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Method for positioning superheaters in biomass burning steam generators, and steam generator

Imported: 24 Feb '17 | Published: 06 Jan '04

Tom Blomberg

USPTO - Utility Patents

Abstract

A method for positioning superheaters (

2, 3, 4, 5) in biomass burning steam generators, and a steam generator. The steam generator comprises a combustion chamber (

1), a flue gas duct (

6), a steam circuit (

7), and the superheaters (

2, 3, 4, 5) positioned for minimizing corrosion at a high temperature. The steam generator is fitted with at least two superheaters (

2, 3, 4, 5), whose positioning in the flue gas duct (

6) and serial arrangement in the steam circuit (

7) are effected in such a way that the superheater's or superheaters' heat transfer surface has its surface temperature remaining below the melting point of KOH, 406° C. (corresponds to a steam temperature of about 350-380° C.) down to the point in the flue gas duct (

6), at which the flue gases' temperature has fallen to 750° C. While the flue gases are within the range of less than 750° C., the final superheating is effected to a higher temperature without significantly increasing the contamination and corrosion hazard for superheater surfaces.

Description

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a schematic diagram illustrating the system and method of the present invention.

Claims

1. A method for positioning superheaters (

2,

3,

4,

5) in biomass burning steam generators for minimizing the corrosion of superheater surfaces at a high temperature, wherein the steam generator is fitted with at least two superheaters (

2,

3,

4,

5), whose positioning in a flue gas duct (

6) and serial arrangement in a steam circuit (

7) are effected in such a way that the superheater's or superheaters' heat transfer surface has its surface temperature remaining below the melting point of KOH, 406° C. (corresponds to a steam temperature of about 350-380° C.) down to the point in the flue gas duct (

6), at which the flue gases' temperature has fallen to 750° C., and that, while the flue gases are within the range of less than 750° C., the final superheating is effected to a higher temperature without significantly increasing the contamination and corrosion hazard for superheater surfaces.

2. A method as set forth in claim 1, wherein, in order to ensure a necessary residence time, the superheaters are fitted in the flue gas duct (

6) in such a way that downstream of a preparatory temperature range of 750° C. for flue gases the duct (

6) is provided with a sufficiently long vacant section (a) upstream of the next superheater (

3).

3. A steam generator using biomass as a fuel, comprising a combustion chamber (

1), a flue gas duct (

6), a steam circuit (

7), and superheaters (

2,

3,

4,

5) positioned for minimizing corrosion at a high temperature, wherein the steam generator is provided with at least two superheaters (

2,

3,

4,

5), whose positioning in a flue gas duct (

6) and serial arrangement in a steam circuit (

7) have been effected in such a way that the superheater's or superheaters' heat transfer surface has its surface temperature remaining below the melting point of KOH, 406° C. (corresponds to a steam temperature of about 350-380° C.) down to the point in the flue gas duct (

6), at which the flue gases' temperature has fallen to 750° C., and that, while the flue gases are within the range of less than 750° C., the final superheating has been effected to a higher temperature without significantly increasing the contamination and corrosion hazard for superheater surfaces.

4. A steam generator as set forth in claim 3, wherein, in order to ensure a necessary residence time, the superheaters have been fitted in the flue gas duct (

6) in such a way that downstream of a preparatory temperature range of 750° C. for flue gases the duct (

6) has been provided with a sufficiently long vacant section (a) upstream of the next superheater (

3).