DE2122063A1 - Waste heat steam generator - Google Patents

Description

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DR. I. MAAS

DR. W. PFEIFFER DR. F. VOITHENLEITNER

8 MUNICH 23 TR — 10 UNeERSTR. 25- TEL. 39 02 pp

Treadwell Corporation New York, N.Y. 10019, V.St.A.

Waste heat steam generator

If its waste heat were used effectively, a Brayton gas turbine cycle would be a very efficient one Power generator as it is capable of working with a very high inlet temperature. The poor efficiency of the currently used waste heat conversion plants however, reduces the possible efficiency to such an extent that the overall efficiency of the cycle is usually even is less than that of a common steam or Rankine cycle.

Than one in the past the overall efficiency too wanted to improve, waste heat boilers were often used and finally there are two waste heat boilers arranged in series, which generate steam at progressively lower pressures have been used.

A thermal efficiency of 35.1% is theoretically with a cycle that works with a waste heat source with an initial temperature of 454 ° C (850 ° F) drops to 38 ° C (100 ° F). This efficiency could be achieved by using a very large number of in Would use horizontal boilers working at progressively lower pressures, but in the In practice, the costs of the system and disruptive losses, such as pressure and temperature drops, limit the number two or at most three boilers in a row.

The present invention provides a waste heat boiler system created in which the intrinsic heat, in particular the intrinsic heat of a Brayton cycle gas turbine, is initially used to superheat the steam of a working medium, as described below, and then used to heat the working medium in the liquid form under a pressure sufficient to Evaporation prevention is essentially high enough. In essence, the present invention is shown in its broadest scope is not concerned with the precise working medium used in each case. Water is by far the cheapest and in many cases the preferred working medium. However, other known working media can also be used, such as suitable fluorocarbons, for example the one under the trade name "Freon RIl"

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ammonia and the like can be used. Other working media can of course also be used taking into account that the selected medium has suitable evaporation properties for the Must have application to which the energy generated by the waste heat is subjected. On a Brayton cycle gas turbine the normal exhaust gas has a temperature on the order of 427 to ^ 82 ° C (800 - 900 ° F) and this means certain restrictions on the type of working medium. For example, one of these Combination of mercury not particularly desirable. According to the invention there is no upper limit for the Temperature of the waste heat source that is not specified by the building materials of the system. The increase in efficiency however, it is much more significant if the temperature of the waste heat source is not extremely high. In the latter In this case, conventional Rankine cycle heating boilers often have a sufficient thermal efficiency so that the need for the present invention is not so great.

In the temperature range occurring in the exhaust gases from gas turbines water is a very suitable working medium and it is preferred because of its cheapness and other properties. To the description as possible To make clear, the invention is described below with reference to water as the working medium, but without this it is intended to limit the invention in its broadest scope to that particular substance.

If you have waste heat in the temperature range from 42 7 to 482 ° C

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(800-900 ° F) can use water at a pressure of 105.5 at (1500 psia) without evaporation to a temperature of 313 ° C (596 ° F). This hot, high-pressure water goes into the high-pressure tank (high pressure receiver) initiated a series of several, for example two or three containers, each row consists of a high pressure, an intermediate pressure and a low pressure vessel. The water in the high-pressure tank can gradually evaporate under reduced pressure to an intermediate pressure and the generated steam is superheated by the exhaust gases, as explained above, and then in a high pressure steam turbine expanded with multiple nozzles. The rate of evaporation under reduced pressure (flashing) is regulated by the number of turbine nozzles used. A single nozzle can be used at the highest pressure are, while with falling pressure and also falling weight of the flowing through a single nozzle Steam gradually more nozzles are switched on in order to keep the power output reasonably constant to keep.

When the water in the high pressure tank evaporates under pressure reduction to a predetermined lower pressure it is fed into an intermediate pressure vessel and the empty high-pressure vessel is filled with hot again Filled with water. As above, the water in the intermediate pressure tank can evaporate down to a lower pressure. The generated steam combines with the exhaust steam of the high pressure turbine and after overheating it is combined Steam introduced into an intermediate pressure turbine with multiple nozzles.

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When the water in the intermediate pressure tank is depressurized to a selected lower level Pressure is evaporated, it is led into a low-pressure container. The empty intermediate pressure vessel will then filled again with the water that was previously able to evaporate in the high-pressure container. The water in the As above, low-pressure tanks can be subjected to pressure reduction Evaporate to condensation pressure. The steam generated combines with the exhaust gas from the intermediate pressure turbine and after overheating, the combined steam is fed into a low-pressure turbine with multiple nozzles, through which it expands to become a condenser.

