(186e) Validation of CFD Prediction Accuracy of VOC Generation Rate for Cost-Effective Design of VOC Recovery Equipment

Volatile organic compounds (VOC) emissions from storage facilities, which significantly affect the atmosphere and human health, have a considerable contribution to the total VOC emissions from chemical, refinery and petro-chemical plants. The emitted VOC amount and composition may significantly differ depending on the local atmospheric conditions and the property of the stored product in the tanks. In recent years, it is required by the environmental regulation that the VOC emitted from oil or chemical product storage tanks be recovered by applying a control process when designing refinery plants or petro-chemical plants. In designing the VOC recovery equipment in a refinery or petro-chemical plant, the maximum instantaneous VOC evaporation rate and its composition from tanks are crucial parameters for selecting the recovery process and deciding the capacity of recovery equipment. Currently American Petroleum Institute (API) Standard is commonly used to predict the VOC evaporation rate when designing the VOC recovery equipment, but the formulation in API standard overestimates the VOC evaporation rate and also has some limitations on application. In view of this, a semi-empirical model, which is based on analogy between mass transfer and heat transfer on a flat plate, has been proposed and incorporated into the CFD code to more properly predict the evaporation rate of VOC under higher ambient temperature and condensation rate of its vapor under lower ambient temperature for a fixed-roof gasoline tank. The present research aims to verify the CFD prediction accuracy of VOC evaporation and condensation rate by comparison with the experimental data from both our laboratory experiments and literature. Our laboratory experiments were performed for single composition (n-C6H14) and multi-composition (i-C5H12, n-C5H12, n-C6H14), while the experimental data in the literature were obtained through site measurement of an industry-scale gasoline tank by Japan Agency for Natural Resources and Energy in the past. The CFD-predicted VOC emission results match well with laboratory and industry-scale experimental data. Hence, it is expected that cost-effective design of VOC recovery equipment can be realized if predicting VOC emission based on the proposed model. Also, the consumption of nitrogen, which is sucked into the tank for protection of storage tank when the VOC condensation occurs under lower ambient temperature, can also be predicted properly by the proposed model. The predicted nitrogen consumption amount can be used to decide the capacity of nitrogen generator of a plant.