Oxygen enriched gas supply arrangement for combustion.

0001The present invention relates to an oxygen enriched gas supply arrangement for combustion purpose.

0002Recently, there has been a tendency towards a remarkable rise in energy cost, and energy saving or conservation is strongly demanded with respect to equipment and appliances which utilize energy. Particularly, with respect to combustion appliances, internal combustion engines, external combustion engines, etc. which directly emolov energy in the form of fuels. various attempts have been made for the improvement of combustion efficiency thereof, one of which attempts is represented by an oxygen enriched combustion process. As is well known, combustion is an oxidizing reaction by oxygen as a fuel from the chemical point of view, in which the reaction heat produced thereby is utilized for various purposes. Generally, the term "combustion" has normally referred to combustion or burning in natural atmosphere, i.e, in the oxygen concentration at 21 Vol.%, through all ages and in any places. The reaction heat generated at this time is imparted to exhaust gases (for example, carbon dioxide, moisture, and nitrogen gas in air, etc.), and if unable to recover, results in the exhaust gas loss, or the combustion temperatures are affected by the capacity of the exhaust gas. In any case, the less the amount of exhaust gas is, the larger is the gain of the heat amount which may be utilized. The factor which has a large influence in exhaust gases is an inert gas, especially, nitrogen which is contained in the moisture produced.and in air, and not related to the combustion. By reducing the amount of nitrogen as described above, increases in combustion speeds and burning temperatures are noticeable, resulting in energy saving in combustion to a large extent. Reduction of nitrogen amount means employment of oxygen enriched air, which makes it possible to achieve a large saving in combustion, even by the oxygen enriching at several % as shown, for example, in Fig. l(a). .In the graph of Fig. 1(a), the abscissa represents oxygen concentration of the oxygen enriched air, while the ordinate denotes fuel saving rate in combustion, with respective combustion temperatures being takes as parameters. Although the above graph shows an example in which natural gas (₁3A) is employed as a fuel, similar trend to the above may be noticed with respect to other kinds of fuels also. As is clear from the graph of Fig. l(a), energy saving performance (i.e. fuel saving effect) is improved towards the high temperature utilizing regions, and the process is effective for the wide applications such as glass melting, glass processing, metal melting, ceramic calcination, general boilers for various forgings, etc. Moreover, it is understood that several to 20% increase or so in the oxygen enriching rate shows a remarkable effect, and that oxygen at high concentration is not necessarily required. For a secondary effect, the employment of oxygen enriched air provides a particularly.. superior effect for precision processing, with flame length becoming short and sharp, for example in the pean burner during combustion.

0003As is seen from the foregoing description, the combustion with the use of oxygen enriched gas has various advantages and conspicuous features especially in the energy saving effect, and for specific realization of such merits in the actual applications, it is strongly required to supply oxygen at low cost, or oxygen enriched air.

0004At present, although oxygen enriched.air required for combustion is generally supplied frcm oxygen cylinders, there are such problems with respect to the use of such cylinders as employment of high pressure gas, or necessity for replacement of the cylinders, danger for leakage of gas, etc. Additionally, use of'liquid oxygen other than the use of oxygen cylinders may also present similar problems to the above.

0005As stated earlier, in the present age in which energy saving is actually required, it is necessary to derive oxygen inexhaustibly present in air in a still more efficient manner, and therefore, the present invention intends to provide an oxygen enriched gas supply arrangement which may be applied to combustion at high efficiency.

0006It has already been known that most of high polymeric membranes have a larger permeability constant with respect to oxygen, than the permeability constant thereof with respect to nitrogen, in the state where no pin holes are present. From tne above fact, it is of course possible to employ such a high polymeric membrane for the selective separation, but in the case where oxygen enriched gas obtained from an arrangement utilizing the high polymeric membrane is used for combustion, conditions as described below must be satisfied, which conditions, however, are considerably different from the conditions required for medical purposes (disclosed, for example, in Japanese Laid Open Patent Applications Tokkaisho Nos. 51/3291, and 51/6876, etc.). The above fact results from the entire difference in the using conditions.

0007Generally, combustion arrangements include various combustion methods and combustion temperatures, different configurations and sizes of the units, etc., and the oxygen concentration and flow rate of the oxygen enriched gas are set forth according to the individual arrangements. Accordingly, in the utilization of oxygen enriched gas for a combustion arrangement, it is necessary to provide an oxygen enriched gas supply arrangement which meets the above requirements. However, for satisfying the above conditions with respect to manufacture of the oxygen enriched gas supply arrangement, an apparatus merely for obtaining oxygen enriched gas is not sufficient for the purpose. In other words, the supply arrangement must be capable of coping with various changes, for example, in the state of operations, using conditions, external conditions for the arrangement, etc., which requirements are considerably different from the requirements for the oxygen enriched gas which is utilized for other purposes.

0008Specific requirements for the oxygen enriched gas supply arrangement for combustion may be raised as follows.

