Abstract:
There is disclosed a steam oven installation, that in certain embodiments, comprises: a steam oven; a supply steam line for receive a superheated steam flow and for delivering supply steam to the steam oven; an injector for injecting a volume of control fluid into the supply steam line; a monitor for monitoring at least one thermodynamic property of steam within the steam oven installation; and a controller for controlling the injection of the control fluid based on the at least one monitored thermodynamic property so that the supply steam flow delivered into the steam oven comprises substantially dry saturated steam. There is also disclosed a corresponding method of controlling the supply of steam to a steam oven in a steam oven installation.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    The present application claims priority to GB 1400807.2, filed on 17 Jan. 2014, which is hereby incorporated by reference in its entirety for any and all non-limiting purposes. 
       BACKGROUND 
       [0002]    The invention relates to a steam oven installation having a steam oven. The invention also relates to a method of controlling the supply of steam to a steam oven in a steam oven installation. 
         [0003]    It is known to provide a steam oven for cooking, amongst other things, foodstuffs. However, it can be difficult to precisely control the conditions within the steam oven. Previously considered steam oven installations allow the flow rate of steam delivered to a steam oven to be adjusted. However, such installations do not allow precise control of the steam conditions within the steam oven. Accordingly, it is desirable to provide an improved steam oven installation. 
       SUMMARY 
       [0004]    According to a first aspect of the invention there is provided a steam oven installation comprising: a steam oven; a supply steam line for receiving a superheated steam flow and for delivering supply steam to the steam oven; an injector for injecting a volume of control fluid into the supply steam line; a monitor for monitoring at least one thermodynamic property of steam within the steam oven installation; and a controller for controlling the injection of the control fluid based on the at least one monitored thermodynamic property so that the supply steam flow delivered into the steam oven comprises substantially dry saturated steam. The steam oven installation is therefore configured to control the enthalpy of the supply steam. 
         [0005]    Dry saturated steam is steam at saturation temperature and in the absence of saturated liquid water, and is typically represented in steam charts by the “dry saturated steam” or “saturated steam” line. Substantially dry saturated steam is steam close to or on the dry saturated steam line, i.e. with a dryness approaching 100% or a small level of superheat. 
         [0006]    The steam installation may further comprise a static mixer for mixing the control fluid with the superheated steam flow. The injector and the mixer may be a single unit. The injector and the mixer may be integrally formed. 
         [0007]    The monitor may comprise at least one sensor. A sensor may be disposed in the supply steam line downstream of the injector. In this regard, certain embodiments may capture data with various electronic sensors and/or devices. In other embodiments, the present invention can be partially or wholly implemented on a tangible non-transitory computer-readable medium, for example, by storing computer-executable instructions or modules. Of course, the methods and systems of embodiments may also include other additional elements, steps, computer-executable instructions, or computer-readable data structures. 
         [0008]    The steam oven installation may further comprise at least one nozzle for ejecting the supply steam into the steam oven. A sensor may be disposed within the steam oven adjacent to the nozzle. 
         [0009]    The monitor may comprise at least one temperature sensor for monitoring the temperature of the supply steam flow. The monitor may comprise at least one pressure sensor for monitoring the pressure of the supply steam flow. 
         [0010]    The monitor may comprise at least one steam dryness sensor for monitoring the steam dryness of the supply steam flow. 
         [0011]    The controller may be arranged to control an injection flow rate at which the control fluid is injected into the supply steam line. The controller may be configured to control the injection of the control fluid so that the supply steam flow delivered into the steam oven is at least at the saturation temperature of the steam and no more than 5° C. above the saturation temperature of the steam. The controller may be configured to intermittently inject control fluid into the supply steam line. 
         [0012]    The supply steam flow delivered into the steam oven may be determined to be substantially dry saturated steam when the temperature of the steam is at least the saturation temperature and no more than 1° C., 2° C., 5° C. or 10° C. above the saturation temperature. Further, the supply steam flow delivered into the steam oven may be determined to be substantially dry saturated steam when the steam dryness is no less than 95%, no less than 98%, no less than 99% or 100%. 
         [0013]    The controller may be configured to control the injection of the control fluid based on the properties of supply steam flow at a monitoring point upstream of the nozzle so that the supply steam flow delivered into the steam oven comprises substantially dry saturated steam. 
