CN103674333B - A kind of real-time identification method of coal fired power plant as-fired coal net calorific value - Google Patents

Abstract

The invention provides a kind of real-time identification method of coal fired power plant as-fired coal net calorific value, step comprises: 1, obtain boiler structure parameter according to boiler operatiopn design discipline, reads the operating condition measuring point instantaneous value given time from the real-time data base of DCS control system; 2, the specific enthalpy of working medium and the specific heat of density and flue gas and density is calculated based on working medium physical parameter storehouse and flue gas physical parameter storehouse; 3, based on the relational model correction main steam mass rate of main vapour pitch aperture and main steam mass rate; 4, the gross energy calculated respectively under corresponding boiler side each several part Energy transmission and this given time according to boiler side whole process mechanism model exports; 5, the transfer function model between feeder coal supply mass rate and as-fired coal mass rate is set up; 6, the transfer function model that as-fired coal mass rate and gross energy export is set up.The present invention is used for on-line identification as-fired coal net calorific value, has the application potential of burning and coal blending optimizing.

Description

A kind of real-time identification method of coal fired power plant as-fired coal net calorific value

Technical field

The present invention relates to a kind of as-fired coal net calorific value real-time identification method of thermal power generation control field, particularly, relate to a kind of as-fired coal net calorific value real-time identification method based on station boiler side mechanism model and DCS real time data.

Background technology

Coal-fired firepower power station is the main body of China's power industry, is also the major fields of energy-saving and emission-reduction.Due to China mine, transport, coal price diversification, most of power plant all faces as-fired coal matter frequent fluctuation, and this affects the bottleneck problem of whole process safe and highly efficient operation.Weighing an important indicator of ature of coal is net calorific value, and the coal that net calorific value is defined as unit mass burns the heat that can produce completely.The change of net calorific value directly affects the coal-fired thermal value at burner hearth thus breaks full-range energy equilibrium.If thermal value raises and do not subtract coal in time, then the input of boiler side gross energy is higher than specified output, causes unit generated energy coal consumption in short-term to be risen; If thermal value declines and do not supplement coal-fired in time, then will directly cause unit short-time rating decline and load tracking precise decreasing.If as-fired coal net calorific value can be measured in real time, then for coal blending workshop section, be equivalent to had feedback signal, can be used for the optimization instructing coal blending; For boiler-turbine coordinated, just can check coal in time, implement compensatory control.

But the sampling analysis cycle of China's major part coal fired power plant ature of coal off-line assay value reaches 6-8 hour, can not as the foundation controlling (as coal-supplying amount feedforward compensation) in real time.Could by " perception " when often will wait until after coal varitation that main steam pressure occurs obviously to change, pass through boiler master system fading margin First air flow subsequently to increase/to reduce furnace coal weight, slowly, whole interference stabilizes that transient process is consuming time reaches 15-30 minute in said process response.Like this, if the period of change of actual as-fired coal net calorific value is a hour level, then whole production just may be in continued jitters state, has a strong impact on the economy of electricity power enterprise's production and steady security.In view of domestic more than 300MW Subcritical Units bears the puzzlement of ature of coal frequent variations to some extent all the year round, be badly in need of the support of as-fired coal net calorific value Fast Identification technology, to improve Control platform.

Through the retrieval to prior art, Liu Fuguo (Liu Fuguo. the identification real time monitoring of fuel coal of power station boiler ultimate analysis and thermal value. Proceedings of the CSEE .25 (6), 139-144,2005) the coal-fired ultimate analysis based on dynamic element balance and thermal value discrimination method is proposed, and being successfully applied to 300MW unit, net calorific value precision of prediction is higher.But, the method needs the real-time measurement of smoke evacuation composition and needs to carry out ash content correction.U.S. thermoelectricity (ThermoElectron, existing name ThermoFisherScientificInc.) develop coal supply elemental analyser based on rapid neutron activation analysis (PGNAA-PromptGammaNeutronActivationAnalysis), real-time net calorific value is calculated by software, but it relates to application and the management of radioactive source, in addition this product price and long-time maintenance cost higher, be widely applied far away at home.

Summary of the invention

For defect of the prior art, the object of this invention is to provide a kind of power station as-fired coal net calorific value real-time identification method, the method makes full use of DCS control system real time data, the whole process mechanism model real-time simulation of bonded boiler side builds dynamic mass and energy balance relations, and then obtains as-fired coal net calorific value; Utilize net calorific value real-time identification value to compensate control to as-fired coal mass rate, the safety and steady obviously contributing to fired power generating unit is produced and thermal efficiency optimization.

For realizing above object, the invention provides a kind of power station as-fired coal net calorific value real-time identification method, the method comprises the following steps:

Step one, according to boiler operatiopn design discipline, obtain boiler following structural parameters: heat exchanger tube at different levels is along the total length in Working fluid flow direction, sectional area distribution, heat interchanger metallic walls quality; From the real-time data base of DCS control system, read the operation condition real time data under given time, specifically comprise: the exhaust gas temperature at the Temperature of Working at drum pressure, main steam mass rate, reheat heat steam mass flow, economizer exit feed-water quality flow, heat interchanger measuring point place at different levels and pressure, heat interchanger metallic walls temperature, flue outlet induced draft fan place, volumetric flow rate, boiler load and environment atmospheric pressure;

Step 2, according to working medium physical parameter storehouse and drum pressure, calculate this given time water drum outlet saturated vapour specific enthalpy and density, establish the temperature of working medium between the adjacent crucial measuring point of heat interchanger at different levels simultaneously, pressure linearly distributes, and by fixing discretize length, heat interchanger at different levels is divided into series of discrete infinitesimal, calculate working medium specific enthalpy and the density of each infinitesimal; According to flue gas physical parameter storehouse and exit gas temperature, pressure, atmospheric pressure, calculate specific heat and the density of exit gas under this given time;

Step 3, relational model based on main vapour pitch aperture and main steam mass rate, according to real-time main vapour pitch aperture correction main steam mass rate, particularly: based on main vapour pitch aperture and main steam mass rate characteristic, the DCS measured data of pitch group and the dynamic perfromance of over-temperature channel heat interchanger at different levels and drum, timely correction main steam maskantflowmeter observation value, thus obtain the main steam mass rate matched with actual furnace coal weight and feedwater flow;

