What began as a small in-house laboratory experiment to find a way to use discarded coal products (fines) has now led to a full-scale demonstration that can boost coal operator profits, reduce waste at their plants, and recover valuable energy sources for consumers, the US Dept of Energy (DOE) reports.

An efficient, cost-effective process for recovering coal fines is significant in today’s energy marketplace because 2,000 Mt of coal fines are impounded in the USA, and about 50 Mt are added to that total each year at more than 700 coal impoundment sites. In full-scale tests conducted by CQ Inc, the GranuFlow process – which was developed and patented by scientists at the Office of Fossil Energy’s National Energy Technology Laboratory (NETL) – has shown that it can recover and clean a significant portion of coal fines to produce an added source of energy for the nation’s future.

The GranuFlow process treats fine-sized coal particles (150 mesh, about 0.1 mm, or less) to improve their dewatering and handling characteristics. To demonstrate commercial viability of the process, CQ employed the process at four commercial coal preparation plants under full-scale operating conditions:

• PBS Coals’ Shade Coal Preparation Plant located near Central City, Pennsylvania
• Edison Mission Energy’s Homer City Coal Preparation Plant located near Homer City, Pennsylvania
• Jim Walter Resources’ No. 7 Coal Cleaning Plant located near Brookwood, Alabama
• PinnOak Resources’ Concord Coal Cleaning Plant located near Hueytown, Alabama 

In addition, combustion tests of the GranuFlow-treated coal were performed at Edison Mission Energy’s Homer City Power Station. The full-scale tests were conducted to confirm previous test results at smaller scale, establish operating parameters for future commercialization, and generate the necessary information and data to commercialize the technology.

In its recently released final report on the tests, CQ noted that the GranuFlow process experienced no operational, permitting, regulatory, or end-user problems at full scale. In addition, economic forecasts indicated that the process can add more than $1 million in annual profits for operators producing metallurgical coal and also add between $600,000 and $3 million for coal market values ranging from $50 to $100/t.

Although other methods are available to capture coal fines, these processes become less efficient as particle sizes decrease. The fines captured through these processes also have a high moisture content, which can reduce their heating value and cause materials handling problems, such as sticking in bins and freezing in winter. The captured fines can be thermally dried, but the process is expensive and energy intensive; moreover, a significant proportion of thermally dried fines can literally blow away with the wind.

In the GranuFlow process, a binder is added to fine-sized coal slurries to make the coal particles stick together. The agglomerated fines are more efficiently captured during subsequent cleaning and dewatering, which reduces the size and number of impoundments. The binder is applied in such a way that cake moisture decreases, possibly eliminating the need for thermal dryers; and the smallest particles are agglomerated, making the filter cake virtually dust-free.

NETL received patents for the process in 1990 and 1995. Early research and scale-up demonstrations were funded by the Energy Department’s Office of Fossil Energy, while the most recent, full-scale demonstrations were conducted under the Mining Industries of the Future Program within DOE’s Office of Energy Efficiency and Renewable Energy.