Belt dryer and method for dewatering microalgae

Abstract

The invention relates to a method and a device for obtaining dewatered biomass from algae and/or microorganisms. The concentrated biomass available as a result of the harvesting process is spread over an endless conveyor belt (1) and exposed to heated air on the conveyor belt (1). The air is heated by the sun and/or an air heater (5) in a closed system, the conveyor belt (1) being enclosed by a light-permeable casing (2). The drying process is carried out until a residual moisture is achieved, the dewatered biomass adhering to the conveyor belt (1) at the end of the drying process. Said biomass is separated from the conveyor belt (1) by means of a doctor- or scraper edge (9) and is gathered in a collection container (8).

Claims

1. A method for drying microalgae, comprising: spreading a suspension comprising microalgae onto a surface of a conveyor belt oriented at an inclination angle of more than 5 degrees relative to an imaginary horizontal plane; drying the suspension while the suspension is adhered to the surface of the conveyor belt, wherein during the drying, the suspension is conveyed by the conveyor belt and is dried utilizing heated air to obtain a microalgal biomass having a residual moisture; separating the microalgal biomass from the surface utilizing a removal device; and collecting the separated microalgal biomass in a container, wherein the microalgae includes microalgae from one of the following orders: the order of Chlorellales; the order of Volvocales; and the order of Eustigmatales.

2. The method of claim 1, wherein the removal device is one of: a scraper edge; and a doctor.

3. The method of claim 1, wherein the spreading occurs as a result of a portion of the conveyor belt being dipped in a container containing the suspension.

4. The method of claim 1, wherein the drying is carried out at a temperature of between 20 C. and 70 C.

5. The method of claim 1, wherein the microalgae have a coccal or spherical cell shape.

6. The method of claim 1, wherein the inclination angle is more than 30.

7. The method of claim 1, wherein the suspension spread onto the surface of the conveyor belt has an average layer thickness of between 0.2 mm and 2 mm.

8. The method of claim 1, wherein the surface is at least one of: a rough surface with an arithmetical average Ra of more than 0.1 m; a textured surface; and a hydrophilic surface.

9. The method of claim 1, wherein the surface is oriented at a contact angle to water of at most 90.

10. The method of claim 1, wherein the surface includes one of: an elastomer; a natural rubber; and a nitrile rubber.

11. The method of claim 1, wherein the residual moisture is less than 50%.

12. The method of claim 1, wherein the residual moisture is less than 25%.

13. The method of claim 1, wherein the residual moisture is more than 5%.

14. The method of claim 1, wherein the residual moisture is more than 5% and less than 50%.

15. The method of claim 1, further comprising, after the separating, drying the separated microalgal biomass using convection drying until a residual moisture of less than 5% is achieved.

16. The method of claim 1, wherein the microalgae have an average cell diameter of more than 3 m.

17. The method of claim 1, wherein more than 50 percent by weight of said microalgal biomass collected in the container is in a form of one of: flakes; flakes with a longest dimension that is more than 1 cm; and flakes with a thickness of between 0.1 mm and 2 mm.

18. The method of claim 1, wherein one of: the order of Chlorellales consists of the family of Chlorellaceae; the order of Volvocales consists of the family of Haematococcaceae; and the order of Eustigmatales excludes Nannochloropsis and consists of the families of Loboceae, Chlorobothryaceae, Pseudocharaciopsidaceae and Eustigmataceae.

19. A method for drying microalgae, comprising: arranging a conveyor belt inside a heated enclosure, said conveyor belt being oriented at an inclination angle of more than 5 degrees relative to an imaginary horizontal plane; placing a suspension comprising microalgae onto a surface of the conveyor belt while the conveyor belt is moving; drying the suspension with heated air to obtain a dried microalgal biomass having a first residual moisture level; removing the microalgal biomass from the surface while the conveyor belt continues to move; and collecting the separated microalgal biomass in a container, wherein the heated air is heated by at least one of: solar energy; and an air heater; wherein the microalgae is from one of the following orders: the order of Chlorellales; the order of Volvocales; and the order of Eustigmatales.

20. A method for drying microalgae, comprising: arranging a conveyor belt inside an enclosure; placing a suspension comprising microalgae onto a surface of the conveyor belt while the conveyor belt is moving; moving the suspension in an upward direction relative to an imaginary horizontal plane and also in a downward direction relative to the imaginary horizontal plane; during the moving, drying the suspension with heated air inside the enclosure for between 0.5 minutes and 20 minutes in order to obtain a dried microalgal biomass having a first residual moisture level; removing the microalgal biomass from the surface while the conveyor belt continues to move; and drying the removed micro microalgal biomass until the removed micro microalgal biomass reaches a second residual moisture level, wherein the heated air is heated by at least one of: solar energy; and an air heater; wherein the microalgae includes microalgae from one of the following orders: the order of Chlorellales; the order of Volvocales; and the order of Eustigmatales.

Description

(1) The invention will be illustrated more in detail with reference to exemplified embodiments represented in the drawings or pictures.

