Fact Sheet This means, one tonne of natural fluorspar (87% CaF2) can be substituted by around 3.2 to 4.7 tonnes of SCL. As SCL contains some ammonia, it may contribute to reduction of NOx once fed into the kiln inlet, thus decreasing the needed amount of additional NOx-reducing agent in SNCR.
Biomass-CO2-value SCL has no biogenic carbon content. The co-combustion of SCL does not save any fossilderived carbon dioxide, thus not contributing to greenhouse gas mitigation. However, as SCL produces hydrogen if it becomes wet (e.g. humidity), the avoidance of hydrogen generation by using SCL as alternative material could be an opportunity for indirect greenhouse gas emission reduction. While molecular hydrogen (H2) is not a direct greenhouse gas, it can reduce hydroxide radicals and thus indirectly increase methane CH4 and hydrofluorocarbons (HFCs) [E-1]. It has to be discussed with local authorities whether hydrogen-avoidance can be recognised in a CDM scheme.
4.3.2 AFR pre-processing Prior to use as alternative fuel in clinker kilns SCL is subject to pre-processing. The preprocessing is done at the smelter’s facility. SCL from the storage is transported to the grinding facility where it is ground in a ball mill. The so-called stage I material (grain size around 60µm, assigned for kiln burner feeding) is transported by special enclosed vessels to the cement manufacturer. However, finely ground SCL develops gaseous product while handling, so SCL is subsequently thermally treated at temperatures of around 600°C. This treatment destroys gas-developing compounds, thus minimising health and safety risks. The following sketch provides an overview of the SCL treatment:
Figure 93: SCL treatment procedure at an Australian smelter (Source: MVW)
Storage
Stage I
SCL storage sheds
Ball mill
Stage II Calciner
Silo
Stage III
KGS
Wet plant
Kiln grade spar storage
Trucks to cement plant
SCL grinding to around 60µm and subsequent calcination is very costly. Therefore, it is suggested to use coarser SCL and another feeding point which is less sensitive than the kiln burner. Crushing of SCL down to less than 10mm and feeding into the backend of a clinker kiln or into the calciner at low rates (some 0.7t/h) showed the viability of this modified treatment and utilisation procedure. However, the refractory parts of SCL cannot be burned in a clinker kiln, so the unburned refractory part will be remaining in the clinker. This phenomenon does not hamper cement grinding. However, if the
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