Patent Description:
A bottom section of a combustion chamber of a fluidized bed boiler may include a sloping floor or sloping floor sections for facilitating removal of solids when transferring the solids into a solids removal opening by means of air jets and gravity, the sloping floor being formed by a protective refractory material layer. The air jets are brought about by nozzle devices providing air for combustion and fluidization. The nozzle devices extend from the protective refractory material layer to varying heights.

The nozzle devices may obstruct the removal of solids or the orientation of the air jets is not optimal. The nozzle devices may be abraded by the air jets carrying solids or fluidized bed material. The height differences in the sloping floor including the nozzle devices may vary strongly depending on the dimensions of the combustion chamber. Thus, the operation of the fluidized bed of the combustion chamber may be affected. The shape and structure of the protective refractory material layer may differ between boilers.

Document <CIT> discloses a grate assembly in a fluidized bed boiler.

Document <CIT> discloses a grate assembly in a fluidized bed boiler, the grate assembly including concentric rings arranged at various levels. Document <CIT> discloses the features in the preamble of the appended independent claim <NUM>.

The grate assembly according to the invention is presented in claim <NUM>.

A fluidized bed boiler including the above-mentioned grate assembly is presented in claim <NUM>.

Other claims present further details of the examples of the invention.

The grate assembly according to the invention is for use in a bottom section of a combustion chamber of a fluidized bed boiler.

The grate assembly comprises a grate bottom wall having a plurality of cooling tubes that are attached to the grate bottom wall; a protective refractory material layer on the grate bottom wall and covering the plurality of cooling tubes; and a plurality of nozzle devices for supplying fluidizing primary air above the grate bottom wall and the protective refractory material layer into the combustion chamber for maintaining combustion of fuel and fluidization of bed material.

The grate assembly further comprises at least one grate module formed on the grate bottom wall, each grate module comprising a solids removal opening in the refractory material layer via which solids on the refractory material layer are guided downwards to a solids removal conduit adapted to guide the solids through the refractory material layer and the grate bottom wall.

Each grate module further comprises a plurality of concentric landings each formed in the refractory material layer, the landings being situated at intervals in a vertical direction and being separated by frontal surfaces between the landings. Each frontal surface surrounds one of the landings and follows the shape of the perimeter of a rectangle or a rectangle with at least one shaped corner. The landings define a stepped structure that descends towards the solids removal opening situated in the center of the landings. Each landing comprises a group of nozzle devices belonging to the plurality of nozzle devices and being embedded in the refractory material layer. The group of nozzle devices is directed to jet the air through one of the frontal surfaces along one of the landings that is adjacent to the frontal surface.

According to an example, the at least one shaped corner includes a chamfer, multiple chamfers, a step, multiple steps, a shape extending inwards the rectangle, and/or a shape extending outwards the rectangle.

According to an example, each landing comprises four rows of nozzle devices each with nozzle devices aligned in a row and belonging to the group of nozzle devices. According to an example, the frontal surface comprises four corners each having at least one nozzle device belonging to the group of nozzle devices and being between two of the rows of nozzle devices.

The fluidized bed boiler for use in steam production comprises a combustion chamber with a bottom section including the above-mentioned grate assembly.

The presented invention is particularly advantageous and solves the above-mentioned problems.

In an example, the grate module of the presented invention provides a modular and expandable system for constructing the bottom section of the combustion chamber of the fluidized bed boiler.

In an example, the use of the grate modules of the presented invention provides a way of restricting the height differences between the nozzle devices. The height differences and the height of the stepped structure of the grate assembly and the grate module can be chosen in such a way that the motion of the fluidizing primary air above the grate assembly takes place in a desired or controlled manner.

In an example, rows of additional nozzle devices are easily integrated into or between the grate modules for facilitating the design of the layout of the grate assembly and the bottom section of the combustion chamber.

