube to record _i, obtain each measuring point feedwater flow rate measurements v by formula (1) _mifor:

$v_{\mathrm{mi}}=\sqrt{\frac{2\mathrm{\Δ}{p}_i}{\mathrm{\ρ}}}---\left(1\right)$

In formula: v _mi---i gets 1 ~ 4, respectively the feedwater flow rate measurements at corresponding r=0, r=0.4R, r=0.8R, r=0.95R measuring point place; Δ p _i---i gets 1 ~ 4, respectively the feedwater dynamic pressure measurement value at corresponding r=0, r=0.4R, r=0.8R, r=0.95R measuring point place;

Step 3: the determination of feedwater flow initial calculation value:

By formula (2), estimate feedwater flow, calculate feedwater flow initial value:

$D_{w1}\≈D_{w0}\frac{P_{\mathrm{el}}}{P_{\mathrm{el}0}}---\left(2\right)$

In formula: D _w1---feedwater flow initial value; P _el---the operating mode power of the assembling unit to be measured;

Step 4: the determination of the radial velocity flow profile of pipeline section

41), by feedwater flow initial value D _w1, feedwater piping internal diameter d, feedwater density p, estimates feedwater mean flow rate initial value v according to formula (3) _a':

${v_a}^{,}=\frac{4D_{w1}}{\mathrm{\ρ\π}{d}^2}---\left(3\right)$

42), by feedwater kinetic viscosity η, feedwater mean flow rate initial value v _a', feedwater piping internal diameter d, feedwater density p, calculates flowing Reynolds number in feedwater piping according to formula (4):

$\mathrm{Re}=\frac{\mathrm{\ρ}{v_a}^{,}d}{\mathrm{\η}}---\left(4\right)$

43), be the feedwater piping of R for radius, in turbulent situation, namely during Re > 2000, the velocity distribution v of feedwater piping cross-section radial is:

$v=v_{\max }{(1-\frac{r}{R})}^{\frac{1}{n}}---\left(6\right)$

V in formula _maxfor feedwater piping axle center place is to water flow velocity, by the reynolds number Re that flows in feedwater piping, according to turbulent velocity distributed constant n in formula (7) computer tube:

$n=10-3e^{{-10}^{-6}\mathrm{Re}}---\left(7\right)$

34), according to velocity distribution v and the pipeline section area of feedwater piping cross-section radial, set up along feedwater piping cross section average velocity v according to formula (8) _amodel:

$v_a=\frac{{\∫}_0^{R}2\mathrm{\πrvdr}}{\mathrm{\π}{R}^2}---\left(8\right)$

Substitute into formula (8) by by formula (6), can be calculated

$v_a=2(\frac{n}{n+1}-\frac{n}{2n+1})v_{\max }---\left(9\right)$

Each measuring point distance cross section circle centre position length r is substituted into formula (6), obtains each measuring point place predicted velocity v ₁, v ₂, v ₃, v ₄, corresponding r=0, r=0.4R, r=0.8R, r=0.95R measuring point respectively:

$\left\{\begin{array}{c}{v}_1=v_{\max }\\ v_2={0.6}^{\frac{1}{n}}{v}_{\max }\\ v_3={0.2}^{\frac{1}{n}}{v}_{\max }\\ v_4={0.05}^{\frac{1}{n}}{v}_{\max }\end{array}\right.---\left(10\right)$

Simultaneous formula (9) and formula (10), cancellation v _max, obtain the mean flow rate predicted value v that each measuring point is corresponding _a1, v _a2, v _a3, v _a4, corresponding r=0, r=0.4R, r=0.8R, r=0.95R measuring point respectively:

$\left\{\begin{array}{c}{v}_{a1}=2(\frac{n}{n+1}-\frac{n}{2n+1})v_1\\ v_{a2}=\frac{2(\frac{n}{n+1}-\frac{n}{2n+1})}{{0.6}^{\frac{1}{n}}}{v}_2\\ v_{a3}=\frac{2(\frac{n}{n+1}-\frac{n}{2n+1})}{{0.2}^{\frac{1}{n}}}{v}_3\\ v_{a4}=\frac{2(\frac{n}{n+1}-\frac{n}{2n+1})}{{0.05}^{\frac{1}{n}}}{v}_4\end{array}\right.---\left(11\right)$

