Variateur de fréquence moyenne tension dans ventilateur de dépoussiérage de mélangeur de métal
2010-1-6 16:03:35
Il y a deux mélangeur de métal, soit 1# et 2#, chez Handan Steel&Iron Group. Chaque mélangeur de métal à un trou de coulée. Durant l’ajout d’acier ou la sortie d’acier, l’acier en fusion réagit intensément à l’air, créant une grande quantité de gaz d’évacuation. C’est nocif pour les ouvriers et pollue également l’environnement. Afin d’améliorer l’environnement et réduire la pollution, un système de dépoussiérage est nécessaire. L’aciérie installe un ventilateur de dépoussiérage Y4-73№29.5F. Le ventilateur nécessite cinq flux d’air pour s’adapter aux besoins de la technique. La vitesse du ventilateur doit être contrôlée afin d’augmenter l’efficacité et l’économie en énergie du ventilateur.

In original projects, hydraulic coupling used to be adopted. With rapid development of high voltage variable frequency technology, hydraulic coupling is losing its advantage gradually. Harsvert-A VFD was selected eventually. The VFD put into service in April, 2003. It has been running stably for a year.

I. Technics requirements of dusting fan

There is 1# mixer and 2# mixer in steel plant. Air flow is not needed when there is no iron input or output. During working of mixer, slag tap needs air flow 350000m³/h；tap hole needs 150000m³/h. 300000m³/h air flow is needed when tap holes of two mixer output iron simultaneously. 500000m³/h is needed when slag tap and tap hole of one mixer work simultaneously. Slag taps of two mixers can not open simultaneously. Tap holes of two mixers can open simultaneously.

Adding iron: by crane of 125t. Melting iron jar has two models : 70t and 100t. Adding period of each jar is 4~6min.

Outputting iron: calculate as per: three converters produce 20 furnaces/shift, single mix outputs iron 30jars/shift. Three shifts a day and 8 hours a shift. Single jar output time: 1~2min. Shortest period of output is 8min. Accumulative time of output of each shift: 30~60min.

A~B: both slag tap and tap hole do not work

B~D: work time of taphole. B~C: fan acceleration time

D~F: work time of two tap holes. D~E: fan acceleration time

F~H: work time of one slag tap. F~G: fan acceleration time

H~J: work time of slag tap and tap hole. H~I: fan acceleration time. During acceleration, it can skip any acceleration point according to need.

J: fan begins to decelerate.

J~L: time of one slag tap work and one tap hole work transferring to one slag tap work.  J~K: fan deceleration time

L~N: time of one slag tap work transferring to two tap holes work. L~M: fan deceleration time.

N~P: time of two tap holes work transferring to one tap hole work. N~O: fan deceleration time.

P~R: time of one tap hole work transferring to no iron adding or output. P~Q: fan deceleration time.

Q~R: both slag tap and tap hole do not work

II. Requirements of speed adjustment

Unit ： m³/h

VFD acceleration time is 46s (0~50Hz), no requirement for deceleration time. VFD should meet requirement of accelerating during deceleration.

Metal mixer of the steel plant uses a HARSVERT-A06/105 VFD to control speed. The VFD is high-high voltage source drive. Its main data is following: capacity is 1050KVA, rated output current is 105A, input frequency 45Hz~55Hz, rated input voltage 6000V, allowable voltage vibration -10%~10%, input power factor ≥0.96, output frequency 0~50Hz (speed adjustment range 0~100%), VFD efficiency ≥98% (not including transformer), frequency resolution is 0.01Hz, stepless speed adjustment, overload capacity: 120% for 1min and 150% immediately. Acceleration time and deceleration time are set as per technics requirement.

III. Energy saving calculation

1. Principle of energy saving

VFD can accelerate /decelerate motor speed according to technics need, change curve of fan, make fan parameter meet requirement of technics. There is following relationship between flow, pressure, power and speed:

Q₁/Q₂=n₁/n₂

H₁/H₂=(n₁/n₂)²

P₁/P₂=(n₁/n₂)³

Q₁、H₁、P₁—flow, pressure and power when pump runs at speed n₁

Q₂、H₂、P₂—flow, pressure and power when pump runs at speed n₂

If speed lowers a half, namely n₂/n₁=1/2，so P₂/P₁=1/8, we see speed reduction can lower shaft power to save energy.

In VFD control, power factor is near to 1 at full load 50Hz. Operation current is far less than rated current. Reason is that filter capacitors inside VFD take effect in improving power factor, saving 20% capacity for power grid.

2. Operation record

 PLC inside VFD and HMI bring convenient for commissioning. Commissioning period shortens a lot. Setting all parameters is very easy. Adjust air flow of each stage in time according to flue gas quantity. After reforming with VFD, environment is improved greatly.

3. Energy Saving

Statistic daily operation time in each stage, we get following data:

VFD input power of each speed stage:

P₁＝1.732×6×5.8×0.8=48.2kW

P₂＝1.732×6×25.1×0.8=208.7kW

P₃＝1.732×6×37.9×0.8=315.1kW

P₄＝1.732×6×23.89×0.8=198.6kW

P₅＝1.732×6×62.50×0.8=519.6kW

Daily power consumption of fan:

48.2×3 208.7×7 315.1×4 198.6×7 519.6×3＝4694.9 kW·h

Power price: 0.4yuan, yearly work time: 300days, yearly power cost:
       4694.9×0.4×300＝563388yuan

In direct on line state, yearly power cost:

P＝1.732×6×76×0.8=631.8kW

631.8×24×300×0.4=1820000yuan

Cost saved: 1257000yuan (USD 184852)

a. Technics is improved. In VFD control, dusting fan can adjust air flow smoothly. Operation personnel can adjust parameters easily.

b. Lifetime of fan and motor is prolonged. Dusting fan is usually centrifugal fan. Its start-up time is long and start curret is big (6~8 times of rated current), which brings big impact on motor and fan. In VFD control, soft start and soft stop cause little impact, which prolongs lifetime of machine.

c. Wear and tear of valve and impeller is reduced. In VFD control, fan usually runs at speed which lowers 150 round/min than rated speed. So wear and tear of impeller, motor and bearing is much reduced. It prolongs maintaince interval of fan and saves maintaince cost.

d. Automatization is easy. Air flow of dusting system changes as per technics requirement. In damper control, there is linearity problem of opening angle and flow relationship. Because of serious wear and tear, valve character changes, causing nonlinearity problem, thereby leading to incorrect adjustment and abnormal work of control system. In technology of variable frequency, it keeps linearity in high precision 0.1～0.01Hz all the time, which creates favourable conditions for automatization.

V. Commissioning concluding

1. Problem of resisting disturbance. VFD is controlled by system PLC. There are 4 routes analogue output. 2 routes enter into instrument of controller cabinet to display. 2 routes enter into PLC to involve protections. During commissioning, signal entering into instrument is fine, but signal entering into system PLC is sporadic. After detecting, PLC analogue signal is normal. Later on, we solve the problem by earthing system PLC reliably.

2. Inrush current problem of dry transformer. HARSVERT-A adopts technology of cell-cascade multi-level, with a dry transformer. In this project, transformer is epoxy casting transformer with F class insulation. As per transformer manual, inrush current shoud be within 6 magnification. Set instantaneous protection of high voltage breaker as 7. Supplying power to VFD is sporadic. Power can not be supplied to VFD sometimes due to instantaneous protection activity of breaker. Later on, problem is solved by increasing instantaneous protection value to 11 from 7.