Patent Description:
Inactivation of microorganisms by means of a steam sterilization process involves the presence of steam (moist heat) and high temperatures over a certain time period. During such a steam sterilization process, the material to be sterilized must be in contact with the steam and its condensate for said time period. However, there is a challenge in such steam sterilization processes because non-condensable gases (NCGs) may accumulate, and may insulate and prevent full steam penetration into for example lumens, such as in long hoses, textile packages and crevices on objects, and may thus impair the ability for inactivation of microorganisms in such locations. It is desirable to remove non-condensable gases (NCGs) to achieve an efficient steam sterilization process.

The NCGs are mainly dissolved O<NUM>, N<NUM>, and CO<NUM> that are absorbed from the atmosphere in lakes, rivers and wells. There may be a seasonal variation of NCG levels due to different temperatures and increased stirring of lakes during spring and fall when temperatures change.

A common method for removing NCGs from water for sterilization processes is hot well degassing. This involves using a heated tank where the feed water is kept at an elevated temperature. The saturation of dissolved gas decreases as the temperature rises. However, the degassing works poorly if sufficient time is not given for the water to heat up and the gases to escape, or if the temperature is too low. Furthermore, the temperature needs to be kept well below the boiling point in order to avoid damaging the pump or even for the water to be able to be pumped at all.

Examples are disclosed by : <CIT> , <CIT> and <CIT>.

In view of the above it should be understood that there is still room for improvement when it comes to degassing the water that is to be used in a steam sterilization process.

An object of the present invention is to present a method and system which at least partly alleviates the drawbacks of the prior art. This and other objects, which will become apparent in the following, are accomplished by a method as defined in claim <NUM>. Some non-limiting exemplary embodiments are presented in the dependent claims.

The applicants have determined that water should be passed through a degassing filter and then recirculated through the degassing filter, thereby enabling a considerable reduction of the NCG content in the water before providing it to the boiler.

Thus, according to at least one aspect of the present inventive concept, there is provided a method of controlling a steam sterilizer system comprising a boiler in which liquid water is turned into steam, the method comprising:.

By recirculating the water through the degassing filter, the NCG content will gradually be reduced, thereby enabling water having a low or substantially no NCG-content to be passed to the boiler for generating improved steam for the steam sterilizer.

Suitably, the steam sterilizer system may comprise a valve located downstream of the degassing filter and upstream of the boiler. In at least some exemplary embodiments of the method, said step of passing at least a portion of the water to the boiler may comprise opening said valve. In other words, the valve being located in a feed passage between the filter and the boiler may be controlled to be closed while recirculating the water through the degassing filter in order to prevent water from prematurely flowing to the boiler (i.e. before a sufficient amount of NCGs has been removed). The opening and closing of the valve may be controlled strategically by means of a control unit of the steam sterilizer system. Such a control unit provides additional advantages, and will be discussed in more detail later in this disclosure.

Said valve in a feed passage between the filter and the boiler may, for convenience, be referred to as a first valve. The steam sterilizer system may also have other valves. For instance, in order to recirculate the water, there is suitably provided a recirculation passage which extends to the container from a point downstream of the degassing filter. In such a recirculation passage, there may be may be provided a valve which, for convenience, may be referred to as a second valve. When the first valve is closed, the second valve may be controlled to be open to allow for recirculation of the water through the degassing filter. When the time comes to open the first valve to allow at least a portion of the water to be passed to the boiler, then the second valve may be closed. It should, however, be understood, that closing of the second valve is not necessary. Indeed, some recirculation may be allowed simultaneously with passing water to the boiler. For instance, instead of a controllable second valve the recirculation passage may be provided with a small orifice which is always open for recirculation. From the above it should be understood that, according to at least one exemplary embodiment of the method, the method may comprise, simultaneously with the step of passing at least a portion of the water to the boiler, continuing recirculating a minor part of the water that has passed through the degassing filter.

It should be understood that the general idea of recirculating the water through the degassing filter while preventing the water from flowing from the degassing filter to the boiler, may be implemented in various ways. For instance, in some exemplary embodiments, a relatively short recirculation loop may conceivable, with or without a separate pump, in which case water that has exited the degassing filter may be returned to the filter without passing through the container. In other words, in at least some exemplary embodiments, the recirculation of the water may bypass the container. However, as has already been indicated above, in at least some exemplary embodiments the recirculation may advantageously be performed via the container. Thus, according to at least some exemplary embodiments, the step of recirculating the water through the degassing filter may comprise returning the water to the container and then pumping it to the degassing filter again.

