The invention relates to a fluidized bed heat exchanger as a component of an associated incineration apparatus, in particular to a so-cailed Circulating Fluidized Bed Apparatus (CFBA). Hereinafter terms like "upper", "lower", "horizontal", "vertical", "inner" etc. always refer to a regular use position of the heat exchanger and/or the CFBA.

A CFBA typically comprises a circulating fluidized bed reactor, designed as a combustor, incineration reactor, boiler, gasifier, steam generator etc., hereinafter called combustor.

The combustor walls are made of tubes, through which water runs, wherein said tubes are either welded directly to each other to provide a wall structure or with fins/ribs between parallel running tube sections.

As most of corresponding fossil fuels like coal, timber etc. contain sulphur and/or harmful substances it is necessary to clean the gases leaving the combustor, in a suitable way.

Typically the combustor has at least one outlet port at its upper end, wherein said outlet port allows a mixture of gas and solid particles (hereinafter called solids or ash) exhausted from the reactor, to flow into at least one associated separator. The separator serves to disengage the f!ue gases and solids. Thereafter the separated flue gases and solids are treated separately. The solids are either directly returned into the combustor and/or fed into an intermediate heat exchanger, in particular into at least one Fluidized Bed Heat Exchanger (FBHE) via a corresponding inlet opening of said FBHE.

A syphon along the way from the separator to the FBHE and/or to the combustor allows decoupling of pressure (fields) between separator and combustor or separator and FBHE respectively.

The at least one FBHE allows to use the heat, provided by the soiids (particulate material), for generating power, for example to heat up and/or increase the pressure of a steam or water, transported as a heat transfer medium via tubes through said FBHE and further to turbines or the like.

The FBHE is equipped with at least one outlet opening, also called return means, for at least part of the solids on their way out of the FBHE and back into the combustor.

The general design of such CFBA and its. components is disclosed in EP 495296 A2.

The typical electrical capacity range of a generic FBHA is around 50 to 600MW and the combustor has a height between 30-60m, a width between 13-40m and a depth: 15-40m, Typical sizes of an FBHA are: height: 3-8 m, width: 3-8 m, depth 3-8 m.

While the overall functionality and reliability of such CFBA, including the FBHE (also called ash cooler) has proven successful over years there is a continuous demand for

improvements.

Against this background it is an object of the invention to provide an FBHE for installation between a separator and a combustor of a CFBA which provides optimizations in

construction, maintenance, service, efficiency and/or solids ^' flow (avoidance of plugging).

The general process engineering of this type of a fluidized bed heat exchanger is more or less defined and includes:

- feeding the solids via an inlet opening,

- fluidizing the solids by air, introduced under pressure via corresponding nozzles in the bottom area of the heat exchanger,

- transferring the energy (heat), stored within the solids, via heat transfer means (in particular tubes, through which a heat transfer fluid like water or steam flows), arranged in the heat exchanger, into said fluid, withdrawing the solids from the heat exchanger via a corresponding outlet opening. Insofar the invention is based on the idea to improve the heat transfer within the heat exchange chamber by optimizing the supply/transport of the solids into the heat exchange zone of the heat exchanger, to avoid any plugging within the heat exchange zone and to extract the solids continuously to allow a continuous flow of the solids within the heat exchanger.

In this respect it has been realized that introducing the solids into the heat exchanger at its bottom end (as disclosed in EP 495296A2) has the disadvantages that additional power is required to feed the solids. if the solids are transported into the heat exchanger via an inlet opening at -an upper end of the heat exchange zone it was realized that the thus initiated counter-flow of the solids and the air introduced by the bottom area of the heat exchange zone leads to an irregular distribution of the solids within the heat exchange zone and correspondingly to a loss of heat transfer efficiency.

These drawbacks can be avoided by a design, characterized by a special feeding channel (runner) to guide the solids from an inlet opening at an upper end of the heat exchanger downwardly towards the bottom area of the heat exchanger, wherein no or substantially no air is introduced into the solids ^' stream flowing within the runner, before the solids ieave the runner at a lower end of the runner. The flow direction of the solids along the runner is therefore substantially downwardly with no or no substantial counterflow within the runner.

This outlet end of the runner is close to the bottom of the heat exchanger, and allows to transfer the solids into the associated (adjacent) heat transfer zone of the heat exchanger.

