US20120227728A1

US20120227728A1 - Burner for boiler using biomass solid fuel

Info

Publication number: US20120227728A1
Application number: US13/509,233
Authority: US
Inventors: Kyo Ung Kim
Original assignee: INTER BIO Co
Current assignee: INTER BIO Co
Priority date: 2009-11-11
Filing date: 2010-11-10
Publication date: 2012-09-13
Also published as: WO2011059230A3; CN102686945A; WO2011059230A2; EP2505916A2

Abstract

The present invention relates to a burner for a boiler using solid fuel such as wood pellets or the like, which are in the spotlight as biomass energy, and realizes a new combustion type, wherein fuel is transported using a screw circulating water inside and burnt in a predetermined section supplied with air (oxygen) by a blower. Therefore, it is possible to secure the durability of the screw even at the high temperature generated during the combustion, and complete simultaneous treatment of sludge and ashes. In addition, it is possible to largely reduce the size of the boiler using solid fuels, thereby simplifying the entire structure of the boiler, while promoting the reduction of manufacturing cost.

Description

TECHNICAL FIELD

The present invention relates to a burner for a biomass solid fuel boiler, and more particularly, to a burner for a boiler using solid fuel, such as wood pellets, which is being spotlighted as biomass energy.
The present invention relates to a biomass solid fuel boiler burner adapted to realize a new type of combustion, i.e. combustion occurs in a specific area, into which air (oxygen) is supplied by a blower, while fuel is being fed by a screw, inside which water circulates, thereby guaranteeing durability of the screw against the high temperature caused by combustion, completely processing sludge and ash, simplifying the overall boiler structure (e.g. substantially reducing the size of the boiler using solid fuel), and reducing manufacturing costs.
In addition, the present invention relates to a biomass solid fuel boiler burner including a screw formed as a hollow pipe inside the combustion chamber of the boiler to discharge sludge and ash, a circulation fan or a compressor adapted to circulate a fluid inside the hollow portion of the screw, and a cooler positioned outside the combustion chamber to cool the circulating fluid (gaseous air, liquid refrigerant, etc.) so that the fluid lowers the high temperature inside the combustion chamber, thereby improving operations and functions for efficient processing of sludge and ash while guaranteeing durability of the screw inside the combustion chamber against the high temperature caused by combustion.

BACKGROUND ART

Recent global warming and resulting climate change are regarded as a serious threat to the survival of mankind, and such recognition is followed by growing interest in renewable energy and soaring investment to replace existing fossil fuels.
In this connection, there is vigorous research on boilers using biomass solid fuel, other than conventional boilers using coal.
Biomass solid fuel typically refers to a type of renewable energy extracted from energy-dedicated crops and trees, agricultural products and fodder crops, farm wastes and leftovers, etc.
Use of such biomass solid fuel is advantageous not only because energy is self-sustained, but also because environment contamination is reduced substantially.
Current boiler combustion types for using biomass solid fuel include a movable grate type, which is conventionally employed when coal is used as a fuel, and which is based on conveyor belt or chain driving, a burner type commonly employed to burn wood pellets, a crucible type, a dish type, etc.
However, conventional boiler combustion types have the following problems.
The movable grate type, which is based on a conveyor belt (chain), etc., has a complicated mechanical structure, which increases the manufacturing cost. And the fact that a large space is occupied below the boiler makes it difficult to manufacture a high-efficiency boiler (burner). Therefore, this type is not suitable for small-sized boilers (e.g. domestic boilers).
The burner type and crucible type, which are commonly employed to burn wood pellets, have problems related to processing of sludge and ash, which are generated in a large amount when low-quality pellets are burnt. This is one of fundamental reasons of malfunctioning of boilers. The burner structure of these types makes it impractical to manufacture medium and large-sized boiler burners for commercial and industrial purposes.

