WO2007060281A1

WO2007060281A1 - Continuous retort

Info

Publication number: WO2007060281A1
Application number: PCT/FI2006/000386
Authority: WO
Inventors: Taisto Raussi
Original assignee: Raussin Metalli Ky
Priority date: 2005-11-25
Filing date: 2006-11-22
Publication date: 2007-05-31
Also published as: FI20051205A0

Abstract

The object of the invention is a continuous retort for the carbonization of pulp. The retort consists of a vertical tank provided with an inner jacket (1) and an outer jacket (2), and the upper end of which has a feeding opening (3) and the lower end an outlet opening (4) and through which the pulp to be treated is organized to flow due to gravity. The upper part of the tank forms a drying chamber (5), the middle part a charcoal kiln (6) and the lower part a cooling chamber (7) .In the area of the drying chamber and the charcoal kiln, the space between the inner jacket and the outer jacket forms a heating channel (8) provided with essentially horizontal flow tubes (13) in order to ensure uniform heating and charring of the entire area of the downwards flowing pulp. Equivalently, the cooling jacket (11) of the cooling chamber is provided with horizontal cooling tubes (16) that reach throughout the tank at which the cooling water of the cooling chamber is organized to circle the coal mass and to pass through it while gradually rising upwards towards the upper part of the cooling chamber.

Description

CONTINUOUS RETORT

Field of the Invention

The present invention relates to a continuous retort defined in the preamble of claim 1.

Background of the Invention

Traditionally, in coal burning, an intermittently functioning retort is used whether in production of mainly coal or in recovery of liquid or gase- ous components separated from the wood pulp, such as burning gases and tar-based and tall oil -based liquids. Different size tanks are filled with wood chips, chopped wood bits of varying size or long beams until they are quite full and then they are closed for the duration of the treatment. In the treatment, these are heated in such a way as to boil out of the wood pulp the liquid and gaseous components so that only the essentially clean coal remains. After this the tank is cooled or it is let to cool down to such a low tem- perature that it can be safely opened without the coal kindling.

The known art has several disadvantages. In the beginning of the process, the drying and heating of the wood pulp up to the generation of gases is slow and requires a lot of additional energy. In the gasification phase, a considerable excess of burning gases is produced than can be utilized in the process so that another use needs to be found for them or they are wasted or released into the air. The cooling phase means simply waiting, since the hot coals kindle very easily. Since cooling with oxygen-rich air or water is not possible, and the use of any cooling gas is not economically feasible, the only economically feasible alternative is waiting for hours. In this way, the treatment of one batch takes usually about 48 hours. This kind of carbonization in batches is energy-economically very disadvantageous. At one stage there is a great need of additional energy, then an extreme excess of energy that is difficult to store and then just waiting around doing nothing.

An additional disadvantage is the availability of gases and foremost steams generated in the process. The liquids vaporized out of the wood pulp consist of several different components, such as tall oils and tars, whose vaporization temperatures vary and which have different industrial uses. In intermittent retorts, however, all vapours are treated together and from the retort a condensation liquid is obtained that is a mixture of all the liquids con- tained by the wood. Its use as such is not possible so that the mixture needs still further downstream operation before its end use.

A device essentially similar to the one depicted above is the device disclosed in Patent Speci- fication GB125439, in which batches of wood are dropped into a vertical tank from the top and from the bottom of the tank batches of coal are gotten. Gaseous and liquid products are recovered in a common condenser and a part of them are burnt in order to pro- duce heat for the process.

The Object of the Invention

The object of the invention is to remove the above-mentioned disadvantages. Particularly, the object of the invention is to disclose a continuous retort, whose production volume may be made to be several times that of an intermittently functioning retort.

Also, it is the object of the invention to disclose a retort, whose energy consumption and energy production can be made to be as even as possible. Also, it is the object of the invention to disclose a retort that the condensation liquid produced by it can be recovered as completely as possible so that the condensation liquid is already separated into liquids of different qualities.

