The primary sources of fugitive emissions from refineries and chemical plants are equipment leaks, process venting, evaporation losses, flaring, and accidents and equipment failures. When monitoring plants, the Environmental Protection Agency (EPA) is heavily focused on methane emissions.
Why such a heavy focus on methane? According to the EPA, methane is the predominant greenhouse gas emitted by the oil and gas sector. It is the second most prevalent greenhouse gas emitted in the U.S. from human activity. Per EPA reports, pound for pound, methane has 25 times the global warming potential of carbon dioxide. Methane’s lifetime in the atmosphere is much shorter than CO2, but it is more efficient at trapping radiation. As such, it is considered detrimental to public health.
The latest EPA reports indicates that methane emissions from all sources in the U.S. have decreased by 11% since 1990. Interestingly, in this period, methane emissions from agricultural sources have increased, and have decreased from sources associated with oil & gas exploration and production. However, this reports also states that methane emissions will increase by the year 2030 if no action is taken. So the EPA is implementing a series of programs, some of them voluntary, to reduce methane emissions from all sources.
Legislation to improve air quality goes back as far as 1955 with the passage of the Air Pollution Control Act. This act primarily provided funds for the federal government to research air pollution. Progressively over the years, amendments were added to continue the studies, define emission limits and establish the EPA.
From the beginning, the EPA’s compliance focus has been on plants monitoring and repairing their own equipment. Owners of the plants turned to standards development organizations for help in improving the sealing performance of gaskets and packing. The result is that numerous emission test standards were written. At the time of this article, there are 11 different fugitive emission standards for packing and valves known by the author. And there are still several more in development. Isn’t this too much already? Why are there so many?
The problem lies in confusion within the standards committees. The question these committees struggle to answer is: How do we prove performance in the plants through laboratory testing? Different tests are required for the wide variety of valve types and services. The discussions and debates in standards committees as to what constitutes a valid test are repetitive.
What measurement method(s) are acceptable? Vacuum, flushing, bagging, sniffing? Should the test be done with helium or methane? Helium is safer to use in the laboratory, but methane is what the EPA is focused on. Several have tried and confirmed it is not possible to correlate test results from one gas with the other.
How many thermal cycles during the test are appropriate? Should packing adjustments be permitted during the test? What is the temperature range the valve should be subjected to during the test? Should the leakage be measured when the stem is stationary (static leakage), when the stem is moving (dynamic leakage) or both? What criteria can be used to extend the test results to other sizes and pressure classes of the product line? And there are several more questions that must be agreed upon before the committee can issue an emission test standard.
Testing and Specifying
Once the standards are issued, plant owners and valve manufacturers begin the work of specifying and testing products. Despite all the work by the standards committees, the test results are still not definitive. The question remains unresolved. Will a valve leaking 2, 5 or some other amount times 10-7 or 10-4 millibar liter per second per millimeter of stem diameter with helium consistently pass an EPA sniff test for parts per million of methane when it is operational in a plant?
This question is not answered because one successful test in a laboratory is no guarantee of future success in the plants. The laboratory tests do not address other influencing factors such as thermal stresses, pipe stress, flow erosion, vibration, internal and external corrosion, mechanical wear, aging, and other environmental situations that can influence packing loads.
Despite the fact that emission standards are a confusing jumble, and comparison of results between them is practically impossible, we have had excellent results. Note the overall reduction of methane emissions from the oil and gas sector since 1990. Testing to the various emission standards has led to significant improvements to packing and seal materials and installation techniques, which in turn has led to lower fugitive emissions.
So what does the future bring? Of course, more change. In March 2014, the U.S. administration launched a new climate action plan including strategies to reduce methane emissions. In 2015, this plan was modified with a new goal to cut methane emissions from the oil and gas sector by 40% to 45% by 2025. Currently the EPA is seeking expert input on how to update and modernize their Leakage Detection and Repair (LDAR) program to help achieve these goals. In addition, the American Petroleum Institute (API) is developing a new fugitive emission test standard for rotary valves that may be released by late 2016 or possibly early 2017.
Ultimately, our industry continues to make good progress despite conflicting legislation and standards.