Anhydrous Ammonia Control for Nitrogen Oxides Reduction
As a technique to reduce the level of Nitrogen Oxides (NOx) in boiler or furnace exhaust gases, Selective Catalytic Reduction (SCR) has been around for years. SCR is a technology which converts Nitrogen Oxides (NOx) with the aid of a catalyst into diatomic Nitrogen (N2) and Water (H2O). A reductant agent is injected into the exhaust stream through a special catalyst. A typical reductant used here is Anhydrous Ammonia (NH3).
A customer of Bronkhorst, who has been selling and servicing boilers and pumps for commercial and industrial applications for over 50 years, had been using a mass flow controller (MFC) which was not reliable and robust enough for the application and thus their customers were suffering from poor ammonia measurement and control.
Why use mass flow measurement in Ammonia Control?
Some NOx reduction systems are liquid ammonia based, and others are gas based ammonia. Whatever the state of the ammonia in the NOx reduction system Bronkhorst can offer accurate ammonia measurement and control. Systems in the field today are using the MASS-STREAM (gas), IN-FLOW (gas) and Mini CORI-FLOW (liquid) to accurately control the ammonia being injected into the exhaust gas stream so that proper reaction takes place without ammonia slip. Ammonia slip is when too much ammonia is added to the process and it is exhausted, un-reacted, from the system; effectively sending money out the exhaust stack.
There are very strict federal and state air quality regulations that specify the allowable level of NOx which can be released into the atmosphere and there can be very heavy fines if those levels are exceeded. The company needs to provide their customers with a reliable and robust solution. The application demands a robust and repeatable mass flow controller that is at home in industrial environments.
What kind of Mass Flow Meter or Controller can be used here?
In the NOx reduction system serviced by our customer the mass flow controllers are used to control the flow of anhydrous ammonia (ammonia in gas state) into the exhaust gas of a boiler or furnace where it is adsorbed onto a catalyst. The exhaust gas reacts with the catalyst and ammonia which converts the Nitrogen Oxides into Nitrogen and Water.
Bronkhorst recommended a mass flow controller – from the MASS-STREAM series - using the CTA (Constant Temperature Anemometer) technology which is ideal to avoid clogging in potentially polluted industrial gas applications.
Let me explain a bit about the working principle of this kind of mass flow controller and why it is suitable for an application like this.
The CTA (Constant Temperature Anemometer) principle is essentially a straight tube with only two stainless steel probes (a heater and a temperature sensor) in the gas flow path. A constant temperature difference between the two probes is maintained with the power required to do so being proportional to the mass flow of the gas. This means the MASS-STREAM is less sensitive to dirt, humidity, or other contaminants in the gas, as compared to a by-pass type flow meter that relies on a perfect flow split between two paths. The thru-flow nature of the CTA technology is ideal to avoid clogging in potentially polluted industrial gas applications. The straight flow path and highly repeatable measurement and control capability, combined with the robust IP65 housing, allows the MASS-STREAM to thrive in tough applications.
- Watch our video animation, explaining the functions and features of the Bronkhorst Mass Flow Meters and Controllers for gases using the CTA principle.
- Check out the top 5 reasons why to use mass flow controllers with CTA measurement.
- Want to stay up to date on new flow solutions? Would you like to receive every month the latest tips in your inbox?
Many people have a traditional inkjet or laser printer in their homes, to print '2D' texts and images on paper. In an extension to this, 3D-printers already show up in our homes, to make gadgets, jewellery and other products. 3D printing is becoming increasingly popular and nowadays large online platforms are being set up where open source designs are accessible to everyone, like Pinshape. 3D-printing, also known as additive manufacturing is a novel production technique where 'real 3-dimensional' products are built layer by layer, made from scratch. This is the opposite of traditional machining operations such as drilling, milling or cutting, where pieces of material are removed to yield the product.
3D printing as ‘rapid prototyping’
3D printing today is often associated with a process called ‘rapid prototyping’ – which is used by research and development (R&D) teams to create a physical representation of a new invention (prototype) so that it can be tested and validated.