Summary of the Invention

A continuous retort according to the present invention is characterized in Claim 1. A continuous retort for carbonization of wood pulp according to the present invention includes a vertical tank provided with an inner jacket and an outer jacket and a feeding opening of wood pulp at the upper end and an outlet opening at the lower end and through which the wood pulp to be treated has been set to flow by means of gravity at a velocity required by sufficient and appropriate drying, heating, charring and cooling of the wood pulp. The vertical and straight tank can have either a round or angular cross section. The upper part of the tank consists of a drying chamber where the fed wood chips or equivalent pulp is initially dried and in which it also begins to heat up. The middle part of the tank consists of a charcoal kiln, in which, in elevated temperature that rises even up to about 400⁰C, the wood is charred i.e. it gasifies and vaporizes out some components. Lowest in the tank is the cooling chamber in which the hot coal that remains of the pulp is cooled down to the temperature in which it can be removed from the tank without the risk of kindling when coming into contact with air. Because heat is needed in the drying chamber and the charcoal kiln in order to carry out the process, the space between the inner jacket and the outer jacket in the drying chamber and charcoal kiln area is formed into a heating channel. In its lower end there is a source of heat with which the hot combustion gases are lead into the heating channel, and in the upper end there is an exhaust channel through which the cooled heating gases are removed from the process. In the area of the cooling chamber, the space between the inner jacket and outer jacket forms a cooling jacket in order to cool the charred pulp before it is removed from the retort. Also, the retort is provided with recovery equipment in order to recover the gases and vapours separating from the charring pulp. Characteristic of the invention is that the drying chamber, charcoal kiln and cooling chamber together form a continuous and open space without limits between one another, in which no intermediary walls between chambers exist nor any openable and closable doors. Therefore, due to gravity, the pulp to be treated is flowing downwards in the chamber and from one chamber into another smoothly, steplessly and continuously. This downward flowing of the pulp and at the same time heating and charring of the pulp as evenly as possible is being controlled according to the invention so, that in the heating channel are provided substantially horizontal flow tubes which extend throughout the tank and into which the circling and rising flows of hot flue gases are guided. Thus, by the flow tubes provided in sufficiently many different heights and even horizontally in different places, the heat is being distributed evenly in the entire area of the downward flowing pulp that requires heating. In equivalent manner, in the area of the cooling chamber, horizontal cooling tubes are provided that extent throughout it so that the cooling water of the cooling chamber is organized to pass also in the middle of the charcoal mass in order to ensure even cooling in the entire area of the charcoal mass . Preferably, in the retort according to the invention, the burning gas recovery equipment is connected to the source of heat in order to burn in the source of heat the burning gases that gasify from the pulp and in order to guide the hot combustion gases into the heating channel .

Preferably, the heating channel around the tank is provided with horizontal and vertical flow guides such as continuous walls or parts thereof. These are used to stop the hot combustion gases from rising straight and too rapidly upwards. Thus, the hot combustion gases flow gradually rising and inter- mittently horizontally to-and-fro or appropriately spirally or circularly towards the exhaust channel so that they efficiently transfer their heat energy through the inner jacket into the pulp to be treated.

The recovery equipment with which the gases and vapours created in the tank are being recovered, are provided with appropriate tubes outside of the tank so that the gases and vapours can be guided into the desired places. Preferably, these include partly downwards open flow channels i.e. downwards open chutes in the tank that are conducted out of the tank. A structure that is downwards open but in other directions closed ensures that the flow channels stay open when the pulp presses downwards around them due to gravity. Extremely preferable place for the partly open flow channels is the lower side of the horizontal flow tubes, for example connected to the lower surface of the flow tubes. Thus, the larger and more robust flow tubes protect the flow channels and small and light structures can be used as flow channels.

Preferably, part of the flow channels of the recovery equipment of the charcoal kiln are conducted to the condenser outside of the retort, where the obtained hot vapours are cooled into liquid substances, for example turpentine, tar and tall oil based liquids that can be used as semi-finished products in chemical manufacturing. Especially when using flow channels which are in different heights and thus in different temperature areas in the tank, different fairly pure liquids from the different channels can be obtained that can be used directly in downstream operations. Due to the high temperature of the tank no oxygen can be let into it because then the pulp would immediately ignite. For this reason, the filling and the emptying of the tank needs to be performed carefully. In the filling of the upper part and the empty- ing of the lower part various different lock feeders, known as such, can be used. They can either be functioning fully continuously or appropriately in batches .

The feeding and removing in batches is, how- ever, organised in such small and repetitive batches that in practice the process seems to be continuous. Thus it does not in any way allocate the continuous carbonization process.

In the lower part of the tank, in the cooling jacket there can be a continuous water space that releases the steam pressure from its upper part and that is filled using the water connection of the lower part. The jacket may also consist of a spiral and upwards circulating water channel. Preferably, however, the main direction of movement of the cooling water is the opposite of the downwards directed movement of the hot coal so that the cooling of the coal can be made more efficient.

Because the temperature of the coal mass flowing into the cooler is around 400⁰C, it contains a considerable flow of energy. This heat energy is recovered in the form of steam which preferably is conducted from the upper part of the cooling chamber through the steam channel to be utilized outside of the retort, for example in a steam turbine to rotate an electric generator. Thus, the retort can be made to produce the electricity required to run and control it and it can be made completely independent of outside energy .

Because considerably more burning gases are produced in the retort than are needed in the heating of the tank, a part of the gases can be burnt in a boiler and/or in a steam superheater provided in connection with the retort and the additional steam thus obtained conducted into a steam turbine .

