WO1998017946A1

WO1998017946A1 - Solid fuel fired boiler plant and furnace unit and flue gas unit for use in such a boiler plant

Info

Publication number: WO1998017946A1
Application number: PCT/DK1997/000456
Authority: WO
Inventors: Hans Erik Askou
Original assignee: Aalborg Energie Technik A/S
Priority date: 1996-10-18
Filing date: 1997-10-17
Publication date: 1998-04-30
Also published as: ATE216475T1; BR9712331A; PL332731A1; EP1015813A1; DK1015813T3; DE69712112T2; CZ9901365A3; EP1015813B1; ES2178007T3; DE69712112D1; AU4551497A; CZ297187B6; PL186730B1

Abstract

The invention relates to a solid fuel boiler plant comprising a combustion section (5) and a flue gas section (6). The invention further relates to a furnace unit and a flue gas unit. The combustion section (5) and the flue gas section (6) have a first lateral wall (1, 11), a second lateral wall (2, 12), a third lateral wall (3, 13) and a fourth lateral wall (4, 14). The lateral walls (1, 2, 3, 4, 11, 12, 13, 14) are formed by pipings (2) with a heat transmission medium, preferably water/steam, inside the pipes (22). The second lateral walls (2, 12) of the combustion section (5) and the flue gas section (6), respectively, coincide. The second lateral wall (2, 12) extends in parallel with a substantial flow direction of the flue gas through the combustion section (5) and the flue gas section (6), respectively, and forms a shelter wall between the combustion section (5) and the flue gas section (6). In a preferred embodiment the combustion section (5) is provided with a lining (8).

Description

SOLID FUEL FIRED BOILER PLANT AND FURNACE UNIT AND FLUE GAS UNIT FOR USE IN SUCH A BOILER PLANT

Background of the invention

The present invention relates to a solid fuel boiler plant burning solid fuel such as wood, straw, coal and sludge, said plant comprising a boiler, which comprises a combustion section extending from a lower part of the boiler upward to an upper part of the boiler, said combustion section being provided with pipings, which form lateral walls including a first lateral wall and a second lateral wall of the combustion section, said boiler also comprising a flue gas section extending in parallel with the combustion section from the upper part of the boiler downward to the lower part of the boiler and being provided with pipings, which form lateral walls, including a second lateral wall of the flue gas section, said boiler comprising a primary fuel inlet device, which is arranged at a lower part of the combustion section, and wherein an opening from the primary fuel inlet device to the combustion section is placed in a first lateral wall, alternatively a bottom, of the combustion section.

The invention further relates to a furnace unit and a flue gas unit for use in a boiler of the above-mentioned type.

In connection with boilers for burning solid fuel it is known to use a boiler unit comprising a combustion section and a flue gas section. The combustion section may also be designated the first section. The flue gas section usually comprises two sections, an empty section designated the second section and an superheater section designated the third section, respectively. The combustion section is formed as a room, which extends from a lower end to an upper end, and the flue gas section is formed as a room, which extends from an upper end to a lower end, and the flue gas section is defined by lateral walls, which are formed by pipings constituting tubular radiators or plate radiators. Positioned at the bottom of the combustion section is a grate, on which the solid fuel is burnt. The grate is further able to retain and discharge ashes from the lower part of the combustion section. The combustion section is provided with an inlet for solid fuel. The inlet is positioned in a first lateral wall of the combustion section. At the top of the combustion section of known plants there is an outlet designed to conduct the flue gas from the combustion section to the flue gas section. The outlet is positioned in a third lateral wall of the combustion section, said third lateral wall being opposite the first lateral wall.

Positioned at the top of the flue gas section there is an inlet designed to conduct flue gas from the combustion section outlet to the flue gas section. The inlet in the flue gas section of known plants is positioned in a first lateral wall of the flue gas section. The flue gas section is divided into a second section and a third section separated by a partition wall, which is formed by pipings. Formed at the bottom of the flue gas sec- tion there is a passage from the second section to the third section. Located inside the third section of the flue gas section there is a heat exchanger in the form of a superheater. The flue gas is conducted from the inlet at the top of the flue gas section down through the second section of the flue gas section through the passage, up through the third section past the superheater and to an outlet in an upper end of the flue gas sec- tion.

