Technical Field

The present disclosure relates to the continuous production of charcoal from chipped hard wood and soft wood, forest and orchard thinning, residues from sawmills and similar wood working industries, and in particular to a non pressurized reactor for carbonizing wood to charcoal in an energy efficient manner while recovering valuable wood vinegar from the wooden biomass fed into the reactor.

Background and Prior Art

Growing demand of charcoal as cooking fuel and other domestic uses because of its light weight and unlimited storability, for metallurgical uses, water treatment and other uses on one hand, and a growing exploitation of renewable energy sources, curbing green house gases and heat emissions on the other hand, have promoted the search for enhanced processing techniques of converting wood to charcoal in an efficient and less polluting way than ancient or traditional practices.

Moreover, continuously operable charcoal production lines are imposed by ordinary industrial productivity constraints.

Vertical retorting apparatuses, often operated with a moving bed of wooden biomass undergoing carbonization to form charcoal and employing specific devices for preventing sawdust and carbonized particles to be dragged out together with streaming carbonization flue gases, and water cooled heat exchanging surfaces for lowering the temperature of the charcoal before it is released through a discharge port of the reactor, have represented the prominent approach in developing efficient carbonization units.

FR 2.416.931, US 5.584.970, US 1.739.786, GB 2285582, GB 198328, FR 2913236, CN 101230280, RU 2201952 and WO 2009/094736, disclose retorting reactors for charcoal production based on the use of an up-right retorting vessel or tower.

A less energy wasteful carbonization process has been sought by collecting the hot pyrolysis gases released by the biomass undergoing carbonization and using them for pre-drying (hot purging) the fresh feed wood, or by burning them in a burner eventually admixed to another fuel for generating hot flue gas to be injected in the pyrolysis zone.

A twin-retort carbonization unit is described in the article "Charcoal production with reduced emissions" by P. J. (Patrick) Reumerman and D. (Burt) Fredericks presented at the 12 ^th European Conference on biomass for energy industry and climate protection, Amsterdam, 2002.

These known apparatuses are all relatively tall and complex structures, generally requiring large investment and having significant maintenance costs.

The document CN 101693842 discloses a biomass high pressure retort for producing charcoal employing a high-pressure retort disposed horizontally at a certain height and employing motor driven mixing means for maintaining the retorting biomass under constant intermixing, a horizontally disposed, charcoal transfer unit, placed below the high pressure retorting vessel, adapted to receive through a vertical pipe the fully carbonized mass of charcoal expelled out the high pressure retort and having a variable pitch screw conveyor adapted to disintegrate the larger pieces of charcoal to reduce the particle size and pack them more and more densely together while advancing the material such to practically form a gas locking diaphragm in the discharge path of the produced charcoal.. A third screw conveyor receives the compacted mass of particles of charcoal expelled at the end of the crush and pack variable pitch screw conveyor, through a vertical pipe, advancing it while being cooled by water flowing in a gap space around the screw conveyor wall. Also in this retorting apparatus hot purging gases are circulated inside the pressurized horizontal retort.

Objectives and Summary of this Disclosure

Orchard and forest thinning, chipped wood from fallen trees and similar wooden wastes, sawdust and discards from wood milling plants before the carbonization process may begin undergo a practically complete drying phase. Normally in an initial section of the retorting reactor the fresh wood is exposed to streaming hot purge gases that gradually strip the moisture and other vaporized substances contained in the wood. This drying process normally occurs at about 140-280°C. The hot purge gases are then ducted to a burner whereat by injection of air, combustible gases are burned for generating new hot purging flue gas to be reinjected inside the retorting vessel.

The applicant has found that by conducting a complete drying phase of fresh chipped wood biomass fed at an inlet of a segmented, substantially horizontally disposed charcoal producing reactor, without forcing a hot purging gas through the drying and successively carbonizing biomass, valuable wood vinegar liquor can be economically recovered instead of burning it.

The content of vinegar in wood varies with type and age of the wood. Freshly cut wood will contain more vinegar that long stocked wood. Freshly cut wood may contain up to 7% by weight wood vinegar; bamboo just about 1.5%.

Extraction of wood vinegar is economically important. For example 1 ton of wood will produce approximately 500 kg of charcoal that can be sold at 10 Baht/kg, generating a revenue of 5,000 Baht. From the same one ton of wood, from 15 liters (1.5%) to 50 liters (5%) of wood vinegar may be recovered that can be sold at 300 Baht/kg generating a revenue of 4,500 - 15,000 Baht, that is generally much higher than that of the corresponding charcoal.

