Apparatus and process for torrefaction of ligno-cellulosic biomasses and mixtures with liquid

Abstract

A method and apparatus for treating a biomass material to produce a torrefied fuel comprising the steps of preheating the biomass material with a hot liquid flowing counter to the direction of travel of the biomass material at a temperature up to 200° C., superheating the preheated biomass material with a liquid flowing counter-current to the direction of travel of the biomass material to a temperature ranging up to 300° C. for a period sufficient to obtain full torrefaction of the biomass material, and cooling the torrefied biomass material with liquid flowing counter to the direction of travel of the torrefied biomass material.

Description

RELATED APPLICATIONS

This is a utility patent application claiming priority from U.S. Provisional Patent Application No. 61/457,192, filed Jan. 25, 2011 and is a continuation-in-part of U.S. patent application Ser. No. 12/656,357, filed Jan. 27, 2010.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not applicable.

REFERENCE TO SEQUENCE LISTING, A TABLE, OR A COMPUTER PROGRAM LISTING COMPACT DISC APPENDIX

None.

FIELD OF THE INVENTION

Torrefaction of biomass is a mild thermo-chemical treatment carried out at 200° C.-300° C., under anoxic conditions to produce a solid bio-fuel. The decomposition of hemi-cellulose in the biomass at this temperature range causes up to about 70% of the mass to be retained while approximately 90% of the initial biomass energy content is kept with the product having a low moisture content.

BACKGROUND OF THE INVENTION

Torrefaction has been a well-known process for more than a century, but presently a large and wide interest is emerging for up-grading the vast range of biomass resources of the planet. The biomass resources that are presently known to have a large potential are forestry, agricultural, herbaceous, algal and aquatic crops and residues. These biomass resources expected to provide a significant contribution to the world primary energy needs.

With the arrival on the market of low-cost petroleum/natural-gas and very-low cost coal, the interest in torrefied wood disappeared in the latter half of the 20^th century for economic reasons.

However, with the emerging problems of environmental sustainability, security and diversification of energy supply, increasing demand and interest for renewable energy (in particular bio-energy that is expected to provide in a longer-term a large contribution to the world primary energy needs) and for mitigation of the CO₂ emission, torrefaction of ligno-cellulosic biomass has undergone a renewed interest. Raw biomass has a low energy density and generally contains too much moisture, is too hygroscopic, can rot during storage and is difficult to comminute into small particles. The fibrous structure and toughness of woody and grass biomass is created naturally through a complex structure of mainly three polymeric constituents; cellulose, hemicellulose and lignin. Cellulose fibres are responsible for the fibrous structure and anisotropic properties of the biomass and they are bound together through a matrix of mainly hemicellulose and to a lesser extent lignin Wood, sawdust and cutter shavings are a favoured feedstock for pelletization and softwood is generally preferred over hardwood.

Another biomass creating great interest throughout the world is peat. Peat is an accumulation of partially decayed vegetation matter or histosol. By volume, there are about 4 trillion m³ of peat in the world covering a total of around 2% of global land mass (about 3 million km²). Peat deposits are found in many places around the world, notably in Ireland, Russia, Belarus, Ukraine, Finland, Lithuania, Latvia, Estonia, Scotland, Poland, northern Germany, the Netherlands, Scandinavia, New Zealand and in North America, principally in Canada, Michigan, Minnesota, the Florida Everglades, and California's Sacramento-San Joaquin River Delta. The amount of peat is smaller in the southern hemisphere, partly because there is less land, but peat can be found in New Zealand and the Falkland Islands/Malvinas, Asia, and Indonesia. Peat material is either fibric, hemic, or sapric. Fibric peats are the least decomposed, and comprise intact fiber. Hemic peats are somewhat decomposed, and sapric are the most decomposed. Phragmites peat is one composed of reed grass, Phragmites australis, and other grasses. It is denser than many other types of peat. The Intergovernmental Panel on Climate Change has taken the position that peat is not a fossil fuel even though the carbon dioxide emissions of peat (106 g CO₂/MJ) are higher than those of coal (94.6 g CO₂/MJ) and natural gas (56.1 g CO₂/MJ). It is estimated that if appropriate harvesting methodology is used to avoid destruction of the peat field that peat will be a long term renewable feed stock lasting thousands of years.

Torrefaction technology when integrated with the agro-pellet technology appears to have great promise. Agro-pellets (produced by direct processing of any type of humid biomass or mixture) are physically very similar to conventional pellets for heating, except for the composition of micro-elements and ashes.

Because the processing cost for torrefaction of agro-pellets seems roughly the same as the long distance logistic-cost saving (transportation) due to the large increase of the energy density of the torrefied biomass. The marketplace will give preference to the import of torrefied pellets economically produced due to their higher quality and lower transportation costs when compared with present commercial pellets.