         [0014]    The injector may be arranged to inject water as the control fluid into the supply steam line. 
         [0015]    The monitor may be arranged to continually or periodically monitor the at least one thermodynamic property. The controller may be configured to continuously or periodically control the injection of the control fluid. 
         [0016]    The steam oven installation may further comprise a supply steam controller which is arranged to control the delivery of the supply steam flow to the steam oven to ensure that steam leaks from the inlet and/or the outlet based on a steam leakage determining module which is arranged to determine whether steam is leaking from the inlet and/or the outlet of the steam oven. 
         [0017]    The supply steam controller may be arranged to increase the steam flow rate at which the supply steam flow is delivered into the steam oven if the steam leakage determining module determines that steam is not leaking from the inlet and/or the outlet of the steam oven. 
         [0018]    The steam leakage determining module may comprise a temperature sensor for monitoring the temperature in the region of the inlet and/or the outlet. 
         [0019]    The steam oven installation may further comprise a conveyor for conveying articles through the steam oven. 
         [0020]    According to a second aspect of the invention there is provided a method of controlling the supply of steam to a steam oven in a steam installation, comprising: injecting a volume of control fluid into a superheated steam flow and delivering the resultant supply steam flow into the steam oven; monitoring at least one thermodynamic property of steam within the steam installation; and controlling the injection of the control fluid based on the at least one monitored thermodynamic property such that the supply steam flow delivered into the steam oven comprises substantially dry saturated steam. The enthalpy of the supply steam delivered into the steam oven is therefore controlled. 
         [0021]    The method may further comprise mixing the control fluid with the superheated steam flow. 
         [0022]    Monitoring the at least one thermodynamic property of the steam may comprise monitoring the temperature of the supply steam flow. Monitoring the at least one thermodynamic property of the steam may comprise monitoring the steam dryness of the supply steam flow. Monitoring the at least one thermodynamic property of the steam may comprise monitoring the pressure of the supply steam flow. 
         [0023]    The supply steam flow may be delivered through at least one supply steam line to the steam oven where it is ejected into the steam oven through at least one nozzle. 
         [0024]    The at least one thermodynamic property of the supply steam flow may be monitored in the supply steam line downstream of the injection of the control fluid. The at least one thermodynamic property of the supply steam flow may be monitored within the steam oven adjacent to a nozzle. 
         [0025]    Controlling the injection of the control fluid may comprise controlling an injection flow rate at which the control fluid is injected into the superheated steam flow. 
         [0026]    The injection of the control fluid may be controlled such that the supply steam delivered into the steam oven is at least at the saturation temperature of the steam and no more than 5° C. above the saturation temperature of the steam. The method may comprise intermittently injecting the control fluid. 
         [0027]    The injection of the control fluid may be controlled based on the properties of supply steam flow at a monitoring point upstream of the nozzle so that the supply steam flow delivered into the steam oven comprises substantially dry saturated steam. 
         [0028]    The control fluid may be water. 
         [0029]    The at least one thermodynamic property may be continually or periodically monitored. The injection of the control fluid may be continuously or periodically controlled. 
         [0030]    The method may further comprise determining whether steam is leaking from the inlet and/or outlet of the steam oven, and based on this, controlling the delivery of the supply steam to the steam oven to ensure that steam leaks from the inlet and/or outlet. The method may comprise increasing the steam flow rate at which supply steam flow is delivered into the steam oven if it is determined that steam is not leaking from the inlet and/or outlet of the steam oven. 
         [0031]    Determining whether steam is leaking from the inlet and/or outlet of the steam oven may comprise monitoring the temperature in the region of the inlet and/or outlet. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0032]    The invention will now be described, by way of example, with reference to the following drawings, in which: 
           [0033]      FIG. 1  schematically shows a first embodiment of a steam oven installation according to the invention; and 
           [0034]      FIG. 2  schematically shows a second embodiment of a steam oven installation according to the invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0035]      FIG. 1  shows a steam oven installation  10  comprising a steam oven  12  and a supply steam line  14  arranged to provide supply steam to the steam oven  12  via an ejector header  16  extending into the steam oven  12 . In use, the enthalpy of the steam within the steam line  14  is controlled by a controller  22  such that the supply steam delivered into the steam oven  12  is substantially dry saturated steam. 
