Choosing the Right Sensing Tech for Power Generation: What Matters Most
The ability of hydrogen to conduct heat over seven times more effectively than air has made it a popular cooling medium in power generation. But the sector’s fascination with hydrogen has been going strong since the commissioning of the first hydrogen-cooled turbo generator by Dayton Power and Light in 1937.
Here’s the thing: as long as hydrogen stays in its purest form within the metal enclosure, cooling the generator windings, everything’s fine and dandy. The trouble arises when it leaks - something it can easily do, considering it’s about 14 times lighter than air. Hydrogen then starts accumulating in clouds, leading to potentially explosive situations.
So, how do we stop that from happening? How do we catch leaks so early that the risk is nipped in the bud? Well,that’s where hydrogen sensing comes into the picture.
In this article, we talk about the use of hydrogen in power generation and how the right sensing technology can enhance not just safety but also improve operational efficiency and save costs.
The Role of Hydrogen in Power Generation
Thanks to its superior thermal conductivity, hydrogen is widely used as a cooling medium in large power generators,typically over 120 MW in capacity. It absorbs heat from the generator and dissipates it while re-circulating through a compressor and dryer system. In the past, this job was done by air. However, hydrogen is 14 times lighter than air, meaning fans can move up to 14 times more hydrogen with the same power.
In other words, more fuel gets converted to electricity with hydrogen-cooled generators. When pitted against air-cooled generators of the same capacity, hydrogen-cooled ones fare better in efficiency, compactness, and cost-effectiveness.
In a power plant, hydrogen is supplied by trucks in the form of high-pressure cylinders or tube trailers. The transfer is either done by replacing empty cylinders with new ones or pumping hydrogen stored in tube trailers into empty high-pressure vessels. The replenishment activity is manual and has significant risks attached to it.
In some cases, hydrogen is produced on-site. This is relatively safer since the transfer happens through permanent piping, with fewer to no manual activities involved. It is still not fail-safe, as hydrogen is notorious for its ability to sneak out of joints and valves.
Building the Case for Hydrogen Detectors - Safety, Costs, and Efficiency
Hydrogen on its own doesn’t support combustion and only becomes flammable after coming into contact with air. It also has a wide explosive range, from as low as 4% to 75% in the air. Hydrogen’s minimum ignition energy is also lower than natural gas and can be set off by the tiniest spark.
There’s more. Hydrogen molecules are eight times smaller than methane, making it very easy for them to leak out of joints, shaft seals, and generator bearings. Add to that the manual process of refilling hydrogen and storingcylinders. What you have is a potentially hazardous situation that requires round-the-clock monitoring through highly selective and subsecond-responsive sensing.
In an ideal scenario, only the amount needed for cooling generator windings should be on site. But the sneaky nature of hydrogen and the high-pressure requirements associated with large-capacity generators results in frequent leakages. Anything from 5 to 25 Nm3/day of hydrogen is consumed at a power plant, depending on the capacity of the power generator.
A low-cost sensor placed optimally at the source and other vulnerable areas can reduce the amount of hydrogen loss, resulting in huge cost savings for the company.
The slightest reduction in purity below 99% can make hydrogen dramatically denser and less effective in drawing away the heat. Impurity increases friction in the rotating rotor, leading to more energy lost to heat than being used to generate electricity.
Depending on the generator capacity, these friction or windage losses can be anything from 600 to 3,650 MWhr/year for every drop in purity below 99%. A sensor that can track, measure and alert every time the purity slips below a certain level can increase power generation efficiency exponentially.
Hydrogen Sensing in a Power Plant - Various Types of Detectors To Choose From
It’s pretty clear that hydrogen sensing is an absolute necessity for safe and efficient power plant operations.But there are different types of hydrogen gas leak detectors to choose from depending on the application. Let’s take a look at what they are:
1.Ceiling Mounted LEL Detectors for Holistic Coverage
Traditional LEL (lower explosive limit) detectors may be based on catalytic combustion, catalytic pellistor, or semiconductor technology. In most power plants, you’ll find them mounted at the ceilings where they display LEL readings. In the case of hydrogen, LEL is 4%.
When the volume of H2 gas reaches 1%, the LEL display will show 25% and 100% when it reaches 4% level, which is an explosive scenario. Also, most LEL sensors don’t hold up well to high exposure. You’ll find them typically installed at the ceilings to improve overall room safety.
2.Fixed Detectors for Instantaneous Leak Detection At Source
Ceiling-mounted sensors can only monitor the accumulation of hydrogen at the ceiling. They cannot detect what’s happening below. The most surefire way to catch and contain a leak before it becomes a problem is to detect it at its source, such as the joint, manifolds, valve, and other areas prone to mechanical failures.
Sensing technology required for detection at source should be highly selective with no cross-interference or false alarms. It should also have rapid responsiveness and be able to withstand exposure to the highest concentrations of hydrogen.
The H2 Intellisense Slim Hydrogen Sensor is highly sensitive and selective to hydrogen and detects leaks with subsecond responsiveness. It continues to monitor with high accuracy even when exposed to the highest hydrogen concentration levels.
3.Portable Gas Leak Detectors to Pin Point Leakage Location
Hydrogen embrittles metal and can even escape from places without joints, manifolds, or connections. In a power plant context, this may translate to small leaks along the welded seams that could go undetected. This is where portable sensors come into play, helping pinpoint the precise location of the leak.
Besides accuracy, the sensor’s speed of response is especially important. An operator may need to check hundreds of points, which can be tedious. A sensor with a response time of 30-50 seconds would require an operator to spend a minute or more at each location.
In contrast, the H2 Intellisense Slim Portable Hydrogen Detector boasts a subsecond response time and zero cross-sensitivity, letting the operator know if there’s a leak in less than 2 seconds.
4.MEMS Nanochip Sensors Purity Measurement and Multi Gas Detection
Hydrogen’s purity directly affects the efficiency of a generator. Even a 1% drop in purity below 99% can trigger a huge drop in overall efficiency. Our ultra-miniaturized PlatfoMEMS Omni-Gas Chip sensors are designed to withstand the harshest conditions. They can be placed inside the generator chamber at multiple points for real-time purity measurement.
That’s not all. During maintenance activity, hydrogen is purged from generators with CO2, which in turn is purged with air to make it safe for personnel to enter. Our smart sensors can be programmed for multiple gas detection, letting operators know whether the mixture inside is 99% hydrogen or 99% CO2, or 100% air.
An arrangement as complex as a power plant comes with its unique safety challenges, all the more if the cooling medium used to cool generator windings is hydrogen - a highly flammable, leak-prone, and odorless gas.At 21Senses, we offer specialized solutions for power generation plants in the form of fixed and portable hydrogen leak sensors. Our sensors are responsive, accurate, selective, and tough enough to function smoothly at any level of overexposure. Reach out to us for any hydrogen sensing need, from leakage detection to purity measurement.