Method for controlling the BTU content of a flare gas
A method for controlling the Btu content of a flare gas to combusted in a flare stack comprising a flare tip is provided. The method includes, introducing a first gas stream including nitrogen to be flared, the first gas stream having an initial Btu content, providing a supplemental fuel gas stream, and combining the first gas stream with the supplemental fuel gas stream, thereby obtaining a flare gas stream having a final Btu content measured at the flare tip.
1. A method for controlling the Btu content of a flare gas to be combusted in a flare stack comprising a flare tip, the method comprising:
introducing a first gas stream comprising nitrogen to be flared, the first gas stream comprising an initial Btu content,
providing a supplemental fuel gas stream, and
combining the first gas stream with the supplemental fuel gas stream, thereby obtaining a flare gas stream comprising a final Btu content measured at the flare tip,
wherein:
the first gas stream has a first flow rate, wherein the first flow rate is measured;
the supplemental fuel gas has a second flow rate, wherein the second flow rate is measured;
the ratio of the second flow rate to the first flow rate is maintained at a predetermined value, thereby maintaining the final Btu content at or above a minimum net heating value measured at the flare tip,
wherein the first gas stream and the supplemental fuel gas stream are combined at a combination point, and
wherein the first flow rate and the initial Btu content are measured upstream of the combination point.
2. The method of claim 1 , wherein the supplemental fuel gas flow is initiated when the initial Btu content falls below a predetermined minimum net heating value measured at the flare tip.
3. The method of claim 2 , wherein the predetermined minimum net heating value comprises the heating value required to achieve combustion efficiency requirements.
4. The method of claim 1 , wherein the first gas stream has a pressure, and wherein the supplemental fuel gas flow is terminated when at least one of the following conditions has been met by the first gas stream:
the hazardous air pollutants (HAP) level is less than 20 ppm,
the pressure is below 5 psig, or
the lower explosive limit (LEL) is less than 10%.
5. The method of claim 1 , wherein the predetermined value of the ratio of the flow rates is a function of the first flow rate and the initial Btu content.
6. The method of claim 5 , wherein the first flow rate, the initial Btu content, and the final Btu content are measured and reported at least every 15 minutes.
7. The method of claim 6 , wherein the Btu measurements are performed by a gas chromatograph, mass spectrometer, or calorimeter.
8. The method of claim 1 , wherein the minimum net heating value is 270 Btu/SCF measured at the flare tip.
9. The method of claim 1 , wherein the supplemental fuel gas stream is provided by a local, external bulk source.
10. The method of claim 9 , wherein the local, external bulk source is portable and temporary.
11. The method of claim 10 , wherein the supplemental fuel gas is selected from the group consisting of hydrogen, ethane, propane, propylene, butane and/or any suitable hydrocarbon with a sufficient heating value.
12. The method of claim 1 , wherein:
the first gas stream has a first flow rate, wherein the first flow rate and the initial Btu content are measured;
the supplemental fuel gas has a second flow rate, wherein the second flow rate is measured and the final Btu content is measured at the flare tip; and
wherein the second flow rate is adjusted to maintain the final Btu content at or above a minimum net heating value at the flare tip.
13. The method of claim 12 , wherein the first flow rate, the initial Btu content, and the final Btu content are measured at least every 15 minutes.
14. The method of claim 12 , wherein the minimum net heating value is 270 Btu/SCF measured at the flare tip.
15. The method of claim 12 , wherein the supplemental fuel gas stream is provided by a local, external bulk source.
16. The method of claim 15 , wherein the local, external bulk source is portable and temporary.
17. The method of claim 15 , wherein the supplemental fuel gas is selected from the group consisting of hydrogen, ethane, propane, propylene, butane and/or any suitable hydrocarbon with a sufficient heating value.