Process for the conversion of biomass of plant origin, and a combustion process

Abstract

The invention provides a process for the conversion of biomass into a biomass product which is suitable for use as a fuel. The biomass is of plant origin and comprises microorganisms naturally occurring in the biomass. The process comprisespreparing a slurry by dispersing the biomass comprising the naturally occurring microorganisms in an aqueous liquid, maintaining the slurry at conditions suitable for aerobic digestion by the microorganisms to obtain a slurry comprising the biomass product as a dispersed solid phase, andrecovering the biomass product. The recovering comprises washing and drying the biomass product. The invention also provides a combustion process.

Claims

1. A process for the conversion of biomass into a biomass product which is suitable for use as a fuel, wherein the biomass is of plant origin and comprises microorganisms naturally occurring in the biomass, which process comprises preparing a slurry by dispersing the biomass comprising the naturally occurring microorganisms in an aqueous liquid, maintaining the slurry at conditions suitable for aerobic digestion by the microorganisms to obtain a slurry comprising the biomass product as a dispersed solid phase, and recovering the biomass product, which recovering comprises washing using water as a washing liquid and drying the biomass product.

2. A process as claimed in claim 1, wherein the process comprises in addition recovering from the slurry a liquid phase, yielding a biomass extract.

3. A process as claimed in claim 1, wherein the aqueous liquid is water.

4. A process as claimed in claim 3, wherein the pH of the water, as measured at 20 C., is in the range of from 6.5 to 8.5, and wherein the slurry is maintained at conditions suitable for digestion by the microorganisms for a time in the range of from 100 hours to 500 hours.

5. A process as claimed in claim 4, wherein the pH is in the range of from 7 to 8, and wherein the time is in the range of from 150 hours to 300 hours.

6. A process as claimed in claim 1, wherein the aqueous liquid comprises at least a portion of a biomass extract obtained by additionally recovering from the slurry a liquid phase, yielding the biomass extract.

7. A process as claimed in claim 6, wherein the pH of the aqueous liquid, as measured at 20 C., is in the range of from 3 to 6, and wherein the slurry is maintained at conditions suitable for digestion by the microorganisms for a time in the range of from 0.5 hours to 150 hours.

8. A process as claimed in claim 7, wherein the pH is in the range of from 4 to 6, and wherein the time is in the range of from 1 hours to 100 hours.

9. A process as claimed in claim 1, wherein the biomass comprises forestry waste or agricultural waste.

10. A process as claimed in claim 9, wherein the biomass comprises mown grass.

11. A process as claimed in claim 1, wherein the naturally occurring microorganisms comprise microorganisms which are capable of converting saccharides into lactic acid or lactic acid salts.

12. A process as claimed in claim 1, wherein the conditions suitable for digestion by the microorganisms comprise a temperature in the range of from 5 C. to 40 C.

13. A process as claimed in claim 12, wherein the conditions suitable for digestion by the microorganisms comprise a temperature in the range of from 10 C. to 30 C.

14. A process as claimed in claim 1, wherein recovery of the biomass product from the slurry comprises employing a filter plate or a screen, while exerting a pressure onto the slurry, which pressure is in the range of from 0.0005 MPa to 0.02 MPa.

15. A process as claimed in claim 1, wherein recovering the biomass product from the slurry comprises a plurality of washing steps in a counter current process, and wherein water is applied as the washing liquid in the last washing step.

16. A process as claimed in claim 1, wherein the recovering comprises drying to achieve a moisture content of the biomass product of at most 20% by weight.

17. A process as claimed in claim 16, wherein the moisture content is at most 10% by weight.

18. A combustion process, which combustion process comprises the steps of preparing a slurry by dispersing a biomass in an aqueous liquid, wherein the biomass is of plant origin and comprises microorganisms naturally occurring in the biomass, maintaining the slurry at conditions suitable for aerobic digestion by the microorganisms to obtain a slurry comprising a biomass product as a dispersed solid phase, recovering the biomass product from the slurry, which recovering comprises washing using water as a washing liquid, and combusting the biomass product.

