GB1577214A - Production of deoxygenated water for use in brewing - Google Patents

Description

(54) PRODUCTION OF DEOXYGENATED WATER FOR USE IN BREWING (71) We, BREWING PATENTS LIMITED, a British Company, of 42, Portman Square, London, W.1, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:- The present invention relates to improvements in the deoxygenation of water eg for use in the production of beer.

It is already known to produce beer by fermenting high gravity worts to produce a beer of more than normal commercial gravity and to dilute the product beer down to the nermal commercial gravity. This technique has a number of advantages. In particular it permits a greater production of normal commercial beer to be achieved in any given processing plant and it also permits some reduction in the energy requirements, in particular because there is a reduction in the volume of wort boiled in relation to the volume of commercial beer produced.

In operating this process it is necessary to pre-treat the diluent water and in particular it is normally necessary that the diluent water should be effectively sterile and its dissolved oxygen content be reduced to below 0.5 p.p.m., being preferably in the range of 0.1-0.3 p.p.m., whereas under normal conditions water contains about 10 p.p.m. dissolved oxygen by weight.

In order to achieve the desired objective of providing sterile water having a low oxygencontent of the order indicated, it is already known to heat a stream of water to a temperature of the order of 70" C and maintain the water at such a temperature for a sufficient period to achieve pasteurisation. The heated water is then sprayed into a tower, in which reduced pressure is maintained by means of a vacuum pump. The pressure in the vacuum tower is maintained slightly below the equilibrium partial pressure of water at the temperature at which it is introduced to the tower so that the water immediately boils and simultaneously dissolved oxygen is flashed off from the water which collects in the bottom of the tower, often below a packing layer. The evolved oxygen and water vapour are drawn off from the tower by means of the vacuum pump.

In order to produce the large volume of sterile, deaerated water required, the size of the vacuum tower vessel is large and the capital cost of the structure is high. It is an object of the present invention to provide an alternative method of producing de-oxygenated, e.g.

deaerated, water e.g. suitable for use in the dilution of beer brewed from high gravity won, which may be performed in a vessel adapted to withstand only a small difference between its internal pressure and the ambient atmosphere.

In order to achieve this result a stream of the water, e.g. employed for diluting beer in a high gravity brewing process, is introduced into the upper region of a vertical column and brought into intimate counter-current contact with a stream of carbon dioxide introduced at a lower region of the column in an amount sufficient to displace dissolved oxygen from the water e.g. to reduce the oxygen level of the water below 0.5 p.p.m. As carbon dioxide is used the deaerated water drawn off from the column will, of course, be substantially saturated with carbon dioxide but that is no disadvantage, since it is almost always necessary to carbonate the deaerated water to a higher level of carbonation before addition to the beer.

In carrying the invention into effect in one system a stream of water is sprayed into the top end of a vertical column, having a layer of ceramic packing near its lower end. The column is provided with a take-off line at its bottom for removal of the deaerated water and with an inlet for carbon dioxide gas in the same locality. Such inlet is below the lower level of the ceramic packing and a gas outlet is provided at the top end of the column.

The gas outlet line may be provided with a vacuum pump to permit displaced oxygen and excess carbon dioxide to be drawn off by maintaining a very small negative pressure in the column. However, it is more usual to maintain a slight super-atmospheric pressure in the column and to allow the oxygen and carbon dioxide to blow off to atmosphere.

In general it may be said that it is preferred to operate the process with a pressure in the column which does not differ by more than 5 p.s.i. from the ambient atmospheric pressure.

In an alternative arrangement the layer of packing material occupies the greater part of the volume of the tower. In this case the bulk of the gas transfer takes place as the water passes down the bed of packing material rather than in the spray droplets. Whilst it it may be more expensive to build a system where the bulk of the tower volume is occupied by packing material, nonetheless this arrangement may often be favoured because the flow of gas up the tower is more truly countercurrent than is likely to be the case in a spray tower where some back mixing of the gas is certain. By operating without significant back mixing the quantity of gas blown-off at the top of the tower can be substantially reduced thus effecting a saving on operating costs.

Where a deep packing layer is employed it is unnecessary to break up the incoming feed water into very fine droplets, since the oxygen transfer from water to the gaseous phase takes place in the packing. It is of course necessary to distribute the incoming water over the top of the packing.

Although it is possible to pasteurise the water after removal from the column, it is preferable to raise the water to above pasteurisation temperature before introduction into the tower, since the quantity of carbon dioxide employed to achieve deaeration decreases with increase in water temperature during the treatment. The water must be retained at a temperature above the pasteurisation temperature for an appropriate period.

This holding period may be partially before and partially after deaerating contact with gaseous carbon dioxide, although it is preferable to complete pasteurisation before introducing the water to the column.

