Abstract:
A procedure and apparatus for generating steam for an autoclave or an equivalent device, so that the load of the autoclave or device can be equalized. Thermal energy is stored in water under pressure which is converted when needed into steam which, in turn, is accumulated and later purified. The present invention also concerns the use of the procedure and apparatus to equalize load in the autoclave or device.

Description:
BACKGROUND OF THE INVENTION 
     The present invention concerns procedure and means for generating and accumulating steam for an autoclave or equivalent device, with which the load of the autoclave or equivalent device can be equalized. The present invention is also directed to the use of such procedure and means for equalizing the load of the autoclave or equivalent steam-operated apparatus. 
     In hospitals and in the pharmaceutical industry, instruments are presently sterilized with steam in an autoclave, this steam being generated in boilers from ordinary, softened tap water. When a steam space of a steam generator is connected with the autoclave which is under vacuum, the pressure is equalized in a moment, and as the pressure quickly drops, the water in the steam generator boils with frothing. Such froth may then also contaminate the objects being sterilized which are lodged in the autoclave. The droplets in the froth contain salts, rust, dead bacteria and germs, in addition to pyrogenic substances, which are normally present in drinking water. The impure steam carries these above-noted substances onto the goods being sterilized, which may, e.g., cause fever or infection in patients being operated upon. 
     In order to achieve a sufficient pressure for sterilizing in a short period of time in the autoclave, a steam generator with a high maximum output is required. 
     In order to prevent some of the above-noted problems, a filter has been used in the prior art for purifying steam. However, the filter tends to become clogged and fails to eliminate the drawbacks which result from the periodic steam discharge. 
     SUMMARY OF THE INVENTION 
     Accordingly, it is an object of the present invention to purify steam to a sufficient degree of purity for meeting requirements of injection solutions, and to prevent access of impure steam to substances being sterilized or into an autoclave and other equipment related to drug preparation and to sterilization, such as distribution pipe systems and ventilation apparatus. 
     It is also an object of the present invention to regulate power consumption of an autoclave or equivalent device as uniformly as possible, so that the autoclave or device will not draw high peak loads from the mains. 
     Accordingly, these and other objects are attained by the present invention which is directed to a procedure for generating and accumulating steam for an autoclave or equivalent steam-operated device, which comprises the steps of storing thermal energy in water that is under pressure, turning at least part of the water stored under pressure into steam as required, and accumulating the steam for use in the autoclave or equivalent device as needed, so that load of the autoclave or device can be equalized by introducing the steam thereinto. Additionally, the accumulated steam may be passed through a purifyer to purify the same, prior to introduction into the autoclave or equivalent device. 
     The present invention is also directed to apparatus for generating and accumulating steam for equalizing load in an autoclave or equivalent steam-operated device, which comprises a boiler or tank for containing water under pressure, means for feeding the water into the boiler or tank, means for heating the water in the boiler or tank, and means for accumulating the steam generated from the water in the tank or boiler. Additionally, means for generating steam from the water inside the boiler or tank are provided. In particular, the feeding means comprise a pump and the heating means comprise a heating element, with a steam withdrawal outlet from the boiler or tank being provided, along with a purifier for purifying the steam generated in the boiler or tank and coupled to the steam withdrawal outlet. 
     For achieving the above-noted objects, the procedure of the present invention is principally characterized by heat energy being stored in water under pressure higher than atmospheric pressure and being turned into steam therefrom as required, such steam being accumulated and later purified with the aid of a purifyer. 
     Apparatus or means of the present invention is characterized by comprising a boiler in which the thermal energy is stored in water under pressure, a heating element for heating the water, a pump for supplying the water to the boiler, centrifugal purifier for purifying the generated steam, members for accumulating steam and a steam withdrawal outlet. 
     The present invention is also directed to a procedure for equalizing the load of an autoclave or equivalent steam-operated apparatus, which comprises the use of the above-noted procedure and/or the above-noted means/apparatus. 
     The steam generator and accumulator of the present invention comprises a sufficiently large tank and a small heating element. The tank capacity contains, e.g., about two thirds water, about one third being reserved for the steam. The pressure that is used has to be considerably greater than the sterilizing pressure, e.g. about 8 bar. The energy is latent in the water in the form of heat capacity, and when the pressure in the boiler falls or the connection to the vacuum in the autoclave is opened, the water is converted into steam. The steam thus-generated is stored in the apparatus and is purified in a manner known per se in the art, e.g. in centrifugal means or in a purifier of another type. 