35), corresponding according to each measuring point mean flow rate predicted value v _a1, v _a2, v _a3, v _a4, calculate along feedwater piping cross section average speed value, shown in (12):

$v_a=\frac{{\mathrm{\Σ}}_{i=1}^4{v}_{\mathrm{ai}}}{4}---\left(12\right)$

Formula (11) is substituted into (12),

$v_a=0.5(\frac{n}{n+1}-\frac{n}{2n+1})v_1+\frac{0.5(\frac{n}{n+1}-\frac{n}{2n+1})}{{0.6}^{\frac{1}{n}}}{v}_2+\frac{0.5(\frac{n}{n+1}-\frac{n}{2n+1})}{{0.2}^{\frac{1}{n}}}{v}_3+\frac{0.5(\frac{n}{n+1}-\frac{n}{2n+1})}{{0.05}^{\frac{1}{n}}}{v}_4---\left(13\right)$

Step 5: the determination of each point velocity flexible strategy:

By turbulent velocity distributed constant n in pipe, substitute into formula (14) and calculate each point velocity flexible strategy K _i, corresponding r=0, r=0.4R, r=0.8R, r=0.95R measuring point respectively:

$\left\{\begin{array}{c}{K}_1=0.5(\frac{n}{n+1}-\frac{n}{2n+1})\\ K_2=\frac{0.5(\frac{n}{n+1}-\frac{n}{2n+1})}{{0.6}^{\frac{1}{n}}}\\ K_3=\frac{0.5(\frac{n}{n+1}-\frac{n}{2n+1})}{{0.2}^{\frac{1}{n}}}\\ K_4=\frac{0.5(\frac{n}{n+1}-\frac{n}{2n+1})}{{0.5}^{\frac{1}{n}}}\end{array}\right.---\left(14\right)$

Step 6: calculate mean flow rate and feedwater flow:

Utilize the flow velocity v that each measuring point is measured _miwith the flow velocity flexible strategy K of each measuring point _i, calculate the feedwater mean flow rate based on point velocity measured value by formula (15):

v _ma＝∑K _iv _mi(15)

Utilize feedwater mean flow rate v _ma, feedwater piping internal diameter d, feedwater density p, calculates feedwater flow by formula (16):

$D_w=\frac{\mathrm{\ρ}{v}_{\mathrm{ma}}\mathrm{\π}{d}^2}{4}---\left(16\right)$

Step 7: error checking

By the feedwater flow D calculated _wwith initial calculation value D _w1relatively, if relative error Δ discontented foot formula:

Then with calculated flow rate D _wfor initial flow, repeat step 4 ~ 7, carry out iterative computation, until relative error meets accuracy requirement.The feedwater flow now obtained is the feedwater flow of operating mode to be measured.

Be below certain unit survey calculation example, detailed calculation procedure is as follows:

Step 1: take design conditions power of the assembling unit P _el0=600MW, design conditions feedwater flow D _w0=1662.2t/h, feedwater piping internal diameter d=0.341m.

Record unit electrical power P _el=400MW, feed pressure p _w=22.071MPa, feed temperature t _w=250.152 DEG C, calculate feedwater density p=817.9kg/m ³, feedwater kinetic viscosity η=115.8 × 10 ^-6pa.s.

Step 2: each point velocity measuring and calculating

The dynamic pressure that each measuring point records:

Δp ₁＝9.037kPa，Δp ₂＝8.255kPa，Δp ₃＝6.658kPa，Δp ₄＝4.978kPa

Then by each measuring point can be obtained to water flow velocity:

v _m1＝4.701m/s，v _m2＝4.493m/s，v _m3＝4.035m/s，v _m4＝3.489m/s

Step 3: the determination of feedwater flow initial value

By formula (2), calculate feedwater flow initial value:

$D_{w1}\≈D_{w0}\frac{P_{\mathrm{el}}}{P_{\mathrm{el}0}}=1108t/h$

Step 4: the determination of the radial velocity flow profile of pipeline section

By the initial feedwater flow D of estimation _w1with give water-mass density, calculate feedwater mean flow rate initial value v by formula (3) _a':