It is believed that the efficaciousness of carbon dixide as a deaeration medium is in part due to the fact that, in a system in which water droplets or streams move through a column counter-current to a carbon dioxide stream, the surfaces of the droplets or of the streams are actually in immediate contact with a gaseous microatmospheric boundary layer in which the pressure of carbon dioxide gas may be significantly reduced below that of the general carbon dioxide macroatmosphere in the vessel. In consequence the dissolved oxygen may, in part, be released into the carbon dioxide macroatmosphere in a similar manner to its release where the macroatmosphere in the vacuum tower of the prior art is at below normal atmospheric pressure.

It is known that vacuum deaeration systems of the type referred to operate most efficiently if the feed water enters the tower at a temperature slightly above the boiling point of water at the reduced pressure maintained by the vacuum pump or ejector system used to draw off vapour from within the tower. As a consequence, an appreciable quantity of steam is flashed off from the water, thus cooling the liquid process stream. If the system is fed with hot water at, for example, 700 C then this boiling will substantially reduce the temperature of the water leaving the tower and represents a heat loss to the system which cannot easily be recovered. Thus, extra energy will be consumed in operating the process.

In the present invention, however, the water does not boil and the heat losses caused by vaporisation of water are consequently much reduced in comparison. Furthermore, it is believed to be possible to operate the new system at substantially higher temperatures, particularly in the range 80--950 C, than is practical in the vacuum deaeration process without sustaining unacceptable heat losses.

The use of higher temperatures will be expected to increase the rate at which dissolved oxygen will leave the water stream.

One system for carrying out the invention is illustrated in the accompanying drawing. The object of the system is to provide a supply of adequately carbonated, deoxygenated water in a tank 1, from which it may be drawn off via pipe 2 for blending with a beer, brewed from a high gravity wort. The tank 1 is supplied with carbon dioxide via pipe 3 so as to maintain a predetermined carbon dioxide pressure in the headspace in the tank 1.

Water is supplied to the system from a supply 4. The inflowing water is heated to pasteurisation temperature in two stages by heat exchange effected by a plate type heat exchanger. In the first stage 5 the incoming water is partially heated by heat exchange with warm water flowing from the deaerater to the tank 1. In the second stage 6, the inflowing water is heated to above pasteurisation temperature, such as 700 C, by heat exchange with a flow of steam 7. From the second stage 6 the water inflow is passed via pipe 8 to a spray head 9. The water from spray head 9 is sprayed into a deaerator column 10, which may have a conventional packing layer 11 to separate the upper space 12, which is essentially gas-filled, from the lower, collection space 14, which is essentially water-filled.

A stream of carbon dioxide is led into the column 10 at 15 and enters the collection zone 14 via a distribution device 13, thence passing upwardly through the packing layer 11 into the upper space 12 and blows off through gas outlet 16.

The deaerated and partially carbonated water collected in space 14 is cooled in the first heat exchanger 5 and then in a second cooling stage 17 by heat exchange with a coolant fluid stream 18 before being passed by pipe 19 to tank 1.

In one example the deaerator column 10 was constructed so as to be able to withstand an internal pressure of no more than 15 psig.

The diameter of the column was 6 inches and the height of the space 12 above the packing layer was 4 inches. The packing layer consisted of ceramic Raschig rings of i inch diameter packed to a depth of 19 inches.

Example 1.

Water at a temperature of 800 C was sprayed into the column in the form of fine droplets at the rate of 1.67 1/mien and carbon dioxide gas was supplied via inlet 1S at the rate of 550 ml/min (at S.T.P.). This rate of carbon dioxide supply was found sufficient to reduce the oxygen content of the water to 0.2-0.3 p.p.m. Exhaust gab was vented via outlet 16 at 220 ml/min (at S.T.P.).

In carrying out the process of the invention with water at a temperature above pasteurisation temperature it is sufficient to supply carbon dioxide gas in amounts approximately in the range of 500 to 1000 p.p.m. by weight to the heated water to reduce the oxygen content to the stated level, provided that adequate contact time between water and carbon dioxide is arranged.

Example 2.

Using the apparatus employed in Example 1 a comparison was made of the deaerator when operated as a vacuum stripping system or as a CO2 flushing system. In the former instance the gas outlet of the deaerator was connected to a vacuum pump which ran continuously.

In both cases the deaerator was run with water entering the top of the stripping column at 79800 C and at a flow rate of 1.66 L67 I/min. The dissolved oxygen content of the water was 9.0 p.p.m. When the deaerator was run under vacuum the internal pressure above the packing layer was measured to be 0.29 atmospheres (absolute pressure) indicating that the water was entering the tower at a temperature above its boiling point at the operating pressure. The water leaving the tower was found to be at a temperature 60 C lower than that at which it entered. However, when the deaerator was run at virtually atmospheric pressure with a 90w of CO2 gas which was vented at the top of the column at 205 ml/min (at S.T.P. and including released gases from the water) then the temperature loss in the water was found to be only 10 C.

Example 3.

The deaeration tower employed in Example 1 was increased in height and the packing depth was increased to 43 inches. The deaerator was then run under a varietv of conditions. The results are shown in Table 1.

