Salt is one of the most troublesome contaminants for gas turbine operators. In the offshore/coastal environment or indeed anywhere close to bodies of saltwater, corrosion of turbines can be swift and severe if airborne salts are not adequately understood and properly filtered. Salt removal is one of the areas that needs to be understood and defined.
The enormous amount of air a gas turbine consumes means even the smallest percentage of salt can have serious consequences. Over time, advanced filtration systems have moved from offering 95% salt removal efficiency to today, greater than 99.9%. This 5% difference seems small but is very significant in terms of the reliability and performance of the turbine.
Salt is perilous to gas turbines for two main reasons;
To rub further salt into the wounds, the hygroscopic/sticky nature (has an affinity for water and absorbs moisture from the surrounding air) of salt when in moisture-rich environments means it easily adheres to the compressor and turbine blades; increasing the rate at which contaminants build up on the surfaces and so more quickly impacting the aerodynamic performance of the turbine and its overall thermal efficiency. Below 40% relative humidity (RH), salt appears in dry form. Above 75% RH, it is in a liquid form. In between these states, salt exists in a particularly problematic, damaging wet and sticky form.A bit of history on measurement
How much salt is in the air was defined by the National Gas Turbine Establishment (NGTE) 30 knot aerosol standard back in the 1970s? Based on the amount of salt present in a series of air samples collected by the UK Royal Navy in the North Atlantic, this figure was set at 3.6 ppm (parts per million). Unfortunately, 3.6 ppm is very high and not a realistic appraisal of the true offshore environment. This was recognised by the NGTE at the time and was only ever meant to be an interim measure until more detailed test information became available. Less salt in the air is of course a good thing, however, it is also key that GT operators have a realistic view of how much salt is in the air in order that they may correctly specify filtration systems that limit the amount reaching the inside of the machine. This anomaly prompted Parker Hannifin, to carry out an ASME paper research project back in 2004, resulting in a new ppm figure for ambient air salt concentration and size distribution in the marine environment. This revised figure, now known as the McGuigan Marine Boundary Layer (MMBL), provides a conservative, realistic figure for the average salt levels in the lower marine boundary layer (MBL) throughout the world. Still a realistic measure today, it puts the salt level at 0.1067 ppm.
Each percentage point counts
The more contaminants that are allowed through to the turbine, the quicker its aerodynamic efficiency will reduce and the greater the risk of damage to the machine. Ultimately this reduction in performance will result in reduced power output, lower system availability and reliability, and higher maintenance costs.
Unlike contaminants that cause compressor fouling (and can be cleaned away by water washing), one of the major problems with salt corrosion is that its effects are often not perceived in turbine performance data until something actually breaks. Unscheduled maintenance can be significant but, in many mechanical drive applications, the cost of lost productivity can also be huge.
If a turbine consumes 350,000 kg of air per hour (typical 30MW GT) and there is 0.1607 ppm of salt by weight in the air to start with (1ppm(w) = 1mg/kg), this equates to an unfiltered gas turbine exposure of nearly 300 kg of salt per year for an 8000hr operating year!. This means each 0.1% improvement in filtration efficiency protects the turbine from an extra 0.3 kg of salt exposure per year.
Designing a filter for salt removal
Salt can exist in a solid, a liquid or a sticky in-between state. Changes in relative humidity affect the state of solidity of the salt. As a liquid salt droplet is transformed through drying to a solid particle, it will also contract to about 25% of its original size. To handle salt effectively, a filtration solution needs to allow for input concentration, aerosol size distribution and aerosol physical state; whether droplet, dry particle or any in-between/sticky state.
A filter system also needs to provide this protection without getting easily blocked itself. The right solution for a given application therefore also has to consider the impact of increased pressure drop from multiple filtration stages with the Gas Turbine salt protection needs and must be designed to handle and remove both salt phases in order to properly protect the turbine. Dust filters will capture solid dry salt particles. Liquid removal stages and hydrophobic filters prevent salt from attacking the turbine internals in liquid form.
One of the vital elements in handling salt corrosion in offshore and coastal environments is to effectively handle the moisture in the air. Filter media with high dry particulate efficiency ratings may not necessarily be effective at handling liquid droplets. Coalescers can manage free moisture and salt in liquid form (brine) by agglomerating droplets to make them larger and heavier so they will fall out of the airstream. Although traditionally associated with large maintenance overheads, coalescers are now available that will run for extended periods without sudden pressure spikes and in configurations that can be easily cleaned with a water or air hose.
