WO2016198725A1

WO2016198725A1 - A gas generating apparatus and a method for treating the particulate matter formed in a gasifier of a gas generating apparatus

Info

Publication number: WO2016198725A1
Application number: PCT/FI2015/050405
Authority: WO
Inventors: Jani Kaaresto; Iikka Ylikoski; Iikka KORVA; Jarno Haapakoski
Original assignee: Volter Oy
Priority date: 2015-06-09
Filing date: 2015-06-09
Publication date: 2016-12-15

Abstract

The invention relates to a gas generating apparatus. The gas generating apparatus comprises: -a gasifier (1) with a pyrolysis space (7) for forming raw synthesis gas from carbonaceous feedstock by burning the feedstock incompletely under oxygen deficiency, and an ash space (8) for collecting ash particles formed in the pyrolysis space (7) and separated from the pyrolysis space (7) by a grate (12) or the like, -a separating device (3) for separating particulate matter from the raw synthesis gas formed in to the gasifier (1) and conducted from the gasifier (1) to the separating device (3) through a conduit, -a return conveyor (5) lead from the separating device into the ash space (8) and arranged to deliver the particulate matter separated from the raw synthesis gas directly in to the ash space (8). The invention relates also to a method for treating the particulate matter formed in a gasifier (1) of a gas generating apparatus.

Description

A GAS GENERATING APPARATUS AND A METHOD FOR TREATING THE PARTICULATE MATTER FORMED IN A GASIFIER OF A GAS GENERATING APPARATUS Field of the invention

The invention relates to a gas generating apparatus and a method for treating the particulate matter formed in a gasifier of a gas generating apparatus.

Background of the invention

Gasifiers of prior art for gasifying carbonaceous feedstock such as wood- based feedstock normally comprise a container-like frame enclosing a pyrolysis space and ash space separated by a grate or the like, in which pyrolysis space the feedstock is gasified by burning the feedstock incompletely under oxygen deficiency to produce raw synthesis gas. Typically the raw synthesis gas exiting from the gasifier contain more or less (depending on the burning efficiency, conditions in the pyrolysis space, fuel type etc.) particulate matter such as ash, soot and unconverted carbonaceous feedstock. Such fine particulate matter is usually separated from the raw synthesis gas before its further processing. Refined synthesis gas is typically utilized e.g. as fuel of a power generation plant or for producing chemicals such as hydrogen, methanol, ammonia, substitute natural gas or synthetic transportation oil.

Most frequently separating is carried out by means of separating devices such as cyclones or filters to which the raw synthesis gas formed in the gasifier is lead. These devices retain fine particulate matter from the raw synthesis gas stream while allowing passage of the synthesis gas and thereby producing cleaner synthesis gas being free of harmful particulate and contamination. In this process the particulate matter accumulates in to the separation device from where it is periodically or continuously removed and transported e.g. to waste disposal sites or corresponding places for further treatment. However, as the particulate matter still contains unconverted carbonaceous feedstock when exiting from the gasifier a portion of the energy concentration of the feedstock is always lost when converted in to the synthesis gas in the known gasifiers. In order to remedy this drawback it has been developed during last decades such gasifiers and gas refining devices for gasifiers in which the fine particulate matter accumulated in to the separating device is returned back to the pyrolysis space of a gasifier. This will enhance the fuel-efficiency of a gasifier but still some proportion of the unconverted feedstock will be lost in such gasifiers since the recycled matter conducted into the pyrolysis space where an intense gas stream causes portion of the recycled matter to return back to the separation device so quickly that gas-conversion cannot have enough time to take place.

Brief summary of the invention

It is an aim of the invention to provide a novel gas generating apparatus, in which the carbonaceous feedstock is converted in to gaseous form more completely and which gas generating apparatus therefore produces less disposable ash and soot-based waste material. The aim of the invention is also to provide a method for processing the particulate matter formed in the pyrolysis space of the gas generating apparatus during the gasification such that better fuel-efficiency is achieved and particulate matter containing still less unconverted carbonaceous feedstock is produced.

