This application is US national stage application of International App. No PCT/FI2014/050736 filed on Sep. 29, 2014, which claims priority on Finnish Application No. 20136013, filed on Oct. 11, 2014, the disclosures of which applications are incorporated by reference herein.
Not applicable.
The invention relates to thermal devices, such as gasification reactors and boilers, particularly fluidized bed boilers, such as bubbling fluidized bed boilers. The invention relates to thermal devices for heating a heat transfer medium. In particular, the invention relates to thermal devices for heating a heat transfer medium, such as steam, to a very high temperature.
Boilers are used for burning combustible material and thereby for producing energy, such as heat. Heat is recovered from the heat transfer surfaces of the boiler by a heat transfer medium, such as water and/or steam. Hot steam can be used to generate electricity, for example by means of steam turbines.
The efficiency of generating energy is improved when the temperature of the heated heat transfer medium is raised. However, some challenges are involved in increasing the temperature. Increasing the temperature will inevitably increase the temperature of the outer surfaces of the heat transfer pipes. Because corrosive substances, such as salts, are condensed on the surfaces, and an increase in the temperature generally accelerates chemical reactions, corrosion is significantly accelerated due to the increase in the temperature.
Furthermore, for producing particularly hot heat transfer medium, the heat transfer pipe for recovering heat should be placed in a very hot environment. The pressure inside the heat transfer pipe is usually considerable (for example, dozens of bars, typically higher than 30 bar); for example, the pressure and the temperature may correspond to the pressure of saturated vapour, at least at low temperatures. At higher temperatures, the steam is normally superheated, wherein its temperature is higher than the temperature of saturated steam at a corresponding pressure, or the temperature of the critical point of the heat transfer medium, i.e. the critical temperature. (374° C. for water), is exceeded. The heat transfer pipe used in such a hot environment has to withstand the pressure prevailing inside the pipe and also the loads from the corrosive environment outside the pipe. Heat transfer pipes which are resistant to a hot environment and a high pressure under corrosive conditions are typically very expensive options.
Protected heat transfer pipes for a loopseal superheater are disclosed in US 2010/0000474. Therein, the superheating piping includes a steam pipe where the steam to be superheated is directed, and the steam pipe is separated by a protective shell. Such a superheater is preferably placed inside a loopseal. Same principles can be applied for a radiant superheater or a superheater arranged in a flue gas channel.
A device and method for altering the heat transfer characteristics of tubes exposed to the heat generated within a boiler is disclosed in U.S. Pat. No. 4,177,765. Therein a fluidized bed boiler is equipped with a plurality of slidable sleeves circumscribing the vapor generator tubes disposed therein. By selectively extending or retracting the sleeves over the tubes, the heat transfer characteristics can be altered.
It is an aim of the present invention to provide a thermal device, such as a gasification reactor or a boiler, for heating a heat transfer medium to a high temperature and simultaneously to apply conventional materials.
In an embodiment, the thermal device comprises
at least a first wall delimiting a flow duct for gases, and
a heat exchanger pipe comprising at least an inner pipe, at least a first section of said heat exchanger pipe being placed in said flow duct for gases and extending from said first wall to said first wall or to a second wall delimiting the flow duct for gases in said flow duct for gases, and
said first section of the heat exchanger pipe comprising a second section of the heat exchanger pipe, which extends in said flow duct for gases.
In the thermal device, the second section of the heat exchanger pipe comprises
at least a section of the inner pipe, for transferring heat transfer medium from the first end to the second end of the inner pipe and for recovering heat by the heat transfer medium,
an outer pipe which radially encloses said section of the inner pipe, and
a layer of medium left between said outer pipe and said section of the inner pipe in the radial direction.
Furthermore,
(A,i)
the inner pipe of the first section of said heat exchanger pipe is noninsulated in one or more noninsulated areas in such a way that
the distance from all the points of the noninsulated areas in the first section of the heat exchanger pipe to the other heat transfer surfaces of the thermal device (except for the heat exchanger pipe itself) is not greater than 15 cm; or
(A,ii)
the inner pipe of the first section of said heat exchanger pipe is, over its entire length, insulated from the flow duct for gases by means of said outer pipe and/or an insulator.
In an embodiment, the thermal device comprises several other heat transfer pipes inside the walls of the flow duct for gases, for recovering heat. Said heat exchanger pipe and said other heat transfer pipes constitute a continuous flow duct for the heat transfer medium, for heating the heat transfer medium.
Furthermore, in one such embodiment,
(B,i)
said flow duct for the heat transfer medium comprises the first section of said heat exchanger pipe as the last heat transfer element placed in the flow duct of gases, in the direction of the flow of the heat transfer medium, or
(B,ii)
said flow duct for the heat transfer medium comprises the last first section of the heat exchanger pipe placed in the flow duct for gases, in the direction of flow of the heat transfer medium, and at least one heat transfer pipe in the flow duct for gases, placed downstream in the direction of flow of the heat transfer medium, and
said last first section of the heat exchanger pipe is arranged, in the flow direction of the gas flowing outside the outer pipe, upstream of said heat transfer pipes in the flow duct for gases, placed downstream in the flow direction of the heat transfer medium.
Preferably, said second section of the heat exchanger pipe extends in a straight line or bends less than 90 degrees.
In an embodiment, said second section of the heat exchanger pipe bends at least 90 degrees and thereby does not extend in a straight line.
The thermal device can be used, for example, for heating steam. In an embodiment of the use of the thermal device,
the heat transfer medium is allowed to flow in said inner pipe,
steam is used as the heat transfer medium, and
the temperature of the heat transfer medium flowing in the inner pipe is at least 500° C., preferably at least 530° C.
The thermal device can be used for heating the heat transfer medium in such a way that the surface temperature of a heat exchanger pipe in operation is considerably high. Thus, condensation of corrosive substances on the surface of the pipe is prevented or at least reduced. In an embodiment of the use, the temperature of the outer surface of the outer pipe exceeds 600° C.
Furthermore, in the presented boiler, the use of auxiliary agents for combustion is intensified when the means for supplying the auxiliary agent are placed in such a location where the operating temperature is typically favourable to the supply of the auxiliary agent.
The use of the thermal device will lead to performing a method. A corresponding method for heating a heat transfer medium comprises
producing gas heated by a thermal device,
conveying said gas into a flow duct for gases,
conveying heat transfer medium into a heat exchanger pipe comprising at least an inner pipe, at least the first section of the heat exchanger pipe being placed in the flow duct for gases and extending in said flow duct for gases from the wall of said flow duct to the same or another wall of said flow duct, and said first section of the heat exchanger pipe comprising a second section of the heat exchanger pipe, extending in said flow duct for gases, and
recovering heat by the heat transfer medium in the heat exchanger pipe.
In the method, the second section of the heat exchanger pipe comprises
at least a section of the inner pipe for transferring heat transfer medium from the first end to the second end of the inner pipe and for recovering heat by the heat transfer medium,
an outer pipe which radially encloses said section of the inner pipe, and
a layer of medium left, in the radial direction, between said outer pipe and said section of the inner pipe.
Furthermore,
(A,i)
the inner pipe of the first section of said heat exchanger pipe is noninsulated from the flow duct for gases in one or more noninsulated areas in such a way that
the distance from all the points of the noninsulated areas in the first section to the other heat transfer surfaces of the thermal device is not greater than 15 cm; or
(A,ii)
the inner pipe of the first section of said heat exchanger pipe is, over its entire length, insulated from the flow duct for gases by means of said outer pipe and/or an insulator.
In an embodiment of the method, too, the thermal device comprises several other heat transfer pipes inside the walls of the flow duct for gases, for recovering heat. Said heat exchanger pipe and said other heat transfer pipes constitute a continuous flow duct for the heat transfer medium, for heating the heat transfer medium.
