Production of Activated Char and Producer Gas Sewage Sludge

Abstract

According to the depletion of fossil fuel and global warming, energy conversion technology for waste has been considered as value added alternative energy source. Among the potential waste that can be converted into energy, waste sludge continues to be increased due to increased amount of waste water treatment facilities, resulting from industry development and population increase. Most of waste sludge was treated through landfill, incineration, and land spreading (Fullana et al, 2003; Inguanzo et al, 2002; Karayildirim et al, 2006). However, landfill requires the complete isolation between filling site and surrounding area due to leaching of hazardous substance in sludge, and has the limited space for filling site. Utilization of sludge as compost incurs soil contamination by increasing the content of heavy metal in soil, and causes air pollution problem due to spreading of hazardous component to atmosphere. Incineration has the benefits of effective volume reduction of waste sludge and energy recovery, but insufficient mixing of air could discharge hazardous organic pollutant especially in the condition of low oxygen region. In addition, significant amount of ashes with hazardous component will be created after incineration. As alternative technology for the previously described sludge treatment methods, researches on pyrolysis (Dominguez et al, 2006; Fullana et al, 2003; Karayildirim et al, 2006) and gasification treatment (Dogru et al, 2002; Phuphuakrat et al, 2010) have been conducted. Pyrolysis/gasification can produce gas, oil, and char that could be utilized as fuel, adsorber and feedstock for petrochemicals. In addition, heavy metal in sludge (excluding cadmium and mercury) can be safely enclosed. It is treated at the lower temperature than incineration so that amount of contaminant is lower in pyrolysis gasification gas due to no or less usage of air. Moreover, hazardous components, such as dioxin, are not generated. However utilization of producer gas from pyrolysis gasification into engine and gas turbine might cause the condensation of tar. In addition, aerosol and polymerization reaction could cause clogging of cooler, filter element, engine inlet, etc (Devi at el, 2005; Tippayawong & Inthasan, 2010). As the reduction methods of tar component, in-pyrolysis gasifier technology (IPGT) and technology after pyrolysis gasifier (TAPG) were suggested. Firstly, IPGT does not require the additional post-treatment facility for tar removal, and further development is required for operating condition and design of pyrolysis gasifier. Through these conditions and technical advancement, production of syngas with low tar content can be achievable, but cost and large scaled complex equipments are needed (Bergman et al, 2002; Devi et al, 2003).