CN103744302A - Isothermal chemical vapor infiltration PLC-IPC control system based on piston flow reaction dynamic model - Google Patents

Abstract

The invention discloses an isothermal chemical vapor infiltration (ICVI) programmable controller (PLC)-industrial personal computer (IPC) control system based on a piston flow reaction dynamic model. The control system comprises an industrial personal computer IPC, a PLC controller, a vacuum diaphragm pump, a heating unit and a mass flow valve which are in communication with the industrial personal computer IPC, and flow, pressure and temperature sensors and an I/O interface. The industrial personal computer IPC comprises a man-machine interface (HMI), an effective residence time computing unit and a flow computing unit. The PLC controller comprises three control loops including a pressure control loop, a temperature control loop and a flow control loop. According to the invention, on the basis of advantages of the industrial personal computer IPC and the PLC controller, comprehensive renovation is performed on the original control system, the existing detailed reaction mechanism is applied into vapor infiltration furnace technological parameter control and optimization, and real-time computation is performed on an intermediate measurement quantity, that is the effective residence time, through the piston flow dynamical model to achieve the advantage of effective control of the intermediate measurement quantity.

Description

A kind of isothermal chemical vapor infiltration PLC-IPC control system based on laminar flow reaction power model

Technical field

The present invention relates to a kind of control system that contains laminar flow reaction power model kernel, for realizing, adopt isothermal chemical vapor infiltration reacting furnace to prepare the process of compound substance to effective control of pressure, temperature and hold-up time.

Background technology

Isothermal/isobaric chemical vapor infiltration technique (Isothermal/Isobaric Chemical Vapor Infiltration, ICVI) is to prepare the technological means that high-performance fiber strengthens carbon back and ceramic matric composite is the most important, be most widely used.Take carbon/carbon compound material manufacture process as example, its basic process is as follows: one or more gaseous precursor, under suitable pressure condition, reach the temperature of expection through preheating zone; In isothermal section, there is pyrolysis and deposition process, in the surface of precast body and hole, generate different RESEARCH OF PYROCARBON components; Residual gas finally leaves gas-phase permeation stove behind cooling zone.Because the RESEARCH OF PYROCARBON character generating is by gas-phase reaction and the common decision of surface deposition process, therefore the process parameter control of gaseous phase permeation process is particularly important.At Bokros[1 in 1969] just clearly illustrated the major parameter that affects pyrolytic carbon deposition: precursor gas kind, pyrolysis reaction temperature and pressure, the gas residence time and the structure of reactor geometric relationship in reactor.And Feron[2] and Huettinger etc. [3] also also emphasized under study for action that the hold-up time is an important parameter, their result shows in level pressure situation, along with the prolongation of gas hold-up time, there is the variation tendency of smooth layer (SL)-> rough layer (GL)-> smooth layer (SL) in the microstructure of pyrolytic carbon.Current for isothermal ICVI process system, if adopt pressure and temperature sensor, these two technological parameters that can directly measure conventionally can reach accurately and control so.And the hold-up time refers to that gas (comprising precursor gas and diluents) discharges the isothermal region at precast body place completely and can flow freely the space time used from being filled to completely, i.e. effective hold-up time.This space just refers to sample cylindric annular space space around in Fig. 1.

The computing formula of lower hold-up time of ideal conditions is as follows:

$\mathrm{\τ}=\frac{V}{Q}\frac{T_0}{T}\frac{P_0}{P}---\left(1\right)$

In formula τ, represent the hold-up time, s; V represents precast body surrounding space volume; Q represents precursor gas volumetric flow rate; T ₀represent porch temperature, K; P ₀represent porch pressure, kPa; T represents isothermal region temperature, K; P represents isothermal region pressure, kPa.When formulating technological parameter, first to determine the hold-up time, and the technological parameter such as temperature, pressure, and then according to formula (1), calculating needed volumetric flow rate according to these parameters, the flow value obviously calculating according to formula (1) and the kind of inlet gas are irrelevant.But for different inlet gas, it is generally unequal that its vapour-phase pyrolysis reaction causes the amount of the gaseous matter before and after reaction, cause ICVI reacting furnace inner volume fluctuations in discharge larger, in actual process, be difficult to measure this parameter of effective hold-up time, so only can rely on formula (1) to calculate the apparent hold-up time, then the experiment statistics based on a large amount of is just likely found out optimum process condition corresponding thereto.

