By Kilian Regan, Chief Product Officer, and Kevin Moses, Director of Operations, LDARtools
The year was 1996 and 11-year-old me (Kevin Moses), and my 9-year-old brother, were up to no good, or so we thought. Mom and Dad left us in the hands of our very capable teenage sister, who was undoubtedly talking on the cordless phone in her room. Recently Dad left a video in the VCR called “Fugitive Emissions” and this was the moment we had been waiting for.
Different Methods Available
- The Correlation Equation method converts ppm to mass flow using equations provided by the EPA. This is the most common method used.
- The Average Emission Factors(AEF) method uses an industry average (generally determined by the EPA) to report unmeasured components. This method is used if components do not have monitoring (ppm) data.
- Others, such as >10,000ppm or < 10,000pmm (aka Leak, No Leak) OR AEF, are created using a facility’s historical data. These are largely unused and highly complex. They are mentioned only to highlight that they will not be covered in this overview.
The Correlation Equation
- Zero Readings Emission Rates. Assumes there is a very small leak on 0 reading components.
- Peg Factors Emission Rates for analyzers that peg at 10,000ppm and 100,000ppm.
- The ppm Correlation Equation for everything in between 0 and analyzer peg.
The following is an example of a Valve in a refinery in Light Liquid Service:
- Zero Reading Emission Rate: 7.8E-6 kg/hr
- Pegged 10,000ppm: 0.064 kg/hr
- Pegged 100,000ppm: 0.14 kg/hr
- Correlation Equation: 2.29E-6(ppm)^0.746
Direct Measurement can also be used to replace or update the estimates. An example would be after finding a leak (ppm), another trip would be made to the component with a specialized device, such as a bagging kit or High Flow Sampler, that can capture all of the leak with a known amount of dilution. While the reading from the device is measured in concentration, the known dilution allows an accurate mass flow rate of the leak to be calculated.
Calculating Emissions Between Data Points
Linear interpolation (trapezoid) is the most commonly used calculation method and assumes that emission rates increase/decrease linearly between routine data points. As with almost everything about emission reporting of fugitives, the only thing known, is the likelihood it is not actually true. The change in the leak was almost certainly caused by an event, but there is no way to prove this with the data available.
There are exceptions to the linear assumption. One example is the emissions after a leak and before a repair attempt. The emissions rate is assumed to continue at the same rate until the repair attempt, as logic would suggest. See Chart 1 for an illustration of this.
Average Emission Factors