FR2549444A1 - IMPROVEMENTS TO PROPULSION SYSTEMS OF MUSIC BOATS BY STEAM TURBINE - Google Patents

Abstract

THE INVENTION RELATES TO A PROPULSION SYSTEM FOR VESSELS DRIVEN BY A STEAM TURBINE WITH THE OBJECT OF REDUCING THE SPECIFIC CONSUMPTION OF FUEL OIL. ACCORDING TO THE INVENTION, IT INCLUDES ONE OR TWO MAIN BOILERS 1, A SUPERHEATER 2, A HIGH PRESSURE STEAM TURBINE 3, A LOW PRESSURE STEAM TURBINE 4, A TURBO-GENERATOR 6, A FEED PUMP DRIVEN BY THE TURBINE 7 , A REDUCER 8, AND A SHAFT AND ITS PROPELLER 9. THE INVENTION APPLIES IN PARTICULAR TO THE DRIVE OF OIL TANKERS.

Description

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  The present invention relates to systems

  propulsion of boats powered by steam turbine.

  The improvements to which the present invention refers are intended to reduce the specific oil consumption of propulsion systems of steam turbine powered vessels in newly built vessels, and more particularly by means of adequate transformations using the

  improvements above, to reduce the specific fuel consumption of propulsion systems.

  existing boats ms by steam turbine.

  The above improvements are based on a completely new idea of the vapor cycle of marine steam turbine systems by introducing into the cycle a gas turbine which has the following tasks: the generation of electricity for the use of the boat; supplying power to the transmission shaft by a pre-reducer or an electric motor powered by a generator driven by the gas turbine; producing exhaust gas that can be used as combustion air in the main boilers and to heat the main steam in an external heater (exhaust gas boiler), or to heat the main steam in an external heater only. The improvements according to the invention also relate to the case where the propulsion system has two boilers, with the use of the superheater of a boiler as main steam heater, this being logically

  only applicable to the transformation of an existing system.

  The above improvements, or a portion thereof, are applicable to a newly constructed system, but are particularly suitable for application to steam turbine systems on existing vessels, which, because of slow training in the steam they are forced to operate, especially the larger boats, first due to the huge increase

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  fuel prices and secondly because of the low level of loading (which particularly affects large oil tankers), must reduce the power of propulsion compared to the original power, and 5 the specific fuel oil consumption at this reduced power increases by remarkable way and as a result the reduction in the price derived from slow steaming in steam turbine vessels decreases

  remarkably because of this increase in the specific consumption of fuel oil.

  Thanks to the improvements of the present invention, it is possible, in newly built boats, to obtain a reduction in the specific consumption of fuel oil compared to that of the conventional system of about 30%; and in existing vessels powered by a steam turbine operating at the usual slow steaming operation, it is also possible to obtain a reduction in the specific fuel oil consumption of about 1%, which for a tanker with a weight tonnage of 30,000 tonnes, under current operating conditions, means a daily saving of about 40 tonnes of heavy fuel oil or about US $ 2.0 million per

  year at the current price of heavy fuel oil.

  Moreover, the increase in the specific consumption of fuel oil in both cases for variations in plus or minus nominal yield is reduced, which in the case of existing systems modified and re-adapted to a reduced power by the improvements of the present invention, allows increases in the reduced power of the modified design of about 15% to 20%, with increases in fuel oil specific consumption of about 4%, which improves the flexibility of the system for adapt to higher power if that

is necessary.

  All this is of double interest Because of its intrinsic character and as until the energy crisis and in some cases a few years later, the propulsion

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  steam coexisted with diesel propulsion in high-powered boats, this coexistence has been

  deeply affected by the energy crisis.

  The propulsion systems of the boats are either diesel engines or steam turbines powered by steam boilers. In some exceptional cases, and in some warships,

  Propulsion consist of gas turbines.

  Until the end of 1973 when the first energy crisis occurred, there was a balance between diesel propulsion and steam turbine propulsion in high-powered boats. steam was its greatest reliability and adaptability to large, high-powered ships, ie large oil tankers, offsetting its

  high fuel oil consumption compared to that of diesel.

