Improved combustion air preheating design using multiple heat sources incorporating bypass flue in large-scale coal-fired power unit

In this study, a new concept of the combustion air preheating system integrated with a bypass flue (BPF) configuration was put forward and its feasibility was evaluated. In the proposed system, the primary air and secondary air are heated separately with cascade heat exchange and the hot and cold bypassing primary air mixing is avoided, which contributes to enhancing the air preheating and waste heat utilization. Thermodynamic analysis was performed based on, a typical 600 MW coal-fired power unit incorporating the new concept. The results indicated that owing to the proposed design, the power generation efficiency promotion reaches 0.78% (absolute value) with a standard coal consumption rate reduction of 5.52 g/kWh as compared to the reference unit, which are 0.14% (absolute value) higher and 0.94 g/kWh larger than those caused by the regular BPF retrofitting, respectively. The energy utilization is more rational in the new design according to the energy and exergy analysis, and the exergy efficiency of the primary air heating process is improved from 75.75% (original design) or 79.62% (regular BPF design) to 84.46% due to the proposed concept. The volume and heat exchange area of the APH decline significantly as well in the modified system. (C) 2018 Elsevier Ltd. All rights reserved.