CN105955020B - A kind of DMC-PID multi-variant control methods of coal water slurry gasification process - Google Patents

Abstract

The invention relates to a DMC-PID multi-variable control method for a coal-water slurry gasification process. Specifically, a cascaded control system of dynamic matrix control and proportional-integral-differential control is used to control the coal-water slurry gasification process in multiple ways. Variable control method (hereinafter referred to as DMC-PID control method). The characteristics of the coal water slurry gasification process control system are as follows: the feed flow control mainly includes the cascade control of the coal water slurry flow and the cascade control of the oxygen-coal ratio; the core of the gasification chamber control is the temperature control of the gasifier furnace; The control mainly includes cascade control of chilled water flow and crude gas temperature. Utilizing the DMC-PID control method of the present invention, the present invention realizes that within the adjustable range of the operating variable, the main controlled variable of the coal gasification process is controlled within the range of industrial requirements, thereby effectively solving the problem of the coal-water slurry gasification process. Issues such as multivariate coupling between gasification temperature and syngas yield.

Description

A DMC-PID multivariable control method for coal-water slurry gasification process

technical field

The invention relates to a process control method in the fields of coal chemical industry and automatic control, in particular to a DMC-PID multivariable control method for a coal-water slurry gasification process.

Background technique

my country is rich in coal resources. In 2013, the proven reserves of coal resources were 114.5 billion tons, ranking third in the world. However, the overall efficiency of my country's coal utilization rate is low and the pollution is serious. Coal gasification technology is the core technology for clean and efficient conversion of coal. Compared with traditional coal resource utilization technology, coal gasification technology has absolute advantages in environmental protection and efficient resource utilization. Therefore, coal gasification technology has been widely used in industry.

In the coal gasification process, the gasifier is the core equipment of the coal gasification process. The chilled coal-water slurry gasifier body can be divided into a gasification chamber and a quenching chamber. After pressurized, the coal-water slurry is sprayed into the gasifier through a nozzle to react with oxygen, and the reactants undergo pyrolysis under high temperature and high pressure. , combustion and coking to produce mixtures such as synthesis gas, the synthesis gas leaves the top of the gasifier through the quenching ring and enters the cooling chamber at the bottom. After water quenching in the quenching chamber, the synthesis gas leaves the bottom of the gasifier and enters other equipment for further Sequential treatment, while slag, most of the bituminous coal and high molecular compounds in water are regularly discharged through the bottom of the gasifier. The coal gasification reaction can be expressed by formula (1-1):

Coal→α ₁ H ₂ +α ₂ CO+α ₃ CH ₄ +α ₄ CO ₂ +α ₅ H ₂ O+α ₆ H ₂ S+α ₇ N ₂ +α ₈ Ash+α ₉ Char

(1-1)

Among them, α ₁ -α ₉ are the coefficients of each component in the coal gasification process, which will change with the difference of coal quality, feed coal water slurry concentration and oxygen-coal ratio. In addition, the main product of the gasification reaction is called effective gas, which is mainly composed of CO, _H2 and _CH4 , and is the main source of chemical products such as hydrogen, methanol and synthetic natural gas.

PID controller is the most widely used in industrial production due to its simplicity, easy to understand, and no need for precise systems in use. However, in the gasification process, there is a strong coupling relationship between gasification temperature and syngas yield. For example, the main reactions in the coal gasification process include steam methane reforming reaction, partial oxidation reaction of coal, oxidation reaction of CO and water gas reaction, etc. Among them, the steam methane reforming reaction and the partial oxidation reaction of coal are both endothermic reactions, and when the furnace temperature rises, the steam methane reforming reaction and the partial oxidation reaction of carbon both react in a positive direction, that is, develop in the direction of CO generation . However, since the steam methane reforming reaction and the partial oxidation of carbon produce more CO, more CO will promote the oxidation reaction of carbon monoxide and the water gas reaction to proceed forward, thereby further increasing the temperature and increasing the The output of H ₂ , and the increase of H ₂ will further affect the steam methane reforming reaction and the partial oxidation reaction of carbon. In fact, since coal gasification is a complex chemical reaction process involving multiphase interactions at high temperature and high pressure, the coal gasification process is affected by coal composition, gasification conditions (such as gasification temperature and gasification pressure), coal slurry concentration, etc. The influence of multiple variables and the coupling relationship will be more complicated. The above problems are difficult to be effectively solved by the conventional PID control method.

