EP0314028A1 - Method for increasing the efficiency of a steam process - Google Patents

Abstract

The subject matter of the invention is a method for increasing the efficiency in the steam process, in which the steam (HT) generated in the steam generating process (1) with a hot material flow (14) is supplied into the steam turbine. The cooled steam flow (HL) coming from the steam turbine is condensed. The supply water (VS) of the steam generating system (1) is preheated. More supply water is pumped through the supply water preheater (9) than is needed for steam generation in the boiler (1). The excess supply water (V1) is cooled in devices (11, 12, 13; 21) generating low-pressure steam (LP steam). The low-pressure steams (H2, H3, H4; HS) produced in this way are supplied into the steam turbine (3), as an intermediate supply, and are fed back, cooled, into the supply water preheater (9). The cooled excess supply water is fed back into the supply water (VS) running in the supply water preheater. <IMAGE>

Description

The invention relates to the method for increasing the efficiency in the steam process, in which the steam generated in the steam generating system with a hot material stream is fed into a steam turbine, the cooled steam stream condenses from the steam turbine and the feed water of the steam generating system is preheated.

In steam turbine processes that use their energy e.g. B. obtained from the waste heat of the gas turbines, the problem is that compared to the gas stream low feed water flow and accordingly low steam flow. The gases can therefore not be cooled down very much without reducing the pressure in the steam process, which in turn reduces the efficiency. In practice, the optimal pressure level of the waste heat boiler of a gas turbine is 30-40 bar and the gases can be cooled to a little below 200 ° C with an 1-pressure boiler.

Attempts have been made to solve this problem in a number of ways which differ only slightly from one another. The most common solution has been to form a 2-pressure process, the optimal pressure level in the waste heat processes of the gas turbine being 60 to 80 bar, and the gases thereafter typically being more than 250 ° C. Of this heat, a part is separated with a separate evaporator recovered lower pressure levels, the steam is fed into the tap of the turbine. In this way, the heat content of the gases can be more accurate used and their initial temperature can be reduced by several tens of degrees. An example of the use of a 2-pressure solution is shown in the Swiss patent SCH-621 186.

A somewhat different solution is shown in the Swiss patent specification SCH-645 433. In the system described in this publication, a separate steam boiler is arranged in addition to the waste heat boiler of the gas turbine, as a result of which the total feed water quantity of the two boilers becomes just large enough to be able to cool the waste gas gas stream of the gas turbine down to almost 100 ° C. Thus, the high pressure steam obtained from the two boilers as a whole is fed into the steam turbine only at one pressure / temperature level.

The Swedish publication SE-416 835 also shows a preheating system that is a 2-printing process. In this system, the steam turbine is fed by the HP part and the LP part gives steam for other general needs, such as preheating the fuel oil and other heating. The system also has a feed water preheater that takes its heat from the LP part of the steam generator. This system also consists of a multi-stage preheating system, with the steam being fed into the steam turbine only at a pressure / temperature level.

In the Finnish contingent publication FI-58681 a method is shown in which a feed water circulation is arranged in the feed water preheater of the waste heat boiler back into the feed water tank on the suction side of the feed water pump. This achieves controllability with regard to the fact that water evaporation in the feed water preheater can be prevented due to the increased amount of water. The system described, the variations of which are also used, generally leads to a deterioration of the flue gas cooling when the feed water circulation is increased, since the feed temperature of the feed water into the feed water preheater increases in practice.

According to the publication, the power output of the steam turbine can be increased with this system, since the tapping quantity to be discharged by the steam turbines is reduced in a situation in which evaporation would otherwise take place in the preheater.

What has been described above is illuminated with regard to the thermodynamics by the scheme 3, in which the temperatures T and the transferred heat quantities Q of the gas flow or other material flow K to be cooled and the cooling water V are shown.

Figure 3a shows a 1-pressure solution in which the evaporation temperature (I) and the so-called "pinch point" temperature difference A 1 limit the cooling available for evaporation and overheating and the amount of heat to be transferred to a value Q₀. The amount of heat required to preheat the corresponding amount of feed water is Q 1, which is sufficient for a very low gas cooling in the usual applications in which the inlet temperature of the gas is low. A considerable amount of heat Q _h is lost. The gas stream to be cooled can at most be cooled to a temperature T _a .

The usual way to remedy this is to install a second evaporator at a lower pressure level, ie a 2-pressure solution, which is shown in Figure 3b. Normally, the steam (II) generated in this way is fed as an intermediate feed into the steam turbine, as in publication SCH-621 186, or in factory processes or the like, as in publication SE-416 835. The amount of heat recovered from the gas stream to be cooled is increased in comparison to the 2-pressure process by the amount Q₂ and the gas stream to be cooled is cooled to a temperature T _{b at the most} .

