Self-flushing anaerobic digester system

1. A digester system comprising:

a primary digester tank containing a primary feed material portion defining a primary feed material level and biogas located within the primary digester tank above the primary feed material level;

a secondary digester tank containing a secondary feed material portion defining a secondary feed material level and biogas located within the primary digester tank above the primary feed material level;

a first conduit connected between the primary digester tank and the secondary digester tank to define a primary tank lower opening within the primary digester tank and a secondary digester tank lower opening within the secondary digester tank, where the primary digester tank lower opening is below the primary feed material level and the secondary digester tank lower opening is below the secondary feed material level;

a second conduit connected between the primary digester tank and the secondary digester tank to define a primary tank upper opening within the primary digester tank and a secondary digester tank upper opening within the secondary digester tank, where the primary digester tank upper opening is above the primary feed material level and the secondary digester tank upper opening is above the secondary feed material level; and

a flow control valve configured to allow or prevent flow of fluid through the first conduit; wherein

the second conduit allows flow of biogas directly between the primary digester tank and the secondary digester tank;

when the flow control valve is configured to allow flow of fluid through the first conduit,

a portion of the primary feed material portion flows from the primary digester tank to the secondary digester tank to form the secondary feed material portion, and

when the portion of the primary feed material portion flows from the primary digester tank to the secondary digester tank, biogas flows from the secondary digester tank to the primary digester tank through the second conduit; and

when the flow control valve is configured to allow flow of fluid through the first conduit, the primary digester tank lower opening is arranged such that solid contaminate that has accumulated at the bottom of the primary digester tank is flushed out of the primary digester tank.

2. A digester system as recited in claim 1 , in which, when the flow control valve is configured to allow flow of fluid through the first conduit and the flow control valve is configured to allow flow of fluid through the first conduit, the primary digester tank lower opening is configured such that fluid flows through the first conduit a first flow rate, where the first flow rate is predetermined such that solid contaminate that has accumulated at the bottom of the primary digester tank is flushed out of the primary digester tank.

3. A digester system as recited in claim 1 , in which, when the flow control valve is configured to allow flow of fluid through the first conduit and the flow control valve is configured to allow flow of fluid through the first conduit, the primary digester tank lower opening is configured and arranged such that fluid flows through the first conduit a first flow rate and solid contaminate that has accumulated at the bottom of the primary digester tank is flushed out of the primary digester tank.

4. A digester system as recited in claim 1 , in which:

the valve allows the first feed material portion to flow from the primary digester tank to the secondary digester tank at a first flow rate;

a pump removes the secondary feed material portion from the secondary digester tank at a second flow rate; and

the first flow rate is greater than the second flow rate.

5. A digester system as recited in claim 1 , flow control valve configured to allow flow of fluid through the first conduit when the primary feed material within the primary digester tank exceeds a predetermined level.

6. A digester system as recited in claim 5 , further comprising a primary feed material level sensor arranged within the primary digester tank to determine a level of the primary feed material within the primary digester tank.

7. A digester system as recited in claim 1 , further comprising a pump configured to remove the secondary feed material portion from the secondary digester tank.

8. A digester system as recited in claim 7 , in which the pump is operatively connected to a separator for separating the secondary feed material portion pumped from the secondary digester tank into liquid and solid components.

9. A digester system as recited in claim 1 , in which the first conduit comprises a downwardly extending portion arrange to facilitate the flushing of the primary feed material portion at a bottom of the primary digester tank.

10. A digester system as recited in claim 1 , further comprising a membrane arranged within the primary digester tank above the primary feed material level to define first and second regions, where the biogas accumulates within the first region.

11. A digester system comprising:

a primary digester tank containing a primary feed material portion defining a primary feed material level and biogas located within the primary digester tank above the primary feed material level;

a secondary digester tank containing a secondary feed material portion defining a secondary feed material level and biogas located within the second digester tank above the secondary feed material level;

a first conduit connected between the primary digester tank and the secondary digester tank to define a primary tank lower opening within the primary digester tank and a secondary digester tank lower opening within the secondary digester tank, where the primary digester tank lower opening is below the primary feed material level and the secondary digester tank lower opening is below the secondary feed material level;

a second conduit connected between the primary digester tank and the secondary digester tank to define a primary tank upper opening within the primary digester tank and a secondary digester tank upper opening within the secondary digester tank, where the primary digester tank upper opening is above the primary feed material level and the secondary digester tank upper opening is above the secondary feed material level;

a flow control valve configured to allow or prevent flow of fluid through the first conduit;

a pump is operatively connected to the secondary digester tank and a separator; wherein

the second conduit allows flow of biogas directly between the primary digester tank and the secondary digester tank;

when the flow control valve is configured to allow flow of fluid through the first conduit,

a portion of the primary feed material portion flows at a first flow rate from the primary digester tank to the secondary digester tank to form the secondary feed material portion, and

when the portion of the primary feed material portion flows from the primary digester tank to the secondary digester tank, biogas flows from the secondary digester tank to the primary digester tank through the second conduit;

the primary digester tank lower opening is arranged such that solid contaminate that has accumulated at the bottom of the primary digester tank is flushed out of the primary digester tank when the flow control valve is configured to allow flow of fluid through the first conduit;

the pump is configured to transfer at least a portion of the secondary feed material portion from the secondary digester tank to the separator at a second flow rate;

the first flow rate is greater than the second flow rate; and

the separator separates the secondary feed material portion pumped from the secondary digester tank into liquid and solid components.

12. A digester system as recited in claim 11 , in which the primary digester tank lower opening is configured such that fluid through the first conduit a first flow rate when the flow control valve is configured to allow flow of fluid through the first conduit, where the first flow rate is predetermined such that solid contaminate that has accumulated at the bottom of the primary digester tank is flushed out of the primary digester tank when the flow control valve is configured to allow flow of fluid through the first conduit.

13. A digester system as recited in claim 11 , in which the primary digester tank lower opening is configured and arranged such that fluid through the first conduit a first flow rate when the flow control valve is configured to allow flow of fluid through the first conduit and solid contaminate that has accumulated at the bottom of the primary digester tank is flushed out of the primary digester tank when the flow control valve is configured to allow flow of fluid through the first conduit.

14. A digester system as recited in claim 11 , further comprising a primary feed material level sensor arranged within the primary digester tank to determine a level of the primary feed material within the primary digester tank, where the flow control valve is configured to allow flow of fluid through the first conduit when the primary feed material level sensor determines that the primary feed material within the primary digester tank exceeds a predetermined level.