NO842913L - PROVIDENT DEVICE FOR STEAM-TOWED SHIPS - Google Patents

Description

The improvements in this patent application relate to intentions to reduce the specific fuel oil consumption of propulsion devices for steam turbine-driven ships both in terms of new construction and in particular, by means of suitable conversions using the above-mentioned improvements, to reduce specific fuel oil consumption of propulsion devices for existing steam turbine-driven ships.

The above-mentioned improvements are based on a completely new idea regarding the steam cycle in sea-based steam turbine plants by inserting into the cycle a gas turbine which has the following tasks: to produce electricity for the ship's use, to supply energy to the propeller shaft through a pre-reduction gearbox or an electric motor fed by a generator driven by the gas turbine, to produce exhaust gases that can be used as combustion air in the main boilers and to reheat primary steam in an external reheater (exhaust gas boiler), or to simply reheat primary steam in an external reheater. The improvements according to this patent application also include, when the propulsion device has two boilers, the use of one boiler's superheater as a primary steam reheater, which logically can only be adapted to the conversion of an existing plant.

The above-mentioned improvements, or parts of them, can be applied, as previously mentioned, to a new build, but they are particularly suitable for application to steam turbine systems for existing ships, where, due to the slow speed of propulsion at which they are forced to work, particularly the large ships, firstly as a result of the enormous increase in the price of fuel oil and secondly as a result of the low freight level (which particularly affects large tankers), it is necessary to reduce the propulsion effect in relation to the originally calculated effect. Thereby, however, the specific fuel oil consumption increases noticeably with this reduced effect, which results in the cost reduction achieved through slow propulsion speed with steam turbine-driven ships noticeably decreases due to this increase in specific fuel oil consumption.

With the help of the improvements covered by this patent application, it is possible for newly built ships to achieve a reduction in specific fuel oil consumption of approx. 30% compared to the conventional plants, and with existing steam turbine-driven ships working according to the current slow speed of progress, it is also possible to achieve a reduction in specific fuel oil consumption of approx. 30%, which for a tanker of 300,000 tonnes dead weight under the current operating conditions means a daily saving of approx. 40 tonnes of heavy fuel oil or approximately 2.0 million US $ per years after today's prices for heavy fuel oil.

In addition, the increase in specific fuel oil consumption is mitigated both when it comes to variations above and below the calculated output, which for existing plants that have been modified and adapted to a reduced output using the improvements covered by this patent application allows increases in said reduced output with the modified design of about. 15 to 20%, together with increases in the specific fuel oil consumption of approx. 4%, which improves the plant's flexibility to adapt to demands for higher output if this is required.

All this has twofold interest: because of its very nature and because steam propulsion, until the so-called energy crisis and in some cases for a few years afterwards, existed side by side with diesel propulsion in ships with very powerful propulsion machinery, which simultaneous existence was strongly affected by said energy crisis.

Propulsion devices for ships consist of either diesel engines or steam turbines fed by steam boilers. In some extreme cases and on some warships, the propulsion devices consist of gas turbines.

Until the end of 1973 when the first oil crisis broke out, there was an equilibrium or balance between diesel operation and steam turbine operation in ships with high power requirements. The advantage of steam was its greater operational reliability and better adaptability to large high-power ships, namely large tankers, which offset its higher fuel oil consumption compared to diesel operation.

In 1973, specific fuel oil consumption for a traditional steam turbine propulsion device was approx. 200-210 g/S.H.P. (axle horsepower) x hour, while for diesel it was approx. 150-160 g/B.H.P.