         [0036]    The steam oven  12  has an inlet  26  and an outlet  28 , and a conveyor  30  extends from the inlet  26  to the outlet  28  for conveying foodstuffs into, through and out of the steam oven  12 . In this embodiment, the inlet  26  and the outlet  28  are at least partially open such that a leakage flow of steam may flow from within the steam oven  12  out of the inlet  26  and/or the outlet  28 . 
         [0037]    The ejector header  16  is arranged to receive supply steam from the steam line  14  and distribute it into the steam oven  12 . The ejector header  16  is coupled to the steam line  14  outside of the steam oven, and has a series of distribution pipes extending into the steam oven  12  terminating at nozzles  18  for ejecting the supply steam into the steam oven  12 . The distribution pipes of the ejector header  16  are all of the same length and are arranged to effect the same pressure drop of the supply steam within the steam line  14 . 
         [0038]    The steam oven installation is configured to control the enthalpy of the supply steam flow, as described in detail below. 
         [0039]    The steam line  14  is coupled to a source of superheated steam  50  so as to receive superheated steam. Superheated steam is steam that is at a temperature higher than the saturation temperature (which is dependent on the pressure of the steam). In this embodiment, the steam line  14  is arranged to receive superheated steam marginally above atmospheric pressure (e.g. 0.2 bar gauge), and so the saturation temperature is marginally above 100° C. (e.g. 105° C.). In other embodiments, the source of superheated steam may be at atmospheric pressure or pressurised (e.g. by 1 bar gauge) and subsequently expanded within the steam line  14  and/or upon entry into the steam oven  12 . 
         [0040]    A steam flow valve  32  is disposed in the steam line  14  for controlling the flow of superheated steam in the steam line  14 . The steam flow valve  32  is controlled by a steam flow controller  34 , which is configured to adjust the steam flow rate at which steam flows through the steam flow valve  32 . 
         [0041]    The steam flow controller  34  is coupled to steam leakage determining modules  36 ,  38  disposed adjacent to the inlet  26  and the outlet  28  of the steam oven  12  respectively. In this embodiment, the steam leakage determining modules  36 ,  38  comprise temperature sensors arranged to monitor the temperature in the region of the inlet and the outlet  26 ,  28 . In this embodiment, the steam flow controller  34  is configured to receive temperature signals from the steam leakage determining modules  36 ,  38  and to determine whether steam is leaking from the inlet  26  and/or outlet  28  respectively depending on whether the respective temperature signal is above a threshold. In this embodiment, the threshold is marginally below the saturation temperature, for example, 1° C. below (i.e. 99° C. when the steam oven operates at atmospheric pressure). 
         [0042]    The steam flow controller  34  is configured to increase the steam flow rate if it is determined that steam is not leaking from the inlet  26  and/or the outlet  28 . Conversely, the steam flow controller  34  is configured to maintain or periodically reduce the steam flow rate if it is determined that steam is leaking from both the inlet  26  and the outlet  28 . The presence of a leakage flow from the inlet and outlet indicates that the steam oven chamber is fully occupied with steam. 
         [0043]    An injector  20  is disposed in the steam line  14  downstream of the steam flow valve  32 , and is arranged to inject a control fluid, which in this embodiment is water, with the superheated steam flow to provide the supply steam flow for the steam oven  12 . 
         [0044]    In this embodiment the injector  20  includes a static mixer that is configured to mix the control fluid (water) with the superheated steam flow to provide a homogeneous mix of water droplets and steam. In this embodiment the static mixer comprises a series of elements for repeatedly dividing and subsequently turbulently mixing the flow. In other embodiments, the mixer may be arranged to mix by virtue of turbulence alone, for example it may comprise an orifice plate, or may be formed by the convolutions (or corrugations) within a flexible hose. Further, the mixer may be a separate unit provided downstream of the injector. 
         [0045]    The water is provided from a water supply  52  to the injector  20  via a water line  40 . A water flow control valve  41  is disposed in the water line  40  for controlling the flow of water to the injector  20 . The water flow control valve  41  is controlled by a water controller  42  of the controller  22 , which is configured to adjust the injection flow rate of water into the injector  20 . 
         [0046]    The water controller  42  is coupled to a monitor  44  arranged to monitor at least one thermodynamic property of steam within the steam oven installation, and is configured to determine whether the supply steam delivered into the steam oven  12  is substantially dry saturated steam. 
