CN101813562B - Method for estimating exhaust enthalpy of low pressure cylinder of steam turbine in real time - Google Patents

Abstract

The invention discloses a method for estimating the exhaust enthalpy of a low pressure cylinder of a steam turbine in real time, which belongs to the field of steam turbine parameter measurement. The method comprises: firstly, defining the exhaust efficiency of the (i+1)th stage of a turboset; secondly, obtaining the exhaust enthalpy of the (i+1)th stage of the turboset accordingly; and thirdly, according to a collected heat balance diagram of the steam turbine, obtaining the design parameters of the steam turbine under various working conditions, fitting the relationship between inter-stage efficiency of steam turbine and pressure ratio and calculating the exhaust efficiency eta i, i+1 of the (i+1)th stage of the seam turbine under different conditions from the exhaust efficiency of the last stage upward stage by stage. The method overcomes the drawback that the calculation speed of a loop iteration algorithm is far insufficient for meeting the demands for on-line monitoring of the machine and estimates the exhaust enthalpy of the low pressure cylinder of the steam turbine in real time when the turboset works under various working conditions.

Description

A kind of method of estimating exhaust enthalpy of low pressure cylinder of steam turbine in real time

Technical field

The invention belongs to the turbine parameters field of measurement, particularly a kind of method of estimating exhaust enthalpy of low pressure cylinder of steam turbine in real time.

Background technology

Steam turbine is being carried out in the process of economic analysis, must confirm the thermodynamic state of steam turbine last stage.Under common operating mode, one section turbine discharge that draws gas all is in wet-steam phase to steam turbine from the end.At wet-steam region, pressure and temperature no longer is an independent variable, and the mass dryness fraction parameter that need be aided with wet steam could be confirmed the state of wet steam.And no matter online low pressure dryness measurement device is from measuring accuracy, and still also there are a lot of problems in measuring speed on cost investment.For the thermodynamic state of online acquisition steam turbine afterbody steam, must do variable working condition to steam turbine and calculate.The design parameter that Under Variable Conditions of Steam Turbine is calculated equipment needed thereby, geometric parameter and necessity is a lot, and needs loop iteration to calculate.The loop iteration algorithm often can not be restrained owing to a variety of causes.Even can restrain, its computing velocity also far can not satisfy the needs of unit on-line monitoring.

Create a kind of not only simply but also convergent steam turbine last stage thermodynamic state computing method, become the problem that the online economic analysis of steam turbine must solve.The estimation of steam turbine last stage thermodynamic state mainly just is meant the estimation of exhaust enthalpy of low pressure cylinder of steam turbine.

Summary of the invention

The method that the purpose of this invention is to provide a kind of estimating exhaust enthalpy of low pressure cylinder of steam turbine in real time.

At first, the definition of analogy System Turbine Relative Internal Efficiency, it is following to provide the draw gas definition of efficient of Steam Turbine:

${\mathrm{\η}}_{i,i+1}=\frac{h_i-h_{i+1}}{h_i-h_{i+1}^{\%}}---\left(1\right)$

Can get the enthalpy that draws gas of Steam Turbine (i+1) level thus:

$h_{i+1}=h_i-{\mathrm{\η}}_{i,i+1}\·(h_i-h_{i+1}^{\%})---\left(2\right)$

In the formula, h _i, h _I+1Be respectively i, (i+1) the level enthalpy that draws gas, η _{I, i+1}Be (i+1) level efficient of drawing gas; h _I+1 ^%It is (i+1) level ideal enthalpy that draws gas;

The present invention adopt with steam turbine last stage draw gas or final stage draw gas upper level draw gas (superheated vapor) be the steam turbine variable working condition accounting method in proper order of zequin; At first collect the heat balance diagram of steam turbine before calculating; Obtain the design parameter of steam turbine under each operating mode; Comprise what extraction pressure of steam turbine end, temperature and enthalpy design load, the practical implementation step is following:

Upwards adjust step by step from the steam turbine last stage beginning of drawing gas, suppose to obtain the i level and draw gas and be the superheated vapor state, its pressure, temperature are respectively P _i, t _i, the enthalpy entropy that draws gas that water of writing through Matlab and steam character software for calculation bag can get this grade is respectively h _i, s _iWherein, at different levels the drawing gas before the superheated vapor state point, level is constant with the pressure ratio of level group, so think that the internal efficiency ratios of drawing gas at different levels before the superheated vapor state point are constant; For at different levels the drawing gas after the superheated vapor state point, desirable adiabatic process is regarded in the expansion in steam turbine as, so desirable entropy (i+1) grade

Calculate h by formula (2) _I+1, combine this stage pressure P again _I+1Get entropy s _I+1With desirable enthalpy h _I+1 ^%

Calculate (i+1) level efficiency eta of drawing gas under the different operating modes _{I, i+1}The time, at first calculate its η under each typical condition according to the steam turbine heat balance diagram _{I, i+1}, through match η _{I, i+1}With P _I+1/ P _iRelation curve, can get the η of Steam Turbine when the operation of each operating mode _{I, i+1}, the 7th grade of efficient fitting formula y=674.15x that draws gas of certain power plant steam turbine group ²-652.92x+159.03, (y is the 6th grade to the 7th grade a efficiency eta ₆₇, x is pressure ratio P ₇/ P ₆, variance R ²=0.9975 o'clock), its fit procedure can realize through the match tool box among Excel or the Matlab.