Dry salt particles can be dealt with by high efficiency (HEPA/EPA) filters but care needs to be taken with media selection to ensure these filters are not quickly blocked by moisture or sticky salt particles. Tests in real-world applications have shown that thicker glass fibre media is less prone to blockage in such environments than ePTFE membranes, which are 10 times thinner. Glass fibre media with effective hydrophobic coatings have been shown to prevent virtually all liquid salt and/or sticky salt particles from entering the turbine.
How offshore installations are different
For an offshore oil and gas installation, a multi-stage filtration system is required to handle the various, harsh environmental challenges faced. As space offshore is at a premium, it often makes sense to install a more compact, high velocity filter system with a multi-stage Vane Coalescer Vane (VCV) salt removal system. Stage one is an inertial vane separator that removes bulk water including rain, sea spray and coarse aerosols. This is followed by a coalescer that coalesces fine salt aerosols into larger droplets (>20 µm). This stage also captures fine dust and dry salt. The final inertial vane separator stage stops and removes the re-entrained larger salt droplets.
A traditional M6 (EN779) VCV inlet filtration system is a popular choice for offshore turbines and offers excellent wet salt and bulk water removal capability. However, at high air velocities (as the units are designed to be compact) these systems are typically limited to an F7 (EN779) dry particulate removal efficiency rating. If the environment is considered dusty then this configuration can have a limited filter life, produce high operating pressure losses and have reduced effectiveness against dry salts. As well as a need to replace filters on a regular basis, maintenance of the drain system on these units is also critical to operation, so overheads can be higher than desired. These VCV systems are therefore typically employed when salt is the main concern rather than a combination of salt and high dust levels.
To address issues that result from a combination of high concentrations of salt as well as high concentrations of dust, the latest high-velocity filtration systems are designed with extra filtration stages that provide very high small particulate removal efficiency with hydrophobic properties; meaning they prevent liquid penetration while still capturing fine (< 3µm) dust and dry salt particles. These F8 (EN779) to H13 (EN1822) rated high-velocity filters can also be configured with deeper glass fibre filtration cells (24” deep) which means that although turbine inlet air velocity is high, the air velocity at the media is similar to low and medium velocity systems. This increases filtration efficiency and reduces pressure loss across the system. The thicker filter media has the added benefit of being less prone to blockage than thinner, high-efficiency alternatives.
Testing salt efficiency removal
Ultimately, whatever the ppm of salt in the air inlet, the more that is removed the better the turbine is protected from deteriorating performance and catastrophic failure. However, salt leaching rates are not covered in standard efficiency tests (EN779, ASHRAE 52.2, EN1822, JIS Z8122). The only real test of the effectiveness of an inlet filtration system is the performance of the turbine over time in the variety of environmental conditions it faces. To simulate the real world, Parker (CLARCOR) created a hydrophobic salt test protocol to help determine salt removal efficiency and in order to correctly and realistically evaluate new filter system designs when they are subject to variations in salt concentration, dust concentration and relative humidity. Specifically designed to test for phenomena such as salt leaching, the test takes the filter through a total of nine wet/dry cycles in a ten-day testing protocol.
The test requires that the filter(s) are clamped and installed as they would be on site. This ensures that the seal and clamping system are not weak points in the unit where liquid and contaminants can bypass the filtering media itself. Salt is first introduced into the test as an aerosol. Repeated tests are then completed (10 days’ worth) when the filter is loaded with dust. This adds back pressure to the system while the dust coats the fibres within the media as it gets captured, simulating real-world particulate build up. This combination of salt aerosol and loaded filter is very important to analyze as captured dust often acts as an alternative flow path for wet salt transfer downstream, in effect acting as a shortcut for wet salt transmittal downstream, bypassing the media!
Testing a filter system in this way provides comprehensive data about performance over time including the amount of water and salt that passes through the filter during various test stages and highlights any pressure loss increase that occurs. There are two widely used filter tests with accepted ratings used in the filtration industry – the EN779 standard and the EN1822 standard. The EN779 test standard has a set of criteria that a filter must meet to achieve a certain rating. Depending on the filter, a rating of G1-G4, M5-M6 or F7-F9 will be given. The higher the rating, the more effective (typically) the filter. The EN1822 standard is used to test higher efficiency filters, in the EPA/HEPA range, and produces a ratings scale of E10-E12, and H13-H17. When the multi-stage hydrophobic high-velocity system was tested against this salt test protocol, it showed salt removal efficiency to be improved by a factor of 10,000 compared with traditional M6 (EN779) units, giving an E11 (EN1822) efficiency rating with similar pressure loss to a standard M6 (EN779) efficiency system. Such units have also been proven to reduce the frequency of offline turbine water washes by up to a factor of 6 (from around four weeks to six months) without creating sudden pressure spikes.