If too much feed water is pumped through the feed water preheater and its excess is returned uncooled to the inlet side, as in publication FI-58681, the inlet temperature of the feed water (T₀-T₁ T₂, Figure 3d) rises and this has the consequence that that in the feed water stored heat decreases. However, this phenomenon is used in partial load control when the inlet temperature of the gas drops (0 - 1 - 2 in Fig. 3d), whereby the steam generation of the boiler decreases, which means that the feed water quantity would decrease. The water would therefore already start to boil in the feed water preheater, which one tries to prevent or keep to a minimum for several reasons, and one method used is the extra circulation of the feed water. On the other hand, in terms of efficiency, it would be necessary for the feed water to be in the preheater up to Would warm the saturation point. A related method is shown in the publication FI-58681. In this process, one can prevent evaporation in the feed water preheater on the one hand by means of certain types of control of the feed water circulation and on the other hand almost reach a cooking temperature. The aforementioned publication SCH-621 186, which is associated with a two-printing process, is also intended to solve the prescribed part-load problem. However, this does not include feed water circulation.

The disadvantage of the systems described above is - because of the multi-stage in HD evaporation - a complicated steam generation side and therefore also a high price. In addition, in the solutions discussed above, the problem generally becomes greater with partial loads of the gas turbine installation when the gas flow from the waste heat boiler remains unchanged, but the energy to be obtained is reduced, and the boiler's steam generation is also reduced.

This also leads to operational problems if the preheaters start to evaporate in the above-mentioned manner because of the reduced water flow, if changes in the process circuit are not carried out - which in turn reduces the efficiency of the partial load - or then a process at the nominal point far away from an economical one Optimal design is planned.

With the help of the process according to the invention, the abuses described above can be decisively improved. To achieve this, the measures described in the patent claims are provided for the method according to the invention.

The most important advantage of the invention can be considered that it enables in a simple way:
- A process that almost corresponds thermodynamically to a multi-pressure process, in which there are separate steam generator circuits for each pressure level of the expansion device of the process described here, which results in high efficiency
- Cooling of the gases reasonably close to the feed water temperature
- Solves the operational problems of partial load in the boilers and other objects in which the amount of gas is independent of the heat output
- Achieving the advantages described above economically cheaper than with the usual processes, both through increased electricity generation and through lower investment costs.

The invention will be explained in detail below with reference to the accompanying drawings.

Figure 1 shows an embodiment of the process according to the invention as a process diagram. Figure 2 shows an alternative arrangement of the evaporation according to the invention as a process diagram. Figures 3a to 3d show the temperature-heat quantity diagrams that explain the invention and its technical level.

The process gains its thermal energy through a boiler arrangement, which is generally marked with a cipher 1. The components of the boiler arrangement 1 are arranged in the energy-generating medium flow 14, which typically arises from the waste gas flow from the gas turbine, the flue gas flow from the other combustion process, other corresponding hot gas flow or liquid flow.

The process shown in the picture would work as a common counterflow system as follows. The feed water VS coming from the feed water tank 4, the temperature of which is approx. 55 ° C., comes via LP preheater 9 into the steam separating drum 2 of the boiler system, of which it is circulated as flow VP into the steam generator 7, around the steam HP into the drum 2 to get. The steam flow HT is taken from the drum 2, which is passed over the superheater 6 and is then led into the HP part of the steam turbine. The exhaust steam HL from the steam turbine 3, which has consumed its energy, runs through the condenser 10 and converts into water flow VL, the temperature of which can be approximately 40 ° C. This condensation water is normally controlled in various ways via the feed water tank 4 into the system as feed water VS.

Only in this process the VH water heater, which in this case is the same as VS, is so small that it does not allow a particularly large reduction in the flue gas temperature, as previously stated, regardless of how cold the feed water is. The usual types of load regulation, i.e. with constant or sliding pressure, have no significant effect on efficiency in this regard.

To solve the efficiency and part-load problems described above, three expansion evaporators 11, 12 and 13 are arranged in this steam process according to the invention (Figure 1 as an example). In normal load situations during operation, both at full load and at part load, if feed water VS according to the invention is fed more when the steam generation of the boiler 1 presupposes, the amount of water used for primary steam generation flows as water VH to be evaporated into the boiler drum 2 and the excess part of the water amount fed into the secondary line as water V1 after the LP preheater 9. The water to be evaporated runs VH continue via the steam generator 7 as previously described.

