US2268074A - Protective means for the heaters of thermal circuits - Google Patents

Description

Dec. 30, 194-1. Q ER 2,268,074

PROTECTIVE MEANS FOR THE HEATERS OF THERMAL CIRCUITS Filed Sept. 26, 1939 2 Sheets-Sheet l Dec. '30, 1941. 4 c. KELLER 2,258,074 PROTECTIVE MEANS FOR THE HEATERS OF THERMAL CIRCUITS Filed Sept. 26, 1939 2 Sheets-Sheet 2 risk that the temperature of Patented Dec, 30, 1941 UNITED STATES PATENT OFFICE 2,268,014 r PROTECTIVE FOR THE HEATERS 0F THERMAL CIRCUITS Curt Keller,

' Zurich, Switzerland,

land

Application September 26 In Switzerland s 1 Claim. The invention relates to an arrangement for plants in which a gaseous working medium describes a closed cycle under a pressure greater than atmospheric, the working medium, which is heated in a tubular gas heater by a. supply of heat from an outside source, being allowed to expand in at least one turbine while giving up Zurich, Switzerland, assignor to Aktiengesellschaft fuer Technische Studien,

a corporation of Switzer- 1939, Serial No. 296,704

October 10, 193.8 (01. 60-59) cooling the heater tubes of thermal powerv energy externally and brought afterwards again to a. higher pressure in at least one compressor, an exchange of heat taking place also in a heat exchanger between the expanded and recompressed current of working medium prior to the supply .ofheat from the outside source in the tubular gasheater.

The tubes of .the gas heater or plants of this kind are subjected to very high temperatures. In addition to this they are subjected to severe mechanical stresses owing to the pressure exi'st lng inside them. If therefore it is intended to bring the working medium to a high temperature in the tubular gas heater, one is compelled to subject the constructional material of the tubes to the utmost limit of its heat resisting power, if it is desired to retain dimensions which are usable in practice. When the tubes are sub- 'Ject to such high stresses by the fire gases on their outsides and on their-insides by the work- 'ing medium which flows through them under a pressure greater than atmospheric pressure and is to be heated to a high temperature, it is im-. portant under all circumstances, to keep the temperature of the tubes at as high a value as possible with only very slight variations. If therefore for example the absorption of heat by the working medium ceases owing to fluctuations in'the load, or, on the other hand, too

much heat is given oil by the furnace, there is the tubes mayrise, at least for a short time, above the particular value permissible so that the tubes are no longer able to cope with the stresses. to. which they are subjected. The risk in overheating of this kind is greater in the tubular gas heaters of plants of the kind herein referred to than in steam boilers, because owing to the comparatively bad transmission of heat on the insides and out sides of the tubes the temperature thereof at a desired working temperature of the working gas to be heated up is considerably higher than it is at the equaily'high working temperature of the of a steam power plant t is therefore all the more important not to a is. value of the tube wall temperature ul. heaters, because in. the range of temperati.

involved, which lies between 600. and 800 C. for example, the strength of steel or corresponding alloys decreases rapidly with increasing temperature. Even increases of temperature of 20 C. for example weaken the strength of the metal very considerably.

The object of the present invention is therefore, to provide an arrangement for cooling the heater tubes of the thermal power plants of the kind hereinabove referred to, which, if the temperature of the tubes of the tubular gas heater he suddenly raised beyond a fixed point, permits of the particular rise of temperature being rapidly and effectively counteracted. According to the present invention this is accomplished by an additional pipe circuit which can be shut off, and permits of working medium supplied by the compressor being passed directly into the inlet of the gas heater without passing through the heat exchanger. i

In the drawings afiixed to the present specification and forming part thereof two embodiments of the invention are shown diagrammatically by way of example.

In the drawings:

Fig. 1 illustrates, partly in longitudinal section, partly in side elevation, a thermal power plant,

wherein use is made of the cooling arrangement according to the invention.

Fig. 2 illustrates a similar modification of a detail.

