The invention relates to a chamber arrangement for a continuously-operated charcoal production retort for treating different types of biological masses.

BACKGROUND OF THE INVENTION

A retort is a furnace for slowly heating wood or other bio-based mass in an oxygen-free space up to approxi ^¬ mately 500 °C. Traditionally, charcoal has been ob ^¬ tained as the main product, the side products being different types of liquids and gases, such as distil ^¬ late and tar. The traditional retorts are batch re- torts, i.e. the chamber of the retort is charged with the mass being treated, and it is heated as long as it yields liquids, or until a specific temperature de ^¬ pending on the mass being treated is reached. As a re ^¬ sult, charcoal is obtained along with a tarry distil- late solution, from which purer liquid fractions may be obtained by various separating methods.

The resulting liquid product contains approximately 25-30 % water and many hundreds of different com- pounds, and it consists of low-molecular compounds up to complex high-molecular lignin material and anhydrous sugars. The proportion of acids in the liquid is typically 4-7 %. The main classes of compounds are ac ^¬ ids, alcohols, aldehydes and terpenes. However, sever- al applications have been found in the recent years also for further fractionated distillates: plant pro ^¬ tection agents, biocides, i.e. substances for controlling harmful organisms, snail and slug, elk and mole repellers, wood impregnating and colouring agents, metal coating agents, and lubricating and skin care agents. Also the charcoal obtained from the process has many applications in addition to the traditional industrial uses. The larger pieces of charcoal are suitable for use as barbeque charcoal, the smaller crushed pieces are an efficient soil conditioner for farmlands, and fine charcoal forms an essential part of different types of filters for removing various un ^¬ desirable components from air and gas flows. Various continuously-operated retorts are also known, where biomass is conveyed in a continuous flow in hot conditions, so that different compounds are gasified at different temperatures, with relatively pure char ^¬ coal remaining at the end. These types of structures are disclosed for example in patent US 4,501,644 and in application WO 2012/032223. The problem in the above solutions is the non-homogeneous quality of the charcoal obtained. The masses being treated roll or are pushed forward in the chambers as thick layers of mass, some of the mass being constantly in contact with the hot heating surfaces and some of the mass re ^¬ maining in the central parts of the mass flow. Thus the end result is often incompletely carbonized mass, the use of which especially in various filter struc- tures is not acceptable.

OBJECT OF THE INVENTION

The object of the invention is to remedy the defects of the prior art mentioned above. Specifically, the object of the invention is to disclose a new chamber arrangement for a retort, which enables a continuous charcoal production process to be carried out, with stable and constant temperatures and other conditions prevailing, such that the result is pure and complete- ly carbonized charcoal mass. A further object of the stable process is to produce distillates that are as pure as possible, and even as such are ready accepta ^¬ ble products for the market.

SUMMARY OF THE INVENTION

The chamber arrangement for a charcoal production re ^¬ tort according to the invention is designed for treat ^¬ ing bio-based mass in an oxygen-free space. The ar ^¬ rangement comprises several elongated treatment cham ^¬ bers one above the other, with conveyor means for con- veying the mass being treated through the chambers as a sequential process from the top to the bottom, while a hot gas partly surrounding and warming up the treat ^¬ ment chambers flows in an opposite direction from the bottom to the top in fire chambers. According to the invention the treatment chambers are paired by means of a scraper conveyor circulating the chambers for moving the mass from a first end of one of the treat ^¬ ment chambers to its second end, down to the other treatment chamber, lengthwise through the chamber and down to the next stage. Further, the fire chambers are arranged one above the other so as to alternate with the treatment chambers, and alternately connected to each other from their ends to form a continuous rising fire conduit between the treatment chambers.

Thus, in the structure according to the invention one scraper conveyor circulates continuously in the same direction, first moving the mass in the upper treatment chamber in one direction and then in the next lower treatment chamber in the opposite direction. After this the mass goes to the next scraper conveyor and into the corresponding two treatment chambers. Further, between each of the treatment chambers, i.e. so as to alternate with the horizontal treatment cham- bers in the vertical direction, there are at each stage corresponding horizontal fire chambers. Preferably in a pair of treatment chambers the first end of the upper treatment chamber, i.e. in the mass flow direction the inlet end, comprises a feeding space for feeding the mass to the treatment chamber. Likewise, preferably in a pair of treatment chambers the outlet end of the lower treatment chamber compris ^¬ es a discharge space for routing the mass out from the treatment chamber to the next treatment chamber or out from the process. These above-mentioned spaces are one and the same sealed chamber structure with the treat ^¬ ment chambers, such that the mass being treated stays in a sealed oxygen-free space throughout the treatment time .