In such an embodiment of the method,
(B,i)
said flow duct for the heat transfer medium comprises the first section of said heat exchanger pipe as the last heat transfer element placed in the flow duct of gases, in the direction of the flow of the heat transfer medium, or
(B,ii)
said flow duct for the heat transfer medium comprises the last first section of the heat exchanger pipe placed in the flow duct for gases, in the direction of flow of the heat transfer medium, and at least one heat transfer pipe in the flow duct for gases, placed downstream in the direction of flow of the heat transfer medium, and said last first section of the heat exchanger pipe is arranged, in the flow direction of the gas flowing outside the outer pipe, upstream of said subsequent heat transfer pipes placed in the flow duct for gases, in the flow direction of the heat transfer medium.
Preferably, said second section of the heat exchanger pipe extends in a straight line or bends less than 90 degrees.
In an embodiment of the method, said second section of the heat exchanger pipe bends at least 90 degrees and thereby does not extend in a straight line.
1 to 1g4 show cross-sectional views of a heat exchanger pipe at different points thereof in a flow duct for gases in a thermal device,
1 to 1h3 show straight and curved second sections of a heat exchanger pipe,
Thermal devices are used for generating energy, such as electricity and/or heat, and/or for producing fuel from combustible material, such as municipal waste and/or raw material of biological origin, such as wood based raw material. For example, the thermal device may refer to a boiler in which combustible material is burnt for producing energy. Boilers can be classified according to the material to be burnt, wherein e.g. the following boilers are known: soda recovery boiler (fired with black liquor), oil fired boiler, coal fired boiler, pulverized fuel boiler, and waste fired boiler (in a waste-to-energy power plant). Boilers can be classified according to the structure of the boiler, wherein e.g. the following boilers are known: fluidized bed boiler, such as circulating fluidized bed boiler (CFB) and bubbling fluidized bed boiler (BFB); grate boiler; water-pipe boiler; and fire-pipe boiler. For example, the thermal device may refer to a gasification reactor, in which combustible material is oxidized to produce synthesis gas. Synthesis gas can be further refined to fuel, such as biofuel. For example, the thermal device may refer to a pyrolysis reactor, in which combustible material is pyrolyzed to produce pyrolysis oil. The pyrolysis oil can be further refined. Moreover, the thermal device may refer to a torrefaction reactor, in which combustible material is thermally treated to evaporate water and light hydrocarbons from the combustible material. The combustible material treated in this way can be later used as fuel in subsequent processes. In a corresponding way, the thermal process refers to a process in which energy and/or fuel is produced. In alignment with the above described reactors, the thermal process may be, for example, a combustion, gasification, pyrolysis, or torrefaction process. The above mentioned combustible material may be, for example, solid material of biological origin, such as wood based material.
Boilers are given here as an example of thermal devices and their use. Boilers are used for burning combustible material and thereby for producing energy, such as heat. Heat is recovered from the heat transfer surfaces of the boiler by a heat transfer medium, such as water and/or steam. Hot steam can be used to generate electricity, for example by means of steam turbines.
A gasification reactor is given as a second example of thermal devices and their use. Gasification reactors are used to oxidise combustible material in oxygen deficient conditions, for producing synthesis gas. Heat can be recovered from the synthesis gas. Heat is recovered from the heat transfer surfaces of the gasification reactor by a heat transfer medium, such as water and/or steam. Hot steam can be used to generate electricity, for example by means of steam turbines.
Pyrolysis reactors are given as a third example of thermal devices and their use. They are used for forming pyrolysis steam which can be condensed. In the condensing, heat can be recovered in the above described way.
The efficiency of energy production is improved when the temperature of the heated heat transfer medium is raised. Water and/or steam is normally used as the heat transfer medium. In the present description, steam also refers to steam at a temperature exceeding the critical point of water (373° C.), which steam is sometimes call gas, because the steam at said temperature cannot be liquefied to water by increasing the pressure.
Thermal devices, such as boilers, comprise walls, which delimit, for example, a furnace, the gasification phase of the gasification reactor, and/or various gas ducts, such as flue gas ducts, synthesis gas ducts, or pyrolysis steam ducts. The term “wall” may refer to, for example, the walls or the ceiling of the reactor. Thermal reactors also comprise heat exchangers for recovering heat generated in the reactions. The surface temperature of the heat exchanger in operation has a significant effect on the corrosion of the surface of the heat exchanger. Basically, if said surface temperature is low, corrosive substances are condensed from the gases into solids. At the low temperature, the solids do not significantly corrode the surfaces. On the other hand, if said surface temperature is high, no significant amounts of corrosive substances are condensed from the gases, wherein the corrosion is relatively slow, too. In between, a range is left in which corrosive substances are condensed from the gases into liquid substances onto the heat recovery surfaces, wherein the corrosion is very rapid. The values of these temperatures will be given in more detail further below.
Raising the surface temperature of the heat exchanger pipe is very challenging, because the pipe has to withstand the pressure prevailing inside it at the operating temperature.
The present invention will be illustrated in the appended drawings. The figures, such as
at least a first wall 112 delimiting a flow duct 115 for gases, and
a heat exchanger pipe 200 comprising at least an inner pipe 210, at least the first section 202 of said heat exchanger pipe being placed in said flow duct 115 for gases and extending in said flow duct 115 for gases from said first wall 112 to said first wall 112 or to a second wall 114 (
said first section 202 of the heat exchanger pipe comprising a second section 240 of the heat exchanger pipe, extending in said flow duct 115 for gases.
In this context, the “heat exchanger pipe” thus refers to a possibly long pipe whose (at least one) first section 202 is, over its entire length, placed in the flow duct 115 for gases. In a corresponding manner, the first section 202 refers to a continuous section of the pipe that is as long as possible and extends in the flow duct; that is, a section that extends from wall to wall (either the same or another wall). The second section 240 of the heat exchanger pipe, comprised in said first section 202, is a shielded assembly in which an inner pipe 210 is shielded by an outer pipe 220. The second section 240 may be shorter than the first section 202, or equal in length.
With reference to
at least a section of the inner pipe 210 for transferring heat transfer medium from the first end to the second end of the inner pipe and for recovering heat by the heat transfer medium,
an outer pipe 220 which radially encloses said section of the inner pipe, and
a layer 230 of medium left between said outer pipe 220 and said section of the inner pipe 210 in the radial direction.
Such a structure has the advantage that because of the medium layer 230, the surface temperature of the outer pipe 220 is, when the thermal device is in operation, so high that no significant amounts of corrosive substances are condensed on its surface. Such a pipe with a layered structure is heavier than a single layered pipe. Furthermore, it has been found that if a pipe with a layered structure is bent, the outer pipe will come into contact with the inner pipe, wherein there will be no medium layer at the bending point. When there is no medium layer, heat will be conducted too well from the outer pipe to the inner pipe, which will reduce the surface temperature of the outer pipe to a range that is critical for corrosion, at least when the present configuration is applied in hot conditions and with a hot heat transfer medium. Furthermore, a relatively straight pipe is easier to make self-supporting than a pipe that bends to a great extent. For these reasons, in an advantageous embodiment,
said second section 240 of the heat exchanger pipe extends in a straight line or bends less than 90 degrees.
It has been discovered that with some technical solutions, it is possible to arrange the inner pipe 210 inside the outer pipe 220, even when the outer and inner pipes are bent, in such a way that a medium layer sufficient for heat insulation is left between these pipes.
In an embodiment, said second section 240 of the heat exchanger pipe is bent at least 90 degrees, wherein said second section of the heat exchanger pipe does not extend in a straight line. Also in this case it is possible, by applying certain technical solutions, to provide a medium layer constituting a sufficient heat insulation between the outer pipe 220 and the inner pipe 210.