19. A combustion process as claimed in claim 18, wherein the combustion process comprises drying the biomass product recovered from the slurry by exposing the biomass product to outside weather conditions.

Description

EXAMPLE 1

In Accordance with the Invention

(1) A container was provided having inner dimensions of 3 m2 m1.7 m (lengthwidthheight), a flat, rectangular, horizontal, concrete bottom and four flat, rectangular, vertical, concrete walls, and having placed therein a solid wooden plank supported by wooden blocks placed on the bottom at regular distances, the plank having been placed such that an open drainage channel (20 cm width and 20 cm depth) was formed at one side of the bottom in the longitudinal direction of the container. The container was charged with 540 kg of mown grass (37% by weight moisture content, representing 200 kg water) and 940 kg of water (a mixture of rain water and tap water) having pH 6.75, electric conductivity 0.62 mS/cm, refraction 0 Brix and temperature 9 C. In order to assist in obtaining and maintaining a slurry of the grass in the liquid phase, liquid phase was circulated by pumping at a rate of 5000 kg/h from the bottom of the drainage channel in one corner of the container onto the upper surface of the mixture of grass and water in the opposite corner of the container. After 1 hour the pH of the liquid phase had reached 6.6, refraction 1 Brix, electric conductivity 4.6 mS/cm, temperature 9.5 C. (Throughout this patent document, values of pH, refraction and electric conductivity are as measured at 20 C.). The circulation of liquid phase was continued.

(2) The next day, this procedure was repeated, yielding a second batch of slurry. After circulating liquid phase for 168 hours the two batches were combined, resulting in the following: a total of about 2960 kg slurry consisting of about 2280 kg of liquid phase and about 680 kg of solid phase, the liquid phase being a slightly foaming, clear, dark brown coloured liquid, and having a fresh sour odour and the following characteristics: electric conductivity 4.8 mS/cm, pH 6.6, refraction 1 Brix, temperature 9 C.

(3) Then circulation of liquid phase was stopped and, instead, liquid phase was pumped into a separate container of similar size. In this manner about 45% by weight of the liquid phase could be separated from the slurry, yielding about 1350 kg of a first lot of biomass extract.

(4) A rubber and nylon-fibre lined bag having dimensions such that the bag fits the horizontal inner dimensions of the container was placed in the container, covering the slurry. Then the bag was filled with tap water and closed. The height of the column of water inside the bag was 50 cm. A second bag of similar dimensions was placed on top of the first bag and filled with tap water until the height of the column of water inside the second bag was 50 cm. Additional liquid phase was drained by pumping from beneath the drainage channel. In this manner about 500 kg of a second lot of biomass extract was obtained.

(5) The biomass product remaining in the container was then washed. To this end, the biomass product was re-dispersed in 1000 kg of tap water and the liquid phase so obtained (1000 kg) was drained by pumping from beneath the drainage channel with the two water filled bags still in place. Washing was repeated two times. The washing effluents were combined and stored for use in Example 2, hereinafter.

(6) 10-kg samples of the washed biomass product were transferred into a hydraulic juice press filling the cylinder of the press and subjected to pressing. For each pressing, the pressure inside the press was increased in 2 minutes from 0.1 MPa to 5 MPa, while pressing juice was drained and collected. After pressing the biomass product had a moisture content of 47% by weight. The weight of each of the blocks of biomass product obtained was about 5 kg.

(7) The biomass product blocks where loaded into open containers (1.5 m length, 1 m width, 1 m height), each container having a wooden pallet as a bottom and four wire nettings supported by a metal framework as side walls. The wire nettings possessed 10 cm10 cm openings for passing drying air. The open containers had no cover. The open containers filled with biomass product blocks were placed in a drying kiln as a stack of three layers of two by three open containers each. The drying kiln was operated as a condenser dryer at temperatures of 45-65 C., for 96 hours. After drying, the biomass product had a moisture content of 10% by weight.