Due to the great advantage of DMC in directly dealing with constraints and unconventional dynamic characteristics, DMC is widely used in chemical industry processes. The cascade control strategy is composed of the primary model predictive control (Model Prediction Control, MPC) and the secondary PID controller. The MPC-PID controller has absolute advantages over the traditional PID controller and pure MPC. The internal model control method (Internal Model Control, IMC) proposed based on the equivalent model using the Smith delay compensator solves the problem of multiple time delays and complex interactions. However, because the Smith predictor and PID controller cannot solve the long delay and model adaptability problems, the DMC-PID cascade control method can predict and reduce the error, which is superior to the traditional PID control and IMC-PID cascade control .

Contents of the invention

In view of the above problems, the purpose of this invention is to provide a kind of DMC-PID cascade control method of coal-water slurry gasification process, realize in the adjustable scope of operating variable, the controlled variable (mainly reaction) in the coal gasification process Device temperature, effective gas production rate, etc.) are controlled within the set industrial value range.

Theoretically, the variables in the control structure of coal gasification process are composed of controlled variables, operating variables and disturbance variables. The manipulated variable is the process input, which is a variable that can be controlled artificially in the control process. On the contrary, the controlled variable is the output of the process. The goal of control is to control the output of the controller within a certain value or within a reasonable industrial range. . Through the analysis of the degree of freedom in the control of the gasification process, it can be concluded that the main operating variables in the gasification process are the feed oxygen flow rate, the feed coal flow rate, the pumped coal water slurry flow rate, and the gasification water flow rate (including the moisture in the coal) , quenching water flow, coal slurry tank liquid level, the main controlled variables in the gasification process are the reactor temperature and the yield of each component of the effective gas. In addition, the relevant operating variables in the gasification process include oxygen-coal ratio, water-coal ratio, nitrogen-coal ratio, etc., and related controlled variables include cold gas efficiency and reactor pressure, etc., but combined with the analysis of control degrees of freedom and actual industrial conditions, The present invention selects coal water slurry flow rate, oxygen flow rate, etc. as operating variables, selects reactor temperature, effective gas yield, etc. as controlled variables, and simultaneously selects coal water slurry concentration as test variable to verify the effectiveness of the control method.

Aiming at the fact that conventional PID control cannot effectively solve the problem of coupling and nonlinear relationship between multivariables in the gasification process, the technical scheme adopted by the present invention is as follows:

A DMC-PID multivariable control method of a coal-water slurry gasification process, comprising the steps of:

(1) variable selection of the control system: select the operating variable and the controlled variable in the coal-water slurry gasification process, and select the test variable for verifying the control system;

(2) Open-loop test of the control system: according to the actual industrial range of the manipulated variable and the set value of the controlled variable, the PID parameters of the controller are adjusted, and a series of steps are performed on the control system jump response test;

The corresponding test method is as follows: analyze the influence of each manipulated variable on the controlled variable, first assume that one of the manipulated variables remains unchanged, and perform a step response test on the other manipulated variables; after a series of step response tests, get Step changes in the feed oxygen flow rate and feed coal flow rate, etc., and the dynamic response data of the controlled variable gasifier temperature and synthesis gas yield;

(3) Identification of the structure model of the control system: using the finite impulse response identification method, after testing, according to the different coefficients of the controlled variable and the corresponding root mean square error, the steady-state duration, control coefficient and smoothing factor are selected as the DMC control The input parameters of the gasifier are obtained to obtain the FIR model prediction curve of the gasifier temperature and the effective gas component yield;

(4) DMC controller design and cascade control system: the input variables of the DMC controller include the volume fraction of effective gas and the temperature of the gasifier, and the output signals are respectively connected in series with the operating variables to adjust the oxygen flow rate and the coal-water slurry flow rate by feedback Each operating variable; adjust the boundary value and preset value of the DMC controller within the industrial range of the operating variable and the controlled variable, so as to carry the DMC controller; use the output of the DMC as the set value of the PID controller to obtain the DMC -PID cascade control structure;

(5) Test of gasification process control system: Select relevant variables that have nothing to do with operating variables as test variables to test and verify the designed control method.

