Reactor for grinding and roasting biomass, biomass processing system and facility incorporating such a reactor, and associated method

Abstract

A reactor for grinding and roasting biomass, including: a chamber interiorly delimited with internal walls; a grinder laid out inside the chamber, including a central rotary shaft rotatably mounted in the chamber and grinding elements present on the central rotary shaft for grinding against internal walls and of biomass, or lingo-cellulosic biomass, present inside the chamber; a heater for heating and maintaining by thermal conduction via the grinder the biomass present inside the chamber, at a predetermined called roasting temperature between 200 C. and 350 C., to simultaneously achieve grinding and roasting of the biomass in the chamber.

Claims

1. A biomass grinding and roasting reactor, comprising: a chamber interiorly delimited with internal walls; grinding means laid out inside the chamber, including a rotary central shaft rotatably mounted in the chamber and grinding elements present on the rotary central shaft for grinding biomass, or ligno-cellulosic biomass, against the internal walls, present inside the chamber; heating means for heating and maintaining by thermal conduction via the grinding means the biomass present inside the chamber, at a predetermined roasting temperature, between 200 C. and 350 C., to simultaneously achieve grinding and roasting of the biomass in the chamber, wherein the heating means is configured to perform at least the maintaining during the grinding and roasting of the biomass, wherein the heating means includes heat piping elements, and wherein one of the heat piping elements is laid out inside the central rotary shaft and contains a liquid such that the liquid is centrifuged when the central rotary shaft is rotated.

2. The biomass grinding and roasting reactor according to claim 1, wherein the grinding means and the internal walls of the chamber have substantially identical heat conductivities.

3. The biomass grinding and roasting reactor according to claim 1, wherein the heat piping elements are in physical contact with at least one portion of the grinding means.

4. The biomass grinding and roasting reactor according to claim 3, comprising a further plurality of heat piping elements uniformly distributed at a periphery and in physical contact against a peripheral wall of the chamber on at least one major portion of its length.

5. The biomass grinding and roasting reactor according to claim 3, wherein the heat piping elements are in physical contact with the grinding elements present on the central rotary shaft.

6. The biomass grinding and roasting reactor according to claim 3, wherein the heat piping elements each include at least at one of their ends fins for forming a heat exchanger between a gas and a heat transfer fluid inside the heat piping elements.

7. The biomass grinding and roasting reactor according to claim 1, wherein the grinding means comprises hammers present on the central rotary shaft rotatably mounted in the chamber, the hammers configured to strike and burst biomass particles against a peripheral internal wall of the chamber.

8. An installation for treating biomass, or ligno-cellulosic biomass, comprising: the reactor according to claim 1; and a granulation press located downstream of the reactor.

9. The biomass treatment installation according to claim 8, further comprising a cyclone laid out between the reactor and the granulation press.

10. The biomass treatment installation according to claim 8, further comprising a combustion chamber distinct from the reactor chamber, the combustion chamber being configured to achieve post-combustion of the gases from the roasting and particles of a size less than a predetermined diameter at a predetermined, post-combustion, temperature between 800 and 1,000 C.

11. The biomass treatment installation according to claim 10, wherein the combustion chamber comprises at least one multifuel burner for simultaneously achieving post-combustion of the gases from the roasting and of the particles with a size of less than the predetermined diameter and of solid material fuels.

12. The biomass treatment installation according to claim 11, wherein the multifuel burner is connected to the granulation press so that the solid material fuels are roasted granules produced by the granulation press.

13. The biomass treatments installation according to claim 10, wherein an outlet of the combustion chamber is connected: to a reactor inlet so as to heat the heating means at the roasting temperature with the post-combustion gases; or to an inlet of the reactor to inject the post-combustion gases at the roasting temperature, into the reactor chamber; or to the heat exchangers formed by fins of heat pipes so that energy for heating a heat transfer fluid of the heat pipes is provided by the post-combustion gases.

