The Science of Sensor Placement For Power Plant Safety: What to Consider
Hydrogen is widely favored in the power generator sector as a heat transfer medium for large-capacity generators. A typical hydrogen-cooled generator of 150-250 MW uses about 1 to 3 cylinders worth of hydrogen every day. With such volumes of hydrogen present, keeping the workers and equipment safe becomes crucial.
Thankfully, modern sensors are becoming smaller, more accurate, and easier to operate. But no matter how high-quality a sensor is, it will not deliver its best performance unless positioned optimally.
In this article, we explore the hows and whys of sensor placement to keep a power plant efficient and incident-free.
Factors to Consider for Ideal Sensor Deployment
Detecting an elusive gas like hydrogen is no easy task. And how quickly and effectively a sensor detects a leak boils down to how selective and responsive it is and where it is installed. Here are some important factors to keep in mind for optimal sensor deployment.
1. Characteristics of Target Gas
Perhaps the first thing you should consider while placing the sensors is the leak behavior of the target gas. Hydrogen is the lightest known element on the planet and is hard to detect. It’s odorless, colorless, and has a wide explosive range extending from 4% to 75% in air. When H2 leaks, it travels up and collects as flammable pockets at the top of the room. Given H2’s extremely low ignition energy, something as small as an electrostatic spark from a human can set off these gas pockets.
2. Small Form Factor and Subsecond Responsiveness
A miniaturized size such as that of our Solid State Electrochemical Sensor allows it to be set up in any hard-to-reach spot. The H2 IntelliSense Slim measures only 5cm in height vs. a typical 22cm tall sensor in the market. It takes lesser time for the leaked gas to arrive on its surface, enabling a faster and subsecond response time compared to the bigger-sized hydrogen gas leak detectors.
3. Close Proximity to Source
A facility as complexly engineered as a power plant requires detection not just at the ceiling but also at generator inlets, stator dome, and vacuum seal oil tank. The sensor should be able to function even when exposed to high concentrations of hydrogen. While most sensors fail beyond 4% Lower Explosive Limit (LEL), both our H2 IntelliSense Slim Hydrogen Sensor and PlatfoMEMS Omni-Gas Chipcontinue to work flawlessly even in 100% hydrogen concentration.
4. Multi-Gas Sensing Capabilities
During the maintenance activity, the hydrogen inside the casing is purged completely with CO2. The CO2 is then purged with Air to make it 100% safe for operators to access all parts of the power generator. The presence of CO2 or H2 during maintenance can cause serious repercussions to the worker’s health. A multi-gas sensor such as PlatfoMEMS Omni-Gas Chip should be placed inside the chamber to monitor the purging procedure. The sensor can be programmed to tell with precision the level of H2 in Air or H2 in CO2 or Air in CO2 inside.
5. Reliable Detection with No False Alarms
An accurate sensing system should not only be able to avert potentially explosive situations but also detect minor leaks. While not as risky, these small leaks cause significant H2 loss through continuous outgassing. Reliable detection also reduces the risk of false alarms, that can cost the company in terms of lost revenue, time, and damage to equipment from production shutdown.
Our H2 IntelliSense Slim sensors are selective and specific to hydrogen alone, with no cross-sensitivity to other combustible and reducing gases. In other words, there’s no risk of false alarms, and every release, no matter how small or big, is caught early, saving companies millions of dollars in H2 refilling.
Conventional Placement vs Robust Placement Approach - Bridging the Gap
While most power companies have started prioritizing procuring good quality hydrogen sensors, the deployment is far from desirable. Mounting a couple of sensors at the ceiling alongside one or two other vulnerable areas like storage sheds and filling stations has become the conventional way. However, such deployment would provide basic coverage.
Securing the entire site, protecting personnel and property, and reducing unplanned downtime requires continuous and accurate hydrogen sensing at all vulnerable areas.
