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:

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

(2) Annual time: 360 days

(3)Power price: 0.65yuan, total cost saved M

2. Before reform

Input voltage U_d：6kV；input current I_d   average ：47A，

P：motor power；I：motor input current；U：motor inout ower；cosφ：power factor

Formula ：P_d =1.732×U×I×cosφ=1.732×6×47×0.47=230kW，

Annual time T=360×24=8640h，

Annual power consumption：C_d= T×P_d=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= C_d－C_b，energy saving rate=（ΔC/C_d）×100% ，

There is:

Annual power saved：ΔC=C_d－C_b = 1987200-535680=1451520kWh

Energy saving rate：（ΔC/C_d）×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.