A power plant in North Dakota decreased their quicklime consumption & operating costs by almost $1 million annually.
It wasn't by replacing an old system, or by reducing their capacity, it was by hiring STT to help them understand the 'Science of Slaking'.
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"STT's System Optimization Study is the most cost effective approach to reducing your quicklime consumption and slaker maintenance costs. More >>"
Kevin Thomas, P.E.
Plant Environmental Superintendent

STT's expertise in lime slaking is unmatched in the industry. With their help we've decreased our quicklime consumption by nearly 10% annually and decreased our maintenance costs. Their System Optimization Study (SOS) is the most cost effective approach to reducing your quicklime consumption and slaker maintenance costs. They are the only name we trust when it comes to understanding lime slaking - and you should too.

Kevin Thomas, P.E.
Plant Environmental Superintendent
Office (701)794-7278
Cell (701)317-1468

The Challenge

The VERTIMILL® lime slaker system was originally designed for 30 tons per hour but was only able to run smoothly at 65% of design capacity. Even at reduced capacity, monthly cleanout of the downstream equipment and piping was required, resulting in lost production and increased operating costs.

The Process

When the system was commissioned there were several factors that were limiting the system's ability to run at design throughput.

STT Enviro Corp took a systematic approach to understanding the capacity limiting issues and developing a solution. First, one of STT's Slaking Specialists completed a Scientific Study on-site to identify the factors affecting performance. The Study concluded that there were six factors contributing to performance issues at the plant:

  • An analysis of the quicklime used at site showed that it was excessively reactive, which resulted in dry quicklime floating on the surface, thus not getting slaked fully before leaving the slaker.
  • Analysis of the available water showed high levels of sulphates which impeded slaking reaction.
  • Due to a lower than optimum set-point for slaking temperature, slaking was not as 'aggressive' as it should have been.
  • Due to the 'buoyant' nature of this particular quicklime, larger quicklime and grit particles carried over to the separating tank.
  • Excessive surface splashing enhanced carryover of unslaked quicklime particles to the separating tank.
  • Large particles carried over beyond the slaker were then settling downstream in tanks & pipes.


Quicklime consumption decreased by

over 10%

Reduced slaker maintenance costs by


Increased Sulphur scrubbing


Reduced carbon dioxide output by

5,300 tons

Increased throughput capacity from 63% to


name-plate capacity


STT then provided four key recommendations that would address all six factors contributing to poor system performance:
  • Remove the VERTIMILL® upper scraper arm to reduce surface splashing and short circuiting of unreacted quicklime.
  • Add grinding media to create seasoned charge to improve the grinding of quicklime and grit and address muted slaking due to the presence of sulphates in the slaking water.
  • Increase the target slaking temperature to ensure proper slaking of quicklime and the production of highly reactive lime slurry.
  • The major bottle neck to capacity was identified as poor hydraulics of the slaking mill which allowed lime to leave it unslaked. A modified feed arrangement (VERTIMILL® Retrofit Kit - patent pending) was installed in the slaker to eliminate quicklime short circuiting, thus ensuring that it is fully slaked before it leaves the slaker.

BEFORE: VERTIMILL® slaker without STT's modified feed arrangement. The absence of the modified feed arrangement allowed unreacted lime to leave the slaker without proper slaking and grinding.

AFTER: The modified feed arrangement (shown in blue) ensures that hydraulic short circuiting is eliminated. All quicklime fed to the slaker is forced below the slurry liquid level for complete slaking and grinding thus resulting in increased throughput and significantly improved lime slurry quality.

The Results

  • Lime slurry reactivity increased by over 8%
  • Quicklime consumption decreased by almost 10% annually
  • Overall carbon dioxide output was reduced by 5,300 tons annually
  • Throughput capacity of the lime slaking system increased from 63% of name-plate capacity to 100% of name-plate capacity
  • Large particle carryover decreased, resulting in decreased maintenance costs ($120,000 annually)
  • Maintenance hours dropped because there was reduced requirement to clean out tanks downstream
  • Sulphur scrubbing efficiency was improved
  • Worker safety increased due to reduced time spent in enclosed spaces performing maintenance

What is the 'Science of Slaking'?

  • Understanding that the slaking 'recipe' for each site is unique
  • Taking into consideration the local conditions, process parameters, and the application of scientific slaking principals
  • Applying system changes & upgrades systematically so the effect of each change is documented
  • Comparing the upgraded system performance data to the ideal performance data so proper financial analysis can be understood

We are so confident in our methodology that if we can't find ways to save you at least 8% of your current quicklime consumption, you won't pay for our study. Don't wait. Call us today.
+1 604-248-8063

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