Login| Sign Up| Help| Contact|

Patent Searching and Data


Title:
METHOD AND DEVICE FOR REMOVING ASHES FROM A COMBUSTION CHAMBER
Document Type and Number:
WIPO Patent Application WO/1998/055802
Kind Code:
A1
Abstract:
The invention concerns a method and a device for removing combustion residues, such as ashes, from a combustion chamber (12) in a combustion device (11) for solid fuel during ongoing combustion. The combustion chamber (12) and/or its space for ashes is connected intermittently to a pressure vessel (21), in which a subpressure has been created, i.e. a pressure which is lower than the pressure in the combustion chamber. Combustion residues and combustion gas are evacuated by the subpressure to the pressure vessel.

Inventors:
Hultmark, G�ran (Fortgatan 5, V�stra Fr�lunda, S-426 76, SE)
Application Number:
PCT/SE1998/001037
Publication Date:
December 10, 1998
Filing Date:
June 02, 1998
Export Citation:
Click for automatic bibliography generation   Help
Assignee:
SCANDINAVIAN SOLAR AB (Stora �v�gen 1, Askim, S-436 34, SE)
HOTAB ELDNINGSTEKNIK AB (Gammeldammsv�gen, Halmstad, S-302 41, SE)
Hultmark, G�ran (Fortgatan 5, V�stra Fr�lunda, S-426 76, SE)
International Classes:
F23J1/00; F23L9/06; (IPC1-7): F23J1/02
Foreign References:
US3776149A
US3949685A
Attorney, Agent or Firm:
G�teborgs, Patentbyr� (Sj�porten 4, G�teborg, S-417 64, SE)
Download PDF:
Claims:
PATENT CLAIMS
1. A method for removing combustion residues, such as ashes, from a combustion chamber (12) in a combustion device (11) for solid fuel, characterized in that the combustion chamber (12) and /or its space for ashes during ungoing combustion are connected intermittently to a pressure vessel (21), in which a subpressure has been created,i.e. a pressure which is lower than the pressure in the combustion chamber, and that combustion residues and combustion gas are evacuated by the subpressure essentially instantaneously to the pressure vessel.
2. A method according to claim 1, characterized in that the combustion residues are allowed to sink to the bottom of the pressure vessel (21) before a new evacuation is started.
3. A method in accordance with claim 2, characterized in that the combustion gases in connection with the generation of the subpressure in the pressure vessel (21) are brought back to the combustion chamber (12).
4. A device for removing ashes from a combustion chamber (12) in a combustion device (11) for solid fuel, characterized in that in the combustion device (12) is arranged at least one opening (19), which via a pipe (20) is connected with a pressure vessel (21), that a vaccum pump (23) or similar is arranged to create a subpressure in the pressure vessel, that in said pipe (20) is arranged a cutoff valve (29), which in open position establishes a connection between the combustion chamber (12) and the interior of the pressure vessel (21), that the cutoff valve (29) is controlled of at least one controll member (30), which during ungoing combustion is arranged to open the cutoff valve (29) a short duration, when the desired subpressure is achieved, whereby combustion residues and combustion gas are evacuated essentially instantaneously to the pressure vessel by the subpressure.
5. A device according to claim 4, characterized in that also the vaccumpump (23) is controlled by said control member (30), which is arranged to intermittently start and stop the vaccum pump (23).
6. A device according to claim 5, characterized in that the suction pipe (22) of the vaccum pump (23) is connected to the pressure vessel (32) alternatively to the combustion chamber (12) and/or to the atmosphere.
7. A device according to claim 4, characterized in that said opening (19) in the combustion chamber (12) is arranged in at least one evacuation pipe (18), which is located in or below the fuel bed (14).
8. A device according to claim 7, characterized in that the opening (19) in the evacuation pipe (18) is a slot or a perforation, which is directed obliquely upwards towards the top of the combustion chamber.
Description:
METHOD AND DEVICE FOR REMOVING ASHES FROM A COMBUSTION CHAMBER.

The present invention concerns a method for removing combustion residues, such as ashes, from a combustion chamber in a combustion device for solid fuel during ongoing combustion.The invention also concerns a device for removal of ashes from a combustion chamber in a combustion device for solid fuel during ongoing combustion.

THE BACKGROUND OF THE INVENTION AND THE PROBLEM When using stoker feeded combustion pans, e.g. of the type which is described in SE-B-457 474, the fuel is normally fed in the same pace as it is combusted towards an outfeeder for ashes in the end of the combustion chamber, where discharge of ashes occurs with the aid of a number of movable rakes arranged below the combustion chamber or its grid. With the aid of one in the glowing bed forwards and backwards movable spear larger slag clods are removed towards the rakes. Air injection to the fuel bed is in this stadium of the of the working cycle low so that any spreading of fly ash does not occur.

One cause for the formation of slag is that the combustion occurs too quickly and that the melt temperature of the ashes is reached , which results in the formation of slag.

With the right construction of the combustion chamber, right dosage of the fuel amount and air supply, (SE-A-9700609-2) the formation of slag can to a certain extent be reduced, at least what concerns the use of granular solid fuel, such as pellets produced from wood, peat, bark, wood chips and similar. High temperatures are however needed in order to achieve an effective gas combustion and thereby lower CO2-content in the flue gas, which again leads to the formation of slag. The removal of the slag demands a relatively extensive device with many movable parts, which in addition must stand high temperatures.