There are numerous uses of torrefied biomasses or mixtures, namely, synthetic gas production and co-firing in power plants of torrefied biomass with the mineral coal. Through torrefaction, the biomass becomes more like coal. Torrefied biomass pellets can be easily handled, are especially attractive rather than using raw biomass because the torrefied biomass pellets have higher heating value and are friable (reducing milling energy needed) and can be blended, pulverized and co-fired with coal as the capital and operating costs for separate biomass fuel feed and firing systems are avoided. Well over half of the electric generation in the United States is derived from coal with more than two-thirds of the power plants using pulverized coal boilers. Because torrefied biomass is a high-quality, environmental friendly, solid bio-fuel and similar, from the operational point of view to coal, a high level of co-firing can be undertaken (50% up to complete substitution). Compared to the coal it replaces, the torrefied biomass reduces sulphur dioxide (SO₂), nitrogen oxides (NOx) and net greenhouse gas emission of CO₂ This offers considerable opportunity for world-wide CO₂ emission mitigation alone, keeping in mind that the substitution of 1 ton of agro-pellets saves ˜1.5 ton CO₂, while 1 ton of torrefied agro-pellets saves ˜1.9 ton CO₂. It is acknowledged that the initial torrefaction treatment has material losses and CO₂ emission, but these can be utilized in the process and can be taken into account in the evaluation of the specific total energy balance.

A generalized world-wide torrefied agro-pellet-coal co-firing activity (level of 20%) could provide a bioelectricity production equivalent to the power generation from about 200 nuclear power plants, with a decrease of about 1 billion tons of CO₂ emissions per year. Furthermore, high quality fossil fuels are rapidly being depleted and the present invention can extend existing supplies.

A number of patents disclose various torrefaction processes. These torrefaction processes are primarily direction towards torrefaction using heated gases in an inert atmosphere. Typical patents referring to gas treated processes are as follows:

U.S. Pat. No. 4,787,917 issued Nov. 29, 1988 is directed to the torrefaction of woody suckers having a diameter between 5 mm and 20 mm. After the suckers are harvested they are cut to a uniform length of between 10 mm and 25 mm. The cut sucker lengths are pre-dried to reduce the high quantity of water in the suckers which ranges between 40% to 60% at a temperature which is two to three times greater than that the temperature applied during the torrefaction process. This pre-drying reduces the water content of the suckers about 50%. The torrefaction is carried on at a temperature range of 250° C. to 280° C. for no more than 10 minutes resulting in a torrefied product having a water content being fixed at 3%.

U.S. Pat. No. 4,954,620 issued Sep. 4, 1990 discloses torrefaction of a ligno cellulose material, in oxygen free hot gases to preheat the material; softwood (conifer species) and hardwood, in a first zone from an ambient temperature up to 200° C. to eliminate humidity to not more than about 5%. The temperature is then rapidly raised to between 220° C. and 280° C. in a second zone by use of a gas burner. The temperature is then maintained at about the same temperature of the second zone in a third zone. The gas is permanently recycled to enable its temperature level to be accurately regulated.

Japanese Patent Number JP 11094463 issued Apr. 9, 1999 has a dry-air generator that releases dry air which absorbs and dissipates dispersed moisture. A dehydrator (2) compresses the raw material conveyed through a band conveyor (6) and press rollers (7), and disperses moisture to the raw material. The press rollers are oscillated by ultrasonic generators (8). It contains a microwave generator and induction heater for direct or indirect heating of raw material and evaporation of dispersed moisture.

Chinese Patent Number CN 101100344 (publication date not available) is directed toward a method and apparatus for desiccation of sewage sludge to minimize the dangers generally associated with this material and ease its handling and disposal. The patent discloses heating sludge (76-78% water content) in a first rotary kiln at 20-75° C., sending the heated sludge to a microwave processing device for 1-3 minutes, heating the cell-water in sludge and desiccating the same. The processed sludge is then sent into a mechanical dehydration device; stirred twice and the dehydrated sludge is placed into a stirring crusher to process crush-into-kernel treatment. The sludge is removed from a second rotary kiln through a sieve device, to produce sludge having a kernel-diameter of 1-8 mm and a water content below 40%.

U.S. Patent Publication 2009/0151251 published Jun. 18, 2009 discloses methods and apparatuses for the production of “syngas” from “carbon-containing feedstock.” It includes a torrefaction step or alternatively, use of “microwave-assisted pyrolysis” in which the feedstock is subsequently fed through a heated reaction vessel, such as a steam reformer or partial-oxidation reactor, to form syngas.

Russian Patent RU2085084 issued Jul. 27, 1997 discloses a dehydrating apparatus for foodstuffs using alternating applications of heat and infrared radiation. In one stage, the spent steam air mixture from another stage is used with a forced feed of drying agent. An oscillating regime of drying with forced feed of drying agent is used at the second stage of dehydration. The density of the supplied heat flow is increased in comparison with the first stage at which there is used the steam-air mixture formed at the second stage.

Various other methods of torrefaction have been, or are proposed as are shown in:

French Patent Number FR2624876 issued Jun. 29, 1989 sets forth a torrefaction process in continuous mode operation where the heating system for biomass is based on hot gas circulation (charged steam).

WO 2010 001137 published Jan. 7, 2010 discloses densifying biomass material and the microwave torrefaction of various biomasses at 2.45 GHz to obtain char and oil fuel products using preheating and torrefaction. Chemical additives such as sulphuric acid are added to improve the microwave efficiency for heating and breakdown of the densified biomass. Several other patents propose as a heating system the use of micro-wave radiation devices. For example WO2008 134835 published Nov. 13, 2008 and BRP 10707567 issued Jun. 16, 2009 both apply micro-wave radiation having a frequency of 2.45 GHz which is the standard microwave frequency utilized for drying (water evaporation).

