EP1396678A2

EP1396678A2 - Combustion equipment for combustible material

Info

Publication number: EP1396678A2
Application number: EP03102690A
Authority: EP
Inventors: Timo Alastalo
Original assignee: PTI-Metalli Oy
Current assignee: PTI-Metalli Oy
Priority date: 2002-09-04
Filing date: 2003-09-03
Publication date: 2004-03-10
Also published as: FI20021574A0; FI114411B; FI20021574L; EP1396678A3

Abstract

The invention relates to combustion equipment for combustible material, which combustion equipment includes a heating boiler (1) and a firebox in it (1.1). The combustion equipment also includes means for feeding the material to the heating boiler (1), and fans (4, 3) for feeding primary and secondary air to the heating boiler (1), in order to burn the material in the firebox (1.1). The equipment includes a briquetting machine (7.1) for forming the combustible material into briquets and a briquet-transfer pipe (7) connected to it, which is arranged to open into the firebox (1.1) thus forming a combustion zone. A larger blast pipe (8) arranged at a distance around the briquet-transfer pipe (7), for feeding primary air to the briquet.

Description

The present invention relates to combustion equipment for combustible material, which combustion equipment includes

a heating boiler and a firebox in it,
means for feeding the material to the heating boiler, and
fans for feeding primary and secondary air to the heating boiler, in order to burn the material in the firebox.

Few heating boilers suitable for the combustion of briquets, pellets, or other similar solid fuels have been developed and manufactured. The aforesaid fuels have been burned in heating boilers designed for the combustion of oil, wood-chips, and sawdust, in the fireboxes of which various types of auxiliary devices, such as pellet burners, stokers, or similar previously known equipment technologies, have been installed. In these boiler plants, the feed of the fuel and particularly of the combustion air has been implemented unsatisfactorily. In addition, the combustion of loose material, such as sawdust and wood-chips is problematic, due to the formation of dust and of the danger of explosions.

The following operating problems have been found to exist in known combustion equipment burning briquets:

The brittle briquets fracture in an uncontrolled way during transportation, storage, and in feed systems, creating fine-particle material, which drops unburned beneath the grates, or travels as carbon particles along with the combustion gas flow to the combustion gas equipment and partly also through the chimney to the environment.
It is difficult to adjust the amount of briquet fuel according to the required output, as it is nearly impossible to feed the cylindrical briquets to form an even layer on the grates, particularly in small boilers.
The thermal value of the dry biomass (moisture content 5 - 15 %) in a tightly pressed briquet is more than three times that of, for example, free-length wood-chips, making it difficult to implement control of the combustion temperature in a conventional grate boiler plant.
In a grate boiler plant, it is difficult to handle light, fine-particle ash in such a way as to prevent it forming dust and spreading outside the combustion equipment.
The temperature of the ash of dry fuel easily becomes too high, causing the ash to sinter, i.e. to form large lumps, which are difficult to remove using a conveyor.

The invention is intended to create a new type of combustion equipment for combustible material, by means of which the drawbacks of the prior art can be eliminated. The characteristic feature of the present invention are stated in the accompanying Claims. According to the invention, the combustible material is briquetted using a briquetting machine, which is connected to the heating boiler using a briquet-transfer pipe. The briquetting machine is used to feed a suitable amount of fuel to the firebox of the heating boiler, steplessly in direct proportion to the heating output. At the same time, the combustion waste is removed from the combustion equipment along the briquet-transfer pipe, in the form of waste briquets. The material to be burned is transferred in the tight briquet-transfer pipe until it begins to heat up. After this, the material is permitted to expand while a regulated amount of primary air (gasification air) is blown into it, causing carbon monoxide and other flammable gases to be discharged in the direction of the combustion zone.

In one form of the combustion equipment according to the invention, at the actual combustion zone secondary air is blown, in the first stage, over all of the briquet from all directions through holes made in the pipe and, in the second stage, into the flames above the aforesaid pipe. In addition, the material to be burned is wetted, for example with water, at the terminal end of the briquet-transfer pipe, so that the material will expand as desired, allowing the gasification air to be able to push into and through the material.

In one combustion equipment according to the invention, all the feed and combustion devices, and their adjustment and control devices (operating devices) are located on a combustion base. The combustion base can thus be tested and test operated as such and the actual heating boiler can be lifted on top of the ready-to-operate combustion base, once the basic tests have been made. The intention is thus to control and regulate and circulate both the combustion airs and the heat-recovery air (HR air) in such a way that the temperatures of the structures of the combustion base will be sufficiently high, but that excessive temperatures do not arise.

