Application case 20: Collector’s pressure control plan

1 Introduction

The existing conditions of gas collector pressure control of Shandong zouping tiexiong energy 400000 t /a coking plant:

★Collector pressure adjustment automatic flap valve (actuator), each has 1 valve. There are two stoves.

★when furnace in coal, using high pressure ammonia, (pressure 40kg, flow 25m3/h).

★induced draft fan has 1 set of VVVF.

1.1 control requirements

★stove in the no coal, gas collector pressure fluctuation range is ± 20Pa.

★stove in the coal, gas collector pressure fluctuation range is ± 50Pa.

1.2 The control objectives

1) To the safe and reliable operation;

2) To complete the normal function of automatic control;

3) To steady 400000 tons of coke oven collector pressure control;

4) Pressure control index 60-100Pa;

2 The hardware and software of control system.

★the control system:

The control system consists of the host operating system and field control station, the system is divided into 2 layer networks, the first layer is a field control station, its main function is to monitor, control valve and frequency control, transmit all data to the main control station and accept the main regulation station to transmit data, carry on processing the field data to control the main data and so on; also can choose a variety of operating mode, manual mode and automatic mode. Second main control room adjusting operation station, concentrated display all visual information of the process, including the mode of operation, the set point value, the alarm value, the running state of the system, variable and command, also can manage the alarm, operation mode etc; senior management station and database management station, can generate history report, store history records, and deal with sudden incidents etc. See Figure 1

★hardware: the controller uses the SIEMENS of Step7-200 series

By using Advantech IPC

17 inch LCD display

Control cabinet

The security gate

★All software:

Operating system using Windows2000 professional

Monitoring software WINCC6.0

Software: STEP7 MICRO/WIN V3.1

2.1 To determine the control scheme

Due to the requirements of process and control target of coking furnace, it is difficult to use the conventional control scheme to complete the control requirements and objectives.

●     The determined Control method

Using the expert control system to determine the control model, using advanced fuzzy, multi variable, line of intelligent control to work out intelligent control system.

● The identified control scheme

Using the appropriate constraint established controller structure to meet the control performance requirements, on the premise of ensure safe and reliable pressure, when furnace is without coal, the fluctuation range gas collector pressure is ± 20Pa; when furnace is coaling, the fluctuation range of gas collector pressure is ± 50Pa.

Solve the problem of normal control when furnace is charging.

2.2 Intelligent control development

★Analysis in system pressure

☆source of data: recording the data of the two.

☆data content: pressure and temperature, opening and frequency of fan.

☆data regression: the associated nonlinear or linear regression to the data, find out the related mathematical model

★Methods in mathematical modeling

Modeling basically using system identification method:

From the input, output data to set up an object mathematical model is a calculus method, namely, system identification method.

Solve the relationship between pressure and the coupling variable of valve opening.

★The number in the controller algorithm

Each of these algorithms require contains: control algorithm

3 Control systems to realize the function

3.1 The controller to realize the function of

★In the temperature conditions permit, in accordance with the target temperature rise curve automatically complete all fire way temperature control , each fire channel has a separate controller.

★completed identification and correction of control mathematical model online.

★completed the prediction of the actual temperature, and participate in the control strategy online.

★completed identification and correction of optimization algorithm online.

★test has the function of on-line and off-line test function, and be able to draw prediction and the actual temperature rise curve.

★the controller is a intelligent controller, has recognition, processing and information notification function of data validity.

★The control parameters of the controller have manual and automatic online modification function.

★control mode

AUTO: in accordance with a certain condition, the automatic input each fire path controller.

When the conditions are not met, the manual to confirm a fire channel controller inputs and stops.

MAN: manual input and stop each the controller.

The test function is divided into two states, offline and online, they respectively have investment function and stop function.

★dealing with the fault of communication controller

When communication failure: should be able to stop controller, and stop all the functions of the controller. At this time the last good value should be ensured.

When communication recovery: firstly should read all the data of that time of each frame in the scene, and then operate each fire channel controller.

★Fault handling in data, error data processing.

The controller has the data recognition function, ensure the correctness of the model, excluding invalid or incorrect data; at the same time to notify the relevant interface, not online to modify the control parameters and model.

★Amplitude limiting functions of all data, overflow handling, gradient (rate of change) limit

The controller should be amplitude limiting and fault handling with all input, output and all the associated variables for the controller.

★controller interface should be able to complete all the controller parameters of artificial modification function (in addition to the core technology).

3.2 The functions achieved by PC

★Display interface of each variable bar graph and data.

★Achieve manual regulating interface of each variable valve

★Achieve manual regulating interface of converter draught fan.

★Computer, display and PLC are with clock synchronization function, can complete control function at the same processing time.

★With safety control security interface at the under-pressure, low fuel pressure and the normal production, to improve and modify control safety.

4 Control system Safety and control strategy

★the input processing for the input, when a fault occurs (such as thermocouple or heat blocking), the underlying program keep outputting, maintain the normal operation of the system.

5 The operation and stop of control system

★In debugging process of the control system, each furnace controller separate operates and stops in debugging interface.

★finished debugging, the debugging interface can be accessed only by trained engineers with inputting specific password to enter

★The system operation in the normal production process is controller’s overall operation and stop.

★The emergency shutdown controller, in the presence of non safety conditions, only after eliminating unsafe conditions, can be normal operation controller.