Eliminating leaks and fire hazards for teal catalyst control valve
This weeks post is discussing about how to eliminate risks at petrochemical production related to TEAL (triethylaluminium), an organoaluminium compound which is highly pyrophoric, igniting immediately upon exposure to air. It is mainly used as a co-catalyst in the production of polyethylene and medium chain alcohols.
For years, a petrochemical plant in the US was experiencing stem leaks with its linear teal catalyst feed control valve. A small amount of teal, a fine powder catalyst, on the stem would crystallize and adhere to the stem, forming a surface like sand paper when the rising stem of the valve exposed teal residue to the air. This abrasive surface would then scar the packing, causing it to leak. One serious problem resulting from the leaking valve was small, fast-starting fires that were ignited when the teal catalyst was exposed to air.
Ongoing accumulation of teal catalyst on the stem would also cause the valve to stick and fail. To combat this, the plant installed a backup globe valve to come online when the primary valve failed. Unfortunately, the sticky teal catalyst would also cause similar problems for the backup valve over time. Once the backup valve’s performance began to degrade, it would only last a few more weeks before it too failed.
Facing unnecessary costs and downtime
At this point, the plant would have no choice but to replace both the primary and the backup valves. If possible, both failed valves would then be repaired and placed into inventory as backup valves. This solution was obviously not an optimal one, as it resulted in unacceptable repair, replacement and labor costs. The downtime also cut into productivity.
High performance through simplicity
In its search for a solution to these problems, the plant considered the Neles RotaryGlobe valve (½” 150# flange CxS with Cv of 0.1). Metso’s Neles RotaryGlobe is an innovative and revolutionary rotary control valve for use in a wide range of applications. It provides high performance in terms of flow control accuracy, reliability and safety. Efficiency, high availability and process safety are standards enabled by features such as low emission packing, and simple and modular top entry construction.
The RotaryGlobe valve solution, in particular, appealed to the plant because the valve did not have a rising stem. This eliminated the issue of the teal sticking to and crystallizing on the stem when exposed to air. In addition, the RotaryGlobe valve’s scraping seat design, which keeps the trim working by automatically scraping the plug and cage, clears debris every time the valve cycles.
The plant observed an on-site demo of the RotaryGlobe valves and the advantages that they bring. The plant also simulated the valve’s performance under actual line conditions using patented Nelprof® 6 expert sizing software. Based on this simulation and an understanding of the process conditions, Metso was able to provide the plant with a guarantee of the valve’s performance. So, the plant decided in favor of installing the valve.
After installation of the Neles RotaryGlobe valve, the plant operators experienced a consistent and unprecedentedly smooth flow of teal catalyst. The valve has also performed very reliably. In fact, the plant installed a spare backup valve, but it was never needed and subsequently removed.
Overall plant performance and uptime have been greatly improved thanks to the new solution. The previously annual USD 20,000 (EUR 14,500) hardware and labor costs created by the repair and replacement of the failed valves have been eliminated. Also eliminated was the approximately USD 50,000 (EUR 36,400) worth of lost productivity due to unscheduled downtime. Safety concerns caused by the teal/air fire potential were also resolved.
As a result of the initial success, the plant brought five additional Neles RotaryGlobe valves into service, with the teal tank farm utilizing two new valves as well. The Neles success story has spread to other parts of the plant, which has led to the installation of several hundred Metso valve solutions in other critical applications.
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