The function of the outer pipe 220 is, among other things, to shield the inner pipe 210. It is possible that in addition to the outer pipe 220 (
Moreover, it is possible that at a point where the temperature is already low in the flow duct 115, the inner pipe is not shielded at all; not with an insulator nor with an outer pipe. Such points are typically found in the vicinity of the heat recovery surfaces, such as the walls 112, 114. Even in this case, the inner pipe 210 is shielded over almost its entire length in the flow duct 115 for gases. Consequently, in some embodiments
(A)
the inner pipe 210 of the first section 202 of said heat exchanger pipe is, in some parts, insulated from the flow duct 115 for gases by means of said outer pipe 220 and/or an insulator 260, and
the inner pipe 210 of the first section 202 of said heat exchanger pipe is noninsulated from the flow duct 115 for gases in one or more noninsulated areas 270 (
(A1)
the length of even the largest noninsulated area 270 of the first section 202 does not exceed 15 cm; preferably, the length of even the largest noninsulated area 270 does not exceed 10 cm, the length being measured in the longitudinal direction of the inner pipe 210; or
(A2)
the distance from all the noninsulated areas 270 of the first section 202 to the other heat recovery surfaces of the thermal device (other than the heat exchanger pipe 200 itself) is not greater than 15 cm; preferably not greater than 10 cm; or
(B)
the first section 202 of said heat exchanger pipe, or the inner pipe 210 of said first section 202, is, over its entire length, insulated from the flow duct 115 for gases by means of said outer pipe 220 and/or an insulator 260 (
With reference to points (A, A1 and A2) and
Point (A2) is also a possible solution, because the temperature of the gases in the flow duct 115 is typically lower in the vicinity of the heat recovery surfaces than far away from the other heat recovery surfaces. In the vicinity of the heat recovery surface, the heat exchanger pipe may also extend in the direction of the heat recovery surface or substantially in parallel with the heat recovery surface in the flow duct 115. Typically, the heat exchanger pipe extends in a direction substantially perpendicular to the wall (
Yet more advantageously, the first section does not comprise any non-insulated areas 270 (
An embodiment of the present invention is illustrated in
a first wall 112 (a wall in the figure) comprising the first area 122 of the wall of the boiler,
a second wall 114 (a wall in the figure) comprising the second area 124 of the wall of the boiler, and
a reaction area 110 for generating gases, such as (a) a furnace 110 for burning material and for forming flue gases, or (b) a gasification phase for oxidizing raw material and for forming synthesis gas, wherein
at least said first wall 112 of the thermal device delimits the flow duct 115 for gases in such a way that a section of the flow duct 115 for gases is left between the first area 122 of the wall of the device 100 and the second area 124 of the wall of the device 100.
In the device according to
Further with reference to
In
In an embodiment, the second section 240 of the heat exchanger pipe extends in a straight line or bends less than 90 degrees, as described above. Advantageously, the second section 240 bends less than 45 degrees, less than 30 degrees, or less than 15 degrees.
In a corresponding manner, in some other embodiments, the second section 240 of the heat exchanger pipe bends at least 90 degrees, at least 45 degrees, at least 30 degrees, or at least 15 degrees.
With reference to
said heat exchanger pipe 200 extends in such a way that the second section 240 extends in the flow duct 115, and
said second section 240 of the heat exchanger pipe has a first longitudinal direction S1 at its first point p1 (
said second section 240 of the heat exchanger pipe has, at all its points p2, a longitudinal direction S2 which is parallel to or forms an angle with a magnitude smaller than said a degrees to the first direction S1 of the second section of said heat exchanger pipe.
In this context, the longitudinal direction of the heat exchanger pipe refers to the longitudinal direction in the flow direction of the heat transfer medium. For example in
For example in
For example in
In the embodiment of
said heat exchanger pipe 200 extends so that the second section 240 of the heat exchanger pipe extends from said first area 122 of the wall of the device to said second area 124 of the wall of the device in such a way that
said second section 240 of the heat exchanger pipe has a central axis having a radius of curvature that indicates, at each point, the direction, or the change in the direction, of the central axis and is at least 25 cm, at least 50 cm, at least 1 m, at least 5 m, and most advantageously at least 10 m.
Thanks to the large radius of curvature, a medium layer 230 is also provided at each point between the outer pipe 220 and the inner pipe 210 when the pipe with a layered structure is bent. Furthermore, such a relatively straight pipe is easier to make self-supporting.
As presented above, with some technical solutions it is possible to arrange the inner pipe 210 inside the outer pipe 220, also when the outer and inner pipes are bent, in such a way that a medium layer sufficient for the heat insulation is left between these pipes.
Consequently, in an embodiment
said heat exchanger pipe 200 extends so that the second section 240 of the heat exchanger pipe extends from said first area 122 of the wall of the device to said second area 124 of the wall of the device in such a way that
said second section 240 of the heat exchanger pipe has a central axis having a radius of curvature that indicates, at each point, the direction, or the change in the direction, of the central axis, and being shorter than 10 m, shorter than 5 m, shorter than 1 m, shorter than 50 cm, or shorter than 25 cm.
In an embodiment, the first area 122 of the wall (such as a wall) of the device is placed on the opposite side of the flow duct 115, with respect to the second area 124 of the wall of the device. In an embodiment, the first wall 112 of the device is opposite to the second wall 114 of the boiler.
In an embodiment, the first area 122 of the wall of the boiler and the second area 124 of the wall of the boiler are parallel to each other, or the angle between the planes parallel to the areas is smaller than 45 degrees, such as smaller than 30 degrees or smaller than 15 degrees. The areas of the walls can also be perpendicular, for example if the first section of the heat exchanger pipe extends between two walls at an angle to each other.
The extension of the second section 240 of the pipe in the flow duct 115 can be represented by one or more of the following:
by the curvature of the second section 240, particularly the angle of curvature (angle α), and
by the radius of curvature of the central axis of the second section 240.
For example, the second section 240 can curve not more than 45 degrees so that the radius of curvature is at least 1 m. In a corresponding manner, the second section 240 can curve more than 45 degrees so that the radius of curvature is shorter than 1 m.
In an advantageous embodiment, as illustrated in
the section 240 of the heat exchanger pipe extends straight from said first area 122 of the wall of the boiler to said second area 124 of the wall of the boiler.
In this embodiment, the section 240 of the heat exchanger pipe has, at all points thereof, a longitudinal direction that is parallel with the first longitudinal direction of said heat exchanger pipe. As presented above, the heat exchanger pipe 200 can bend in the flow duct 215, for example, less than 90 degrees, or according to the radius of curvature, but bending is not technically advantageous in view of the manufacture. In view of the manufacture, it is technically advantageous that the inner pipe 210 can be inserted through the outer pipe 220 in its longitudinal direction. This is possible, for example, when the outer pipe 220 is straight.
As presented above and in
the thermal device 100 comprises insulator 255 adjacent to the first wall 112 and extending from said first area 122 of the wall of the device to the flow duct 115 for gases,
said insulator 255 adjacent to the first wall 112 is arranged to insulate at least the inner pipe 210 of the heat exchanger pipe 200 from the flow duct 115 for gases,
the thermal device 100 comprises insulator 257 adjacent to the second wall 114 and extending from said second area 124 of the wall of the device to the flow duct 115 for gases,
said insulator 257 adjacent to the second wall is arranged to insulate at least the inner pipe 210 of the heat exchanger pipe from the flow duct 115 for gases, and
said second section 240 of the heat exchanger pipe extends from said insulator 255 adjacent to the first wall of the device to said insulator 257 adjacent to the second wall of the device.
