The invention relates to a feed water treatment system for steam boilers and other applications.

Prior Art

Oxygen free water is preferred/necessary for:

• Steam boiler systems - for prohibition of corrosion

• Injection water for drilling operations - for prohibition of corrosion

• Reduce alcohol content in brews/wine

• Diluting chemicals that react (reduction chemicals) or breaks down (organic solutions ie glycol, ethanol) with dissolved oxygen.

Traditionally, degassing and oxygen elimination of feed water for steam boilers, is done with in heated feedwater tanks with deaerator towers and chemicals/oxygen scavengers ie sodium sulfate, hydrazine etc.

Deaerator towers and heated feedwater removes dissolved gases by heating water above 100°C thus boiling off the dissolved gases. The feedwater tanks spend approximately 0,5% of nominal boiler output to keep the overpressure in the feed tank and keep the gas/steam flow out the venting pipe from the degasser tower, but cases of spending of up to 3 % of nominal boiler output have been reported. Since feed water tanks often are kept warm almost continuously, this can sum up to considerable amounts of lost energy and wasted water. In steam boiler systems dimensioned with high nominal output and with unsteady or an average steam production/use well below the nominal output, the degassing energy percentage use of the total can be as high as above 10%. This also represents a loss of water. It is possible to recycle both the energy and water from the degassing system, but the efficiency depends much upon the use of feed water vs mass flow of return condensate. In the most cases other sources of waste heat can cover the same recovery potential better. Thermal degassing isn't perfect and is most commonly combined with use of chemicals - oxygen scavengers - to get the concentration down to 0 ppb (parts per billion). The most common oxygen scavenger, hydrazine, is poisonous and carcinogenic. This method is also known as thermal degassing. Vacuum deaerators are commercially available, but the size of the facility is increasing rapidly when the demanded concentration of dissolved oxygen in the process is closing to 0 ppb. Vacuum deaerators can also remove other dissolved gases (ie nitrogen) which also is an unwanted element in steam systems, but not due to corrosion causes, as for oxygen, but can cause gas pockets which are unwanted in closed steams circuits.

Catalytic removal of oxygen has been a known technique for making oxygen free of dissolved oxygen since the 1950s. There are a few catalytic feedwater treatment processes for steam systems and district heating/cooling circuits. Reaching 0 ppb with this use of catalytic resin has some limitations. As an example, the manufacturer of Lewatit K3433 has listed these critical dimensioning factors:

Lowest column height: 600 mm (probably for obtaining 0 ppb for water with initially low oxygen content).

Maximum column height: 1100 mm (probably for not getting too high pressure drop over the resin and too hard to backwash in an effective and satisfactory way)

Water flow speed through column: max 80 m/h

To remove oxygen completely from a flow at temperatures of make-up water, calculations for needed column height could get as high as 3000 mm. Therefore, the catalytic feedwater facilities were dimensioned to treat 3 times the needed flow and 2/3 of the flow was recirculated water.

Hydrogen is for all known facilities supplied by "bottle batteries" of 12 x 50 I gas cylinders. Lewatit is a commonly used catalyst, supplied by Lanxess.

Thermal degassing of water is an efficient way to remove huge amounts of dissolved gases, and in processes containing heating of water - ie steam production - a good way to do the heavy load.

Vacuum treatment can remove huge amounts of dissolved gases very effectively and cost-effectively. However - reducing dissolved oxygen to non-corrosive contents ie under 20 ppb demands time - and huge facilities for continuous production.

Catalytic "wet combustion" eliminates dissolved oxygen very efficiently, especially the last pps down to 0 ppb. Though the need for expensive catalyst is rising when inlet content of dissolved oxygen rises. Running cost of circulation pumps and other infrastructure are rising with rising need of catalyst. A prior version of catalytic feedwater treatment had a 40% utilization grade of hydrogen. Excess hydrogen remains in the steam system, and needs to be vented in the plant. It also adds to the operating cost.

The object of the invention is to provide a feedwater treatment system, with a good compromise between performance and cost.

The idea of this invention is to combine two degassing/oxygen removal techniques - vacuum treatment and "catalytic wet combustion" to create a more energy-, water- and space efficient and chemical free feed water treatment facility for steam boilers.

The technique/process is called "Vacuum-catalytic elimination of dissolved oxygen in water".

