In different kinds of applications like aging processes, validation testing and/or in research on plant growth, often a specified flow of moist air is needed to achieve specific ambient conditions in a test chamber. Nowadays, we have multiple solutions for these kinds of applications, one of them with the help of controlled evaporation and mixing systems. Let me explain what the benefits are of these systems in comparison with the more conventional bubbler systems.
How does a Bubbler System work?
Small concentrations of moist air can be created using a bubbler system. This conventional method requires optimal pressure and temperature control of the bubbler system. A complete bubbler level measurement system therefore consists of a source of compressed air, an air flow restrictor, sensing tube, and pressure controller. The latter converts the back pressure to provide output to a controller, which calculates the liquid level. The quality of the moist air fully depends on the theoretical calculation of the degree of saturation of the air flowing through the liquid and the accuracy of pressure and temperature control. With this conventional approach it is difficult to achieve a specific air moisture content.
Figure 1. Set-up Conventional Bubbler System
Bronkhorst evaporation systems
In addition to this approach, Bronkhorst developed a CEM-system, based on Controlled Evaporation and Mixing, which can be used for moist air applications. This CEM-system is an innovative vapor delivery solution, based on a liquid flow controller (LIQUI-FLOW or mini CORI-FLOW), a gas flow controller and a temperature controlled mixing and evaporating device.
Compared to the more conventional bubbler system, a CEM-system offers a more direct approach. The method is very straightforward, and theoretically any concentration can be made in a matter of seconds with high accuracy and repeatability. Moreover, it’s possible to adjust a relative humidity between 5 and 95 percent.
Figure 2. Set-up Bronkhorst CEM System
The moisture content is accurately controlled by the liquid flow controller and the amount of air flow can be adjusted by the gas flow controller. On top of the CEM a mixing valve allows for a correct atomization of water in the air flow. Because of the relatively low pressure ratio of the water mist in the air flow, the water can be evaporated at a low temperature in the spiralized heater tube at the outlet of the mixing valve.
The set-up of a CEM-system basically consists of:
- A Mass Flow Controller for gases for measurement and control of the carrier gas flow (e.g. EL-FLOW Select series).
- Mass Flow Meter for Liquids for measurement of the liquid source flow (e.g. LIQUI-FLOW series, mini CORI-FLOW series).
- Temperature controlled mixing and evaporating device (CEM) for control of the liquid source flow and mixing the liquid with the carrier gas flow resulting in total evaporation; complete with the Temperature Controlled Heat-Exchanger to add heat to the mixture; Basic Bronkhorst CEM-systems are available as a complete solution, including control electronics, offering total flexibility in realizing a vaporizing solution in virtually any situation.
Do you want to learn more about CEM technology? Visit the Bronkhorst Vapour Flow Control section on our website and read all about our different products and applications in vapour control.
Selecting the right flow meter is the key to success while selecting the wrong one means nothing but trouble. Flow meter technology has significantly increased the available choices for every kind of application. The right flow meter is essential for crucial data collection and the wrong one can lead to grief in the budget and costly lost production time. In this blog I will discuss some of the important elements that go into the decision-making process of a flow meter.
Price versus popularity, Most common criteria to select the flow meter
Beware of relying on two of the most common criteria that people tend to use in the selection process: cost and popularity. If you place price at the top of your criteria, it will be easy to get the wrong flow meter for the application or one that does not hold up physically or performance-wise. That bargain will quickly turn into a budget nightmare. If the measuring device and its ancillary equipment need frequent and expensive maintenance, what you saved on that flow meter will quickly dissipate. Moreover, a flow meter that has a higher initial investment can also make up for it by costing less to maintain and operate. Coriolis mass flow meters are more expensive in purchase initially than many other types of flow meters, but can save a great deal of money over time because they are easier to maintain, translating into less downtime.
A Set-up of Coriolis Mass Flow Meters (mini CORI-FLOW)
While it is important to research what type of flow meter is most commonly used in your industry, just selecting what is popular can also lead to disaster. If the flow meter is not appropriate for the application, measurements can be under or over which means valuable material can be lost and revenue negatively impacted.
