The present invention relates to a method and an arrange- ment for continuous deaeration of a particle free liquid as water.

For the present time different methods are used to deaerate liquids depending upon the liquid and the aim of the deaeration. Deaeration of liquids is usually carried through in order to diminish the amount of dissolved oxygen in said liquids.

Driving off air by cooking a liquid at atmospheric pressure has been used since long, but this is a relatively energy demanding method which is not suitable for all kinds of liquids.

Another way of driving off air from a liquid at atmospheric pressure means that the air in the liquid is forced away for example by use of carbon dioxide or some other suitable inert gas. The liquid is distributed over a column with filling material and meets the gas flow in countercurrent. The deaerated and possibly carbonated liquid is withdrawn from the bottom of the vessel.

Deaeration may also take place in an expansion vessel connected to vacuum. A certain vacuum level corresponds to a certain boiling point of the liquid. The liquid is transported to the expansion vessel with a certain temperature which is some degrees above the boiling point which has been adjusted by way of the vacuum value. When the liquid enters the vessel the temperature falls immediately and air and a certain amount of liquid boils

off. The liquid vapours condense against cooled areas in the vessel, while the air which has boiled off is sucked away from the vessel by the vacuum pump.

According to the invention there is now proposed a method and an arrangement for deaeration of liquids which is advantageous both in consideration of the investment and the operational costs.

The method according to the invention is mainly charac¬ terized in that the liquid in an upper part of a vessel which is connected to a vacuum source is divided over a packing material. The liquid is forced to pass over a packing material which completely fills the cross section of the vessel to the largest part of its extension vertically. The liquid films which are formed at the division are diverted and reformed during the passage through the packing material in such a way that an incessantly newly formed exposure area towards the surrounding vapour space in the vessel is available during a necessary contact time. Deaerated liquid is removed at the bottom part of the vessel. During the deaeration the vessel is maintained at or near to absolute vacuum. The pressure is advantageously less than 15 mbar.

The method according to the invention is with advantage carried through in such a way that the temperature of the liquid is below 15 ^C C. If the temperature of the liquid is higher it is of course possible to carry through deaeration at this temperature, but according to the invention an effective deaeration may be obtained at such low tempera¬ ture as below 15°C. This temperature 10-15°C often corre¬ sponds to the prevailing temperature of the water when drawn off from some water source.

According to the method of the invention a liquid the initial air content of which is 8-10 ppm may have an air content of 0.5 ppm after an accomplished deaeration.

An arrangement for deaeration of liquid according to the method of the invention comprises a vacuum vessel, which in its upper part has a connection to a source of liquid and at its lower part a connection for withdrawing deaerated liquid. The vacuum vessel has also a connection to means which cause vacuum in the vessel. In its upper part there are arranged means to divide the incoming liquid into a number of thin liquid films. To its main part the vessel is filled by an inert packing material of thin corrugated sheets provided with holes which create a large exposure area between the liquid and the vapour space in the vessel.

The arrangement according to the invention is with advantage designed such that the vessel has a certain height, which guarantees a certain contact time, while the volume (diameter) of the vessel is adjusted to the desired capacity of the deaeration arrangement. If an increased capacity is desired the diameter of the vessel is increased.

The present invention is described with reference to the attached drawing which schematically shows an embodiment of the arrangement chosen as an example.

In the drawing there is shown a vacuum vessel 1. In the upper part of the vessel there is a connection to a conduit for liquid 2. At the bottom of the vessel there is a connection to a conduit 3 through which deaerated liquid is withdrawn from the vessel. In the upper part of the vessel there is also a connection to a vacuum pump 4 arranged to

evacuate the vessel to a pressure near to absolute vacuum. The vessel is to the main part of its height filled with a packing material 5. The bottom part of the vessel is intended to be filled with deaerated liquid to a certain level. In close vicinity to the upper level of the packing material there is a distributor which divides the liquid into the form of thin films which flow downwards over the packing material.

The packing material consists of filling material available on the market, thin corrugated sheets or plates provided with holes which force the liquid films to incessantly change flow direction during the passage through the packing material. As a consequence of this diversion and reforming there is a large and all the time newly formed exposure area towards the surrounding vapour space in the vessel, which means that the air content of the liquid rapidly falls. The packing material which is inert against the liquid may consist of stainless steel, a suitable synthetic or ceramic material.

During the deaeration the liquid is supplied through the conduit 2 to the vessel 1 which is evacuated by the vacuum pump 4 to a pressure close to absolute vacuum e.g. below 15 mbar. The liquid which is divided into a number of thin liquid films by the distributor 6 falls due to the gravitational pull through the packing material to the bottom of the vessel and the air content in the liquid falls rapidly. In the bottom of the vessel the deaerated liquid is collected and withdrawn from the vessel by a pump 7. The pump is controlled by a level sensor (not shown) in the vessel 1.

Due to the deaeration the air content in the liquid may be lowered with up to 95 %. The height of the vacuum vessel is determined by the desired contact time between the liquid film and the evacuated vapour space in the vessel. According to the invention a satisfactory deaeration may be obtained with a vacuum vessel with a height below 4 m. The height of packing material in the vessel is less than 2.5 m. With this arrangement an efficient deaeration may be obtained with a simple equipment with low demands on available room height. The arrangement does not require supplementary gas in order to obtain a low oxygen level.