The apparatus is called "Vacuum-catalytic feed water treatment"

The combination of vacuum and catalytic oxygen removal is taking advantage of the best characteristics of both methods. The vacuum treatment removes amounts of dissolved oxygen and gases. This also makes dissolving hydrogen gas into the water before catalytic process easier and more efficient due to low partial pressure of dissolved gases in the water. The vacuum modules dimension requirements are much smaller than if vacuum was to be the only degassing process. The catalytic process requires much less catalyst resin and hydrogen than if the catalytic process was to be the only oxygen removing process. This makes the combination of vacuum and catalytic degassing more space-, cost- and energy efficient.

Combined, this mixer and vacuum treated water gives an over 90% utilization rate of hydrogen compared to theoretical need of hydrogen gas.

The combination of feed pump, diffuser, pump with low NPSH and vacuum pump to generate continuous vacuum treatment of the water. Vacuum can be generated efficiently with change of water level in the vacuum tank, thus giving the vacuum pump the task to evacuate gas from the vacuum tank when pressure is rising due to degassing process.

Results have shown obtaining 0 ppb with conditions exceeding the prior dimensioning limits for catalytic wet combustion of hydrogen and oxygen. With vacuum treatment before the catalyst, the need for recirculating water through the catalyst is eliminated. The necessary column height has been reduced to 400 mm and water flow speed through resin is up to 115 m/h, showing a reduction of needed catalyst resin of over 80% and total electric power use by 75% of prior version, that did not use vacuum degassing.

The invention consists of 2 main sub systems: a vacuum treatment part, and a catalytic wet combustion part.

The vacuum treatment part, where sub atmospheric pressure moves the equilibrium of dissolved gases in the liquid to release the gas as bubbles, which can be vented away from the liquid. This can be done in several ways.

Keep the liquid in a vessel where a vacuum pump maintains a sub atmospheric pressure.

Run the liquid through a vessel where suction pressure of a circulation pump pumping the water out of the tank, and the feed/flow of water into the vessel is controlled, so the pressure can be maintained at a desired low level. The released gas from the water needs to be vented. This can be done by a vacuum pump connected to the vessel (continuous process), or by releasing gas through an automatic vent by periodically changing water-level in the vessel (batch process).

By condensation of steam. Humid air, which condenses in a closed volume will create a vacuum. This method can also be used to create the sub atmospheric pressure to degas water in a vessel.

Method ii) is chosen as the most feasible for continuous production of degassed water.

Dissolving hydrogen into the water for catalytic reaction can be done in several ways.

• Injected into the water stream before the catalyst tank, and mixed with a: o in-line mounted obstruction/reduced aperture wich creates turbulence and pressure drop ie a solid cone spray. Here is hydrogen introduced in the water in front of the spray at a higher pressure than the water. The obstruction and pressure drop creates microbubbles of the hydrogen, thus making a large contact area between the water and hydrogen to dissolve as much as possible of the hydrogen. How ever the pressure drop also releases other dissolved gases in the water, this can make the process inefficient. The pressure drop is also a factor increasing the need for pump energy. o in-line mounted venturi nozzle (see figure 4b).

Here the hydrogen is mixed with water after a pressure drop in a venturi nozzle. This also makes microbubbles of hydrogen in a turbulent environment, thus making good contact between hydrogen and water. The water pressure at the injection point can be very low, making it possible to inject low pressure hydrogen ie at atmospheric pressure. o in-line mounted vessel with diffusing microbubbles of hydrogen into the vessel.

By using one or more diffusers with small mesh microbubbles of hydrogen is induced into water in a general vessel, with the purpose to expose as much hydrogen to the water to dissolve as much hydrogen into the water. The inlet, outlet and direction of flow flow can be done in several ways.

• Injected into the catalyst tank o By diffuser above, into or below catalyst. o By separate circuit circulating water with hydrogen induced and released into the catalyst tank

We have chosen a solution based of the principle in i) c.

Short summary of the invention

A first aspect of the invention is a system (0) for reducing the concentration of dissolved oxygen in a flow of feedwater comprising,

- a feedwater line (1),

- a vacuum degassing system (A), said vacuum degassing system (A) in connection with said feedwater line (1),

- a catalytic wet combustion system (B), said catalytic wet combustion system (B) in connection with said vacuum degassing system (A) and

- an outlet (28) in connection with said wet combustion system (B), said outlet is arranged for discharge of treated feedwater.