On a professional level, 3D-printing is already becoming a popular solution to manufacture products in small series, fast and custom-made. 3D-printing of polymers and metals already occurs on an advanced scale, alongside this 3D-printing of ceramics is rising.
3D-printing at Bronkhorst
3D-printers are very useful within the production environment. This is demonstrated by their use here at Bronkhorst - for product as well as process development. It really has become a new and very accessible way of manufacturing.
We use several 3D-printers mainly for visualisation purposes - 'the rapid prototyping way' - and to print useful tooling to facilitate the production of mass flow controllers and meters. Prior to using 3D-printing, a prototype of a component had to be manufactured at an external tool shop, which took some time - and investment - before it was ready. The use of 3D-printing has allowed us to increase our productivity: it is much faster to print a component or a tool ourselves.
Within a few hours, we can evaluate the design of a component: will it really work in the way we expected it, does it really fit? Moreover, for small quantities, no investment is required for manufacturing a mould.
In addition to its speed, 3D-printing has some convincing advantages. It is much more powerful to deal with a real component - a plastic model, with some real look & feel - than a 3D-rendered image which may look fantastic but isn't in real life. In addition, the communication between R&D, engineering and production works that much better having a component in your hand to talk about. Which are the key problems we will encounter, what can be the risks of a new design? In the R&D department, 3D-printing is mainly used to test the functionality of a design. The engineering department goes one step beyond, in making the design feasible and realisable.
3D printer Kaak
Cooperation with external partners
K3D, part of Kaak Group in Terborg, acquired the first real industrial 3D-printer for metal. Since September 2016, the printer is fully operational. The MetalFab1 machine is based on selective laser melting (SLM), a 3D-printing technique where a layer of metal powder is deposited, after which a part of these powder particles is selectively melted together by means of laser heat. It is the first local step in real production of metal parts with a 3D-printer.
Want to learn more about Mass Flow Controllers in 3D-printers? Read the blog of Jens Kiene about how a MASS-STREAM mass flow controller is used for selective laser melting.
Kaak approached seven companies in the region to experiment with the 3D-technique together, with the aim to turn the eastern part of the Netherlands into a 'print valley'. Each week, Bronkhorst has access to the printer for several hours. Bronkhorst is constantly looking for possibilities to improve the production process of flow meters, e .g. whether it’s possible to integrate more functions in the modules without interfering with the modular design. Moreover, local educational institutes are invited to get access to the machine, in order for their students to become acquainted with this technology.
Mass flow controllers for 3D-printers
Besides the fact that we use 3D-printing for our own product and process development, it also goes the other way around: mass flow controllers are used inside 3D-printers for metals. In selective laser melting, it is essential to have an inert gas atmosphere around the to-be-melted metal powder particles inside the 3D-printer, to prevent the metal from oxidation during the laser melting with oxygen from the surrounding air. To that end, an inert shielding gas has to be applied: argon gas for steel and titanium, and nitrogen gas for aluminium. Bronkhorst helps 3D-printer manufacturers with a system that generates and controls the flows of these inert shielding gases.
3D-printing is a way of additive manufacturing, a novel production technique essential for Bronkhorst to keep up with all new trends in the market for product- as well as process development.
Read more about this application using 3D-printing of metal products.
Check out the mass flow controller MASS-STREAM D-6300 that is used for 3D-printing
Watch the video
It is real common nowadays to use 3D printing techniques as process optimization in industrial production evironments. In our Bronkhorst premises in Ruurlo we also use 3D-printers for our own product and process development. 3D-Printers are indispensible within our production environment, it has brought us a new and very accessible and flexible way of manufacturing.
Within a few hours, we can evaluate the design of a component: will it really work in the way we expected it, does it really fit? You can read all about our experiences here in our blog
‘Product & process optimization by use of 3D printers’
But it also goes the other way around. Not only do we use 3D printers in the production proces of flow meters, but these flow meters and flow controllers are also used inside 3D-printers as well.
