United States Lime & Minerals, Inc.,
St. Clair, Marble City, Oklahoma

The St Clair plant was founded in 1938 with the construction of two simple shaft kilns and extracted its limestone from an open pit. As early as 1953, mining was partially moved underground to continue to have access to the excellent limestone. In 1964, the first rotary kiln was built, followed by another in 1971. Due to the age of the rotary kilns, a replacement investment became more and more urgent - of course according to the latest state of the art.

The limestone in St Clair is special in two respects: particularly pure and particularly fragile - the second a challenge for the production of quicklime. After many intensive technical discussions between the US Lime and Maerz teams, the PFR C-series kiln, which had just been developed at the time, emerged as the optimal kiln type for this project. In 2016, US Lime placed an order with Maerz for a 550 t/d (600 short tons/d) natural gas-fired C3F PFR kiln.

Expectations were high: best quality quicklime, optimal utilisation of the underground mine and lowest possible fuel consumption - not only to save costs, but also to keep CO₂ emissions as low as possible.

The construction of this new type of kiln was accompanied particularly intensively by Maerz to ensure that the construction work went smoothly. In spring 2019, the time had come: shortly after firing up, the new Maerz kiln reliably produced the required high quality of quicklime, so that the rotary kiln could even be sent into well-earned retirement before the scheduled date.