Background

Biomass is a promising renewable source of energy, which can be converted into different fuels, such as oil, gas and charcoal. The conversion can be achieved by heating biomass in the absence of oxygen in a process termed "pyrolysis". The combustion of the biomass derived fuels can be C0 ₂ neural, as the C0 ₂ released by combustion is recycled into biomass again by photosynthesis.

Pyrolysis has been used by mankind since ancient times for the production of charcoal form wood. However the successive use of wood as source of biomass contributes to the global problem of deforestation. An alternative source of biomass are agricultural waste products.

The olive tree is abundant in the whole Mediterranean basin and is extensively used for olive oil production. The waste generated from olive oil production, including olive stones and pomace, has a high calorific value and therefore represents a good biomass for the production of charcoal by pyrolysis. Other common agricultural wastes in the Mediterranean region are almond shells and palm waste. Production of charcoal from these materials therefore represents a possibility to provide fuel to many people without promoting deforestation.

Pyrolysis reactions can be classified as "slow", "fast" and "flash" according to their solid residence time, heating rate and pyrolysis temperature. "Slow" pyrolysis is characterized by a long solid residence time (minutes to hours), and comparative low heating rate and temperature, whereas "fast" and "flash" pyrolysis have short residence times in the second to minute ("fast") or millisecond ("flash") range, higher heating ranges and pyrolysis

temperatures. "Slow" pyrolysis results in the highes charcoal product yield, which decreases in "fast" and "flash" pyrolysis in favour of increasing oil yields. The pyrolysis of olive waste to charcoal is already known in the art.

Hmid et al. (Hmid et al. 2014. Production and characterization of biochar from three-phase olive mill waste through slow pyrolysis. Biomass & Bioenergy. 71 , 330-339) discloses the pyrolysis of olive mill waste by slow pyrolysis at maximal temperatures of 430°C - 530°C at different heating rates at laboratory scale conditions.

Encinar et al. (Encinar et al. 1996. Pyrolysis of two agricultural residues: Olive and grape bagasse. Influence of particle size and temperature. Biomass and Bioenergy. 1 1 (5), 397- 409) investigated the pyrolysis of olive bagasse at temperatures between 300°C - 900°C. Anincrease of fixed carbon content and heating value was observed over this temperature range, while the yield of the obtained charcoal steadily decreased. The authors concluded that a pyrolysis temperature of 600°C - 700°C would be required to obtain charcoal for standard briquette production.

Especially for large scale charcoal production by pyrolysis, ecological process conditions and systems which recycle side products of the process to reintroduce them into the process are highly desirable. WO 2014/ 46206 discloses a system for pyrolysis of biomass, wherein the pyrolysis gas is combusted to heat the pyrolysis reactor. Furthermore the document discloses a process with a stepwise increasing pyrolysis temperature. However, the document does not disclose specific pyrolysis conditions or systems optimized for the production of charcoal from olive waste.

In view of the of the described art it was the object of the present invention to provide an optimized large scale process for the production of charcoal from olive waste or other common agricultural residues in the Mediterranean region, an optimized system for carrying out the process and a superior charcoal which can be produced in said large scale process.

Description of the invention

The afore mentioned problem is solved according to the present invention by a process for the production of charcoal from biomass selected from olive waist, preferably olive pomace, and/or olive stones, or almond shells, or palm waste, comprising, i) feeding the biomass to a reactor, ii) ii) subjecting the biomass to pyrolysis at a temperature increasing from between about 180°C and about 220°C to between about 380°C and about 470°C for between about 10 min and about 20 min, and

withdrawing pyrolysis gas, and charcoal from the reactor.

More specifically, during the process of the invention, the biomass is subjected to a temperature profile, wherein: a) the biomass is initially subjected to a temperature of between about 180°C and about 220°C, preferably between about 190°C and about 210°C, over about 4 min to about 8 min, preferably over about 5 min to about 7 min,

b) the temperature is subsequently increase to between about 280°C and about 340°C, preferably between about 290°C and about 330°C, most preferably to about 320°C over about 1 min to about 5 min, preferably about 2 min to about 4 min, and c) the temperature is finally increase and maintained to between about 380°C and about 470°C, preferably between about 390°C and about 460°C, most preferably to about 450°C over about 4 min to about 8 min, preferably about 5 min to about 7 min.

