Apparatus For Filling And, If Desired, Emptying Inert Gas Poor In Oxygen Into Or From Holds In Ships, Respectively

Abstract

Exhaust gases from an emergency or auxilliary gas turbine/generator set are passed to an afterburner in which the rather high oxygen content of said exhaust gases is reduced to an acceptable level for use of the resulting gas as an inert explosion-proof gas for empty oil tanks. Before the gas is supplied to the tanks it is cooled by water supplied by a pump driven by the electric current produced by the generator. No blowers are required, since the turbine may operate against the pressure required for feeding the gas through the afterburner and the cooler and into the tanks. For displacing the inert gas from the tanks when desired, compressed air from the compressor unit of the turbine/generator set is tapped off and passed through an injector in which additional air from the atmosphere is entrained. The combined air is passed through the cooler and fed to the tanks through a suitable distribution system.

Description

BACKGROUND OF THE INVENTION

The present invention relates to a method and an apparatus for filling and, if desired, emptying inert gas, poor in oxygen, into or from holds or rooms in ships, respectively, in which method and apparatus combustion gases are produced in a combustion device, which gases are cooled and supplied to the holds to be filled.

A number of serious explosion accidents in tankers have proved that it is important to control the gas content of ships' tanks so that the gas mixture is explosion-proof. Plants or apparatus have therefore been developed, in which the exhaust gases from the burners serving for the production of steam for the main engine and/or auxilliary engines of the ship are supplied to the tanks of the ship as the tanks are emptied of oil. Such an apparatus has the advantage that the costs thereof are moderate, and that it has a relatively low power demand (for the operation of a blower supplying the exhaust gases to the tanks with the desired overpressure). However, such apparatus also have several disadvantages. Firstly, the oxygen content of the exhaust gases varies considerably. The apparatus further depends upon the steam boilers being in operation and upon the operating condition of the boilers. The exhaust gases entrain impurities and cause deposits on the blowers, valves and conduits. Sulphuric or sulphurous acid may be present in the exhaust gases, and the required blower is seriously exposed to corrosion. Therefore, the apparatus requires a rather large amount of maintenance. In addition, the blower required for blowing the exhaust gases into the tanks of the ship produce rather much noise.

Further, the system depends upon the presence of a burner for a steam boiler.

There have also been developed plants or apparatus working with separate gas generators, i.e. burners especially adapted for the production of an inert gas, poor in oxygen, for use in ships' tanks. Such apparatus produce a very pure gas with low oxygen and sulphur contents and is, of course, independent of a firing of steam boilers. The disadvantages of such an apparatus are that it is extremely expensive and has a very large power demand and fuel consumption.

SUMMARY OF THE INVENTION

The object of the present invention is to provide a method and an apparatus of the kind initially referred to, which does neither depend on steam boiler burners nor require any blower for providing the required pressure of the inert gases, but is still substantially cheaper than an apparatus having a separate gas generator. The inert gas is primarily intended for the filling of empty oil tanks, but may also be used for instance in extinguishing fire in engine rooms.

The method of the invention is characterized in that as a combustion device there is used a gas turbine which also serves other purposes, for instance the operation of a generator, the exhaust gases of the turbine being supplied to an afterburner for reduction of the oxygen content of the gases and then to the desired holds by the pressure downstream of the turbine and without the aid of blowers.

The apparatus of the invention is primarily characterized in that it is adapted to be connected to the exhaust conduit from a gas turbine which also serves other purposes, for instance the operation of a generator, said apparatus comprising an afterburner for reduction of the oxygen content of the exhaust gases, a cooler for reduction of the temperature of the gases, a discharge conduit for the cooled combustion gases and a valve for controlling the supply of exhaust gases to maintain the pressure of the inert gas within the desired limits.

Gas turbines are often installed as an auxilliary or emergency set onboard ships. Such sets are mostly not in use when the ship is unloading, and the set is then available for the production of inert gas for the filling of the oil tanks of the ship as these tanks are emptied. It is true that the exhaust gases from a gas turbine are not directly suited as an inert gas for said purpose, since the oxygen content is comparatively high. However, the oxygen content is relatively constant, and the exhaust gases therefore lend themselves to an afterburning for reduction of the oxygen content. The essential advantage in using a gas turbine for producing the desired inert gases is primarily that no blower whatsoever is required, since the turbine may supply the exhaust gases at the pressure required for introducing the gases into tanks and other holds or rooms in the ship. Such a back-pressure downstream of the turbine will of course reduce the output of the turbine. However, the remaining output will be sufficient not only for operating a cooling water pump for cooling the exhaust gases, but also for supplying electric current to the electric distribution network of the ship during the unloading period. As an example, it may be mentioned that a gas turbine which normally delivers 1,100 to 1,200 kW to the network will still deliver about 600 kW to the network when the back-pressure is increased from 14.2 psia (1 atmosphere) to about 18.5 psia. Approximately half of said output is required for the operation of the cooling water pump, but there still remains a net output of approximately 300 kW.