No single filtration solution is right for all installations
Understanding the nature and impact of salt is a vital consideration in designing a filtration system for use in offshore or coastal environments. Systems need to be tested and evaluated for their performance in handling wet, dry and sticky salt to protect turbines from serious damage without sudden pressure spikes. If filters are selected solely on efficiency rating, operators may be left with systems that are difficult to maintain and, although higher rated, may not protect assets as well as lower efficiency solutions. With a careful assessment of conditions and selection of filter configuration, modern filtration solutions have been shown to virtually negate corrosion of turbine blades over 20,000 fired hours in real-world conditions.
About Parker Gas Turbine Filtration Division
Parker Hannifin supplies a full range of inlet systems and filters engineered to meet your operating goals, including:
We are the choice for advanced filtration for new units and replacement filters. Our inlet system designs include self-cleaning (pulse) and static inlet systems for all gas turbine OEMs. We supply a full range of filter types at all efficiency levels. The predictable and reliable performance of our air filters significantly reduces compressor contamination and the need for unplanned maintenance.
This article was contributed by Peter McGuigan, global LNG market manager, Parker Gas Turbine Filtration Division. It was originally published in Gas Turbine World, September 2017.
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27 Aug 2021
Floating liquefied natural gas (FLNG) vessels are processing facilities that float above offshore gas fields. They treat and process natural gas using marine versions of the same technologies found on a land-based LNG plant -- only much more compact – floating LNGs are approximately 1/4 the size for the same LNG output. They offer operators the ability to process gas at or very close to the source field. The value of FLNGs is that they can tap into smaller and more remote fields. When a resource is exhausted, they can be unmoored and reconfigured for a new feed gas composition range and/or consumer non methane component specification and can be moved to another location to continue operations.
Offshore operation underscores the importance of maintaining the reliability of equipment on these vessels for extended periods. Operational shutdown of a key piece of equipment, such as a gas turbine (GT), can cost millions of dollars per day in lost production. Limited personnel and access to spare parts could mean further delays. Continue reading to learn more about the benefits and challenges of FNLGs as well as recommendations to ensure dependable GT operation.
The benefits of operating and processing gas offshore, at source, using a nonpermanent structure are clear.
Space is the biggest challenge facing FLNG engineers. LNG production requires a large amount of specialized equipment, including pretreatment systems, gas turbines, compressors, expanders, head exchangers, etc. Storage space for the LNG in its super cooled stage and natural gas liquids (NGLs) is also necessary. On top of that, all the systems and facilities needed for the ship and crew must be considered.
In contrast to land-based sites where designs may be considered as field proven, layout optimizations, design experiences, and engineering best practices with regards to implementing FLNG production are still relatively new and are evolving. To date, only a handful of FLNG production vessels have been commissioned - Petronas’ FLNG Satu and Dua, Golar’s Hilli Episeyo, Exmar’s Tango FLNG, and Shell’s Prelude. Projects currently under construction include Golar’s Gimi and ENl’s Coral South.
The importance of maintaining equipment
The refrigerant compressors hold the key to maximizing production. In most cases, refrigerant compressors are mechanically driven (rotated) by gas turbines. That said, the reliability of the GT becomes equally critical to production. Aeroderivative GTs are preferred as refrigerant compressor drivers over frame engines because they are smaller and lighter and have components that are quick and easy to interchange, making maintenance easier. They are also designed to offer high reliability, and can be quickly ramped up and down, allowing for any forced interruptions caused by adverse weather conditions to not have a prolonged effect on
Gas turbine air intake system
One key piece of GT equipment is the GT combustion air intake system. GTs take in huge amounts of air as part of their combustion process. Air that is left untreated contains several destructive contaminants, which can cause serious damage, erosion, corrosion, and fouling of the precision engineered GT internals. The harsh weather conditions found in offshore environments are particularly brutal on any piece of equipment, let alone one that needs to run continuously.
Gas turbine filtration requirements
Issues relating to the ingestion of ambient air particulate, salts and hydrocarbons account
for 60 - 80% of overall gas turbine losses. Controlling these contaminants with the right air intake filtration is a huge step in assuring reliable plant operations and maximizing LNG output for extended intervals.