EP 0 566 099 describes a boiler for burning fuel in a fluidised bed in a plant of the type discussed above. The flue gases are let out of the furnace from an upper part of the furnace through a lateral wall of the furnace. The lateral wall of the furnace coin- cides with a lateral wall of the flue gas section. The coinciding lateral walls have been chosen in such a manner that the flue gas is let through the combustion section, through the outlet of the combustion section, through the inlet of the flue gas section, through the flue gas section and out through the outlet of the flue gas section in such a manner that the flue gas extends in one and the same plane throughout the boiler.

Thus, known boilers have their combustion section and flue gas section arranged next to one another so that the inlet of the combustion section is positioned in a first lateral wall of the combustion section and the outlet of the combustion section is positioned in a third opposite lateral wall of the combustion section, and in such a manner that the inlet of the flue gas section is placed in a first lateral wall of the flue gas section, which coincides with the third lateral wall of the combustion section. Initially, this results in an uncomplicated flow of flue gas through the boiler. However, it leads to several drawbacks.

Firstly, the boiler will be very elongated when the combustion section and the flue gas section are positioned next to one another. This means that during transport of the boiler from the place of manufacture to the plant site it is always necessary to transport the furnace unit and the flue gas unit separately due to big dimensions of the entire boiler consisting of both the furnace unit and the flue gas unit next to one another.

In large plants a boiler volume is sufficiently large compared to a surface area of the boiler to maintain a required burning temperature since a distance from the inside of the combustion section to the lateral walls of the combustion section is larger. In smaller plants a volume of the boiler is smaller compared to a surface area of the boiler. This means that it may be difficult or energy-consuming to maintain a sufficient burning temperature in small plants since a distance from the inside of the com- bustion section to the lateral walls of the combustion section is smaller. This applies particularly to small plants with elongated furnaces.

Thirdly, the large ratio of surface area to volume also means that especially in smaller plants it is difficult to control the temperature in the combustion section, which is of great importance by the decomposition of different noxious flue gases.

Fourthly, it is difficult to utilise secondary fuel inlet devices as both the first and the third lateral walls of the combustion section are occupied by the primary fuel inlet device and of the coincidence between the third lateral wall of the combustion section and the first lateral wall of the flue gas section, respectively. Secondary fuel inlet devices may only be used on the second lateral wall and the fourth lateral wall of the combustion section, and the flue gas section, respectively. This means that secondary fuel inlet devices perform firing crosswise of the combustion section. Especially, in elongated combustion sections, the flame length or the throw length of the secondary fuel inlet devices is limited by the lesser distance from the second lateral wall to the fourth lateral wall. Secondary fuel inlet devices also perform firing perpendicularly to a plane of symmetry of a direction of flow of a flue gas and thereby disturb the flow of the flue gas through the boiler. A plane of symmetry for the flow direction of the flue gas extends in parallel with the direction of firing of the primary fuel inlet device.

Thus, it is the object of the present invention to provide a boiler that does not have the above-mentioned drawbacks, and which thus has a design that to an appreciably higher degree makes allowance for a better combustion and control of the temperature at the same time as the costs of construction are reduced.

This object is achieved with a boiler characterised in that the second lateral wall of the combustion section is adjacent to the first lateral wall of the combustion section, the primary fuel inlet device being arranged in said first lateral wall, that an outlet from the combustion section is positioned in the second lateral wall of the combustion section, and that the second lateral wall of the flue gas section coincides with the second lateral wall of the combustion section, and that an inlet into the flue gas section from the combustion section is positioned in the second lateral wall of the flue gas section.