The pyrolysis may be performed in a system for the pyrolysis of biomass according to a different aspect of the invention, comprising,

- a reactor comprising an inlet at the upstream end of the rector,

- a first outlet for solid products at the downstream end of the reactor,

- one or more further outlets for volatile products at the downstream end of the reactor,

- a gas cleaning system comprising a cyclone separator connected to the one or more outlets for volatile products, a condenser connected to the cyclone separator and a baffle separator connected to the condenser, and

- at least one burner positioned after the baffle separator for heating the reactor.

"About" in the context of the present disclosure refers to an average deviation of maximum +/- 10 %, preferably +/- 5 % based on the indicated value. For example, a temperature of about 200°C refers to 200°C +/- 20°C and preferably 200°C +/- 10°C. "Pyrolysis" is understood herein to mean thermal decomposition of organic matter in the absence or limitation of oxygen.

"Biomass" refers to living or formerly living organic matter.

It has been surprisingly found, that the processing of biomass selected from olive waist, preferably olive pomace, and/or olive stones, or almond shells, or palm waste through slow pyrolysis according to the described process parameters enables the conversion of the biomass into charcoal with a high heating value and high carbon content with good yields at a large scale. However, it has also been found, that the process produces an excess of combustible gases and tar, which requires an adaptation of the processing of these intermediates and the parts of the system employed for the process as described below in detail.

To make the process more ecologic and cost efficient, side products such as pyrolysis gas, water and thermal energy can be reintroduced into the process, as described in more detail below.

The charcoal obtained from the disclosed process can be agglomerated into briquettes, which burn without smoke or smell and have a long burning time. Furthermore the briquettes can be produced at relatively low costs.

Biomass employed in the present process may be olive waist, preferably olive pomace and/or olive stones, or almond shells, or palm waste. Olive pomace comprises small pieces of skin, pulp, seeds and stones. The olive waste may be derived from two-phase or three- phase extraction of olives which is the most common waste in the production of olive oil. Palm waste may comprise empty fruit bunches, fibres, shells, and crushed kernels. In general "waste" refers to residues from the recited agricultural products mentioned herein.

Before being subjected to pyrolysis, the biomass needs to be processed to obtain optimal overall process yields and product characteristics.

In an optional pre-treatment step, biomass might be washed and/or screened for non- biomass components. It has been found that optimal process yields and product characteristics are obtained in the inventive process with biomass, which has a particle size of between 0.1 mm and 10 mm prior to pyrolysis. Therefore, in one embodiment, the inventive process comprises the step of sizing the biomass to a particle size of lower than 25 mm, preferably lower than 15 mm, most preferably between 0.1 mm and 10 mm prior to pyrolysis. Sizing may be accomplished by milling, cutting, or grinding for example.

It has also been found that the moisture content of the biomass influences product yields and characteristics. In a preferred embodiment of the present invention, the biomass used in the process has a moisture content of between about 2,5% to about 20% total weight, preferably between about 2,5% to about 10%, most preferably about 5% prior to pyrolysis. To ensure the desired moisture content, the process may comprise a step of drying the biomass to the afore mentioned moisture content prior to pyrolysis.

In a specific embodiment, the biomass is dried with thermal energy, such as provided by hot air, recovered by heat exchange from the exhaust gases of the combusted pyrolysis gases. In a certain embodiment of the process, the water evaporated during the drying of the biomass may be condensed and used in the agglomeration of the charcoal obtained from the pyrolysis of the biomass.

After the described optional preconditioning, the biomass is fed through an inlet to theupstream end of a reactor by a suitable assembly. Such assembly may include a feed auger or a rotary feeder valve.

