CN101256418A - Combination control method for exit temperature of heating furnace - Google Patents

Abstract

The invention relates to a comprehensive control method for the outlet temperatures of a heating furnace, belonging to the field of furnace temperature control technology. The invention is characterized in that branch balance control makes the outlets temperatures of a multi-branch heating furnace uniform, and automatic load lifting and dropping can be realized. By using state feedback prediction control of measured states and feedforward control, the method effectively improves the anti-interference ability. A state space model of the heating furnace is obtained by mechanism modeling, in no need of testing devices. An on-line model is self-adaptive, which effectively overcomes process characteristic change and improves the rate of putting into operation. Low-value fuel can realize idea valve location interval control, thus saving high-value fuel. The comprehensive control of the outlet temperatures ensures the uniform and stable outlet temperatures of the heating furnace, which is easy to operate and economical.

Description

A kind of integrated control method of furnace outlet temperature

Technical field

The present invention relates to the autocontrol method of tubular heater, belong to petrochemical complex tubular heater and production run automation field.

Background technology

Tubular heater (to call heating furnace in the following text) occupies crucial status in oil refining and petrochemical complex production, almost tubular heater is all arranged, decompression heating furnace as usual, delay coking heating furnace, reformer etc. in every suit oil refining and the petrochemical unit.Realize the steady control of furnace outlet temperature, remain on the technological requirement value and can guarantee separating effect or reaction depth direct influence is arranged to guaranteeing product quality and realization " long period safety, steady running ".

For Large-scale Heater,, usually it is divided into a plurality of branch roads because the heated medium treatment capacity is big.Since the adjustment of fuel atomization situation, nozzles, the variation of air quantity, and the heating-furnace bore temperature distributes and is inhomogeneous; Reason such as coking and the outer black dirt of pipe in the boiler tube, each branch road furnace tube heat transfer characteristic there are differences, and these situations cause each heating furnace branch road outlet temperature difference, easily cause tube coking and energy loss.Therefore, the temperature balance of multiple branch circuit furnace outlet is the important control index of heating furnace.

Heating furnace is a process that has more interference, and wherein comparatively significantly to disturb be the variation etc. of fuel gas pressure and calorific value, inlet amount and variation of temperature, feed properties in influence.The load of heating furnace is often adjusted with production, causes process characteristic to change.In addition, for the high heating furnace of some temperature, as delay coking heating furnace because at heating furnace inevitable tube coking in running period, initial stage in an operating cycle and latter stage parameter such as furnace tube heat transfer coefficient have time-varying characteristics.How effectively suppressing these disturbs and the process characteristic variation is the key of design of Controller.

Existing heating furnace branch balance control method has, and differential type branch balance control algolithm, its thought are to adopt temperature difference PID controller that each arm flow setting value is revised; Forecast Control Algorithm based on dynamic mathematical models.But it implements still comparatively complicated.

The existing controlling schemes of heating furnace mainly is PID control, the control of outlet temperature (or middle furnace tube temperature) single loop, outlet temperature and fire box temperature or fuel flow rate (pressure) tandem is arranged, but conventional tandem scheme can not be taken into account the interference that enters flow (pressure) subloop and fire box temperature subloop, under numerous interference effects, the control effect is unsatisfactory sometimes.Control methods such as nerve-fuzzy control, Smith Prediction Control, Non-Model Controller and Predictive function control also are used to the control of heating furnace.When model can obtain, can obtain better effect based on the control of model, simultaneously, also need to consider the versatility of algorithm and be easy to realization property.Be controlled at when implementing based on the advanced person of input and generally will carry out step test, device is caused disturbance.But make full use of the measurement information of process, comprise output variable, state variable and disturbance variable, will help the raising of control system performance.

Summary of the invention

Purpose of the present invention: propose the temperature integrated control method of furnace outlet that a kind of novel branch balance control based on the stable state energy equilibrium combines with self-adaptation feedback of status PREDICTIVE CONTROL.Branch balance control makes multiple branch circuit furnace outlet temperature unanimity, and can realize carrying automatically load down.By setting up the simplification mechanism model of heating furnace, do not need device is tested the acquisition state-space model, adopt the actual measurement state to carry out the feedback of status PREDICTIVE CONTROL, to improve anti-jamming capacity.The process characteristic that causes at factors such as load variations and cokings changes, and model adaptation is carried out in the change of online judgment task point, to improve operational percentage.The interval control of the desirable valve position of low value fuel is to save high value fuel.

