Our world is moving faster and flow processes are not immune to this. Newer industrial communications protocols can deliver flow data from hundreds of flow meters in less than a second. This increased speed of data acquisition can improve your process, but the speed of your flow sensor can improve the data itself. In this post, we’ll take a look at two examples of how Alicat’s sensor speed can make your flow data better.
Fast flow totalization of transient flow events at oil and natural gas wells
When you need to know the total amount of a gas that has flowed, instead of just the live flow rate, the measurement speed of your flow meter becomes much more critical. If your gas or liquid is already flowing, a flow totalizer can start and stop a timed measurement to take a sample of the total amount flowed during that time period. However, when you need to know the entire amount that has flowed from start to finish, significant amounts of your data can be lost as your flow meter comes up to speed. One of the more striking examples of this came through a research application with the US Environmental Protection Agency (EPA).
Alicat was contacted by an EPA researcher who needed to quantify how much gas was being emitted by pneumatic controllers at oil and natural gas well pads. At these sites, the natural gas that is already present is typically used to drive these controllers, and when they actuate some of the natural gas escapes into the atmosphere. The challenge was that most of these controllers were intermittent pneumatic controllers whose actuation periods lasted just a few seconds. A previous study had used thermal mass flow meters to totalize these emissions. However, the 1-3 second response rate of these meters meant that a significant proportion of the flow data was lost as the thermal flow meter tried to catch up with the transient flow rate.
In order to preserve the greatest amount of flow data, the EPA turned to Alicat’s pressure-based laminar flow meters. These instruments measure flow rates 1000 times each second and have a pneumatic measurement response time of 5 ms. With these flow meters installed, the researcher was able to follow the precise curve of the pneumatic controller’s actuation, from its explosive opening to its sudden shutting. The response speed of the sensor itself recorded much more of the available data compared to the thermal flow meter, making these measurements more accurate and reliable. The Alicat flow meter’s sensor speed was able to improve the quality of the data that the researchers obtained. You can read the resulting paper published in Earth and Environmental Sciences.
Improving the temporal resolution of flow readings for environmental monitoring and beyond
Another example of the benefits of fast flow measurement comes from the realm of ambient air monitoring. The gas analyzers that measure the concentrations of greenhouse gases in the air we breathe must be periodically calibrated to ensure they are measuring these small concentrations accurately. To do this, air monitoring technicians use dynamic dilution calibrators to generate known concentrations of the gas that the analyzer is designed to measure. Because this process is dynamic, the mass flow controllers inside these dilution calibrators must also be calibrated on a regular basis.
As gas analyzers have become more sensitive, the dilution calibrators have added mass flow controllers with lower flow rates, typically 10-20 sccm at the lowest, in order to simulate smaller gas concentrations. In the past, a positive-displacement (PD) flow meter was commonly used to calibrate these mass flow controllers. This type of flow meter provides an averaged flow rate that is calculated by dividing the total amount flowed by the duration of the measurement, but the very low flow rates required hid some critical data. At a flow rate of 20 sccm, such a flow meter takes about 20 seconds to complete a single measurement (see this video). At 1 sccm (the lowest point in the required 20-point calibration), the measurement time is more than 6 minutes.
When a mass flow controller failed its calibration, there was no indication of what was happening to the flow rate during the long measurement, because the only recorded data came at the end of the measurement. Perhaps the flow controller was oscillating on a regular cycle, or perhaps it started out well and then got clogged. Sometimes, the fault was that the PD meter got stuck in the middle of its measurement, but there was no way to diagnose this scenario without continuously observing the meter.
Air monitoring technicians in these situations have turned to Alicat’s fast flow meters to make visible the data that was hidden from the other flow meter. Because an Alicat responds pneumatically to changes in flow rates within 5-10 ms, the technicians are able to diagnose the cause of a failed calibration. When data is captured in real time, recurring oscillations that come from an underperforming mass flow controller are easily distinguished from a clog in the flow path. Indeed, when an Alicat is connected to a positive-displacement flow meter, it can diagnose failures that result when the puck of the PD meter stutters in its cylinder or when the puck takes too long to accelerate to match the speed of the flow.
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