(brake horsepower) x hour. It is necessary to add that both consumptions are not homogeneous, namely for the following reasons: A steam turbine propulsion device's specific fuel oil consumption is always given on the basis of heavy fuel oil or bunker oil C, which has a lower calorific value of 9,700-9,800 kcal/kg, while that for a diesel engine is given on the basis of gas oil, which has a lower calorific value of 10,200-10,250 kcal/kg, which means a difference of

about. 5%. A steam turbine propulsion device's specific fuel oil consumption, on the other hand, always includes the consumption of the plant's auxiliary equipment and also the consumption of the turbogenerator that supplies the electrical energy required on board, which was not common for diesel-powered ships and could involve a further difference of 4-6% . When comparing real consumption, the specific fuel oil consumption of the diesel engine plant should be increased by approx. 10-11% plus the amount corresponding to the consumption of cylinder lubricating oil which is of the order of 5 g/B.H.P. x hour of heavy fuel oil equivalents.

Despite this, in 1973 there was a difference in "homogeneous" fuel oil consumption of approx. 15% in favor of diesel, which was partly compensated for through the propeller's better efficiency in steam turbine-powered ships (lower rpm on the propeller),

and through less weight and less space required for the steam turbine plant, as well as lower maintenance costs and shorter layover time (off-hire) for steam turbine-powered ships. And of course through the very low price of oil fuel, which for small differences in consumption was only of secondary importance.

In 1973/74, the first oil price increase took place which, based on the oil price fob PG in 1970, meant an increase of eleven times the 1970 price. And at the end of 1979 came the second oil price increase, which brought the oil price twenty-eight times higher, relative to the aforementioned 1970 fob PG basis. Oil prices then fell slightly at the beginning of 1983, but the high exchange rate of the dollar in many cases offset the cost reduction that would otherwise have been achieved.

On the engine builder side, it was noticed that the largest diesel engine builders in 1975/76 launched a competition to reduce specific fuel oil consumption for diesel engines, which after several reductions is now in the range of 118-125 g/BHP x hour. At the same time, the speed of two-stroke diesel engines decreased as the stroke/bore ratio increased, which in large engines eliminated the propeller speed advantage of the geared steam turbine.

Finally, there is a very important feature that distinguishes the two types of propulsion systems from each other. This consists in the fact that when the speed and thus the effect must be reduced for one reason or another, diesel engines work better past their specific fuel oil consumption varies very little with varying power, while specific fuel oil consumption in steam turbine plants increases significantly when the power is reduced, namely in such a way that a steam turbine plant with a specific fuel oil consumption of 210 g/SHP x hour at its normal operating power, which is usually of the order of 90% of the maximum continuous performance (MCR), can reach a specific fuel oil consumption of 240 and 250 g/SHP x hour for performances of 70 to 50% of the maximum performance.

The great importance the fuel bill has today for the ships' operating costs, together with the persistently low freight level of large tankers, led to the general precaution of reducing speed and consequently propulsion power, in order to optimize income and minimize losses. Steam turbine-powered ships are thus very disadvantaged in relation to ships powered by diesel engines, namely due to the former's significantly higher specific fuel oil consumption, particularly at reduced power. This situation and the steam turbine bed's less flexibility

working at varying outputs as far as specific fuel oil consumption is concerned has practically eliminated steam turbine operation in merchant shipbuilding.

However, due to the fact that there were a very large number of ships powered by high-power steam turbine plants, the above situation led to engine replacement (so-called re-engining) in quite a large number of cases, i.e. the steam turbine plant was replaced by a diesel engine plant, usually unless effect. Such a conversion can, depending on engine performance (specific fuel oil consumption), lead to savings of up to 40% at slow speeds compared to the plant's previous consumption. However, such a conversion involves a very significant investment and a very long layover time for the ship to carry out the conversion. Engine replacement therefore results in rather large costs.

Parallel to this, albeit on a smaller scale, a number of transformations of the steam-to-steam type have been developed, which consist in an improvement of the steam cycle and in the restoration of the plant's operational conditions at the reduced power the ship is powered by. This type of conversion results in a specific fuel oil consumption for the converted plant (with the new reduced power) which is in the range of 195-205 g/SHP (axle horse power)

x hours. These conversions are cheaper than engine replacement and the required storage time is shorter, but the fuel oil savings are significantly less compared to engine replacement.

