Energy efficient system and process for treating sludge

Patent metadata

Field	Value
Publication number	US-9527760-B2
Application number	US-201313791919-A
Country	US
Kind code	B2
Filing date	Mar 9, 2013
Priority date	Mar 9, 2013
Publication date	Dec 27, 2016
Grant date	Dec 27, 2016

Abstract

Apparatus and process is provided for hydrolyzing sludge from water treatment and for conditioning the hydrolyzed sludge for optimal anaerobic digestion. Methods provided include dewatering to produce dewatered sludge, hydrolyzing the dewatered sludge in a steam fed process, preheating the dewatered sludge before hydrolysis with sludge-to-sludge heat transfer, and cooling and diluting the sludge using sludge-to-water heat transfer and water injection, and anaerobically digesting the hydrolyzed sludge. Apparatus provided includes a generally vertically oriented counterflow sludge-to-sludge heat exchanger, a hydrolysis reactor and associated source of steam, sludge-to-water heat exchangers, and a dilution unit. Temperature and pressure sensors are configured to command various variable flow pumps and valves for controlling the process.

First claim

What is claimed is:

1. A method for treating sludge comprising:
(a) dewatering the sludge;
(b) directing the dewatered sludge to a generally vertically oriented heat exchanger, the heat exchanger having a sludge inlet placed at a lower portion of the heat exchanger, a sludge outlet placed at an upper portion of the heat exchanger, a hydrolyzed sludge inlet placed at an upper portion of the heat exchanger, and a hydrolyzed sludge outlet placed at a lower portion of the heat exchanger;
(c) directing the dewatered sludge into the sludge inlet and upwardly through the heat exchanger and out the sludge outlet and into a hydrolysis reactor;
(d) hydrolyzing the dewatered sludge in the hydrolysis reactor;
(e) passing the hydrolyzed sludge into the hydrolyzed sludge inlet of the heat exchanger;
(f) providing sludge-to-sludge heat transfer by directing the hydrolyzed sludge downward through the heat exchanger as the dewatered sludge moves upward and through the heat exchanger;
(g) directing the hydrolyzed sludge out the hydrolyzed sludge outlet of the heat exchanger to an anaerobic digester; and
(h) anaerobically digesting the hydrolyzed sludge in the anaerobic digester.

2. The method of claim 1 including directing at least a portion of the dewatered sludge around the heat exchanger and to the hydrolysis reactor without the dewatered sludge passing through the heat exchanger.

3. The method of claim 1 including directing at least a portion of the dewatered sludge around the heat exchanger and to the hydrolysis reactor to increase the temperature of the hydrolyzed sludge entering the anaerobic digester.

4. The method of claim 1 including directing dilution water into the hydrolyzed sludge to adjust a proportion of dry matter in the sludge.

5. The method of claim 1 including directing dilution water into the hydrolyzed sludge to cool the hydrolyzed sludge.

6. The method of claim 1 including heating dilution water and directing the heated dilution water into the hydrolyzed sludge to heat the hydrolyzed sludge.

7. The method of claim 6 wherein the heated dilution water is directed into the hydrolyzed sludge during a startup period in the method.

8. The method of claim 1 , wherein the heat exchanger includes a cylinder, including directing the hydrolyzed sludge into a top portion of the cylinder and downwardly through the cylinder; and directing the dewatered sludge upwardly through a series of spaced apart conduits extending through the cylinder so as to give rise to sludge-to-sludge heat transfer as heat is transferred from the hydrolyzed sludge passing through the cylinder to the dewatered sludge passing upwardly through the conduits in the cylinder.

9. The method of claim 1 including,
cooling the hydrolyzed sludge upstream of the anaerobic digester by directing the hydrolyzed sludge through one or more additional heat exchangers disposed upstream of the anaerobic digester; and
reducing the dry solids concentration of the hydrolyzed sludge by mixing dilution water with the hydrolyzed sludge at a point between the hydrolysis reactor and the anaerobic digester.