Step 4, according to boiler side whole process mechanism model, calculate corresponding boiler side each several part Energy transmission respectively and gross energy exports, wherein as-fired coal burns produce and the gross energy Q transmitted completely _sumwhereabouts is divided into two parts: Part I is that boiler system effectively utilizes heat Q ₁, water-cooling wall caloric receptivity Q can be decomposed into further _slbwith heat interchanger at different levels, comprise superheater at different levels, reheater, economizer heat exchange amount Q _heatex; Part II is thermal loss, can be decomposed into heat loss due to exhaust gas energy Q further ₂, heat loss due to unburned gas energy Q ₃, heat loss due to combustibles in refuse energy Q ₄, boiler radiation loss energy Q ₅, heat loss due to sensible heat in slag's energy Q ₆; Boiler radiation loss energy Q ₅in gross energy, proportion is q ₅, q ₅be easy to obtain by experimental formula, therefore as-fired coal burns produce and the gross energy Q transmitted completely _sumcan be expressed as:

Q _sum=(Q _heatex+Q _slb+Q ₂+Q ₃+Q ₄+Q ₆)/(1-q ₅)(1)

Step 5, set up transfer function model between feeder coal supply mass rate and as-fired coal mass rate, obtain as-fired coal mass rate;

Step 6, fire coal entered phase relation between stove to the Energy transmission based on main steam and be decomposed into coal dust and transmit two processes in burner hearth combustion and heating power to working medium, and then set up as-fired coal mass rate and gross energy export between phase relation transfer function model, obtained by parameter identification and export corresponding as-fired coal mass rate and net calorific value with gross energy under this given time.

Preferably, in step 3, described main vapour pitch aperture and main steam mass rate characteristic, refer to the sectional type nonlinear function that main vapour pitch aperture is corresponding with main steam mass rate.Described correction main steam mass rate D _msmethod be:

$D_{\mathrm{ms}}=\underset{n=1}{\overset{5}{\mathrm{\Σ}}}\frac{\mathrm{\αf}\left(L_n\right)p_0}{\sqrt{T_0}}---\left(2\right)$

In formula, α is model parameter, f (﹒) represent the aperture-mass rate characteristic of main vapour pitch, L _nrepresent revised main vapour pitch aperture, p ₀represent main steam pressure, T ₀represent main steam temperature;

Wherein:

L _n(k)=ΔL _n(k)+L _n0(3)

$\frac{\mathrm{\Δ}{L}_n\left(s\right)}{{\mathrm{\ΔL}}_{\mathrm{ms}}\left(s\right)}=\frac{1}{1+\mathrm{Ts}}---\left(4\right)$

The difference form of formula (4) is:

${\mathrm{\ΔL}}_n\left(k\right)={\mathrm{\ΔL}}_n(k-1)\·e^{-\frac{\mathrm{\Δt}}{T}}+{\mathrm{\ΔL}}_{\mathrm{ms}}(k-1)\·(1-e^{-\frac{\mathrm{\Δt}}{T}})---\left(5\right)$

In formula, Δ L _msfor the main vapour pitch aperture increment of Real-time Feedback; Δ L _nrepresent revised main vapour pitch aperture increment; L _n0represent the main vapour pitch aperture before working conditions change; S represents Laplace operator; T represents the equivalent time constant of main steam pressure control loop and pulverized coal preparation system; Δ t is the sampling period; K is current given time, and k-1 is previous moment.

Preferably, in step 4, described boiler side whole process mechanism model comprises: water-cooling wall caloric receptivity computation model, at different levels overheated/reheater changes heat Calculation model, economizer changes heat Calculation model, thermal loss computation model; Particularly:

Described water-cooling wall caloric receptivity computation model, calculates by setting up drum, downtake, the energy of whole boiler circuit of water-cooling wall composition and penetration quality dynamic mechanism model;

Described at different levels overheated/reheater changes heat Calculation model, be establish at different levels overheated/between the adjacent measuring point of heat exchanger, the temperature of working medium, pressure linearly distribute again, and divide infinitesimal with fixing discretize length pipeline section, according to quality, energy dynamics balance equation, try to achieve at different levels overheated/reheating heat interchanger heat exchange amount;

Described economizer changes heat Calculation model, and because water in economizer is liquid, compressibility is very little, and energy is accumulated hardly, therefore adopts energy homeostasis to account model calculating;

Described thermal loss computation model, for calculating each several part thermal loss, model adopts experimental formula.

More preferably, in step 4, described at different levels overheated/reheating heat interchanger changes heat Calculation model and is:

Penetration quality dynamic balance equation:

$\mathrm{dD}=D\left(k\right)-D(k-1)=\underset{i=1}{\overset{L/0.1}{\mathrm{\Σ}}}{\mathrm{\ρ}}_i\left(k\right)A_i\·0.1-\underset{i=1}{\overset{L/0.1}{\mathrm{\Σ}}}{\mathrm{\ρ}}_i(k-1)A_i\·0.1---\left(6\right)$

$D_{\mathrm{in}}=\frac{\mathrm{dD}}{\mathrm{dt}}+D_{\mathrm{out}}---\left(7\right)$

In formula, D is working medium total mass flow rate in overheated/reheating heat exchanger system, ρ _ifor overheated/density of working medium in the passage of heat i-th discrete infinitesimal again, A _ifor the equivalent circulation area of the overheated/passage of heat i-th discrete infinitesimal again, D _in, D _outbe respectively overheated/reheating feeder connection, outlet vapor mass rate, dt is the differential to time t.

