Smelting Jarosite and Sulphur Residue in a Plasma Furnace
395
reductive stage or further reduction in the same reactor are still required to fume Zn
and Pb into acceptable levels. However based on the experience from this work, it
could be possible to reach acceptable levels of Pb and Zn only using one stage after
further optimization of the process. Length of the fuming period depends on final
slag composition requirements as well on legislation. In this work, the target was set
as Zn < 1% and Pb < 0.03%.
The leaching test target has been to reach inert criteria status according to standard
leaching test (CEN).
In the reducing stage, coke is used to enable fuming, further volatilization of
Zn and Pb. Consequently, CO 2 emissions are created. Firstly, in the test work, it
was noticed that no coke was required in the smelting stage, avoiding a significant
part of the direct CO 2 emissions. In the fuming stage on the other hand, a reductant
such as coke is required. Further studies have been carried out in laboratory scale and
comparing bio-based reducing agents such as bio-coal. Thermochemical models have
been developed, and laboratory studies are being carried out to further investigate
different phenomena [5, 6].
It should be noted that it will be more and more important to avoid direct and
indirect CO 2 emissions in the future. Sufficient amount of electrical energy with
reasonable prices is required for plasma operation with as low as possible CO 2
footprint.
Principles of ScanArc Plasma Process
The plasma reactor itself is a twin-shelled water-cooled steel construction with a
number of openings for feed, plasma generators, slag tapping, sampling, and gas
outlet [7].
Energy is added to the process by plasma generators (PGs). Oxygen potential in
the PG gas is controlled by addition of hydrocarbon into the water-cooled tuyeres in
front of the PG. In the pilot plant, LPG (propane) is used for this purpose. By not
using a combustion reaction to provide heat, temperature and oxygen potential is
decoupled allowing to separate the heat from chemistry, a feature that is not possible
in a process with energy supplied by conventional fossil fuels.
Heat generation by a PG is simple and straight forward and is presented in Fig. 4.
Compressed air flows through the PG where it is heated to a temperature of about
3000–5000 °C by the rotating electric arc between up- and downstream electrodes.
The energy content in the outgoing PG gas is about 3.5–4.5 kWh/Nm
3 .
The superhot PG air is mixed with propane in the tuyere in front of the PG to
control the oxygen potential in the gas. NOx formation is controlled by keeping the
gas composition at a low level of free oxygen. The very hot gas is thereafter injected
into the slag bath where its heat is transferred to the slag. In the pilot plant, the reactor
is equipped with two PGs, a lower submerged PG1 (1 MW) that supplies heat and
395
reductive stage or further reduction in the same reactor are still required to fume Zn
and Pb into acceptable levels. However based on the experience from this work, it
could be possible to reach acceptable levels of Pb and Zn only using one stage after
further optimization of the process. Length of the fuming period depends on final
slag composition requirements as well on legislation. In this work, the target was set
as Zn < 1% and Pb < 0.03%.
The leaching test target has been to reach inert criteria status according to standard
leaching test (CEN).
In the reducing stage, coke is used to enable fuming, further volatilization of
Zn and Pb. Consequently, CO 2 emissions are created. Firstly, in the test work, it
was noticed that no coke was required in the smelting stage, avoiding a significant
part of the direct CO 2 emissions. In the fuming stage on the other hand, a reductant
such as coke is required. Further studies have been carried out in laboratory scale and
comparing bio-based reducing agents such as bio-coal. Thermochemical models have
been developed, and laboratory studies are being carried out to further investigate
different phenomena [5, 6].
It should be noted that it will be more and more important to avoid direct and
indirect CO 2 emissions in the future. Sufficient amount of electrical energy with
reasonable prices is required for plasma operation with as low as possible CO 2
footprint.
Principles of ScanArc Plasma Process
The plasma reactor itself is a twin-shelled water-cooled steel construction with a
number of openings for feed, plasma generators, slag tapping, sampling, and gas
outlet [7].
Energy is added to the process by plasma generators (PGs). Oxygen potential in
the PG gas is controlled by addition of hydrocarbon into the water-cooled tuyeres in
front of the PG. In the pilot plant, LPG (propane) is used for this purpose. By not
using a combustion reaction to provide heat, temperature and oxygen potential is
decoupled allowing to separate the heat from chemistry, a feature that is not possible
in a process with energy supplied by conventional fossil fuels.
Heat generation by a PG is simple and straight forward and is presented in Fig. 4.
Compressed air flows through the PG where it is heated to a temperature of about
3000–5000 °C by the rotating electric arc between up- and downstream electrodes.
The energy content in the outgoing PG gas is about 3.5–4.5 kWh/Nm
3 .
The superhot PG air is mixed with propane in the tuyere in front of the PG to
control the oxygen potential in the gas. NOx formation is controlled by keeping the
gas composition at a low level of free oxygen. The very hot gas is thereafter injected
into the slag bath where its heat is transferred to the slag. In the pilot plant, the reactor
is equipped with two PGs, a lower submerged PG1 (1 MW) that supplies heat and