In a typical application of the above method, the temperature of a gas is measured in a combustion chamber, which temperature may be in the order of 700-1200°C. The combustion chamber may for example be a chamber in an incinerator in which for example refuse, especially household refuse, is burned. Alternatively, the combustion chamber may be a combustion chamber of a power station or a heating station, in which combustion chamber fossil fuel is burned, especially coal, oil, gas or another combustible material, for example straw, etc., or a corresponding combustion chamber in a factory or the like. The measurement of the temperature of the combustion gas firstly serves the purpose of monitoring that, on one hand, a complete combustion takes place, and on the other hand, a combustion which does not take place at such a temperature, especially such a low temperature, that toxic combustion products are formed, especially dioxin. For measur¬ ing the temperature of the combustion gas which, as already men¬ tioned, may have a temperature of above 1000 ^β C, a pyrometer is used in accordance with this method, which pyrometer has a thermal sensor which may be constituted by a thermocouple or a resistive element the resistance of which changes as a function of the temperature in a known manner. In order to ensure that the temperature registered by the thermal sensor is the gas temperature and not a random tempera¬ ture determined by hot and/or cold bodies or zones, particularly radiation sources detected by the thermal sensor, the thermal sensor in such a known pyrometer used for measuring the temperature of a gas, particularly a combustion gas, is encased in the radiation screen or radiation screens which serves or serve to ensure that the temperature registered by the

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thermal sensor is determined by the gas with which the thermal sensor is in contact or is brought into contact.

In accordance with the known art a pyrometer for carrying out the above, known method is usually formed as a suction pyrometer, i.e. a pyrometer whose gas inlet is placed inside the space in which the gas whose temperature is to be measured, is present, while the gas outlet of the pyrometer is arranged outside the space. Through the pyrometer a strong gas flow is produced from the gas inlet to the gas outlet and thus past the thermal sensor and consequently expelled from the space by means of an ejector pump, an electric fan or the like. Apart from polluting the environment, these known pyrometers work with ex¬ tremely high gas velocities, typically in the order of 150 m/s, in order to obtain a correct registration of the gas temperature. Consequently fairly large amounts of gas are sucked out from the space, which in itself may be unfortunate and further result in pollution.

The suction of gas from the space through the suction pyrometer takes place, as will be understood, via a channel from the gas inlet to the gas outlet of the pyrometer, which channel is connected to the ejec¬ tor or fan. By the suction of gas with a temperature typically in the order of 700-1200 ^β C through the channel, a cooling off of the gas in the channel takes place. Consequently, considerable amounts of fly ash or cinders are most often deposited in the channel. In measuring the temperature in incinerators in which the pyrometer has been introduced through an opening in the wall of the incinerator, espe¬ cially in the top wall of the incinerator, the known suction pyrometers can only be used for measurement for fairly short time periods of a few hours, typically a maximum of 5-10 hours, after which time period the suction from the throughflow or suction pyrometer through the said channel is stopped or blocked by fly ash or cinders, whereupon the measuring procedure has to be interrupted.

An object of the present invention is to provide a method for pyrometric measurement of the temperature of a gas in a space, by which method a continuous monitoring of the gas temperature may be carried out, i.e. measurement of the gas temperature for up to 1000 hours or more. A further object of the present invention is to

eliminate the sometimes unfortunate effects of polluting the en¬ vironment by the suction of gas from the space in which the gas is present, the temperature of which is to be measured.

These and other objects are obtained in accordance with the present invention by a method of the above-described type, which method is characterized in that the pyrometer is arranged with its gas inlet and its gas outlet inside the space, that a pressure fluid is passed from a pressure fluid source arranged outside the space through a pressure fluid conduit to a nozzle or pressure fluid discharge open¬ ing of the pressure fluid conduit arranged inside the space, from which nozzle or pressure fluid discharge opening the pressure fluid is discharged, and that a relative low pressure is generated at the gas outlet by the discharge of pressure fluid from the nozzle or the pressure fluid discharge opening for generating a gas flow through the inside of the radiation screen from the gas inlet, past the thermal sensor arranged inside the radiation screen and to the gas outlet.