A second aspect of the invention is a method for reducing the concentration of dissolved oxygen in a flow of feedwater comprising • leading feedwater through a feedwater line (1), to a vacuum degassing system (A),

• withdrawing vacuum from the vacuum degassing system (A), feeding said feedwater from said degassing system (A) to a catalytic wet combustion system (B), and

1. after said catalytic wet combustion system (B) transmitting the treated feed water to an outlet (28) in connection with said wet combustion system (B).

Figure captions

Figure 1 illustrates a process and instrumentation diagram of the invention.

Figure 2 is a detailed drawing of the hydrogen mixer, which is part of the invention.

Figure 3 illustrates 5 alternative solutions for hydrogen mixing

Figure 4 illustrates an alternative solution for vacuum degassing.

Component list

Component list for Figure 1

A: Vacuum unit

B: Catalytic unit

1 : Feedwater inlet

2: Feed pump

3: Gate valve

4: Oxygen transmitter

5: Optional heat exchanger for waste heat recovery

6: Pig tail diffusors

7: Vacuum tank

8: Gate valve

9: Vacuum pump

10: Pressure transmitter

11: Level transmitter

12: Main pump

13: Check valve

14: Hydrogen mixer

15: Hydrogen diffuser

16: Check valve

17: PEM-cell

18: Inlet demineralized water 19: Pneumatic valve

20: Meshed pipe

21: Catalyst tank

22: Pressure transmitter

23: Catalyst resin

24: Meshed pipe

25: Pressure transmitter

26: Oxygen transmitter

27: Pneumatic valve

28: Outlet feedwater

29: Pneumatic valve inlet backwash water

30: Pneumatic valve inlet pressurized air

31: Pneumatic valve for bypass

32: Optional bypass for circulation during hydrogen saturation of catalyst resin

33: Outlet backwash water

Component list for Figure 2

34: Water inlet

35: Water outlet

36: Stainless steel housing

37: Pipe with conical reducer

15: Hydrogen diffuser

38: Tubing

39: Check valve

40: Hydrogen supply line

Component list for Figure 3

34: Water inlet

35: Water outlet

41: General reducer/aperture for pressure drop ie solid cone spray

42: Hydrogen supply

43: Venturi nozzle

44: General tank

45: Circulation pump

46: Pipe with multiple outlets

47: General reducer/aperture for pressure drop ie solid cone spray Component list for Figure 4:

49: Water inlet

50: Motorized valve

51: Vaccuum pumpe

52: Water vacuum treatment tank

Detailed description of the figures and embodiments of the invention

The invention will in the following be described and embodiments of the invention will be explained with reference to the accompanying drawings.

Figure 1 shows the main parts of the invention. Feedwater enters the system through the feedwater inlet (1), flows through a feed pump (2), and a controlled gate valve (3). An oxygen transmitter (4) measures the concentration of the dissolved oxygen in the feedwater before its treatment. An optional heat exchanger (5) may be installed to heat the feedwater and said heat exchanger may be heated by waste heat from other processes in the plant where the feedwater system is installed, or from other low-grade heat sources. The feedwater enters a vacuum tank (7), through diffusors (6). As thermal heating of the water increases the release of dissolved gases from the feedwater, the optimal position of said heat exchanger (5) is between said gate valve (3) and said vacuum tank (7). The feedwater is turned into a mist of small droplets by said diffusors (6), so that the combined surface area of the droplets is much larger than the horizontal cross section of said vacuum tank (7). The purpose of said feed pump (2) is to raise the water pressure to a level where said diffusors (6) function as intended, and the purpose of said gate valve, is to control the flow of feedwater to within the operating specifications of said diffusors (6). Said feed pump (2) is not needed if the supply pressure of the water is sufficiently high. In one embodiment of the invention, said diffusors (6) is of the pig tail type, which are designed for a supply pressure higher than 3 barg. In other embodiments of the invention, different types of diffusors can be used, that generate smaller droplets, but it has been found that the pig tail diffusors generate sufficiently small droplets that the oxygen concentration can be reduced to below 2500 ppb (parts per billion). Tests have shown that 2500 ppb is the maximum level of oxygen content the catalytic part of the process can handle to 0 ppb. The effectiveness of the vacuum depends on the water temperature and vacuum pressure. When the temperature rises above 40 °C it is possible to get the water in the vacuum tank (7) to boil, which gives even more effective degassing. But this results in vapor being drawn out with the vacuum pump (9). This results in water and energy loss, but most significant is the increase of volume the vacuum pump (9) has to remove - and needs to be of a larger size and has to run more. Boiling is an unwanted condition, therefore a regulating curve for pressure relative to temperature is implemented in the process.