  In 1973, the specific fuel consumption of a conventional steam turbine propulsion system was about 200-210 g / h horsepower x hour, while that of diesel was about 160 g / hr. horsepower x brake It is imperative to add that the two consumptions are not homogeneous for the following reasons: the specific fuel consumption of a steam turbine propulsion system 25 is still given on the heavy fuel oil , or Bunker C (bunker fuel), which has a lower calorific value of 40600-41000 k J / kg while that of a diesel engine is given on diesels with a low heating value of 42700 to 42900 k J / kg, which means a difference of 5% Furthermore, the specific fuel consumption of a steam system always includes the consumption of ancillary facilities and also of a turbine generator that supplies the electrical energy required on board, some cho which was not usual in diesel-powered boats and that could mean an additional difference of 4-6%. Therefore, when comparing actual fuel consumption, the specific oil consumption of the diesel engine system must be increased by about 10-11% plus the amount corresponding to the consumption of the oil of the cylinders which is of the order of 5 g / horsepower brake x hour equivalent fuel oil. Despite this, in 1973, there was a difference in the "homogeneous" fuel oil or fuel oil consumption of about 15% in favor of diesel, which was partially offset by the better propeller efficiency in the steam turbine (lower number of turns of the propeller); and by less weight and less need of volume of the steam system; and lower maintenance prices as well as shorter off-leash times for steam turbine powered boats And of course, the very low price of fuel oil which, for small differences in fuel consumption,

marginal value.

  In 1973/1974, the first increase in the price of oil, which referred the price of free-on-board oil to the producer in 1970, meant an increase of 11 times. At the end of 1979, the second increase in oil prices occurred. put the price of oil at 28 times more, still referring to 1970, on a free-on-board basis to the producer. The price of oil dropped slightly in early 1983, but the strength of the dollar in many cases

  price that would otherwise result.

  On the machine construction side, it should be noted that diesel engine builders began a race in 1975/76 to reduce the specific fuel oil consumption of diesel engines, which, after several jumps downwards, is now in the order of 118 to 125 g / horsepower x hour At the same time, the number of revolutions per minute of two-stroke diesel engines has decreased with the increase of the stroke / bore ratio, thus eliminating the need for large engines. advantage of

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  number of turns of the steam turbine propeller.

  Finally, there is a very important characteristic that differentiates the two types of propulsion: when for one reason or another the speed and consequently the power must be reduced, the diesel engines work better because the specific consumption of fuel oil varies very much. with the variation in power, while in steam turbine systems the specific fuel oil consumption increases considerably with the reduction in power so that a steam turbine system with a specific fuel oil consumption The amount of 210 g / horsepower per hour at its normal operating power, which is usually in the order of 90% of its MCR value (maximum continuous power), can reach specific fuel consumption levels. oil of 240 and 250 g / power of the honeymoon x hour or SHP xh for powers

from 70% to 50% of MCR.

  The current weight of the fuel bill in the operating costs of a boat with the persistence of the low freight level in the large oil tankers has led to a reduction in speed and, consequently, to optimizing gains or reducing losses Thus, steam turbine powered boats are considerably disadvantageous compared to those powered by diesel engines, because of the considerably higher specific fuel oil consumption of the former, especially at a lower fuel consumption. Reduced power This fact, and the reduced flexibility of the steam turbine system to operate at various powers, with respect to the specific fuel oil consumption, have practically eliminated steam turbine propulsion in the construction of commercial vessels. . However, given the large number of vessels propelled by high power steam turbine systems, the above situation has led to the re-equipping of the vessels in a relatively large number of cases, which means the introduction of the steam turbine installation by a diesel engine installation, generally of a lower power This type of conversion, depending on the engine output (specific consumption of fuel oil) makes it possible to obtain savings of up to 40% at a low steam training compared to the previous consumption of the system However, such a conversion involves a very significant investment and a very long downtime

  long to perform it, so it is therefore quite expensive to perform.