${v_a}^{,}=\frac{4D_{w1}}{\mathrm{\ρ\π}{d}^2}=4.121m/s$

Flowing Reynolds number in feedwater piping is calculated by formula (4):

$\mathrm{Re}=\frac{\mathrm{\ρ}{v_a}^{,}d}{\mathrm{\η}}=9925819$

By turbulent velocity distributed constant n in formula (7) computer tube

$n=10-3e^{{-10}^{-6}\mathrm{Re}}=9.99985$

The velocity flow profile of feedwater piping cross-section radial is then obtained by formula (6):

$v=v_{\max }{(1-\frac{r}{R})}^{\frac{1}{9.99985}}$

Step 5: the determination of each point velocity flexible strategy

By turbulent velocity distributed constant n in pipe, formula (14) is utilized to calculate each point velocity flexible strategy K _i:

$\left\{\begin{array}{c}{K}_1=0.5(\frac{n}{n+1}-\frac{n}{2n+1})=0.2164\\ K_2=\frac{0.5(\frac{n}{n+1}-\frac{n}{2n+1})}{{0.6}^{\frac{1}{n}}}=0.2278\\ K_3=\frac{0.5(\frac{n}{n+1}-\frac{n}{2n+1})}{{0.2}^{\frac{1}{n}}}=0.2542\\ K_4=\frac{0.5(\frac{n}{n+1}-\frac{n}{2n+1})}{{0.5}^{\frac{1}{n}}}=0.2921\end{array}\right.$

Step 6: calculate mean flow rate and feedwater flow

Utilize each point velocity measured value v _miwith the flow velocity flexible strategy K of each measuring point _i, calculate the feedwater piping cross section mean flow rate based on point velocity measured value by formula (15):

v _ma＝∑K _iv _mi＝4.087m/s

By feedwater mean flow rate v _ma, feedwater piping internal diameter d, feedwater density p, calculates feedwater flow D by formula (16) _w

$D_w=\frac{\mathrm{\ρ}{v}_{\mathrm{ma}}\mathrm{\π}{d}^2}{4}=1098.82t/h$

Step 7: error checking

The feedwater flow relative error of the feedwater flow calculated and initial setting:

$\mathrm{\Δ}=\frac{|1108-1098.82|}{1108}=0.0083>0.001$

Then make feedwater flow initial value D _w=1098.82t/h, re-starts the calculating of step 4 ~ 7.

1st iterative step 4: the determination of the radial velocity flow profile of pipeline section

By the initial feedwater flow of estimation with to water-mass density, calculate feedwater mean flow rate by formula (3):

${v_a}^{\′}=\frac{4D_w}{\mathrm{\ρ\π}{d}^2}=4.087m/s$

Feedwater Bottomhole pressure Reynolds number is calculated by formula (4):

$\mathrm{Re}=\frac{\mathrm{\ρ}{v_a}^{\′}d}{\mathrm{\η}}=9843607$

By turbulent velocity distributed constant n in formula (7) computer tube

$n=10-3e^{{-10}^{-6}\mathrm{Re}}=9.99983$

Then obtain feedwater piping cross sectional flow rate by formula (6) to distribute:

$v=v_{\max }{(1-\frac{r}{R})}^{\frac{1}{9.99983}}$

Iterative step 5 for the first time: the determination of each point velocity flexible strategy

By turbulent velocity distributed constant n in pipe, formula (14) is utilized to calculate each point velocity flexible strategy K _i:

$\left\{\begin{array}{c}{K}_1=0.5(\frac{n}{n+1}-\frac{n}{2n+1})=0.2164\\ K_2=\frac{0.5(\frac{n}{n+1}-\frac{n}{2n+1})}{{0.6}^{\frac{1}{n}}}=0.2278\\ K_3=\frac{0.5(\frac{n}{n+1}-\frac{n}{2n+1})}{{0.2}^{\frac{1}{n}}}=0.2542\\ K_4=\frac{0.5(\frac{n}{n+1}-\frac{n}{2n+1})}{{0.5}^{\frac{1}{n}}}=0.2921\end{array}\right.$

