Steps for determining the regulatory compliance of thermally reclaimed bonded sand
- Establish assumptions for composition
- Measure total %LOI
- Determine CO2, SO2 separately
Thermal sand reclamation oxidizes binder and catalyst residuals completely for mechanically reclaimed sand, resulting in carbon dioxide, water, sulfur dioxide and nitrogen. Some NOx may be present, too.
Q: In our thermal sand reclamation unit we run a 60:40 blend of reclaimed and new sand, at rate of three short tons (6,000 lb.) per hour. The regulatory agency needs to know the emissions from our thermal reclaimer unit. What laboratory testing can estimate the emission associated with the use of furan binders?
A: Emissions from a proposed thermal reclaiming system can be calculated based on the binder and catalyst composition. The proposed thermal reclaimer runs at three short tons (6,000 lb.)) per hour and the feed is 60% mechanically reclaimed sand blended with 40% new sand. An assumption is made that the thermal reclaiming unit completely oxidizes the binder and catalyst residual on the mechanically reclaimed sand.
At first, the percentage of the total composition lost on ignition (%LOI) for the 60:40 blend of mechanically reclaimed and new sand has to be measured. Then, we must determine the type and the percentage of binder BOS (“based on sand weight”) and the type and the percentage of catalyst BOB (“based on binder weight”). The composition of
the LOI residual on the mechanically reclaimed sand will be the weighted average of the binder and the catalyst composition, less the water content of the combination. This assumed composition does not account for changes due to curing, casting, shakeout or the mechanical reclaiming processing.
The thermal reclaiming unit completely oxidizes the binder and catalyst residual on the mechanically reclaimed sand. Combustion products are carbon dioxide, water, sulfur dioxide and nitrogen. Some NOx could be present but should be minimal at typical thermal reclaiming fluidized bed temperatures.
Emissions of water and nitrogen will not be estimated. For a known binder and catalyst, the total amount of carbon, sulfur and nitrogen can be calculated. Based on the information and assumptions above, the emissions of carbon dioxide and sulfur dioxide can be calculated as pounds per hour (lb./hr.):
But, this does not include the carbon dioxide generated from the combustion of the fuel (natural gas) used as the ignition source for the mechanical reclaimer. A better estimate of emissions definitely will result if the mechanically reclaimed sand is analyzed.
In addition, it is unknown whether or not the thermal reclaiming unit is capable of complete combustion. This will depend on the operation of the unit itself and is a question for the manufacturer.
Finally, be aware that NOx emissions are possible. Again, this will depend on the operation of the thermal reclaiming unit and cannot be estimated. It is advised to consult with the manufacturer of the thermal reclaiming unit regarding NOx emission and to ask them for typical emission information from other units they have reclaiming furan no-bake sand.
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