Most of the volume of said vacuum tank (7) contains a mix of low-temperature steam and air, while the feedwater droplets fall to the bottom of said vacuum tank (7). The feedwater is pumped out of said vacuum tank (7) by a pump (12), being the main pump of the system. A level transmitter (11) mounted in conjunction with the vacuum tank (7) ensures that the water level of the vacuum tank (7) is sufficient for the operation of said pump (12), and as low as necessary to ensure a large vacuum volume for the droplets to fall. The vacuum pressure is mainly maintained by the level control of the water by said main pump (12). It is desirable to keep the water level low in the tank to expose the sprayed water to vacuum as much as possible before hitting the surface of water. The level of water must also be kept above a minimum to meet the required NPSH (net pressure suction head) of the main pump (12) to avoid cavitation. In one embodiment of the invention, said main pump (12) is a multi-stage pump with low NPSH demand, to produce low enough pressure in said vacuum tank (7) and to operate satisfyingly in the conditions.

A vacuum pump (9) evacuates air, oxygen and low-pressure steam from said vacuum tank (7). Said vacuum pump (9) together with said pump (12) maintain a sufficiently low pressure in said vacuum tank (7), to ensure that the oxygen concentration in the mixture of steam and air is much lower than the typical oxygen concentration in tap water. A controlled gate valve (8) in conjunction with the vacuum tank (7) prevents air to leak back into said vacuum tank (7) when the said vacuum pump (9) is not running. A check valve (13) in the flow downstream from said pump (12), prevents reverse flow of feedwater back into said vacuum tank (7).

The rate of oxygen transport from the liquid feedwater to the gas phase in said vacuum tank (7) is dependent on the combined surface area of the droplets, the vacuum pressure, the oxygen concentration in the gas phase, and the feedwater temperature. If the water temperature exceeds the boiling point at the pressure in said vacuum tank (7), the liquid water will boil, resulting in an increase in water surface area, and a reduced partial pressure of oxygen in the gas phase in said vacuum tank (7), both of which will increase the rate of oxygen transport from the liquid phase to the gas phase. But this results in vapor being drawn out with said vacuum pump (9). This results in water and energy loss, but most significant is the increased volume said vacuum pump (7) has to remove - and it would have to be of a larger size and have to run more of the time. The experience is that boiling is an unwanted condition, and in one embodiment of the invention, the pressure in the vacuum tank is controlled to ensure that the boiling point of the feedwater is above the feedwater temperature.

Said main pump (12) pumps the feedwater to a hydrogen mixer (14), in which a hydrogen diffusor (15) dissolves hydrogen into the water flow. Said hydrogen mixer is described in more detail in figure 2. In one embodiment of the invention, hydrogen is produced locally in a PEM cell (17) mounted in a serial configuration, which are fed with demineralized water and electric current at 12 V. The dosing of hydrogen is controlled by the system's automation. The PEM-cells are dimensioned to be run on half of capacity or below for prolonged longevity of the PEM-cells. Delivery pressure of hydrogen gas needs to be higher than the pressure in the hydrogen mixer - and is by default 4,5 bar.

The demineralized water for the PEM-cells is produced by water running through small cartridges of mixed-bed cation and anion ion-exchange resin resulting in water with conductivity below 1 pS/cm.

The feedwater with dissolved hydrogen is fed into a catalyst reactor tank (21), through a meshed inlet pipe (20). Said catalyst reactor tank (21) contains catalyst resin (23). In one embodiment of the invention, said catalyst resin (23) is in the form of small pellets coated with catalyst material. The function of said meshed inlet pipe (20) is to prevent said catalyst resin (23) from exiting said catalyst reactor tank (21) during backwash or other backflow events. Said meshed inlet pipe (20) has a smaller mesh width than the size of the smallest fragments of said catalyst resin (23). A small amount of gas in the feedwater flow is not dissolved in the water, and it will rise to the top of said catalyst reactor tank (21). An automatic vent valve (not shown) can be installed at the top of said catalyst reactor tank, to let out such un-dissolved gas.