DISCLOSURE

Technical Problem

In order to develop a burner for burning solid fuel capable of automatically discharging ash, which is an unavoidable byproduct of complete combustion of solid fuel, and sludge, which is generated when alien substances and impurities included in the solid fuel are burnt at a high temperature and intermingled with the ash, there could be found usefulness by using a spring-type screw to feed fuel at a low rate, completely burn it as it goes through a combustion area, and automatically transfer resulting ash and sludge to the outlet. However, application of this type has a fundamental problem in that conventional screw material, e.g. iron or stainless steel, cannot endure high-temperature flames occurring in the combustion area, only to be deformed or melt down.
Therefore, the present invention has been made in view of the above-mentioned problems, and an aspect of the present invention is to provide a biomass solid fuel burner and a boiler burner adapted to realize a new type of combustion, i.e. combustion occurs in a specific area, into which air is supplied by a blower, while fuel is being fed by a screw, inside which water circulates, thereby guaranteeing durability of the screw against the high-temperature flames caused by combustion, accurately controlling the amount of combustion by adjusting the rotation and feed rates of the screw, completely processing sludge and ash generated by combustion, simplifying the overall boiler structure (e.g. substantially reducing the size of the boiler combustion chamber), and reducing manufacturing costs.
Another aspect of the present invention is to improve durability of the screw by using a refrigerant (e.g. gas or liquid) injected separately, not using water existing in the piping of the boiler, as the fluid circulating inside the screw, thereby lowering the temperature of the screw, which is inside the high-temperature combustion chamber, sufficiently.
Another aspect of the present invention is to improve durability of the screw, which is adapted to discharge sludge and ash from the boiler combustion chamber, by lowering the temperature of the screw more efficiently using a cooler adapted to separately cool the high-temperature fluid, which circulates inside the screw, outside the boiler combustion chamber.

Technical Solution

In accordance with an aspect of the present invention, there is provided a biomass solid fuel boiler including a fuel supplier adapted to supply solid fuel; a combustion device adapted to burn the solid fuel; and a boiler body adapted to heat water using combustion heat, wherein the combustion device includes a combustion chamber having a solid fuel supply hole on a front side and a sludge/ash discharge hole on a rear side, the solid fuel being burnt in the combustion chamber; a screw arranged along and in parallel with the interior of the combustion chamber and installed so as to rotate, the screw including a hollow pipe, inside which water circulates so that the screw can endure high temperature inside the combustion chamber, the screw being adapted to both feed the solid fuel and discharge sludge and ash through a rotating operation; a driver installed on a front portion of the combustion chamber to rotate the screw; and an igniter installed on a lateral portion of the combustion chamber to ignite the solid fuel. This construction improves fuel efficiency and effectively processes sludge and ash.
The biomass solid fuel boiler preferably further includes a blowing device installed below the combustion chamber to inject air necessary for combustion into the combustion chamber. The screw is preferably wound in the shape of a spring having straight portions on both ends adapted to act as fulcrums during rotation. Alternatively, the screw is preferably connected to a boiler water tube to receive water in the boiler water tube forcibly circulated by a circulation pump.
The screw may be adapted so that its size can be adjusted based on boiler capacity, and a plurality of screws can be arranged in parallel and used.
Besides the construction of connecting the screw to the water tube of the boiler to circulate water, it is also possible to employ fluid (gas or liquid refrigerant), which can be cooled by an external cooler, and use a separate compressor or a fan.

Advantageous Effects

The biomass solid fuel boiler according to the present invention has the following advantages:
The circulation pump forcibly circulates water inside the screw, which is adapted to feed solid fuel during combustion and discharge sludge and ash, so that the screw can endure high-temperature combustion conditions. This guarantees perfect processing of sludge and ash, which is a problem of solid fuel boilers, and enables complete combustion. The fact that the overall boiler structure, specifically structure of the burner, can be simplified makes the present invention applicable to domestic small-sized boilers. Furthermore, adjustment of the size of the screw, inside which water circulates, and possibility of multi-rowed arrangement structure make the present invention applicable to large-capacity boilers, such as industrial large-sized boilers and cogeneration plants.
In addition, durability of the screw is improved by using a refrigerant (e.g. gas or liquid) injected separately, not using water existing in the piping of the boiler, as the fluid circulating inside the screw, thereby lowering the temperature of the screw, which is inside the high-temperature combustion chamber, sufficiently.
Furthermore, durability of the screw, which is adapted to discharge sludge and ash from the boiler combustion chamber, is improved by lowering the temperature of the screw more efficiently using a cooler adapted to separately cool the high-temperature fluid, which circulates inside the screw, outside the boiler combustion chamber.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view illustrating the overall shape of a biomass solid fuel boiler according to an embodiment of the present invention;

FIGS. 2 and 3 are perspective views illustrating a combustion device of a biomass solid fuel boiler according to an embodiment of the present invention;