Wood vinegar has may uses. It is used in form of diluted solution (1-2 ml/liter) sprayed on agriculture fields once or twice a month, with the following benefits:

^stimulates vegetable growth and strengthens roots and leaves

■S enhances soil fertility

curbs odor

as flavor enhancer effect on cultivated products, improves fruit yield and quality, increasing sugar content;

^■ S repels insects

^• prevents bacteria and virus diseases and increases the quantity of useful microbes

^• f nourishes seeds for germination

facilitates composting

Wood vinegar is also employed as an integrator in animal food with the following benefits:

S enhances resistance to diseases

improves quality of meat and milk.

According to the applicant's studies and findings, and effective segmentation of a generally horizontally extending tubular reactor (or with a slight inclination) can be implemented by deploying motor driven carousel valves in relatively short vertical chutes connecting the outlet end of a tubular segment of the reactor to the inlet end of the successive segment, and at a wood feed inlet port at the inlet end of the first segment and at a cooled charcoal discharge port at the outlet end of the last segment of the tubular reactor. Carousel valves so deployed practically provide effective gas locks between adjacent segments of the reactor as well as at the fresh chipped wood loading port and at the cooled charcoal discharge port.

Missing a pervasive streaming of hot purging flue gases through the wooden biomass during the drying phase and through the carbonizing biomass during the successive pyrolysis phase, and missing the possibility of exploiting a gravity fall of the material as in vertically disposed retorting apparatuses, an effective continuous intermixing of the loose material being treated and progressive advancement of it along the sequential segments of the reactor are ensured by motor driven screw conveyors that advance the mass of loose material from an inlet end to an outlet end of each tubular segment of the reactor. Intermixing of loose particles and small pieces of the material being processed while being advanced by the screw conveyor, is enhanced by disposing the segments with a slight upward inclination that may be generally comprised between 5 and 20°, such to advance the mass of loose particles and small pieces up a sloping tube, thus enhancing the dragging action of the leading surface of the screw.

Moreover, a slight inclination creates the condition to connect the upper outlet end of a tubular segment of the reactor to the lower inlet end of the following segment of the reactor with a substantially vertical tubular chute along which is installed a motor driven carousel valve adapted to continuously transfer loose material urged by the screw conveyor to fall upstream onto the carousel valve, downstream, releasing it by gravity through the inlet port of the successive tubular segment of the reactor, while ensuring a perfect gas lock between segments.

Alternatively, the segments may even be perfectly horizontal and placed at different heights, staggering them or alternating the direction of transit of the mass of loose material being processed in the successive segment. In this case, the urging (leading) surface of the screw may have stumps adapted to mix the loose material while advancing it along the tubular segment.

In any case these arrangements avoid the need of tall structures that are generally onerous to erect and maintain. The whole processing line may be assembled and sustained on a pavement and has a comparably low profile such to be easily serviced without cumbersome lifting means.

Basically the reactor of this disclosure consists of an inner conduit composed of at least three tubular segments, disposed horizontally or with a slight inclination and having inside a screw conveyor, connected in series by tubular chutes. Along each connecting tubular chute is present a motor driven rotary multi vane carousel valve adapted to bring the loose material, fallen between vanes on the upstream side of the carousel, to fall off down-stream, into the inlet end part of the successive tubular segment.

The whole inner conduit and the rotary multi vane (carousel) valves are made of a corrosion resistant metal adapted for operation at a temperature of up to 600- 750°C.

The first two processing segments are both surrounded by a hot flue gas circulation gap space defined between an outer surface of the tubular segment and an inner surface of a thick thermal insulating jacket, and a third segment is surrounded by a cooling fluid circulation gap space defined between an outer surface of the tubular segment and an inner surface of a thick thermal insulating jacket.

The first segment constitutes a fresh wood drying and wood vinegar recovery, stage and has liquor trap channel longitudinally extending along a bottom part of the horizontally disposed or slightly inclined tubular segment, adapted to collect a liquid phase of wood vinegar exuded by the drying wood and discharge it in a liquor collecting vessel, and a vapour vent pipe of a vapour phase of wood vinegar at a top part of the segment connecting to a condenser having a condensed liquor discharge pipe duct to said liquor collecting vessel.

The second segment constitutes a pyrolysis stage of the wood dried in the first segment, transforming it into charcoal.

The third tubular segment constitutes a charcoal cooling stage prior to discharge it from the reactor at safely low temperature when coming in contact with the air.

