Accurate Level Measurement Contributes to Heat Rate Reduction

Industrial steam turbine

Steam production is a costly operation in any facility, but is of paramount importance in power generation plants. The bottom line of a combustion based power generation facility is sensitive to the cost of input fuel. Measures that can be taken to reduce fuel input for a unit of power output (called heat rate) can translate directly into profitability. An additional benefit of reducing heat rate is a commensurate reduction in emissions.

A major contributor to heat rate reduction is the recovery of heat from the process and transference of that heat into the boiler feedwater. A sizable feedwater preheater of the shell and tube type is used to recover the heat. Shell and tube heat exchanger efficiency can be maximized with accurate control of liquid level.

Magnetrol, globally recognized leader in level measurement technology, makes the case for using guided wave radar level measurement technology as the most advantageous means for this application. The video below describes the process and how the guided wave radar level transmitter can provide the best performance.

Magnetrol has an information kit devoted to heat rate reduction. Share your steam system and level measurement challenges with a product specialist, and ask how you can get the Heat Rate Reduction Kit. Combining your facility and process knowledge with the product application expertise of a specialist will result in effective solutions.

Applying Coriolis Flowmeters

Coriolis Flowmeter
Courtesy Yokogawa

Coriolis mass flow meters are widely used throughout the process measurement and control field. Their basic operating principle, combined with modern sensor and signal processing technology, provide a list of potential application advantages.

• Directly measure mass flow based on the principle of measurement.
• No "moving" parts (except the slightly vibrating sensor tubes).
• Coriolis sensors have the ability to measure flow of non-conductive fluids.
• Measure the mass flow rate with high accuracy.
• Instruments can be applied across a wide usable measurement range.
• Deliver density measurement based on oscillating frequency.
• Not materially impacted by fluid viscosity or density.
• Coriolis flow meters also do not need lengthy straight pipe sections upstream or downstream of the sensing unit.

SELECTION AND INSTALLATION RECOMMENDATIONS

Some considerations for product selection and installation of Coriolis mass flow meters:

• Rapid temperature changes within the measured medium can impact measurement accuracy.
• Wide ranges of connection types are available, specify the best match for your system.
• Select sensor tube construction material to accommodate media characteristics.
• For liquid measurement, the sensor tube will extend downward from a horizontal pipe run. 
• As with most industrial products, there may be restrictions on where the device may be used. For example, not for use in aircraft. Assure that your application conforms with the intended usage of the instrument.
• Install at least one tight shutoff valve adjacent to the instrument for purposes of zeroing. Isolation valves for inlet and outlet are preferred.
• Follow manufacturer recommendations for pipe supports, if required, at inlet and outlet sides of the unit
• Avoid installation at locations with high levels of vibration or strong electrical fields.
• Locate the sensor unit at the lowest practical level in the piping system. This helps avoid collection of gas bubbles in the sensor tubes.
• Sensor tubes need to be completely filled with subject medium to obtain accurate measurement.
• Avoid the use of flexible connections and reducers at the unit connection points, unless in accordance with specific manufacturer guidelines.

The Coriolis flow meters of different manufacturers may have some particular recommendations, all of which should be followed to insure the best available performance, safety, and longevity of the unit.

Share your process instrumentation challenges and requirements with process measurement specialists, combining your process knowledge and expertise with their product application experience to develop effective solutions.

Quick Reference Guide for Pressure and Flow Instrumentation

Mass Flow Controller
Courtesy Brooks Instrument

Brooks Instrument is a globally recognized manufacturer of flow and pressure instrumentation for scientific and industrial use. The company's product line ranges through:

Variable Area Flowmeters - Armored metal, glass tube and plastic for reliable measurement of liquids and gases

Mass Flow Controllers - Coriolis and thermal mass flow technology for precision fluid measurement and control

Pressure Controllers - Digital and mechanical pressure regulators and controllers deliver high precision gas control

Pressure and Vacuum Products - Pressure transducers, gauges, and capacitance manometers

Vaporization Products - Deliver controlled high purity vapor to processes from source liquid

There are many products and variants. The company developed a summary document that provides an overview of the various product types, enabling potential users to focus quickly on the instruments that will meet their requirements. The document is included below.

Share your pressure, vacuum, and flow measurement and control challenges with product application specialists, combining your process knowledge and experience with their product application expertise to develop effective solutions.

Flow, Pressure & Vapor Instrumentation from Miller Energy, Inc.

Thermal Mass Flow Meter Q&A From Magnetrol

Thermatel® thermal mass flow meter
Courtesy Magnetrol®

Sometimes you discover that others do something better than you. When that happens, watch and listen.

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.

Question: What is the difference between the flow units Nm3/h, Sm3/h, and actual m3/h?

Answer: Actual m3/h is a flow rate at operating temperature and pressure. Normal or standard m3/h (Nm3/h = Sm3/h) is a flow rate at standard temperature and pressure (STP). I tend to reference the natural gas industry, where it is not possible to compare flow rates at every operating condition, so it is preferable to reference all flow rates back to a set of base conditions, such as 60°F and 1 atm. STP is not universal so it may be unique based on the region or industry.

Most flow meters output a flow rate at operating conditions and need to correct this measurement. This may be accomplished with a multivariable transmitter or external to the device. A few examples that do not need to correct the measurement are thermal mass flow meters, such as the ones produced by MAGNETROL, and Coriolis flow meters.

