Validation of Primary Water Dew-Point Generator for Methane at Pressures up to 6 MPa

Abstract

In this paper, the validation of the water dew-point generator with methane as a carrier gas in the temperature range from \(-41\,^{\circ }\hbox {C}\) to \(+15\,^{\circ }\hbox {C}\) and at pressures up to 6 MPa is reported. During the validation, the generator was used with both nitrogen and methane to investigate the effect of methane on the generator and the chilled mirror dew-point meters. The effect of changing the flow rate and the dew-point temperature of the gas entering the generator, on the gas exiting the generator was investigated. As expected, methane at high pressures created hydrates in combination with water and low temperatures, thus limiting the temperature range of the generator to \(+8\,^{\circ }\hbox {C}\) to \(+15\,^{\circ }\hbox {C}\) at its maximum operating pressure of 6 MPa. A lower operating pressure extended the temperature range; for example, at 3 MPa, the temperature range was already extended down to \(-15\,^{\circ }\hbox {C}\), and at 1 MPa, the range was extended down to \(-41\,^{\circ }\hbox {C}\). The validation showed that, in its operating range, the generator can achieve with methane the same standard uncertainty of \(0.02\,^{\circ }\hbox {C}\) frost/dew point already demonstrated for nitrogen and air carrier gases.