The water flows downwards through said catalyst reactor tank (21) and through the bed of catalyst resin (23). Said catalyst resin (23) absorbs the dissolved hydrogen and facilitates a catalytic reaction that eliminates dissolved oxygen in the water. It has been found that if the concentration of dissolved oxygen in the feedwater entering said catalyst reactor tank (21) is below 2500 ppb, the oxygen concentration can be reduced to 0 ppb in the water exiting said catalyst reactor tank (21) through a meshed pipe exit (24). An oxygen transmitter (26) monitors the performance of said catalyst reactor tank (21) in real time. A pressure transmitter (25) monitors the pressure in said catalyst reactor tank (21). The oxygen free feedwater exits the feedwater treatment system through a controlled valve (27) and the outlet pipe (28). An inlet valve (29) for backwash water and an outlet (33) for backwash water, controlled by a controlled valve (19), are for cleaning of said catalyst resin (23). Pressurized air can be introduced during backwash through a controlled valve (30), for improved cleaning efficiency.

When the system is started after a period of standstill, or filled with fresh water, the oxygen concentration will not reach 0 ppb immediately. An optional bypass line (32) from said catalyst reaction tank (21), through a controlled valve (31) to the line into said vacuum tank (7), will allow circulation and cumulative reduction of oxygen concentration in the water in the system, before flow through the system, and feedwater production is started.

Published dimensioning limits for catalytic oxygen removal have been found to be too conservative, if the oxygen concentration in the water entering said (catalytic reactor tank (21) is lower than 2500 ppb. The water exiting said vacuum tank (7) has been shown to be below that level. With vacuum treatment the need for recirculating water through said catalytic resin (23) is eliminated in normal operation. A column height of said catalytic resin (23) of as low as 400 mm and water flow speed through said catalytic resin (23) of up to 115 m/h, have been tested with 0 ppb of dissolved oxygen in the feedwater exiting the system through said outlet (28). 0 ppb has been obtained, with conditions exceeding the prior dimensioning limits. The pre-treatment in said vacuum tank (7) has been shown to reduce the amount of said catalyst resin (23) by more than 80% compared to systems that use catalytic treatment only, and total electric power use has been shown to be 75% lower than a system that uses catalytic treatment only, with a similar capacity.

Backwashing procedure is conducted when pressure drop over the reactor tank exceeds a set value, or oxygen content of the outlet water doesn't get down to desired level under normal conditions. Backwashing is done with water with different temperature than normal operating temperature for the resin. If treated water is cold - warm water (preferably 60 K warmer than normal operating temperature) is used for backwash. Cold water is used for facilities treating hot water. This is because thermal expansion and contraction of the resin is an effective way to remove fouling on the resins surface. Adding pressurized air in the backwash water stream gives good stirring of the resin - and dirt is easily passed to the backwash outlet and drain. If backwash doesn't give the desired results, changing the resin is recommended. The exchanged resin is then cleaned with a lye solution at the provider's workshop and ready for use later.

Area (A) confines the components for vacuum degassing, and area (B) confines the components for catalytic wet combustion shown in Figure 1. In other embodiments of the invention, alternative solutions for vacuum degassing and catalytic wet combustion can be used, some of which are described in figure 3 and figure 4.

Figure 2 shows one embodiment of the hydrogen mixer according to the invention, in more detail. The hydrogen mixer is a container (e.g. a stainless steel filter housing) with a concentric reducer, part of (37) in the center in which feed water flows downwards. Near the bottom of the housing is a fine meshed (5 pm) diffuser (15), where hydrogen is fed into the downwards flowing water stream. The hydrogen feed is through a tubing (38) connected to the bottom of the hydrogen mixer. There is a check valve (39) to prevent backflow of hydrogen or hydrogen mix. Said check valve (39) is the same as the check valve (16) in figure 1. The small hydrogen bubbles are rising towards the water flowing downwards through the concentric reducer. The smallest gas bubbles will rise slowest and also be easily dissolved in the water, unsaturated with dissolved gases. Larger bubbles will rise faster and will thus meet water with higher counter speed. The larger bubbles will then be torn into smaller bubbles by the water with higher speed. This gives a good efficiency of the hydrogen dissolving process.

The series in Figure 3 shows alternative solutions of mixing in hydrogen for the process.