The pyrolysis reactor may be a fixed cylinder comprising a conveying mechanism, preferably a screw. In an alternative embodiment, the pyrolysis reactor may be a rotating cylinder. In the latter case, the walls of the rotary cylinder may be equipped with structures, such as rims for example, that promote the movement of the biomass in the reactor. Preferably the parts of reactor consist of steel or hard materials to withstand the olive stones that may be comprised in the biomass.

For a high-throughput of biomass, several reactors might be used in parallel.

The reactor might be sited together with at least one burner in a combustion and exhaust chamber, which might be designed to guide the hot combustion gases generated by the burners around the reactor and discharge the gases from the chamber through a chimney or exhaust pipe.

In the reactor, the biomass is subjected to pyrolysis at a temperature increasing from between about 180°C and about 220°C to between about 380°C and about 470°C in between about 10 min and about 20 min. Preferably the temperature increases from about 190°C to about 460°C, most preferably the temperature increases from about 200°C to about 450°C. Preferably the biomass is subjected to pyrolysis for between about 13 min and about 17 min, most preferably about 15 min.

In a preferred embodiment of the invention, the biomass is subjected to a temperature profile, wherein: a) the biomass is initially subjected to a temperature of between about 180°C and about 220°C, preferably between about 190°C and about 210°C, over about 4 min to about 8 min, preferably over about 5 min to about 7 min, b) the temperature is subsequently increase to between about 280°C and about 340°C, preferably between about 290°C and about 330°C, most preferably to about 320°C over about 1 min to about 5 min, preferably about 2 min to about 4 min, and c) the temperature is finally increase and maintained to between about 380°C and about 470°C, preferably between about 390°C and about 460"C, most preferably to about 450°C over about 4 min to about 8 min, preferably about 5 min to about 7 min.

In a specific embodiment: a) the biomass is initially subjected to a temperature of about 200°C for about 6 min, b) the temperature is subsequently increase to about 320°C in about 3 min, and c) the temperature is finally increased and maintained to about 450°C for about 6 min in the process in accordance to the present invention.

In another specific embodiment: a) the biomass is initially subjected to a temperature of about 200°C for about 6 min, b) the temperature is subsequently increase to about 300°C in about 3 min, and c) the temperature is finally increased and maintained to about 400°C for about 6 min in the process in accordance to the present invention.

In one embodiment, the biomass is heated with a heating rate of about 10°C/min to about 25°C/min, preferably about 15°C/min to about 20°C/min during the pyrolysis.

A pyrolysis process carried out with the disclosed temperatures and heating rates is generally considered to be a "slow pyrolysis" in the art.

During the pyrolysis reaction, the biomass is conveyed along the axis of the reactor to expose the biomass to different temperatures for certain times, as disclosed above.

Therefore, different reaction zones along the longitudinal axis of the reactor may be heated to different, increasing temperatures.

Alternatively, the pyrolysis reaction might be carried out in more than one reactor. In this embodiment the reactors are heated to different temperatures. To expose the biomass to the different temperatures, the biomass is withdrawn from one reactor and fed to the next reactor with a higher temperature, thereby exposing the biomass to the above described

temperature profile.

In a preferred embodiment of the process according to the invention, the biomass is heated only by its contact to the wall of the reactor, which is heated directly by at least one burner from the outside of the reactor. In an alternative embodiment, a heat transfer medium, such as sand might be introduced into the reactor together with the biomass. The convection of the biomass through the reactor may be facilitated by a rotating screw inside the reactor, or by the rotation of the reactor itself. The speed of transport, and accordingly the time of expose of the biomass to different temperatures, can be controlled by the speed of the rotation of the screw, or the rotation speed of the reactor respectively.

The system may comprise one or several thermosensors inside the reactor, which measure the temperature inside the reactor and/or the biomass and communicate with a controlling unit. The controlling unit controls the speed of the motor that drives the screw or the rotation of the reactor and may also control the intensity of the burner flames, for example by regulating valves which determines the flow of combustion gas.