According to at least one exemplary embodiment, said step of recirculating the water through the degassing filter comprises:.

Thus, the water is suitably recirculated "multiple times", so that all of the water in the container has passed through the degassing filter, on average, at least twice. The more times the water is recirculated, the higher amount of NCGs will be removed from the water. The actual control of the recirculation may, of course, be volume-based, e.g. using a flow meter. However, suitably, the recirculation may be time-based, i.e. recirculating for a certain time period, which may correspond to a certain volume of water having been passed through the degassing filter.

According to at least one exemplary embodiment, the step of recirculating the water through the degassing filter is continued until determining that either (i) the water has been circulated through the degassing filter for at least a minimum time period, T1, or (ii) the water has completed at least a minimum number of cycles through the degassing filter.

The minimum time period T1 may, for example, be determined empirically, or through a look-up table, or be calculated based on known or estimated NCG content, flow rate, volume, etc. The minimum time period T1 is suitably selected such that a satisfactory reduction of NCGs in the circulating water is achieved before water is allowed to pass to the boiler. If time allows, and there is no urgent or pending request to supply the boiler with water, then recirculation may suitably continue for a longer time period than said minimum time period T1, in order to even further reduce the NCG content. In case the control of the recirculation is not time-based, and instead a minimum number of cycles is to be completed, then such control may be implemented by using a flow meter to measure the volume of water that has passed through the degassing filter. Thus, one cycle may suitably correspond to passing a volume of water through the degassing filter which corresponds to the volume that was initially present in the container before starting to pump water from the container. In some embodiments, the volume of water passing through the degassing filter before the water is passed to the boiler is at least double the volume of water initially present in the container, or at least double the volume of water initially present in a degassing circulation loop.

In addition to the above-mentioned time-based and cycle-based alternatives for controlling the duration of the recirculation, another conceivable alternative is a pressure-based control. Such a pressure-based control may suitably be implemented in connection with a vacuum tank being used for drawing NCGs from the degassing filter. This will be explained in more detail below.

According to at least one exemplary embodiment, the method comprises applying, by means of a vacuum tank, a vacuum to the degassing filter to draw NCGs from water passing through the degassing filter.

Applying a vacuum to the degassing filter improves the gas removal efficiency of the degassing filter. The vacuum tank may, for example, be connected to a central vacuum arrangement of the sterilizer system or may instead be connected to a separate ejector or an additional vacuum pump.

As indicated above, a pressure-based control of the recirculation duration may suitably be implemented, Thus, according to at least one exemplary embodiment, the step of recirculating the water through the degassing filter is continued until determining that there is a pressure rate of change below a predefined threshold in the vacuum tank.

Since a vacuum tank will normally be provided with a pressure sensor, use of such a pressure sensor may be convenient for monitoring the change in gas content during recirculation of the water. In particular, it should be understood that, initially, when you start the degassing process, the water will have a high NCG content, and a rather steep pressure rise in the tank is expected at the beginning of the degassing (recirculation) process. However when the water is fully degassed, then continued recirculation should not result in a pressure rise. Thus, by monitoring the pressure rate of change, the control unit may determine when the recirculating water is sufficiently degassed.

Although it may be convenient to measure the pressure rate of change in the vacuum tank as discussed above, it should be understood that such pressure rate of change may instead, or additionally, be measured at other locations. Indeed, regardless of using a vacuum tank or some other device for creating a vacuum, the pressure rate of change may be measured in any suitable closable volume which can be arranged in gaseous communication with the degassing filter. Thus, in a general sense, and according to at least one exemplary embodiment, the step of recirculating the water through the degassing filter is continued until determining that there is a pressure rate of change below a predefined threshold in a closable volume in fluid communication with the degassing filter.

A pressure sensor may be provided in any such volume, be it the previously discussed vacuum tank or another volume in fluid communication with the degassing filter. By fluidly connecting the volume to a dry side of the filter and then closing the volume during measurement, a pressure value may be obtained from the pressure sensor. Gas molecules passing through the degassing filter will raise the pressure in the volume. If there is already a pressure in the volume (e.g. no or poor vacuum) then there will be no or little transport of gas molecules.

Although the above-mentioned time-based, cycle-based and pressure-based control strategies have been presented as different conceivable alternatives, it should be understood that combinations thereof are also conceivable. For instance, another possibility is to control the recirculation based on a combination of the pressure rate of change and the minimum time period T1, which will result in an even more robust control strategy.