14. The biomass treatment installation according to claim 13, further comprising an additional heat exchanger, distinct from the heat exchangers of the heat pipes, a hot fluid circuit of which is connected to the outlet of the combustion chamber and a cold fluid circuit of which is connected to a dryer configured to apply the biomass before being fed into the reactor, to provide energy for heating the dryer by the post-combustion gases.

15. The biomass grinding and roasting reactor according to claim 1, wherein a portion of the one of the heat piping elements extends beyond an end of the central rotary shaft and includes fins mounted on the portion of the one of the heat pipe elements to form a heat exchanger.

16. The biomass grinding and roasting reactor according to claim 1, wherein the liquid in the one of the heat piping elements is naphthalene.

Description

SHORT DESCRIPTION OF THE DRAWINGS

(1) Other advantages and features of the invention will become better apparent upon reading the detailed description of the invention given as an illustration and not as a limitation with reference to the following figures wherein:

(2) FIG. 1 is a diagram showing the heat exchange coefficient levels depending on the fluids or solids in mutual contact;

(3) FIG. 2 is a diagram showing the purge gas flow rates according to the technology of grinders used according to the state of the art;

(4) FIG. 3 is a schematic longitudinal sectional view of a biomass grinding and roasting reactor according to the invention of applying hammer grinder technology;

(5) FIGS. 3A and 3B schematic transverse sectional views of the reactor of FIG. 3;

(6) FIG. 4 is a schematic view of a first embodiment of a biomass treatment installation integrating a biomass grinding and roasting reactor according to the invention;

(7) FIG. 5 is a schematic view of a second embodiment of a biomass treatment installation integrating a biomass grinding and roasting reactor according to the invention.

DETAILED DISCUSSION OF PARTICULAR EMBODIMENTS

(8) In the following description, the terms of inlet, outlet upstream, downstream are used with reference to the transfer direction of the biomass and of the fluids both in the reactor according to the invention, in a system and an installation integrating such a reactor. Further, the terms of upper, lower, above, below are used with reference to the vertical or horizontal physical orientation of the reactor and of the dryer of the installation according to the invention.

(9) By diameter of the particles, is meant to their equivalent diameter, i.e. the diameter of the sphere which would behave identically during a selected grain size analysis operation.

(10) FIGS. 1 and 2 have been commented on above. So they will no longer be commented on here.

(11) In FIGS. 3 to 3B, is illustrated a reactor for concomitant grinding and roasting ligno-cellulosic biomass, like wood, according to the invention.

(12) The reactor 1 according to invention comprises a single chamber 10 delimited at its cylindrical periphery with a side wall 11, and respectively on either side with two end walls 12, 13.

(13) The illustrated reactor 1 is made from a hammer grinder. Thus the reactor comprises a central rotary shaft 14 mounted on bearings 140 arranged on the outside of the chamber 1.

(14) A plurality of hammers 15 is attached onto the rotary shaft 14 defining stages regularly spaced along the chamber. Each stage also comprises a number of regularly distributed angularly hammers 15.

(15) As visible in FIGS. 3 and 3B, a number of eleven stages is thus provided along the chamber, each stage comprising a number of four hammers positioned from 15 to 90 relatively to each other.

(16) Thus, when the biomass, dried beforehand to a humidity level preferably comprised between 10 and 15%, is supplied into the reactor 1, the rotating hammers 15 via the shaft 14 will strike and burst the biomass particles against the peripheral internal wall 110 of the chamber.

(17) According to the invention, in order to simultaneously achieve grinding and roasting of biomass within the chamber 10, while controlling at best the heat exchanges between the different elements of the reactor (side wall, hammers, rotary shaft) and the biomass particles being roasted, implantation of suitable heat pipes 16 is provided for heating the hammers 15 and the rotary shaft 14 on which they are mounted, maintaining their temperature via thermal conduction, heating the side wall 11 of the chamber to a predetermined so-called roasting temperature comprised between 200 C. and 350 C.

(18) More specifically, a first heat pipe 160 is inserted into the inside of the rotary shaft 14. The provided assembly is such that the relevant heat pipe rotates with the shaft 14. The efficiency of the heat pipe 160 is even further improved by the centrifugation effect of the liquid which it contains, the latter will be distributed over the whole of the internal wall of the heat pipe during rotation.

