Technical field

The present invention relates to a method and a system for

determining the amount of non-dissolved gases in liquid product. More particularly, the present invention relates to an in situ method and system for determining the content of gas bubbles in a liquid processing plant.

Background art

In liquid processing a flow of liquid product is transported through various processing units, such as heaters, tanks, separators, homogenizers, etc. In cases were the liquid processing plant is configured to modify an initial liquid product, e.g. water, to a final product, such as juice, or milk, it is often required to provide additional mixers and additive inlets.

When introducing an ingredient into a liquid processing plant, no matter if it is the initial liquid product or additives, there will always be a certain amount of gas present. Gas, such as air, will either be present as non- dissolved bubbles, or as dissolved gas. During processing non-dissolved gases may dissolve, and vice versa.

Air incorporation may cause major problems in liquid processing and end-product quality. Air in the product may cause increased fouling in heat exchangers, cavitation in homogenizers, and unwanted whey formation in fermented products. In terms of product quality, air in the product can cause oxidation, both during processing and in the package on the way to

consumers. Further to this, air incorporation can also lead to significant product losses in production if the air creates large volumes of unwanted foam in mixing tanks and other equipment. Air incorporation may also reduce the accuracy of standardizing milk in terms of fat content.

It is therefore of great importance to monitor the content of air, or other gases, being present in the liquid product during processing. So far this is done by off-line methods, in which a sample of the liquid product is extracted from the liquid processing line and thereafter analyzed. This is not only a time-consuming method, but it also will induce product losses since the extracted sample may not be introduced again into the product flow, e.g. due to hygienic reasons.

Therefore there is a need for an improved method and system for determining the amount of non-dissolved gases in a liquid product.

Summary of the invention

It is an object of the present invention to improve the current state of the art, to solve the above problems, and to provide an improved system for determining the amount of non-dissolved gases in liquid product.

An object of the present invention is to provide a method and system solving the above-mentioned drawbacks of prior art solutions.

An idea of the present invention is to provide an in-situ method and system for determining the amount of non-dissolved gases in liquid product, especially the amount of non-dissolved oxygen and nitrogen.

According to a first aspect, a sensor system for a liquid processing line is provided. The sensor system comprises sensor means for determining the amount of dissolved gases in a liquid product flowing past said sensor means; pressure means for increasing the pressure of the liquid product; and a controller being configured to receive i) a first signal corresponding to the amount of dissolved gases at a state for which the pressure means does not provide a pressure increase; and ii) a second signal corresponding to the amount of dissolved gases at a state for which the pressure means do provide a pressure increase. The controller further comprises a calculating module being configured to calculate the amount of non-dissolved gases from the first signal and the second signal.

The first signal may correspond to the amount of dissolved gases at a specific point of interest.

The second signal may correspond to an amount corresponding to

100% of dissolved gases.

The sensor means may comprise a single sensor arranged at a specific position, and wherein said pressure means is a pressure control valve. In an embodiment, the sensor means comprises a first sensor arranged at a specific point of interest, and a second sensor arranged downstream said first sensor, and wherein said pressure means comprises a pump arranged between said first sensor and said second sensor.

The pressure means may further comprise a pressure control valve arranged downstream said second sensor.

The sensor means is preferably configured to sense the amount of dissolved oxygen, and the calculating unit is configured to calculate the amount of non-dissolved oxygen.

The calculating unit may further be configured to calculate the amount of non-dissolved nitrogen from the calculated amount of non-dissolved oxygen.

According to a second aspect, a tank for holding a liquid is provided. The tank comprises a loop with an entry in fluid communication with said tank and an outlet in fluid communication with said tank, a pump arranged along said loop for pumping said liquid trough said loop, and a sensor system according to the features above arranged downstream said pump.