  In parallel, but to a lesser extent, a series of steam-steam conversions have been developed, including an improvement of the steam cycle and a restoration of the design conditions of the system to the reduced power at which the boat operates. conversions result in a specific fuel oil consumption of the converted system at the new

  reduced power, which is of the order of 195 to 205 g / SH Pxh.

  These conversions are less expensive than retrofitting and also require less downtime, but fuel oil savings compared to retrofitting are considerably lower. In both cases, either diesel steam or steam, the boat is left at a nominal power reduced to a percentage of the original power which is variable, and there is no possibility, in a practical way, to return to the original power, in particular in re-equipped versions. The invention will be better understood and other purposes,

  characteristics, details and advantages of it will appear more clearly during the explanatory description

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  which will follow with reference to the accompanying schematic drawings given solely by way of example illustrating several embodiments of the invention and in which: Figure 1 shows a conventional system of a steam turbine driven boat; Figure 2 shows a propulsion system comprising a cycle with intermediate heating; Figure 3 shows a modification of Figure 1; Figure 4, including the reheat arrangements of Figure 3, schematically shows a cycle with two intermediate reheats; Figure 5 shows schematically a cycle with fully external intermediate heating and a gas turbine according to another arrangement of the cycle schematically shown in Figure 4; Figure 6 shows a modification of the arrangement of Figure 5; Figures 7a, 7b, 7c and 7d show some modifications of Figures 4, 5 and 6; FIG. 8 schematically shows the recovery of the exhaust gases from the main boilers in the recovery boiler; and

  Figure 9 shows an installation showing a significant simplification from those shown in Figures 4 and 5.

  The system shown in FIG. 1 consists of one or two main boilers 1, a superheater 2, a high-pressure steam turbine 3, a low-pressure steam turbine 4, a main condenser 5, a turbo-generator 6, a feed pump 6 driven by the turbine, a gearbox 8, and a shaft

with its propeller 9.

  As typical values in marine installations for pressure and temperature, the following figures can be cited: vapor pressure at the inlet of the high pressure turbine 60 bar, temperature

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corresponding 505 C.

  On the other hand, in order to clarify and define certain terms and expressions that will be commonly used, it would be wise to note the following: Overheating: heating of the saturated steam that is normally accomplished by the same boiler as that producing that steam and before its Utilization, hence the words "superheater" and "superheated steam" Reheating: the reheating is to heat the steam again after using it Usually, reheating is performed in a heater arranged in the same boiler, o the words "heater" and

"warmed vapor".

  External Heating: This is a reheating process performed in a heater which is arranged outside the boiler producing the steam to be heated, contrary to the practice established to date of heating the steam in a heater arranged in the boiler producing Steam When this reheat is not external, it is assumed that it is accomplished in a

  heater arranged in the boiler producing steam.

  In order to increase the efficiency of the steam cycle, it is necessary to increase the drop of the enthalpy of the vapor through the turbines, and there are various ways to achieve this: to increase the pressure of the steam. steam increase the temperature of the steam increase the vacuum at the condenser use a cycle with an intermediate reheat. 30 And while in a new design installation it would be possible to take all the measures described above, it will be practically impossible in an existing installation or system, or in any

clearly anti-economic case.

  The systems schematically represented in FIG. 2 comprise a main boiler 1, a superheater 2, a high-pressure steam turbine 3, a medium-pressure steam turbine 3a, a low-pressure steam turbine 4, a main condenser 5, a turbo generator 6, a feed pump driven by the turbine 7, a gearbox 8, a shaft and its propeller 9 and a heater 10. In some of these systems with intermediate heating, the-turbo-generator and the feed pump driven by the turbine were replaced by a generator driven by the shaft or respectively by an electrically powered feed pump, thereby obtaining further improvement in overall efficiency. It is very difficult and very expensive to adopt this cycle in existing systems, by means of the corresponding conversion and in the manner known hitherto, since this may involve either a considerable modification of the main boilers to adapt a heater. or to arrange an external heater with its corresponding burner, to obtain,

  in both cases, a moderate improvement in effectiveness.

  In FIGS. 1 and 2 as well as in the other figures, the continuous lines represent the steam sheaths. The dashed lines of equal length represent the electric lines. The lines in mixed lines represent sheaths of feed water or

of condensate.