When the water in the low-pressure tank evaporates under pressure reduction up to a preselected pressure is, the container is emptied and then refilled with the water that was previously in the intermediate pressure tank has evaporated.

The water from the low-pressure tank subjected to the evaporation process and the condensate are combined and pumped back through the exhaust gases for reheating.

Since the pressure of the steam generated by the evaporation of a hot water filling drops continuously from the initial pressure of 105, .Bat (1500 psia) to the preselected condensation pressure, each hot water filling forms the equivalent of an unlimited number of boilers, which work at progressively lower pressures. The efficiency of the cycle can therefore closely approximate the maximum theoretical efficiency of 35.1% mentioned above ¹ .

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If you neglect heat and friction losses, according to the invention, from a given amount of exhaust gases having a temperature of 454 ° C (850 ° F) 5H% generates more work than a single waste heat boiler, 30% more work than with two waste heat boilers in series and 23% more work than with three in-line boilers.

The evaporation of the water in the high-pressure, intermediate-pressure and low-pressure tanks was described as as if they happened one after the other. It is noted, however, that the water in all three containers in the Practice is evaporated at the same time, with steam being delivered to the respective turbines. If the selected lower pressure is reached in all three tanks, the water is pumped out of the low-pressure tank, the water in the intermediate pressure tank is transferred to the low pressure tank the water in the high pressure tank is directed into the intermediate pressure tank and into the A new filling of hot water is initiated in the high-pressure tank.

The dead point in power generation that occurs could, while the fillings are being transferred from container to container, can be switched off, by using an alternating series of three tanks that share the same three turbines Food.

The uniformity of the power flow from the waste heat boilers can be guaranteed by using a hot water buffer tank, into which the pressurized hot water

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flows before it enters the high pressure water tank and a cold water buffer tank is used into the .the chilled water after evaporation from the low pressure water tank and is pumped by the condenser. The capacity of the buffer tanks must be sufficient to accommodate the periodic water requirements of the rows of tanks with the uniform water flow rate of the waste heat Balance recovery plant.

It can be seen that the number of required per row Containers both by the number of nozzles available in a given turbine and is determined by the steam pressure ratio with which the turbine must work.

Because the water in the low pressure tank is always cooler than the water in the intermediate pressure tank, which in turn is always cooler than the water in the high-pressure tank, causing any steam space that remains in the tanks, when the water is passed on, due to the irreversible nature of the evaporation of the hotter ones Liquid with constant enthalpy in the temporarily lower pressure chamber of the container, in which the same is passed on, a loss of efficiency. However, a small vapor space is made up of mechanical ones Reasons needed to ensure that there is no flow siges water is introduced into the steam turbines, and the resulting small loss of efficiency must be considered Safety factor must be accepted. However, it should be kept as low as practically possible.

Since it is desirable to

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to carry out exercises with minimal mutual heat exchange, the interface contact areas of the Containers should be kept as small as possible. A practical embodiment has an upper and lower pressure vessel, which by relatively long Pipes or small diameter pipes are connected.

It is noted that the heat efficiency of the waste heat boiler according to the invention is so great that often the best overall efficiency is obtained when used with a Brayton cycle gas turbine maximized with a much fewer number of turbine stages than is normally the case is desirable if no waste heat system with such a high degree of efficiency is available. Indeed, in many Cases a single-stage gas turbine can be used, which of course saves investment costs that would otherwise have to be achieved a maximum turbine efficiency with several stages, reheating and the like are necessary would be. This savings option with the preferred Embodiment according to the invention is practical extremely important.

The figure shows a flow diagram in purely schematic form a plant for the recovery of power from the waste heat of a Brayton cycle gas turbine.

According to this figure, air 1 "enters" from the atmosphere the compressor 2 of a Brayton cycle turbine and is compressed in this and passed to the burner 6 4, which is supplied with a suitable fuel 65. The hot high pressure air flows after relaxing and

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partial cooling in the expander 63 of the Brayton cycle gas turbine to the heat recovery part 3, in which they heat to the top heater 4, 5 and 6 as well as the water heater 7 releases and is finally vented to the atmosphere at 66 in a cooled state.

Since the drawing is purely schematic, only a single-stage compressor 2 is shown. Of course, this one can be multi-stage and cooling or cold generation can be provided between the stages. That I the present invention, even in its preferred embodiment, does not go into particular details of the Brayton cycle concerned, from which the waste heat is obtained, the figure is kept simple by adding all the design features which are not essential for the schematic representation of a Brayton cycle system are. However, as noted above, one of the advantages of the invention is when used with a Brayton cycle system as a heat source in that the efficiency with a much smaller number of turbine stages, preferably only one level, maximum, can be made, and this is just shown in the figure. In this regard it can be said that the heat recovery system according to the invention is the formation of the Brayton cycle power generation system can convert appropriately.