In our robust placement approach, we recommend installing hydrogen-selective sensors at key locations like ceiling and storage rooms, as well as overlooked but risky places where leakages usually go undetected. Let’s go over these locations one by one.
1. Generator Inlets:
Fixed detectors detect with the fastest response time and accuracy when placed right above the flanges on the hydrogen supply side of the generator as well as around the rotor’s seal-bearing system.
2. Storage Sheds:
Whether the hydrogen supplied to the generator is supplied or generated, a certain amount of stored H2 is usually kept on site for refilling. When there’s a leak, H2 travels upwards and gathers at the ceiling. We recommend installing sensors on each beam that supports the roof to minimize the chances of hydrogen and air mixing.
3. Hydrogen Filling Stations:
In order to secure an on-site hydrogen filling station, it’s essential to place an appropriate number of sensors near the ceiling. This will help catch leaks from joints, allowing operators enough time to take remedial action. Another location for speedy detection would be immediately above the cylinders that supply hydrogen to the generator.
4. RYB Copper Bus Bar:
A potential leak location but often overlooked from a sensor deployment perspective is the RYB busbars that carry the current from the generator. There’s always the threat of hydrogen collecting near the adaptor box in case of leakage, making it the ideal spot for sensor placement.
5. Dryer Unit:
A dryer unit is used for continuously removing moisture from recirculated hydrogen, making it a key spot for sensor placement. We recommend installing the sensor above the connecting joints in the dryer to prevent leaks.
6. Vacuum Seal Oil Tank:
Sensors aren’t just required to detect hydrogen escaping outside but also to keep a watch on internal leakages. Hydrogen escaping from the vacuum seal oil tank means that it has already leaked internally into the oil tier. A robust detector that can withstand extremely high concentrations of hydrogen should be placed here to trigger alerts in the event of a leak.
7. H2, CO2, Air Exchange Skid:Continuous monitoring is also required above connecting joints in the gas exchange skid.
8. Stator Water Dome: While the generator’s rotor and core are cooled by hydrogen, its stator windings are water-cooled. A sensor is needed to continuously monitor and alert if hydrogen accidentally leaks into the water cooling tier. Only sensors that can sustain exposure to high hydrogen concentrations and high moisture conditions should be placed in the stator water dome.
9. Purity Monitoring Connection:
If the hydrogen in the casing gets contaminated by even 1% of air, the density of the coolant increases dramatically and results in significant windage losses. A purity analyzer continuously samples hydrogen to ensure it’s at the desired purity level. We recommend placing a miniaturized sensor such as our PlatfoMEMS Omni-Gas Chip at the purity system’s connection to alert whenever hydrogen flowing in and out of the monitoring system starts leaking at the joints.
10. Air Vent Pipe Near the Rooftop:
A hydrogen-cooled power generator also has water cooling and air cooling tiers. A sensor is needed to detect when hydrogen leaks internally in any of these tiers. If a leak happens in the air cooling layer, a detector placed at the air vent pipe near the rooftop will instantly sense the presence of H2 in the air stream and trigger an alert.
11. Portable Hydrogen Leak Locator:
Hydrogen is known to cause embrittlement and can escape even through the smallest pores in welded seams. A portable hydrogen leak detector such as the H2 Intellisense Slim Portable Hydrogen Detector detects with a subsecond response time to identify the precise leak points. Its rugged enclosure allows it to be taken as close to the leak source as the operator wants without the fear of damage.
Conventional vs. Robust Placement - Which Approach Would You Choose?
Power plants are large, sprawling sites with numerous potential leak points that need continuous monitoring. But the way the sensors are currently deployed is not enough and requires a makeover. This is where we step in.
The 21Senses sensors are designed to detect leaks and monitor H2 purity with high specificity and sensitivity under the harshest conditions. Our proprietary technology and industry expertise allow us to offer a highly cost-competitive and scalable sensing solution. Reach out to us to learn more about our solutions and how we help our clients secure their sites through a robust placement approach.