Methods for anaerobic waste digestion

Patent metadata

Field	Value
Publication number	US-11465922-B2
Application number	US-202117156250-A
Country	US
Kind code	B2
Filing date	Jan 22, 2021
Priority date	Dec 5, 2019
Publication date	Oct 11, 2022
Grant date	Oct 11, 2022

Abstract

Methods for generating methane from animal waste by anaerobic digestion using bacteria. A screen separator removes suspended solids greater in size than a predetermined size ranging from about 50μ to about 150μ. An electrocoagulation unit electrochemically hydrolyses the waste, causing particles to settle out. A dissolved carbon air flotation has a CO2 bubbler for separating large particles from small particles by flotation. An anaerobic digester produces biogas. The digester has a biocurtain for growing the bacteria and a heat exchanger for heating the bacteria. The biocurtain surface is convoluted to retain the bacteria. A membrane module removes CO2. A knock out pot for removes droplets of water. A scrubber removes water vapor, particulates, and contaminant gas. A compressor boosts pressure. A gas chromatograph monitors the biogas composition. A flare skid lowers excess pressure for safety. Biogas is injected into a local pipeline system. A process control is used for controlling the anaerobic waste digestion system.

First claim

What is claimed is:

1. An anaerobic waste digestion system for use in connection with a source of waste comprising anaerobically digestible material, for generating methane from the waste by anaerobic digestion using bacteria, the waste being a water-based slurry comprising solid particles having a particle size larger than a predetermined size unsuitable for digestion, the slurry further comprising solid particles having a particle size smaller than a predetermined size suitable for digestion, the anaerobic waste digestion system comprising:
a first phase particle separator, including a screen separator adapted for receiving the slurry, the screen separator being adapted for removing from the slurry solid particles having the particle size larger than the predetermined size unsuitable for digestion, the first phase particle separator being adapted for allowing passage therethrough of the slurry;
a second phase particle separator including an electrocoagulation unit connected in fluid communication with the screen separator for electrochemically inducing hydrolysis of the slurry, so as to cause particles to settle out of the slurry, the electrocoagulation unit being adapted for allowing passage therethrough of the slurry;
a third phase particle separator including a dissolved carbon air flotation (DCAF) separator connected in fluid communication with the electrocoagulation unit, the DCAF separator having a CO 2 bubbler for separating by flotation the solid particles having the particle size larger than the predetermined size unsuitable for digestion from the solid particles having the particle size smaller than the predetermined size suitable for digestion, the DCAF separator being adapted for allowing passage therethrough of the solid particles having the particle size smaller than the predetermined size suitable for digestion as feedstock;
a fourth phase gas producer configured to provide an operating temperature in a range from approximately 68 to 140° F., the fourth phase gas producer including at least one low solids anaerobic digester connected in fluid communication with the DCAF separator, wherein an influent comprising the solid particles having the particle size smaller than the predetermined size suitable for digestion enters the anaerobic digester as feedstock, biogas exits as a product, an effluent exits as wastewater, and a slurry exits as settled solids, the anaerobic digester having at least one biocurtain for growing the bacteria, the anaerobic digester being adapted for allowing passage therethrough of the biogas; and
a process control operatively connected to the anaerobic waste digestion system for controlling the anaerobic waste digestion system;
wherein the predetermined size suitable for digestion is less than about 150 μm.

2. The anaerobic waste digestion system of claim 1 , wherein the waste is an animal waste comprising bedding sand and manure, and wherein the first phase particle separator further comprises:
a sand lane for receiving the animal waste, the sand lane adapted for attachment to a source of animal waste and adapted to receive water from a water source, wherein the bedding sand is separated from the animal waste and water to form the water-based slurry;
an equalization pit connected in fluid communication with the sand lane for receiving the water-based slurry, the equalization pit being adapted for allowing passage therethrough of the slurry to an equalization tank.

3. The anaerobic waste digestion system of claim 1 , wherein the first phase particle separator further comprises:
at least one equalization tank adapted for attachment to the source of waste for receiving the water-based slurry;
at least one slurry pump connected in fluid communication with the equalization tank, for reducing particle size of the solid particles by hydraulic shear;
the screen separator being connected in fluid communication with the equalization tank and the slurry pump; and
a solids tank connected in communication with the screen separator, for receiving solid particles having the particle size larger than the predetermined size unsuitable for digestion.

4. The anaerobic waste digestion system of claim 3 , wherein the at least one equalization tank and the at least one slurry pump comprises:
a first equalization tank;
a first slurry pump adapted for receiving slurry from the first equalization tank and returning the slurry to the first equalization tank, so as to reduce particle size by hydraulic shear, the first slurry pump being adapted for discharging the slurry to the screen separator;
a second equalization tank; and
a second slurry pump adapted for receiving slurry from the second equalization tank and returning the slurry to the second equalization tank, so as to reduce particle size by hydraulic shear, the second slurry pump being adapted for discharging the slurry to the screen separator; wherein
one of the first and second equalization tank is adapted for receiving slurry while the other equalization tank is discharging.

5. The anaerobic waste digestion system of claim 1 , wherein the first phase particle separator further comprises a solids tank for receiving phosphorus-containing solids removed by the screen separator.

6. The anaerobic waste digestion system of claim 1 , wherein the electrocoagulation unit further comprises a collection basin including:
an outlet wall extending between an upper edge and a lower edge;
an internal baffle adjacent the outlet wall;
a sloping floor;
a first outlet disposed adjacent the outlet wall upper edge adapted for discharging solid particles having a particle size smaller than the predetermined size suitable for digestion;
a second outlet disposed below the first outlet and adjacent the internal baffle, adapted for discharging solid particles having a particle size larger than the particles discharged by the first outlet; and
a third outlet disposed below the second outlet and adjacent the sloping floor for discharging solid particles having a particle size smaller than the predetermined size suitable for digestion and solid particles having a particle size larger than the predetermined size suitable for digestion.

7. The anaerobic waste digestion system of claim 1 , further comprising:
a fifth phase gas refiner including a membrane module connected in fluid communication with the anaerobic digester for removing heavy hydrocarbons, CO 2 , and contaminant liquids, the fifth phase gas refiner being adapted for allowing passage therethrough of the biogas.

8. The anaerobic waste digestion system of claim 7 , wherein the fifth phase gas refiner further comprises:
a knock out pot connected in fluid communication with the anaerobic digester, the knock out pot being adapted for removing entrained droplets of water from the biogas;
a scrubber connected in fluid communication with the knock out pot for removing water vapor, particulates, and contaminant gas from the biogas; and
a compressor connected in fluid communication with the scrubber and the membrane module.

9. The anaerobic waste digestion system of claim 8 , further comprising:
a collection pit connected in fluid communication with the anaerobic digester effluent outlet and the knock out pot for receiving the effluent from the anaerobic digester and the water from the knock out pot; and
at least one lagoon connected in fluid communication with the collection pit for receiving the effluent and water therefrom, the lagoon being connected in fluid communication with the first phase particle separator for conveying the water thereto.

10. The anaerobic waste digestion system of claim 8 , wherein the anaerobic digester further comprises:
a digester first cell having a first c

Assignees

• Trane Int Inc

Inventors

• Yochum Charles Don
• Selman Stanley Scott
• Shaffer Nathalie

Classifications

• C02F1/463

  by electrocoagulation · CPC title

• C02F3/2806

  Anaerobic processes using solid supports for microorganisms · CPC title

• C02F3/284

  using anaerobic baffled reactors · CPC title

• C02F2303/24

  Separation of coarse particles, e.g. by using sieves or screens · CPC title

• C02F2103/20

  from animal husbandry · CPC title