0009In the first place, it is necessary that the oxygen concentration is variable as required by the combustion apparatus, because in the case where the oxygen enriched gas is burnt through mixing thereof with gas or liquid fuel, combustion temperatures and combustion speeds remarkably vary depending on the oxygen concentration at that time. More specifically, a temperature rise of about 80°C is noticed upon increase of the oxygen concentration by only 1%, while simultaneously, flame length is largely altered due to the marked variation in the combustion speed. From the above facts, in the oxygen enriched gas supply arrangement, it is necessary that the concentration of oxygen required by the combustion apparatus is arranged to be variable.

0010In the second place, it is required that the flow rate of the oxygen enriched gas is arranged to be variable in the similar manner as in the above first requirement. In other words, in order to meet the conditions of the combustion apparatus or for burning at a value close to the stoichiometric or theoretical combustion, the llow rate must be adapted to be variable.

0011Thirdly, the oxygen enriched gas supply arrangement is required to be adaptable for external conditions, mainly with respect to the variations in temperatures. More specifically, in the arrangement of the present invention empolying a selective gas permeable membrane, since the gas permeation amount of the membrane is varied by the temperature variations, thus resulting in alterations in the flow rate of the oxygen enriched gas, it is necessary to eliminate such variations.

0012In the fourth place, it is required to be adaptable also to humidity as well as to external temperatures. Generally, permeation of moisture with respect to a high polymeric membrane is knownto be larger than that of oxygen and nitrogen, and in fact, under the state of high humidity, a large amount of moisture is contained in the permeated gas, which may give rise to variations in heat conduction and oxygen concentration during combustion due to presence of water vapor in the enriched gas, and therefore, it is necessary to maintain the moisture at a constant level as far as possible.

0013In the fifth place, with respect to oxygen supply arrangements, although a vacuum pump is employed in the arrangement or the present invention ror proviaing a pressure difference between a primary side and a secondary side of the selective gas permeating membrane, the flow speed of the oxygen enriched gas as obtained thereby tends to be fluctuated (pulsated) to a large extent, thus resulting in pulsations of flames during combustion. Therefore, such pulsations must also be prevented.

0014By solving the problems as described in the foregoing, oxygen enriched gas efficiently usable for combustion can be obtained.

0015Hereinbelow, the requirements as stated so far will further be described in detail.

0016Generally, as one of the practice for obtaining optimum amounts of oxygen concentration and flow rate of the oxygen enriched gas for effecting theoretical combustion suitable for combustion gas amount or calorific amount thereof, it is conceived to vary the differential pressure at opposite sides of the selective gas permeating membrane within the arrangement. However, the object as described above can not be achieved by merely changing the differential pressure, because there is a relation as follows with respect to the differential pressure and permeating flow rate. The permeating flow rate is represented by the following equations.<maths id="math0001"><img file="EP0054941A2_D0001.tif" /></maths><maths id="math0002"><img file="EP0054941A2_D0002.tif" /></maths>where F(N₂) and F(O₂) are respectively permeating amounts of nitrogen and oxygen, K is a physical constant for the membrane p (N₂) and P (O₂) respectively denote permeability coefficients for nitrogen and oxygen according to the membrane materials, and ΔP (N₂) and ΔP (O₂) represent partial differential pressures of nitrogen and oxygen.with respect to the membrane surface. More specifically, as is understood from the above equations, the total flow rate Ft permeated through the membrane is represented as Ft = F(N₂) +F(O₂) , and the permeating flow rate Ft may be controlled to the required level upon alteration of the differential pressure, but meanwhile, the oxygen concentration (F(O₂)/F(t)) is also varied simultaneously. The state as described above is shown in Fig. l(b) based on the results of experiments. In the graph of Fig. l(b), air (21% oxygen) is employed for the primary side, and the abscissa represents a pressure ratio (B/A) between the pressure A at the primary side and the pressure B (permeated gas) at the secondary side of the selective gas permeating membrane, while a curve P and the left side ordinate denote the oxygen concentration (%) at that time. A curve Q and the right side ordinate show the flow rate with respect to a permeation amount assumed to be 1 at a pressure ratio B/A=0.5. As is seen from the above results, upon lowering of the differential pressure, the permeating amount Ft is also reduced, with consequent reduction in the oxygen concentration (F(O₂)/F(t)). Although the absolute value for the above will be altered depending on the permeating performance of the membrane and exhaust capacity of the pump, the trend as described above may be said to apply to any state. Therefore, the problems related to achieving the necessary oxygen concentration and flow rate can not be solved through mere alterations of differential pressures, but effects as follows should also be taken into account.

0017In general, most of the high polymeric membranes tend to be increased in the permeating rate thereof through temperature rise, as represented by the following equation<maths id="math0003"><img file="EP0054941A2_D0003.tif" /></maths>

0018As is seen from the above equation, the increase in the permeating amount follows the increase of the permeability coefficient P due to rise of the temperature _T, further being correlated with activating energy Ep.

