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INTRODUCTION

This Technical Report discusses the existing definitions of "wet gas flow" and provides suggested definitions for use. Common wet gas flowmetering terminologies, principles, and limitations of the available wet gas meter technologies are also discussed.

Wet gas flowmetering is an important flow measurand in many industries. If a relatively small volume of liquid is present in a gas it is generally said to be "wet." Wet gas flows are not new occurrences in industry (e.g., wet saturated steam flows have been produced since the industrial revolution) but it is only recently that attempts to meter wet gas flows (e.g., by the oil and gas industry) with improved and a perhaps better understood uncertainties have been made. Measurement techniques are being continuously developed but accepted single-phase (dry) gas meter uncertainty is as yet not attainable when a wet gas flow is present. Due to the difficulties involved in wet gas metering it is unlikely that the same level of uncertainty seen with single-phase gas metering will be achieved in the foreseeable future.

There are two distinct wet gas-metering situations:

(a) Where some flow rate knowledge is initially known, for example,

(1) the total mass flow rate is known (such as in a closed cycle system, e.g., a steam power cycle) and either the ratio of liquid-to-gas flow rates or one of the phase flow rates is required to be metered.

(2) one phase flow rate is known (from some other means) and the other phase flow rate is to be metered.

(b) No flow rate information is known (e.g., unprocessed wet natural gas flows) and either or both the liquid and gas phase flow rates are required to be metered. This is a considerably more difficult metering situation as extra information is required and meters being developed for this situation are considered to be at the cutting edge of fluid flowmetering technology.

NOTE: Most of the current technologies ignore the effects of multi-component liquids present in wet gas flows. However, some metering systems are designed to estimate the different quantities of liquid components in a wet gas flow.