Thermal Mass Flow Measurement of Tank Blanketing Gas

Insertion style thermal mass flow meter can measure
low flow rates of gas for tank blanketing.
Courtesy Magnetrol

Closed liquid tanks and other vessels contain two substances, liquid and not liquid. The liquid, in this case, is the subject material of a process. The "not liquid" is whatever fills the space not filled by the subject liquid. There are many cases where the process, the subject liquid, and safety are best served by filling the space with a known gas. There may be concerns about ignition of the vapor from the liquid, reactivity of the liquid with oxygen, or a wide range of other issues that call for filling the tank space with a known gas.

Nitrogen is a commonly employed gas for tank blanketing. It is comparatively inexpensive and widely available. It can inhibit combustion by displacing atmospheric oxygen and is not reactive with most industrial process chemicals.

Vessels with rapidly changing levels, or those of very large size, will require larger available flow capacity of blanketing gas to maintain the desired conditions within the tank. There are regulating valves designed specifically for tank blanketing operations. Vents intended for use in the same application are also commercially available.

Monitoring tank liquid level and gas flow are part of best practices for a tank blanketing operation. Confirming that gas flow rate is commensurate with the requirements for current tank level confirms proper operation. Too high a flow rate could indicate a leak or malfunction of a blanketing system component. It may also be useful to totalize gas flow for use in operational planning.

Thermal insertion flow meters are suitable for measuring the wide range of gas flow rates employed in tank blanketing applications. The instruments are available for insertion installation, as shown in the image near the top of this article, or as inline units. Either configuration delivers accurate measurement with no moving parts, a high turndown ratio, and minimal maintenance requirement.

Share your tank blanketing requirements and challenges with process measurement and control specialists, combining your own process knowledge and experience with their product appliction expertise to develop effective solutions.

Thermal Mass Flow Meter Questions Answered by Experts

Thermatel, insertion style thermal mass flow meter
Image courtesy of Magnetrol

Knowledgeable individuals that share expertise and experience with others in their field are a valuable resource, worthy of our attention.

Tom Kemme, from Magnetrol®, expertly fielded some questions about thermal mass flow meters in a recent blog post. Mr. Kemme's responses were so useful and clear that I decided, with all the credit flowing his way, to share them here for those of you that may not closely follow the Magnetrol® Blog.

Will thermal mass flow meters be affected by changes in the composition of gas (i.e. will they require recalibration every time the composition changes)?

Thermal mass flow meters measure a flow rate based on convective heat transfer. Fluid properties are some of the many factors that influence convection. Each gas has unique properties, which is why these flow meters are calibrated for a specific application. You would not want a meter calibrated for an air application placed into a natural gas application without recalibration or some type of field adjustment if applicable.

All gas mixes are not created equal. If you had a gas mix with high hydrogen content, a variation in hydrogen would have a much greater effect than typical variation in natural gas content. Hydrogen has a tendency to create more heat transfer than most gases. For natural gas, it is common to have some slight variation in composition between the calibration of the device and the application itself. However, the effect is minimal for slight changes in methane or ethane at different times of the year. Natural gas fuel flow is one of the most prevalent applications for thermal mass.

Based on our experience, the biggest cause of malfunction in flow meters is improper installation. If you do not install a flow meter per the manufacturer’s recommendation this will greatly influence the performance of the meter. For thermal mass, this includes proper straight run, depth into the pipe (insertion probes) and flow arrow alignment.

Each application presents unique difficulties for every flow meter technology, and each end user has unique needs. There is no exact answer as to when a recalibration would be needed for thermal mass flow, as it is application dependent. You do not always need recalibrations for variation in gas composition.

What role do thermal flow meters play in emissions monitoring applications?

Thermal flow meters are at the forefront in flow measurement for emissions reporting and energy management projects. The energy management arena spans many markets, including some of the largest in the oil & gas and power industries. Some popular applications include monitoring gas fuel flow to a combustion source to report SO2 (sulfur dioxide) emissions, stack (flue) gas flow in power plants as part of a continuous emissions monitoring (CEM) system of NOX (nitrous oxide) and SO2, and flares in a gas field that need to be reported to environmental authorities. These applications prove difficult for many flow meter technologies.

For example, in a flare application most of the time gas is not being flared off, but it needs to be measured in case of an event. The user will want to monitor the low flow of pilot gas keeping the flare lit. This requires a flow meter with a very high turndown with good low flow sensitivity, which is a limitation of some technologies, such as differential pressure flow meters.