TABLE 1

Oxygen Oxygen Water content content Water Gas Inlet of feed of product Stripping flowrate blow-off temp. water water gas ' Zmin 1/mien* OC p.p.m. p.p.m.

CO2 1 6.32 0.18 78 9.05 0.20 CO2 6.15 0.37 77 9.5 0.20 CO, 6.32 0.62 78 9.0 0.12 CO, 6.38 0.62 77 30+ 0.14 N2 6.67 0.62 77 8.9 0.20 CO, 15.7 0.62 79 8.75 0.17 N, 14.4 0.62 75 8.8 0.25 CO, 6.32 0.36 18 8.7 0.40 CO2 6.27 0.62 18 8.1 0.35 CO, 6.36 1.99 18 8.7 0.23 * Volume at S.T.P.

The dissolved oxygen content of the feed water was increased by injecting a super-saturated solution of oxygen in water into the feed line to the tower.

The results obtained in Example 2 demonstrate that the thermal energy required for the process of the present invention is substantially decreased as compared with the requirements of the reduced pressure process previously employed.

The figures given in Table 1 indicate that, in comparable circumstances, CO is operationally a more efficient medium than nitrogen, which is known for use in the deaeration of feed water for boilers. In boiler operation the removal of both oxygen and CO, from the feed water is required for the purpose of reduction of corrosion. It is a surprising result of the present invention that CO, may be applied to the production of deaerated water for beverages and provide superior results to those obtained with nitrogen.

WHAT WE CLAIM IS: 1. A process for the removal of dissolved oxygen from water, which process comprises introducing the water into an upper region of a vertical column, introducing a stream of carbon dioxide into a lower region of said column, effecting intimate countercurrent contact between the water and the carbon dioxide in the column whereby oxygen originally present in the water is transferred to the gas phase, removmg a stream of gas from the said upper region, and recovering deoxygenated water from the said lower region of the column.

2. A process as claimed in claim 1, wherein the water entering the column is at a temperature in excess of 70" C.

3. A process as claimed in claim 1, wherein contact between the water and the gas stream is assisted by providing packing within the column.

4. A process as claimed in any one of claims 1 to 3, wherein the deoxygenated water recovered from the column contains not more than 0.5 ppm of oxygen.

5. A process according to any of claims 1 to 4 in which the water is introduced as a spray in an upper region of the column.

6. A process according to any of claims 1

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (7)

**WARNING** start of CLMS field may overlap end of DESC **. TABLE 1 Oxygen Oxygen Water content content Water Gas Inlet of feed of product Stripping flowrate blow-off temp. water water gas ' Zmin 1/mien* OC p.p.m. p.p.m. CO2 1 6.32 0.18 78 9.05 0.20 CO2 6.15 0.37 77 9.5 0.20 CO, 6.32 0.62 78 9.0 0.12 CO, 6.38 0.62 77 30+ 0.14 N2 6.67 0.62 77 8.9 0.20 CO, 15.7 0.62 79 8.75 0.17 N, 14.4 0.62 75 8.8 0.25 CO, 6.32 0.36 18 8.7 0.40 CO2 6.27 0.62 18 8.1 0.35 CO, 6.36 1.99 18 8.7 0.23 * Volume at S.T.P. The dissolved oxygen content of the feed water was increased by injecting a super-saturated solution of oxygen in water into the feed line to the tower. The results obtained in Example 2 demonstrate that the thermal energy required for the process of the present invention is substantially decreased as compared with the requirements of the reduced pressure process previously employed. The figures given in Table 1 indicate that, in comparable circumstances, CO is operationally a more efficient medium than nitrogen, which is known for use in the deaeration of feed water for boilers. In boiler operation the removal of both oxygen and CO, from the feed water is required for the purpose of reduction of corrosion. It is a surprising result of the present invention that CO, may be applied to the production of deaerated water for beverages and provide superior results to those obtained with nitrogen. WHAT WE CLAIM IS:

1. A process for the removal of dissolved oxygen from water, which process comprises introducing the water into an upper region of a vertical column, introducing a stream of carbon dioxide into a lower region of said column, effecting intimate countercurrent contact between the water and the carbon dioxide in the column whereby oxygen originally present in the water is transferred to the gas phase, removmg a stream of gas from the said upper region, and recovering deoxygenated water from the said lower region of the column.

2. A process as claimed in claim 1, wherein the water entering the column is at a temperature in excess of 70" C.

3. A process as claimed in claim 1, wherein contact between the water and the gas stream is assisted by providing packing within the column.

4. A process as claimed in any one of claims 1 to 3, wherein the deoxygenated water recovered from the column contains not more than 0.5 ppm of oxygen.

5. A process according to any of claims 1 to 4 in which the water is introduced as a spray in an upper region of the column.

6. A process according to any of claims 1

to 5 in which the column is maintained at an internal pressure close to the ambient atmospheric pressure.

7. A process according to any of claims 2 to 6 in which the stream of feedwater is in part heated by heat exchange with the stream of water withdrawn from the column.