A boiler with these features opens the possibility for a quite new and appreciably different boiler structure that does not have the previously mentioned drawbacks, but instead implies several advantages. However, a boiler according to the invention im- plies another and less uniform flow of flue gas through the combustion section and the flue gas section, but this is compensated by the advantages which the boiler has. The flow of the flue gas through the combustion section and through the flue gas section takes place in two different planes in parallel and different from earlier known boilers where the flow of the flue gas takes place in one and the same plane.

A furnace unit for use in a boiler of the above-mentioned type is characterised in that the furnace unit comprises lateral walls, that the lateral walls are formed by pipings, that a first lateral wall has an inlet to a combustion section, that a second lateral wall is adjacent to the first lateral wall, and that the second lateral wall has an outlet from the combustion section.

In known boilers there is provided a fuel inlet device in a first lateral wall of the combustion section, alternatively, at the bottom of the combustion section, and the outlet of the combustion section is provided in a third lateral wall of the combustion section. In known boilers the third lateral wall is provided opposite and not as in the present invention adjacent to the first lateral wall.

An embodiment of a furnace unit according to the invention is peculiar in that the combustion section is provided with a lining, that the lining extends from a position over the lower part of the combustion section in a direction towards the upper part of the combustion section, preferably from a position over the lower part of the combus- tion section corresponding to a fourth of the vertical extension of the combustion section to a position corresponding to three quarters of the vertical extension of the combustion section, preferably from a position over the lower part of the combustion section corresponding to half of the vertical extension of the combustion section to a position corresponding to three quarters of the vertical extension of the combustion sec- tion.

A flue gas section for use in a boiler of the kind mentioned above is peculiar in that the flue gas unit comprises lateral walls, that the lateral walls are formed by pipings, that a second lateral wall has an inlet to a flue gas compartment, and that the second lateral wall is intended to be coincident with a second lateral wall in a furnace unit.

In known boilers the inlet for the flue gas section is provided in what corresponds to a first lateral wall of the flue gas section. The first lateral wall of the flue gas section is coincident with the third lateral wall of the combustion section in known boilers, and it is not as in the present invention coincident with the second lateral wall of the combustion section. A boiler according to the invention has a structure implying that especially smaller boiler plants achieve a greater efficiency and become easier to transport from the place of production to the construction site. The efficiency is increased by the surface area being relatively small compared to the volume. This means, that the possibility of maintaining a sufficient temperature in the combustion section and the possibility of controlling the temperature in the combustion section are increased. The transport of the plant from the place of production to the construction site is eased by it being possible for smaller plants to transport the whole boiler in assembled condition and comprising both the furnace unit and the flue gas unit. This means that it is possible to perform almost all machining operations at the place of production while at the same time the transport only comprises one single shipment.

The efficiency may be further increased by providing a lining according to the invention in the combustion section. The lining according to the invention implies that for small boilers it becomes possible to remove both NO_x-compositions and noxious un- burnt gases, e.g. CO-compositions, before the flue gas is conducted to the flue gas section. In that connection it is important that the lining does not extend down to the lower part of the combustion section in order not to risk to high combustion temperature by the burning of e.g. dry wood refuse. It is also important that the lining does not extend in the full height of the combustion section in order not to risk a too high temperature in the uppermost part of the combustion section with the consequence of lacking decomposition of NO_x-compositions. If the boiler according to the invention is provided with a lining it is possible to improve the temperature for fire up through the combustion section, so that a sufficiently low combustion temperature is achieved in order to reduce corrosion and creation of clinker at the same time as a sufficiently high combustion temperature is achieved in order to ensure burning off of noxious gases like CO.

Description of the drawing

The invention will be described in more detail below with reference to the accompanying drawing, in which Fig. 1 is a section through an embodiment of a boiler plant according to the invention viewed perpendicularly to a first lateral wall and in parallel with a second lateral wall,

Fig. 2 is a section through a furnace unit for a boiler plant according to the inven- tion as seen parallel with the first lateral wall,

Fig. 3 is a section through a flue gas unit for a boiler plant according to the invention as seen in parallel with the first lateral wall,

Fig. 4 is a section through the embodiment of a boiler plant according to the invention as seen from above in a first plane in parallel with the first lateral wall and the second lateral wall, and

Fig. 5 is a section through the embodiment of a boiler plant according to the invention as seen from above in another plane in parallel with the first lateral wall and the second lateral wall.