Some additional discussion relating to the use of a vacuum tank will now follow. In particular, various tests may be executed in connection with such a vacuum tank. One such test, may be a leak test, to make sure that the provided vacuum functions to satisfaction. Another such test, is a performance test.

Thus, according to at least one exemplary embodiment, the method comprises:.

Additionally, according to at least one exemplary embodiment, the method comprises:.

The above leak test and performance test are clearly beneficial for reducing the risk of incorrect control and degassing. The leak test and/or the performance test may form part of separate maintenance cycles, or may be integrated into the production cycles. Any leak will make degassing more difficult, requiring more vacuum support and may result in the above-mentioned pressure-based recirculation control to become ineffective. A lack of pressure rise in the vacuum tank during initial degassing of water that has not been degassed before, may be indicative of a faulty, worn or clogged filter that needs to be replaced.

As an alternative or a supplement to the above-discussed control strategies (time-based, volume-based and/or pressure-based), another control strategy may be to monitor the actual NCG content in the container. Thus, according to at least one exemplary embodiment, the method comprises:.

Thus, this is another way to avoid premature filling of water (with high NCG content) into the boiler. Monitoring the NCG content of the water in the container may, for example, be achieved by using an in situ Total Dissolved Gas (TDG) sensor between in the discharge passage from the container to the degassing filter. Suitably, such a TDG sensor may be arranged in the discharge passage between a circulation pump and the degassing filter. Another possibility is to use a single-gas sensor, e.g. an oxygen gas (O<NUM>) sensor. Since a certain relationship between the quantities of O<NUM>, N<NUM> and CO<NUM> can be expected in the fresh water, a sensor which only measures the quantity of one of the gases may therefore be sufficient for estimating/calculating the total NCG content.

As explained above, there may be various control strategies to reduce the risk of the water being passed prematurely to the boiler, in particular to reduce the risk of filling the boiler with water having too high NCG content. There may, however, be other considerations for determining when to allow water to enter the boiler. This is reflected in at least one exemplary embodiment, according to which the method comprises:.

Thus, by monitoring the liquid water level in the boiler the control unit may determine if there remains sufficient water for steam generation for an upcoming sterilization of articles to be sterilized in a sterilizer downstream of the boiler. The boiler may therefore suitably be provided with a level control system including level sensors for detecting when the level in the boiler is low, as a consequence of water therein having been converted into steam by means of for example heating elements.

According to at least one exemplary embodiment, the method comprises:.

Supplying fresh water to the container results in an increased NCG content when mixed with any degassed water already present in the container. It is therefore advantageous to prevent fresh water from being supplied to the container if the boiler is to be filled in the near future.

The determined time period T2 may suitably be calculated based on current circumstances, and may vary from one occasion to another. If the determined time period T2 is short, which may be indicative of a re-filling of the boiler being required shortly, then it is advantageous to suspend supplying of fresh water to the container until after the re-filling of the boiler has been completed, and thus only use degassed water already present in the container. This may be particularly relevant if the container volume is significantly larger than the re-filling volume normally passed to the boiler, as the water in the container can then be used for several batches of re-filling and steam generation operations. Conversely, it should be understood that if the determined time period T2 is relatively long, then there may be sufficient time to fill up the container with fresh water and have it recirculated through the degassing filter to reduce the NCG content sufficiently before re-filling of the boiler is expected to be requested. For instance, if using the time-based control, if the time period T2 is longer than the sum of the time it takes to fill the container and the minimum time period T1 for recirculating the water through the degassing filter, then fresh water may suitably be supplied to the container. Naturally, the control unit may be configured to calculate, based on time periods T2 and T1 and the fresh water supply rate, how much fresh water is allowed to be supplied to the container (if a complete filling would take too long), such that the supplied amount of fresh water can be degassed in a timely manner within the time period T2.

It should be understood that supplying fresh water to the container may be made from a fresh water conduit directly to the container. However, another conceivable option is to add the fresh water upstream or downstream of the container in the degassing arrangement. For instance, the fresh water may be added to the above mentioned recirculation passage which interconnects a point downstream of the degassing filter with the container, or the fresh water may be added to a discharge passage which interconnects the outlet of the container with the degassing filter. If a pump is provided in the discharge passage than the fresh water may be added to the discharge passage upstream or downstream of the pump. Thus, it should be understood that the fresh water may be supplied to the container by letting the fresh water enter at any suitable location of the recirculation path of the water in the degassing arrangement where it will reach the container during degassing circulation.