Energy dynamics balance equation:

$\begin{array}{c}\mathrm{dE}=E\left(k\right)-E(k-1)=\underset{i=1}{\overset{L/0.1}{\mathrm{\Σ}}}{\mathrm{\ρ}}_i\left(k\right)h_i\left(k\right)A_i\·0.1-\underset{i=1}{\overset{L/0.1}{\mathrm{\Σ}}}{\mathrm{\ρ}}_i(k-1)h_i(k-1)A\left(i\right)\·0.1\\ +c_{\mathrm{metal}}{M}_{\mathrm{metal}}\·{\mathrm{dT}}_{\mathrm{metal}}\end{array}---\left(8\right)$

$Q=\frac{\mathrm{dE}}{\mathrm{dt}}+D_{\mathrm{out}}{h}_{\mathrm{out}}-D_{\mathrm{in}}{h}_{\mathrm{in}}---\left(9\right)$

In formula, E is overheated/reheating passage working medium gross energy, h _ifor overheated/specific enthalpy of working medium in the passage of heat i-th discrete infinitesimal again, c _metal, M _metalwith Δ T _metalfor the specific heat of overheated/reheating channel metal wall, gross mass and metallic walls temperature increment, Q is the energy that overheated/reheating passage working medium obtains from flue gas, h _in, h _outbe respectively overheated/reheating feeder connection, outlet vapor specific enthalpy.

More preferably, in step 4, described economizer is changed heat Calculation model and can be obtained by energy balance

Q _sm=D _fw·(h' _out-h _i' _n)(10)

In formula, D _fwfor feed-water quality flow, h ' _inand h ' _outbe respectively economizer entrance feedwater specific enthalpy and economizer exit feedwater specific enthalpy.

More preferably, in step 4, described thermal loss computation model, wherein each several part thermal loss adopts experimental formula to calculate, particularly:

Q ₂=K ₁(Q _py-Ql _f)(11)

Q ₃=0(12)

Q ₄=Q _cc·(G _fh·C _fh+G _lz·C _lz)(13)

$q_5=5.82\·{\left(D_e\right)}^{-0.38}\·\frac{D_e}{D}---\left(14\right)$

Q ₆=c _fh·G _fh·t _fh+c _lz·G _lz·t _lz(15)

In formula: K ₁the imperfect combustion modified value of as-fired coal solid, Q _pysmoke evacuation energy, Ql _fcold air energy, Q _ccrepresent the net calorific value of carbon, Q _cc=32.7MJ/kg, G _fh, G _lzthe mass rate of flying dust and slag respectively, C _lzthe carbon content of slag, C _fhunburned carbon in flue dust, D _ebe the volume of boiler, determine evaporation capacity, D is actual evaporation, equal with main steam mass rate, c _fh, c _lzthe specific heat capacity of flying dust and slag respectively, t _fh, t _lzthe temperature of flying dust and slag respectively;

Above-mentioned involved parameter is obtained by following formula:

K ₁=1-q ₄(16)

q ₄=A _ad·A _fh·C _fh/F _cad(17)

Q _py=c _py·ρ _py·V _py·(t _py+273.15)(18)

Ql _f=cl _f·ρl _f·Vl _f·(tl _f+273.15)(19)

c _fh=0.71+0.000502·t _fh(20)

c _lz=0.71+0.000502·t _lz(21)

In formula, q ₄as-fired coal solid-unburning hot loss number percent, A _adas-fired coal ash content, A _fhthe fly ash content in ash content, F _cadbe as-fired coal fixed carbon content, c is the specific heats of gases, and ρ is gas density, and V is gas flow, and t is gas temperature, and subscript py and lf represents smoke evacuation and cold air respectively.

Preferably, in step 5, the transfer function model between described feeder coal supply mass rate and as-fired coal mass rate adopts first order inertial loop model to characterize:

$\frac{D_{\mathrm{coal}}\left(s\right)}{D_{\mathrm{belt}}\left(s\right)}=\frac{1}{1+\mathrm{Ts}}---\left(22\right)$

Turn to difference form can obtain:

$D_{\mathrm{coal}}\left(k\right)=D_{\mathrm{coal}}(k-1)\·e^{-\frac{\mathrm{\Δt}}{T}}+D_{\mathrm{belt}}(k-1)\·(1-e^{-\frac{\mathrm{\Δt}}{T}})---\left(23\right)$

In formula, D _coalrepresent as-fired coal mass rate, D _beltrepresent feeder coal supply mass rate, T represents coal pulverizer closed-loop control link and grinds the total equivalent time constant of link.

Preferably, in step 6, phase relation transfer function model between described as-fired coal mass rate and gross energy export, refers to and adopts first order inertial loop to transmit two processes in burner hearth combustion and heating power to working medium, the order transfer function model finally obtained to characterize as-fired coal respectively:

$\frac{Q_{\mathrm{sum}}\left(s\right)}{D_{\mathrm{coal}}\left(s\right)}=\frac{Q_{\mathrm{furnace}}\left(s\right)}{D_{\mathrm{coal}}\left(s\right)}\·\frac{Q_{\mathrm{sum}}\left(s\right)}{Q_{\mathrm{furnace}}}=\frac{K}{1+T_{1}s}\·\frac{1}{1+T_2\text{s}}---\left(24\right)$

In formula, Q _furnacerepresent that as-fired coal released energy at hearth combustion, Q _sumrepresent the summation of boiler side whole process each several part Energy transmission, K is amplification coefficient, and its physical significance is as-fired coal net calorific value, T ₁for the time constant of as-fired coal combustion process, T ₂for heating power is to the equivalent time constant of refrigerant heat transfer process.

Preferably, in step 6, carrying out to the phase relation transfer function model between described as-fired coal mass rate and gross energy export the difference equation model that discretize obtains is:

$Q_{\mathrm{furnace}}\left(k\right)=Q_{\mathrm{furnace}}(k-1)\·e^{-\frac{\mathrm{\Δt}}{T_1}}+K\·D_{\mathrm{coal}}(k-1)\·(1-e^{-\frac{\mathrm{\Δt}}{T_1}})---\left(25\right)$

$Q_{\mathrm{sum}}\left(k\right)=Q_{\mathrm{sum}}(k-1)\·e^{-\frac{\mathrm{\Δt}}{T_2}}+Q_{\mathrm{furnace}}(k-1)\·(1-e^{-\frac{\mathrm{\Δt}}{T_2}})---\left(26\right)$

Preferably, in step 6, amplification coefficient K, namely described as-fired coal net calorific value is obtained by parameter identification method, and objective function is:

In formula, N represents the time window width carried out selected by parameter identification, represent the predicted value of high-temperature flue gas transferring energy summation, the restriction range of K is determined according to the fire coal species of concrete unit, T ₁, T ₂time of flowing through in flue according to the combustion process of concrete unit and flue gas of restriction range determine.

