STEAM GENERATOR

Abstract

The invention relates to a steam generator (D1, D2) having a first passage, which is formed by one or more pipes (R1, R2) and through which a medium can be conducted in liquid and/or vapour form, and having a second passage (F1, F2), through which a hot gas can be conducted along the outer side of each of the pipes (R1, R2) which form the first passage. Each of the pipes (R1, R2), which form the first passage, of the steam generator (D1, D2) is surrounded by a pressure-resistant casing (M1, M2) which has a heat-insulating coating (W1, W2) on the inner side thereof and through the interior space of which the second passage (F1, F2) runs.

Description

The invention relates to a steam generator with a first passage that is formed by one or more tubes and through which a medium can be directed in liquid and/or vapor form, as well as a second passage through which a fuel gas can be guided along the outer side of each of the tubes forming the first passage.

Steam generators of the generic type have been state of the art for many years and are used, for example, as so-called water-tube boilers for generating steam in thermal power plants. A water-tube boiler has a reaction chamber that is penetrated or bounded by water-carrying or steam-carrying tubes the so-called water tubes. A carbon-containing fuel is usually burned in the reaction chamber at low underpressure. The heat that is released during the combustion is taken up to a large extent by the media that flow through the water tubes and is used for generating and superheating steam. The superheated steam thus generated is then expanded in various pressure stages into a steam turbine connected to a generator, whereby electrical current is generated.

The electrical efficiency of the above-described process is increased with the temperature and the pressure of the steam introduced into the steam turbine. For this reason, it is desired to generate steam at the highest possible pressure and the highest possible temperature and to feed it to the steam turbine. According to the state of the art, it is possible, with the assistance of a water-tube boiler, to generate high-pressure steam at a maximum of 600° C. and 280 bar (a) as well as medium-pressure steam at a maximum of 620° C. and 60 bar (a). In order to further increase the electrical efficiency, it is desired to considerably increase these values and to provide high-pressure steam at 700° C. and 350 bar (a) as well as medium-pressure steam at 720° C. and 60 to 120 bar (a). The main difficulty that is to be overcome in this connection consists in developing suitable materials from which water tubes can be manufactured at reasonable cost and which have a sufficiently long service life under such extreme conditions. In the opinion of experts, this may take until the next decade.

The object of this invention is therefore to indicate a steam generator of the above-described type, which can be manufactured from materials that can currently be obtained on the market and which nevertheless makes it possible to generate steam at higher temperatures and pressures than that which is possible according to the state of the art.

This object is achieved according to the invention in that each of the tubes forming the first passage is surrounded by a pressure-resistant casing, which has a heat-insulating coating on its inner side and through whose inner space the second passage runs.

A shell construction, which is configured and sized in such a way that it is able, under operating conditions, to tolerate an internal pressure that exceeds the external pressure by at least 1 bar, is to be provided under a pressure-resistant casing.

Because of the pressure-resistant casing, it is possible to guide a fuel gas at a pressure that is elevated relative to the atmospheric pressure through the second passage. Since the pressure of the fuel gas acts on the outer sides of the tubes forming the first passage, the pressure of the media guided into the interior of the tubes can be completely or partially compensated and thus the mechanical stress of the tubes can be at least reduced. For this reason, it is possible to reduce the wall thickness of the tubes in comparison to the state of the art and/or to operate the tubes at higher internal pressure and/or at higher temperatures. In addition, the transfer of heat to the tubes forming the first passage is improved by the elevated pressure of the fuel gas, by which it is possible to reduce the fuel gas temperature with the same heat output.

Configurations of the steam generator according to the invention specifically call for a pressure-resistant casing or several pressure-resistant casings, whereby each casing specifically surrounds a tube or several tubes of the first passage.

Preferably, a pressure-resistant casing consists of steel, especially preferably a steel that is used according to the state of the art for the construction of steam generators. The steel can be refractory steel.

Because of the heat-insulating coating, it is possible to reduce the thermal stress of the pressure-resistant casing to the extent that even non-refractory steel can be reasonably used. In particular, when the casing temperature in the operation of the steam generator can be limited to lower than 70° C., the use of fiber composite material is also conceivable. In this case, a fiber composite material is defined as a material that usually comprises a plastic matrix, which is reinforced by embedded fibers, such as, for example, glass or carbon fibers. In addition, a pressure-resistant casing, which consists of a combination of steel and/or aluminum and/or a fiber composite material, is also conceivable.

