METHOD FOR THE CONTINOUS THERMAL HYDROLYSIS OF ORGANIC MATERIAL AND A PLANT SUITABLE FOR IMPLEMENTING SUCH METHOD

Abstract

A method for the continuous thermal hydrolysis of organic material, which includes at least the stages of: a) pressurizing starting organic material at a pressure setpoint P1; b) inline mixing organic material with steam to obtain a mixture at a controlled temperature setpoint T1, selected below the steam saturation temperature of the mixture; c) continuously introducing the mixture obtained, which is in a liquid phase, into a hydrolysis reactor; d) continuously extracting hydrolyzed mixture from the hydrolysis reactor; and e) suddenly depressurizing the hydrolyzed mixture separating a liquid fraction from a steam fraction, which is recovered. The steam employed to produce the mixture in stage b) includes steam recovered in operation e) which is recompressed.

Claims

1. A method for the continuous thermal hydrolysis of organic material, which comprises at least the stages of: a) pressurizing starting organic material (3) at a pressure setpoint P1; b) inline mixing pressurized organic material with steam (7) to obtain a mixture (8) at a controlled temperature setpoint T1, selected below the steam saturation temperature of the mixture to ensure that the mixture is in a liquid phase; c) continuously introducing the mixture (8) obtained, which is in a liquid phase, in a hydrolysis reactor (9); d) continuously extracting hydrolyzed mixture (11) from the hydrolysis reactor (9); and e) suddenly depressurizing said hydrolyzed mixture separating a liquid fraction (13) from a steam fraction, which is recovered (14); wherein the steam (7) employed to produce the mixture in stage b) comprises steam recovered (14) in operation e) which is recompressed.

2. The method according to claim 1, characterized in that the starting organic material (3) is at room temperature.

3. The method according to claim 1, characterized in that the working pressure of the hydrolysis reactor (9) is kept above the steam saturation pressure at the temperature at which the process is carried out.

4. The method according to claim 1, characterized in that the recovered steam (14) is recompressed employing steam recompressing methods either mechanical, thermal or a combination of both.

5. The method according to claim 1, characterized in that the steam (7) employed for producing the mixture (8) in step b) is obtained by mixing new steam (17) with steam (14) recovered from stage e) which is recompressed.

6. The method according to claim 4, characterized in that the recovered steam (14) is recompressed in a first step, by a steam compressor, which rises the pressure thereof between 4 and 6 bar; and subsequently in a second step the mechanically recompressed steam (18) is thermally compressed by mixing it with new steam (17), the differential pressure provided in this second step being between 1 and 1.5 bar.

7. The method according to claim 5, characterized in that the inline mixture of pressurized organic material and steam is carried out in a liquid-steam mixing valve.

8. The method according to claim 1, characterized in that the Temperature setpoint T1 is between 5 and 10 C. lower than the steam saturation Temperature of the mixture for pressure P1.

9. The method according to claim 1, characterized in that the stay time of the mixture in the hydrolysis reactor (9) is between 5 and 60 min.

10. The method according to claim 1, characterized in that stage e) of depressurization is carried out by means of a regulating valve causing a differential pressure ranging between 4 and 8 bar.

11. The method according to claim 1, characterized in that the liquid fraction (13) obtained in stage e) of depressurization is at a pressure sufficient to pump by pressure difference said liquid fraction (13) to digestion tanks.

