The upgrades will increase the city’s ability to reclaim lime and sell it to other jurisdictions, reducing the facility’s operating costs.
“(We) are the only kiln that actually provides a commodity to other uses,” said Tammi Clements, Dayton’s deputy city manager.
Lime is put in water to soften it and remove minerals, which can build up in pipes and result in problems for common consumer usages.
Lime sludge is the waste residual that comes from the softening process.
Often, the sludge is put into a lagoon or applied to farmers’ fields to adjust the pH of the soil, said Shannon Zell, the city’s kiln supervisor.
But the city takes the lime sludge, processes it through the kiln and returns it pebble lime, a form that can again be used for softening, Zell said.
Wet residuals are dried, and unwanted minerals are removed. The sludge is thickened and moved into storage tanks. The sludge is put into centrifuges and then through the kiln.
The kiln is a 265-foot long furnace that has a 60-foot flame that burns at about 2,000 degrees.
The city has been in the lime-recovery business since the mid-1950s. The city provides lime for its own Ottawa and Miami water treatment plants.
But in recent years, the city has started to draw significant revenue from the sale of lime to other jurisdictions.
In 2008, the city made $5,500 from lime sales. In 2013, it received $254,232. Revenue is expected to soar.
The city sold about 3,500 tons of lime in 2014. It sold 5,000 tons in 2015 and hopes to sell 6,000 this year.
The city brings in residuals from Troy and Middletown that are cleaned out of their lime lagoons.
That has allowed the kiln to run at a higher production rate, increasing efficiency and saving the city on every ton of lime it produces, Zell said.
The kiln is designed to handle 158 tons per day, but it was operating at less than half its capacity.
Recently, Dayton commissioners approved a $9.1 million contract with Danis Industrial Construction Company.
The contract calls for constructing truck scales, a wet residuals receiving facility and dilution tanks, a blending tank and other facilities for recarbonation, thickening, dewatering and other processing needs, according to city documents. The money is coming from the city’s water capital funds.
The facility expansion will allow the city to bring in more residuals to put through the recycling process, which then can be sold as pebble lime to other municipalities, said Clements.
The project will allow the kiln to operate at its optimal level and produce more than 100 tons of pebble lime per day, she said.
The process keeps residuals out of the landfill. The sale of lime pebbles provides a strong revenue source, and the payback for the investment should be about eight years, Clements said.
“It is an innovative approach, and it is a green and sustainable approach to recycling,” she said.
The city currently sells recycled lime to nine water utilities, and it has been in talks with a dozen others to become their provider, officials said.
The city anticipates lime sales revenue could be $1.6 million annually through 2035, which will offset operational costs at the lime reclamation facility. Dayton also will benefit from lower operating costs.
On the open market, the city would have to spend $3.4 million annually on lime to soften its water, officials said.
“This shows creativity, resourcefulness and helps us a great deal in terms of maximizing our capacity …” said Commissioner Joey Williams.
The expansion should break ground in April and is expected to take about 420 days to complete.
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