The basis of the invention is the realization that it is rendered possible to measure the temperature of the gas in the space con¬ tinuously by arranging the pyrometer in the manner characteristic of the invention, i.e. by arranging the gas inlet and the gas outlet inside the space and by generating a gas flow through the pyrometer, i.e. from the gas inlet, past the thermal sensor arranged inside the radiation screen and to the gas outlet, as no substantial cooling takes place of the gas or the particles present in the gas and, consequently, that there is no stopping or blocking of the pyrometer or of a suction conduit or channel associated with the pyrometer, such as is the case with the known suction pyrometers. The gas flow through the radiation screen of the pyrometer, particularly past the thermal sensor arranged inside the radiation screen, which is manda¬ tory for a correct measurement of the temperature of the gas, is generated in accordance with the invention by generating a relative low pressure at the gas outlet of the pyrometer. The low pressure is generated by the discharge of a pressure fluid supplied to the space via a pressure fluid conduit, from a nozzle or pressure fluid dis¬ charge opening of the pressure fluid conduit and consequently by an ejector effect. SUBSTITUTE SHEET

It is to be noted that the relative low pressure may be generated just outside the radiation screen, alternatively and preferably in¬ side the radiation screen, as the pressure fluid may be discharged from the nozzle or pressure fluid discharge opening which may be ar¬ ranged outside the radiation screen or preferably inside or at the radiation screen as long as it is ensured that the low pressure generated at the gas outlet is sufficient for the generation of a gas flow through the inside of the radiation screen.

The pressure fluid may be any pressure fluid which is compatible with the measuring procedure in question, but will normally be pressurized air, pressurized water or pressurized steam. For certain applica¬ tions, it may be advantageous to use a gas, such as nitrogen, which is inert to a process or combustion. Alternatively, the gas may be used whose temperature is to be measured and which is sucked out from the space, cooled off, compressed in a compressor unit and fed back into the space via the pressure fluid conduit.

In accordance with the invention it has surprisingly been found that in order to generate a gas flow through the inside of the radiation screen for obtaining a correct gas temperature measurement it is sufficient to supply the pressure fluid in fairly small amounts. Thus, it has been found that by using pressurized air in carrying out the method according to the invention a sufficient gas flow may be generated through the radiation screen of the pyrometer by supplying pressurized air and discharging the pressurized air from the nozzle or the pressure fluid discharge opening in an amount of 15-100 1/ min. , or preferably 15-50 1/min.

It has further surprisingly been found that a correct temperature measurement may be obtained at flow velocities through the pyrometer which are considerably smaller than the flow velocities which have so far been considered necessary in accordance with the above known art for obtaining correct temperature measurements. Thus it has been found that said relative low pressure at the gas outlet may be generated with a gas flow through the radiation screen of the pyrometer having a flow velocity in the order of 30-50 m/s. As a result of this low flow velocity the risk of blocking or stoppage is

further reduced as lower amounts of gas are passed through the pyrometer than in the known art.

The present invention also relates to a pyrometer for measuring the temperature of a gas in a space and having a thermal sensor for generating a gas temperature dependent, electrical signal and having a radiation screen in which a gas inlet and a gas outlet are pro¬ vided, and which substantially encases the thermal sensor arranged inside the radiation screen, which pyrometer in accordance with the invention is characterized in that the pyrometer is adapted to be arranged with its gas inlet and its gas outlet in said space, that the pyrometer has a pressure fluid conduit which is adapted to be supplied with a pressure fluid from an outer pressure fluid source, and which ends in a nozzle or pressure fluid discharge opening for discharging the pressure fluid and for generating a gas flow through the inside of the radiation screen from the gas inlet, past the thermal sensor arranged inside the radiation screen and to the gas outlet by generating a relative low pressure at the gas outlet by the pressure fluid discharge.

In the pyrometer according to the invention, the nozzle or pressure fluid discharge opening may be arranged in any manner in relation to the radiation screen of the pyrometer as long as it is ensured that a gas flow is generated through the inside of the radiation screen from the gas inlet, but it is preferred that the nozzle or pressure fluid discharge opening is arranged inside the radiation screen and down¬ stream relative to the thermal sensor referring to the direction of the gas transportation from the gas inlet to the outlet.

