FLUE GAS PURIFICATION DEVICE WITH RETAINER FOR COLLECTING LOOSE

PARTS

The invention relates to a flue gas purification device, comprising

- a heat exchanger, featuring

- a first section, comprising a first inlet port for a raw gas and a first outlet port for said raw gas, a second section, comprising a second inlet port for a clean gas and a second outlet port for said clean gas, and means for a heat exchange between said first section and said second section of the heat exchanger,

- a raw gas duct, extending from said first outlet port vertically

downwardly to a raw gas entrance at a lower end of a gas scrubber, wherein said raw gas duct defines a raw gas flow direction,

- said gas scrubber comprises a main part, which extends vertically upwardly from said raw gas entrance and provides an upper end with a clean gas exit, followed by the second inlet port of the heat exchanger, as well as inlet means between the raw gas entrance at its lower end and the clean gas exit at its upper end to apply an absorbent into the gas on its way from the raw gas entrance through the gas scrubber to the clean gas exit.

The general construction of such a scrubber and associated components may be derived from EP 2644252 B1. The general design of a corresponding heat exchanger is disclosed in EP 2258462 Bl .

Although corresponding flue gas purification devices have been used successfully in terms of cleaning the flue gas and in particular to extract sulphur oxides from the flue gas, the following problem could not yet been solved satisfactorily:

The flue gas, passing the first section of the heat exchanger, typically enters the heat exchanger with a temperature of more than 100°C, for example 120° C to 150° C, while leaving the first section at a

temperature of 40° C to 60° C less. Besides the high temperature the flue gas, deriving e. g. from a power plant, a furnace or a steam generator, is usually composed of carbon dioxide, nitrogen, carbon monoxide, sulphur oxides as well as particulate (solid) matter. The aggressive flue gas is responsible for a high degree of corrosion within the heat exchanger. The corrosive environment may even cause a "disintegration" of the mechanical parts of the heat exchanger and as a consequence, parts of the heat exchanger may loosen and fall down into the raw gas duct, which follows the heat exchanger and which serves to further transport the gas into the subsequent scrubber.

Such disintegration of mechanical parts (like plates, hinges, bolts, screws etc., often in a size of up to 50cm in one direction of the coordinate system) may damage the inner surface of the raw gas duct if they hit this inner surface of the raw gas duct.

This is true as well if the inner surface of the raw gas duct provides a protective sheeting against the chemically aggressive gas. The protective cover is often made of polytetrafluoethylene (PTFE). The necessary repair work causes standstill periods of the whole device and extensive costs. To better protect the inner surface of the raw gas duct against such mechanical attack (impact) it is known to fit additional baffle plates on the inner surface of the raw gas duct. As loose parts may hit the wall of the raw gas duct at any area it is necessary to protect the inner surface of the raw gas duct more or less completely.

This increases the costs dramatically in view of the size of such a raw gas duct (for example: height: 10 - 30 m, diameter: 4 - 12 m, flue gas: 2.000 - 4.000 m ³ /h).

It is an object of the invention to provide means to reduce or avoid mechanical impact onto the inner surfaces of the flue gas duct (raw gas duct) within a flue gas purification device as described.

The invention is based on the following considerations.

Because of the chemically aggressive behaviour of the flue gases to be purified, corrosion of the mechanical parts of the heat exchanger cannot be avoided. Insofar it cannot be avoided either that corroded parts may fall downwardly into the subsequent raw gas duct.

However, such loose (not fixed) parts may be "collected" before hitting the wall (inner surface) of the raw gas duct and/or before hitting further areas of the raw gas duct and/or before entering subsequent sections of the raw gas duct and/or before entering the scrubber if the worst comes to the worst.

"Collection" means to prevent the particulate matter (for example plates, flanges, hinges, etc. deriving from the heat exchanger) from further falling down along the flue gas path defined by the raw gas duct

(channel) between the heat exchanger and the scrubber. Insofar, the invention is based on the idea to provide some kind of a barrier (retainer, retaining means, shield, net) for said loosened

particulate material within the raw gas duct.

