For forty years, the kilns at Permanente had used the wet-process method to produce clinker. One-half million gallons of water a day carried the limestone, clay and iron ore in a slurry to the kilns, where the mixture was calcined. In the aftermath of the 1973 oil embargo, the fuel for heating the water, along with the minerals, was now too costly.
Although a dry-process had been used before, it wasn’t until the late ‘70s that technology came together to make it truly cost-effective. By combining a precalciner with a preheater to reclaim heat from a single kiln, energy use could be cut dramatically. A $112 million program was launched in 1977 to replace Permanente’s six kilns with a single dry-process one. It would be equipped to burn coal as well as fuel oil and natural gas.