The pyrometer may be embodied in numerous ways determined by the measuring location, particularly the space in which the pyrometer is to be arranged during measurement, by the environment, particularly the gas to which the pyrometer is exposed, and further by the re¬ quirements to the durability of the pyrometer, particularly its ability to stand a high temperature for a long period of time, and further reactive gasses if any. Even though the radiation screen may be formed in any appropriate manner and have any appropriate shape, for example be formed as a ball, a cube or be constituted by any other geometrical shape, the radiation screen is, in accordance with

the presently preferred embodiment of the pyrometer according to the invention, preferably embodied comprising a cylindrical pipe of a high temperature resistant material, which cylindrical pipe is open at one end, which open end constitutes the gas outlet, one or more peripheral openings constituting the gas inlet being provided in the cylindrical pipe, and the thermal sensor and the pressure fluid dis¬ charging nozzle or pressure fluid discharge opening of the pressure fluid conduit being arranged consecutively between said peripheral opening or openings and said open end.

In accordance with another embodiment of the invention the radiation screen has two circularly cylindrical pipes arranged coaxially inside each other, and in the space between these coaxially arranged circu¬ larly cylindrical pipes either an insulating material may be provided or a space be formed which forms a cooling jacket which is supplied with a cooling medium, particularly cooling water, and which encases and protects the thermal sensor of the pyrometer against a too strong, sudden thermal influence from a possible, strongly radiating heat source present in the space. In this embodiment comprising a cooling jacket, the circularly cylindrical pipes may be made from different materials. Thus, the outer cylindrical pipe may be made from a material which can withstand particularly strong radiation action, while the inner cylindrical pipe merely has to withstand the thermal action from the gas whose temperature is to be measured. The radiation screen is advantageously made from heat resistant stainless steel, such as A.I.S.I. (American Iron and Steel Institute) 310 steel or 25/20 Ni/Cr steel possibly containing a small amount of Si, quartz glass or a high temperature resistant ceramic material, such as aluminium and beryllium oxide.

The thermal sensor of the pyrometer may, like in the conventional pyrometers, be constituted by a thermocouple or a resistive tempera¬ ture measuring element, i.e. a resistor element, the temperature variation of the resistance value of which is detected for determin¬ ing the temperature of the element. Naturally, other thermal sensors, such as high temperature resistant semiconductor elements, etc., can also be used for special applications.

In accordance with the invention the pyrometer preferably has further means for fastening the pyrometer in an opening in a wall delimiting the space. Thus, in the preferred embodiment of the pyrometer ac¬ cording to the invention the pyrometer preferably has a flange pro¬ jecting from the radiation screen of the pyrometer.

The invention will now be explained with reference to the drawing which is a schematic and partially sectional view of a presently preferred embodiment of a pyrometer according to the invention for carrying out the method according to the invention.

The pyrometer according to the invention shown in the drawing is generally designated 10 and comprises two circularly cylindrical pipes 11 and 12 arranged coaxially inside each other and made of a high temperature resistant material, such as heat resistant stainless steel, for example A.I.S.I. (American Iron and Steel Institute) 310 steel, quartz glass or a high temperature resistant ceramic material. It is to be noted that the two circularly cylindrical pipes 11 and 12 need not be of the same material. Thus, the outer pipe 11 may advan¬ tageously be of a material which can withstand higher temperatures than the material of the inner circularly cylindrical pipe 12, par¬ ticularly higher temperatures produced by heat radiation sources. In the two circularly cylindrical pipes 11 and 12 adjacent to the upper ends of the pipes 11 and 12, several peripheral openings 13 and 14, respectively, are provided which are arranged coaxially in alignment and establish a connection from the environment of the pyrometer 10 to an inner space defined by the inner, circularly cylindrical pipe 12. The connection from the environment of the pyrometer 10 to the inner space of the pipe 12 constitutes a channel which is designated 15 in the drawing, and which is further defined by two circular plate-shaped parts 16 and 17, of which the plate-shaped part 16 has an inner circular opening and is arranged so as to seal the space between the outer and the inner cylindrical pipes 11 and 12, respec¬ tively, i.e. the part 16 is arranged in a sealing relationship with the inner wall of the pipe 11 and in a sealing relationship with the outer wall of the pipe 12, while the other circular plate-shaped part 17 is arranged in a sealing relationship with the inner wall of the pipe 11 and sealingly abutting the upper end of the pipe 12.

