At CalPortland’s Mojave cement plant, kiln production and efficiency were adversely impacted by the reliability of the raw mill, which struggled with the increasing demands of a hot market. The decision was made to invest in a new mill. FLSmidth tells the story.
The Mojave plant’s K6 line, operated by CalPortland Company (CPC), was built in the early 1980s and has been upgraded a number of times since then, but the plant was still operating the original raw mill – a non-FLSmidth brand VRM rated for about 250 stph. With cement demand running high in California, the plant was pushing the mill beyond its limits, but still not achieving the desired throughput – and experiencing reliability and quality issues as a result. CPC was ready to make the change.
Choosing the right supplier
When it came to choosing which raw mill would be the right fit for the plant, CPC went out to competitive bid for an EPC contract to supply and install a new grinding circuit.
“We gave a basic design,” explains Alan Simmons, Director Electrical and Control Engineering, CPC. “It included some slightly novel concepts, based on our preferences and experiences. We found that some suppliers were more willing to accommodate our requests than others, and FLSmidth was one of those that was willing to work with us on the engineering. We narrowed it down to several suppliers, but in the end FLSmidth came out on top. It was a question of the technical ability, the financial offering, and the fact that we were already operating an OK mill, which was a real advantage. For one thing, it gave us the economic benefits of common spare parts, but it also meant we were familiar with the workings of the mill and its control system.”
Commonality of spare parts is a major benefit for cement producers because it cuts their investment in half. In this case, the new mill was actually with an over-sized gearbox, just to ensure that commonality and provide CPC with these benefits.
“The old mill wasn’t just curtailing throughput,” says Alan, “it was also impeding our process efficiency. We wanted the new mill to enable us to overcome those challenges.
For example, because the old mill was running so hard, we couldn’t control the product fineness as much as we would have liked. Moreover, running the kiln below optimal feed rates was preventing us from achieving optimal fuel efficiency. The OK mill enables us to target product fineness to optimise efficiency. And by increasing capacity, we’re getting a better burn and less emissions per tonne.”
Another consideration that factored into CPC’s decision was the U.S. EPA’s NESHAP guidelines, which hold cement producers to extremely stringent emissions limits. The emphasis is on managing and measuring pollutants at the kiln stack, but 40-year-old kilns are not necessarily designed to operate in the manner required to control the emissions within the NESHAP limits. The new mill, however, can accommodate all the kiln gases through the mill system, giving the plant more flexibility in managing emissions.
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Read the article online at: https://www.worldcement.com/special-reports/09112022/new-raw-mill-increases-productivity-at-mojave/
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