The aim of the invention is achieved because in the gas generating apparatus according to invention the particulate matter such as ash and soot being collected by a separating device is returned back to gasifier such that direct accession of it in to the pyrolysis space is prevented by delivering the particulate matter in to ash space where it remains so that long enough conversion time is ensured that at least most of its unconverted feedstock will be gasified. More precisely, the gas generating apparatus according to the invention is characterized in what will be presented in the independent claim 1 and the method for processing particulate matter formed in a gasifier of a gas generating apparatus what will be presented in the independent claim 8. The dependent claims 2-7 will present some preferred embodiments of the gas generating apparatus according to the invention and the dependent claims 9-11 will present some preferred embodiments of the method according to invention. The advantage of the gas generating apparatus and the method according to invention is that better fuel efficiency is achieved and less disposable waste material such as ash and soot is produced. Description of the drawings

Next the invention is described in more detail by referring the attached drawing wherein

figure 1 shows a principal drawing of a gas generating apparatus according to the invention.

Detailed description of some preferred embodiments of the invention

A gas generating apparatus shown in figure comprises a gasifier 1 , a cooler 2 and a separating device 3. The gas generating apparatus of figure 1 comprises also an ash discharge conveyor 4 arranged to deliver the ash fallen in to the ash space outside the gasifier 1 as well as a return conveyor 5 arranged to convey the particulate matter separated from the cooled raw gas in the separating device 3 from the separating device 3 to the ash space 8 of the gasifier 1.

In the embodiment shown in figure 1 the gasifier 1 has a container like frame 6 comprising a pyrolysis space 7, an ash space 8 as well as feeding device 9 for feeding the feedstock to be burned in to the pyrolysis space 7 of the gasifier 1 and an exit conduit 10 for transporting the raw synthesis gas formed in the pyrolysis process 7 to the cooler 2 and further from the cooler 2 by cooled raw synthesis gas conduit 11 to the separation device 3. The ash space 8 and the pyrolysis space 7 in the gasifier 1 of figure 1 are divided from each other by a grate 12. The grate 12 is configured such that it allows ash particles being too heavy to fly with the raw synthesis gas stream to fall through the slits of the grate 12 in to the ash space 8. Furthermore, it has been arranged at least one air/oxygen inlet (not shown in the drawing) in to the pyrolysis space to provide suitable amount of oxygen to maintain suitable conditions for enabling gas-conversion process where the carbonaceous feedstock burns incompletely in to the raw synthesis gas. The cooler 2 of the apparatus is a formed of a heat exchanger comprising primary channel and secondary channel configured with respect to each other such that heat of the medium flowing in the primary channel is exchanged to the secondary medium flowing in the secondary channel. Typically the heat exchanger applied herein is constructed such that it comprises one primary channel formed of single pipe with large diameter inside which the secondary channels are formed of one channel with spiral form or plurality of adjacent channels having smaller diameter than the primary channel. In the cooler 2 of the apparatus the raw synthesis gas coming from the pyrolysis space of the gasifier 1 acts as a primary medium from which a certain amount of heat is exchanged in to the secondary medium in order to reduce the temperature of the raw gas in to a desired level before leading it in to the separation device 3. The secondary medium to be circulated in the secondary channels of the cooler 2 may be e.g. water or watery solution comprising some suitable additive such as e.g. some antifreezing medium. The heat exchanged in to the secondary medium may be utilized e.g. for heating of commercial or residential buildings nearby the site of the apparatus. The separating device 3 is in this embodiment a filtration device comprising input chamber 13 and output chamber 14. The raw synthesis gas coming from the gasifier 1 through the cooler 2 is conducted at first in to the input chamber 13 and from there through the filter 15 in to the output chamber 14 from where it is lead outside the apparatus for further processing or use as a fuel. The filter 15 is in this embodiment a fabric filter made of some suitable filter fabric having suitable size of pores being arranged to catch the particles accompanying with the incoming raw gas. The filter 15 is arranged in to separating device such that it allows the raw synthesis gas coming in to input chamber 13 to flow to the output chamber 14 only through the filter 15. Therefore, during the use of such apparatus the particulate matter accumulates on to the pores the filter 15 while the raw synthesis gas flows through the filter 15. Hence, the particulate matter separated from the raw synthesis gas forms little by little a growing deposit layer on the side of the filter being on the side of the incoming raw synthesis gas (i.e. on the side of input chamber 13). Growing deposit layer will finally block the filter 15 and prevents the gas stream through it if the said layer (i.e. so called "filter cake") is not removed every now and then.