The invention is characterized in that described method is set up successively according to the following steps in host computer:

Step (1): pass under the condition that the heat of boiler tube inner fluid is directly proportional with the difference of fluid temperature (F.T.) with fire box temperature and the thermal property of fluid remains unchanged ignoring extension thermal loss, burner hearth, setting up according to the following steps with furnace outlet temperature, fire box temperature and fuel flow rate is the simplification mathematical model based on energy equilibrium of state variable:

Step (1.1): when using fuel gas as heating furnace fuel, the described simplification mathematical model when setting up the fuel gas flow PID regulating loop that is similar to first order inertial loop by following formula:

${\mathrm{\ρ}}_1{V}_1{C}_1\frac{{\mathrm{dT}}_{\mathrm{out}}}{\mathrm{dt}}={\mathrm{FC}}_1(T_{\mathrm{in}}-T_{\mathrm{out}})+\mathrm{UA}(T_l-T_{\mathrm{out}})$

${\mathrm{\ρ}}_2{V}_2{C}_2\frac{{\mathrm{dT}}_l}{\mathrm{dt}}=-\mathrm{UA}(T_l-T_{\mathrm{out}})+K_3{F}_3+K_4{F}_4$

${\mathrm{\τ}}_3\frac{{\mathrm{dF}}_3}{\mathrm{dt}}=-F_3+F_{3s}$

${\mathrm{\τ}}_4\frac{{\mathrm{dF}}_4}{\mathrm{dt}}=-F_4+F_{4s}$

Wherein: ρ ₁, ρ ₂Be respectively feedstock oil density and atmospheric density, known;

V ₁, V ₂Be respectively boiler tube volume and heating furnace burner hearth volume, known;

C ₁, C ₂Be respectively feedstock oil specific heat and air specific heat, known;

T _In, T _Out, T _lBe respectively heating furnace temperature in, outlet temperature and fire box temperature;

F is the furnace charge total flow;

U is mean heat transfer coefficient, and is known;

A is total heat conduction area, and is known;

F ₃, F _3sBe respectively the flow and the setting value thereof of fuel 1;

F ₄, F _4sBe respectively the flow and the setting value thereof of fuel 2;

K ₃, K ₄For unit mass fuel is passed to the available heating value of fluid, known;

τ ₃, τ ₄For the first order inertial loop time constant, known.

Step (1.2): choose the working point $O=(T_{\mathrm{out}}^{*},T_l^{*},T_{\mathrm{in}}^{*},F^{*},F_{3s}^{*},F_{4s}^{*}),$ To the various linearization process of doing of step (1.1), obtain the state space equation of system at working point O place, " ^*" number the expression O place, working point parameter;

Step (2): when comprising load variations or coking when interior factor causes in the step (1.2) selected changing operate-point, the change of online judgment task point as follows, model described in the automatic setting procedure (1.2):

Step (2.1): read real time data.

Step (2.2): whether be in stable state by following criterion deterministic process:

$\frac{1}{N_y\&CenterDot;N}\underset{i=1}{\overset{N_y}{\mathrm{\&Sigma;}}}\underset{j=1}{\overset{N}{\mathrm{\&Sigma;}}}\left|\frac{y_{\mathrm{ij}}-{\stackrel{\&OverBar;}{y}}_i}{{\stackrel{\&OverBar;}{y}}_i}\right|<\mathrm{\&epsiv;}$

Wherein: N _yBe the number of the characteristic variable of selection, known;

N is historical data length, and is known;

y _iBe mean value to i the selected N of a characteristic variable historical data.

ε is preassigned stable state decision threshold, and interval is (0,0.02).

When stability criterion described in the step (2.2) was set up, process was in stable state, obtains a new working point O _New

Step (2.3): press following formula and judge new steady operation point O _NewAnd whether departing between the selected former working point O surpasses the scope d that sets:

${||O_{\mathrm{new}}-O||}_2^2>d,$ || || ₂Be 2 norms.

Wherein the interval of d is (0,1).

If following formula is set up, then recomputate the described model of step (1.2) with new working point.

