Design Of Control System For Heat-conduction Oil Boiler Based On PLC

This paper's purpose is to transform a heat-conducting oil heating furnace control system in a certain highway maintenance unit in Zhangye city of Gansu province. We use PLC automatically to control the heating furnace,through PLC controls the several parts of heating furnace for making the coal burning under the best condition and improving the efficiency of heating furnace,reducing the cost and pollution, improving the safety of the production process; heating temperature has good control result, and it keeps the original quality of the asphalt for giving material security of paving high quality road.In this paper, we complete the hardware design of temperature detection of heat conduction oil, detection of furnace negative pressure, control of the coal feed,control of the blower,control of the fan, fault alarm as well as the software design of the programmable controller.With heating load demand(as measured by the temperature of heating furnace outlet oil) controls the burning of coal in heating furnace, finally it realizes the automatic operation of the heating furnace.This design's main idea is to send the temperature signal of outlet oil in heating furnace,rotating speed signals of grate motor and blower motor to the programmable controller through the analog-to-digital conversion.The programmable controller(PLC) compares the temperature signal with default value, which sends out the instruction to adjust the stoker motor speed(adjust the coal feed) and the blower motor speed(adjust the air fuel ratio).It sends the negative pressure signal to induced draft fan converter,and processes fan speed(adjust the negative pressure in the heating furnace),so that the coal combustion can be in the best state,and the heating furnace can realize the automatic control.This design uses the cpu224 xp of Siemens S7-200 as the control module, PT100 thermal resistance to detect the temperature of heat-conducting oil, EM231 RTD modules to send the signals to control module, PTP708 F pressure sensor detects the negative pressure in heating furnace and sends current signal to the wind frequency converter.Finally we use the frequency converter to control the speed of the grate motor, blower,induced draft fan and program with SIEMENS STEP7 software.