     If, for example, a 130 dm 3  steam autoclave is used, it operates normally with 25 kW boiler power, while due to the present invention, only 5 kW are needed for the boiler. When this power input of the apparatus is maintained, its pressure will only fall to a critical level when the autoclave is used 8 to 10 hours per twenty four hours. The steam generator of the present invention may be used in two ways: either with overnight charging or periodically. For example, the load of the autoclave or equivalent steam-operated apparatus is equalized on a twenty-four hour basis. 
     If, for example, 6 kW power input is used, sterilization can be continued around the clock, the normal breaks associated with working stretches being taken into consideration. In this case, a uniform loading will be achieved which is about 4.5 kW per 100 liters of chamber volume. It is also feasible to construct large chambers designed for 1/4 power and operated on a round-the-clock uniform basis. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention will be described in greater detail below, with the aid of the accompanying drawings, and to which, however, the present invention is not intended to be restricted. In the drawings, 
     FIG. 1 is a schematic, cross-sectional view of an embodiments of the means or apparatus of the present invention, in which a heating element is connected inside a boiler and a centrifugal purifier is connected outside of the boiler; 
     FIG. 2 illustrates a pressure graph of an autoclave chamber in accordance with the present invention; 
     FIG. 3 illustrates a steam consumption graph of an autoclave used in conjunction with the means and procedure of the present invention; and 
     FIG. 4 is a graph illustrating coupling and loading of an autoclave boiler in accordance with the present invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In FIG. 1, the means or apparatus of the present invention is generally denoted by reference numeral 1, said means containing water 4 about 2/3 of the volume of a tank 5, while the remainder of the tank 5 is reserved as a steam space 8 as illustrated. This energy is in latent form in the water 4, constituting the heat capacity of the water. When the pressure drops, the energy is converted to free steam. The water does not boil violently in the procedure of the present invention, and therefore, the released steam does not contain water drops. The heating element, with which the water 4 is heated to the requisite temperature, and which, in the embodiment illustrated in FIG. 1 is connected inside the boiler 5, is denoted by reference numeral 2. Alternatively, the heating element 2 may be connected outside of the boiler 5. 
     The pump with which water 4 is fed into the tank or boiler 5, is denoted by reference numeral 6. The steam stored in the apparatus and taken from boiler 5 through an outlet 7, is purified with a centrifugal purifier denoted by reference numeral 3. When the steam exits from the centrifugal purifier 3, further along a pipe or outlet 7 as illustrated, the degree of purity meets the standard which is required of water intended for injection solutions. The purifier, advantageously a centrifugal purifier, is connected out-side of the boiler 5 as illustrated in FIG. 1. However, the purifier may alternatively be connected in conjunction with the boiler 5 itself, i.e. inside thereof. 
     FIG. 2 presents a pressure graph of the autoclave. As described above, the pressure can be made to conform without delay to this graph, with the aid of the steam accumulator 1 of the present invention. Without the steam accumulator 1, the steam from the boiler will not suffice to produce the rapid pressure elevation (graph a) and the sterilizing time will be prolonged if the temperature rises slower (graph b). Plot (b) is denoted as a dotted line in FIG. 2. 
     FIG. 3 illustrates a steam consumption graph of an autoclave used in conjunction with the steam generator 1 of the present invention, plotted over time. Before sterilization, the apparatus is allowed to be preheated for a period of time indicated by t 1 , at the beginning of which, when the autoclave is switch on, the steam consumption is greatest, and after which the steam consumption quickly decreases to a given, relatively low level as illustrated. The actual sterilizing time is denoted by t 2 , in the course of which the steam consumption after first rising steeply, reaches its peak, after which the steam consumption again descends steeply, being at a given, relatively low level during the drying process which is denoted by t 3 . 
     It is thus understood that the steam consumption of the autoclave has two peaks during the sterilizing process: the first and smaller peak occurring while the autoclave is being preheated (t 1 ) when the autoclave is started; and the second peak during the actual sterilization (t 2 ). With the aid of the steam accumulator 1 of the present invention, steam at sufficiently high pressure is available for the autoclave at all times, this being very important in view of speedy processing. In other words, only the peak loads of the autoclave or equivalent steam-operated apparatus need be equalized with the present invention herein. 
