Submerged combustion vaporizer with low NOx

1. An apparatus comprising:

heat exchanger tubing;

a tank structure configured to contain a water bath for the heat exchanger tubing;

a burner;

a duct system that includes sparger tubes with outlet ports and is configured to convey exhaust from the burner to the sparger tubes; and

a fuel delivery system configured to provide the burner with primary fuel, and including a staged fuel injector structure configured to inject a staged fuel stream into the exhaust in the duct system separately from the primary fuel at a location downstream of the burner.

2. An apparatus as defined in claim 1 wherein the staged fuel injector structure is configured to inject a staged fuel stream into the duct system at a location upstream of the sparger tubes.

3. An apparatus as defined in claim 1 wherein the staged fuel injector structure is configured to inject multiple staged fuel streams into the duct system at locations upstream of the sparger tubes.

4. An apparatus as defined in claim 1 wherein the staged fuel injector structure is configured to inject staged fuel streams directly into the sparger tubes.

5. An apparatus as defined in claim 4 wherein the staged fuel injector structure is configured to inject a single staged fuel stream directly into each sparger tube at a location upstream of the outlet ports in the sparger tube.

6. An apparatus as defined in claim 4 wherein the staged fuel injector structure is configured to inject staged fuel streams directly into each sparger tube at locations adjacent to the outlet ports in the sparger tube.

7. An apparatus as defined in claim 1 wherein the fuel delivery system includes fuel lines and valves arranged to deliver fuel from a common source to both the burner and the staged fuel injector structure, whereby the primary fuel and the staged fuel stream include the same fuel from the common source.

8. An apparatus as defined in claim 1 wherein the fuel delivery system is configured to provide the staged fuel injector structure with only fuel.

9. An apparatus as defined in claim 1 wherein the fuel from the common source is natural gas.

10. An apparatus for use with heat exchanger tubing, a tank structure configured to contain a water bath for the heat exchanger tubing, a burner configured to receive primary fuel, and a duct system that includes sparger tubes with outlet ports and is configured to convey exhaust from the burner to the sparger tubes, the apparatus comprising:

a staged fuel injector structure configured to inject a staged fuel stream into the exhaust in the duct system separately from the primary fuel at a location downstream of the burner; and

a fuel delivery system including fuel lines and valves arranged to deliver fuel from a common source to both the burner and the staged fuel injector structure, whereby the primary fuel and the staged fuel stream include the same fuel from the common source.

11. An apparatus as defined in claim 10 wherein the staged fuel injector structure is configured to inject a staged fuel stream into the duct system at a location upstream of the sparger tubes.

12. An apparatus as defined in claim 10 wherein the staged fuel injector structure is configured to inject multiple staged fuel streams into the duct system at locations upstream of the sparger tubes.

13. An apparatus as defined in claim 10 wherein the staged fuel injector structure is configured to inject staged fuel streams directly into the sparger tubes.

14. An apparatus as defined in claim 13 wherein the staged fuel injector structure is configured to inject a single staged fuel stream into each sparger tube at a location upstream of the outlet ports in the sparger tube.

15. An apparatus as defined in claim 13 wherein the staged fuel injector structure is configured to inject staged fuel streams into each sparger tube at locations adjacent to the outlet ports in the sparger tube.

16. An apparatus as defined in claim 10 further comprising a fuel delivery system configured to provide the staged fuel injector structure with only fuel.

17. An apparatus as defined in claim 10 wherein the the fuel is natural gas.

18. An apparatus comprising:

heat exchanger tubing;

a tank structure configured to contain a water bath for the heat exchanger tubing;

a duct system including sparger tubes with outlet ports arranged to discharge gas into a water bath in the tank structure;

a premix burner including an oxidant plenum, mixer tubes with open inner ends in the oxidant plenum, and fuel conduits configured to direct fuel into the mixer tubes, with the mixer tubes having open outer ends arranged to discharge premix into the duct system; and

a water injection system operatively associated with the premix burner to mix water into the premix;

wherein the oxidant plenum is part of an oxidant flow path extending from a blower to the oxidant plenum and the mixer tubes, and the water injection system is configured to inject water into the oxidant flow path; and

wherein the water injection system is configured to inject water into the oxidant flow path upstream of the oxidant plenum.

19. An apparatus comprising:

heat exchanger tubing;

a tank structure configured to contain a water bath for the heat exchanger tubing;

a duct system including sparger tubes with outlet ports arranged to discharge gas into a water bath in the tank structure;

a premix burner including an oxidant plenum, mixer tubes with open inner ends in the oxidant plenum, and fuel conduits configured to direct fuel into the mixer tubes, with the mixer tubes having open outer ends arranged to discharge premix into the duct system; and

a water injection system operatively associated with the premix burner to mix water into the premix;

wherein the oxidant plenum is part of an oxidant flow path extending from a blower to the oxidant plenum and the mixer tubes, and the water injection system is configured to inject water into the oxidant flow path; and

wherein the water injection system is configured to inject water directly into the oxidant plenum.