Abstract
According to the study of basic Rankin thermal cycle, the steam exhaust pressure of a typical steam turbine toward the condenser, plays a great role in the efficiency and the net output power of the steam turbine, so most surface condensers that are working in thermal power plants are kept at vacuum condition so that the maximum power of thermal cycle can be achieved. The vacuum pressure at condenser leads to the entering of air and Non-condensable gases from turbine gland seals to condenser so that the special air ejection equipment is being used to take apart air from steam and vent it to out of condenser. In this study, a special steam and air separator mechanism in an evacuating system called “Aircooler” at a 16 MW steam turbine condenser is being studied and the Fluent CFD software is utilized to analyze the behavior of steam plus air in a typical aircooler system of 16 MW steam turbine condenser of Neka power plant to find a way to reduce the risk of cooling tube rupture in aircooler ducts. The critical condition which tube rupture happens is determined and it is demonstrated that in hot seasons of year, by increasing the seawater cooling temperature and increasing in turbine steam exhaust pressure and temperature, the risk of tube rupture due to more mixture velocity at the first row of aircooler cooling tubes increases and also the effect of tube plugged condition on the performance of aircooler shows that the risk of other tubes rupture will increase and thus the efficiency of aircooler decreases due to more aircooler exhaust temperature. Finally, two modified plans at aircooler system design will be studied and simulated via Fluent CFD software which leads to reduce the risk of tube rupture. The results show that by modification of aircooler ducts and holes, the mixture air and steam flow velocity to first aircooler cooling tube row decreases significantly and causes the risk of tube rupture to decrease remarkably and also the exhaust temperature of aircooler decreases and causes the higher ejector performance.
Highlights
According to the study of basic Rankin thermal cycle, the steam exhaust pressure of a typical steam turbine toward the condenser, plays a great role in the efficiency and the net output power of the steam turbine, so most surface condensers that are working in thermal power plants are kept at vacuum condition so that the maximum power of thermal cycle can be achieved
A special steam and air separator mechanism in an evacuating system called “Aircooler” at a 16 MW steam turbine condenser is being studied and the Fluent CFD software is utilized to analyze the behavior of steam plus air in a typical aircooler system of 16 MW steam turbine condenser of Neka power plant to find a way to reduce the risk of cooling tube rupture in aircooler ducts
The critical condition which tube rupture happens is determined and it is demonstrated that in hot seasons of year, by increasing the seawater cooling temperature and increasing in turbine steam exhaust pressure and temperature, the risk of tube rupture due to more mixture velocity at the first row of aircooler cooling tubes increases and the effect of tube plugged condition on the performance of aircooler shows that the risk of other tubes rupture will increase and the efficiency of aircooler decreases due to more aircooler exhaust temperature
Summary
Lux et al [3] presented a computer model that could predict the performance of a condensing heat exchanger with circular tubes This model ignored the effect of condensation and diffusion processes. A new mechanistic model for the prediction of condensation in the presence of non-condensable gas using a commercial computational fluid dynamic code, CFX-4, was presented by Karkoszka and Anglart [6]. Mokraoui and Souayed [8] performed a simulation of water-vapor condensation in the presence of non-condensable gas between two vertical plane plates and in a plate fin-and-tube heat exchanger in a stationary mode using FLUENT software and Mohammad Saraireh [9] used FLUENT CFD method to solve Condensation of water vapor from humid air in compact heat exchangers. The FLUENT CFD software is used to analyze the behavior of steam plus air in a typical aircooler system of 16 MW steam turbine condenser of Neka power plant to find ways to reduce the risk of cooling tube rupture in aircooler ducts
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