Hydrocarbon Liquid Properties

Hydrocarbon Liquid Properties

Generalization of liquid petroleum products by density light density hydrocarbon liquids: ethylene, propylene, ethane propane butane medium density/mixed light products: natural gas liquids. natural gas condensate, natural gasoline, LPG Heavy hydrocarbon products: conventional, heavy crude, waxy crude and bitumen NGL: extracted from natural gas and contains propane, butane pentanes and traces of ethaneClassification of NGL dependent on vapor pressure: Condensate: C5, C6, and a small amount of heavier hydrocarbons Natural gasoline: C5+ and some amounts of butanes Liquefied petroleum gas: propane, normal and iso-butane LPG: gravity around 120, used as a feedstock in refineries, liquefies under pressure that is high than its vapor pressure

Phase Behavior hydrocarbons can exist as a vapor a liquid or a mixture of both. Important Points on the phase diagram: Bubble Point: the point at which the first drop of liquid mixture begins to vaporize Dew Point: the point at which the first drop of gaseous mixture begins to condense Critical Point: is the state of pressure and temperature at which all intensive properties of the gas and liquid phases are equal The limits where the two phases of gas and liquid mixtures can also coexist must be defined as: Circondentherm (Tct): maximum temperature at which two phases; liquid and vapor can coexist. above this temperature no liquid can be formed regardless of the pressure Circondenbar (Pcb): maximum pressure at which two phases; liquid and vapor can coexist. above this pressure no gas can be formed regardless of temperature Quality lines: the pressure and temperature conditions for constant percentage volumes of liquids. The Equation of state: determines the thermodynamic state of the liquid as it is transported through a pipeline. Five Universally accepted methods for predicting fluid properties for gas and liquid (slide 9)

heavier hydrocarbon liquids remain mostly in the liquid forms while light hydrocarbons such as ethane can be transported in a dense phaseThe liquids in a dense phase have physical properties somewhere between that of the liquid and gas. density of a liquid viscosity of gas

Properties of Petroleum Liquids Mass: the amount of matter contained in a body the amount of the inertial property of that body meaning its resistance to the change of motion Volume the space occupied by a particular mass dependent upon temperature and pressure changes minutely with temperature Density depends on liquid and temperature lower density --> higher temp higher density --> higher prep Thermal expansionliquids expand as their temperature rises density decrease with temperature increase :the decreasing ratio with increasing temperature is referred to as thermal expansion coefficient density increase with pressure increase and volume decrease: the increasing ratio with the increasing pressure is referred to as the bulk modulusCompressibility : the extent to which a fluid can be compressed. change in pressure--> change in volume it is the main cause of pressure surge in pipeline systems Bulk Modulus k: defines the compressibility of a liquid. the higher the bulk modulus the stiffer the liquid.(lecture 2 slide 13) Specific Gravity and API Gravity SG: measure of how heavy the liquid is compared with water. some change with pressure and temperature equations ( lecture 2 slide 16-17) Viscosity Newtonian Vs. Non-Newtonian viscosity: relative measure of resistance to flow measure of friction between adjacent layers of a flowing fluid velocity gradient is caused by viscosity. Sheer Stress : the frictional forces within a fluid that oppose the flow function of pressure Sheer Rate: the velocity with which an individual layer moves relative to neighboring layers function of geometry and average velocity of a fluidNewtonian Fluids dynamic/absolute viscosity is constantNon-newtonian fluids Time dependent Time independent Viscoelastic VAPOR PRESSURE the pressure that maintains a liquid in equilibrium at a given temperature.it is a measure of volatility Pipeline transportation of hydrocarbon liquids requires that a minimum pressure greater than the vapor pressure be maintained throughout the pipeline to avoid: Slack flow two-phase flow conditions avoid cavitation in pumps REMARK: Cavitation occurs when the pressure at the pump is below the Vapor pressure. Pressure must be ABOVE the vapor pressure at all points in time True Vapor Pressure: the equilibrium partial pressure exerted by a volatile organic fluid as a function of pressure. Evaporation losses in tankage systems are related to the TVPpartial vapor pressure Reid Vapor Pressure:absolute vapor pressure For liquid hydrocarbons having a vapor pressure greater than the atmospheric pressure at base temperature, the base pressure must be the equilibrium vapor pressure at base temperature. FLUID PROPERTIES AFFECTING MEASURMENT ( lecture 2 slides 34-35)

EQUATIONS FOR THE CALCULATION OF VISCOSITY WITH STEPS (lecture 2 slides 22-23)Hydrocarbon Liquids Blending & Volume Shrinkage :shrinkage occurs when two or more petroleum products are blended, the mixture experiences a volume reduction which is a function of gravity/density between the light & heavy components. shrinkage decreases as the % of light component volume increases Pour Point : lowest temperature at which a liquid will flow under prescribed conditionspour point is influenced by the precipitation or solidification of certain components ex: parrafins POUR POINT TEST ( Lecture 2 slide 24) once the temperature falls below the pour point, liquids begin to exhibit non-newtonian behavior and pipeline operation and design must be modified to be effective. examples: Heating the hydrocarbon liquid &/or insulating the pipeline : this helps in maintaining the temperature of the material above the pour point until they reach their destination. Injection lightweight hydrocarbon liquids: these liquids are miscible with the heavier hydrocarbon liquid, they dilute and lower the effective viscosity and pour point temperature. Boiling range fives information on the composition, properties, behavior of the hydrocarbon liquid during transportation storage and use FLASH POINTthe lowest temperature at which the hydrocarbon liquid's vapor can ignite momentarily when exposed to a flame. Equation ( lecture 2 slide 28)SPECIFIC HEAT CAPACITY the amount of heat required to increase the temperature of a unit quantity of a liquid by a specific amount. at constant pressure --> Cp if high Cp --> low heat gain if low Cp--> high heat gain at constant temp --> Ct THERMAL CONDUCTIVITY property of a material used in heat transfer calculation.it is the amount of heat transferred across a unit area of the solid material with unit thickness