Characteristic of the production of hydrogen-rich combustible gas by pyrolysis of high-ash sewage sludge

Pyrolysis is considered a promising way to treat sewage sludge and extract energy. This paper first studied the applicable conditions and characteristics of high-ash sewage sludge (HASS) pyrolysis to produce hydrogen-rich combustible gas. The yields and characteristics of three-phase products of pyrolysis gas, tar, and solid product of HASS were determined. The weight-loss behavior and kinetic characteristics of pyrolysis were analyzed by thermogravimetric experiment. HASS mainly decomposed at 540–901 °C and the weight loss rate was between 2.399 %⋅min⁻¹ and 3.372 %⋅min⁻¹. The activation energies of the main decomposition process of HASS ranged from 137.081 to 198.673 kJ⋅mol⁻¹. Devolatilization is more likely to occur than the cracking of macromolecular organic compounds and the decomposition of minerals. Naphthalene occupies the highest proportion of tar, ranging from 18.88 to 61.15%. H₂, CO₂, CO, CH₄ are the major components of pyrolysis gas. The H₂ content and lower heating value of the hydrogen-rich combustible gas obtained by pyrolysis of HASS with a particle size of 0.15–0.18 mm at 800 °C, which is the most suitable condition for producing hydrogen-rich combustible gas, reached the highest values of 51.477% and 13.960 MJ⋅m⁻³, respectively. H₂ is the product of cracking, decarboxylation, aromatization, and cyclization of macromolecular organic matter in the HASS.