SOLID AND BIOMASS FUEL

Technical Field of the Present Invention

The present invention relates to a multi chamber incinerator for turbulent two-stage combustion of fuel, such as coal or biomass fuel, with increased efficiency and low emission.

Background of the Present Invention

A wide variety of combustion methods and incinerators are available in the prior art, such as stoker-type combustors, fluidized bed combustion, pulverized coal combustion and cyclone combustors. However, these systems have many issues.

One major issue is low efficiency. The cause for low efficiency can be twofold. First cause is the incomplete burning of the fuel, such as coal, due to build-up of slag around unburnt coal preventing its access to oxygen. For this reason, coal having higher calorific content, such as bituminous coal, which is harder to mine and more expensive than coal having lower calorific content, such as lignite, is preferred. Second cause is the incomplete oxidation of carbon monoxide to carbon dioxide, which both lowers the overall efficiency of the incinerator and causes emission of harmful carbon monoxide into the atmosphere.

Another issue is fly ash that is released to the atmosphere along with flue gas, which requires the use of scrubbers, electrostatic precipitators or other filtering devices in order to comply with air pollution standards. Strict emission standards also limit the amount of carbon monoxide, NO _x and SO _x , all of which are byproducts of coal combustion that is allowable to be released into the atmosphere. To comply with this, it is imperative that complete combustion is achieved.

The attempts made in the state of the art to alleviate these problems associated with incinerators are disclosed by European patent no. 2 402 651, US patent no. 4,007,697, US patent no. 4,633,790, US patent no. 4,430,948, US patent no. 5,588,378 and US patent no. 5,299,532, among others.

The present invention aims to improve on the problems described in the prior art. The invention makes use of two-stage double cyclone turbulent combustion in order to achieve improved efficiency and low emission values. First stage of combustion takes place in the main combustion chamber where fuel is fed onto a grate, from the openings of which oxygen enriched air is blown upwards. Burning fuel particles are suspended by turbulence and carbon is oxidized to carbon monoxide. These combustion gases are transferred to the second combustion chamber where second stage combustion takes place. Due to the shape of the second combustion chamber, turbulent flow of gases occurs which provides improved mixing of combustion gases and air. In the second stage carbon monoxide is oxidized to carbon dioxide, with very low NO _x produced. The multi chamber incinerator is suitable for burning solid fuels with lower calorific content, such as lignite, as well as biomass fuel, or a combination thereof. The present invention can be used in any application requiring heat transfer, such as industrial or domestic-type heating (boilers) and power generation. The present invention provides a multi chamber incinerator for turbulent combustion of fuel as provided by the characterizing features defined in Claim 1.

Objects of the Present Invention

The object of the invention is to provide multi chamber incinerator for complete turbulent two-stage combustion of fuel with increased efficiency and low emission.

Brief Description of the Technical Drawings

Accompanying drawings are given solely for the purpose of exemplifying multi chamber incinerator, whose advantages over prior art were outlined above and will be explained in brief hereinafter.

The drawings are not meant to delimit the scope of protection as identified in the Claims, nor should they be referred to alone in an effort to interpret the scope identified in said Claims without recourse to the technical disclosure in the description of the present invention.

Figure 1 demonstrates a vertical sectional view of an embodiment of the present invention.

Figure 2 demonstrates an enlarged view of the components of the secondary combustion chamber of the present invention as depicted in Figure 1. Figure 3 demonstrates a vertical sectional view of another alternative embodiment of the present invention with dome channels.

Figure 4 demonstrates a vertical sectional view of yet another alternative embodiment of the present invention with dome channels and bottom feed.

Figure 5 demonstrates a vertical sectional view of yet another alternative embodiment of the present invention with multiple secondary combustion chambers and bottom feed.

Figure 6 demonstrates a vertical sectional view of yet another alternative embodiment of the present invention with fuel recycle system.

