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Selection of melting furnace

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Selection of products
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2017/12/22 17:17
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[Abstract]:
Usually the melting rate for an induction furnace is determined based on annual production.And the power utilization
Power utilization coefficient
  Usually the melting rate for an induction furnace is determined based on annual production.And the power utilization coefficient does not get enough attention during the estimating of annual production,which influence the correct final result frequently.
  Power utilizationcoefficient means the ratio of average output power to its rated power in a melting operation period,the higher value means the furnace's rated capacity to play a more fully.
  A typical melting cycle consists of charging time,melting time,test time and the pouring time.Obviously,the furnace does not require high output power during the test time and pouring time,this lower output power period caused the power utilization reduced.For example,in a conventional melting furnace,the charging and melting time is about 60 minutes,the test time is 10 minutes,and the pouring time is five minutes.After a simple calculation to know its power utilization coefficient is 80%only.In fact,even in a melting time the furnace can not always rated power output for some type of furnace,so the actual power utilization coefficient is usually around 75%.
  The effective way to improve the mentioned power utilization coefficient is to select the melting furnace equipped with the power supply with power sharing system.Based on two inverters with series resonant circuit,this power supply can feed the power to two furnaces at same time,one for melting and another for holding,so that the test time/pouring time in one furnace will be overlapped with the melting time in another furnace.(See article<The technology of power sharing system and its application>),the power supply with series resonant inverter has a characteristics of constant power output,so the full power will feed to furnace during the whole melting process.By the two factors above mentioned,the power utilization coefficient can make up to 95%when this type of power supply was selected.
  Type of power supply
  Because of different working principle,different selected semiconductors and different control ways in the different type of intermediate frequency power supply,the different final operating characteristics could be got.Although some characteristics unrelated to melting operation,but will influence to power grid.So it is needed to take careful consideration in the selection of furnaces.The following table show you the comparison in important features in three type of power supply,which XMEI provided.
 

Type of power supply

PS type power supply

CAS type power supply

CA type power supply

Working principle

SCR rectifying
SCR invert with parallel resonant circuit

SCR rectifying
SCR invert with series resonant circuit

Diode rectifying
IGBT invert with series resonant circuit

Power regulating

Phase shift control in rectifier
Output power fluctuates with load

Frequency control in inverter
Constant power output

Constant power output

Power factor in grid side

Max. 0.9
It will go down with reduced output power

0.9
Keep constant

0.97
Keep constant

Harmonic in grid side

Depending upon the pulses
numbers in rectifier

Depending upon the pulses
numbers in rectifier

Depending upon the pulses
numbers in rectifier

Melting rate

1

1.07

1.12

Power consumption

1

0.98

0.97

 
  Note.
  The data for melting rate and power consumption listed in above table are calculated on basis of same power and same furnace size.The sample furnace is 10t/6000kW IF induction furnace for iron melting.
  The regulation of output power in PS type power supply to be done in rectifier side and there is one load can be fed only.Generally,one power supply to feed one furnace or to feed one of two furnaces alternatively by switching,on which one furnace for running and another for standby.
  The regulation of output power in CAS type and CA type power supply to be done in inverter side,the output power in rectifier is fixed,thus it is possible to let one set of rectifier to feed power to multi sets of inverters,that means one rectifier can drive multi-loads.Generally,one power supply feeds power to two furnaces at same time.
  Power density
  According to the standard power configuration,the melting rate equal furnace size,that means 10t/h melting rate matches to 10t furnace,in which the power density is about 600kW/t appr.Because of higher electrical efficiency in CAS and CA type power supply,so the melting rate for the furnace configurated with CAS or CA type power supply will higher than that configurated with PS type power supply at same furnace size.Of course the power density could be higher than 600kW/t,take example 800 kw/t,but we don’t suggest to take this higher density,it will cause the melting efficiency go down.
  Application
  Requirement:Annual productivity:10000t/y,300 working days/y,10 working hours/day.
  So,the productivity should be 33.3 t/day.Assuming that furnace is running in Intermittent operation,so preheating of lining is needed and maintenance operation also is needed after furnace shut down.Assuming the preheating operation will take 1 hour and maintenance operation after furnace shut down will take 0.5 hour,so far the total actual operation time is 8.5 hours.
  If the PS type power supply is selected,the power utilization coefficient is about 0.75,the actual melting time is 6.38 hours,the melting rate is 5.22 t/h.From the specification of PS type power supply,we can select 5t/3200 kW furnace and the transformer to eb 3800 kVA appr..
  If the CA type power supply is selected,the power utilization coefficient is about 0.95,the actual melting time is 8.00 hours,the melting rate is 4.16 t/h and the melting power is about 2200 kW.Considering the another furnace to be in holding status,From the specification of CA type power supply,we can select 5t/2500 kW furnace with power sharing system and the transformer to be 2750 kVA appr..
  Obviously,for same annual production,if the CA type of power supply with power sharing system d 38%.to be selected the rated power of furnace could be saved 28%and the capacity of transformer could be saved 38%.
  The result is that CA type of power supply is energy saving and no increasing investment for equipment to be needed.

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