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Original Story URL:
http://www.dairynet.com/environment/ash.php


Using Coal Combustion Byproducts to Create a Green Economy

DPC Ash Recycling Rate is Best Ever

Reduce-reuse-recycle is a mantra for the times, and one that Dairyland is committed to following as much as possible in our business operating practices. For instance, the coal combustion process used to generate electricity at Dairyland’s Genoa and Alma power plants creates an ash byproduct. Dairyland has a strong history of recycling the majority of the fly ash annually, but 2008 beat all records with 98 percent of the fly ash recycled at the Genoa #3 power plant and 89 percent recycled at Alma’s John P. Madgett (JPM) power plant. To put this recycling rate in perspective, the national average for coal fly ash recycling is 44 percent. In addition, 100 percent of the bottom ash was recycled at the Genoa power plant.

Benefits of Dairyland’s ash recycling program

For each ton of coal Dairyland power plants burn to produce electricity, approximately 5 percent, or 100 pounds, results in an ash byproduct. Approximately 80 percent of this ash byproduct is referred to as fly ash, a light powdery substance captured in the emission control systems at the power plant. The remaining 20 percent is bottom ash, a coarse granular material collected at the bottom of the coal furnace. Both fly and bottom ash consist of chemical compounds that are commonly found in natural clays and limestone, and are the major components of Portland cement.

Fly ash is used extensively in concrete, from lightweight applications to ultra strong, load-bearing columns in high-rise buildings. Regionally, Dairyland also markets our fly ash to pipe manufacturers for use in underground piping.

Using coal combustion byproducts to replace the natural clay and limestone in the manufacturing of Portland cement is the most common recycling option used at Dairyland, with benefits for both business and the environment. Most concrete today in our area is 30 percent fly ash, contributing to stronger, less permeable concrete—at a lower price. Since fly ash is less than half the price of Portland cement, consumers save money when building roads, bridges, buildings and other community projects with concrete that contains fly ash.

By using a recycled product, less virgin clay and limestone needs to be extracted from quarries. Fuel costs are lower for the cement manufacturer as fly ash doesn’t need to be “preheated,” since it was already heated during the coal combustion process. This correlates with a major air-quality benefit of using fly ash in place of Portland cement. The production process required to make traditional Portland cement from limestone and clay releases significant amounts of greenhouse gases, such as carbon dioxide, largely due to the fuel required to manufacture and heat the “raw” limestone. When Portland cement is replaced with fly ash, the greenhouse gas emissions can be exponentially reduced as the ash does not need to be heated. Therefore, using Dairyland’s fly ash is good for the road we drive on… and the air we breathe.

Dairyland also recycles our bottom ash as a substitute for crushed rock or sand in road construction and as an anti-skid material in lieu of sand or salt on winter roads. As with the use of fly ash, an environmental benefit to recycling bottom ash is that it reduces the need to quarry rock, since bottom ash is used as a substitute for natural crushed rock.

Last, but not least, a positive result of Dairyland’s ash recycling program is that it lessens the need to dispose of the product in landfill storage. Ash from Dairyland facilities that cannot be recycled is safely stored in a landfill facility near Alma, Wis. Many people have heard about Tennessee Valley Authority’s (TVA) ash pond spill incident, and may wonder how the TVA facility differs from Dairyland’s. There are critical engineering and storage method differences between TVA’s and Dairyland’s landfill.

At Dairyland, the remaining dry fly ash is conditioned to achieve optimum moisture content in order to prevent dusting. It is then delivered by truck to the landfill storage cell. There, the ash is carefully compacted and managed to prevent dusting and to ensure construction of a stable, engineered structure designed to resist accumulation of additional moisture. In fact, the fly ash itself is somewhat like cement, which adds to the stability of the landfill storage cell. In contrast, TVA was managing ash as a “wet stack,” in which fly ash was slurried at that particular facility into a pond-like containment area which had been raised over a period of years. The exact cause of the TVA failure has not yet been determined, but once the containment dike failed, the water-saturated ash within the facility overflowed.

Notably, the state of Wisconsin no longer permits wet ash pond storage facilities, such as the TVA facility that experienced the failure.

Building Stronger Roads and Sidewalks in Our Community

An especially satisfying beneficial reuse accomplishment for Dairyland has been to harvest our own fly ash from the JPM plant for internal construction projects. In particular, some of the concrete used during the installation of environmental control equipment at the Genoa power plant was made using recycled fly ash from the JPM plant. Another unique application of Dairyland’s fly ash is the use of JPM ash in the construction of two wind turbine renewable energy projects in southern Minnesota.

The sidewalk in front of Wendy’s Restaurant on South Avenue near Dairyland’s Administration Building was poured with cement containing fly ash from the JPM plant.

Residents who live or work near our Genoa and Alma power plants have no doubt driven on roads containing Dairyland’s recycled bottom ash. Specifically, Hwy. 35 and Hwy. K near Genoa, and Hwy. 35 to Alma contain the bottom ash, utilized as a “surface coarse” gravel overlay material. You may be able to recognize it as the ash overlay “sparkles” more than standard road overlay. The bottom ash material provides better traction, is very durable and doesn’t break windshields as readily as standard gravel. It also melts ice faster… a real bonus for drivers this winter.