Detailed Description of the Present Invention

The following numerals are referred to in the detailed description of the present invention:

10 Turbulent Combustion Incinerator

11 Main Combustion Chamber

12 Secondary Combustion Chamber

13 Insulating Ceramic Fiber Wool

14 Refractory Material

15 Fuel Hopper

16 Fuel Feeder Motor

17 Fuel Transfer Auger

18 Support Element

19 Ball Bearing 20 Fuel Feed Pipe

21 Fuel Feed Inlet

22 Heat Collecting Dome

23 Dome Opening

24 Rotatable Sweeper

25 Fuel Spreader

26 Slag Mill

27 Sweeper Motor

28 Grate

29 Grate Holes

30 Air Blower

31 Air Transport Pipe

32 Gas Acceleration Nozzle

33 Funnel Pipe Bend

34 Ash Collection Cone

35 Ash Transfer Auger

36 Counter-Weight Cover

37 Dome channels

38 Gas flow channels

39 Recirculation pipe

40 Fuel recycle system

Figure 1 illustrates an embodiment of the present invention, referred to as turbulent combustion incinerator (10). Turbulent combustion incinerator (10) consists of a two-stage double cyclone turbulent combustion system. The first stage takes place in the main combustion chamber (11), where solid or biomass fuel is burned. The second stage takes place in the secondary combustion chamber (12) where components of combustion gases, such as CO are combusted completely. Inside surface of turbulent combustion incinerator (10) is of refractory material (14) and the outside is insulated by ceramic fiber wool (13) to prevent loss of heat. The present invention can be used in a variety of applications that require heat transfer, such as boilers and power generation. Harvest of heat energy from the turbulent combustion incinerator may occur via a jacket or pipes placed in the outside walls of the turbulent combustion incinerator where desired fluid can flow, or some other heat exchange method can be used.

Fuel, such as lignite or biomass, is fed into the system from above by fuel hopper (15). The fuel is transferred along the fuel hopper (15) by fuel transfer auger (17) driven by fuel feeder motor (16) and mechanically borne by ball bearing (19). Fuel hopper is attached to the main body of the turbulent combustion incinerator by support element (18). From the top, fuel is transferred directly to the main combustion chamber (11) via fuel feed pipe (20) and fuel feed inlet (21). Fuel feed inlet (21) is made of ceramic material resistant to temperatures above 1200°C and is preferably insulated from fuel feed pipe (20).

Secondary combustion chamber (12) will be described in more detail hereinbelow. In brief, fuel entering the main combustion chamber (11) from above via fuel feed inlet (21) is met with air flowing from below via grate holes (29) of the grate (28). Air is supplied to the main combustion chamber (11) from air blower (30) via the air transport pipe (31). Fuel is evenly distributed across grate (28) by rotatable sweeper (24), rotated by sweeper motor (27) to ensure more efficient combustion. Bottom ash produced by combustion is collected by ash collection cone (34) and removed by ash transfer auger (35) with counter-weight cover (36) which disposes of bottom ash when a certain weight of ash is reached. Due to the turbulent flow within turbulent combustion incinerator (10), ash produced by combustion is flung towards the walls of turbulent combustion incinerator (10) and is transferred to ash collection cone (34) by gravity, thereby reducing particulate matter (PM) emissions.

Combustion gases, fly ash and other volatiles resulting from combustion are passed through the dome openings (23) around the heat collecting dome (22) to the secondary combustion chamber (12), where the second stage combustion of CO occurs. Completely combusted flue gas is collected by gas acceleration nozzle (32) and released into the atmosphere, or transferred for further processing, such as scrubbing, filtering and/or electrostatic precipitation, via funnel pipe bend (33).

Figure 2 illustrates secondary combustion chamber (12) in detail. Secondary combustion chamber (12) comprises heat collecting dome (22), fuel feed inlet (20) and gas acceleration nozzle (32). Inside surface of secondary combustion chamber (12) is of refractory material. Secondary combustion chamber (12) is where second stage combustion occurs. Uncombusted air and flue gas enter into secondary combustion chamber (12) from main combustion chamber (13) via dome openings (23). The higher volume of secondary combustion chamber (12) allows CO and other gases to expand and combust more freely. The outer surface of fuel feed inlet (20) and the lateral and concave top surface of secondary combustion chamber (12) allow formation of double cyclone turbulent air flow inside secondary combustion chamber (12) for more efficient combustion of CO. Completely combusted flue leaves secondary combustion chamber (12) through gas acceleration nozzle (32) and is released into the atmosphere, or transferred for further processing, such as scrubbing, filtering and/or electrostatic precipitation, via funnel pipe bend (33).