New flow technologies offer new solutions
Advances in technology can also put instruments on the market that may not be as well-known, but provide a better solution. For instance, in the past, inline ultrasound flow meters had to be re-calibrated when a new fluid was introduced and could not be used in applications where hygiene was important. Nowadays new ultrasonic flow meters have solved those concerns and opened up the use of inline ultrasound flow meters to those types of applications.
A flow meter is a highly technical device that is influenced by lots of variables. We’ll breakout the most important ones, but realize that every application is unique.
Ultrasonic volume flow meter (ES-FLOW)
Volume or Mass flow measurement
There are two basic measurements of fluids, volume and mass flow measurement, so a flow meter is either a volumetric flow meter or a mass flow meter. However, you can calculate volume from mass and mass from volume if you know the density and agreed upon variables. Whether a volumetric flow meter or mass flow meter is the best depends on the application, its components and the purpose of the measurement.
Flow meter categories
Some flow meters can be easily eliminated because they simply will not work with the application. For instance, electromagnetic flow meters will not work with hydrocarbons and require a conductive liquid to function. Many flow meters cannot measure gases or slurries. Listed below are some of the main flow meter categories paired with the fluid type the meters can handle.
- Gas – Coriolis Mass, Thermal Mass, Ultrasonic, Variable Area, Variable Differential Pressure, Positive Displacement, Turbine
- Liquid – Coriolis Mass, Thermal Mass, Ultrasonic, Variable Differential Pressure, Positive Displacement, Turbine, Electromagnetic
- Slurry – Coriolis Mass, some subsets of Variable Differential Pressure, Electromagnetic, Ultrasonic
- Vapour – Vortex, Ultrasonic, Diaphragm, Floating Element
It is crucial to know the properties of the fluid being measured, below are some of the primary components:
- Type of fluid – liquid, gas, slurry, vapour
- Condition of the fluid – foreign objects in it, suspended particles, air bubbles,
- Other contaminants
- Flow consistency – consistent or breaks, fill the pipe or partially fill or varies
- Flow range – the minimum and maximum of the flow
- Corrosive nature of the material – corrosive liquid or gas can deteriorate inline sensors
It is also important to know about the physical dynamics of the application site. Some of the physical properties of the site to consider are:
- Configuration of the pipe before and after the flow meter and the length of straight pipe at the inlet and outlet of the flow meter.
- The size of the pipe. Some flow meters have a poor performance with very small pipes and some cannot measure fluids in larger pipes
- The material the pipe is made from
- The surrounding environment and whether it is stable or variable
- Will the flow meter work at a certain angle? This can seriously affect a flow meter’s performance
Read in our previous blog why the choice of piping is important for thermal mass flow meters
Flow meter specifications
Last but not least, also the specifications itself have to be taken into consideration when selecting the right flow meter.
Accuracy – Naturally, an important factor of a flow meter is accuracy. To even suggest that accuracy is a variable seems ridiculous. Who would want an inaccurate meter? However, not all flow meters possess the same accuracy; some applications do not even require precision.
Thermal mass flow meters for gas (EL-FLOW Prestige)
Repeatability – Repeatability means the number of times (%) you get the same results running the same test or measurement under the same conditions. Accuracy requires repeatability, but repeatability does not require accuracy. It just needs consistency. Therefore, it can be said that repeatability of a flow meter is often considered even more important than accuracy.
Turndown Ratio or Rangeability – This implies the range that a flow meter can accurately measure the fluid. Usually, it’s best to choose a flow meter with the greatest range available without compromising other components that are more critical.
Hygiene requirements – Flow meters for food, pharmaceuticals, and the medical industry especially demand sterile environments.
Cost – As stated above, this should include installation, maintenance and repairs over time. How much the meter costs to operate, like its electrical demands, can also increase the overall cost of the flow meter.
As you can see, there are a lot of variables to finding the right flow meter and the ones we have listed are only the basics. This does not even touch on the various options in different models. The best way to get the right meter is to get help with your search and team up with experts in the field. Experience matters.
It is important to get your information from people who know these complex and important devices. To let Bronkhorst help in the search for the right flow meter for your needs, please contact us.
