WO2003018963A1

WO2003018963A1 - Procedure for treating the gas flow, operating in the final part of the steam turbines and the equipment for performing this procedure

Info

Publication number: WO2003018963A1
Application number: PCT/RO2002/000014
Authority: WO
Inventors: Dan Andreescu
Original assignee: Dan Andreescu
Priority date: 2001-08-24
Filing date: 2002-05-31
Publication date: 2003-03-06
Also published as: WO2003018963A9

Abstract

The invention 'Procedure for treating the steam flow operating in the final part of steam-turbines and the equipment performing this procedure' applied in the field of thermo power-plants with condensation and of the nuclear power plants. The aim of this invention consists in the implementation of the final part of steam turbines in a reduced number of turbine parts, by transferring a part of the flow, 40 60 %, preferably 50 %, from upstreams the final part, respectively the last 2 or 3 stages, into a secondary turbine which drives the boiler feed water supply pump, with the final part producing more power by the increase of the air extraction efficiency from the condenser by means of an additional assembly for reduction of the steam amount in the air-steam mixture, extracted therefrom, as well as by reducing the humidity in the steam passing through the final part, especially through the last stage, by a separator assembly placed between two successive stages, passed through by the whole steam flow which reduces the effect of braking and corrosion of the drops on the rotoric blades.

Description

Procedure for treating the gas flow, operating in the final part of the steam turbines and the equipment for performing this procedure.

1_ The invention is referring to a procedure of treating the gas flow, operating in the final part, the last two or three stages of condensation steam turbines, and the equipment performing this procedure, for turbines used in thermo-power plants and nuclear power plants.

A very high volumetrical steam flow is specific to this final part of steam turbines, due to

2 the very low condensation pressure needed for obtaining an as high as possible yield of the thermal cycle, respectively an as big as possible turbine power.

Consequently, the final axial flow section becomes very large and restrictive for the turbine power, due to the length of the final rotor blades, which are built at the edge of the admissible resistance to the strains they are undergoing, especially the centrifugal force. At the

3- same time, the rotor blades, especially the final ones, with high peripherical speeds, undergo a certain errosion process with very severe consequencies, due to the humidity produced in the steam by distension below the saturation limit curve, the intensity of the errosion process increasing proportionnaly with steam pressure decrease.

At the same time with the steam which is drained out of the final turbine stage, there is

4. also air penetrating into the condenser through different unsealings, due to the sensibly underatmospherical pressure at which the condensation occurs, this air having to be extracted in order to maintain constant pressure in the condenser.

This extraction is inevitably performed, with an 3 ÷ 4 times bigger amount of steam, and the air-steam mixture is brought to the atmospheric outlet draining pressure, by means of a

5 compression gauge, placed outside the condenser.

In order to treat the steam flow in the final part of the steam turbines' low pressure part, there is known a procedure consisting, in the first step, in introducing the steam flow-rate from the previous middle-pressure turbine part, into one or several low pressure turbine parts, usually with two opposite flows, aiming to increase the final total section, followed, in the second step, β by the distension of the whole steam flow in successive stages up to the final pressure, corresponding to the pressure in the turbine condenser, where, in the third step, occurs the steam condensation, followed by a phase of air elimination of the condenser, consisting in the extraction, in the condensation finalising zone, of an aer-steam mixture which is afterwards, in a last step, compressed outside the condenser, up to the atmospheric outlet pressure.

7 Simultaneously with the second distension phase for the final stages, which operate in wet steam, there is performed a separation phase, of collecting the humidity out of the steam at the stage periphery, through natural centrifugation of drops, which occurs when the steam flows through the turbine stages or/and through humidity collection, deposed in a film layer, through special channels practiced in the statoric blades. The disadvantage of this procedure consists in the folio wings:

- it determines a most complicated constructive solution, needing the existence of several low-pressure turbine parts usually in double flow, which are lengthenning the turbine and rendering it more expensive, leading also to the increase of the machine hall size, where this turbine is placed in. - Additional power consumption needed for compressing the steam extracted at the same time with the air of the condenser, which is 3÷4 times more than the air.

- Reduced effeciency of the separation, only 15÷25% of the humidity contained in the steam being eliminated, because only a part of the wet steam flow-rate is participating in the separation process, resulting in the decrease of the inner efficiency of the final turbine part and the intensive errosion of the rotoric blades, especially at the last stage.