In its most general embodiment the invention relates to a flue gas purification device, comprising the features mentioned on page 1 and further:

- at least one retainer, arranged within the raw gas duct at or beneath the first outlet port of the heat exchanger and at a distance to the raw gas entrance of the gas scrubber, which retainer extends at least partially transverse to said raw gas flow direction and has a plurality of openings, each of a size, allowing the raw gas to flow through the retainer and preventing solid particles of a size larger than one opening, to pass said retainer.

The bespoke arrangement of the retainer(s) depends on the device. In any case an arrangement as close as possible to the first outlet port of the heat exchanger is favourable to collect any undesired external parts and to avoid that such parts hit (bump) further surface areas on their way through the raw gas duct.

This double task (collecting solid particles, gas permeability) leads to embodiments of the retainer, wherein the retainer features at least one pattern of the group comprising: knitted fabrics, woven fabrics, punched foils, cut foils, bands arranged at a distance to each other, trays, grids and grates. While the physical sections of the retainer are responsible for stopping (and collecting) the loosened solid parts, the openings (gaps, slots, holes) between the physical parts of the retainer allow the raw gas to continue its flow along the raw gas duct. It becomes apparent from this that the size of the physical parts and the holes respectively (in other words: the "mesh size") is decisive to separate solid parts.

A suitable material for the retainer may be selected of a material of the group comprising: polyarylene; polymethylpentene; inorganic materials based on SiO ₂ , AI ₂ O ₃ , CaO, MgO, ZrO ₂ , TiO ₂ or mixtures thereof; glass; acid resistant metals; carbon; polytetrafluorethylene (PTFE) or mixtures thereof.

The retainer may extend over the whole cross section of the raw gas channel or just part of it, depending on the design and orientation of the raw gas duct and a corresponding heat exchanger, which may be further dependent on the design and orientation of the associated gas scrubber.

According to one embodiment the gas scrubber features a horizontal cross section, which diminishes in a section above the inlet means for the absorbent and towards the second inlet port for the clean gas. This section of the gas scrubber of reduced cross section may feature the shape of an inverted funnel (i.e. with inclined outer walls), wherein its upper end, which is connected to the second inlet port of the heat exchanger, may have a constant cross-section again.

In such a case, as the lower part of the gas scrubber is "bigger" (wider) than the upper part with inclined walls, the raw gas duct often follows this design. In other words: According to one embodiment the raw gas duct extends substantially parallel to an adjacent outer profile of the gas scrubber, including a section, inclined to the vertical and horizontal.

In the embodiment of the gas scrubber with inclined upper walls the inclination angle may be in the range of 20° to 70° to the vertical, often between 35° and 55° to the vertical. The raw gas duct, arranged parallel to the scrubber, then features a corresponding inclined section at its upper part.

A corresponding layout is represented in Figure 1 of the attached drawing.

It derives from this design that at any solid particles, falling out of the heat exchanger, will hit the inclined inner surface of the wall of the raw gas duct, namely the wall of the raw gas duct which is adjacent to the scrubber.

In order to collect this solid material, the retainer may protrude from the corresponding inner wall section of the raw gas duct.

The arrangement of the retainer at the wall of the raw gas duct may easily be achieved by the skilled person. For example the retainer may be screwed, bolted or welded to said wall.

Especially in embodiments defined by a retainer which extends

completely across the raw gas duct, hooks may also serve to fix the retainer to the wall.

In order to remove the solid particles as collected by the retainer (shield) a corresponding inspection chamber (window, door) may be provided adjacent to the retainer in the wall of a raw gas duct.

To increase the lifetime (service time) of the retainer it can be

advantageous to sheet the retainer with a suitable material like

polytetrafluoethylene (PTFE).