The secondary flow V1 of the water comes into the first expansion steam generator 11, in which it can be expanded, whereby it is divided into steam flow H2 and residual water flow V2. Thereafter, the steam stream H2 is overheated with the help of the gas stream 14 in the low-temperature superheater 8 and conducted into the steam turbine 3 at a point corresponding to this pressure. The pressure of the superheated steam is typically 15 bar and the temperature is 250 ° C. The residual water stream V2 is again fed into the next expansion evaporator 12, in which it can be expanded further, dividing it into steam stream H3 and into residual water stream V3. The pressure of the steam stream H3 is typically 5 bar and the temperature is 153 ° C. This stream is mainly led into the stage of the steam turbine 3 corresponding to this pressure as partial steam H31.

Part of this steam flow can be fed as part flow H32 into the feed water tank 4 for heating the feed water. The corresponding residual water stream V3 is fed further into the next expansion evaporator 13, in which it is allowed to expand further, in order to form the steam stream H4 and the water stream V4. In this phase the pressure of the steam flow H4 can be 1 bar and the temperature 100 ° C. This residual water flow V4 is via the condenser 10 into the condensation water VL led, the temperature is typically about 40 ° C.

The arrangement implemented with the surface heat exchanger 5 with regard to the condensation water VL and VLK and the feed water VK and VS relates to the degassing of the feed water and as such is not associated with this invention.

From a thermodynamic point of view, the heat recovery according to Figure 3c is increased in this invention by increasing the water flow through the feed water preheater and increasing the heat area of the feed water preheater, which is as much as necessary and profitable. The flue gas can in principle be cooled down to the temperature of the feed water coming from the condenser. B. to the temperature T _c , the amount of heat recovered also increases compared to the 2-pressure solution by the amount Q₃. By suitably designing the equipment and regulating the water flow, saturated HD water is obtained more than the amount of heat Q available to the evaporation and overheating part of the boiler can evaporate and overheat. Therefore, the excess feed water is removed from the boiler and used to generate vapors of lower pressures, in the alternative ways described in this application and thus cooled again in the feed water preheater (the cooling phase of the water is not shown in Figure 3c).

The resulting LP vapors are fed into the steam turbine as an intermediate feed, whereby the electrical power of the turbine increases.

In a case corresponding to this example (Figure 1), the effect of the feed water circulation via the expansion evaporators was unchanged with the design of the equipment as follows: circulation Steam turbine output (net) Performance increase 0 kg / s 40.73 MW 0 MW 7.38 " 41.58 " 0.75 " 16.08 " 42.24 " 1.51 " 25.91 " 42.60 1.87 " 36.72 " 42.48 1.75 "

The primary steam flow HT into the steam turbine 3 remained constant at 37.4 kg / s.

Figure 1 shows only one example process according to the invention. The principle of the invention can be applied in many different ways, by adhering to its principle of feeding in excess feed water and z. B. evaporated with the expansion methods 11, 12 and 13 mentioned and this steam leads into the steam turbine 3. In the example, there are expansion vaporizers at three pressure / temperature levels, but expansion vaporizers can only have one or more than three. The steam obtained from these expansion evaporators can be superheated with gas flow in one or more superheaters 8, or the vapors can be fed into the turbine without overheating.

A particularly favorable way of realizing the overheating (shown in FIG. 2) is to overheat the steam HS available in each case from the expansion evaporator in the heat exchanger 23 with the water V1 coming into this evaporator. Applied to the example in Figure 1, the steam flow H3 is accordingly overheated with the water flow V2, the steam flow H4 with the water flow V3 etc. You can also combine the overheating with the gas stream 14 and the overheating with the water streams V1, V2 and / or V3. Likewise, partial steam streams H32 can be taken at various points in the evaporation process and led to the feed water heating or this phase can be omitted and the entire steam into the Guide turbine 3.

It goes without saying that the number and construction of the low temperature preheaters 9, superheaters 8, steam generators 7 and superheaters 6 are planned according to the flow and the type of the heat source using all constructions known as such. Likewise, the overheating with the water streams V1, V2 and / or V3 can be achieved using any heat exchanger construction known as such between the water stream and the corresponding steam stream HS, H2, H3 and / or H4.

The arrangements connected to the feed water tank 4 and the heat exchanger 5 itself can also be different. Depending on the process requirements, the excess feed water to be circulated can either be returned to the suction side of the feed water pump 16 or, using a separate circulating pump, to the pressure side thereof.

In addition to the expansion evaporators ("flash" drum) described above, low-temperature circulating water V1 can also be used to evaporate using a surface heat exchanger combination 21 (Figure 2), this excess water flow V1 being the stream to be cooled or, if desired, the superheating stream as well Is medium.

A lower water flow for evaporation can also be taken from this at the same time, from which the corresponding steam flow HS is created in the steam turbine. This water can of course also be taken elsewhere. The system described above is shown in Figure 2. Otherwise, the variations of the system described above are applicable in connection with this or similar evaporators (if these evaporators are available at several pressure levels).