FIG. 4 is a perspective view illustrating a screw of a combustion device of a biomass solid fuel boiler according to an embodiment of the present invention;

FIG. 5 illustrates a schematic operating condition of a biomass solid fuel boiler according to an embodiment of the present invention;

FIG. 6 illustrates fluid circulation inside a screw of a biomass solid fuel boiler according to another embodiment of the present invention;

FIG. 7 illustrates fluid circulation operation in a screw of a biomass solid fuel boiler according to another embodiment of the present invention; and

FIG. 8 illustrates a schematic operating condition of a biomass solid fuel boiler according to another embodiment of the present invention.

MODE FOR CARRYING OUT THE INVENTION

Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.
FIG. 1 is a perspective view illustrating the overall shape of a burner for a biomass solid fuel boiler according to an embodiment of the present invention.
As shown in FIG. 1, a boiler body 12 is provided as a means for heating water, which flows through internal piping, using combustion heat obtained by burning biomass solid fuel; a combustion device 11 is installed below the boiler body 12 as a means for burning solid fuel; and a fuel supplier 10 is installed in front of the boiler body 12 and the combustion device 11 as a means for supplying solid fuel.
The fuel supplier 10 may be any means capable of supplying biomass fuel, such as wood pellets, in a predetermined size condition continuously or periodically in a controlled manner (a spring screw is commonly used), detailed description thereof being omitted herein. The boiler body 12 is adapted to heat water inside the piping through heat exchange with combustion heat in a conventional manner, detailed description thereof being omitted herein.
Reference numeral 20 refers to a fuel supply tube, which is connected to a solid fuel feeder (not shown) in front of the combustion device 11, so that solid fuel is fed into the inner front area of the combustion device 11.
FIGS. 2 and 3 are perspective and sectional views of a combustion device of a biomass solid fuel boiler according to an embodiment of the present invention.
As shown in FIGS. 2 and 3, the combustion device 11 is structured to use a screw 16 of a special type, which has excellent durability against the high-temperature condition inside the combustion chamber 15, to both feed solid fuel and efficiently process sludge and ash generated during combustion.
To this end, a combustion chamber 15 is provided as an elongated housing installed along and in parallel with the lower portion of the boiler body 12, and a screw 16 is installed in parallel inside the combustion chamber 15 to substantially feed solid fuel and discharge sludge and ash.
A solid fuel supply hole 13 is formed on the front portion of the combustion chamber 15 so that solid fuel can be introduced through it, and a sludge/ash discharge hole 14 is formed on the rear portion so that sludge and ash, which are generated after combustion, are naturally discharged and processed by the operation of the screw 16.
Specifically, as shown in FIG. 4, the screw 16 consists of a hollow pipe, inside which water circulates. The overall shape of the screw 16 is as follows: it has straight portions 16 a on both ends, and is wound in the shape of a spring 16 b so as to push solid fuel or sludge and ash towards one side.
Such construction of the screw 16, inside which water flows, enables the screw to endure any high temperature occurring during combustion, meaning that it can fulfill the role of feeding solid fuel and discharging sludge and ash without being deformed or burnt down by heat.
The screw 16 is supported on the front and rear wall surfaces of the combustion chamber 15 via bearings, for example, using the straight portions on both ends, respectively, so that the screw 16 rotates, as a driver 17 is actuated, and pushes solid fuel, sludge, and ash towards one side.
The driver 17 includes a motor 21, a belt 22, and pulleys 23. The motor 21 is installed on one side of a frame 24. The pulleys 23 are installed on a shaft of the motor 21 and on a straight portion of the screw 16, which extends to the outside through the front portion of the combustion chamber 15, respectively. The belt 22 is installed to connect between the two pulleys 23.
As a result, actuation of the motor 21 is transmitted via the pulleys 23 and the belt 22 to the screw 16, which then rotates around a center axis defined by the straight portions on both ends.
Those skilled in the art can understand that, besides the pulley/belt transmission type, the driver 17 can adopt any other transmission type, such as chain transmission, gear transmission, motor direct-connection transmission, etc.
As the water circulating inside the screw 16, water inside the boiler water tube may be used.
For example, the front and rear straight portions of the screw 16 are provided with valves 25, respectively, and are connected to piping 26 (e.g. hose) extending from the boiler water tube through a coupler (not shown), so that water forcibly circulated by a boiler-side circulation pump (not shown) can also circulate inside the screw 16.