According to a third aspect, a method for determining the amount of non-dissolved gases in a liquid product is provided. The method comprises the steps of determining the amount of dissolved gases in a liquid product; increasing the pressure of the liquid product; and determining an amount corresponding to 100% of dissolved gases in the liquid product after said pressure increase. The method further comprises the steps of calculating the amount of non-dissolved gases from a first signal corresponding to the amount of dissolved gases at a state for which the pressure means does not provide a pressure increase; and a second signal corresponding to the amount of dissolved gases at a state for which the pressure means do provide a pressure increase.

In an embodiment the method further comprises the step of calculating the amount of non-dissolved nitrogen from the calculated amount of non- dissolved oxygen.

Generally, all terms used in the claims are to be interpreted according to their ordinary meaning in the technical field, unless explicitly defined otherwise herein. All references to "a/an/the [element, device, component, means, step, etc.]" are to be interpreted openly as referring to at least one instance of said element, device, component, means, step, etc., unless explicitly stated otherwise. Brief description of the drawings

The above objects, as well as additional objects, features and advantages of the present invention, will be more fully appreciated by reference to the following illustrative and non-limiting detailed description of preferred embodiments of the present invention, when taken in conjunction with the accompanying drawings, wherein:

Fig.1 is a schematic view of a liquid product processing line according to an embodiment;

Fig.2 is a schematic view of a liquid product processing line according to another embodiment;

Fig. 3 is a diagram showing the dissolved amount of 0 ₂ as a function of time;

Fig. 4 is a schematic view of a method according to an embodiment; and

Fig. 5 is a schematic view of a tank according to a further embodiment.

Detailed description of preferred embodiments of the invention

Starting with Fig. 1 a liquid product processing line 10 is shown schematically. The processing line 10 may be configured to various

applications; however a preferred use is for processing liquid food products, such as juices, dairy products, etc. The liquid product processing line has an inlet 1 1 , at which an initial liquid product is introduced, and an outlet 12 at which the processed liquid product is discharged to further equipment such as filling machines, storage tanks, etc. The liquid product processing line 10 comprises several processing units arranged in series, such as heaters, homogenizers, mixers, pumps, tanks, etc. The processing line 10 is shown as an example only; the initial liquid product flows to a tank 13, a heater 14, a pump 15, a further heater 1 6, and a yet further tank 17. However, these equipment could be exchanged by other equipment being suitable for other applications. The liquid product processing line 10 further comprises a sensor system 100 arranged in-line, i.e. the sensor system 100 is positioned in the liquid product flow. The sensor system 100 comprises sensor means 1 10 for determining the amount of dissolved gases in a liquid product flowing past said sensor means 1 10, and pressure means 120 for increasing the pressure of the liquid product. Further to this, the sensor system 100 comprises a controller 130 being configured to receive a first signal Si corresponding to the amount of dissolved gases at a state for which the pressure means 120 does not provide a pressure increase; and a second signal S ₂ corresponding to the amount of dissolved gases at a state for which the pressure means do provide a pressure increase. The controller 130 further comprises a

calculating unit 132 being configured to calculate the amount of non-dissolved gases at the state of non-increased pressure from the first signal Si and the second signal S ₂ .

In the embodiment shown in Fig. 1 the sensor means 1 10 is a single sensor being configured to sense, or monitor, the amount of dissolved oxygen in the liquid product. Such sensors are readily available and will not be described in further details herein. The pressure means 120 is a pressure control valve for regulating the pressure of liquid product.

For liquid and air contained in a pipe or other channel or container, the relationship between dissolved and non-dissolved air or other gases depend on the temperature and pressure. Thus it is important to define at which circumstances the amount of non-dissolved air is to be measured. Hence the preferred point of measurement should be at the specific point of interest. For example, if- due to the impact of air bubbles on fouling -the specific point of interest is in the heating section of a heat exchanger, then the sensor system 100 should be arranged at that position such that the oxygen measurements take place there, and then preferably at the hot exit side since that is the point where the pressure is lowest and the temperature highest, thus lowest equilibrium level of dissolved air.

