WO2017025215A1

WO2017025215A1 - Circulating fluidized bed furnace

Info

Publication number: WO2017025215A1
Application number: PCT/EP2016/063093
Authority: WO
Inventors: Alexander Baum
Original assignee: Doosan Lentjes Gmbh
Priority date: 2015-08-11
Filing date: 2016-06-09
Publication date: 2017-02-16
Also published as: ES2687791T3; EP3130849B1; PL3130849T3; ZA201800809B; DK3130849T3; CN209325767U; EP3130849A1; KR20180040152A; PH22018500003U1

Abstract

A circulating fluidized bed furnace (10) comprising an outer furnace wall (10r), surrounding an inner combustion space (10c) of a circulating fluidized bed type, and a heat exchange chamber (20), which is friction-locked to said outer furnace wall, wherein said heat exchange chamber is further supported by one or more structural elements (50), each of which being provided with two ends, a first end (50f) being fixed to a section of the furnace wall, while a second end (50s) being fixed to the heat exchange chamber at an offset to the furnace wall,

Description

Circulating Fluidized Bed Furnace

Description

The invention relates to so-called Circulating Fluidized Bed Furnace (CFBF) being part of a Circulating Fluidized Bed Apparatus (CFBA), which main components are:

- The said CFBF, also called a Circulating Fluidized Bed Reactor, designed as a combustor, incineration reactor, boiler, gasifier, steam generator etc. as disclosed - i.a. - in US 6,802,890 B2. In a typical CFBF gas (air) is passed through a permeable grate-like bottom area of the furnace (so-called air plenum), which grate (grid) supports a circulating fluidized bed of particulate material, the so-called incineration charge, mostly including a fuel-like material such as coal, sand etc. In typical applications aeration is achieved by corresponding nozzles, feeding air and/or gas into the particulate material present within the furnace space. The aerated particulate material/fuel mixture (air plenum) allows to promote the incineration process and effectivity.

The outer walls of the furnace, which define the combustion chamber (reaction chamber), are usually so-called tube walls, comprising welded tubes with or without fins in between. In operation a heat transferring fluid like water and/or steam is fed through said tubes/pipes of said furnace walls in order to cool the same and to transfer heat therefrom for further purposes.

The CFBF typically has at least one outlet port at its upper end, via which a mixture of gas and solid particles, exhausted from the reactor, may flow into at (east one associated separator.

- The separator, for example a cyclone separator, serves to

separate solid particles (the particulate material, including ash) from said gas. A typical design of such a separator is disclosed in US 4,615,715. Again the outer walls of the separator can be designed with hollow spaces to allow water flowing through.

- While the gas is extracted from the separator and fed into

subsequent installations of the plant, there are means for the transfer of said separated solid particles out of the separator and into at least one heat exchange chamber, often designed as a Fluidized Bed Heat Exchanger (FBHE), via a corresponding inlet port of said heat exchange chamber. These means may be ducts/pipes/channels or the like. As far as reference is made in the following to an FBHE this refers to a preferred heat exchange chamber, but includes all types of a heat exchanger suitable for that purpose, independently of whether constructed as a

superheater etc.. - A syphon along the way from the separator to the CFBF and/or heat exchanger to allow decoupling of pressure (fields) between separator and CFBF.

- The at least one heat exchange chamber allows to use the heat, provided by the particulate material, for generating power, for example to heat up and increase the pressure of a steam

transported as a heat transfer medium via tubes or the like, through said heat exchanger and further to turbines or the like.

- Typically the heat exchange chamber is equipped with at least one outlet port, being part of return means, in order to transport at least part of the solid particles out of the heat exchanger and back into the Circulating Fluidized Bed Furnace CFBF.

US 5.840.258A discloses a design of such CFBA, wherein the CFBF and the FBHE have been integrated closely together; in other words: FBHE and CFBF have a common wall (tube wall). In operation, i.e.

under temperature load, this design provides the advantage of close (similar) temperatures in both units and thus, minimizes any thermal stresses between both units.

Indeed these temperature expansions and temperature stresses are a major problem in such installations. The thermal expansion of a CFBF of a height of ca. 35 to 50m may range from 0, 1 m to 0,3m and may cause serious stresses within the furnace walls, independently of whether the furnace is bottom supported (according to US 5.840.258A) or top-supported (suspended), as shown in US 6,305,330B1.