It may also increase the lifetime of the whole device to cover at least part of the wall of the raw gas duct, in particular sections above of the retainer, with protection plates as known from prior art. These plates may be mounted onto the inner surface of the corresponding wall- section, as mentioned above.

Contrary the prior art devices such additional protection plates may be limited to an area above said retainer, as the retainer avoids further falling down of the solid particles and avoids further impacts caused by these solid particles at surface sections in the lower part of the raw gas duct. These plates can be metal plates sheeted with a foil of PTFE or other suitable material.

If these protection plates are installed it becomes possible to integrate a retainer into such protection plate. For example the retainer may be fixed to and protrude from a protection plate.

The retainer itself may be rigid or flexible (deformable), as well under load. Insofar one embodiment of the retainer is characterized by a netlike structure (crossing fibres or bands) within a corresponding outer frame which frame is attached to the wall of the raw gas duct. The fibres/filaments/bands of such net (or tray-like construction) can be made of polytetrafluoethylene or other materials withstanding

temperatures of up to 150°C and chemical attack by flue gases.

In another example carbon fibres as such or covered with

polytetrafluoethylene are used as a material to construct a retainer for the flue gas purification device.

Further constructions and materials are quoted hereinafter:

- ECTFE (ethylenechlorotrifluorethylene)

- PFA (perfluoralkoxy-polymers)

- PTFE-M (modified polytetrafluorethylene). The retainer may be fixed to the wall of the gas duct by welding, clamping, glueing etc. It may be designed as a net between two outer bands. It may be mounted fixedly or detachably at the raw gas duct.

Although the heat exchanger may be of any type and design one embodiment provides to arrange the first section and the second section of the heat exchanger along a common horizontal level to allow closer arrangement of the gas scrubber and the raw gas duct as well as associated components. The heat exchanger can be a rotating heat exchanger. While the hot flue gases increase the temperature of corresponding heat exchange elements (like heat exchange tubes) of the rotating parts of the heat exchanger on their way through the first section of the heat exchanger, the heat exchange elements release the heat to the low temperature clean gas within the second section of the heat exchanger after their rotational movement into the corresponding position.

Further features of the invention will derive from the features of the subclaims and the other application documents, including the following description of various embodiments, including features which may not only be realized within said specific embodiment but also in other combinations if technically possible and not explicitly excluded.

In the drawings the following is schematically shown:

Figure 1 : A vertical cross section of a flue gas purification device

according to the invention,

Figure 2: An enlarged perspective view onto that part of the raw gas duct encircled in Figure 1 , Figure 3: A front view onto a retainer used according to Figure 1 into embodiments,

Figure 4: Optional arrangement of a retainer within the raw gas duct of Figure 1.

In the Figures identical components or components of equivalent function are represented by the same numerals.

Figure 1 represents a flue gas purification device, comprising a heat exchanger 10, featuring a first section 12, comprising a first inlet port 12i for a raw gas RG and a first outlet port 12o for said raw gas RG; further featuring a second section 14, comprising a second inlet port 14i for a clean gas CG and a second outlet port 14o for said clean gas CG as well as means (not displayed) for a heat exchange between said first section 12 and said second section 14 of the heat exchanger 10. The heat exchanger may be a rotary one, including heat exchange elements turning around a central rotation axis.

A raw gas duct 20 extends from said first outlet port 12o vertically downwardly to a raw gas entrance 32 at a lower part 301 of a gas scrubber 30, wherein said raw gas duct 20 defines a raw gas flow direction RGD.

Said gas scrubber 30 comprises a cylindrical main part 34, which extends vertically upwardly from said raw gas entrance 32 and provides an upper part 30u with a clean gas exit 38, connected to the second inlet port 14i of the heat exchanger 10.