Salt is particularly damaging to the GTs on FLNGs because there is such a large quantity of it churned up from the sea. While the filterhouse and internals are typically manufactured from 304 or 316 grade stainless steel, sodium from sea salt (NaCl), if allowed to get downstream of the filters, will combine with sulfur in the fuel to create sodium sulfate (Na2SO4). This chemical reacts with the base metal of the turbine blades in the high temperatures of the hot gas path, causing rapid corrosion and component failures. This is a common effect known as hot corrosion or sulfidation. Chlorine in the salt also acts as a pitting corrosion initiator in colder parts of the turbine, potentially leading to catastrophic damage.
Because of its hygroscopic nature, salt can be difficult to control. It readily absorbs water and can easily move from solid to liquid form with changes in ambient relative humidity.
Filtration recommendations to defend against salt contamination:
Sand and dust
Sand and dust can cause numerous issues for an installation in terms of both damage to machinery and degradation of turbine performance. Large dust particles greater than 2μm in size can cause erosion and affect turbine efficiency. If the erosion causes parts in the front end of the equipment to fail, contaminants may travel through and cause severe machine damage.
Finer dust can stick to parts of the machine and change the operating aerodynamics. This, in turn, reduces turbine efficiency, requires online and eventually offline water washing, reduces availability, and increases operational costs. Moisture in the inlet air stream can combine with dust to form mud which can block a filter.
Filtration best practices for sand and dust:
Turbine air inlet filtration system design considerations
There are several factors that should be considered in the design of an FLNG turbine air inlet system:
To ensure profitability, the reliability of the systems used to liquefy gas onboard an FLNG vessel is critical and, although GT filtration systems may seem like a smaller part of the overall puzzle, they are vital to ensuring ongoing smooth operations. GT air intake systems need to be designed for the real-world environment in which they will be used.
They must also be able to effectively and efficiently handle a diverse range of seasonally varying contaminants such as salt, dust, oily hydrocarbons, and moisture. For FLNG vessels, it is essential that these systems are physically compact and flexible enough to allow operators to easily change filter types depending on location. Designing GT air intake solutions for the offshore environment requires a thorough understanding of the very specific challenges such systems will face, but when undertaken correctly offers operators a rapid return on investment.
This post was contributed by Pete McGuigan, global LNG market manager, Parker Gas Turbine Filtration Division, Parker Hannifin Ltd, UK.
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27 Aug 2021
Pleasure craft owners and commercial ship staff rely on watermakers for their supply of purified water for drinking and process applications. Watermakers remove salt and contaminants from sea and brackish water. They offer a continuous supply and a cost-effective alternative to other sources of water.
Are you thinking about purchasing a Parker watermaker or do you have questions about how they are installed and maintained? To help, we've compiled a list of our most frequently asked questions.
Parker watermakers reduce the time, physical effort and concern related to assuring a continuous supply of fresh water on your vessel. Installation and maintenance are easy and require little time, leaving users more time for other activities while aboard. Parker products are backed by a dedicated, highly trained support team and over 350 sales and service dealers worldwide.
This article was contributed by Paul Kamel, product manager II, Parker Bioscience and Water Filtration.
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19 Aug 2021
If semiconductor manufacturers had any question about the complexity of their industry ecosystem, COVID-19 eliminated that doubt.
Riding a wave of growing demand for semiconductors, buoyed in part by a 5.4% increase in 2020 sales attributed to stay-in-place home electronics orders and surprised by a boom in early 2021 automotive sales, the semiconductor industry found itself in the midst of production shortage.
While chipmaking capacity has kept pace with sales for the most part, consolidation of advanced manufacturing players has created scarcity in the market. The scarcity was enough for automotive manufacturers to halt production.
Things only worsened when the industry discovered a growing shortage of raw materials essential to component manufacturing. That shortage has spread to multiple sectors, leaving original equipment manufacturers to deal with pricing volatility, extended lead times and stock-outs in the near future.
The semiconductor industry is not alone
Many semiconductor and semiconductor tool companies lessen supply chain disruption with a dual-sourcing plan, a strategy that paid off during the pandemic.
But the semiconductor industry is hardly the only industry to deal with disruption. Nearly 94% of Fortune 1000 companies are dealing with supply chain disruptions due to the pandemic, according to a recent Accenture research study.
Supply chain disruption can extend delivery times and build product backlogs that can turn into customer concerns. Demand, disruption and innovation trickles down, as well. And nowhere is that clearer than in the ultrapure water industry.Demand for ultrapure water is growing
Ultrapure water consumption in the semiconductor industry is higher than any other industry, and technological advances in clean room and wafer manufacturing have created the need for even higher-grade ultrapure water.