In this blog I would like to share an application with you explaining how mass flow meters are used in the 3D printing machines of one of our German customers in the machine building industry.
Selective laser melting (SLD)
3D-printing, also known as additive manufacturing, is a technique where products are made by building a product layer by layer. This is the opposite of machining operations such as drilling or milling, where pieces of materials are removed to yield the product.
Selective laser melting (SLM) is a 3D-printing technique where a layer of powder is deposited, after which a part of these powder particles is selectively melted together by means of laser heat.
The customer is a machine builder who makes 3D-printing machines that print metal parts out of steel, aluminium or titanium powder using this selective laser melting technique. Their customers are in the fields of aerospace, automotive and medicine & dental. High purity inert gases are necessary around the metal powder bed within the 3D-printer.
It is essential to have a gas atmosphere around the to-be-melted metal powder particles that is oxygen-free, to prevent the metal from oxidation during the laser melting. To that end, an inert shielding gas has to be applied: argon gas for steel and titanium, and nitrogen gas for alumium.
Flow solution with MASS-STREAM mass flow controller
For the end user of SLM's 3D-printing machine, there are two ways to establish a nitrogen atmosphere: either from the in-house nitrogen supply mains - if present - or from a nitrogen generator, which is an accessory to the 3D-printer. In the latter option, Bronkhorst becomes involved.
Pressurised air from a compressed air supply or a compressor is supplied to the nitrogen generator, and its molecular sieve separates the air flow into two flows. Constituents such as oxygen, water vapour and argon are removed, and nitrogen with high purity (grade 5.0) remains.
Downstream of the generator, a mass flow controller (using direct through-flow measurement technique) is installed to control the nitrogen flow to the 3D-printer. This controller works in two operating modes.
Prior to the printing process, the 3D-printer has to be flushed, in order to establish the shielding gas atmosphere. To this end a high nitrogen flow of 60 to 90 liters per minute is necessary. Next, during the printing process itself, a small nitrogen flow of 3 to 10 liters per minute has to be supplied, for refreshing purposes and to compensate for leakage.
• Read more about this application using 3D-printing of metal products
• Check out the mass flow controller (MASS-STREAM™ D-6300 ) used in this application
What is FLUIDAT?
FLUIDAT is Bronkhorst’s online calculation software. It allows our end users to make many theoretical calculations for their instruments and also have access to over 1800 different fluid properties and corresponding data.
Working with fluids and ever changing process conditions can provide many challenges, especially when trying to understand the behaviour of the given fluid depending on the actual pressure and temperature of the process. Along with understanding the behaviour of your particular fluid or fluid mixture making sure that you select an instrument that is able to operate effectively to the level you expect and that meets your application’s demands. In this case the initial selection of the correct instrument is fundamental, understanding what is possible for the future of your instrument can however be just as important.
This is where FLUIDAT can assist by allowing our end users to fully understand their instruments capability. If it’s working at different pressure conditions or using a completely different fluid for example, FLUIDAT can allow you to make an informed decision about whether or not the instrument is up for the task at hand. Of course, sometimes we have to accept that returning the instrument for recalibration is the only option but with FLUIDAT at your fingertips you have the ability to make an informed choice.
Traditionally, fluid data has been stored in technical handbooks and manuals with graphs and tables of data in a listed format demonstrating fluid properties along with their coefficients. However, this is a very inflexible format and does not allow immediate access to changing fluid behaviour (due to external factors) without making what can sometimes be complex calculations.
Knowing that these challenges were sometimes a hindrance to our end users, Bronkhorst released this on-line fluid management programme to support our customers in a way we never had before. This on-line programme allows immediate data and calculations relating to the behaviour of thousands of fluids under different working conditions.
One example of this is our Controlled Evaporation Mixing (CEM) vapour generation calculation tool. To calculate the output vapour to the process you need to calculate the combination and vaporisation properties of both a liquid and gas at differing temperatures and flow rates. Our CEM calculation tool can make this task easy, at just a click of a button.
