Modelling of Alkali Contaminant Flows in Evaporative Gas Turbines

A new advanced gas turbine cycle, called the Evaporative Gas Turbine (EvGT), also known as a Humid Air Turbine (HAT), has recently been demonstrated in Sweden, with a pilot plant built and operational. As the EvGT cycle involves complex interactions between air and water streams, air quality aspects need to be carefully examined. This article examines different strategies to prevent contamination and turbine corrosion and presents a theoretical model simulating the flow of alkali salts in the EvGT cycle for different ambient salt concentrations, cycle configurations and equipment performance.Similar to the existing pilot plant, the EvGT cycle studied in this article requires no external water source to meet its water demands. Instead, water is condensed from the flue gas and recycled to the humidification tower. Recirculating the condensate implies that the best strategy to ensure a high air quality and hinder impurity build up and transfer within the cycle is to filter the incoming air. Furthermore, air intake filters could simplify or eliminate the need for condensate treatment. The humidification tower is an important area for the transfer of contaminants to and from the water and air streams. Minimising droplet entrainment and bleeding off a fraction of the humidifying water are key strategies to protect the turbine, while the capture of airborne particles in the humidifying water film improves the air quality.The model constructed predicts that a small blow down from the water circuit (typically 0.1-3.5% of the feed water flow) is sufficient to ensure that the alkali concentration does not exceed those in an equivalent dry gas turbine. This blow down can then be treated and partly recycled to the water circuit or discarded.Copyright © 2001 by ASME