STEAM CRACKING CONTROL FOR IMPROVING THE PCI OF BLACK GRANULES

Abstract

The present disclosure relates to a method for continuously preparing a pulverulent material having a calorific power greater than the calorific power of the initial biomass, the method comprising a steam cracking step, wherein the initial biomass consists of elements having a grain size distribution of between P25 and P100, having a humidity of less than 27%, and directly subjected to a steam cracking treatment.

Claims

1. A process for the continuous preparation of a powdered material having a calorific value greater than the calorific value of an initial biomass, comprising: a steam cracking stage, wherein an initial biomass subjected to the steam cracking stage is constituted of elements with a particle size class of between P16 and P100, having a moisture content of less than 27%, the initial biomass being directly subjected to a steam cracking treatment in the steam cracking stage.

2. The process of claim 1, wherein a severity factor of the steam cracking stage is greater than 3.7 and less than 4.2.

3. The process of claim 1, wherein a severity factor of the steam cracking stage is controlled in line with a carbon content in an off-gas.

4. The method of claim 1, wherein a severity factor of the steam cracking stage is controlled as a function of a carbon content in a sample of steam-cracked biomass.

5. The process of claim 1, wherein a severity factor of the steam cracking stage is controlled as a function of a pH of a steam-cracked biomass sample.

6. The process of claim 1, wherein a pH of a steam-cracked biomass sample obtained via the steam cracking stage is adjusted by adding lime, carbon dioxide, or dissociated forms of carbon dioxide.

7. The process of claim 1, further comprising a biomass pelletizing step for preparation of pellet fuels.

8. The process of claim 2, wherein a severity factor of the steam cracking stage is controlled in line with a carbon content in an off-gas.

9. The method of claim 2, wherein a severity factor of the steam cracking stage is controlled as a function of a carbon content in a sample of steam-cracked biomass.

10. The process of claim 2, wherein a severity factor of the steam cracking stage is controlled as a function of a pH of a steam-cracked biomass sample.

11. The process of claim 2, wherein a pH of a steam-cracked biomass sample obtained via the steam cracking stage is adjusted by adding lime, carbon dioxide, or dissociated forms of carbon dioxide.

12. The process of claim 2, further comprising a biomass pelletizing step for preparation of pellet fuels.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0037] The present disclosure will be better understood from reading the following detailed description of a not-limiting example of the disclosure, wherein FIG. 1 represents a schematic view of a continuous production facility according to the disclosure.

[0038] FIG. 1 is an example of the realization of a steam cracker unit 10, in particular for the manufacture of a combustible material using biomass chopped down to a particle size between P16 and P100, according to the disclosure. In the preferred embodiment, the biomass will have a particle size between P20 and P100 or even between P25 and P100.

[0039] FIG. 2 is a table representing the characteristics of the different particle size classes according to the nature of the elements that compose the material.

DETAILED DESCRIPTION

[0040] The steam cracker unit is fed with biomass consisting of elements with particle size classes between P16 and P100, with a moisture content of less than 27%.

[0041] Particle size is defined by the particle size of the main fraction (P) and the particle size defining the coarse fraction (G). Particles smaller than one millimeter are considered to belong to the fine fraction. The main fraction P must represent at least 80% overall of the fuel.

[0042] According to the size and percentage of the elements constituting the main fraction (P), the coarse fraction (G) and the fine fraction, the particle size of the elements of the biomass is defined according to reference class. These reference classes are pre-established by the European Committee for Standardization (CEN/TS 14961) in the technical specification document (CEN/TS), which serves as a normative document in domains wherein the current state of the art is not yet stable enough for a European standard.

[0043] CEN/TS also specifies that 80% (overall) of the fuel must pass through a sieve corresponding to the particle size class and must be retained in the sieve corresponding to a particle size of 3.15 mm.