In an example, the central location of the solids removal opening in the grate module provides an efficient way of removing solids. The size and dimensions of the grate module can be chosen in such a way that solids are efficiently transferred to the solids removal opening.

In an example, the presented invention provides a simple structure in which the grate bottom wall and the plurality of parallel cooling tubes extend horizontally.

In an example, the presented invention provides the plurality of nozzle devices embedded in the refractory material layer constituting the stepped structure and thereby unobstructed removal of solids is facilitated by the surfaces of the stepped structure of the grate module.

In an example, the nozzle devices in corners of the grate module are oriented to remove solids efficiently from the surfaces of the stepped structure.

These and other non-limiting features, characteristics and advantages of the presented invention are more particularly disclosed below.

The following is a brief description of the drawings, which are presented for the purposes of illustrating the exemplary embodiments disclosed herein and not for the purposes of limiting the same.

In the description, reference is made to the figures with the following reference numbers and denotations:.

A more complete understanding of the features disclosed herein can be obtained by reference to the accompanying drawings. These figures are merely schematic representations and are not intended to indicate relative size and dimensions of the devices or components thereof or to define or limit the scope of the embodiments. The specific terms used in the following description are intended to refer only to the embodiments selected for the drawings and are not intended to define or limit the scope of the disclosure. In the drawings and the description below, like numeric designations refer to devices or components of like function.

In the following, the terms "horizontal" and "vertical" refer to the intended operating positions of the device or component in question when installed in place for implementing the functions of the described solution. The terms "horizontal" and "vertical" are used to indicate direction relative to an absolute reference, i.e. ground level. In the figures, the vertical direction is denoted by an arrow Z and the two orthogonal, horizontal directions are denoted by arrows X and Y. The horizonal directions are orthogonal in relation to the vertical direction.

Also, the terms "upper", "lower", "on top", "below", "upward", and "downward" relate to the above-mentioned, intended operating positions. The terms "parallel" and "perpendicular" should not be construed to require structures to be absolutely parallel or absolutely perpendicular to each other. The term "opposite" should not be construed to require opposite directions to be absolutely parallel to each other.

Referring to <FIG>, one embodiment of a steam generator or a fluidized bed boiler <NUM> in which the present invention is applied is shown. The fluidized bed boiler <NUM> may be a part of a power plant, a steam boiler plant, or a hot water boiler plant, adapted for the production of electric energy, steam, and/or heating energy.

The boiler <NUM> includes a combustion chamber <NUM>, i.e. a furnace, for the combustion of fuels and a flue gas channel <NUM> for conveying flue gases, i.e. combustion product gases, coming from the combustion chamber <NUM>.

The boiler <NUM> may comprise further devices that are relevant for the design in question but are not necessarily shown in the figures. The boiler <NUM> may additionally comprise a cyclone separator <NUM> connected to the combustion chamber <NUM> for separating solid particles from the flue gases coming from the combustion chamber <NUM> and for guiding the flue gases to the flue gas channel <NUM>. The boiler <NUM> may further comprise a support frame <NUM> for supporting the combustion chamber <NUM> and the flue gas channel <NUM> to the ground. The support frame <NUM> may, for example, include columns <NUM>, supporting beams <NUM> and/or hangers <NUM> for supporting the combustion chamber <NUM> and/or the flue gas channel <NUM> to the support frame <NUM>.

The boiler <NUM> may be a fluidized bed boiler of CFB design (circulating fluidized bed) or BFB design (bubbling fluidized bed). The fuel may be a gas, solid fuel or solid waste from various sources, e.g. municipal waste. Fluidizing air realizing a fluidized bed and to be used as primary air for combustion is fed into the combustion chamber <NUM> via a bottom section <NUM> constituting the lower part of the combustion chamber <NUM>.

As shown in <FIG> and <FIG>, the grate assembly for use in the bottom section <NUM> of the combustion chamber of the fluidized bed boiler <NUM> comprises a grate bottom wall <NUM>, a protective refractory material layer <NUM>, a plurality of nozzle devices <NUM>, and at least one grate module <NUM>.

