Based on the PID control function to regulate inverter in the coal application - heat conduction oil boiler control system

One, the introduction

this paper, taking jiangyin xiangshan printing and dyeing coal-fired thermal oil boiler as the object, the modification of control system, PID regulating function of the yonghong PLC controller control frequency converter, PID control, the practice also have PI and PD control. PID controller is based on the error of the system, the use of proportion, integral, differential calculate the control quantity control. Ratio ( P) Control of proportional control is one of the most simple control method. The controller output to the input error signal is proportional to the relationship. When only proportional control system output steady-state error ( 稳定的, 状态误差) 。 In the fan and induced draft fan to replace the original system through frequent start-stop way to control the oil temperature, realize the output points and reduction in the number of relay accurate temperature control, the effect of coal saving. At the same time, through the touch screen can be interactive advantage, realize the freedom of temperature setting and moderate oil furnace negative pressure real-time monitoring.

second, the system introduced

this system is a coal-fired boiler, the need of heating medium is heat conduction oil, oil boiler 6 oil motor, transmission of the oil pump and motor and slag remain in operation, power frequency to variable frequency control of motor has three: induced draft fan, air blower, the blower is mainly composed of the following six parts: the motor, air filter, blower, air chamber, the base of ontology, And fuel tank) , drip nozzle. Blower run by cylinder offset in the rotor eccentricity, and between the blades of the rotor slot of volume change in air, compressed, spit out. Using the pressure difference between the blower in operation automatic lubrication to drip nozzle, drop into the cylinder to reduce friction and noise, and can keep the gas inside the cylinder does not return, this kind of blower is also called sliding-vane blower. Blower medium to clean air, clean gas, sulphur dioxide and other inert gases. Can also be on-demand production conveying inflammable, explosive, easy corrosion and other toxic and special gas. Thus can be widely used in metallurgical, chemical, fertilizer, petrochemical, food, building materials, petroleum, mine, textile, gas station, pneumatic conveying, sewage treatment and other industrial department sent to the boiler coal of coal machine. Two analog signals need to detect, is pressure testing, all the way along the way is out of the oil temperature detection. Three

equipment and technique requirement of boot sequence is to start the induced draft fan first, and then start the blower, finally to start the fire grate. Shutdown sequence is to stop blower first, and then stop the induced draft fan, the last stop grate. Circulation pump is running, can not stop, sent to scuttle start stop of the motor and the slag of coal is controlled by manual. Main control furnace temperature blower, indirectly control the oil temperature, the impact pressure in the furnace, induced draft fan is depending on the input mechanical energy, improve the gas pressure side by side to send the machinery of the gas, it is a kind of driven fluid machinery. Induced draft fan is widely used in factories, mines, tunnels, cooling towers, vehicles, ships, and the structure of the ventilation, dust and cooling; The ventilation of the boilers and industrial furnaces and wind; Air conditioning equipment and household appliances in cooling and ventilation; Grain drying and submitted; Wind tunnel and become a hovercraft inflatable and propulsion, etc. Working principle of induced draft fan and the turbine compressor are basically the same, just due to the low gas flow rate, pressure changes small, generally does not need to consider the change of the gas volume, namely the gas as incompressible fluid handling. System requirements out of the oil temperature in a 270 - degree, error of plus or minus five degrees. Keep the pressure in the furnace is in - 10Pa. Four, system hardware configuration

the PLC host of this system is the FBs - yonghong company 20 ma a, FBs - analog input module 2 da a, FBs - analog template B2A1D one, PC's touch screen, frequency converter of the three.

5, the design of the software:

5. 1 options:

boiler system is a system to maintain constant temperature and constant pressure, due to the pressure and temperature between the various elements have influence, so in the early stage of system design to develop a variety of solutions.

boiler scheme of the original system is controlled by temperature control table of induced draft fan and blower motor start-stop, frequent start-stop motor of electric energy waste is extremely serious, through analysis, using inverter control motor instead of relay control, the features of the PID control through PLC temperature and pressure.

scheme one: single PID control scheme, through the temperature signals were collected by PID arithmetic, control the frequency of the blower, again through the frequency control the frequency of the induced draft fan blower, the corresponding relationship between them is to keep furnace pressure for - 10Pa。

scheme 2: double PID control scheme, through the temperature signals were collected after PID arithmetic, control the frequency of the blower.

then collected through the pressure signal is PID operation, control the frequency of the induced draft fan. Make two stable frequency values in equilibrium state and to keep furnace temperature of 270 degrees at the same time, the pressure is maintained in - 10Pa。

through debugging results show that the scheme one and two schemes of a result is not very ideal, temperature and pressure fluctuation is bigger, the effect of the scheme, is very good, two frequency values in a state of dynamic balance, temperature and pressure are to satisfy the control requirement.

6, conclusion:

for increasingly prominent energy tension and the increasing cost, coal boiler of power saving and section, more and more attention from the industry. Boiler combustion situation by drum, wind turbines and grate motor speed control, the transformation cost has been accepted by the user. So the automatic control system of boiler system reform is more and more widely used.

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