Compared with prior art, the present invention has following beneficial effect:

Present invention achieves the on-line identification to as-fired coal net calorific value, processing speed fast (computing time is level second), net calorific value identification precision is high, and implementation cost is low; Can implement coal-supplying amount based on the present invention to compensate and Optimized Coal Blending, to the steady production of thermoelectricity flow process, the thermal efficiency, excellent and energy-saving and emission-reduction have Great significance.

Accompanying drawing explanation

By reading the detailed description done non-limiting example with reference to the following drawings, other features, objects and advantages of the present invention will become more obvious:

Fig. 1 is one embodiment of the invention main vapour pitch structural drawing;

Fig. 2 is one embodiment of the invention high-temperature flue gas energy transferring schematic diagram;

Fig. 3 is one embodiment of the invention coal supply energy release process schematic diagram;

Fig. 4 is one embodiment of the invention as-fired coal net calorific value identification result figure.

Embodiment

Below in conjunction with specific embodiment, the present invention is described in detail.Following examples will contribute to those skilled in the art and understand the present invention further, but not limit the present invention in any form.It should be pointed out that to those skilled in the art, without departing from the inventive concept of the premise, some distortion and improvement can also be made.These all belong to protection scope of the present invention.

As shown in Figure 1, the present embodiment relates to the as-fired coal net calorific value real-time identification of certain subcritical 300MW firepower power station, boiler model HG-1025/17.3-WM18 type, boiler is Natural Circulation, resuperheat, " W " flame combustion mode, two arch list burner hearth, balanced ventilation, afterbody twin flue, gas baffle temperature adjustment, dry ash extraction, outdoor layout, all steel frame suspension type drum boiler.Heat transmission equipment in this natural circulation boiler flue mainly comprises superheater, reheater, economizer three part.In Fig. 1: 1-valve rod, 2-valve pocket, 3-valve seat, 4-sleeve, 5-valve disc, position 0 refers to the steam inlet of valve pocket, and position 1 refers to the steam (vapor) outlet of valve pocket.

The present embodiment provides a kind of coal fired power plant as-fired coal net calorific value real-time identification method, and the method specifically comprises the following steps:

Step one, according to boiler operatiopn design discipline, obtain boiler following structural parameters: heat exchanger tube is 568m along the total length L in Working fluid flow direction, and wherein superheater overall length is 396.7m, and reheater total length is 123.5m; Total length L is divided into the short tube that 5202 sections isometric, every section of short tube length setting is 0.1m; Heat interchanger is along heat exchanger tube sectional area distribution A (i) (i.e. the sectional area of i-th section of short tube) in Working fluid flow direction; Heat interchanger metallic walls quality 1244871kg;

The operation condition real time data under given time k is read: drum pressure 17.6MPa from the real-time data base of DCS control system, main steam mass rate 233.6kg/s, reheat heat steam flow 192.1kg/s, economizer exit feedwater flow 236.6kg/s, heat interchanger at different levels each section of short tube Temperature of Working (first 387.9 DEG C of superheater one-level attemperator, after superheater one-level attemperator 379.1 DEG C, first 472.9 DEG C of superheater secondary attemperator, after superheater secondary attemperator 472.0 DEG C, superheater outlet is 538.7 DEG C, reheater entrance 304.5 DEG C, reheater exports 535.3 DEG C, economizer entrance 263 DEG C, economizer exit 286.2 DEG C) and pressure (superheater entrance is 17.46MPa, superheater outlet is 16.61MPa, reheater entrance 2.871MPa, reheater outlet 2.682MPa, economizer entrance 17.963MPa, economizer exit 17.6MPa), heat interchanger metallic walls temperature 380.5 DEG C, the exhaust gas temperature 120.2 DEG C at flue outlet induced draft fan place and the volumetric flow rate 320m of smoke evacuation ³/ s, boiler load 230MW and environment atmospheric pressure 0.087MPa.

Step 2, according to working medium physical parameter storehouse and drum pressure, calculate this given time water drum outlet saturated vapour specific enthalpy h _bhand density p _bh, establish the temperature of working medium between the adjacent crucial measuring point of heat interchanger at different levels simultaneously, pressure linearly distribute, the working medium specific enthalpy h of the infinitesimal section divided in calculation procedure one _gz(i) and density p _gz(i); According to flue gas physical parameter storehouse and exit gas temperature, pressure, atmospheric pressure, calculate the specific heat c of exit gas under this given time _pyand density p _py.

Described working medium physical parameter storehouse, refer to according to water and steam thermodynamic properties industry formula (IAPWS-IF97) develop have can parallel calling, region automatic discrimination, the feature such as batch processing computing for the working medium physical parameter storehouse in line computation, can list of references: Wang Xuhui, Yu Tong, Hui Zhaoyu, Yuan Jingqi, for the working medium physical parameter database of thermoelectricity gamut emulation, control engineering, 2011; 18:131-133.

Described flue gas physical parameter storehouse, refers to the specific heat at line computation flue gas and the Data Base of Chemical Compound of density by flue gas pressures and temperature real time data.Can list of references: Cai Wei, Yu Tong, Hui Zhaoyu, Yuan Jingqi, Zhang Ruifeng, Chen Yu, the On-line Estimation of apparatus of thermo-electric power boiler heat loss due to exhaust gas, control engineering, 2011; 18:149-151.

Step 3, relational model (main vapour pitch structure as shown in Figure 1) based on main vapour pitch aperture and main steam mass rate, according to real-time main vapour pitch aperture correction main steam mass rate, particularly: based on main vapour pitch aperture and main steam mass rate characteristic, the DCS measured data of pitch group and the dynamic perfromance of over-temperature channel heat interchanger at different levels and drum, timely correction main steam maskantflowmeter observation value, thus obtain the main steam mass rate matched with actual furnace coal weight and feedwater flow.

Described main vapour pitch aperture and main steam mass rate characteristic, refer to the sectional type nonlinear function that main vapour pitch aperture is corresponding with main steam mass rate.Can list of references: the foundation and application of Liu Xin, Yu Tong, Yuan Jingqi, 300MW steamer owner vapour pitch group model, control engineering, 2012; 19:1183-1186.

