Utilization of mill rejects with biomass pellets in the existing coal power plants- a novel approach towards sustainability & fuel security

ABSTRACT

The present work is focused on the possible utilization of mill rejects blended with the biomass non-torrefied pellets (made of paddy straw, dry grasses and fallen sal leaves) in the existing tangential coal-fired boiler through the gasification process. The physio-chemical analysis and combustion behavior study of the materials is done based on thermo-gravimetric analysis (TGA) and differential thermal analysis (DTA). The result shows that the gross calorific value (GCV) of the developed bio-mass pellet is about 3900–4300 kCal/kg with the mass percentage of fixed carbon (FC) and volatile matter (VM) of about 15% and 70%, respectively. From the TGA and DTG study, it is observed that about 7% weight loss was found in all pellets at a temperature range of about 85–110°C but for the mill rejects, it is about 5–6%. At the peak temperature, the maximum weight loss of pellets and mill rejects is about 0.90 gm/min and 0.16 gm/min, respectively. The combined use of mill rejects and pellets (1:1) in the updraft gasifier generates combustible syngas with mole fractions of CO and H₂ of about 0.29 and 0.30, respectively with a lower heating value of about 159 kJ/mole. The direct use of generated combustible syngas into the coal-fired boiler of a 500 MW power plant increases the net energetic and exergetic performance by about 0.09 and 0.07% points, respectively and resulting in a reduction of annual CO₂ emissions by about 9452 tons. Cost-benefit analysis is used to determine the feasibility of the system.

KEYWORDS:

• Biomass pellet
• gasifier
• DTG
• coal power plant
• mill rejects
• syngas
• TGA
• efficiency
• CO₂

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Notes on contributors

G. Khankari

Dr. Khankari working as Senior Manager (R&D) at Research and Development Section, Damodar Valley Corporation, Kolkata, and he has more than 15 years of industrial experience in thermal power generation. He has many national and international publications in the field of energy research.

D.V. Rajan

Dr. Dhavala Venkata Rajan has been employed at Damodar Valley Corporation since 1994, and currently works as Senior General Manager (R&D) and he has vast experience more than 28 years of industrial experience in erection, commissioning and O&M of thermal power generation. He has enormous input in the national and international level publications in the field of power /electrical systems, energy research etc. His current area of research is power flow techniques, state estimation, power system operation and planning, Grid integration with RES and application of soft computing techniques in various power system problems.