Investigation of effect of cooling water characteristics on flue gas condensation along vertical tube heat exchanger

Abstract

Flue gas condensing heat exchangers obtain the highest thermal efficiency of power boilers through the recovery of sensible and latent heat of condensation from flue gases containing certain amount of water vapor. Many parameters influence the operation of economizers, among them the amount of water vapor in the flue gas and cooling water parameters. This paper presents experimental results obtained for various local parameters of vertical tube bundle economizer when the flue gas water vapor mass fraction is 6 % and 14 % and when different cooling water inlet flow rates and temperatures are applied. The results showed that the change in the water flow rate had negligible effect on variation of the local flue gas and cooling water temperature along heat exchanger. However, its effect on the condensate flux and the local Nusselt number was significant. The cooling water temperature and, especially, water vapor mass fraction had a great impact on the average Nu number, but the effect of the flue gas Re number was less evident. It was determined that there exists a ratio of cooling water to flue gas mass flow rate, where the operation of the economizer is optimal in terms heat transfer and condensation efficiency.