Reducing Emissions from Vessels, Valves, and other Equipment

by , , , | Nov 8, 2022 | Sustainability, Valves, Actuators & Regulators | 1 comment

Marcel Dultra, Dan Myers, and Emily Thomas of Emerson recently published an article in the September 2022 issue of Valve World Americas. It is titled “Greening Process Equipment One Device at a Time” and it discusses a host of recently introduced technologies designed to significantly reduce emissions. A summary of the article follows.

Numerous government standards targeting greenhouse gas emission reductions, as well as a multitude of corporate initiatives, are driving companies to reduce, and ideally eliminate, releases to the atmosphere. Fortunately, several new technologies can help them achieve these goals.

Understanding emission sources

There are two types of emissions that typically occur in an operating process plant or facility: fugitive emissions and vented emissions (Figure 1).

Figure 1: Emissions generally fall into one of two types: fugitive emission from unintentional leaks (left) and intentionally vented emissions (right).

Fugitive emissions are unintentional leaks that discharge from pressure-containing equipment. These usually include valve packing leaks, relief valve seat leaks, pump seal leaks, and flange leaks. The second type of emissions are vented. These emissions result from intentional releases from relief valves and pressure vents, and from pneumatic equipment which use natural gas instead of air.

Fugitive emission reduction solutions

Valve packings are a common source of fugitive emissions. Fortunately, recent advances in materials and engineering designs have yielded dramatic improvements in valve packing performance (Figure 2).

Figure 2: The picture on the left shows a typical rising stem control valve with standard packing. The latest Fisher ENVIRO-SEAL™ (right) reduces fugitive emissions to 100 ppm or less.

The authors describe the new offerings:

The latest environmental packing designs utilize spring-loaded washers to continuously compress the packing seals, paired with a combination of different packing ring materials to achieve extremely low leak rates of less than 100 parts per million (ppm), yet still handle a wide range of process temperatures and pressures.

Older valve styles do not usually incorporate this type of packing, so a plant should start by evaluating existing valve packing installations and quantifying their performance. A plant walkdown targeting valves that handle volatile organic products and other targeted materials can be an excellent place to start, as the authors explain:

If a valve has a history of leaks, a simple and inexpensive packing upgrade to a more advanced design will typically yield dramatic reductions in emissions. Improved positioner diagnostics also provide a means to continuously monitor packing performance and alarm if problems are detected.

Another common source of fugitive emissions comes from relief valve seat leaks, which can be difficult to detect, especially when the valve vents into a flare header. In this case, WirelessHART® acoustic sound and temperature monitors can be strapped to the discharge piping to detect leaks (Figure 3).

Figure 3: This graph illustrates a typical relief valve leakage event. After the first blow down, the valve does not shut completely. Leakage is indicated by elevated acoustic noise (blue line) and an elevated temperature (green line).

The monitoring device allows the plant to immediately respond to leaks, eliminating emissions and avoiding lost product.

Vented emission reduction solutions

Vented emissions often result when a pressure relief device opens to protect the process from an overpressure event. This protects the equipment, but results in an environmental release which must be documented and reported. The authors comment:

The obvious solution to reducing vented emissions is to avoid the overpressure event in the first place, but these issues cannot be addressed until the plant has an easy way to detect and quantify pressure relief events.

The WirelessHART acoustic and temperature transmitter discussed previously helps detect relief valve discharge events, but there are other sources of vented emissions, including open thief hatches, gauge hatches, and pressure relief manways. A simple switch or position sensor can be mounted on these devices to indicate when a tank vent is operating, or when a hatch has been left open (Figure 4).

Figure 4: A WirelessHART gateway communicating with a variety of wireless field devices can help plant personnel reduce vented emissions by detecting open hatches, tank blanketing issues, and tank pressure vent releases.

A wireless network provides a practical method for capturing this data and alerting the operators to emission problems.

Another significant source of vented emissions occurs at remote oilfield sites when natural gas is used to actuate pneumatic equipment. Automation providers have introduced a broad array of very low bleed and zero emission alternatives for these remote sites, as the authors describe.

The most common solution involves low power, electric valve actuators and electronic transmitters. These devices cut methane vented emissions to zero, while providing information to enable a host of advanced process control strategies, each of which can be implemented from a remote location.

Real world savings

Several facilities have employed these technologies and achieved dramatic emission reductions, as well as significant cost reductions. One refinery installed flow meters and relief valve acoustic detectors on their flare header system. The project paid for itself in five months by allowing plant personnel to immediately detect and stop relief events. This reduced overpressure events, saving $2,500 to $50,000 per release.

Several oil companies are actively pursuing wholesale electrification of their well site valves and instrumentation. They expect to save nearly $1 million per well due to increased production, reduced losses, remote control capability, and significantly improved operation.

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The opinions expressed here are the personal opinions of the authors. Content published here is not read or approved by Emerson before it is posted and does not necessarily represent the views and opinions of Emerson.

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