This is because during main vapour pitch change, not changed by feedwater and Coal-fired capacity in the dynamic increment short time of main steam mass rate and cause, but the vapour that make use of over-temperature channel heat interchanger and drum holds characteristic.After the change of main vapour pitch aperture, main steam can instantaneous change, but coal-supplying amount and feedwater flow need just to change through main steam pressure control and pulverized coal preparation system controlling unit, therefore need to observe value revise to main steam maskantflowmeter.

Described correction main steam mass rate D _msmethod be:

$D_{\mathrm{ms}}=\underset{n=1}{\overset{5}{\mathrm{\Σ}}}\frac{\mathrm{\αf}\left(L_n\right)p_0}{\sqrt{T_0}}---\left(1\right)$

In formula: α value 0.137, f (﹒) represent the aperture-mass rate corresponding relation of main vapour pitch, L _nrepresent revised main vapour pitch aperture, p ₀represent main steam pressure, T ₀represent main steam temperature;

Wherein L _ncomputing method be:

L _n(k)=ΔL _n(k)+L _n0(2)

$\frac{\mathrm{\Δ}{L}_n\left(s\right)}{{\mathrm{\ΔL}}_{\mathrm{ms}}\left(s\right)}=\frac{1}{1+\mathrm{Ts}}---\left(3\right)$

The difference form of formula (3) is:

${\mathrm{\ΔL}}_n\left(k\right)={\mathrm{\ΔL}}_n(k-1)\·e^{-\frac{\mathrm{\Δt}}{T}}+{\mathrm{\ΔL}}_{\mathrm{ms}}(k-1)\·(1-e^{-\frac{\mathrm{\Δt}}{T}})---\left(5\right)$

In formula: Δ L _msfor the main vapour pitch aperture increment of Real-time Feedback, Δ L _nrepresent revised main vapour pitch aperture increment, L _n0represent the main vapour pitch aperture before working conditions change, s represents Laplace operator, and T represents the equivalent time constant of main steam pressure control loop and pulverized coal preparation system, and Δ t is the sampling period, is 5 seconds in the present embodiment, and k is current given time, and k-1 is previous moment.

Step 4, according to boiler side whole process mechanism model, calculate boiler side each several part Energy transmission under this given time respectively and gross energy exports (high-temperature flue gas energy transfer process is as shown in Figure 2), wherein:

As-fired coal burns produce and the gross energy Q transmitted completely _sumwhereabouts is divided into two parts: Part I is that boiler system effectively utilizes heat Q ₁, water-cooling wall caloric receptivity Q can be decomposed into further _slbwith heat interchanger at different levels, comprise superheater at different levels, reheater, economizer heat exchange amount Q _heatex; Part II is thermal loss, can be decomposed into heat loss due to exhaust gas energy Q further ₂, heat loss due to unburned gas energy Q ₃, heat loss due to combustibles in refuse energy Q ₄, boiler radiation loss energy Q ₅, heat loss due to sensible heat in slag's energy Q ₆; Boiler radiation loss energy Q ₅in gross energy, proportion is q ₅, q ₅be easy to obtain by experimental formula, therefore as-fired coal burns produce and the gross energy Q transmitted completely _sumcan be expressed as:

Q _sum=(Q _heatex+Q _slb+Q ₂+Q ₃+Q ₄+Q ₆)/(1-q ₅)(5)

In the present embodiment, described boiler side whole process mechanism model comprise water-cooling wall caloric receptivity computation model, at different levels overheated/reheater changes heat Calculation model, economizer changes heat Calculation model, thermal loss computation model, concrete:

Described water-cooling wall caloric receptivity computation model, calculating by setting up drum, downtake, the energy of whole boiler circuit of water-cooling wall composition and penetration quality dynamic mechanism model, the technology in patent of invention " method for real-time measurement (patent ZL2010112300066930) of boiler water wall caloric receptivity " specifically can be adopted to realize;

Described at different levels overheated/reheating heat interchanger changes heat Calculation model, refers to divide based on the infinitesimal section described in step one, utilizes quality, energy dynamics balance equation, under calculating this given time at different levels overheated/reheating heat interchanger working medium heat exchange amount; Particularly:

Penetration quality dynamic balance equation:

$\mathrm{dD}=D\left(k\right)-D(k-1)=\underset{i=1}{\overset{L/0.1}{\mathrm{\Σ}}}{\mathrm{\ρ}}_i\left(k\right)A_i\·0.1-\underset{i=1}{\overset{L/0.1}{\mathrm{\Σ}}}{\mathrm{\ρ}}_i(k-1)A_i\·0.1---\left(6\right)$

$D_{\mathrm{in}}=\frac{\mathrm{dD}}{\mathrm{dt}}+D_{\mathrm{out}}---\left(7\right)$

In formula: D is working medium total mass flow rate in overheated/reheating heat exchanger system, ρ _ifor overheated/density of working medium in the passage of heat i-th discrete infinitesimal again, A _ifor the equivalent circulation area of the overheated/passage of heat i-th discrete infinitesimal again, for superheater, D _infor drum outlet (i.e. over-temperature channel entrance) saturated vapour mass rate, D _outfor over-temperature channel outlet (i.e. high pressure cylinder entrance) superheated vapor (i.e. main steam) mass rate, for reheater, D _infor reheating feeder connection (i.e. high pressure cylinder outlet) cold reheated steam mass rate, D _outfor reheating channel outlet (i.e. intermediate pressure cylinder entrance) reheat heat steam mass flow; Dt is time differential.