For the purpose of realising the final part of steam turbines, there is known the equipment aimed to distend the whole steam flow-rate received from the previous, intermediate pressure turbine part, up to the final pressure in the condenser, built up by one or several double-flow low-pressure turbine parts, having as main element the turbine stages coupled on the same shaft line and providing the steam into a condenser having collecting channels, through which is extracted directly an air-steam mixture from the final condensation zone, being further compressed outside, in a compression equipment; at the same time, in the zone of the stages operating with wet steam, there are used constructive solution consisting in collecting torroidal statoric chambers at stage periphery and/or slits in the statoric blades, by which is extracted and suctionned up the deposed water film.

The disadvantages of this technical solution are:

- Lengthenning of the turbine, rendering it more expensive, increase of the machine hall size, where the machine is placed. - Significant decrease of the turbine final part power, also as an effect of the thermal cycle efficiency at an increase of the steam percentage in the air-steam mixture extracted from the condenser and, especially, at the increasing air flow-rate penetrated into the condenser, with respect to the dimensioning values, which is an usual situation in the operationnal practice. This way, it results an increased power consumption for the air-steam mixture compression, as well as a pressure increase in the condenser, leading to the decrease of the final turbine part power. - The partial separation, only of the humidity contained in the steam being in the close vicinity of the torroidal chambers or of the extraction slits and not from the entire steam flow passing through the stage, whereas the summed length of the collecting channels is constructively limited by the circumference of the stage, which reduces the efficiency of the separation, and in the case of the extraction slits on the statoric blades, the efficiency is reduced as the need of achieving an aerodynamical prophyle, adequate for the statoric blade, is in contradiction with an effective constructive shape of the collecting slits. This leads to a pronounced wear and an efficiency decrease of the turbine final part, especially of the final rotoric blade.

The technical problem solved by the present invention consists in the direct atenuation, as well as through a sinergical effect, of the technical conditions usually occurring at the realisation of the final part, the last 2 or 3 stages respectively, of steam turbines, by transferring a part of the flow-rate, about 40 ÷ 60%, preferably 50%,in order to make constructively identical the flow- parts which follow, upstream the final part, in a secondary turbine, with the final part producing more power by the decreased pressure in the condenser, which is performed increasing the effectiveness of the air extraction thereof, as well as by reducing the humidity of the air passing through the final part, especially the last stage, which reduces the effect of braking and errosion of the drops upon the rotoric blades. The procedure used in this invention reduces the disadvantages presented above, by reducing the antagonistical constraints which occur at steam flowing through the final part of the low pressure parts of steam turbines, by the introduction of a new phase, i.e.:

- a first new extraction phase of a part, preferably half, of the steam flow-rate passing through the low-pressure part, from upstreams the last 2 or 3 stages, this amount being further sent into a secondary turbine, which is part of the boiler feed-water supply turbopump assembly;

- a second new phase of internal separation of the humidity from the steam, where all the wet steam in the turbine is precipitating, the separator equipment taking all the flow-room, similarly to a turbine stage and placed between the turbine stages; - a third new phase, which leads to the significant reduction of the steam amount extracted together with the air from the condenser, consisting in the partial condensation of the steam in the mixture. The equipment as per the invention reduces the above mentioned disadvantages by the fact that it reduces even to the half, the number of flows, respectively of low pressure parts of the main turbine, by transferring of a part, preferably one half, from the last 2 or 3 stages, into another shaft line, belonging to the boiler feed-water supply turbopump; at the same time it contains additionnally a humidity separator assembly, placed in the turbine final part, made of several distinct and successive, cavil type stages for mechanical, inertial separation, which increase considerably the length of the collecting channels, as well as the film layer

22 concentration of the drops in the collecting zone; as well, it contains additionnaly an assembly consisting mainly in a heat exchanger with condenser role, placed on the air-steam way after the extraction zone in the turbine condenser and upstreams of the compression equipment for the air- steam mixture.

The invention has the fallowing advantages:

23 - Reduction, even to the half, of the flows through the main turbine low pressure parts, with considerable economic effects, due to the reduction of length and weight of the main turbine and, consequently, reduction of the machine hall size.

- Reduces the steam/air ratio in the mixture extracted from the condenser from 3/l÷4/l to 1/1÷2/1, which results in the decrease of the power consumed for compressing by

24 the air-steam mixture compressing equipment.

- Increase of the humidity separation efficiency from 15% ÷ 25% up to 75% ÷ 85%, by performing separation throughout the whole wet air flow, as well as by the considerable increase of the summed length of the collecting channels.

- Reduction of the constraint degree upon the final part, especially of the final flow- 5 section upon the dimensions of the main turbine, which permits, from case to case, the decrease of the final pressure and/or the reduction of the absolute outlet speed, with important positive effects on the specific heat consumption and the interval efficiency of the turbine.

