Poland
emits 10.58 Mg of mercury to the atmosphere annually. More
than 90% of this emission is generated by combustion and thermochemical
usage of coal, including coking. In Poland, the coking industry consumes
more than 12 million Mg of bituminous
coals each year. Contrary to lignites and subbituminous coals used
in power plants, there is not much reliable data on mercury content
in Polish bituminous coals. The purpose of this paper was to determine
mercury content in bituminous coals delivered to Polish coke plants
and to analyze possible removal of mercury during coal cleaning processes.
Eighty-two samples from 9 mines were analyzed. The average mercury
content varied from 28.4 to 182.6 μg kg–1,
with a mean value of 75.9 μg kg–1. The analysis of mercury content in three coals
treated by (i) flotation, (ii) dense-media washing, and (iii) jig
washer cleaning, revealed that mercury content in relation to net
calorific value can be reduced by 27% (flotation) to 71% (dense-media
washing). In addition, distribution of mercury, ash, and sulfur between
products and rejects in the process of coal cleaning was determined.
For this purpose samples of raw coals, clean coals, middling products
and rejects derived from six coal preparation plants were examined
(67 samples). The publication presents the mercury balance results
for bituminous coal coking. The mercury is transferred to coal tar
(75%, mean mercury content 2007 μg kg–1),
coke (6%, 7.5 μg kg–1), sulfur (2%, 2998 μg
kg–1) and purified coke oven gas (3%, 7.5 μg
m–3). Balance data shows that almost 14% of mercury
is emitted to the atmosphere during the process of filling the coke
oven chambers with coal.