While this is a boon for the ultrapure water industry – projections call for an $11 billion overall industry appraisal by 2026 – it is a bit of conundrum for manufacturers.
First, ultrapure water has become more expensive. Some estimates suggest that for every dollar’s worth of water purchased, it costs $20 to make it ultrapure and another $10 to properly manage wastewater disposal. Increased water usage can impact local communities and farms, and when water levels dip too low, there’s an environmental cost to wildlife habitats, as well.
There are other environmental concerns, as well. Most notably, the impact global fabs have on local watersheds and consumption. For example, the work of one Stanford University student shows that industry fab feedwater use was comparable to overall regional water use in China. That, along with long-term arid climate forecasts, could prolong – or excerabate – an already growing industry water shortage.
To mitigate both challenges, semiconductor manufacturing plants are exploring ways to reduce, reuse and recycle the ultrapure water they use during the high technology manufacturing process. But those efforts are just as challenging.
Water applications in microelectronics and chemical purity for semiconductor manufacturing
As chip technology advances, it becomes critical that the silicon wafer surface be as clean and clear of debris as possible to prevent damage and maximize yield.
This gets tricky on the nanometer level since there are more and more chances for contaminants to strike the wafer surface. Semiconductor innovation relies heavily on advanced materials research now to maintain the trend of achieving more computing power in smaller footprints. With an increase in chip yield per wafer, any defect could create a level of chip scrapping larger than years past, when fewer chips were housed on smaller wafers.
To eliminate the possibility, manufacturers must further reduce the level of contaminants in the water to avoid defects as small as 2 nm. In some instances, eliminating contamination associated with liquids has become more important than that from gases and cleanroom air.
Tackling the challenges of ultrapure water reclamation
A big challenge for semiconductor manufacturers is what to do with spent ultrapure water. Contaminated rinse water usually winds up in a manufacturer’s industrial waste treatment system and cannot be reused because of added contamination.
Overall, reclaiming spent ultrapure water for semiconductor fabrication is almost unheard of, though some methods to reclaim and deionize contaminated ultrapure water for semiconductor use are being tested. That hasn’t stopped some industries from recycling water for other purposes, including chemical aspirators, cooling towers and point-of-use abatement systems.
But the cost of acquiring ultrapure water combined with wastewater systems management is becoming a financial burden for many manufacturers and may encourage further study into effective reclamation and recycling technology.
In the meantime, an effective water management solution that handles the quality and quantity of supply water, treats wastewater discharge properly and secures industrial water for effective recycling is paramount for semiconductor companies, according to SK hynix.
Mitigating supply shortages
Supply chain disruptions also are impacting the rather straightforward creation of ultrapure water. How so?
During the purification process, or pretreatment, water is carried through a water filter, clearing it of most contaminants, and then deionized through either ion exchange or electrodeionization.
But polymer raw material shortages – especially polyethylene (PE), polypropylene (PP), and monoethylene (MEG) – are causing factory shutdowns, price increases and production delays across multiple industries, according to Harvard Business Review. Almost universally, the filters critical to the purification of ultrapure water are built with these polymers, which means extended lead times both in component and semiconductor manufacturing.
This is where a dual-sourcing strategy like the one employed by Parker can pay dividends. Dual-sourcing, or multi-sourcing, is a risk-management strategy in which an organization uses two or more suppliers to acquire certain components, raw material, products and services.
For example, when a major diversified chip manufacturer’s original filter supplier unexpectedly extended lead times and couldn’t deliver those critical components within the promised time frame, Parker was able to supply those filters in less than half the lead time.Investigating fluid impurities
Semiconductor manufacturers also are combating wafer defects caused by process and fluid impurities. Often, filter leaching is the culprit – or what the defects are attributed to. The right vendor can help deduce the issue through expert technical assistance.
That was the case when one major chip manufacturer discovered a correlation between its wafer yield and the improved resolution of metals extractables measurement in their process water. The fluid transfer components, including Parker’s Clariflow filter line, could also be a source of added contamination that was not previously detected. To identify root cause, the manufacturer reached out to Parker, who then recommended a technical team further investigate to ensure the problem had been properly identified. Parker’s Technical Counsel provides field and lab service for customer application troubleshooting. They conduct fluid and filter analysis into the parts per trillion range.
After a thorough investigation, including a best-practices review with some of the customer’s peer manufacturers, the Parker team concluded the very nature of the filter’s construction materials, polypropylene and polyethersulfone membrane, tend to leach trace metals over time regardless of how the final filter product is manufactured or flushed.