In order to provide the process with continuous gas flow moving through and heating the process, the inlet end of the lowermost fire chamber is connected to a combustion chamber, such that the hot gases produced during combustion of a fuel therein are conveyed to the fire chambers. Further, the outlet end of the last fire chamber is connected to an exhaust flue for rout ^¬ ing the flue gases out from the process after being cooled. Thus, the hot gases flow and rise from the combustion chamber through all of the fire chambers one after the other, whereby they cool down, at the same time warming up the biomass that flows in the op ^¬ posite direction in the treatment chambers. Preferably there is one more fire chamber than there are treat- ment chambers, such that the biomass is warmed up in each of the treatment chambers from above and from be ^¬ low .

As the bio-based mass circulating in the treatment chambers is carbonized, different types of distillates are separated from it at different temperatures, whereby preferably at least one of the treatment cham ^¬ bers comprises a tapping point for drawing these gases out from the process. When the tapping point is locat ^¬ ed within the right temperature range, it gives out gas that may be burnt for producing the heat needed for the process. Thus, the process produces its own energy, and only at start-up is there need for exter ^¬ nal heating energy, such as firewood in the combustion chamber. In one embodiment the charcoal production re- tort comprises at least one gas extractor for routing the gases to a desired location or out from the pro ^¬ cess, and/or for circulating the gases.

Preferably, all of the distillates separated from the mass at different temperatures are not burnt in the gaseous state; instead, at least one, and appropriate ^¬ ly even more, of the treatment chambers are provided with an intermediate tapping point for drawing a specific type of distillate, such as acetic acid, out from the process and for condensing it to a liquid.

Further, the charcoal obtained from the process re ^¬ quires intensive cooling. At the end of the process its temperature is on the order of 500°C, which must be reduced to a temperature below 100°C so that it does not ignite when coming into contact with oxygen of the air. The heat obtained from the cooling may be recovered and utilized as known per se for various ap ^¬ plications, which are not described more specifically in this connection. In one embodiment the charcoal is cooled by means of heat exchangers or water cooling, e.g. by means of water jets. In one embodiment the charcoal production retort comprises one or more screens for screening the charcoal product formed. Preferably the treatment chambers have a uniform height, the height of the scraper of the scraper con ^¬ veyor substantially corresponding to the height of the treatment chamber. The wide, low and long treatment chambers and substantially equally wide and long fire chambers form a pack of chambers one above the other, where the height of the treatment chambers and the fire chambers is not necessarily the same. The essen ^¬ tial feature is that the structure is wide and planar, such that the mass moves therein as a wide and thin, even layer conveyed by the scrapers. Thus, the carbon ^¬ ization takes place evenly and homogenous charcoal mass is obtained irrespective of its grain size. Preferably the chain tension of the scraper conveyor is sufficiently loose, so that when moving back the scrapers do not hang in the air, but scrape the bot ^¬ toms of both of the treatment chambers when moving in both directions. Thus, the operation of the scraper conveyor is identical in both directions and the mass moves at a steady speed through the whole process, i.e. through all of the treatment chambers. This en ^¬ sures that the mass is carbonized homogeneously and completely .

For example, the size ranges may be described such that the height of the treatment chamber is on the or ^¬ der of 5-20 cm, for example approximately 10 cm and its width is on the order of 1-4 m, for example ap- proximately 2-3 m. The length of the chambers may in this case be 5-10 m. Within these size ranges, the process yields about 1-2 m ³ of carbon per hour, and 1- 2 m ³ of acetic acid per day. The chamber arrangement according to the invention can be provided as a very compact and tightly-packed structure, where the heat is conducted efficiently from the hot flue gases to the mass being treated since the treatment chambers and the fire chambers al ^¬ ternate such that the bottom of the treatment chamber always forms the top of the fire chamber and the bot ^¬ tom of the fire chamber forms the top of the treatment chamber. The tightly-packed structure and sufficient thermal insulation of the outer jacket guarantee that the different chambers maintain an efficient heat con- duction contact with each other. Thus, the thermal balance of the process is stable and it is easy to control based on measurement data obtained from ther ^¬ mometers installed at suitable locations by adjusting the mass feeding rate to the process and the rotating speed of the scraper conveyors.