The prior art has previously disclosed the torrefaction of various biomasses using fluids. A liquid is approximately 1000 times denser than an inert gas; thus more molecules are in contact with the biomass surface with a liquid than a gas. U.S. Pat. No. 4,553,978 issued Nov. 19, 1985 discloses torrefaction of ligneous matter in a liquid bath at a temperature ranging from at least 200° C. to 280° C. Two published patent publications are directed toward the torrefaction of biomass (wood pellets) using a heat transfer fluid (HTF). Each of these references discloses a preheating section, a torrefaction section and a cooling section. U.S. Patent Publication No. 2010251616 published Oct. 7, 2010 uses a HTF with a higher vapor pressure than petroleum based fluids taken from a group comprising Jatropha oil and other vegetable, algae, nut and bean oils. It is noted that during the process, oils are driven out of the biomass mix which results in altering or degrading the physical properties of the HTF. The process uses a sequential batch process using wood pellets placed on caged carts on tracks immersed in the HTF for preheating the pellets and torrefaction of the pellets. This invention replaced a previous continuous conveyor system by the same inventor which is disclosed in Patent Publication No. 2007266623 published Nov. 22, 2007, now U.S. Pat. No. 7,942,942, issued May 17, 2011. The '942 patent is directed towards a serpentine batch flow using separate wire cages immersed in a petroleum derived heat transfer Paraffinic fluid maintained at a very low vapor pressure to provide torrefaction of the wood pellets. The vapor chambers constantly received steam vapor and volatile organic compounds gasses during the torrefaction wood processing which exited at exhaust ports on the top of the vapor chambers.

The present invention is generally directed toward a process for the conversion of a variety of ligno-cellulosic biomass products (pellets, chips, briquettes, granules, powder and other small-size piece materials) by partial mild carbonization, into an high value bio-energy-commodity in particular direct conversion of an agro-pellet to a torrefied pellet. In fact, pellets are the ideal form of torrefaction heat transfer conditions. Pellets have the typical advantages of high specific density, low moisture content (less than 10%), low bulk density and an ideal shape for good heat transfer.

The process is preferably undertaken in a continuous operation mode which allows a continuous feed of pellet product to flow through multiple treating sections at different temperatures where the pellet product is heated by liquid torrefaction.

The continuous operation mode of the present invention envisions an apparatus constituted by a chain of different contiguous separated processing chambers. Each chamber is characterized by a specific set of chemical-physical parameters, energetic fluxes, temperature, etc., determined according to the function of the chamber (e.g. pre-heating, torrefaction and cooling), and these remain stable during the process. The material can be transported along the chambers by means of several well-known conveyor devices, such as: belt-type conveyor system, screw-type conveyor system, gravity-based conveyor system, etc.

The use of heated liquid in a counter flow to the direction of the transport of the pellets during the torrefaction step specifically increases the energy transfer to the considered type of material (agro-pellets), improving the speed and uniformity of the heating of the material down to its core. Its use is more efficient in this stage of the process when the water content of material is already reduced to low values.

Because the heat transfer from liquid to solid biomass is very high (especially if the liquid is agitated or pumped), the total processing energy need by using hot liquid heating can be reduced by about ⅔ with respect to conventional gas ovens.

A critical element for process optimization is the supply of controlled high rate heat input on the biomass; this can be more easily accomplished by using a liquid as shown by the present apparatus process.

Torrefaction under the present invention is of significant interest for the following reasons:

• • 1) Increase in efficiency of heat transfer to biomass and easy control of the torrefaction process;
  • 2. Decrease in time required for torrefaction;
  • 3) Increase (20%) of the heating-value of the processed feedstock;
  • 4) Low energy loss during processing because of the limited amount of volatilized biomass;
  • 5) Increased energy density during the process, reducing the specific costs of the material to be transported;
  • 6) Very low moisture content of 3% or less;
  • 7) Biologically stable;
  • 8) High friability (easy grinding);
  • 9) Hydrophobic (easy storage).

Although the inventive process and typical apparatus may be applied to any ligno-cellulosic agro-forestry biomass feedstock, algae, dedicated energy-crops, or aquatic crops of any given dimensions, for economic, large-scale supply and for convenience of use, the preferred biomass products to be processed are preferably peat and agro-forestry-pellets preferably softwood and more preferably conifers. These pellets have dimensions in the general range of 6-8 mm in diameter and up to 30 mm in length.

SUMMARY OF THE INVENTION

The present invention is directed toward a process and apparatus for manufacturing a “solid torrefied bio-fuel” from ligno-cellulose biomass pellets/chips/granules using a liquid preheating step which dries and heats the pellets in a range of 140° C. to 200° C. Torrefaction of the preheated biomass is accomplished in a second step in a chamber also using heated liquid to obtain a mild carbonization of the pellets around 280° C. without affecting the cellulose and lignin components of the biomass. The torrefied pellets are then cooled in a separate chamber after the torrefaction step.

It is an object of the invention to manufacture a pellet/chip/granular product which has been uniformly torrefied by quickly heating the same with a heated liquid to be able to produce a more homogeneous refined biomass product at a much faster processing rate when compared with gas-heating processes by the adoption of hot liquid heating of the pellets.

