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VFD application in ID fan of flue gas purification system

Abstract: this paper introduces HARSVERT-A series VFD application in ID fan of flue gas purification system, and indicates its function and effect.
Key words: medium voltage variable frequency technology, ID fan, energy saving, harmonic

I. Preface
In most middle/large mining companies, power consumption of motor accounts for 50% of total power consumption. LV VFD is very common. But, defectiveness of MV variable frequency technology, and voltage withstand capacity of components have been restricting MV VFD development and its application. In recent years, with rapid development of MV technology and voltage withstand function, MV VFD has been used widely. Its energy saving effect is considerable.

II. Project introduction
There were 4 low voltage motors (Y355M-4,315kW,562A,1476r/min) in flue gas purification system. In general, 2~3 motors worked and another was spare. Fans connected in parallel. Subpressure was controlled by valve. Valve opening was controlled just by personnel experience. In 2005, plant decided to reform purification system with medium voltage VFD. Mode of one work and one spare was suggested to ensure safety and reliability.

Fig1: purification system layout drawing
1. Driving equipments
MV asynchronous motor: YP7560-6, 1000kW, 50Hz , Ve=6300V,Ie=108.95A;ne=994r/min;cosφ=0.876, insulation class: F, connecting: Y, allowed to start once in hot state and twice in cold state, produced by Lanzhou Motor Co., Ltd.
2. Centrifugal ID fan
Model: Y7-2X36-22F;338600m3/h;7500Pa;ne=990r/min; 1000kW.

III. VFD structure and principal

HARSVERT-A adopts technology of cell-cascaded, high-medium voltage source, 6kV input. Medium voltage is transferred to low voltage through transformer. Then it goes through diode and IGBT inverter. Then cells cascaded output 6.3kV.

Fig 3:6kV VFD system drawing

IV. Effect
MV VFD has been running stably in flue gas purification system for 3 years since Augst, 2005. System also runs healthily. Energy saving is considerable and achieves expected goal. It also meets technology requirement and improves purification effect, which makes plant be prized by local environmental protection bureau. According to related statistics, power consumption of purification system has been down 19%. Actual data is in following:

NO Furnace Subpressure (Pa) Frequency (Hz) Current (A) Result Remark
1 1system 960-1020 19 26 Up to standard
2 2 systems 1000-1100 24 34 Up to standard
3 3 systems 1050-1150 27 41 Up to standard
4 4 systems 1100-1200 31 47 Up to standard
5 5 systems 1160-1250 35 52 Up to standard
6 6 systems 1200-1130 38 58 Up to standard

V. Concluding remarks
VFD application in purification system optimizes the system performance, improves purification effect, reduces power consumption greatly. According to related statistic, flue gas consumption reduces 19m3/t. Total power consumption reduces 137000kW.h per month.
[1] HARSVERT-A series VFD operation instruction, Beijing Leader Harvest Technologies Co., Ltd. 2005.1
[2] Power Smart TM series VFD manual 2006.8

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