Thermal analyses on high and medium pressure steam flow in a steam conditioning valve with a steam nozzle using CFD

An essential part of controlling steam flow and pressure in industrial systems is a pressure control valve which lowers and regulates steam pressure prior to its delivery process. Unplanned plant shutdowns and large operating losses could cause damage like a hairline crack near a valve diffuser on the inside surface of the control valve caused by high pressure steam. Experienced in chemical industry, a pressure control valve located in a utility area has exhibited signs of internal surface cracking might due to continuous operation in high and medium pressure steam, whereby a valve replacement is needed. This study is exploratory and not intended for quantitative prediction with a scope involving modelling of steam conditioning valve using 3D modelling software. Based on the valve specifications, the study analysed the cause of hairline crack due to steam flow within the valve using Computational Fluid Dynamics (CFD) simulation with appropriate boundary conditions in determining temperature distribution along the inner surface. The objective was to investigate the effect of temperature distribution of the valve with and without a steam nozzle at Point A-B as the hairline crack area is predicted to be initiated based on real life occurrence. The impact of flow temperature in Steam Conditioning Valve contributing to the cracking event in valve body might be due to rapid expansion of high-pressure steam, which induces cooling due to energy conversion from internal energy to kinetic energy during compressible flow. By comparing high-pressure steam (HPS) and medium-pressure steam (MPS) conditions, the nozzle inlet’s pressure was reduced to compare the flow behaviour of valve under MPS condition. The overall temperature difference was significantly lower for MPS which is only 38% reduction compared with under HPS conditions of 59%. However, the temperature drop for HPS from Point A to B exhibited immediate drop compared to MPS condition which may cause cracking due to rapid cooling. The identification of critical regions with elevated temperature values, which can be related to the actual problem of chemical industry, may contribute to the ongoing MPS letdown of control valve replacement project in chemical industry.