Step (3): according to the following steps, be state variable self-adaptation feedback of status predictive control algorithm, realize the STATE FEEDBACK CONTROL of heating furnace with actual measurement furnace outlet temperature, fire box temperature and fuel flow rate:

Step (3.1): the outlet temperature setting value that is provided with on the described host computer read operation operator interfaces, and the constraint condition that comprises pipe surface temperature.

Step (3.2): selected host computer reads the measured value of following each variable by the communication modes of setting:

As the temperature and the flow of the feedstock oil of charging,

Send into the flow of the fuel 1 in the heating furnace,

The fire box temperature of heating furnace,

The outlet of still place temperature of heating furnace;

Step (3.3): after selected host computer carries out computing with the mathematical model of described simplification, result data F _3sGive a PID regulator, the PID regulator carries out PI by following formula to be regulated:

$\mathrm{\&Delta;OP}=P(\mathrm{\&Delta;}(\mathrm{PV}-\mathrm{SP})+\frac{1}{I}(\mathrm{PV}-\mathrm{SP}))$

Wherein: OP is the output valve of PID regulator, outputs to a variable valve;

SP is the setting value of PID regulator, the result of calculation of receiving step (3.3);

PV is the real-time detected value of PID regulator;

P, I are the parameters of PID regulator, set by instrumentation engineering teacher,

And remove to regulate the flow of the fuel 1 that enters heating furnace by a variable valve.

For the pluralities of fuel heating furnace, as the flow of the fuel 2 of high value fuel, be according to the interval control of desirable valve position of described fuel 1, in desirable valve position interval, fuel 1 valve position after described PI regulates is opened greatly as far as possible, and fuel 2 and fuel 1 are sent to heating furnace jointly.

Described F when making fuel 1 with fuel gas ₃, F _3oBe respectively the flow-compensated value and the meter reading of fuel 1, wherein:

$F_3=F_{3o}\sqrt{\frac{T_{\mathrm{ref}}}{T}\frac{P+P_0}{P_{\mathrm{ref}}+P_0}}$

Wherein: P _Ref, T _RefFor design temperature and pressure, known;

P, T are actual temperature and pressure;

P ₀For the actual measurement atmospheric pressure, be used for instrument is shown that pressure is converted to absolute pressure.

For heating furnace, implement the Balance Control of heating furnace multiple branch circuit outlet temperature successively according to the following steps with multiple branch circuit outlet:

Step (4.1): calculate the flow Δ F that each branch road e of described heating furnace need adjust according to the following steps _e:

Step (4.1.1): the outlet medial temperature that is calculated as follows heating furnace:

$T_{\mathrm{wa}}=\frac{\mathrm{\&Sigma;}\left(F_e{T}_{\mathrm{oe}}\right)}{\mathrm{\&Sigma;}{F}_e}$

Wherein, F _eBe the flow of heating furnace branch road e, and F=∑ F _e

T _OeOutlet temperature for each branch road e of heating furnace.

Step (4.1.2): be calculated as follows branch road e outlet temperature by T _OeAdjust to T _WaRequired fluctuations in discharge is:

${\mathrm{\&Delta;F}}_e=\frac{T_{\mathrm{oe}}-T_{\mathrm{wa}}}{T_{\mathrm{wa}}-T_{\mathrm{in}}}{F}_e$

Step (4.2): carry out if the fluctuations in discharge of each branch road not within the maximum permission of the single step variation range of branch road flow, need be divided into several cycles.Be calculated as follows execution cycle number that the out branch flow adjusts and phase variable quantity weekly:

$T_n=\underset{e}{\max }\left\{\mathrm{ceil}\left(\frac{{\mathrm{\&Delta;F}}_e}{{\mathrm{\&Delta;F}}_{e,\max }}\right)\right\}$

${\mathrm{\&Delta;F}}_{\mathrm{ne}}=\frac{{\mathrm{\&Delta;F}}_e}{T_n}$

Wherein, T _nBe the execution cycle number that guarantees that all branch road flows are all set in maximum allows variation range; Ceil represents the real number carry is rounded;

Δ F _{E, max}For the maximum permission variable quantity of branch road e flow, known;

Δ F _NeAmount for the per performance period change of branch road e flow.

When the furnace charge total flow changes, increase the proportional distribution amount of each branch road flow:

$K_e=\frac{F_e}{\mathrm{\&Sigma;}{F}_e}$

${\mathrm{\&Delta;F}}_e=\frac{T_{\mathrm{oe}}-T_{\mathrm{wa}}}{T_{\mathrm{wa}}-T_{\mathrm{in}}}{F}_e+K_e\mathrm{\&Delta;F}$

Wherein, K _eAccount for the ratio of total flow for branch road e flow;

Δ F is the variable quantity of charging total flow.

