A North Carolina State University course, Introduction to Fugitive Emissions Monitoring, defines fugitive emissions as:
…used in air quality control, generally refers to any emission escaping from regulated processes (sources) other than via the designed release point (smoke stack, etc.). The point source for a fugitive emission is simply called “a leak.” These leaks and emissions are most often associated with the equipment necessary for the movement of process fluids and gasses.
The term “fugitive” is used because these emissions are neither calculated in the source design, captured by the emission control equipment/systems, nor are they detected through normal equipment monitoring processes. Since these emissions bypass control equipment, they are also referred to as “uncontrolled emissions.”
I mention this as background for a Valve World article, Reduce fugitive emissions with a HIPPS solution, written by Emerson’s Carsten Thøgersen. Regulatory pressures drive this need to reduce these emissions:
Oil and natural gas producers are under continual scrutiny to lower fugitive emissions by the Environmental Production Agency (EPA) in the United States, TA-Luft in the European Union (EU), and similar regulatory bodies in other producing countries. As an industry, they have responded positively with tighter pollution control standards and reduced greenhouse gas emissions.
A High Pressure Protective System (HIPPS) can help oil & gas producers to reduce fugitive emissions from pressure protection:
Protection against pressure build up is mainly provided by conventional pressure relief and blow down valves that will discharge gases and liquids to the ﬂare when process design pressures are exceeded.
Carsten defines a HIPPS as:
…a part of the Safety Instrumented System (SIS) and is designed to prevent overpressure by shutting off the source and capturing the pressure in the upstream side of the system, thus providing a barrier between the High Pressure and Low Pressure sides of the process plant. The tight shutoff will prevent loss of the containment and eliminate fugitive emissions. HIPPS is seen as the “last line of defense”.
What’s found in a typical HIPPS:
…2 or 3 ﬁnal elements in series, isolating the upstream pressure source from the downstream side, to avoid any pressure build up. The system is often required to shutdown within 2-3 seconds for gas and 6-8 seconds for liquids, depending on the pipeline pressure, ﬂow rate and the diameter and class of the pipeline.
When a pressure sensing system, typically 3 pressure sensors connected to the SIS logic solver in a 2-out-of-3 (2oo3) voting logic configuration, detects a peak pressure surge exceeding the shutdown limits, the logic solver will initiate a shutdown sequence with the final elements (shutdown valves).
Designing a HIPPS can be complex, because they:
…require the successful functioning of multiple devices to achieve the same performance as a single pressure relief. That is the calculated reliability of the multiple devices needs to meet or exceed the reliability of a conventional pressure relief valve. In addition, the design needs to be verified through Site Integration Test (SIT) and also needs to be validated through compliance to EIC 61511 and the SRS given by the end user.
Carsten notes that Emerson can combine technology and expertise to deliver HIPPS applications [hyperlinks added]:
Emerson manufactures control equipment with adequate certiﬁed failure data to meet SIL3 requirement for HIPPS. The well regarded and ﬁeld-proven components include Bettis actuators, Fisher DVC controllers, ASCO solenoids, DeltaV SIS logic solvers and Rosemount pressure transmitters.
This solution is different in that it includes safety consultancy to make sure there is a holistic view of the process from front end engineering over SRS to the validation of the system.
HIPPS has many advantages compared with conventional pressure relief. Although it will not be able to fully replace existing systems for pressure relief using ﬂares in the near future, it is a sound and safe way to help operators and end users reduce fugitive emissions.