In both cases, whether from steam to diesel or from steam to steam, the ship is left with reduced power/output which is only a percentage of the original power which is variable, and there is no possibility of returning to the original effect, especially not when it comes to engine replacement.

In the following, a traditional plant or propulsion device for a steam turbine-driven ship is described with reference to fig. 1, where the system shown schematically is made up of the following components:

The following figures are given as typical values for sea-based plants for pressure and temperature: Steam pressure at the inlet of the high-pressure turbine 60 kg/cm 2, corresponding temperature 505°C.

On the other hand, and to clarify and define certain words and expressions that are commonly used in the present description, it will be useful to state the following: Superheating: Heating of the saturated steam, which is normally carried out by the same boiler that produces such steam and before it is used, hence the words "superheated" and "superheated steam". Reheating: Reheating consists of reheating steam after it has been used. Reheating is usually carried out in a reheater (reheater) arranged inside the same boiler, hence the words "reheater" (reheating unit) and "reheated damo".

External reheating: This is a reheating process

which is carried out in a reheater that is placed outside the boiler that produces the steam to be reheated, this in contrast to the hitherto established practice, which now involves reheating the steam in a reheater arranged inside the boiler that produces the steam . When it is not stated that the reheating is external, it can be assumed that it takes place in a reheater arranged inside the boiler that produces the steam.

To increase the efficiency of the steam cycle, it is necessary

to increase the drop in the heat content of the steam through the turbines, and to achieve this there are the following possible ways:

- To increase vapor pressure

- To increase steam temperature

- To increase condenser vacuum

- Using a cycle with intermediate reheating.

And while in a newly constructed plant it will be possible

to take into account each of the precautions stated above, this will be practically impossible in an already existing facility or clearly uneconomical.

In some cases, propulsion devices have been developed and utilized, which include a cycle of intermediate reheating. Such devices can be represented schematically as shown in fig. 2, where each part is set out as follows:

In some of these propulsion devices with intermediate reheat, the turbogenerator and the turbine-driven feed pump have been replaced by a shaft-driven generator and an electrically driven feed pump, respectively, so that a further improvement in overall efficiency is achieved.

To insert such a cycle in existing propulsion devices, by means of corresponding conversions and in the hitherto known manner, is very difficult and expensive as it would involve either a significant modification of main boilers for the arrangement of an afterheater or to arrange an external afterheater with its associated burner, a moderate improvement in efficiency being achieved in both cases.

In as well as fig. 1 as in 2 as well as in the subsequent figures, solid lines represent steam ducts. Dotted lines of mutually equal line segment length represent electrical wires. Dotted lines represent channels for feed water or condensate.

The improvements which are the subject of this patent application

and which is described below in connection with the attached drawings, has taken into account the new situation created by the new price of oil and the need for slow propulsion speed, as well as to a certain extent the need for flexibility in the plant (the propulsion device ) with regard to power variations versus power for a new design, and the variation in the specific fuel oil consumption with varying power, since according to the invention, one has been particularly concerned with the conversion of existing steam turbine-driven ships, in whose propulsion devices it is possible, by means of the improvements we are applying for a patent to achieve specific fuel oil consumption of the order of 160-170 g/SHP x hour compared to 240-250 g/SHP x hour, which today represents normal consumption for these ships under slow propulsion speed. The improvements are described in principle for the conversion of the propulsion device for an existing ship, but they can also be used in connection with a newly designed device for a new ship. The difference is that, if we exclude tankers for LNG (liquefied natural gas), there is absolutely no need for steam turbine propulsion devices in the construction of merchant ships, while there is a fairly significant market for the conversion of steam turbine propulsion devices in existing merchant ships, except precisely tankers for LNG.

What distinguishes tankers for LNG or ships for the transport of liquefied natural gas is that they use as fuel a mixture of heavy fuel oil and boiled-off gas which originates from the ship's cargo and which would otherwise be lost to the atmosphere. The mixing ratio depends on the evaporation rate of the cargo, which is of the order of 0.20 to 0.25% per day and of propulsion the fuel consumption of the remediation device, and therefore varies with the ship's size and propulsion power, as the proportion of gas is generally greater than 50%.