Small alterations to the said combustion base will allow it to be used to manufacture grill charcoal. The briquet-transfer pipe, the gasification air blast pipe, and the pre-heater pipe, which are set inside each other, are arranged in such a way that the pyrolysis gases are removed from the fuel, but the carbonaceous material (i.e. wood charcoal) remains unburned. The grill charcoal is thus pushed out of the combustion base by the material. The combustion equipment can also be used to make briquets, by not gasifying the material, or by guiding the material to the side before the combustion zone.

By means of the pipes fitted inside each other according to the invention, the gasification process can be regulated in such a way that the desired amount of pyrolysis gases can be separated by heating the fuel. The pyrolysis gases can be lead either to a separate heating boiler for burning, or else a heating boiler unit, specifically suitable for the combustion of clean pyrolysis gas, can be installed on top of the combustion base. The tight briquet-transfer pipe for the material to be burned terminates before the combustion zone, so that the primary air blast pipe, which is larger than the briquet-transfer pipe, will permit the material to expand and the gasification process to succeed. A secondary air perforated pipe, the area of effect of which forms the actual combustion zone, is fitted in the gasification zone as an extension of the primary air blast pipe. The pyrolysis gases discharge into the combustion zone from the primary air blast pipe, the secondary air perforated pipe, and through a discharge frame, as well as tertiary air from the sloping side walls of the flame cone of the base, through the tertiary air blast cones. According to the invention, the amount, direction, and temperature of all of the separate combustion airs can be adjusted using common control logic. In addition, just before the gasification stage the moisture content of the material to be burned is made suitable by spraying with a liquid, for example water, through a wetting pipe into the material to be burned.

A sufficient number of circulation baffles are fitted to the casing structures of the outer jacket and partition walls of the combustion base, by means of which the tertiary air is circulated and preheated to a suitable temperature. Thus an adjustable amount of tertiary air discharges through the tertiary-air blast channels and cones to the flame cone of the base and from there to the boiler firebox. The remainder of the tertiary air is passed through a bypass duct past a damper to the smoke duct of the boiler.

The following advantages are achieved with the aid of the combustion equipment according to the invention:

fine-particle fuel is not formed during the transportation, storage, or feed stages, because the briquetting machine compresses the material directly along the briquet-transfer pipe to the boiler firebox to be burned.
The amount of fuel can be regulated steplessly, in such a way as to be directly proportional to the heating output requirement.
The high thermal value of a briquet is not a drawback, because it can be controllably gasified and burned, by regulating steplessly the amount and temperature of the fuel and combustion air and the oxygen content of the combustion gases.
The fuel is gasified and completely burned in the briquet-transfer pipe, at the latest in the rear part of the combustion zone, after which the combustion waste is transferred in the closed part of the same pipe and compressed to form waste briquets and drops out of the combustion equipment. Thus the combustion waste, such as fine-particle ash, cannot at any stage form dust outside the equipment, or in the environment.
By adjusting the amount of air flowing around the briquet-transfer pipe, the temperature of the ash can be kept below the sintering temperature.

In the following, the invention is examined in greater detail with reference to the accompanying drawings, which depict some embodiments of the invention, in which

Figure 1: shows a cross-section, along the centre-line, of the combustion base according to the invention and the heating boiler raised on top of it (cross-section A - A of Figure 2),
Figure 2: shows a cross-section of the combustion base, along the centre-line of the combustion pipes (cross-section B - B of Figure 1),
Figure 3: shows a vertical cross-section of the combustion base and the heating boiler (cross-section C - C of Figure 1),
Figure 4: shows a control and operating diagram of the combustion equipment,
Figure 5: shows a schematic cross-section of the combustion base, with additionally a control and operating diagram of the amount and temperature of the tertiary air,
Figure 6: shows a top view of the combustion base, level D - D of Figure 7 (the arrows show the direction of flow of the tertiary air),
Figure 7: shows a cross-section along the centre-line of the combustion base, without the combustion pipes (cross-section A - A of Figure 6),
Figure 8a: shows a cross-section of the combustion base (cross-section E - E of Figure 6),
Figure 8b: shows a cross-section of the combustion base (cross-section F - F of Figure 6),
Figure 9: shows a detail drawing of the tertiary-air blast duct and the blast cone control member (cross-section C - C of Figure 1),
Figure 10: shows another embodiment of the combustion equipment according to the invention with the addition of a control and operating diagram,
Figure 11: shows a cross-section of the heating boiler of the combustion equipment of Figure 10.