The pyrolysis reaction according to the process of the invention is preferably performed under a pressure of lower than 1000 mbar, preferably lower than 750 mbar, most preferably at about 500 mbar. The reduced pressure may be generated by a pump downstream of the reactor and upstream of further means for processing the pyrolysis gases. A suitable pump which withstands the hot gas produced by the pyrolysis reaction is employed. The use of this mild vacuum generates non-oxidative reaction conditions which are required for the pyrolysis reaction. Alternatively non-oxidative might be generated by an inert-gas atmosphere.

The pyrolysis reaction in accordance with the disclosed reaction conditions results in fine charcoal as solid product and combustible pyrolysis gases as a volatile product. The pyrolysis gas is composed of a complex mixture of non-condensable constituents such as hydrogen, carbon monoxide, carbon dioxide, and methane. Furthermore the pyrolysis gas comprises condensable constituents such as water vapour, heavy tars and other hydrocarbons.

The obtained charcoal is discharged from the reactor through an outlet at the downstream end of the reactor by a suitable assembly. Such assembly may include an auger or a rotary valve.

After discharging the charcoal from the pyrolysis chamber, the charcoal may be cooled in a cooling reactor. Water or air might be used as cooling agents for the cooling reactor.

Alternatively the charcoal may cool by transporting the charcoal on a conveyor belt.

The charcoal initially obtained from the pyrolysis process may be stored in a silo or other type of suitable storage container.

In a preferred embodiment of the invention, the charcoal may subsequently be agglomerated into briquettes, especially ball shaped briquettes, pellets or other similar objects for storage, transport and convenient use by end user. For this purpose, the charcoal is mixed with water and optionally a binding agent. In one embodiment of the invention, the water used for agglomeration comprises water extracted from the pyrolysis gas as described herein or recovered in the drying process of the biomass. The binder might be selected from starch, bentonite, molasses, tar or other suitable matter. In case tar is used as a binder, the tar extracted from the pyrolysis gas might be used. After thorough mixing in a suitable mixer, charcoal, water and optionally binder, the mixture is pressed into briquettes, especially ball shaped briquettes, of a desired size, or pelleted by a briquetting or pelleting machine. For example a YHQ 650-4 briquette machine making balls from Huaye Heavy Industry & Machinery Co., Ltd (Hanan, China) might be used. Other suitable machines are commercially available, for example from C.F. Nielsen SA (Baelum, Denmark) or K.R. Komarek Inc. (Wood Dale, USA).

The pressed briquettes or pellets might subsequently be dried. For the drying process, thermal energy recovered from combustion gases as explained below might be used. Drying of briquettes or pellets might be performed in a large scale drying chamber through which the briquettes or pellets are conveyed on a conveyor belt, while a current of hot air is flowing through the chamber. Hot air is provided to the chamber by means of hot air generators and fans.

The dried briquettes or pellets might optionally be stored in a silo or other suitable container. Finally dried charcoal briquettes or pellets might be packed in sacks by a suitable machine for storage and sale.

The pyrolysis gases generated in accordance with the inventive process as described before are discharged from the reactor by one or more further outlets and processed by a three- phase gas cleaning system.

As mentioned before, it has been surprisingly found, that the processing of biomass selected from olive waist, preferably olive pomace, and/or olive stones, or almond shells, or palm waste according to the disclosed process generates an excess of combustible gas and tars in comparison to a classical pyrolysis process. Consequently, it is a further aspect of the present invention to employ an increased gas cleaning system comprising pipes with an increased diameter and an increased baffle separator and tar collector in comparison to systems described in the art and known to the skilled person for pyrolysis processes for other biomass of different origin or according to other process parameters. The dimensioning of the gas cleaning system is also adapted in relation to the capacity of the pyrolysis reactor.

In a first step of the gas cleaning process, the pyrolysis gas may be provided by a tubing from the outlet of the reactor to the inlet of a cyclone separator, where solid particles are separated from the pyrolysis gas. Within the cyclone separator, a high speed rotating gas flow is established within a cylindrical or conical container which enables the separation of solid particles from the gas. The separated solid particles may consist mainly of charcoal generated by the pyrolysis process and may be collected and subjected to further processing together with the main charcoal product stream.