Similarly to the above discussed timing of preventing fresh water from being supplied to the container, according to at least one exemplary embodiment, the method comprises:.

The predetermined time period may, for example, correspond to the previously discussed predetermined time period T2.

The idea of timing the supply of fresh water to the container is also reflected below. Thus, according to at least one exemplary embodiment, the method further comprises:.

If the container is filled with approximately the same volume of water that is later passed to the boiler, then the above steps may suitably be repeated for each new batch of water to be evaporated in the boiler.

By monitoring the water level in the container, unnecessary dilution may be avoided. The control unit may suitably be configured to determine if the current water level is sufficient for another batch of steam generation in the boiler, and if that is the case, then supply of fresh water to the container may be prevented. In other words, it may be better to make use of the already degassed water available in the container before supplying fresh water to the container, as the fresh water would increase the NCG content in the container and require further circulation of the water through the degassing filter.

According to at least one exemplary embodiment, said step of controlling the supply of fresh water to the container based on the current water level in the container comprises:.

As understood from the previous discussions, supplying water into the container when the water level is low is advantageous as it reduces a rise in dissolved gas level.

The prevention of providing fresh water to the container may suitably be achieved by means of a further valve, a container-filling valve, which can be opened and closed. Such a container-filling valve may be controlled by the control unit based on level sensor input (e.g. from one or more sensors monitoring the water level in the container). However, in at least some alternative exemplary embodiments, the container may be provided with a float valve instead of the container-filling valve and the level sensors.

According to at least one exemplary embodiment, the method further comprises at least one of:.

In embodiments in which the method also takes uses the previously discussed time-based control and the predetermined time period T1, then said first time period T3 should normally be greater than the time period T1, since in addition to the recirculation time (T1), time will also elapse during the actual feeding of fresh water to the container. Said second time period T4 may, however, in at least some exemplary embodiments correspond to the previously discussed predetermined time period T2, i.e. a predicted time period for the water to fall to or fall below a predefined level in the boiler.

In other words, according to this exemplary embodiment, the control of supplying fresh water may advantageously be based on completed/finished filling of boiler, e.g. directly after (within a short time period after) filling the boiler.

In other exemplary embodiments, the container may be associated with a predefined low water level and a predefined high water level. In such embodiments, and when the NCG level is assumed to be low as a result of degassing, you will normally not add fresh water to the container when the current water level is between said predefined low and high water levels. Instead, the water already present in the container will be used for filling the boiler with degassed water when the boiler may require it. This may be done as long as there is no risk of running out of degassed water in the container. When the current water level has dropped to or below said predefined low water level, then fresh water may again be supplied to the container. This will raise the NCG content in the container, and a new degassing/circulation phase will be initiated. This is at least partly reflected in the following exemplary embodiment. According to at least one exemplary embodiment, the method comprises:.

Although it may be advantageous and convenient to have a clear threshold in the form of said predefined low water level for supplying fresh water to the container, the control unit may suitably be configured to handle other scenarios as well. For instance, the control unit may suitably determine that water may be supplied even though the current water level has not dropped to said predefined low water level, i.e. the current water level is still between the predefined low and high water levels. This will, however, be performed proactively if the control unit has determined that there is sufficient time for degassing supplied fresh water before water needs to be passed to the boiler.

According to at least another aspect of the invention, there is provided a control unit configured to carry out the steps of any of the above described methods (including any exemplary embodiment thereof) method according to any preceding claim, the control unit being configured to:.

The advantages provided by said control unit are largely analogous to the advantages provided by the previously disclosed method (including any exemplary embodiment thereof).

The control unit may include a microprocessor, microcontroller, programmable digital signal processor or another programmable device. The control unit may also, or instead, include an application specific integrated circuit, a programmable gate array or programmable array logic, a programmable logic device, or a digital signal processor. Where it includes a programmable device such as the microprocessor, microcontroller or programmable digital signal processor mentioned above, the processor may further include computer executable code that controls operation of the programmable device. The control unit is preferably configured for use with steam sterilizer systems, and provided with electronic instructions to perform and control any of the methods described herein.

According to at least yet another aspect of the present inventive concept there is provided a steam sterilizer system comprising the control unit according to the above-presented aspect (including any exemplary embodiment thereof), and further comprising a boiler and a sterilization chamber.