The fact that this mixture is used is the reason why steam turbines are still used in tankers for LNG, because the combustion of natural gas in diesel engines has not yet found its solution.

On the other hand, and due to the large capital costs of LNG tankers and their peculiar form of operation, always long-term contracts, these ships have been far less affected by the increased oil prices than other ship types, and operating speed and propulsion power have therefore only been exposed to small variations .

As a result of the reasons outlined above, there has so far been no need to transform the propulsion device in existing tankers for LNG.

In this connection, it seems appropriate to state that when it comes to the application/adaptation of the improvements that are the subject of this patent application to the propulsion device for a new ship, it is possible to bring the specific fuel oil consumption down as low as 145 to 135 g/SHP x hour, values which, after correction for the previously mentioned homogenization, agree well with those that can be achieved today with diesel engine plants. It goes without saying that the lower consumption of the new steam turbine plant compared to the redesigned plant is due to the first-mentioned being a new plant.

In accordance with the principles of the improvements

which is the subject of this patent application, and where the plant comprises two main boilers, a first important purpose can be achieved by using the superheater for one of the boilers as reheater for a cycle with intermediate reheating. Such a plant, which is derived from that in fig. 1 shown, is schematically reproduced in fig. 3, where the various components are indicated as follows:

This new cycle allows, by means of a redesign with very simple modifications in the steam circuit, and by replacing the high-pressure steam turbine with a high-pressure/medium-pressure steam turbine, to achieve a cycle with intermediate reheating at a reasonable cost, and to improve the efficiency . Furthermore, by making a suitable reduction of the utility power and replacing the turbo generator and the steam turbine-driven feed pump with a reduction gear-driven generator and an electrically driven feed pump respectively, the specific fuel oil consumption can be lowered to 195-200 g/SHP

x hour compared to 240-250 g/SHP x hour at the parent plant at reduced power (as it is assumed that the modified plant will have a usage effect that corresponds approximately to the reduced power at the original plant).

Another way to improve the efficiency of the cycle and

which can possibly be combined with the one described above as well as covered by the improvements that form the subject of this patent application, and with the help of which an even lower specific fuel oil consumption can be achieved, consists in installing as a further or additional component for the entire cycle a gas turbine driving an electric generator, and in utilizing the exhaust gases from the gas turbine, which exhaust gases contain a large amount of energy,

to implement one or more (generally one or two) intermediate reheatings which will have a very high degree of efficiency and which by nature will be of the type we have called "external".

The gas turbine-driven electric generator will supply electrical energy to the ship as well as to an electric motor, which in turn will supply power to the propeller shaft via a reduction gear. (As an alternative described later, the gas turbine can deliver power directly to the reduction gear and not via an electric motor).

In fig. 4, which includes the reheating devices according to fig. 3, a cycle with two intermediate reheatings is shown schematically, where the first takes place in the superheater of the second boiler and the second in a reheater arranged in the recovery boiler for the gas turbine exhaust gases, as in fig. 4 also includes a gas turbine with the previously described functions.

Those in fig. 4 schematically shown components are indicated as follows:

Using the cycle illustrated in fig. 4 can

the specific fuel oil consumption, which in the original plant is of the order of 240-250 g/SHP x hour, is reduced to a value of the order of 160-165 g/SHP x hour for the same reduced effect. In this connection, it is worth mentioning that the figures given above correspond to a steam cycle and that, taking into account what was previously stated about homogenization, 160-165 g/SHP x hour in a steam turbine plant corresponds to 135-140 g/CV x hour in a diesel plant, i.e. less than the specific fuel oil consumption of diesel plants from 1974 and earlier as well as immediately after 1974, which represent those which today exist side by side with steam plants in large tankers.