Inlet means 40 between the raw gas entrance 32 at the lower part 301 and the clean gas exit 38 at its upper part 30u serve to apply an absorbent into the gas on its way from the raw gas entrance 32 through the gas scrubber 30 to the clean gas exit 38. In the embodiment displayed the absorbent is seawater, which is brought into contact with the raw gas in a space between the raw gas entrance 32 and spray nozzles 42, connected to said inlet means 40.

While the flue gas, after contact with the seawater based absorbent, moves upwardly within the scrubber 30 and leaves the scrubber 30 as clean gas CG via the second section 14 of the heat exchanger 10, the used absorbent drops downwardly within the scrubber tower 30 into a sump S at the bottom of the scrubber 30 and from there into subsequent installations (arrow A).

It may be seen from Figure 1 that the clean gas exit 38 at the upper part 30u of the scrubber has the shape of an inverted funnel and thus inclined outer walls. The angle of inclination in this embodiment is about 45° to the horizontal.

The upper part 22 of the raw gas duct 20, subsequent to the first outlet port 12o, is as well inclined by approximately 45°, i.e. part 22 of duct 20 and clean gas exit 38 of scrubber 30 extend parallel to each.

Section 22 of raw gas duct 20 is followed by a vertically downwardly oriented section 24 and substantially horizontally oriented end section 26, followed by the raw gas entrance 32.

The inclined section 22 of raw gas duct 20 extends parallel to the adjacent funnel shaped clean gas exit 38 of the scrubber 30 and section 22 extends offset to section 24.

While the raw gas duct 20 is made of metal its inner surface is sheeted with polytetrafluorethylene 28 to protect the corrosive metal wall against chemical attack by the aggressive flue gasses passing the raw gas duct 20. Further: protection plates 28p are mounted on a (limited) section of the inner wall 22w of the flue gas duct 20 which extends upwardly from a retainer 50 to further protect the hitting area.

The retainer 50 extends at a right angle to the lower wall 22w of section 22 into the raw gas duct 20. The retainer 50 comprises a metal frame 52, covered with polytetrafluorethylene, and a net-like structure (left part of Figure 3) with crossing filaments 54, 56, which are fixed to said frame 52 at their respective ends.

The filaments 54, 56 are made of carbon fibres and covered by

polytetrafluorethylene.

The frame 52 itself is clamped (not shown) to said wall 22w.

The net-like structure of the retainer 50 is selected to allow solid particles, falling-down from the heat exchanger 10 into the raw gas duct 20 to be collected by said retainer 50 while at the same time the retainer 50 allows the raw gas to pass through openings 58 defined within said net, i.e. between the filaments 54, 56.

In Figure 3 (right part) an alternative to design the retainer 50 is shown. In this embodiment the retainer is designed as a shield is made of a polyaryIen-/polymethylpentene compound foil, into which openings 58 were punched to allow the gases to pass through.

The dimensions displayed do not correspond reality. In particular the openings 58 are smaller, i.e. the mesh size is smaller to allow smaller particles to be collected by said retainer 50.

Figure 4 displays three alternatives to arrange a retainer 50 within the raw gas duct 20. Alternative I is characterized by a grid-like retainer 50, which extends all over the gas duct 20 and penetrates the duct walls, wherein the free ends 50e of said retainer 50 are bent and fixedly secured to the external part of the wall of the raw gas duct 20. The embodiment I is realized with a substantially rigid retainer 50.

The embodiment according to II displays a flexible retainer 50 made of a knitted fabric of inorganic glass fibres and fixed to the inner surface of the wall of raw gas duct 20 by corresponding hooks 50h.

The embodiment of III is similar to that of Figure 2 with the proviso that an outer frame 52 of the retainer is fixed to a flange-like part 50f which is screwed onto said wall of the raw gas duct 20.

Shortly above said retainer 50 (alternative III) a service window 60 allows to remove any solid particles collected by said retainer 50 and schematically displayed in Figure 2 by numeral 70.

A similar window installation is also displayed with respect to

embodiment I in Figure 4 in its open state (in dotted lines).