Emerson Exchange 365

Sometimes a level reading may be deceptive, even when the measuring instrument is working as it should. Addressing this type of issue can often result in substantial benefits, as in this situation where payback was realized in a week.

A plant was struggling with a production bottleneck because operators weren’t sure how much liquid they were putting in their tanks because they didn’t understand the liquid’s characteristics well enough to interpret the level reading. Sound confusing? We helped straighten out the problem, and you can read the full story in my article in the February 2020 issue of Flow Control, Improving Level Measurement to Solve a Production Bottleneck.

The situation in question was at a large ethanol fuel plant trying to maximize production with the existing set of fermenter tanks. Operators were never entirely sure they had filled the tanks to maximum capacity.

Each fermenter has a differential pressure (DP) level transmitter. This is a common level measuring technology and is an ideal choice, provided the liquid involved has known density characteristics that do not vary. Unfortunately, when making mash for ethanol, density is not predictable. Moreover, when the mash goes into the fermenter, there is always some foam, but the amount varies based on a number of factors. For those reasons, the DP level transmitters did not provide the degree of precision needed without cumbersome density compensation.

There was no problem with the DP transmitters. They were working perfectly, but given the lack of a precise handle on the liquid density and the amount of foam, operators felt they had to stay on the safe side. They ended up leaving more open head space in the tank than they realized. This open head space was wasted production capacity. The solution: installing a second level transmitter using a different technology to provide a final reading.

Getting the last bit of capacity required a different technology: guided-wave radar (GWR). With GWR, a metal probe extends down through the air or vapor space and into the process medium. The probe helps concentrate the signal, which helps when there are multiple levels, such as liquid below foam, or where there is an interface level, such as oil on top of water. GWR devices are easy to install and can be used in tanks of all sizes. The main drawback of GWR is the probe itself, making its use impractical if there are moving agitators or other equipment inside the tank.

The plant inserted a short GWR probe into the tank using Emerson’s Rosemount 5300 Level Transmitter. It was short enough to clear the agitators but deep enough to know when the liquid level reached maximum capacity, including foam. Having both the DP reading and the actual liquid height provides more information about the liquid itself and the fermentation process. So, in addition to gaining this “free” capacity, plant operators can more closely monitor and control processes and reactions in the tank.

With more accurate volume measurement, it is possible to add enzymes and yeast more precisely, rather than wasting money overdosing additives to be on the safe side. Also, with a known volume from the GWR and liquid weight from the DP transmitter, it is possible to calculate the specific gravity at the time the mash is pumped into the fermenter. This information can be used to optimize the mash-making process.

And, with the ability to determine specific gravity, it is possible to monitor the fermentation process more closely to determine the optimal residence time in the fermenters. This supports ongoing analysis to characterize the fermentation itself and evaluate the practicality of increasing production without sacrificing ethanol yield.

The plant has realized multiple benefits for a simple and economical improvement. The increased capacity paid for the whole project in about a week. Could you imagine similar benefits?

• Are there parts of your process where there might be a mismatch of measuring technology and the needs of the process?
• This plant selected DP because it worked well in a large tank with moving agitators, but never fully resolved the density issue. Are there areas where you have similar struggles?

Tell us about the troubles you’re dealing with on a daily basis and the ideas that work great. You can share with others about your implementations and experiences at the Emerson Exchange 365 community forum, a place where you can exchange ideas and experiences with others in the same situation. It’s a site where you can communicate with experts and peers in all sorts of industries around the world. Look for the Level Community, plus other specialty areas for opportunities to provide input, suggestions, and answers.