In one embodiment of the invention, the gas inlet of the pump which generates the reduced pressure inside the reactor is connected to the outlet of the reactor, and the outlet of the pump is connected to the inlet of the condenser.

In a next step, the pyrolysis gas may be provided by a tubing from the outlet of the cyclone separator to the inlet of a condenser. Within the condenser, water is withdrawn from the pyrolysis gas. In the condenser, the pyrolysis gas might pass tubes comprising a refrigerated liquid and/or plates connected to such tubes. In a further embodiment other condensable constituents of the pyrolysis gas, such as heavy hydrocarbons, may be withdrawn from the pyrolysis gas. The water withdrawn from the pyrolysis gas may be used for the

agglomeration of the charcoal to reduce the water consumption and waste water production of the process.

In a final step of the gas cleaning process, the pyrolysis gas may be provided by a tubing from the outlet of the condenser to a baffle separator, and passed through the baffle separator, whereby tar is withdrawn from the gas. The tar may be collected in a tar collector (3).

Figure 1 depicts a baffle separator in accordance with the present invention.

The baffle separator comprises a gas input (1 ), a tar output (2) and a tar collector (3) at the bottom part and a gas outlet (4) at the top part of the separator. The single baffles (5) are connected to each other, to form baffle segments extending from the bottom part of the separator to the top end part. The single baffles in a baffle segment may be arranged in a staggered manner. The bottom facing end of one baffle might be arranged to overlap with the top end of the previous baffle. The baffle segments are arranged in a parallel fashion to constitute channels, through which the pyrolysis gas passes the separator from the bottom to the top. The collected tar might be further processed. For example, the tar might be used in the processing of the charcoal derived from the pyrolysis as a binder in the agglomeration process as described above.

After passing the baffle separator the pyrolysis gas might be combusted to heat the reactor. For this purpose, several burners along the axis of the chamber are positioned to direct a flame towards to wall of the chamber. Thereby, the reactor is heated by the flames of the burners and the combustion gases flowing around the reactor. Instead of pyrolysis gas, natural gas might be used to supply the burners. In one embodiment, the pyrolysis reaction might be started by heating the reactor by combusting natural gas. Once the pyrolysis reaction has started and pyrolysis gas is produced in sufficient amount, the reactor might be further heated by combusting pyrolysis gas. When the pyrolysis gas is used to supply the burner, a pilot flame of natural gas is always maintained.

Thus, it is a further embodiment of the invention, that the reactor is heated from the outside by combustion of the pyrolysis gas withdrawn from the reactor.

In the embodiment of the invention, wherein pyrolysis is carried out in more than one reactor, the first reactor might be heated by the combustion of natural gas. The subsequent reactor might be heated by combustion of the pyrolysis gas produced by the pyrolysis in the first reactor.

Finally, the combustion gases are exhausted via a chimney or pipe. Since it is one of the underlying ideas of the present invention to make an efficient use of the natural resources, the combustion gases might be passed through a heat exchanger within the chimney or exhaust pipe to recover the thermal energy comprised in the hot gas. The thermal energy recovered from the combustion gases might then be used to dry the biomass prior to pyrolysis or the briquetts or pellets derived from agglomeration of the charcoal.

Since the pyrolysis of biomass selected from olive waist, preferably olive pomace, and/or olive stones, or almond shells, or palm waste in accordance with the inventive process produces large amounts of combustible gas, the combustible gas which is not used to heat the reactor might be combusted by an auxiliary burner, which is also connected to the gas cleaning system. Preferably the auxiliary burner is connected to the system after the outlet of the baffle separator. The above described process yields a high quality charcoal product with a high calorific or heating value, high carbon rate and low ash rate. Therefore, ina further aspect, the invention relates to charcoal obtained or obtainable by the process disclosed above.

Therefore the present invention relates to charcoal characterised by a higher heating value (HHV) of at least about 28 MJ/Kg of dry matter, preferably at least about 30 MJ/Kg. Within the meaning of this invention, higher heating value (HHV) is determined according to standard NF EN 14918.