THE PURPOSE WITH THE INVENTION AND THE SOLUTION OF THE PROBLEM The purpose with the invention is to attain a method for removing combustion residues from a combustion chamber and an ash exhaust for achieving this, which - does not include any movable parts in the combustion chamber or in connection with this, - mainly prevents the forming of slag, - gives an effective combustion of gas and thereby low CO2-contents, - can be shaped as a closed system, - has high capacity, and - is fireproof.

These tasks have been solved by means of that the combustion chamber and/or its space for ashes is connected intermittently to a pressure vessel, in which a subpressure has been created,i.e. a pressure which is lower than the pressure in the combustion chamber, and that combustion residues and combustion gas are evacuated by the subpressure to the pressure vessel.

DESCRIPTION OF THE DRAWINGS The invention will in the following be more closely described in connection with an embodiment and with reference to the enclosed drawings.

Figure 1 shows an endview of a combustion device provided with an ash exhaust in accordance with the invention.

Figure 2 shows a longitudinal section along the line II-II in figure 1.

DESCRIPTION OF AN EMBODIMENT The combustion device ii, shown in figure 1 and 2, can be of an arbitrary type, but is in the shown embodiment of the type as is more closely described in SE-9700609-2

and which has been shown to give good results with regards to the combustion as well as the discharge of ashes during ongoing combustion.

The combustion device 11 includes a combustion chamber 12, suitably comprising a ceramic pipe, one end of which is connected to a fuel conveyor 13, e.g. a screw conveyor, and the opposite end of which leads out the flue gas. The fuel bed is designated with 14, which fuel bed either can be arranged directly on the bottom of the combustion chamber or on a not shown grid. Primary air is delivered to the combustion chamber through the fuel conveyor 13, while secondary air reach the fuel bed 14 via a perforated pipe 15, located at some distance above the bottom of the combustion chamber 16 and which extends axially along a main part of the combustion chamber.

The perforations, i.e. the holes 17 in the pipe 15, are preferably directed downwards towards the bottom 16 of the combustion chamber.

Adjacent the perforated pipes 15 is arranged an evacuation pipe 18, which has at least one opening 19, e.g. an axial slot or nozzle, which is directed obliquely upwards. The evacuation pipe is connected to a first pipe 20, which leads to a pressure vessel 21, which serves as a receptacle. A suction pipe 22 from a vaccum pump 23 is likewise connected to the cover 24 of the pressure vessel 21, which cover is removable when the vessel shall be drainaged. The drainage can also occur through a drainage pipe 25. A three way valve 26 is via a pressure pipe 32 connected to the pressure side of the vaccum pump 23, which valve can connect the vaccum pump either with the atmosphere via a filter 27 or with a by-pass pipe 28, which is connected to the pipe upstreams a cut-off valve 29. With the aid of a control member 30, which can be a timer, a program work, a micro processor or similar, the connection and disconnection of the cut-off valve 29 and the vaccum pump 23 are controlled, and possibly also the drainage valve 31 and the three way valve 26 depending on how automatic the combustion device is.

DESCRIPTION OF THE FUNCTION During ongoing stoking in the combustion chamber 12 the control member 30 starts intermittently the vaccum pump 23, which in a short time, e.g. within a few minutes, creates a subpressure in the pressure vessel 21. When the predetermined subpressure of for instance 600 millibar is achieved the vaccum pump is turned off and the cut-off valve 29 is opened. The subpressure in the pressure vessel 21 causes an equalisation ofthe pressure difference between the pressure vessel and the combustion chamber 12, which occurs very quickly (within half a second) which means, that loose particles -mainly ashes- and combustion gases instantaneously are evacuated to the pressure vessel. When the cut-off valve has been open a few seconds it is turned off again and the mixture and combustion residues and combustion gases are allowed to separate in the pressure vessel.

The separation time can vary depending of the type of fuel, but can take from for instance 10 to 30 minutes. Thereafter the vaccum pump 23 is started again to initiate a new cycle.

The gas-air mixture in the pressure vessel can either exhaust to the atmosphere via the filter 27 or be brought back in a closed cycle to the combustion chamber 12, depending on how the three way valve is controlled. If the last mentioned way is chosen a disintegration of the fuel bed will occur when the gas-air mixture enter the combustion chamber, which disintegration effectively prepares the evacuation of the combustion residues.

Depending on how big volyme the pressure vessel has, the discharge of it will take place every week or every month. Possibly, the vaccum pump can be used to discharge the pressure vessel. In such a case (not shown) a further pipe from the suction side of the vaccum pump is arranged, which further pipe is connected to the outgoing pipe of the valve.

The invention is not limited to the shown embodiment but a lot of variations are possible within the scope of the following claims.

LIST OF REFERENCE NUMBERS 11 combustion device 12 combustion chamber 13 fuel conveyor 14 fuel bed 15 perforated pipe 16 bottom of combustion chamber 17 perforation, e.g. holes 18 evacuation pipe 19 axial slot or nozzle 20 first pipe 21 pressure vessel/ ash bin 22 suction pipe 23 vaccum pump 24 cover 25 drainage pipe 26 three way valve 27 filter 28 by-pass pipe 29 cut-off valve 30 control member 31 drainage valve 32 pressure pipe