Combustion characteristics of waste sludge at air and oxy-fuel combustion conditions in a circulating fluidized bed reactor

• Comparative combustion performance of waste sewage sludge in air and oxy-fuel conditions.
• Pressure drop and temperature distribution in air and oxy-fuel combustion.
• Comparison of ash composition in air and oxy-fuel combustion.
• Comparison of flue-gas composition in air and oxy-fuel combustion.

Oxy-fuel combustion and circulating fluidized bed (CFB) technologies were applied to waste sewage sludge using a cold-bed and a 30 kWth CFB pilot test bed. In the cold-bed tests, the minimum fluidization velocity (umf) and the superficial velocity were determined as 0.120 m/s and 2.5 m/s, respectively. In pilot tests, the combustion characteristics of waste sewage sludge in oxy-fuel condition were very distinctive compared with that in air condition in terms of operation parameters such as the distribution of pressure drop and temperature, flue-gas temperature, and the composition of ash and flue-gas. Based on cold-bed and pilot bed tests, the oxygen injection rate was optimized in the range from 21% to 25% in oxy-fuel condition for waste sludge combustion to apply oxy-fuel combustion and CFB technologies with considering technologies for stable and economic operation.