Iterative step 6 for the first time: calculate mean flow rate and feedwater flow

Utilize each point velocity measured value v _miwith the flow velocity flexible strategy K of each measuring point _i, calculate the feedwater piping cross section mean flow rate based on point velocity measured value by formula (15):

v _ma＝∑K _iv _mi＝4.086m/s

By feedwater mean flow rate v _ma, feedwater piping internal diameter d, feedwater density p, calculates feedwater flow D by formula (16) _w

$D_w=\frac{\mathrm{\ρ}{v}_{\mathrm{ma}}\mathrm{\π}{d}^2}{4}=1098.52t/h$

Iterative step 7 for the first time: error checking

The feedwater flow relative error of the feedwater flow calculated and initial setting:

$\mathrm{\&Delta;}=\frac{|1098.82-1098.52|}{1098.82}=0.00027<0.001$

Meet accuracy requirement, namely recording feedwater flow is 1098.52t/h

Interpretation of result: result of calculation contrast is as shown in table 1, as can be seen from table, through twice calculating, feedwater flow convergence is stable, each measuring point calculating flow velocity is also quite close with measured value simultaneously, shows that the feedwater flow calculating method that the present invention proposes reduces comparatively accurately to the velocity distribution of water flow.

Table 1

The above is only the preferred embodiment of the present invention; it should be pointed out that for those skilled in the art, under the premise without departing from the principles of the invention; can also make some improvements and modifications, these improvements and modifications also should be considered as protection scope of the present invention.

Claims (1)

1. a fired power generating unit feedwater flow assay method, is characterized in that, comprises the steps:

(1), point layout and point velocity are calculated:

Be measuring point along four positions of radial direction selected distance cross section circle centre position length r=0, r=0.4R, r=0.8R, r=0.95R in the arbitrary cross section of feedwater piping, utilize Pitot tube to measure the dynamic pressure Δ p of feedwater _i, then each measuring point place feedwater flow rate measurements v _mifor:

$v_{\mathrm{mi}}=\sqrt{\frac{2\mathrm{\&Delta;}{p}_i}{\mathrm{\&rho;}}}---\left(1\right)$

In formula: v _mi---i gets 1 ~ 4, respectively the feedwater flow rate measurements that records of corresponding r=0, r=0.4R, r=0.8R, r=0.95R measuring point place; Δ p _i---i gets 1 ~ 4, respectively the feedwater dynamic pressure measurement value that records of corresponding r=0, r=0.4R, r=0.8R, r=0.95R measuring point place; ρ---to water-mass density; R is feedwater piping radius;

(2), estimate feedwater flow, obtain feedwater flow initial value:

$D_{w1}\&ap;D_{w0}\frac{P_{\mathrm{el}}}{P_{\mathrm{el}0}}---\left(2\right)$

In formula: D _w1---feedwater flow initial value; P _el---the operating mode power of the assembling unit to be measured; D _w0---the design conditions feedwater flow of taking; P _el0---the design conditions power of the assembling unit of taking;

(3), each point velocity flexible strategy are calculated:

31), described feedwater flow initial value D is utilized _w1, feedwater piping internal diameter and give water-mass density, estimate feedwater mean flow rate initial value v _a':

${v_a}^{\&prime;}=\frac{4D_{w1}}{\mathrm{\&rho;\&pi;}{d}^2}---\left(3\right)$

In formula: v _a'---feedwater mean flow rate initial value; D---feedwater piping internal diameter;

32), according to feedwater mean flow rate initial value, the reynolds number Re of flowing in feedwater piping is calculated:

$\mathrm{Re}=\frac{\mathrm{\&rho;}{v_a}^{\&prime;}d}{\mathrm{\&eta;}}---\left(4\right)$

In formula: η---feedwater kinetic viscosity;

33), in turbulent situation, namely during Re>2000, the velocity distribution v calculating feedwater piping cross-section radial is:

$v=v_{\max }{(1-\frac{r}{R})}^{\frac{1}{n}}---\left(6\right)$

V in formula _maxfor feedwater piping axle center place is to water flow velocity, turbulent velocity distributed constant n calculates such as formula shown in (7):

$n=10-{3e}^{-10^{-6}\mathrm{Re}}---\left(7\right)$

34), according to velocity distribution v and the pipeline section area of described feedwater piping cross-section radial, set up along feedwater piping cross section average velocity v according to formula (8) _amodel:

