Assessing Fugitive Emissions Performance in Valves and Packing
8 februari 2016
Abstract
If you are a refinery end-user that has to comply with environmental regulations for fugitive emissions, you know how important it is to select valves that will meet or exceed Volatile Organic Compound (VOC) fugitive emission limits. You also know the costs involved when a valve fails to meet these limits, and how hard it has been to get test data that will allow direct comparisons between valve and packing manufacturers. Without data that can be used to directly compare performance results, end-users are left with educated guess work, field trials and past experience from others as a basis for their valve and packing selection decisions.
While most end users would like to see realistic testing done that will provide comparable VOC results in PPM levels of hydrocarbons, and include multiple thermal and mechanical cycles that are representative of real plant operating conditions, up to now this testing has not been easily available from an independent laboratory at a cost effective price. That has now changed.
ChevronTexaco, together with Yarmouth Research, has developed a simple test and testing procedure that can be easily adjusted to accommodate any off the shelf valve and provide the VOC data needed to understand how a valve is likely to perform once in service. For the recent set of screening tests performed on valves from 5 major US valve suppliers, an off the shelf 4 inch class 300 valve was used with Methane gas at 600 psi (41.37 Bars). A stuffing box temperature of 500F (260C) was obtained every 500 cycles, and the test was run for 5,000 cycles or until a leak rate of 500 PPM was reached for the third time. Not only was each valve’s Original Equipment Manufacturer (OEM) packing tested, but a second valve was tested using off the shelf spool packing that might be used for repacking valves in the field.
Both packed valves and Bellow Seal valves were tested, along with different packings from major suppliers and small bore forged steel valves. The results are amazing. No two valves performed the same, and there exists a very significant difference in VOC performance. As an example, two new four inch packed valves failed to complete the first 500 cycles without leaking >500 PPM. Only one new packed valve made it theentire 5,000 cycles. Spool packing results were equally diverse, with one packing only lasting 1,000 cycles while another packing combination went 5,000 without ever exceeding 500 PPM.
This type of testing benefits end-users by providing the data they need to reduce plant emissions and negative environmental impacts, as well as reducing maintenance costs and environmental fines. It also benefits the manufacture by providing a relatively inexpensive way to obtain comparable product emission performance results which can lead to valve designs with lower emissions levels.