It is another objection of the invention to produce a torrefied fuel from peat.

It is yet another object of the invention to utilize a process which produces a torrefied fuel which consumes less energy during the torrefaction process making the torrefied fuel more economically feasible and with better energy balances.

It is still another object of the invention to produce a pellet fuel which contains a significant amount of the energy content 90%) of the starting material being processed.

It is an additional object of the invention to convert peat pellets to produce a torrefied fuel pellets and integrate peat pelletization plants with torrefaction plants by reducing the moisture level of the feedstock from 70% to 10% prior to torrefaction.

It is still another object of the invention to minimize the torrefaction liquid consumption in the process by controlling liquid evaporation, recovery and regeneration.

It is yet another object of the invention to minimize environmental issues involved in the torrefaction process by adoption of a separate recovery, treatment of condensable and non-condensable emissions.

It is still another object of the invention to minimize the energy process consumption by recovery and utilizing the V.O.C. for the processing heating.

It is further object of the invention to allow all types of biomasses/mixtures including soft woods such as conifers to be pelletized and further refined into “torrefied agro-pellets”.

These and other objects, advantages, and novel features of the present invention will become apparent when considered with the teachings contained in the detailed disclosure along with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic block diagram representing the stages of the liquid torrefaction process showing the heat exchange between the stages and the direction of liquid flow contra to the direction of transportation of the biomass;

FIG. 2 is a schematic diagram of the inventive liquid torrefaction apparatus;

FIG. 3 is a schematic diagram of the apparatus of FIG. 2 used with gas and vapors recovery apparatus used to separate and remove condensable and non-condensable gases and vapors during the various stages of the process;

FIG. 4 is a schematic diagram showing filtration of the liquid used in the torrefaction process; and

FIG. 5 is a schematic showing the liquid level sensing and additional liquid reservoir of the process.

DETAILED DESCRIPTION OF THE INVENTION

The present Invention relates to a liquid torrefaction (mild carbonization) process and apparatus for the conversion of ligno-cellulosic biomass materials or mixtures pre-formed in a substantially uniform form (pellets, chips, briquettes, granules, etc.) into a novel refined high value, solid torrefied bio-fuel using a finely controlled processing-heating-combination using recirculating liquid at specific temperatures. The terms “biomass” and “biomass materials” as used in the specification and claims should be construed as covering softwood and hardwood, sawdust, peat, plant material such as sorghum and plant suckers, algae and other organic materials or mixtures thereof. While conventional pellets are refined products obtained by drying and compaction of wood, sawdust, agro-pellets are refined products physically similar to conventional pellets but are obtained from any type of biomass mixtures. For the purposes of this application, the term “pellets” is used to describe both wood based pellets, agro-pellets and peat pellets.

During torrefaction (beyond about 240° C.), biomass undergoes a process which is difficult to control for the presence of biomass hot spots. To avoid this risk, normally the torrefaction process is generally carried out at temperature between 240° C. and 280° C. However, the higher the temperature, the faster is the torrefaction process can be accomplished. Therefore, in the apparatus, because of the level and uniformity of material temperature can be controlled easily and with high accuracy, the torrefaction can be carried out at very high temperature. Normally in the torrefaction processes (using gas), 280° C. is considered critical maximum level to avoid exothermal (uncontrollable) process conditions. In the apparatus, the process occurs naturally in oxygen-free atmosphere (in liquid or under of Oxygen-free atmosphere), and thus it is possible to operate the torrefaction at a temperature above this critical temperature of 280° C., without the risk of fire because of the absence of oxygen.

The preferred embodiments and best modes of the invention are shown in FIGS. 1 and 2. While the invention is described in connection with certain preferred embodiments, it is not intended that the present invention be so limited. On the contrary, it is intended to cover all alternatives, modifications, and equivalent arrangements as may be included within the spirit and scope of the invention as defined by the appended claims and description.

In addition, the originality of the invention relies also on the combined use of high heat exchange, agitation and high flow of heating liquid allowing for a faster and better control and uniformity of the temperature of the material to be processed; an improved control of the temperature of the entire material (not only its skin temperature, but also its core temperature) as the same is actually crucial for improving the quality and homogeneity of the final torrefied product and also for avoiding the risk of non-controllable exothermic reactions.

The process and apparatus of the invention is basically a continuous three step or stage process as shown in FIG. 1 using a liquid for torrefaction which has a flow current which runs counter to the directional transport of the biomass. The invention uses a number of receptacles for the process steps which provide a number of advantages by facilitating the heat recovery while allowing better temperature control and process regulation. The receptacles preferably are formed as troughs having an upper open configuration to allow the recovery of biomass emissions during the process.

Since liquid is much denser than a gas, the transfer of energy to the biomass pellets is much faster than when torrefaction is done by a gas. The heat energy is in some cases transferred by conduction, between the liquid adjacent to the biomass surface. During the process, water vapor, V.O.C. and other gases are also driven out of the biomass and are carried off by the extraction chimneys.

The torrefaction liquid used in the process may be a vegetable oil such as sun flower, corn oils or mixtures of any type of vegetable oil or petroleum based oil, used oil, synthetic oils, including silicone oil, organic liquids such as Dowtherm oil, coal/peat distilled liquid, or other particular liquids including low temperature melting metals such as bismuth or metal alloys. Oils derived from soy beans, palm, seeds, nuts and micro-algae can also be used as the torrefaction liquid. It is also envisioned that exhausted or previously used oils for food cooking such as palm oil, olive oil, grape seed oil, and peanut oil could be used.

