Stamped and pressed coal cakes for carbonisation in by-product and heat-recovery coke ovens

• Meaning of the coal compaction in the cokemaking.
• Methods of the coal compaction.
• Energy demand for stamping.
• Model of the densification.
• Assessment of the cake stability.

Coking of coal blends using high volatile coals with poor coking abilities to produce a high quality coke for blast furnace application can be achieved by compacting the coal blend prior to the carbonization process. Here densification up to a relative material density of 80%, i.e. a compact density around 1100 kg/m3, has proven to be advantageous. Coal is compacted by stamping, if the so-called stamp charging process applied. Compacting of the coal by pressing is used in case of the cokemaking with so called heat-recovery ovens.Stamped and pressed coal cakes require over the cake volume uniform high density and mechanical stability. Besides the aspects of the coal selection, the efficiency of the process is mainly determined by the operating parameters compacting time and compacting energy for coal cake making and by the sufficient cake mechanical stability to ensure trouble-free charging the ovens.At the Department for Mechanical Process Engineering & Solids Processing of the Technical University Berlin the two sub-processes of densification and strengthening during stamping and during pressing are theoretically and experimentally investigated using specially developed lab-scale compacting test units for stamping and for pressing and a coal cake strength test device.Describing cake density in terms of coal properties for a given coal and measured compacting energy input then leads to a compacting equation with the so-called Stampability as the integral model parameter for the stamping process. For the pressing process the cake density can be calculated with the measured compacting pressure and the Compressibility factor, respectively. Investigations were carried out to provide evidence of a significant influence of coal type, coal surface moisture, coal granulometric properties on the densification process.In order to investigate the mechanical strength properties of the stamped and pressed coal cakes, a specific strength tester has been developed, combining the possibilities of investigating compressive/tensile strength as well as shear strength.Based on the tests on the densification behaviour and cake strength for a given coal, the stability criterion of a coal cake with the required density and height can now be calculated.