Energy dynamics balance equation:

$\begin{array}{c}\mathrm{dE}=E\left(k\right)-E(k-1)=\underset{i=1}{\overset{L/0.1}{\mathrm{\Σ}}}{\mathrm{\ρ}}_i\left(k\right)h_i\left(k\right)A_i\·0.1-\underset{i=1}{\overset{L/0.1}{\mathrm{\Σ}}}{\mathrm{\ρ}}_i(k-1)h_i(k-1)A\left(i\right)\·0.1\\ +c_{\mathrm{metal}}{M}_{\mathrm{metal}}\·{\mathrm{dT}}_{\mathrm{metal}}\end{array}---\left(8\right)$

$Q=\frac{\mathrm{dE}}{\mathrm{dt}}+D_{\mathrm{out}}{h}_{\mathrm{out}}-D_{\mathrm{in}}{h}_{\mathrm{in}}---\left(9\right)$

In formula: E is overheated/reheating passage working medium gross energy, h _ifor overheated/specific enthalpy of working medium in the passage of heat i-th discrete infinitesimal again, c _metal, M _metalwith Δ T _metalfor the specific heat of overheated/reheating channel metal wall, gross mass and metallic walls temperature increment, Q is the energy that overheated/reheating passage working medium obtains from flue gas, h _inand h _outbe respectively overheated/reheating feeder connection specific steam enthalpy and outlet vapor specific enthalpy;

Described economizer working medium caloric receptivity computation model, because water in economizer is liquid, compressibility is very little, and energy is accumulated hardly, therefore adopts energy homeostasis to account model calculating:

Q _sm=D _fw·(h' _out-h _i' _n)(10)

In formula: D _fwfeed-water quality flow, h ' _inand h ' _outbe respectively economizer entrance feedwater specific enthalpy and economizer exit feedwater specific enthalpy;

Described thermal loss computation model, wherein each several part thermal loss adopts experimental formula to calculate, and is namely calculated according to following prior art:

Q ₂=K ₁(Q _py-Q _lf)(11)

Q ₃=0(12)

Q ₄=Q _cc·(G _fh?C _fh+G _lz·C _lz)(13)

$q_5=5.82\·{\left(D_e\right)}^{-0.38}\·\frac{D_e}{D}---\left(14\right)$

Q ₆=c _fh·G _fh·t _fh+c _lz·G _lz·t _lz(15)

In formula: K ₁the imperfect combustion modified value of as-fired coal solid, Q _pysmoke evacuation energy, Ql _fcold air energy, Q _ccrepresent the net calorific value of pure carbon, Q _cc=32.7MJ/kg, G _fh, G _lzthe mass rate of flying dust and slag respectively, C _lzthe carbon content of slag, C _fhunburned carbon in flue dust, D _ebe the rated capacity of boiler, D is actual evaporation, equal with main steam mass rate, c _fh, c _lzthe specific heat capacity of flying dust and slag respectively, t _fh, t _lzbe respectively fly, ash and the temperature of slag;

Above-mentioned involved parameter is obtained by following formula:

K ₁=1-q ₄(16)

q ₄=A _ad·A _fh·C _fh/F _cad(17)

Q _py=c _py·ρ _py·V _py·(t _py+273.15)(18)

Q _lf=c _lf·ρ _lf·V _lf·(t _lf+273.15)(19)

c _fh=0.71+0.000502·t _fh(20)

c _lz=0.71+0.000502·t _lz(21)

In formula: q ₄as-fired coal solid-unburning hot loss number percent, A _adas-fired coal ash content, A _fhthe fly ash content in ash content, F _cadbe as-fired coal fixed carbon content, c is the specific heats of gases, and ρ is gas density, and V is gas flow, and t is gas temperature, and subscript py and lf represents smoke evacuation and cold air respectively.

Step 5, set up transfer function model between feeder coal supply mass rate and as-fired coal mass rate, first order inertial loop model can be adopted to characterize:

$\frac{D_{\mathrm{coal}}\left(s\right)}{D_{\mathrm{belt}}\left(s\right)}=\frac{1}{1+\mathrm{Ts}}---\left(22\right)$

Turn to difference form:

$D_{\mathrm{coal}}\left(k\right)=D_{\mathrm{coal}}(k-1)\·e^{-\frac{\mathrm{\Δt}}{T}}+D_{\mathrm{belt}}(k-1)\·(1-e^{-\frac{\mathrm{\Δt}}{T}})---\left(23\right)$

In formula: D _coalrepresent as-fired coal mass rate, D _beltrepresent feeder coal supply mass rate, T represents coal pulverizer closed-loop control link and grinds the total equivalent time constant of link.

Step 6, fire coal entered phase relation between stove to the Energy transmission based on main steam and be decomposed into coal and transmit two processes in burner hearth combustion and heating power to working medium, characterize this two processes with first order inertial loop respectively, thus set up as-fired coal mass rate and gross energy export between phase relation transfer function model:

$\frac{Q_{\mathrm{sum}}\left(s\right)}{D_{\mathrm{coal}}\left(s\right)}=\frac{Q_{\mathrm{furnace}}\left(s\right)}{D_{\mathrm{coal}}\left(s\right)}\·\frac{Q_{\mathrm{sum}}\left(s\right)}{Q_{\mathrm{furnace}}}=\frac{K}{1+T_{1}s}\·\frac{1}{1+T_2\text{s}}---\left(24\right)$

In formula: Q _furnacerepresent that as-fired coal released energy at hearth combustion, Q _sumrepresent that the boiler side whole process gross energy under given time k exports, K is amplification coefficient, and its physical significance is as-fired coal net calorific value, T ₁for the time constant of as-fired coal combustion process, T ₂for heating power is to the equivalent time constant of refrigerant heat transfer process.

Discretize is carried out to obtained transfer function model and obtains difference equation model:

$Q_{\mathrm{furnace}}\left(k\right)=Q_{\mathrm{furnace}}(k-1)\·e^{-\frac{\mathrm{\Δt}}{T_1}}+K\·D_{\mathrm{coal}}(k-1)\·(1-e^{-\frac{\mathrm{\Δt}}{T_1}})---\left(25\right)$

$Q_{\mathrm{sum}}\left(k\right)=Q_{\mathrm{sum}}(k-1)\·e^{-\frac{\mathrm{\Δt}}{T_2}}+Q_{\mathrm{furnace}}(k-1)\·(1-e^{-\frac{\mathrm{\Δt}}{T_2}})---\left(26\right)$

Further identification amplification coefficient K, its physical significance is exactly export corresponding as-fired coal net calorific value with gross energy under this given time, and obtained by simplex discrimination method, objective function is:

In formula: N represents the time window width carried out selected by parameter identification, represent the predicted value of high-temperature flue gas transferring energy summation, in the present embodiment, N is taken as 120, K restriction range is [13,25], T ₁restriction range is [0,600], T ₂restriction range is [0,600].