Such an insulated structure is illustrated in
It is obvious that the insulator can be alternatively used in connection with only one wall, for example the first wall (not shown in the figure). Thus,
the thermal device 100 comprises insulator 255 adjacent to the wall and extending from said first area 122 of the wall of the device to the flow duct 115 for gases,
said insulator 255 adjacent to the wall is arranged to insulate at least the inner pipe 210 of the heat exchanger pipe from the flow duct 115 for gases, and
said second section 240 of the heat exchanger pipe extends from said insulator 255 adjacent to the wall to said second area 124 of the wall of the device.
Alternatively, it is possible, for example, that
the thermal device 100 comprises insulator 255 adjacent to the wall and extending from said first area 122 of the wall of the device to the flow duct 115 for gases,
said insulator 255 adjacent to the wall is arranged to insulate at least the inner pipe 210 of the heat exchanger pipe from the flow duct 115 for gases,
the inner pipe of the first section of said heat exchanger pipe is non-insulated from the flow duct for gases in one noninsulated area 270 in such a way that
said noninsulated area 270 extends from the second area 124 of the wall of the device to the flow duct 115 for gases, and
said second section 240 of the heat exchanger pipe extends from said insulator 255 adjacent to the wall of the device to said noninsulated area 270.
The length of the noninsulated area 270 is advantageously short, as presented above.
With reference to
Thus, the heat exchanger pipe comprises a thermally insulated section 250, in which section 250 the first section 202 of the pipe can bend even abruptly. In the thermally insulated section 250, the insulator 260 (
said first section 202 of the heat exchanger pipe comprises a thermally insulated section 250 in said flow duct 115 for gases, in which thermally insulated section 250
the inner pipe 210 is not enclosed by the outer pipe, and the inner pipe 210 in said thermally insulated section 250 is thermally insulated by means of a thermal insulator 260 from the gases of the flow duct 115, as shown in
the inner pipe 210 is enclosed by the outer pipe 220, and the outer pipe 220 in said thermally insulated section 250 is thermally insulated by means of the thermal insulator 260 from the gases of the flow duct 115, as shown in
For example ceramics, mortar, or putty can be used as the insulator 255, 257 adjacent to the wall and/or as the insulator 260 in the thermally insulating area 250. The thermal conductivity κ of the insulator (255, 257, 260) is advantageously lower than 75 W/mK (Watts per meter and Kelvin), more advantageously lower than 50 W/mK, or even more advantageously lower than 10 W/mK, the thermal conductivities being given at room temperature 20° C. For example mortar can be used as the insulator. For example in this case the thermal conductivity of the insulator (255, 257, 260) can be lower than 2.5 W/mK. The thermal conductivity of e.g. some ceramics is some dozens of W/mK, for example 60 W/mK for silicon carbide (SiC), 32 W/mK for aluminium oxide (Al2O3), and 20 W/mK for silicon nitride (Si3N4). The thickness t of the insulator (255, 257, 260) is advantageously at least 0.5 mm, more advantageously at least 1 mm, and even more advantageously at least 2 mm. If necessary, the ceramic coating can be thin. Preferably, the coating is thicker when mortar or putty is used. Thus, the outer surface of the heat exchanger pipe can be equipped with protrusions, such as pins, to keep the insulator in place. This can be done particularly when fastening the insulator 255, 257 adjacent to the wall. In this case, the thickness of the insulator can be, for example, 10 to 30 mm. In an embodiment, the insulator 255, 257 adjacent to the wall is fastened to the heat exchanger pipe (outer pipe or inner pipe) by means of protrusions.
The insulator 255, 257, 260, for example gunning or ceramics, can be selected so that the insulator 260 is heat resistant and it provides the desired heat transfer level from the flow duct 115 to the heat exchanger pipe 200. The desired heat transfer level may depend on e.g. the location of the heat exchanger pipe. For example, the thickness and the thermal conductivity can be selected so that the ability to conduct heat (i.e. conductance) of the insulation layer, as determined by the thermal conductivity κ and the thickness t by the formula κ/t, is not higher than 80,000 W/m2K, more advantageously not higher than 30,000 W/m2K, where the thermal conductivity κ is given at room temperature 20° C. Furthermore, the insulator (255, 257, 260) should withstand temperatures corresponding to the operating temperature. Advantageously, the insulator (255, 257, 260) withstands temperatures higher than 900° C., such as higher than 1000° C., without melting or burning; optionally, the insulator does not have to withstand temperatures higher than 1500° C.
With reference to
Advantageously, in such a bending insulating area 250, the heat exchanger pipe 200 does not comprise an outer pipe 220. This is due to the fact that the heat exchanger pipe is normally made of a straight pipe by bending. During the bending, damage, such as microfractures, takes place particularly at the bending point. If no outer pipe 220 is used at the point to be bent, the condition of the bent point of the inner pipe 210 after the bending can be secured more easily than the condition of a structure in which the inner pipe 210 would enclosed by the outer pipe 220.
As can be seen from
at least the inner pipe 210 extends from said first area 122 of the wall to the outside of the flow duct 115 for gases, and
at least the inner pipe 210 extends from said second area 124 of the wall to the outside of the flow duct 115 for gases.
According to
Yet some embodiments are shown in
In the embodiment of
said first wall 112 comprises the first area 122 of the wall of the device, and
the thermal device 100 comprises insulator 255 adjacent to the wall and extending from said first area 122 of the wall of the device to the flow duct 115 for gases,
said second section 240 of the heat exchanger pipe extends from said insulator 255 adjacent to the wall of the device to said thermally insulated section 250, and
said insulator 255 adjacent to the wall is arranged to insulate at least the inner pipe 210 of the heat exchanger pipe from the flow duct 115,
In the embodiment of
said first wall 112 comprises a first area 122 of the wall of the device, and
said second section 240 of the heat exchanger pipe extends from said first area 122 of the wall of the device to said thermally insulated section 250.
In
In the embodiments according to
Preferably, and as shown in
Such a structure has some technical advantages.
Firstly, the medium layer 230 insulates the inner pipe 210 thermally from the outer pipe 220. Thus, there is little transfer of heat from the outside to the inner pipe 210 and further to the heat transfer medium. As a result, heat losses in such a duct take place mostly in the medium layer 230 and not in the inner pipe 210.
Consequently, even if the heat exchanger pipe 200 is placed in an environment (duct 115) in which a very high temperature prevails, wherein the surface temperature of the heat exchanger pipe 200 rises high, the temperature of the inner pipe 210 does not become too high in view of the regulations for designing the material of the inner pipe. In a corresponding manner, if the temperature of the inner surface of the inner pipe 210 is to be raised in order to form a hotter heat transfer medium, the layered structure according to
Secondly, the outer pipe 220 shields the structures inside it, that is, the medium layer 230 and the inner pipe 210, from corrosion and mechanical wear. The outer pipe 220 is advantageously a single piece, wherein the outer pipe effectively shields the medium layer 230 and the inner pipe 210 from mechanical wear. Such a single-piece outer pipe 220 is, for example, weldless. In addition or alternatively, such a single-piece outer pipe 220 is, for example, without holes. Moreover, the outer pipe 220 can shield the insulation layer 230 and the inner pipe 210 over at least the whole length of the flow duct 115 for gases. Consequently, the second section 240 of the duct advantageously comprises a single-piece outer pipe 220 extending over its entire length. Yet more advantageously, such a second section extends over the entire length of the first section 202.
Thirdly, because the surface temperature of the outer pipe 220 is high, as described above, no corrosive substances, such as salts, will condense on its surface. The same also applies to the insulated area 250. Salts condense from flue gases onto heat recovery services when the partial pressures of steam in the flue gas exceeds the pressure of saturated steam. The pressure of saturated steam, in turn, is significantly dependent on the temperature. In a combustion process, salts in steam phase are formed in flue gases in such amounts that condensing takes place, typically for example when the temperature of the heat recovery surface is lower than 500° C., lower than 550° C., or lower than 600° C. In a corresponding manner, condensing does not take place if the surface temperature of the heat recovery surface is higher. Advantageously, during the operation, the temperature of the outer surface of the outer pipe 220 of the heat exchanger pipe 200 is at least 550° C., at least 600° C., or at least 650° C., such as about 670° C. or higher. In a use of the thermal device,
the heat transfer medium is allowed to flow in said inner pipe in such a way that
the temperature of the outer surface of the outer pipe is higher than 600° C. Furthermore, steam is advantageously used as the heat transfer medium.