Length and inner diameter of the tubular segments, heat conduction and heat exchanging characteristics of the metallic walls of the tubular segments, volumes of particulated material contained at any time in each single segments of the inner conduit may be similar or different from one another according to thermal balance considerations and retorting characteristics of the contemplated feed wood, made at the design stage of the reactor for a specific usage. Motor driven carousel valves, respectively at a chipped wood feed loading port at the inlet end of the first segment and at a cooled charcoal discharge port at the outlet end of the third segment, prevent leakages of gaseous substances from the segmented inner conduit.

Hot pyrolysis gases exit the second segment through a vent pipe ducting them to an inlet port of an ordinary burner that produces hot flue gas that is ducted into the flue gas circulation gap space surrounding the second segment at its charcoal outlet end and thence enters at a reduced temperature into the flue gas circulation gap space surrounding the first segment at its dried wood outlet end and exits at said chipped wood feed inlet end of the first segment.

The still hot flue gas, exiting the reactor may be ducted to a heat exchanger for recovering heat in form of hot water and the cooled flue gas may serve as source of C02 being fed to growing algae in a algae farming unit for nullifying green house pollutants release in the atmosphere and producing valuable biomass from which may be obtained bio-fuel, fertilizers and/or edible substances for human and animal consumption.

The cooled flue gas is also exploited for lowering the temperature of the hot flue gas stream that is ducted into the hot flue gas circulation gap space of the second tubular segment of pyrolysis and/or into the hot flue gas circulation gap space of the first tubular segment of wood drying and wood vinegar recovery, by injecting it into the gas stream to lower the heat input as needed in order to independently regulate the temperature in the two stages of the reactor.

Of course, combustion conditions in the burner are adjusted/controlled in order to ensure that the excess air remains below 10 % to limit the oxygen content in the cold flue gas to be injected into the charcoal cooling segment below a safe value. Moreover, cold flue gas is exploited as cooling fluid for injecting it into the third tubular segment to cool the charcoal before releasing it outside the reactor. The injected cool flue gas is made to flow through the mass of loose charcoal stripping heat from the charcoal; practically cooperating with the cooling fluid, generally water to be heated, that circulates in the gap space in contact with the outer surface of the metal tube, which may advantageously be finned in order to enhance heat transfer.

Of course, the so re-heated flue gas will be re-cycled back to the heat exchanger for recovering heat from the produced charcoal and avoiding heat releases in the atmosphere.

At start-ups, any suitable fuel will be fed to the burner to raise the temperature inside the second segment up to about 400-550 °C in order to trigger carbonization of the dried wood and fuel will be added for as long as the pyrolysis process reaches a self sustaining state, and it may be occasionally added if needed to restore optimal processing conditions.

The claims as filed are integral part of this description and are herein incorporated by reference.

Brief description of the drawings

FIGURE 1 is a schematic illustration of an exemplary embodiment of the reactor of this disclosure.

Description of exemplary embodiments

The attached drawings and the ensuing description of preferred embodiments have a purely illustrative purpose of the novel reactor of this disclosure. As such, the illustrated spatial arrangement of the various parts of the reactor, dimensions and materials used are not intended to limit the scope of the claims, other equivalent arrangements and alternative materials of constructions being possibly preferred, subject merely to ordinary design choices. With reference to FIG. 1 , the exemplary embodiment of reactor according to this disclosure, indicated as a whole with 1, comprises at least three distinct stages with 2, 3 and 4, respectively, connected in series (cascaded).

An inner segmented processing conduit that may be made of stainless steel pipe or of other corrosion resistant metal or metal alloy, has a common chipped wood feed toggle and inlet port provided with a motor driven rotary vane (carousel) valve 9 for introducing fresh feed material into the first stage 2 of reactor, and a cooled down charcoal discharge port provided with a motor driven rotary vane (carousel) valve 10 for releasing produced charcoal out of the last stage 4.

The mass of loose particles and small pieces introduced at an inlet end of a first tubular segment 12 of the inner conduit, advances progressively urged by a screw conveyor 15, driven by a motor 19, inside the first tubular segment 12, as far as falling by gravity down a terminal tubular chute 5, in which is present a rotary vane (carousel) valve 7, driven by a motor not shown in the drawing. The carousel valve passes the loose material into the inlet end of the second tubular segment 13, along which the loose material advances, urged by the screw conveyor 16, driven by a motor 19', as far as reaching the outlet end of the second tubular segment and falling down the terminal tubular chute 6, where the rotary vane (carousel valve) 8 passes the loose material into the inlet end of the third tubular segment 14, along which the material advances, urged by the screw conveyor 17, driven by the motor 19, as far as reaching the outlet end of it from where the loose material falls through a discharge port of the conduit wherein a third rotary vane (carousel) valve 10 releases the processed material out of the reactor.