The first stage as shown in FIGS. 1 and 2 depicted as block 20 (pre-heating) is used to heat the material by means of a recirculated liquid loop. Pellets are fed into the preheating open chamber from the feed stock hopper. It should be noted that each of the staging blocks 20, 40 and 60 represent receptacles which hold the torrefaction liquid and the material. The material is introduced into each receptacle and moved by mechanical transfer systems from one end to the other end of the receptacle then extracted from one receptacle and transferred to a subsequent receptacle for additional processing. These mechanical systems insure a controlled transport of the material in the receptacle against the pressure of a current of liquid in a counter direction. The material is transported by a conveyor against a flow of liquid which is at a higher temperature at the upstream end of the flow than the temperature at the downstream end of the flow which allows for maximum heating efficiency of the material. While the conveyor shown in the drawings used in the receptacles is a screw conveyor, it should be noted that belt conveyors, troughs, trommels, or other conveyors known in the art can be used. It should also be noted that the material transport systems (conveyors) are designed and manufactured to allow flow of the torrefaction liquid and are unaffected by being immersed. In order to increase the heat transfer, the heating liquid can be agitated mechanically or hydraulically in each of the receptacles. It should be noted that the agitation must be operated without interfering with the counter current liquid flow.

Stage two (torrefaction) as shown in block 40 is a torrefaction receptacle and is the core stage of the conversion process and is used for the torrefaction of the material using a closed liquid torrefaction loop system. In this stage, as shown in FIG. 2, the liquid is heated in heater 54 and transported by pump 52 to the base of conveyor 44 and flows toward conveyor 24 with an optimized energy transfer to the material and for uniform material torrefaction as the material is carried along the torrefaction conveyor against the liquid flow. In such way a better control and uniformity of the temperature of the material itself can be achieved with quick torrefaction time. Consequently the insurgence of hot spots is avoided, eliminating the risk of triggering exothermic reactions.

The use of a neutral atmosphere such as CO₂, Argon or Nitrogen is not required in the torrefaction chamber to eliminate the risk of triggering uncontrollable exothermic reactions such as pyrolysis because the material undergoing torrefaction is already protected by the liquid itself or by the upper liquid vapors presence. Because the material is totally immersed in a nonoxidative liquid, the maximum process temperature can be elevated to 300° C. or more, thus allowing a fast and economic torrefaction process.

Based on a combination of well controlled and diversified heat inputs the torrefaction process temperature is kept between 230° C. and 280° C., but preferably around 280° C. Ligno-cellulosic material or mixtures such as softwood (conifers), grasses or peat in appropriate form and size such as pellets, briquettes chips, granules, powder, etc. are placed in contact with heated liquid.

Torrefaction is generally operated below 280° C. because above 280° C. there is great risk of start-up of an uncontrollable pyrolysis process with great-loss of material and implementation of the carbonization process. When using the present invention, torrefaction has been successfully undertaken up to 300° C., thus allowing the material to be moved through the process much faster.

The torrefaction stage of the process is based on the direct heat inputs to the material to sustain the endothermic reactions of the process.

The third stage 60 is a cooling stage where the torrefied material is cooled by low temperature liquid through heat exchange loop and immersing the torrefied material in the lowertemperature liquid.

The third stage as indicated by block 60 and FIG. 2 provides for the cooling of the torrefied material in cooling chamber 61 of the trough at least below 100° C. and the flow of the heated liquid to preheating trough 21 of the trough via pump 63 and conduit 65.

An optional fourth stage as shown in block 80 provides for the draining of the liquid from the torrefied material. The draining effect is completed as shown in FIG. 1.

Depending on the material to be processed (and particularly its initial water content), the first step 20 constitutes a pre-treatment material heating. Such pre-treatment is thus used to achieve low water content in the material, which are preferably pellets, of no more than 10%, preferably 3% before processing it in the second torrefaction step. As shown in FIG. 1, heated liquid can be recycled from the cooling step (block 60) back to first stage (block 20) for pre-heating the biomass. This can be accomplished by an external loop with heat exchanger, or pumping the heated liquid from the cooling chamber block 60. Maximum heat exchange is accomplished by transporting the material against the flow direction of the torrefaction liquid so that the material is carried into progressively cooler liquid temperatures before discharge into the block 80.