Many operators are most concerned with measuring CO2 (carbon dioxide) emissions. However, with thermal flow meters we are increasingly finding applications with the need for methane measurement. Methane is a greenhouse gas that has more than 20 times the global warming potential as CO2. No longer can coalmines or landfills emit this directly to the atmosphere. If not flaring the gas off, the owners are beginning to capture it, treat it, and produce usable natural gas from it. Some facilities that emit landfill gas, or facilities that produce biogas, are involved in carbon credit programs or clean development mechanisms. Similar applications can be found in wastewater treatment plants where customers are reporting digester gas emissions and even capturing this gas to produce electricity and reduce energy costs. Thermal dispersion flow meter technology, such as the MAGNETROL Thermatel® TA2, has become well accepted in all of these markets.

You can easily tap into Magnetrol® expertise to solve your flow measurement challenges. Reach out to a product specialist and combine your process knowledge with their flow measurement expertise to develop effective solutions.

Thermal Dispersion Flow Switches For Pump Protection

Thermal dispersion flow switches have advantages
when applied for pump protection
Image courtesy Magnetrol

Good practice for installing industrial pumps calls for inclusion of protective devices to assure that the pump is not exposed to conditions beyond its design intent. Monitoring liquid flow is a useful method for determining if a pump is operating within a safe range.

There are numerous methods of verifying flow in piping connected to a  pump. Magnetrol, globally recognized manufacturer of flow and level measurement technologies, offers up their assessment of various pump protection measures and a recommendation for what they consider an advantageous choice for flow measurement in a pump protection application.

Magentrol's white paper is included below, and you can share your flow and level measurement challenges with application experts for help in developing effective solutions.

Thermal Dispersion Flow Switches For Pump Protection from MSJacobs-Cali

Corrosion Resistant Flow Meter

There are numerous flow measurement technologies available for application in process measurement. Each technology is represented by a broad array of product variants, each with a set of attributes making it suitable for certain applications.

ICON Process Controls specializes in corrosion resistant industrial fluid handling and process control equipment, offering the most complete line of all plastic instrumentation products supported by the largest inventory in North America. Applications for their corrosion resistant instruments include Municipal and Industrial Water & Wastewater Treatment, Bulk Chemicals, Steel Processing, Metal Finishing, Chemical Dosing Skids, Food & Beverage.

Share your process measurement and control requirements with instrumentation specialists. Combine your own knowledge and experience with their product application expertise for effective solutions.

Hydrostatic Pressure Measurement for Determining Liquid Level

Pressure transmitters can be used to provide liquid level in
pressurized or open vessels.
Photo courtesy Azbil North America

Pressure measurement is an inferential way to determine the height of a column of liquid in a vessel in process control. The vertical height of the fluid is directly proportional to the pressure at the bottom of the column, meaning the amount of pressure at the bottom of the column, due to gravity, relies on a constant to indicate a measurement. Regardless of whether the vessel is shaped like a funnel, a tube, a rectangle, or a concave polygon, the relationship between the height of the column and the accumulated fluid pressure is constant. Weight density depends on the liquid being measured, but the same method is used to determine the pressure. 

A common method for measuring hydrostatic pressure is a simple gauge. The gauge is installed at the bottom of a vessel containing a column of liquid and returns a measurement in force per unit area units, such as PSI. Gauges can also be calibrated to return measurement in units representing the height of liquid since the linear relationship between the liquid height and the pressure. The particular density of a liquid allows for a calculation of specific gravity, which expresses how dense the liquid is when compared to water. Calculating the level or depth of a column of milk in a food and beverage industry storage vessel requires the hydrostatic pressure and the density of the milk. With these values, along with some constants, the depth of the liquid can be calculated.

The liquid depth measurement can be combined with known dimensions of the holding vessel to calculate the volume of liquid in the container. One measurement is made and combined with a host of constants to determine liquid volume. The density of the liquid must be constant in order for this method to be effective. Density variation would render the hydrostatic pressure measurement unreliable, so the method is best applied to operations where the liquid density is known and constant.

Interestingly, changes in liquid density will have no effect on measurement of liquid mass as opposed to volume as long as the area of the vessel being used to store the liquid remains constant. If a liquid inside a vessel that’s partially full were to experience a temperature increase, resulting in an expansion of volume with correspondingly lower density, the transmitter will be able to still calculate the exact mass of the liquid since the increase in the physical amount of liquid is proportional to a decrease in the liquid’s density. The intersecting relationships between the process variables in hydrostatic pressure measurement demonstrate both the flexibility of process instrumentation and how consistently reliable measurements depend on a number of process related factors. 

Share your process measurement and instrumentation requirements and challenges with professionals that specialize in their proper selection and application. Combining your own process knowledge and experience with their product application expertise will help to develop effective solutions.