• When you have selected the right flow meter, the next step is installing this instrument. Graham Todd gives some useful tips when installing a mass flow meter.
The so-called ‘Graphene Flagship’ originitated from the European Commission. This initiative has set a goal to concretise the development of Graphene before the start of 2020, from laboratory level to the consumer market.
What is graphene?
Graphene can be subdivided in three different types: single-layered, double-layered and multi-layered graphene:
- Single-layered graphene is the purest form available with with unique characteristics. These characteristics make (single-layered) graphene an attractive product for a large number of applications.
- Double-layered as well as multi-layered graphene have other (less qualitative) characteristics.
As the number of layers increases, it also becomes increasingly cheaper to produce.
In this blog I limit myself to only single-layered graphene, because as of today this type still gives the best result in various research.
Graphene is the world’s first 2D material that consists of only a single atomic layer of carbon; the same material that’s used in diamonds and penciltips. The carbon atoms in graphene are ranked in a hexagon structure. Single-layered graphene is characterized by the following properties
- 200 times stronger than steel
- 1.000.000 times thinner than a single human hair
- The world’s lightest material (1 m² weighs about 0,77 milligram)
- Impenetrable for molecules
- Excellent electrical and heat conduction
Graphene can also be combined with other materials, such as gases and metals, to produce new materials with the abovementioned properties or to improve existing materials.
At this point there isn’t a method available yet to produce graphene on a larger scale against acceptable costs. However, this is still being researched.
Plasma Enhanced Chemical Vapour Deposition (PE-CVD)
There are a couple of different methods to produce graphene. One of the most common methods in single-layered graphene production is Plasma Enhanced Chemical Vapour Deposition (PE-CVD). In this method, a mixture of gases - in which at least one gas contains carbon – is heated until a plasma has formed. Mass flow meters and controllers are used in CVD processes to dose gases and liquids accurately.
In PE-CVD the plasma forms a graphene layer on a nickel or copper substrate. Heating takes place in a vacuum, but a more ‘green’ CVD process can be used as well, in which heating takes place under atmospheric pressure. By using Chemical Vapour Deposition large sheets of graphene can be produced.
Some of the precursors are liquids that need to be evaporated first, to be used in the CVD process in its gaseous form. It’s very important that the plasma is created with the right proportions and precision. This can be achieved by using highly accurate flow instruments. A deviation in the plasma can cause defects in the graphene layer. Defects can be impurities in the 2D structure that can change the unique properties of the material.
3D-Model structure of graphene
Grootschalige productie van grafeen door plasma gebaseerde technieken
(ENG: Research for high quality graphene by using atmospheric pressure plasma-based techniques)
Our Spanish distributor, Iberfluid Instruments S.A, recently cooperated with the University of Cordoba in a research to investigate the opportunities regarding graphene production on a large scale by using a plasma based technique under atmospheric pressure. In this research ethanol was evaporated with the use of Bronkhorst evaporation system, the so-called Controlled Evaporation and Mixing (CEM) system, to form a plasma. With the use of an evaporation system liquids are being evaporated directly to create the right gas for the plasma. A possible setup of such an evaporation system can consist of a CEM system with an additional liquid flow meter (i.e. a Coriolis mass flow meter, from the mini CORI-FLOW series) for ethanol, a gas flow controller (i.e. an EL-FLOW mass flow controller) for argon, which functions as a carrier gas and finally a temperature-controlled control valve or mixing valve.
An evaporation system like the Bronkhorst CEM system can deliver excellent performance in terms of stability and accuracy. These properties guarantee a reliable creation of plasma, which eventually leads to higher quality graphene.
Bronkhorst CEM system for research at the University of Cordoba
In the research document ‘Scalable graphene production from ethanol decomposition by microwave argon plasma torch’ is described why the University of Cordoba (ES) uses the Bronkhorst Controlled Evaporation and Mixing system in the PE-CVD graphene production process.