In DCS control system, configuration realizes the method at the scene, be illustrated in figure 4 the result run investigation continuously and draw after (totally 816 hours) for 34 days, wherein: solid black lines is identification net calorific value, black round dot is every 6 hours off-line chemical examination net calorific values once.

Present invention achieves the on-line identification to as-fired coal net calorific value, processing speed fast (computing time is level second), net calorific value identification precision is high, and implementation cost is low; Can implement coal-supplying amount based on the present invention to compensate and Optimized Coal Blending, to the steady production of thermoelectricity flow process, the thermal efficiency, excellent and energy-saving and emission-reduction have Great significance.

Above specific embodiments of the invention are described.It is to be appreciated that the present invention is not limited to above-mentioned particular implementation, those skilled in the art can make various distortion or amendment within the scope of the claims, and this does not affect flesh and blood of the present invention.

Claims (7)

1. a real-time identification method for coal fired power plant as-fired coal net calorific value, it is characterized in that, the method comprises the following steps:

Step one, according to boiler operatiopn design discipline, obtain boiler following structural parameters: heat exchanger tube at different levels is along the total length in Working fluid flow direction, sectional area distribution, heat interchanger metallic walls quality; From the real-time data base of DCS control system, read the operation condition real time data under given time, specifically comprise: the exhaust gas temperature at the Temperature of Working at drum pressure, main steam mass rate, reheat heat steam mass flow, economizer exit feed-water quality flow, heat interchanger measuring point place at different levels and pressure, heat interchanger metallic walls temperature, flue outlet induced draft fan place, volumetric flow rate, boiler load and environment atmospheric pressure;

Step 2, according to working medium physical parameter storehouse and drum pressure, calculate this given time water drum outlet saturated vapour specific enthalpy and density, establish the temperature of working medium between the adjacent crucial measuring point of heat interchanger at different levels simultaneously, pressure linearly distributes, and by fixing discretize length, heat interchanger at different levels is divided into series of discrete infinitesimal, calculate working medium specific enthalpy and the density of each infinitesimal; According to flue gas physical parameter storehouse and exit gas temperature, pressure, atmospheric pressure, calculate specific heat and the density of exit gas under this given time;

Step 3, relational model based on main vapour pitch aperture and main steam mass rate, according to real-time main vapour pitch aperture correction main steam mass rate, particularly: based on main vapour pitch aperture and main steam mass rate characteristic, the DCS measured data of pitch group and the dynamic perfromance of over-temperature channel heat interchanger at different levels and drum, timely correction main steam maskantflowmeter observation value, thus obtain the main steam mass rate matched with actual furnace coal weight and feedwater flow;

Step 4, according to boiler side whole process mechanism model, calculate corresponding boiler side each several part Energy transmission respectively and gross energy exports, wherein as-fired coal burns produce and the gross energy Q transmitted completely _sumwhereabouts is divided into two parts: Part I is that boiler system effectively utilizes heat Q ₁, water-cooling wall caloric receptivity Q can be decomposed into further _slbwith heat interchanger at different levels, comprise superheater at different levels, reheater, economizer heat exchange amount Q _heatex; Part II is thermal loss, can be decomposed into heat loss due to exhaust gas energy Q further ₂, heat loss due to unburned gas energy Q ₃, heat loss due to combustibles in refuse energy Q ₄, boiler radiation loss energy Q ₅, heat loss due to sensible heat in slag's energy Q ₆; Boiler radiation loss energy Q ₅in gross energy, proportion is q ₅, q ₅obtained by experimental formula, as-fired coal burns produce and the gross energy Q transmitted completely _sumbe expressed as:

Q _sum＝(Q _heatex+Q _slb+Q ₂+Q ₃+Q ₄+Q ₆)/(1-q ₅)

Step 5, set up transfer function model between feeder coal supply mass rate and as-fired coal mass rate, obtain as-fired coal mass rate;

Step 6, fire coal entered phase relation between stove to the Energy transmission based on main steam and be decomposed into coal dust and transmit two processes in burner hearth combustion and heating power to working medium, and then set up as-fired coal mass rate and gross energy export between phase relation transfer function model, obtained by parameter identification and export corresponding as-fired coal mass rate and net calorific value with gross energy under this given time.

2. the real-time identification method of a kind of coal fired power plant as-fired coal net calorific value according to claim 1, is characterized in that, in step 3, and described correction main steam mass rate D _msmethod be:

$D_{ms}=\underset{n=1}{\overset{5}{\Σ}}\frac{\mathrm{\α}f\left(L_n\right)p_0}{\sqrt{T_0}}$

In formula, α is model parameter, f (﹒) represent the aperture-mass rate characteristic of main vapour pitch, L _nrepresent revised main vapour pitch aperture, p ₀represent main steam pressure, T ₀represent main steam temperature;

Wherein:

L _n(k)＝ΔL _n(k)+L _n0

$\frac{{\mathrm{\ΔL}}_n\left(s\right)}{{\mathrm{\ΔL}}_{ms}\left(s\right)}=\frac{1}{1+Ts}$

Above formula is turned to difference form, that is:

${\mathrm{\ΔL}}_n\left(k\right)={\mathrm{\ΔL}}_n(k-1)\·e^{-\frac{\mathrm{\Δ}t}{T}}+{\mathrm{\ΔL}}_{ms}(k-1)\·(1-e^{-\frac{\mathrm{\Δ}t}{T}})$

In formula, Δ L _msfor the main vapour pitch aperture increment of Real-time Feedback, Δ L _nrepresent revised main vapour pitch aperture increment, L _n0represent the main vapour pitch aperture before working conditions change, s represents Laplace operator, and T represents the equivalent time constant of main steam pressure control loop and pulverized coal preparation system, and Δ t is the sampling period, and k is current given time, and k-1 is previous moment.

