Selecting the Proper Lime Kiln Technology

Lime is a key industrial mineral used as a chemical additive by many industries. The industrial facilities that utilize Lime in various forms are metal ore processing, metallurgy, steel, paper, pharmaceuticals, sulfur removal, and water treatment. It is also used for generating many basic chemicals used to manufacture consumer goods.

Lime is produced through the calcination of carbonate minerals, calcium and magnesium in Rotary Kilns or Vertical Kilns.

The main types of Lime Kilns are:

Long Rotary Kilns

Main Advantages:

    • Large production volumes
    • Wide range of feed sizes
    • Medium to high reactivity Lime
    • Low sulfur Lime
    • Flexibility in fuels used
    • Production not affected by limestone decrepitation
    • Can use high sulfur coal and petcoke

Main Disadvantages:

    • High CAPEX
    • Highest OPEX (high energy usage)
    • Contact cooler may not be applicable if product is very fine
long-rotary-kiln-southern-peru-copper
Long Rotary Kiln (Southern Peru Copper).
Long rotary lime kiln
Long Rotary Kiln (Courtesy of alibaba.com).

Preheater Rotary Kilns

Main Advantages:

    • Large production volumes
    • Wide range of Limestone feed sizes
    • Medium to high reactivity Lime
    • Fuel flexibility

Main Disadvantages:

    • Limestone decrepitation can cause "plugging" in the preheater
    • High CAPEX
    • OPEX higher then shaft kiln
    • Low fuel efficiency of rotary kilns
    • Cannot use high sulfur coal and petcoke for steel customers
preheater-rotary-kiln
Rotary Kiln Preheater.
Blue Circle-lime-kiln-preheater-metso
Rotary Kiln Preheater (Courtesy of Metso).

Single Shaft Vertical Kilns

Main Advantages:

    • Low CAPEX
    • Short Schedule
    • Competitive fuel efficiency

Main Disadvantages:

    • Low production volumes
    • Will not work if Limestone decrepitates
    • Limited Limestone feed range
    • Low Lime reactivity
vertical-shaft-kiln-newmontgold
Single Shaft Vertical Shaft Kiln (Newmont Gold).

Annular Shaft Kilns

Main Advantages:

    • High concentration of CO2 in off-gas for use in further chemical processes
    • Good fuel efficiency
    • No need to wash limestone feed
    • Capable to adjust Lime reactivity production levels
    • Effective in producing dead-burned lime

Main Disadvantages:

    • Limited production volumes
    • Will not work if Limestone decrepitates
    • Limited Limestone feed range
    • Limited Lime reactivity
annular-shaft-kiln-fercalx
Annular Shaft Kiln (Courtesy of Fercalx).

Parallel Flow Vertical Shaft Kilns

Main Advantages:

    • Best fuel efficiency of all Lime Kilns
    • Capable to produce medium to very high reactivity Lime

Main Disadvantages:

    • Will not work if Limestone decrepitates
    • Limited range of feed sizes
regenerative-dual-shaft-kiln-maerz
Parallel Flow Vertical Shaft Kiln (Courtesy of Maerz).


The decision on the technology to be used is based on many factors, including the desired product characteristics, limitations of the geographical area, fuel properties and cost, etc. Some of the most important aspects to be considered are:

  1. Market (Lime use): Lime reactivity (low, medium or high) and sulfur contents are common specifications that depend directly on the technology used.
  2. Availability of Limestone resources and industry capability to manage large amounts of fines:Rotary kilns allow kiln feed size variations. This allows utilizing the smaller stone particle [down to ¼” (6mm)] generated in mining, crushing and screening; hence, increasing the mine’s life.
  3. Physical Properties of the Limestone and Lime: Although the fuel efficiency of vertical kilns is much higher than that of rotary kilns, limestone could break down into smaller pieces during calcination due to the “decrepitation” phenomenon which clogs vertical kilns, making the process not feasible. Likewise, the lime created during the calcination process should have sufficient physical strength to carry the weight of the limestone bed in the kiln.

 

LIME INDUSTRY– PEC Consulting Group’s Active Participation

PEC Consulting Group has provided technical assistance to industries and processing facilities that benefit from the use of lime. In doing so, we have actively helped industries meet the ever increasing demand for the production of quality lime. Sample Scopes of Work have included:

  • Feasibility and Technical Studies for Greenfield lime production facilities
  • Technical Studies for capacity increase of existing plants
  •  Investigation of potential raw material deposits such as sea shells, travertine, and limestone through Geological exploration, core drilling programs, and testing for raw material physical and chemical properties
  •  Mining Plans
  •  Conceptual design of mine and plant
  •  Flow sheets, layouts, equipment lists and basic designs.  Basic equipment specifications. Technology comparisons of major process equipment tenders
  •  Capital cost and operating cost estimates
  •  Logistics for supplying the mine facilities
  •  Economic viability analysis of the projects

A study forms the foundation for future development and it is an absolute necessity for successfully carrying a project to completion. By delivering a well prepared and thorough study, PEC Consulting Group helps its clients achieve their desired goals and competitive edge.

Article contributed by Jorge L. Lerena

Jorge Lerena has extensive experience as a Consultant and Project Manager at PEC Consulting Group. His expertise also includes financial and economic valuation and design of industrial facilities. He has participated internationally in Brownfield and Greenfield lime plant projects, and in studies for the geological evaluation and process selection of Greenfield lime plants.

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