As for other noninsulated areas 270 in the vicinity of the heat recovery surfaces, it is noted that at lower temperatures, the corrosion problem is reduced for the above described reasons.
Fourthly, the structure makes it possible to use fuels having a higher content of heavy metals or chlorine than usual. As presented above, the temperature of the outer surface of the outer pipe 220 rises high because of the insulation layer 230. Thus, the condensing of heavy metals and/or chlorides (e.g. NaCl, KCl) on the outer surface of the outer pipe 220 is prevented or at least reduced to a very significant extent. Consequently, the boiler 100 can be used even for long times without maintenance even if the contents of heavy metals and/or chlorides in the flue gases were higher than in the flue gases of boilers of prior art. Further, this enables the application of said fuels in the boiler.
Fifthly, even though the presented layered structure of the heat exchanger pipe 200 increases the mass of the heat exchanger pipe 200, the presented structure will carry the mass of the heat exchanger pipe 200, because the second section 240 of the heat exchanger pipe extends in the flow duct 115 for flue gases approximately in the same direction over its whole length, or it does not have abrupt bends, as described above in more detail. If the second section 240 of the pipe twisted in the flow duct 115 for flue gases, the second section 240 of the heat exchanger pipe would subject its supporting structures to a relatively high torque, or the flow duct 115 should be fitted with separate supporting structures. Due to this supporting, the length of the second section 240 is advantageously relatively short, at least when the second section is horizontal, as will be presented further below.
Advantageously, the ducts 210, 220 have a circular cross section. Pipes of this kind are technically easy to manufacture, and furthermore, they are more resistant to pressure than pipes of other shapes.
The inner diameter of the inner pipe 210 can be, for example, 30 to 60 mm, such as 40 to 50 mm, advantageously about 45 mm, such as 42 to 46 mm. The thickness of the shell of the inner pipe can be, for example, 4.5 to 7.1 mm. The thickness of the shell refers to the thickness of the wall of the duct, that is, the half of the difference between the outer diameter and the inner diameter. The inner pipe 210 can comprise for example steel. The inner pipe 210 can comprise for example ferritic or austenitic steel. Advantageously, the inner pipe 210 comprises austenitic steel.
The thickness of the medium layer 230 is advantageously 0.5 to 4 mm, such as 1 to 2 mm. The medium layer may comprise solid, liquid or gaseous medium. The medium layer may comprise at least one of the following: gas (such as flue gas, air, synthesis gas, pyrolysis steam), putty, and ceramics. Advantageously, the medium layer comprises putty, and the thickness of the putty layer is 1 to 2 mm. The putty can be selected, for example, so that the putty is resistant (without burning and/or melting) to temperatures higher than at least 700° C. but possibly not higher than 1000° C.
The inner diameter of the outer pipe 220 is dimensioned according to the outer diameter of the inner pipe 210 and the thickness of the medium layer 230. Because the medium layer 230 can comprise gas, increasing the inner diameter of the outer pipe 220 will increase the thickness of the insulation layer 230 if the outer diameter of the inner pipe 210 is not increased in a corresponding way. The inner diameter of the outer pipe 220 can be, for example, 35 to 70 mm. The thickness of the shell of the outer pipe 220 can be, for example, 4.5 to 7.1 mm. The outer pipe 220 can comprise for example steel. The outer pipe 220 can comprise for example ferritic or austenitic steel. Advantageously, the outer pipe 220 comprises austenitic steel.
Typically, in a thermal device, such as a boiler, the temperature depends on the location, and particularly the height in view from the furnace 110. In
said first section 202 of the heat exchanger pipe is horizontal, or the longitudinal direction of said first section forms an angle smaller than 30 degrees at its every point with the horizontal plane. The angle can also be, for example, smaller than 20 degrees, smaller than 10 degrees, or smaller than 5 degrees. The term “horizontal” refers to a line in the horizontal plane, such as a pipe curved in the horizontal plane, or a horizontal pipe. The term “every point” specifies that the longitudinal direction of the pipe depends on the point of viewing, if the pipe is not straight.
This gives the advantage that the whole outer pipe 220 of the second section 240 of the heat exchanger pipe will be substantially at the same temperature. By the placement of the second section 240 in the height direction it is possible to make sure that the whole outer pipe is at the same, sufficiently high temperature in view of condensing of corrosive substances. When the whole second section 240 of the heat exchanger pipe 200 is placed at substantially the same temperature, it is considerably easier, on one hand, to dimension the structure to enable the production of hot heat transfer medium and, on the other hand, not to exceed or go below the operating temperatures of the materials even locally, than in a situation in which the heat exchanger pipes extended for example vertically (
In an advantageous embodiment, the length of the first section 202 of the heat exchanger pipe 200 is, for example, shorter than 6 m, wherein the first section 202 of the heat exchanger pipe 200 is self-supporting in the horizontal direction as well. Self-supporting refers to a structure which is supported at its ends only. Thus, no separate supporting structures will be needed for the first section 202 of the pipe in the flow duct 115 for flue gases. The heat exchanger pipe 200, particularly the inner pipe 210, is supported to the first and second areas (122, 124), from which the inner pipe is conveyed through the wall or walls. The length of the first section 202 is advantageously not greater than 5 m and more advantageously not greater than 4.5 m. For achieving a sufficient heat transfer capacity, the length of the first section 240 is advantageously at least 1 m, such as at least 2 m, and more advantageously at least 3 m. The length of the first section 240 can be, for example, about 4 m. What has been said here about the length of the first section 202 also applies to the length of the second section 240.
Moreover, in the self-supporting structure, there is no need to support the heat exchanger pipe 200 or its sections in the flow duct 115 for flue gases. In an embodiment, the first section 202 of the heat exchanger pipe extends freely in the flow duct 115. Thus, the first section 202 of the heat exchanger pipe is not supported to the rest of the structure, such as the wall (112, 114) of the thermal device 100, the top of the thermal device 100, another heat exchanger pipe 200, another first section 202b of the same heat exchanger pipe 200, or another second section 240b of the same heat exchanger pipe 200. Such a freely extending structure is technically easier to manufacture than a supported structure. Furthermore, the freely extending structure does not involve supporting structures which would conduct heat to the heat exchanger pipe. Moreover, the presence of supporting structures would make it more difficult to design the suitable operating temperature and to maintain the thermal device.
With the presented solution, it is possible to raise the outer temperature of the outer pipe 220 of the heat exchanger pipe 200 so high that no corrosive substances condense on its surface, such as heavy metals and/or alkali salts, particularly sodium chloride (NaCl) or potassium chloride (KCl). During the operation, the temperature of the outer surface of the pipe 200 is advantageously high, as described above. In a corresponding manner, during the operation, the temperature of the heat transfer medium, such as steam, flowing inside the inner pipe 210, is, for example, at least 500° C., such as at least 530° C., and advantageously at least 540° C. In a use of the thermal device,
the heat transfer medium is allowed to flow in said inner pipe 210,
steam is used as the heat transfer medium, and
the temperature of the heat transfer medium flowing in the inner pipe 210 is at least 500° C., preferably at least 530° C.
In such use, the temperature of the inner pipe 210 is, for example, between 500° C. and 700° C. and advantageously between 500° C. and 600° C.
