How to Accurately Measure Solvent Recovery Yield

Accurately calculating solvent recovery yield is essential to ensuring you’re getting maximum performance out of your distillation unit. Discover why this one metric is so vital to monitoring your distillation units health.

How to Accurately Measure Solvent Recovery Yield

Accurately calculating solvent recovery yield is essential to ensuring you’re getting maximum performance out of your distillation unit. Discover why this one metric is so vital to monitoring your distillation units health.

Table of Contents

Solvent recovery yield measures the percent of solvent that’s recovered from the distillation process.

The yield of a solvent recovery unit is one of the best indicators available of a distillation units’ overall health. Which makes it a vital piece of data in making sure you’re getting the most output you possibly can from your distillation units.

Unfortunately, it’s often an over promoted number on some solvent recovery units with no system of accurately measuring the yield. 

Calculating Solvent Recovery Yield as a Percent of the Feed Material

There are two ways to measure the yield for solvent recycling equipment:

1.       The volume of solvent recovered as a percent of the total waste stream (feed).

2.       The volume of solvent recovered as a percent of the available solvent in the waste stream (feed).

The second approach is often cited by companies that sell solvent distillation equipment.  This approach is used for two reasons.

First, it sounds impressive to say, “our equipment recovers 90% to 95% of the available solvent.”

Second, the percent of solvent in the waste material varies from drum to drum or tote to tote. And almost no one knows the exact percent of solvent in the waste stream.  In other words, it’s easy to make a claim no one can feasibly check.

Traditional distillation units are not designed to measure the volume of recovered solvent as a percentage of available solvent. To do so, you would have to constantly measure the percent of solvent in the feed material which is impractical.

The alternative, is to use the first approach, measure the yield as a percent of the total waste. This is the recommend method of the two available options as it doesn’t matter if the percent of solvent changes in the feed stream.  

Formula for Calculating Solvent Recovery Yield as a Percent of the Feed Material

Recovered Solvent Yield Percent = Volume of Solvent Recovered /Volume of Feed Material Processed

How Do You Track Recovered Solvent Yield?

On a traditional distillation unit, this is typically a manual process done by logging the approximate amount of feed material that’s processed into the distillation unit and logging the approximate amount of solvent recovered.  

The challenge with this approach, is ensuring it’s consistently completed.  One glance at a solvent recovery log often shows gaps between entries. 

This is an example of a manual solvent recovery log:

Manual solvent recovery log to track yield

With advanced units however, you can ditch this old method of manually tracking. 

These units automatically measure the volume/weight of spent solvent material or feed material (input) and volume/weight of recovered solvent (output), giving you the yield number. And then they track and record those numbers every time they run so you can see the performance over time.

CleanPlanet Chemical’s AlwaysClean distillation unit coupled with the proprietary Athena online system automatically tracks these numbers. So, all you have to do is login and all the information is right at your fingertips.

Here’s an example of how this looks with the Clean Planet Chemical Athena Solvent Recovery Tracking and Notification System:

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How Often do you Calculate Recovered Solvent Yield?

Due to the cycle of cooking and discharging that a solvent recovery unit undergoes, it’s impractical to measure yield until many multiples of these cycles are completed.

A day or a week cannot be used to calculate yield because not enough cycles have been completed to produce a reliable yield calculation. Instead, yield should be reviewed on a monthly and quarterly basis.

When you look at these monthly and quarterly numbers, if the yield falls more than 5% month over month or quarter over quarter, a review needs to be completed for both process issues and any unit mechanical problems.

The recovered solvent yield is critical to measure and track for these four reasons:

  1. Provides a snapshot on the health of a distillation unit and establishes a baseline
  2. Indicator that the unit needs repair or replacement
  3. Provides a point of comparison for competitive units
  4. Provides some insight into how much solid material is being wasted
  5. Combining the recovered solvent and still bottom volume and deducting it from the feed volume will provide the rough volume of VOC material lost as fugitive emissions

What to Do if Yield Drops

If you do see a drop in your yield, it could be due to one of the following reasons:

  1. Unit has mechanical problems
  2. The settings have changed on the unit
  3. The solvent or contaminate have changed
  4. Too much contaminate (solids) in the feed material
  5. Poor recovery of the clean distillate

Yield as a Measurement of a Distillation Units Health

As a distillation unit ages, it’s natural to see the yield percent decrease due to wear and tear. If the yield percent is calculated every month and tracked, it can be a barometer on the unit’s overall performance and health.

Performing annual preventative maintenance and repairs in a timely manner will help maintain the units yield. 

Maintenance and Repair Warnings from Low Yield

Falling yield will sometimes indicate that the distillation unit needs mechanical attention. 

Establishing the baseline for the yield percent will enable the maintenance department to have a scorecard to review when completing a quarterly review of the unit. 

Consistently tracking the yield percent will be a key to ensuring the unit gets timely attention from the maintenance department and will result in better uptime and ultimately better overall solvent recovery.

Settings have Changed on the Distillation Unit

If you see a sudden change in the yield it may be that someone has inadvertently adjusted the settings on your distillation unit.

Record the original settings in three places: on the unit via a label, in a hard file folder and in an electronic file.  If the yield falls unexpectedly, compare the time and temperature settings on your unit against your records and make sure nothing has changed.

Excessive Solid Waste

In addition, monitoring the yield percent will provide some insight to the volume of contaminate material in the feed stream. A low yield percent may mean that too much paint, ink or oil is being wasted.

Sometimes changes in personnel or process can result in overmixing paint or ink material resulting in excessive solids in the cleaning stream. 

Another possible cause of more than normal solids in the spent solvent cleaning stream is solid ink/paint waste being put in the wrong container.  Posted signage in the drum storage area and clear drum labeling will minimize this problem.

Poor Recovery of the Clean Distillate

State air regulators often view solvent distillation equipment as pollution devices because they often lose up to 20% of the recovered solvent to the air. Low yield can indicate that the condensing process is not working properly. 

A quick way to evaluate if low yield is due to poor recovery is to calculate the loss of material from the distillation process:

Loss of Clean Distillate = (Feed material – (Clean distillate + Still bottom material))

If observations indicate this may be a problem, weigh the feed drums, the clean distillate drums and the still bottom drums and use the formula above to calculate the material loss.  If the material loss is excessive, it may be due to over cooking the capability of the condensing process (check the temperature) or there is a mechanical issue related to the condensing process.

ANOTHER (BETTER) WAY

CleanPlanet partners with its customers to ensure they are maximizing their solvent recovery yield. Our Athena system delivers reliable metrics you can see at any time to monitor your solvent distillation units health. If you aren’t getting the yield you expected from your distillation unit reach out to our team to see how we can help.

Learn how to get even more value out of your solvent waste.  

Learn how to get even more value out of your solvent waste.  

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