Summary of the invention

Due to the problems referred to above of prior art existence, the object of the invention is to propose a kind of isothermal chemical vapor infiltration PLC-IPC control system based on laminar flow reaction power model, by the intrinsic heat scission reaction mechanism of given presoma, solve reaction Kinetics Model, in gaseous phase permeation process, realize the real-time calculating to effective hold-up time of isothermal region section, and according to the relation of this indirect measurement and entrance volumetric flow rate, accurately control each key process parameter in isothermal chemical vapor infiltration technique, raising forms the understanding of mechanism to RESEARCH OF PYROCARBON matrix or ceramic matrix, a kind of control system of the controllability of micromechanism and composition in enhancing preparation process.

To achieve these goals, the present invention is achieved by the following technical programs: the isothermal chemical vapor infiltration PLC-IPC control system based on laminar flow reaction power model, comprises industrial computer IPC, the PLC controller that carries out communication with industrial computer IPC, vacuum diaphragm pump, heating unit, flow valve, and flow, pressure and temperature sensor and I/O interface, industrial computer IPC comprises HMI, effectively hold-up time and flow rate calculation unit, this PLC controller comprises three control loops, is respectively pressure control loop, temperature control loop and hold-up time control loop, this pressure control loop is that gas is successively through the first gas admittance valve, pressure transducer, pressure controller, vacuum diaphragm pump, ICVI reactor returns this first gas admittance valve and forms, and this temperature control loop is that gas is successively through the second gas admittance valve, temperature sensor, temperature controller, heating unit, ICVI reactor returns the second gas admittance valve and forms, and this hold-up time control loop is that gas is successively through the 3rd gas admittance valve, flow sensor, flow controller, flow valve, ICVI reactor returns the 3rd gas admittance valve and forms, industrial computer IPC is the setting value to effective hold-up time according to user, provides the expectation value of mass rate, and sends to flow controller.

As further feature of the present invention, described effective hold-up time computing unit is an XAE(Extended Automation Engineer who operates on IPC) the TcCOM assembly of engineering, be the Component Object Model Component Object Model under TwinCAT automated software environment), it comprises laminar flow reaction power model and a PI control algolithm, can, according to pressure and the temperature of the default parameter of described HMI and actual measurement, calculate the effective hold-up time in isothermal section.

As further feature of the present invention, described flow rate calculation unit is another TcCOM assembly, it adopts (Lookup Table) module of tabling look-up of MATLAB, effective hold-up time according to different presomas under given deposition process conditions in reactor and the relation of its presoma volume space velocity under the status of criterion, the modified value of calculated mass flow.

As further feature of the present invention, described pressure, temperature and flow control circuit concentrates on a PLC controller and completes, for realizing pressure, temperature and the effectively control of hold-up time in isothermal section to the gas phase presoma in above-mentioned ICVI reactor.

As further feature of the present invention, between described industrial computer IPC and PLC controller, adopt TCP/IP or RS232 communication modes.

As further feature of the present invention, described I/O interface carries out communication by EtherCAT bus and host CPU.

Owing to adopting above technical scheme, the isothermal chemical vapor infiltration PLC-IPC control system based on laminar flow reaction power model of the present invention compared with prior art has following advantage:

In traditional ICVI control technology, the hold-up time, always as a reference quantity, adopts the formula of a simplification in actual control system, obtain corresponding volumetric flow rate, by controlling volumetric flow rate, reaches the object of controlling the hold-up time.But this formula of reduction is not considered the complicated cracking process of presoma in ICVI reacting furnace.In cracking process, the volumetric flow rate of mixed gas can change a lot, and therefore needs constantly to regulate in real time the volumetric flow rate of entrance, cannot realize the accurate control to the hold-up time at all.Current going deep into along with the research of presoma pyrolysis mechanism, increasing detailed reaction mechanism is suggested and verifies, the present invention is exactly the advantage of utilizing PLC programmable logic controller (PLC), original control system has been carried out to comprehensive transformation, existing complex reaction meachanism is applied in the process parameter control and optimization of gas-phase permeation stove, reaction Kinetics Model by laminar flow is carried out real-time calculating to this middle measuring amount of effective hold-up time, reach it is effectively controlled, in addition by exploitation, control software, control system is the switching value based between IPC and PLC also, the communication of analog quantity and digital quantity, real-time demonstration and the storage of controlling technological parameter have been realized.Putting into operation of this control system show, its working stability is reliable, and control accuracy is high, has greatly improved research and production efficiency.

Accompanying drawing explanation

The invention will be further described with specific embodiment with reference to the accompanying drawings below:

Fig. 1 is isothermal chemical vapor infiltration poke schematic diagram;

Fig. 2 is the annexation of control system each several part;

Fig. 3 is isothermal chemical vapor infiltration steering logic figure;

Fig. 4 is hold-up time control loop schematic diagram;

Fig. 5 is hold-up time and its graphs of a relation in status of criterion lower volume air speed of different presomas in reactor;

Fig. 6 is cracking of ethylene reaction rate figure (1000 ℃ of temperature, pressure 2kPa, hold-up time 1s, the relative consumption speed of numeral component);

Fig. 7 is the graph of a relation (curve lines are expectation value, and symbol is measured value) that in cracking of ethylene process, main gas composition changed with the hold-up time

Embodiment

As Fig. 2, shown in 3, isothermal chemical vapor infiltration PLC-IPC control system based on laminar flow reaction power model, the PLC controller, vacuum diaphragm pump, heating unit, mass rate valve, flow, the pressure and temperature sensor that comprise industrial computer IPC, carry out communication with industrial computer IPC.Industrial computer IPC comprises HMI, effective hold-up time and flow rate calculation unit, this PLC controller is controlled respectively three control loops, for pressure control loop, temperature control loop and hold-up time control loop, this pressure control loop is that gas is successively through the first gas admittance valve, pressure transducer, pressure controller, vacuum diaphragm pump, ICVI reactor, return this first gas admittance valve and form, this temperature control loop is that gas is successively through the second gas admittance valve, temperature sensor, temperature controller, heating unit, ICVI reactor, return the second gas admittance valve and form, this hold-up time control loop is that gas is successively through the 3rd gas admittance valve, flow sensor, flow controller, flow valve, ICVI reactor, returning the 3rd gas admittance valve forms, industrial computer IPC is the setting value to effective hold-up time according to user, provide the expectation value of mass rate, and send to flow controller.

Industry IPC comprises Human machine interface, effective hold-up time and three of flow rate calculation unit part.User can by HMI carry out the definition of model parameter, online show and Data Post.By this part, user can arrange the equivalent dimension of intrinsic reaction mechanism, tubular reactor, initial flow and expectation hold-up time curve; The journal file of output parameter in experimentation, and parameter is carried out to aftertreatment.Effectively hold-up time computing unit is an XAE(Extended Automation Engineer who operates on IPC) the TcCOM assembly of engineering, be the Component Object Model Component Object Model under TwinCAT automated software environment), it comprises laminar flow reaction power model and a PI control algolithm, can, according to pressure and the temperature of the default parameter of described HMI and actual measurement, calculate the effective hold-up time in isothermal section; It adopts (Lookup Table) module of tabling look-up of MATLAB flow rate calculation unit, effective hold-up time according to different presomas under given deposition process conditions in reactor and the relation of its presoma volume space velocity under the status of criterion, the modified value of calculated mass flow, and provide thus the instruction of modified flow rate.Because the real-time aspect of flow correction instruction is less demanding, therefore the communication between IPC and controller adopts TCP/IP or RS232 communication modes just can meet the demands, and can simplify like this system, reduces costs.PLC controller mainly completes the instruction of heating unit, membrane pump and flow valve to gas-phase permeation stove, and the dynamic perfromance of temperature, pressure and flow is controlled.

