COMPUTER AIDED DESIGN OF FLARE

Abstract

In case of plant failure or shutdown safe disposal of hydrocarbon gases in petroleum and alied industries is a must. Waste gases are burned at flare tip. Since flare is an utility, it is necessary to design flare system for optimum conditions. This can be achieved by computer aided design based on different available model and to study at the same time dispersion of pollutants around the flare stack. In the present work computer program in FORTRAN 77 has been developed by selecting two types of models, (i) Point source model (Kent, Brzustowski) and (ii) Surface source model (Thronton) These modes heavily rely on the amount of heat released from the burned gases, which in turn is based on the equilibrium composition of gases product and adiabatic flare temperature. In the present work. The equilibrium composition and adiabatic flame temperature generated is estimated using methods of equilibrium constants and enthalpy balance respectively. The input parameters for flare design models are composition and nature of gas, ambient conditions, maximum allowable heat flux, Mach No. Wind velocity and downward distance. The output parameters are equilibrium composition, adiabatic flame temperature, dimensions of flame and flare stack from the result it appears clear that the models of Brzustowski or Kent which are based on the point source model predict around the same flame length as well as Stotek height with an error of 10 % infact Kent model is more sophisticated than Brzustwski model. The results obtained also agree well with that of Tan with an error of 2-3%. Thronton model is one of the most sophisticated and accurate model for prediction of flame dimensions and radiation from flame. It is seen that this model predicts the maximum stack height for a particular level of heat flux. In the present work environmental aspect of flare is considered pollutant dispersion is predicted using Gaussian model also the noise generated by combustion process is estimated.