vacuum ejector system

7/30/2019 Vacuum Ejector System

1/11

CFFP VACUUM EJECTOR SYSTEM

14/07/06


2/11

INTRODUCTION

CFFP is manufacturing alloy steel castings and

forgings which include turbine & generatorrotors and casings for steam turbines. CFFP isalso planning to produce 250MW & 500MW IProtors. These products require clean steel.

The purpose of VOD/VAD/ Vacuum degassing isto ensure hydrogen below 1ppm, oxygen below20ppm and nitrogen below 50ppm for cleansteel production.

Gas levels and oxide inclusions are highlydependent on vacuum in the refining unit.


3/11

Results Achieved After CFD

Modification

Vacuum achieved in VAD During vacuum degassing of VAD melt,the vacuum achieved was 3 to 4 torr for

35 as well as 70tonne melt against therequired vacuum of less than 1 torr.

Vacuum achieved during vacuum casting:

During vacuum casting the vacuumachieved was 1.2 to 1.8 torr against arequirement of less than 1 torr


4/11

Studies of Corporate R&D at CFFP

The facilities at CFFP were shown and VAD/VODprocess was explained to Corp. R&D team.

Witnessed the pouring of VAD heat no. 70297 of 56tonne (Grade Hy 19375, 1Cr MoV turbine rotor)

under the following conditions.Heating stage: 430mbar, Duration: 40min.Deep degassing: 1.8 torr

Duration 20 min.Rinsing: 420mbar, Duration: 50 min.One ingot was poured under vacuum (1300 size in pitside) another one (1200 size) bottom poured.Pouring rate :3 ton/min under vacuum for 9 minutes.

Vacuum: 0.5 torr


5/11

Studies of Corporate R&D at CFFP(contd.)

The vacuum achieved in this heat during deepdegassing is 1.8 torr versus 3 to 4 torr in earlierheats.

The deterioration in the ejectors earlier was due toclogging, dust loading and leakages.

Leakages were plugged and cleaning of the nozzles,ejectors were carried out prior to the visit. Thishas improved the performance of the system.

It has been examined that during vacuum pouringthe time to achieve the desired vacuum shall be 1.5minutes. Other wise it increases the croppercentage due to entrained defects.


6/11

Dissolved Gas Analysis of VAD/VOD Heats

Heat No. Process Material [O]

ppm

[N]

ppm

[H]

ppm20614

26/06/06

VAD

36.1tonne

Generator

rotor

57 97 3.5

7029601/07/06

VAD51tonne

Generatorrotor (Ni:3.0,Cr:1.5 Mo:0.4)

104 81 3.4

20629

11/07/06

VOD

29.5tonne

AA 19542

12%Cr, 4%Ni

98 170 4.5

70297

13/07/06

VAD

56tonne

1CrMoV rotor 41 56 1.8

The results show that the gas levels are higher than required for clean steel


7/11

Vacuum Oxygen Decarburisation at 120 torr for 50 minute duration

Melt

Size CO gas Oxygen Ar TotaL Rate/hr

Dust

Load,

kg/hr

Leakage

Kg/hr

Total

kg/hr

Add 20%

Excess

Capacity

50 tons 292 690 7 989 1186.8 300 20 1506.8 1808.16

75 438 1035 10.5 1483.5 1780.2 300 20 2100.2 2520.24

90 525.6 1242 12.6 1780.2 2136.24 300 20 2456.24 2947.488

The above values are in Kgs during the process

Vacuum Decarburisation at 1 torr for 20 minute duraiton

Melt

Size CO Gas Ar Gas Total Rate /hr

Dust

load Leakage Total 20% Excess

50 58 15 73 219 25 10 254 304.8

75 87 22.5 109.5 328.5 25 10 363.5 436.2

90 104.4 27 131.4 394.2 25 10 429.2 515.04

GAS CALCULATIONS (BASED ON HITACHI GUIDELINES)


8/11

The present vacuum system capacity after

CFD modifications is 200kg/hr at 1 torr. It is considered that if vacuum requirement

of VOD/VD is met, it will meet VAD/VDrequirement also. Since we do not have datafor VAD/VD and only VOD/VD available, thecalculation has been carried out for VOD/VDonly.

The existing vacuum capacity of 200kg/hr isnot sufficient for 50tonne VOD/VD processas against the requirement of 304.8 kg/hr at1 torr as derived from the calculations.

Studies of Corporate R&D at CFFP(contd.)


9/11

The suction capacity used by some wellknown specialty steel makers are as

follows: Cruseot Loire: For 51 to 95 tonne VADunit, required suction capacity is 235 Kg/hrof dry air @ 200C at 0.5 torr.

Slovenske Zelezarne Acronis 90T VD/VODunit: the ejector system capacity is250Kg/hr of dry air at 0.5 torr.

Hitachi suggested for 50Tons VD/VOD unitthe required ejector system capacity as250kg/hr at 0.5 torr.

Midhanis proposed 25tonne VAD system,:suction capacity of 140Kg/hr at 0.5 torr.


10/11

RECOMMENDATIONS

From the calculation of gas content for theVD/VOD process, the present ejectorcapacity is not adequate for 50tonne andabove. This is also reflected in the dissolvedgases such as hydrogen, nitrogen and oxygencontent in the samples for clean steelproduction.

The gas calculations were carried out at 1torr. However to remove the dissolved gases

the vacuum to be achieved shall be 0.5 torr.The recommended capacity of ejector is250kg/hr at 0.5 torr for 50-90tonne meltbased on available VAD/VOD units with userslike Cruseot Loire, Slovenske ZelezarneAcroni and Hitachi.


11/11

RECOMMENDATIONS (CONTD.)

To meet the above requirement of 250kg/hr at 0.5

torr, following may be considered:a) It is possible to add another similar ejectorsystem to make up the present capacity to 250Kg/hr at 0.5 torr. It will require additionalequipment like boiler, condenser, etc. Howeveroperational constraints may be examined.

b) It has been observed that users all over theworld prefer a dedicated vacuum system for theirVAD/VOD units.

c) Since six stations (2VADs, 1VOD, 3 Vacuumpouring units) are being catered by a combinedejector system it leads to operational constraintslike leakages due to more number of valves andlosses due to extra pipe lines .

vacuum ejector system

Documents