New generation of pebble lime preheaters

 MCP Preheater

MCP Preheater

In 2012, FLSmidth introduced its new patented Multiple Cassette Preheater (MCP preheater), which represents the rise of a new generation of pebble lime preheaters.

“The MCP unit looks radically different from what has been applied to limestone preheating in the past,” says Michael Prokesch, FLSmidth Global Manager of Process Design. “Not only does it look good, it offers improved heat transfer while reducing power consumption, reduced stone degradation and reduced buildup potential. The MCP technology is a novel approach in an industry that has been somewhat stagnant over many years. The technology is primarily geometry-based and derived from prototype/scaled R&D testing in FLSmidth facilities. The testing gave results that countered the common design assumptions, thus making radical design changes which resulted in significant improvements in operation.”

FLSmidth’s conventional preheater was adequate and delivered results that were on par with the competition at a comparable or higher capital cost. Being adequate, though, provided incentive to create something better—something that would provide a clear differentiation between FLSmidth and the competition.

“The MCP preheater has satisfied this goal, and the result is lower CAPEX and OPEX levels for our clients,” Prokesch said.

In the MCP preheater, hot gases leaving the kiln are drawn around the full circumference at cassette level. Gas enters the cassette from all sides equally due to the unique MCP preheater geometry. From there the gas is drawn up through the descending stone. The gas exits the stone bed and moves through a dedicated aspirator.

The stone bin is separate from the preheating area, requiring chutes to feed stone to the preheating zone. These stone chutes serve as restrictions to help reduce stone bin false air. Upon a ram stroke, stone moves from stone bin periphery to a stone chute. From there the stone is directed and discharged to the preheating zone. Stone is delivered to the cassette on the centerline—to help with uniform stone distribution—where it moves counter-current to hot kiln gasses effecting preheating and precalcining.

When stone reaches the cassette bottom, it spills out at its angle of repose into adjacent ram stone piles, the back wall and feed apron. This configuration establishes a free gas path to the full cassette circumference. Upon reaching the ram level, hot precalcined stone is pushed out the fully annular stone discharge opening and onto the feed apron. From here it is pushed into the kiln.

A few of the unique aspects of the MCP preheater include:

  • A stone bed that can be adjusted while running, which allows operation with multiple stone size distribution while easily maintaining optimal fuel efficiency
  • Symmetrical cassettes that are constructed from a refractory lined cylinder, which result in fewer outages and a decrease in longer-term maintenance costs
  • A flat roof that is offset from the back wall and adjacent cassettes, creating a full circumference for hot kiln gasses to enter the cassettes
  • Smaller shelf-to-roof dimensions that effectively eliminate the dead zone where material commonly sits and stagnates
  • Greatly reduced hydraulic pressure and less stone crushing, resulting in reduced wear on the hydraulic components and less fines generation

In short, the MCP preheater has superior heat transfer (which leads to industry-leading efficiency) and can operate for longer periods of time without requiring maintenance. These features make the MCP a vast improvement over previous models.

“With conventional preheater technology, the stone is retained in an enclosed annulus generally containing multiple partitions to produce separate rectangular stone beds to improve gas flow distribution and heat transfer,” Prokesch said. “Access to these stone beds during operation is limited to one side only, and hot kiln gas can only enter the stone bed from one side. The right angle corners are also susceptible to buildup formation. In the MCP design, each stone bed is retained in an independent cylinder. This means there is 360° access to each stone bed and there are no corners to encourage build-up. Hot kiln gas can also penetrate the stone bed around the full circumference of the bed, resulting in superior gas distribution and thus heat transfer. In addition, the configuration of the MCP cassettes enables us to easily configure preheaters to easily retrofit different kiln sizes and configurations.”

While the MCP preheater offers versatility and new possibilities, it’s important to note that FLSmidth will continue to develop and deliver products that satisfy the demands of an ever-evolving market.

“This technology provides a competitive edge for FLSmidth in the pebble lime industry,” Prokesch said. “It also gives us a state-of-the-art device to consider for new applications to allow us to develop a foothold in new areas for Pyromet equipment supply. While we are pleased with the performance of the MCP preheater, we are busy adding new features that will offer more operational benefits to our clients.”

CONTACT: Michael Prokesch