To sum up at different levels the drawing gas before the superheated vapor state point can calculate h by formula (2) _I+1, combine this stage pressure P again _I+1Can get entropy s _I+1Can calculate steam turbine parameters at different levels thus step by step until the exhaust enthalpy of low pressure cylinder of steam turbine h that calculates under each operating mode _c

The invention has the beneficial effects as follows and overcome the loop iteration algorithm often owing to a variety of causes causes and can not restrain; Even can restrain; Its computing velocity also far can not satisfy the deficiency of the needs of unit on-line monitoring, can estimate to obtain the η of Steam Turbine when each operating mode operation in real time _{I, i+1}

Description of drawings

Fig. 1 is certain power plant steam turbine group the 7th pumping efficiency η ₆₇With pressure ratio P ₇/ P ₆The matched curve instance.

Embodiment

The present invention provides a kind of method of estimating exhaust enthalpy of low pressure cylinder of steam turbine in real time.At first defining Steam Turbine (i+1) the level efficient of drawing gas is:

${\mathrm{\η}}_{i,i+1}=\frac{h_i-h_{i+1}}{h_i-h_{i+1}^{\%}}---\left(1\right)$

Can get the enthalpy that draws gas of Steam Turbine (i+1) level thus:

$h_{i+1}=h_i-{\mathrm{\η}}_{i,i+1}\·(h_i-h_{i+1}^{\%})---\left(2\right)$

In the formula, h _i, h _I+1Be respectively i, (i+1) the level enthalpy that draws gas, η _{I, i+1}Be (i+1) level efficient of drawing gas; h _I+1 ^%It is (i+1) level ideal enthalpy that draws gas.

Below in conjunction with accompanying drawing the present invention is further specified, concrete steps are following:

1) collects the heat balance diagram of steam turbine, obtain the design parameter of steam turbine under each operating mode, mainly comprise what extraction pressure of steam turbine end, temperature and enthalpy design load;

2), and provide fitting formula according to the relation between efficient and the pressure ratio between each operating mode design parameter match stage;

3) adopt curve-fitting method, begin to calculate from the afterbody superheated vapor through the match tool box among Excel or the Matlab, till calculating turbine discharge.

To sum up, calculate h by formula (2) _I+1, combine this stage pressure P again _I+1Can get entropy s _I+1Can calculate steam turbine parameters at different levels thus step by step until the exhaust enthalpy of low pressure cylinder of steam turbine h that calculates under each operating mode _c

The instance explanation

Below will be calculated as example explanation implementation process of the present invention with certain power plant steam turbine group low pressure (LP) cylinder exhaust enthalpy.

Certain power plant's what steam parameter of typical condition tubine group end of table 1

	P 6	t 6	h 6	P 7	t 7	h 7	P 8	t 8	h 8	P c	h c
												TNL	0.1337	144.2	2761.9	0.06421	87.7	2640.8	0.0247	64.7	2510	0.0052	2340.4
75％	0.1019	133.9	2744	0.04918	80.9	2626.4	0.01914	59.1	2499.1	0.0052	2351.4
												50％				0.03425	72.6	2631.5	0.0135	518	2506.8	0.0052	2402.2
40％	0.0588	126.2	2732.8	0.02842	67.9	2617.1	0.01133	48.3	2495.4	0.0052	2418.5
												30％	0.0463	116.9	2716	0.02246	62.6	2603.6	0.009	43.8	2484.7	0.0052	2445

Table 1 is what steam parameter of several typical conditions end of certain power plant steam turbine heat balance diagram mark, in the table: P _i, t _i, h _iBe followed successively by i level extraction pressure, temperature and enthalpy, P _cBe turbine low pressure cylinder exhaust steam pressure, h _cBe the exhaust enthalpy of low pressure cylinder of steam turbine value, the form font-weight representes that partly this grade steam condition is a superheat state, and all the other all are in wet-steam phase.At first nominal operating mode TNL is calculated:

(1) from steam turbine last stage draw gas the beginning adjust steam conditions at different levels step by step forward, until the superheated vapor state occurring.Under the TNL operating mode: the 6th grade is drawn gas and is superheated vapor state (P ₆The pairing saturated-steam temperature of=0.1337Mpa is 107.945 ℃, and current actual temperature is 144.2 ℃), and 7,8 two-stages are drawn gas and are wet steam.