This heat transfer zone can be designed in a conventional way, namely with a fluidized bottom (nozzle bottom, grate) to allow a fiuidization of the solids and an optimized heat transfer into heat transfer means arranged in said heat transfer zone and means to extract the solids from the heat exchanger. Contrary to the solids ^' flow direction within the runner the main flow direction of the solids in the heat transfer zone is upwardly and again without or with no substantial counterflow, notwithstanding the fiuidizing effect caused by the fluidized bottom of the heat transfer zone.

The runner is a part and an important component of the heat exchanger and allows said downwardly oriented flow of the solids. It provides the advantage of an inlet opening at the upper end of the heat exchanger, in particular close to or in its ceiling and thus at a short distance to the associated separator which is arranged above the heat exchanger. The material flow can be affected by gravity with no or little external power being required.

As the solids may flow within the runner without any substantial external forces, in particular without any air supply and as there are no heat transfer means within the runner space, the solids ^' stream can be controlled easily and effectively. Any counter-flows can be avoided along the runner space.

This design does not exclude means to break up (loosen up) the solids ^' stream on its way along/through the runner. These means can be: mechanical mixing means, vibration or pulsation means arranged at runner walls or within the runner space, spiral conveyors within the runner space or air nozzles, blowing air bubbles into the solids ^' s stream, whithout influencing the main flow direction of the solids through the runner.

The heat transfer zone and the runner can be arranged side by side and with a common wall to achieve a compact design.

A type of a transition region is arranged beneath the lower end of feeding channel (runner), which extends into the adjacent heat exchange zone of the heat exchanger. Along this transition region the material flow makes a substantially 90 degrees turn (from a

substantially vertical and downwardly oriented movement into a substantially horizontal flow), before the solids get under the influence of the fluidized bed of the heat exchange zone, which pushes the solids ^' stream upwardly, while at the same time fluidizing the solids. It is important that the heat exchange zone again is designed in such a way to avoid any substantial counter flow between air and solids.

To allow a smooth movement of the solids from the runner into the heat exchange zone a baffle, in particular a curved baffle, may be provided and installed within the transition region. in its most general embodiment the invention provides a fluidized bed heat exchanger, which comprises at least one iniet opening , a heat exchange zone and at least one outlet opening , arranged to each other in a way to allow a stream of solids, deriving from an associated combustor, to enter the heat exchanger via said opening, to pass through said heat exchange zone and to leave the heat exchanger via said outlet opening, wherein the inlet opening is arranged at an upper part of a runner (20), the runner extends downwardly from an upper section of the heat exchanger towards a bottom-section of the heat exchanger and ends close to said bottom-section, thereby allowing a downwardly oriented flow of the solids through said runner, the runner is open at its end close to said bottom-section, thereby providing at least one passage for the solids to leave the runner and to flow into at least one heat exchange zone, which is arranged adjacent to said runner and provided with a fluidized bottom, the outlet opening is arranged at an upper part of the heat exchanger and extends from the at least one heat exchange zone. Although the outer shape of the heat exchanger is not crucial, a box-shaped (cubic) apparatus with 4 vertical outer walls, a horizontal (lower) bottom and a horizontal (upper) ceiling is a favourable design and is the starting point for the following disclosure, but not limiting the scope of the invention.

Accordingly the inlet opening can be arranged in the ceiling, while the outlet opening is typically arranged in a vertical wall of the heat exchange zone. The outlet opening may be a part of an outlet channel, which outlet channel extends from said heat exchange zone through said runner to a corresponding aperture in the outer vertical wall of the heat exchanger. This gives the solids ^' stream a loop-shape, as will be further explained with reference to the attached drawing.

In an embodiment characterized by an inlet opening at the very top end of the heat exchanger the outlet channel and the outlet opening are arranged at a lower elevation than the inlet opening, which again optimizes the overall flow behaviour of the solids within the heat exchanger.

A very compact design provides for a heat exchanger, wherein an outer vertical wall of the heat exchanger constitutes an outer wall of the runner, i.e. the runner extends substantially parallel to one of the outer vertical walls while the opposite wall extends between opposite wall sections of the heat exchanger. This design allows to build a runner with a horizontal cross section being characterized by a length being larger than its width, for example 2:1 to 8:1.