The advantages provided by said steam sterilizer system are largely analogous to the advantages provided by the previously disclosed control unit and the previously disclosed method (including any exemplary embodiments thereof).

In the following some additional aspects of the disclosure will be presented.

The skilled person realizes that different features of the present invention may be combined to create embodiments other than those described in the following, without departing from the scope of the claims.

The present invention will now be described more fully hereinafter with reference to the accompanying drawings, in which certain aspects of the system are shown. The system may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, the embodiments are provided by way of example so that this invention will be thorough and complete, and will fully convey the scope of the system to those skilled in the art.

<FIG> is a schematic view of a steam sterilizer system <NUM> according to at least one exemplary embodiment. On a general level, the steam sterilizer system <NUM> comprises a container <NUM>, a boiler <NUM> and a steam sterilizer <NUM>. Water from the container <NUM> can be delivered to the boiler <NUM>. The boiler <NUM> turns the delivered water into steam. The steam is then passed from the boiler <NUM> to the steam sterilizer <NUM>. The steam sterilizer <NUM> is schematically depicted by a dashed rectangle and it should be understood that the present approach is not limited to the use of any particular type of steam sterilizer, but may be implemented with any suitable steam sterilizer having a sterilizing chamber in which articles, such as medical goods, to be sterilized can be subjected to steam generated by the boiler <NUM>. An example of a steam sterilizer which could be used will be discussed later in connection with <FIG>.

Continuing with <FIG>, the boiler <NUM> may be provided with any suitable means for turning water into steam. For instance, the boiler <NUM> may be provided with one or more heating elements <NUM> within the boiler <NUM>. Furthermore, the boiler <NUM> may be provided with one or more level switches <NUM> for interrupting the filling of water into the boiler <NUM>.

The water may be fed to the boiler <NUM> from the container <NUM> by operating a pump <NUM> in order to pump water from the container <NUM>. The container <NUM> may have an inlet <NUM> for supplying fresh water into the container <NUM> and an outlet <NUM> for discharging water from the container <NUM>. The outlet <NUM> of the container <NUM> opens into a discharge passage <NUM> (conduit) which could be a pipe, tube, hose, or similar structure. The pump <NUM> is suitably provided in said discharge passage <NUM>. As explained previously in this disclosure, if the water that is fed to the boiler <NUM> contains non-condensable gases (NCGs), these will together with the steam generated by the boiler <NUM> be passed on to the sterilizing chamber of the steam sterilizer <NUM>. The presence of NCGs lowers the chances of achieving full steam penetration to all parts of the articles that are to be sterilized for the entire duration of a sterilization cycle. It is therefore desirable to remove most of the NCGs from the water before water is fed into the boiler <NUM>. To achieve this effect, the steam sterilizer system <NUM> comprises a degassing filter <NUM>.

The discharge passages <NUM> extends from the outlet <NUM> of the container <NUM> to the degassing filter <NUM>. The degassing filter <NUM> may be of standard type used for vacuum or sweep gas degassing in various technical fields where water processing is performed. The degassing filter <NUM> may have a shell side, where the water passes along a hydrophobic membrane, and a lumen side (dry side), which is the other side of the membrane. The lumen side may be connected to a vacuum tank <NUM> held at low pressure. The degassing filter <NUM> works by striving for equilibrium of the gases on both sides of the membrane and thus moves gas dissolved in the water through the membrane to the vacuum side, where the gas is removed due to the connection to the vacuum tank <NUM>. The water, however, does not pass through the membrane of the degassing filter <NUM>.

A vacuum tank <NUM> may be use to maintain a vacuum, which may be created by means of a vacuum pump, which may be part of a dedicated vacuum system or shared vacuum system (e.g. shared with the steam sterilizer <NUM>). Alternatively, the vacuum may be provided by a vacuum pump or system without a vacuum tank <NUM>.

The water that exits the degassing filter <NUM> may continue downstream of the degassing filter <NUM> along a feed passage <NUM> for feeding water into the boiler <NUM>. A first valve <NUM> may be provided in the feed passage <NUM> for controlling the flow of water through the feed passage <NUM>. In particular, the first <NUM> valve may be controlled to a closed state in order to prevent water from passing to the boiler <NUM> from the degassing filter <NUM> when the pump <NUM> is pumping the water from the container.

