PROCESS TO PREPARE A CHAR PRODUCT

Abstract

The invention is directed to a process to prepare a char product by pyrolysis or mild gasification of a solid biomass feed thereby obtaining a gaseous fraction comprising hydrogen, carbon monoxide and a mixture of gaseous organic compounds and a solid fraction comprising of char particles having a reduced atomic hydrogen over carbon ratio and a reduced oxygen over carbon ratio relative to the solid biomass feed. The solid biomass feed are pellets of a solid torrefied biomass feed. The pyrolysis or mild gasification is performed at a temperature of between 500 and 800° C. and at a solid residence time of between 10 and 60 minutes.

Claims

1.-16. (canceled)

17. A process to prepare a char product the method comprising mild gasification of a solid biomass feed, thereby obtaining a gaseous fraction comprising hydrogen, carbon monoxide and a mixture of gaseous organic compounds and a solid fraction comprising of char particles having a reduced atomic hydrogen over carbon ratio and a reduced oxygen over carbon ratio relative to the solid biomass feed; wherein the solid biomass feed are pellets of a solid torrefied biomass feed having a content of volatiles of between 50 and 75 wt %; and wherein the mild gasification is performed at a temperature of between 500 and 800° C. and at a solid residence time of between 10 and 60 minutes and in the presence of oxygen and steam.

18. The process according to claim 17, wherein the mild gasification is performed in an elongated reactor wherein the biomass is continuously transported from a solids inlet at one end of an elongated reactor to a solids outlet at the other end of the elongated reactor.

19. The process according to claim 17, wherein the solid biomass feed is subjected to a mild gasification by contacting the solid biomass feed with an oxygen comprising gas and wherein the amount of oxygen is between 0.1 and 0.3 mass oxygen per mass biomass.

20. The process according to claim 19, wherein the oxygen comprising gas is air.

21. The process according to claim 17, wherein the amount of oxygen is between 0.1 and 0.3 kg per kg of the solid biomass feed and wherein the content of oxygen is between 20 and 40 vol. % O.sub.2 per combined O.sub.2 and H.sub.2O at 300° C.

22. The process according to claim 18, wherein oxygen comprising gas is supplied to the elongated reactor at two or more axially spaced away positions along the length of the reactor between the solids inlet and the solids outlet.

23. The process according to claim 17, wherein in the mild gasification the hydrogen over carbon (H/C) ratio is reduced by more than 70% and the atomic oxygen over carbon (O/C) ratio is reduced by more than 80% when comparing the pellets of a solid torrefied biomass and the char particles.

24. The process according to claim 17, wherein the char product has a BET (N.sub.2) surface area of between 300 and 500 m.sup.2/g.

25. The process according to claim 17, wherein the gaseous fraction comprising hydrogen, carbon monoxide and a mixture of gaseous organic compounds is subjected to a continuously operated partial oxidation at a temperature of between 1100 and 1600° C.

26. The process according to claim 25, wherein a syngas mixture obtained in the partial oxidation is contacted with a carbonaceous compound to chemically quench the syngas mixture.

27. The process according to claim 17, wherein the char product is separated from the gaseous fraction and activated to obtain an activated carbon product having a BET (N.sub.2) surface area of above 700 m.sup.2/g.

28. A combustion process comprising use of a gaseous fraction obtained by the process of claim 17 as a fuel.

29. The process according to claim 28, wherein the fuel is combusted by contacting with an oxygen containing gas having an oxygen content of above 90 vol. %.

30. A partial oxidation process to prepare a syngas, the process comprising use of a gaseous fraction obtained by the process of claim 17 as a feedstock.

Description

EXAMPLE 1

[0046] To one end of an elongated tube reactor 70 kg/h torrefied feedstock was continuously fed. The torrefied feedstock was pelletised torrefied wood having a cylindrical shape. The properties of the feedstock are listed in Table 1. The reactor had an internal diameter of 0.6 m and was provided with an axial mixing means which slowly moved the feedstock and the solid reaction products in an axial direction and over a length of 1.1 m to a solids outlet provided at the other end of the tubular reactor.

