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Precious Metals Recovery LLC RCRA Permit Application Dry Hills ...

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The retort off-gas first passes through an afterburner which uses oxygen and air to oxidize any<br />

sulfur vapor and other combustibles in the retort off-gas. The off-gas then passes through a<br />

condenser, where the majority of the mercury and moisture from the gas condenses. Sulfur<br />

dioxide (SO2) may also condense with moisture in the form of sulfuric acid in the condenser. The<br />

condensate will be collected in a tank, from which elemental mercury will be drained into pigs.<br />

The remaining condensate waste solution will be sent to the waste solution treatment circuit for<br />

further treatment.<br />

Localized ventilation is also designed for the retort dome when it is opened for material loading<br />

and unloading. Dust laden gas will be drawn from the hoods to the hygiene exhaust system for<br />

filtering prior to carbon filtration of the building exhaust. Dust removed by the hygiene exhaust<br />

system will be sent back to the retort for processing. The hygiene exhaust system is further<br />

discussed in Section 1.2.6.<br />

The retort cycle will take longer than 8 hours per batch (i.e., longer than normal working hours),<br />

thus the equipment will be designed to operate safely without supervision. Design features<br />

included to ensure safe retort operation outside of working hours are as follows:<br />

Automatic fail-safe shutdowns in design (e.g., over-pressure, over-temperature).<br />

Surveillance monitoring (CCTVs).<br />

Automated alarms and communication systems (see Section 1.5.2 for a description of<br />

response to alarms).<br />

1.2.4 Retort Off-Gas System<br />

The retort off-gas drawn off the condensate tank will be sent through a series of sulfur<br />

impregnated activated carbon (S-AC) columns which will remove residual mercury from the gas<br />

stream, before entering a rotary vacuum pump (see Appendix 1-C Process Flow Diagrams).<br />

Gas will be sent to a small packed tower SO2 scrubber (see Figure 1.2-5 below) where SO2<br />

generated in the retort will be removed from the gas according to the following overall reaction:<br />

SO2 + 2NaOH Na2SO3 + H2O<br />

PMR <strong>RCRA</strong> <strong>Permit</strong> <strong>Application</strong>, <strong>Dry</strong> <strong>Hills</strong> Facility Page 26<br />

JBR Environmental Consultants, Inc. | HATCH March 2013

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