0019Table 1 gives examples of the activating energy Ep, while a graph in Fig. l(c) shows the relation-between temperatures and oxygen permeability coefficients for polydimethyl siloxane having small activating energy Ep, in which graph, an increase of the permeability coefficient as much as by about 10% is noticed upon rising of temperature by 10°C. In other words, the above fact implies that the oxygen enriched gas supply arrangement depends largely on the temperature variations under the circumstances where it is installed, and should be adaptable for such temperature variations. Normally, circumstances under which combustion apparatuses are to be installed are considerably strict, with temperatures around the apparatus varying in the range from 0°C or so to 40°C or thereabout through four seasons of the year, and therefore, the permeating flow rate should be controlled at all times with respect to the temperature variations of several tens of degrees. Furthermore, as is noticed from Table 1, since the activating energy Ep for oxygen is not equal to that of nitrogen, and the pormeability coefficient p due to the activating energy Ep and temperature T is different with respect to oxygen and nitrogen, it is natural that the flow rate variations of oxygen and nitrogen with respect to the temperature variations are not in agreement with each others. <tables id="tabl0001" num="0001"><img file="EP0054941A2_D0004.tif" /></tables>

0020With respect to the external circumstances, similar state also applies to the humidity. As described earlier, in most cases, the permeation coefficient for water is larger than that for nitrogen and oxygen gases, and this fact means that, when it is intended to selectively separate oxygen in the atmosphere through utilization of a membrane, moisture is naturally permeated therethrough simultaneously, with the result that the partial pressure of the water component in the gas subjected to the permeation, becomes larger than that in the atmosphere, and thus, dew may be formed in correspondence to external temperatures. In the phenomenon as described above, the humidity increase in the permeated gas has a particular effect to the combustion. In other words, there are cases where the combustion efficiency may be lowered due to variations of partial pressure for each gas, and variations in the heat conduction during combustion through mixing of water vapor, by the humidity increase in the enriched gas. The effect of humidity may differ dependinq particularly on the places of installation of the arrangement in the similar manner as in temperatures, but in the case where the apparatus is used for combustion, external circumstances are as poor as for temperatures, and in the similar conditions as in outdoors. In other words, the humidity variations in Japan throughout the year are in the range of several tens to 90%, and under such situation, the requirements for cominustion use are not related to how to reduce the humidity, but how to maintain the humidity constant, and as a matter of fact, it may be contrived how to bring the humidity close to the minimum level throughout the year.

0021Subsequently, it becomes important to see how the oxygen enriched gas thus obtained is stable. In the arrangement according to the present invention, transportation of gas is effected by a vacuum type pump for providing a pressure difference between the primary side and secondary side of the selective gas permeating membrane, and what is brought into question in such arrangement is the.characteristics of the pump itself. In other words, in the pump which is normally operated through a cycle of pressure reduction to compression, the gas to be transported thereby is intrinsically subjected to pulsations. Therefore, if the oxygen enriched gas fed by the vacuum type pump is merely employed as a combustion gas, there are cases where flames are pulsated, if the pulsation is excessive, and further, where optimum burning state is broken in the worst case. Accordingly, it is an essential requirement for a combustion gas supply equipment to provide a gas as stable as possible.

0022Accordingly, an essential object of the present invention is to provide an oxygen enriched gas supply arrangement for combustion purpose which is capable of satisfying the requirements as described in the foregoing for a combustion oxygen enriching apparatus.

0023Another important object of the present invention is to provide an oxygen enriched gas supply arrangement of the above described type which is simple in construction and stable in functioning at high reliability.

0024In accomplishing these and other objects according to one preferred embodiment of the present invention, there is provided an oxygen enriched gas supply arrangement which comprises a housing, a selective gas permeating membrane cell provided in the housing, means for supplying air to the selective gas permeating membrane cell for. obtaining oxygen enriched gas therethrough and means for controlling flow rate and/or oxygen concentration of oxygen enriched gas to be obtained through the selective gas permeating membrane cell. The arrangement further includes means for controlling humidity of the oxygen enriched gas to a predetermined value, and means for removing pulsation in the oxygen enriched gas.

0025By the arrangement according to the present invention as described above, an improved oxygen enriched gas supply arrangement for combustion has been presented, with substantial elimination of disadvantages inherent in the conventional arrangements of this kind,

0026These and other objects and features of the present invention will become apparent from the following description taken in conjunction with the preferred embodiment thereof with reference to the accompanying drawings, in which; <ul id="ul0001" list-style="none"><li>Fig. l(a) is a graph showing the relation between the oxygen concentration and combustion fuel saving rate (already referred to),</li><li>Fig. l(b) is a graph showing the relation among the pressure difference at opposite sides of a selective gas permeating membrane, oxygen concentration and flow rate (already referred to),</li><li>Fig. l(c) is also a graph showing the relation between the temperature of the selective gas permeating membrane and permeability coefficient (already referred to) ,</li><li>Fig. 2 is a schematic sectional view explanatory of the principle and construction of an oxygen enriched gas supply arrangement for combustion according to'one preferred embodiment of the present invention,</li><li>Fig. 3 is a block diagram explanatory of the structure and principle of functions of the oxygen enriched gas supply arrangement of the present invention,</li><li>Fig. 4 is a fragmentary diagram illustrating the structure of a membrane cell to be enployed in the arrangement of Fig. 1,</li><li>Fig. 5 is a schematic perspective view explanatory of an oxygen enriched gas supply system in the arrangement of the present invention,</li><li>Figs. 6 and 7 are a perspective view and a cross sectional view of a humidity eliminating or dehumidifying section to be employed in the arrangement according to- the present invention,</li><li>Figs. 8(a) and 8(b) are a perspective view, and a cross section taken along the line VIII(b)-VIII(b) in Fig. 8(a), of a humidity eliminating section according to another embodiment of the present invention,</li><li>Fig. 9 is a block diagram illustrating the overall construction of the arrangement according to the present invention,</li><li>Fig. 10 is a view similar to Fig. 2, which particularly shows a further modification thereof,</li><li>Fig. 11 is a block diagram illustrating a control system of the arrangement of Fig. 10,</li><li>Fig. 12 is a flow-chart explanatory of functions of the control system of Fig. 11, and</li><li>Fig. 13 is an electrical block diagram showing electrical circuits employed in the arrangement of Fig. 10.</li></ul>