The grate bottom wall <NUM> includes a plurality of cooling tubes <NUM> that are attached to the grate bottom wall <NUM>.

According to an example in <FIG>, the grate bottom wall <NUM> extends horizontally and the plurality of cooling tubes <NUM> are parallel, extend horizontally, and are attached to the grate bottom wall <NUM> at intervals along the grate bottom wall <NUM>.

According to an example in <FIG>, the grate bottom wall <NUM> is constituted by the plurality of cooling tubes <NUM> separated by fins attached between the cooling tubes <NUM>.

The protective refractory material layer <NUM> is situated on the grate bottom wall <NUM> and covers the plurality of cooling tubes <NUM>.

The plurality of nozzle devices <NUM> are for supplying fluidizing primary air for maintaining combustion of fuel and fluidization of bed material above the grate bottom wall <NUM> and the protective refractory material layer <NUM> into the combustion chamber <NUM>. Each nozzle device <NUM> is adapted to guide primary air that arrives through the grate bottom wall <NUM> and the refractory material layer <NUM> and to jet the air to be used as the fluidizing primary air.

According to an example in <FIG>, the nozzle device <NUM> includes a conduit section attached to and going through the grate bottom wall <NUM>, and a mouth section for jetting out the air guided via the conduit section.

The grate assembly <NUM> comprises, for example, one grate module <NUM> or <NUM> to <NUM> adjacent grate modules <NUM>. According to an example, the grate modules <NUM> constitute a N x M grid, with N equaling <NUM>, <NUM>, or <NUM> and M equaling <NUM>, <NUM>, or a whole number between <NUM> and <NUM>.

According to an example in <FIG>, all the grate modules <NUM> of the grate assembly <NUM> are similar. Alternatively, the grate assembly <NUM> may include similar and/or dissimilar grate modules <NUM>.

Each grate module <NUM> comprises a solids removal opening <NUM>, a solids removal conduit <NUM>, and a plurality of concentric landings <NUM>.

The solids removal opening <NUM> is formed in the refractory material layer <NUM> via which solids removal opening <NUM> solids on the refractory material layer <NUM> are guided, by means of air in motion and gravity, downwards through the refractory material layer <NUM> and the grate bottom wall <NUM>.

According to an example in <FIG>, the solids are guided downwards to a solids removal conduit <NUM> of the fluidized bed boiler <NUM> or the grate assembly.

Each landing <NUM> is formed in the refractory material layer <NUM>. The landings <NUM> are situated at intervals in relation to a vertical direction and are separated from each other by frontal surfaces <NUM> that are situated between the landings <NUM>.

The landings <NUM> constitute a stepped structure, e.g. a funnel, that descends towards the solids removal opening <NUM> that is situated in the centre of the landings <NUM>.

According to an example in <FIG>, the frontal surfaces <NUM> extend vertically.

Each frontal surface <NUM> surrounds one of the landings <NUM> and follows the shape of the perimeter of a rectangle, or the shape of the perimeter of a rectangle with at least one shaped corner. Alternatively, each frontal surface <NUM> surrounds one of the landings <NUM> and follows the shape of the perimeter of a square, or the shape of the perimeter of a square with at least one shaped corner. The square, representing a rectangle, is a special case of the rectangle with four sides of equal length.

According to examples in <FIG>, the at least one shaped corner includes a chamfer (<FIG>), multiple chamfers (<FIG>), a step (<FIG><FIG>), multiple steps (<FIG><FIG>), a shape extending inwards the rectangle (<FIG><FIG><FIG><FIG>), and/or a shape extending outwards the rectangle (<FIG><FIG>). According to an example, all the four corners of the rectangle are similar. According to an example, the corner is formed of two perpendicular edges (<FIG>).

