JPH01280604A - Method of improving efficiency of steam process - Google Patents

Abstract

PURPOSE: To improve heat efficiency by feeding through a preheater a greater amount of feed water than the amount predetermined from steam generation amount in a boiler, and supplying the excessive feed water to a low-pressure steam generation apparatus so as to generate low-pressure steam and introduce the same into a steam turbine. CONSTITUTION: Feed water Vs is fed from a feed water tank 4 to a steam separation drum 2 of a boiler apparatus through a low-pressure preheater 9. After the feed water is separated, steam generated by a steam generator 7 is supplied to a steam turbine 3 through a superheater 6. The steam after finishing work is introduced to a condenser 10 and then returned to the feed water tank 4 after being condensed. In this case, a plurality of expansion evaporators 11 to 13 are disposed. The excessive component of the feed water supplied to the drum 2 is introduced into the expansion evaporator 11 as a branch flow V1. The branch flow V1 is separated into a steam flow H2 and a residual water flow V2, and the steam flow H2 is introduced into the steam turbine 3. Further, in the same manner, steam flows H3 and H4 separated by the second and the third expansion evaporators 12 and 13 are introduced to the steam turbine 3.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention is directed to a steam generating system in which steam generated by a high temperature medium flow is supplied into a steam turbine, and the cooled steam is discharged from the steam turbine. The present invention relates to a method for increasing the efficiency of a steam process in which a stream is condensed and the feed water of the steam generation system is preheated.

[Conventional technology]

In steam turbine processes where energy is obtained, for example, from the waste heat of a gas turbine, a problem is that the feed water flow is low compared to the gas flow, and therefore the steam flow is low. Therefore, the gas cannot be cooled particularly significantly without reducing the pressure during the steam process,
Therefore, efficiency is further reduced. In practice, the optimal pressure level for the waste heat boiler of a gas turbine is 60-40 par, and the gas is transported by the 1-pressure boiler to about 2
It can be cooled down to around 00°Q.

Many attempts have been made to solve this problem, with little difference from each other. The most common solution was to set up a 2-pressure process. In this case, a suitable pressure level in the gas turbine waste heat process would be between 6° and 80 par, and the gas would then typically be above 2508C. From this heat, one part
my D due to the separate evaporator at a relatively low pressure level.
Steam at the same pressure level is returned to the turbine bleed port. In this way, the calorific value of the gas is utilized finely, and the gas outlet temperature is lowered by several tens of degrees. 2-pressure)
An example of application of screen release is Swiss Patent Invention No. 621 18
A somewhat different solution is described in Swiss Patent Invention No. 645466, 1ifl. In the system described in the published specifications, a separate simmering boiler is installed in addition to the waste heat boiler of the gas turbine, so that the total amount of water supplied by both boilers is controlled by the waste heat boiler of the gas turbine. There will be sufficient volume to cool the hot gas stream to about 1°C. In this way, the combined high pressure steam obtained from both boilers is fed to the steam turbine at only one pressure/temperature level.

Swedish Patent Application No. 416 835 describes a preheating system for a two-pressure process. In this system, a steam turbine is fed by a high pressure section and a low pressure section provides steam for other general needs, such as fuel oil preheating and other heating. This system further
It has a feedwater preheating system that extracts heat from the low pressure section of the steam generator. This system also consists of a sophisticated multi-stage preheating system in which steam is supplied to the steam turbine at only one pressure/temperature level.

Finnish patent application publication no. 58681 describes a method in which a feed water circulation returning to the water tank on the suction side of the water pump is provided in the feed water preheater of the waste heat boiler. . This provides a regulating function in the sense that the evaporation of water in the feedwater preheater is prevented as the water volume increases. The system described here (variations of which may also be used) invariably reduces the cooling of the flue gas as the feed water circulation increases, since the intake temperature of the feed water to the ship water preheater actually increases. Causes a decrease in effectiveness. According to this specification, if this system is used, the amount of oil to be discharged from the steam turbine is reduced in a state where evaporation would normally occur in the preheater, so the output of the steam turbine is increased. It will be elevated.