         [0047]    In this embodiment, the monitor  44  is a temperature sensor disposed adjacent to an ejector nozzle  18  of the ejector header  16 . It will be appreciated that in other embodiments the monitor  44  may comprise a plurality of temperature sensors disposed adjacent to respective ejector nozzles  18  of the ejector header  16 . The monitor  44  may further comprise one or more pressure sensors so that the saturation temperature within the steam oven  12  may be determined. The water controller  42  is configured to receive a temperature signal from the monitor  44  and determine whether the supply steam flow delivered to the steam oven  12  is substantially dry saturated steam depending on whether the temperature signal is at or above a lower threshold and at or below an upper threshold. The lower threshold and upper threshold are set with respect to the saturation temperature of the supply steam, which in this embodiment is 100° C. as the steam oven  12  operates at atmospheric pressure. 
         [0048]    The water controller  42  is configured to increase the injection flow rate at which water is supplied to the injector  20  if it is determined that the temperature of the supply steam flow is above the upper threshold, and is configured to decrease the injection flow rate of water to the injector if it is determined that the temperature of the supply steam flow is below the lower threshold. 
         [0049]    Operation of the steam oven installation will now be described. In the following description, given values of steam properties are provided by way of example only. 
         [0050]    In a start-up phase of operation, the steam oven  12  is cool. A supply of superheated steam at 0.2 bar gauge pressure and at a temperature of 110° C. is provided to the steam line  14 . The saturation temperature of steam at 0.2 bar gauge is approximately 105° C., and so the steam is superheated. The steam flow controller  34  controls the steam flow valve  32  to allow steam to flow to the injector  20  and into the steam oven  12  via the ejector header  16 . 
         [0051]    The water controller  42  periodically determines the properties of the steam flow delivered into the steam oven  12  by monitoring the temperature signal from the temperature sensor  44  at a frequency of once every 10 seconds. The lower threshold temperature is set at 100° C. and the upper threshold temperature is set at 102° C. In other embodiments, different lower and upper thresholds may be set, for example, they may be 100° C. and 104° C. respectively, or 102° C. and 105° C. respectively. 
         [0052]    The water controller  42  periodically controls the water flow control valve  41  to adjust the injection flow rate until the water controller  42  determines that the temperature of the supply steam delivered into the steam oven  12  lies between the lower and upper thresholds. 
         [0053]    In this embodiment the superheated steam is received above atmospheric pressure at 0.2 bar gauge. Accordingly, when water is injected and mixed with the superheated steam at the injector  20  the resultant supply steam is a homogeneous mix of water droplets and steam (i.e. wet steam). As the pressure of the supply steam is reduced in the steam line  14  and in the distribution pipes of the ejector header  16 , the steam undergoes isenthalpic expansion and vaporises the surrounding water droplets, rather than becoming superheated. The water controller  42  controls the injection of water such that the supply steam expands to substantially dry saturated steam at atmospheric pressure upon delivery into the steam oven. 
         [0054]    The steam controller  34  of the controller  22  periodically determines whether steam is leaking from the inlet and/or the outlet at a frequency of once every 10 seconds based on the signals provided by the steam leakage determining modules  36 ,  38 . In the start-up condition, there will be no leakage flow. Accordingly, the steam controller  34  controls the steam flow valve  32  to adjust the steam flow rate until the steam controller  34  determines that steam is leaking from both the inlet  26  and the outlet  28 . In other words, the steam controller  34  controls the steam flow valve  32  to increase the steam flow rate until it is determined that the temperature signals from the steam leakage determining modules  36 ,  38  correspond to a leakage flow temperature greater than the lower leakage threshold, which in this embodiment is marginally below the saturation temperature (e.g. 1° C. below, or 99° C. when the steam oven operates at atmospheric pressure). 
         [0055]    The steam controller  34  may periodically execute an economising operation in which it controls the steam flow valve  32  to reduce the steam flow rate until it is determined that steam is not leaking from at least one of the inlet  26  and the outlet  28 , and then once more increases the steam flow rate a sufficient amount so that steam leakage is determined at both the inlet  26  and the outlet  28 . This economising operation ensures that the steam flow rate is not unnecessarily high. 