  The improvements concerned by the present invention, which will be described below with reference to the drawings, take into account the new situation created by the new oil price and the need for slow steam entrainment as well as to a certain degree, the need for flexibility of the system with respect to the variation of power with respect to the new nominal power and the specific variation of the fuel oil consumption when the power varies; these enhancements are specially designed for the conversion of existing steam turbine powered boats into

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  the propulsion systems from which it is possible, by the improvements according to the invention, to obtain specific consumption of fuel oil of the order of 170 g / SHP xh compared to 240-250 g / SHP xh which is currently These improvements are in principle described for the conversion of the propulsion system of an existing boat, but they also apply to a newly designed system for a new boat. that, with the exception of liquefied natural gas carriers, there is absolutely no demand for steam propulsion systems for the construction of commercial vessels and that there is a sizeable market for conversion steam-propulsion systems of existing commercial vessels with the exception, specifically, of

liquefied natural.

  The special feature of liquefied natural gas carriers or vessels for the transport of liquefied natural gas is that they use, as fuel, a mixture of heavy fuel oil and boil-off gas from the cargo that

  otherwise would be lost to the atmosphere.

  The proportion of the mixture depends on the evaporation rate of the cargo which is of the order of 0.20 to 0.25% per day and the consumption of the propulsion system and therefore varies with the size of the boat and the propulsion power, the proportion of gases being generally

greater than 50%.

  The use of this mixture as fuel is the reason why steam turbines are still used in liquefied natural gas carriers because the combustion of natural gas in diesel engines

has not been resolved yet.

  On the other hand, and given the large capital of liquefied natural gas carriers and given their particular form of operation, still by long-term charter, the influence on these vessels of increased fuel oil prices has been much greater. low than in other types of boats and therefore the speed and the corresponding power of propulsion

  have only undergone slight variations.

  For the reasons described above, there has so far been no request for conversion of the

  propulsion system of existing liquefied natural gas carriers.

  It seems wise to indicate here that, in the case of the application of the improvements forming the subject of the present invention to the propulsion system of a new boat, the specific consumption of fuel oil can reach only 145. at 135 g / SHP xh, values which are close to those which can be obtained at present with the diesel-engine systems, with the homogenization correction described above. It goes without saying that the least consumption of the new steam system with respect to the system converted is due

  because it's a new system.

  According to the invention, when the system has two main boilers, one can achieve a first important goal by using the superheater of one of the boilers as a heater of a cycle with intermediate heating. FIG. 3 schematically shows this case, on which one can see the main boilers 1, the superheater 2, the high pressure steam turbine 3, the medium pressure steam turbine 3a, the low pressure steam turbine 4, the main condenser 5, the turbine generator 6, the feed pump driven by turbine

  7, the gearbox 8, the shaft and its propeller 9 and the heater 10.

  This new cycle makes it possible, by a transformation with very easy modifications of the steam circuit, as well as the replacement of the high-pressure steam turbine by a high-pressure medium-pressure steam turbine.

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  to obtain a cycle with intermediate reheating at a reasonable price and to improve the efficiency With in addition a significant reduction of the nominal power and the replacement of the turbo-generator and the pump of supply brought to the steam by a generator driven by a gearbox or respectively an electrically powered feed pump, the specific consumption of fuel oil can be lowered to 195-200 g / SHP xh compared to 240-250 g / SHP xh from the parent system to a power reduced (it is assumed that the modified system will have a nominal power approximately equal to the power

reduced from the original system).

  Another way to improve the efficiency of the cycle, which can or can not be combined with that described above, and to obtain an even lower specific fuel oil consumption, includes the installation, as another component of the complete cycle, a gas turbine that drives an electric generator, and the use of gas turbine exhaust gases, which contain a large amount of energy, to produce one or more (usually a or two) intermediate reheating which will be very efficient and which, on their own

  nature, will be of the type we have called "external".

