Conversion of nitrogen compounds and tars obtained from pre-composted pig manure pyrolysis, over nickel loaded brown coal char

Fuel gas production and nitrogen transformation during pig manure pyrolysis from room temperature to 900 °C are investigated. The catalytic decomposition of the derived volatiles is also studied. Ammonia, HCN and N2 were obtained as the main N-containing gases. Ammonia was mainly emitted below 700 °C, which corresponds to 24.8 wt% of the nitrogen in the manure. Hydrogen cyanide and N2 gases obviously formed at temperatures above 700 °C, while the HCN concentration was as low as one ninth that of NH3 and one fifth of the concentration of nitrogen even at 900 °C. Thermal cracking of the pyrolysis volatiles produced little NH3, but noticeably increased HCN formation. When the prepared nickel-loaded brown coal char (LY-Ni) was added to the second part of the reactor (second stage) as a catalyst, most of the N-containing species in the volatiles converted into N2 gas. It suggests that LY-Ni has high catalytic activity for the conversion of N-containing compounds. Significant quantities of light fuel gases (H2, CO and CH4) were also generated. Compared with sand, 5.8 times (H2 and CO) the amount of gases was produced with the LY-Ni char at 650 °C. Decomposition of the manure volatiles depends on the catalyst temperature. Total product gases approximately doubled in yield when the catalyst temperature increased from 450 to 550 °C, and the volatiles conversion (based on carbon balance of the manure volatiles) increased from 72.4 wt% to 92.0 wt%. At 600–700 °C, the volatiles conversions stabilized at high levels of 96.7–98.2 wt%. •The main N-containing gases from pig manure pyrolysis were NH3, HCN and N2.•Thermal cracking for the pig manure volatiles promoted HCN formation noticeably, and did little effect on NH3.•A nickel-loaded brown coal char converted the N in the pig manure volatiles mostly into N2 gas.•Light fuel gases, such as H2, CO and CH4, were significantly generated under the prepared nickel-loaded brown coal char.