The screw 16 can be arranged in various numbers and configurations depending on the boiler capacity.
For example, in the case of a small-sized boiler (e.g. domestic boiler), a single row of small screw may be arranged and used. In the case of a large-sized boiler (e.g. industrial boiler), a large screw or multiple rows of a plurality of screws may be arranged in parallel and used.
That is, boilers of various capacities can be obtained by properly setting the screw size, the number of screws, the capacity of the blowing device (described later), etc.
The combustion device 11 is provided with a blowing device 19 to help efficient complete combustion of solid fuel.
The blowing device 19 includes a blowing fan, etc., and is installed in a predetermined position below the combustion chamber 15, preferably on an introduction portion into which solid fuel is introduced, to supply an adequate amount of wind necessary for combustion into the combustion chamber 15, thereby guaranteeing more efficient solid fuel combustion.
An igniter 18 is installed in a lateral area of the combustion chamber 15, e.g. next to the introduction portion into which solid fuel is introduced, to enable initial ignition of solid fuel during boiler operation.
The igniter 18 may be an ignition means used for a conventional solid fuel boiler (electric ignition rod, electric heat wind ignition, etc.).
The operating condition of the biomass solid fuel boiler, which has the above-mentioned construction, will now be described.
FIG. 5 illustrates a schematic operating condition of the biomass solid fuel boiler according to an embodiment of the present invention.
As shown in FIG. 5, in order to activate the boiler, biomass solid fuel (e.g. wood pellets) is introduced into the combustion chamber 15 of the combustion device 11 from the fuel supply tube 20 of the fuel supplier 10 through the solid fuel supply hole 13 of the combustion chamber 15. The following ignition by the igniter 18 starts combustion of the solid fuel, and following injection of air by the blowing device 19 results in the main phase of combustion of the solid fuel.
The heat exchange action of combustion heat, which is generated by intense combustion of the solid fuel, heats water flowing through the boiler's internal piping and thus provides hot water and steam as needed.
A suitable amount of solid fuel is continuously or periodically supplied into the combustion chamber 15 of the combustion device 11 (the amount of supplied fuel can be controlled using a fuel introduction screw), and the concurrent slow rotation of the screw 16, which is driven by the driver 17, feeds the solid fuel to the combustion area (area into which air is injected by the blower) to be burnt therein.
Water flows inside the screw 16, and the cooling action of water flowing inside the screw 16 guarantees that the screw 16 can endure the high-temperature environment inside the combustion chamber 15 without being deformed. When the water has passed through the hollow pipe and then the combustion area, the water, in a high-temperature condition, is introduced into a water tube inside the boiler, in the case of a hot-water boiler. In the case of a steam boiler, the water is transferred to a condensation water tank and fed into the boiler at a high temperature to be recycled. This prevents the minimum heat loss that would otherwise occur due to the cooling action of the screw inside the combustion chamber.
In addition, sludge or ash, which is generated by combustion of the solid fuel, is repeatedly pushed back by rotation of the screw 16, and is eventually discharged to the outside through the sludge/ash discharge hole 14, which is on the end of the combustion chamber 15, to be processed.
That is, the rotation action of the screw 16 simultaneously feeds solid fuel and discharges sludge and ash.
As such, the present invention employs a screw, which has a special shape and a cooling type, and substantially improves problems of conventional solid fuel boiler burner structures, i.e. excessive manufacturing cost, bulky combustion furnace, difficulty in processing sludge and ash, etc.
Furthermore, use of the screw provided by the present invention makes it possible to manufacture a boiler capable of properly using various types of fuel, which has a predetermined particle size or less, including not only wood pellets, which are being spotlighted as biomass energy, but also wood chips, farm byproducts, livestock excretion pellets, etc.
In addition, adjustment of the size and number (e.g. parallel arrangement) of the type of screw provided by the present invention makes it possible to manufacture a remarkable solid fuel boiler burner, which is applicable not only to a domestic small-sized boiler, but also to an industrial large-sized boiler or a cogeneration plant.
Other embodiments of the present invention will now be described in detail with reference to the accompanying drawings.
FIG. 6 illustrates fluid circulation inside a screw of a biomass solid fuel boiler according to another embodiment of the present invention, FIG. 7 illustrates fluid circulation operation in a screw of a biomass solid fuel boiler according to another embodiment of the present invention, and FIG. 8 illustrates a schematic operating condition of a biomass solid fuel boiler according to another embodiment of the present invention.