Further, the feed water flow and feed coal flow of the feed flow control module are cascaded to control the concentration of the coal water slurry; the core of the gasification chamber control module is the temperature control of the gasifier furnace; the quenching chamber control module The chilled water flow control is cascaded with the crude gas temperature control.

The selected controlled variable in the coal gasification process is the input variable of the DMC controller, including the gasifier temperature and the yield of each component of the syngas; the selected operating variable is the output variable of the DMC controller, including the feed oxygen volume and feed coal slurry flow.

In the control process, the output of the DMC is used as the set value of the PID controller, and the DMC controller and the PID controller are cascaded.

The control parameters of DMC include steady state duration, control coefficient and smoothing factor.

Within the adjustable range of the operating variable, the controlled variable of the gasification process is controlled within the range required by the industry.

The whole control system includes the following control contents:

In the entire coal-water slurry gasification control system, in addition to flow control, liquid level control, pressure control and temperature control, etc., a PID cascade control method is specially added, including: oxygen-coal ratio ratio controller and oxygen flow control Cascade control of feed water flow controller and feed coal flow controller, cascade control of synthesis gas flow addition controller and coal water slurry flow controller, quenching water flow controller and synthesis gas Cascade control of temperature.

The DMC open-loop prediction mechanism can be expressed by formula 1-2:

f＝f _u +D _d +f _d +f _n (1-2)

Among them, f _u is the system response of the past control behavior, D _d + f _d is the response to suppress the disturbance, and f _n represents the unknown disturbance or model error. While using the finite impulse response identification method, the control parameters of DMC are mainly composed of steady-state duration, control coefficient and smoothing factor. After testing, according to the different coefficients of the controlled variables and their corresponding root mean square errors, a certain steady-state duration, control coefficient and smoothing factor are selected as the input parameters of the DMC controller, and the gasifier temperature and effective gas group can be obtained. The FIR model prediction curve of fraction yield etc.

After the design of the DMC-PID cascade control structure is completed, the variable that will not directly change the value of the operating variable is selected as the test variable to test the test performance of the gasification control system. If the concentration of coal water slurry can be selected as the test variable, by changing the concentration of coal water slurry ± 8%, the step response test of the control structure is carried out, and by observing the dynamic response curve of the DMC-PID cascade control structure, it can be seen that DMC- The relevant dynamic characteristics of the PID cascade control method.

Description of drawings

Figure 1 is a schematic diagram of the furnace body structure of the chilled GE coal-water slurry gasifier;

Fig. 2 is the impact diagram of variables; wherein (a) is the step excitation diagram of the manipulated variables MV1 and MV2, and (b) is the dynamic response diagram of the controlled variables CV1 and CV2;

Figure 3 is the FIR model identification results; where (a) and (b) represent the results of gasifier furnace temperature and carbon monoxide, respectively;

Fig. 4 is the flowchart of DMC-PID multivariable control method;

Figure 5 is the dynamic response diagram of the control system under the disturbance of ±8% of the concentration of coal water slurry, where (a), (b), (c), and (d) represent the feed coal water slurry (Coal Water Slurry, CWS ) flow rate, feed oxygen (O ₂ ) flow rate, gasifier furnace temperature (POX) and carbon monoxide (CO) volume fraction dynamic response curves.

Symbol Description

1 oxygen; 2 coal slurry; 3 nozzle; 4 gasification layer; 5 refractory brick;

6 Chilling water; 7 Chilling section; 8 Ash lock bucket;

9Synthesis gas (the main effective gas components are CO, H ₂ , CH ₄ , enter the follow-up process).

