Wastewater sludge management is a significant challenge for small-scale, urban wastewater treatment plants (WWTPs). Common management strategies stabilize sludge for land disposal by microbial action or heat. Such approaches require large footprint processing facilities or high energy costs. A new approach considers sludge to be a fuel which can be used on-site to produce electricity. Electrical power generation fueled by sludge may serve to reduce the volume of hazardous waste requiring land disposal and create economic value for WWTP operators. To date, no detailed system designs or techno-economic analyses have been found for small scale sludge fueled power plants. Fortunately, a literature base exists describing the fundamentals of applying thermochemical conversion (TCC) technologies to sewage sludge. Thermochemical conversion of sludge is established for large WWTPs, however large system design techniques may not be applicable to small systems.To determine the feasibility of small scale power generation fueled by sludge, this work evaluates several thermochemical conversion technologies from the perspective of small urban WWTPs. Literature review suggests wet oxidation, direct combustion, pyrolysis, and gasification as candidate front-end TCC technologies for on-site generation. Air and steam blown gasification are found to be the only TCC technologies appropriate for sludge. Electrical power generation processes based on both air and steam blown gasification are designed around effective waste heat recovery for sludge drying. The systems are optimized and simulated for net electrical output in ASPEN Plus R . Air blown gasification is found to be superior. Sensitivity analyses are conducted to determine the effect of fuel chemical composition on net electrical output. A technical analysis follows which determines that such a system can be built using currently available technologies. Finally, an economic analysis concludes that a gasification based power system can be economically viable for WWTPs with raw sewage flows of 0.115 m 3 /s, or about 2.2 million gallons per day.

No abstract

Highly porous ceramic fiber insulations are beginning to be considered as a replacement for firebrick insulations in high temperature, high pressure applications by the chemical process industry. However, the implementation of such materials has been impeded by a lack of experimental data and predictive models, especially at high gas pressure. The goal of this work was to develop a general, applied thermophysical model to predict effective thermal conductivity, keff, of porous ceramic fiber insulation materials and to determine the temperature, pressure, and gas conditions under which natural convection is a possible mode of heat transfer. A model was developed which calculates keff as the sum of conduction, convection, and radiation partial conductivities. The model was validated using available experimental data, including laboratory measurements made by this research effort. Overall, it was concluded that natural convection is indeed possible for the most porous insulations at pressures exceeding 10 atm. Furthermore, keff for some example insulations was determined as a function of temperature, pressure, and gas environment.