Coal Preparation » Dewatering
This report summarises the results of a two stage study aimed at demonstrating the use of heavy fuel oil emulsions as a dewatering aid to reduce the moisture content of fine coal products from vacuum filters. Stage 1 of this project had previously indicated that moisture reductions up to 8 wt% were achievable. The main objectives of Stage 2 were:-
- to perform further bench-scale experiments in equipment that could be readily scaled up
- to use this information to design and build a rig for demonstrating the process at the pilot scale.
The treatment process involves preparation of the emulsion, conditioning of the coal with the emulsion and vacuum filtration of the conditioned slurry.
During the bench scale testwork, two coals and three heavy fuel oils were used. Although moisture reductions of around 7-8 wt% could be achieved, there were significant differences in the response of the two coals to some of the important dewatering parameters, in particular oil dose. In addition, the two samples of fuel oil procured for the pilot scale trials gave moisture reductions of only ca 5 wt% in preliminary bench scale tests compared to the 7-8 wt% achieved with the first oil sample obtained.
The pilot scale trials used a 0.9 m2 drum filter, the same type as the filters at the plant where the trials were undertaken. With conventional flocculant, the pilot scale filter gave an excellent simulation of the full scale machines. The oil emulsions achieved moisture reductions up to ca 5 wt% compared to polymer flocculants, in good agreement with the bench scale predictions. The moisture reductions were accompanied on occasions with large increases in throughput.
Further work is needed to optimise the treatment and to understand the underlying reasons why performance varied with different feedstocks, in particular for the oils. Success in this program could lead to a treatment cost, based on current spot market prices for fuel oil, of less than 10 cents / tonne of coal wt% moisture reduction.