Fast-neutron and gamma-ray transmission method for coke-humidity determination

Efficient and highly automated metallurgical processes require the on-line control of coke moisture which assures high steel quality and fuel economy. The present paper dealt with the feasibility study of the Fast Neutron and Gamma-ray Transmission (FNGT) technique for the determination of the moisture content of coke in a hopper-mounted gauge arrangement. In the experimental assembly, a Pu-Be source was used. Two separate detectors: [phi]25x120 mm 3He (surrounded by paraffin moderator) and [phi]100x100 mm NaI(Tl) were applied. The temperature of the moderator was controlled and a suitable correction of the neutron count rate was done as the hydrogen H capture cross-section shows a 1/v dependence, where v is the neutron velocity. The optimisation of the FNGT arrangement was done by the modelling calculations using MCNP 4C code and was focused on obtaining a high sensitivity of the transmitted neutron flux to the moisture changes and on lowering the neutron-counting error, both leading to a more accurate humidity determination. Laboratory measurements were carried out for lump-coke and crushed-coke samples, with added moisture up to 8 wt.% and 17.1 wt.% respectively, and showed a good agreement between the moisture content determined from the FNGT measurements and the moisture determined from an oven-drying method.