0027Before the description of the present invention proceeds, it is to be noted that like parts are designated by like reference numerals throughout several views of the accompanying drawings.

0028Referring now to the drawings, there is shown in Fig. 2 the general construction of an oxygen enriched gas supply arrangement according to one preferred embodiment of the present invention. It should be noted here that Fig. 2 merely illustrates general dispositions of each component and flow of non-permeated gas from an inlet to an outlet of air for general understanding of the arrangement of the present invention, and that the processing of permeated gas or oxygen enriched gas by the arrangement will be described in detail with reference to Fig. 3 and thereafter.

0029In Fig. 2, the arrangement generally includes a housing Hofa cubic rectangular box-like configuration, a metallic net or filter 21 provided at one side or an air inlet I of the housing H for protecting a membrane cell 1 provided in the housing H in a position subsequent to the filter 21, a fan 22 disposed next to the membrane cell 1 for introducing atmospheric air therethrough into the housing H, a humidity eliminating or dehumidifying section 23 provided in the housing H subsequent to the fan 22, a vacuum pump 24 disposed next to the humidity eliminating section 23, and a pulsation removing section or a buffer 25, for example, in the form of a tank for storing therein the oxygen enriched gas provided subsequent to the vacuum pump 24 and adjacent to an outlet O of the housing H.

0030In the above construction, atmospheric air is introduced by the fan 22 via the metallic net or filter 21 into the housing H, and oxygen and water vapor in the atmospheric air are passed through selective gas permeating membranes of the mmebrane cell 1 (to be described later with reference to Fig. 4) for selective removal of oxygen and water vapor from the atmospheric air. Subsequently, nitrogen enriched gas (i.e. gas having less oxygen and water vapor) which does not pass through the selective gas permeating membranes, further flows into the rear portion of the housing H by. the action of the fan 22 or is directly discharged from the housing H, and in the case where the nitrogen enriched gas is caused to flow further into the rear portion of the housing H, it is cooled by evaporating water component therefrom at the humidity eliminating section 23, and passed through the vacuum pump 24, and then, may be discharged outside by changing its direction .of flow through a flow direction control member 26 provided at the outlet O for regulating the flow direction of the gas. In Fig. 2, although the flow direction control member 26. includes a plurality of control plates arranged in the longitudinal direction, such plurality of control plates may be modified to be arranged laterally with respect to the outlet O, or the flow direction control member 26 may be provided at a side portion or lower portion of the arrangement.

0031The arrangement in Fig. 2 further includes a sound insulating material 27 provided along inner faces of the housing H and an atmospheric air introducing portion or atmospheric air intake port 28 (to be described.later with reference to Fig. 5) provided in one wall of the housing H in a stage subsequent to the membrane cell 1. Since the atmospheric air introducing portion 28 is required to be in contact with atmospheric air having constant oxygen concentration, it is necessary to provide said portion 28 in a position spaced from the flow direction control member 26 for discharging gas..

0032It should be noted here that in the embodiment of Fig. 2, although the fan 22 is provided behind the menbrane cell 1, the arrangement may be so modified as to provide the fan 22 at the air inlet I or at the air outlet O, since it is merely intended to cause gas to flow.

0033Subsequently, the flow of the oxygen enriched gas passing through the membrane cells will be described with reference to Fig. 3.

0034In Fig. 3, air indicated by the arrow 30 is passed through a main membrane cell 31 which is normally used at all times and an auxiliary membrane cell 32 for controlling oxygen concentration and flow rate, with oxygen selectively permeating through the membranes. The oxygen enriched gas thus obtained is advanced to a vacuum pump 33, while, at an intermediate portion therebetween, there are provided an inner pressure detecting portion 34 for the gas and the atmospheric air introducing portion 28 (equivalent to the portion 28 in Fig. 2) for controlling oxygen concentration and flow rate. The atmospheric air introducing portion or external air inlet port 28 which is intended to introduce ordinary external atmospheric air (oxygen at 20 vol.%), thereby to control oxygen concentration and flow rate by diluting oxygen enriched gas, may be provided in plurality or may be disposed either before or after the vacuum pump. The enriched gas which has passed through the vacuum pump 33 is further introduced, if necessary, into a humidity eliminating or dehumidifying chamber 36 for removing water content or moisture in the gas. Part of the gas obtained here is fed back by a feed back control 37 for further controlling concentration and flow rate.