Areas of application for graphene
Due to a large amount of unique properties research takes place in numerous areas of application. The main focus is on single-layered and double-layered graphene. For now it seems that single-layered graphene still gives the best results. At the same time the use of so-called flakes has been taken into account. These flakes are tiny pieces of graphene which can be mixed with another material, such as polymers. The properties of these materials can be improved by adding graphene flakes, which makes graphene widely applicable in different industries. A couple of examples based on single-layered graphene:
- Water purification: Scientists are currently developing an advanced filtration system based one graphene oxide that is being used to make polluted water drinkable.
- Medical industry: Since graphene isn’t poisonous for the human body, research is being done to the possibilities to use graphene in medicine transport in the body, by attaching the medicine to the graphene. Graphene also has the properties to prevent bacteria formation, which makes it ideal to use as a coating for implants.
- Energy industry: Because of the large surface and excellent electrical conduction, graphene could be used in energy storage. The goal is to make graphene batteries more compact than they are now, while increasing the capacity to make it possible to charge batteries within seconds.
- Textile industry: Graphene could be used to process electronics in textiles, such as effective, efficient and highly accurate sensors. Furthermore, graphene anti-corrosion coatings and conductive inks can be made.
- Semiconductor industry: Thanks to good electrical and thermal conductivity, graphene offers possibilities to increase the speed and capacity of chips (for computers and smartphones).
We continue to closely monitor the developments of graphene and we will keep you informed.
The emission of nitrous oxides (e.g. NO2) into our atmosphere is a global issue these days. Everywhere researchers and developers are working on better and more accurate simulation and measurement methods, as well as on the development of more efficient catalysts. This applies both to stationary combustion processes (e.g. power plants, steel production and chemical base materials) and to mobile applications in the automotive sector to reduce the NO2 with selective catalytic reduction (SCR). Ammonia or ammonia forming compounds (urea) are added to form pure nitrogen and water.
NOx, a generic term for nitrogen oxides that are most relevant for air pollutions, is a mixture of different nitrogen oxides; nitric oxide (NO) and nitrogen dioxide (NO2). The focus here is on NO2 radicals and its dimer dinitrogen tetroxide N2O4. NO2 is toxic and emissions to the environment should be kept as low as possible. However, NO2 occurs as a by-product in a large number of combustion processes, so that both technical developers in the industry and developers of occupational and preventive medicine have to deal with this substance.
However, this equilibrium also poses the problem of measuring and controlling gas flows containing NO2 in higher concentrations. Especially when using pure NO2, which is in balance with its dimeric form N2O4, which is temperature and pressure dependent and additionally influenced by light and surface conditions (at 27°C only 20% is present as NO2, the remaining 80% as dimer N2O4). The mixture is very sensitive to moisture and can react with humidity to nitric acid (HNO3) and nitrous acid (HNO2), which in turn are highly corrosive.
Gas mixtures with NO2
For investigations of combustion processes with NO2 emission or the testing/ new development of catalysts, a precisely known flow rate of gas mixtures with NO2 must be realised. This applies not only to catalysis but also to the effect of NO2 on the organism and the environment, because NO2 is highly toxic due to its reactivity.
In one of our projects a system consisting of a gas cylinder, needle valve, backwash unit, transfer lines and mass flow controller should be constructed, which can dose nitrogen dioxide (NO2) in the range between 0- 6 g/h against room pressure.
Challenges with thermal mass flow
Common mass flow meters and mass flow controllers work with thermal measuring principles (with bypass sensor or according the CTA principle (Constant Temperature Anemometry)). Thermal sensors operate on the principle of heat transport in the sensor element. This method depends on the type of gas, since the heat transport depends directly on the heat capacity and the thermal conductivity of the gas to be metered.
Since NO2 has a temperature and pressure-dependent equilibrium with N2O4, the parameters in the sensor element can change constantly. Consideration of the equilibrium using a single conversion factor to a reference gas is not sufficient, especially for pure NO2 or N2O4. Through gravimetric tests, we have determined that massive under-dosing can occur at a dosage of pure NO2 (approx. 10 % of the target value).
A further challenge with a thermal mass flow controller in the closed state, corresponding to a flow rate of 0 ml/min, is that it can produce pseudo signals of up to 10% of the maximum dosing range. The reason for this is that the sensor element contains a mixture of NO2 and N2O4, which is constantly influenced by the active heating of the sensor element. Thus, a heat transport in the device is faked and a flow rate is indicated.