A recirculation passage <NUM> extends from a point <NUM> of the feed passage <NUM> upstream of the first valve <NUM>, but down of the degassing filter <NUM>. The recirculation passage <NUM> is used for recirculating water that has passed through the degassing filter <NUM>, back to the container <NUM>, so that the same water may be passed through the degassing filter <NUM> multiple times before allowing at least a portion of the circulated water to be fed to the boiler <NUM>. The container <NUM>, the discharge passage <NUM> and the recirculation passage <NUM> can thus be regarded as forming part of a circulation loop.

The steam sterilizer system <NUM> also comprises a control unit <NUM> which is configured to communicate with various components of the steam sterilizer system <NUM>, and is also configured to control the operation of certain components and to receive input signals from various components. The control unit <NUM> may be configured to communicate, send/receive instructions, etc. wirelessly or by wire. As such the control unit <NUM> is configured to perform the steps of the methods disclosed herein. The control unit <NUM> may be inside the same physical housing as the steam sterilizer <NUM>, but in principal, it can also be at other locations. The control unit can include electronics, processors, memory, electronic instructions, and other elements that are useful to control any of the systems and methods described in this disclosure.

<FIG> discloses schematically a method <NUM> according to at least one exemplary embodiment of the present inventive concept. In particular, <FIG> discloses a method <NUM> of controlling a steam sterilizer system comprising a boiler in which liquid water is turned into steam. The steam sterilizer system may, for instance, be the steam sterilizer system <NUM> presented in <FIG> or a different one.

If said method <NUM> is to be implemented for the steam sterilizing system <NUM> of <FIG>, the control unit <NUM> may suitably be configured to control the pump <NUM> so that water is pumped from the container <NUM> through the outlet <NUM>, along the discharge passage <NUM> and through the degassing filter <NUM>, where NCGs dissolved in the water would be removed as water passes through the degassing filter <NUM>. Thereby, the NCG content of the water becomes reduced. The control unit <NUM> may also control the first valve <NUM> to be actuated or maintained in a closed state, thereby closing off the feed passage <NUM>, and thereby preventing water from flowing from the degassing filter <NUM> to the boiler <NUM>. Instead water will be guided by the recirculation passage <NUM> back to the container <NUM> in order to recirculate the water through the degassing filter <NUM> for additional removal of NCGs. When sufficient degassing has been achieved, then the control unit <NUM> may control the first valve <NUM> to become actuated into an open state so that at least a portion of the water in the circulation loop can be delivered to the boiler <NUM>.

Although not illustrated in <FIG> the recirculation passage <NUM> may in at least some exemplary embodiments be provided with a second valve in order to prevent recirculation, for example, when water is fed to the boiler <NUM>. In other exemplary embodiments, however, the recirculation passage <NUM> may always be open, thus allowing some amount of water to be recirculated even when water is passed to the boiler <NUM>. In such case, the recirculation passage <NUM> may suitably be provided with a flow reducing orifice, so that the flow to the boiler <NUM> is larger than the flow back to the container <NUM>.

When executing the method steps disclosed herein, the control unit <NUM> may suitably execute the step (S2) of recirculating the water through the degassing filter <NUM> in such way that the water is recirculated through the degassing filter <NUM> so that the total volume that is passed through the degassing filter <NUM> before said at least a portion of the water is passed to the boiler <NUM> is at least double the volume of water that was initially present in the container <NUM> or in the circulation loop before starting to pump water from the container <NUM>.

In particular, the control unit <NUM> may continue to control the recirculation of the water through the degassing filter <NUM>, keeping the first valve <NUM> closed and continuing to operate the pump <NUM> so that the water circulates in the circulation loop, until a satisfactory degassing has been achieved. The control unit <NUM> may, for instance, continue the recirculation until it determines that the water has been circulated through the circulation loop, and thus through the degassing filter <NUM>, for at least a minimum time period, T1. Such a minimum time period T1 may, for instance, be available from a look-up table or may be calculated by the control unit <NUM>, for example based on the volume of water available in the circulation loop. A larger water volume may require a longer time period T1 than a smaller water volume to arrive at the desired low or zero NCG content in the water. Instead of, or as a supplement to, such a time-based recirculation control, the control unit <NUM> may instead execute a volume-based recirculation control. In the latter case, the control unit <NUM> controls the circulation of the water (operating the pump <NUM> and closing the first valve <NUM>) until at least a minimum number of cycles through the degassing filter <NUM> has been completed, i.e. the volume of water present in the circulation loop should have passed the degassing filter <NUM> a minimum number of times. For this purpose, there may suitably be provided a flow meter in the circulation loop.