The present invention has each branch road furnace outlet temperature unanimity of assurance, realizes carrying load down automatically, and antijamming capability is strong, saves high price matter fuel, the advantage that adaptivity is good.

Description of drawings

Fig. 1. the heater control system overall construction drawing.

Fig. 2. the heater control system overall construction drawing.Among the figure, F _E1, F _E2, F _E3, F _E4Be respectively the flow instrumentation of 4 branch roads, T _E1, T _E2, T _E3, T _E4Be respectively the outlet temperature measuring instrument of 4 branch roads, F ₁C, F ₂C, F ₃C, F ₄C is respectively the flow regulator of 4 branch roads, and TT is the general export temperature instrument, F ₃T, F ₄T is respectively the flow instrumentation of fuel 1 and fuel 2.

Fig. 3. the model online adaptive.

Fig. 4. a kind of mode that control program is realized in host computer.

Embodiment

The method of the invention contains following outlet temperature self-adaptation feedback of status PREDICTIVE CONTROL and 2 parts of branch balance control, and its implementation theory diagram and overall construction drawing are referring to accompanying drawing 1 and accompanying drawing 2.

Outlet temperature self-adaptation feedback of status PREDICTIVE CONTROL partly comprises following steps:

Steps A 1: setting up with furnace outlet temperature, fire box temperature and fuel flow rate (pressure) is the simplification mechanism model of state variable; This steps in sequence is undertaken by following substep:

Steps A 1.1: suppose: (1) thermal efficiency of heating furnace changes when little, and the ratio that the net heat that the boiler tube inner fluid absorbs accounts for the burning gross calorific power remains unchanged, and ignores the flue gas heat loss when the burner hearth heat balance; (2) the burner hearth heat of passing to the boiler tube inner fluid is directly proportional with the difference of fluid temperature (F.T.) with fire box temperature; (3) thermal property of fluid remains unchanged; (4) be similar to fuel gas flow PID regulating loop with first order inertial loop.

Steps A 1.2: when using fuel gas as heating furnace fuel, because the fuel gas meter reading is the normal flow under design temperature and the pressure condition, when off-design temperature and pressure condition, meter reading and actual flow have deviation, therefore need carry out the temperature, pressure correction to obtain actual flow to meter reading, the adjustment of PID controller be flow after compensation, this helps eliminating the interference to fuel of pressure, temperature.Correction formula is:

$F_3=F_{3o}\sqrt{\frac{T_{\mathrm{ref}}}{T}\frac{P+P_0}{P_{\mathrm{ref}}+P_0}}$

Wherein: F ₃, F _3oBe respectively flow-compensated value of fuel 1 (being assumed to be fuel gas) and meter reading;

P _Ref, T _RefFor design temperature and pressure, known;

P, T are actual temperature and pressure;

P ₀For the actual measurement atmospheric pressure, be used for instrument is shown that pressure is converted to absolute pressure.

Steps A 1.3: according to energy equilibrium:

${\mathrm{\&rho;}}_1{V}_1{C}_1\frac{{\mathrm{dT}}_o}{\mathrm{dt}}={\mathrm{FC}}_1(T_i-T_o)+\mathrm{UA}(T_l-T_o)$

${\mathrm{\&rho;}}_2{V}_2{C}_2\frac{{\mathrm{dT}}_l}{\mathrm{dt}}=-\mathrm{UA}(T_l-T_o)+K_3{F}_3+K_4{F}_4$

$T_3\frac{{\mathrm{dF}}_3}{\mathrm{dt}}=-F_3+F_{3s}$

$T_4\frac{{\mathrm{dF}}_4}{\mathrm{dt}}=-F_4+F_{4s}$

Wherein: ρ ₁, ρ ₂Be respectively feedstock oil density and atmospheric density;

V ₁, V ₂Be respectively boiler tube volume and heating furnace burner hearth volume;

C ₁, C ₂Be respectively feedstock oil specific heat and air specific heat;

T _o, T _lBe respectively furnace outlet temperature and fire box temperature;

F is the furnace charge total flow;

U is a mean heat transfer coefficient;

A is a total heat conduction area;

F _3sBe respectively fuel 1 flow setting value;

F ₄, F _4sBe respectively fuel 2 flows and setting value thereof;

K ₃, K ₄Pass to the available heating value of fluid for fuel;

T ₃, T ₄Be the first order inertial loop time constant.