Each tubular segment 12, 13, 14, is surrounded by a gap space, 18 defined between the outer surface of the tubular segment and a thermally insulating jacket 11.

Practically, the whole segmented conduit of the reactor is thermally insulated from the environment by a thick jacket 1 1 that apart from an inner lining of metal, and optionally also an outer cladding of reflective metal foil, includes a thick mat or layer of thermal insulation material, for example rock wool, alumina or other refractory material.

Heat input to the feed material introduced in the reactor at start ups and eventually during operation, is provided a burner 23, adapted to burn any available fuel of choice, adapted to generate hot flue gas that is ducted through a pipe 24 to the gap space 18 of the second tubular segment 13, where it circulates around the outer surface of the tubular segment 13.

The hot flue gas gives out part of its heat to the inner metal tube and thence to the mass of loose material inside the tubular segment 13 rising its temperature beyond the threshold temperature that triggers the beginning of a pyrolytic carbonization of wood that once started will itself generate hot pyrolysis gases that will eventually exit the sealed segment through the duct 22 connecting to an inlet of the burner 23, wherein the combustible fraction of the pyrolysis gas mixture, mainly CO, will be burned alone or together with added fuel to generate other hot flue gas that is continuously ducted through the pipe 24 into the hot flue gas circulation gap space 18 surrounding the second tubular segment 13 of the reactor.

The so injected hot flue gas eventually pass through the duct 30 entering the hot flue gas circulation gap space 18 surrounding the first tubular segment 12 of the reactor at a temperature adapted to progressively dry the fresh chipped wood, fed to the reactor through the fresh wood inlet port and passed inside by the gas sealing motor driven rotary vane (carousel) valve 9, before exiting the reactor through a vent pipe 25.

Optionally, according to the preferred exemplary embodiment shown in the figure, the vent pipe 25 ducts the still hot flue gas to a heat exchanger 32 for recovering heat and thence, the pipe 25' that eventually would leads the cooled gas to an ancillary draught regulation butterfly valve 41, followed by a non-return (check) valve 42 and a chimney 43, for ensuring viable working conditions to the burner 23 as long as the vented out flue gas is sufficiently hot (during start ups and eventual electrical supply interruptions), has an upstream derivation branch 25", along which during normal steady state operation of the reactor, a fan 44 drafts the cooled flue gas to a reservoir 33 serving as a source for supplying C02 to growing algae through the pipe 25' ", in order to practically nullifying C02 release into the atmosphere.

Under normal working conditions, the fan 44 is driven for producing an up-stream vacuum that ensures an air intake rate at the burner 23 that matches the oxygen requirement for correctly and efficiently burning the combustible being fed to the burner 23 (contained in the pyrolysis gas and other fuel eventually fed). This maintains a correct/acceptable amount of excess air in the flue gas. In practice, the fan 44 substitutes a natural draught that would be generated by venting out hot flue gas through the chimney 43. The check valve 42 isolates the ancillary chimney path during operation of the fan 44.

The processing temperature inside the first tubular segment 12 is generally regulated to remain within a range of about 140°C and 240°C, thus well below the threshold temperature of carbonization that is around 400-450°C.

The chipped fresh wood introduced in the first segment of the reactor is not contacted by streaming hot purging gases and the wood being driven exudes a liquor that is generally referred to as wood vinegar that is only partly vaporized and its liquid phase percolates down the constantly moved loose material advancing along the first tubular segment 12, and collects in a liquor trap 28 running along the lower part of the tubular conduit, leading to a wood vinegar discharge pipe 29, connecting to a wood vinegar collecting vessel (not show in the drawing). The vaporized fraction of the wood vinegar is ducted by the pipe 20 to a condenser 21, from where through a condensed liquor discharge pipe 29bis, is conveyed to the wood vinegar collecting vessel.

The liquor trap 28 may be in the form of a narrow deep channel at the bottom of the tube 12 connecting to a stainless steel discharge tube 29.

The fresh wood introduced at the inlet end of the first segment is practically completely dried once it reaches the outlet end part of the first tubular segment 12, from where it falls down the tubular chute 5, between vanes of the motor driven carousel valve 7 that releases the loose material down into the inlet end part of the second tubular segment 13, where the temperature is maintained well over the pyrolysis threshold temperature, generally between 450°C and 550°C, by modulating the heat input in form of hot flue gas produced by the burner 23, according to needs.

