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.
For many years, Mass Flow Controllers (MFCs) and Mass Flow Meters (MFMs) have been used in Analytical instrumentation. There are some distinctive applications like carrier gas control or mobile phase control in Gas Chromatography (GC) and Liquid Chromatography (LC). I discovered that there are a lot more applications of Mass Flow Controllers in analyzers then I could imagine when entering the world of Mass Flow Controllers after many years working in Analytical Chemistry.
One application I would like to focus on in this blog is Mass Spectrometry or shortly, as chemists like to use abbreviations, MS. Mass Spectrometry comes in many forms and is often coupled to Gas Chromatography and Liquid Chromatography. A Mass Spectrometer coupled to a Gas Chromatography (GC) is called a GC-MS and a Mass Spectrometer coupled to a Liquid Chromatography (LC) is called a LC-MS.
Where are Mass Spectrometers applied?
The market for Mass Spectrometers is huge and expanding. The instruments are used for Analytical Research in general but increasingly important in Food Research. Research concerning aging of whiskey and fingerprinting of red wine to determine the origin of the grapes are some examples. Another emerging market is Biopharmaceutical Research where Mass Spectrometers are used to study proteins and how these proteins are digested in living organisms. There are even Mass Spectrometers on Mars (!), where the martian soil is studied.
Figure 1: Mass Spectrometer (schematic)
What is a Mass Spectrometer?
The Mass Spectrometer is often compared with a weighing scale for molecules. Every molecule is built up from atoms and every atom has its own atomic mass and this is “weighted” by a Mass Spectrometer. Before it can weigh the different atoms that are present in one sample, the atoms have to be separated from each other. This is done by charging the atoms (to form ions) and using a magnet to deflect the path that the ion is following. The lighter the ion, the more influence the magnet has and the bigger the deflection. The detector detects where the ion hits and this is a measurement of the weight.
The place where the ionization takes place is called the ion source and there are a lot of different types of ion sources, depending on the matrix of the sample and on the ions that you want to form. The ionizing part is the most interesting part from a Mass Flow point of view because in this part different gases are used, depending on the technique of ionization.
There are two main techniques: hard ionization and soft ionization. With hard ionization techniques, molecules in the sample are heated and fragmented down to atomic levels giving information about the atomic structure of the molecule. With soft ionization techniques the molecule stays more intact giving mass information of the molecule. This is used in Food and Pharma research and has become very popular in the last decade.
Let’s look into detail to one of the most popular soft ionization techniques, the Electrospray Ion Source. The EIS vaporizes the liquid (coming from a Liquid Chromatograph, for example) by leading gas alongside a charged needle to form an aerosol spray. Leading a counter gas flow through the formed spray will evaporate most of the liquid that you do not want to measure, leaving the charged droplets going into the Mass Spectrometer.
Figure 2+3: Electrospray ionization (ESI)
Mass Flow Controllers and Evaporation used in Electrospray Ion source
The interesting part is that the flow needs to be very constant as you want the process of forming droplets and evaporating solvent to be the same, day after day and at different locations with different circumstances. An important parameter in this reproducibility is the gas flow. By using Mass Flow Controllers for Nebulizer gas and Evaporation or Drying gas, the ion source will always have reproducible gas flows.
Our solutions department can design compact gas modules for analytical applications to supply gases for ion-source combined with other gas flows with high accuracy and good reproducibility. Combining components like pressure switches and/or shut-off valves with the flow channels can give a compact gas handling module to fit in the small footprint demanding designs of the Mass Spectrometers. Furthermore, the changes on leaks are decreased significantly as the whole manifold can be leak and pressure tested before it is shipped to the customer.
If you would like to learn more about Bronkhorst customized flow solutions, you can watch this Video or visit our website.
You would think that measurements of mass flow would be expressed in units of mass, such as grams/hour, milligrams/second etc. Most users, however, think and work in units of volume.
Let’s start with an example:
Imagine you have a cylinder of 1 liter, which is closed by means of a moveable piston of negligible weight. This cylinder contains 1 liter of air at ambient pressure, approximately 1 bar. The weight of this volume of air at 0°C is 1.293 g, this is the mass.
When we move the piston half way to the bottom of the cylinder, then the contained volume of air is only ½ liter, the pressure is approximately 2 bar, but the mass hasn’t been changed, 1.293 g; nothing has been added, or left out.
According to this example, mass flow should actually be expressed in units of weight such as g/h and mg/s. Many users, however, think and work in units of volume. This not a problem, provided conditions under which the mass is converted to volume are agreed upon.
