​ Overview

The KCA Carbon Converter is a modular, self-contained unit for converting carbon fines into a fine-dry ash.  Dirty-wet carbon fines are fed directly into the roasting chamber, and the resulting ash is fully captured as a dry product.  A three-stage exhaust scrubbing system fully captures mercury to satisfy emission standards of every U.S state and foreign country. Gold and silver recovery up to 99% has been demonstrated in operation.  For more information, please download the Carbon Converter brochure .

Process Description

The Carbon Converter is designed to process 300kg of clean-dry carbon per day.  The actual throughput is based on the carbon composition and moisture content of the feed material.

Two (2) interchangeable bottom sections of the furnace allow for semi-continuous operation.  The semi-continuous batch system is easily operated by one person through a sophisticated PLC interface.

The process begins as carbon fines are loaded into the feed hopper.  An automated conveyor then transfers the fines material to the top of the furnace.  The carbon is continuously and evenly distributed over a bed of silica sand by a rotating distributor head.  A burner is used to preheat the furnace.  Hot air is pulled down through the carbon which combusts to provide operational heat.  Excess water is evaporated, and the carbon begins to ash.

Carbon is continuously burned in the furnace, until the level of accumulated ash alerts the operator to exchange bottom sections for the next ashing cycle.  The carbon ash is then easily collected and removed for gold and silver recovery.

​​​While the carbon is burning, hot exhaust gas flows through a series of two (2) venturi wet scrubbers, using water at ambient temperature to remove the bulk of volatiles, including most of the mercury.  Mercury is collected in a conical sump below each scrubber.  Water for this stage is process solution, flowing into the system and discharging back into the leach process.  As a final polishing step, the cooled exhaust gas passes through a tank filled with sulfur-impregnated carbon to remove any trace amounts of mercury from the exhaust gas stream.  Once the ashing cycle is complete, the ash, which has been roasted at high temperature, contains no mercury.

Frequently Asked Questions​

Q: How sensitive is the process to variability in the feed?

A: The process is semi-continuous batch, with the batch cycle time dependent on the feed material.  We have seen cycle times as short as one (1) hour, and as long as twenty-four (24) hours.  Feeds which are very high in clay may require agglomeration, which can be done by the operator in a modified drum concrete mixer.  Agglomerating the feed has shown to increase cycle times, and increase overall throughput in feeds with high clay content.

Q: What test work is recommended for each site/carbon product?

A: Test work is recommended for each carbon product on site.  The test work consists of gathering small representative samples of potential carbon fines feed material, and sending them to the KCA laboratory in Reno, Nevada USA.  Once received, KCA will complete analyses on each sample provided, including assays for gold, silver, carbon, and moisture content, along with some basic physical characterization.  Based on the results, KCA will conduct a design/cost analysis and determine the projected payback period, as well as determine design factors and optimal operating conditions for the equipment.

Q: What is the actual product I'm getting from the unit? How much product does it yield?

A: The ash product containing the gold will be a mix of carbon ash, a small amount of silica sand from the sand bed hearth, and any non-combustible material that was fed in with the carbon fines feed.  The actual amount of ash product is highly dependent on how much non-combustible material is present in the feed.

Q: How do I treat the ash to get my gold?

A: There are two options for ash treatment.

Option 1: Direct Smelting

Option 2: Fine Grinding & Leaching

Q: How much floor space/footprint does the unit require?

A: The installed Carbon Converter footprint with the feed system is approximately 7.5m x 7.5m.  This includes space required for proper operation and maintenance access.

An additional 6m x 8m carbon preparation space is also recommended to facilitate daily operations.

Q: How is mercury controlled/captured?

A: Hot exhaust gases from the furnace are cooled and treated with two wet venturi scrubbers in series, which condense liquid mercury for periodic collection from their respective tanks.  The exhaust exiting the second venturi then passes through a bed of sulfur impregnated carbon to capture any residual mercury vapor.

In some cases, it is possible that a minuscule amount of condensed mercury can be carried out with the cooling solution stream.  If this is not acceptable, then filters can be installed on the solution outlet.

Q: What are the utility requirements?

A: An electrical feed requirement capable of supporting a 100HP / 75KW maximum, and 40HP / 30KW continuous electrical load.

A burner requirement of 500,000 BTU/hr (125,000 kcal/hr), which can be powered by either natural gas, propane, or diesel.

A cooling/scrubber solution requirement of 20gal/min (4.6 m3/hr), which can be pregnant solution, barren solution, or raw water

Q: What is the cost to run the unit?

A: Operating costs can range from US$50,000 – US$100,000 per year, excluding labor costs.  These costs depend in large part on the nature of the feed.  KCA provides a more concise operating cost estimate upon evaluation of each operation’s carbon.

Generally, with clean carbon and long furnace runs, we expect minimal operator time will be required.  Dirty carbon may cause more difficult materials handling which may result in higher labor costs.

KCA will help define these costs more accurately as information is received regarding your carbon.

Q: I need to process more than the designed throughput. Do you have a larger unit?

A: Currently, there is one size unit, but multiple units can be provided to reach the desired throughput.  The modular design of the Carbon Converter allows for efficient shipping and installation of multiple units at a central location.  The size is convenient for a single person to operate one or multiple units.

Q: Does the unit have to be installed indoors?

A: The unit is designed to be installed indoors, but can be installed outside with proper protection from the elements

Q: How soon can the unit be delivered?

A: Upon receipt of purchase order and down payment, KCA can be ready to ship from our shop in Reno, Nevada USA in approximately 16-20 weeks.

Q: What is your warranty/guarantee on the equipment?

A: KCA will guarantee equipment performance for a period of 12 months after completion of commissioning.  The equipment is warranted against component failure due to faulty equipment or construction.  KCA will repair or replace components at KCA’s cost and responsibility during the 12 month warranty period.  KCA will include one follow-up visit at no charge after commissioning, to assess the performance of the unit and perform repairs/adjustments if necessary.

For additional services/equipment offered by KCA, please visit our home page.