Fig. 5 schematically reproduces a cycle with complete external intermediate reheating and a gas turbine with the functions described above, as fig. 5 more or less represents an alternative arrangement to. that in fig. 4 schematically shown system, but has a specific fuel oil consumption that is insignificantly higher, although not greater than 170 g/SHP x hour, while it is simpler, cheaper and easier to install in an existing plant, as it is not necessary to modify the main boilers and there are no regulation problems. Furthermore, it can be used in plants where there is only one boiler.

This system is shown schematically in fig. 5, where the various components are indicated as follows:

The previously described arrangement, which is schematically shown in fig. 4, exhibits four characteristic features which are unique and novel and which are indicated as follows: - The use of a gas turbine in a steam turbine system for the propulsion of ships. - The utilization of the exhaust gases from the gas turbine in the main boilers for the production of steam and superheating. - The use of one boiler overhead as a reheater. - The use of a second external reheater as for its own

function utilizes the energy in the gas turbine exhaust gases in a recovery boiler.

With regard to the arrangement described above, which is schematically shown in fig. 5, this exhibits four distinctive features, which are unique and new, in particular: - The use of a gas turbine in a steam turbine system for ship propulsion. - The arrangement of a first external reheater in the recovery boiler for the gas turbine exhaust gases, which reheater utilizes the energy in said gases for its function. - The arrangement of a second external reheater, i.e. in the recovery boiler for the gas turbine exhaust gases, in series with the first reheater, and which for its function utilizes the energy in said gases. - The fact that no primary steam (main steam) is produced in the recovery boiler for gas turbine exhaust gases, which is a characteristic feature of land-based combined steam systems.

In the arrangements discussed above, the gas turbine drives an electric generator which feeds an electric motor, which in turn supplies power to the shaft line via a reduction gear. Alternatively, the gas turbine could deliver power directly to the reduction svek se len.

This arrangement, which is schematically shown in fig. 6, would be more advantageous on the basis of overall efficiency, and even if it is mechanically more complicated when converting existing facilities, it is overall cheaper.

Notwithstanding the above, the significant characteristic features of the improvements according to this patent application will not be changed.

As an alternative to that in fig. 5 shown arrangement, shows fig. 6 schematically the above-mentioned alternative. In this figure, the various parts are indicated as follows:

Alternatively and in a mechanically deviant design, the gas turbine could, depending on the type of ship or facility to be converted or rebuilt, be arranged in series with the high-pressure/medium-pressure steam turbine, and the electric generator be driven through a suitable alternator.

In some cases and for the sake of simplification, the second, intermediate reheater as well as other non-essential components could be eliminated, after the number of intermediate reheaters is increased beyond two.

In some cases and depending on the slow forward speed, it could be useful between the steam turbines and the reduction gear to insert a further speed reduction stage, to bring the turbines back to the operating speed and thus reduce investment and costs.

All of the steam turbine systems described above and shown in the figures are, as several times pointed out, schematic. What has been omitted in particular are the outlet valves for the steam turbines as well as the associated heating units for feed water, but also many other parts which are accessories to the improvements which are the subject of this patent application and which remain unmodified and do not themselves require modifications to the improvements according to this patent application.

Finally, it must be pointed out that the improvements that are the subject of this patent application deviate significantly from the well-known utilization of combined gas turbine/steam turbine systems in land-based installations. This is due to the significant disparity that exists between arrangements for sea-based facilities compared to land-based facilities, and it is a fact that a gas turbine has so far never been used on board a ship in a combined system with a steam turbine. On the other hand, the arrangement of afterheaters in the systems, and the feature that no primary steam is produced in the recovery tank or boiler for gas turbine exhaust gas, are completely new features of both sea-based installations and land-based installations.

It is finally possible to achieve further improvements in some cases by means of additional heating of the exhaust gases from the gas turbine at their inlet in the recovery boiler, or by heating the gases before their entry into the power turbine, in both cases a burner is used.