Fig. 1 illustrates a boiler plant according to the invention. The boiler plant comprises a combustion section 5 and a flue gas section 6. The illustration is seen from the front and perpendicularly to a first lateral wall 1 (see Fig. 2 and Fig. 3) and a third lateral wall 3 (see Fig. 2 and Fig. 3) of the combustion section 5 and the flue gas section 6, respectively, and in parallel with a second lateral wall 2 and a fourth lateral wall 4 of the combustion section 5 and the flue gas section 6. The combustion section 5 comprises a grate 7 in a lowermost part of the combustion section 5 and a lining 8 along the lateral walls 1,2,3,4 of the combustion section 5. The flue gas section 6 comprises a first superheater 9 and a second superheater 10. The second lateral wall 2 of the combustion section 5 and the second lateral wall 12 of the flue gas section 6 are coin- cident and form a screen wall between the combustion section 5 and the flue gas section 6. A passageway 15 (see Fig. 5) between an upper part of the combustion section 5 and an upper part of the flue gas section 6 forms an outlet for flue gases from the combustion section 5 and inlet for flue gas to the flue gas section 6.

The course of the flow of the flue gas is illustrated by arrows. The flue gas flows from the lower part of the flue gas section 5 upwards through the interior 16 of the combustion section 5 past the lining 8 and out through the passageway 15 (see Fig. 5) in the second lateral wall 2. The flue gas then flows into the flue gas section 6 and downwards through a first zone 17 (see Fig. 3). In the illustration of Fig. 1 the second section 17 is positioned before the first superheater 9 and the second superheater 10 in a plane above the plane of the paper. The flue gas is further conducted from a lower part of the second section 17 to the lower parts of a second zone 18 (see Fig. 3) through a passageway 19 (see Fig. 3) under a partitioning wall 20 (see Fig. 3) between the second section 17 and the third section 18 in the flue gas section 6. The flue gas then flows upwards through the third section 18 past the second superheater 10 and the first superheater 9 and through an outlet 21 (see Fig. 3) in the upper part of the flue gas section 6.

The first lateral wall 1,11, the second lateral wall 2, 12, the third lateral wall 3,13, and the fourth lateral wall 4,14 of the combustion section 5, the flue gas section 6, and the partitioning wall 20, respectively, are formed by pipings 22. Between the pipings 22 there are mounted plate elements 23 (se Fig. 4 and Fig. 5) to form a tight side wall.

The pipings 22 are mutually connected at upper ends and at lower ends with further pipings 24, so-callled connectors. The pipings 22 contain a heat transmission means, preferably water/steam. The boiler plant according to the invention is provided with a steam tank 25 in which steam under pressure created by the heating of water in the pipings 22 is collected and conducted further on to the first superheater 9 and the second superheater 10. The superheated steam may be conducted further on from the first superheater 9 and the second superheater 10 to e.g. a steam turbine in an electric power plant or to another kind of energy transformation.

Fig. 2 illustrates a furnace unit according to the invention for use in a boiler plant according to the invention. The furnace unit comprises a combustion section 5. The combustion section 5 has a first lateral wall 1, a second lateral wall 2 (see Fig. 1), a third lateral wall 3, and a fourth lateral wall 4 (see Fig. 1). The lateral walls 1,2,3,4 are formed by the pipings 22 (see Fig. 4 and Fig. 5).

