324
N. Starev and G. Doganov
HF at less than 0.25 mg/Nm
3 . Gas properties, e.g. fluctuating SO 2 content depending
on the stages in the furnace, are the main challenge of the batch TSL process. The
technology adopted in KCM’s New Lead Plant is based on the wet gas sulphuric
acid process, which does not require any sulphur burning during the furnace stages
with low SO 2 . The operation temperature in the converter is maintained by natural
gas burning in a direct-fired preheater controlled by the converter inlet temperature.
At the acid plant inlet, the gas is diluted by fresh air to 5.5–6% SO 2 before entering
the direct-fired preheater. After pre-heating to 390–400 °C, the gas enters the reactor,
which consists of three catalyst beds loaded with vanadium–caesium catalyst. The
heat generated by the exothermal catalytic process is recovered by a liquid salt system
using two interpass heat exchangers. The gas temperature at the third bed outlet is
around 400 °C and has to be decreased for the next step—acid condensation. The
cooling to 265 °C is carried out in a heat exchanger with molten salt as a heat
transfer media. Downstream the SO 3 –water vapour–acid mist mixture is condensed
in a condensation column through glass tubes heat exchangers. Additional cooling
downstream to 60 °C is applied by blowing ambient air into the glass tubes. Product
acid with concentration of 97–98% is collected in a tank and is further cooled down
to 40 °C by flowing through a plate heat exchanger. Acid production is as low as
0.5 t per 1 t lead bullion. After condensation, the process gas still contains some
acid aerosols, which are removed in a wet electrostatic precipitator downstream. The
weak acid, collected in the precipitator sump, is sprayed in the condensation column
head over the glass tubes in counter-current to the gas flow.
Final SO 2 capture to 99.8% is performed in a tail gas scrubber by hydrated lime
solution sprayed in counter-current to the gas flow. The generated 20% gypsum solution is periodically transferred and mixed with the slurry from the wet gas cleaning
plant and is recycled with the raw material feed. By utilizing the calcium from the
gypsum, the total demand for fresh lime-ash required as a flux is decreased by almost
30%. Final gas prior to releasing to the atmosphere contains less than 300 mg/Nm
3
of SO 2 .
Conclusion
The New Lead Plant commissioned in KCM represents a unique combination of subsystems and applies the best available techniques. The smelting technology allows
treatment of primary and secondary lead-containing materials in a wide range of
ratios. The TSL furnace process off-gas with SO 2 content varying from 0 to 10% is
treated in the wet gas sulphuric acid plant. This process allows versatility in choosing
raw materials and corresponds to the challenges of the raw materials market. Sulfuric
acid production is reduced to the lowest possible rates and depends solely on sulphur
content in the TSL input. The specific acid production is as low as 0.5 tons acid
per ton of lead bullion produced. The residual gypsum solution, generated in the
final gas-purifying unit, is recycled in the smelting stage allowing reduction of the
N. Starev and G. Doganov
HF at less than 0.25 mg/Nm
3 . Gas properties, e.g. fluctuating SO 2 content depending
on the stages in the furnace, are the main challenge of the batch TSL process. The
technology adopted in KCM’s New Lead Plant is based on the wet gas sulphuric
acid process, which does not require any sulphur burning during the furnace stages
with low SO 2 . The operation temperature in the converter is maintained by natural
gas burning in a direct-fired preheater controlled by the converter inlet temperature.
At the acid plant inlet, the gas is diluted by fresh air to 5.5–6% SO 2 before entering
the direct-fired preheater. After pre-heating to 390–400 °C, the gas enters the reactor,
which consists of three catalyst beds loaded with vanadium–caesium catalyst. The
heat generated by the exothermal catalytic process is recovered by a liquid salt system
using two interpass heat exchangers. The gas temperature at the third bed outlet is
around 400 °C and has to be decreased for the next step—acid condensation. The
cooling to 265 °C is carried out in a heat exchanger with molten salt as a heat
transfer media. Downstream the SO 3 –water vapour–acid mist mixture is condensed
in a condensation column through glass tubes heat exchangers. Additional cooling
downstream to 60 °C is applied by blowing ambient air into the glass tubes. Product
acid with concentration of 97–98% is collected in a tank and is further cooled down
to 40 °C by flowing through a plate heat exchanger. Acid production is as low as
0.5 t per 1 t lead bullion. After condensation, the process gas still contains some
acid aerosols, which are removed in a wet electrostatic precipitator downstream. The
weak acid, collected in the precipitator sump, is sprayed in the condensation column
head over the glass tubes in counter-current to the gas flow.
Final SO 2 capture to 99.8% is performed in a tail gas scrubber by hydrated lime
solution sprayed in counter-current to the gas flow. The generated 20% gypsum solution is periodically transferred and mixed with the slurry from the wet gas cleaning
plant and is recycled with the raw material feed. By utilizing the calcium from the
gypsum, the total demand for fresh lime-ash required as a flux is decreased by almost
30%. Final gas prior to releasing to the atmosphere contains less than 300 mg/Nm
3
of SO 2 .
Conclusion
The New Lead Plant commissioned in KCM represents a unique combination of subsystems and applies the best available techniques. The smelting technology allows
treatment of primary and secondary lead-containing materials in a wide range of
ratios. The TSL furnace process off-gas with SO 2 content varying from 0 to 10% is
treated in the wet gas sulphuric acid plant. This process allows versatility in choosing
raw materials and corresponds to the challenges of the raw materials market. Sulfuric
acid production is reduced to the lowest possible rates and depends solely on sulphur
content in the TSL input. The specific acid production is as low as 0.5 tons acid
per ton of lead bullion produced. The residual gypsum solution, generated in the
final gas-purifying unit, is recycled in the smelting stage allowing reduction of the