In operation, the material such as biomass pellets 200 are stored in a silo-hopper 10 and discharged from the silo-hopper 10 into a funnel structure 23 which discharges the material (pellets) onto the proximal end of a preheat conveyor 22 which rotates through upper open trough 21. The spiral heat exchanger 12 in the silo 10 is used to heat the material stored in the silo. The conveyor 22 transports the preheated material against the liquid flow onto a belt conveyor or elevator 24 which dumps the material into the receiving area of the torrefaction conveyor 42. The material is carried by conveyor 22 through the preheating chamber 20 formed by a trough 21 having an open upper section where the material is preheated so that their moisture content is reduced preferably to about 3%. Heating the material drives some of the resident moisture, gases, and V.C.O out of same. As shown in FIG. 3, temperature sensors 128 can be mounted in the channel of trough 21 and can be used to determine the temperature of the liquid. The chimney recovery system 120 allows a recovery of gases and chemicals discharged from the biomass during heating which have an economic value or must be dispersed of. The speed of conveyor 22 can be adjusted to submit the material at various increasing liquid temperatures below specific designated condensation chimney columns 120. The material is heated by the moving torrefaction liquid which is used during the process. The hot torrefaction liquid is returned from the cooling receptacle chamber 60 and trough 61 to the preheating open receptacle of trough 21 via heat recovery pump 64 and conduit 65. The liquid preheats the biomass material coming into the preheating trough 21 from the silo 12 through the funnel structure 23. All of the conduits, troughs and receptacles used in the present invention are insulated to prevent heat loss. The conveyor 22 carries the material so that the material is constantly moved and brought into contact against the current of the heated moving liquid. A pump 23 transports heated liquid from the proximal end of the preheating receptacle chamber 20 through filter 28 via conduits 25 and 26 back through the hopper 10 and through the stored material in the feed hopper 10 via a coiled (serpentine) heat conduit 12. The heated liquid is drawn off of the hopper coil conduit 12 by a recycling pump 15 and transported through conduit 16 into cooling receptacle chamber 60 of upper open housing 61 to reduce energy costs. A reservoir 70 is connected to conduit 16 for automatic resupply of torrefaction liquid to receptacle chamber 20 when the liquid level in the chamber is sensed to be below a certain critical level.

After the preheating step, the preheated materials shown as pellets 200 are then carried by a belt or elevator conveyor 24 or mechanical system into an open torrefaction receptacle in the form of a trough 41 filled with hot torrefaction liquid. As shown in FIG. 2, the heating liquid is transported out of the proximal end of the trough 41 by pump 52 through conduit 51 into and through a heater 54 which can be fuelled by gas, electricity, steam, microwave or the cheapest heat source available at the site. The heated torrefaction liquid is maintained at a temperature level of about 280° C. to 300° C. so that the material undergoes torrefaction. Torrefaction consists in a fast uniform heating of all the material volume, avoiding that no portion of the material being heated exceeds the 300° C. to avoid the presence of hot-spots and the risk of triggering the exothermal uncontrolled pyrolysis process described above. The material immersed in the hot liquid will be submitted to the torrefaction process for a typical process period ranging from about 5 to about 30 minutes depending upon the capacity and type of apparatus and upon the size of the material. The final torrefaction stage 41 of the process as shown in FIG. 4 is based on the combined utilization of micro-wave radiation (preferentially 5.8 GHz) thermal inputs from a microwave generator 46 at the end of the torrefaction state toward the rear of block 40 to heat the interior of the biomass pellets to a desired temperature of at least 240° C. up to about 300° C.

The micro-wave radiation with frequency of 5.8 GHz is utilized, rather than the 2.45 GHz micro-wave radiation normally utilized. It should be noted that the 5.8 GHz microwaves radiation is more efficient than the 2.45 GHz radiation when the material moisture content is very low the moisture having been previously reduced in the previous torrefaction area. Therefore, to quickly reach a temperature level of 240° C. or greater throughout the biomass pellets, the use of a micro-wave radiation of a 5.8 GHz is desirable.

The pellets 201 are transported to the distal end of the torrefaction receptacle block 40, having been subjected to the continuous flow of liquid flowing in a direction counter to that of the material, where they are deposited onto an elevator or belt conveyor 44 which carries the torrefied material 201 into cooling open receptacle block 60. The material is then carried by a conveyor to a drainage stage 80.

The materials are deposited by torrefaction conveyor 44 (FIG. 2) into cooling block 60 formed by an open trough housing having an open upper section. The upper open housing trough 61 forming the cooling block 60 houses a conveyor 62 which carries the torrefied material counter to the flow of liquid in chamber 60 to elevator or belt conveyor 64 which transports the cooled torrefied material 202 to a drying conveyor 81.

In the cooling step, cooled liquid is deposited from conduit 16 into the distal end of block 60 and removed at the proximal end by pump 63 and conduit 65 to the upper open trough 21. As the torrefied material is carried by conveyor against the flow of the liquid, they give up their heat to the cooler liquid and the liquid becomes progressively hotter by the effect of forced heat convection.

In all of the open troughs, an agitating pump can be used to circulate the liquid in the chamber below the respective conveyors.

It is recognized that there may be a liquid depletion in the system as the liquid is absorbed by the torrefied materials as they are processed and transported out of the cooling block 60 onto the draining area 81. A small percentage of the liquid remains on and within the torrefied material. This can be kept at a minimal level by centrifuge recovery or other known technology. As shown in FIG. 5, replenishment of the system uses a liquid reservoir 70 as seen in FIG. 5 which feeds liquid into the cooling block 60 via conduit 71, valve 72 and conduit 73 when sensors 75 indicate a low liquid level. The sensors 75 serve to open valve 72 allowing liquid to pass from reservoir 70 into cooling housing 61. Further it is also recognized that pieces of the material may be generated by the conveyors rotation, pumped liquid and oils from the devolatized material may impact progressively on the effectiveness of the torrefaction liquid. In order to remove such impurities, filter and regeneration systems 26, 56 and 66 are provided as shown in FIG. 4.