In a similar embodiment , three outer vertical walls of the heat exchanger constitute three outer walls of the runner and a fourth wall of the runner is provided by a partition wall, which extends between two opposing outer vertical walls of the heat exchanger.

The heat exchange zone comprises a number of heat exchange means, preferably designed as tubes and arranged at a distance to each other to provide chamber like compartments between adjacent heat exchange tubes. The tubes as such as well as their orientation within the heat exchange chamber belong to prior art. For example, one or more of said heat exchange tubes can be arranged in a wall-like pattern and/or mounted in an outer wall of the heat exchanger.

The new construction of the heat exchanger allows further improvements with respect to the heat exchange means. One favourable arrangement is achievable, if one or more of said heat exchange tubes are mounted in a discrete and detachable section of an outer wall of the heat exchanger. This allows to dismantle part of the outer wall of the heat exchanger and thus to pull the heat transfer means out of the heat exchange zone, for replacement purposes, for maintenance purposes etc.

At the same time, the fitting of the heat exchange means becomes much easier. Another advantage, which results from the described detachable arrangement of the heat transfer means, is the opportunity to select that part of the outer vertical wall of the heat exchanger for fitting the heat transfer means, which provides the largest space adjacent to said wall. In numerous plants that will be the wall which is arranged parallel to but at a distance to the combustor wall. This is true in particular in arrangements where the heat exchanger has a common wall with the combustor. Heat transfer tubes, arranged in a wall- like pattern and at a distance to each other, then extend substantially perpendicular to the combustor wall.

A similar arrangement is achievable if one or more of said heat exchange tubes are mounted in a discrete and detachable section of a vertical outer wall of the heat exchanger, in particular the vertical outer wall, which extends opposite to the outer wall, which is part of the runner.

The heat transfer means, even if arranged in a so-called "wall like pattern" (which may be realized, for example, be a meandering profiling of a tube) do allow a substantial amount of the solids to pass through these "heat exchange walls", for example through spaces provided between adjacent tube sections. It is also possible to arrange the outlet opening of the heat exchanger in a wall section, which. extends parallel to these wall like heat exchangers.

As already mentioned above the heat exchanger may comprise a baffle downstream of the runner, to redirect the stream of solids from a predominantly vertical and downwardly oriented direction within the runner into a predominantly horizontal direction when entering the heat exchange zone. The baffle can be a discrete construction part of formed in- situ by a corresponding shape of the outer wall of the heat exchanger.

The described heat exchanger is typically used as part of an incineration apparatus, comprising a fossil, fuel fired combustor with at least one outlet port at its upper end, wherein said outlet port allows a mixture of gas and solids exhausted from said combustor to flow into at least one associated separator for separating said solids from said gas, means to transfer at least part of said separated solids from said separator into at least one of said fluidized bed heat exchangers, wherein the outer wall of the heat exchanger, comprising the outlet opening, can form a common wall with an outer combustor-wal!. This common wall can be the outer wall of the runner.

Further features of the invention are disclosed in the subclaims and the other application documents.

The invention will now be described with reference to the attached drawing, showing in a very schematic away in

Fig 1: a vertical cross section of a 1st embodiment of a heat exchanger Fig 2: a horizontal cross section of the 1st embodiment of a heat exchanger

Fig 1: a vertical cross section of a 2nd embodiment of a heat exchanger

Fig 2: a horizontal cross section of the 2nd embodiment of a heat exchanger

In the Figures identical construction parts or construction parts of same or similar function are displayed by the same numeral.

Fig. 1 shows a circulating fluidized bed heat exchanger 10 for use in a circulating fluidized bed apparatus of the type mentioned above. The heat exchanger is box shaped with six outer walls, a ceiling (upper wall) 12, four vertical outer walls 14 a, b ,c, d and a lower bottom 16.

One of the four vertical side wall 14 a,b,c,d, namely wall 14a, displayed on the left in Fig. 1, is part of an outer wall CW of an associated combustor C.

Close to the combustor wall CW, the ceiling 12 provides an inlet opening 18 for a stream of solids (ash), which derives from an associated separator (not displayed, as known in prior art). The flow direction at inlet opening 18 is symbolized by arrow I. The inlet opening 18 is followed by a so-called runner 20, which is a channel along which the solids flow

downwardly until the end of the runner at a distance to the bottom 16 of the heat exchanger. Typically the solids stream has free-flow properties on its way through runner 20.

