Technology Update in Geothermal Steamflow Measurement

Abstract

Increases in the cost of energy have encouraged users to be more accountable for losses. The first step in loss accounting is accurate measurement of the energy source. In the past the typical flowmeters used in the measurement of geothermal steam were Orifice Plate, Averaging Pitot and Venturi's. Inherent problems with these technologies and the need to retrofit flow meters into existing pope work have encouraged the investigation of more robust measurement techniques.

Flow meter design for geothermal steam applications needs to take into amount several factors.

There may be a significant amount of noncondensable gasses such as H2S, CO2, N, Ar, Hg, (vapor). These gases cause the measurement to deviate from the steam tables so the meter should have a method of correcting for the effect of those gasses.

In order to consider the contaminated steam as a homogenous fluid some form of mixing will be advantageous to ensure a stable and repeatable signal.

The meter must be able to handle the stress of extreme velocities, sometimes in excess of 60 m/s that can be expected in Geothermal Steam Applications.

As many new installations will be in existing pipe work the meter must be very tolerant of flow disturbances cause by adjacent elbows, valves and other pope fittings.

The meters performance on wet steam application should be understood and it should show good tolerance to dirty and corrosive fluids.

The meter should be accurate, repeatable and have a good turn down.