Analysis of chemical-looping method for production of hydrogen gas from sewage sludge

The objective of this study is to develop a highly efficient technology for producing hydrogen from sewage sludge using chemical-looping technology. In this study, laboratory-scale gasification experiments were conducted on sewage sludge samples. The effects of CaO as a carrier of oxygen or carbon (C) and as a gasification accelerator were evaluated. Lab-scale tests using a tube-type electric furnace showed that gasification of CaO-mixed dry sludge with steam resulted in substantial absorption of CO₂ by CaO at 600 ℃ and 700 ℃ and the concentration of H₂ in the gas reached 70 vol.%. The gasification was significantly accelerated in CaO-mixed steam gasification compared with pyrolysis gasification and steam gasification of dry sludge in the absence of the CaO mixture. The hydrogen gas (H₂) recovery rate also increased, and tar with a high C weight ratio and high calorific value was recovered. Almost the entire C in the sewage sludge was gasified at 800 ℃. Therefore, this method (pyrolysis with steam and CaO) was shown to be effective as one of the hydrogen production methods from sewage sludge.