One further problem in this context is to properly adapt associated parts of the CFBA, for example the separator and/or the heat exchanger. In many of the known constructions, special expansion joints are required to accommodate motions between associated parts. The integrated design according to US 5,840,285 A may avoid such expansion joints to some extent, but has the disadvantage of

considerable loads (forces) onto and into the furnace wall by said adjacent cyclone and/or heat exchanger.

It is an object of the invention to provide a compact design for a furnace of the circulating fluidized bed type in combination with at least one associated unit, in particular a heat exchange unit, of an overall CFBA.

The invention is based on the following findings:

A compact design may be realized by bringing associated units of the CFBA as close as possible or even better to fix one unit to another (as known from US 5,425,412), but any such friction-locked arrangement of adjacent/associated units causes serious structural problems in view of the extreme weights/loads of such units.

A generic heat exchanger of a CFBA has a size of for example 5x5x5m and a corresponding weight of 100.000kg in an empty state. Additional loads by the solid material transported through said heat exchanger vary strongly and may be in a range up to 100.000kg or more.

The furnace wall, to which the heat exchanger may be friction-locked, typically a so-called tube wall, cannot withstand/compensate such high and varying loads unless constructed as a "castle-wall", being

unacceptable in view of costs and the thermal conditions of a CFBA. The thermal expansions/constrictions mentioned above cause further structural problems.

In other words: The extreme forces and moments, caused by a heat exchange unit which is friction-locked (for example welded) to a conventional furnace wall (like a tube wall) cannot be compensated yet in an economically and mechanically acceptable way. The invention now provides a technical solution for this problem and furthermore a technically relatively simple construction, by further providing at least one structural element, by which the heat exchanger is mechanically linked to the furnace wall, which structural element allows to compensate any such additional loads caused by the heat exchanger and/or the material passing there through.

In its most general embodiment the invention relates to a circulating fluidized bed furnace, comprising

- an outer furnace wall, surrounding an inner combustion space of a circulating fluidized bed type, and

- a heat exchange chamber, which is friction-locked to said outer furnace wall,

- wherein said heat exchange chamber is further supported by one or more structural elements, each of which being provided with two ends, a first end being fixed to a section of the furnace wall, while a second end being fixed to the heat exchange chamber at an offset to the furnace wall.

The structural element "absorbs" all (additional) forces, which have not been absorbed by the furnace wall, to which the heat exchanger is fixedly secured for example by welding.

Insofar it is advantageous that the first end of the structural element is fixed to the furnace wall at a vertical distance above the heat

exchanger, while it is important for the second end being affixed to the heat exchanger at a horizontal distance to the furnace wall and best to a vertically extending wall of the heat exchanger, for example its outer wall, being the wall opposite to the furnace wall.

Although a direct (linear) run of said structural element between first and second end (thereby forming a triangle between furnace wall, ceiling of the heat exchanger and structural element) is within the scope of the general concept, it^'s technical realization is limited to CFBAs with a small or light weight heat exchanger as the furnace walls are of limited stability/structural integrity (German: Stabilitat/Festigkeit).

In this respect further embodiments are characterized by one or more of the following features, which can be realized individually or in arbitrary combinations if not explicitly excluded or technically absurd:

- The structural element is an element, which only transfers (or at least predominantly only transfer) axial forces; in other words: which does not transfer moments/momentums.

- Suitable elements of the type mentioned before are: rope, cord, wire, chain, cable. Use of such a structural element does not exclude to combine the rope etc. with other construction

elements, for example a nut, a screw, a bar, a spring or a rod , especially to simplify the fixation of the structural element at its ends to the furnace wall and/or heat exchanger respectively and/or to integrate such other construction elements into the run of a structural element.

- The use of such structural elements leads to the important option to arrange the structural element in a way to respect the limited structural integrity of the associated units of the CFBA. It is known, i.a., that tube walls have very limited compressive

strength (low pressure resistance) but that these tube walls (tube panels) can easily endure tensile stresses.

