Off-shore power station

(54) Designation: Off-shore power plant to exploit natural gas deposits

7502539-5

The present invention relates to an off-shore power plant for utilizing ground gas deposits under the seabed by combustion of the ground gas in the combustion chamber into a power plant built on an artificial island consisting of steam generators, turbines and generators. This is understood to mean such facilities, which are established in the coastal area or on the open sea and flow on the water or stand on the seabed and are intended for energy generation.

It is previously known to build off-shore power plants at the extraction sites for the deposits and to directly consume the extracted natural gas at the extraction site instead of transporting it over pipelines to the mainland. The natural gas would then be combusted in series-connected gas turbines. The efficiency of clean gas turbines is low. The device for such gas turbines also requires a large platform, so that the effect calculated on the surface is small.

At the off-shore power plants, due to the high construction costs of the support structure, the lowest possible building volume is sought.

The object of the invention is therefore to provide such power plants with high efficiency at minimum possible building volume.

The task is solved according to the invention by providing an expansion turbine driven by ground gas driven by the originating pressure in a combustion chamber which is connected to a compressor for compressing the combustion air to the combustion chamber of the steam generator. As a result, the building volume can be degraded and the support structures required in any case can be used to accommodate parts of the power plant.

Such a construction is possible, if steam generators are used, which are operated under overpressure in the fireplace, and to whose flue gas line a gas turbine and to whose steam line a steam turbine is connected. Thus, a combined steam-gas process will be used with the aid of pre-compression steam boilers. Such steam boilers have a cylindrical shape and are therefore advantageous for placement in the support structure. In addition, the combined gas-vapor process provides an improvement in efficiency, resulting in a better power per unit area.

The low volume of buildings enables an advantageous building method. The tires can be made flowable and equipped with all heating and mechanical engineering devices on the yards. The tires thus produced can then be towed as finished units on a waterway to the destination. In this way, the assembly is extensively located to the shipyard and expensive lake mounting is reduced to a minimum.

An embodiment of the invention is illustrated in the drawing and. will be described in more detail below. Fig. 1 shows the gas vapor circuit and Fig. 2 shows the basic structure of the power plant according to the invention.

The shown off-shore power plant is arranged for operation with natural gas. However, mineral oil can also be used. For highly nitrogen-containing weak gas, the described plant is particularly well suited.

According to Fig. 1, natural gas is passed over a natural gas line 16 to an expansion turbine 17, which is connected to a compressor 4 for compressing the combustion air to the combustion chamber of the steam generator 1. Part of the resulting combustion heat is used for steam generation. The heat of the heat is utilized in a gas turbine 2 which is supplied to the hot flue gases. The gas turbine 2 drives a generator 3. The steam generated in the steam generator is supplied to a steam turbine 5, which drives a generator 6. After discharge, the steam enters a seawater cooled condenser 7. The condensate is preheated in a steam heated feed water preheater 8 and in a flue gas heated feed water preheater 9 and is fed back to the steam generator 1.

If the pressure of the absorbed natural gas is high enough, another expansion turbine, powered by natural gas, can be deployed. This expansion turbine can drive compressor 4 to compress the combustion air.

According to Fig. 2, the power plant is arranged on an artificial island. It consists of support legs 10 arranged in a triangle, which supports a platform. The support legs 10 are submerged on the seabed. Line 11 indicates the height of the sea surface. The support legs 10 occasionally occupy a steam boiler trained as a pre-compression boiler 1. The ground gas and combustion air are introduced into the lower part of this standing boiler 1, while the steam and flue gas are supplied to the turbines from the upper part of the boiler. This device is thermodynamically particularly advantageous, in contrast to the otherwise onshore devices in combination processes.

The platform consists of several superimposed tires. The lower deck 12 accommodates the gas treatment and the water treatment units as well as all the equipment required to supply the platform. On the overlying tire 13 are the gas turbines 2, the steam turbines 5 and the generators 3 and 6, of which only one gas turbine 2 and the generator 3 connected to the gas turbine are indicated in Fig. 2. The units are available from above. Therefore, the tire 13 is provided with removable mounting hatches. Furthermore, a crane track is located on deck 13 for a circular crane rotating around the central shoe.

Generators 3 and 6 cooperate. The current generated by them is converted into direct current by high voltage. For this purpose, inverters (thyristors) are available, the direct current is carried over sea cable to land.

The power plant described above allows a particularly favorable assembly. The necessary assembly units are mounted on the tires and in the support structures immediately on the shipyard. The tires are made floating and can be towed out in position. In this way, the expensive sea installation work is reduced to a minimum. At smaller water depths down to 30 meters and smaller units, the support legs are already fixed in the platform holders and the whole is immersed only in the lake. Greater water depth requires a support-like structure for each support leg. These can be transported independently of the platform to the installation site, then immersed and secured in the holders of the equally floating platform tires.

At the subsequent installation on the lake, the support legs are first lowered to the seabed. In addition, the tires are raised to their final level above sea level. Then follows the steel-based mounting connection of support structures and tires. The described essentially pre-assembled position on the yard is also possible and advantageous when the steam generator is not, as described, arranged in the support legs but on one of the tires.