Figure 3 illustrates another embodiment of turbulent combustion incinerator (100. ^In this embodiment, heat collecting dome (22) contains dome channels (37). Dome channels (37) are aligned to provide air flow that is focused towards the part of fuel feed inlet (21) that is beneath gas acceleration nozzle (32), meaning the angle of dome channels (37) gets more acute radially, so that air flow is tangentially diverted from the outer surface of the fuel feed inlet (21). Concave structure of the top of secondary combustion chamber (12) diverts air flow back towards heat collecting dome (22), creating a double cyclone turbulent flow of air and combustion gases coming from main combustion chamber (11), thereby expediting further oxidation of combustion gases such as CO.

Figure 4 illustrates another embodiment of turbulent combustion incinerator (10"). For convenience, the numerals assigned to each part remain unchanged. Those that are changed are denoted by an apostrophe, such as fuel hopper (150. ^In this embodiment, the fuel is fed from the bottom of turbulent combustion incinerator (100 by fuel hopper (150- The fuel is transferred along the fuel feed pipe (200 by fuel transfer auger (170 driven by fuel feeder motor (160- Fuel is fed directly into grate (28) from the bottom by elbow-shaped fuel feed inlet (210- In order to not interfere with air transport pipe (31), fuel feed pipe (200 is placed eccentrically to grate (28). As with the first embodiment of the invention, combustion gases, fly ash and other volatiles resulting from combustion are passed through the dome openings (23) and dome channels (37) to the secondary combustion chamber (12), where the second stage combustion of CO occurs. Turbulent flow is obtained via tangential air flow along concave top surface of secondary combustion chamber (12). Completely combusted flue gas is collected by gas acceleration nozzle (32) and released into the atmosphere, or transferred for further processing, such as scrubbing, filtering and/or electrostatic precipitation, via funnel pipe bend (33).

Figure 5 illustrates an alternative embodiment of turbulent combustion incinerator (100). In this embodiment, secondary combustion chamber (12) is divided into two sections: first division (12a) and second division (12b) of secondary combustion chamber (12) which are concave shaped at the top and at the bottom. 50% of total air feed is supplied to the main combustion chamber (11) via the air transport pipe (31) and the remaining 50% is supplied to the secondary combustion chamber (12) via transport pipe (310. First division (12a) of secondary combustion chamber (12) and main combustion chamber (11) are separated by first heat collecting dome (22a). Flow of combustion gases from main combustion chamber (11) to first division (12a) of secondary combustion chamber (12) is facilitated by first dome channels (37a), which provide tangential flow along the walls of first division (12a) and fuel feed inlet (21) leading to double cyclone turbulent flow within first division (12a), and also by gas flow channels (38). First division (12a) and second division (12b) of secondary combustion chamber (12) are separated by second heat collecting dome (22b). Flow of combustion gases from first division (12a) to second division (12b) is facilitated by second dome channels (37b), which provide tangential flow along the walls of second division (12b) of secondary combustion chamber (12) and fuel feed inlet (21) leading to double cyclone turbulent flow within second division (12b), and also by gas flow channels (38). Additionally, as mentioned above, 50% of total air feed is supplied to the second division (12b) to ensure complete combustion. Overall air-fuel equivalence ratio used for the operation of turbulent combustion incinerator (100) is λ≥1.30. However, since only 50% of total air feed is supplied to the main combustion chamber (11), first stage of combustion occurs with a rich mixture λ,≥0.65. For this reason, most of the fuel is only oxidized to carbon monoxide and as there is an air deficiency, formation of NO _x is minimized.

In addition, a fraction of flue gas is recirculated into secondary combustion chamber (12) via recirculation pipe (39). Recirculation flue gas lowers the overall oxygen content by dilution. In addition, as flue gases are cooled, the temperature of combustion gases decreases as well. Both these effects lead to reduction of formation of NO _x .

In addition, the fuel is fed from the bottom of turbulent combustion incinerator (10'") by fuel hopper (150 as mentioned above.

Figure 6 illustrates another alternative embodiment of turbulent combustion incinerator (1000- In this embodiment, the bottom ash collected by ash cone (34) is recycled in to the feed stream by fuel recycle system (40). A fraction of bottom ash transferred by ash transfer auger (350 is fed into fuel feed pipe (200, so that unburnt fuel contained within can be added to fresh fuel feed. The remaining bottom ash is removed via counter-weight cover (360- In addition, this embodiment comprises sweeper motor (270 on top of funnel pipe bend (33). In summary, the invention proposes a turbulent combustion incinerator (10) comprising a main combustion chamber (11) and a secondary combustion chamber (12) for turbulent combustion of fuel.