TABLE-US-00001 TABLE 1 Average pellet dimensions: length (cm) 6 (length, diameter) Average pellet dimensions: diameter (mm) 8 Bulk density (kg/m3) 0.35 content of volatiles (wt %) 70 atomic hydrogen over carbon (H/C) ratio 0.55

[0047] The pressure in the tubular reactor was 0.1 MPa. The start temperature in the reactor was 520° C. and achieved by electrical heating of the tubular wall of the reactor. The solid residence time was between 15 and 20 minutes.

[0048] The gaseous effluent and the solids leaving the reactor were collected separately. The solids were analysed and their properties and char yields are listed in Table 2.

EXAMPLE 2

[0049] Example 1 was repeated except that the temperature in the reactor was achieved by feeding hot air at three axially spaced positions along the length of the reactor. The total air flow was 20-25 Nm3/hour. The temperature of the air was 300° C. The achieved temperature varied (see Table 2). The solids residence time was as in Example 1. The char yield and solids composition are listed in Table 3.

EXAMPLE 3

[0050] Example 1 was repeated except that the temperature in the reactor was achieved by feeding a mixture consisting of oxygen and steam at three axially spaced positions at a feed temperature 300° C. The oxygen content was 24 vol. %. The achieved temperature varied (see Table 2). The solids residence time was as in Example 1.

[0051] The solids were analysed and their properties and yields are listed in Table 2. In Table 3 some additional process conditions and results are listed.

TABLE-US-00002 TABLE 2 Example 2 Example 2 Example 2 Example 3a Example 3b Example 3c Heating electrical Air Air Steam/Oxygen Steam/Oxygen Steam/Oxygen Reactor 520 640 680 520 622 640 temperature Biomass 70 70 62 flow (kg/h) Pyrolysis 1.3 1.3 1.4 gas production (kg/kg feedstock) Yield char 0.28 0.26 0.22 0.21 0.17 0.14 particles (kg/kg feedstock) BET 238 128 88 377 387 440 surface area (m2/g) C (wt %) 88.4 91.4 91.9 87.1 90.5 88.5 H (wt. %) 1.5 0.6 0.6 1.2 1.0 1.1 O (wt %) 1.0 0.6 0.5 3.2 0.9 2.2 Ash (wt %) 5.7 6.6 6.0 6.6 6.9 7.9 Volatiles 9.6 2.3 2.4 4.2 3.9 5.1 (wt %)

TABLE-US-00003 TABLE 3 Example 3a Example 3b Example 3c Heating Steam/Oxygen Steam/Oxygen Steam/Oxygen Reactor 520 622 640 temperature Biomass flow 70 70 62 O2/biomass 0.17 0.17 0.17 (kg/kg) O2/(H2O + O2) 24 24 22 (expressed in vol. % at 300 C.) Yield char 0.21 0.17 0.14 particles (kg/kg feedstock) Char analysis: BET surface area 377 387 440 (m2/g) C (wt %) 87.1 90.5 88.5 H (wt. %) 1.2 1.0 1.1 O (wt %) 3.2 0.9 2.2 Ash (wt %) 6.6 6.9 7.9 Volatiles (wt %) 4.2 3.9 5.1

EXAMPLE 4

[0052] The gaseous mixture obtained in Examples 3a-3c were partially oxidised to a syngas mixture of carbon monoxide and hydrogen at 0.1 MPa. The composition of the obtained syngas mixture and conditions of the partial oxidation are listed in Table 4. The listed yield was 1.5-1.7 kg syngas per kg biomass fed to the mild gasification process.

TABLE-US-00004 TABLE 4 Experiment 3a 3b 3c Syngas yield 1.5 1.6 1.7 (kg/kg biomass feedstock) Syngas composition Hydrogen (vol. %) 23.7 23.7 23.7 Carbon Monoxide 20.7 21.7 21.7 (vol. %) Carbon dioxide 19.5 19.6 19.6 (vol. %) Water (vol. %) 34.6 33.9 33.9 Methane (vol. %) 1.5 1.2 1.2 Lower heating 5.7 5.7 5.7 value (MJ/Nm3)