- This leads to embodiments wherein the structural element has at least three sections, a first section, extending from the first end of the structural element downwardly and substantially parallel to the outer furnace wall, a second section, extending from the second end of the structural element upwardly, and at least one

intermediate section in-between said first and second sections. Again the second section should extend substantially parallel to the outer furnace wall. "Substantially parallel" includes a sloped orientation within technical tolerances, with an angle between furnace wall and a longitudinal axis of the structural element of at most 15°, better less than 10°, less than 5° or less than 3°.

The run of the structural element (e.g. the rope or wire)

downwardly and parallel to the furnace wall allows to largely avoid mechanical moments to act on said rope but to stress the rope predominantly or even exclusively in its axial direction.

- This is true in particular if the structural element has at least

three sections, a first section, extending vertically downwardly from its first end, and/or a second section, extending vertically upwardly from its second end (and insofar as well parallel to the furnace wall), and at least one intermediate section, extending in- between especially in a substantially horizontal orientation.

The vertical orientation of the tensile means (rope etc), parallel to the furnace wall, to which it is fixed at its first end, causes any forces to be absorbed by said rope to be forces in an axial direction of said means, i.e. in a direction, where the said rope features its highest stability.

- The structural element can be made of a material from the group comprising: metal, steel, plastic, carbon, textile.

- According to another embodiment, the second end of the

structural element is fixed to the heat exchange chamber at an offset to the furnace wall, being larger than 50% of a

corresponding length of the heat exchange chamber, seen in a direction perpendicular to the furnace wall (i.e. horizontally). Accordingly the second section may extend substantially parallel to the outer furnace wall and at a horizontal distance to the first section.

- The farther the second fixation point from the furnace wall is

selected, the better gets the stress distribution within the

structural element. A fixation of the second end of the structural element to any of the vertically extending exposed walls of the heat exchanger is preferred by the same reasons as explained in relation to the fixation of its first end to the vertically extending furnace wall.

- Depending on the specific plant (its size, weight, temperature load etc.), two or more structural elements may be fixed at their second ends in spaced relationship at the heat exchange chamber and extending substantially parallel to each other between their respective first and second ends.

- According to the above disclosure the outer furnace wall, an

inner/adjacent wall of the heat exchange chamber, or both are tube walls and characterized by tubes (for water and/or steam passing there through), either directly fixed to each other (for example by welding) or with fins in between (as well fitted by welding) and mostly made of metal.

- The inventive concept allows a design, wherein outer furnace wall and an inner wall of the heat exchange chamber, being the wall adjacent to the furnace wall, represent a common wall, to realize the most compact arrangement. This further allows to provide one or more (common) through opening(s) within said common wall, representing the outlet opening of the heat exchange chamber as well as the corresponding inlet opening of the furnace (CFBF), which further simplifies the overall construction. - Generally spoken: the heat exchange chamber features at least one outlet port and the circulating fluidized bed furnace features at least one corresponding inlet port to allow a re-transport of solid particles from said heat exchange chamber into said

circulating fluidized bed furnace.

- In an alternative the heat exchanger is arranged at a small

distance to the furnace wall, wherein anchors between and furnace wall and the corresponding outer wall of the heat

exchanger are responsible for a friction-locked attachment of the heat exchanger to said furnace wall, while at least one bridge-like channel with openings to the interior of the heat exchanger and furnace respectively allows for the necessary material transport between both units.

- A further embodiment is characterized by one or more suspension means, for example hangers, which are arranged between the heat exchange chamber and an associated support structure.

The support structure can be the same discrete support (steel) structure, for example a (rigid) frame, to which the furnace and other units of the CFBA are fixed in a suspended manner. A corresponding design is known from US 6,305,33061 .

The support structure can be as well a separate structure or any of the corresponding units of the CFBA can be used as such support structure to hang the heat exchanger.

- The suspension means can be so-called constant hangers

(German: KonstanthSnger, Konstantlast Hanger), for example constant load springs (German: Konstantlast Federn). Constant hangers are known as such and distributed i.a. by www.liseQa.de , according to which a constant hanger is defined as follows: "Their job is to transfer the working load over the whole travel area while maintaining constancy, i.e. , without any considerable deviations." This behaviour can be favourably used for the invention, namely to compensate different loads of the heat exchange chamber (by varying loads of solid materials).