Another essential advantage of the combination of an inert gas apparatus with a gas turbine is that thereby a simple possibility is provided for removing the inert gas from the holds of the ship when this is required. Thus, according to the invention, air having the required pressure for displacing the inert gas from the holds of the ship may be supplied from the compressor unit of the gas turbine, a portion of the air compressed in the compressor being passed through an injector in which the pressure is reduced and additional air is drawn in. Air of suitable pressure supplied from the injector is passed through the cooler of the apparatus to reduce the temperature of the air and further to the tanks in order to displace the inert gas therein. In the apparatus of the invention this possibility is provided for by the fact that the apparatus comprises an air conduit for connection to the pressure side of the compressor unit of the turbine and delivery of compressed air to the discharge conduit through the cooler and an injector inserted in said air conduit and operated by the compressed air from the compressor to draw additional air into the air conduit.

Further features of the invention will appear from the following description of an embodiment, reference being had to the accompanying drawing, which illustrates the operating principles of an apparatus according to the invention.

DETAILED DESCRIPTION OF THE DRAWING

In the drawing, the elements included in a conventional auxilliary and/or emergency set driven by a gas turbine are indicated within a frame G shown by a dot-and-dash-line. These elements consist of the gas turbine itself, which in the drawing has been divided into its three functional units, viz. a compressor 1, a combustion chamber 2 and a turbine 3. The generator is indicated at 4, whereas 5 is an oil tank for operation of the gas turbine, the oil being supplied to the combustion chamber 2 of the gas turbine set by a pump 6. The exhaust gases from the gas turbine are ordinarily let out into the atmosphere through an exhaust conduit 7 and an exhaust pipe 8 within the ship's funnel.

The inert gas apparatus according to the invention is based upon the presence of such a gas turbine set and is connected to this set in the following way:

An exhaust conduit 9 is connected to the exhaust conduit 7. The distribution of the exhaust gases on the exhaust pipe 8 and the exhaust conduit 9 is controlled by a throttle valve 10 in the exhaust pipe 8 in a manner which will be described later in more detail. When the inert gas apparatus is not in operation, the exhaust conduit 9 is closed by a valve 11.

The exhaust gases from the exhaust conduit 9 are passed to an afterburner 12 having a fuel nozzle 13 fed from the fuel tank 5 through a conduit 14 by means of a pump 15. The fuel amount is controlled in a manner which will be described later in more detail.

The afterburner is required primarily to reduce the oxygen content of the exhaust gases from the gas turbine. Typically, such exhaust gases from the gas turbine may have the following analysis:

percent by volume:

Co.sub.2 -- 3.25

h.sub.2 0 -- 2.32

so.sub.2 -- 0.0056

o.sub.2 -- 16.1

n.sub.2 -- 77.8

downstream of the afterburner the exhaust gases may have the following composition:

percent by volume:

Co.sub.2 -- 15

co -- 0.1

h.sub.2 -- 0.1

o.sub.2 -- about 1

N.sub.2 -- 83.8

the exhaust gases from the afterburner 12 are passed into a cooling tower 16 in which they are cooled by spraying with sea water supplied through a conduit 17 by means of a cooling water pump 18. The cooling water collects in the bottom of the cooler 16 and is discharged into the sea through a conduit 19.

The cooled gases are passed through a water separator 20 and further through a discharge conduit 21 leading to a distributing system not shown.

A pressure indicator 22 measures the pressure in the discharge conduit 21, and a feedback 23 actuating the throttle valve 10 in the exhaust pipe 8 controls the pressure in the discharge conduit 21 so as to maintain the pressure constant at the desired value, which may for instance be 16.4 psia.