Recognizing the material, rather than the construction, was the root cause, Parker encouraged the customer to consider its all-fluoropolymer filter product, Fluoroflow. Testing confirmed improved fluid purity and extended on-stream life. This, in turn, increased wafer yield through decreased defects, reduced equipment downtime, and more than $100,000 in annual filter spend.
Parker solutions for the semiconductor industry
Regardless of supply chain disruption and wastewater reclaimation efforts, the demand for ultrapure water in the semiconductor fabrication process will only grow. Through strategic dual-sourcing and unparalled industry expertise, Parker helps manufacturers meet demand with high-purity filtration solutions that enhance processes and meet ultrapure water needs.
Polypropylene filters, like the Parker Clariflow and Polyflow, are designed for general-purpose use in the filtration of high-purity liquids and aqueous chemicals. Our fluoropolymer product, Flouroflow, is designed for general-purpose use in the filtration of high-purity liquids and aqueous chemicals.
To learn more, download our white paper on semiconductor trends.
Article contributed by the Parker Filtration Team with our Bioscience Filtration Division.
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18 Aug 2021
A lot has changed in the transportation industry since the introduction of fuel and its use in internal combustion engines in the late 19th century. As environmental concerns have driven more stringent emissions regulations over the years, today’s diesel fuel needs to be cleaner than ever to protect critical engine components. This has led to the wide use of water-fuel separation filtration technologies in engine designs. Fuel filter water separators are typically used to remove contaminants in the form of water droplets and solid particles from the fuel before it enters the engine.
In a fuel-water separator, the separated water falls to the lower bowl of the filter assembly — the water bowl — and is drained at regular intervals. If the water isn’t drained effectively, it can be re-entrained with the fuel causing significant damage to the engine and its performance.
In this blog, we outline a case study of simulation models used to construct design tools that contribute to creating a good first prototype design for water bowls and drainage in water-fuel filters for combustion engines.
A fine line between simple and complex
While this drainage mechanism in a fuel-water separator seems simple, the design is quite complex primarily due to three factors:
To best and most efficiently understand these factors, high-fidelity numerical simulations can be used. These simulations will lower the reliance on and requirement for experimental testing. They can be used to understand the physics of water drainage from inside a filter’s water bowl. Further, an analytical solution can be formulated to provide a design engineer with a very good first approximation of the most effective physical attributes that will assure proper water collection and drainage.
How it works
When water droplets are separated from fuel by a fuel-water separator, they coalesce and grow larger and heavier. Gravity causes the water droplets to settle and collect down as clean fuel is pulled in the opposite direction. The example shown below is our Fuel Filter / Water Separator – Racor GreenMAX™ Series.
The collected water is drained regularly to assure that it does not re-contaminate the cleaned fuel. If the water collected in the water bowl does not drain due to clogging or other malfunction, the separated water will re-contaminate the cleaned fuel and the performance of the fuel-water separator will dramatically diminish.
An increase in water content in the fuel supplied to the engine can:
An analytical solution – case study
Parker Hannifin specializes in fuel-water separator solutions for a variety of applications from marine to gasoline engines. Parker’s engineers found that given the varied geometries and materials used in their solutions, a simplistic physics-based tool to understand critical design features that prevent effective drainage of water from the water bowl is beneficial. The purpose of a study using this tool will provide initial design guidelines to a design- engineer even before a prototype is made for testing.
Computational fluid dynamic model (CFD)
From the base geometry of the water bowl, the internal fluid volume was extracted. Key geometric variables were refined, and the internal volume extraction was automated so that several different geometric variations could be simulated in the design space. The extracted internal volume was discretized for computational fluid dynamics (CFD) using unstructured polyhedral elements with finer resolutions where water curvature is of significance (for example, when geometry gaps are small). The cell aspect ratios and skewness factors were the key quality factors monitored to estimate meshing quality. Multiple levels of refinement were considered, and results were monitored.
The workflow used for the analysis is shown below.
A 3D transient, multiphase (volume-of-fluid) method was used to model the two-phase flow. To introduce water drops in the fuel domain, periodically, drops of specified volume were introduced into the water bowl. The estimate of water sizes came from experimental observations. The contact angle for water-fuel-surface interface was also specified from experimental measurements for all the different surfaces with which the water comes in contact.
In this application, the interface curvature was very critical, therefore a continuum surface stress (CSS) model was chosen to model the surface tension force.
The local pressure drop at key geometry points was monitored to indicate the event of water clogging the water bowl. The simulation was run for a pre-set time and the pressure and movement of water drops were observed to see if the clogging event was registered.