(2) In the drawings:

(3) FIG. 1 shows a schematic representation of a side view of a device for obtaining dewatered biomass,

(4) FIG. 2 shows a schematic representation of a plurality of conveyor belts arranged one next to the other,

(5) FIG. 3 shows illustrations of the dewatered biomass according to the invention in the form of flakes of Chlorella vulgaris with a residual moisture of about 22.5%, and

(6) FIG. 4 shows illustrations of the dewatered biomass according to the invention in the form of flakes of Chlorella vulgaris with a residual moisture of less than 5% after the final convection drying step on a conveying belt.

(7) According to FIG. 1, the device for obtaining dewatered biomass, i.e. for drying it, comprises a conveyor belt 1, in particular an endless conveyor belt, for receiving the biomass. The conveyor belt 1 is a rough textured belt which is coated with nitrile rubber. Furthermore, this conveyor belt 1 is surrounded by a transparent enclosure 2, for example a tube or a channel-like hull structure, to form a closed system. A reflection surface 3, preferably a mirror, in particular a flat or paraboloidal-type reflector, is placed under the enclosure 2 with the conveyor belt 1 inside. The transparent enclosure 2 preferably consists of plastics or glass.

(8) The conveyor belt 1 with the enclosure 2 is arranged at a freely selectable angle with respect to the horizontal line. The dimension of the angle is selected corresponding to the altitude of the sun and the insolation, but is in this embodiment in any case more than 40. The conveyor belt 1 with the enclosure 2 is arranged to be rotatable, preferably on a star handle 4.

(9) To heat the air for drying the biomass, an air heater 5 is provided if there is not sufficient sunlight.

(10) At the lower end of the conveyor belt 1, i.e. at the rising part of the conveyor belt 1, a supply 6 for the moist biomass is provided. At the back of the conveyor belt 1, i.e. in the region of the star handle 4, at the end of the endless conveyor belt 1, a collection belt 7 for final drying and the transport of the dewatered biomass into a collection container 8 is provided. To scrape off the dewatered biomass, a doctor- or scraper edge 9 is arranged at the back of the conveyor belt 1, that means at the end of the endless conveyor belt 1.

(11) At the beginning and/or in the region and/or at the end of the drying section, moisture and/or temperature measuring devices are provided. These measuring device are preferably sensors.

(12) According to FIG. 2, a plurality of devices consisting of the conveyor belt 1 with the enclosure 2 are arranged on the star handle 4. For each conveyor belt 1, one supply 6 for the moist biomass is provided. Equally, the collection belt 7 transports the dewatered biomass into the collection container 8.

(13) Below, with reference to FIG. 1 and FIG. 2, the method for obtaining dewatered biomass from algae and/or microorganisms, for example after the process of harvesting the algae and/or microorganisms from a suspension consisting of a nutrient solution, in particular in cultivation and production or hydro-cultivation, is shown in detail.

(14) The present concentrated biomass of Chlorella vulgaris (concentration: 150 g/L) is spread over a preferably endless conveyor belt 1 via the supply 6. The biomass spread at the conveyor belt 1 is exposed to heated air, the heating of the air being effected by the sun and/or an air heater 5 in a closed system. The drying process is carried out until a residual moisture of 22.5% is achieved, wherein the dewatered biomass adheres to the conveyor belt 1 at the end of the drying process in the form of flakes. The drying of the biomass is carried out at 50 C. This flake-like form of the biomass is separated from the conveyor belt 1 by a doctor- or scraper edge 9 and collected in a collection container 8 via the collection belt 7.

(15) The application of the concentrated biomass on the conveyor belt 1 is continuous. Equally, the heating of the biomass at the conveyor belt 1 and/or the separation of the biomass from the conveyor belt 1 is continuous.

(16) To heat the air for drying the biomass, the conveyor belt 1, with the biomass adhering to the conveyor belt 1, is directed corresponding to the solar altitude. For this purpose, the star handle 4 is provided.

(17) As already illustrated, the air surrounding the conveyor belt 1 for drying the biomass is heated directly via insolation and indirectly via reflection surfaces 3 provided behind the closed system.

(18) The biomass to be dried is initially transported from the bottom to the top at the conveyor belt 1 arranged at an angle () of 70 and exposed to direct insolation, and after the deflection of the conveyor belt, the biomass to be dried is transported at the conveyor belt 1 from the top to the bottom and exposed to indirect insolation.

(19) To optimize the drying process, both in the spreading of the biomass at the conveyor belt 1 and/or in the drying section and/or in the region of the collection container, the moisture and/or the temperature of the air and/or the biomass is measured.

(20) FIG. 3 shows the dewatered biomass obtained according to the embodiment of FIG. 1 in the form of flakes of Chlorella vulgaris (drying temperature: 50 C.). The residual moisture amounts to about 22.5%. The region marked by the rectangle in a white dashed line in the upper picture is shown in an enlarged illustration in the lower picture. The final drying step is usually carried out on the same or the following day (see the following paragraph).

(21) FIG. 4 shows the dewatered biomass according to FIG. 3 after the final drying step (convection drying on the conveyor belt, temperature: 50 C.). The residual moisture now amounts to less than 5%. The thickness of the flakes now is about 0.7 mm (median of all flakes of one sample), the flakes have, along their longest dimension, an extension of about 7 cm (median of all flakes of one sample). The region marked by the rectangle in a white dashed line in the upper picture is shown in an enlarged illustration in the lower picture. The flakes of FIG. 4 are filled into a closable container and can be preserved for at least some months.