To achieve these values, some measurements have been presented above. Furthermore, in an embodiment of the thermal device 100, the heat exchanger pipe according to the invention is placed in such a way with respect to the other heat exchanger pipes and flow directions that said temperature values are fulfilled. In some embodiments, said first section of the heat exchanger pipe is placed in a desired temperature zone in the thermal device 100, by selecting a desired height position for said first section 202 of the pipe in the thermal device 100, such as a boiler.
the thermal device 100 comprises several other heat transfer pipes, such as superheaters 154 and 156, inside the walls of the flow duct 115 for gases for recovering heat,
said heat exchanger pipe 200 and said other heat transfer pipes (154, 156) constitute a continuous flow duct for the heat transfer medium, for heating the heat transfer medium, and
said flow duct for the heat transfer medium comprises, as its last heat transfer element placed in the flow duct 115 for gases in the flow direction of the heat transfer medium, a first section 202b of said heat transfer pipe 200. Because the different first sections can be named as desired, such a first section can be said first section 202 (not shown in the Figure).
For example in
Another advantageous height position is also realized in the embodiment of
the thermal device 100 comprises several other heat transfer pipes 152, 156 inside the walls of the flow duct 115 for gases, for recovering heat,
said heat exchanger pipe 200 and said other heat transfer pipes 152, 156 constitute a continuous flow duct for the heat transfer medium, for heating the heat transfer medium, and
said flow duct for the heat transfer medium comprises the last first section 202 of the heat exchanger pipe placed in the flow duct for gases, in the direction of flow of the heat transfer medium, and at least one heat transfer pipe (such as pipe 152 in
said last first section 202 of the heat exchanger pipe is arranged, in the flow direction of the gas flowing outside the outer pipe, upstream of said heat transfer pipes (pipes 152 in
For example, the flow duct for heat transfer medium shown in
In such use, the noninsulated heat transfer pipe downstream of the last first section 202 of the heat exchanger pipe in said medium circulation may be placed, in the flow duct for flue gases, in an area whose temperature is, for example, below 500° C. In addition, when the temperature of the heated medium in said last first section 202 of the heat exchanger pipe is advantageously at least 500° C., no condensing takes place on the surface of the noninsulated pipe. In a use
heat transfer medium is heated to a first temperature in said first section 202 of the heat exchanger pipe placed last in the flow duct for gases, in the direction of the heat transfer medium,
at least one said heat transfer pipe 152 downstream in the flow direction of the heat transfer medium is arranged in an area where a second temperature is prevailing in the flow duct for gases, and
the second temperature is not higher than the first temperature.
Thus, the heat exchanger pipe 200 with a layered structure, particularly the first section 202, 202b of the heat exchanger pipe placed last in the flow duct for gases, is arranged in a hotter place than the other heat transfer pipes. In the first section 202, 202b of the heat exchanger pipe placed last in the flow duct for gases, the heated heat transfer medium is, in such a solution, typically so hot that no significant condensing of corrosive substances will take place on the surface of the heat transfer pipes downstream. If the heat transfer element placed last in the flow duct 115 for gases, in the flow direction of the heat transfer medium, is a structure of the above described kind, the structure comprises no heat transfer pipes on which corrosive substances would condense downstream.
Advantageously, the heat exchanger pipe 200 is arranged close to the point of forming heat. For example in a boiler, the distance between the first section 202 of the heat exchanger pipe 200 with a layered structure, closest to the grate 102 (in the flow direction of flue gases), and the grate 102 can be, on one hand, at least 5 m or at least 10 m, to secure a sufficiently large furnace 110. On the other hand, the distance between a first section 202 of the heat exchanger pipe 200 with a layered structure and the grate 102 can be, for example, not greater than 50 m, not greater than 40 m, or not greater than 35 m, to secure the hotness of the environment of the heat exchanger pipe 200 during the operation. In a corresponding manner, the height of the first section 202 of the heat exchanger pipe 200 in the thermal device 100 above the earth's surface can be, for example, not greater than 50 m, not greater than 40 m, or not greater than 35 m. In a corresponding manner, the height of the first section 202 of the heat exchanger pipe 200 in the thermal device 100 above the earth's surface can be, for example, at least 5 m or at least 10 m.
With reference to
means 300 for feeding an auxiliary agent, for feeding an auxiliary agent for the process, such as an auxiliary agent for the combustion process, for example to the furnace or the process area,
a part of which means 300 for feeding an auxiliary agent is placed in the flow duct 115 for gases, and
said part of the means 300 for feeding an auxiliary agent is placed downstream of the first section 202 or another first section 202 of said heat exchanger pipe 200 in the flow direction of gases.
This gives the advantage that the auxiliary agent is only supplied to the flue gases cooled by the heat exchanger pipe 200, whereby the effect of the auxiliary agents is improved.
The auxiliary agent is preferably liquid, for example an aqueous solution of a reacting agent. The means 300 comprise a pipe or the like for feeding the liquid auxiliary agent to the flow duct 115 for gases, and one or more nozzles 310. Advantageously, the feed means 300 extend through the flow duct 115 over its entire length in one direction, wherein auxiliary agent can be supplied over substantially the entire area of the flow duct in the direction of its cross section.
The auxiliary agent comprises at least one of the following: ammonia (NH3), ammonium ion (NH4+), ferric sulphate (Fe2(SO4)3), ferrous sulphate (FeSO4), aluminium sulphate (Al2(SO4)3) ammonium sulphate ((NH4)2SO4), ammonium hydrogen sulphate ((NH4)HSO4), sulphuric acid (H2SO4), and sulphur (S), as well as aqueous solutions of these. Advantageously, the auxiliary agent comprises ammonia (NH3) or ammonium ions (NH4+). One way of operating the boiler 100 is to use said means for feeding auxiliary agent to supply the boiler with an auxiliary agent that comprises ammonia (NH3) or ammonium ions (NH4+). In a use of the thermal device,
said means for feeding an auxiliary agent are used for supplying the thermal device with an auxiliary agent,
the auxiliary agent comprising at least one of the following: ammonia (NH3), ammonium ion (NH4+), (Fe2(SO4)3), (FeSO4), (Al2(SO4)3), ((NH4)2SO4), ((NH4)HSO4), (H2SO4), and sulphur (S), as well as aqueous solutions of these. In an advantageous embodiment, the auxiliary agent comprises ammonia (NH3) or ammonium ions (NH4+).
Further with reference to
a first heat exchanger comprising said heat exchanger pipe 200 and further several heat exchanger pipes 200 which comprise some inner pipe 210, at least one outer pipe 220 and a medium layer 230 remaining between the outer pipe and a section of an inner pipe,
a second heat exchanger comprising several heat transfer pipes,
the first heat exchanger being arranged upstream of said second heat exchanger in the flow direction of gases,
the second heat exchanger being spaced from the first heat exchanger, wherein a space 350 is left between the second heat exchanger and the first heat exchanger,
part of the means 300 for feeding an auxiliary agent being placed in the flow duct 115 for gases, and
said part of the means 300 for feeding an auxiliary agent being arranged in said space 350.
For example, the second heat exchanger can be arranged in the top of the process area 110 of the thermal device 100, as shown in
Obviously, a part of the pipes of the means for feeding an auxiliary agent is placed outside the boiler. Furthermore, it is obvious that other means for feeding an auxiliary agent can be placed in other parts of the boiler.
With reference to
a first section 202 of said heat exchanger pipe, that is, the first first section 202 of the heat exchanger pipe,
said heat exchanger pipe comprises a second first section 202b extending from one wall (the second wall 114,
the second first section 202b or the inner pipe of said second first section 202b being insulated over its entire length from the flow duct for gases by means of a second outer pipe and/or an insulator, and
said inner pipe 210 connecting said first first section of the heat exchanger pipe to said second first section of the heat exchanger pipe outside said flow duct for gases.
In this way it is easy to guide the inner pipe 210 back to the duct 115, and a separate insulated area 150 is not necessarily needed although the first sections extend straight in the flow duct 115.
