Claims
- 1. A process for producing a powder by spin flash drying, thereby drying a paste or a filter cake comprising the steps of,
- feeding the material to be dried to a dryer chamber (1),
- contacting said material with a stream of drying gas to obtain dry particles,
- adjusting the amount of introduced material with the amount and drying capacity of introduced drying gas thereby controlling to a desired moisture content and size of the particles leaving the dryer chamber (1),
- subjecting said particles to a size classification into at least two fractions in a classifier (6),
- which first fraction comprises particles with the predetermined particle size distribution, which is withdrawn as product, suspended in a first exit gas stream,
- and which second undersize fraction is withdrawn from the classifier (6) as an entrained suspension in a second exit gas stream and is returned to the dryer chamber (1) as solid particles.
- 2. The process according to claim 1, comprising the step of collecting the gas of the first and second exit gas streams from the classifier (6) after separation of the particles from the gas streams,
- and returning the collected gas as drying gas to the dryer chamber (1).
- 3. The process according to claim 1, wherein the recycled drying gas is reheated by indirect heating.
- 4. The process according to claim 1, wherein the recycled drying gas is reheated by direct heating.
- 5. The process according to claims 1 and 4, wherein the excess of drying gas is controlled in such a way that the moisture content in the drying gas is 0.4 kg water pr kg dry drying air or higher.
- 6. An apparatus comprising,
- a spin flash dryer with a vertical, cylindrical dryer chamber (1), having a rotating coaxial placed stirrer, with a variable speed drive screw feeder (5) and with apertures (2) for supply of hot drying gas and for the removal of the spent drying gas and removal of the dried material,
- a first classifier means (7) in the upper part of the dryer chamber (1),
- a second classifier means (8) in the upper part of the dryer chamber (1),
- means (9) for separating suspended desired particles from drying gas,
- means (10, 11) for separating and recycling undersize particles to the dryer chamber (1).
- 7. Apparatus according to claim 6, wherein each of the first and second classifier means comprises a central annular orifice (7, 8).
- 8. Apparatus according to claim 6, wherein the distance between the annular orifices of the first and the second classifier means (7,8) is 0.1 to 1 times, the diameter of the dryer chamber (1).
- 9. Apparatus according to claim 6, wherein the diameter of the lower annular orifice (7) is 0.1 to 0.95 times the diameter of the dryer chamber (1), and the diameter of the upper annular orifice (8) is 0.05 to 0.9 times the diameter of the dryer chamber (1).
- 10. Apparatus according to claim 6, wherein
- the orifices of the classifier means (7, 8) are adjustable.
- 11. Apparatus according to claim 6, comprising means (12)for collecting streams of exit drying gas,
- means (13) for separating drying gas into an excess stream, which is led to a cooler (14) and a stream which is recycled as drying gas to the dryer chamber (1).
- 12. Apparatus according to claim 11, wherein means (16) to reheat the recycled drying gas are provided.
- 13. A process according to claim 2, wherein the excess of drying gas is controlled in such a way that the moisture content in the drying gas is 0.4 kg water pr kg dry drying air or higher.
- 14. A process according to claim 3, wherein the excess of drying gas is controlled in such a way that the moisture content in the drying gas is 0.4 kg water pr kg dry drying air or higher.
- 15. A process according to claim 4, wherein the excess of drying gas is controlled in such a way that the moisture content in the drying gas is 0.4 kg water pr kg dry drying air or higher.
- 16. The process according to claim 5, wherein the moisture content in the drying gas is 0.6 kg/kg dry drying air or higher.
- 17. Apparatus according to claim 8, wherein the distance between the annular orifices of the first and second classifier means (7,8) is 0.2 to 0.5 times the diameter of the dryer chamber (1).
- 18. Apparatus according to claim 9, wherein the diameter of the lower annular orifice (7) is 0.5 to 0.95 times the diameter of the dryer chamber (1), and upper annular orifice (8) is 0.45 to 0.9 times the diameter of the dryer chamber (1).
- 19. A process according to claim 2, wherein the excess of drying gas is controlled in such a way that the moisture content in the drying gas is 0.6 kg water pr kg dry drying air or higher.
- 20. A process according to claim 3, wherein the excess of drying gas is controlled in such a way that the moisture content in the drying gas is 0.6 kg water pr kg dry drying air or higher.
- 21. A process according to claim 4, wherein the excess of drying gas is controlled in such a way that the moisture content in the drying gas is 0.6 kg water pr kg dry drying air or higher.
Priority Claims (1)
Number |
Date |
Country |
Kind |
1308/95 |
Nov 1995 |
DKX |
|
Parent Case Info
This application is the national phase under 35 U.S.C. .sctn.371 of prior PCT International Application No. PCT/DK96/00480 which has an International filing date of Nov. 21, 1996 which designated the United States of America, the entire contents of which are hereby incorporated by reference.
PCT Information
Filing Document |
Filing Date |
Country |
Kind |
102e Date |
371c Date |
PCT/DK96/00480 |
11/21/1996 |
|
|
7/15/1998 |
7/15/1998 |
Publishing Document |
Publishing Date |
Country |
Kind |
WO97/19307 |
5/29/1997 |
|
|
US Referenced Citations (9)
Foreign Referenced Citations (1)
Number |
Date |
Country |
0141403 |
May 1985 |
EPX |