In a lower part of the first lateral wall 1 there is provided an orifice 26 for introducing solid fuel to the combustion section 5. The grate 7 is provided lowermost in the com- bustion section 5. The orifice 26 forms a passageway between a feeding device (not shown) for solid fuel, preferably a Spreader- stoker or a pneumatic feeding device. A Spreader-stoker or pneumatic feeding device may be used in combination with different kinds of grates 7 like moving grate, stair grate, vibrating grate, pushing grate, or another grate. A Spreader-stoker or another pneumatic feeding device is intended to be mounted outside the orifice 26 and to conduct the solid fuel from a silo (not shown) into the combustion section 5 by mechanical or pneumatic feeding into the combustion section 5. Spreader-stoker and pneumatic feeding device may be used separately or in combination. The grate is utilised by conducting solid fuel onto the grate 7 and burning it to ashes on the grate 7, whereafter the ash is conveyed from the grate 7 by its movement down in a removal duct 27 and further on by means of a screw conveyor 28. As alternative to the screw conveyor 28 another removal device may be used. Spreader-stoker, pneumatic feeding device, pushing grate, stair grate, vibrating grate, moving grate, or another kind of grate all constitute known art. Other known art for the feeding of solid fuel, for burning off and for removal of burned fuel may also be utilised. Thus, it will be possible to provide a primary feeding device at the lower part of the combustion section in the form of an external pre-furnace, in which primary combustion and gasification take place.

As indicated, the combustion section 5 is provided with a lining 8 along the first lateral wall 1, the second lateral wall 2, the third lateral wall 3 and the fourth lateral wall 4. The lining 8 extends from a position pi over the lower part of the combustion section 5 to a position p2 under the upper part of the combustion section 5. In the shown embodiment, the lining 8 extends from a position pi over the lower part of the com- bustion section 1 corresponding to about half of the vertical extension h of the combustion section to a position p2 corresponding to about three fourth of the vertical extension h of the combustion section. The lining 8 is made from a ceramic material and is placed between the side walls 1,2,3,4 of the combustion section 5 and the interior 16 of the combustion section 5. The lining 8 covers in this way some of the extension of the side walls 1,2,3,4 of the combustion section 5. Fig. 3 illustrates a flue gas unit according to the invention for use in a boiler plant according to the invention. The flue gas unit comprises a flue gas section 6. The flue gas section 6 has a first lateral wall 11, a second lateral wall 12 (see Fig. 1), a third lateral wall 13, and a fourth lateral wall 14 (see Fig. 1). The lateral walls 11,12,13,14 are formed by the pipings 22 (see Fig. 4 and Fig. 5).

The flue gas section is divided into a second section 17 and a third section 18, which are separated by a partitioning wall 20. The partitioning wall 20 is formed by the pipings 22 and extends from a position p3 uppermost in the flue gas section 6 to a posi- tion p4 over a lower part of the flue gas section 6. A passageway 19 under the partitioning wall 20 is formed between the second section 17 and the third section 18. The second section 17 of the flue gas section 6 is provided in the uppermost part with a passageway 15 (see Fig. 5) extending between the uppermost part of the combustion section 5 through the second lateral wall 2 of the combustion section 5 and the flue gas 6, respectively, to the uppermost part of the flue gas section 6. The third section 18 of the flue gas section is provided with the first superheater 9 and the second superheater 10. An uppermost part of the third section 18 is provided with the outlet 21 for flue gas from the flue gas section 6.

Flue gas from the combustion in the combustion section 5 is intended to be conducted into the flue gas section 6 through the passageway 15 in the uppermost part of the second section 17, further on downwards in the second section 17 through the passageway 19 under the partitioning wall 20 between the second section 17 and the third section 18, further on upwards through the third section 18 and past the second super- heater 10 and the first superheater 9 and out through the outlet 21 in the upper part of the third section 18.

Fig. 4 illustrates a boiler plant seen in a first plane from above and from an uppermost part of the combustion section 5 and the flue gas section 6, respectively. The figure shows the first lateral wall 1,1 1, the second lateral wall 2,12, the third lateral wall

3,13, and the fourth lateral wall 4,14 of the combustion section 5 and the flue gas section 6, respectively. The second lateral wall 2,12 of the combustion section 5 and the flue gas section 6, respectively, are coincident and form a screen wall between the combustion section 5 and the flue gas section 6. The Figure also shows the partitioning wall 20 between the second section 17 and the third section 18 of the flue gas section 6 and the first superheater 9 and the second superheater 10, which are illustrated superimposed .