Steps A 1.4: choose the working point $O=(T_{\mathrm{out}}^{*},T_l^{*},T_{\mathrm{in}}^{*},F^{*},F_{3s}^{*},F_{4s}^{*}),$ In working point place's linearization.Obtain the state space equation of system after the arrangement.

Steps A 2: when factors such as load variations or coking cause changing operate-point, the change of online judgment task point, self-optimizing model, the self-adaptation of implementation model;

When bigger variation took place the load of heating furnace, system can depart from original working point.In addition because at coking furnace inevitable tube coking in running period, initial stage in an operating cycle and latter stage coking furnace parameters such as furnace tube heat transfer coefficient have time-varying characteristics.Bigger mismatch can appear in the mechanism model of the heating furnace that drew originally, and is unfavorable to the performance of controller.For guaranteeing controller performance, improve operational percentage, in control system, designed online model adaptation.

The principle of model adjustment is to keep determining new working point according to operating mode on the mechanism model structure basis of invariable, calculating new model parameter.In each control cycle, whether the controller checking process is in stable state, i.e. the certain characteristics variable that selection is concerned about sees whether satisfy following stable state judgment basis

$\frac{1}{N_y\&CenterDot;N}\underset{i=1}{\overset{N_y}{\mathrm{\&Sigma;}}}\underset{j=1}{\overset{N}{\mathrm{\&Sigma;}}}\left|\frac{y_{\mathrm{ij}}-{\stackrel{\&OverBar;}{y}}_i}{{\stackrel{\&OverBar;}{y}}_i}\right|<\mathrm{\&epsiv;}$

Wherein: N _yBe the number of the characteristic variable of selection, known;

N is historical data length, and is known;

y _iBe mean value to i the selected N of a characteristic variable historical data.

ε is preassigned stable state decision threshold, and interval is (0,0.02).

When system is in stable state, obtained a new steady operation point O _NewFor reducing the frequency that model switches, give full play to the advantage of PREDICTIVE CONTROL strong robustness, if depart from above certain limit new working point and former working point, then recomputate model with new working point.Judgment criterion is

${||O_{\mathrm{new}}-O||}_2^2>d,$ || || ₂Be 2 norms.

Wherein the interval of d is (0,1).

Model online adaptive flow process with reference to the accompanying drawings 3.

Steps A 3: with actual measurement furnace outlet temperature, fire box temperature and fuel flow rate (pressure) is state variable, realizes the feedback of status PREDICTIVE CONTROL of heating furnace;

The feedback of status PREDICTIVE CONTROL scheme of heating furnace adopts the feedback of status predictive control algorithm, with the fuel flow rate setting value is performance variable, with the outlet temperature is controlled variable, furnace outlet temperature, fire box temperature and fuel flow rate (pressure) are state variable, feed rate, feeding temperature are feed forward variable, and adopt the actual measurement state value to carry out feedback of status.

Consider the constraint condition of burner hearth and correlated variables such as pipe surface temperature in the controlling schemes, and added the anti-saturated measure of integration.Controlling schemes structural drawing with reference to the accompanying drawings 4.

The advantage of scheme is: (1) has overcome the shortcoming that normal reheating furnace outlet temperature tandem controlling schemes can not be taken into account the interference that enters flow subloop and fire box temperature subloop; (2) when performance variable is fuel gas, as state variable, overcome that conventional to be principal parameter, fuel gas flow with the heater outlet temperature can not suppress the problem of the fuel gas flow disturbance that the fuel gas pressure surge causes fully as the tandem controlling schemes of second parameter with the fuel gas flow behind the temperature and pressure compensation.And flow carries out feedback of status as state, and the anti-saturated measure of integration of employing when valve position reaches height in limited time, is avoided continuing increase or reduce fuel flow rate given; (3) feedforward compensation has alleviated the influence to outlet temperature of feed rate and temperature variation.

Steps A 4: to the pluralities of fuel heating furnace, by the interval control of the desirable valve position of low value fuel, to save high value fuel;

Low value fuel is provided with desirable valve position interval, with reference to the accompanying drawings 4.