$v_a=\frac{{\&Integral;}_0^{R}2\mathrm{\&pi;rvdr}}{\mathrm{\&pi;}{R}^2}=2(\frac{n}{n+1}-\frac{n}{2n+1})v_{\max }---\left(8\right)$

35), when the velocity distribution v of feedwater piping cross-section radial, the mean flow rate that each measuring point is corresponding is estimated:

Each measuring point distance cross section circle centre position length r is substituted into formula (6), obtains each measuring point place predicted velocity v ₁, v ₂, v ₃, v ₄:

$\left\{\begin{array}{c}{v}_1=v_{\max }\\ v_2={0.6}^{\frac{1}{n}}{v}_{\max }\\ v_3={0.2}^{\frac{1}{n}}{v}_{\max }\\ v_4={0.05}^{\frac{1}{n}}{v}_{\max }\end{array}\right.---\left(9\right)$

Simultaneous (8) and formula (9), cancellation v _max, obtain the mean flow rate predicted value v that each measuring point is corresponding _a1, v _a2, v _a3, v _a4:

$\left\{\begin{array}{c}{v}_{a1}=2(\frac{n}{n+1}-\frac{n}{2n+1})v_1\\ v_{a2}=\frac{2(\frac{n}{n+1}-\frac{n}{2n+1})}{{0.6}^{\frac{1}{n}}}{v}_2\\ v_{a3}=\frac{2(\frac{n}{n+1}-\frac{n}{2n+1})}{{0.2}^{\frac{1}{n}}}{v}_3\\ v_{a4}=\frac{2(\frac{n}{n+1}-\frac{n}{2n+1})}{{0.05}^{\frac{1}{n}}}{v}_4\end{array}\right.---\left(10\right)$

36), corresponding according to each measuring point mean flow rate predicted value v _a1, v _a2, v _a3, v _a4, calculate along feedwater piping cross section average speed value, shown in (11):

$v_a=\frac{{\mathrm{\&Sigma;}}_{i=1}^4{v}_{\mathrm{ai}}}{4}---\left(11\right)$

Formula (10) is substituted into (11),

$v_a=0.5(\frac{n}{n+1}-\frac{n}{2n+1})v_1+\frac{0.5(\frac{n}{n+1}-\frac{n}{2n+1})}{{0.6}^{\frac{1}{n}}}{v}_2+\frac{0.5(\frac{n}{n+1}-\frac{n}{2n+1})}{{0.2}^{\frac{1}{n}}}{v}_3+\frac{0.5(\frac{n}{n+1}-\frac{n}{2n+1})}{{0.05}^{\frac{1}{n}}}{v}_4---\left(12\right)$

According to formula (13), calculate each point velocity flexible strategy K ₁, K ₂, K ₃, K ₄:

$\left\{\begin{array}{c}{K}_1=0.5(\frac{n}{n+1}-\frac{n}{2n+1})\\ K_2=\frac{0.5(\frac{n}{n+1}-\frac{n}{2n+1})}{{0.6}^{\frac{1}{n}}}\\ K_3=\frac{0.5(\frac{n}{n+1}-\frac{n}{2n+1})}{{0.2}^{\frac{1}{n}}}\\ K_4=\frac{0.5(\frac{n}{n+1}-\frac{n}{2n+1})}{{0.05}^{\frac{1}{n}}}\end{array}\right.---\left(13\right)$

(4), iterative logical:

By the feedwater flow rate measurements v of described each measuring point _miwith the flow velocity flexible strategy K of each measuring point _i, calculate the mean flow rate in the feedwater piping cross section based on point velocity measured value:

v _ma＝∑K _iv _mi(14)

Then the feedwater flow of surveyed operating mode is:

$D_w=\frac{\mathrm{\&rho;}{v}_{\mathrm{ma}}\mathrm{\&pi;}{d}^2}{4}---\left(15\right)$

By the feedwater flow D calculated _wwith initial calculation value D _w1carry out error checking, if relative error is greater than preset value, be then initial flow with calculated flow rate, recalculate, until flow relative error is less than or equal to preset value, the feedwater flow now obtained is the feedwater flow of operating mode to be measured.