Preferably the structure of the fire chamber is such that a large number of intermediate support elements are arranged between its top and its bottom for join- ing, such as welding, the bottom and the top to each other as a rigid assembly. When the fire chambers, de ^¬ spite the wide and varying temperature differences, keep their measures accurately, the measures of the treatment chambers are also maintained constant, such that the plates are not able to bend and buckle even under great temperature fluctuations. This ensures that the relatively tightly fitted scrapers of the scraper conveyor move unobstructed in the treatment chambers, as the height of the treatment chambers can be maintained constant. The fire chambers may be formed from any suitable material that withstands the temperatures used in the process. In one embodiment the fire chambers are formed from or coated by a ceramic material. The chamber arrangement according to the invention ensures that the mass being treated moves during the treatment process from one chamber to another, and from one end of each of the chambers to its other end, under conditions where all of the mass particles un ^¬ dergo exactly the same treatment process at the same temperatures and within the same treatment times. Thus, by setting a sufficient temperature and suffi ^¬ cient treatment time, high-quality and homogeneous bi- ochar is obtained as the end result.

In the retort according to the invention, in terms of its use and the homogeneous quality of the products obtained, it is essential that the properties in dif- ferent chambers remain constant with sufficient accu ^¬ racy. Therefore, each of the chambers preferably com ^¬ prises a heat measuring arrangement, one of more heat sensors or the like. The burner power and mass circu ^¬ lating speed, i.e. conveyor power, may then be adjust- ed by means of the measured temperature data and the retort control arrangement. When constant temperatures can be maintained in the chambers, also gasification in the chambers will be maintained constant, i.e. only specific materials are gasified in a specific chamber and thus the gas discharged from a specific chamber and the distillate obtained from it are maintained the same .

In the retort the first treatment chamber as seen in the mass flowing direction may be a drying chamber in which the temperature is kept low enough that the mass is only dried, i.e. water is removed from it. Thus, only water vapour is discharged from the chamber, and not yet any more valuable distillates to be recovered. In principle the retort according to the invention could have any number of successive treatment cham ^¬ bers, but in practice 4-10 successive chambers with different temperature levels rising step by step have been found sufficient for treating different types of bio-based masses and for sufficient separation of dif ^¬ ferent types of end products from each other.

In one embodiment of the invention, one of the conden- sers, for example a condenser connected to the exhaust of the flue gases, comprises heat transfer means for using the heat obtained from the condenser to pre- treat the biological mass. In the pre-treatment the mass may be pre-dried and/or pre-heated before being fed to the first chamber of the retort. Thus, the waste heat that would otherwise be wasted in the pro ^¬ cess can be utilized, and the mass can be made drier and more homogeneous . The charcoal and distillates conveyed to different condensers are relatively hot, so the heat volumes processed therein are significant enough to be recov ^¬ ered. Therefore the condensers are preferably provided with means for recovering the heat as steam, hot water or hot air and for routing it to be utilized outside of the retort. The utilization may vary according to the energy needs found in the operating environment and in the vicinity of the retort. The waste heat may be utilized for example as steam, hot water, warm wa- ter, hot air or for rotating a turbine with steam to obtain electricity.

Most suitably, woodchips with a relatively small chip size that will be homogeneously carbonized are used in the retort according to the invention. Further, the scraper conveyors in the chambers mix the mass while moving it forward, whereby the mass is maintained ho ^¬ mogeneous and only specific components are evenly gas ^¬ ified at specific stages from the mas, i.e. the mass warms up evenly and thoroughly as the process pro- gresses.

ADVANTAGES ACHIEVED WITH THE INVENTION

The retort according to the invention has significant advantages over the prior art. The retort according to the invention provides a continuous process, whereby separate and time consuming heating stages and cooling stages are avoided. This significantly increases the production capacity. According to the invention the treatment of the mass can be made very uniform and ad- justable, such that the different material components gasified from the mass may be obtained in a pure state as required. Just by adjusting the temperatures in different chambers and arranging desired temperature ranges in different chambers, the composition of the distillate obtained from a specific chamber may be predetermined as desired. The number of different types of distillates to be recovered may be easily limited by connecting a desired number of chambers one after the other. Process adjustment is simply effected by adjusting the mass feeding rate and the burner power based on the measured temperatures. Generally it is sufficient to arrange only one temperature measurement point/chamber; however, in order to more specifically monitor the distillates being produced and their qual- ity, the temperatures may also be measured at several points in one chamber.

The retort according to the invention provides a good- quality and homogeneous charcoal product. The charcoal product formed may be used in various applications, such as in filter structures, as a soil conditioner or as other charcoal products, such as barbeque charcoal.