The torrefied material produced by the present inventive process and apparatus is greatly different from charcoal and from the so called “brown-charcoal” process, obtained by carbonization of wood at low-temperature. Typical physical characteristics of the torrefied pellets of the invention are:

1) It is highly friable and can be milled easily;

2) It has very low hygroscopicity (about 3%);

3) It is stable (no biological degradation);

4) Its reactivity to combustion is high;

5) Its heating-value is high: ˜5,300 kcal/kg.

It appears that during torrefaction-treatment only the hemi-cellulose component of the material is modified, without substantially affecting the cellulose and lignin components of material and that the same are relatively stable and not affected by the temperature level of the novel process.

The direct exposure of the material to the high temperature heated fluid quickly heats the material as previously discussed. Most of the water and gases are driven out of the material in the preheating chamber prior to reaching the torrefaction chamber. The general order of gases driven out is carbon dioxide gas, carbon monoxide and other volatile compounds. Torrefied material produced with the invention generally have a typical volume change reduction ranging from about 8% to about 13% and a typical weight change reduction ranging from about 7% to about 15%.

In the present process, the original material preferably are pellets sized with a diameter ranging from 6 mm to 14 mm, and more preferably 6 mm to 8 mm with a length less than 30 mm. It will be understood that the cylindrical size of the pellets is an ideal form to accomplish uniform heating and thus homogenous torrefaction within a short period of time

FIG. 3 shows the recovery systems for various gasses and vapors emitted from the biomass during the treatment process. During the entire process, significant emissions are produced in the form of steam vapour, condensable vapors, non-condensible gases as effects of the biomass drying and devolatization. Extraction columns or chimneys 120 are placed on top of various processing troughs for a separate recovery of emitted products. Each chimney or extraction column 120 recovers different products (steam, acetic-acid, V.O.C., etc. as the material is subjected to different temperatures while providing abatement of noxious emissions (Cl/CO) by presently known prior art devices. It should be noted that the series of continuous chimneys which are schematically shown are located in appropriate sites in order to selectively recover the local emissions. At given process conditions, local emissions have constant temperature and composition and the number of continuous chimneys determines the selectivity in order to maximize the energy efficiency and economics of the torrefaction process.

The principles, preferred embodiments and modes of operation of the present invention have been described in the foregoing specification. However, the invention should not be construed as limited to the particular embodiments which have been described above. Instead, the embodiments described here should be regarded as illustrative rather than restrictive. Variations and changes may be made by others without departing from the scope of the present invention as defined by the following claims:

Claims

1. A method of treating a biomass material to continuously produce a torrefied product comprising the steps of:

a. transporting a biomass material through a first processing station containing moving heated liquid and immersing said biomass material in said heated liquid preheating said biomass until said biomass material reaches a desired preheated temperature to remove the moisture from the biomass until the biomass material has a maximum equilibrium water content of about 10%;

b. transporting said preheated biomass material from said first station to a second torrefaction station;

c. applying a flow of heated torrefaction liquid in said second station in a continuous liquid flow circuit opposite to the direction of travel of said biomass material to transfer heating energy to preheated biomass material until said biomass material reaches a temperature suitable to create torrefaction of said biomass material;

d. transporting said torrefied biomass material from said second station to a third cooling station;

e. cooling said torrefied biomass material in said third station with a moving flow of cooler liquid in a chamber separate from said torrefaction liquid flow circuit by transporting said biomass material in a counter-current direction to that of the moving cooling liquid; and

f. transporting heated liquid from the downstream flow area of the carried biomass of said third station chamber to said first station to transfer heat generated by said torrefied biomass material to said first station.

2. A method as claimed in claim 1 wherein said biomass material is pre-formed pellets.

3. A method as claimed in claim 1 wherein each station is an upper open ended receptacle.

4. A method as claimed in claim 3 wherein said receptacle is a trough with an open upper section.

5. A method as claimed in claim 1 wherein said second station is additionally heated with micro-wave radiation having a frequency of 5.8 GHz.

6. A method as claimed in claim 1 wherein said torrefaction liquid is contained in a closed flow circuit including a housing defining a torrefaction chamber, a pump for moving liquid out of said torrefaction chamber to a heater for heating said liquid from about 230° C. to about 300° C. and conduit means for returning said heated liquid from said heater back to said housing.

7. A method of treating biomass material as claimed in claim 1 wherein said torrefaction liquid has its flow directed in a counter-current direction opposite to the direction of travel said biomass material during said preheating, torrefaction and cooling steps.

8. A method of treating biomass material as claimed in claim 1 wherein the heating liquid for each of the steps a), c) and e) is separately filtered and regenerated.

9. A method of treating biomass material as claimed in claim 1 wherein gases and waste products emitted during the heating of said biomass material are collected by a plurality of continuous collection chimneys mounted over said first and second stations.

10. A method of treating biomass material as claimed in claim 1 wherein said torrefaction temperature is at least 300° C.

