Alternative Energy

Alternative Energy – The Benefits of Coal Fly Ash

By Pat V. Sonti

Introduction

Coal fly ash is one of the residues generated in the combustion of coal.  Fly ash is generally captured from the chimneys of coal-fired power plants and is one of two types of ash that jointly are known as coal ash.  The other is bottom ash, which is removed from the bottom of coal furnaces.  Depending upon the source and make-up of the coal being burned, the components of fly ash vary considerably, but all fly ash includes substantial amounts of silicon dioxide (SiO₂) (both amorphous and crystalline) and calcium oxide (CaO).  Toxic constituents include arsenic, beryllium, boron, cadmium, chromium, chromium VI, cobalt, lead, manganese, mercury, molybdenum, selenium, strontium, thallium, and vanadium, along with dioxins and PAH compounds.

The U.S. and Uses of Fly Ash

In the past, fly ash was generally released into the atmosphere, but pollution control equipment mandated in recent decades now requires that it be captured prior to release. In the U.S., fly ash is generally stored at coal power plants or placed in landfills.  About 43 percent is recycled, often used to supplement concrete production.  It is increasingly being used in the synthesis of geopolymers and zeolites.

Coal fly ash has become a very important issue, receiving much attention from policymakers and agencies such as the U.S. Environmental Protection Agency (EPA). The U.S. has laid great emphasis on the safe handling and processing of coal fly ash as part of its clean energy agenda.  Millions of tons of toxic coal fly ash are piling up in power plant ponds in 32 states across the country.  The federal government has long recognized the risk to human health and environment but has left much of the area unregulated.

The reuse of fly ash as an engineering material, via coal fly ash processing technologies, primarily stems from its pozzolanic nature, spherical shape, and relative uniformity.  Fly ash recycling, in descending frequency, includes usage in:

1. Portland cement and grout
2. Embankments and structural fill
3. Waste stabilization and solidification
4. Raw feed for cement clinkers
5. Mine reclamation
6. Stabilization of soft soils
7. Road sub-base
8. Aggregate
9. Flowable fill
10. Mineral filler in asphaltic concrete
11. Other applications

U.S. Government Agencies

U.S. Department of Energy (DOE) data found that 156 coal-fired power plants store coal fly ash in surface ponds similar to one that recently collapsed in the Tennessee Valley Authority (TVA) power plant in Tennessee in December 2008, which has been declared a disaster much worse than the Exxon Valdez oil spill in Alaska two decades ago.

Currently, man-made lagoons hold a mixture of non-combustible coal and fly ash trapped by equipment designed to reduce air pollution from power plants.  Over the years, this volume of waste grew as demand for electricity increased and the federal government clamped down on emissions from power plants.

The EPA is establishing national standards for ponds or landfills that are used to dispose of waste produced from burning coal.  The EPA’s Administrator testified at her U.S. Senate confirmation hearings in early 2009 that targeting coal fly ash is one of the top three areas of her focus as the head of the EPA.

The EPA estimates about 300 ponds exist for coal fly ash nationwide.  The U.S. power industry estimates that ponds contain tens of thousands of pounds of toxic heavy metals.  Storing coal fly ash is getting more expensive and power utilities will be pushed to find more ways to recycle or process it safely via fly ash processing plants.  Some beneficial uses of coal fly ash are to process it and use it in concrete because it binds heavy metals and prevents them from leaching, or use it as a base for roads, where the ash is covered by an impermeable material.  But using the coal fly ash as backfill or to level abandoned mines requires intensive study and monitoring.

Positive Steps Going Forward

As with any effective policy, until the U.S. Congress enacts a comprehensive regulatory framework, the task of dealing with coal fly ash will be left solely to each state and the private sector.

The U.S. currently is a global leader in coal fly ash processing technologies, which have been developed with an “academia-public-private” sector partnership. Some of these technologies are in various stages, and most of the private sector parties involved in the process are in need of further capital for investments but bring the requisite “know-how” to the table.

With the currently weak investment scenario for equity, working capital and debt, it is vital to leverage a “private-public-partnership” model where the U.S. government will provide grants, loans, and loan guarantees via either the DOE and/or EPA.  This can be matched with equity from technology promoters and owners, project developers, private equity groups and venture capitalists.  Additionally, we should enact tax and carbon credits in order to spur active private sector investment.  With long-term planning, the U.S. can become a net exporter of coal fly ash processing technologies thereby increasing U.S. exports, creating jobs, and improving our economic output.