The newly added interactive Vapour-Pressure line allows users to simply glide the cursor over the chosen fluid graph to establish the phase at the given temperature and pressure. Added value comes from the ability to create and save your own fluid mixtures, which alone can remove hours of calculations and research from a single project.
OK, so let’s have a look in more detail at some of the calculation tools available in FLUIDAT.
Gas Conversion Factor:
Here, the end user can choose a pure gas or create a gas mixture to find the conversion factor for a different gas to which an instrument can be sized on. As with most thermal mass flow controllers the output signal from the MFC is determined by which gas it has been calibrated for. With the gas conversion factor tool you simply choose the ‘Fluid from’ and ‘Fluid to’ to find out the conversion / correction factor. You can also select your exact model to improve the accuracy of the conversion. This function also allows you to add the specific pressure and temperature conditions you are converting from and to, for even more accuracy. The conversion factor can then be applied to the output measurement of the MFC to know the actual flow of the new gas.
Example of a gas conversion made in FLUIDAT:
Controlled Evaporation Mixing (CEM) Calculation Tool:
A CEM system can be an extremely versatile addition to any vapour generation requirement. FLUIDAT allows the end user to make various calculations to not only enable the correct CEM heater temperature setting , the flow rates required for both the liquid and gas instruments and the relative humidity of the generated vapour. It is also possible to back calculate the flow rates needed to achieve the required relative humidity of your vapour. All of the fluid data is stored within the FLUIDAT software, the heat capacity, thermal conductivity and heat of vaporisation to name a few. This data can also be accessed by the user under the ‘Fluid Properties’ calculation.
The possibilities of the CEM calculation tool are endless, from knowing the pressures needed to supply the liquid and gas MFCs to calculating the vapour temperature on the outlet, or knowing the flow of the vapour output and having the ability to choose between thousands of different fluids to make your calculations. This makes FLUIDAT a ‘must-have’ for any Bronkhorst customer using our CEM vapour delivery systems.
Example of a CEM calculation in FLUIDAT:
Pressure Drop Calculations:
For most applications it is important for the end user to understand the pressure drop across the instrument. It is not only important to understand the pressure loss across a device but sometimes it can also be critical to know the required pressure for the instrument to function correctly, especially when using control valves.
In FLUIDAT it is possible to calculate the pressure drop for both our gas instruments and our mini-Coriolis Series. Calculating the pressure drop using FLUIDAT is easy, all you need to do is select the correct pressure drop calculation tool. You have the choice of selecting our MASS-STREAM, EL-FLOW/IN-FLOW or Coriolis Instruments.
The calculation tool for the Coriolis Instruments is called ‘CoriCalc’ and for the other instruments are referred to as ‘Pressure Difference D-6300’ or ‘Pressure Difference LOW-dP-FLOW and EL-FLOW'. Once you have selected the correct tool and instrument type you can then select the fluid and flow rate and simply hit the calculate button. You can choose to readout the pressure drop in many different units from mbar to psi for example. For meters this is pretty straight forward, the pressure drop will be displayed across the sensor and fittings and yes, you can also choose the fitting size and type in many situations.
This calculation tool can also demonstrate the minimum required inlet pressure to flow the fluid you want at the required flow rate. Without the complication of the control valve calculating for meters is relatively straight forward. When making calculations involving both a meter and control valve (e.g. in a controller), it is important to make sure your calculation includes the correct selected orifice for your given controller, the easiest way to do this is using the inlet and outlet pressures to be used.
Example of a Pressure Drop Calculation in FLUIDAT:
FLUIDAT is an extremely useful and powerful tool for those using Bronkhorst instruments. It allows an end user access to additional information which can be used to not only enhance the potential of our instruments but also allows our customers to gain an advantage over competitors and gain an understanding of mass flow. The above examples are just a snippet of some of the tools available.
Please register at www.fluidat.com to take full advantage of this free online software.
Within the medical arena there is increased pressure on budgets and financial accountability, with a significant trend for the sector to look again at how resources are used and where savings can be made.