Both of these possible solutions are schematically illustrated in fig. 7a, 7b, 7c and 7d, which refer to fig. 4, 5 and 6. In fig. 7a, 7b, 7c and 7d correspond to reference numbers and components to those according to fig. 4, 5 and 6, while the burner is indicated by 19 when the heating of the exhaust gases takes place at the inlet of the recovery boiler and by 20 when the heating of the gases takes place before their inflow into the power turbine.

In the relevant figures, as well as in the preceding and following ones, the inlet or outlet for air or gases as well as the corresponding channels are represented by two parallel lines with intermediate arrows, which indicate the direction of flow.

In fig. 8 is a diagrammatic illustration of recovery of the exhaust gases from main boilers in the recovery boiler, as fig. 8 corresponds to the schematic representation in fig. 4 and whose principles, which represent an alternative, could also have been applied to those in fig. 5 and 6 schematically shown arrangements. Reference numbers in fig. 8 corresponds to the reference numbers in fig. 4.

Finally, it must be taken into account that the ship's age and/or other conditions may lead to a solution that is not among those with the lowest specific fuel consumption, but to a solution that adequately combines investment, specific consumption and conditions certain ships. In consideration of this, it has been developed in fig. 9 shown installation, which entails a significant simplification compared to those shown in fig. 4 and 5, as the recovery boiler for waste gas is bypassed, and where the high-pressure steam turbine is not replaced by a new high-pressure/medium-pressure steam turbine, but where, on the other hand, the existing steam turbine is subjected to a modification for the new use effect (design power). It can also be considered a noticeable simplification of the one in fig. 6 showed the installation, since in addition to the same simplifications as before, there has also been a looping of the pre-reduction gearbox, and where the mechanical transmission has been replaced by an electrical transmission similar to that shown in fig. 4 and 5.

The one in fig. 9 schematically shown installation, for which we also claim a patent, essentially consists in arranging the gas turbine as an electric generator set, and in injecting the exhaust gases from the gas turbine into the main boilers as combustion air. The generator set feeds the main switchboard and an electric motor, which either directly or via a reduction gear drives the ship's reduction gear, the most applicable solution probably being that this electric motor directly drives the other reduction gear for the low-pressure steam turbine. Alternatively, where this is possible, electric transmission could be replaced by a mechanical transmission that has a better degree of efficiency.

Components and parts included in the one in fig. 9 schematically rendered installation is indicated as follows:

According to this solution, due to additional, small modifications at the main boilers (looping of preheaters for air, modification of the air boxes and installation of an additional waste heat utilizing device (preheater) in each boiler's exhaust gas duct), the specific fuel oil consumption will only increase to a maximum of 180 g/SHP x hour, this in connection with an investment, which, as previously mentioned, is much lower than with the previous solutions and in certain cases more profitable. Moreover, it has advantages in terms of its greater flexibility and easier installation. To sum up: By means of the described improvements, which are shown in the drawings and which are the subject of this patent application, a significant reduction of the specific oil consumption of the propulsion devices for steam turbine-driven ships is achieved,

for the reduced propulsion power that is normally used today in sea-based steam turbine plants, which reduced propulsion power/speed, as previously mentioned, is a consequence of the enormous increase in the price of oil fuel and of the low freight rate level, as the reduction takes place from today's usual specific fuel oil consumption of 240 to 250 g/SHP x hour down to specific fuel oil consumption in plants modified in accordance with the improvements that are the subject of this patent application, namely of the order of magnitude 160 to 170 g/SHP x hour, which is achieved through a moderate investment and with a quite a short period of time to carry out the transformation/remodeling, i.e. in an economical and profitable way.

In the event that the solution schematically illustrated in fig. 9, specific fuel oil consumption will go up to 180 g/SHP x hour, but the investment required here will be significantly lower, and the residence time will be correspondingly shorter. It is also more flexible and easier to install.

The new arrangement which is the result of these improvements has the added advantage that the increase in specific fuel oil consumption for variations of 15% more or less than the new reduced use effect, for which the plant has been redesigned and which reduced effect must be determined jointly by the owner and designer, is only of the order of 4%. This significantly favors the flexibility of the converted plant for variations in output as far as specific fuel oil consumption is concerned. Another benefit associated with flexibility is the ability to retrofit back to the original facility in the event of a large increase in freight rates, canceling the new cycle and retaining only some of the aforementioned improvements with consequent improvement in efficiency .

