Prime-mover dynamo plants – Turbogenerators
Reexamination Certificate
1999-06-08
2001-06-05
Enad, Elvin (Department: 2834)
Prime-mover dynamo plants
Turbogenerators
C290S00100C, C290S00100C, C290S00100C, C290S043000, C290S054000
Reexamination Certificate
active
06242819
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to an arrangement for a gas urbine for use in gas supply pipe systems particularly in long distance gas transmission lines for supplying gas to low pressure end consumers.
In today's long distance gas piping systems particularly natural gas is conducted over long distances of over thousand kilometers to the end consumer for domestic or industrial heating purposes. In order to be able to transport the gas over such long distances at the least possible losses, it is highly compressed to typically 80 bar and above. In order to feed the gas into the low pressure duct systems of the end consumer with substantially lower safety provisions, the gas pressure must be reduced possibly in several expansion stages arranged in series.
In each expansion stage, a part of the energy stored in the compressed gas is released. For economical reasons, it has not been particularly attractive to try to regain the energy released in the final expansion stages in the long distance piping system between local centers (for example, community gas plants) and the final end users (for example, private gas heating systems for domestic use) and to utilize it, (for example, to generate electricity). The reason for omitting such utilization resides in the high investment and maintenance costs for present gas turbine generators including the necessary safety systems which are not in an economically reasonable relation to the advantages that can be obtained by such local electrical power generation.
EP 000 438 discloses a gas expansion turbine in a gas supply system including a motor generator with a shaft provided with a bladed-turbine wheel.
It is the object of the present invention to provide a turbine plant which is simple, compact, and adequate from a safety and from an economical point of view for decompressing the gas at the end stages of long distance gas transmission lines whereby the energy released by the gas expansion can be converted to electrical energy.
SUMMARY OF THE INVENTION
In accordance with the invention, a gas expansion turbine is provided in a gas distribution piping system which includes a gas supply pipe section with at least one separating wall disposed at the supply (high pressure) side. At or near this at least one separating wall which includes nozzles for the depressurization of the gas supplied thereto an asynchronous motor or an asynchronous generator is disposed. The shaft of the asynchronous motor/generator carries at the downstream side (low pressure side) behind the nozzles a turbine wheel which is light-weight and is driven by the gas flow. Furthermore, means are provided for conducting away the electrical energy generated during operation of the generator and for feeding it into the electric power net. Furthermore, a control arrangement is provided which provides a control signal to a safety valve arranged upstream ahead of the asynchronous motor/generator for (partially) closing the gas supply pipe section when the shaft speed exceeds a critical value.
With the arrangement according to the invention, a number of components otherwise needed with gas turbine generators such as a valve housing, a turbine housing and a steam discharge cover are omitted, so that there are no investment and maintenance expenses for these components.
Furthermore, the turbine wheel, which is light-weight particularly by the use of plastic instead of steel as the construction material, provides for an essentially explosion-proof design even without the use of thick-walled housings for the relatively thin-walled standard low pressure pipes. With the relatively light turbine wheel blades used in accordance with the invention, any parts which might fly off at high speeds because of material fatigue as a result of long term use because of crack formations at the rotating blades and which hit the surrounding low pressure pipe walls are retained by the pipe walls because of the relatively low mass and high elasticity of the materials used and the low kinetic energy and low impulse transmission of the parts thrown off.
Furthermore, with the arrangement of a gas decompression turbine according to the invention, the shaft supported in the separating wall does not require a special gas-tight seal which also saves investment and maintenance expenses.
In order to provide for an automatic shut down or respectively, a reduction of the gas flow when the speed of the asynchronous motor/generator becomes excessive because of a break down of the electric power net, a speed-dependent control signal may be supplied to a control device such as a local SPC (storage programmable control) which supplies a control signal to a safety valve disposed upstream of asynchronous motor/generator for (partially) closing the gas supply pipe section. For this purpose, valves can be used which are provided in the various gas supply pipe sections anyhow so that again there are no additional investment and maintenance costs.
The SPC already mentioned can additionally be used for the permanent surveillance of the asynchronous motor/generator speed during start up and also during generator operation.
Since the asynchronous motor/generator is disposed directly in the gas supply flow, there is also no need for the installation of a fan wheel since the asynchronous motor/generator is sufficiently cooled by the gas flow.
Any heat losses caused by mechanical friction in the asynchronous motor/generator and the losses in the copper and iron of the coils of the asynchronous motor/generator are utilized for preheating the gas flow. This will result in an increase of the thermodynamic efficiency during expansion of the gases in the nozzles to the low pressure side pressures and temperatures.
In asynchronous motor/generators with a second free shaft end (as they are provided in series for example for mounting a cooling fan wheel for other applications), it is possible, in a simple manner, to provide for a two-stage expansion for accommodating larger pressure drops by providing on the shaft two impeller wheels in series. In this case, an additional separation wall is disposed in front of the second impeller wheel, which also includes nozzles for the expansion of the gas. In such an arrangement, the gas is subjected to a pre-expansion in the nozzles of the first separating wall, is then conducted onto the first impeller wheel. Subsequently, the gas is directed onto the second impeller wheel (in a second expansion stage) in the same way as it is directed onto the first impeller wheel.
It is of course also possible to arrange several gasexpansion turbines in series in a gas pipe section.
Furthermore, it is possible in a cost-efficient manner to provide for pre-heating of the gas at the supply side for increasing the efficiency.
In order to increase the operational safety of the arrangement according to the invention, in a preferred embodiment, a reinforcement ring is disposed at the inner circumference of the gas supply pipe in the area of the turbine wheel. The distance between the inside wall of the reinforcement ring and the outer circumference of the turbine wheel is so selected that, at speeds below a predetermined speed, the turbine wheel is freely movable within the reinforcement ring. However, upon exceeding the predetermined speed, the turbine wheel comes into contact with the reinforcement ring because of a radial stretching of the blades caused by the centrifugal forces.
If in this preferred arrangement, the asynchronous motor/generator speed becomes excessive because of a failure of the electric power net, that is, if the speed increases in an uncontrolled manner, the blades of the turbine wheels are radially stretched, particularly if they consist of an easily stretchable material such as plastic, until they come into contact with the surrounding reinforcement ring. The friction forces activated in this manner provide for a counter force which retards the rotation of the shaft so that excessive speeds of the asynchronous motor/generator are prevented even if the forced shut do
Heintz Theo
Keiper Rudolf
Muller Thomas
Aktiengesellschaft Kuhnle, Kopp & Kausch
Bach Klaus J.
Enad Elvin
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