EP0533652B1 - Process and device for operating a gas turbine with introduction of additives - Google Patents

Abstract

In a process involving at least one burner in a combustion chamber, damage to the components of the gas turbine due to the presence of vanadium in the fuel is prevented by spraying an aqueous solution of a magnesium compound separately into the combustion chamber. A device for carrying out the process consists of a burner (1) known per se with devices for spraying water (2) or steam (3). Said device communicates with a reservoir (4) through a dosing device (5). The invention replaces the use of expensive, oil-soluble magnesium compounds by the simpler, more economical use of water-soluble magnesium salts.

Description

The present invention relates to a method for operating a gas turbine according to the preamble of claim 1 and a corresponding device according to the preamble of claim 7.

From AU-B-496757 a method for operating a gas turbine fired with vanadium-containing fuel is known, which has at least one burner in a combustion chamber and means for feeding a magnesium compound dissolved in water as an additive into the combustion chamber, the burner acting on the fuel becomes.

From EP-A-0 193 838, for example, a so-called hybrid burner is known, which also provides options for injecting water or steam into the combustion zone. Reference is expressly made to this document for details of the burner construction. Further variants of burners with additional injection of inert substances are also known from DE-A 36 06 625. Water and / or steam are e.g. B. injected into the combustion zone of a combustion chamber to lower the temperature there and thus reduce the generation of environmentally harmful NO _x .

It is also known from the prior art to add additives to the fuel when firing gas turbines, for example in order to protect the components of the gas turbine from damage. In particular, there are problems with fuels containing vanadium, for example certain heavy oils. The vanadium forms low-melting vanadium compounds on the hot gas-carrying components, in particular the blades of a gas turbine, which are very aggressive and quickly dissolve protective oxide layers. This leads to strongly accelerated high-temperature corrosion. To avoid this form of corrosion, it is known to add metal compounds to the fuel which react with the vanadium during combustion and form vanadates which are characterized by such high melting points that they are in solid form at the usual blade temperatures. Among numerous metal compounds, those of magnesium have proven particularly effective, since magnesium orthovanadate (Mg₃V₂O₈) forms, which only melts at 1159 ° C. The resulting magnesium-containing deposits, on the other hand, are easy to remove from the blades. So far, the magnesium has been added to the fuel either in the form of oil-soluble compounds, colloidal suspensions or in the form of water-soluble salts that have to be emulsified.

The production of oil-soluble additives is very complex and entails high costs, which can make the use of a fuel uneconomical, for example at high vanadium contents. The addition of less expensive, non-oil-soluble magnesium compounds as a suspension or emulsion causes serious stability problems and requires considerable equipment. Magnesium oxide suspensions can cause burner nozzles to wear out. From AU-B 496 757, from which the present invention is based, the use of magnesium sulfate dissolved in water, which is emulsified with the fuel, is known. However, metering and mixing with the fuel is relatively complex and difficult to keep constant. In almost all applications, the expensive oil-soluble additives have had to be used.

Against this background, it is an object of the present invention to provide a method and an associated device which allow reliable and inexpensive admixture of magnesium in the combustion process while avoiding the problems mentioned. In particular, the admixture of magnesium sulfate dissolved in the water in the combustion process of fuels containing vanadium should be made easier and cheaper.

To achieve this object, a method according to the characterizing part of claim 1 and a device according to claim 6 are specified. Advantageous refinements are specified in the respective dependent claims.

The separate injection of a magnesium compound dissolved in water In terms of process engineering, it is much easier to control together with the water in the combustion chamber than the emulsification of a magnesium compound dissolved in water with the fuel. As a result, an exact dosage of the magnesium content to be introduced in relation to the vanadium content in the fuel can be achieved without any problems. The necessary additional devices on the burner are not particularly complex and have already proven themselves in connection with the reduction of NO _x in the exhaust gas. By spraying the magnesium compound dissolved in water directly into the flame, practically the same effect is achieved as with an injection together with the fuel. Magnesium sulfate is preferably an inexpensive magnesium compound which is easily soluble in water. About three parts by weight of magnesium should be added per part by weight of vanadium in the fuel. The concentration of the water-soluble magnesium compound in the water can be adjusted so that about one tenth of the volume of water with dissolved magnesium compound must be injected per volume of fuel. From a technical point of view, this is not a problem because the injection of much larger portions of water is already solved in another context.