SHORT DESCRIPTION OF THE DRAWINGS

The invention will now be described in detail with reference to the accompanying drawing 1 that schemati ^¬ cally illustrates one chamber arrangement for a char ^¬ coal production retort according to the invention. DETAILED DESCRIPTION OF THE INVENTION

Fig. 1 schematically illustrates one chamber arrange ^¬ ment for a charcoal production retort according to the invention with some of its other components. The cham ^¬ ber arrangement comprises eight treatment chambers 1 connected one above the other as described below. The treatment chamber is formed of a relatively long and wide, planar structure that is horizontal, having a relatively small height compared to its width and length. All of the treatment chambers are stacked one above the other, with corresponding planar fire chambers 3 arranged in each space between them as well as at the top and at the bottom.

The treatment chambers 1 are paired by means of a com- mon scraper conveyor 2 that moves in one direction in the upper treatment chamber and returns back in the next lower treatment chamber. Attached to the conveyor chains of the scraper conveyor there are transverse scrapers 10. The tension of the chains is selected to be sufficiently loose, so that in both directions the scrapers will scrape the bottom of the respective treatment chamber and thus push forward the mass being treated on the bottom of the treatment chamber. A feeding hopper 12 with mass feeding means is arranged at the inlet of the first treatment chamber for feeding the bio-based mass being treated to the pro ^¬ cess. The mass flows through a feeding space 4 to the inlet of the first treatment chamber 1 from where the scraper conveyor moves it through the first treatment chamber and through the second treatment chamber to a discharge space 5 arranged at the outlet of the second treatment chamber. From there the mass drops into the next corresponding pair of treatment chambers, and the corresponding circulation is repeated. This is effect- ed four times.

Planar and hollow fire chambers 3 are arranged above and below each of the treatment chambers 1. A first end of the lowermost fire chamber 3a is connected to a combustion chamber 6 for burning a combustible material to provide a hot gas flow as desired into the fire chambers 3. A second end of the fire chamber 3a is connected to the inlet end of the next fire chamber by means of a connecting conduit 13, all fire chambers being connected to each other in a corresponding manner to provide a circulating hot flue gas flow between the treatment chambers. Finally the flue gases are routed to an exhaust flue 7 at the outlet of the last, i.e. the uppermost fire chamber.

While the biomass moves back and forth in the treat ^¬ ment chambers in the downward direction, the hot flue gases move upwardly back and forth in the adjacent conduits, the heat applied on the mass thus rising steadily throughout the process. The large areas of hot surfaces and thin layers of mass rolling in front of the scrapers heat up evenly and thoroughly, whereby in different treatment chambers, different types of distillates, gases and gasified liquids are separated from the mass. Some of the gases are easily combustible fuels, and may be used as a heat source for the process itself. Thus, from at least one of the treatment chambers la there is arranged a tapping point 8 from which the gases are directly routed to the combustion chamber 6 to be burnt. This way, the process does not require external energy after start-up.

Other types of distillates also separate from the bio- mass being treated before it is completely carbonized. Therefore, an intermediate tapping point 9 is arranged in at least one of the treatment chambers lb for rout ^¬ ing a hot gas to a suitable condenser arrangement 14 in order to cool and condense the gas to a liquid and out from the process. For example, acetic acid may be obtained this way from the process, even in signifi ^¬ cant amounts.

After the last treatment chamber the completely car ^¬ bonized biochar is extremely hot, approximately 500°C, and may not be allowed to come into contact with air and oxygen. Therefore, the biochar is routed to a cooling arrangement 15 where the biochar is cooled with suitable heat exchangers and for instance water jets, such that it may be discharged to the outside air for final cooling.

The fire chambers and treatment chambers that alter ^¬ nate one above the other are structures with a uniform section, i.e. they have a constant height. This means that with a suitably selected height of the scrapers 10 being used, it may be guaranteed that the mass moves forward along the hot heating surfaces as an even flow rolling in front of the scrapers. No intermediate support elements may be arranged in the treat- ment chambers because the scrapers move along their full area. Therefore, preferably, as illustrated in the fire chamber arranged between the lowermost pair of the treatment chambers, inside the fire chamber 3 there are a number of intermediate support elements 11 for securing the top and the bottom of the fire chamber to each other as a rigid assembly. This guarantees the dimensional stability of the fire chambers 3 even under great temperature fluctuations. As the top of the fire chamber always forms the bottom of the over ^¬ lying treatment chamber, and the bottom of the fire chamber always forms the top of the underlying treat ^¬ ment chamber, the above mentioned rigid structure of the fire chambers also guarantees reliable dimensional stability of the treatment chambers. Therefore, the scrapers of the scraper conveyor are always able to freely move through the treatment chambers, even when they are sized rather close-fittingly according to the height of the treatment chamber.

The invention has been described above by way of exam ^¬ ple with reference to the accompanying drawing; however, different embodiments of the invention are possi ^¬ ble within the scope defined by the claims.