Cold, low pressure water is pumped to a pressure of about 105.5 at (1500 psia) brought to about 313 ° C (596 ° F) in the water heater 7 heated and passed through the buffer tank 15 and the valve 16 to the high pressure vessel 17 of row A.

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In row A, the containers 24 and 31 and the work Capacitor 11 with progressively lower absolute Pressures, which ideally at the beginning of the cycle should be such that it applies

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The pump 18 circulates the water from the container 17 via the valve 19 to the steam separation stage 20, in which the water evaporated with progressively falling temperature and falling pressure, since the evaporated by relaxation Steam is removed. The flash vapor generated is passed through the superheater 4 via the valve 21 directed to the multiple nozzles of the turbine 8, through which he see relaxed in the line 60, where he with the generated in the same way in the steam separation stage 27 Qitspannun ^ steam is combined.

The combined steam flow is heated in the superheater 5 and flows through to the multiple nozzles of the turbine 9 which he relaxes in the line 61, where he generated with the in the same way in the steam separation stage 34 Flash steam is combined.

The combined steam flow is in turn in the superheater 6 heats and flows to the multiple nozzles of the turbine 10, through which it expands to the condenser 11. the Shafts of the turbines 8, 9 and 10 generate power, which is shown schematically at 62. It can turn out to be some power-consuming element, such as one

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Generator, act. The power output level is in the same way the turbine 63 of the Brayton cycle with a power consuming element 68 shown connected. In the latter case, the power delivered is natural the difference between the generated power and the power consumed by the compressor 2 driven by the turbine 63.

A second row of tanks and vacuum evaporators, which is labeled B, contains the containers 39, 46 and 53, which the containers 17, 24 and 31 of the series A. Flash evaporators 42, H9 and 56 correspond to components 20, 27 and 34 and pumps 40, 47 and 54 correspond to pumps 18, 25 and 32. Valve connections in row B are denoted by 38, 43, 45, 50, 52, 57 and 55 and 59, respectively. In the same way are the Check valves 44, 45 and 58 are provided.

When the pressure of the container '17 equates to the initial pressure of the Container 24 has fallen, the pressure of which has dropped to the initial pressure of the container 31, the pressure of which If again, in the ideal case, it has fallen to that of the condenser, then the steam valves 21, 2 8 and 3 5 closed and the valves 43, 50 and 57 of the steam separation stages 42, 49 and 56 of the steam generation row B are opened simultaneously, thus ensuring continuity of the supply of driving steam to the turbines 8, 9 and 10 is guaranteed.

The pump valves 19, 26 and 33 are then closed, but pumps 18, 25 and 32 continue to operate for automatic return to the cycle, not shown.

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The water inlet valves 16, 23 and 30 are then opened, whereby the bank A is pressurized and causes the shut-off valves 22, 29 and 36 to close so that the liquid and steam content of the steam separation stages 20, 27 and 3 ^ are included at the pressures prevailing at the end of the cycle. It it is necessary that a certain remaining steam space is in the separation stages to allow liquid to enter the turbines when operation resumes is prevented. The volumes of these steam rooms should however, must be kept as small as possible since they cause a loss of cycle efficiency, such as explained below.

Then the water outlet valve 37 is opened, whereby hot, high pressure water that in the water tank; 17 displaces the water contained at a lower temperature, which in turn displaces the water in the Water container 2 U displaces water contained, which in turn displaces the water contained in the water container 31 repressed.

The flow rate of the water to the buffer tank 15 is regulated by the valve 67, which regulates the temperature of the heater 7 leaving the heater Keeps water constant. The capacity of the tank 15 must be sufficient to meet the periodic water requirements the steam generator rows A and B with the substantially uniform flow rate to Tank 15. balance.

The valves 37, 30, 23 and 16 close when the

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Liquid level in tank 15 falls by a predetermined amount, which is the displacement volume of the cycle is equivalent to. The pump valves 19, 26 and 33 are then reopened and row A is again ready to enter the productive process.

Row B works in the same way as it does for row A has been described, with the corresponding pumps, valves, flash evaporators and the like including the operation of the check valves 44, 51 and 58 operate in the same way when the series B has given up its performance and is being pressurized again.

When the pump valves 19, 26 and 33 open again first causes the resulting irreversible relaxation ν evaporation of the hot liquids with constant Enthalpy in the temporarily lower pressures, which in the remaining steam chambers in the Steam separation stages prevail, the above-mentioned loss of efficiency of the cycle. The same phenomenon occurs when the valves 41, 48 and 55 are first opened again to put row B into operation.