The present invention is at an XAE engineering of industrial computer IPC operation, the TcCOM assembly that it has comprised multiple execution different tasks.First task is the C program in machine code calculating effective hold-up time of the ICVI reactor of operation based on laminar flow reaction Kinetics Model, obtains the effective hold-up time of presoma in reactor; Second task is the Lookup Table module that adopts MATLAB, by hold-up time of obtaining in advance and the family curve of presoma volume space velocity, obtains the revision directive of mass rate; The 3rd task completes setting, storage, calculating, demonstration and the aftertreatment to important parameter in gaseous phase permeation process.

Fluid in pipe, do laminar flow flow there is following feature: the mobile phase on vertical cross-section can be ignored for axial flow velocity; There is not the mixing between fluid particle in the direction mobile at fluid, without air-teturning mixed phenomenon.Therefore can adopt plug flow model to carry out to occur in equivalent simulation gas-phase permeation the chemical dynamics process of isothermal section, fast and effectively calculate effective hold-up time of precursor gas.

For first order reaction, the concentration of hold-up time and reactant is obeyed the distribution of exponential function, and for multistage complicated cracking reaction, must be as follows from the mobile governing equation of the mass conservation, transfer components and the energy conservation equation derivation laminar flow of control volume:

$\frac{d\left(\mathrm{\ρu}{A}_c\right)}{\mathrm{dz}}=0---\left(2\right)$

$\mathrm{uA}{\mathrm{\ρ}}_c\frac{d\left(Y_k\right)}{\mathrm{dz}}=M_k{A}_c{\stackrel{.}{\mathrm{\ω}}}_k---\left(3\right)$

${\mathrm{\ρuA}}_c\frac{d\left(C_{p}T\right)}{\mathrm{dz}}+\underset{k=1}{\overset{k_g}{\mathrm{\Σ}}}{\stackrel{.}{\mathrm{\ω}}}_k{h}_k{M}_k{A}_{\mathrm{cs}}={\mathrm{UA}}_s(T_w-T)---\left(4\right)$

pM＝ρRT (5)

Here ρ represents the density kgm of mixed gas ^-1, u is axial speed ms ^-1, A _cfor the cross-sectional area m of pipeline ², Z is axial position m, A _sfor the surface area m in unit length, the quantity that kg is gaseous component, M _kfor the molal quantity kgmol of component k ^-1, Y _kthe massfraction of component k,

mole increment molm of the component k causing for gas-phase reaction ^-3s ^-1, C _pfor the specific heat Jkg of mixed gas ^-1k ^-1, the temperature K that T is gas, scope is 273～1500K, h _kfor the specific enthalpy Jkg of component k ^-1, the heat transfer coefficient J m that U is mixed gas ^-2k ^-1s ^-1, p is pressure Pa, scope is 0～100kPa, the average molar mass kg mol that M is mixed gas ^-1, T _wfor the temperature K of reacting furnace wall.

Can be by following Solving Partial Differential Equations in effective hold-up time of isothermal section:

${\mathrm{\τ}}_{\mathrm{cal}}=\∫\frac{1}{u}\mathrm{dz}---\left(6\right)$

Here τ _calrepresent effective hold-up time, scope is at 0～30s, i.e. the hold-up time of mixed gas in reaction chamber.Initial volumetric flow rate can be arranged by formula (1).According to the structure of reactor and the arrangement of precast body in reaction chamber, can determine the cross-sectional area of equivalent plug flow model, this area can change with axial location from the inlet to the outlet.Then by laminar flow reaction Kinetics Model formula (2-6) is solved, obtain effective hold-up time τ _cal.In this control system, this part work is to be completed by one section of C code implanting in IPC, and concrete steering logic is as Fig. 4.And the volume space velocity family curve of the hold-up time of the different presomas by based on this model generation in reactor and its presoma under the status of criterion is as Fig. 5, adopts two-dimentional look-up table to calculate the volumetric flow rate of correction.