In the event that the circulating water VH coming from the preheater already contains steam, i.e. if the preheater has evaporated, the excess feed water V1 taken for circulation can be fed into a steam separator of the same pressure (not shown in the pictures). The steam obtained from this separator is fed into the boiler or into the boiler drum 2 and the remaining water is fed into devices 11, 12, 13; 21 cooled, which generate LP steam. ND vapors H2, H3, H4; HS are treated as described above. If the getting of salts of the cooling water in the LP circulation is to be avoided, the feed water V1 in the boiler drum 2 is taken from a special feed water channel before the preheated feed water VH has mixed into the boiler water VP.

Regardless of the aforementioned and in addition, the waste heat from the process, e.g. B. flue gas flow, can still be used with the help of the boiler device 15 for heating the water used for other purposes. The waste heat energy of the flue gas can thus be used extremely effectively.

The use of the waste heat of the gas turbines is mentioned above as the application object of the process. However, the application of the process is not limited to this, but the heat flow 14 can also be another flue gas flow or an exhaust gas flow from any engine, e.g. B. a ship machine, or a hot medium flow from any process, the medium can be gaseous, liquid or a combination of the two. Stream 14 may also include solid particles.

Claims (12)

1.Method for increasing the efficiency in the steam process in which the steam (HT) generated in the steam generation process (1) with hot material flow (14) is fed into the steam turbine, the cooled steam flow (HL) coming from the steam turbine condenses and the feed water ( VS) of the steam generating system (1) is preheated,
characterized,
that the feed water preheater (9) pumps more feed water than the steam generation of the boiler (1) requires that the excess feed water (V1) is cooled in low-pressure steam (LP steam) generating devices (11, 12, 13; 21) and that the resulting low-pressure vapors (H2, H3, H4; HS) are fed as intermediate feed into the steam turbine (3) and cooled and fed back into the feed water preheater (9) and that the cooled excess feed water is fed into the one running into the feed water preheater Feed water (VS) is returned. 2. The method according to claim 1,
characterized,
that the circulating excess feed water (V1) is cooled by expanding it to lower pressure in one or more stages (11, 12, 13) and that any expansion steam partial flow (H2, H3, H4) is fed into the steam turbine (3) as an intermediate feed at a point corresponding to the pressure level in question. 3. The method according to claim or 2,
characterized,
that the excess feed water (V1) to be circulated is fed back into the feed water (VK) running into the feed water preheater on the suction side of the feed water pump (16). 4. The method according to claim 1,
characterized,
that the excess feed water (V1) to be circulated is cooled in surface heat exchangers (21), and the steam (HS) formed during the cooking of the cooler is fed as an intermediate feed into the steam turbine (3). 5. The method according to claim 1 or 4,
characterized,
that the excess feed water (V1) to be circulated is returned to the pressure side of the feed water pump (16) using a special circulating pump (22). 6. The method according to one or more of the preceding claims,
characterized,
that the excess feed water (V1) used for cooling is taken after the feed water preheater (9) before the feed water reaches the boiler drum (2). 7. The method according to claim 6,
characterized,
that the excess feed water (V1) taken into the circulation is first led into a steam separating device of the same pressure, of which the steam is led into the boiler drum (2) and the remaining water in low pressure steam generating devices (11, 12, 13; 21) is cooled and that the resulting LP vapors (H2, H3, H4; HS) are fed into the steam turbine as an intermediate feed. 8. The method according to one or more of the preceding claims,
characterized,
that the excess feed water (V1) taken for cooling in the boiler drum (2) is taken from a special feed water channel before the preheated feed water (VH) has mixed into the boiler water (VP). 9. The method according to one or more of the preceding claims,
characterized,
that the excess feed water (V1) taken for cooling is taken from the boiler water (VP) located in the boiler drum (2). 10. The method according to one or more of the preceding claims,
characterized,
that the circulation water quantity (VS) of the feed water preheater (9) is set so that the feed water (VH) reaches the boiling temperature corresponding to the pressure of the boiler drum (2) before the excess feed water portion (V1) going into the circulation is separated from it. 11. The method according to one or more of the preceding claims,
characterized,
that the steam (H2, H3, H4) generated in at least one of the LP steam generating devices (11, 12, 13) is overheated with the corresponding circulating excess feed water (V1, V2, V3) coming into the device in question. 12. The method according to one or more of the preceding claims,
characterized,
that the steam (H2, H3, H4) generated in at least one of the LP steam generating devices (11, 12, 13) is overheated with a superheater (8) which is in the hot material stream (14) at a temperature level which corresponds to the temperature between the preheater (9) and the evaporator (7) of the primary circuit.

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