Desulfurization system process

1 Introduction

China is a big coal-fired country and SO2 emission from coal combustion has become the major pollutant affecting the air quality in our cities. Therefore, boiler flue gas desulfurization is an important means of reducing SO2 emissions.

Boiler flue gas desulfurization system has a high complexity, and its control system requirements are often high. The use of PLC control has become a more advanced, strong momentum of application, more widely used as a control device. It has high reliability, can withstand the harsh environment test, full-featured, cost-effective features, widely used in boiler flue gas desulfurization project. The author involved in the design of a heat source plant in Shandong 2 × 75t / h boiler flue gas desulfurization control system, the use of Siemens S7-200 programmable controller, the host computer using Beijing YAC Kingview configuration KINGVIEW6.53 industrial control software to achieve the desulfurization System monitoring.

2, desulfurization system process

The heat source plant limestone - gypsum wet flue gas desulfurization technology. Limestone slurry technology as the desulfurization agent in the absorption tower flue gas washing and washing, the flue gas sulfur dioxide to form calcium sulfite, while the absorption tower to the air drums, forced to make calcium sulfite conversion As calcium sulfate, by-product of desulfurization agent is gypsum. The method desulfurization efficiency (greater than 95%), high reliability.

The system includes flue gas heat exchange system, absorption tower desulfurization system, feeding system, gypsum dehydration and wastewater treatment system. This article is designed to feed system PLC control system.

3, boiler desulfurization system introduction

(1) This system is 2 × 75t / h boiler flue gas desulfurization project. There are three pneumatic double-deck valves in front of each boiler. When the system is running, it is closed and closed when the system is stopped. It can be operated on site and operated by the control room operator station. The system has a 22kw Roots blower for blowing the limestone into the boiler for desulfurization; with local / remote changeover switch that can be operated by the field control cabinet or control room operator station and interlocked with the front pneumatic valve , Pneumatic valves can not be fully opened, Roots blower can not run.

(2) Each system has a 4kw feeder, frequency control. Control panel with door mounting allows operator control of on-site control cabinets or control room operators Feeder start-stop, fault reset and feeder speed control, and can be linked to Roots blower, Roots blower is not running , Feeder also can not run.

(3) The two systems share a limestone silo. The bunker is equipped with a high material level and two low material levels. The three RF admittance level switches with local / remote switch can be controlled by the on-site control cabinet , On-site duster operation box or control room operator station operation; site duster operation box installed in the 0m layer, near the limestone powder silo inlet for the operation of the powder silo feeding dust collector and can detect limestone inside the silo The height of the flour.

4, PLC control system hardware components

(1) Central Processing Unit

The S7-200 uses the CPU226CN as its central processing unit, with 24 digital inputs and 16 digital outputs that can be expanded to 248 digital and 35 analogues. S7-200CPU instruction powerful, digital logic control can be carried out, data processing and closed-loop process control.

(2) expansion module

Digital expansion modules include: EM223CN, 8 input DC24V / 8 relay output; EM221CN, 8 input DC24V.

Analog expansion module: 2 EM231CN, 4 analog inputs, 12-bit resolution; EM232CN, 2 analog outputs, 12-bit resolution.

5, PLC control system functions

PLC control system to complete the data acquisition, analog control and sequence control and other functions.

(1) data acquisition function

PC (IPC) installed KingView KINGVIEW6.53 monitoring software, it communicates with the S7-200 through the free port to establish a connection to achieve data transmission.

Data acquisition function will be in accordance with the required sampling speed, A / D conversion accuracy and scan cycle, the production process of a variety of information (analog, digital) for collection, processing, computing, retrieval and storage, and text , Charts, curves and other forms of configuration into a variety of screens, through the LCD display on the host computer to the operator in time to provide information on the operational status of the unit.

Specific functions of data acquisition:

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(2) analog control

Desulfurization system operating parameters input to the PLC, the use of PLC and PID software controllable analog output, automatic adjustment function. The function of this analog control will control the feeder frequency converter. Limestone amount of desulfurizer how much is controlled by the feeder frequency converter, due to the amount of material directly affect the efficiency of desulfurization, in order to achieve environmental protection and economic standards, the need to control the amount of feed according to the SO2 content. SO2 content of the set value can be modified on the host computer, SO2 after desulfurization monitoring the value of the set value is compared, after PID operation to adjust the frequency of feeder inverter and then to control the amount of feed.

(3) Sequential control of SCS

SCS control objects include the unit motor, pneumatic door, solenoid valve, the project SCS system, will be optional functional group level, sub-group level, single control mode to consider, each sub-group control function Kai, stop independent run. Operators can choose automatic program control or manual operation on the CRT keyboard. During automatic program execution, any error can be signaled to the operator to interrupt the running program and return to a safe state. The cause of the program interruption is displayed on the screen. When manual operation mode is selected, the license file set by SCS system can prevent operator misoperation. The interlocking and protection command of the device has the highest priority. The manual command takes precedence over the automatic command. The "Start", "Stop" or "On" and "Off" commands of the controlled device lock each other, Direction of action. The protection and blocking functions of the SCS are always active and are not allowed to be manually removed by the operator.

6, control software design ideas

The software part is the key part to realize desulfurization control. The software is designed according to a modular structure in order to achieve strong portability and future functional expansion.

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