Abstract: In low-pressure standby circulation mode, the oil supply pump can maintain the minimum circulation pressure, at which point the pump's inlet and outlet valves are fully open. Since the frequency converter is equipped with a single-loop regulator, closing the return valve to maintain system pipeline pressure while ensuring the oil temperature in the main oil supply pipe is a very economical method.
High oil pressure and high flow rate circulation pose safety risks and increase equipment maintenance. First, the system operates under high oil pressure and high flow rate year-round, leading to more frequent and increased leakage points. Furthermore, the large return oil volume and high pressure accelerate the flow of oil within the storage tank, hindering impurity settling and increasing the impurity content of the oil during operation.
This shows that the constant high oil pressure and high flow rate operation significantly increases the workload of system and equipment maintenance. The fuel oil system operates in a rated standby state year-round, wasting a large amount of electrical energy. To better ensure safe production, eliminate various safety hazards, effectively reduce plant power consumption, reduce financial waste, lower power generation costs, and reduce equipment maintenance workload, it is necessary to modify the fuel oil system accordingly. Specifically, through analysis of the fuel oil system and in-depth research on the mechanical performance of the fuel pump, with the fundamental goal of ensuring boiler fuel oil supply and the ultimate aim of eliminating all safety hazards and maximizing energy conservation and consumption reduction, we believe that adopting variable frequency technology is the best solution.
After the frequency converter is installed, the system has two operating states: low-voltage standby circulation state and normal oil supply state.
In low-pressure standby circulation mode, the oil supply pump can maintain the minimum circulation pressure, at which time the inlet and outlet valves of the oil supply pump are fully open. Since the frequency converter is equipped with a single-loop regulator, closing the return oil valve to ensure the system pipeline pressure while ensuring the oil temperature of the main oil supply pipe is a very economical method. In addition, it can effectively control the oil temperature of the large tank in summer, and can also ensure that the system can switch to normal oil supply mode at any time when the boiler needs oil.
The system works by detecting the outlet pressure of the main pipe via an oil pressure sensor. Then, after PID control calculations within the frequency converter, the output frequency of the frequency converter is adjusted to change the motor speed, thereby achieving constant pressure oil supply. Specifically, the adjustment method is as follows: the pressure of the main pipe before the furnace is compared with the pressure value set by the potentiometer at regular intervals (generally set at 23 seconds). When the pressure of the main pipe before the furnace is lower than the pressure value set by the potentiometer, the motor speed increases, and the pressure of the main pipe before the furnace increases. When the pressure value set by the potentiometer is reached, the motor speed decreases, and the pressure of the main pipe before the furnace decreases, thus achieving automatic constant pressure converter operation. The main pipe pressure adjustment is manually set by the operator at any time according to the needs of the operating conditions. Equipment commissioning and setting of operating parameters: The commissioning process mainly includes the following:
(1) Put the oil pump into operation of the frequency converter, adjust it using the local potentiometer, and observe whether the performance of the frequency converter can meet the technical requirements.
(2) After the local potentiometer adjustment test is successful, the furnace-side potentiometer is adjusted to observe whether the operation effect is good.
(3) After the entire equipment has been successfully commissioned, the parameters for normal oil supply pressure and optimal energy saving should be set. During normal oil supply, the oil pressure in the boiler front main pipe should be maintained above 410MPa. During the commissioning process, the normal oil supply parameters, i.e., the maximum pressure value adjusted by the frequency converter, should be determined. After setting, the pressure stabilization operation of this parameter should be performed to observe whether the operation is normal.
(4) After the operating parameters are set, a test should be conducted to switch from standby to normal oil supply. To ensure the boiler can be supplied with oil and stabilize combustion in the shortest possible time under abnormal conditions, and considering the specific performance and requirements of the equipment, we believe the time for the oil supply pump outlet main pipe pressure to adjust from the energy-saving cycle pressure to the normal oil supply pressure should be controlled within 100 seconds. Afterwards, a low-pressure injection combustion stabilization test should be conducted, with the time for the oil pressure to rise from the lowest oil pressure to the low-pressure injection pressure controlled within approximately 10 seconds.
After various debugging and testing, the performance of the frequency converter and the operation of the system were confirmed, proving that the oil supply system can meet production needs and achieve the expected purpose after the frequency converter was installed.
