A Cost-Effective Option
We initially considered magnetic flow meters, as they provide accurate measurement and long-term reliability at the right price. However, they require external power — and no power wiring ran to the separator columns. We estimated the cost to run power to the 50-ft. columns at about $4,000 per column. Coordinating the efforts of separate groups for electrical and instrumentation work also would affect project cost and schedule. With everything factored in, the total cost to run power was prohibitive.
Coriolis technology appealed to us. After all, Coriolis is the most accurate technique available for measuring process mass and volume flows. However, conventional Coriolis meters also require external power, but the introduction of Emerson's Micro Motion 2200 two-wire transmitter made our use of Coriolis meters possible.
We already had standardized on Micro Motion Coriolis flow meters wherever possible throughout Eli Lilly. Around 200 devices are installed at the Clinton plant, mostly working directly on the manufacturing process. We also have some meters reading natural gas flows into the plant. When the availability of the new two-wire device came to our attention, it was an easy choice for the recovery process.
In September 2009, the first Coriolis meter was installed on the feed line of Column 1 during a routine maintenance shutdown. The device was positioned in the "flag" orientation in a vertical section of pipe (see lead photo). Because Coriolis technology doesn't require a long straight pipe run before or after the device, it was very easy to fit without serious pipe-work reconfiguration. Installation was simple and incredibly smooth. It took just a few minutes to get the meter up and running; after a couple of calls to the control room to confirm it was performing correctly, we were done.
The installation cost totaled $3,258, which included electrical and piping contractors' charges. We incurred some additional costs for piping changes not essential for the new meter install — because we decided to put the meter at a height that would provide easy ergonomic access rather than 12 ft. in the air like the old meter.
The Micro Motion two-wire Coriolis device ideally suits continuous process and mass balance applications. The new meter delivers ±0.2% liquid flow and ±0.002 g/cm3 liquid density accuracy. Once the device was in place, we immediately found that feed flow rates were about 100 liters/minute higher than expected. This was far more than we had anticipated and demonstrated the difficulties we had to overcome when controlling the process.
We also have seen a good improvement in the stability of the recovery process. While operators before often were "shooting in the dark" regarding feed flow rates, they now have a stable starting point from which to make process adjustments. As a result there've been no upsets caused by the feed.
Not needing to move the process into recycle mode also means we no longer waste energy by being in that mode.
In early September we replaced three of the remaining eight meters for feed, overhead and bottom flows on the three columns. We expect to swap out the rest by the end of September. The new devices will allow us to perform an accurate mass balance on the separator. The mass balance information will enable us to optimize the process, maximizing solvent recovery while minimizing energy costs. We hope to improve the efficiency of the process by at least 5% if not much more.
An additional bonus is that the Coriolis meters have no moving parts and require very little maintenance. We expect that over time this will create more savings and further improve the uptime and efficiency of the recovery process.
LARELL PALMER is a senior instrument engineer for Eli Lilly & Co., Clinton, Ind. ERIK SCHROEPPEL is a process engineer for Eli Lilly & Co. in Clinton. JOSEPH ALMON is a senior sales engineer for Micro Motion, Emerson Process Management, Indianapolis, Ind. E-mail them at Palmer_Larell_K@Lilly.com, Schroeppel_Erik_F@Lilly.com and JosephAlmon@Emerson.com.