Valve position by slow adjustment high value fuel, realization makes low value fuel adjusting valve opening reach the optimization aim of desirable valve position interval (generally near standard-sized sheet) as far as possible, reach as far as possible low value fuel that burn more, burn the energy-conservation of high value fuel less and reduce the target of polluting.

The branch balance control section contains following steps:

Step B1: calculate the flow that each branch road need be adjusted according to the stable state energy equilibrium, make the outlet temperature unanimity;

By adjusting each branch road flow and keeping total flow constant, make that each road boiler tube is heated evenly, each way outlet temperature unanimity, prevent local overheating.

The outlet medial temperature of heating furnace is:

$T_{\mathrm{wa}}=\frac{\mathrm{\&Sigma;}\left(F_e{T}_{\mathrm{oe}}\right)}{\mathrm{\&Sigma;}{F}_e}$

Wherein, F _eBe the flow of heating furnace branch road e, and F=∑ F _e

T _OeOutlet temperature for each branch road e of heating furnace.

Under the constant situation of fuel, with branch road e outlet temperature by T _OeAdjust to T _WaRequired fluctuations in discharge is:

${\mathrm{\&Delta;F}}_e=\frac{T_{\mathrm{oe}}-T_{\mathrm{wa}}}{T_{\mathrm{wa}}-T_{\mathrm{in}}}{F}_e$

The fluctuations in discharge of each branch road is considered the minimum and maximum scope of branch road flow.

The fluctuations in discharge of each branch road is considered the maximum rate of change that allows.

Step B2: adopt Steady-State Control and Region control, to avoid the frequent Dynamic Coupling that causes of adjusting;

If after the branch road fluctuations in discharge, it is T that outlet temperature reaches the steady required time _s, getting control cycle is T _sThis is to consider that the rapidity to the branch road temperature balance does not have high requirement, and each branch road flow is adjusted the response time of each branch road outlet temperature short, after calculating the flow that each branch road need adjust and carrying out, after reaching steadily, wait carries out the adjusting of next cycle again, so just avoided the identification of dynamic model and the dynamic stability problem of control, the long-term steadily control of the serious a plurality of branch road outlet temperature control systems of coupling is the very problems of difficulty when many for branch road.

It is target that branch balance is adopted weighted mean, but adopts Region control.When each branch road temperature difference in a scope of allowing, controller output is fluctuateed among a small circle near steady-state value, the adjustment of carrying out the branch road flow again just there is no need.

Step B3: the furnace charge total flow is proposed load down control automatically under the branch road temperature equalization;

Given new total flow, automatically change each branch road flow set by current because of consistent each the required branch road flow proportional of maintenance branch road outlet temperature, reduce the steadily not new imbalance that causes each branch road outlet temperature because of the lifting amount as far as possible, finally make each branch road flow sum equal new total flow setting value with generation.

If it is K that branch road i flow accounts for the ratio of total flow _e, the variable quantity of the current relatively total flow of new total flow is Δ F, then the variable quantity of the branch road flow of branch road e is:

$K_e=\frac{F_e}{\mathrm{\&Sigma;}{F}_e}$

ΔF _e＝K _eΔF

To all branch roads, take identical execution cycle number.And the maximum of considering each branch road allows rate of change.

Above-mentioned branch road temperature balance control method be by each branch road present flow rate and the temperature difference automatically estimation each branch road outlet temperature of sening as an envoy to reach consistent flow adjusted value, to each branch road heat transmission resistance with furnace flame is inhomogeneous and frequent variation has self-reacting ability.For the pluralities of fuel situation, inhomogeneous and the frequent variation of furnace flame is a serious problem, this is because the nozzles skewness of the various fuel of burning, as a kind of fuel of regulating because of causing the hot strength difference of each branch road after load variations the has tangible adjusting.

Control method among the present invention can realize by host computer.Fig. 5 is a kind of scheme that realizes in host computer.Control program is by real-time data base or by OPC (OLE for Process Control) mode retrieve processed data, and main data processed result is calculated and finished the back and show or send into the DCS demonstration at host computer.Display control interface is used for carrying out the controlled variable adjustment on host computer and DCS.