From the CFD analysis, key geometric features that result in clogging were identified. Analysis of these results paved the way to develop physics-based analytical expressions to predict obstruction of water in a water bowl design. Using the guideline of the analytical expression, experimental testing was performed on some known water bowl designs. The comparison between the analytical expression, CFD results and the experimental observation is shown below. The plot shows that the CFD observations of water buildup with respect to critical geometric gap as well as the experimental observations are within ± 5% of the analytical expression derived. This validates our physical understanding derived from the CFD analysis as well as the analytical expression simplified for this problem.
Equipped with this knowledge, Parker engineers created a simplistic design guide. This is highly valuable to a design engineer as it avoids time consuming CFD and/or experimental prototype analysis and provides a direct pathway to constructing a good first prototype. A sample design guide shown below provides a visual of the simplicity of use. The design engineer would input design parameters and the design guide would provide inputs on issues with geometric parameters.
Engine manufacturers rely heavily on creating prototypes and testing concepts to find appropriate design solutions. Engineers can use high-fidelity numerical simulations to provide quick guidelines and resolutions to water clogging issues they might face in their testing. Apart from that, since this tool provides design guidelines as well, the first prototype built with it is often more accurate than without it. This lowers testing requirements and prototype iterations by a significant number thus helping the engineer get to the final design faster and more effectively.
This post was contributed by Sucharitha Rajendran, advanced system design and modeling engineer, Parker Filtration Innovation Center.
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17 Aug 2021
The COVID pandemic impacted the way many industries do business, and the HVAC industry is no exception. Ongoing concerns regarding infection risk and indoor air quality have prompted an unprecedented demand for filters with a Minimum Efficiency Reporting Value (MERV) value of 13, commonly known as MERV 13 filters, as well as those with even higher MERV ratings. As part of its COVID response, ASHRAE recommends increasing outside air within buildings as much as possible, as well as upgrading air filters to a minimum MERV 13 efficiency rating.
The rush to upgrade to high MERV filters, however, opens the door to a practical discussion about whether that is the best action in all cases. The reality is that using the wrong filter for the wrong application in the wrong place can substantially limit HVAC systems’ efficiency. The result is that air quality will suffer, and the system will consume more power than it should to function.
Is MERV 13 really the best choice for your HVAC system?
A MERV rating is determined by the filter’s particle-size removal efficiency. The higher the number, the higher the filter efficiency. Before considering ratings, however, it’s important to determine the purpose of the filter.
If the primary purpose is to keep heating and air conditioning systems clean and block contaminants from interfering with the operation of key components, you likely don’t need as high a MERV rating. If the primary objective is to protect breathing air quality, then a higher MERV rating might make sense.
An option worth considering in some applications is the use of a multi-filter system that includes final filters and pre-filters. A less expensive, lower MERV-rated filter, functioning as a pre-filter, can trap dirt and large particles before the air reaches the final filters downstream which then remove the small particles. Multi-filter systems can extend the life of the more expensive final filters, creating overall cost savings.
When choosing a filter, it’s also important to consider the conditioned space’s activities and the types and sizes of particles those activities generate. Contaminants of greatest concern need to be evaluated to determine the level of filtration efficiency required for that contaminant’s size (measured in micrometers/microns). Once a full list of contaminants of concern has been identified, you can use the ANSI/ASHRAE Standard 52.2-2017 to select the proper filter with the appropriate MERV.
Additional considerations when choosing a filter
Of course, particle-capture efficiency matters. But there are also other filter characteristics that should be considered when determining the best filter for a specific application. Cost is always a consideration and should include the purchase price, as well as service life and maintenance requirements. The filter’s resistance to airflow also is a key consideration, as it is proportional to the energy consumed by the filter. Energy expenditures can account for about 81% of an air filtration system’s annual operating costs, while its purchase price and maintenance can account for about 18.5%.
Other considerations include the design and materials used in filters. Some designs are easier to install, seal better, and don’t absorb moisture or shed. Pleated filters, which are commonly made with a blend of cotton and polyester or synthetic media, provide a larger filter-surface area than panel filters. Most pleated filters are MERV 6 to 13. Depending on the filter, capture efficiencies for particles in the 3 to 10-micron range can be 35% to 90%.
There are also extended-surface filters that are made with synthetic, fiberglass or cellulose/glass-fiber media. These include bag or pocket, rigid-cell, aluminum-separator and V-bank filters. Pocket filters provide an even greater filter surface area than pleated filters to provide maximum efficiency with the lowest pressure drop and longest life. They typically have MERV ratings of 11 to 15.
