Application of China-made high-voltage VFD (Variable-frequency Drive) in energy-saving transformation of auxiliary equipment in power plants

I. Introduction

Comprehensively build a conservation-oriented enterprise, vigorously carry out energy conservation and consumption reduction, and actively explore new ways of energy conservation with the purpose of improving corporate economic benefits. With the continuous development and progress of power electronics technology, it is an effective measure for enterprises to use new technologies to improve the management level of enterprise production equipment and save energy and reduce consumption. With the continuous improvement of China's domestic high-voltage VFD (Variable-frequency Drive) manufacturing technology and the reduction of the overall cost, the application of high-voltage VFD (Variable-frequency Drive) in power plant auxiliary equipment has become more common, and its safety, stability and energy saving have been It reaches or is close to the foreign imported brand VFD (Variable-frequency Drive).

2. Analysis of auxiliary engine operating conditions

1. Boiler induced draft fan

Our company's #2 boiler is a 410T/H boiler, which adopts double induced draft fan type. The fan model is Y4-73N0.23.5F. It is configured with a three-phase AC asynchronous motor with a power of 800kW and a rated voltage of 6kV. The damper is adjusted by a baffle. It is normal. The operating opening is about 50%, and the actual air volume of the fan is about a part of the rated air volume. The fan operates far away from the rated point, and its actual operating efficiency is very low. Due to the existence of the baffle, the air pressure difference between the front and rear of the baffle is formed, causing throttling losses. At the same time, the fan baffle actuator is a high-torque electric actuator, which has many faults and the fan automatic rate is low.

2. Boiler feed water pump

Our company's soda and water system is a common female pipe type, using 4 water supply pumps running in parallel. Under normal operating conditions, 3 pumps are working and 1 is standby. Among them, #1 and #2 water supply pump motors have a rated power of 3200KW and a rated voltage of 6KV, and use a hydraulic coupler to drive the water supply pump; #3 and #4 water supply pump motors have a rated power of 2800KW and a rated voltage of 6KV, which are directly connected to the motor. A fixed speed pump that drives the feed water pump. Since the outlet pressure of #3 or #4 water pump is high when running, in order to prevent overload operation, the other two hydraulic coupling water pumps can only increase the outlet pressure, so that the pressure of the water supply pipe reaches 13.5MPa, while during normal operation The drum pressure is 9.4MPa, and the difference from the normal drum pressure is about 4.0MPa. Not only is a large amount of electrical energy wasted, but the higher water pressure also causes damage to pipes, pump impellers and valves.

In order to solve the above situation, we have carried out variable frequency speed regulation technology transformation on the boiler induced draft fan and feed water pump of the power plant auxiliary equipment, which has achieved the purpose of saving energy, reducing losses, extending the service life of the equipment and optimizing process control. Some of the work during the transformation process are introduced as follows.

3. Energy Saving Analysis of Auxiliary Engine Frequency Conversion Transformation

1. Boiler induced draft fan

Using VFD (Variable-frequency Drive) as an air volume regulator, the most direct benefit is energy saving and consumption reduction. The main feature of using variable frequency speed regulation is to eliminate or reduce the throttling loss of the baffle. The energy-saving effect is related to the performance of the fan, operating conditions, the opening of the baffle, etc. The following is an example of the estimation and calculation of the induced draft fan modification of furnace #2 of our company.

1.1 Operating parameters before transformation (the load of #2 boiler is 370T/h)

1.2 Calculation formula of power frequency power before transformation:

1.3 Power calculation formula after transformation:

1.4 #2 boiler induced draft fan energy saving calculation

Comparing the electric power of the #2 boiler induced draft fan before and after frequency conversion speed regulation: a single induced draft fan reduces the electric power by 180kW, and the energy saving rate is 33%. The above is the power saving rate under ideal conditions. In actual application, in order to consider the VFD (Variable-frequency Drive) failure to switch to power frequency operation, the damper needs to be reserved for other purposes. Even though the damper is fully open during variable frequency adjustment operation, there is still a certain obstruction, which affects the calculation results. In addition, the power saving effect is also different under various operating conditions, so the actual power saving rate is somewhat different from the above estimated results. . However, judging from the above results, the power saving is significant and it is worth transforming.

2. Boiler feed water pump

The #3 and 4 water supply pumps run at a fixed speed. The main feature of using variable frequency speed regulation is to eliminate or reduce the energy waste caused by large throttling losses in valve adjustment, high outlet pressure, serious pipe damage, and low system efficiency. The following is an example of our company's #4 water supply pump transformation calculation situation to introduce.

2.1 Operating parameters before transformation (#4 boiler feed water pump)

#1, 2, and 4 water supply pump energy saving calculation (normal operation of 3 pumps with mother pipe operation)

2.2 Calculation of power frequency operation