The emphasis of the improved ICVI control system of the present invention is to have added a hold-up time controller to existing ICVI control system.The logic of control system as shown in Figure 3, has comprised four control loops: pressure control loop, temperature control loop, flow control circuit and hold-up time control loop.First three loop has been mainly the control to system dynamic characteristic, reaches the control of constant temperature, constant voltage and flow, and real-time is very strong.And be non real-time to the control of hold-up time, there is a time cycle, when the deviation in mass rate limited range can be allowed, after going beyond the scope, according to IPC, recalculate effective hold-up time, and provide the flow correction instruction of flow controller.The logic of hold-up time controller as shown in Figure 4.

On industrial computer IPC, also move based on Matlab the gui interface of GUIDE too development, mainly in order to realize:

(1) input of user to temperature, pressure and hold-up time expectation value;

(2) the real-time demonstration of data;

(3) storage of various data and history data inquiry and data sheet are printed;

(4) demonstration of system running state, as normal, warning, fault etc.

In the present invention, industrial computer adopts times good fortune built-in industrial control IPC, Intel i5 dual core processor, 8GB CFast card, in-built WES7 embedded OS.Have multiple PORT COM (RS232, CANopen, Ethernet), its I/O is by EtherCAT bus and host CPU communication, and analogue collection module is EL3124, gathers 4-20mA standard signal, and electric current resolution is 16.Analog output module is EL4124, output 4-20mA standard signal, and electric current resolution is 16.

Controller comprises three parts: mass rate control loop, temperature control loop and pressure control loop.Mass flow controller adopts pid control algorithm, for the mass rate of the gas phase presoma to ICVI technique, controls.Gas enters from the gas access of mass flow controller, and its flow, after flow sensor is measured, flows out from the outlet of flow control valve.Thereby PLC controller continuously changes the aperture flow of adjustments of gas continuously of flow valve by sending mass rate instruction, the measuring-signal of flow is carried out to communication by ICP/IP agreement and industrial computer IPC simultaneously, and the accuracy of flow is ± 1%S.P.Temperature controller also adopts pid control algorithm, take temperature control as core.In control loop, the temperature at K type thermocouple measurement ICVI reacting furnace uniform temperature zone middle part, and be the temperature control loop that electric signal sends PLC controller to by the temperature transition recording, controller output 0-5V standard control signal, thereby control the heating of heating unit, realize the close-loop feedback control of temperature.The measuring-signal of temperature is carried out to communication by ICP/IP agreement and industrial computer IPC simultaneously.Pressure control is made as major control object with negative pressure control.Vacuum diaphragm pump adopts variable frequency control, by inverter motor and PLC controller, makes membrane pump rotating speed adjustable, can more accurately control vacuum pressure, the measuring-signal of pressure is carried out to communication by ICP/IP agreement and industrial computer IPC simultaneously.

During concrete enforcement: 1. the reference value of user's setting pressure, temperature, initial flow and hold-up time on gui interface, these data can provide by the file of function and discrete point.Then in reaction mechanism storehouse, select the reaction of high order mechanism of presoma, as the splitting mechanism of ethene.Then according to the putting position of the structure of reactor and precast body, calculate the equivalent cross-sectional area of piston flow reactor, and set the parameter of laminar flow kinetic model;

2.IPC read flow measurements by certain sampling period, flow expectation value and the flow measurements fed back by PLC are compared, if the difference of measured value and expectation value exceedes certain limit, according to user to the input data run of the model C code of built-in effective hold-up time of calculating, obtain effective hold-up time, then according to the family curve of the hold-up time of different presomas in reactor and its presoma volume space velocity under the status of criterion under given deposition process conditions as Fig. 5, obtain the modified value of volumetric flow rate, and send the instruction of volumetric flow rate reference value to mass flow controller,

3. adopt the HMI user of IPC can self-defined hold-up time curve, by IPC, by ICP/IP protocol, send to flow expectation value in PLC controller and the feedback of flow sensor, instruction is sent to actuator flow valve, reach the control to flow;