In order to use density in converting mass flow to volumetric flow, we must pick a set of specific pressure and temperature conditions at which we use the density value for the gas.
The conditions that are agreed upon contain various references, normal reference and standard reference, available in European or American style. What is the difference?
Normal reference, European style
Following the ‘European’ definition, a temperature of 0°C and a pressure of 1.013 bar are selected as ‘normal’ reference conditions, indicated by the underlying letter “n” in the unit of volume used (mln/min or m3n/h). The direct thermal mass flow measurement method is always based on these reference conditions unless otherwise requested.
An example conversion to volumetric units using Normal reference conditions: The mass flow meter indicates 100 g/h of Air flow. • Density Air (@ 0°C) = 1.293 kg/m3 • X ln/m Air = 100 g/h / (60 minutes x 1.293 kg/m3) • Flow = 1.29 ln/m Air
Standard reference, European style
Alternatively, a temperature of 20°C and a pressure of 1.013 bar are used to refer to ‘standard’ reference conditions, indicated by the underlying letter ‘s’ in the unit of volume used (mls/min or m3s/h).
An example conversion to volumetric units using Standard conditions: The mass flow meter indicates 100 g/h Air flow. • Density Air (@ 20°C): 1.205 kg/m3 • X ls/m Air = 100 g/h / (60 minutes x 1.205 kg/m3) • Flow = 1.38 ls/m Air
If the prefix ‘s’ has been used, it refers to the American style.
Standard reference, American style
According to the ‘American’ definition the prefix ‘s’ in sccm, slm or scfh refers to ‘standard’ conditions, 101.325 kPa absolute (14.6959 psia) and temperature of 0°C (32°F).
Please be aware of the reference conditions when ordering an instrument. ‘Normal’ and ‘Standard’ can be relative to each customer.
Why is this important? Because mixing up these reference conditions causes an offset in what the customer expects to see by greater than 7%!
Did you know that natural gas is odorless? I didn’t… I always find it having a penetrating sulfur scent. Well, it appears that this penetrating scent is added to the natural gas on purpose. Let’s see why this is.
As natural gas is combustible and odorless by nature, the government requires some safety measures here. Many countries have established safety regulations how to handle natural gas and which gas needs odorisation. This is mostly done by the Health and Safety department (HSE) of the local government.
What about natural gas odorisation?
Today’s question is about this subject. Why does gas smell when it is odorless by nature? This is the point where gas odorisation comes in.
Odorisation of natural gas is done to act as a ‘warning agent’ in case of leakage. The idea is that people can smell the gas prematurely if it is present. Because, if there is too much gas present it can be explosive.
As shown in the picture, the LEL (Lower Explosive Limit) and UEL (Upper Explosive Limit) are crucial here. If the concentration of the combustible substance present in the air is too low (< LEL), than no combustion will occur. It the mixture is too rich (> UEL), there is a huge amount of gas in the air and only partial combustion will occur. Gases become dangerous in between the LEL and UEL. Therefore, it is most important for people in the surroundings to smell the gas in time, before the concentration is too high and it exceeds the LEL.
As a result, it is stated in the safety regulations that natural gas has to be detectable at a concentration level of 20% of the LEL and this is done by odorisation. Needless to say that the odor used in the gas is not dangerous to people’s health.
When is an odor added to gas?
This depends on the type of gas line. We know ‘distribution lines’ and ‘transmission lines’.
Distribution lines are local natural gas utility systems that include gas mains and service lines, such as the commercial gas used at domestic environments. All these distribution lines need to be odorised. For the transmission lines it is stated in the regulations when to odorise it.
Picture LEL and UEL
For the odorisation there are many different odorants available, such as Tetrahydrothiophene (THT) and Mercaptan. Selecting the odorant depends on the properties of the gas to be odorised, pipeline layout, ambient conditions etc. Tetrahydrothiophene or THT is a well-known odor. THT is under ambient conditions a colourless volatile liquid with an unpleasant smell.
Controlled supply of THT using mass flow controllers
Bronkhorst had the pleasure of developing a solution for a Dutch customer to add THT to their biogas. Biogas was generated from anaerobic decomposition of organic matter and upgraded to natural gas quality to inject into the Dutch natural gas main. As commercial natural gas in the Netherlands has to contain at least 18mg of THT per cubic meter gas, the process of adding this to the commercial gas had to be done really accurately.
