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UPFRONT CFD IN POWER PLANT APPLICATIONS
We would like to share some information on the latest success of the CFD Engineering Solution Center. Our task was to determine the transient fluid flow and heat transfer relations inside a steam generator of a Hungarian power plant.
A steam generator is a large pressure vessel which has a very important role in the operation of a power plant: it safely separates the primary heat transfer agent from the secondary agent and generates steam which is led to the turbines. As far as fluid flow and heat transfer is concerned it can be seen as a heat exchanger: the extreme hot primary water under high pressure transfers the heat via several batches of tubes to the water inside the secondary volume. This secondary water is boiled and the high pressure steam is led to the turbines.
Our task was to determine the fluid flow situation under normal operating conditions inside the steam generator and to figure out the fluid flow and heat transfer conditions while the steam generator is cooled down to execute maintenance operations.
The first step was to create the 3D CAD model of the steam generator. In the Upfront CFD philosophy the geometry (the basis of all simulations) is made in the best tool available: a 3D CAD system and then the model is read directly into CFdesign. This model contained all necessary details of the steam volume like water drop separator, feedwater tubes, the main steam tubes to turbines and other details important to analyse heat transfer. It also contained the primary collectors with bolted flange connections, stiffening ribs and shock rings on the top of the primary collectors. Primary collectors are slender steel towers inside the steam generator which distribute the primary agent to the tube batches. The towers are closed on the top with a blank flange and bolted connections.
During the analysis the steam generator was split into two parts: secondary steam and secondary water volumes. Our analysis focused on the steam part of the two volumes. The fluid was high pressure saturated steam which was characterized by material properties appropriate for such pressure and temperature conditions.
The normal operating conditions were analysed by stead-state simulations, for non-standard operating conditions transient fluid flow and heat transfer simulations were used. From the stead-state analyses it could be derived that in the volume above the primary collector (we call it the collector dome) the flow was dominated by buoyancy forces, while inside the main steam volume pressure driven flows determined the release of 450 ton/hour steam.
Transient simulations were focused on the collector dome. Fine details of the 20 pieces of bolted connections (including studs, special nuts and washers), small gaps inside the flow volume gave the beauty of the geometry. In v9 extruded mesh can be created and where it was applicable we used this mesh to reduce the number of nodes.
The heat loads of the primary collector included many cooling speeds of primary and secondary agents. Those were given as transient boundary conditions in °C/hour units. With these analyses the temperature field of steel parts and the steam itself were determined, those could be analysed throughout any cross-sections at any time steps. The picture above shows the temperature field of the bolted connections of the primary collector.
Based on the results conclusions on the transient heat load and temperature fields of steel parts were presented and CFD Engineering gave solution to a question being unanswered for many years: what happens inside the steam generator when the required cooling speed is modified.
2007.02.02 - CFD Engineering Hungary Kft. |
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