Each landing <NUM> comprises a group of nozzle devices <NUM> belonging to the plurality of nozzle devices <NUM>. The group of nozzle devices <NUM> is embedded in the refractory material layer <NUM> and are configured, directed, or oriented to jet the air through one of the frontal surfaces <NUM> and further along one of the landings <NUM> that is adjacent to the one frontal surface <NUM>. According to an example, the one landing <NUM> is between the one frontal surface <NUM> and another frontal surface <NUM> situated lower in relation to a vertical direction. According to an example, the one landing <NUM> is between the one frontal surface <NUM> and the solids removal opening <NUM> at the centre of the grate module <NUM>.

According to an example in <FIG>, the solids removal opening <NUM> is circular. Alternatively, the solids removal opening <NUM> may be, for example, of rectangular, e.g. a square, or polygon shape.

According to an example in <FIG>, the nozzle devices <NUM> are adapted to jet the air to horizontal directions. According to an example in <FIG>, each nozzle device <NUM> is adapted to jet the air to a predetermined horizontal direction specific to the nozzle device <NUM>.

According to an example in <FIG> and <FIG>, each frontal surface <NUM> is formed by surfaces of the group of nozzle devices <NUM> or by the refractory material layer <NUM>, or by both the surfaces of the nozzle devices <NUM> and the refractory material layer <NUM>. According to an example there are alternating nozzle devices <NUM> and sections of refractory material layer <NUM> in the frontal surface <NUM>.

According to an example, a front surface of the nozzle device <NUM> constitutes a part of the frontal surface <NUM>. According to an example, the front surface is included in the mouth section of the nozzle device <NUM>. According to an example, the air is jetted out via an opening in the front surface.

According to an example, the group of nozzle devices <NUM> is embedded in the refractory material layer <NUM> in such a way that the air is jetted out from the nozzle device <NUM> to a conduit and an opening formed in the refractory material layer <NUM> for jetting the air through the frontal surface <NUM>.

According to an example in <FIG>, the group of nozzle devices <NUM> is embedded in the refractory material layer <NUM> in such a way that a top surface of the nozzle device <NUM> constitutes a part of the landing <NUM>. According to an example there are alternating nozzle devices <NUM> and sections of refractory material layer <NUM> on the landing <NUM>. According to another example the nozzle device <NUM> is embedded below the surface of the landing <NUM>.

According to an example in <FIG>, each landing <NUM> comprises a first row <NUM> of nozzle devices <NUM>, a second row <NUM> of nozzle devices <NUM>, a third row <NUM> of nozzle devices <NUM>, and a fourth row <NUM> of nozzle devices <NUM>. The nozzle devices <NUM> in each row are aligned in a row and belong to the above-mentioned group of nozzle devices <NUM>. The rows are arranged horizontally in such a way that the first and second rows <NUM>, <NUM> are parallel and are situated on opposite sides of the landing <NUM>, and that the third and fourth rows <NUM>, <NUM> are parallel, situated on opposite sides of the landing <NUM>, and perpendicular to the first and second rows <NUM>, <NUM>.

According to an example in <FIG>, two or more nozzle devices <NUM> belonging to the plurality of nozzle devices <NUM> and being situated on different landings <NUM> are aligned in a row along a direction perpendicular to one of the rows <NUM>, <NUM>, <NUM>, <NUM>.

According to an example in <FIG>, each nozzle device <NUM> in each row <NUM>, <NUM>, <NUM>, <NUM> is configured, directed, or oriented to jet the air in a horizontal direction perpendicular to the above-mentioned opposite row towards the opposite row along the landing <NUM>.

According to an example, there are eight to eighty nozzle devices <NUM> in the above-mentioned group of nozzle devices <NUM>.

According to an example, there are three to seven concentric landings <NUM> in the grate module <NUM>. Alternatively, there are eight or more, for example at least ten, concentric landings <NUM>. According to an example, the landings extend horizontally.