ATEX Zone 1 Coriolis Mass Flow Meter
The traditional approach to add THT is using a pump with a fixed stroke volume. However, low gas flow rates using a pump for batch-wise injection may lead to liquid THT remaining in the gas lines. THT may not be mixed well with the gas and might have the wrong concentration. A homogeneous injection of THT is therefore much better. Besides this, THT is a relatively expensive odor which also makes an accurate injection very much desired.
A better solution here would be using a combination of a pump with a Coriolis mass flow controller, in our case the mini CORI-FLOW™ series mass flow controllers. The Coriolis instruments make it possible to dose both continuously as well as accurately.
For the complete application, please download our application note.
Something to be taken into account is the classification of the area. As gases in principle are explosive, it is very common for the environment around gases to be classified as a hazardous area. Most common classifications (in Europe) are marked as ATEX zone 1 or zone 2. Just make sure to select the right material to use.
For solutions such as THT odorisation processes, Bronkhorst can offer both ATEX/IECEx zone 1 and zone 2 solutions. Our mini CORI-FLOW Exd mass flow meter, for zone 1 applications, is a collaboration with one of world’s leading manufacturers in explosion protection, Electromach member of the R.STAHL Technology Group.
To optimize a chemical reaction, chemists must find the best combination of compounds and introduce these in precise proportions into the reaction chamber. This reactor may be kept at a certain pressure and temperature and a catalyst may be added to accelerate the reaction. The input of the reaction gases must be accurately measured at all times, even while pressurizing the reactor. An overshoot in flow (outside the scale of the mass flow meter) should be avoided, because this will introduce inaccuracy.
Bronkhorst has developed a specialized combination of electronic pressure and thermal mass flow controllers for automated pressure control of reactor vessels. This standard solution can be applied for low flow lab reactor systems as well as for high flow industrial applications like in hydrogenation processes in the food industry industry or at chemical plants.
At the inlet of the reactor, an EL-FLOW Mass Flow Controller (MFC) provides the process gas delivery, while an EL-PRESS Electronic Pressure Transmitter (EPT) measures the reactor pressure. At the outlet of the system there is a flow restriction which could simply be a (needle) valve or, as shown in the illustration, a MASS VIEW Mass Flow Regulator (MFR) with local display. The reactor pressure is controlled by giving a setpoint to the pressure transmitter.
In the illustration this is achieved by a script programmed into a PC and delivered via RS232. The integrated PID-controller of this pressure meter (Master) controls the valve position of the MFC’s control valve (Slave). When building up the pressure in the reactor, the maximum inlet flow is restricted by the MFC, thus preventing a flow peak. By using the ‘slave factor’ option, the maximum flow can be adjusted. When the process pressure has reached the desired value, it is kept constant while the required amount of reaction gas is controlled with a constant flow.
It is also possible to pre-set the total amount of reaction gas allowed into the system by using a batch control function. Once the total amount is reached, the set-point for the MFC can be programmed to be reset to zero, thus switching off the gas supply, independent of the process pressure.
The application of paint or labels to surfaces can be trickier than one would expect. Just as in applying paint to a wall in one’s home, if the surface is not properly prepared the result will be less than perfect. A leading manufacturer of ceramic and glass coating equipment was looking for a way to improve their coating process and increase their competitive advantage.
The process involves driving HMDSO vapor through a flame for surface treatment of glass. The end result is obtaining a hard SiOx-like thin film leading to a more wetable surface prior to painting or labeling. Initially the customer had tried using a syphon tube in the liquid HMDSO source that sucked up liquid into the fuel stream and into the burner. This was unsuccessful as it resulted in a very unreliable liquid flow because liquid draw was based on gas velocity. Next, the customer tried using a bubbler system. With the bubbler the customer found that the vaporization changed with bubbler liquid depth, delta P, temperature, and other un-controllable factors. Also, neither of these two processes provided recordable data feedback, so variations in surface treatment could only be detected at final product QC.
The Bronkhorst solution was to provide a system where the HMDSO vapor added to the flame could be accurately and precisely controlled. This was done through using a mini CORI-FLOW for the control of HMDSO liquid, an EL-FLOW Select thermal mass flow controller for the carrier gas, a Controlled Evaporator Mixer (CEM) to completely vaporize the HMDSO, and an E-8000 readout/control unit to power and control the vaporizer system.
Since implementing the Bronkhorst CEM system this customer has reduced the cost of materials as they are using precisely what is needed in the process, improved product quality as any variations can be seen and adjusted early in the process, and now has archived data for documentation and review.
Download our CEM brochure.