This open lower end of runner 20 is provided by a shortened inner wall 22, which extends parallel. to wall 14a, while side walls of runner 20 are provided by corresponding sections of the two vertical walls 14b, 14d, being the sections adjacent to waif 14a.

This channel (runner 20) is free of any heat transfer means, although its outer walls 14a, 14v, 22, 14d can be designed as heat transfer walls.

It is further important that no air is blown into the stream of solids passing said runner 20 and insofar this embodiment is characterized by a non-fluidized bottom section 16r at its part beneath runner 20. Nevertheless, if appropriate, means like vibrators to break up the solids stream (to avoid any clogging effects) may be arranged along or within the runner section.

A space between runner 20 and bottom section 16r is called transition area TR as the solids are redirected in that zone from a substantially vertical downward-movement (along runner 20) into a substantially horizontal flow, when passing the gap between the lower end 22e of inner wall 22 and bottom 16, wherein the solids flow is symbolized by arrow U.

That part of bottom 16, which extends after said gap (transfer passage) is designed as a conventional fluidized bottom and referenced 16c. As a fluidized bottom is state of the art it will not be explained here in more detail. It is the main object of such bottom to allow air or gases to pass through said bottom and to enter the space above said bottom 16c, being the heat transfer zone 40 of the heat exchanger 10. Typically air is blown in via corresponding nozzles, symbolized in the Figures by arrow A.

As can best be seen in Fig. 2 a number of wall-like heat transfer tubes 42a-e are arranged within said heat transfer zone 40, being tubes, through which water or steam as a heat transfer fluid flows. Each "heat transfer wall" is characterized by a meandering run of the corresponding tube(s), symbolized in Fig. 1 by six loops 42t for one heat transfer tube 42a, with a distance between adjacent tubes sections to allow the solids to pass through said "wall". Each tubes 42a-e is mounted in wall 14c and fluid ly connected to a central feeding line 43 at its end, protruding wall 14c of the heat exchanger 10.

The tubes 42a-e are arranged at a distance to each other so that chamber like compartments 45 are arranged between adjacent tubes 42a, b; 42b,c; 42c,d; 42d,e.

Each of said tubes (walls) 42a-e is mounted in the outer vertical wall 14c of the heat exchanger 10 in a way to allow individual replacements at any time. For this purpose the corresponding mounting section for each of said heat transfer tubes 42a-e is a detachable part of said wall 14c and displayed by numeral 44. This allows to fit or extract the tubes 42a- e individually or in groups at any time. The preferred mounting and extracting path is symbolized by arrow M in Fig. 2.

This is the same direction along which the solids leave the heat transfer zone 40 in this embodiment, namely by an outlet channel 46, which extends from an outlet opening 48 in said inner wall 22 through said runner 20 to a hole (aperture) 47 within said outer wall 14a. In this embodiment, the channel 46 extends in a slightly inclined fashion downwards between outlet opening 48 and hole 47 and two distinct outlet channels 46 are arranged at a distance to each other and accordingly two outlet openings 48 and two holes 47 are provided.

The solids, leaving the heat exchanger zone 40 via this outlet opening 48 (arrow O), are recycled into the combustor C.

The new heat exchanger urges the solids to make a kind of a loop, symbolized in Fig. 1 by arrow L

It is within the scope of the invention to extract other parts of the solids separately, for example by one or more further outlet openings in any of the outer walls 14b, c,d.

The embodiment of Fig. 3,4 is similar to that of Fig. 1,2. Insofar only the differences will be explained hereinafter: instead of two outlet openings 48, each with a circular cross section, the heat exchanger of Fig. 3,4 has only one, slot-!ike outlet opening 48, which is arranged in an upper part of one of the wall 14b, i.e. an outer wall of the heat exchanger, while the outlet opening 48 in Fig. 1,2 is .arranged in the partition wall 22, being also the outer wall of the heat exchange zone 40.

This wall 12b is a common wall with the combustor wall CW. in other words: Compared with the embodiment of Fig.1,2 the heat exchanger 10 of Fig. 3,4 is turned by 90° into the displayed position.

A further distinctive feature is the arrangement of a curved baffle 20b at the lower end of an inner face of wall 14a to allow a smooth transition of the solids ^' stream from vertical to horizontal, displayed by arrow U.