In the inner space defined by the inner, circularly cylindrical pipe 12 a thermocouple 23 is arranged extending from a threaded junction bushing 22 at the upper end of the pyrometer 10 through a central opening in the circular plate-shaped part 17 into the inner space of the pipe 12.

Apart from the circular plate-shaped parts 16 and 17 the pyrometer 10 has a circular plate-shaped part 27 at its lower end. The circular plate-shaped part 27 has a central opening and is arranged in a sealing relationship with the outer wall of the pipe 12 and the inner wall of the pipe 11, so that a space 24 is defined between the pipes 11 and 12 and between the plate-shaped parts 16 and 17 in which space 24 a thermally insulating material, such as KERLANE ^® 60 may be en¬ closed. Instead of a thermal insulation an inlet and an outlet chan¬ nel for the supply and discharge, respectively, of a cooling medium, such as cooling water, may be provided in the space 24. The plate- shaped parts 16, 17 and 27 may be of the same material as the pipes 11 and 12 or of another, preferably thermally insulating material, such as a ceramic material.

As is evident from the drawing, the pyrometer 10 has an open lower end 21, as the plate-shaped part 27 does not close the lower end of the inner circularly cylindrical pipe 12. There is, thus, connection from the environment of the pyrometer through the openings 13, the channel 15, the openings 14 and the inside of the pipe 12 and further through the opening 21 to the environment. In accordance with the invention a forced gas flow is generated from the environment of the pyrometer through the openings 13, the channel 15 and the openings 14 and further down past the thermocouple 23 and through the opening 21 by the generation of a relative low pressure at the lower end of the pyrometer. According to the invention, this low pressure is generated by discharging a pressure fluid, preferably pressurized air, from a pressurized air nozzle 20 which may be arranged outside the pyrometer or, as shown in the drawing, inside the pyrometer or rather inside the pipe 13. The drawing shows a threaded connection bushing 18 for mounting a pressurized air conduit (not shown in the drawing) , which piece is connected to a pressurized air conduit or pipe 19 which ends

in the pressurized air discharge nozzle 20. By discharging pres¬ surized air from the nozzle 20 a relative low pressure is generated in accordance with generally known physical laws just below the noz¬ zle 20, at which place the gas flow velocity is high owing to the discharge of pressurized air.

It is to be noted that the two pipes 11 and 12 together with the as¬ sociated plate-shaped parts 16, 17 and 27 constitute a radiation screen having an upper flange 26 firmly connected to the pipe 11 and serving the purpose of maintaining the pyrometer 10 in a vertical or upright position as shown in the drawing when the pyrometer 10 is suspended in an inner space in an incinerator, introduced through an opening in the upper wall of the incinerator. As will be evident to persons having skill in the art, the pipes 11 and 12 and further the plate-shaped parts 16, 17 and 27 of the radiation screen may advan¬ tageously have radiation reflecting and radiation absorbent surfaces which may be provided in accordance with technical radiation princi¬ ples known per se for optimization of the performance of the radia¬ tion screen. Although the drawing shows several openings 13 and 14 in the pipe 11 and the pipe 12, respectively, it is preferred, espe¬ cially for use of the pyrometer 10 for measurement of the gas tem¬ perature in incinerators in which there is a circulation of gas con¬ taining particles of soot, cinders and fly ash, that peripheral openings 13 and 14 are only provided in the pipes 11 and 12, respec¬ tively, on one side of the pyrometer, which side is arranged in the lee side in relation to the circulation of the waste gas so as to prevent an introduction of particles of soot, cinders or fly ash by the waste gas circulation through the peripheral openings otherwise resulting in stoppage and blockage of the pyrometer.