In other exemplary embodiments, the control unit <NUM> may as an alternative or as a supplement, perform a pressure-based control of the recirculation. As illustrated in <FIG>, a pressure sensor <NUM> may be provided to monitor pressure, for example in the vacuum tank <NUM>. By monitoring the pressure rate of change, the control unit <NUM> may determine when the recirculating water has become sufficiently degassed, as discussed previously in this disclosure. <FIG> also illustrates that the steam sterilizer system <NUM> may, in at least some exemplary embodiments, be provided with a Total Dissolved Gas (TDG) sensor <NUM>, for example located in the discharge passage <NUM> between the pump <NUM> and the degassing filter <NUM>. The control unit <NUM> may then control the duration of the recirculation based on the NCG content measured by the TDG sensor <NUM>.

In addition to controlling that the duration of the recirculation is sufficient for adequate degassing, the control unit <NUM> may suitably also receive input from level sensors or level switches <NUM> of the boiler for determining that the liquid water level in the boiler <NUM> has sunk to or below a predefined water level, and that a new batch of water may be filled into the boiler <NUM> for steam generation. Thus, the control unit <NUM> may monitor the liquid water level in the boiler <NUM> and proceed from the step (S2) of recirculating the water through the degassing filter <NUM> to the step (S3) of passing at least a portion of the water to the boiler <NUM> when the liquid water level if the boiler <NUM> has reached or fallen below said predefined water level.

The control unit <NUM> may also perform control actions based on predictions. For instance, the control unit may, based on various input signals, including signals indicative of the water level in the boiler <NUM>, predict that the water level in the boiler <NUM> will within a predetermined time period T2 fall to or below said predefined water level. In such case, the control unit <NUM> may, for instance, close the inlet <NUM> of the container <NUM>, or close a further valve <NUM> at the inlet <NUM> of the container <NUM>, in order to prevent fresh water (carrying high NCGs) from being supplied to the container <NUM> until said predefined water level in the boiler <NUM> has been reached and degassed water from the container <NUM> has been passed to the boiler <NUM> to refill the boiler <NUM>. When the boiler <NUM> has been refilled, the control unit <NUM> may again enable fresh water to be supplied into the container <NUM>. As previously explained in this disclosure, in other exemplary embodiments, the fresh water may be supplied to the container <NUM> in other ways as well, for example upstream or downstream of the container <NUM> somewhere along the circulation loop. In such cases, the entry of fresh water into the circulation loop may similarly be closed to prevent fresh water from being supplied to the container <NUM>.

As should be understood from the above discussion, the control unit <NUM> may be configured to prevent fresh water (e.g. by closing the further valve <NUM>) from being supplied to the container <NUM> while water is recirculated through the degassing filter <NUM>, and to subsequently pass at least a portion of said water to the boiler <NUM>, and subsequently supplying fresh water to the container <NUM>.

In addition to receiving input about the water level in the boiler <NUM>, the control unit <NUM> may also receive input (e.g. from one or more level sensors or level switches <NUM>) about water level in the container <NUM>, and may determine whether or not it is appropriate to supply fresh water to the container <NUM>. In other words, the control unit <NUM> may monitor the water level in the container <NUM> and control the supply of fresh water to the container <NUM> based on the current water level in the container <NUM>. Typically, when the current water level in the container <NUM> has fallen to or below a predefined water level, the control unit <NUM> may decide to supply fresh water to the container <NUM>. Naturally, the control unit <NUM> may take other considerations into account as well, before deciding on supplying fresh water to the container <NUM>, such as if water is currently being fed to the boiler <NUM>, or expected to be fed to the boiler within a certain (short) time period, in which case the risk of fresh water having a high NCG content being blended with the degassed water already present in the circulation loop should suitably be avoided.

If the control unit <NUM> predicts that refilling the boiler <NUM> will not be required soon, then fresh water may suitably be provided to the container <NUM>. Conversely, if the control unit <NUM> determines that within a certain (short) period of time water will be required to be provided to the boiler <NUM>, then the control unit <NUM> may prevent the provision of fresh water to the container <NUM>.

It should be understood that after fresh water has been supplied to the container <NUM>, the water in the container <NUM> needs to be circulated and subjected to degassing. Therefore, the control unit <NUM> is configured to reiterate the pumping and recirculation of water through the degassing filter <NUM> while preventing water from flowing from the degassing filter <NUM> to the boiler <NUM> (i.e. keeping the first valve <NUM> closed while operating the pump <NUM> in the example shown in <FIG>).