(19) As better illustrated in FIGS. 3A and 3B, second heat pipes 161 are in physical contact with the side wall 11 of the reactor. These second heat pipes 161 are regularly distributed angularly.

(20) As visible in FIGS. 3A and 3B, a number of eight heat pipes 161 is thus provided on the perimeter of the chamber and on the whole height thereof, the eight heat pipes 161 being distant from each other at 45.

(21) As visible in FIG. 3, the ends 1600 of the heat pipes comprise fins so as to form an optimum heat exchanger between a hot gas flowing in each cavity 17 and the heat transfer fluid inside each heat pipe. This heat transfer fluid is preferably naphthalene or Gilotherm DO.

(22) Further, according to the invention, the dimensioning of the reactor 1 essentially takes into account the adjustment of the required dwelling time for the relevant biomass particles. This adjustment depends on two parameters: the actual temperature of the internal wall 110 of the side wall 11, of the rotary shaft 14, of the hammers 15 in physical contact with the biomass particles, and on the size of the particles. The adjustment may be different depending on the type of biomass used and requires depending on the install configuration of the reactor 1 suitable means downstream from the reactor.

(23) Thus, when the reactor 1 which has just been described is in the vertical position in the install configuration, the implantation of a first dynamic selector 2 adapted for forcing large diameter particles to dwell in the reactor for a longer time in order to combine the size reduction by grinding and the roasting heat treatment.

(24) This configuration is shown in FIG. 3. The ground and roasted particles at the outlet of the reactor are thus calibrated by the first dynamic variable speed selector 2. Typically the speed of rotation is comprised between 2,000 et 4,000 rpm for calibrating the particles with a diameter of the order of 500 m at the outlet. In FIG. 4, outlet particles calibrated to a diameter of 1 mm are mentioned. The use of the first dynamic selector 2 requires a carrier gas allowing transport of the powder (agglomerated biomass particles) and maintaining the temperature of the latter.

(25) When the reactor 1 which has just been described is in a horizontal position in an installed configuration, a suction is performed downstream from the reactor 1 by means of a fan not shown and through a cyclone 3, which considerably reduces the grain size distribution inside the chamber 10 and improves the yield of the reactor. In other words, it is possible to do without the first dynamic selector 2. This configuration is illustrated in FIG. 5. Biomass particles (roasted biomass meal) calibrated to a diameter of 1 mm were moreover mentioned in this figure.

(26) Preliminary tests according to TGA (acronym of Thermo Gravimetric Analysis) analysis were conducted on small particles for validating the application of the reactor 1 according to the invention, and for defining the conditions of its dimensioning. The obtained results on hard wood (beech) show that the minimum dwelling time for sizes of particles of 200 m at a temperature of 280 C. should be one minute.

(27) In FIGS. 4 and 5, a complete installation is illustrated, for treating biomass, integrating the reactor 1 according to the invention and allowing granules to be produced by means of a granulation press.

(28) Both illustrated installations are provided for having less energy consumption.

(29) Except for the first the dynamic selector 2 which has just been described and the installed configuration of the reactor 1 (vertical position in FIG. 4; horizontal position in FIG. 5), both installations comprise the same elements with the same relative functions and layout. Also a single detailed description is made for the two distinct configurations.

(30) As mentioned, the installation in FIG. 4 is rather intended for producing granules with the press 4 from roasted wood meal for which the particles have a diameter of less than 1 mm while the installation in FIG. 5 is rather intended for producing granules with the press 4 from roasted biomass meal for which the particles have a diameter of less than 1 mm.

(31) Some biomass is dried beforehand in a dryer 5 at a temperature preferably comprised between 100 and 125 C. This dried biomass is fed by gravity into the grinding and roasting reactor according to the invention 1, the latter being preheated.