In the drawing a space defined above the circular plate-shaped part 17 within the pipe 11 is further filled with a deposit or casting 25 which is preferably a thermally insulating, high temperature resis¬ tant deposit or casting, such as a high temperature resistant epoxy deposit or casting. In an alternative embodiment the deposit or casting 25 is omitted, and the space is consequently empty.

It is especially to be noted that the pyrometer according to the in¬ vention and shown in the drawing is adapted to be arranged in a space

in which a gas is present, the temperature of which is to be mea¬ sured, having its gas inlets 13 and 14 and its gas outlet 21 arranged in the space in question so that in accordance with the principles of the invention a gas flow is generated past the thermocouple 23 in the space, without extraction or suction of gas from the space, as is the case with the known suction pyrometers. Thus, any problems are avoided in connection with stoppage of the suction channel of the suction pyrometer, unintentional pollution in consequence of suction of toxic suction gases from the space, etc. Whereas, most frequently, it has only been possible to use the known suction pyrometers for 5- 10 hours owing to stoppage or blockage of the suction channel, the pyrometer 10 according to the invention shown in the drawing and im¬ plemented in accordance with the below example has been used con¬ tinuously for measuring the temperature in a combustion chamber in an incinerator for burning household refuse for a period of more than 1000 hours.

EXAMPLE

A pyrometer 10 according to the invention was constructed from the following components: the inner pipe 12 was a pipe of heat resistant stainless steel, A.I.S.I. 310 steel or so-called 25/20 Ni/Cr steel and had a length of 500 mm, an inner diameter of 14 m and a wall thickness of 1 mm, the outer pipe 11 was also of heat resistant stainless steel,

A.I.S.I. 310 steel and had a total length of 3000 mm, an outer di¬ ameter of 40 mm and a wall thickness of 1.5 mm, the plate-shaped components 16, 17 and 27 were also made from heat resistant stainless steel, A.I.S.I. 310 steel of a plate thickness of 1.0 or 1.5 mm, the space 24 was filled with thermally insulating material of the type KERIANE* 60, the thermal sensor 23 was a thermocouple of a commercially available type, e.g. a type K, NiCr/Ni thermal sensor of a diametre of 3 mm and having a jacket of 25/20 Ni/Cr steel, the holes or openings 13 and 14 had a diameter of 10 mm, the pressurized air conduit 19 was a stainless steel pipe of A.I.S.I

310 steel of an outer diameter of 4 mm and a wall thickness of

SUBSTI - ' "- ^*■

0.5 mm , and the nozzle 20 had an inner bore of a diameter of 1 mm.

For a period of more than 1000 hours (corresponding to continuous measuring for 2 months) temperatures were measured continuously in an incinerator within the range of 900-1200°C, a gas flow of a velocity of 30-60 m/s being generated by supply of pressurized air in an amount of 15-50 1/min. in the radiation screen of the pyrometer, or rather in the inner space defined by the pipe 12.

Although the invention has been described above with reference to a special embodiment of a pyrometer according to the invention, it is obvious that numerous modifications and amendments may be made within the scope of the invention without deviating from the spirit and aim of the invention. The materials stated in the example thus merely serve to illustrate the invention, as these material statements must not be considered limiting. It is thus expected that instead of the heat resistant stainless steel type stated, A.I.S.I. 310 steel, stainless steel with a higher oxide scale may be used, particularly another type of 25/20 Ni/Cr steel with a small content of Si to ob¬ tain an increased oxide scale temperature compared with traditional 25/20 Ni/Cr steel. Instead, it is possible that especially quartz glass or ceramic materials, such as aluminium or beryllium oxide, are usable for the components in the radiation screen of the pyrometer and probably also for the components of the pressure fluid conduit and the pressure fluid discharge nozzle. It should further be noted that the radiation screen may possibly be formed with a neck and a subsequent enlargement for the generation of a venturi effect, just as instead of pressurized air, it is probably possible to use pres¬ surized water or pressurized steam, possibly a gas, such as nitrogen or the like, which is inert in relation to the gas whose temperature is to be measured, or possibly a gas sucked out from the measuring chamber and compressed in a compressor unit after cooling.