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Rotary kiln

Process description

The raw meal is continuously fed into the rotary kiln via cyclone pre-heaters and feed hoppers. The material is transported towards the burner from the inlet to the outlet side utilising a slight incline and rotation.  At temperatures of 1250°C to 1450°C in the rotary kiln, the raw meal is fired to cement clinker and cooled with air in the clinker cooler on the outlet side. The heated cooling air is then supplied to the rotary kiln as secondary air. Meanwhile the combustion exhaust gases flow counter current towards the inlet of the rotary kiln and are used in the calciner (cyclone preheater) for drying and calcination. Optionally, some of the heated cooling air is also used for the burners in the pre-calciner as tertiary air. The heat in the rotary tube is generated by the direct energy input from a multi-fuel burner. Various fuels can be fired at the same time.

Gas application

Oxygen increases the quality of the combustion locally, which means that the replacement fuel rate can be further increased.

Advantages:

  • Optimisation of energy costs through cheap, low caloric secondary fuels 
  • Higher adiabatic flame temperature
  • Faster reaction speed 
  • Fossil fuels replaced by waste materials 
  • More rapid ignition of low caloric fuel particles makes total combustion possible before reaching the clinker bed
  • Use of replacement fuels with even lower heating temperatures (solid and liquid) 
  • Replacement of compressed air for atomisation
  • Additional parameters for kiln control (fast and easy to control)
  • Stabilisation of kiln operation  
  • Reduction in CO2 Certificate
  • CO2 Certificate for O2 production is Messer’s responsibility   
  • Greater gas radiation
  • Constant NOx through adjusted oxygen input
  • Less strain on the induced draft
  • Increase in production also possible 

Messer-solution

In addition to the gases required for your process, Messer offers a variety of equipment for its optimisation under the brand names Oxipyr and Oxijet. 

In order to select the optimum system, experts from Messer first carry out a comprehensive process analysis. Following calculations and basic engineering, suggestions are made for optimisation and further procedures. 

  

Oxijet – atomizing lance implemented in cement rotary kiln burner

The gas input system must be specific to the type of burner and furnace. Various nozzles can be used for this purpose:  

  • Messer Oxijet - basic                  Impulse lance for burner or hood
  • Messer Oxijet - swirl                   Swirling lance for burner or hood for rapid mixing  
  • Messer Oxijet - supersonic         Laval lance for burner, adjusted to O2 throughput
  • Messer Oxijet - atomising           Atomisation of lowest caloric liquid fuels with oxygen   

Application:

50 MW Rotary kiln main burner:

  • +700 ÷ 1200 kg/h             shredder light fraction
  • +250 ÷ 330 Nm³/h            oxygen
  • -250 Nm³/h                       compressed air
  • +80 ÷ 150 K                     “developed flame body temperature"
  • Flame approx. 2 to 3m shorter
  • 1/3 less FeO in the clinker  
  • More stable kiln operation 
  • No increase in annual carbamide consumption 
  • Kiln stability not affected

Pulsating Oxijet

Oxygen is introduced directly into the kiln using lances with the oxygen discharge speed in the supersonic range. The laval lances used only generate the required momentum when there is a defined design point. Pulsation guarantees constant oxygen content in the air/oxygen mixture. The regulation communicates with the kiln control unit.   

It is important that the special rapid-switching valves are mounted as close as possible to the lances in order to provide supersonic speed during each phase of oxygen input. With controlled oxygen input the oxygen volume can be adjusted as desired for the melting performance. In addition to all its process technology advantages, the system with its well thought-out simple construction, requires little maintenance, is easy to assemble and operate and has low investment costs with a long service life. The fine-tuning of the regulated frequency is carried out during on-site commissioning; the optimised parameters are stored and can be called-up for each product and/or melting performance.