In this embodiment the filter cleaning is performed by giving periodically pressure air pulses on the side of the filter being opposite to the side of the growing "filter cake" (i.e. on the side of output chamber 14). Also other cleaning methods for cleaning the filter such as mechanical scraping, vibrating or ultrasound cleaning may be alternatively or additionally applied. During the filter cleaning the "filter cake" is broken up in to crumb with smaller and larger particles which mostly has larger particle size than the particle size of the original particulate matter in the raw synthesis gas before deposition in the separating device 3.

As can be seen from figure 1 the return conveyor 5 is in this embodiment formed of three conveyor portions 16-18 two of which (i.e. the first conveyor portion 16 and the third conveyor portion 18) have been arranged in horizontal position and one of which (i.e. the second conveyor portion 17) in vertical position. It should be notified that orientation of conveyor portions 16 and 18 need not to be in horizontal but the orientation of the conveyor portions 16 or 18 can be also such that one or both of these the conveyor portions have oblique angle with respect to a horizontal plane. In such case the angle between the conveyor portion 16 and 17 as well as 17 and 18 may differ from the right angle shown in figure 1. The orientation of the conveyor portion 17 is preferably at least substantially vertical since it should be ensured that the crumb transported at the first end of the conveyor portion 17 will fall from the first end to the second of the conveyor portion 17.

In to the first conveyor portion 16 and third conveyor portion 18 it have been fitted conveyor screws 19 and 20 inside the conveyor tubes 21 and 23. These conveyor screws 19 and 20 have vortex being configured such that when the respective conveyor screw is rotated in a first direction the material such as crumb from the filter 15 being placed at the first end of the respective conveyor portion 16 or 18 the material is transported by the respective conveyor screw 19 or 20 to the second end of the respective conveyor portions 16 or 18. The reason for having the second vertical conveyor portion is that the ash space of the gasifier 1 is located remarkably lower than the bottom of the input chamber 13.

The second conveyor portion 17 do not comprise any screws but two airlock valves 25 and 26 which the first airlock valve 25 is provided at the first end of the second conveyor portion 17 and the second airlock valve 26 at the second end of the second conveyor portion 17. The first airlock valve 25 and the second airlock valve 26 can be any kind of airlock valves that are able to prevent air and/or gas flowing from the first conveyor portion 16 to the third conveyor portion 18 or vice versa but allows the crumb to be transported through the valves from first conveyor portion 16 to the third conveyor portion 18. Thus, the first airlock valve 25 and the second airlock valve 26 can be e.g. devices that has cylindrical case with an airtight rotatable drum inside the case divided in sections which each can receive the crumb through an opening at one position and deliver it out through an another opening at the other position. When the rotation of the drums of the first airlock valve 25 and the second airlock valve 26 are synchronized such that only one of the airlock valves 25 and 26 are open at time the air or gas flow from the first conveyor portion 16 to the third conveyor portion 18 or vice versa through the second conveyor 17 portion is prevented while the crumb is moved through the airlock valves 25 and 26. The two airlock valves 25 and 26 may be replaced with one airlock valve which may be, in that case, a rotary feeder, a lock feeder, a locker feeder or corresponding single valve device which allows the crumb to go from the first conveyor portion 16 through the second conveyor portion 17 to the third conveyor portion 18 but prevents air/gas flow from the first conveyor portion 16 to the third conveyor portion 18 or vice versa. Alternatively, airlock valves 25 and 26 may be further replaced with three or more airlock valves by means of which the respective function as the above mentioned is achieved.

