Application du variateur de fréquence dans système de décrassage
2010-1-4 11:44:58
Résumé: cette page introduit la réforme avec variateur de fréquence VFD dans la centrale de Jiaxing et analyse ses bénéfices économiques.
Mots clés: système de décrassage à eau, fréquence variable, application.

1. Preface

There are 2 sets of 300MW units and 4 sets of 600MW units in the power plant. Total capacity is 6000MW. 300MW unit is equipped with 1025t/h boiler. In 2000, dry deslagging system is changed into water power deslagging system. AC motor variable frequency is a new developing technology. It is not only better than conventional DC motor speed adjustment, but also better than pressure adjustment, pole-changing control and cascade control. It has advantages of smooth adjustment, wide adjustment range, high efficiency, easy structure, hard mechanical characteristic, completed protection and good reliability. In 2005, the plant reformed deslagging system with VFD.

2. Pump operation

Water power deslagging system is composed of bottom bucket, deslagging system, feed water system and dehydrate chamber. After cooling and cracking, mixture of water and slag is removed to transfer chamber by high pressure water. In outlet of transfer chamber, slurry pump sends slurry to dehydrate chamber 1km away. The dry slag is taken outside and water is recycled by pump. Because of defectiveness of calculation, it can not meet water recycle requirement. It needs pump to keep minmium flow. When load varies, slag also varies, water demand is also different. Therefore, pump does not work at full load for about 15 hours, which increases cost. We reform motor with VFD. VFD control can keep water system balance and its full use. It can provide smooth and stepless control, reduce surge and has important meaning for energy saving.

3. Selection

3.1 Scheme selection

In order to save cost, we considered to use hydraulic coupling ever. But we finally gave up this method as its much maintenance, long installation period. After research, considering advanced technology and mature product, we decide to use medium voltage variable frequency drive (VFD). In several VFD brands such as Leader Harvest, AB, Siemens, we decide to use Leader Harvest VFD because of its advanced technology and the cost-effective.

3.2 Model selection

(1) Motor is 6kV/450kW. VFD current is a key parameter. VFD capacity is designed according to motor rated current and max current. So VFD should meet following conditions:

P_M: output power

η:efficiency 0.85

cosφ: power factor 0.75

U_M: voltage

I_M: current

K：revised coefficient of current waveform (1.05~1.1).

P_CN：VFD capacity (KVA)。I_CN：VFD rated current(A)。

(2) connecting method: one drive one bypass circuit

(3) Control principle: PLC implements pressure PI control, ensures pipe pressure constant, outputs 4~20mA signal to VFD to implement auto control of speed. Equip upper PC on VFD. Install upper PC in control room, start/stop, adjust VFD through upper PC. VFD data and state shows in upper PC.

(4) Link lock protection of isolator, inlet valve, outlet valve and pump fault.

(5) Set over current protection, low speed protection.

(6) Protection action: by PLC.

4. Benefit analysis

Annual work hour: 6000 hours, average load rate: 80%, price: 0.37 yuan/kW.h, total power consumption of pump is 2.5% before reform and 1.4% after reform.

Before reform, annual power generation: 100000×0.8×6000=480000000kWh, power consumption of pump: 480000000×2.5%=12000000kwh.

After reform, power generation of pump is 480000000×1.4%=6720000kwh.

Power saved is 12000000-6720000=5280000kwh, that is 1.95 million yuan (USD 286764) saved.

Soft start resulted from variable frequency can greatly reduce impact on motor, pump, valve and MV switch and prolong equipments lifetime. In addition, high precision and wide range of stepless control not only meets requirement of peak adjustment, but also communicates with ethernet well, improving automatization level and work&production environment.

　　

Reference:

1. Wu Zhongzhi, Wu Jialin. VFD application manual Beijing: machinery industry publishing company

2. Wu Shiqiang technology of pump and fan China power publishing company

3. HARSVERT-A VFD manual