(2) get the thermal parameter value of the 6th grade (superheated vapor level) by enthalpy-entropy diagram.Under the TNL operating mode: by P ₆=0.1337MPa, t ₆=144.2 ℃, get h ₆=2762.4180kJ/kg, s ₆=7.4482kJ/ (kgK).

(3) be isoentropic process, then s by the 6th grade to the 7th grade ₇=s ₆=7.4482kJ/ (kgK) is again by P ₇=0.06421MPa can get: mass dryness fraction x ₇=0.9905;

Utilize cylinder efficiency calculation software to get simultaneously: η _6,7=0.95249.

(4) can know by formula (2):

Bring into and can get h ₇=2640.1972kJ/kg combines P simultaneously ₇Can get S ₇=7.4651kJ/ (kgK).

(5) be isoentropic process, then s by the 7th grade to the 8th grade ₈=s ₇=7.4651kJ/ (kgK) is again by P ₈=0.0247MPa can get: mass dryness fraction x ₈=0.9468,

Utilize cylinder efficiency calculation software to get simultaneously: η _7,8=0.8774506481.

(6) same step (4) can get: h ₈=2510.3735kJ/kg combines P simultaneously ₈Can get s ₈=7.5188kJ/ (kgK).

(7) be isoentropic process, then S by the 8th grade to steam discharge _c=S ₈=7.5188kJ/ (kgK) is again by P _c=0.0052MPa can get: mass dryness fraction x _c=0.8909,

Utilize cylinder simultaneously

Efficiency calculation software can get: η _{8, c}=0.7965530897.

(8) same step (4) can get: h _c=2341.1147kJ/kg.

More than each step all can realize through program.In like manner, also can calculate the exhaust enthalpy of low pressure cylinder of steam turbine of other several typical conditions.Gained result and its design load are compared, see Table 2.Can know that by table 2 the method maximum relative error that the present invention adopts is no more than 0.05%, has higher precision, and need not to detect the mass dryness fraction parameter of wet steam, can be applied to the on-line monitoring of unit exhaust enthalpy.

Certain Turbo-generator Set exhaust enthalpy design load of table 2 and estimated value are relatively

Claims (2)

1. the method for an estimating exhaust enthalpy of low pressure cylinder of steam turbine in real time is characterized in that, concrete steps are following:

(1) at first defining Steam Turbine (i+1) the level efficient of drawing gas is:

${\mathrm{\η}}_{i,i+1}=\frac{h_i-h_{i+1}}{h_i-{\tilde{h}}_{i+1}}---\left(1\right)$

Can get the enthalpy that draws gas of Steam Turbine (i+1) level thus:

$h_{i+1}=h_i-{\mathrm{\η}}_{i,i+1}\·(h_i-{\tilde{h}}_{i+1})---\left(2\right)$

In the formula, h _i, h _I+1Be respectively i, (i+1) the level enthalpy that draws gas, η _{I, i+1}Be (i+1) level efficient of drawing gas;

It is (i+1) level ideal enthalpy that draws gas;

(2) collect the heat balance diagram of steam turbine, obtain the design parameter of steam turbine under each operating mode, comprise what extraction pressure of steam turbine end, temperature and enthalpy design load;

(3) upwards adjust step by step from the steam turbine last stage beginning of drawing gas, suppose to obtain the i level and draw gas and be the superheated vapor state, its pressure, temperature are respectively P _i, t _i, water of writing through Matlab and the steam character software for calculation Bao Dedi i level enthalpy entropy that draws gas is respectively h _i, S _iWherein, at different levels the drawing gas before the superheated vapor state point, level is constant with the pressure ratio of level group, so think that its internal efficiency ratio is constant; For at different levels the drawing gas after the superheated vapor state point, desirable adiabatic process is regarded in the expansion in steam turbine as, so desirable entropy (i+1) grade

Calculate h by formula (2) _I+1, combine this stage pressure P again _I+1Get entropy S _I+1With desirable enthalpy

(4) (i+1) under the different operating modes of calculating grade of efficiency eta of drawing gas _{I, i+1}The time, at first calculate its η under each operating mode according to the steam turbine heat balance diagram _{I, i+1}, through match η _{I, i+1}With P _I+1/ P _iRelation curve, can get the η of Steam Turbine when the operation of each operating mode _{I, i+1}

To sum up at different levels the drawing gas before the superheated vapor state point can calculate h by formula (2) _I+1, combine this stage pressure P again _I+1Can get entropy S _I+1Can calculate steam turbine parameters at different levels thus step by step until the exhaust enthalpy of low pressure cylinder of steam turbine h that calculates under each operating mode _c

2. according to the method for the said estimating exhaust enthalpy of low pressure cylinder of steam turbine in real time of claim 1, it is characterized in that the η of said match _{I, i+1}With P _I+1/ P _iRelation curve be to realize through match tool box among Excel or the Matlab.

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