Hereinafter, the feed pipe for the combustible material to be burned will be referred to by the term briquet-transfer pipe 7. The same type of combustion equipment can of course be used to transfer and burn, for example, pellets and other similar solid fuels. In addition, particularly the combustion of loose material, such as sawdust and wood-chips, is controlled, as the material is briquetted prior to being fed to the heating boiler.

Figure 1 shows one combustion equipment according to the invention, which includes pre-heating and combustion piping comprising four pipes set inside each other. The entire combustion equipment is shown in Figure 4. With the aid of a separate press apparatus, briquetting machine 7.1, or similar, the material to be burned is pushed at a regulated speed along the briquet-transfer pipe 7 to the combustion base 2 of the heating boiler 1. The briquet-transfer pipe 7 terminates before the combustion zone and a primary-air blast pipe 8, which is larger than the briquet-transfer pipe 7 and through which a regulated amount of primary air is fed to the gasification zone, is fitted around it. Once the narrow briquet-transfer pipe 7 ends, the material to be burned is able to expand. In the end part (gasification zone) of the blast pipe 8, the primary air is then able to penetrate through the billet of fuel, forming carbon monoxide and other flammable gases, which discharge at the actual combustion zone into the flame cone 24 (Figures 1 and 3) of the base.

In addition, a secondary-air blast pipe 9, which is larger than the primary-air blast pipe 8, is fitted around the latter. A regulated amount of preheated secondary air is fed through the secondary-air blast pipe 9, to the flame cone 24 of the base, through the holes of the perforated pipe 12 and the openings remaining in the upper edge of the discharge frame 21. By adjusting the gap between the discharge frame 21 and the secondary-air blast pipe 9, the ratio between the aforementioned amounts of air can be altered (Figure 9). The dimensioning of the pipes is such as to achieve an adequate expansion of the material in the gasification stage, as well as a sufficient flow of air to the combustion zone.

After the perforated secondary-air pipe 12 of the actual combustion zone, an ash-transfer pipe 13 and a combustion-ash transfer screw 14 attached to its outer circumference, and which can be rotated by the drive wheel 15 of the ash-transfer pipe, are fitted, thus moving combustion waste, which may remain in the secondary-air blast pipe 9, through the combustion-ash drop opening 16, to the lower part of the base 2. The fly ash collecting in the lower part of the combustion base 2 is moved outside the base 2, by means of a fly-ash transfer screw, a transfer-screw drive device 18, and a fly-ash discharge screw 19 in the lower combustion base 2.

According to the invention, tertiary-air circulation baffles are fitted to the casing structures of the outer jacket and partitions of the combustion base 2 (Figures 5 - 9). The lower flat level 34.1 circulates the tertiary air to the rear part of the base 2 and from the opening there it moves above the flat level 34.1 and from there to the front end of the base 2, from where is moves, from an opening in the flat level 34.2, to the next air space. Air circulation is also arranged into the intermediate casings of the combustion base, through small openings (not shown). After the final flat level 34.3, adjustable amounts of preheated tertiary air are able to discharge, through both the tertiary-air blast ducts 25 and the blast cones 25.1, to the flame cone 24 of the base, and through the tertiary-air bypass duct 31, through the smoke duct 35 of the heating boiler 1 to the chimney, or alternatively to the combustion-gas heat exchanger. In the tertiary-air blast channels 25, there are openings at the jacket of the combustion base 2, from which the tertiary-air can flow, through the blast ducts 25 and blast cones 25.1, to the firebox of the boiler. According to the invention, the rate of flow and discharge direction of the tertiary-air can be regulated using the discharge-rate damper 26, a regulator rod 27 that moves in the direction of the cone, and a regulator rod moving member 30, which can be moved manually, hydraulically, or in some other similar manner. The centred movement of the discharge-rate damper 26 can be ensured by means of centring shafts 28 and regulator rod attachment flanges 29.

The combustion regulation method according to the invention includes wetting of the material to be burned by water, or by some other liquid, which can be regulated by dosing. The temperature of the firebox 1.1 of the heating boiler 1 can be stabilized, in such a way that a temperature transmitter 2.1 gives an impulse to the firebox temperature regulator 2.2, which uses a wetting-water regulator valve 2.3 to direct an adjustable amount of moisture into the material being burned, through a wetting-pipe connection 11 (Figure 4). The wetting water is fed, just before the discharge of the material into the wider primary-air blast pipe 8. By regulating the moisture content of the fuel, the temperature of the heating boiler's firebox is kept within the set values.

