Technical Field
-
The invention concerns a boiler, especially a biomass-burning boiler, particularly a boiler for burning whole bales of biomass and containing a combustion chamber and at least one heat exchanger.
State of the Art
-
At the present time, there exists a whole series of biomass-burning devices as well as a whole series of biomass-burning methods. Such devices also include boilers burning whole bales of straw. Such devices can be divided into those with a device dosing the straw from the bale before it is loaded in the combustion space and those enabling whole bales of straw to be loaded in the combustion space.
-
The above-described devices can also include a device intended for burning mass of plant origin described in Patent Document
CS 228635 . The device consists of a pressing chamber connected to a storage bunker for bulk fuel. The pressing chamber is provided with a pressing worm placed on a hollow shaft. The chamber is connected to an air intake and mouthed into the combustion chamber along with the pressing chamber outlet. One major disadvantage of this device is the fact that the pressing worm facilitates loading the mass that consists of small particles but it does not facilitate loading e.g. whole bales of straw.
-
Patent Application
CZ PV 2001-1178 describes a method of burning biomass compressed into large-volume bales and a device facilitating this method of burning. This method lies in the fact that a longitudinally placed bale is conveyed, using a horizontal conveyer, from a storage bunker into a tilting bridge tilted into the horizontal plane. Then the bridge is tilted into the vertical plane and the sliding arm of the bridge holds the bottom face of the bale. Then, a charging chamber moves above the tilted bridge, the sliding arm of the bridge shifts the held bale vertically upwards into the charging chamber where inside-mounted grips of its vertical conveyer grip the inserted bale. The charging chamber with the gripped bale then moves above the vertical burning shaft of the combustion chamber and lowers the gripped bale vertically into the burning shaft of the combustion chamber where the bottom face of the bale touches down on the aerating mechanism. The device using this method consists of a charging line and of a combustion boiler provided with an aerating mechanism and connected with a heat exchanger. A disadvantage of this device is its big size, complexity and expensiveness.
-
Another device that can burn whole bales of straw is known from Utility Design
CZ 16473 . This device is provided with a waste-gas exhaust fan and waste-gas pipe. The combustion chamber is walled with a partition wall and a back wall and is located inside a shell consisting of a left wall on the ground surface, of a right wall and a ceiling. Further, the respective fore-chamber is marked off with an openable front wall and a partition wall, with a left wall, right wall and a ceiling. Its back wall covers the whole height of the shell and stretches up to the ceiling under which the back wall is provided with holes for waste gases. The partition wall is shortened at its bottom and provided with one or more pipes connected (under the partition wall) to the right and left walls with a clearance. Further, a travelling grate is located above the ground surface in the inclination from the openable front wall to the back wall. The travelling grate partly protrudes into the combustion chamber, and between the upper surface of the travelling grate and the lowest pipe is a gap for feeding straw into the combustion chamber. The fore-chamber space is closed with the travelling grate at its bottom part but the combustion chamber is, at its bottom part, marked off with the travelling grate only behind the partition wall. The ground surface is provided with an ash pan located at the back wall and with a waste-gas flue behind the hole for waste gases.
-
Another method of burning bales of straw is known from Patent
CZ 303224 . This patent describes burning bales of biomass in a boiler with controlled intake of combustion air into the combustion chamber using a blower or a waste-gas exhaust fan. The air is blown into the combustion chamber with at least one nozzle whose position can be changed in the vertical plane. The combustion air is, for the whole burning time, blown tangentially to the upper surface of the burning bale and the waste gases are exhausted in the sense of the air blown inside. The boiler is provided with at least one nozzle for the intake of the combustion air which points away from the wall of its combustion chamber in the level of the upper surface of the bale. The nozzle is rotatable around its horizontal axis and the exhaust hole is located in the place opposite to the nozzle. A disadvantage of this boiler is the fact that the mechanism of the primary air intake is rather complicated while the advantages arising out of this design do not enhance the general utility value of the boiler as a whole.
-
Utility design
CZ 17061 describes a biomass- and coal-burning combustion chamber additionally provided with a device for feeding whole bales of straw into the combustion chamber and with a screw conveyer to remove ash and other non-combustible particles out of the chamber. The combustion chamber is divided into the first and second combustion spaces between the travelling grate at the bottom, the ceiling at the top, the front and the back walls and the left-side and right-side walls. These walls consist of water-cooled pipes and the ceiling is, behind the bending, a continuation of the front wall, its ceiling pipes lead upwards at an angle towards the back wall and are connected to the upper chamber of the back wall, and the front wall is provided with an opening for feeding bales of straw under which the travelling grate is located in the inclination from the front wall towards the back wall and behind the travelling grate, the first chamber of the inclined wall is connected to the back wall which consists of pipes and ceramic materials. These pipes lead upwards at an angle, are connected to the second chamber and the chamber is (with vertical pipes) connected to the ceiling pipes. Further, load-bearing pipes with gaps between them are connected to the bottom side of the second chamber and to the front wall and these pipes bear two ceramic blocks which are placed on their top and which cover the whole width of the combustion chamber, thus forming a passage hole between the first combustion space below the inclined wall and the ceramic blocks and the second combustion space above the ceramic blocks and the inclined wall. The hole is provided with a first ceramic partition wall placed behind the vertical pipes in the direction of the back wall and connected to the ceiling. This partition wall leads vertically downwards towards the inclined wall and protrudes into the second combustion space. Another ceramic partition wall is placed closer to the back wall. It leads from the inclined wall vertically upwards in such a manner that its upper edge ends closely below the lower edge of the first ceramic partition wall thus forming a waste-gases flue between the second ceramic wall and the back wall. The waste-gas flue is connected to the waste-gas hole in the back wall. A disadvantage of this design is the fact that it does not contain any accessory device for dosing individual bales of straw.