     FIG. 4 illustrates an example of the autoclave boiler load graph as plotted over time. The highest power demand of the steam autoclave (about 25 kW) is indicated by a solid line (f). A 25 kW boiler was previously needed (f) for the problem solution of the prior art. During pre-heating of the autoclave, the power uptake varies from zero to the highest value. During sterilization, the power is at its maximum, being variable again from zero to maximum during drying. The power uptake while the steam generator is on (c) and during the so-called off times (d) is illustrated in FIG. 4 with dotted lines for the exemplary case. This power demand can be levelled out with the steam generator 1 and the procedure of the present invention, at about 6 kW (e) in the present example, whereby only 6 kW continuous power consumption is required. 
     The apparatus and procedure described above may be used as a steam source for other purposes, such as heating, air or gas humidifying, etc., where sterile particle-free and pyrogen-free steam is needed. 
     A few examples in which the steam generator of the present invention is used in conjunction with a sterilizing autoclave, are presented below. The results are presented in Tables 1 and 2. 
     The preceding description of the present invention is merely exemplary, and is not intended to limit the scope thereof in any way. 
     
                                           TABLE 1__________________________________________________________________________          Sterilization No.          1     2  3  4  5  6  7    8__________________________________________________________________________SteamFeed water quan-          200   188                   182                      178                         173                            169                               164  156Accumu-tity in column (1)latorHeating time (min)          11Pressure before          6.2   5.0                   4.5                      4.0                         3.6                            3.3                               3.0  3.8sterilizing (bar)Pressure after          5.0   4.5                   4.0                      3.6                         3.3                            3.0                               2.5sterilizing (bar)Condensate          10    0.5                   0.5                      0.5                         0.5                            0.5                               0.5quantity (1)Condensatetemperature (°C.)Steam conduc-tivity (μS/cm)Remarks   During the           No more                                    Heat-          preheating           transi-                                    ing of          time the             tion to                                    steam          pressure             steri-                                    gener-          fell 7.5             lizing                                    ator,          to 6.2 bar                no                                    steriliz.Sterilization          09.25 09.55                   10.30                      11.05                         11.35                            12.07                               12.37                                    14.40starting timeAuto-Steam     2.4   2.4                   2.4                      2.4                         2.4                            2.4                               2.4  2.4clavepressure (bar)Sterilizing          12    12 12 12 12 12 12   12time (min)Total time (min)          30    30 30 30 30 30 30   30Remarks   Pre-          heating          time          25 min.          Cold          chamber!__________________________________________________________________________ At the end, 161 l water in the apparatus. Interruption of run at 13.00 hrs. 
    
     
                                           TABLE 2__________________________________________________________________________          Sterilization No.          1   2  3  4  5  6  7  8  9  10__________________________________________________________________________SteamFeed water quan-          192 182                 178                    173                       164                          169                             158                                151                                   147                                      143Accum-tity in column (1)latorHeating time (min)          Warm          jacketPressure before          7.9 7.2                 7.0                    6.6                       6.4                          6.2                             6.5                                6.2                                   6.0                                      6.1sterilizing (bar)Pressure after          7.2 7.0                 6.6                    6.4                       6.2                          6.5                             5.2                                6.0                                   6.1                                      6.0sterilizing (bar)Condensate           1  0.5                 0.5                    0.5                       0.5quantity (1)Condensatetemperature (°C.)Steam conduc-          0.8 0.5                  0.45                    -- 0.6                          --    0.5tivity    (μS/cm)RemarksSterilization          08.10              09.22                 09.55                    10.25                       10.55                          13.30                             12.12                                12.55                                   13.27starting timeDuringSteam     2.4 2.1                 2.1                    2.1                       2.2                          2.2                             2.2                                2.2                                   2.2                                      2.2Steril.pressure (bar)Auto-Sterilizing          12  12 12 12 12 12 12 12Clavetime (min)Total time (min)          70  30 30 30 30 30 30 30 30 30Remarks   Auto-          clave          temp.          adjusted          to cor-          rect          value__________________________________________________________________________ In the evening at 16.00 hrs, 250 l water in the column. Autoclave jacket hot through the night. Power of heating resistances, 6 kW. During the night, about 13 l condensate came from the centrifugal separator. Note: In the evening, feed water cold; pressure 0.