The foregoing description is based on the sixth section, which indicates the temperature T and the amount of heat transferred, Q, of the gas stream or other medium stream K to be cooled and of the cooling water.
The diagram clarifies the thermodynamics.

In FIG. 6a, a 1-pressure release is shown, where the evaporation temperature (1) and the so-called ``pinch point'' temperature difference A1, which can be used for evaporation and sacrificial heating, are shown in Figure 6a. Limit the cooling effect and the amount of heat transferred to a value Q. It is limited to. The amount of heat required to preheat a corresponding quantity of water supply is Q-factor, and is sufficient for a truly slight cooling effect of the gas in normal use where the gas introduction temperature is low. be. , the gas stream to be cooled is cooled only to a temperature Ta at most.

The usual way to solve this is to incorporate a second evaporator at a lower pressure level, ie the 2-pressure relief shown in Figure 6b. Usually, the steam (IT:) produced in this way is
6 as an intermediate feed into a steam turbine, or used in a factory process or similar process as described in Swedish Patent Application No. 416 835. The heat recovered from the cooled gas stream increases by a heat quantity Q, 2 compared to 1-pressure release, but the same cooled gas stream is cooled only to a temperature T'b at most.

As described in Finnish Patent Application Publication No. 58 681, a large amount of K (lj
When water is pumped and the excess water is returned to the inlet side without being cooled, the inlet temperature of the feed water rises a little, as shown in Fig. 6d.
TollT2), and this will result in a reduction in the amount of heat stored in the feed water. However, if the gas introduction temperature decreases (0-1-2 in Fig. 6d), this phenomenon is exploited in part load control.

In this case, the steam production of the boiler will be reduced and therefore the water supply will be reduced. However, the feed water will already begin to boil in the feed water preheater, but attempts have been made to prevent or limit this to a minimum for a number of reasons, and methods utilized include temporary circulation of the feed water. be. On the other hand, efficiency would require that the feed water be already heated to the saturation point in the preheater.

Finnish Patent Application Publication No. 58681 describes a method in this regard.

In this method, on the basis of a certain control strategy for the circulation of the feed water, it is possible on the one hand to prevent evaporation in the feed water preheater and, on the other hand, to obtain approximately boiling temperatures. The aforementioned Swiss patent invention No. 621 186 related to the two-pressure process is also one! It is also intended to solve the partial load problem mentioned above. However, this does not include the circulation of feed water.

[Problem that the invention seeks to solve]

The disadvantages of each of the systems described above are that - due to the multi-stage high-pressure evaporation action, the steam generation is complicated and, therefore, it is also expensive. Moreover, this problem in the aforementioned solutions is due to the partial loading of the gas turbine unit when the gas flow in the waste heat boiler remains unchanged but the energy to be obtained is reduced and the steam output of the boiler is also reduced. It is generally more serious when

If the preheater starts an evaporative action as described above due to the reduction in water flow, if no process treatment changes are carried out - in which case the efficiency at part load is reduced again - or, moreover, the process at the nominal point However, if the design is far from the economically optimal design, operational technical problems will also arise.

[Failure to solve the problem]

Using the process of the invention, the deficiencies mentioned above can be decisively remedied. The features of claim 1 characterize the inventive method for realizing this.

The most important advantages of the invention are that it achieves the following in a simple way:

- a process that is approximately thermodynamically equivalent to a multi-pressure process, providing a separate steam generation circuit for each pressure level of the expansion process of the process described herein, resulting in high efficiency; Cooling of the gas to near the temperature of the feed water, - solving technical problems of partial load operation in heating boilers and other objects where the gas quantity does not depend on the waste heat capacity, increasing the power generation. Achieving the above-mentioned advantages is more economical than in the case of conventional processes, both in terms of cost and relatively low investment costs.

〔Example〕

In the following, the invention will be explained in more detail with reference to the accompanying drawings.

This process receives and takes off thermal energy through a boiler, indicated generally by the numeral 1.

The components of the boiler 1 include an energy-producing medium stream 14
The medium stream typically consists of a waste heat gas stream of a gas turbine, a flue gas stream of another combustion process, or another relatively hot gas or liquid stream. .