The crumb being conveyed is moved by gravity in the conveyor tube 21 from the first end to the second end of the second conveyor portion 17 because the second end is located lower than the first end. Since the first conveyor portion 16 ends to the first end of the second conveyor portion 17 and the first end of the third conveyor portion 18 begins from the second end of the second conveyor portion 17 the crumb material brought by the conveyor screw 19 from the first end of the first conveyor portion 16 goes through the first airlock valve 25, falls through the vertical conveyor tube 22 and goes through the second airlock valve 26 from the second end of the first conveyor portion 16 to the first end of the third conveyor portion 18. Therefore, when the conveyor screw 19 of the first conveyor portion 16 and the conveyor screw 20 of the third conveyor portion 18 are rotated (to the said first direction) by rotating devices (e.g. electric motors) thereof as well as when the airlock valves 25 and 26 are operated the material (i.e. crumb formed by breaking up the "filter cake" on the filter 15) is transported from first end of the first conveyor portion 16 to the second end of the third conveyor portion 18 and hence from the input chamber 13 of the separating device 3 in to the ash space 8 of the gasifier 1 such that no any air or gas can flow from the ash space 8 of the gasifier 1 to the input chamber 13 of the separating device 3 or vice versa

The walls and the bottom of the input chamber 13 is designed such that the crumb falling towards the bottom of the input chamber 13 during the filter 15 cleaning phase run in between the vortex of the conveyor screw 19 of the first conveyor portion 16 placed on the bottom of the input chamber 13. The bottom of the input chamber 13 has such design that the rotating conveyor screw 19 on the bottom of the input chamber 13 sweeps all the fallen crumb and starts to transfer it towards the second end of the first conveyor portion 16. The crumb is also crushed in to the smaller particles when it gets between the vortex of the conveyor screws 19 and 20 and the walls of the input chamber 13 as well as of the conveyor tubes 21 and 23. Thus, at the second end of the third conveyor portion 18 the particle size of the crumb is much smaller than what it was before getting in to the beginning of the first conveyor portion 16. Therefore, the return conveyor 5 being conducted from the input chamber 13 of the separating device 3 to the ash space 8 of the gasifier 1 has in this embodiment two effects; Firstly, it returns the particulate matter separated from the raw synthesis gas stream at the separating device 3 into the ash space 8 of the gasifier 1 , and secondly it crushes the particles of the crumb and therefore ensures that the particle size of the crumb formed of broken "filter cake" has small enough particle size. Hence, by using conveyor with a conveyor tubes 21 and 23 with a conveyor screws 19 and 20 in these conveyor tubes 21 and 23 the returned particulate matter in the form of crumb is got during its transportation in to the form wherein its burning properties for utilizing the energy content in its containing unconverted carbonaceous feedstock is improved. However, it should be notified that in most cases the "filter cake" will be crushed enough when it falls and hits against the bottom of the input chamber 13 after it has been disentangled from the filter 15. Hence, the returned particulate matter in form of crumb will have enough small particle size even if the conveyor would be such type of conveyor which would not crush the crumb during the transportation.

Furthermore, in order to ensure that the conversion of the unconverted feedstock will take place as completely as possible there may be arranged one or more air/oxygen blowing channels 24 in to the ash space 8 for dusting the returned particulate matter in the ash space 8. Such dusting will fly the ash particles in the ash space 8 and therefore provides them more oxygen which will enhance the conversion process. Alternatively or wholly or partly in addition to the blowing channels 25 the air/oxygen blowing can be provided through the third conveyor portion 18. Furthermore, the gas for dusting the ash may be also some other gas than air or oxygen. However, if air or oxygen is used for dusting the ash the total amount of air or oxygen provided in to the gasifier 1 should be controlled such that it is not provided too much air or oxygen in to the pyrolysis space 7 to ensure that a conversion process under appropriate conditions is achieved.