Commercial and Industrial Process Heating Methods

Electric heating element of special design

Many industrial processes involve the use of heat as a means of increasing the energy content of a process or material. The means used for producing and delivering process heat can be grouped into four general categories.

• Steam
• Fuel
• Electric
• Hybrid

The technologies rely upon conduction, convection, or radiative heat transfer mechanisms, solely or in combination, to deliver heat to a substance. In practice, lower temperature processes tend to use conduction or convection. Operations employing very high temperature rely primarily on radiative heat transfer. Let's look at each of the four heating methods.

STEAM

Steam based heating systems introduce steam to the process either directly by injection, or indirectly through a heat transfer device. Large quantities of latent heat from steam can be transferred efficiently at a constant temperature, useful for many process heating applications. Steam based systems are predominantly for applications requiring a heat source at or below about 400°F and when low-cost fuel or byproducts for use in generating the steam are accessible. Cogeneration systems (the generation of electric power and useful waste heat in a single process) often use steam as the means to produce electric power and provide heat for additional uses. While steam serves as the medium by which heat energy is moved and delivered to a process or other usage, the actual energy source for the boiler that produces the steam can be one of several fuels, or even electricity.

FUEL

Fuel based process heating systems, through combustion of solid, liquid, or gaseous fuels, produce heat that can be transferred directly or indirectly to a process. Hot combustion gases are either placed in direct contact with the material (direct heating via convection) or routed through tubes or panels that deliver radiant heat and keep combustion gases separate from the material (indirect heating). Examples of fuel-based process heating equipment include furnaces, ovens, red heaters, kilns, melters, and high-temperature generators. The boilers producing steam that was described in the previous section are also an example of a fuel based process heating application.

ELECTRIC

Electric process heating systems also transform materials through direct and indirect means. Electric current can be applied directly to suitable materials, with the electrical resistance of the target material causing it to heat as current flows. Alternatively, high-frequency energy can be inductively coupled to some materials, resulting in indirect heating. Electric based process heating systems are used for heating, drying, curing, melting, and forming. Examples of electrically based process heating technologies include electric arc furnace technology, infrared radiation, induction heating, radio frequency drying, laser heating, and microwave processing.

HYBRID

Hybrid process heating systems utilize a combination of process heating technologies based on different energy sources or heating principles, with a design goal of optimizing energy performance and overall thermal efficiency. For example, a hybrid steam boiler may combine a fuel based boiler with an electric boiler to take advantage of access to low off-peak electricity cost. In an example of a hybrid drying system, electromagnetic energy (e.g., microwave or radio frequency) may be combined with convective hot air to accelerate drying processes; selectively targeting moisture with the penetrating electromagnetic energy can improve the speed, efficiency, and product quality as compared to a drying process based solely on convection, which can be rate limited by the thermal conductivity of the material. Optimizing the heat transfer mechanisms in hybrid systems offers a significant opportunity to reduce energy consumption, increase speed and throughput, and improve product quality.

Many heating applications, depending on scale, available energy source, and other factors may be served using one or more of the means described here. Determining the best heating method and implementation is a key element to a successful project. M.S. Jacobs and Associates specialize in electric heating applications and facets of the industrial production of steam. Share your process and project challenges with them and combine your facilities and process knowledge and experience with their product application expertise to develop effective solutions.

Wireless Communications Deliver Real Time Process Data From Remote Operating Sites

Oil is where you find it, with many prospecting and production sites located where the communication options taken for granted in developed areas do not exist. Oil is big and serious business, with tremendous sums of money at risk on the prospect of reaping even greater returns. Every business operation, though, is of great importance to the stakeholders. Countless operations in little known industries and endeavors are located beyond the boundaries of modern communications infrastructure.

If you want a data connection, bring your own.

Remote operating sites, whether for oil extraction or other purposes, will often be automated. Some decision making system or individual is responsible for the safe and effective operation of the remote site, or has a use or need for real time data being gathered at the remote site. Radio transmission is a viable, maybe the best, option for delivering real time data from a remote site to a central office.

• Transmission options for 900 MHz, 2.4 GHz, cellular, and satellite systems are readily available.
• Equipment operates on low voltage, low power. Suitable for solar or other remote site power source.
• No special instrumentation needed. Radio transmitting and receiving equipment interfaces directly with analog signals from common industrial process transmitters.
• No "across the land" cabling needed.
• Equipment can be configured to resist extreme environmental conditions.

Analynk manufactures transmission and receiving equipment that builds the bridge between remote sites and the home office. From elemental componentry to integrated, ready to run systems, Analynk specializes in wireless communications for industrial process control. Share your wireless process data connection challenges with process measurement and control specialists. Whether an expansive multipoint, or a single point application, application specialists can combine standard or customized products into a practical solution for every application.