Shanghai Laogang Renewable Energy Utilization Center incinerates and treats 3,000 tons of municipal waste per day, with an advanced flue gas treatment system and power generation equipment, making it one of the largest domestic waste treatment facilities in Asia and one of the most environmentally demanding. Construction of the project started in August 2010 and was completed and put into trial operation in May 2013. After the project is put into operation, while treating 1 million tons of domestic waste per year, the annual power generation capacity can reach about 250 million kilowatt hours, and the annual grid power is about 200 million kilowatt hours. The slag from waste incineration will be comprehensively reused, such as landfill cover material, brick making, road base paving, etc.

The project uses 13 sets of NewSky AS800 series high voltage inverters, including 4 sets of primary fans, 6 sets of feed pumps and 3 sets of circulation pumps. Taking this project as an example, this paper introduces the characteristics of AS800 high voltage inverters used on fans and pumps in the power industry, and explains the process, inverter technology features and application effects of the field application.

Introduction to the field application process

Circulating water pump process

In the circulating water pump system, the circulating water pump realizes the recycling of water resources, the hot water from the condenser outlet enters the cooling tower, and the heat of circulating water is transferred to the atmosphere to lower the temperature, and then it enters the condenser for cooling low-pressure cylinder discharge after the circulating water pump is raised with pressure, because the water level of the system is basically stable, so the head of the circulating water pump is also basically stable, which means the size of the circulating water pump determines the power consumption of the circulating water pump.

Due to the changes in the unit load and external environment, the vacuum is constantly changing, so it is necessary to adjust the circulating water volume in time to ensure the safe and economic operation of the unit. In normal operation in winter, one circulating water pump running at low speed is sufficient to meet the cooling needs of the unit; however, in the season of large temperature difference and load change, although the circulating water pump is regulated at high and low double speed, it cannot ensure the operation of the unit in an economic way, resulting in high electricity consumption rate and high cost of power generation, so it is necessary to adjust the water pump with frequency.

The use of high-voltage inverter according to the actual needs of the circulating water pump motor speed regulation, and then adjust the size of the water pump cooling water, that can reduce the power of the motor, but also to achieve the most favorable vacuum control, so as to ensure and improve the operating conditions of the generator set, but also to achieve the effect of energy saving and consumption reduction.

In order to reduce the power consumption rate of the plant and reduce the cost of power generation, Shanghai Laogang Renewable Energy Utilization Center decided to retrofit one circulating water pump of the power plant with a new Timex AS800 series high voltage inverter to achieve an economical and efficient operation.

Boiler process for waste-to-energy plants

Figure 1 Boiler process flow of waste power plant

The boiler process of waste power plant is shown in Figure 1. waste power plant boiler system includes primary fan, induced draft fan system, in the actual operation process, the primary fan system mainly inside the waste storage pit combustible gas pumped to the waste incinerator, combustion to generate heat to supply the boiler, steam to promote the turbine power generation, while preventing gas leakage (gas containing poison), in the application of important equipment, must ensure its reliability of operation. The induced draft fan system is the process of power generation to form a negative pressure to the furnace to suck away the exhaust gas, the impact on the entire power generation system is also more important, the shutdown of the induced draft fan may lead to boiler fire.

On-site AS800 high voltage inverter

Inverter system configuration

According to the working condition of the site load, considering that the inverter will not affect the production and ensure the normal operation of the system, the system needs to be equipped with an industrial frequency bypass to switch the motor to industrial frequency when the inverter fails. One-tow automatic bypass solution is suitable for one-tow working condition that requires easy operation or the inverter can be automatically switched to I.F. after failure during frequency operation.

In order not to affect the production after the inverter is out of operation and to ensure the normal operation of the system, the system needs to be equipped with an industrial frequency bypass, which will throw the motor into operation under industrial frequency when the inverter fails. The three contactors in Figure 2 are installed in the bypass cabinet. In order to ensure that no power is back-fed to the inverter output, KM2 and KM3 achieve a natural mechanical interlock. When KM1 and KM2 are closed and KM3 is open, the motor runs in the inverter state; when KM1 and KM2 are open and KM3 is closed, the motor runs in the industrial frequency.

Figure 2 Frequency conversion system primary circuit

AS800 High Voltage Inverter Technical Features

The ideal power for machinery：The output current contains extremely small high harmonic components, and the resulting pulsating torque has a negligible effect on the shaft system, reducing the vibration of the motor.

Multiple curve selection function: Since the compactor machinery is a multi-stage drive mechanism, different machinery will have different characteristics, providing a variety of curve algorithms to suit different mechanical process requirements.

The high voltage inverter must meet the site pump load requirements, as well as the need for dynamic response to fast braking operation.

Figure 3 Field measured output current waveform

Adjust the speed of the motor by inverter to adjust the water volume, so that the power output of the motor is basically proportional to the water demand, always making the motor work with high efficiency to achieve obvious power saving effect.

The system has an automatic control bypass cabinet that provides sufficient contacts for the configuration of the furnace front operating table.

The system has 2 sets of control circuits for frequency conversion and industrial frequency, with single module bypass function to increase the redundancy capability of the inverter.

It makes the current rise gently when starting and loading the motor without any impact; it can make the motor realize soft stop, avoiding the harm caused by anti-generation current and helping to extend the service life of the equipment.

The grid-side input harmonic current is greatly suppressed by the phase-shifting rectifier transformer, and the voltage is superimposed by the cascade of multi-stage H-bridge power units to obtain a nearly perfect high-voltage sinusoidal output, which can directly drive high-voltage motors without any additional filters.

As the motor operates in a high efficiency state, the power factor is high, which reduces reactive power loss and saves a lot of power.

Application Effect Analysis

Energy saving. Frequency converter-controlled fan and water pump compared with the traditional control of the fan and water pump, energy saving is the most practical significance, according to the site of the demand for raw materials to adjust the speed of the fan and water pump is an economic operation state.

Lower operating costs. The operating cost of traditional fan pumps consists of three components: procurement cost, maintenance cost, and energy cost. Among them, energy cost accounts for about 60% of the fan pump running cost. Through the reduction of energy costs, coupled with the reduction of the impact on the equipment after the frequency start, maintenance and repair volume also follow the reduction, so the operating costs will be greatly reduced.

Extend the service life of fan pumps. The inverter starts the fan water pump from 0Hz, and its starting acceleration time can be adjusted, thus reducing the impact caused to the electrical and mechanical parts of the fan water pump when starting, enhancing the reliability of the system and extending the service life of the pump. In addition, the inverter control can reduce the fluctuation of current when the unit starts, this fluctuation current will affect the power grid and other equipment, the inverter can effectively reduce the peak of the starting current to a minimum.

Reduce the noise of equipment. According to the requirements of the working conditions of the fan and water pump, after the transformation of frequency conversion, the motor running speed is significantly slowed down, so the noise of the fan and water pump operation is effectively reduced.

Energy saving benefit description. According to the analysis of the operation of the site, the power consumption of the site with inverter is more than 20% compared with the power consumption without inverter, which brings huge economic benefits to the users.