- By steam wetness reduction, increase of the inner efficiency of the stages 2 downstreams, by up to 8 percentage points, increase which has to be reduced maximally by 2 percentage points due to the negative effect of the pressure loss within the separator equipment. »

- Wear-out reduction of the rotoric blades, (especially of the final one), proportionally to the additionnally extracted amount of humidity.

2? - Reduces substantially the power drops effect in the final turbine part and the decrease effect of the thermal cycle efficiency, by maintaining the pressure in the condenser due to the increase of the air extraction efficiency, even in the case of increasing air infiltrations into the condenser above the expected computation value.

- It assures a better vacuum, i.e. a lower pressure at steam inlet into the condenser and 2.8 _ thereby, a power gain of the turbine, for the same amount of power consumed by the air-steam mixture compressing equipment. In the followings is given an implementation example of the invention, related to the figures 1;2;3 and 4, which represent:

Fig.1 : Equipment for treating the steam flow through the final part of a steam turbine. Fig.2: Location of the humidity separator assembly in the final part of the steam turbine.

Fig.3: Humidity separator equipment, outspread cylindrical section. Fig.4: The assembly separating the steam out of the air-steam mixture extracted from the condenser. The procedure as per the invention consists, in the first phase, in introducing the steam flow into the low-pressure part and distending it in successive stages up to the upstream of the last two or three stages where, as new phase, one part of the steam flow-rate is taken over,preferably 50%, which are transferred outside, where, in the next phase, it is distended in a secondary turbine, which is driving the shaft-line of the boiler feed water supply pump and a secondary electric generator which closes up the powers balance, at the same time with the distension phase of the steam flow-rate remained in the main turbine downstreams of the taking- over point; in parallel to this phase, there is introduced a new separation phase for the humidity of the whole steam flow passing through the turbine, by introducing a humidity separating equipment, in the zone where its humidity is of about 5 ÷ 9%, which takes all the axial flow- section between two successive stages, the separation of drops being performed inertially, by the alternating deviation of the whole wet steam flow, so that the water drops are gathering in a film layer, being drained afterwards gravitationnally to an intake port or to the condenser, where the steam drained from the turbine is condensing to a underatmospheric pressure, for which, in order to be maintained, there is created a phase of extracting an air-steam mixture amount from the zone of the condensing process finalisation in the condenser, at a pressure value of usually 0,035 ÷ 0,060 bar and in a ratio of 3 ÷ 4 times more steam than air, followed by a new condensing phase of the steam in the mixture, made with the cooling water from the turbine condenser inlet, this reduces the steam / water ratio to 1/1 ÷ 2/1 and consequently the total air- steam flow-rate, which, in a last phase, is compressed up to the atmospheric pressure for draining to the outlet into the atmosphere. The simultaneous introduction of the three phases consisting in the reduction of the steam content in the air-steam mixture extracted from the condenser, in the efficiency increase of separating the water drops out of the steam flow which passes through the final turbine part and in the transfer of 40 - 60%, preferably 50% of the steam flow to the secondary turbine, assure a sinergy effect, i.e. it leads to a cummulated effect, superior to the effects resulted at single application, which attenuates the contradictions appearing when there is realised the final part, respectively the last two or three stages of the steam turbines. Thus, the pressure reduction in the condenser, by introducing a reduction phase of the steam amount in the extracted air-steam mixture, which increases the efficiency of the air extraction from the condenser, results in the negative effects of corrosion increase and the increase of turbine flows number and, consequently the turbine length increase, these effects being balanced by the efficiency increase of the humidity separation and transferring of some flows from the main turbine to the secondary turbine.

As well, the separation efficiency increase by placing a water drops separator of the whole steam flow which is passing through the turbine final part results in the negative effect of turbine lengthenning, this effect being balanced by mounting of some flows to the secondary turbine, as well as an additional pressure loss at the steam flow through the separator, which is balanced by the pressure drop in the condenser.

Likewise, the transfer of a part of the steam flow to the secondary turbine, 40÷60%, preferably 50%, leads to a pressure loss in the connection pipes, thus a decrease of the turbine power, which is balanced by the efficiency increase of the separation and by the pressure drops in the condenser.