(8) The first lot of biomass extract was processed by means of a membrane filter installation provided with commercially available spirally wound polymer nano-filtration membranes and protective filter candles positioned up-stream relative to the membranes. The membrane filter installation was operated at 2.5 MPa (25 bar) and at a rate of 200 kg/h, producing 70-100 kg/h of permeate and 100-130 kg/h of concentrate. During the operation the concentrate was recycled into the container comprising the biomass extract, and permeate was collected in another, similar container. Accordingly, the concentrate became progressively more concentrated in mainly proteins, mono- and disaccharides, and it became more dark brown and cloudy. The permeate, comprising chlorides, nitrates and other salts and lactic acid, had a water clear appearance.

(9) During the nano-filtration process, the temperature of the concentrate increased slowly from about 10 C. to about 40 C., caused by the supply of energy to the pumping equipment of the membrane filter installation. The higher temperature resulted in 200% more filtration capacity of the process. The membrane filtration appeared to be a very efficient process for the removal of salts and lactic acid from the biomass extract and for concentrating the biomass extract. It is remarkable that the nano-filtration process could proceed with long run times andwith no pre-filtering other than by applying the filter candleswithout significant fouling of the filter candles and the membranes.

(10) The permeate was concentrated by removing water by means of reverse osmosis applying a pressure of 7 MPa.

(11) The first lot of biomass extract, the concentrate obtained at the end of nano-filtration process, and permeates obtained at the start and at the end of the nano-filtration process were analysed (see Table I, below; COD means chemical oxygen demand). The results depicted in Table I are indicative for a concentration factor of 15-20 for the concentrate, relative to the biomass extract, and that potassium chloride is present in the permeate in a high concentration.

(12) TABLE-US-00001 TABLE I Electric conductivity Density Refraction KCl content COD Dry matter (mS/cm) pH d.sub.20 (g/l) ( Brix) (g/l) (g/l) (% by weight) Biomass extract 6.52 3.83 1.002 1 6.5-7.5 Concentrate 104 4.4 1.072 17 140-150 19.5 Permeate at start 2.3 3.9 0 1.0-1.25 Permeate at end 11 3.7 1 15.0-20.0 : not analysed

EXAMPLE 2

In Accordance with the Invention

(13) Example 1 was repeated with the difference that the container was charged with 1000 kg of the mown grass and then filled with 2000 kg of washing effluent obtained in Example 1, instead of water. After circulating liquid phase for 96 hours, the liquid phase had reached pH 6.0. 1800 kg of biomass extract and 1200 kg of wed biomass product were obtained. After pressing the biomass product had a moisture content of 50% by weight and after drying, the biomass product had a moisture content of 10% by weight. The pressing juice obtained from pressing in the hydraulic juice press (about 200 kg) was collected.

EXAMPLE 3

In Accordance with the Invention

(14) Example 2 was repeated with the difference that, after charging with 1000 kg of the mown grass, the container was charged with 1800 kg of the biomass extract obtained in Example 2 and 200 kg of the permeate obtained in Example 1, instead of the washing effluent obtained in Example 1. After circulating liquid phase for 48 hours, the liquid phase had reached pH 4.2. 1800 kg of biomass extract and 1200 kg of wed biomass product were obtained. After pressing the biomass product had a moisture content of 50% by weight and after drying, the biomass product had a moisture content of 10% by weight.

EXAMPLE 4

In Accordance with the Invention

(15) Example 3 was repeated with the difference that, after charging with 1000 kg of the mown grass, the container was charged with 1800 kg of the biomass extract obtained in Example 3, and 200 kg of the permeate obtained in Example 2, instead of the biomass extract obtained in Example 2, and the permeate obtained in Example 1. After circulating liquid phase for 48 hours, the liquid phase had reached pH 3.8. 1800 kg of biomass extract and 1200 kg of wed biomass product were obtained. After pressing the biomass product had a moisture content of 50% by weight and after drying, the biomass product had a moisture content of 10% by weight.