One of the largest expenditures in most hospitals is the cost of purchasing or producing the various medical gases needed, such as Medical Air, Nitrogen, Oxygen and Nitrous Oxide. Often the usage and consumption of these gases is neither monitored nor measured or, whenever it is done, it is often a crude estimation, inaccurate and recorded only by pen and paper.
Most hospitals rely on the rate at which the cylinders (in which the gas is supplied) empty to determine the amount and rate of gas used. There are of course many issues associated with this method, such as:
- The amount of gas in a particular sized cylinder can vary greatly, even when directly delivered by the gas supplier
- Total gas consumption and peak times of consumption cannot be accurately determined
- Leaks can go undetected
- Specific point of use consumption is impossible to determine
This makes it very difficult to manage costs overall and to assign invoicing costs to individual departments and sections.
A company specialising in the design, installation and maintenance of gas systems was asked to install the medical gas network in a new hospital. An approach was made to Bronkhorst UK Ltd for the supply of gas meters which could then be communication-linked to the building maintenance system.
Thermal mass flow Instruments with integrated multi-functional displays were offered to fulfil both the accuracy and reliability requirements . As a result of their through-flow measurement (Constant Temperature Anemometry - CTA technology) the thermal mass flow instruments offered the additional benefits of no risk of clogging, no wear as there are no moving parts, minimal obstruction to the flow of the gas and hence ultra-low pressure drop, all based upon the fact that the instrument body is essentially a straight length of tube.
In addition to the local integrated displays both 4…20 mA and RS232 output signals were available ensuring integration with the Building Management System (BMS). This gave the end user real time continuous data logging and remote alarming should the gas supply enter low- or high-flow status for any given event. As a double failsafe the instrument offers both on-board flow totalization and further hi/lo alarms.
The installation of the mass flow instruments for this hospital application provided the following benefits to the client:
1. On primary networks:
- Separated invoicing for hospital/clinic/laboratory departments sharing the same source of medical gas
- Monitoring and acquisition of consumption data
- Leak detection within gas line, safety vent and medical gas source
2. On secondary networks:
- Independent gas consumption invoicing between the health institution departments
- Over-consumption detection
- Monitoring and acquisition of consumption data
- Leak detection within gas line
Subsequent installations across Europe have followed the trend of increased accountability by installing a Mass Flow Meter for the incoming bulk delivery, obtaining a totalized flow reading and cross matching this to the bulk invoice. This could be useful in the event of inadvertent errors or typos when a bulk delivery invoice is being raised.
Thermal mass flow instruments that make use of a bypass (capillary bypass or bypass sensor) are what most people have in mind when they think of thermal mass flow instruments. What are the differences?
In instruments based on the thermal principle, power is applied to heat the sensor tube. Accordingly the temperature of the tube is measured at two points. With no flow measured, the temperature differential between the two points will be zero.
When the flow increases, the temperature at the first measuring point will decrease, as fluid carries away the heat. At the same time the temperature at the second measuring point will increase as the fluid carries heat to it. More flow will result in a greater temperature differential and this temperature differential is proportional to the mass flow.
Another technology used to measure mass flow is CTA (Constant Temperature Anemometry).
In a CTA (through flow, straight tube) instrument there are two measurement “probes” inserted into a straight tube flow path. The first “probe” both heats and measures the temperature of the fluid, as the second “probe” measures the temperature of the fluid.
Again, as the gas flow increases the gas will carry heat from the first measuring point to the second one. In a CTA, however, the power is varied to keep the temperature between the two measuring points constant, and it is this power level that is proportional to the mass flow.
Each technology has its advantages and disadvantages which generally are application specific.
A clean, dry gas application where higher accuracy is as important as repeatability, may be a better application for a bypass instrument like the Bronkhorst EL-FLOW series.
An application with a dirty or slightly moist gas, or where lower accuracy but high repeatability and robustness is required, may be a better application for a CTA instrument like the Bronkhorst MASS-STREAM™ series.
Curious about using a thermal Mass Flow Meter or Controller? Or the top 5 reasons why we use Mass Flow Meters with CTA measurement?.
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