11. A method of treating biomass pellet feedstock by torrefaction to produce a refilled solid bio-fuel comprising the steps of:

a. loading biomass pellet feedstock into a continuous feed container for depositing said pellets into a preheating receptacle;

b. preheating the biomass pellets in said preheating receptacle with a recycled heated liquid moving in a counter-current flow to that traveled by the biomass feedstock to a temperature less than about 200° C.;

c. applying a heated liquid substantially contained in a closed flow circuit to the preheated biomass pellets which have been transported to a second receptacle heating said biomass pellets until the pellets reach a temperature of up to about 300° C. for sufficient time allowing uniform torrefaction of said pellets;

d. cooling the torrefied biomass pellets outside of said torrefaction closed flow circuit which have been transported to a third receptacle with a cooler liquid moving in a counter-current flow in respect of the pellets;

e. recycling the liquid used to cool the pellets in step d. to the biomass pellets of step b); and

f. transporting the cooled pellets from said third receptacle to a draining station.

12. A method of treating biomass pellets as claimed in claim 11 wherein said heated liquid is taken from a group of liquids consisting of one or more of the following liquids: silicone oil, vegetable oil, petroleum based oil, synthetic oil, used oil, coal/peat distilled liquid, low temperature metals.

13. A method of treating biomass pellets as claimed in claim 11 wherein said liquid in contact with said pellets is agitated in step c).

14. Apparatus for torrefaction of biomass material using a liquid for torrefaction comprising:

a. a biomass feed housing;

b. a preheating receptacle defining a preheating chamber with an open upper section adapted to hold liquid and receive biomass from said feed receptacle and conveyor means mounted in said preheating receptacle for carrying biomass material through said preheating receptacle and the liquid contained therein;

c. a torrefaction receptacle defining a chamber with an open upper section positioned downstream of said preheating receptacle, conveyor means mounted in said torrefaction receptacle to received preheated biomass material from said preheating conveyor means and carry biomass material through said torrefaction receptacle;

d. a closed fluid circuit means connected to said torrefaction receptacle, heater means connected to said fluid circuit to heat liquid passing through said fluid circuit and pump means to pump liquid through said fluid circuit from one section of said torrefaction receptacle back to another section of said torrefaction receptacle;

e. a cooling receptacle defining a cooling chamber with an upper open section positioned downstream of said torrefaction receptacle, conveyor means mounted in said cooling receptacle for carrying torrefied biomass material received from said torrefaction receptacle through said cooling receptacle; and

f. discharge means discharging said torrefied biomass material from said cooling receptacle.

15. Apparatus as claimed in claim 14 including heat exchange means connecting said cooling chamber with said preheating chamber and carrying liquid from said cooling chamber to said preheating chamber.

16. Apparatus as claimed in claim 14 wherein said biomass feed housing is a feed hopper with a heat exchange means mounted thereto.

17. Apparatus as claimed in claim 16 wherein a heat exchange means in the form of a coil shaped conduit is mounted in said biomass feed housing.

18. Apparatus as claimed in claim 17 wherein at least one pump is connected to coil shaped conduit leading to or away from said feed hopper.

19. Apparatus as claimed in claim 16 wherein said heat exchange means comprises a conduit means with one end connected to the proximal end of said cooling receptacle and communicates with said cooling chamber, another end connected to said preheating receptacle and communicating with said preheating chamber and a pump mounted to said conduit means to transport liquid from said cooling chamber back to said preheating chamber.

20. Apparatus as claimed in claim 16 including separation columns mounted over various sections of said preheating receptacle and said torrefaction receptacle to collect by products from said biomass material when the same is subjected to different liquid temperatures.

21. Apparatus as claimed in claim 16 including a liquid reservoir receptacle activated by sensor means in one of said receptacles to replenish liquid into said cooling receptacle.

22. Apparatus as claimed in claim 21 wherein said sensor means is mounted to said cooling receptacle to sense the liquid level in cooling chamber.

23. Apparatus as claimed in claim 15 wherein said torrefaction receptacle has microwave generating means mounted thereto to provide 5.8 GHz microwaves.

24. Apparatus for torrefaction of biomass material using a liquid for torrefaction comprising:

a. a biomass feed receptacle with a first heat exchange means mounted thereto communicating with a preheating receptacle and a cooling receptacle;

b. a preheating receptacle comprising an open ended trough housing defining a preheating chamber adapted to hold liquid and receive biomass from said feed receptacle and conveyor means mounted in said preheating receptacle for carrying biomass material through said preheating receptacle and the liquid contained therein;

c. a torrefaction receptacle comprising an open ended trough housing defining a chamber positioned downstream of said preheating receptacle, conveyor means mounted in said torrefaction receptacle to received preheated biomass material from said preheating conveyor means and carry biomass material through said torrefaction receptacle;

d. a closed fluid circuit means connected to said torrefaction receptacle, heater means connected to said fluid circuit to heat liquid passing through said fluid circuit and pump means to pump liquid through said fluid circuit from an end of said torrefaction receptacle back to the other end of said torrefaction receptacle so that biomass material is transported by said torrefaction conveyor means against the flow of liquid heated by said heater means;

e. a cooling receptacle comprising an open ended trough housing defining a cooling chamber positioned downstream of said torrefaction receptacle, conveyor means mounted in said cooling receptacle for carrying biomass material received from said torrefaction receptacle through said cooling receptacle; a second heat exchange means connecting said cooling chamber with said preheating chamber and carrying liquid from said cooling chamber to said preheating chamber.

25. An apparatus as claimed in claim 24 wherein said agitation means is mounted to said torrefaction receptacle housing.