0035The remaining gas may be taken out in the form of a combustion enriched gas through a buffer chamber or pulse eliminating chamber 38 for removing pulsations thereof, if necessary. There are further provided a temperature detector 35 coupled to the cell portion, and a flow rate detector 90, a pressure detector 91, a combustion apparatus 92 and a pressure and flow rate control discharge outlet 93, etc. provided at stages subsequent to the buffer chamber 38 as shown.

0036Subsequent to the general constructions and flow of gas for the oxygen enriched gas supply arrangement of the present invention described so far, specific constructions and functions of each component thereof will be described in more detail hereinbelow.

0037In the manufacture of the oxygen enriched gas supply arrangement for combustion, although it is possible to produce an arrangement which may catisfy tho required oxygen concentration and flow rate, by preliminarily taking into account, general operating conditions and the like, since control for effecting optimum combustion is further required depending on operating conditions, using circumstances, etc., the method for making the oxygen concentration and flow rate variable will be described hereinbelow in the first place.

0038The factors which solely determine oxygen concentration and flow rate in the oxygen enriched gas are the total membrane area and pump capacity. If the membrane area is constant, pressure and air flow rate corresponding to the pump capacity may be obtained, and accordingly, the oxygen concentration and flow rate can be automatically determined. However, it.is generally considerably difficult to arrange capacity of the pump itself to be variable. Therefore, according to the present invention, it is so arranged that part of the gas discharged from the discharge opening of th'e pump is returned to the inlet of said pump. By providing a by-pass for feed-back as described above, the pump capacity, although tending to be rather lowered, may be adapted to be variable. By the above system, it becomes possible to control the pressure, and consequently oxygen concentration and flow rate. The system as described above requires only a simple construction in which the inlet and discharge opening of the pump are merely connected by a pipe, with a valve therebetween, and cost increase thereby may be neglected. The specific construction of the above system will be described later with reference to Fig. 5.

0039In a second system, oxygen concentration and flow rate are arranged to be variable at the membrane cell portion. In Fig. 4, there is shown the construction of such membrane cell section 1 which includes a main membrane cell 45 composed of one or more membrane cells and working at 100% in the normal operating state, and a plurality of sets of auxiliary membrane cells 46 each composed of a plurality of membrane cells for use upon variations in operating conditions or external conditions and occupying approximately 20% of the entire mmebrane cell, although the above rate may differ depending on various conditions. The membrane cell section 1 further includes one or more control valves 47 for controlling the auxiliary membrane cells 46, said valves 47 being arranged to deal with one or more sets of the auxiliary membrane cells 46. These valves 47 may be of a manually operated type or electrically driven type based on on/off control. In operation, upon opening of the valves 47 the oxygen enriched gas in the auxiliary membrane cells 46 passes through a piping 48 and introduced into another piping 49 through which the oxygen enriched gas of the main membrane cell 45 is passing. By properly controlling the number of the auxiliary membrane cells to be opened through the valve 47, the flow rate or oxygen concentration of the oxygen enriched gas obtained from the membrane cell section 1 may be controlled. When the auxiliary membrane cells 46 are used, the oxygen enriched gas is subjected to such changes that the flow rate increases with constant oxygen concentration, if pressure is kept at a constant level..

0040Since the gas permeating films employed for the membrane cells '45 and 46 are intended for combustion purpose, a membrane material containing polydimethyl siloxane which has a favorable permeating performance is preferable for obtaining flow rate larger than 20ℓ/min. at the minimum.

0041Referring also to Fig. 5 schematically showing the oxygen enriched gas supply system according to the present invention, while passing through the piping 49, the flow of the oxygen enriched gas from the membrane cell 1 is introduced into a pressure sensor 50 on the way, which is arranged to detect the pressure at the permeating gas side of the membrane, thereby to find the state of the permeating gas from membrane characteristic temperature, flow rate, etc. Meanwhile, for alterning the state of the oxygen enriched gas in a passage through a piping 51; an external air intake port 52 corresponding to the atmospheric air introducing portion 28 in Figs. 2 and 3 is provided. In this embodiment, the air intake port 52 is provided with a filter 52a, and the amount of intake air is arranged to be adjusted by a valve 53 inserted in a line between the piping 51 and the air intake port 52. The valve 53 is of a flow rate variable type which may be controlled either manually or by a motor. The arrangement as described in the.foregoing may be applied to a case where oxygen concentration is higher than specified level, with a less flow rate, and the control thereof is of course based on. the combination of the valves 47 for the auxiliary membrane cells and a control by a valve 57 for by-passing in the feed back to be described later. Subsequently, the gas which has passed through the pipe 51 is introduced into a pressure reduction vacuum pump 55 which is connected to the pipe 51 through an inlet pipe 54 and an outlet pipe 56, with the valve 57 being provided in the pipe 51-at a position between the pipes 54 and 56 for connecting said inlet pipe 54 with the outlet pipe 56. The valve 57 is of a flow rate variable type similar to the valve 53, and may be controlled either manually or by a motor. The valve 57 also has a function to establish a by-pass passage for reducing pressure at the side of the pipings 49 and 51, and when opened, reduces the oxygen concentration and flow rate of the permeating gas so as to reach specified values. Meanwhile, the control of the valve 53 is of course correlated to various conditions, i.e. factors such as applicability of the auxiliary membrane cell valve 47 and feed back by-passing valve 57, temperature, pressure; flow rate, etc. Described so far is the control section for achieving the specified flow rate and oxygen concentration required in oxygen enriched gas for combustion, and also for obtaining a constant value with respect to variations in the external conditions. In the above case, the concentration of oxygen ultimately used for combustion in the arrangement of the present invention as described so far, should be less than 39%, which is suitable for burning.

