Vacuum is necessary during various steps of vegetable
oil processing. These steps essentially include hydrogenation, fractionation, bleaching, deodorization and de-acidification.
Out of all vacuum equipments, Ejector Vacuum System has established the superiority and versatility of their use as compared to the mechanical vacuum pump.
The most outstanding advantage of the Steam Jet Ejector is the total absence of moving parts, which eliminate mechanical breakdown, and assures constant and dependable operation with freedom from repairs.
No adjustment or lubrication is required nor are any specially trained operators necessary as their operation is very simple.
Over and above this, as Steam Jet Vacuum System convey at very high velocity which are many times the speed of sound, they are capable of handling large volume under vacuum thus making them eminently suitable for deodorization application wherein high quantity of open / sparging steam has to be handled.
- Bleaching / drying
- Distillative de-acidification
Ejector & Booster
- Mixing chamber
The Nozzle discharges a high velocity Steam Ejector across a suction chamber that is connected to the equipment to be evacuated. The process vapours are entrained by this Steam Jet and carry into a Venturi shape diffuser, which convert the velocity energy of the steam into pressure energy enabling discharge ultimately to atmosphere.
The Ejectors are generally categorized into one of four types:
- Single Stage.
- Multi-stage condensing.
- Multi-stage non-condensing.
- Multi-stage with both condensing and non-condensing stages.
Lower suction pressure is obtained by staging of the Ejectors. The number of stages of Ejectors is depended on the suction pressure required. Nominal range of suction pressure for number of Ejector is stated below:
|Stages||Nominal range of pressure (in torr)||Nominal range of Vacuum (in mm Hg (v)|
|Single stage||80 – 300 torr||460 – 680 mm Hg (v)|
|Second stage||12 – 100 torr||660 – 748 mm Hg (v)|
|Third stage||4 – 25 torr||735 – 756 mm Hg (v)|
|Fourth stage||4 – 0.06 torr||756 – 759.4 mm Hg (v)|
|Fifth stage||0.6 – 0.02 torr||759.4 – 759.98 mm Hg (v)|
|Sixth stage||0.05 – 0.01 torr||759.95 to 759.99 mm Hg (v)|
Effect of Operational change on critical flow Booster / Ejector Performance
|Motive Pressure||Discharge Pressure||Suction Pressure||Suction Capacity|
|Decrease||Constant||Increase rapidly||Decrease rapidly|
|Constant||Increase||Increase rapidly||Decrease rapidly|
A four stage Ejector System is normally used for Continuous Deodorizers where In the nominal operating suction pressure is 1.5- 2.5 torr while a three stage Ejector System is used for Batch Deodorizer where a nominal suction pressure is 5 6 torr. However, nowadays, physical refining of some of the oil including rice barn, Soya involves very low operating suction pressure of about 0.5 torr for optimum deodorization which calls for installation of a five stage Ejector System.Due to high cost of power available from most of the State Electricity Boards, many of the large refineries are installing their own captive power plants. Many a times, low- pressure steam is available as exhaust from the backpressure turbine of their captive power plant. Instead of condensing this waste low-pressure steam and using it as boiler feedwater, the same can be utilized to motivate Ejectors for deodorizers or De-acidifiers.
As the cost of this low-pressure waste steam is very less, the running cost of the Plant reduces drastically as the Booster/Ejector Vacuum System utilizes majority of the steam in a refinery.
Boosters and Ejectors have been supplied for as low as 0.5 Kg/cm2 (g) motive steam pressure and as high as 40 Kg/cm2 (g). Cooling water temperature also plays a very major role for the efficiency of the Ejector System. Roughly, for every 2°C, increase in the cooling water inlet temperature of the inter-condenser from 32°C will increase the steam consumption by about 10% and vice versa. Therefore, cooling tower should always be properly maintained.
Also, nowadays, considering high cost of energy, mainly steam, most of the installations have incorporated multiple nozzle Boosters which consume about 15 20% lesser steam compared to conventional single nozzle Booster designed for the same motive and suction pressure and capacity.Mazda Limited in India supplies these special multiple nozzle Boosters since last ten years in collaboration with world leaders
Mazda can therefore, claim to be instrumental in improving the efficiency of various refineries and saving India’s precious natural resources.