The process shown in the drawings functions as a normal reflux system as follows. Sent from water tank 4,
The feed water VS at a temperature of about 55° C. passes through a low-pressure preheater 9 into the steam separation drum 2 of the boiler installation, from where it is fed as streams v, p in order to receive the steam HP into the drum 2. It is sent to the steam generator 7. The steam stream HT leaving the drum 2 is sent via a superheater 6 and then directed to the high pressure part of the steam turbine.

Steam H that has exhausted its energy comes out of steam turbine 3
L is a water stream V flowing through the condenser 10 and having a temperature of about 40°C.
Changes to L. This condensate is usually controlled in various ways and directed into the system via a water tank 4 as feed water V, S.

Since the water t V H (in this case the same as It is not possible to achieve a particularly large reduction in gas temperature. Conventional load control schemes with constant or smoothly varying pressures do not substantially affect efficiency in this regard.

In order to solve the aforementioned efficiency and part-load problems, this steam process is equipped according to the invention (as an example in FIG. 1) with six expansion evaporators 11° 12.13. . In normal load conditions during operation, whether at full load or at partial load, the feed water VS
However, when a larger amount of water is supplied than the planned amount based on the steam generation of the boiler 1, the amount of water used for the main steam generation flows into the boiler drum 2 as water VH to be evaporated, and The amount of water produced: Water after the low-pressure preheater 9 flows into the side channel as 1. Water to be evaporated V
H flows further through the steam generator 1 as described above.

The water branch stream (1) reaches the first expansion evaporator 11 which expands the water branch stream, where it is split into a vapor stream (H2) and a residual water stream (2).

The steam stream H2 is then heated by the gas stream 14 in the cryogenic superheater 8 and introduced into the steam turbine 3 at a point corresponding to its pressure. Typically in this case the superheated steam pressure is 15 par;
The temperature is 250°C. The residual water stream v2 is again introduced into the adjacent expansion evaporator 12 which further expands the water stream, where it is separated into a vapor stream H6 and a residual water stream v6. The pressure of this vapor stream H6 is typically 5 bar and the temperature is 156°C. This flow is mainly introduced into the crotch of the steam turbine 3 corresponding to the same pressure as a steam partial flow H31. A portion of this steam stream can be introduced as partial stream H32 into the introduction water tank 4, which heats the feed water. The corresponding residual water stream 6 is introduced anew into an adjacent expansion evaporator 13 which further expands the same residual water stream for the purpose of producing a steam stream H4 and a water stream 4. At this stage, the pressure of the steam stream H4 is 1 bar and the temperature is 100°C. This residual water stream V4 is passed through the water supply device 10 and typically has a temperature of about 40°.
It is led to condensate VL, which is C.

Regarding the condensate VL, VLKfi and the feed water VK, VS, the arrangement realized with the surface heat exchanger 5 concerns the degassing of the feed water and is not per se relevant to the invention.

From a thermodynamic perspective, the present invention achieves this by increasing the water flow through the feedwater preheater, and by increasing the surface area of the feedwater preheater as much as is necessary and cost-effective. , heat recovery is increased correspondingly to FIG. 6C. The flue gases are in principle up to the temperature of the feed water leaving the condenser (in practice, e.g. up to the temperature 're).
cooled down. In this case, the amount of heat recovered is further increased by the amount of heat Q3 compared to 2-pressure release. Therefore, by proper design of the equipment and proper control of water flow, saturated high pressure water is maintained in excess of the amount of water that can be evaporated and superheated by the amount of heat Q available in the evaporation and superheating sections of the boiler. To this end, excess feed water is diverted from the boiler and utilized to generate relatively low pressure steam in the alternative manner described herein, which is then cooled and recycled again. Returned into the feedwater preheater (the cooling stage of the water is not clear from Figure 6c).

The low-pressure steam generated is fed as an intermediate feed to a steam turbine, which increases its electrical output.

In the case corresponding to this example (FIG. 1), the effect of sending the feed water through the expansion evaporator, without changing the arrangement of the devices, was as follows.