To the discharge conduit 21 there is further connected an oxygen analyser 24. This analyser actuates a valve 25 in a return conduit 26 for the fuel supplied by the pump 15. When the oxygen content in the discharge conduit 21 is excessive, the flow of fuel through the valve 25 is further throttled, whereby more fuel will be supplied to the afterburner 12 through the fuel nozzle 13. If the oxygen content in the exhaust gases lies below a certain limit, this must be taken as an indication that an incomplete combustion may take place in the afterburner 12, and that the exhaust gases may contain an excessive amount of carbon monoxide. The flow through the valve 25 will then be increased so that the fuel supply to the fuel nozzle 13 is reduced.

The oxygen analyser 24 also actuates a valve 27 in the discharge conduit 21 and a valve 28 in a conduit 29 branched from the discharge conduit 21 and leading to the atmosphere. The valves 27 and 28 are so controlled that the exhaust gases are passed to the ship's holds through the distribution system not shown, only when the oxygen content lies within predetermined limits, whereas the gases are passed to the atmosphere through the conduit 21 when the oxygen content is too high or too low, a low oxygen content being, as already mentioned, interpreted as an indication of an excessive carbonmonoxide content. 34 is a safety valve.

When the apparatus according to the invention is to be used for displacing the inert gas from the holds in the ship by means of fresh air having the required pressure, the valve 11 will be closed and the afterburner 12 and the described control devices will be out of operation. A portion of the air compressed by the compressor 1 is diverted through a conduit 30. This, of course, reduces the output of the gas turbine 3, and it must be expected that the generator 4 cannot be subjected to a load during this period. The compressed air from the conduit 30 is supplied to an injector 31 which reduces the pressure of the air and at the same time draws in additional air through an air inlet 32. From a gas turbine set of the capacity previously referred to it is possible to tap off about 9,000 standard m.sup.3 air per hour at a pressure of approximately 37 psia. A corresponding amount of air may be drawn into the injector so that in the conduit 33 from the injector 31 there may flow about 18,000 standard m.sup.3 air per hour having a pressure of about 18.5 psia. The temperature of the air tapped from the compressor is about 170.degree. C. This temperature is reduced in the injector partly because of the expansion and partly because of admixture with air drawn in through the air inlet 32. The air in the conduit 33 will therefore have a temperature of about 100.degree. C. For further cooling this air is passed into the cooler 16 and further through the discharge conduit 21 into the distribution system (not shown) for fresh air.

A gas turbine set of the capacity previously referred to will produce about 31,000 standard m.sup. 3 exhaust gas per hour, and when the pressure in the exhaust conduit downstream of the turbine is to be 18.5 psia, the temperature of the exhaust gases will be about 550.degree. C. The exhaust temperature will of course rise further in the after-burner, and when the apparatus is to supply inert gas, comparatively large amounts of cooling water (about 1,500 m.sup. 3 per hour) will be required in the cooler 12. As previously indicated the pump 18 for circulating this amount of cooling water may be operated with an input of about 300 kW, which may be provided by the gas turbine set. When the set supplies air for displacing the inert gas from the tanks, a substantially lower amount of cooling water is required, since in this case only about 18,000 standard m.sup.3 air per hour must be cooled from a temperature of about 100.degree. C.

Claims

What I claim is

1. Apparatus for filling and, if desired, emptying inert gas, poor in oxygen, into or from holds in ships, respectively, said apparatus being connected to the exhaust conduit from a gas turbine, said apparatus comprising an afterburner for reduction of the oxygen content of the exhaust gases of the turbine, a cooler for reduction of the temperature of the gases, a discharge conduit for the cooled combustion gases and a valve for controlling the supply of exhaust gases to maintain the pressure of the inert gas within the desired limits.

2. Apparatus as claimed in claim 1, characterized by an oxygen analyser for analysing the oxygen content of the supplied inert gas and a valve for controlling the supply of fuel to the afterburner said valve being controlled in accordance with the result of the analysis.

3. Apparatus as claimed in claim 2, characterized by a branch conduit leading from the discharge conduit for inert gas into the atmosphere and one or more valves controlled by the oxygen analyser for supplying gas to the branch conduit instead of the discharge conduit when the oxygen content is not within the prescribed limits.

4. Apparatus as claimed in claim 3, characterized by an air conduit for connection to the pressure side of the compressor unit of the turbine and delivery of compressed air to the discharge conduit through the cooler and an injector inserted in said air conduit and operated by the compressed air from the compressor to draw additional air into the air conduit.