These constant hangers are further able to carry a significant share of the total load and insofar relieve the structural

element(s).

They can be arranged, i.a. , between heat exchanger and a rigid frame (the same as to suspend the furnace or another one) or between heat exchanger and a cyclone arranged above said heat exchanger.

The invention will now be described by way of an example and

reference to

Fig. 1 , which displays a highly schematic drawings of a furnace

arrangement according to the invention.

Fig. 1 displays part of a circulating fluidized bed apparatus (CFBA), namely a circulating fluidized bed reactor (furnace) 10 with a particulate material inlet port 101, an air plenum at a bottom area (symbolized by arrow 10a), a fluidized bed of particulate material above said air plenum, being part of its combustion chamber 10c, and at least one outlet port 12 at its upper part, wherein said outlet port 12 allows a mixture of gas and solid particles exhausted from the circulating fluidized bed furnace chamber 10c to flow into at least one associated separator 14 for separating solid particles from said gas, means 16 (including a non-illustrated syphon) to transfer said separated solid particles into at a circulating fluidized bed heat exchanger 20 and return means 22 to transport the solid particles back into the circulating fluidized bed furnace 10, wherein the circulating fluidized bed furnace 10 (also called a boiler), the separator 14 (also called a cyclone) and the circulating fluidized bed heat exchanger 20 (or any other type of a heat exchanger) are mounted in a suspended manner as will be described hereinafter. A plurality of vertically extending steel support columns 30r,l extends from the ground (symbolized by foundations 32) to a plurality of spaced horizontally extending beams 34. A plurality of hanger rods 36 (alternatively ropes, wires, textile strings etc. can be used) extends downwardly from said beams 34 for supporting the furnace 10 and the separator 14 in a suspended manner.

According to the invention the heat exchange chamber (unit) 20 (wherein heat exchange means like heat exchange tubes are symbolized by wave 20w) is friction- locked to the furnace 10 (its tube wall 10r) by welding. It derives from this that part of the right wall 10r of said circulating fluidized bed furnace 10 represents as well the left wall of said heat exchanger 20, which other walls - as well as the furnace walls - are all designed as tube walls (made of tubes in a spaced relationship with fins in between and water and/or steam flowing through said tubes).

The circulating fluidized bed heat exchanger 20 is further suspended by a steel rope 50, having a first end 50f, fixed to the right furnace wall 10r, and a second end 50s, fixed to the upper end section of the right wall 20r of the heat exchanger 20, i.e. at the largest possible horizontal offset to the furnace wall 10r.

The steel rope 50 has three sections, a first section 50fs, extending vertically downwardly from its first end 50f and parallel to the furnace wall 10r, a second section 50ss, extending vertically upwardly from its second end 50s (and insofar as well parallel to the furnace wall 10r), and one intermediate section 50is, extending in- between in a substantially horizontal orientation and insofar perpendicular to the furnace wall 10r.

The first rope section 50fs runs closely to the furnace wall 10r; insofar fixation means 50fm of said first rope section 50fs are displayed larger than in reality (for the purpose of a better illustration).

The intermediate rope section 50is winds around a lower part of a first rotating disk (roller) 52fd, mounted to a beam 52, which extends horizontally from column 30r, at its left end (following the first rope section 50fs) and, at a distance thereto, winds around an upper part of a second roller (rotating disk) 52sd (followed by the second rope section 50ss).

Said rope 50 not only fulfils the function of a structural element to support the heat exchanger 20 in a suspended manner, but provides the advantage, that the strain on the first section 50fs of said rope 50 is predominantly parallel to the right tube wall 10r and underdoes predominantly (nearly exclusively) only vertically downwardly directed tensile forces.

The same is true with respect to the tube wall 10r, which now can easily endure the tensile stress caused by the load of the heat exchanger 20, independently of whether in the "cold state" (non-loaded with solid particles) or loaded, and independently of varying loads.

Corresponding advantages may be achieved by the described vertical orientation of the second rope section 50ss and its fixation to the outer vertical tube wall 20r of the heat exchanger.