12. The method according to claim 1, characterized in that the pressure setpoint P1 is between 3 and 16 bar.

13. The method according to claim 1, characterized in that the Temperature setpoint T1 is between 130 and 190 C.

14. A plant (1) for the continuous thermal hydrolysis of organic material, especially suitable for sludge having low solids content, comprising means (2) for feeding the starting organic material (3), which comprise a duct (4) and a supply pump (5) capable of rising the circulating organic material to an absolute pressure setpoint P1 between 3 and 16 bar; a mixing device (6), connected to the feeding means (2) and a steam source (7), suitable for mixing the pressurized organic material with the steam and obtaining a mixture (8) in a liquid state at a controlled temperature setpoint T1, between 130 and 190 C., below the steam saturation temperature of the mixture; a hydrolysis reactor (9) with at least an inlet (9a) and an outlet (9b), the inlet (9a) being connected at the outlet of the mixing device (6) and the reactor being prepared to maintain the mixture under absolute pressure conditions ranging between 3 and 16 bar and at a temperature ranging between 130 and 180 C. during the stay thereof inside the reactor; a regulating valve (10), connected at the outlet (9b) of the hydrolysis reactor (9), capable of promoting the decompression of the hydrolyzed mixture (11) coming out from the reactor; an expansion chamber (12), connected to the regulating valve (10), where a liquid fraction (13) is separated from a steam fraction (14), which is recovered; at least one recompression device (15) of the steam (14) recovered in the expansion chamber (12); and at least one mixing device (16) for adding new steam (17) to the recovered and recompressed steam (18), supplied by the steam source (7) connected to the mixing device (6).

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0043] FIG. 1, is a schema of a plant according to the invention.

DETAILED DESCRIPTION OF ONE EMBODIMENT

[0044] The plant 1 of FIG. 1 is an example of a plant for the continuous thermal hydrolysis of organic material, especially suitable for sludge having low solids content.

[0045] With reference to the schema of FIG. 1, the stages of the method and the pieces of equipment included in the exemplary plant for the implementation thereof are indicated below.

[0046] The organic material to be hydrolyzed, in the example a starting sludge 3 at room temperature, is fed by means of feeding means 2, which in the example comprise a duct 4 and a supply pump 5 capable of rising the circulating sludge to an absolute pressure setpoint P1 between 3 and 16 bar.

[0047] The plant 1 comprises downstream the supply pump 5 a mixing device 6, connected on one side to the feeding means 2 and on the other side to a steam source 7 at a pressure Pv higher or equal to the pressure setpoint P1. The mixing device 6, which may be a liquid-steam mixing valve, mixes the pressurized organic material with steam, thus obtaining a mixture 8, which contains sludge in a heated liquid state.

[0048] A characteristic of the method is that said heating is carried out by inline mixing, and controlling that the temperature of the obtained mixture 8 is a controlled temperature setpoint T1 lower than the steam saturation temperature of the mixture, so as to obtain a mixture 8 without steam, essentially in a liquid state. In the example, the Temperature setpoint T1 may be between 5 and 10 C. lower than the saturation temperature for pressure P1, said Temperature setpoint T1 being comprised between 130 and 190 C.

[0049] The mixture 8, in liquid phase, is introduced in a hydrolysis reactor 9 through an inlet 9a, provided for such purposes on the upper portion thereof, and is extracted through an outlet 9b, provided in the lower portion of the reactor. In the example, the balance of the material being introduced in and extracted from the reactor 9 is zero.

[0050] The working pressure in the reactor 9 is kept above the saturation pressure at the temperature at which the process is carried out, such that the sludge and steam mixture 8 remains in a liquid phase.

[0051] The dimensions of the reactor 9 are selected such that the time of stay of the mixture 8 is the appropriate one, preferably being comprised between 5 and 60 min.

[0052] Additionally, the reactor 9 is internally provided with a stirring mechanism to prevent eventual problems during the startup and shutdown phases of the plant 1.

[0053] A regulating valve 10, connected at the outlet 9b of the hydrolysis reactor 9, brings about the sudden decompression of the hydrolyzed mixture 11 extracted from the reactor 9.

[0054] In this stage of sudden decompression, the breaking of the cell walls of the sludge contained in the hydrolyzed mixture 11 takes place. The decompression is carried out using a regulating valve that causes a pressure difference ranging between 4 and 8 bar relative to the pressure setpoint P1, and is confined in an expansion chamber 12, connected to the regulating valve 10, wherein a liquid fraction 13 is separated from a steam fraction 14, which is recovered.

[0055] In the example, this recovered steam 14 is subjected in a first step to a mechanical recompression by means of a recompression device 15, in the form of a compressor, the differential pressure provided in this step being between 4 and 6 bar. Then, in a second step the mechanically recompressed steam 18 is thermally compressed by mixing it, in a mixing device 16 based on the Venturi effect, with new steam 17, the differential pressure provided in this second step being between 1 and 1.5 bar, thus obtaining the steam source 7 that feeds the mixing device 6.