0042It should be noted here that the auxiliary membrane described as employed in the foregoing embodiment may be omitted, if not required depending on the operating conditions, and that the control valves may be arranged to be all or partially operated manually.

0043As already described earlier, in order to control the variations due to temperatures, a temperature sensor 59 is provided at the membrane cell 1 for monitoring temperatures at all times, and upon variations in the temperature, the specified value is achieved through analysis on suitability of the use of the auxiliary membrane 46, introduction of external air, and opening or closing of the by-pass valve 57. As stated previously, in the arrangement according to the present invention, temperature, pressure, permeating flow rate, and oxygen concentration are respectively correlated with each other, and it is possible to manually control these tactors, but it is also possible to effect the control based on real time through employment of an automatic central control system to be described in detail later with reference to Fig. 11.

0044In Fig. 5, since a certain amount of water component or moisture is contained in the oxygen enriched gas obtained through a discharge port 58 of the pump, it is required to remove such moisture. therefrom, if necessary. Particularly, when atmospheric humidity is high, if the gas is brought from the pressure reduction state into normal pressure or pressure higher than that through the pump 55, water vapor forms dew due to the relative temperature difference with respect to the external temperature. By utilizing the above phenomenon, the gas is normally passed through a spiral pipe to be described later so as to take out the water vapor through dew formation thereof by bringing the spiral pipe into normal temperature. In the above case, however, there is such a problem that the humidity and amount of dew formation depending on the external air temperature. According to the arrangement of the present invention, the inconvenience as described above has been removed by the following method intended to lower the humidity in the permeated gas as far as possible. Ideally, although the humidity may be lowered by passing the permeated gas through a temperature below 0°C, it is impossible by the above practice to avoid increased size of the arrangement, and an increase in the cost for maintenance. Therefore, in the arrangement of the present invention, the problem has been solved by lowering the temperature below normal temperature through a simple construction as far as practicable. More specifically, a material through which water readily penetrates and another material having a favorable heat conduction held in close contact with each other, are connected to the piping for the permeating gas. The above arrangement is based on a principle that, when water vapor in the permeating gas forms dew in the piping, the temperature .is further lowered for expediting the dew formation through lowering of the temperature by latent heat when the water taken out by osmotic pressure or internal pressure is vaporized.

0045The specific constructions for the arrangement as described above are shown in Figs. 6, 7, 8(a) and 8(b).

0046Particularly, owing to the fact that the oxygen enriched gas for combustion is used in a large amount and subjected to the external conditions of high humidity, and from the necessity for bringing humidity close to the external low humidity conditions, the arrangement of the present invention is characterized in that, water in the form of dew is utilized to achieve a still lower temperature in addition to the dew formation merely by external atmospheric temperatures, so that the latent heat during evaporation of water in the form of dew is fully utilized. The amount of water available from the permeating gas is such that, according to actual measurements, water more than 2 t/hr. in amount is collected at a permeating rate of 30 m³/hr., with the effect being particularly conspicuous during rainy weather, etc. The construction of the humidity eliminating section as shown in Figs. 6 and 7 is suitable for a case where the external temperatures are low all through the year or where the arrangement is of a compact size. In Figs. 6 and 7, the humidity eliminating section 62 includes a plurality of plate members 63 each composed, for example, of a rectangular metallic plate 65, and another plate 64 of a similar shape made of capillary material and closely piled upon said metallic plate 65, with said plate members 63 being arranged on the piping from the pump 55 in spaced relation from each other as shown. Each of the capillary material plates 64 is adapted to take out water component in the form of dew through capillary action, and the water component thus taken outside is evaporated by the nitrogen enriched'gas (low humidity gas), while the temperature lowered by the latent heat at this time is transmitted into the oxygen enriched gas through the metallic plates 65 through heat conduction. In Figs. 6 and 7, there is further provided a filter 66 in the piping for removing solid matters, oil, etc. from the pump, and such a filter 66 may be omitted, if a pump free from discharging of impurities is employed.

0047Referring further to Figs. 8(a) and 8(b), there is shown another embodiment of the humidity eliminating section of a still larger size, which is particularly suitable for dealing with a large amount of dew forming water, although based on the same principle as described above. The humidity eliminating section of Figs. 8(a) and 8(b) includes an evaporating pad 84 composed of the capillary material plate 64 and metallic plate 65 as described earlier, a conduit pipe 87 provided along one surface of the inclined metallic plate 65 opposite to its other surface for the capillary material plate 64, and directed in a zigzag manner into a trap 82 provided at one end of said pipe 87, and another conduit pipe 83 connected between the bottom portion of the trap 82 and the surface of the capillary material plate 64 of the evaporating pad 84.

