LPG blending

By GSS Ops Team 21 January, Monday

The program Ship LPG EU or Ship LPG EU Cal can help you to calculate the quality of the LPG blend for every stage of loading-on-top of the OBQ and then after the loading of every subsequent layer.

You just need to know either the gas composition of OBQ and of each component being blended on board or at least the density at 15˚C and the molar mass of each component and the mass of OBQ and of each component from shore tank quantity calculations or from LPG LACT meter.

If the “Loading” option was selected for cargo operations, then you will see a more complicated User menu containing 2 tabs “Calculation based on GC” and ”Calculation based on Molar Weights and Densities of Each Grade” allowing to calculate the density at 15°C and molar mass for the mix on board: of either OBQ and the first cargo loaded on top of OBQ or the mixture of OBQ and the first and the second cargo loaded on the top of OBQ as shown in the example below: When filling Ullage reports you will notice that like when you worked over shore tank reports, if you select the cells for input values of either densities at 15°C or molar mass, a popup menu “Input GC Tests” appears preventing you from further entering the data as shown below. Blog In order to get on your screen the built-in density and mass molar calculator, you need to click on the pop-up menu.
Now you have 2 options for such a calculator when the mode of cargo operations is "Loading":

Tab 1: “Calculation based on GC” (i.e. based of test results based on Gas Chromatographer test results) Blog

  • Note, that the difference of the built-in calculator of a density at 15°C and molar mass for “Discharge” option with the same calculator for “Loading” option is that you must fill in quantities in metric tons in vacuo for OBQ and each grade to be mixed otherwise the last column for the Mix will not calculate pro rata quality for the Mix and therefore you will not be able to transfer calculated data into your Ullage Report.
  • Also Note, that the total percentage of each column must be 100%. You must check and correct your input data for every column and click “Calculate Test Results“ again until you get 100% in every column with the data. Only after that and after you filled in Metric tons in vacuo for every grade you can click buttons “Density @ 15°C (in vacuo)” and “Molecular Weight”, to transfer calculation results into appropriate cells of the “Main” page. Usually Metric tons used for such calculations are based on shore quantities except OBQ.
  • Also Note, that in order to get correct calculation results of Molar weights and the densities at 15˚C for each grade and for their mix you need to select using option buttons at the very top of the user form what type of percentage you are going to fill in: by mass %, mol.% or by vol.%.
  • Note, that the filled in data are “remembered” by the program and they can be repeated for every ship’s tank which is very convenient, if you use the same density and molar mass for calculation of all ship’s tanks.

  • Tab 2: ”Calculation based on Molar Weights and Densities of Each Grade” (i.e. calculation of pro rata density at 15°C and molar mass of the mix on board based on known densities at 15°C and molar masses of each grade used for the mix on board). Blog If densities at 15°C and molar masses of each grade mixed on board the ship is known then you can calculate a pro rata weighted quality of the mix of up to 4 grades or of OBQ and 3 grades. You just need to fill in for every grade the density at 15°C, molar mass and a quantity of such grade in Metric tons in vacuo. The quantities used for calculations can be obtained from shore calculations based on either shore tank measurements of on meter measurements.

    If you pre-selected the option of "Discharge" then when you click on the pop-up menu, you will get a more simplified the density and molar mass calculator as shown below:
    Blog

    As you can see, it is very easy to calculate quality of the blend using the above described built-in density and molar mass calculator!

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