According to the invention, the amount of primary air (gasified combustion air) is regulated according to the required heating output. The temperature of the input water of the heating boiler 1 is stabilized according to the set value of a PI regulator 3.2 at the temperature transmitter 3.1. This is achieved by using a frequency converter 33 to adjust the speed of rotation of the electric motor 3.4 of the primary-air fan 4. The electric motor 3.4 is controlled in such a way that an amount of air corresponding to the heating output requirement is provided in the primary-air blast pipe 8 of the gasification zone of the material to be burned.

In addition, according to the invention, the secondary air is preheated to a temperature according to a set value. The temperature of the combustion air entering the secondary-air blast pipe 9 is stabilized according to the set value of a temperature regulator at the temperature transmitter 5.1. This is achieved by using the operating device 5.3 of the HR duct damper 23 to allow the requisite amount of bypass flow from the lower part of the base 2 of the heating boiler 1 to the convection part of the heating boiler 1, and from there through the smoke duct 35 to the chimney.

Further, according to the invention, the tertiary air is preheated and its amount and temperature are regulated. The temperature of the combustion air entering the tertiary-air blast duct 25 is stability according to the set value of the temperature regulator 6.2 at the temperature transmitter 6.1. This is achieved by using a frequency converter 6.3 to regulate the rotation speed of the electric motor 6.4 of the tertiary-air fan 5 so as to hold the temperature of the tertiary air within the set values. The amount of tertiary air is regulated in such a way that the oxygen content, at the oxygen sensor 7.1, of the combustion gases of the heating boiler 1 is stabilized according to the set value of the combustion-gas analyser 7.2. This is achieved by using the PI regulator of the gas analyser to regulate the operating device 7.3 of the tertiary-air damper, so as to use the amount of the bypass flow to provide a suitable amount of tertiary air going to the firebox of the boiler.

Figures 10 and 11 show another embodiment of the combustion equipment according to the invention. In this case, the combustion piping is installed inside the heating boiler 1.1. In the first embodiment shown, the heating boiler is set on top of a special combustion base. The same reference numbers are used for operationally similar components. In the embodiment of Figure 11, there are three pipes inside each other, the innermost of which is a briquet-transfer pipe 7 according to the invention. The briquet-transfer pipe 7 extends through the heating boiler and has a discharge frame 21, which opens into the combustion zone of the firebox 1.1. After the discharge frame, the combustion waste is pushed by the material in the briquet-transfer pipe 7 and exits from the combustion equipment, in the form of waste briquets. The primary air between the two outer pipes 8 and 8.1 is preheated and guided into the middle primary-air blast pipe 8 at the front of the heating boiler, from which the primary air meets the material in the gasification zone. The flows of air and combustion gases are shown by arrows in Figure 11.