10. The method of claim 1 including heating the hydrolysis reactor with steam produced by a steam generator; and directing steam generator feed water and hydrolyzed sludge to a heat exchanger disposed downstream of the hydrolysis reactor and reducing the temperature of the hydrolyzed sludge by transferring heat from the hydrolyzed sludge to the steam generator feed water.

11. The method of claim 1 wherein the heat exchanger is tilted from vertical to increase heat transfer from the hydrolyzed sludge to the dewatered sludge.

12. The method of claim 11 wherein the heat exchanger is tilted about 15° relative to vertical to prevent the formation of boundary layers in the hydrolyzed sludge about tubes disposed within the heat exchanger that conduct the dewatered sludge through the heat exchanger.

13. The method of claim 1 wherein the heat exchanger includes an air pocket disposed in a top portion of the heat exchanger for absorbing pressure surges.

14. The method of claim 1 wherein the hydrolysis reactor includes a vent system for venting non-condensable gases from the hydrolysis reactor.

15. A method of treating sludge comprising:
(a) dewatering the sludge;
(b) directing the dewatered sludge to a hydrolysis reactor and hydrolyzing the dewatered sludge;
(c) directing the hydrolyzed sludge to an anaerobic digester;
(d) anaerobically digesting the hydrolyzed sludge;
(e) providing a heat exchanger on the outlet side of the hydrolysis reactor for heating at least a portion of the dewatered sludge prior to the dewatered sludge entering the hydrolysis reactor wherein the heat exchanger provides for sludge-to-sludge heat transfer between the hydrolyzed sludge and the dewatered sludge;
(f) varying the flow of the dewatered sludge through the heat exchanger during certain periods of sludge treatment by:
(i) during a startup mode directing at least a part of the dewatered sludge through a heat exchanger bypass line and to the hydrolysis reactor; and
(ii) during a steady state mode, directing a majority of the dewatered sludge through the heat exchanger and then to the hydrolysis reactor.

16. The method of claim 15 , including during an initial portion of the startup mode, directing substantially all the dewatered sludge through the heat exchanger bypass line to the hydrolysis reactor.

17. The method of claim 16 , after the initial portion of the start-up mode, increasing over time the flow of dewatered sludge through the heat exchanger and decreasing the flow of dewatered sludge through the heat exchanger bypass line during the startup mode.

18. The method of claim 15 , further including during a selected period of the steady state mode, directing substantially all of the dewatered sludge through the heat exchanger prior to reaching the hydrolysis reactor.

19. The method of claim 15 , including during the steady state mode, increasing the temperature of the hydrolyzed sludge directed to the anaerobic digester by decreasing the flow of dewatered sludge through the heat exchanger and increasing the flow of dewatered sludge through the heat exchange bypass line.

20. The method of claim 15 including directing dilution water into hydrolyzed sludge for adjusting a proportion of dry matter in the sludge.

21. The method of claim 20 wherein directing dilution water into the hydrolyzed sludge includes cooling the hydrolyzed sludge due to the dilution water.

22. The method of claim 15 including directing dilution water into the hydrolyzed sludge for adjusting a temperature of the sludge or for adjusting a dry matter proportion of the sludge.

23. The method of claim 22 wherein directing the dilution water into the hydrolyzed sludge includes heating the dilution water before directing the dilution water into the sludge and heating the sludge with the heated dilution water.

Assignees

• Hojsgaard Soeren J
• Rohold Lars
• Veolia Water Solutions & Tech

Inventors

• Hojsgaard Soeren J
• Rohold Lars

Classifications

• C02F11/12

  by de-watering, drying or thickening · CPC title

• C02F1/008

  Control or steering systems not provided for elsewhere in subclass C02F · CPC title

• F23G2900/50208

  Biologic treatment before burning, e.g. biogas generation · CPC title

• C02F2209/03

  Pressure · CPC title

• C02F2209/10

  Solids, e.g. total solids [TS], total suspended solids [TSS] or volatile solids [VS] · CPC title