In Figure 3a) the most used process in former models of catalytic oxygen removal is in general described. The hydrogen is induced in front (42) of a reducer (41). Several inserts of reducers with different apertures have been used in former models. The principle is to create a strong turbulence to both crush hydrogen bubbles into as small bubbles as possible, and high speed currently exposes hydrogen to water for a highest possible dissolving into the water. The process is demanding a relatively high pump energy to create the pressure drop across the reducer (41). The pressure drop can without pretreatment with vacuum of the water release other dissolved gases in the water, thus making the process less efficient. Former models have shown 40% efficiency in use of the added hydrogen gas. In figure 3b) the hydrogen is injected in a venturi nozzle (43). The purpose here is the same as the previous method principle - by creating a strong turbulence to crush hydrogen bubbles into small microbubbles for a best possible dissolving of the hydrogen gas into the water. By injecting the hydrogen at the back of the end of the nozzle (42), where the nozzle produces a low pressure, the hydrogen supply may be at a lower pressure i.e. atmospheric or sub atmospheric.

In figure 3c) the principle is to induce hydrogen through a fine meshed diffuser (15) creating microbubbles down to the size of 2pm into a vessel/tank (44), where the microbubbles dissolve on their way upwards in the tank (44).

In figure 3d) the hydrogen is induced in a separate circuit where a circulation pump (45) is circulating water from the reactor tank (21) and mixing in hydrogen by one of the former principles described above. But by returning the hydrogen enriched water through a pipe with multiple outlets (46) into the catalyst mass (23). The nature of the catalyst will absorb the surplus hydrogen bubbles, making the use of hydrogen efficiency better.

In figure 3e) the hydrogen is induced directly into the reactor tank (21). This can be done above the catalyst (23) or into the catalyst (23). This is an alternate version of the principle in figure 3c), but is assumed to be less efficient, as the speed of flow downwards isn't very high, and the diameter of the tank makes the distribution of the hydrogen inefficient and inefficient over the volume of catalyst.

Figure 4 shows in general the principle of vacuum treatment of water.

Figure 4a) shows a water volume in a tank under vacuum pressure maintained by a vacuum pump (51). The degree of degassing depends on the pressure and time of exposure to the vacuum pressure. This is a typical batch process setup.

In figure 4b) the process in 4a) is set up in parallel of two (or more) units/tanks, where a series of batches can make a continuous production flow of degassed water.

In an embodiment of the invention the diffusor (15) is a fine meshed 5p diffusor.

In an embodiment of the invention a vacuum tank (7) is arranged with pig tail diffusers (6), where the diffusers (6) introduce droplets in the vacuum tank (7). It has been found that pig tail diffusors generate sufficiently small droplets that the oxygen concentration can be reduced to below 2500 ppb (parts per billion). Tests have shown that 2500 ppb are the maximum level of oxygen content the catalytic part of the process can handle to 0 ppb.

In an embodiment of the invention the dissolved oxygen content is maximum 5 ppbs (parts per billion).

In an embodiment of the invention the velocity of the feedwater through said catalytic reactor tank (21) is exceeding 115 m/h.

In another embodiment of the invention the height of the catalytic resin column (21) is equal to or less than 40 cm.

The combination of vacuum degassed better hydrogen dissolving has also shown better efficiency of the catalyst resin. The producer of Lewatitt K3433 says in their product data sheet that the speed of water flow has to be lower than 80 m/h through the resin and a minimum resin column height of 60 cm to obtain a concentration of 0 ppb dissolved oxygen. This invention achieves 0 ppb with a flow speed of approx. 115 m/h and a column height of 40 cm.

In an embodiment of the invention a heat exchanger (5) is arranged upstream the vacuum tank (7). This heat exchanger (5) may be installed to heat the feedwater. The heat exchanger (5) may be heated by waste heat from other processes where the feedwater system is installed, or from other low-grade heat sources available in the plant.

In an embodiment of the invention a bypass valve (31) is arranged in the discharge port of the catalytic reactor tank (21) where the bypass valve (31) is connected to a feed water line (1) though a bypass circulation line (32), providing means for recirculating said feed water (1) during hydrogen saturation of the catalytic reactor tank (21).

In an embodiment of the invention an oxygen sensor (25) is arranged in said outlet feed water (28) for measuring the oxygen content of the discharge water.

The essence of the invention relates to a feed water treatment system for steam boilers and other applications. Other applications can be to utilize the treated feedwater in the process of diluting beer with a high alcohol percentage.