One should also bear in mind that the majority of ships, practical

all of them, in the case of large tankers, to which these improvements can be applied are of the same age as the diesel-powered ships that have a high specific fuel oil consumption, so that steam turbine-powered ships remodeled or rebuilt in accordance with the improvements that are the subject of this patent application, after said homogenization will have a specific fuel oil consumption that is smaller

than with diesel plants of the same age, so that the current situation has been reversed.

In the aforementioned special case of LNG tankers, the improvements that are the subject of this patent application have additional advantages, which are described as follows: By having natural gas as fuel, it can be burned in the gas turbine, for which natural gas is the most appropriate fuel and enables the gas turbine to operate at higher temperatures and, as a result, to achieve higher power and higher efficiency. As the exhaust gas temperature is higher, the recovery of the energy in such gases in the recovery boiler is also facilitated and improved.

As the gas turbine's power and therefore consumption is low

when compared with total propulsion power and consumption, the gas turbine will burn natural gas at all times, so that the plant's overall efficiency will improve due to the two above-mentioned reasons.

On the other hand and as a result of the fact that the gas turbine in tankers for LNG always burns natural gas instead of bunker oil C, said gas turbine can be of the so-called light type instead of the extra powerful construction required to burn bunker oil C, whereby the price of the gas turbine will be noticeably lower, while the degree of efficiency will again be promoted due to the better degree of efficiency of gas turbines of the light type in relation to the aforementioned extra powerful construction, so that a more profitable installation is obtained as a result of these conditions.

Continuing with LNG tankers, the above considerations ultimately mean that the improvements which are the subject of this patent application can be applied to existing ships, whether in operation or under construction, and also to newly built LNG tankers, as the propulsion device for these for the present seems to continue to be steam turbines. In both cases, reshaping, rebuilding or applying the improvements according to this patent application to a new ship construction will result in significant reductions in fuel oil consumption compared to ships with traditional propulsion machinery.

Finally, it should be mentioned that after rebuilding/transformation in accordance with the previously described improvements, the ship will have two propulsion devices, i.e. the steam turbine and the gas turbine, so that if one of them should fail, there is the additional security that the other can bring the ship to port without the need for a tugboat.

Claims (7)

1. Propulsion device for steam turbine-driven ships, intended to reduce the specific fuel oil consumption of the propulsion device for steam turbine-driven ships and comprising as main components one or two main berths, each provided with a superheater, high-pressure and low-pressure steam turbines, main condenser, turbogenerator, turbine-driven feed water pump, and reduction gear, shaft line and propeller, characterized in that the propulsion device includes a gas turbine which feeds the device with energy, partly in thermal form and partly in mechanical form. 2. Propulsion device in accordance with claim 1, characterized in that one of the main boiler heads, when the device comprises two boilers, is used as a reheater. 3. Propulsion device in accordance with claims 1 and 2, characterized by the use of an external reheater which utilizes and recovers the energy in the gas turbine's exhaust gases. 4. Propulsion device in accordance with claim 1, characterized in that the exhaust gases from the gas turbine are injected into the main boilers and utilized as combustion air. 5. Propulsion device in accordance with claim 1, characterized in that the gas turbine exhaust gases are used to reheat only once, in one recovery boiler for gas turbine exhaust gas, the main steam, without producing main steam in said recovery boiler. 6. Propulsion device in accordance with claims 1 and 5, characterized in that two or more intermediate reheatings are carried out in an external reheater using the gas turbine exhaust gases. 7. Propulsion device in accordance with one of claims 1-6, characterized in that a burner is arranged to increase the temperature in the gas turbine exhaust gases, either at the gas inlet of the exhaust gas recovery boiler or at the inlet of the relevant gas turbine's drive turbine.