Claims (5)

1. a kind of integrated control method of furnace outlet temperature is characterized in that, described method is set up in host computer successively according to the following steps:

Step (1): pass under the condition that the heat of boiler tube inner fluid is directly proportional with the difference of fluid temperature (F.T.) with fire box temperature and the thermal property of fluid remains unchanged ignoring extension thermal loss, burner hearth, setting up according to the following steps with furnace outlet temperature, fire box temperature and fuel flow rate is the simplification mathematical model based on energy equilibrium of state variable:

Step (1.1): when using fuel gas as heating furnace fuel, the described simplification mathematical model when setting up the fuel gas flow PID regulating loop that is similar to first order inertial loop by following formula:

${\mathrm{\&rho;}}_1{V}_1{C}_1\frac{{\mathrm{dT}}_{\mathrm{out}}}{\mathrm{dt}}={\mathrm{FC}}_1(T_{\mathrm{in}}-T_{\mathrm{out}})+\mathrm{UA}(T_l-T_{\mathrm{out}})$

${\mathrm{\&rho;}}_2{V}_2{C}_2\frac{{\mathrm{dT}}_l}{\mathrm{dt}}=-\mathrm{UA}(T_l-T_{\mathrm{out}})+K_3{F}_3+K_4{F}_4$

${\mathrm{\&tau;}}_3\frac{{\mathrm{dF}}_3}{\mathrm{dt}}=-F_3+F_{3s}$

${\mathrm{\&tau;}}_4\frac{{\mathrm{dF}}_4}{\mathrm{dt}}=-F_4+F_{4s}$

Wherein: ρ ₁, ρ ₂Be respectively feedstock oil density and atmospheric density, known;

V ₁, V ₂Be respectively boiler tube volume and heating furnace burner hearth volume, known;

C ₁, C ₂Be respectively feedstock oil specific heat and air specific heat, known;

T _In, T _Out, T _lBe respectively heating furnace temperature in, outlet temperature and fire box temperature;

F is the furnace charge total flow;

U is mean heat transfer coefficient, and is known;

A is total heat conduction area, and is known;

F ₃, F _3sBe respectively the flow and the setting value thereof of fuel 1;

F ₄, F _4sBe respectively the flow and the setting value thereof of fuel 2;

K ₃, K ₄For unit mass fuel is passed to the available heating value of fluid, known;

τ ₃, τ ₄For the first order inertial loop time constant, known.

Step (1.2): choose the working point $O=(T_{\mathrm{out}}^{*},T_l^{*},T_{\mathrm{in}}^{*},F^{*},F_{3s}^{*},F_{4s}^{*}),$ To the various linearization process of doing of step (1.1), obtain the state space equation of system at working point O place, " ^*" number the expression O place, working point parameter;

Step (2): when comprising load variations or coking when interior factor causes in the step (1.2) selected changing operate-point, the change of online judgment task point as follows, model described in the automatic setting procedure (1.2):

Step (2.1): read real time data.

Step (2.2): whether be in stable state by following criterion deterministic process:

$\frac{1}{N_y\&CenterDot;N}\underset{i=1}{\overset{N_v}{\mathrm{\&Sigma;}}}\underset{j=1}{\overset{N}{\mathrm{\&Sigma;}}}\left|\frac{y_{\mathrm{ij}}-{\stackrel{\&OverBar;}{y}}_i}{{\stackrel{\&OverBar;}{y}}_i}\right|<\mathrm{\&epsiv;}$

Wherein: N _yBe the number of the characteristic variable of selection, known;

N is historical data length, and is known;

y _iBe mean value to i the selected N of a characteristic variable historical data,

ε is preassigned stable state decision threshold, and interval is 0～0.02;

When stability criterion described in the step (2.2) was set up, process was in stable state, obtains a new working point O _New

Step (2.3): press following formula and judge new steady operation point O _NewAnd whether departing between the selected former working point O surpasses the scope d that sets:

${||O_{\mathrm{new}}-O||}_2^2>d,$ || || ₂Be 2 norms,

Wherein the interval of d is 0～1,

If following formula is set up, then recomputate the described model of step (1.2) with new working point;

Step (3): according to the following steps, be state variable self-adaptation feedback of status predictive control algorithm, realize the STATE FEEDBACK CONTROL of heating furnace with actual measurement furnace outlet temperature, fire box temperature and fuel flow rate:

Step (3.1): the outlet temperature setting value that is provided with on the described host computer read operation operator interfaces, and the constraint condition that comprises pipe surface temperature;

Step (3.2): selected host computer reads the measured value of following each variable by the communication modes of setting:

As the temperature and the flow of the feedstock oil of charging,

Send into the flow of the fuel 1 in the heating furnace,

The fire box temperature of heating furnace,

The outlet of still place temperature of heating furnace;

Step (3.3): after selected host computer carries out the computing of feedback of status PREDICTIVE CONTROL with the mathematical model of described simplification, result data F _3sGive a PID regulator, carry out the PI algorithm and regulate, and remove to regulate the flow of the fuel 1 that enters heating furnace by a variable valve.

