Impact of boiler unit load changes on furnace processes

Abstract

Relevance. The need to assess the stability of combustion, thermal stress and nitrogen oxides (NOx) emission during load reduction of a steam boiler. Since renewable energy sources and nuclear power plants will receive great attention in the future, coal-fired thermal power plants are to operate at reduced loads, so it is important to investigate the reliability of operation and environmental parameters of the boiler unit in case of load adjustment. Aim. To investigate pulverized coal fuel burnout, temperature parameters and NOx emission at 50 % reduction of boiler unit load in the base configuration and taking into account installation of tertiary blast nozzles. Objects. Furnace chamber of a natural circulation boiler unit with steam capacity of 220 t/h in the baseline layout and with tertiary air nozzles. Methods. The package of application programs FIRE-3D for numerical study was applied. Combustion of pulverized coal fuel is a complex physical and chemical process, therefore the interaction of gas flow and solid particles was modeled using Eulerian and Lagrangian schemes, respectively. In the gas phase, the combustion of volatiles and CO with further combustion of carbon residue are modeled. NOx emission is modeled using post-treatment models including formation of fast, fuel and thermal nitrogen oxides. Results. Temperature fields, flow characteristics, NOx emissions for different loads of the furnace chamber of the boiler unit with steam capacity of 220 t/hour are obtained on the basics of numerical modeling. The authors have obtained quantitative estimations of furnace environment parameters corresponding to several levels of boiler load reduction up to 50% of the nominal one. Installation of four tertiary blast nozzles allows reducing NOx emissions by 12.75% at theoretically required amount of air in burner devices (α=1.0).

Keywords

• furnace chamber
• pulverized coal fuel
• vortex burners
• numerical modeling
• load