According to an example in <FIG>, each frontal surface <NUM> comprises four corners <NUM> constituting the corners of the rectangle, each corner includes at least one nozzle device <NUM> belonging to the above-mentioned group of nozzle devices <NUM> and being between two of the rows <NUM>, <NUM>, <NUM>, <NUM> that are perpendicular to each other. The at least one nozzle device <NUM> is configured, directed, or oriented to jet the air in a horizontal direction towards the solids removal opening <NUM> or the one of the four corners <NUM> that is situated diagonally opposite. According to an example in <FIG>, the at least one nozzle device <NUM> jets the air at an angle of <NUM> degrees or at an angle of <NUM> to <NUM> degrees, or at an angle of <NUM> to <NUM> degrees, in relation to the above-mentioned two rows that are perpendicular to each other.

According to an example, there are not more than one, two, or three nozzle devices <NUM> in the above-mentioned corner <NUM>. Alternatively, there are more than three nozzle devices <NUM> in the above-mentioned corner <NUM>.

According to an example in <FIG>, the grate assembly <NUM> further comprises on at least one side of at least one of the grate modules <NUM> an additional landing <NUM>. The additional landing <NUM> is formed in the refractory material layer <NUM>. The additional landing <NUM> forms an extension to the stepped structure of the grate module <NUM>. According to a first example in <FIG>, the additional landing <NUM> is separated from the uppermost landing <NUM> of the grate module <NUM> by an additional frontal surface <NUM> between them. According to a second example, the additional landing <NUM> is separated from another additional landing <NUM> by an additional frontal surface <NUM> between them.

According to an example in <FIG>, the additional landing <NUM> and/or the additional frontal surface <NUM> follows the shape of a line, i.e. the additional landing <NUM> and/or the additional frontal surface <NUM> extends rectilinearly. According to an example, the additional landings <NUM> extend horizontally. According to an example, the additional landing <NUM> extends rectilinearly along one side of at least two of the grate modules <NUM> that are adjacent.

The additional landing <NUM> comprises a group of additional nozzle devices <NUM> embedded in the refractory material layer <NUM> and are configured, directed, or oriented to jet the air through one of the additional frontal surfaces <NUM> and further along the above-mentioned uppermost landing <NUM> or the above-mentioned other additional landing <NUM> that is adjacent to the one additional frontal surface <NUM>. According to an example, the additional nozzle devices <NUM> are adapted to jet the air to horizontal directions.

According to an example in <FIG>, the landings <NUM> of the grate module <NUM> and the additional landings <NUM> situated on one side, on two adjacent or opposite sides, or on three adjacent sides of the grate module <NUM> form a grate module <NUM> following a rectangular shape. According to another example, the grate module <NUM> follows a square shape which grate module <NUM> together with the additional landings <NUM> forms a non-square, rectangularly shaped structure. According to an example in <FIG>, the additional landings <NUM> are to be situated between two adjacent grate modules <NUM>.

According to an example in <FIG>, the additional landing <NUM> comprises an additional row <NUM> of additional nozzle devices <NUM>. The additional nozzle devices <NUM> in the additional row are aligned in a row and belong to the above-mentioned group of additional nozzle devices <NUM>. The additional row is arranged horizontally in such a way that the additional row <NUM> is parallel to the first and second rows <NUM>, <NUM> or the third and fourth rows <NUM>, <NUM>.

According to an example in <FIG>, each additional nozzle device <NUM> in the additional row <NUM> is configured, directed, or oriented to jet the air in a horizontal direction perpendicular to and towards the above-mentioned rows that are parallel to the additional row <NUM>. Alternatively, at least one additional nozzle device <NUM> at one or both ends of the additional row <NUM> is configured, directed, or oriented to jet the air in a horizontal direction towards the solids removal opening <NUM> or the one of the four corners <NUM> that is situated diagonally opposite, the at least one additional nozzle device <NUM> belonging to the above-mentioned group of additional nozzle devices <NUM>. According to an example, the at least one additional nozzle device <NUM> jets the air at an angle of <NUM> degrees or at an angle of <NUM> to <NUM> degrees, or at an angle of <NUM> to <NUM> degrees, in relation to the other additional nozzle devices <NUM> of the additional row <NUM>.