2. a kind of integrated control method of furnace outlet temperature according to claim 1, it is characterized in that, for the pluralities of fuel heating furnace, flow as the fuel 2 of high value fuel, be interval control of desirable valve position according to the setting of described fuel 1, in desirable valve position interval, fuel 1 valve position after described PI regulates is opened greatly as far as possible, and fuel 2 and fuel 1 are sent to heating furnace jointly.

3. a kind of integrated control method of furnace outlet temperature according to claim 1 is characterized in that, described F when making fuel 1 with fuel gas ₃, F _3oBe respectively the flow-compensated value and the meter reading of fuel 1, wherein:

$F_3=F_{3o}\sqrt{\frac{T_{\mathrm{ref}}}{T}\frac{P+P_0}{P_{\mathrm{ref}}+P_0}}$

Wherein: P _Ref, T _RefFor design temperature and pressure, known;

P, T are actual temperature and pressure;

P ₀For the actual measurement atmospheric pressure, be used for instrument is shown that pressure is converted to absolute pressure.

4. a kind of integrated control method of furnace outlet temperature according to claim 1 is characterized in that, wherein for the heating furnace with multiple branch circuit outlet, implement the Balance Control of heating furnace multiple branch circuit outlet temperature successively according to the following steps:

Step (4.1): calculate the flow Δ F that each branch road e of described heating furnace need adjust according to the following steps _e:

Step (4.1.1): the outlet medial temperature that is calculated as follows heating furnace:

$T_{\mathrm{wa}}=\frac{\mathrm{\&Sigma;}\left(F_e{T}_{\mathrm{oe}}\right)}{\mathrm{\&Sigma;}{F}_e}$

Wherein, F _eBe the flow of heating furnace branch road e, and F=∑ F _e

T _OeOutlet temperature for each branch road e of heating furnace;

Step (4.1.2): be calculated as follows branch road e outlet temperature by T _OeAdjust to T _WaRequired fluctuations in discharge is:

${\mathrm{\&Delta;F}}_e=\frac{T_{\mathrm{oe}}-T_{\mathrm{wa}}}{T_{\mathrm{wa}}-T_{\mathrm{in}}}{F}_e;$

Step (4.2): if the fluctuations in discharge of each branch road does not allow within the variation range in that the single step of branch road flow is maximum, need be divided into several cycles to carry out, be calculated as follows execution cycle number that the out branch flow adjusts and phase variable quantity weekly:

$T_n=\underset{e}{\max }\left\{\mathrm{ceil}\left(\frac{{\mathrm{\&Delta;F}}_e}{{\mathrm{\&Delta;F}}_{e,\max }}\right)\right\}$

${\mathrm{\&Delta;F}}_{\mathrm{ne}}=\frac{{\mathrm{\&Delta;F}}_e}{T_n}$

Wherein, T _nBe the execution cycle number that guarantees that all branch road flows are all set in maximum allows variation range; Ceil represents the real number carry is rounded;

Δ F _{E, max}For the maximum permission variable quantity of branch road e flow, known;

Δ F _NeAmount for the per performance period change of branch road e flow.

5. a kind of integrated control method of furnace outlet temperature according to claim 4 is characterized in that, when the furnace charge total flow changes, increase the proportional distribution amount of each branch road flow:

$K_e=\frac{F_e}{\mathrm{\&Sigma;}{F}_e}$

${\mathrm{\&Delta;F}}_e=\frac{T_{\mathrm{oe}}-T_{\mathrm{wa}}}{T_{\mathrm{wa}}-T_{\mathrm{in}}}{F}_e+K_e\mathrm{\&Delta;F}$

Wherein, K _eAccount for the ratio of total flow for branch road e flow;

Δ F is the variable quantity of charging total flow.

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