Avoiding Carbon Bed Hot Spots in Thermal Process Off-Gas Systems

Conference · Sun May 01 04:00:00 EDT 2011

OSTI ID:1017891

Soelberg, Nick; Enneking, Joe

Mercury has had various uses in nuclear fuel reprocessing and other nuclear processes, and so is often present in radioactive and mixed (radioactive and hazardous) wastes. Test programs performed in recent years have shown that mercury in off-gas streams from processes that treat radioactive wastes can be controlled using fixed beds of activated sulfur-impregnated carbon, to levels low enough to comply with air emission regulations such as the Hazardous Waste Combustor (HWC) Maximum Achievable Control Technology (MACT) standards. Carbon bed hot spots or fires have occurred several times during these tests, and also during a remediation of tanks that contained mixed waste. Hot spots occur when localized areas in a carbon bed become heated to temperatures where oxidation occurs. This heating typically occurs due to heat of absoption of gas species onto the carbon, but it can also be caused through external means such as external heaters used to heat the carbon bed vessel. Hot spots, if not promptly mitigated, can grow into bed fires. Carbon bed hot spots and fires must be avoided in processes that treat radioactive and mixed waste. Hot spots are detected by (a) monitoring in-bed and bed outlet gas temperatures, and (b) more important, monitoring of bed outlet gas CO concentrations. Hot spots are mitigated by (a) designing for appropriate in-bed gas velocity, for avoiding gas flow maldistribution, and for sufficient but not excessive bed depth, (b) appropriate monitoring and control of gas and bed temperatures and compositions, and (c) prompt implementation of corrective actions if bed hot spots are detected. Corrective actions must be implemented quickly if bed hot spots are detected, using a graded approach and sequence starting with corrective actions that are simple, quick, cause the least impact to the process, and are easiest to recover from.

• Research Organization: Idaho National Laboratory (INL)
• Sponsoring Organization: DOE - EM
• DOE Contract Number: AC07-05ID14517
• OSTI ID: 1017891
• Report Number(s): INL/CON-10-18125
• Country of Publication: United States
• Language: English

Related Subjects

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE WASTES FROM NUCLEAR FACILITIES
ABSORPTION HEAT
CARBON
COMBUSTORS
GAS FLOW
HEATERS
HEATING
HOT SPOTS
IMPLEMENTATION
MERCURY
MONITORING
NUCLEAR FUELS
OFF-GAS SYSTEMS
OXIDATION
PACKED BEDS
RADIOACTIVE WASTES
REGULATIONS
REPROCESSING
TANKS
VELOCITY
WASTES
mercury
mixed waste treatment
nuclear fuel reprocessing