Characterization of a novel two-stage high ash coal gasifier for low tar and high calorific value gas

Abstract

The high ash content of coal poses two critical challenges in conventional gasifiers: (a) ash agglomeration and (b) low-quality syngas. The ash agglomerations are caused by the interaction of alkali and alkaline earth metals with other inorganic compounds, localized temperature generation, and unoptimized process parameters. Whereas low-quality gas is due to moderate temperature operations and the mixing of syngas with pyrolysis products. Recognizing these challenges, the current work discusses the design, development, and performance characterization of a novel two-stage gasification system that strategically segregates oxidative pyrolysis in a cyclone reactor and oxy-steam char gasification in a packed bed reactor. Such segregation provides explicit control over parameters like local temperatures, particle and gas residence time, enabling the configuration to handle coal with a wide range of ash content. Thermodynamic analysis and performance characterization experiments have been carried out with varied temperatures, oxygen, and steam flow rates. While operating the system up to 950˚C, there was no indication of clinker formation. The gravimetric tar content was found 52 ± 3 mg/Nm3. The concentration of CO, CO2, CH4, and H2 in the product gas during experiments was 40 ± 5, 20 ± 5, 2 ± 1, and 45 ± 5%, respectively. The carbon conversion was greater than 77%, with further scope for improvement.