Detailed ways

Below, the content of the present invention is further described with examples, but the protection scope of the present invention is not limited to examples. Other changes and modifications made by those skilled in the art without departing from the spirit and protection scope of the present invention are still included in the protection scope of the present invention.

Example 1

This embodiment is a DMC-PID multivariable control method of a coal-water slurry gasification process. The specific implementation steps of the multivariable control method are as follows:

Step (1): Variable selection for the control system

The present invention selects the coal-water slurry flow rate and the oxygen flow rate as the operating variables, and selects the reactor temperature and the CO gas component yield as the controlled variables to construct a DMC-PID multivariable control method. The concentration of coal water slurry is selected as the test variable to verify the control method.

Step (2): Control system open loop test

According to the actual industrial conditions of the gasifier, it is equipped with a conventional PID control structure. The control system of coal water slurry gasification process can be divided into feed flow control module, gasification chamber control module and quenching chamber control module. The main feature of the feed flow control module is that the feed water flow and the feed coal flow are cascaded to control the concentration of coal water slurry; the core of the gasification chamber control module is the temperature control of the gasifier furnace; the quenching chamber control module The main feature is the cascade control of the chilled water flow controller and the crude gas temperature controller.

The main controllers of the coal gasifier control system are described as follows:

1) Feed controllers include dry coal flow controller, feed water flow controller, chilled water feed controller and feed oxygen flow controller;

2) Proportional controllers include water-coal ratio controllers and oxygen-coal ratio controllers;

3) The pressure of the gasification chamber is adjusted by controlling the syngas flow rate in the quenching chamber through the pressure control valve;

4) Adjust the liquid level of the coal slurry tank by controlling the feed coal water slurry flow through the cascade coal flow level controller. Similarly, the liquid level control of the quench chamber is realized by adjusting the control valve to control the discharge of slag;

5) By adjusting the ratio of oxygen to coal and the flow of chilled water to control the temperature of the gasifier and the temperature of the gas in the chilled chamber respectively.

Configure PID parameters for the controller of the above-mentioned coal-water slurry gasification process. Among them, the adjustment value of the coal slurry concentration is set to 66.67%, the ratio of oxygen to coal is set to 1.04, and the delay time of the delayer is set to 1 minute.

A series of step response tests were performed on the open-loop PID control structure by disconnecting the feedback control loops for temperature and syngas yield, according to the industrial range of the manipulated variables. In order to analyze the influence of each operating variable on the controlled variable, it is assumed that the flow rate of coal water slurry is constant, and an independent step response test is made on the flow rate of oxygen. Assuming that the step response time interval is 0.3 hours, and the entire test duration is 12.6 hours, the step change curves of feed oxygen flow rate and feed coal flow rate are shown in Figure 2a (top) and Figure 2a (bottom), respectively. After simulation, the dynamic response curves of controlled variable furnace temperature POXT and carbon monoxide component CO can be obtained as shown in Figure 3b (top) and Figure 3b (bottom), respectively.

Step (3): Identify the structural model of the control system

Using the finite impulse response identification method, the control parameters of DMC are mainly composed of steady-state duration, coefficient and smoothing factor. After testing, according to the different coefficients of the controlled variable and the corresponding root mean square error, the steady-state duration is 36, the control coefficient is 30, and the smoothing factor is 5 as the input parameters of the DMC controller, and the gasifier temperature POXT is obtained The FIR model prediction curves of CO and carbon monoxide component yield CO are shown in Figure 3a and Figure 3b, respectively. It can be seen that the industrial value of the gasification process is in good agreement with the model prediction value.

Step (4): DMC controller design and cascade control system

The input variables of the DMC controller are the volume fraction of CO and the temperature of the gasifier, and the output signals are connected in series with the oxygen flow rate and the coal-water slurry flow rate respectively, so as to adjust the oxygen flow rate and the coal-water slurry flow rate through feedback. Set the current value of the DMC controller and the industrial value range of each variable, adjust within the industrial value range of the manipulated variable and the controlled variable, and use the output of the DMC as the oxygen flow controller MV1 and the coal-water slurry flow controller respectively The set value of MV2, the DMC-PID cascade control structure is obtained as shown in Figure 4.