COMPONENTS LIST

1.: Heating boiler
1.1: Firebox
2.: Base of heating boiler
3.: Secondary-air fan
4.: Primary-air fan
5.: Tertiary-air fan
6.: Preheating-air HR duct
7.: Briquet-transfer pipe
7.1: Briquetting machine
8.: Primary-air blast pipe
8.1: Primary-air pre-heater pipe
9.: Secondary-air blast pipe
10.: Secondary-air pre-heater pipe
11.: Wetting-pipe connection
12.: Secondary-air perforated pipe
13.: Ash-transfer pipe
14.: Combustion-ash transfer screw
15.: Ash-transfer pipe drive wheel
16.: Combustion-ash drop opening
17.: Fly-ash transfer screw
18.: Fly-ash transfer screw operating device
19.: Fly-ash discharge screw
20.: Pyrolysis-gas discharge frame
21.: Secondary-air discharge frame
22.: Boiler-base masonry liner
23.: HR-duct damper
24.: Base flame cone
25.: Tertiary-air blast duct
25.1: Tertiary-air blast cone
26.: Discharge-rate damper
27.: Discharge-rate regulator rod
28.: Centring axles
29.: Regulator rod attachment flanges
30.: Regulator rod movement member
31.: Tertiary-air bypass duct
32.: By-pass duct damper
33.: Boiler firebox pressure damper
34.1-3: Tertiary-air circulation baffles
35.: Combustion-gas duct
36.: Ash-briquet holder
36.1: Ash-briquet conveyor
36.2: Ash-briquet container
37.: Primary-air blast duct
1.1: Input-water temperature transmitter No. 1
1.2: Input-water temperature PI regulator No. 1
1.3: Briquetting machine frequency converter
1.4: Briquetting machine electric motor
2.1: Firebox temperature transmitter
2.2: Firebox temperature regulator
2.3: Wetting water regulator valve
3.1: Input-water temperature transmitter No. 2
3.2: Input-water temperature PI regulator No. 2
3.3: Primary-air fan frequency converter
3.4: Primary-air fan electric motor
4.1: Combustion-gas oxygen sensor
4.2: Combustion-gas analyser
4.3: Secondary-air fan frequency converter
4.4: Secondary-air fan electric motor
4.5: Tertiary-air fan frequency converter
4.6: Tertiary-air fan electric motor
5.1: Secondary-air temperature sensor
5.2: Secondary-air temperature regulator
5.3: HR-duct damper drive motor
6.1: Tertiary-air temperature transmitter (UK)
6.2: Tertiary-air temperature regulator (UK)
6.3: Tertiary-air fan frequency converter (UK)
6.4: Tertiary-air fan electric motor (UK)
7.1: Combustion-gas oxygen sensor (UK)
7.2: Combustion-gas analyser (UK)
7.3: Tertiary-air damper operating device (UK)
8.1: Boiler firebox pressure transmitter
8.2: Boiler firebox pressure regulator
8.3: Firebox pressure damper operating device

Claims

Combustion equipment for combustible material, which combustion equipment includes

a heating boiler (1) and a firebox in it (1.1),

means for feeding the material to the heating boiler (1) , and

fans (4, 3) for feeding primary and secondary air to the heating boiler (1), in order to burn the material in the firebox (1.1),

characterized in that the equipment includes

a briquetting machine (7.1) for forming the combustible material into briquets,

a briquet-transfer pipe (7), connected to the briquetting machine (7.1), which is arranged to open into the firebox (1.1) thus forming a combustion zone,

a larger blast pipe (8) arranged at a distance around the briquet-transfer pipe (7), for feeding primary air to the briquet.
Combustion equipment according to Claim 1, characterized in that a second larger blast pipe (9) is arranged at a distance around the primary-air blast pipe (8), for feeding secondary air to the combustion zone, or for preheating the primary air.
Combustion equipment according to Claim 2, characterized in that perforations are arranged in the primary-air blast pipe (8) in the location the combustion zone, for feeding secondary air from the secondary-air blast pipe (9) through the perforations to the combustion zone.
Combustion equipment according to any of Claims 1 - 3, characterized in that the briquet-transfer pipe (7) extends after the heating boiler (1) outside it, in order to remove the combustion waste, fed by a briquet from the combustion equipment.
Combustion equipment according to any of Claims 1 - 4, characterized in that the combustion equipment includes a combustion base (2), into which the pipes (7, 8, 9) are fitted, and on top of which the heating boiler (1) is intended to be installed.
Combustion equipment according to any of Claims 1 -5, characterized in that, before the combustion zone, a wetting-pipe connection (11) is arranged to the briquet-transfer pipe (7), for leading liquid to the briquet and thus for wetting the briquet.
Combustion equipment according to any of Claims 1 - 6, characterized in that the combustion equipment includes sensor and regulator devices (3.1, 3.2, 3.3) for controlling the fan (4) intended to feed the primary air, according to the input water of the heating boiler (1), in order to regulate the heating output of the heating boiler (1).
Combustion equipment according to any of Claims 1 - 7, characterized in that the part of the primary-air blast pipe (8) following the combustion zone, in the direction of travel of the briquet, is arranged to rotate to form an arranged ash-transfer pipe (13), on the outer circumference of which a transfer screw (14) is arranged, to transfer the combustion waste away from the secondary-air blast pipe (9), by rotating the ash-transfer pipe (13).
Combustion equipment according to Claim 5, characterized in that the combustion base (2) includes two tertiary-air blast ducts (25), at right-angles relative to the primary-air blast pipe (8), for feeding preheated tertiary air into the combustion zone.
Combustion equipment according to Claim 9, characterized in that the blast duct (25) terminates in a narrowing blast cone (25.1), to which is fitted a rotatably arranged damper (26), for regulating the amount of tertiary air, by moving the damper (26).