The equipment, as per the invention, formed by low pressure turbine part or parts Number 1, which drive the main electric generator Number 2, and the steam is drained into the condenser 3, having upstreams of the last two or three final stages an extraction port 4, dimensionnedHbr-the^taken-over steam flow-rate, preferably 50%, by which is supplied the double-flow secondary turbine 5, coupled with the secondary generator 6 and with the boiler feed water supply pump 7 and the booster pump 8, intermediated by the multiplier 9 with speed variation and respectively the demultiplier 10, the speed admission into the secondary turbine being controlled by the valve 11, and in the most rational case of the taking-over, of 50% , there results the constructive identity between the final part, the last two or three stages of the turbines and of the main turbine condenser, with the condenser 12 of the secondary turbine; the separator assembly A as per the invention, placed upstreams the final stage 13 and fixed dismountably on its statoric diaphraggm, of the main turbine 1 and similary in the secondary turbine 5, passed through by the whole steam flow of the location zone, is radially limited by the tapered walls, inner one 14 and outer one 15, each of them having a horizontal joint, dismountably assembled, walls between which are fixed, in flow direction two successive circular rows of elements, the journal statoric separator blades 16 and 17, made of tear checkered sheet, having an angle at the center of 30 ÷ 60°, increasing from base to top, the leading edge of the first row 17 and the trailing edge of the second row 18 being perpendicular to the peripheric "u" rotation direction of the turbine rotor and the relativ pitch being of 0,35 ÷ 0,45, so that in every journal section, the projection of the leading edge on direction "u" is superposed onto the trailing edge of the neighbour blade, at the outlet blades of the separator blades is fixed the pocket 18, made of thin metal-sheet, bent in "U"-shape and fixed tightly sealed onto the outer-backside of the separator blade and by the other side forming an interspace with the inner-backside of the blade, of 3÷5 mm by which the humidity collected in a film-layer especially on the inner-backside is gravitationnally guided towards the ends, where there are the circular collecting channels 19 of the tapered walls 14 and 15, wherefrom it is gravitationnally drained and, by the pressure difference, the collected humidity is driven to the condenser, where the steam-separating assembly B of the air-steam mixture extracted from the condenser 3 of the main turbine and similarly 21 of condenser 12 is composed of a collecting channel 20 provided with slits assuring an uniform extraction of the air-steam mixture of the condensation terminal zone, the channel being continued in the inlet chamber 21 of the cooling water, with respect to which the channel is waterproof sealed; to the collector is joined the pipes bundle 22, immersed in cooling water and since the air-steam mixture is circulating through them, there occurs partial condensation of the steam up to the partial pressure limit in the mixture, corresponding to the saturation temperature, which is correlated with the cooling water temperature, the remaining air-steam mixture is taken-over by the draining collector 23 to which is joint the pipes bundle; in this collector occurs, at the same time, the separation of the condensate from the remaining air-steam mixture, which is gravitationnally drained in condenser 3 through the siphon 24, which is also a hydraulic latch, having a visualisation zone and a non-return valve to avoid inverse flowing; from the collector 23, the remaining air-steam mixture, wherefrom the condensate has been separated out, is sent to the compressing equipment, which is draining it out into the atmosphere.

Claims

_1 1.Procedure for treating the steam flow which operates in the final part of the steam turbines, consisting, in a first phase, in introducing the steam flow coming from the previous intermediate pressure turbine part into one or several low pressure turbine parts, usually with two flows running in opposite directions, for increasing the total final cross-section, followed in the

.

2 second phase by the distension of the whole steam flow-rate in successive stages up to the final pressure, corresponding to the pressure in the turbine condenser where, in the third phase is carried out steam condensation, followed by a phase of eliminating the air from the condenser consisting in the extraction, in the condensation finalisation zone, of an air-steam mixture which afterwards, in a last phase, is compressed outside the condenser up to the atmospheric pressure

3. for being drained out. Simultaneously with the second distension phase for the final stages, which operate in wet steam, there is carried out a separation phase, i.e. of collecting the humidity out of the air at the periphery of the stage, based on the natural centrifugation of the drops, which occurs as steam is flowing through the turbine stages or/and by collecting the humidity deposed in film layer, by special channels practiced in the statoric blades characterised in a first step by introducing the steam flow into the low pressure turbine part and its distension in successive stages up to the upstreams part of the last two or three stages, where, in the next phase is taken over a part of the steam flow-rate, between 40 - 60%, preferably 50% , in order to make identical the following part flows which are transferred out where, in the next step, occurs distension in a secondary turbine driving the shaft line of the boiler feed water supply pump and a secondary

„5 electric generator which closes the power balance, at the same time with the distension phase of the steam flow-rate remained in the main turbine, down-streams with respect to the take-over point; in parallel with this phase, there follows a phase of humidity separation out of the whole steam flow passing through the turbine by introducing a humidity separing device in the zone where its humidity is of about 5 ÷ 9%, which occupies the whole thrust cross-section of flow

