Variateur de fréquence moyenne tension pour application dans le ventilateur de dépoussiérage de l'aciérie de Hangzhou
2010-1-7 9:38:01
Résumé : combinant les techniques de production de ventilateur de dépoussiérage de convertisseur, cette page introduit les caractéristiques de performance du variateur de fréquence VFD et explique le schéma de construction complet et démontre l’effet d’économie d’énergie.
Mots clés : mélangeur de métal, variateur de fréquence moyenne tension VFD, projet clé en main, économie en énergie et réduction des émissions.

I.Preface

　There are 2 sets of 600t metal mix in Hangzhou Steel&Iron Group, as well as a tipping and a station of big bag to small bag. Each metal mix has a slag tap and tap hole. Tipping is corresponding to slag tap. When metal mix inputs or outputs iron, high temperature liquid iron reacts with air violently and the reaction creates lots of gas. It is not healthy for workers and it is also pollutes environment. Air flow of metal mix is changing at any time. So dusting fan needs variable speed to adapt. In original operation, hydraulic coupling could not adjust speed frequently, furthermore, valve signal and fan speed control belonged to different control systems and no connecting signal between them. So fan speed was constant and kept about at 680rpm, current 150A. It eliminated dust just by valve and starting furnace cover. In order  to avoid big vibration caused by full valve close, one valve opened all the time. Much air direct emptying resulted in much power wasted. In addition, efficiency was low when hydraulic coupling run in low speed. Fan speed adjustment mode must improve in order to heighten efficiency and save energy.

After investigation and research, we decided to select HARSVEST-A VFD. The project was turn key project and VFD put into service in December, 2006. it has been running stably for 4 months and brings benefits for our plant.

II. Parameters and technics

1.Dusting fan:

Air flow：660000m³/h

Leakage air loss of duct： 10％

Air flow of iron input：250000m³/h

Air flow of iron output： 60000m³/h

Dusting time of liquid iron input：10 min

Dusting time of liquid iron output: 3 min

Daily times of liquid iron output: 180 times

Daily times of liquid iron input:120 times

When iron inputs, after catching cover closes well, related valve opens. When iron outputs, after metal mix leaves zero position, valve of tap hole opens.

2.Motor:

：Y710－8

Rated power：1600kW       

Rated voltage：6300V

Rated current：183.2A

Power factor：0.84

3.Technics requirements

There are 6 stages of state in site.

a. one slag tap work needs 250000 m³/h；

b. one tap hole work needs 60000 m³/h；

c. two tap holes work needs 120000 m³/h；

d. one slag tap and one tap hole open simultaneously : 310000 m³/h；

e. one slag tap and two tap holes open simultaneously : 370000 m³/h；

f. two slag taps open simultaneously : 500000 m³/h；

III. Variable frequency scheme

1. Main circuit

Because inlet of fan does not have door, bypass cabinet is not installed. Namely VFD connects between grid and motor directly.

2. In order to simplify control logic, PLC controls VFD speed according to furnace cover position of slag tap and tap hole. VFD presets 3 speed points and adjusts motor speed in light of air flow needed.

Site sends 6 digital signals to PLC. Make programme to implement high, middle and low speed of VFD.

State introduction:  0：air inlet close

                             1：air inlet open

                        ——：any state

3. Because VFD has protection for motor, such as over current protection, overload protection, lack-phase protection, over voltage protection, earth protection, short circuit protection, over frequent protection. In variable frequency state, medium voltage cabinet protection is spare. Medium voltage switch protection is only for bypass state. In bypass state, start current is 6~8 times of rated current. No need to add start-up device if grid or upper transformer can stand the big impact, otherwise water resistance or reactor should be installed for bypass system to avoid failed start-up.

IV. Turn key project scheme

1. Because hydraulic coupling is working now. Taking account of stable operation, we remove hydraulic coupling and move motor ahead to connect it to VFD. Make new steel base for motor. In order to ensure safe operation, installation precision should be guaranteed. Concentricity between motor and fan is not more than 0.05mm.

2. Medium voltage VFD is installed in fan room. Take advantage of original cable between medium voltage switch and motor as input cable. Lay cable between VFD and motor. Lay 3 screen control cables between site PLC and VFD controller to start/stop in remote, to collect valve state signal and implement 3 speed stages operation and feedback. In addition, it needs to lay a control cable between medium voltage switch and VFD to implement MV allowable and trip-off.

3. Because of strict requirement of IGBT for temperature, we adopt 3 methods to prevent VFD from stopping due to over heat protection.

a. Add duct on top of VFD. Most heat is discharged outside via duct.

b. Change existing window to double glazing.

c. Add air conditioner.

4. Construction

V. Energy saving calculation

1. Data

2. Power consumption of dusting fan with hydraulic coupling.

       Pd =1.732×U×I×cosφ =1.732×6.3×150×0.8=1309.4 kW

Yearly work time: 7920h (about 330 days); price: 0.5yuan/kW.h

Yearly power consumption is 10370000kW.h, corresponding to 5185000yuan

3. Power consumption of dusting fan in VFD control

a. In high speed of 667rpm

There may be 2 furnaces need dusting simultaneously, daily high speed work time is 12h (including VFD accelerating time)

P1 =1.732×U×I×cosφ =1.732×6.3×110×=1140 kW

b. In middle speed of 520rpm

at least one tap hole works, running time is 10h

P2 =1.732×U×I×cosφ =1.732×6.3×45×0.95=466.5 kW

c. In low speed of 300rpm

work time is 2h

P3 =1.732×U×I×cosφ =1.732×6.3×4.4×0.95=45.6 kW

d. Yearly work time: 7920h (about 330 days); price: 0.5yuan/kW.h

power consumption is 6974000kW.h, yearly cost is 3487000yuan

4. We get power saved is 3396000kW.h, corresponding to 1698000yuan (USD 249705)

In addition to above economic benefit, there are other advantages:

a.       Limit start current and reduct power loss.

b.      Rise power factor to 0.95

c.       Eliminate impact caused by motor start/stop and prolong device lifetime

d.      Make motor connect to fan directly

e.       Lower speed of fan and motor, make drive device less fault.

5. Investment analysis

Pay back period of cost of VFD project is 16 months. The cost includes equipment cost, auxiliary cost, transportation cost, design cost, installation cost, inspection cost, maintenance cost, financing cost and risk cost.

VI. Concluding remarks

Medium voltage VFD plays an important and positive role in heightening efficiency, reducing cost and ensuring fan safe operation and automatization level for Hangzhou Steel&Iron Group. This can be looked upon high-tech project of good applicability and fast repay.