The fluid circulating inside the screw 16 is not used as water inside the boiler water tube, unlike the above-described embodiment of the present invention. That is, according to another embodiment of the present invention, it is preferable to use a separate gas or liquid refrigerant, for example, which is introduced from the outside.
According to the above-described embodiment of the present invention, gas, liquid, or water in the boiler piping flows inside the screw 16 as a fluid (refrigerant), so that the cooling action of the fluid flowing inside the screw 16 enables the screw 16 to endure the high-temperature environment inside the combustion chamber 15 without being deformed.
The above-mentioned construction, as has been explained, directly introduces water, which exists in the boiler piping, into the hollow pipe-shaped screw 16, to seek a cooling effect. However, the water existing in the boiler piping is not a low-temperature fluid, and the cooling effect is insufficient when high-temperature water is reintroduced into the screw 16 with no separate cooling means.
Therefore, the present invention does not use the water, which exists inside the boiler, for the hollow pipe-shaped screw 16, but injects a separate fluid (e.g. gas or liquid), which acts as a refrigerant, from the outside to lessen the high temperature inside the combustion chamber and enable the screw to fulfill its role.
Thus, as shown in FIG. 6, the present invention may include, in order for a separate fluid to circulate, fluid circulation piping 28, a circulation fan or a compressor 30, a fluid injection/discharge hole 31, an injection/discharge valve 32, and a cooler 33.
The present invention, as shown in FIGS. 6 and 7, includes a fluid injection/discharge hole 31 for injecting a fluid into the fluid circulation piping 28 from outside the combustion chamber or discharging the fluid from it. Thus, a fluid circulating inside the screw 16 is injected into a separate fluid injection/discharge hole 31, and, when the lifetime of the fluid is over or when it needs to be replaced, the fluid is discharged through the fluid injection/discharge hole 31, thereby guaranteeing that it fulfills the role of lowering the high temperature.
The fluid injection/discharge hole 31 is typically opened/closed by the injection/discharge valve 32, as shown in FIGS. 6 and 7, to adjust the injection/discharge of the fluid.
The fluid circulation piping 28 is, as shown in FIG. 7, connected to both ends of the screw 16 so that the fluid is circulated to the outside of the boiler's combustion chamber, and the circulated fluid is cooled outside the boiler.
The fluid circulation piping 28 includes a circulation fan or a compressor 30, which is adapted to push the fluid into the hollow pipe-shaped screw 16, to introduce the fluid into the hollow pipe-shaped screw inside the combustion chamber.
The high-temperature fluid, which is circulated from the screw 16 through the fluid circulation piping 28, is cooled down by a cooler 33, which is adapted to cool the fluid outside the combustion chamber, and is re-circulated into the screw 16. This improves durability of the screw 16 while it is enabled to operate in the high-temperature combustion chamber.
The circulation fan or compressor 30, as shown in FIGS. 6 and 7, is adapted to push the fluid into the hollow pipe-shaped screw 16, and is installed on the fluid circulation piping 28.
Typically, the fluid circulating inside the hollow portion of the screw 16 may be gas functioning as refrigerant, or a liquid-state refrigerant. When the circulating fluid is gas, the circulation fan or compressor may consist of a blowing fan or a compressor, for example; and, when the circulating fluid is liquid (e.g. refrigerant), it may consist of a compressor or a screw fan, for example.
The cooler 33, as shown in FIG. 8, exists outside the combustion chamber of the boiler to cool down the fluid, the temperature of which has increased in the screw 16 of the combustion chamber, and re-circulate the fluid to the screw 16. That is, the high-temperature fluid, which has passed through the screw 16, is cooled down outside the combustion chamber to lower the temperature of the fluid, which is to circulate to the combustion chamber, and improve durability inside the high-temperature combustion chamber.
In this case, when the fluid circulating through the screw 16 and the fluid circulation piping 28 is water existing in the piping of the boiler, no separate cooler can be installed on the piping of the boiler. Therefore, a cooler 33 is installed, while the fluid circulation piping 28 is separately circulated outside the boiler, to lower the temperature of the fluid and fulfill its function.
The present invention has been illustrated and described with regard to specific preferred embodiments. However, the present invention is not limited to the above-described embodiments, and those skilled in the technical field of the present invention is capable of any variation, modification, or implementation without departing from the principles of technical ideas of the present invention disclosed in the accompanying claims.