(32) In the vertical position in the installed configuration of the reactor 1 (FIG. 4), downstream from the latter, is provided a cyclone 3 in series with a second dynamic separator 30. The cyclone feeds under the effect of gravity the granulation press 4 with the ground, roasted and calibrated particles at the outlet of the reactor 1 on the one hand and under the effect of the ascending vortex a post-combustion chamber 6 with finer particles (diameter of less than 10 m) at the outlet of the cyclone 3 on the other hand. This second dynamic selector 30 gives the possibility of adjusting the amount of entrained roasted biomass dusts and preferably is installed in the upper portion of the cyclone/separator 3. Typically, the speed of rotation of this second separator 30 is of the order of 10,000 rpm for particles of 10 m. This second dynamic selector 30 gives the possibility of adjusting the LCV (low calorific value) of the roasting gas by enrichment in roasted solid before feeding the post-combustion chamber 6, more exactly its burner 60 and therefore controlling the temperature thereof. This post-combustion chamber 6 has the main function of destroying tars generated by the roasting (acetic acid, formic acid . . . ).

(33) The combustion chamber 6 comprises a multifuel burner 60 which gives the possibility of producing a mixed combustion of both roasted gases in which are suspended the finest particles 30 separated by the cyclone 3 and of solid granules. The combustion temperature is of the order of 850 C. As mentioned in FIGS. 4 and 5, the solid granules feeding the mixed burner 60 may be roasted or crude and advantageously they are produced by the granulation press 4.

(34) Finally a heat exchanger 7 is laid out downstream from the post-combustion chamber 6. More specifically, the hot fluid circuit is connected to the outlet of the combustion chamber 6 and the cold fluid circuit is connected to the aforementioned dryer 5.

(35) As mentioned in FIGS. 4 and 5, the heat exchanger may be of the gas/gas or gas/steam type. Still more specifically, the hot fluid circuit is connected to the inside of the chamber 10 of the reactor according to the invention on the one hand and to the cavities 17 in which are housed the heat exchanger fins 1600 of the heat pipes 16 (FIG. 3).

(36) Thus, in installations for complete treatment of biomass which have just been described, the energy required for the roasting operation is supplied by two distinct heat transfer means: by thermal conduction through the external shell (side wall 11) of the reactor 1 pre-heated with the gas produced by post-combustion in the combustion chamber 6 and if necessary by the central shaft and the grinding means, homogenized by the heat pipes (components with a phase change) on the one hand, and by direct injection of the hot gas produced by post-combustion in the chamber 6, inside the chamber 10 of the reactor 1 on the other hand. Adjustment of the temperature of the gases is ensured by the heat exchanger 7, which, with the heating of the heat pipes, allows very accurate adjustment of the roasting temperature.

(37) As mentioned above, and according to the technology of the grinder used in the reactor 1 according to the invention, additional provisions of energy may be contemplated. For example, for installations of great capacity (flow rate of more than 3 t/hr), pre-heating the hammers may be contemplated.

(38) Although not shown, decoupling the provisions of energy may be contemplated. Thus, providing the heat energy of the heat transfer fluid for the heat pipes may be envisioned by independent combustion of roasted granules and by using the totality of the energy of the gases produced by the post-combustion in the combustion chamber 6 for producing the drying in the dryer 5.

(39) According to this alternative, it is also possible to obtain better control of the roasting temperature in the reactor 1, the totality of the post-combustion energy being dedicated to the drying.

(40) Although the only illustrated application of the reactor 1 according to the invention is the production of biofuel granules, other applications for producing biofuel may also be contemplated. In the latter applications, it is then possible to install the grinding and roasting reactor according to the invention directly upstream from a unit for conditioning/storing the actual roasted powder upstream from a gasification reactor.

CITED REFERENCES

(41) [1]: Torrefaction of wood, part1 Weight loss kinetics (Mark J. Prins & al) March 2006, JAA77 (Journal of Analytical and Applied Pyrolysis), pp 28-34. [2]: Heat transfer Handbook of Adrian Bejan and Alland D. Kraus; [3]: CaloducTechniques de l'ingnieur [B9 545].