Gas separation: processes – Degasification of liquid – Plural successive degassing treatments
Reexamination Certificate
2000-06-21
2002-04-23
Smith, Duane S. (Department: 1724)
Gas separation: processes
Degasification of liquid
Plural successive degassing treatments
C095S247000, C095S262000, C095S266000, C096S157000, C096S197000, C096S201000, C096S203000
Reexamination Certificate
active
06375718
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to a fuel system for a gas turbine plant, which has a heat exchanger for cooling and/or a heat exchanger for heating gaseous fuel, the cooling or heating medium being water which flows in a water circuit. The invention relates, in particular, to a gas/liquid separation apparatus in this water circuit, and to a process for separating gas from such water. The separation apparatus serves to separate gas from the water and to detect the gases separated from the water, and thus to increase the operational reliability of the system. Denoted below as fuel is a gaseous fuel such as, for example, CH
4
, C
2
H
6
, CO, H
2
or a gas mixture.
BACKGROUND OF THE INVENTION
Gaseous fuel which is intended for a gas turbine plant is generally led, coming from a natural gas feed line, firstly through a fuel system in which the parameters, required for the further combustion of the fuel, are controlled.
For example, temporal pressure fluctuations of the fuel occur in the natural gas feed line. In order to equalize these fluctuations, the pressure in the fuel system is appropriately raised or reduced. After a pressure reduction, the fuel can have, for example, a temperature which could cause icing of valves or damage to other subassemblies of the plant. In order to prevent this, the fuel is, for example, already heated before the pressure reduction in a heat exchanger, a so-called dew-point heater. Hot water, for example, is used as heating medium for such dew-point heaters. Furthermore, such a fuel system can be used to enhance or optimize the efficiency of the gas turbine plant. The fuel is preheated for this purpose in a heat exchanger to a prescribed temperature.
A system for heating the fuel in order to enhance or optimize the efficiency of the gas turbine plant is disclosed, for example, in EP 0 918 151, which is hereby incorporated by reference. There, the fuel is guided through the tubes of a heat exchanger around which water flows as a heating medium which flows in a water circuit and has been preheated in a waste-heat recuperator of a gas turbine plant. In particular, the pressure of the fuel is higher than that of the water, in this case.
In particular, the pressure of the fuel is higher than that of the water, in this case.
In order to control a gas compressor for example in a load range below 80%, the fraction of the mass flow not going to the gas turbine plant is recirculated and thereby fed once again to the compressor inlet. Connected in the recirculation line is a heat exchanger in which the fuel is cooled by means of water. Heating of the compressor is thereby avoided in the recirculation operation.
The fuel is led for this purpose through the tubes of the heat exchanger, about which cooling water flows. The cooling water is pumped by means of a delivery pump through a cooling-water circuit which essentially comprises the delivery pump, the heat exchanger, a water-to-water cooler and a gas/liquid separation apparatus. The pressure of the fuel is significantly higher than that of the cooling water in the heat exchanger for cooling the fuel.
Since in both above described heat exchangers, for cooling and for heating the fuel by means of water, the pressure of the fuel is higher than that of the water, there is the risk of a leak occurring, in which case fuel passes into the water. This results in a two-phase flow in the water circuit, which constitutes a safety risk for operating the plant. For example, there is the risk of ignition or explosion in the case of mixing with air at the suction connection of the delivery pump. Furthermore, running dry or cavitation of the delivery pump can occur. Consequently, it .is very important to detect gas leaks at an early stage in order to avoid sizable damage in the system.
In order to limit the level of risk, a gas/liquid separation apparatus, called a separation apparatus here, for short, is connected in the water circuit downstream of the heat exchanger. It serves to separate gases contained in the water, and to detect the gases separated from the water. These are principally methane, hydrogen and further combustible gases. For this purpose, the gases are fed via a gas extraction line to a gas detector, for example a mass spectrometer. In the case of a measurable gas concentration, an appropriate warning is then released, so that necessary countermeasures can be undertaken.
Conventional separation apparatuses which are currently being used have no defined water level as a free surface in the separation apparatus itself, at which the gas bubbles entrained in the water can escape and pass into a gas extraction line. Consequently, the separation and detection of the gases is not sufficiently ensured, with the result that it is not possible to detect a leak reliably in good time.
SUMMARY OF THE INVENTION
In view of the above-named prior art, it is the object of the invention to create a gas/liquid separation apparatus for a water circuit of a fuel system for a gas turbine plant, and a process for separating gas from the water, by means of which the separation of gaseous fuel from the water is improved so that the reliability of the gas detection is raised and, consequently, the level of risk for the operation of the water circuit of a fuel system is reduced.
This object is achieved in accordance with the invention by means of a gas/liquid separation apparatus in a water circuit of a fuel system for a gas turbine plant which has a container with a water inlet and water outlet, and a gas extraction line which leads to a gas detector. According to the invention, the separation apparatus is partitioned by a separating wall in the interior of its container into a water entry chamber and a water exit chamber which are hydraulically interconnected at least in the upper region of the container, thus producing in the water entry chamber a columetric flow flowing upward from the water inlet. This columetric flow then flows from the water entry chamber into the water exit chamber and from there into the water outlet. Furthermore, particularly in the region of it upper termination, the container has a line for feeding into the container a gas which fills a space above the water, as a result of which the water in the container has a free surface.
The partitioning of the container volume into a water entry chamber and a water exit chamber is intended to form a calming section in the water entry chamber at which gas can be separated from the water, and a water outlet in the water exit chamber, which is separated from the calming section. In this case, the free surface is defined by the pressure in the gas-filled space. The hydraulic connection in the upper region of the two water chambers produces in the water entry chamber an upwardly flowing volumetric flow with the aid of which gas bubbles disperse in water rise. The calming section also effects an upwardly directed, non-turbulent flow with a homogeneous velocity profile. This is achieved in conjunction with a suitable duct guidance and low Reynolds numbers, re <700 for water, for example. The gas bubbles can escape at the free and calm surface of the calming section without disturbance from the water into the gas-filled space situated thereabove. In the process, the gas fed into this space differs from the gases from the water. The water exit chamber, which is separate from the water entry chamber, permits an irrotational water outlet, as a result of which as few gas bubbles as possible are entrained into the water outlet.
In a preferred embodiment, the two water chambers are hydraulically connected in their upper region as follows.
The partition which separates the two chambers from one another is tightly connected to the base of the container. There is a free space between the upper edge of the partition and the upper termination of the container. The water flowing upward in the water entry chamber flows over the edge of the partition in the manner of an overflow weir into the water exit chamber. Because of the large width of the overflow weir, slight cros
Blangetti Francisco
Doehler Stephan Werner
Liebig Erhard
Schlageter Rainer
Alstom (Switzerland Ltd
Burns Doane Swecker & Mathis L.L.P.
Smith Duane S.
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