Anti-Freezing Mechanism Analysis of a Finned Flat Tube in an Air-Cooled Condenser

Yonghong Guo,Tongrui Cheng,Xiaoze Du,Lijun Yang

doi:10.3390/en10111872

Abstract

In cold winter weather, the air-cooled condensers (ACCs) face serious freezing risks, especially with part load of the power generating unit. Therefore, it is of benefit to investigate the heat transfer process between the turbine exhaust steam and cooling air, by which the freezing mechanism of the finned tube bundles can be revealed. In this work, the flow and heat transfer models of the cooling air coupling with the circulating water, are developed and numerically simulated for the anti-freezing analysis on basis of the finned tube bundles of the condenser cell. The local air-side heat transfer coefficient, condensate film development, and non-condensable gas development are obtained and analyzed in detail. The results show that, the most freezing risk happens at the fin base due to the highest air-side cooling capacity, besides the windward velocity, ambient temperature and turbine back pressure all determine the freezing risk with the constant inlet flow rate of the non-condensable gas. Furthermore, increasing fin thickness and decreasing fan rotating speed are the most effective anti-freezing measures. Additionally, increasing turbine back pressure can also be adopted to avoid ACC freezing, however the adjustment of outlet steam-air flow is not recommended.

Highlights

Air cooled condensers (ACCs) have been increasingly developed in large scale thermal power plants around the world, owing to their substantial water conservation [1]
An ACC consists of dozens of condenser cells in a rectangular array, and each condenser cell is composed by “Λ” frame finned tube bundles with an axial flow fan below so that ambient air can be driven to pass through the heat exchangers to remove the heat rejection from exhaust steam
In cold winter, the cooling air can take away the entire heat load of the exhaust steam, which result in a freezing risk of the finned tube bundles

Summary

Introduction

Air cooled condensers (ACCs) have been increasingly developed in large scale thermal power plants around the world, owing to their substantial water conservation [1]. In cold winter, the cooling air can take away the entire heat load of the exhaust steam, which result in a freezing risk of the finned tube bundles. In such a case, it is necessary to study the heat transfer mechanism between the cold air and exhaust steam, which may be beneficial to the safe and energy efficient operation of ACC in power plants. Most attention was paid to the thermal resistance of cooling air, and few studies have been carried out on the anti-freezing issues of ACCs. It’s worth noting that the cooling air in cold winter has a huge heat capacity when it flows through the condenser cell, and can carry off the maximum heat load of the turbine exhaust steam.

Methods

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Discussion

Conclusion