Application du variateur de fréquence à Jinxi Petrol Chemical Industry Co., Ltd
Application du variateur de fréquence à Jinxi Petrol Chemical Industry Co., Ltd et analyse des bénéfices économiques.
2009-12-31 14:17:34

1. Préface
Il y a trois ensembles de chaudière 75t (1#, 2#, 3#) et trois ensembles de chaudière 220t (4#, 5#, 6#) dans la société d’énergie thermique de Jinxi Petrol Chemical Industry Co., Ltd. Les chaudières sont équipées de ventilateur aspirant, de ventilateur de soufflage et autres. Les moteurs sont dessinés en fonction de la charge maximum. Toutefois, les chaudières ne sont généralement pas totalement chargées, mais juste au 2/3. Aussi, le flux actuel que la chaudière demande doit être ajusté avec les changements de charge. Pour répondre au besoin, on ajuste généralement l’ouverture du registre, ce qui ne peut ajuster la vitesse du moteur, aussi l’énergie est gâchée et le coût augmente.

2. Purpose of reform

To reduce the cost of manufacture and energy waste, and to accord with requirement of low consumption, low emission and high efficiency, VFD is needed in technical reform for improving the work and saving energy. We have achieved a very good effect and experience through the application of LV VFD. With the MV VFD improving maturely, we put the perfect technique into MV VFD. In May 2006, we reformed with MV VFD for three motors of 4# boiler.

parameters of the motor in 3, 4# boiler

3. Reform scheme

3.1 Main circuit

According to the load of fan, we choose proposal of one drive one, namely one VFD drives one motor. We also added the bypass circuit to ensure the reliability and security. details as below:

The bypass circuit is composed of 3 medium voltage isolator switches QS1, QS2 and QS3 (as figure 1, in which QF is the original medium voltage switch ). QS2 and QS3 can not close together and they are interlocked mechanically. When the motor is driven by medium voltage VFD, QS1 and QS2 are closed and QS3 is open; when the motor is in direct on line, QS3 is closed and QS1 and QS2 are open.
For the purpose of protection, medium voltage VFD is link locked with the switch QF. Once medium voltage VFD faults, QF switches off. It requires user to make suitable change in the switching circuit. During bypass operation, medium voltage VFD will allow QF switch-on and cancel the switch-off signal to enable the motor to start in direct on line.

3.3 Control mode

LEADER&HARVEST provides three modes, local control manually, DCS close loop automatically, DCS open loop manually.

3.4 Cooling proposal

As the process of VFD is AC-DC-AC, there is some heat radiation(2%). The heat heightens the temperature of VFD, even burns it down. For stable operation, VFD should transmit the heat timely. Heat radiation of medium voltage VFD is important for operation. According to the study, we take air-cooling which is the simplest, the most effective and stable. It needs to install duct on top of VFD which could bring the heat out of the room through cooling fan on top of the VFD. Only duct is needed without any other rotating devices so that it is reliable and less fault point. Through fully-load test in the room 40℃, maximum point of VFD is 68℃, which is quite ideal contrast to the design value 140℃.

4. Benefit of reform

4.1 Effect of technical process

After the reform for fans, the damper which used to adjust the flow is fully-opened. Resistance loss is greatly reduced. In addition, as the motor operates in V/F mode in which operating frequency varies so resonance is avoided. It is unexpected that the problem of pipeline cracking is solved.

4.2 Impact on the grid

When motor starts in direct on line state, its starting current might be 7~8 times of rated. The peak current would increases the electric stress of the windings and leads to additional heat so that the motor’s lifespan reduces. After the reform, soft-start becomes a reality by which motor current starts from zero speed/voltage (torque lifting is available) to work current. The load driven by VFD operates in V/F control mode or vector control mode, hardly impact on the grid.

4.3 Maintenance

By VFD, the motor usually runs in range of 30~40Hz. It reduces the speed of fan contrast to line frequency. In addition, soft-start could prolong the lifespan of spare parts, insulation, shaft. Moreover, it reduces the maintenance labour and cost.

4.4 Energy-saving of VFD

In addition to the benefits above, what is more, the perfect energy saving effect is gained. Details as below:

NOTE：power factor is 0.97 after the reform contrast to 0.85 before。

From the chart, we can see the energy saving effect decreases as the boiler’s load increases, and vice versa. But it runs about 8 months at 140~150t/h, 2 months at 200t/h, 1 month at 180t/h, 1 month for maintenance. There is about 9219822 kWh saved in a year, Power saving rate is about 49.5%. If we take account of the power price, we can recover all the investment in less than a year.

5. Conclusions

The reform was one of the most important projects in our corporation in 2006. It is the practical measures that our management changes from extensive form to conservative-minded form. It is embodiment of managers’ forward-looking awareness. The benefits from the reform inspires the staff enthusiasm, and makes us know the importance of energy saving. The perfect economic performance indicates the great potential of energy-saving.