  The electric generator entrained by the gas turbine will supply electrical energy to the boat as well as an electric motor which will deliver power to the transmission shaft by a gearbox (as an alternative described hereinafter, the gas turbine delivers directly from the current

  to the gearbox and not via an electric motor).

  Figure 4 schematically shows a cycle with two intermediate heatings, the first in the superheater of the second boiler and the second in a

  heater arranged in the exhaust gas recovery boiler of the gas turbine, the turbine being also incorporated in the functions described above.

  In FIG. 4, there can be seen an electrically controlled feed pump 7a, the first heater, the gas turbine exhaust gas recovery boiler 11, a second (external) heater 12, a low pressure vaporizer 13 in the recovery boiler, a gas generator of the gas turbine 14, a turbine 15 supplying the gas turbine, an electric motor 16 connected to the reducer and a main switching board 17, and an electric generator 6 driven by With the cycle shown in FIG. 4, the specific fuel oil consumption has a reduced power which is in the original system of the order of 240-250 g / SHP × h can be lowered to a value of the order of 160-165 g / SH Pxh for the same reduced power It should be mentioned here that the figures given above correspond to a steam cycle and taking into account what has been indicated above concerning homogenis a 160-165 g / SHP xh in a steam system equals 183-190 g / k W xh in a diesel system, i.e., this is lower than the value for 1974 and before, and immediately after 1974, existing value with steam systems in large tankers. The cycle shown in FIG. 5 has a slightly higher specific fuel oil consumption, although not greater than 170 g / HPS xh, but it is simpler, less expensive and easier to install in an existing system because It is not necessary to modify the main boilers and there is no problem of regulation. Moreover, it can be used in

  systems where there is only one boiler.

  In Figure 5, 10a denotes the first heater (external). The arrangement described above and schematically shown in FIG. 4 presents four features which are unique and novel and which are as follows: The use of a gas turbine in a cycle of

  steam for the propulsion of the boat.

  The use of gas turbine exhaust gases in the main boilers for production

of steam and overheating.

  The use of the superheater of a boiler as a heater. The use of a second external heater which uses for its operation the energy of the gas turbine exhaust gas in a recovery boiler. With regard to the arrangement described above and shown schematically in FIG. 5, it has four features that are unique and novel and which are as follows: The use of a gas turbine in a cycle

  steam for the propulsion of the boat.

  The arrangement of a first external heater in the exhaust gas recovery boiler of the

  gas turbine which uses, for its operation, the energy of these gases.

  The arrangement of a second external heater, also in the exhaust gas recovery boiler 25 of the gas turbine, in series with the first heater, and which uses, for its operation, the energy of these gases. not to produce the main steam in the exhaust gas recovery boiler of the gas turbine which is a characteristic of the cycles

  combined steam on a land base.

  In the arrangements mentioned above, the gas turbine drives an electric generator which supplies an electric motor which, in turn, delivers its current to the shaft by a gearbox. Alternatively, the gas turbine could supply current directly.

to the reducer.

  This arrangement, which is schematically shown in FIG. 6, will be more advantageous from the point of view of overall efficiency and, although it is mechanically more complicated in the case of the conversion of existing systems, it is, on the whole, less expensive. Notwithstanding the foregoing, the essential features of the improvements achieved by this

invention will not be modified. In Figure 6, one can see, in addition to what was previously

  described, an electric generator 6b

and an intermediate gear 18.

  Alternatively, and in a different mechanical configuration, the gas turbine, depending on the type of vessel or system to be converted, could be arranged in series with the medium pressure high pressure steam turbine and the electric generator be driven by a suitable gearing. . In some cases, and for simplicity, the second intermediate heater as well as other non-essential components could be removed, and

  also increase to more than two intermediate heaters.

  In other cases, and depending on the low rate of steam entrainment, it might be useful to provide between the steam turbines and the reducer, a further reduction in speed in order to bring the turbines back

  at their nominal speed and thus reduce investment and price.

  All vapor cycles described and illustrated herein are schematized. In particular, steam steam purges and the corresponding feed water heaters have been omitted, and many other items which are incidental to improvements which are the subject of the present invention, and which are neither modified nor modified

  the improvements of the present invention.