The continuous retort according to the inven- tion has considerable advantages compared with prior art. The invention enables a continuous process whose production is 3-5 times that of traditional retorts of the same volume functioning in batches. The process can be made uniform so that no outside energy is re- quired at any stage after start-up. On the contrary, the retort can be used to produce excess electricity and heat. Furthermore, the retort does not only produce one multi-compound liquid, but it gives fairly pure different turpentine, tar and tall oil based liq- uids, when fractionated.

List of Figures

In the following section, the invention is explained in detail through an example by referring to the accompanying drawing which presents schematically a side projection of one of the continuous retorts according to the invention.

Description of the Invention The retort according to the drawing consists of a vertical and high straight tank which has an inner jacket 1 and an outer jacket 2. Due to the high temperatures prevailing during the process, the inner jacket and the outer jacket are made of appropriate material, for example vertically corrugated steel plate, so that it is flexible and adapts to the thermal expansion movements caused by temperature fluctua- tion. The upper part of the tank forms a drying chamber 5 , the middle part of the tank forms a charcoal kiln 6 and the lower part of the tank forms a cooling chamber 7. Although the tank has three functionally different parts, it has no intermediary walls and it is a continuous space throughout its height. The upper end of the tank is closed and it has an openable and closable feeding opening 3 or alternatively an appropriate lock feeder. Furthermore, the upper end has a decompression tube 20 which can be provided with a shutter that opens itself due to the pressure. The lower end of the tank is provided with a outlet opening 4 which is also provided with appropriate shutters or equivalent organs with which the access of oxygen into the tank is prevented when the coal is being removed from it .

A space circulating the tank has been created between the inner jacket 1 and the outer jacket 2 of the tank that forms a heating channel 8 in the area of the drying chamber 5 and charcoal kiln 6. In this same area, the outer jacket 2 is wrapped in heat insulation 21 in order to prevent significant heat flow out of the retort through the outer jacket. The equivalent space between the jackets in the area of cooling cham- ber 7 forms a cooling jacket 11 surrounding the cooling chamber .

The lower end of the heating channel 8 is provided with a source of heat 9 which by burning gases produces hot combustion gases that are conducted upwards through the heating channel and when cooled, out through the exhaust channel 10 of the upper part.

An integral part of the heating channel are horizontal flow tubes 13 that are lead through the tank in order to conduct hot combustion gases into the middle area of the tank and thus to guide heat uniformly into the entire area of the tank. In the heating channel 8 there are flow guides, vertical and horizontal or curved plates or equivalent with which the hot flue gases can be made to circulate horizontally, circularly, spirally and/or appropriately upwards both in the surrounding heating channel and the horizontal flow tubes 13 so that they transfer heat uniformly into the entire area of the tank while rising upwards when cooling.

To recover the created gases, the retort has recovery equipment 12, which consist of downwards open flow channels 14 that are attached to the lower surface of the horizontal flow tubes 13. In the area where burning gases are created, the flow channels 14 are connected to each other by tubes 22 which conduct the burning gases to the burner which functions as a source of heat 9 in which the gases are burnt. Other flow channels 14 attached to the lower surface of the flow tubes 13 are connected by tubes 23 to an external condenser 15 in which the recovered vapours condense into liquids. The condenser can be organized so that the condensates are not mixed with one another but that vapours created in different parts of the retort are recovered separately.

In the cooling part 7 water is fed from the lower part of the jacket into the cooling jacket 11 and the water circulates and cools the jacket and the hot coal mass inside it. Also in the cooling part, there are transverse and horizontal cooling tubes 16 so that the cooling effect can be gotten as uniformly as possible into the entire area of the coal mass. The heat gotten from the coal into the water and the vaporizing water can be conducted with a steam tube 17 directly into a steam turbine 18 which rotates the generator 25. If the steam pressure and temperature are not sufficient, the steam can first be conducted through another route 26 into a separate superheater 19 or a boiler that is heated with the excess burning gases remaining from the process which are not needed in the source of heat 9.