3. the real-time identification method of a kind of coal fired power plant as-fired coal net calorific value according to claim 1, it is characterized in that, in step 4, described boiler side whole process mechanism model comprises: water-cooling wall caloric receptivity computation model, at different levels overheated/reheater changes heat Calculation model, economizer changes heat Calculation model, thermal loss computation model; Particularly:

Described water-cooling wall caloric receptivity computation model, calculates by setting up drum, downtake, the energy of whole boiler circuit of water-cooling wall composition and penetration quality dynamic mechanism model;

Described at different levels overheated/reheater changes heat Calculation model, be establish at different levels overheated/between the adjacent measuring point of heat exchanger, the temperature of working medium, pressure linearly distribute again, and divide infinitesimal with fixing discretize length pipeline section, according to quality, energy dynamics balance equation, try to achieve at different levels overheated/reheating heat interchanger heat exchange amount; Wherein:

Penetration quality dynamic balance equation:

$dD=D\left(k\right)-D(k-1)=\underset{i=1}{\overset{L/0.1}{\Σ}}{\mathrm{\ρ}}_i\left(k\right)A_i\·0.1-\underset{i=1}{\overset{L/0.1}{\Σ}}{\mathrm{\ρ}}_i(k-1)A_i\·0.1$

$D_{in}=\frac{dD}{dt}+D_{out}$

In formula, D is working medium total mass flow rate in overheated/reheating heat exchanger system, ρ _ifor overheated/density of working medium in the passage of heat i-th discrete infinitesimal again, A _ifor the equivalent circulation area of the overheated/passage of heat i-th discrete infinitesimal again, D _in, D _outbe respectively overheated/reheating feeder connection, outlet vapor mass rate, dt is time differential;

Energy dynamics balance equation:

$\begin{array}{c}dE=E\left(k\right)-E(k-1)=\underset{i=1}{\overset{L/0.1}{\Σ}}{\mathrm{\ρ}}_i\left(k\right)h_i\left(k\right)A_i\·0.1-\underset{i=1}{\overset{L/0.1}{\Σ}}{\mathrm{\ρ}}_i(k-1)h_i(k-1)A_i\·0.1\\ +c_{metal}{M}_{metal}\·{\mathrm{dT}}_{metal}\end{array}$

$Q=\frac{dE}{dt}+D_{out}{h}_{out}-D_{in}{h}_{in}$

In formula, E is overheated/reheating passage working medium gross energy, h _ifor overheated/specific enthalpy of working medium in the passage of heat i-th discrete infinitesimal again, c _metal, M _metaland dT _metalfor the specific heat of overheated/reheating channel metal wall, gross mass and metallic walls temperature increment, Q is the energy that overheated/reheating passage working medium obtains from flue gas, h _in, h _outbe respectively overheated/reheating feeder connection, outlet vapor specific enthalpy;

Described economizer changes heat Calculation model and adopts energy homeostasis to account model calculating:

Q _sm＝D _fw·(h' _out-h _i' _n)

In formula, D _fwfor feed-water quality flow, h ' _inand h ' _outbe respectively economizer entrance feedwater specific enthalpy and economizer exit feedwater specific enthalpy;

Described thermal loss computation model, wherein each several part thermal loss adopts experimental formula to calculate.

4. the real-time identification method of a kind of coal fired power plant as-fired coal net calorific value according to claim 1, it is characterized in that, in step 5, the transfer function model between described feeder coal supply mass rate and as-fired coal mass rate adopts first order inertial loop model to characterize:

$\frac{D_{coal}\left(s\right)}{D_{belt}\left(s\right)}=\frac{1}{1+Ts}$

Turn to difference form can obtain:

$D_{coal}\left(k\right)=D_{coal}(k-1)\·e^{-\frac{\mathrm{\Δ}t}{T}}+D_{belt}(k-1)\·(1-e^{-\frac{\mathrm{\Δ}t}{T}})$

In formula, D _coalrepresent as-fired coal mass rate, D _beltrepresent feeder coal supply mass rate, T represents coal pulverizer closed-loop control link and grinds the total equivalent time constant of link, and s represents Laplace operator, and k is current given time, and Δ t is the sampling period.

5. a kind of power station as-fired coal net calorific value real-time identification method according to any one of claim 1-4, it is characterized in that, in step 6, phase relation transfer function model between described as-fired coal mass rate and gross energy export, refer to and adopt first order inertial loop to transmit two processes in burner hearth combustion and heating power to working medium, the order transfer function model finally obtained to characterize coal dust respectively:

$\frac{Q_{sum}\left(s\right)}{D_{coal}\left(s\right)}=\frac{Q_{furnace}\left(s\right)}{D_{coal}\left(s\right)}\·\frac{Q_{sum}\left(s\right)}{Q_{furnace}\left(s\right)}=\frac{K}{1+T_{1}s}\·\frac{1}{1+T_{2}s}$

In formula, Q _furnacerepresent that as-fired coal released energy at hearth combustion, Q _sumrepresent the summation of boiler side whole process each several part Energy transmission, K represents model amplification coefficient, and its physical significance is as-fired coal net calorific value, T ₁for the time constant of process of coal combustion, T ₂for heating power is to the equivalent time constant of refrigerant heat transfer process, s represents Laplace operator, D _coalrepresent as-fired coal mass rate.

6. the real-time identification method of a kind of coal fired power plant as-fired coal net calorific value according to claim 5, it is characterized in that, in step 6, carrying out to the phase relation transfer function model between described as-fired coal mass rate and gross energy export the difference equation model that discretize obtains is:

$Q_{furnace}\left(k\right)=Q_{furnace}(k-1)\·e^{-\frac{\mathrm{\Δ}t}{T_1}}+K\·D_{coal}(k-1)\·(1-e^{-\frac{\mathrm{\Δ}t}{T_1}})$

$Q_{sum}\left(k\right)=Q_{sum}(k-1)\·e^{-\frac{\mathrm{\Δ}t}{T_2}}+Q_{furnace}(k-1)\·(1-e^{-\frac{\mathrm{\Δ}t}{T_2}}).$

7. the real-time identification method of a kind of coal fired power plant as-fired coal net calorific value according to claim 6, is characterized in that, in step 6, and amplification coefficient K, namely described as-fired coal net calorific value is obtained by parameter identification method, and objective function is:

In formula, N represents the time window width carried out selected by parameter identification, represent the predicted value of high-temperature flue gas transferring energy summation.