4. adopt the HMI of IPC, user defines pressure and temperature reference value, by ICP/IP protocol, send to pressure control loop and the temperature control loop in PLC controller, and finally send to corresponding actuator by pid control algorithm: membrane pump and heating unit, reach the control of constant voltage and constant temperature;

5. in the exit of gas-phase permeation stove, can adopt gas chromatography mass spectrometry equipment GC/MS to carry out the analysis of effective ingredient to the mixed gas that leaves reacting furnace, whether the complex reaction meachanism that checking adopts under predefined hold-up time condition has predicted the variation of gaseous component exactly;

Fig. 6 has provided and has selected under cracking of ethylene reaction mechanism, expects that the hold-up time is the result of 0～1s even variation.In temperature, it is 1000 ℃, when pressure is 2kPa, the mixed gas that leaves reacting furnace is carried out to the analysis of effective ingredient, curve lines are the expectation value that generates gas mole fraction, symbol is measured value, and result represents that control system can reach the set goal substantially as Fig. 7.In figure, cyclopentadiene is cyclopentadiene, butadiene butadiene, butyne butine, propine propine, diacetylene diacetylene, indene benzo ring third is rare, toluene toluene, benzene benzene, biphenyl biphenyl, phenylacetylene phenylacetylene, phenanthrene phenanthrene, penzylbenzene benzyl benzene.

But above-mentioned embodiment is exemplary, be to be the restriction that this patent is comprised to scope in order better to make those skilled in the art can understand this patent, can not to be interpreted as; As long as any being equal to done according to spirit that this patent discloses changes or modify, all fall into the scope that this patent comprises.

Claims (6)

1. the isothermal chemical vapor infiltration PLC-IPC control system based on laminar flow reaction power model, comprises industrial computer IPC, the PLC controller that carries out communication with industrial computer IPC, vacuum diaphragm pump, heating unit, flow valve, and flow, pressure and temperature sensor and I/O interface, is characterized in that: industrial computer IPC comprises HMI, effectively hold-up time computing unit and flow rate calculation unit, this PLC controller comprises respectively controls three control loops, is pressure control loop, temperature control loop and flow control circuit, this pressure control loop is that gas is successively through the first gas admittance valve, pressure transducer, pressure controller, vacuum diaphragm pump, ICVI reactor returns this first gas admittance valve and forms, and this temperature control loop is that gas is successively through the second gas admittance valve, temperature sensor, temperature controller, heating unit, ICVI reactor returns the second gas admittance valve and forms, and this flow control circuit is that gas passes through flow sensor successively, the 3rd gas admittance valve, flow controller, flow valve, ICVI reactor returns the 3rd gas admittance valve and forms, industrial computer IPC is the setting value to effective hold-up time according to user, provides the expectation value of mass rate, and sends to flow controller.

2. control system according to claim 1, it is characterized in that: described effective hold-up time computing unit is a TcCOM assembly that operates in the XAE engineering on IPC, it comprises laminar flow reaction power model and a PI control algolithm, can, according to pressure and the temperature of the default parameter of described HMI and actual measurement, calculate the effective hold-up time in isothermal section.

3. control system according to claim 1 and 2, it is characterized in that: described flow rate calculation unit is another TcCOM assembly, it adopts the table look-up module of MATLAB, effective hold-up time according to different presomas under given deposition process conditions in reactor and the relation of its presoma volume space velocity under the status of criterion, the modified value of calculated mass flow.

4. control system according to claim 3, it is characterized in that: described pressure, temperature and flow control circuit concentrates on a PLC controller and complete, for the gas phase presoma of realizing in above-mentioned ICVI reactor, in pressure, temperature and effective hold-up time of isothermal section, control.

5. control system according to claim 4, is characterized in that: between described industrial computer IPC and PLC controller, adopt TCP/IP or RS232 communication modes.

6. control system according to claim 5, is characterized in that: described I/O interface carries out communication by EtherCAT bus and host CPU.

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