Control of the optimal processing temperatures into the carbonization stage of pre-dried wood inside the second tubular segment 13 of the conduit as well as of the wood drying and wood vinegar extraction stage, that is inside the first tubular segment 12 of the conduit of the reactor, advantageously avail itself of means for admixing a relatively cold flue gas to the hot flue gas to reduce the heat input to the pyrolysis stage 3 and/or to the drying and wood vinegar extraction stage 2 of the reactor. To this end, the cooled flue gas collected in the reservoir 33 is exploited as a source of cool gas for injecting it into the hot flue gas stream that is ducted into the hot flue gas circulation gap space of the second tubular segment 13 of pyrolysis and/or into the hot flue gas circulation gap space of the first tubular segment 12 of wood drying and wood vinegar recovery, to lower the temperature of the mixed flue gas streams and consequently the heat input rate to the carbonizing and/or to the drying wooden biomass as needed in order to independently regulate the temperature in the two stages of the reactor.

Temperature sensors 34 and 35 generate electrical control signals for respective flow rate regulating valves 37 and 38 of the cool flue gas being admixed to the hot flue gas entering the circulation gap space of the respective tubular segments 13 and 12, and, in a logic OR combination, control a fan 40 dedicated to re-circulate the cool flue gas toward the reactor segment requiring it. The mass of loose material undergoing pyrolysis while advancing along the second tubular segment 13, urged by the respective screw conveyor 16 driven by the motor 19', transforms to charcoal before reaching the outlet end of the second tubular segment 13 from where it eventually falls down the tubular chute 6, between vanes of the motor driven carousel valve 8 that releases the hot charcoal into the inlet end part of the third tubular segment 14 along which it is advanced by the screw conveyor 17, driven by the motor 19".

Inside the circulation gap space 18 surrounding the third tubular segment 14 circulates cool water introduced through the pipe 26, for contributing to cool the mass of loose charcoal being constantly moved by the rotating screw 17, while recovering heat in form of hot water. The heated water exits the circulation gap space 18 through the outlet pipe 27. The outer surface of the third tubular segment 14 of the charcoal cooling stage 4 of the reactor may have fins and/or baffles 31 for enhancing the exchange of heat between the stainless steel tube 14 and the streaming water being heated. Moreover, the cooled flue gas collected in the reservoir 33 is also exploited as a source of cooling fluid that is directly injected into the third tubular segment 14 to cool the loose charcoal advancing therein before releasing it outside the reactor.

The cooled flue gas generated by the burner 23 and collected in the reservoir 33 must have a relatively low excess air content that generally must be kept between 6 and 10 % by suitably controlling the combustion conditions in the burner 23, in order to ensure that the oxygen fraction remains safely below 1.0 %. This makes the collected cooled down flue gas ideally suited to be forced to flow through the mass of loose charcoal "stripping" heat from the hot charcoal; practically cooperating with the cooling water flowing through the circulation gap space 18 of the charcoal cooling stage 4.

A third temperature sensor 36 generates an electrical control signal for a respective flow rate regulating valve 39 of the cool flue gas being forced to circulate through the loose charcoal inside the third tubular segment 14, and, in a logic OR combination with the signals generated by the other temperature sensors 34 and 35, controls the fan 40.

In progressing through the cooling stage of the produced charcoal of the third segment 4 of the reactors the conditions of operation provide for cooling the charcoal reaching the outlet end of the segment the cool down below a temperature of about 70-100 °C, to facilitate handling and avoid the risk of self ignition when coming in contact with the air that normally would arise with a charcoal temperature 80 °C.

The so cooled down charcoal eventually falls down through the discharge port of the reactor, where the motor driven rotary vane (carousel) valve 10 practically impedes the escape of gas while continuously releasing the cooled down charcoal out of the reactor.

In the preferred embodiment illustrated in the drawing, the segments are not perfectly horizontal but all disposed with a slight upward inclination that may be comprised between 5° and 20°.

Making the relative screw conveyors 15, 16 and 17 urge the loose material up a sloping conduit, enhances intermixing of the particles and small pieces making up the mass of loose material being advanced because of an enhanced drag exerted by the lead surface of the screw on the particles and pieces in contact therewith. Intermixing may also be enhanced by having short stubs projecting from the lead helical surface of the screw and encroaching into the mass of loose material and displacing pieces thereof while being the mass as a whole pushed forward by the rotation of the screw.