In one embodiment, said secondary combustion chamber (12) comprising a first division (12a) and a second division (12b).

In a further embodiment, said main combustion chamber (11) in flow communication with the first division (12a) being separated by the first heat collecting dome (22a) and said first division (12a) in flow communication with said second division (12b) being separated by a second heat collecting dome (22b). In a further embodiment, said first heat collecting dome (22a) facing the first division (12a) is concave shaped.

In a further embodiment, said first division (12a) is configured as a substantially toroidal volume.

In a further embodiment, said first heat collecting dome (22a) comprises first dome channels (37a), each one aligned to provide air flow focused towards the longitudinally central axis of said turbulent combustion incinerator (10) so as to effectuate flow of combustion gases from main combustion chamber (11) to said first division (12a) and tangential diversion of air flow within said first division (12a) to provide double cyclone turbulent flow therein.

In a further embodiment, gas flow channels (38) are provided between inner walls of said turbulent combustion incinerator (10) and the first heat collecting dome (22a) to allow flow of combustion gases from main combustion chamber (11) to said first division (12a) and second division (12b).

In a further embodiment, said second heat collecting dome (22b) comprises second dome channels (37b), each one aligned to provide air flow focused towards the longitudinally central axis of said turbulent combustion incinerator (10) so as to effectuate flow of combustion gases from first division (12a) to said second division (12b) and tangential diversion of air flow within said second division (12b) to provide double cyclone turbulent flow therein.

In a further embodiment, said second heat collecting dome (22b) facing the first division (12a) is concave shaped.

In a further embodiment, gas flow channels (38) are provided between inner walls of said turbulent combustion incinerator (10) and the second heat collecting dome (22b) to allow flow of combustion gases from the first division (12a) to the second division (12b).

In a further embodiment, the turbulent combustion incinerator (10) comprises an air transport pipe (31) and a further air transport pipe (310 respectively supplying 50% of total air feed to the main combustion chamber (11) and the remaining 50% to the secondary combustion chamber (12).

In a further embodiment, the remaining 50% of total air feed is either supplied to the first division (12a) or to the second division (12b). In a further embodiment, overall air-fuel equivalence ratio used for the operation of turbulent combustion incinerator (10, 100) is λ≥1.30. In a further embodiment, first stage of combustion within the main combustion chamber (11) occurs with a mixture of λ,≥0.65.

In a further embodiment, a fraction of flue gas is recirculated into said secondary combustion chamber (12) via a recirculation pipe (39).

In a further embodiment, inclination of first and second dome channels (37a, 37b), with respect to horizontal plane is gradually decreased in the radial direction. In a further embodiment, solid or biomass fuel is usable.

In a further embodiment, two-staged combustion is effectuated such that combustion of solid or biomass fuel takes place in said main combustion chamber (11) and combustion of carbon monoxide and other flue gases takes place in said secondary combustion chamber (12).

In a further embodiment, inner surface of said turbulent combustion incinerator (10) is of refractory material (14) and the outside is insulated by ceramic fiber wool (13).

In a further embodiment, fuel is fed into the system from above by fuel hopper (15). In a further embodiment, said fuel hopper (15) comprises a fuel transfer auger (17) that is driven by fuel feeder motor (16) and mechanically borne by ball bearing (19). In a further embodiment, said fuel hopper (15) is attached to the main body of said turbulent combustion incinerator (10) by support element (18).

In a further embodiment, fuel is transferred directly to the main combustion chamber (11) via fuel feed pipe (20) and fuel feed inlet (21).

In a further embodiment, said fuel feed inlet (21) is made of ceramic material resistant to temperatures above 1200°C.

In a further embodiment, combusted flue gas leaves secondary combustion chamber (12) through gas acceleration nozzle (32).

In a further embodiment, bottom ash produced by combustion is collected by ash collection cone (34). In a further embodiment, bottom ash produced by combustion is removed by ash transfer auger (35).

In a further embodiment said turbulent combustion incinerator (10) comprises fuel recycle system (40) whereby a fraction of the bottom ash produced by combustion and removed by ash transfer auger (35) is fed into fuel feed pipe (20).

In a further embodiment, air used is oxygen enriched air. In a further embodiment, said turbulent combustion incinerator (10) comprises a fuel hopper (150 from which fuel is fed into the system from below.