The sensor system 100 operates as follows. The sensor means 1 10 determines the amount of dissolved oxygen during normal conditions, i.e. when the flow control valve is fully opened. The sensed amount is transmitted to the controller 130 as a first signal S-i . Thereafter, the control valve is gradually closed, preferably by means of the controller 130 transmitting a control signal to the pressure control valve 120, while the change of the amount of dissolved oxygen is observed. Due to the pressure increase the amount of dissolved oxygen will increase, until the amount of dissolved oxygen does not increase. At that point, all oxygen is assumed to be dissolved, and the sensor means 1 10 transmits a further signal S ₂

representing the amount of dissolved oxygen when no undissolved oxygen is present. So far, a prerequisite is that the flow is controlled to compensate for varying pressure drops.

By receiving Si and S ₂ , the calculating unit 132 of the controller is able to calculate the amount of non-dissolved oxygen at normal operating conditions, i.e. when the control valve is fully open, as the difference in dissolved oxygen between the second measurement, i.e. the saturated amount of dissolved oxygen, and the first measurement.

Now turning to Fig. 2 another example of a liquid processing line 10 is shown, being equipped with a sensor system 100 according to a further embodiment. The shown example is preferred in situations where it is desired to measure the amount of non-dissolved gases, but where the pressure is not yet raised by means of a pump. This may for example be the case at the outlet of a balance tank 13 or similar.

In this embodiment, the sensor system 100 comprises sensor means 1 10 for determining the amount of dissolved gases in a liquid product flowing past said sensor means 1 10, and pressure means 120 for increasing the pressure of the liquid product. Further to this, the sensor system 100 comprises a controller 130 being configured to receive a first signal Si corresponding to the amount of dissolved gases at a state for which the pressure means 120 does not provide a pressure increase; and a second signal S ₂ corresponding to the amount of dissolved gases at a state for which the pressure means do provide a pressure increase. The controller 130 further comprises a calculating unit 132 being configured to calculate the amount of non-dissolved gases from the first signal Si and the second signal S ₂ . So far, the description of the sensor system 100 is identical to what has previously been described with reference to Fig. 1 .

However, the sensor system 100 of Fig. 2 differs from the embodiment shown in Fig. 1 in that the sensor means 1 10 comprises a first sensor 1 10a being arranged at a specific point of interest, i.e. at the position where it is desired to monitor the amount of non-dissolved gases. The position of the first sensor 1 10a is upstream the pressure means 120, which in this embodiment is realized by means of a pump 120a. The sensor means 1 10 further comprises a second sensor 1 10b being arranged downstream the pump 120a.

The first sensor 1 10a is configured to transmit the signal Si , while the second sensor 1 10b is configured to transmit the signal S ₂ .

If the pressure after the pump is raised considerably, one may assume that all oxygen has been dissolved at the position of the second sensor 1 10b. Hence, the calculating unit 132 of the controller 1 30 is able to calculate the amount of non-dissolved oxygen at normal operating conditions, i.e. when the control valve is fully open, as the difference in dissolved oxygen between the second measurement, i.e. the amount of dissolved oxygen at the position of the second sensor 1 10b, and the first measurement at the position of the first sensor 1 10a.

If the above assumption is not applicable, i.e. if the pressure increase caused by the pump does not provide a pressure high enough to dissolve all gases, the pressure means 120 may further comprise a pressure control valve 120b arranged downstream of the second sensor 1 10b. If operating the pump 120a at constant conditions, the sensor system 100 may operate in the same manner as described above with reference to Fig. 1 . That is, the first sensor 1 10a determines the amount of dissolved oxygen during normal conditions, i.e. when the flow control valve 120b is fully opened. The sensed amount is transmitted to the controller 130 as a first signal S-i . Thereafter, the control valve 120b is gradually closed, preferably by means of the controller 130 transmitting a control signal to the flow control valve 120b, while the change of the amount of dissolved oxygen is observed by means of the second sensor 1 10b. Due to the pressure increase the amount of dissolved oxygen will increase, until the amount of dissolved oxygen stops increasing. At that point, all oxygen is assumed to be dissolved, and the second sensor 1 10b transmits a further signal S ₂ representing the amount of all oxygen being dissolved.

