Engineering Primer – Errors between % volume and mass -Take 1

April 8, 2008

Liquid flowrate can be measured using two methods:

  1. Volumetric, where flow is directly measured (turbine meters), or calculated using other process variables (pressure differential in the case of orifice meters). In this case, the volume is multiplied by some form of density to get mass.
  2. Mass, which is measured using coriolis type meters. To get volumetric flowrates, the mass must be divided by density.

An example where confusion between the two types of methods can result in a financial or accounting problem is determining the amount of free water in a crude flowstream.

The volume fraction of water ismp typically determined on-site using a ‘shakeout’ method. A crude sample is extacted from the process and spun down in a centrifuge to get good separation between the crude and water. A de-emulsifier is typically added to break up the emulsion layer in the sample. The volume of water in the cylinder is the volumetric amount of water in the sample, say anything between 0.5 – 40%.

The details of the above method can be read up in the Manual of Petroleum Measurement Standards (MPMS), Chapter 10-Sediment and Water, Section 4-Determination of Water and/or Sediment
in Crude Oil by the Centrifuge Method (Field Procedure)

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Article – Haze reduces GT power output

March 26, 2008

An interesting article appeared in the pages of the Feb 2008 issue of the Jurutera, the Institution of Engineers, Malaysia’s monthly bulletin. It claims that during the haze season, a gas turbine (GT) can lose as much as 3% of its power output.

For those of you who are not from south east Asia, the haze is a polite term for seasonal smog mostly generated by Indonesia and generously shared with the rest of the region.

To quote the article, written by Engr. Dr Philip Tan, Mr. Loh Tian Ek and Mr. Ng Yan Fu,:

  • ‘The (GT) output reductions could reach as much as 3%.”
  • “However, to our amazement, the additional power loss would recover when the haze is (sic) cleared.”
  • “… hypothesized that during the haze period, the oxygen concentration per volume of air could be lowered.”

The article provides stoichiometric equations demonstrating the effects of lowered oxygen content.

I would say that if the air quality is bad enough to cause a GT to have a reduced power output, pity the lungs of biological machines.

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