  Finally, it should be pointed out that these improvements which form the subject of the present invention differ essentially from the well-known use of combined steam turbine gas turbine cycles in shore-based installations. This is due to the essential difference which exists between arrangements of marine installations compared to onshore facilities, and in reality, to date, a gas turbine has never been used, on board a ship, in a combined cycle with a steam turbine. the arrangement of the heaters in the cycles and the non-production of main steam in the exhaust gas recovery boiler of the gas turbine are totally

  new in marine systems as well as in lowland installations.

  Finally, it is possible to obtain further improvements in some cases by additional heating of the exhaust gases of the gas turbine at their entry

  in the recovery boiler or by heating the gases 20 before entering the power turbine, using in both cases a burner.

  These two possibilities are diagrammatically shown in FIGS. 7a, 7b, 7c and 7d, which relate to FIGS. 4, 5 and 6. In these FIGS. 7a, 7b, 7c and 7d, the reference numerals correspond to FIGS. to those already mentioned for FIGS. 4, 5 and 6, the burner being identified at 19 when the exhaust gas is heated at the inlet of the recovery boiler and at 20

  when the gases are heated before entering the turbine.

  In these figures as well as the preceding and the following, the air or gas inlets or outlets and the corresponding sheaths are shown.

  by two parallel lines with arrows on the inside indicating the direction of flow.

  FIG. 8, showing the recovery of the exhaust gases from the main boilers in the recovery boiler, corresponds to the diagram of FIG. 4, the principle of which could also be applied to the diagram of FIGS. 5 and 6. The reference figures in FIG.

  8 correspond to those of Figure 4.

  Finally, it must be taken into account that the age of a boat and / or other considerations may lead to a solution that is not among those with the lowest specific consumptions but allows

  adequately combine the investment, specific consump- tion and circumstances of that boat.

  With this in mind, the installation shown in FIG. 9 has been developed, a simplification of that of FIGS. 4 and 5. The recovery exhaust gas boiler is eliminated and the high pressure steam turbine is not replaced. by a new medium-pressure high-pressure steam turbine, but the existing boiler is modified taking into account the new nominal power It can also be considered, for a simplification of the installation of Figure 6, 20 in addition to the same simplifications as those above, the elimination of the pre-reducer and the mechanical transmission substituted by an electric transmission such as

  shown in Figures 4 and 5.

  Essentially, the installation schematically shown in FIG. 9 consists in arranging the gas turbine as an electricity generator group and injecting the exhaust gases of this turbine into the main boilers as combustion air. generator feeds the main switching board and an electric motor that drives directly or by gear reducer of the boat, the most useful solution is probably that this electric motor drives directly the second reduction gear of the low-pressure steam turbine Alternately and where possible, an electric transmission may be replaced by a mechanical transmission which has a

better efficiency.

  The elements represented in FIG. 9 bear the same reference numerals as in the preceding figures. With this solution, thanks to slight additional modifications of the main boilers (elimination of air preheaters, modification of the air chambers, installation of an additional economizer in the exhaust duct of each boiler), the specific consumption of fuel oil increases only up to 180 g / SHP xh with an investment, as previously indicated, much lower than in the previous solutions and in some cases more profitable Moreover, this has the advantage of 'a bigger

  flexibility in terms of the volume required and the ease of installation.

  In summary, with the improvements described above, it is possible to achieve a considerable reduction in fuel oil or fuel oil specific fuel consumption in steam turbine driven propulsion systems for the reduced propulsion power normally used today in the production of steam. at sea, as a consequence of the enormous increase in fuel oil prices and low freight 240 to 250 g / SHP xh currentadays to specific consumptions of the modified system according to the invention of 160 to 170 g / SHP xh by means of a moderate investment and a stop enough

  short-to convert, that is, economically and profitably.

  In the case where the solution schematically represented in FIG. 9 is used, the specific consumption of fuel oil will reach 180 g / SHP × h, but the investment required will be considerably less and the shutdown time shorter. this solution is

  more flexible and easier to install.