Claims

1. A biomass solid fuel boiler comprising:

a fuel supplier (10) adapted to supply solid fuel;

a combustion device (11) adapted to burn the solid fuel; and

a boiler body (12) adapted to heat water using combustion heat, wherein

the combustion device (11) comprises:

a combustion chamber (15) having a solid fuel supply hole (13) on a front side and a sludge/ash discharge hole (14) on a rear side, the solid fuel being burnt in the combustion chamber (15);

a screw (16) arranged along and in parallel with the interior of the combustion chamber (15) and installed so as to rotate, the screw (16) comprising a hollow pipe, inside which water circulates so that the screw (16) can endure high temperature inside the combustion chamber, the screw (16) being adapted to both feed the solid fuel and discharge sludge and ash through a rotating operation;

a driver (17) installed on a front portion of the combustion chamber (15) to rotate the screw (16); and

an igniter (18) installed on a lateral portion of the combustion chamber (15) to ignite the solid fuel.

2. The biomass solid fuel boiler as claimed in claim 1, further comprising a blowing device (19) installed below the combustion chamber (15) to inject air necessary for combustion into the combustion chamber (15).

3. The biomass solid fuel boiler as claimed in claim 1, wherein the screw (16) is wound in the shape of a spring having straight portions on both ends adapted to act as fulcrums during rotation.

4. The biomass solid fuel boiler as claimed in claim 1, wherein the screw (16) is connected to a boiler water tube to receive water in the boiler water tube forcibly circulated by a circulation pump.

5. The biomass solid fuel boiler as claimed in claim 1, wherein the screw (16) is adapted so that its size can be adjusted based on boiler capacity, and a plurality of screws (16) can be arranged in parallel and used.

6. A biomass solid fuel boiler comprising:

a fuel supplier (10) adapted to supply solid fuel;

a combustion device (11) adapted to burn the solid fuel; and

a boiler body (12) adapted to heat water using combustion heat, wherein

the combustion device (11) comprises:

a screw (16) arranged along and in parallel with the interior of the combustion chamber (15) and installed so as to rotate, the screw (16) comprising a hollow pipe, inside which fluid circulates to lower temperature inside the combustion chamber so that the screw (16) can endure high temperature, the screw (16) being adapted to both feed the solid fuel and discharge sludge and ash through a rotating operation;

an igniter (18) installed on a lateral portion of the combustion chamber (15) to ignite the solid fuel, and

the boiler comprises a circulation fan or a compressor (30) adapted to push fluid into the hollow pipe-shaped screw (16) so that the fluid is introduced into the hollow pipe-shaped screw inside the combustion chamber.

7. The biomass solid fuel boiler as claimed in claim 6, further comprising a circulation fan or a compressor (30) adapted to push fluid into the hollow pipe-shaped screw (16) so that the fluid is introduced into the hollow pipe-shaped screw inside the combustion chamber.

8. The biomass solid fuel boiler as claimed in claim 7, further comprising:

fluid circulation piping (28) connected to both ends of the screw (16) so that the fluid circulates outside the combustion chamber; and

a cooler (33) adapted to cool the high-temperature fluid, which has passed through the screw (16), outside the combustion chamber, so that durability inside the high-temperature combustion chamber is improved by lowering the temperature of the fluid circulated to the combustion chamber.

9. The biomass solid fuel boiler as claimed in claim 8, further comprising a fluid injection/discharge hole (31) adapted to enable injection of a fluid into the fluid circulation piping (28) from outside the combustion chamber or discharge of the fluid.

10. The biomass solid fuel boiler as claimed in claim 7, wherein the fluid circulating inside the hollow portion of the screw (16) comprises gas.

11. The biomass solid fuel boiler as claimed in claim 7, wherein the fluid circulating inside the hollow portion of the screw (16) comprises a liquid-state refrigerant.

12. The biomass solid fuel boiler as claimed in claim 11, wherein the circulation fan or compressor adapted to push the fluid into the screw (16) is a compressor or a screw fan adapted to circulate liquid.