Since it is desirable that the successive displacements of water with minimal mixing of the respective water flows and with minimal amount of heat exchange occur, the interface contact areas of the containers must be kept as small as practically possible will. This is achieved simply in that the containers 17, 24 and 31 of the row A and 39, 46 and 53 of series B formed from upper and lower pressure vessels

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which are connected by relatively long pipes or pipes with small diameters, such as shown schematically in the figure.

The control of the cycle is automatically set so that the uppermost liquid level in the buffer tank 15 kept constant and thereby the inflow and outflow is balanced. In the case of series A will be the multiple nozzles of the turbine 8 automatically operated so that the pressure drop ratio of the steam separation stage 20 so is set to do so with both this cycle control and the need for an essentially constant power generation. The absolute pressure of the steam separation stage 27 is automatically increased a desired percentage of the absolute pressure of the separation stage 20 through the operation of the multiple nozzles Turbine 9 is regulated and the desired absolute pressure ratio between the separation stages is set in the same way 3U and 2 7 by the operation of the nozzles of the turbine 10 regulated automatically. "

The pressure of the steam generated in the steam separation stages drops from a high value at the beginning of a cycle a low value at the end of a cycle with a comparable reduction in flow weight a given turbine nozzle which passes steam at a given temperature and a given expansion ratio. To performance in one essence To produce a uniform amount, steam is fed to a progressively larger number of nozzles when the vapor pressure drops.

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The exhaust steam from the turbine 8, which as a result of his Relaxation is cooled, combines with the steam generated in the separation stage 2 7 and is in the top heater 5 heated again. The same process occurs with the exhaust steam from the turbine 9. Improve reheating the efficiency of the cycle.

In the case of the B row, the same operation of the multiple nozzles represents in turbines 8, 9 and 10 the pressure drop ratio in steam separation stages 42, 49 and 56 a. The reheating of the exhaust steam from the turbines 8 and 9 proceeds in the same way as above for the operation of the turbines from row A was described.

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Claims (3)

Claims Generating the steam of a working medium with waste heat Plant with heat exchangers and devices for supplying waste heat gases to the same, the heat exchangers Fluid heaters and steam superheaters, characterized in that a plurality of liquid containers operating at high pressure and high temperature are provided in series parallel to each other are, the temperature and pressure in each container in each row decrease progressively, hot working fluid with a print above hers. Evaporation point in the liquid container with the highest temperature in each row of at least one of the heat exchangers in the waste heat steam generator system is pumped, multi-stage steam turbines are provided, which have a number of stages, the containers for the hot liquid in each row, each turbine stage has a plurality of steam inlet nozzles has, a number of relaxation Ver vaporization chambers is provided, which the liquid containers' correspond to the hot liquid from the liquid container with the highest temperature is introduced into a flash evaporation chamber, where it evaporates under progressively lower temperatures and pressures, provided with valves Connection devices from the evaporation chamber to a steam overheating heat exchanger in the waste heat - 17 - 109847/1322 part and from there to the nozzle sets in the high pressure part of the steam turbine are provided, the nozzle sets in certain Sequence and cumulative open when temperature and pressure of the steam in the evaporation chamber are reduced, so that substantially uniform power generation in the turbine stage is maintained, the connection device to the high pressure evaporation chamber is interrupted after the predetermined lower temperature and the prescribed lower pressure in the container with the highest Pressure is reached and liquid is pumped to a second flash evaporation chamber where it is below progressing up to a predetermined value falling pressures evaporated, this second evaporation chamber via a second superheater heat exchanger in the waste heat section and from there with another set of In the next section of the steam turbine connected in a certain sequence switched nozzle sets, the nozzles can be opened in a certain sequence and cumulatively if the temperature and pressure of the steam are in the same Drop off way, like in the high temperature part of the turbine, the liquid containers and evaporation stages lying in series are connected in a certain sequence Nozzle sets are connected to the turbine stages as in the high temperature part of the turbine, the liquid container with the highest temperature in a second row after the flash evaporation of the liquid is connected under the lowest prescribed pressure of the system and the steam connections to the top heaters are interrupted by the evaporation chambers in the first row, the working periods in the second - 18 109847/1322 Series of liquid containers and evaporation chambers be repeated and the cycle in the first row with fresh, high temperature liquid is repeated after the temperature of the liquids of the second series by flash evaporation has dropped to the predetermined level. 2. Plant according to claim 1, characterized in that? the working medium is water. 3. Plant according to claim 1 and 2, characterized in that that the waste heat in the exhaust gas of the gas turbine of a power generating plant operating with an open Brayton cycle is included. 109847/1322 BATH ORIGINAL