PRACTICAL USES OF EQ-COMP
EQ-COMP chemical process simulation software can be used for pressure vessel design, distillation column design, natural gas pipeline design and designing of other hydrocarbon handling equipments and can also be used for oil well simulation and in natural gas contract drafting. EQ-COMP can predict phase equilibrium properties of multicomponent hydrocarbon mixtures very accurately. It has been designed to provide correct properties for almost any composition of the 100 + hydrocarbons and 3 inorganic gases mentioned on the LIST OF HYDROCARBONS – EQ-COMP document. Some of the possible applications of EQ-COMP are described below:
1. When a pure hydrocarbon is placed in a closed chamber under isothermal conditions (maintained at a constant temperature) then a part of it exists in the form of gas/ vapor whereas the remaining exists in the form of liquid. Some molecules constantly migrate from vapor to liquid phase and also from liquid to vapor phase. Under equilibrium conditions the amount of liquid evaporating to vapor phase and amount of vapor condensing to liquid phase is the same. This condition is known as phase equilibrium and the pressure that the vapors exert on the walls of the container under equilibrium is known as equilibrium vapor pressure or saturation vapor pressure. The plot of saturation vapor pressure with temperature is known as Phase equilibrium curve. The pressure and temperature values at the upper extreme of Phase equilibrium curve of pure compounds correspond to critical properties. Beyond the critical point the pure compounds cannot be distinguished between liquid and vapour. The Phase equilibrium curves for pure compounds are open curves. In case the equilibrium pressure of a pure hydrocarbon is known at a given temperature and corresponding liquid and vapour densities are known at these conditions then this information can be used to design storage tanks and pressure vessels for hydrocarbons. EQ-COMP can be used to predict Phase equilibrium curves for pure hydrocarbons and supercritical properties so it can be used to design storage tanks and pressure vessels for pure hydrocarbons.
2. When a hydrocarbon mixture is placed in a closed chamber under isothermal conditions then under equilibrium conditions the composition of the liquid phase and composition of the vapor phase is different with the vapor phase being rich in more volatile component and liquid phase being richer in less volatile component. Vapor phase if taken out of the chamber and condensed under different condition will give us a liquid containing higher percentage of more volatile components resulting in separation of the initial hydrocarbon mixture into two mixtures of different compositions. This method of separation of hydrocarbon mixture based on the volatility of the components is known as distillation. The equilibrium vapour pressure and temperature plot for hydrocarbon mixtures is a closed curve known as Phase envelope consisting of two open curves namely dew point curve and bubble point curve. These two open curves intersect at critical point and form Phase envelope. Hydrocarbon mixtures unlike pure hydrocarbons do not have a single vaporization temperature at a given pressure but vaporize over a range of temperatures and are characterized by an initial vaporization temperature known as bubble point and a final vaporization temperature known as hydrocarbon dew point. The hydrocarbon mixture is 100 % liquid at bubble point where it just starts to vaporize whereas it converts to 100 % vapour at hydrocarbon dew point. Between bubble point and hydrocarbon dew point, the hydrocarbon mixture exists partly in liquid phase and partly in vapour phase. Bubble point, hydrocarbon dew point and two phase properties can be used to design hydrocarbon mixture separation equipments like distillation columns and flash chambers. EQ-COMP can be used to predict the bubble point, hydrocarbon dew point and two phase properties for multicomponent hydrocarbon mixtures so it can be used to design multicomponent distillation columns and multicomponent flash chambers/ storage tanks/ pressure vessels.
3. The maximum pressure at which hydrocarbon mixture can exist in two phases is known as cricondenbar whereas the maximum temperature at which hydrocarbon mixture can exist in two phases is known as cricondentherm. Generally as we decrease the pressure of a two phase system, more and more liquid vaporizes. But sometimes, for a hydrocarbon mixture existing in two phases, the decrease in pressure results in condensation of more and more vapour into liquid phase. This phenomenon is known as retrograde condensation and is generally observed at conditions near the cricondentherm which generally exist in oil wells. Accurate prediction of cricondentherm, cricondenbar, critical point, retrograde condensation region, hydrocarbon dew point, bubble point and other VLE properties is required for oil well simulation studies which are carried out during oil well planning. EQ-COMP can predict all these values very accurately so it can be used for oil well simulation studies during oil well planning.