Steam turbine output incremental feed9 amount Output (net) (net) O
kg/S 40.73MW OMW7.38
// 41.58// 0.75
/116.08 // 42.24 //
H5,,1//25.91 //
42.60 // 1.87 // 36.72
// 42.48// 1.75 1
/Here, the main steam inflow amount HT to the steam turbine 3
i was a constant 67.4 kg/S.

Only one exemplary process of the present invention is shown in FIG. Relying on this principle of supplying feed water in excess, the recirculating section can be used, for example, for the expansion evaporation 2%11,12.13
The principles of the invention can be applied in many different ways, such as by evaporating the steam using a steam turbine and introducing the steam into the steam turbine 3. In this example, an expansion evaporator with three pressure/temperature levels is installed, but one
It is also possible to install only one or six or more expansion evaporators. The steam obtained by these evaporators is 1
In one or more superheaters 8, the gas stream 14 is either subheated or introduced into the turbine without superheating.

According to a particularly advantageous method, a superheating method is realized in which the steam HS that can be obtained in each case from the expansion evaporator is superheated in the heat exchanger 23 using the water v1 flowing into the evaporator ( Figure 2). If applied to the example in Figure 1,
Accordingly, the steam flow H is reduced by the water flow v2.
4 will be heated by water filtration.

Heat transfer by gas flow 14 and water flow v1, v2 and/or ■
It is also possible to combine the overheating by 6. Similarly, a partial steam stream H filter 2 can be obtained at the bottom of the evaporation process and introduced into the feedwater heating section, or that step can be omitted and all the steam can be introduced into the turbine 3.

The number and configuration of the low-temperature preheaters 9, superheaters 8, steam generators 7 and superheaters 6 are determined, depending on the flow direction and the type of heat source, by the use of all structures known per se. Of course.

Similarly, water flow v1. Overheating due to V2 and/or V6 is
The same water flow and corresponding steam flow ns, H2°H3 and/or H
This can be realized by applying any known heat exchange structure between the heat exchanger and the heat exchanger.

The arrangement connected to the water tank 4 and the heat exchanger 5 itself is also
Can be in other formats. The feed water to be conveyed is returned to the suction side of the feed pump 16 or to the pressure side of the pump using a separate water pump, depending on process requirements.

In addition to the expansion evaporator described above (“flash”-drum), a surface heat exchanger complex 21 (FIG. 2) can also be used to evaporate the cold water feed. v1 is a stream to be cooled, or optionally also a superheating medium as mentioned above, from which a still relatively small water stream is simultaneously taken off for evaporation, from which a corresponding steam stream HS is taken. The water is generated towards the steam turbine. This water can, of course, also be obtained at a side location. Said system is shown in FIG. In relation to vessels (
applicable when the same evaporator is provided with multiple pressure levels).

If the feed water VH coming out of the preheater already contains steam, i.e. if the preheater has been evaporated, the excess feed water V1 taken out to the water pump will not be separated but will be sent to the same pressure steam separator (
(not shown). The steam obtained from this separator is introduced into a boiler or boiler drum 2, and the residual water is transferred to a device 11, 12. for generating low-pressure steam.
13; Cooled at 21. The low-pressure steam H2, H3, H4; He thus generated is treated as described above. If you are trying to avoid a rise in salinity of cold water during the low pressure cycle, preheated feed water VH can be used as boiler water vp
Before being mixed into the boiler drum 2, the supplied water 1 in the boiler drum 2 is taken out through a specific water pipe.

Irrespective of the foregoing, and in addition, the waste heat discharged from this process, e.g. from the flue gas stream, can be used to convert the waste heat, e.g. from the flue gas stream, into the immediate heat of the water used for other purposes, using a boiler device 15. It can be used for. In this way, the waste heat energy of the flue gas is utilized most effectively.

The application of this process was mainly explained to the utilization of waste heat from gas turbines. However, the application of this process is not limited to this. Thermal flow 14 may be any process hot medium stream, be it another flue gas stream or the exhaust stream of any engine, e.g. a marine engine, in which case the medium may be gaseous or liquid, or a combination of both names). This flow 14 is
It may also contain solid particles.