Fig. 1 further displays an optional, but favorable feature of the invention, namely constant load hangers (only one of which is shown in Fig. 1) and identified by numeral 54. Said constant load hangers 54, which can be for example constant load springs and/or constant load coils, are attached with their upper ends to said beam 52 and with their lower ends to the ceiling (upper tube wall 20u) of the heat exchanger 20 and are able to relieve said rope 50.

The suspended construction of said furnace 10 (and the heat exchanger 20 attached thereto) allows to follow the thermal expansions of the respective construction elements and avoids mechanical forces, thermo-mechanical forces and/or moments between adjacent construction parts.

The common section of tube wall 10r (with its corresponding overflow opening(s) from the heat exchanger 20 into the furnace 10, symbolized by 22) brings the temperatures within heat exchanger 20 and furnace 10 into closer conformity and thus minimizes any thermal and mechanical stresses between these units of the CFBA, avoiding special expansion joints in between to great extent.

Claims

1. A circulating fluidized bed furnace (10), comprising an outer furnace wall (10r), surrounding an inner combustion space (10c) of a circulating fluidized bed type, and a heat exchange chamber (20), which is friction-locked to said outer furnace wall (10r), wherein said heat exchange chamber (20) is further supported by one or more structural elements (50), each of which being provided with two ends, a first end (50f) being fixed to a section of the furnace wall (10r) , while a second end (50s) being fixed to the heat exchange chamber (20) at an offset to the furnace wall (10r).

2. The circulating fluidized bed furnace according to claim 1, wherein the

structural element (50) is one which only transfers axial forces.

3. The circulating fluidized bed furnace according to claim 1, wherein the

structural element (50) is one of the group comprising: rope, cord, wire, chain, cable.

4. The circulating fluidized bed furnace according to claim 1 , wherein the first end (50f) of the structural element (50) is fixed to a section of the furnace wall (10r), which is above said heat exchange chamber (20).

5. The circulating fluidized bed furnace according to claim 1, wherein the second end (50s) of the structural element (50) being fixed to the heat exchange chamber (20) at an offset to the furnace wall (10r) being larger than 50% of a corresponding length of the heat exchange chamber (20), seen in a direction perpendicular to the furnace wall (1 Or).

6. The circulating fluidized bed furnace according to claim 1, wherein the

structural element (50) has at least three sections, a first section (50fs), extending from the first end (50f) of the structural element (50) downwardly and substantially parallel to the outer furnace wail (10r), a second section (50ss), extending from the second end (50s) of the structural element (50) upwardly, and at least one intermediate section (50is) in-between said first and second sections (50fs, 50 ss).

7. The circulating fluidized bed furnace according to claim 6, wherein the second section (50ss) of the structural element (50) extends substantially parallel to the outer furnace wall (10r) and at a horizontal distance to the first section (50fs).

8. The circulating fluidized bed furnace according to claim 1 , wherein the

structural element (50) has at least three sections, a first section (50fs), extending vertically downwardly from its first end (50f), a second section (50ss), extending vertically upwardly from its second end (50s), and at least one intermediate section (50 is), extending in-between in a substantially horizontal orientation.

9. The circulating fluidized bed furnace according to claim 1 with two or more structural elements (50) being fixed at their second ends (50s) in spaced relationship at the heat exchange chamber (20) and extending substantially parallel to each other between their respective first and second ends (50f, 50s).

10. The circulating fluidized bed furnace according to claim 1 , wherein the outer furnace wall (10r), an inner wall of the exchange chamber (30), or both are tube walls.

11.The circulating fluidized bed furnace according to claim 1 , wherein the outer furnace wall (10r) and an inner wall of the exchange chamber (20) represent a common wall.

12. The circulating fluidized bed furnace according to claim 1, wherein the heat exchange chamber (20) features at least one outlet port (22) and the circulating fluidized bed furnace (10) features at least one corresponding inlet port (22) to allow a re-transport of solid particles from said heat exchange chamber (20) into said circulating fluidized bed furnace (10).

13. The circulating fluidized bed furnace according to claim 1, further including one or more suspension means (54) between the heat exchange chamber (20) and a support structure (52).

14.The circulating fluidized bed furnace according to claim 1 , suspended to support structure (301, 30r, 34).

15.The circulating fluidized bed furnace according to claim 13 or 14, wherein the suspension means (54) is a constant load hanger.