  The new layout resulting from the improvements

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  has the additional advantage that for variations of plus or minus 15% of the new reduced rated power for which the system is re-studied, which reduced power must be set jointly by the owner and the designer, the increase in consumption This significantly improves the flexibility of the converted system with respect to power variations with respect to the specific fuel oil consumption. Another advantage is that the fuel oil is only about 4%. Flexibility is the possibility of reconversion, returning to the original system in the case of a sharp increase in freight, or canceling the new cycle and maintaining some

  improvements with consequent improvement in efficiency.

  It should also be borne in mind that the majority of vessels, practically all in the case of large oil tankers, to which these improvements can be applied, are contemporary with diesel-fueled ships with high fuel oil consumption, so the steamboats converted according to the improvements which are the subject of the invention will, after homogenization, have a specific consumption in

  fuel oil lower than their contemporaries in diesel, 25 thus reversing the current situation.

  In the particular case of the aforementioned liquefied natural gas carriers, the present invention offers the additional advantages which are described as follows: With natural gas as fuel, it can be burned in the gas turbine, for which it represents the fuel best This makes it possible for this gas turbine to operate at higher temperatures and thus to obtain higher power and higher efficiency. Moreover, since the temperature of the exhaust gas is higher, this facilitates and improves the recovery of energy from such gases in the

recovery boiler.

  Since the power and, as a result, the consumption of the gas turbine are small compared to the total power and consumption for propulsion, this gas turbine will still burn natural gas and thus the total efficiency of the system will be better thanks to

  both reasons mentioned above.

  On the other hand, and given that a gas turbine in liquefied natural gas carriers will still burn natural gas instead of Bunker C, this gas turbine may be of the light type instead of the heavy duty type required for to burn the Bunker C, and therefore the price of the gas turbine will be lower and the efficiency will be improved again 15 thanks to the better efficiency of the gas turbine of the light type compared to the gas turbine for service severe, thus having a more profitable facility

thanks to these facts.

  Finally, and still with respect to liquefied natural gas carriers, it emerges from the above considerations that the improvements that are the subject of the invention can be applied to existing vessels, whether in service or under construction. , and also to new liquefied natural gas carriers, since the propulsion of liquefied natural gas carriers continues to be by steam turbine In both cases, the conversion or application to a new form of liquefied natural gas object of the invention will result in substantial reductions in fuel oil consumption by

  compared to the boats having a conventional system.

  Finally, it should be mentioned that the boat after having been converted according to the improvements described above will have two propulsion systems, that is to say the steam turbine and the gas turbine, therefore, in case of failure of the engine. one of them, it remains an additional security thanks to the other for a return to the port without requiring

towing.

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Claims (7)

R E V E N D I C A TI O N S   1 Steam turbine driven propulsion system designed to reduce the specific fuel oil consumption of propulsion systems of steam turbine powered vessels and comprising, as a basic component, one or two main boilers, each of which is provided with a superheater; high pressure and low pressure steam turbines; a main condenser; a turbo-generator; a pump driven by a water supply turbine; and a gearbox, a shaft and a propeller, characterized in that in the system is incorporated a gas turbine which feeds it   in energy, partly in thermal form and partly in mechanical form.   System according to Claim 1, characterized in that the superheater (2) of one of the boilers   main (1) is used as heater and when the installation includes two boilers.   System according to one of the claims   1 or 2, characterized by the use of an external heater (12) utilizing and recovering the energy of the gases   Exhaust gas turbine.   4 System according to claim 1, characterized in that the exhaust gases of the gas turbine   are injected into the main boilers and used as combustion air.   System according to claim 1, characterized in that the exhaust gases of the gas turbine are used to heat only once, in a boiler (11) for recovering the exhaust gases of the gas turbine, the main steam without producing   main steam in said recovery boiler.   6 System according to any one of claims I or 5, characterized in that two reheating   intermediates or more are performed in an external heater using turbine exhaust gas.   System according to any one of the claims   preceding, characterized in that a burner is provided to increase the temperature of the gas turbine exhaust gas, this being done either at the inlet of the exhaust gas recovery boiler gas or at the the entrance of the turbine power turbine gas itself.