The solution: Use of a Coriolis mass flow controller
The remedy here is a Coriolis mass flow controller instead of a thermal mass flow controller due to its different working principle. It does not matter to what extent the balance of NO2 and N2O4 is on one side or the other, since it is all about the transported mass. When using a Coriolis mass flow controller, however, it must be ensured that the medium to be metered is in a defined physical state, i.e. either in a completely liquid or gaseous state.
The boiling point of NO2 at atmospheric pressure is 21 °C, so the complete dosing system, consisting of gas cylinder, needle valve, backwash unit, transfer lines and mass flow controller, can be heated here. Since evaporative cooling occurs inside the mass flow controller when dosing NO2 at the pressure relief point, the temperature there must be set significantly higher than 21 °C. Only at a temperature of at least 45 °C is it ensured that the dosing functions in the range between 0-6 g/h without fluctuations due to condensing and re-evaporating NO2. In this setup a Bronkhorst mini CORI-FLOW ML120 was used, which is the Coriolis instrument with the lowest flow control range in the world. So it is possible to dose even these small gas amounts of NO2.
Check the nitrous oxides (NO2) dosage
The dosed NO2 quantity is checked with the aid of gravimetric measurements. NO2 is transferred via a heated transfer line to a glass U-tube with stopcocks where it is frozen out at -50 °C. The shut-off valves are then closed, the condensate thawed to room temperature and weighed. A total of five different mass flows were tested. The figure shows the result of the check and confirms the very small deviations between the desired and actual dosing quantities. In addition, it can be seen that the mass flow controller operates linearly in the tested range between 0.1 and 4.0 g/h (single points: 0.1; 1.0; 2.5 and 4.0 g/h with error bars drawn in).
This proves that precise control for small quantities of NO2 can be achieved even at low inlet pressures.
As mentioned, nitrogen dioxide (NO2) is a substance of the mixture nitrogen oxides (NOx). Reducing the level of NOx can also be done with Selective Catalytic Reduction (SCR). In case of Selective Catalytic Reduction (SCR) Ammonia or ammonia forming compounds are added to form pure nitrogen and water.
As a scientist at the University of Cambridge, I’m closely involved in a fascinating project on Carbon Nanotubes. In cooperation with Bronkhorst, we are working on a reactor to control the fabrication of this exceptionally strong and conductive material. Let me explain more about this subject and why I consider Carbon Nanotubes to be a material of the future.
History and future of Carbon Nanotubes (CNT)
In the beginning, carbon came in three molecular forms:
• amorphous carbon
Suddenly, in the mid-1980’s, a new molecular form of carbon surfaced in research and ignited the multidisciplinary field of nanotechnology. This all carbon molecule, Buckminsterfullerene, is a nanometre-sized cage of carbon atoms with a molecular structure that resembles a football.
A few years later, another molecular carbon cousin came to light: carbon nanotubes (CNT). Similar to Buckminsterfullerene, the football structure is vastly elongated into a nanometre-wide tube with length millions of times greater than its diameter. Captivating scientific attention; CNT’s strong carbon bonds with its ordered molecular structure make it the strongest material ever made. Electrons glide down CNT’s effortlessly, as stable one-dimensional conductors, which makes CNT’s electrical conductivity four times greater than copper and with a maximum current carrying capacity 1,000 times greater than copper.
3D model of Buckminsterfullerene
By the early 2000's, researchers created processes to fabricate textiles composed of CNT’s with densely packed and aligned microstructure. Initially, the bulk properties of CNT textiles lagged well behind the exciting properties of their individual molecules. After steady incremental improvement, the state-of-the-art CNT fibre is as strong as conventional carbon fibre and about four times more conductive. With continued development we expect CNT fibres that are substantially stronger than conventional carbon fibre with an electrical and thermal conductivity greater than traditional metals like Copper and Aluminium.