[0044] The coarse fraction G should not exceed 1% of the overall mass. The fine fraction should not exceed 5% of the overall mass. [0045] P16 corresponds to a grain size with 3.15 mm≤P≤16 mm, and G>45 mm [0046] P25 corresponds to a grain size with 3.15 mm≤P≤25 mm, and G>63 mm [0047] P100 corresponds to a grain size with 3.15 mm≤P≤100 mm, and G>200 mm

[0048] The particle size of a wafer sample can be determined using an oscillating sieve system, a rotary sieve or an imaging measurement system.

[0049] The biomass is shredded with sharp tools (mill blades), and is directly subjected to steam cracking treatment without humidification or any other treatment.

[0050] The thermal treatment of the biomass is carried out with slightly saturated steam at a temperature between 195° C. and 215° C. The processing time is between 5 and 30 minutes.

[0051] The Treatment Severity Factor is defined using the formula: FS=Log10(time(min)*exp((T° C.-100)/14.75)). The higher the temperature and the longer the treatment time, the greater the severity and the more transformation in the product.

[0052] The lower calorific value on a dry basis increased on average by 0.7 joules per gram, with a variation of 0.25 to 2 joules per gram depending on the severity of the heat treatment, starting from 17 to 19 joules per dry gram of initial wood, that is to say a gain of between 2 and 12% in LHV, around 4% on average.

[0053] Depending on the severity of the heat treatment, the material losses ranged from just a few % to 24%.

[0054] The higher the severity, the greater the loss and the greater the gain in Inferior Calorific Power. During steam cracking, it is mainly the hemicelluloses that are attacked. The main soluble volatiles generated are furfural, acetic acid and formic acid. These soluble volatiles are found in the emitted steam (“evaporates”). Depending on the type of gasoline used, the nature of the condensates varies. Therefore, furfural is more important for oak (up to 60% of VOCs) while for pine, acetic acid is dominant (up to 50% of VOCs).

[0055] Description of the Facility

[0056] This steam cracker unit (10) comprises a hammer mill (11) fed with biomass by means of an auger (12). A separator removes any oversized elements before the chips enter the hammer mill (11). In this wet hammer mill (11), the biomass is ground into fragments with a particle size of between P25 and P100.

[0057] The silo (13) is filled by a bucket loader that collects the biomass from piles formed on the ground storage areas. The biomass is discharged from the hammer mill (11) onto a conveyor belt (14), which is equipped with a weighing belt, and which then transports it to the feed hopper of a hot air dryer (15).

[0058] A moisture sensor continuously monitors the moisture content of the biomass. The biomass fragments are extracted from the silo (16) by a planetary screw and deposited onto a conveyor belt that transports them to a feed silo (17) of a reactor (18) allowing for the continuous treatment of 15 tons of biomass per hour.

[0059] The reactor (18) is a pressure reactor into which superheated steam is injected from its lower part with a pressure of 18 bar and a temperature of 250° C. This vertical reactor has a conical shape to avoid the formation of plugs. The steam flow is extracted from the reactor at its upper level. At the output of the reactor, the steam is returned to the CH boiler in which it was produced.

[0060] It is noted that in the reactor (18) the temperature of the steam is 203° C. and the pressure is 16.7 bar. The feed silo (17) is shaped like a truncated ellipsoid in order to facilitate the flow of the biomass fragments.

[0061] In addition, a rotating scraper in the feed silo (17) pushes the biomass fragments towards a feedscrew (19). This conical feedscrew (19), which has a cross-section that narrows as the screw enters the reactor (18), continuously takes a predetermined quantity of biomass fragments from the feed silo (17), pre-compresses it and pushes it through a screw passage into the reactor (18) under pressure. The dimensions of the conical orifice and the screw were selected respectively, in order to minimize the pressure loss in the reactor and expel the air contained in the biomass fragments.

[0062] It should be noted that the compression force exerted by the screw on the fragments of biomass makes it possible to advantageously expel part of the residual water present in the fragments of biomass.

[0063] At the end of the feedscrew (19), the compacted biomass fragments form a compact block that is dispersed in the reactor by the steam flow. Dispersed biomass fragments fall into the reactor due to gravity upon being heated by the steam flow, and settle on top of the fragments that have previously accumulated on the bottom of the reactor, where they continue to be heated by the steam flow.