By receiving Si and S ₂ , the calculating unit 132 of the controller is able to calculate the amount of non-dissolved oxygen at a position upstream the pump 120a, as the difference in dissolved oxygen between the second measurement, i.e. the amount of dissolved oxygen downstream the pump 120a, and the first measurement.

In Fig. 3 the amount of dissolved oxygen is shown as a function of time. At t=0 a certain amount of oxygen is dissolved, represented by the solid line coinciding with the lower dashed line. The lower dashed line represents the level of dissolved oxygen, while the upper dashed line represents the maximum level of dissolved oxygen. The upper solid line represents the saturation level.

At ti the pressure is increased, whereby un-dissolved oxygen will start to dissolve. S1 thus represents the amount of dissolved oxygen at t<t-i, while S2 represent the amount of dissolved oxygen at t»t-| .

The amount of non-dissolved oxygen should in most cases be enough to know, but should the amount of non-dissolve nitrogen also have to be known, it could be determined by the relationship between the solubilities of oxygen and nitrogen. By measuring the amount of non-dissolved oxygen, as well as the sum of non-dissolved gases, it is possible to determine the amount of non-dissolved nitrogen. Since the ratio between oxygen and nitrogen in air is well known, it will be sufficient to determine the amount of oxygen in order to calculate the amount of nitrogen. However, since the solubility of nitrogen may differ from the solubility of oxygen, the amount of dissolved nitrogen needs to be determined when there is no pressure increase.

Now turning to Fig. 4, a method 200 in accordance with an

embodiment will be described. The method 200 is performed in order to determine the amount of non-dissolved gases in a liquid product, and comprises a first step 202 of determining the amount of dissolved gases in a liquid product at a specific point of interest. Step 202 may preferably be performed by a sensor, whereby the specific point of interest corresponds to the position of the sensor. In a following step 204, the pressure of the liquid product is increased, e.g. by means of a flow control valve or a pump as has been described above. The method further comprises a step 206 of determining a saturated amount of dissolved gases in the liquid product after said pressure increase, either at the position of the first sensor, or at a position of a second sensor. A step 208 is thereafter performed in which the amount of non-dissolved gases is calculated from a first signal corresponding to the amount of dissolved gases at a state for which the pressure means does not provide a pressure increase; and a second signal corresponding to the amount of dissolved gases at a state for which the pressure means do provide a pressure increase.

In some embodiments, the method further comprises a step 210 of calculating the amount of non-dissolved nitrogen from the calculated amount of non-dissolved oxygen, in accordance with the description above. The method 200 may preferably be used for an additional aspect, namely in order to reduce the amount of non-dissolved gases in the flow of liquid product. Hence, a method for reducing the amount of non-dissolved gases in a liquid product is provided, comprising the steps 202, 204, 206, and 208, as well as a further step 212 of maintaining a pressure - by means of the control valve 1 10, 1 10b - to keep the amount of non-dissolved air at an acceptable level.

In Fig. 5, another embodiment of the present invention is illustrated. The embodiment includes a tank 500 for holding a liquid. The tank 500 comprises a loop 501 comprising an entry 502 in fluid communication with said tank 500 and an outlet 503 in fluid communication with said tank 500. A pump 504 is arranged along the loop 501 for pumping the liquid trough the loop 501 . In addition, the sensor system 100 is provided on the loop 501 downstream the pump 504.

The invention has mainly been described with reference to a few embodiments. However, as is readily understood by a person skilled in the art, other embodiments than the ones disclosed above are equally possible within the scope of the invention, as defined by the appended claims.