It is also possible that the second first section 202b is only insulated over almost its entire length from the flow duct 115, as presented earlier (see alternatives A, A1, A2, and B above). The second first section comprises at least an inner pipe which is, in the above described way, insulated, for at least the most part, from the flow duct 115 for gases. Furthermore, the second first section may, and advantageously does, comprise a second second section where an outer pipe encloses the inner pipe of the second first section.
In
As described above, the first first section 202 comprises the first second section 240. Advantageously, the second first section 202b also comprises a second second section 240b. Furthermore, it would be possible for either of the first sections 202, 202b to comprise several second sections, as shown in
Advantageously, the sections 240, 240b extend straight in the flue gas duct 115. In an embodiment,
said first second section 240 of the heat exchanger pipe extends straight in the flow duct for gases, wherein said first second section 240 extends in a longitudinal direction Sx parallel with the flow direction of the medium flowing in the first pipe,
the heat exchanger pipe comprises a second second section 240b extending straight in the flow duct for gases, wherein said second second section 240b extends in a longitudinal direction −Sx parallel with the flow direction of the medium flowing in the second pipe,
the second longitudinal direction −Sx is opposite to the first longitudinal direction Sx, and
said inner pipe 210 connects said first first section 202 of the heat exchanger pipe to said second first section 202b of the heat exchanger pipe outside said flow duct 115 for gases.
Advantageously, only the inner pipe 210 connects said first first section 202 of the heat exchanger pipe to said second first section 202b of the heat exchanger pipe outside said flow duct 115 for gases, because the structure will thus become simpler. It is naturally possible that also the outer pipe 220 extends outside the flow duct 115. This solution has the advantage that in this way, the heat exchanger pipe 200 or a corresponding heat exchanger can be connected to the water circulation of the device 100 in such a way that the feed and return circulations are on the same side of the boiler, in
a feed circulation 410 of heat transfer medium, for feeding heat transfer medium to the heat exchanger pipe 200, and
a return circulation 420 of heat transfer medium, for returning heat transfer medium from the heat exchanger pipe 200, and
the heat exchanger pipe 200 is connected to the feed circulation 410 and the return circulation 420 on the same side of the first wall 112 of the boiler.
Advantageously, the heat exchanger pipe 200 is used as the last superheater of the boiler 100. Thus, the boiler comprises
means for conveying heat transfer medium from a tertiary superheater 156 to said heat exchanger pipe 200.
At this stage, superheated steam typically acts as the heat transfer medium.
If the thermal device 100 comprises two or more insulated first sections 202 of the above described kind in such a way that at least two sections (202, 202b) of the heat exchanger pipe are spaced in the flow direction of gases, the sections (202, 202b) are advantageously placed downstream in the flow duct for gases; downstream with respect to both the medium and the gases. To put it more precisely, in such a thermal device,
said second first section 202b of the heat exchanger pipe is placed downstream of said first first section 202 of the heat exchanger pipe in the flow direction of the medium flowing in the inner pipe 210, and
said second first section 202b of the heat exchanger pipe is placed downstream of said first first section 202 of the heat exchanger pipe in the flow direction of the gas flowing outside the heat exchanger pipe.
For example, in
In such an arrangement, both sections 202 and 202b are heated more evenly with respect to each other than in an arrangement in which the sections 202, 202b were placed upstream relative to said flows. Said more even heating will reduce thermal stresses caused and will improve durability.
Preferably, the tertiary superheater 156 is also directed downstream, as shown in
During the operation of the thermal device, the heat transfer medium and the flue gas flow in the above described way. At other times, the heat transfer medium and the flue gas in the boiler 100 are arranged to flow in the above described way. The flow direction from the thermal device is obvious for a person skilled in the art. The heat transfer medium flows from the input to the use, such as to power production or to the use of heat. Gases flow from the process area to the use, such as to heat recovery or discharge.
In the embodiment shown in
the wall of the thermal device, such as a boiler, comprises a nose 180, and
said first section 202 of the heat exchanger pipe extends from said nose 180.
In
When the nose 180 comprises said first 122 or second 124 area of the wall of the device, the span of the first section 202 (or 202b) of the heat exchanger pipe 200 becomes shorter, because the nose 180 extends from the wall of the boiler towards the flow duct 115 for gases. In this way, the nose forms a protrusion in the wall, extending into the flow duct for gases. The nose makes the flow duct for gases narrower. The shorter span stabilizes the structure of the heat exchanger pipes 200. Above, advantageous lengths were presented for the first section 202 and the second section 240 of the heat exchanger pipe 200, the length corresponding to said span.
The wall 112 of the boiler shown in
In the embodiment shown in
the first 122 or second 124 area of the wall of the thermal device 100 comprises a housing 450,
which housing 450 protrudes from the wall of the thermal device, for example from the first 112 or second 114 wall, outwards from said flow duct 115 for gases, the housing 450 comprising a through hole for conveying said inner pipe 210, 210a to 210e out from the reaction area 110 of the thermal device 110, such as from a furnace 110 of a boiler or from the flow duct 115 for gases, and
Preferably, the outer pipe 220 is tightly fastened to the inner surface of the housing 450 so that the flue gases of the flue gas duct 115 cannot contact the insulation layer 230 or the inner pipe 210. The outer pipe can be, for example, welded to the housing 450.
The housing 450 can also be applied in the embodiments shown in FIGS. 1b and 1c. Thus,
the insulator 255 adjacent to the wall extends from the inner surface of the housing 450 to the flow duct 115 for gases, for shielding the inner pipe of the heat exchanger pipe.
Furthermore, as shown in
When the housing 450 protrudes from the wall of the boiler in the above described way, the flow of gases in the housing 450 is very slow compared with the flow in the flow duct 115 for gases. Thus, very little corrosive condensation takes place in the housing. Firstly, because the flow is very slow, the amount of gas from which condensation can take place, is reduced. Thus, the condensing is reduced as well. Secondly, because heat is recovered from the gases in the housing, too, the gas in the housing will cool down to a lower temperature than the gas flowing in the flow duct 115. In such colder ranges, corrosion is slow, as described above.
Furthermore, the temperature in the housing 450 increases from the edge area towards the flow duct 115. In the embodiment with the housing, the temperature of the outer pipe 220 increases over a clearly greater length of travel than in a situation in which there is no such protruding housing. The greater length of travel, in turn, means a lower temperature gradient, which increases the service life compared with an embodiment without said housing. To reduce corrosion and to sufficiently reduce the temperature gradient, the depth L of the housing (
Advantageously, at least one of the walls of the housing 450 does not comprise the heat exchanger pipe 510, to maintain a high temperature of the housing. This will further reduce said temperature difference. For technical reasons relating to the construction, one heat transfer pipe 510′ which in the normal design would extend in the wall 112, can be moved aside, out of the way for the housing 450 and the heat exchanger pipes 200 (210, 220). Advantageously, as shown in
The presented housing 450 can also be applied in connection with such a heat exchanger pipe which does not comprise the outer pipe at all but only the first, at least partly insulated part. The presented housing 450 can also be applied in connection with a heat exchanger pipe that does not comprise a substantially straight outer pipe. Such a thermal device comprises
at least a first wall delimiting a flow duct for gases, and
a heat exchanger pipe comprising at least an inner pipe, at least the first section of said heat exchanger pipe being placed in said flow duct for gases and extending, in said flow duct from gases, from said first wall to said first wall or another wall delimiting the flow duct for gases, in such a way that
(A)
the inner pipe 210 of the first section 202 of said heat exchanger pipe is, in some parts, insulated from the flow duct 115 for gases by means of said outer pipe 220 and/or an insulator 260, and
the inner pipe 210 of the first section 202 of said heat exchanger pipe is noninsulated from the flow duct 115 for gases in one or more noninsulated areas 270 (
(A1)
the length of even the largest noninsulated area 270 of the first section 202 does not exceed 15 cm; advantageously, the length of even the largest noninsulated area 270 of the first section 202 does not exceed 10 cm, the length being measured in the longitudinal direction of the inner pipe; or
(A2)
the distance from all the noninsulated areas 270 of the first section 202 to all the other heat recovery surfaces of the thermal device (other than the heat exchanger pipe 200 itself) is not greater than 15 cm, advantageously not greater than 10 cm; or
(B)
the first section of said heat exchanger pipe or the inner pipe of the first section of said heat exchanger pipe is insulated over its entire length from the flow duct for gases by means of an outer pipe and/or an insulator.
