Fossil fuel oil is used in Egypt providing close to 90 % of entire power needs. Upon combustion of the oil, it produces fly and bottom ashes. Water used in electricity generating plants is supplied from River Nile. Assiut electric power plant has a maximum power of 2 ” 312 MW/h (1) Solid wastes from power plants can be classified into three categories. Partial utilization of ash has been commonly practiced, as fill for roads, runways, construction sites -cement and brick admixtures. Burning heavy fuel oil yields about 3 kilogram of ash per cubic meter of oil (2) whereby most of the remaining was ash (approximately 90 %). In some cases, ash may be collected by electrostatic precipitators or cyclones (3). It has been reported that some ashes from the flue-gas and boiler residue were fed to the agriculture growing area to reclaim the soil. The minerals in ashes may improve or increase the land fertility, crop growth and yield more agriculture productivity (4)
Fuel oil ash may contain vanadium and other noncombustible and potentially toxic chemicals that may be present in the oil (5, 6). The recovery methods of vanadium from the vanadium-containing ashes showed that there was no single approach to directly recovering vanadium. Specific leaching mode from each ash depended on its chemical and phase compositions (Clean Air Task force, 2003) (7). Moreover, the amount and characteristics of each ash depended on the type of fuel. Boiler Coal produced a relatively large amount of both fly and bottom ashes, while oil produces little bottom ash and more ash. On the other hand, gas produces little of either the two types of ashes. U.S. Geological Survey reported that fossil fuel combustion resulted in concentration of most trace elements in ash by approximately 10 times the concentration in the original fuel (8, 9) Heavy oil ash (HOFA) consisted of inorganic substances such as silicon dioxide (SiO2), iron oxide (Fe2O3), aluminum oxide (Al2O3) and 70’80 % unburned carbon (10). The HOFA contains a good amount of valuable metallic compounds such as vanadium (V, 20’30 %), nickel (Ni, 0.8’6 %), arsenic (As), cadmium (Cd), mercury (Hg), chromium (Cr) and copper (Cu) (11, 8).. Worldwide several million tones of HOFA are generated each year, and only a small portion of these ashes is re-used for productive purposes (12).
Recently, recycling concern of ash is due to increasing landfill costs and current interest in sustainable development. In U.S, coal-fired power plants produced 71.1 million tons of ash, of which 29.1 million tons were reused in various applications (13) (Mo’tlip et al. 2010). If the nearly 42 million tons of unused ash had been recycled, it would have reduced the need for approximately 27,500 acres (33,900,000m3) of landfill space.(13,14). Other environmental benefits to recycling ash includes reducing the demand for virgin materials that would need quarrying and cheap substitution for materials such as Portland cement(13,14) As of 2006, about 125 million tons of coal-combustion byproducts, including ash, were produced in the U.S. each year, with about 43% of that amount used in commercial applications, according to the American Coal Ash Association Web site. As of early 2008, the United States Environmental Protection Agency hoped that figure would increase to 50% as of 2011 (14).
The aim of the present study is to reuse fly ash to prepare valuable carbon products such as active carbon and alumina-magnesia-carbon bricks. The impurities amounting to 21%wt were leached with sulphuric acid that decreased it to 4.78 %. Carbon increased to 95.22, S ; 4.35% and impurities to 0.36%. Activated carbon (AC) having pores of meso size and surface area of 1050 m2/g was obtained by gasification with steam at 1000”C. The study focused on the effect of mass ratio of water vapour: carbon on the quality of the produced activated carbon at temperatures around the traditional one. Also it shows that leaching of the ash with sulphuric acid has no harmful effect on the thermal and mechanical properties of the prepared bricks samples
The objectives are
1. To treat the waste ash by leaching with sulphuric acid to remove the major part of its impurities mainly of mineral source.
2. To prepare active carbon by steam gasification at temperature ‘1000 ”C for time up to 90 minutes.
3. To prepare alumina-magnesia-carbon bricks by mixing alumina, magnesia and purified carbon and use of coal tar pitch as a binding agent.
4. To improve the thermal and mechanical stability of the fired bricks by multi impregnation using coal tar pitch. Each impregnated sample was claimed at 750 ”C to carbonize the tar pitch.
5. To predict that the method is effective, simple and friendly environmental.