Steam generator

Abstract

A steam generator is provided. The steam generator has a combustion chamber having a peripheral wall formed at least partially from gas-proof, welded steam generator pipes, at least two additional inner walls formed at least partially from additional steam generator pipes which are arranged inside the combustion chamber. The inner walls are connected one behind the other on the flow medium side by an intermediate collector. The steam generator has a high service life and is reliable. The flow medium on the inlet of the inner wall upstream of the intermediate collector has a lower temperature than that of the flow medium on an inlet of the peripheral wall.

Claims

1. A steam generator, comprising: a combustion chamber having a peripheral wall formed at least partly from gas-proof, welded steam generator pipes; an inner wall and a further inner wall formed at least partly from additional steam generator pipes, wherein the inner wall and the further inner wall are arranged inside the combustion chamber, wherein the further inner wall is connected downstream from the inner wall on a flow medium side by an intermediate collector, and wherein a flow medium has a lower temperature at an inlet of the inner wall than a flow medium at an inlet of the peripheral wall, wherein an economizer device is connected upstream of the inlet of the inner wall and upstream of the inlet of the peripheral wall on the flow medium side and uses waste heat to preheat flow medium admitted to the economizer device to produce a preheated flow medium, wherein the flow medium at the inlet of the inner wall has a smaller heat input than the flow medium at the inlet of the peripheral wall, wherein the peripheral wall and the inner wall form an evaporator such that flow medium introduced to the evaporator is evaporated, wherein the steam generator is designed as a once-through boiler, wherein the temperature of the flow medium supplied to the inlet of the inner wall is such that no steam content arises in the intermediate collector, wherein a bridging line branches off before an inlet of a flow medium side of the economizer and opens out into the inlet of the inner wall, and wherein a first part of the preheated flow medium is supplied directly to the peripheral wall from the economizer device and a second part of the preheated flow medium is conveyed via a line to the bridging line such that the second part of the preheated flow medium is mixed with flow medium from the bridging line that has not been preheated by the economizer device thereby making the flow medium at the inlet of the inner wall have a lower temperature than the flow medium at the inlet of the peripheral wall.

2. The steam generator as claimed in claim 1, wherein the combustion chamber comprises a fluidized-bed firing device.

3. The steam generator as claimed in claim 1, wherein the inner wall is arranged symmetrically in the combustion chamber and is connected upstream of the intermediate collector on the flow medium side.

4. The steam generator as claimed in claim 1, wherein the bridging line comprises a flow regulation valve.

5. A method for operating a steam generator having a combustion chamber with a peripheral wall formed at least partly from gas-proof, welded steam generator pipes, comprising: forming an inner wall and a further inner wall at least partly from additional steam generator pipes; arranging the inner wall and the further inner wall inside the combustion chamber; connecting the further inner wall downstream from the inner wall on a flow medium side by an intermediate collector; connecting an economizer device upstream of an inlet of the peripheral wall on the flow medium side; preheating a flow medium admitted to the economizer device utilizing waste heat to produce a preheated flow medium; supplying by the economizer device a flow medium having a lower temperature at an inlet of the inner wall than a flow medium supplied at the inlet of the peripheral wall such that no steam content arises in the intermediate collector; and providing a bridging line that branches off before an inlet of a flow medium side of the economizer and opens out into the inlet of the inner wall, wherein the peripheral wall and the inner wall form an evaporator such that flow medium introduced to the evaporator is evaporated, wherein the steam generator is designed as a once-through boiler, and wherein a first part of the preheated flow medium is supplied directly to the peripheral wall from the economizer device and a second part of the preheated flow medium is conveyed via a line to the bridging line such that the second part of the preheated flow medium is mixed with flow medium from the bridging line that has not been preheated by the economizer device thereby making the flow medium at the inlet of the inner wall have a lower temperature than the flow medium at the inlet of the peripheral wall.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) An exemplary embodiment of the invention is explained in greater detail with reference to a drawing, in which:

(2) FIG. 1 shows a schematic of the lower part of the combustion chamber of a once-through boiler with fluidized-bed combustion with a partly-bridged economizer,

(3) FIG. 2 shows the once-through steam generator from FIG. 1 with parallel economizers, and

(4) FIG. 3 shows the once-through steam generator from FIG. 1 with series economizers.