Referring now to the drawings, and first to Fig. 1, l denotes a tubular gas heater, in which the gaseous working medium, which continuously describes a closed cycle under a pressure greater than atmospheric is'heated by heat supplied from an external source l8. The actual heating of the working medium takes place in coils 2, around which the fire gases-flow. The working medium thus heated passes through a pipe 3 into a multi-stage turbine 4 of the axial flow type wherein it expands while giving up energy simultaneously to an electric generator 5 and a turbo-compressor 6 for example. T denotes pipings connected to different points of the casing of the turbo-compressor t and-supplying cooling water to the latter. The water heated in the turbo-compressor E is discharged through pipings 8. The working medium on leaving t a turbine t passes through a pipe if into a texchanger til which is constructed in the "i of a cohtrafiow apparatus contain-- ing; a sys of i i, whereby heat is given to the part of the working medium at the plant, showing a i id, tor pressure, which passes through a pipe 32 l3 into a collector heater l. device 20. The adjustment of this shut 011 detively cold I of the tubular gas heater l without passing out of the turbo-compressor 6 into the heat exchanger l and out of this latter through a pipe I M of the heater I. of the working medium which is cooled down in the heat exchanger i0 passes through a pipe l into the turbo-compressor 6, wherein it is raised .to' av higher pressure and cooled simultaneously. From the pipe l2.there branches off at IS an additional pipe I! in which an intermediate cooler I9 is interposed, and which is connected to the collector ll of the tubular gas This pipe 11 also includes a shut oil! vice 20 is controlled by a thermostatic arrangement 2!, the activity of which in its' turn is dependent on the temperature at the point 22 y or a coil 2 of the tubular gas heater l.

In the plant described the pipe ll forms a by-pass through which, when the shut off device 20 is open, working medium coming from the compressor 6 and which is still comparaean pass directly into the collector through the heat exchanger III. Under normal working conditions this py-pass I1 is shut off, so that the working medium compressed in the compressor 6 passes whollythrough the pipe l2 into the pipe ll of the heat exchanger ill, in which it is preheated-and therefore enters in a preheated state into the tubular gas heater in If however for anyreason the walls ofthe tubes 2 of the heater l are raised to too high a temperature, the thermostatic arrangement 2| will open the by-pass I! at least partially, so that now comparatively cool working medium passes, without going through the heat exchanger l0, directly into the collector H of the tubular gas heater l and then out of this collector l4 into" the tubes'2 which are too hot, where'it mixes with the working medium which has been already preheated and comes from the heat exchanger iii. In this way the temperature of the tubes 2 will be rapidly lowered hereby the temperature of the walls of the tubes is naturally also reduced. If then in the meantime the working conditions of the gas heater l have .been readapted to the modified loads'-by adjusting the amount'of heat supplied by the furnace and if therefore the temperature of the walls of tubes.

2 has dropped again to the permissible upper limit, the thennostatic'arrangement 2| closes the shut off device 20, so that the flow of the working medium through the by-pass I1 is interrupted.

The auxiliary cooler l8 ensures that the portion of the working medium'flowing through the by-pass I1 shall be particularly effective as regards the reduction of the temperature of 'the The part some circumstances tubes 2, in that it permits this part to be brought to a low temperature in the cooler l9. Under however it is possible to dispense with such an auxiliary cooler.

The by-pass IT can also be used, when the tubular gas heater 5 is shut off, that is to say when the plant isstojpped, to deliver colder workdown naturally.

ing medium to the coils of tube 2, so as .to cool them down as rapidly as possible. This is important under certain circumstances, when there is but little time available and there is no opportunity' of allowing the gas heater to slowly cool Fig. 2, the portion of through the addi- In the plant shown in the working medium flowing tional pipe 23 is not delivered to the collector 24 of the tubular gas heater 25 but to pipes 26,

21 connected to tubes 28 and 29 respectively, of

the tubular gas heater 25. In Fig. 2, 30 denotes a turbine, 3| a compressor and 32 a heat exchanger, all of similar designs as the corresponding parts 4, B and HI respectively, of the plant.

shown in Fig. 1. In thatpart of the pipe 33 which leads from the branch oint 34 to the heat exchanger 32 is'provided a throttling device 35 ensuring that in certain cases by far the greater part of the working medium shall be driven through the open by-pass 23. This throttling device 35 is so coupled to the shut ofi device 36 of the additional pipe 23 that when the one is closed the other is open and vice versa.

What is claimed is:

A thermal power plant comprising a closed circuit containing a gaseous working medium which, under operating conditions, is throughout the circuit above atmospheric pressure, said circuit including a surface heater in which heat from an external source is transmitted to the 40, medium, an expansion motor in which the working mediumheated in the surface heater expands while doing external work, a compressor driven by said expansion motor and serving to recompress the medium expanded in-the motor to a higher pressure and deliver it to said surface heater, said circuit including a normal and a supplementary path from said compressor to said heater: 9. heat exchanger in said normal path in which medium leaving the compressor exchanges heat with medium flowing from said expansion motor to said compressor, the supplementary path supplying medium issuing from the compressor directly to said heater; controllable means for causing the diversion of at least a portion of the medium through said supplementary path; and cooling means interposed in said supplementary path.

, CURT KELLER.

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