Experimental investigations on plasma-assisted wood pellet ignition for the start-up of biomass-fired power stations

Abstract

The share of power production from biomass-fired plants in the fuel mix energy system is increasing. These plants are responsible to compensate the residual load and therefore need to provide a high level of flexibility. Plasma-assisted ignition for biomass power plants is an alternative start-up technology that offers a carbon-free start-up with high flexibility. The application of an electrical ignition system, using a plasma torch, is investigated in a 400 kW pilot-scale facility at the Institute of Combustion and Power Plant Technology at the University of Stuttgart. A DC arc plasma torch is integrated centrally in a movable block swirl burner which is to be used as a start-up burner. Milled wood pellets are considered for this study to investigate the applicability of the electrical ignition system for cold start-ups of biomass-fired power plants. An evaluation method is developed to characterize the ignition and flame status under various operational conditions. Additionally, the flame stability is evaluated by post-processing the flame images recorded by a high-speed camera. Several operational parameters, such as burner load, air ratio, and primary air flow rate are used to optimize the burner configurations for a successful ignition and a stable flame. The results showed that biomass particles can be ignited at the burner load of 25%, but a rise of 13% in the load is required to produce a stable flame cloud. The flame is formed at the burner mouth with the support of the plasma torch. Nevertheless, when the plasma system is turned off, a flame lift-off is observed in most cases. The investigation of the effect of air ratio on combustion performance highlights the importance of the available heat for the combustion reactions, which is directly related to the burner load.