Fig. 5 illustrates the boiler plant as seen in a second plane from above and from the upper part of the combustion section 5 and the flue gas section 6, respectively. The Figure shows the first lateral wall 1,11, the second lateral wall 2,12, the third lateral wall 3,13, and the fourth lateral wall 4,14 of the combustion section 5 and the flue gas section 6, respectively. The second lateral wall 2 of the combustion section 5 and the flue gas section 6, respectively, are coincident and form a screening wall between the combustion section 5 and the flue gas section 6. The Figure also shows the partitioning wall 20 between the second section 17 and the third section 18 of the flue gas sec- tion 6 and the first superheater 9.

The second lateral wall 2,12 of the combustion section 5 and the flue gas section 6, respectively, forming screen wall and separation between the combustion section 5 and the flue gas section 6 in the shown illustration is provided with the passageway 15 forming outlet for the flue gas from the combustion section 5 and the inlet for the flue gas to the flue gas section 6. The passageway 15 is formed in a known way by placing the pipings 22 that form the screen wall as triples in a plane Q perpendicularly on a plane P for the screen wall.

It appears from Fig. 4 and Fig. 5 that precisely that lateral wall forming screening wall between the combustion section 5 and the flue gas section 6 is the second lateral wall 2, 12 of the combustion section 5 and the flue gas section 6, respectively. This means that the first lateral wall 1,1 1 and the third lateral wall 3,13 of the combustion section 5 and the flue gas section 6, respectively, have external surfaces that are free. The ex- ternal surfaces of the first lateral wall 1,11 and the third lateral wall 3,13 are mostly suited for mounting of secondary equipment (not shown) like air supply devices and devices for combustion of secondary solid fuels like grinding dust from the wood working industry.

The first lateral wall 1,11 and the third lateral wall 3,13 are mostly suited for this as the first lateral wall 1,11 and the third lateral wall 3,13 extend perpendicularly from a plane of symmetry S for a direction of flow of the flue gas in the combustion section 5 and the flue gas section 6. The equipment that is mounted on the first lateral wall 1,11 and/or the third lateral wall 3,13 will thus conduct e.g. air into the combustion section 5 in a direction in parallel with and not perpendicularly to the plane of symmetry S for the direction of flow of the flue gas. This means that the throw length or the flame length will become as large as possible for plants with elongated combustion space. This also means that firing performed with secondary equipment does not disturb the flow of flue gas through the boiler.

In a possible embodiment the boiler according to the invention has a volume of 90 m and an external surface area of the lateral walls of 165 m of which 120 m constitutes the outer lateral walls.

The invention is described in the above with reference to a specific embodiment for a boiler plant according to the invention. Other embodiments with the combustion section and the flue gas section placed side by side may be provided in order to produce a boiler plant with better possibilities for transporting from the place of production to the construction site and with lesser external surface compared to the volume of the boiler plant.

Claims

1. A solid fuel boiler plant burning solid fuel such as wood, straw, coal and sludge, said plant comprising a boiler, which comprises a combustion section (5) extending from a lower part of the boiler upward to an upper part of the boiler, said combustion section (5) being provided with pipings (22), which form lateral walls (1, 2, 3, 4) including a first lateral wall (1) and a second lateral wall (2) of the combustion section (5), said boiler also comprising a flue gas section (6) extending in parallel with the combustion section (5) from the upper part of the boiler downward to the lower part of the boiler and being provided with pipings (22), which form lateral walls (1 1, 12, 13,

14), including a second lateral wall (12) of the flue gas section (6), said boiler comprising a primary fuel inlet device, which is arranged at a lower part of the combustion section (5), and wherein an opening (26) from the primary fuel inlet device to the combustion section (5) is placed in a first lateral wall (1), alternatively a bottom, of the combustion section (5), c h a r a c t e r i s e d in that the second lateral wall of the combustion section (2) is adjacent to the first lateral wall (1) of the combustion section (5), the primary fuel inlet device being arranged in said first lateral wall (1), that an outlet (15) from the combustion section is positioned in the second lateral wall (2) of the combustion section, and that the second lateral wall (12) of the flue gas section (6) coincides with the second lateral wall (2) of the combustion section (5), and that an inlet (15) into the flue gas section (6) from the combustion section (5) is positioned in the second lateral wall (12) of the flue gas section (6).