[0064] It should be noted that (18) the hold time for the biomass fragments in the reactor is controlled according to the level of the biomass fragments that have accumulated on the bottom of the reactor. In this particular embodiment of the disclosure, the hold time is set at 7 minutes, which corresponds to a severity factor of 3.8. At the bottom of the reactor (18), a scraper mounted on a vertical axis (not shown in FIG. 1) pushes the biomass fragments towards a discharge feedscrew (20) allowing for the extraction of the biomass fragments from the reactor (18).

[0065] This discharge feedscrew (20) pushes the biomass fragments out of the reactor toward a valve (21) with a controlled opening. The opening of this valve is continuously adjusted to control the flow of biomass fragments extracted from the reactor. Under the pressure of the steam present in the reactor and/or the discharge feedscrew (20), biomass fragments are continuously expelled through the valve openings (21) at a very high speed into an expansion line (22) and are carried by the steam flow leaving the reactor with these biomass fragments into the pressure reduction line (22) to a separation unit (23).

[0066] Note that the pressure in the pressure reduction line gradually decreases until it reaches a pressure of about 1.1 bar at the separator. Thus, an explosive decompression of the biomass fragments occurs, due to a revaporization of part of the condensation water present in the biomass fragments. This sudden expansion of the water vapor leads to the appearance of shear forces in the combined fragments of biomass, which causes the mechanical rupture of the structure of the latter.

[0067] In the separation unit (23), the mixture of biomass fragments and steam enters tangentially to a rapidly rotating blade. Under the effect of the centrifugal force generated by this blade, the biomass fragments are projected into a discharge pipe (24), while the steam is ejected from the separator through a valve.

[0068] In a variant of this embodiment of the disclosure, a pressurized cyclone may be implemented to separate the biomass fragments from the residual steam. It should be noted that the rejected steam contains volatile materials that can be advantageously burned in a boiler.

[0069] The biomass fragments projected into a discharge pipe (24) are discharged into a storage silo (25), and will then be transformed into pellets with a diameter of approximately 7 millimeters and an average length of 22 millimeters in a pellet press (26).

[0070] Adjustment of the Steam Cracking Conditions

[0071] The continuous operation of the steam cracker allows a real time control of the operating conditions and in particular: [0072] Of the severity factor [0073] Of the pH of the biomass.

[0074] For this purpose, a measurement of the chemical characteristics of the effluents, or of the chemical characteristics of the solubilized samples of the steam-cracked biomass, can be taken.

[0075] Real-Time Analysis of Effluents

[0076] The real-time measurement of the chemical characteristics of the effluents allows for the evaluation of the material losses of the steam-cracked biomass, resulting in an increase in the carbon content of the effluents. This information can be acquired in real time by an infrared probe positioned in the effluent evacuation pipe.

[0077] The signal provided in real time by the probe is representative of the variations of the carbon level in the effluents. This signal is used by a computer to modify the steam cracker parameters, namely the severity rate, according to a function predetermined by the objectives: for example, maximization of the LHV.

[0078] The probe can also analyze other organic compounds, particularly oxygenated compounds, and provide mapping information for the organic compounds in the effluents in order to control the steam cracking parameters.

[0079] Real-Time Analysis of Steam-Cracked Biomass Sampling

[0080] The steam cracker unit can also comprise a system for real-time sampling of the steam-cracked biomass, with solubilization of this sample in order to collect information on the chemical composition using one or more physico-chemical probes, for example, a pH measurement or a measurement of the organic compound composition.

[0081] This information is then used by a computer to automatically optimize the steam cracker unit parameters in real time.

[0082] Pelletizing Application

[0083] For the production of pellet fuels with a moisture content of less than 10%, the moisture content of the final product before pelletizing must be controlled.

[0084] For this purpose, the initial biomass has a low moisture content prior to steam cracking, which is namely less than 14% and preferably less than 10%.

[0085] Alternatively, the initial biomass can be steam-cracked with a moisture content higher than 14%, but lower than 27%. In this case, a drying step of the steam-cracked biomass is provided downstream of the steam cracker unit, before or after pelletizing.