0048In the above structure, when the dew forming water 81 is collected by a predetermined amount in the trap 82 through the pipe 87, the water thus collected in the trap 82 penetrates into the evaporating pad 84 composed of the capillary material plate 64 and metallic plate 65 through the pipe 83 so as to be evaporated by the nitrogen enriched gas for lowering the temperature. The trap 82 is made of a high polymeric material such as heat insulating material or Teflon and the like for insulation against external temperatures. Meanwhile, in the case where a large amount of water exceeding the amount of evaporation on the pad 84 is recovered, such water is discharged outside through a pipe 86 provided at one edge of the pad 84 in a position adjacent to the trap 82. It is to be noted here that according to this embodiment, the inner pressure of the pipe 87 is in the range of 1500 to 2000 mmHg, although different depending on the conditions of the combustion portion. Therefore, it is possible in terms of principle to increase a height H of the pipe 83 for feeding water up'to such level, but in the actual practice, the height H should preferably be less than 50 cm.

0049It should be noted here that the humidity eliminating section for the oxygen enriched gas supply arrangement according to the present invention as described in the foregoing may further be modified in various ways, for example, in such manners that, the humidity eliminating section as described with reference to Figs. 6 and 7 are provided in plurality, or that shown in Fig. 8 is connected in multiple stages, or the constructions in Figs. 6 and 7 and Figs. 8(a) and 8(b) may be mixed or combined with each other for actual applications.

0050The humidity eliminating sections described so far are arranged to expedite evaporation by the non-permeating gas (nitrogen enriched gas) passing through the surface of the membrane, and since the effect is still more improved owing to the fact that the non-permeating gas is of a gas having less moisture contrary to the permeating gas, the humidity eliminating section is required to be disposed behind the membrane in the form of the humidity eliminating section 23 as shown in Fig. 2. For the capillary material 64 for leading water into atmosphere in Figs. 6 and 7, there may be employed paper, cloth, inorganic fibers or mixtures thereof, and, as the metallic plate 65 for conduction of heat, any metallic materials may be adopted, while the number of such plates may be determined based on the capabilities of the arrangements.

0051As is seen from the foregoing description, according to the construction of the present invention, oxygen enriched gas at a low humidity which could not be achieved at normal temperature, has been advantageously obtained. In the system as desgribed so far, leakage of gas from the penetrating material may seemingly be expected, but as a result of actual measurements, there have been no problems even when the pressure is brought up to 2000 mmHg.

0052Reference is further made to Fig. 9 showing the flow of gas in the arrangement of the invention in further detail, in which like parts in Fig. 5 are designated by like reference numerals, with detailed description thereof abbreviated for brevity. As shown in Fig. 9, it is particularly necessary to provide the humidity eliminating section 62 as described earlier (Figs. 6 and 7) immediately after the pump -55. In other words, the humidity eliminating section 62 should be inecrted in the by-pace portion between the inlet 54 and outlet 56 for the pump 55, If the dehumidification is effected without passing through the section 62 disposed as described above, dew formation takes place in the vicinity of the valve 57, and thus, water vapor counterflows simultaneously with the variation in the flow rate. There are cases where the oxygen enriched gas dehumidified as described above still has pulsations in its flow, and therefore, such pulsations are prevented by the buffer 25, for example, in the form of a tank as described earlier (Fig. 2). The gas from the buffer 25 is further passed through a flow rate- sensor 90 and also a pressure gauge 91. The pressure gauge 91 mav be adapted to be associated with a pressure control releasing valve 93, and it is so disposed that, in the case where the pipe 92 at this portion is subjected to an abnormally high pressure (for example, when the pipe leading to the combustion burner system is stopped, etc.) or where the flow rate is excessive, the pressure is automatically reduced or discharged by the valve 93 into a relief discharge port (not particularly shown). The oxygen enriched gas for combustion as described above is fed into the pipe 92, and is mixed with the combustion gas or combustion liquid fuel from a pipe 94. Moreover, for a burning portion or fuel combustion portion (surrounded by dotted lines in Fig. 9) other than the arrangement as described above, there may be provided a flow rate sensor 95, a pressure sensor 96, etc. for producing oxygen enriched gas of a still higher quality.

0053Referring to Fig. 10, there is shown a further embodiment of the oxygen enriched gas supply arrangement according to the present invention, in which the overall length of the arrangement is shortened for a compact size, with the membrane cell portion 1 being provided on the upper stage and other portions disposed at the lower stage so as to form the flow of gas into U-shape. In Fig. 10, like parts in Figs. 2, 4, 5 and 9 are designated by like reference numerals, with the detailed description thereof abbreviated for brevity.

0054In the above embodiment of Fig. 10, since the air inlet I and nitrogen enriched gas discharge port O are directed in the same direction, in the case where a large amount of nitrogen enriched gas is to be discharged by the air flow direction control plates 26, it is necessary to avoid entry of the nitrogen enriched gas towards the air intake port 21, for example, by spreading the control plates 26 in the lateral directions.

