Summary
To allow the combustion and destruction efficiencies of a flare system to be estimated, the molecular weight of the flare gas can be helpful. This is normally derived from the composition of the flare gas.
If taking a sample for laboratory analysis or on-line compositional analysis is not possible, then, if a gas ultrasonic meter is installed on the flare system and the speed of sound is available as an output, then the molecular weight of the gas can be derived as a direct relationship to the SoS.
How it Works
To derive MW from the SoS, we need to understand the relationship of SoS in an ideal gas, this is as follows:
This calculation can then be entered into either the flare meter controller/ flow computer or within the DCS / ICSS and the corresponding MW can be utilised to enable the calculation of the combustion and destruction efficiency.
Utilisation of the inference of MW from SoS is not a common application but can be used when no sampling or analysis facilities are available on the flare systems.
Advantages
No Equipment costs
Minimal Maintenance costs
On-line continuous calculation
Limitations
An assumption on the adiabatic constant must be made, based on the likely composition of the flare gas
Low Accuracy
High Uncertainty
Case study
No case study available at this time.
On-line analytical methods involve extracting a sample from a flare system via an automatic sampling system and analysing it continuously with a field installed analyser system.
