Gas purification and recovery of calcine dust
The mixed furnace gas escaping from the second stage roaster passes through two Dukang cyclone dust collectors installed in series, and each cyclone dust collector discharges all the collected sand dust into a separate quenching tank. The quenched calcined product is pumped to the calcine scrubbing system. The remaining roasting dust and cyclone dust collector gas is 880 o F and is adjusted to 700 o F with air before entering the electrostatic precipitator .
This electrostatic precipitator is two - model K, Kurt type dust collecting apparatus with rods Neill air barrier, each dust collector is composed of two sets of equipment arranged in parallel, and this equipment is the air flow branch Enter into two intervals arranged in series. Each - Interval contains 882 to 1/8-inch (diameter) of the stab receiving electrode 272 and the winding 3/16 inch square discharge electrode. The trapping electrodes are arranged in 18 wind barriers (
In order to strike the soot from the electrode, the number of times the top hammer hits the trapping electrode and the discharge electrode frame must be controlled. The calcine dust is shaken down into the V -shaped bin and sent to the quenching tank. The gas flow rate and its distribution through the electrostatic precipitator are regulated by a multi-directional vane air lock installed in the inlet and outlet of each dust collector. Today only two of the four sets of devices are working, while the remaining two are used as backups. When - when groups of devices or other severe short-circuit fault, stop its work, while the other - set of equipment put into use until the equipment is repaired.
High-voltage direct current is generated by a transformer, which is raised from a low voltage of 500 volts to a high voltage of 500 volts. High-potential alternating current is converted to high-voltage direct current by using a mechanical rectifier. The negatively charged discharge electrode ionizes the surrounding gas, thereby causing the conductive baking dust to carry a charge, and the charged dust particles are attracted and deposited on the grounded collecting electrode. The dust remaining on the trapping electrode is removed until it is shaken by the top hammer.
The maximum voltage that does not generate an arc allows the electrostatic precipitator to achieve the highest capture yield. The operating voltage is related to the composition of the gas, the temperature and the concentration of the dust, all of which are a function of the operating parameters of the furnace.
Transformer primary winding - voltage and current edge may play a role to monitor for displaying the collector electrode of the discharge is discontinued, since the insulator and by a short circuit between the wind barrier or contamination due to dust caused increased. To overcome the accident occurred while the installation of such equipment, must be based on - to be installed and checked by a detailed project plan comparison table. It seems less important items, such as: an insulating housing and duct damage can cause cold spots, cold spots appear to promote the formation of a hard calcine dust and antimony aggregate. These aggregates can cause damage or short circuit to the hopper screw conveyor. Sufficient leakage near the entrance of arsenic trioxide condensed from the gas, dust and pollution calcined arrested received.
The electrostatic capture of this electrostatic precipitator has an average yield of 94.5% (in terms of the amount of gold in the cyclone exhaust).
Table 3 Â Working parameters of electrostatic precipitator
Inlet temperature | 700 o F |
output temperature | 600 o F |
Primary voltage | 550 volts |
Secondary voltage | 50,000 volts |
Typical analysis results of electrostatic precipitator dust
Au | Fe | S | As | Sb |
1.43 | 18,00 | 2.75 | 2.29 | 0.30 |
(oz / ton) | ( % by weight ) | ( % by weight ) | ( % by weight ) | ( % by weight ) |
Gas cooling
The exhaust of the electrostatic precipitator is cooled to 220 o F by adding conditioned air drawn by a hybrid fan outside the furnace . Contained in the gas phase As 2 O 3 in the expansion chamber positioned below the hybrid condensed into Ventilator - dust kind of fine particles. The temperature of the baghouse is maintained at 220 o F using a pneumatically controlled damper mounted on a hybrid fan to adjust the air inlet . The damper is automatically positioned by a thermocouple and temperature controller.
Electrostatic precipitator evolved gases is about 6500 SCF / min, a temperature of 600 o F, this gas is adjusted to an air flow rate of about 3500 standard cubic feet / minute, a temperature of 220 o F. The condensed arsenic trioxide is recovered from the gas discharged from the cooled calciner in a 300 -type Draco bag collection chamber of eight compartments . Each - compartment 300 with a diameter
In 1978 the federal government announced - Emission Standard gold roaster chimney of God, defined as 15 mg / Scm. During this period, the dust efficiency was improved by improving the operating conditions of the main baghouse.
Baghouse temperature
In order to increase the percentage of arsenic trioxide is condensed from the gas phase into solid phase, by a bag filter operating temperature is reduced to 230 o F 220 o F. Progress - further lowering the temperature is considered to be impractical because the temperature must be kept above the dew point at SOz.
Bag vibration period
   Bag filter by initially - when the shock table referred playing means from the dust bag shock. In the Jat mine, the shock period is shock - week every 45 minutes . A total of 32 weeks per day . Studies have shown that when the bag is subjected to vibration operations, its collection efficiency is the lowest. This is presumably due to the vibration of the bag, causing some fine-grained arsenic trioxide dust to penetrate the micropores of the filter cloth, so that the amount of As 2 O 3 discharged from the chimney is increased.
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