0055Subsequently, a control method for stably supplying the specified flow rate and oxygen concentration as described earlier will be explained. The control portions for achieving the above may be concentrated upon three points, i.e. opening and closing of the auxiliary membrane, operations of the atmospheric air introducing valve and by-pass valve, and any of these operations is a function with respect to the flow rate and oxygen concentration. Meanwhile, means for finding the flow rate and oxygen concentration as related to the above operations may be present at several points, i.e. temperature in the vicinity of the membrane, pressure of the permeating gas, and flow rate or pressure at the final intake port. Although the above relations may apparently seem to require complicated operations, it is possible to apply automatic control therefor. More specifically, since the characteristics of the membrane to be employed are those inherent in the membrane material, the automatic control is possible through mere calculating processing by finding out the differential pressure AP, permeating amount J, oxygen concentration N02, and permeability coefficient PT with respect to temperature, of the membrane itself.

0056In the practical applications, with the employment of a micro-computer, a plurality of spots at the sensor portion are measured, and based on the findings therefrom, variations from the specified values are observed for comparative calculations with respect to the characteristics of the membrane itself, and decision is made by predicting which of the control valves at several places should be operated to achieve best result for obtaining the optimum flow rate and oxygen concentration.

0057More specifically, the control as described above is effected by the construction as shown in Fig. 11.

0058In Fig. 11, an input from the pressure sensor 50 in Fig. 5 for a line 111 is regularized by an operational amplifier 114 and then, fed, through a selector 115 into a processing circuit 116 so as to be subjected to A/D conversion thereat for effecting calculations and other processings. Meanwhile, the output of the temperature sensor 59 in Fig. 5 applied to a line 112 is fed,.after room temperature correction, into the operational amplifier 1l4, and is then, applied to the processing circuit 116 through the selector 115. Similarly, the output from the flow rate sensor 90 in Fig. 9 for a line 113 is applied to the processing circuit 116 through the operational amplifier 114 and selector 115. The data obtained at the processing circuit 116 through calculation and processing thereat are compared with the membrane characteristics memorized in a read only memory ROM 117, for example, the characteristics as shown in Fig. 1(b), which are the fundamental data of the membrane to be employed.

0059On the other hand, for setting the initial values for the combustion conditions, input is effected by a keyboard 63, which is coupled to a display device 64 therefor. The conditions to be designated are determined by the comparicon of the values input by the keyboard 63 and the membrane characteristics, with subsequent determination of the control method for display. Simultaneously, instructions are given to a valve driving motor controller 120 for driving the valve 53. Similarly, the valve 57 is controlled by a valve controller 121 and the valve 47 by a valve driving controller 122. By the repetition of the functions as described above, accuracy is gradually improved. The data and corrected data at this time are stored in a random access memory RAM 118. The control is effected in the manner as described above.

0060It is to be noted that in Fig. ll, the portion 66 surrounded by dotted lines shows one example of a CPU (central processing unit), and, although different according to the kinds, is intended to determined optimum conditions for control method through comparative calculations of various data with membrane characteristics, and that according to this method, it is possible to further correct membrane characteristics with respect to the complicated changes in external conditions for achieving'optimum results.

0061The flow-chart in Fig. 12 shows the foregoing method as observed from the view point of soft ware.

0062Referring now to Fig. 13, the electrical circuit and safety device circuit employed for the oxygen enriched gas supply arrangement according to the present invention will be described hereinbelow, in which solid lines are related to a power supply circuit, while chain lines are coupled to a control circuit.

0063Firstly, powers from a vacuum pump driving three phase power source 131 and a single phase 100 V power source 132 are fed into an open/close control box 135 respectively through power supply prevention breakers 133 and 134 coupled thereto, and further supplied to corresponding components through thermal type overcurrent preventing breakers 136 and 137, to which indicator lamps or LED indicators 152 and 153 are coupled for indication of state of functions. The power supply of 100 V flowing through a line 140 from the breaker 137 is subjected to DC conversion by each controller, and is fed to the CPU 66, a fan 22, indicator lamps 154, an alarm buzzer 150, and also to a controller 144 for each valve, which are all connected to the line 140. A power supply or a battery 145 is coupled through a line 102 to the CPU 66 as a CPU back-up power source for use in case of trouble in the 100 V power supply 132 or power failure, and also as a power source for an alarm buzzer 146 connected to the CPU 66. Secondly, with respect to the control circuit, when the data input through a line 147 are detected to be of abnormal values (for example, values largely deviated from the specified values, or values uncontrollable), the control box 135 is driven through a line 148 connected between the CPU 66 and the control box 135 for cutting off the power supply, and the alarm buzzer 150 is actuated through a line 149 connecting the CPU 66 to said buzzer 150, while the controller 144 is driven by a line 151 connected between the CPU 66 and said controller 144. An indicator 155 is further connected to the CPU 66 for indicating the state of functions thereof.

0064As is clear from the foregoing description, the oxygen enriched gas supply arrangement for combustion purpose according to the present invention is suitably utilized as an air aupply source for various combustion equipment and apparatuses, and is especially superior as the air supply source for combustion apparatuses utilizing high temperatures such as burners used for glass melting, glass processing, metal melting, ceramic calcination, etc., boilers for.general purpose or various forging operations, and further, high temperature furnaces and the like.

0065Although the present invention has been fully described by way of example with reference to the accompanying drawings, it is to be noted here that various changes and modifications will be apparent to those skilled in the art. Therefore, unless otherwise such changes and modifications depart from the scope of the present invention, they should be construed as included therein.