What is the difference between weathering and RVP?
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24/09/2015
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Sudhakara Babu Marpudi, Dangote Oil Refinery Company, m_sudhakarababu@yahoo.com
Weathering test is an indicator of De-butanizer LPG -Naptha separation. 95 ml out of 100 ml sample must evaporate at 2 Deg C (leaving 5 ml only unevaporated). The amount of liquid remained unevaporated at 2 Deg C is the amount it C5+ material present in LPG (which is clearly undesirable). Similarly, < 5 ml left over in the weathering tube indicate the under recovery of LPG (presence of C4+ / C5 material that overloads thedownsream Aromatics / Propylene recovery units, for recovering this as LPG). De-butanizer reboiler temp is adjusted accordingly.
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11/09/2015
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Sridhar Balakrishnan, Bharat Oman Refineries Limited , laksrid@yahoo.com
Weathering : LPG sample is chilled by means of a cooling coil and collected 100 mL of liquid is taken in a weathering tube. Allowed to evaporate at atmospheric pressure under speciļ¬ed conditions . Correct the observed temperature, when 5 mL of liquid test portion remains, for barometric pressure and report as the 95 % evaporation temperature. Significance of the test is intended to find out the presence of heavier hydrocarbons in LPG like pentanes and hexanes etc , which may not readily evaporate.
RVP : Vapour pressure is an important physical property of volatile liquids. It is the pressure that a vapour exerts on its surroundings. For volatile petroleum products, vapour pressure is used as an indirect measure of evaporation rate. High vapour pressures and a low distillation temperature for 10% evaporated both help cold starting. Under hot-operating conditions, high vapour pressure also contributes to vapour lock and increases vapour formation in fuel tanks. The most commonly used method for petroleum products has been the Reid vapour pressure , as determined by ASTM D323 (American Society for Testing of Materials) method (Reid Method). This test method determines vapour pressure at 37.8 'C (100 'F) of petroleum products with initial boiling point above 0 'C (32 'F). It is measured by saturating a known volume of oil in an air chamber of known volume and measuring the equilibrium pressure, which is then corrected to one atmosphere (101.3 kPa).
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10/09/2015
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keith bowers, B and B Consulting, kebowers47@gmail.com
Reid Vapor Pressure (RVP) is a test that measures the vapor pressure of the test material under simulated storage conditions . It is NOT the 'true vapor pressure', but is the apparent vapor pressure measured at 100F and saturated with water and a 4:1 test liquid: water saturated air ratio inside a closed cylinder.
"Weathering" is a description of what happens when a liquid containing volatile components is continuously exposed to atmospheric pressure through an open vent or open top tank, allowing the more volatile components to evaporate into the atmosphere or vapor space in the tank, with continuous vapor removal.
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