Data analysis of kinetics and production of biofuels from pyrolysis of sewage sludge
Thermogravimetric analysis data from a thermogravimetric analyzer (TGA) was used to investigate the kinetics of sewage sludge pyrolysis. In a TGA, sewage sludge was pyrolyzed, and mass loss data was recorded as a function of temperature and time. The coats-Redfern method was used to compute the activation energy and pre-exponential factor of pyrolysis of sewage sludge, which may be reused in large-scale pyrolysis reactor design. To measure the Arrhenius factors, various models used in Coats-Redfern methods were applied, regression coefficient (R2) was deciding factor to understand the reaction mechanism. Data on sewage sludge pyrolysis products was acquired using a lab-scale reactor at various temperatures. The metal oxide content of biochar formed from the process was determined using X-Ray Fluorescence (XRF) spectroscopy, while non-condensable gases were determined using Gas chromatography – Thermal conductivity detector (GC-TCD). The fuel gas produced by the sewage sludge pyrolysis process was quantified using GC-TCD data. The original publication included more biochar characterization.
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Thermogravimetric analysis: TGA study of sewage sludge was carried out at a scientific lab at IIT Roorkee, India, using a thermogravimetric analyzer (EXSTAR TG/DTA 6300) nitrogen atmosphere. Bio-oil was characterized by a GC-MS (Perkin Elmer, USA) equipped with a DB-5 capillary column (30 m X 0.25 mm). The oven temperature was initially fixed at 75°C for 5 minutes, then amplified with a heating rate of 10°C min-1 up to 250°C under the isothermal condition and then held for 25 minutes. Characterization of non-condensable pyrolysis gases: was carried out using Gas chromatography (NUCON manufactured, model 5700 series) equipped with a thermal conductivity detector (TCD). Two packed column, Porapak Q column and molecular sieve 5A, 60/80 mesh connected in series were employed to detect gases. Pyrolysis kinetics was derived using Coats-Redfern approaches. Because of the varying chemical composition of sewage sludge, pyrolysis is a particularly complicated process A number of reactions takes place simultaneously in a fraction of a second during heat degradation. As a result, it is not possible to determine the exact reaction mechanism. Scheme I depicts the total reaction mechanism of sewage sludge in the pyrolysis process. Sewage Sludge → Volatile (gases + tar) + Char (Solid residue) I The pyrolysis experiment was performed using a cylindrical quartz glass tube having following dimensions: 45-centimeter length and 6-centimeter internal diameter. The reactor was instrumented with an electric heater furnace, a K-type thermocouple temperature probe and a PID temperature controller and. Before each experiment, the reactor was fully sealed with vacuum grease to avoid leaking. Glass wool packing was used to insulate the reactor. The reactor was connected with three glass bottle condenser to collect condensed pyrolysed vapors. During each experiment, the reactor was fed with 100 g of sewage sludge. The experiments were conducted from 250°C to 700°C under inert atmosphere. Pyrolysed vapors coming out from reactor was passed through water cooled bottle condenser condensed so that maximum volatile gases (bio-oil) will be condensed were collected in the condenser while non-condensable pyrolysis gases were collected in a bag. Biochar, a byproduct of the process, was collected and tested using several analytical procedures to determine its utility.