4. Natural gas fired turbine power plants and cogen plants require natural gas to run the turbine. In case liquid condensate exists in the natural gas being fed to the turbines then the emissions may increase and turbines may get damaged resulting in turbine maintenance costs and unscheduled shut-downs causing loss of production, time and money. To avoid all this, Natural gas contracts specify a super heat of 50 F for the supplied natural gas which means that the supplied natural gas must be heated to 50 F (28 C) above the cricondentherm temperature before being supplied so as to ascertain that all the heavier hydrocarbons present in the gas are vaporized and do not condense before natural gas is supplied to the turbine. Equation of state prediction of cricondentherm is one of the prominent methods to predict cricondentherm for a typical natural gas composition. EQ-COMP predicts cricondentherm very accurately using Peng-Robinson cubic equation of state so it can be used to fix the temperature at which the natural gas should be supplied to the power plants and this temperature specification is mentioned in Natural gas contracts for natural gas based power plants and cogen plants.
5. Various planetary atmospheres contain varying proportions of hydrocarbons and inorganic gases like Nitrogen and Carbon dioxide. EQ-COMP can predict various phase equilibrium properties for such mixtures so it can also be used to simulate planetary atmospheres like that of Titan, the moon of Saturn which contains mixture of Nitrogen and Methane in varying proportions.
6. Concentration diagrams (x-y plots) and Temperature Concentration diagrams (T-x-y plots) for binary mixtures are required for design calculations of distillation columns to separate these binary mixtures. These diagrams with or without Enthalpy Concentration diagrams can be used to find out theoretical number of trays, feed tray location, reflux ratio etc. of the distillation column using McCabe-Thiele or Ponchon-Savarit method to carry out the required separation of a given binary mixture. For low pressures, simpler methods of vapour-pressure determination like Antoine’s equation are used for plotting these curves with some loss of accuracy but these simpler methods are significantly inaccurate and thus cannot be used at higher pressures. EQ-COMP can accurately find out various VLE properties at low as well as high pressures and can further post-process the data generated by running various modules of EQ-COMP number of times to generate Concentration diagrams, Temperature-Concentration diagrams and Enthalpy Concentration diagrams for any binary mixture comprising of non-polar or mildly polar hydrocarbons at any pressure so it can be used directly for designing distillation columns for binary hydrocarbon mixtures.
7. Latent heat of vaporization (enthalpy change), entropy change, gibbs free energy change and specific heats of pure hydrocarbons and hydrocarbon mixtures is required in numerous chemical engineering calculations involving systems where vaporization of pure hydrocarbons or hydrocarbon mixtures is taking place. EQ-COMP can calculate accurate values of these properties for pure non-polar or mildly polar hydrocarbons or any mixture of non-polar or mildly polar hydrocarbons at any pressure and temperature values on the phase envelope for hydrocarbon mixtures.
8. Gas hydrate formation temperature and pressure conditions are to be avoided for hydrocarbon mixtures being pumped through a pipeline along with water so as to avoid plugging of pipelines. Hydrate plugging in a pipeline is difficult to remove requiring shutting down of pipeline resulting in loss of time, resources and money. Also hydrate formation conditions are also required for many applications of gas hydrates like hydrate based desalination, storage of gases in the form of hydrates etc.. EQ-COMP can predict hydrate dissociation curve for hydrocarbon mixtures which can be used to prevent hydrate plugging of a pipeline resulting in saving of time, resources and money.
These are some of the possible practical applications of EQ-COMP. Apart from these, EQ-COMP can be extensively used in various other natural gas processing, petrochemical and refinery design applications apart from pressure vessel design/ hydrocarbon storage tank design and distillation column design like hydrocarbon pump design, natural gas compressor design and hydrocarbon/ oil and natural gas pipeline design and in research studies in various research laps wherever accurate prediction of vapor liquid equilibrium properties for pure hydrocarbons or hydrocarbon mixtures is required.