According to some examples, the details of the structure, operation, and characteristics of the above-mentioned nozzle device <NUM> explained above, for example in relation to the refractory material layer <NUM>, the frontal surface <NUM>, and the landing <NUM>, apply also to the additional nozzle device <NUM> in relation to the refractory material layer <NUM>, the additional frontal surface <NUM>, and the additional landing <NUM>.

According to an example, the fluidized bed boiler <NUM> includes a solids collecting and handling system for receiving the solids coming via one or more of the solids removal opening <NUM> and/or the solids removal conduit <NUM>.

According to an example, the fluidized bed boiler <NUM> or the grate assembly further comprises one or more air plenum chambers <NUM>. The air plenum chamber <NUM> is adapted to receive the air to be supplied via the plurality of nozzle devices <NUM>, <NUM> as the fluidizing primary air. The air plenum chamber <NUM> is situated below the grate bottom wall <NUM>. According to an example, for conveying the air, the conduit section of the nozzle device <NUM>, <NUM> is in communication with the air plenum chamber <NUM>.

In this description, the singular form "a", "an", and "the" referring to a device or component does not exclude additional or a plurality of corresponding devices or components, unless where specifically specified.

In the description, various devices and components may be described as "comprising" other components. The terms "comprise(s)", "comprising", "include(s)", "having", "has", and variants thereof, are intended to be openended phrases that do not exclude the possibility of additional components, unless where specifically specified.

Claim 1:
A grate assembly for use in a bottom section (<NUM>) of a combustion chamber (<NUM>) of a fluidized bed boiler (<NUM>),
the grate assembly (<NUM>) comprising:
- a grate bottom wall (<NUM>);
- an arrangement for supplying fluidizing primary air above the grate bottom wall into the combustion chamber for maintaining combustion of fuel and fluidization of bed material;
- at least one grate module (<NUM>),
- wherein each grate module (<NUM>) comprises:
- a solids removal opening (<NUM>) via which solids are guided downwards through the grate bottom wall (<NUM>);
- a plurality of concentric landings (<NUM>) situated at intervals in a vertical direction and being separated by frontal surfaces (<NUM>) between the landings,
- wherein each frontal surface (<NUM>) surrounds one of the landings and follows the shape of the perimeter of a rectangle;
- wherein each landing comprises a group of nozzle devices belonging to the plurality of nozzle devices (<NUM>), the group of nozzle devices being adapted to jet the air through one of the frontal surfaces (<NUM>) along one of the landings (<NUM>) that is adjacent to the frontal surface; and
- wherein the landings (<NUM>) define a stepped structure that descends towards the solids removal opening (<NUM>) situated in the center of the landings; and
the grate assembly being characterized in that the grate assembly further comprising:
- a plurality of cooling tubes (<NUM>) of the grate bottom wall (<NUM>) and attached to the grate bottom wall; and
- a protective refractory material layer (<NUM>) on the grate bottom wall (<NUM>) and covering the plurality of cooling tubes (<NUM>),
- wherein the at least one grate module (<NUM>) is formed on the grate bottom wall (<NUM>) and each one of the plurality of concentric landings (<NUM>) is formed in the refractory material layer (<NUM>);
- wherein the solids removal opening is in the refractory material layer (<NUM>) to guide the solids on the refractory material layer downwards through the refractory material layer and the grate bottom;
- wherein the arrangement for supplying fluidizing primary air includes a plurality of nozzle devices (<NUM>) for supplying fluidizing primary air above the grate bottom wall and the protective refractory material layer into the combustion chamber; and
- wherein in each landing the group of nozzle devices is embedded in the refractory material layer (<NUM>).