Suitably, if the control unit <NUM> determines that after filling the boiler <NUM> with water, there is still sufficient remaining water in the container <NUM> (or in the circulation loop) for a subsequent batch when water will again be required to the boiler <NUM>, then the control unit <NUM> may suitably postpone supplying fresh water to the container <NUM>. For instance, the control unit <NUM> may be configured to monitor the water level in the container <NUM>, and prevent providing fresh water to the container <NUM> as long as the water level in the container <NUM> is above or equal to a predefined water level (indicative of a sufficient volume of water remaining in the container for at least another batch of water to be delivered to the boiler <NUM>). Subsequently to operating the boiler <NUM> to generate steam (and as long as the water level in the container <NUM> is above or equal to said predefined water level), the control unit <NUM> may control a further portion or portions of the water to be passed to the boiler <NUM> and operate the boiler <NUM> to turn said further portion or portions of the water into steam.

It should be understood that, normally, degassing will be more time-consuming then filling the container <NUM> with fresh water. Therefore, the control unit <NUM> may be programed to optimize the filling and/or the degassing based on the current needs and requirements from for example the boiler <NUM>. For instance, the control unit <NUM> may determine to only fill the container <NUM> halfway. Degassing half the water volume is expected to take approximately half the time compare to degassing the otherwise full water volume. This may be a strategy if the control unit <NUM> determines that the boiler <NUM> will shortly need refilling.

From the above, it should thus be understood that the general approach of recirculating the water through a degassing filter <NUM> (that is, passing the water through the degassing filter, on average, two or more times) before allowing at least a portion of the water to be delivered to a boiler (e.g. boiler <NUM> in <FIG>) will result in a lower amount of NCGs in the steam provided to a steam sterilizer (e.g. sterilizer <NUM> in <FIG>), thereby enabling an improved sterilization of articles such as medical goods. In addition to this concept of recirculating water through a degassing filter, other control actions may be included to further reduce the risk of an undesirable NCG content following the steam to the steam sterilizer. For instance, before filling the boiler with water, or at start-up, vacuum-puling in the boiler may be performed in order to remove air in the boiler to prevent air residuals to follow the steam to the steam sterilizer. Such vacuum-pulling is schematically indicated by the arrow above the boiler <NUM> in <FIG>.

<FIG> is a schematic diagram of a steam sterilizer <NUM> which could be used with the disclosed system <NUM> of <FIG>. Thus, the steam sterilizer <NUM> in <FIG> could suitably take the place of the generally indicated steam sterilizer <NUM> in <FIG>. However, other steam sterilizers are also conceivable.

The steam sterilizer <NUM> comprises a sterilization chamber <NUM>. Steam from the boiler <NUM> is passed through an inlet <NUM> into the sterilization chamber <NUM>. A drain system <NUM> is provided for controlling the discharge of fluid from the sterilization chamber <NUM> via an outlet <NUM>. A vacuum system <NUM> (which may be a separate vacuum system or shared with the degassing arrangement in <FIG>) is connected to the drain system <NUM> for evacuating the steam from the sterilization chamber <NUM> and condensing the evacuated steam using a flow of coolant <NUM>. The control unit <NUM> may be configured to control the flow of steam from the boiler <NUM> to the sterilization chamber <NUM> via a controllable valve <NUM>. The control unit <NUM> may use information received from a temperature sensor <NUM> in the flow of coolant <NUM> to determine the amount of steam/condensate admitted from the sterilization chamber <NUM> to the drain system <NUM>. The control unit <NUM> may receive other input signals than temperature signals. For instance, the control unit <NUM> may monitor the pressure inside the sterilization chamber <NUM> by means of a pressure sensor <NUM> configured to detect the pressure inside the sterilization chamber <NUM>.

Claim 1:
A method of controlling a steam sterilizer system (<NUM>) comprising a boiler (<NUM>) in which liquid water is turned into steam, the method comprising:
- pumping water from a container (<NUM>) and passing the pumped water through a degassing filter (<NUM>) located upstream of the boiler (<NUM>) in order to remove non-condensable gases (NCGs) dissolved in the water,
- subsequently to passing the water through the degassing filter (<NUM>), recirculating the water through the degassing filter (<NUM>) for additional removal of NCGs, while preventing water from flowing from the degassing filter (<NUM>) to the boiler (<NUM>), and
- subsequently to recirculating the water through the degassing filter (<NUM>), passing at least a portion of the water to the boiler (<NUM>).