Other factors that can affect efficiency
Even a filter with the highest MERV rating can’t achieve high-quality air if some of the air is not going through the filter. Gaps around high-efficiency filters or filter housings can decrease filter performance. They occur when filter media are not sealed properly in the filter frame, when filters are not gasketed properly in filter racks, or when air-handler doors and duct systems are not sealed properly.
For a 1-mm gap, bypass flows can increase to 25% to 35% of the total airflow. The percentage increases based on the filter’s efficiency because air naturally flows through areas with the least resistance. Since higher efficiency filters have a greater resistance to airflow, bypass air has a larger effect. This, in turn, reduces the efficiency rating. For a 1-mm gap, for instance, a MERV 15 filter will perform only as well as a MERV 14 filter. A 10-mm gap, in contrast, causes a MERV 15 filter to perform as a MERV 8 filter. That’s why building operators and maintenance personnel should perform regular field inspections to ensure filter seals and gaskets are installed properly.
To combat gap problems, Parker created its QuadSEAL® HVAC filters with proprietary E-Pleat® media technology. The molded polyurethane frame incorporates a QuadSEAL integrated gasket on all four sides and can flex without damage. Since the media pack is 100% bonded into the foamed frame, bypass is eliminated as is the need for additional sealants or adhesives.
Challenges with MERV 13 filters (and what can be done)
If it were just a matter of choosing the filter that produced the best air quality, the decision would be simple. Everyone would install filters with the highest MERV ratings they could find. Unfortunately, it’s not quite so simple. The challenge facing engineers, building owners and maintenance personnel tasked with specifying and installing filters is that more efficient filters cause higher pressure drops because the smaller pores create more resistance to air flow.
Not only are higher efficiency filters less energy efficient (causing increased energy consumption by the fan), but your air handling unit simply may not have enough capacity to function with a high-efficiency filter. The reality is that most commercial HVAC systems today can only handle MERV 8 filter or MERV 9 filter types.
So, what are your options?
When COVID hit, suddenly industries that, for years, had functioned well with filters with MERV ratings of 8, 10 or 11, were scrambling for MERV 13, 14 and 16 filters. The reality, though, is that there are filter options even more efficient than MERV 16 filters.
High Efficiency Particulate Air (HEPA) and Ultra-Low Particulate Air (ULPA) filters are designed to trap the smallest airborne particles and contaminants. HEPA filters have a minimum efficiency of 99.97% at 0.3 microns, whereas ULPA filters have an efficiency rating of 99.999% at 0.12 microns or higher. This does not mean that ULPA filters are better than HEPA filters when taking air flow and other variables into account. In fact, HEPA filters cost less, have a lower resistance to air flow and offer a longer service life than ULPA filters.
Parker offers a complete line of HEPA and ULPA standalone and pre-filters for removing particles and contaminants with efficiencies up to 99.9995%. They also are designed to reduce energy consumption and operating costs.
So why doesn’t everyone simply switch to a HEPA or ULPA filter since they represent the gold standard in air quality? Because most commercial and industrial HVAC systems on the market today simply aren’t compatible with them. Since they are so efficient, HEPA and ULPA filters cause a higher pressure drop than filters with lower MERV ratings.
The best option today for using HEPA and ULPA filters is as part of stand-alone systems. Many school districts are looking at options for installing portable air filtration systems with HEPA filters in each classroom to augment their central air filtration systems. HEPA and ULPA filters are also frequently found in critical medical applications and cleanrooms.Newer innovations offer superior efficiency while overcoming problems with air flow
Parker’s approach to balancing the need for efficiency with minimum pressure drops has been the development of its LoadTECH® filter that utilize Parker’s proprietary E-pleat® technology. This patented design molds filtration media into a series of pre-formed channels that direct the air smoothly through the filter, allowing for even loading, minimum resistance and complete media utilization. The previously mentioned QuadSEAL® filters offer a similar benefit of improving efficiency without restricting air flow. The advanced media used in these filters also resists tearing, damage, moisture and microbial growth, leading to a long filter life and the need for fewer filter changeouts.
The decision to use a filter with a MERV 13 rating (or higher), in accordance with the latest guidance from the Centers for Disease Control (CDC) and ASHRAE, is complicated by the fact that most commercial HVAC systems cannot handle the highest efficiency-rated filters. While there are options for upgrades, redesigns that include a multi-filter system, and new technologies that balance efficiency and air flow, specifiers need to be careful that they choose the right filter after considering all the variables, including cost, maintenance requirements, operating efficiency and, of course, air quality.
This article was contributed by the Parker HVAC Filtration Division.
24 Jun 2021