Beijing Leader & Harvest Electric Technologies Co., Ltd.
Home » Application » Oil, Gas » Medium voltage VFD application in centrifugal compressor

Medium voltage VFD application in centrifugal compressor
Abstract: this paper introduces variable frequency technology on compressor process and its energy saving benefit.
Keywords: centrifugal compressor medium voltage VFD enery saving

I. Project induction
Zibo Nuoao Chemical Industry Co., Ltd was set up in 2006. The company has 20000t/a propanal equipment, 10000t/a propanal equipment, 15000t/a reclaiming device of butanol and octanol remnant water, 30000t/a octanol equipment. Medium voltage VFD is used on compressor of propanal. Load is centrifugal circulating compressor. Parameters are following:

Compressor Model 4V-2S Motor model YB450M1-2
Manufacturer Jinxi Chemical Industry Mechnical Plant Manufacturer Nanyang Motor Plant
Medium Mix gas(such as CO,H2) Rated power Pdn 450kW
Power 323 kW Rated speed n0 2980 r/min
Rated speed 14029 r/min Rated voltage U0 6kV
Rated flow 20190 m3/h Rated current I0 52.1A
Inlet pressure 1.35 MPa Rated power factor 0.88
Outlet pressure 1.85 MPa
Acceleration rate 1:4.7

II Production process
Mix gas from butanol and octanol workshop and ethene enter into synthesis reaction tower. Gas phase of propanal is created by the action of catalyst, after cooling, coarse propanal is created. Air returns synthesis reactor through compressor. Liquid phase propanal enters into rectifying tower and propanal product is output. Process is as drawings:

In actual operation, in direct on line state, compressor starts on heavy load every time. It is not easy, meanwhile, there is hidden danger in technology process, such as big noise, big start current. in addition, due to load vibration, motor runs in full load seldomly. So valve adjustment mode wastes lots of energy. In this waty, economic benefit is inferior. In order to solve the problems, after investigation, we decide to reform with VFD.

III. Reform project
1. Data in site
(1) Comparison data

Line frequency Variable frequency
Motor speed 2980r/min 1200r/min
Input current 47A 7A
Power factor 0.47 0.85
Valve opening(FV1001) 35%-40% 100%
Inlet pressure 1.35MPa 1.35MPa
Outlet pressure 1.85MPa 1.43MPa
Pressure difference 0.5MPa 0.08MPa
Outlet flow 20190m3/h 8455m3/h

(2) Annual time: 360 days
(3)Power price: 0.65yuan, total cost saved M
2. Before reform
Input voltage Ud:6kV;input current Id average :47A,
P:motor power;I:motor input current;U:motor inout ower;cosφ:power factor
Formula :Pd =1.732×U×I×cosφ=1.732×6×47×0.47=230kW,
Annual time T=360×24=8640h,
Annual power consumption:Cd= T×Pd=8640×230=1987200kWh
Power cost=1987200×0.65=1291680yuan
3. After reform
Input voltage Ub=6KV;input current Ib=7A,
Formula: Pb =1.732×6×7×0.85=62kW,
Annual power consumption Cb=8640×62=535680kWh,
Annual power cost=535680×0.65=348192yuan
4.Energy saving calculation
ΔC= Cd-Cb,energy saving rate=(ΔC/Cd)×100% ,
There is:
Annual power saved:ΔC=Cd-Cb = 1987200-535680=1451520kWh
Energy saving rate:(ΔC/Cd)×100% =1451520/1987200=73.0%,
Cost saved M=1291680-348192=943488yuan(USD 138748)
IV. Operation after reform
There are following advantages:
1. With soft start, motor start current is far less than rated current. That prolongs start time and reduces impact on power grid.
2. Inlet pressure of compressor reduces a lot. Before, pressure difference was 5kg and equipment squealed loudly, about 120dB. After reform, pressure difference becomes 0.8kg, noise is 75dB. That lightens mechanical damage on motor, reduces noise and prolongs equipment lifetime. Meanwhile, impact on pipe is reduced a lot, which prolongs maintenance period of pipe and reduces maintenance cost.
3. Input current is reduced a lot.
4. Power factor is heightened.
V. Concluding
With technology of variable frequency, problems of hard start-up is solved. VFD improves production process, prolongs maintenance period and gains better economic benefit. With VFD developing, there will be more and more equipments need speed adjustment. VFD makes great contribution on energy saving.

Variable Frequency Drive
  • A VFD HARSVERT-A series VFD is a masterpiece of outstanding performance and high reliability, which is widely used for the energy-saving application of the normal motors of fans, pumps ...
  • VS VFD Vector control for the speed-adjustment of synchronous motor;
    Start ability for starting the synchronous motor with load;
    The response time of dynamic torque: less ...
  • FVS VFD PWM rectifier technology. Energy can flow bi-directionally between power grid and the motor;
    Vector control for synchronous motor;
    Strong start up with load in ...
  • FVA VFD Auto re-start after the recovery of main medium voltage;
    Fly-start at any rotating speed;
    Bypass the faulty power cell automatically( OPTIONAL FUNCTION) ...