Step (5): Gasification process control system test

After the design of the DMC-PID cascade control structure is completed, the concentration of coal water slurry is selected as the test variable. By changing the concentration of coal-water slurry to ±8%, the step response test of the control structure is carried out, and the dynamic response curve of the DMC-PID cascade control structure is obtained as shown in Figure 5. It can be seen that the DMC-PID cascade control strategy can control the gasification process The main variables are controlled within the industrial range, thus effectively solving the coupling problem and multivariable control problem of the coal-water slurry gasification process.

Claims (7)

1. a kind of DMC-PID multi-variant control methods of coal water slurry gasification process, which is characterized in that include the following steps：

(1) variables choice of control system：Performance variable and controlled variable during selected coal water slurry gasification, and select and be used for Verify the test variable of the control system；

(2) open-loop test of control system：According to the setting of the actual industrial range and the controlled variable of the performance variable Value, adjusts the pid parameter of controller, and carries out a series of step response test to the control system；

The wherein described open-loop test includes：Influence of each performance variable to controlled variable is analyzed, first assumes one of operation Variable is constant, and carries out step response test to other performance variables；After the test of a series of step response, fed The dynamic response phase of the Spline smoothing and controlled variable gasification furnace furnace temperature and synthesis gas yield of oxygen flow and feed coal flow Close data；

(3) Control system architecture model is recognized：Using finite impulse response (FIR) discrimination method, by test, according to controlled variable Different coefficients and its corresponding root-mean-square error select stable state duration, control coefrficient and smoothing factor as DMC controllers Input parameter obtains the FIR model prediction curve of gasifier temperature and effective gas component yield；

(4) DMC controller designs and cascade control system：The input variable of DMC controllers include effective gas volume fraction and Gasifier temperature, output signal are in series with performance variable respectively, include oxygen flow and water-coal-slurry flow with feedback regulation Each performance variable；The boundary value and preset value of DMC controllers are adjusted in the industrial scale of performance variable and controlled variable, To carry DMC controllers；Setting value by the output of DMC as PID controller, obtains DMC-PID serials control structures；

(5) gasification control system is tested：It selects the correlated variables unrelated with performance variable as test variable, is surveyed with this It tries and verifies designed control method.

2. control method according to claim 1, which is characterized in that the feed water flow of feed rate control module and into Coal flow phase tandem is expected, to control water coal slurry concentration；The core of vaporizer control module controls for gasification furnace fire box temperature；Swash The chilled water flow control of cold house's control module controls phase tandem with raw gas temperature.

3. control method according to claim 1, which is characterized in that the controlled variable selected in coal gasification course is The input variable of DMC controllers includes the yield of gasifier temperature and synthesis gas each component；Selected performance variable, that is, DMC The output variable of controller, including charging amount of oxygen and charging coal slurry flow.

4. control method according to claim 1, which is characterized in that during control, the output of DMC is controlled as PID The setting value of device processed, DMC controllers and PID controller phase tandem.

5. control method according to claim 1, which is characterized in that the control parameter of DMC includes stable state duration, control system Number and smoothing factor.

6. control method according to claim 1, which is characterized in that in the adjustable extent of performance variable, gasification Controlled variable be controlled within the scope of industrial requirements.

7. control method according to claim 2, which is characterized in that entire control system includes content control as follows：

In entire coal water slurry gasification control system, other than flow control, Liquid level, pressure control and temperature control, PID cascade control methods have been specifically added, have been specifically included：Tandem control of the oxygen coal than proportional controller and oxygen flux control device The serials control, synthesis throughput addition controller and water-coal-slurry of system, feed water stream amount controller and feed coal flow controller The serials control of flow controller, the serials control of Quench water flow controller and synthesis gas temperature.