Part II of Greenhouse Gas Emissions Monitoring Using Thermal Mass Flow Meters
In my post Greenhouse gas emissions reporting regulations, I discussed the EPA’s GHG reporting mandate, which requires facilities emitting 25,000+ metric tons of CO2e each year to report GHG emissions. The new rules create a need to measure greenhouse gases. Here I explore the pros and cons of various mass flow measurement technologies, except for thermal flow meters, which will be discussed subsequently.
Coriolis flow meters provide a direct mass flow measurement based upon the fluid’s deflection force moving through a vibrating tube.
Advantages: very accurate with high turndown capabilities, independent of fluid properties
Disadvantages: costly to purchase and install, not suitable for larger pipe sizes
Differential Pressure flow meters calculate the flow by measuring the pressure drop over an obstruction inserted in the flow. Common types of differential pressure meters are Orifice Plates, Flow Nozzles, and Venturi Tubes.
Advantages: commonly accepted method of flow measurement
Disadvantages: limited turndown, poor low flow sensitivity, requires pressure and temperature measurement to get mass flow
Positive Displacement meters need fluid to displace components and measure volumetric flow mechanically.
Advantages: good accuracy
Disadvantages: because the meter has moving parts, must consider gas cleanliness, it requires pressure and temperature compensation
Turbine Flow meters measure volumetric flow based on fluid flowing past a free-spinning rotor, with each revolution corresponding to a specific volume of fluid.
Advantages: high turndown and accuracy
Disadvantages: because the meter has moving parts, the user must consider gas cleanliness. It also requires pressure and temperature compensation
Ultrasonic Flow meters measure the difference in pulses transit time that travels from a downstream transducer to the upstream transducer, compared to the upstream transducer’s time back to the downstream sensor.
Advantages: extremely accurate
Disadvantages: expensive, they require pressure and temperature measurement
Vortex Flowmeter, a bluff object or shedder bar, is placed in the flow path. As gas flows around this shedder bar, vortices are cyclically generated from opposite sides of the bar. The frequency of vortex generation is a function of the gas velocity.
Advantages: frequency of vortex shedding is independent of fluid composition
Disadvantages: requires pressure and temperature compensation, needs a minimum flow rate to generate vortices
As you can see, many of these common flow technologies have inherent challenges when measuring greenhouse gases. In part III of this series, we reveal how thermal mass flow meters excel in measuring greenhouse gas emissions.
To read the Sage Metering white paper in its entirety, visit “Greenhouse Gas Emissions Monitoring Using Thermal Mass Flow Meters.”