Superabsorbent polymers (SAPs) are a key technology for safe, fast, and efficient stabilization of wet and saturated coal combustion residuals (CCR), a major waste management challenge for electric power utilities in the US. Traditional pozzolanic stabilization reagents, such as quicklime, lime kiln dust (LKD), and Portland cement, often perform inadequately with CCR material that is heavily layered, unusually difficult to dewater, or when operating in excessively wet weather conditions. However, the introduction of small dosage rates of SAPs (0.3%-1.0%), either as a standalone technology or as a component of a pozzolan blend, provides CCR management contractors a modern tool for reliable and predictable CCR drying.
Predictable Drying Reagent Costs in Wet Weather
Heavily layered CCR, which contains excess carbon and trapped water, is typically discovered after excavation has already begun and dewatering strategies have been designed. The unexpected water and carbon often require extremely large quantities of additional drying media to eliminate free liquid and to stabilize the wet, layered ash prior to placement in a landfill. While a dosage rate of 8% quicklime may be specified, layers of CCR material can require quicklime dosage rates exceeding 20%, a $140,000 increase in reagent costs for a 10,000-ton batch of CCR. On-site mixing, hauling, processing, and chemical delivery charges represent additional surprise charges that excessively layered CCR (or excessively wet weather conditions) can create. The superior absorption capacity and reaction speed of SAPs allow CCR management contractors to rapidly eliminate excess moisture with minimal reagent.
SAP Enhances Performance of Lime and Other Pozzolanic Reagents
While SAPs offer unrivaled absorption capacity as a standalone drying technology, small dosage rates (0.2% - 0.5%, by weight) of SAP also promote ideal curing of lime, cement, and other pozzolanic reagents. SAPs slowly release absorbed water to the curing reagent which minimizes crack formation and enhances the longevity of stabilized CCRs.
For more details on how SAPs can help you with CCR pond closures, download our Technical Brief No. 1
CCR Blend Optimization with Zappa-Stewart SAPs
Zappa-Stewart’s team of engineers and scientists offers a 3-step approach to optimizing CCR stabilization reagent blends:
- Evaluate the chemical and geotechnical material properties of the coal fly ash to determine SAP compatibility utilizing Zappa-Stewart’s in-house laboratory.
- Determine optimized blend ratios of SAPs and other drying additives based on site-specific CCR samples.
- Provide large-volume SAP samples to CCR closure sites for field demos to demonstrate efficiency, ease of use, and potential cost/time savings.
CCR pond closures involve many variables and unknowns. Superabsorbent polymers help to protect against escalating CCR processing costs by rapidly absorbing excess moisture, and allowing quicklime and other stabilization reagents to react under optimal conditions.
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