Application of Carbon Nano Tube fibres is in strain-resistant textiles (protective clothing, bullet-proof vests), composites, construction compounds (ceramics, lighter car bodies) and cables because of their strength. Using carbon nanotubes could have enormous impact on day-to-day life, similar to the way plastics changed the world in the mid-20th century.
Carbon Nanotubes (CNT) at the University of Cambridge
Our laboratory invented a production process that not only creates Carbon Nanotubes in industrially competitive volumes, but does so with unparalleled graphitic perfection into a macroscopic textile with aligned microstructure, all in one production step. This production process is intrinsically simpler than other fibre production processes such as conventional carbon fibre and Kevlar.
The floating catalyst chemical vapour deposition reactor (F-CVD) that is used for this process just requires a carbon source (toluene), a catalyst source (ferrocene) and a Sulphur based promotor (thiophene), which are mixed together and fed into a 1300°C tube reactor by a carrier gas (hydrogen). A floating CNT cloud is formed. Mechanically extracting the CNT cloud out of the tube reactor condenses the cloud into a bulk fibre with aligned microstructure. This is called “CNT spinning”. Specially protected personnel, also known as “the spinner”, mechanically extracts the CNT cloud into a fibre.
Consistent reactor control however, is challenging. The CNT material properties vary substantially between runs and the relationship between controlled and uncontrolled reactor input parameters are not fully understood yet.
Control of the Carbon Nanotubes Reactor
Our program seeks to implement a robust feedback loop to control the reactor’s CNT material properties.
Every reactor input variables and output variables, which are specifically selected CNT material properties, are automatically measured and recorded into a database; from the outside weather, to the operating personnel, to the age of the tube, to the precursor concentrations, gas flows, etc.. The database is continually data mined for correlations, parameter interaction, and multidimensional linear regression models that statistically predict reactor behaviour using the data exploratory software JMP™.
For example, figure 1 shows a statistical model for the material’s G:D ratio, this is the ratio between graphite (G) and graphitic defects (D) from Raman spectroscopy, which indicates the degree of graphitic perfection. The model is a function of various reactor input parameters that were found the most statistically significant to the G:D ratio. On the horizontal axis in the plot below, there are the predicted G:D values of the model and, on the vertical, the actual measured vales. In a perfect model with perfect control, we would expect a straight 45 degree line. Clearly, the data points are widely spread along the red line, which indicates a low level of reactor control.
The setup here involved simply mixing the precursors together (toluene, ferrocene, and thiophene) and injecting the solution into a hydrogen carrier gas via a simple gear pump. It became evident a more sophisticated system was required for greater reactor control.
Bronkhorst solution for control of the Carbon Nanotubes Reactor
Figure 2 shows our improved system. Separate liquid precursors are now independently controlled with Bronkhorst Coriolis instruments (mini CORI-FLOW series)(link product page). The Coriolis mass flow meters give precise mass flow rates without the need of recalibration between different precursors, which greatly facilitates trying out different CNT recipes. Bronkhorst is the only one who succeeded in applying the well-known high-precision Coriolis principle to an extremely small scale by applying MEMS technology.
Figure 2. Carbon Nanotubes Reactor Scheme
The flow rates are in the range up to 200 g/h for toluene and even below 100 mg/h for thiophene. Hydrogen carrier gases are controlled by robust, plug-and-play Bronkhorst mass flow controllers. Finally, the precisely metered precursors are vaporized and combined with the controlled hydrogen carrier gases with vaporizer technology.
With this new and more sophisticated instrumentation, statistical modelling of the floating catalyst chemical vapour deposition reactor is much more effective. Here, the actual versus predicted values for the graphitic perfection are much more agreeable, as is shown in figure 3. This model has substantially less noise, which means the reactor’s response is predictable and repeatable. So far, with this controllable and well modelled reactor system, we have more than doubled typical CNT production rates and tripled the degree of graphitic crystallinity.
Stay tuned! With Bronkhorst and other important commercial, academic, and government partners we hope to surpass conventional carbon fibre soon!
If you are active in reactor technology, do not hesitate to contact us for solutions for your processes.
Please contact us for more information.
• Read more about MEMS technology that is used for the research in Carbon Nanotubes in the previous blog of Wouter Sparreboom.
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.