The charcoal of the present invention is characterized by a carbon content of at least about 70% of dry matter, preferably at least about 75%, most preferably about 80%. In specific embodiments the hydrogen content of the charcoal may be between about 1% and about 6% of dry matter, or between about 1 ,5% and about 5%, or between about 2% and about 3,5%. In specific embodiments, the nitrogen content of the charcoal may be between about 0,01 % and about 1 % of dry matter, or between about 0, 1 % and about 0,7%, or between about 0,2% and about 0,5%. Within the meaning of this invention, the carbon, nitrogen and hydrogen content is determined according to standard NF EN 15104.

In specific embodiments, the sulphur content of the charcoal may be between about 400 and 550 mg/kg of dry matter. Within the meaning of this invention, the carbon content is determined according to standard NF EN 15289.

Furthermore the charcoal of the present invention is characterized by an ash content of below about 15% of dry matter, preferably below about 12%, most preferably of below about 6%. Within the meaning of this invention, the ash content is determined according to standard ISO 1 171. In specific embodiments, the charcoal may have a volatile matter content from about 10% to about 25%, or from about 15% to about 20% of dry matter. Within the meaning of this invention, the volatile matter content is determined according to standard NF EN 15148.

In a specific embodiment the charcoal is characterised by a higher heating value (HHV) of at least about 28 MJ/Kg, a carbon content of at least about 70% and an ash content of below about 15% of dry matter. Preferably the charcoal has a higher heating value (HHV) of at least about 30 MJ/Kg, a carbon content of at least about 75% and an ash content of below about 12%. Most preferably the charcoal has a higher heating value (HHV) of at least about 30 MJ/Kg, a carbon content of about 80% and an ash content of below about 6%. Preferably the charcoal described in the above embodiments is obtained from biomass selected from olive waist, preferably olive pomace, and/or olive stones, or almond shells, or palm waste. Most preferably the charcoal is derived from olive waist, preferably olive pomace, and/or olive stones.

Also the present invention relates to briquettes or pellets comprising the charcoal as describe above.

A specific embodiment of the present invention relates to briquettes or pellets comprising charcoal derived from olive waste, which has a higher heating value (HHV) of at least about 30 MJ/Kg, a carbon content of about 80% and an ash content of below about 6%.

Examples

1 .1. Olive waste biomass was subjected to pyrolysis at a final temperature of 400°C to 500°C over 10 min as described above.

Typically the following products were obtained per ton of dried biomass:

• 480 kg combustible, non-condensable gas comprising hydrogen, carbon

monoxide, methane (380 kg) etc.

• 190 kg of heavy tars or hydrocarbons

• 330 kg of charcoal

1.2. Olive waste biomass was subjected to pyrolysis at a final temperature of 500°C to 600°C with a short processing time.

Typically the following products were obtained per ton of dried biomass:

• 1 10 kg combustible, non-condensable gas

• 730 kg of heavy tars or hydrocarbons

• 160 kg of charcoal . Olive waste biomass was subjected to pyrolysis as described above with the following temperature profile: 1 . 200°C for 6 min.

2. Subsequent temperature increase to 300°C in 3 min

3. Subsequent temperature increase to 400°C for about 6 min

The charcoal was subsequently analysed and the following characteristics were obtained:

Physical Analysis

Total moisture 22 % gross

Dry matter 78 % gross

Basic Analysis

Ash 5,6 % of dry

4,4 % gross

Volatile matter at 815°C 17,4 % of dry

over 7 min

13,5 % gross

Elementary Analysis

Total carbon 80,4 % of dry

6,7 % gross

Total hydrogen 2,87 % of dry

4,7 % gross

Total nitrogen 0,42 % of dry

0,33 % gross

Total sulphur 471 mg/kg of dry

Total chlorine 2692 mg/kg of dry

Thermal Analysis

Higher heating value 7379 Cal/g

30894 J/g

Higher heating value 5755 Cal/g

24095 J/g

Lower heating value 7238 Cal/g

30304 J/g

Lower heating value 5525 Cal/g

23132 J/g