The apparatus according the invention can be accomplished in many ways differently as it is described in connection with the above mentioned advantageous embodiment shown in the figure 1. For instance as a return conveyor other kind of conveyors than a screw conveyor such as e.g. pneumatic, scraper or chain conveyor can be applied. In such embodiment where the crumb is not crushed in the conveyor a separate crumb crushing can be arranged. For instance, there may be some mechanical element, crushing plates or jaws between the filter and the first end of the return conveyor which is arranged to split the crump before it gets in to the conveyor. The crushing of the crumb formed of the "filter cake" may also not be necessary at all if the cleaning of the filter is made more frequently or even continuously such that deposition of the particulate matter cannot take place. In such embodiments where the return conveyor is a screw conveyor it is also possible to make the conveyor of one portion having one conveyor tube and one conveyor screw. In case of different heights between the first end and second end of such conveyor the conveyor can be positioned in suitably inclined orientation. It may be also possible to use conveyor tube where the particulate matter removed from the filter in form of crumb or powder will be conveyed to the ash space of the gasifier by means of gravity only e.g. placing the separation device such that a tube lead from the separation device to the ash space of the gasifier can have so steep inclination angle that particulate matter in form of crumb or powder would run along such tube without any external energy. It should be also notified that the separation device can be also other kind of separation device than a filtration device. It may be e.g. a cyclone or can include cyclone in addition to a filtration device as a second stage cleaner. Also the gasifier and the cooler may have configuration being different from the ones described above. Thus, the invention should not be limited to the embodiments described above but can be varied within the scope of the appended claims.

Claims

Claims:

1. Gas generating apparatus, comprising

-a gasifier (1 ) with a pyrolysis space (7) for forming raw synthesis gas from carbonaceous feedstock by burning the feedstock incompletely under oxygen deficiency, and an ash space (8) for collecting ash particles formed in the pyrolysis space (7) and separated from the pyrolysis space (7) by a grate

(12) or the like,

-a separating device (3) for separating particulate matter from the raw synthesis gas formed in to the gasifier (1 ) and conducted from the gasifier (1 ) to the separating device (5) through a conduit,

-a return conveyor (3) lead from the separating device into the ash space (8) and arranged to deliver the particulate matter separated from the raw synthesis gas directly in to the ash space (8).

2. Gas generating apparatus according to claim 1 wherein the separating device (3) is a filtration device comprising a filter (15) arranged to collect the particulate matter from the incoming raw synthesis gas flowing downstream through the filter (15).

3. Gas generating apparatus according to claim 2 wherein the separating device (3) comprises input chamber (13) in to which the raw synthesis gas is arranged to enter and an output chamber (14) being separated from input chamber (13) by a filter such that the raw synthesis gas can get into the output chamber (14) only through the filter (15).

4. Gas generating apparatus according to claim 3 wherein the input chamber

(13) is located below the filter (15) and the beginning end of a return conveyor (5) is located on the bottom of the input chamber (13).

5. Gas generating apparatus according to claim 4 wherein the separating device (3) includes a releasing arrangement configured to disentangle the particulate matter being deposited on the filter (15) such that it falls on the bottom of the input chamber (13).

6. Gas generating apparatus according to claim 5 wherein the side walls and/or the bottom of the input chamber (13) is designed such that particulate matter disentangled from the filter (15) is arranged to run in to the return conveyor (5).

7. Gas generating apparatus according to any of claims 4 to 6 wherein the return conveyor (5) is a screw conveyor arranged in to the conveyor tube (21 ) and having vortex configured to sweep the disentangled particulate matter from the bottom of the input chamber (13) in to the conveyor tube (21 ).

8. Method for treating the particulate matter formed in a gasifier (1 ) of a gas generating apparatus, comprising a pyrolysis space (7) and an ash space (8) separated from each other by a grate (12) or the like, the method comprising method steps of

-collecting the particulate matter formed in the gasifier (1 ) of the gas generating apparatus by a separating device (3)

-conveying the particulate matter from the separating device (3) directly in to the ash space (8) of the gasifier (1 ) by a return conveyor (5) conducted from the separating device (3) into the ash space (8) of the gasifier (1 ).

9. Method according to claim 8 wherein the separating device (3) is a filtration device comprising a filter (15) arranged to collect particulate matter from raw synthesis gas flowing through the filter (15) and wherein the filter (15) is periodically or continuously treated in order to disentangle the particulate matter deposited on the filter (15).

10. Method according to claim 9 wherein the deposited particulate matter being disentangled from the filter (15) is arranged to fall on the bottom of an input chamber (13) locating below the filter (15) for feeding the particulate matter into the return conveyor (5) which beginning end is located on the bottom of the input chamber (13).

11. Method according to claim 9 or 10 wherein the deposited particulate matter disentangled from the filter (15) is crushed before or during its transportation from the separating device (3) to the ash space (8) of the gasifier (1 ).