The retort is used as follows. Wood chips which are usually relatively humid are dropped through the feeding opening 3 into the tank so that the tank remains always relatively full . The wood chips are dried initially in the drying chamber 5 and humidity comes out of it and is removed through the decompression tube 20 whenever the pressure in the tank rises to be sufficiently high. It is even possible that the decompression tube is a continually open tube the flow resistance of which has been adjusted so that there is always a small over pressure inside the tank to stop the flowing in the other direction. The dried wood chips flow downwards due to gravity both when it dries and because completely carbonized mass is being removed from the lower end of the retort. Thus the wood chips end up in a hotter area and vapours and burning gases start to separate from it. These are recovered in different stages by different flow channels 14 so that the burning gases are conducted into the burner 9 where the retort is being heated and the vapours are conducted into the condenser in order to be liquefied. Near the burner 9 i.e. in the lower end of the charcoal kiln 6, the temperature is around 400⁰C at which even the rest of the gases and liquids separate from the coal and only essentially pure wood coal remains. As the mass flows downwards, it ends up in the area of the cooling chamber 7, where the mass is surrounded by a cooling jacket i.e. a jacket filled with water. In the area of the cooling jacket the coal is cooled to under 100⁰C at which it can be safely removed from the closed space into the outside air with- out risk of fire. The energy of the steam formed in the cooling is recovered and turned into electricity in the generator 25 in the manner described above. It is also possible that temperature probes and/or gas detection probes are used at different heights in the retort, with which the process is being controlled essentially continually or periodically. For example, the end of gas formation in the lower part of charcoal kiln 6 can be detected, which indicates that completely carbonized coals can be moved lower i.e. cooled coal can be removed from the lower part . In the same way it is possible to detect forma- tion of gases and vapours in the drying chamber 5 and in the charcoal kiln 6, and even recognize them. Thus it is also possible that the tubes 22 and 23 have valves with which the gases flowing in them can be conducted alternatively either to being burned or into the condenser.

Preferably, the process is being controlled only by regulating the quantities of heat at which the wood chips are being fed and coal removed from the process in a continuous and steady flow. Thus, with the help of regulated heating and cooling, the wood chips are made to carbonize uniformly and the gases and liquids separating from them can be recovered in a controlled manner or used immediately.

The invention is not limited to the examples presented above, but many variations are possible while remaining in the framework defined in the claims .

Claims

1. Continuous retort for carbonization of pulp,

- retort consist of a vertical tank provided with an inner jacket (1) and an outer jacket (2) , a feeding opening (3) in the upper end and an outlet opening (4) in the lower end and through which the pulp to be treated is organized to flow due to gravity, - the upper part of the tank forms a drying chamber (5) , the middle part a charcoal kiln (6) and the lower part a cooling chamber (7) ,

- in the area of the drying chamber and the charcoal kiln, the space between the inner jacket and the outer jacket forms a heating channel (8) in the lower end of which there is a source of heat (9) and in the upper end an exhaust channel (10) in order to remove the cooled heating gases. in the area of the cooling chamber, the space between the inner jacket and the outer jacket forms a cooling jacket (11) in order to cool the carbonized pulp before its removal from the retort and

- the retort is provided with recovery equipment (12) in order to recover the gases and vapours separating from the carbonized pulp, characterized in that

- the drying chamber (5) , the charcoal kiln (6) and the cooling chamber (7) form together an open and continuous space, - the heating channel (8) is provided with essentially horizontal flow tubes (13) that reach throughout the tank in order to ensure uniform heating and charring in the entire area of the downwards flowing pulp and - the cooling jacket (11) is provided with horizontal cooling tubes (16) that reach throughout the tank at which the cooling water of the cooling chamber is organized to circle the coal mass and to pass through it while gradually rising upwards towards the upper part of the cooling chamber.

2. Continuous retort according to claim 1 characterized in that the recovery equipment (12) has been connected to a source of heat (9) in order to burn in the source of heat the burning gases gasifying out of the pulp and in order to conduct the hot combustion gases into the heating channel (8) .

3. Continuous retort according to claims 1 and 2, characterized in that the heating channel (8) is provided with horizontal and vertical flow guides in order to conduct the hot combustion gases in gradually rising and intermittently horizontal to-and- fro flows towards the exhaust channel .

4. Continuous retort according to anyone of claims 1 to 3, characterized in that the recovery equipment is provided with partly downwards open flow channels (14) in the tank, which have been lead out of the tank.

5. Continuous retort according to claim 4, characterized in that the partly open flow channels (14) are positioned below the horizontal flow tubes (13) , preferably attached to their lower sur- face.

6. Continuous retort according to claim 4, characterized in that a part of the flow channels (14) are lead into a condenser (15) outside of the retort in order to condense the hot vapours and to recover the turpentine, tar and tall oil based liquids gotten from the pulp.

7. Continuous retort according to anyone of claims 1 to 6, characterized in that the feeding opening (3) of the upper end and/or the outlet opening (4) of the lower end are provided with a lock feeder in order to prevent the air from entering into the tank when adding pulp into it or when removing coal from it .

8. Continuous retort according to anyone of claims 1 to 7, characterized in that the upper part of the cooling chamber (11) is provided with a steam channel (17) in order to conduct the vaporized water to be utilized externally, such as in a steam turbine (18) .

9. Continuous retort according to claim 8, characterized in that in connection with the retort a boiler and/or a superheater (19) is provided in order to burn a part of the burning gases in order to reheat the vapour in them before utilization.