         [0056]    The steam controller  34  and the water controller  42  of the controller  22  continue to periodically monitor the steam flow and control the enthalpy of the supply steam so as to maintain the delivery of substantially dry saturated steam into the steam oven  12  throughout operation of the steam installation  10 . 
         [0057]      FIG. 2  shows a second embodiment of the invention which differs from the first in that the monitor  44 ′ comprises a sensor disposed in the steam line  14  downstream of the injector  20  and upstream of the ejector nozzles  18 . 
         [0058]    The properties of the supply steam may change between the monitor  44 ′ and the ejector nozzles  18 . For example, the supply steam may be superheated at the monitor  44 ′, and may be cooled to provide substantially dry saturated steam at the ejector nozzles  18 . 
         [0059]    As with the first embodiment, the pressure within the steam line  14  may be higher than the pressure in the steam oven  12 . Accordingly, the supply steam within the steam line may comprise wet steam (i.e. a mixture of saturated steam and saturated liquid water at saturation temperature) at a first high pressure (for example, 0.2 bar gauge), and subsequently expand within the steam line or upon entry into the steam oven chamber to atmospheric pressure to provide substantially dry saturated steam at the ejector nozzles  18 . 
         [0060]    As with the first embodiment, the water controller  42  and the monitor  44 ′ are calibrated to control the injection of water based on lower and upper thresholds for steam properties monitored by the monitor  44 ′, which are set to correspond to the delivery of substantially dry saturated steam into the steam oven. 
         [0061]    In this embodiment, the monitor  44 ′ comprises a steam dryness sensor, and the lower and upper thresholds are therefore lower and upper thresholds of steam dryness. 
         [0062]    In one example mode of operation, the pressure of the steam at the monitor  44  is 0.2 bar gauge, and the pressure within the steam oven  12  is atmospheric pressure. The lower and upper thresholds in this embodiment are 90% and 95% steam dryness respectively, and so the supply steam at the monitor  44 ′ is wet steam, but will expand in the steam line  14  and ejector header  16  to form substantially dry saturated steam. 
         [0063]    Accordingly, the controller  22  controls the enthalpy of the supply steam at a point upstream of the steam oven  12  to reach particular conditions which correspond to the downstream delivery of substantially dry saturated supply steam into the steam oven  12 . 
         [0064]    An advantage of the invention is that the supply of steam to the oven can be controlled to ensure that the steam within the oven is substantially dry saturated steam. Substantially dry saturated steam may be desirable for a steam oven because it enables a high rate of heat transfer between the steam and the articles within the oven, such as foodstuffs. Further, unlike superheated steam, substantially dry saturated steam will not dry the foodstuffs. 
         [0065]    It will be appreciated that the term “substantially saturated” is intended to cover the region on and around the dry saturated steam line of a steam chart. This typically includes wet steam which has a high steam dryness (e.g. at least 90%, at least 95%, at least 98%, at least 99% or 100%). Further, it typically includes steam that is 100% dry having a relatively low level of superheat (i.e. a temperature above the saturation temperature), such as up to 1° C., up to 2° C., up to 5° C. or up to 10° C. of superheat. 
         [0066]    The mixer, provided integrally with the injector or downstream of it, ensures a homogeneous mix of water droplets and steam in the supply line. Since the various distribution pipes of the ejector header are of the same length and, as a consequence, configured to effect the same pressure drop, this ensures that in each pipe (or branch) the steam expands in the same way to form substantially dry saturated steam. 
         [0067]    Although embodiments of the invention have been described in which there are two steam leakage determining modules at the inlet and outlet of the steam oven respectively, it will be appreciated that in other embodiments there may be a single steam leakage determining module or there may be more than two steam leakage determining modules. 
         [0068]    Although embodiments of the invention have been described in which the steam flow controller determines whether steam is leaking from the inlet and/or the outlet of the steam oven based on a temperature signal from a respective steam leakage determining module, it will be appreciated that in other embodiments the steam leakage determining module may determine whether steam is leaking and communicate that determination to the steam flow controller. 
         [0069]    Although embodiments of the invention have been described in which superheated steam is received in the steam line at approximately atmospheric pressure, it will be appreciated that in other embodiments superheated steam may be received at a positive gauge pressure, and may be expanded in the steam line or upon entry to the steam oven. Further, the superheated steam may be at higher pressure upstream of the steam flow valve, and may expand as it flows through the steam flow valve.