Dimensionering av fläktsystem till ett kraftvärmeverks rökgaskondensering

Combined heat and power (CHP) plants play a central role in Sweden’s energy transition by producing both electricity and heat from renewable sources, thereby helping to reduce the use of fossil fuels and greenhouse gas emissions. This study focuses on the flue gas condensation system at the Johannes biomass CHP plant in Gävle, where operational issues have arisen due to system upgrades that were not fully matched by adjustments to all subsystems. By adapting the flue gas fan to actual operating conditions, the capacity of the condensation process can be optimized, enabling more energy-efficient operation and reduced operational costs.The purpose of this work is to increase the performance of the flue gas condensation system in order to ensure cost-effective and environmentally sustainable heat production. The goal is to provide a decision-making basis that supports increased condensation capacity from a cost-efficiency perspective. A comprehensive system analysis was carried out using flow diagrams, measurement instruments, and staff input to create a complete picture of the system’s operation. Data were collected from Gävle Energi’s monitoring system during the winter months, allowing for performance analysis under high load conditions. Particular focus was placed on the performance of the flue gas fan, where differential pressure and rotational speed were analyzed against the manufacturer’s specifications. It was found that the fan does not reach its specified capacity, causing the bypass valve to open and thereby reducing condenser efficiency.Operational data show that the existing flue gas fan is underutilized, despite its capability to handle higher mechanical loads at increased rotational speed. By raising the motor frequency to 60 Hz, the fan’s capacity can be increased by 9 percent. The highest measured volumetric flow was 257 000 m³/h, which significantly exceeds the current capacity. To meet demand 99 percent of the time, a flow rate of 232 000 m³/h is required. According to the manufacturer’s data, this can be achieved by equipping the fan with a larger motor.Increasing the fan speed to 1200 rpm by adjusting the frequency has been identified as a viable solution to increase flow rate. However, this would require further investigation into the motor’s mechanical integrity, as well as checks on alignment and bearing load. The study also shows a correlation between increased flow, higher power consumption, and reduced pressure, which should be further evaluated from an energy efficiency perspective. Since the purpose of the flue gas condensation system is to conserve energy and reduce environmental impact, it is essential to ensure that the system operates efficiently and without unnecessary losses.