DETAILED DESCRIPTION OF THE INVENTION

(5) Parts which are the same are provided with the same reference characters in all figures.

(6) The steam generator 1 shown schematically in accordance with FIG. 1 is embodied as a once-through steam generator. It comprises a number of pipe walls formed from steam generator pipes through which there is an upwards flow, namely a peripheral wall 2 as well as symmetrically-arranged inner walls 4 aligned inclined, downstream from which a further inner wall 8 is connected by an intermediate collector 6 on the flow medium side. The once-through steam generator 1 is thus embodied in what is referred to as the pant-leg design.

(7) Flow medium enters the pipe walls through inlets 10, 12 assigned to the peripheral wall 10 or the inner walls 4 respectively. In the inner space 14 solid fuel is burned in a type of fluidized bed combustion and thus an input of heat into the pipe walls is achieved, which causes a heating and evaporation of the flow medium. If the medium now enters all pipe walls with the same enthalpy, a steam content can already arise in the intermediate collector 6 that is so high that an uneven distribution to the pipes of the inner wall 8 occurs and the pipes with high steam content overheat here.

(8) To avoid the consequential disadvantages such as a shorter service life or greater need for repairs for example, the flow medium supplied to the inner walls upstream from the intermediate collector 6 is at a lower temperature than the medium supplied to the peripheral wall 2. In this case an economizer 16, which guarantees different heat inputs into the different medium flows, is provided in the steam generator 1.

(9) To this end, the economizer device 16 in accordance with FIG. 1 comprises an economizer 18, connected upstream from which on the flow medium side is a branching point 20. A part of the flow medium is thus diverted around the economizer 18 in a bridging line 22. In the flow medium-side direction, connected downstream from the economizer 18 is a further branching point 24, from which a line is routed to the inlets 10 of the peripheral wall 2. A part of the preheated flow medium is thus supplied to the peripheral wall 2. Another part of the preheated flow medium is conveyed in a line, which meets the bridging line 22 at a mixing point 26. Here a medium of slightly lower temperature is obtained by the mixing of the medium flows, which is then conveyed to the inlets 12 of the inner walls 4. The amount of the bridged flow medium and thus the temperature of the flow medium conveyed to the inner walls 4 can easily be regulated by a throughflow regulation valve 28 in the bridging line 22 in this case.

(10) FIG. 2 shows an alternative embodiment of the invention. The steam generator 1 is identical here to FIG. 1 except for the economizer device 16. The economizer device 16 includes at its flow medium-side inlet a branching point 30, from which two lines lead into two economizers 18, 32. The outlet of the economizer 18 is connected in this case 10 to the peripheral wall 2, while the economizer 32 is connected to the inlets 12 of the inner walls 4. The economizer 32 is now embodied such that it has a lower heat input into the flow medium than the economizer 18. Thus a lower temperature is achieved at the inlets 12 of the inner walls 4 than at the inlets 10 of the peripheral wall 2. A suitable design of the economizers 18, 32 enables the temperature to be adapted to the desired boundary conditions.

(11) A further embodiment of the invention is shown in FIG. 3. Here too the steam generator 1 is identical to FIG. 1, except for the economizer device 16. The economizer device 16, after its flow medium-side inlet, initially contains an economizer 18 in which the entire flow medium is heated. Then a bridging line 22 branches off, which opens out into the inlets 12 of the inner walls 4. A further part of the flow medium is conveyed into a further downstream economizer 32. Here it is heated further and then conveyed through the peripheral wall 4. The additional heating in economizer 32 means that this medium has a higher temperature than the medium conveyed into the inner walls 4.