2. A solid fuel boiler plant according to claim 1, c h a r a c t e r i s e d in that the combustion section (5) has a rectangular cross-section seen in parallel with the vertical extension (h) of the combustion section (5), that the first lateral wall (1) of the combustion section (5) extends in a substantially vertical plane, that the second lateral wall (2) of the combustion section extends in a second substantially vertical plane (P) perpendicular to the first plane, and that the second lateral wall (12) of the flue gas sec- tion (6) also extends in the second substantially vertical plane (P).

3. A solid fuel boiler plant according to any one of claims 1 or 2, characterised in that the boiler has a width of between 2m and 7m, preferably between 2m and 4m, more preferably between 2.5m and 3.5m, and a depth of between 2m and 5m, preferably between 3m and 4m.

4. A solid fuel plant according to any one of the preceding claims, characterised in that the combustion section (5) has a width of between lm and 4m, preferably between lm and 2m, more preferably between 1.5m and 2m, and that the flue gas section (6) has a width of between lm and 4m, preferably between lm and 2m, more preferably between lm and 1.5m.

5. A solid fuel plant according to any one of the preceding claims, characterised in that the outlet (15) from the combustion section (5) is positioned in the upper part of the second lateral wall (2) of the combustion section (5), that the outlet (15) extends along at most half of the horizontal extension of the second lateral wall of the combustion section and along at most half of the vertical extension of the second lateral wall of the combustion section.

6. A solid fuel plant according to any one of the preceding claims, characterised in that the combustion section (3) has a third lateral wall extending opposite the first lateral wall (1), and that the third lateral wall is provided with secondary fuel inlet devices.

7. A furnace unit for use in a solid fuel plant according to any one of the preceding claims, characterised in that the furnace unit comprises lateral walls (1, 2, 3,

4), that the lateral walls (1, 2, 3, 4) are formed by pipings (22), that a first lateral wall (1) has an inlet to a combustion section (5), that a second lateral wall (2) is adjacent the first lateral wall (1), and that the second lateral wall has an inlet (15) from the combustion section (5).

8. A flue gas unit for use in a solid fuel plant according to any one of the preceding claims, characterised in that the flue gas unit comprises lateral walls (11, 12, 13, 14), that the lateral walls (11, 12, 13, 14) are formed by pipings (22), that a second lateral wall (1) has an inlet for a flue gas section (6), and that a third lateral wall (13) is adjacent the second lateral wall (12), and that a third lateral wall (13) has an outlet (21) from the flue gas section (6).

9. A furnace unit with a combustion section (5) that extends from a lower part of the combustion section (5) upward to an upper part of the combustion section (5) and is provided with pipings (22), which are arranged along lateral walls (1, 2, 3, 4) of the combustion section (5), c h a r a c t e r i s e d in that the combustion section (5) is provided with a lining (8), that the lining (8) extends from a position (pi) over the lower part of the combustion section (5) in a direction towards the upper part of the combustion section (5), preferably from a position (pi) over the lower part of the combustion section (5) corresponding to half of the vertical extension (h) of the combustion section (5) to a position (p2) corresponding to three quarters of the vertical extension (h) of the combustion section.

10. A furnace unit according to claim 9, c h a r a c t e r i s e d in that the lining (8) consists of a ceramic material, and that the lining (8) extends in the combustion section between at least one of the lateral walls (1, 2, 3, 4) of the combustion section (5) and an inside (16) of the combustion section (5).