Sealing the Unseen: Creating Efficiency through Emission Control
Darshan Parekh
Technical Director
PILOT Gaskets And Engineers

On 22 April 2016 (Earth Day), 174 countries signed the Paris Agreement focusing on reducing Greenhouse Gas emissions across the world. This again increases the focus on regulatory standards for Fossil Fuel industries like Refineries and Thermal Power Stations which are anyways stringent. Refineries continue to be pushed towards remaining efficient, hazard free, and environmental friendly all against the global outcry towards renewable source of energy. While emission standards are globally managed by the respective Pollution Control Boards, fur ther controlling Emissions means Refineries need to look at other avenues for complying with these regulations.

Fugitive Emission is defined as; any chemical or mixture of chemicals in any physical form which represents an unanticipated or spurious leaks from anywhere on an Industrial Site. It basically refers to all losses(usually volatile) materials from a process plant through evaporation, flaring, spills and unanticipated or spurious leaks. The focus of this article is primarily on Volatile Organic Compound (VOC). Majority of these volatile materials is not visible to the naked eye and to accurately measure appropriate thermal sensing devices need to be used to "sniff ", detect and measure the leakage loss.

To put things in perspective, the United States of America estimates loss of material in excess of 300,000 Tonnes per year. Besides the obvious environmental effects this is a huge loss of valuable material and an important consideration in Plant inefficiency.


EPA Report on Emission Standard in United States of America in 2008

Sources of VOC Fugitive Emissions:
A significant por tion of Fugitive Emissions can be losses from unsealed sources like storage tanks, open-ended lines, pressure relief valves, vents, flares, blow-down systems, spills and evaporation from water treatment facilities.

Usually these losses are calculated by the Process Engineer and taken into consideration during design however a significant amount of losses are caused by leaks in the sealing element of equipment such as
  • Agitators / Mixers
  • Compressors
  • Flanges
  • Pumps
  • Tank Lids
  • Valves
In a study in Netherlands, 72% of Emissions from a single Refinery was attributed to leakage losses from Equipments, 18% from flaring, 5% from Combustion, 1% from storage and 4% from process emissions.



Sources of Fugitive Emissions

The primary purpose of a Seal is to contain a fluid and protect the immediate environment from contamination. Hence although losses per piece of equipment might be deemed small there are usually so many items of equipment in a Refinery that the total loss via Fugitive Emission is very significant. For e.g. In a refinery for every pump there are usually 32 Valves, 135 Flanges, 1 Safety Valve and 1.5 Open Ended lines. Hence with so many potential sources, leaking losses are high and difficult to ascertain in value without proper help and planning.

LDAR (Leak Detection and Repair).
Leaking Losses are generally higher from dynamic equipment (compared to static equipment) and from older equipment. Furthermore the majority of actual emission will come from only a small fraction of sources (i.e. less than 1% of valves in gas/ vapour ser vice can account for more than 70% of Fugitive Emission in a refinery.)



LDAR Program using infrared Cameras.

Leaking Losses from equipment can be significantly reduced by use of monitoring and maintenance programs such as LDAR (Leak Detection and Repair ). Leaks are detected by monitoring equipment and repairs must be carried out if the leakage rate exceeds cer tain levels. LDAR consists of Volatile Organic Compound (VOC) detecting "sniffers" that help in detecting leaks from flanges, pumps and valves. A correctly implemented LDAR program could reduce Fugitive Emissions by 40% to 60% depending upon the frequency of inspections, the process control and the fluid used.

Leak Control
Valves

Studies have indicated that leaking valve stems are by far the single largest source (60%) of fugitive emissions in a Refinery. Majority of valves are sealed with Gland Packings or various combination of these solutions.

When selecting the correct Packing seal, considerations have to be given to the temperature, media and pressure to which the valve seal will be subjected, as well as the level of sealing performance required to comply with the Emission standard.

Packing Certification
Packings can be tested to qualify them for various types of service, which also helps to assure fugitive emissions requirements are met. ISO 15848 (Parts 1 and 2), API 622, API 624 and VDI 2440, have been in use for evaluation and testing valves and/or stem packings to meet the relevant fugitive emission limits and requirements.





Different types of Gland Packings used in Valves.



The fundamental difference, between ISO 15848-1 and API 622 is that the ISO standard qualifies the seal in the valve, while API tests the packing material independent of the valve. In addition to fugitive emissions, API 622 also assesses the corrosion effect the packing has on the valve stem material and tests for a number of physical attributes, including high -temperature oxidation resistance.



Testing of Valve Packing for Fugitive Emission (Image courtesy FSA)

Refineries and petrochemical processors such as Chevron and Shell have established their own criteria for qualifying stem seals. These standards specify temperature, thermal c ycling, test media, number of actuations, allowable adjustments to maintain the seal during testing and emissions -measuring methods. The Shell specifications for fugitive emissions testing are covered in MESC SPE77-300 for prototype qualification testing and SPE77 -312 for production testing.

Flanges
While individual flanges might not contribute to a large leaking loss, each Refinery utilizes so many flange joints that overall they contribute heavily to Emission loss. There can be enforcement of a combination of preventive measures to reduce these Emissions such as:
  • Regular Maintenance or Controlled Tightening of the Flange an
  • Selecting the Right selection of the Gasket.
In India, there is a still a common usage of Compressed Asbestos Fiber(CAF) Gasketing material or Spiral Wound Gaskets with CAF Filler due to their economical nature. CAF is extremely poor for Fugitive Emissions and selecting application specific certified nonAsbestos Gasketing Solution can itself reduce Fugitive Emission by 400%. The nonAsbestos Gasketing technology in soft gasket material combined with Flexible Graphite Sheets and KAMMProfile ensures that Asbestos based Seals are being phased out due to ineffectiveness when dealing with Emission loss.

Gasket Certification
While selecting the right Gasket, ensuring compliance with cer tification is of primarily impor tance. For Gasketing material the primarily focus should be on TA-LUFT & VDI 2440 cer tification and approval.

Note, TA-Luft only gives guidelines for compliance with permissible leakage limits and refers to other regulations for specific situations to measure and certify static and dynamic leakage values. Specific leakage rate limits for these seals are stated in VDI 2440. VDI 2440 utilizes Helium for testing with values of 10-4 mbar*l/(s*m) at temperatures < 250°C (482°F) and 10-2 mbar*l /(s*m) at temperatures > 250°C.

These tests are able to determine the efficiency of the Gasket (Spiral or Soft) for fugitive Emission and can ensure ease of compliance with Gasket Material Selection.

The Cost Effective
While the loss of valuable material is an obvious advant age for controlling Fugitive Emissions there are hidden advantages too such as Material Cost, Labour Cost, Wasted Energy, Plant in efficiency, Environment Cleanup or Environmental Fines.

In most cases, the cost of the actual sealing technology is negligible when compared to the investment made in the plant as a whole. While, changing from non-certified to correct certified solutions might seem expensive the actual unit cost is completely over whelmed by the savings in labour costs & plant downtime itself. Controlling Fugitive Emissions with the proper cer tified Sealing Solutions will mean greater compliance to LDAR and result in an overall Plant Efficiency with increased production.