Steam Flow Measurement

Application
The application is the measurement of low-pressure steam flows. Such flows are measured and controlled for purposes such as controlling the temperature of vessels, the speed of steam turbines, and the heating of process fluids.



Background
Traditionally, orifice plates have measured steam flows. With that technique, users were faced with pressure drops, which cause energy loss and produce water droplets in low- pressure, saturated steam. These water droplets cause erosion of the internal metal surfaces such as valve seats, elbows, turbine blades, and even the orifice plate used to measure the flow. An additional problem is the limited range of orifice plates, typically a maximum of 10 to 1. More recently, other types, including shedding-vortex meters have been tried.

Problem
A GE customer had installed insertion, shedding-vortex meters in the 60 psig and 235 psig steam-supply system for a new operating unit. These meters were selected because of low-pressure drop. The installed meters, however, could not handle the high velocities encountered and performed poorly in measuring very low flows.

Advantages
The GE Steam Flowmeter system gives excellent measurements from zero flow through 70 fps. There is no pressure drop to cause droplet formation and energy loss. The insertion mechanisms allow transducer replacement and removal without disrupting plant operations.

Equipment
The customer was familiar with GE ultrasonic flowmeters in stack flows and asked if they could measure steam flow. Temperature and pressure inputs were fed into the steam flowmeter electronics so that the meter could calculate mass flow of the system. High-temperature, high-pressure transducers were used to withstand a large range of steam process conditions.

Installation
The installation includes three meters in a diagonal 45° configuration. Steam velocities range from 0 to 70 fps. Line sizes include one 10 in, two 12 in, and one 18 in line.