-
Patent
DK 621286 describes a method of burning whole bales of straw through controlled burning along with the respective device. This method is based on burning whole bales of straw without any previous division. A bale of straw burns from one of its ends and the burning process is continual. This is attained by feeding individual bales of straw into the combustion chamber, one after another, using a hydraulic piston. The output of the boiler depends on the speed at which the piston pushes the bales of straw into the combustion chamber. The design of this boiler is, again, relatively complicated and therefore expensive.
-
It is obvious from the above that the existing state of the art brings a series of disadvantages, the most important one being the relative complexity of the designs of boilers that have so far been described. Moreover, in spite of the complexity of the design there is no radical enhancement of the general utility value of the boiler as a whole. Another disadvantage of most boilers that are known so far is their big size.
-
The goal of this invention is a simple and inexpensive design of a boiler that will facilitate effective burning of whole bales of straw, corn and grass while following all the emission limits providing always that the dosing of these masses will consist in the single filling of the combustion chamber.
Principle of the Invention
-
The aforementioned weaknesses are, to a large extent, eliminated and the goals of the invention accomplished by a boiler, especially a biomass-burning boiler consisting of a combustion chamber and at least one heat exchanger, especially a boiler burning whole bales of biomass based on the invention the nature of which lies in the fact that the combustion chamber consists of a waste-gas flue arranged in its top part and that the waste-gas inlet into the waste-gas flue is arranged on the side of the combustion chamber opposite to the side on which at least one intake of combustion air is arranged. This design extends the path of the waste gases in such a manner that the rest of them finishes burning in the waste-gas flue at the latest which increases effectiveness of the whole boiler and considerably decreases the volume of harmful waste gases exhausted.
-
In the most advantageous design, the waste-gas flue is marked off with the heat- resistant arch and the ceiling of the combustion chamber on the understanding that the heat-resistant arch is made of sheet metal which minimizes its size. The design of this arrangement is simple. It is also advantageous in view of the extended path of the waste gases and in view of more perfect after-combustion of the waste gases before they enter the heat exchanger which increases effectiveness of the boiler.
-
It is advantageous if the intake of the combustion air is connected to the source of the combustion air which is ideally connected to the combustion chamber with a pipe provided with a distributor connected to a primary-air pipe and a secondary-air pipe. The distributor distributes the stream of the combustion air into a primary-air stream and a secondary-air stream before it enters the combustion chamber.
-
The primary-air pipe is advantageously connected with at least one primary-air nozzle arranged in the fixed horizontal plane at the bottom level of the rear side of the combustion chamber, while the secondary-air pipe is connected with at least one secondary-air nozzle arranged in the fixed horizontal plane below the heat-resistant arch in the top level of the rear side of the combustion chamber. The combustion air flows, depending on the volume of O2 in the waste gases, either into the primary-air nozzle or into the secondary-air nozzle. Ideally, the primary-air pipe is provided with a primary-air-control flap and the secondary-air pipe with a secondary-air-control flap. By controlling these two-way flaps, effective burning with low waste-gas emissions is ensured.
-
The combustion chamber is provided with a door arranged in the whole of its section. The door is mostly arranged in the front side of the combustion chamber. This enables the designers to minimize the overall dimensions of the boiler and, at the same time, to maximize the size of the fuel supplied (mostly a bale of straw) which is advantageously inserted all at one go. This is advantageous because no big and expensive dividing device or a complicated dosing device (as those known from the Existing State of the Art) is necessary. Another advantage of this boiler is its inexpensive, simple and easy-to-operate design. The door arranged in the whole section of the boiler which opens sideward enable operator to insert the whole cylindrical bale of straw into the boiler.
-
The combustion chamber is, advantageously, cylinder-shaped and is completely cooled, ideally with water. This design is the most advantageous in view of cutting the respective production costs and in view of good burning of culm plants where a lower burning temperature is necessary if compared to wood burning. The design is even simpler and the whole boiler even cheaper if the door of the combustion chamber is circular and uncooled. In addition to that, it is advantageous if at least part of the combustion chamber is provided with a heat-resistant insulation material which ensures the optimal temperature in the combustion chamber.
-
Further, the boiler is advantageously provided with a waste-gas extraction fan to ensure controlled draught for the whole burning period.