A variant of the invention calls for a pressure-resistant casing to be designed as a tube. In this case, the cross-section of the tube can have any shape, whereby it preferably has a circular shape, however.

Another variant of the invention calls for a pressure-resistant casing to be formed from flat or profiled sheets.

The first passage of a steam generator according to the invention can consist of tubes of any shape. The first passage preferably comprises, however, at least one straight tube or one coiled tube.

A pressure-resistant casing of the steam generator according to the invention is designed for an operating pressure of between 2 and 100 bar (a) and an operating temperature of between 60 and 350° C.

The heat-insulating coating consists of a material that is chemically-resistant and physically-resistant relative to the fuel gases used in the operation of the steam generator according to the invention, in the case of which fuel gases these are primarily gases that are generated by combustion or gasification of carbon-containing feedstocks. The heat-insulating coating preferably consists of aluminum oxide (Al₂O₃) and/or zirconium oxide (ZrO₂) and/or silicon oxide (SiO₂) and/or silicon carbide (SiC).

The evaporator according to the invention can be used to evaporate any liquid and/or to superheat the steam thereof. Preferably, however, it is suitable for evaporating water and/or for superheating steam.

Below, the invention is to be explained in more detail based on two embodiments depicted diagrammatically in FIGS. 1 and 2.

FIG. 1 shows the sectional view of a steam generator according to the invention, whose first passage is formed by several tubes, which together are surrounded by a pressure-resistant casing.

FIG. 2 shows the sectional view of a steam generator according to the invention, whose first passage is formed by several tubes, of which each individual tube is surrounded by a pressure-resistant casing.

The steam generator D1 shown in FIG. 1 has tubes R1, which form a first passage, through which, for example, water and/or steam can be directed at a pressure of up to 350 bar (a) and at a temperature of up to 700° C. The tubes R1 are surrounded by a pressure-resistant casing M1 that consists of refractory steel, which is designed as a tube with a round cross-section. In order to protect the pressure-resistant casing M1 from excessive thermal stress during the operation of the steam generator D1, a heat-insulating coating W1 is arranged on its inner side. The free space F1 within the pressure-resistant casing M1 forms a second passage, through which fuel gas at an elevated pressure can be guided along the outer sides of the tubes R1.

The steam generator D2 that is shown in FIG. 2 has tubes R2, which form a first passage, through which, for example, water and/or steam can be directed at a pressure of up to 350 bar (a) and at a temperature of up to 700° C. Each of the tubes R2 is surrounded by a pressure-resistant casing M2 that consists of refractory steel, which is made of sectional sheets. In order to protect the pressure-resistant casing M2 from excessive thermal stress during the operation of the steam generator D2, a heat-insulating coating W2 is arranged on its inner side. The free spaces F2 within the pressure-resistant casing M1 form a second passage, through which fuel gas at an elevated pressure can be guided along the outer sides of the tubes R2.

Claims

1. Steam generator with a first passage that is formed by one or more tubes and through which a medium can be directed in liquid and/or vapor form, as well as a second passage through which a fuel gas can be guided along the outer side of each of the tubes forming the first passage, characterized in that each of the tubes forming the first passage is surrounded by a pressure-resistant casing that has a heat-insulating coating on its inner side and through whose inner space the second passage runs.

2. Steam generator according to claim 1, wherein it specifically comprises a pressure-resistant casing or several pressure-resistant casings, whereby a pressure-resistant casing surrounds at least one tube of the first passage.

3. Steam generator according to claim 1, wherein a pressure-resistant casing consists of steel and/or aluminum and/or a fiber composite material.

4. Steam generator according to claim 1, wherein a pressure-resistant casing is designed as a tube or is formed from flat or profiled sheets.

5. Steam generator according to claim 1, wherein the first passage is designed with one or more straight tubes.

6. Steam generator according to claim 1, wherein the first passage is designed with one or more coiled tubes.

7. Steam generator according to claim 1, wherein a pressure-resistant casing is designed for an operating pressure of between 2 and 100 bar (a) and an operating temperature of between 60 and 350° C.

8. Steam generator according to claim 1, wherein the heat-insulating coating consists of aluminum oxide (Al2O3) and/or zirconium oxide (ZrO2) and/or silicon oxide (SiO2) and/or silicon carbide (SiC).

9. Steam generator according to claim 1, wherein it is suitable for evaporating water and/or for superheating steam.