Furthermore,
the wall of the thermal device comprises a housing,
the housing protruding outwards from the wall of the thermal device, seen from the flow duct for gases,
the housing comprising a through hole for conveying said inner pipe out of the process area of the thermal device or from the flow duct for gases.
Said outer pipe can be connected to the inner surface of the housing. Insulator adjacent to the wall may extend from the inner surface of the housing to the flow duct for gases, for shielding the inner pipe of the heat exchanger pipe.
For example
at least one wall 452 of said housing 450 forms at least two bends 455, wherein
said wall 452 of the housing 450 constitutes a flexible structure in the housing 450, arranged to receive the thermal expansion of the thermal device 100, such as the boiler 100 and the heat exchanger pipe 200.
Further,
at least one wall 452 of said housing 450 forms at least one fold 460 which deviates from the line of the wall of the housing 450, wherein
said fold 460 constitutes a flexible structure in the housing 450, arranged to receive the thermal expansion of the thermal device, such as the boiler 100 and the heat exchanger pipe 200. The fold 460 converts the housing 450 into bellows, i.e. a tubular structure that becomes shorter and longer when pressed and pulled, respectively. The length of such a bellows-like housing 450 is arranged to change by the effect of thermal stresses.
The line of the wall of the housing 450 refers to a plane that is best fitted to the shape of the wall of the housing (with a fold). When the wall of the housing comprises a fold 460, it comprises at least three bends 455 (not shown with reference numerals in
In
Above, receiving the thermal expansion of the thermal device 100 and the heat exchanger pipe 200 refers to the fact that even if the heat exchanger pipe 200 and the thermal device 100 (such as a boiler, for example a boiler wall) expand to a different extent due to the different operating temperatures and/or different heat expansion coefficients of the thermal device 100 and the heat exchanger pipe 200, no significant thermal stresses are formed in the structure because the structure is flexible, i.e. receives the thermal expansion. In such a structure, at least part of the wall 452 of the housing 450 is arranged to bend as a result of thermal stresses. When the wall 452 of the housing comprises a bend, as a result of thermal expansion the bend is straightened out or curved more, which requires considerably smaller stresses than, for example, expanding or compressing the straight wall of the housing 450 in the direction of the wall of the housing.
The heat exchanger pipe (such as the pipe 200) extends from the first wall 112 to the opposite wall 114 of the boiler. In
A housing 450a is provided in the first area 122 for conveying inner pipes 220, such as the inner pipe 210f, from the outside of the flow duct 115 for flue gases to the flow duct 115. Furthermore, on the side of the flow duct 115, the inner pipes are provided inside the outer pipes 220, such as the outer pipes 220a,f and 220b,f, as presented above. In a corresponding manner, a second housing 450b is provided in the second area 124, for conveying the inner pipe 210 out from the side of the flow duct 115 into the nose 180. The second housing 450b comprises two folds 460b for receiving thermal expansion.
In
The embodiment of
a pyrolysis reactor,
a gasification reactor, or
a boiler, such as a fluidized bed boiler, for example a bubbling fluidized bed boiler or a circulating fluidized bed boiler; preferably a bubbling fluidized bed boiler.
In addition to the thermal device, a method has been presented above for heating a heat transfer medium. The method comprises:
producing gas heated by the thermal device 100,
conveying said gas to a flow duct 115 for gases,
introducing heat transfer medium to a heat exchanger pipe 200, at least a first section 202 of said heat exchanger pipe being placed in the flow duct 115 for gases and extending, in said flow duct 115 for gases, from the wall (112, 114) of said flow duct to the same (112, 114) or another (114, 112) wall of said flow duct 115, said first section 202 of the heat exchanger pipe comprising a second section 240 of the heat exchanger pipe, extending in said flow duct 115 for gases, and
recovering heat into the heat transfer medium by means of said heat exchanger pipe 200.
In the method, the heat exchanger pipe 200 used for recovering heat is such that said second section 240 of the heat exchanger pipe 200 comprises
at least part of an inner pipe 210 for transferring heat transfer medium from the first end to the second end of the part of the inner pipe, and for recovering heat by the heat transfer medium,
an outer pipe 220 radially enclosing said part of the inner pipe 210, and
a medium layer 230 placed between said outer pipe and said part of the inner pipe in the radial direction, and
(A)
the inner pipe 210 of the first section 202 of said heat exchanger pipe is, in some parts, insulated from the flow duct 115 for gases by means of said outer pipe 220 and/or an insulator 260, and
the inner pipe 210 of the first section 202 of said heat exchanger pipe is noninsulated from the flow duct 115 for gases in one or more noninsulated areas 270 (
(A1)
the length of even the largest noninsulated area 270 does not exceed 15 cm; advantageously, the length of even the largest noninsulated area 270 does not exceed 10 cm; the length being measured in the longitudinal direction of the inner pipe; or
(A2)
the distance from all the points of the noninsulated areas 270 to the other heat recovery surfaces of the device (other than the heat exchanger pipe 200 itself) is not greater than 15 cm, advantageously not greater than 10 cm; or
(B)
the first section 202 of said heat exchanger pipe 200, or the inner pipe 210 of the first section 202 of said heat exchanger pipe 200 is, over its entire length, insulated from the flow duct 115 for gases by means of said outer pipe 240 and/or an insulator 260.
In an advantageous embodiment of the method, the thermal device comprises several other heat transfer pipes inside the walls of the flow duct for gases, for recovering heat. Said heat exchanger pipe and said other heat transfer pipes constitute a continuous flow duct for the heat transfer medium, for heating the heat transfer medium.
In such an embodiment,
(C,i)
said flow duct for heat transfer medium comprises a first section of said heat exchanger pipe as the heat transfer element placed last in the flow duct for gases in the flow direction of the heat transfer medium, or
(C,ii)
said flow duct for the heat transfer medium comprises the first section of the heat exchanger pipe placed last in the flow duct for gases, in the flow direction of the heat transfer medium, and at least one heat transfer pipe placed downstream in the subsequent flow duct for gases, in the direction of flow of the heat transfer medium, and
said first section of the heat exchanger pipe placed last is arranged, in the flow direction of the gas flowing outside the outer pipe, upstream of said heat transfer pipes placed downstream in the flow duct for gases in the flow direction of the heat transfer medium.
In an advantageous embodiment of the method, said second section 240 of the heat exchanger pipe extends in a straight line or bends less than 90 degrees.
In an embodiment of the method, said second section 240 of the heat exchanger pipe bends at least 90 degrees.
Features of the method relating to temperatures have been presented above in connection with the use of the device. Features of the method relating to the supply of auxiliary agent have been presented above in connection with the use of the device. Technical features of structures used in the method have been presented above as features of the thermal device.
Number | Date | Country | Kind |
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20136013 | Oct 2013 | FI | national |
Filing Document | Filing Date | Country | Kind |
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PCT/FI2014/050736 | 9/29/2014 | WO | 00 |
Publishing Document | Publishing Date | Country | Kind |
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WO2015/052372 | 4/16/2015 | WO | A |
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Number | Date | Country | |
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20160258692 A1 | Sep 2016 | US |