[Brief explanation of the drawing]

In FIG. 1 an embodiment of the process of the invention is shown as a process diagram. In FIG. Figures 6a, 6b, 3c, and 6d show temperature-calorific diagrams for explaining the present invention and its state of the art. 1. Steam generation system, 2 ...boiler drum, 3.
・Steam turbine, 7. Evaporator, 8. Heater, 9. Preheater, 1112.13. Expansion evaporator, 14. Gas flow.
16...Water pump, 21...-Surface heat exchanger complex,
HT, HT, , HS, H2. H3+ H4- vapor, V j , V S , V K
, V.H. vp...supply water

Claims (1)

[Claims] 1. High temperature medium flow (1) in steam generation system (1)
4) The steam (HT) produced by the steam generation system (HT) is fed into a steam turbine, the cooled steam stream (HL) exiting from the steam turbine is condensed and
In the method of increasing the efficiency of the steam process in which the feed water (VS) of 1) is preheated, a large amount of the feed water is heated to the feed water preheater ( 9) Excess feed water (
V1) is a device (11, 12, 13) that generates low pressure steam.
; 21), the low-pressure steam (H2, H3, H4; HS) thus generated is fed into the steam turbine (3) as an intermediate supply and cooled to supply the feed water. being returned into the preheater (9);
A method for increasing the efficiency of a steam process, characterized in that the cooled excess feed water is returned to the feed water (VS) flowing into the feed water preheater. 2. The excess feed water (V1) to be sent is cooled by expansion to low pressure in one or more stages (11, 12, 13), and a portion of each generated expanded steam 2. Method according to claim 1, characterized in that the streams (H2, H3, H4) are fed into the steam turbine (3) as an intermediate feed at a position corresponding to the pressure level in question. 3. The excess feed water (V1) to be sent is supplied to the feed water (VK) flowing into the feed water preheater by a water pump (16).
3. The method according to claim 1, wherein the method is directed back toward the suction side of the tube. 4. The excess feed water (V1) to be sent is cooled in a surface heat exchanger (21), and the steam (HS) generated when the radiator boils in the heat exchanger is used as an intermediate feed. Method according to claim 1, characterized in that it is fed into the steam turbine (3). 5. The method according to claim 1 or 4, characterized in that the excess feed water (V1) to be sent is returned to the pressurized side of the water pump (16) using a specific water pump (22). . 6. The above, characterized in that, before the feed water reaches the boiler drum (2), excess feed water (V1) used for cooling is withdrawn after the feed water preheater (9). A method according to any one of the claims. 7. The excess feed water (V1) taken into the water conduit is first introduced into a steam separator at the same pressure, from where the steam is introduced into the boiler drum (2), and the residual water is The low pressure steam (H2,
7. A method according to claim 6, characterized in that H3, H4; HS) is fed into the steam turbine as an intermediate supply. 8. Excess feed water (V1) taken up for said cooling in said boiler drum (2) before the preheated feed water (VH) mixes with boiler water (VP)
A method according to any one of the preceding claims, characterized in that the water is removed by a specific water pipe. 9. Excess feed water taken in for said cooling (V1
) is the boiler water (
5. A method according to any one of the preceding claims, characterized in that the method is retrieved from a VP). 10. The excess supply water (V1) that is distributed becomes the supply water (
The flow rate (VS) of the feed water preheater (9) is adjusted such that the feed water (VH) reaches a boiling temperature corresponding to the pressure of the boiler drum (2) before being diverted from the feed water preheater (9). A method according to any one of the preceding claims, characterized in that the method is regulated. 11. The device for generating low pressure steam (11, 12,
13) The steam (H
2, H3, H4) is superheated by excess feed water (V1, V2, V3) flowing into the device and circulating accordingly. Method described. 12. The device for generating low pressure steam (11, 12,
13) The steam (H
2, H3, H4) are superheated by a superheater (8), which superheater is connected to the preheater (9) and the evaporator of the main circuit in the hot medium stream (14). A method according to any one of the preceding claims, characterized in that the temperature step corresponds to a temperature between (7) and (7).