-
The boiler according to this invention has an advantageous boiler-size-to-fuel-size ratio on the understanding that the fuel is mostly a cylinder-shaped bale of straw or hay. The boiler does not require any other specials devices (such as devices for preparation and division of large compressed bales of biomass) for its operation. The overall design of the boiler is simple and cheap and its requirements for the installation space are minimal.
Overview of the Figures
-
The invention will be better clarified on the drawing on which Fig. 1 shows a lateral view of the biomass-burning boiler with a partial sectional view, Fig. 2 shows a front view of the biomass-burning boiler, Fig. 3 depicts a lateral view of the biomass-burning boiler with the heat exchanger placed above the combustion chamber, and Fig. 4 represents a lateral view of the biomass-burning boiler with the heat exchanger placed next to the combustion chamber.
Examples of the Performance of the Invention
-
The boiler for burning whole bales 20 of biomass - straw (Fig. 1, Fig. 2) consists of a combustion chamber 1 and a heat exchanger 2.
-
Front side 17 of the combustion chamber 1 is provided with a door 15 which is arranged in the whole of its section.
-
In the top part of the combustion chamber 1 is a waste-gas flue 3 which is marked off with the sheet-metal heat-resistant arch 6 and the ceiling 19 of the combustion chamber 1.
-
The inlet 24 of waste gases into the waste-gas flue 3 is arranged on the side of the combustion chamber 1 which is opposite to the side with the intakes 25 supplying the combustion chamber 1 with combustion air.
-
The combustion air intakes 25 which include the primary-air nozzles 14 and the secondary-air nozzles 23 are connected by pipes 26 with the source 13 of the combustion air. Before entering the combustion chamber 1, the combustion air is divided into two streams - the primary-air stream and the secondary-air stream. For that reason, the pipe 26 is provided with a distributor 27. The pipe then forks into the primary-air pipe 28 and the secondary-air pipe 29. A ventilator fan is used as the combustion-air source 13.
-
The primary-air pipe 28 is connected to the primary-air nozzles 14 which are arranged in the fixed horizontal plane in the bottom level of the rear side 18 of the combustion chamber 1. The primary-air pipe 28 is provided with a driven primary-air-control flap 21.
-
The secondary-air pipe 29 is connected to the secondary-air nozzles 23 which are arranged in the fixed horizontal plane below the heat-resistant arch 6 in the top level of the rear side 18 of the combustion chamber 1. The secondary-air pipe 29 is provided with a driven secondary-air- control flap 22.
-
The heat exchanger 2 is a horizontal fire-tube exchanger. It is placed (Fig. 3) above the top section of the combustion chamber 1, has two draught passages 8, 10 and is connected through a reversing chamber 7 with the combustion chamber 1. The reversing chamber 7 is connected with the waste-gas flue 3. The heat exchanger 2 is provided with a waste-gas exhaust fan 12.
-
The heat exchanger 2 can also be placed next to the combustion chamber 1 (Fig. 4).
-
The combustion chamber 1 is cylindrical and is provided with a circular uncooled door 15. The entire combustion chamber 1 is water-cooled.
-
The wall of the rear side 18 of the combustion chamber 1 is covered with a heat-resistant insulation material 5 or with a refractory lining. The ceiling 19 of the combustion chamber 1 is covered with a heat-resistant insulation material 4 or with a refractory lining.
-
The middle level of the rear side 18 is provided with an ignition door 16.
-
The boiler is further provided with a control thermostat (not shown) which decreases the output of the boiler in case the preset water temperature has been attained. The boiler is further provided with a temperature limiter (not shown) and with a safety valve (not shown) to prevent overheating and exceeding maximum pressure.
-
The boiler for burning whole bales 20 of biomass works as follows: First, a whole bale 20 of straw (it is advantageous if the bale is cylinder-shaped) is inserted into the boiler. Then the door 15 and the combustion chamber 1 are closed. At the same time, the source 13 of the combustion air is started-up and the bale 20 of straw is lighted through the ignition door 16.
-
Waste gases from the combustion chamber 1 come out through the waste-gas flue 3 via the first reversing chamber 7 into the first draught passage 8 of the heat exchanger 2 and then, via the second reversing chamber 9, into the second draught passage 10 of the heat exchanger 2 from which they are exhausted by the waste-gas exhaust fan 12 via the waste-gas outlet 11 into the chimney (not shown). The source 13 of the combustion air changes its speed during the burning process depending on the volume of O2 in the waste gases. The waste-gas exhaust fan 12 at the waste-gas outlet 11 thus maintains constant negative pressure in the combustion chamber 1.
-
When the bale 20 of straw is burning out, the door 15 to the combustion chamber 1 is opened and another bale 20 of straw is inserted into the combustion chamber 1 which is usually lighted by the previous burning-out bale 20. Then the whole burning process repeats itself.
-
In case of need, the ash from the combustion chamber 1 is removed manually through the door 15 using an ash scraper and put in an ashbin (not shown).
Industrial Application
-
The boiler according to this invention can be used for burning biomass, especially if the biomass is in the form of bales, especially if the biomass is in the form of big cylinder-shaped bales of straw or hay.
