Automatic control of steam injection is difficult because the volume of relief gas is not easily measured because of the wide rangeability (more than 100 to 1). Even if the volume of relief gas is known, molecular weight and composition have a major effect on the steam requirement. Depending on the type of combustion tip, several separate steam injection valves may be needed, requiring split-range control signals.
Currently the Company uses three methods to automatically control steam injection:
1. Flaregas Flarescan—Measuring the flame radiation with thermocouples set around the flare tip. Steam is increased until smoke is suppressed, resulting in lower infrared radiation.
2. John Zink Zoom—Measuring the infrared radiation with a television camera. Steam is increased to reduce the amount of infrared radiation.
3. Panametrics—Measuring the volume and the density of the relief gas with an ultrasonic flowmeter. The required amount of steam is calculated by a microcomputer.
All three methods work for low-to-medium relief rates. Smoke is produced with large rapid changes in the relief rate. Adjusting steam rate with manual controls is not acceptable.