2012-11_LPG Chem Gas Quantity

8/12/2019 2012-11_LPG Chem Gas Quantity

http://slidepdf.com/reader/full/2012-11lpg-chem-gas-quantity 1/4

TECH TALKLPG/CHEMICAL GASES QUANTITY DETERMINATION

OIL, GAS AND CHEMICALS SERVICE NOVEMBER 2012

Introduction

The principal standard for the inspection of LPG is API MPMS Chapter 17.10.2 / EI HM 55 - Measurement ofRefrigerated and/or Pressurized Cargoes on Board Marine Gas Carriers - Liquefied Petroleum and ChemicalGases and it is our policy to follow this standard within the limitations specified by our clients or by regulation.However, the calculation routines specified in API MPMS Chapter 17.10.2 / EI HM 55 are broad based ratherthan rigorous, which can result in multiple calculation processes.

To reduce the confusion and client dissatisfaction associated with multiple calculation processes, we havedeveloped procedures to provide a common platform for quantity determination of LPG and chemical gasses onboard of vessels and in shore tanks. Unless otherwise instructed, only methods in these procedures should beapplied. In special cases the customer may request the use of a different method or procedure. This isacceptable provided that this is fully detailed in the order acceptance and agreed to by ALL of the commercial

parties. Full details must also be included in the written instructions to the field inspector.

Definitions

For the purpose of these procedures the following definitions apply:

Liquefied gasses : products with a vapour pressure exceeding 3 bar absolute at a temperature of 50°C Liquefied Petroleum Gas [LPG] : propane, butane, mixtures of propane and butane, ethane, pentane,

promix Chemical gasses : ethylene, propylene, butadiene, butylenes, ammonia, vinyl chloride monomer True or absolute density : density in vacuum; i.e. - Mass per unit of volume [kg/l vac] Apparent densi ty : density in air; i.e., weight per unit of volume [kg/l air] Saturated conditions : Situation in which the vapor phase is in equilibration with the liquid phase at a

certain liquid temperature.

Methods

The quantity determination is based on the measurements executed by the inspector. As gasses are stored inclosed containers, manual measurement is not possible. Level, temperature and pressure readings are notedfrom local available systems. The reference of the instruments, date and validation of calibration data must bereported. The instructions mentioned in the equipment guide must always be followed.

The following measurements are to be performed or observed by inspector:

Level per tank Tank pressure per tank Temperature per tank for vapour and liquid Trim (for vessels only) List (for vessels only) Atmospheric pressure (optional)

All calculations must initially be performed with the units as mentioned in the capacity tables. Conversion toadditional units starts from the final obtained quantity (kg vac). The total quantity of product in the tank is thesum of the quantity from the liquid phase and the vapour phase. For each phase the volumes are multiplied bytheir respective densities.





Density d etermination for vapour phase of LPG

The density of vapour is calculated according the formula of the gas law.

23.6451

·1.01325 . .

1.01325 ·

288.15273.15 . .

Where:MW = molecular weightObs. pres. = observed pressure in barvap.temp. = vapour temperature23.6451 = molar volume of ideal gas at 15°C and 1.01325 bar

In above equation, a temperature of 15°C is used as reference temperature. The presence of nitrogen in the gasphase is taken into account and the vapour quantity corrected.

Density determination for vapour ph ase of Chemical Gases

For saturated vapour conditions and pure gasses (chemical gasses) the vapour density can be obtained directlyfrom the density table of the product. The presence of nitrogen in the gas phase is taken into account and thevapour quantity corrected.

Density determination liqui d p hase of LPG and Chemical Gases

The method to determine the density is depending of the purity of gases. All densities are in vacuum. For puregases and chemical gases the density is based on the product tables starting from the observed liquidtemperature. For mixtures of gases the density is calculated on the basis of the method imposed, such as ASTMD2598.

Volume determination

Follow any requirements as specified in the tank capacity table. The volume determination is based on the dataof the tank capacity table. The volume of the liquid phase shall be determined by means of a levelmeasurement, corrected as appropriate for:

Trim correction (for vessels only) List correction (for vessels only) Float correction Tape correction

Thermal contraction of temperature Thermal contraction of pressure

The volume of the vapour phase is the difference of the total tank volume and the liquid volume.

Quantity determination

The quantity calculation is done by multiplying the volume with the density, provided that both quantities arereduced to the same temperature. The quantity of the liquid phase is depended of the product:





Observed liquid volume x volume correction factor x Density liquid at reference temperature (i.e. 15°C) Observed liquid volume x Density at observed temperature <<for chemical gasses only>>

Volume correction factor: The volume laid down in current temperature should be converted to the volume atreference temperature based on ASTM table 54.(1952) or ASTM table 54E (2007) for LPG and based upon theappropriate product table for chemical gases.

Conclusion

The procedures that this Tech Talk was based upon can be found on the following SharePoint site:

http://chsites01.sgs.net/sites/ogc/Inspection/SGS%20Work%20Instructions/Forms/AllItems.aspx

Additionally, we have provided two calculation spreadsheets, one for LPG and one for Chemical Gases. Thesecan also be found on the above referenced site in addition to being attached to the message that delivered thisTech Talk. My thanks go to Werner Robaeys for developing the procedures and spreadsheets.





Minutes of Tech Talk Meeting:

Branch:_______________________________ Divis ion: ______________________________

Person Conducting Meeting:__________________________________________________

At ten dees :

Addi ti onal It ems Discu ss ed:

Problem Areas o r Concerns:

Comments:

The original is to b e maintained at the Branch forreference and audit purpo ses. Data from this fo rm isrequired as part of you r mont hly Global QHS&E reporting

2012-11_LPG Chem Gas Quantity

Documents

Transcript of 2012-11_LPG Chem Gas Quantity