6 between two successive stages, the drops' separation being carried out inertially by the alternative deviation of the whole amount of wet steam so that the water drops gather in a film layer being then drained gravitationnaly to an extraction port or in the condenser, where the steam drained from the turbine is condensed at a subatmospheric pressure for whose maintaining there is carried out an extraction phase of an air-steam mixture of the zone of condensation

7 process finalisation in the condenser, at a pressure value of usually 0,035 ÷ 0,060 bar and in a ratio of 3 ÷ 4 times more steam than air, followed by a condensation phase of the steam in the mixture, carried out with the cooling water from the inlet into the turbine condenser, which reduces the steam/air ratio to 1/1 ÷ 2/1 and consequently, the total air-steam flow-rate which is compressed lately to the outlet atmospheric pressure. 2. An equipment to carry out the flow of the steam operating in the final part of the steam turbines, which is aimed to distend the whole steam flow received from the previous turbine part, of intermediate pressure, up to the final pressure in the condenser, formed by one or several low pressure turbine parts, in double flow, having as main element the turbine stages, coupled on the same shaft line and driving the steam into a condenser provided with collecting channels by which an air-steam mixture is extracted directly from the condensation finalisation zone, and then compressed outside in a compression equipment and simultaneously, in the zone of the stages operating in wet steam there are used constructive solutions consisting in statoric torroidal collecting chambers at the stage periphery and/or slits in the statoric blades by which is extracted and absorbed the water film layer, where there is applied the procedure compliant to the requirement of Point 1, characterised by the fact that is made of one or several low pressure turbine parts which are driving the main electric generator (2), and the steam is drained into the condenser (3), having upstreams the last two or three final stages an extraction port (4) dimensionned to stand the taken-over flow-rate of 40÷60%, preferably 50%, of the total, by which is fed the secondary turbine in double flow (5), coupled to the secondary generator (6) and with the boiler feed- water supply pump (7) and the booster pump (8) by the intermediate of the multiplier with speed variation (9) respectively the demultiplier (10), the steam admission into the secondary turbine being controlled by the valve (11) and, in the most rational case of taking- over 50%, the result is the constructive identity between the final part, the last two or three stages of the turbine and of the main turbine condenser, with the condenser (12) of the secondary turbine; the separator assembly (A) placed upstreams of the final stage (13) and fixed dismountably on its statoric diaphragm of the main turbine (1) and similarly in the secondary turbine (5), passed through by the whole steam flow of the location zone, is radially limited by the tapered walls inside (14) and outside (15), having a horisontal joint each, dismountably assembled, walls between which are fixed in the sense of the flow, two successive circular rows of elements, radial statoric separating blades (16) and (17), made of tear checkered sheet, with a center angle of 30 ÷ 60°, increasing from base to top, the attack edge of the first row (17) and the trailing edge of the second row (18) being perpendicular to the peripheric rotation direction "u" of the turbine rotor and the relative pitch being 0,35 ÷ 0,45, so that in any journal section, the projection of the attack edge on the "u"-direction is superposed onto the trailing edge of the adjacent blade, at the trailing (outlet) edges of the separating blades is fixed the pocket (.18) made of thin steel-sheet, bent in "U" -shape and fixed tightly sealing by one side to . the outer- backside of the separating blade and by the other side forming an interspace of 3 ÷ 5 mm, with the inner-backside of the blade, by which the humidity collected in a film layer especially on the inner-backside is guided gravitationnaly towards the ends where there are corresponding circular

L5 collecting channels (19) on the tapered-walls (14) and (15), wherefrom the collected humidity is drained gravitationally and by the pressure difference to the condenser, where the steam separating assembly (B) of the air-steam mixture extracted from condenser (3) of the main turbine and similarly (21) of the condenser (12) is composed of a collecting channel (20) with slits providing an uniform extraction of the air-steam mixture of the condensation finalising j_g . . zone, the channel being continued in the inlet chamber (21) of the cooling water, with respect to which it is sealed tight, to the collector is joined the pipes bundle (22) immersed in cooling water and, in the air-steam mixture circulating through it there occurs partial condensation of the steam up to the limit of the partial pressure in the mixture corresponding to the saturation temperature, which is related to the cooling water temperature, the remaining air-steam mixture is taken-over

L . by the draining collector (23) to which is connected the pipes bundle, in this collector is carried out, at the same time, the condensate separation out of the remaining air-steam mixture, which is gravitationnaly drained in the condenser (3), through the siphon (24), which plays also the part of a hydraulic latch, provided with a visualisation zone and a check- valve for hindering the reverse flowing; of the collector (23), the remaining air-steam mixture wherefrom the condensate has

L8 .. been separated is sent to the compressing equipment which drains it out into the atmosphere.