The following data are given to explain the whole process:

Die Menge des durch das Sulfat zusätzlich eingeführten Schwefels fällt gegenüber derjenigen Schwefelmenge, die gewöhnlich im Brennstoff enthalten ist, nicht ins Gewicht. Auch ansonsten ergeben sich gegenüber der Beimischung einer öllöslichen Magnesium-Verbindung keine Nachteile für den Verbrennungsprozeß und die entstehenden Emissionen.At 20 ° C 25.8%, at 0 ° C 20.9% MgSO₄ dissolve in water. The following reaction then takes place in the burner flame: $$\text{3 MgSO₄ + V₂O₅ → Mg₃V₂O₈ + 3SO₃.}$$

The amount of additional sulfur introduced by the sulfate is insignificant compared to the amount of sulfur usually contained in the fuel. Otherwise there are no disadvantages for the combustion process and the resulting emissions compared to the addition of an oil-soluble magnesium compound.

The required quantities are explained using the following example:

With an assumed, relatively high vanadium content of 300 ppm in the fuel and a metering ratio of magnesium to vanadium of 3: 1, a gas turbine with a fuel consumption of 10 kg / s requires about 160 kg MgSO₄ / h. If a 20% solution of MgSO₄ in water is used, which is sufficiently far from the solubility limit, the amount of solution required is 800 kg or 670 l solution / h.

Devices for carrying out the method are specified in claims 6, 7 and 8. Accordingly, the burners known per se require additional devices for carrying out the method according to the invention, namely at least one additional storage container for a magnesium compound dissolved in water and a metering device which enables feeding into the combustion chamber via water nozzles.

An embodiment of the invention is shown schematically in the drawing. A burner was selected as an example, as is described in detail in EP-A-0 193 838. There is no explanation of the structural details of the burner itself. It is only important that the burner 1 has devices for injecting water 2 and / or steam 3. It is not decisive whether it is a premix burner, a diffusion burner or a so-called hybrid burner. According to the invention, such a burner is assigned at least one storage container 4, which is connected via a metering device 5 to the injection devices 2, 3 for water and / or steam.

The present invention is particularly suitable for gas turbine plants in which vanadium-containing fuel is to be burned always or temporarily.

Claims (8)

1. Method for operating a gas turbine using fuel containing vanadium, which has at least one burner in a combustion chamber and means for supplying a magnesium compound dissolved in water as an additive into the combustion chamber, wherein the fuel is supplied to the burner, characterised in that the magnesium compound dissolved in water is nozzle-injected into the combustion chamber with the water but separately from the fuel.
2. Method according to claim 1, characterised in that the water with the dissolved magnesium compound is injected directly into the flame of the burner.
3. Method according to claim 1 or claim 2, characterised in that the magnesium compound is a magnesium salt, preferably magnesium sulphate (MgSO₄).
4. Method according to one of the preceding claims, characterised in that for each part by weight of vanadium about 3 parts by weight of magnesium are supplied to the combustion chamber.
5. Method according to one of the preceding claims, characterised in that the concentration of the water-soluble magnesium compound in the water is adjusted so that about one tenth of a part, or less, by volume of water with dissolved magnesium compound is injected for each part by volume of fuel.
6. Device for operating the method according to one of the preceding claims using a burner (1) equipped for nozzle-injection of water (2) and/or steam (3), characterised in that at least one additional reservoir for storing water with a magnesium compound dissolved therein communicates with the water or steam injection device (2, 3) in the burner by way of a metering device (5).
7. Device according to claim 6, characterised in that the reservoir (4) has a capacity greater than 1 m³.
8. Device according to claim 6 or claim 7, characterised in that the dimensions of the water or steam injection device (2, 3) are such that water with dissolved magnesium compound can be injected in an amount of about one tenth part of the volume of fuel supplied per unit of time.

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