Question: Do you have any certified failure rate data on your units to perform an SIL verification?

Answer: A Failure Modes, Effects, and Diagnostics Analysis (FMEDA) is completed during development to determine failure rates and Safe Failure Fraction (SFF). The SFF is utilized to determine Safety Integrity Level (SIL), which is often the published value.

Question: What should my meter be reading with no air flow in the pipe?

Answer: At zero flow and a dry pipe, a thermal mass flow meter should measure zero. Different thermal meters may have varying stability at no flow due to differences in operation.

There are two different types of operation: constant temperature (CT) and constant power (CP). CT devices start with a low power and this power increases with the flow rate to maintain the constant temperature difference (ΔT) between the RTDs. CP devices start with a high ΔT between RTDs at low flow and the ΔT decreases as the flow rate increases. CP may lack stability at zero flow due to possible convection currents associated with the high ΔT. CT will hold zero better, particularly devices that add less heat. For example, the maximum surface temperature of a TA2 probe is 4 C above process temperature. This is extremely low heat, eliminating convection currents due to the sensor. Convection currents could also occur through the pipe due to temperature variations.

It is also possible for a thermal meter to measure above zero during a no flow condition when there is pressure buildup in the line (typically a valve closed downstream). There may be low flow cutoff settings that can be changed to ignore nuisance measurements.

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.

Mounting Options For DP Transmitters With Universal Mounting Bracket

This short video illustrates the ease with which numerous mounting configurations of DPharp transmitters can be accomplished in new and existing operations. The DPharp line of pressure transmitters utilize Yokogawa's top flight digital sensing technology for accurate process measurement of pressure and differential pressure in a multitude of applications.

Share your process measurement challenges with application experts, combining your process knowledge with their product application expertise to develop effective solutions.

Dynamic Compensation for Static Pressure Effects in Differential Pressure Measurement

DPharp Gauge Pressure Transmitter
Courtesy Yokogawa

Attaining the best available performance and accuracy from any measuring device utilized in an industrial process is always advantageous. The scale of most industrial processes is such that even small inaccuracies in process measurement produce financially tangible impact. Differential pressure measurement, with wide application in the industrial process sphere, can be improved with the addition of a means to compensate for the real world effects of static pressure upon instrument performance.

Yokogawa Corporation has developed a means to dynamically compensate for static pressure effects in field measurements. The brief technical presentation below will help you understand how static pressure effects can impact your field measurements, as well as how Yokogawa’s Real-time Dynamic Compensation works to offset its impact.

More detailed product and application information is available from your Yokogawa specialist.

Dynamic Compensation for Static Pressure Effects in Differential Pressure Measurement from Miller Energy, Inc.

Summary of Technologies Used For Continuous Liquid Level Measurement in Industrial Process Control

Non-contact radar liquid level transmitter
Courtesy Magnetrol

Automated liquid processing operations in many fields have requirements for accurate and reliable level measurement. The variety of media and application criteria demand continuous improvement in the technology, while still retaining niches for older style units utilizing methods that, through their years of reliable service, inspire confidence in operators.

Here is a synopsis of the available technologies for instruments providing continuous liquid level measurement. All are generally available in the form of transmitters with 4-20 mA output signals, and most are provided with additional outputs and communications. What is notably not covered here are level switches or level gauges that do not deliver a continuous output signal corresponding to liquid level.

Whether considering a new installation or upgrading an existing one, it can be a good exercise to review several technologies as possible candidates for a project. None of the technologies would likely be considered the best choice for all applications. Evaluating and selecting the best fit for a project can be facilitated by reaching out to a product application specialist, sharing your applications challenges and combining your process knowledge with their product expertise to develop an effective solution.

Displacer – A displacer is essentially a float and a spring that are characterized for a particular liquid and range of surface level movement. The displacer moves in response to liquid level, changing the location of a core connected to the displacer by a stem. The core is within a linear variable differential transformer. The electrical output of the transformer changes as the core moves.

Guided Wave Radar – A radar based technology that uses a waveguide extending into the liquid. The radar signal travels through the waveguide, basically a tube. The liquid surface level creates a dielectric condition that generates a reflection. Calculations and processing of the emitted and returned signals provide a measure of distance to the liquid surface. No moving parts.

Magnetostrictive – A method employing measurement of the transit time of an electric pulse along a wire extending down an enclosed tube oriented vertically in the media. A magnetic float on the exterior of the tube moves with the liquid surface. The float’s magnetic field produces the return signal to the sensor. Processing the time from emission to return provides a measure of distance to the liquid surface.

Pulse Burst Radar - A radar based technology employing emissions in precisely timed bursts. The emission is reflectex from the liquid surface and transit time from emission to return is used to determine distance to media surface.  Not adversely impacted by changes in media conductivity, density, pressure, temperature. No moving parts.

Frequency Modulated Continuous Wave Radar – Another radar based technology that employs a radar signal that sweeps linearly across a range of frequencies. Signal processing determines distance to media surface.  Not adversely impacted by changes in media conductivity, density, pressure, temperature. No moving parts.

RF Capacitance - As media rises and falls in the tank, the amount of capacitance developed between the sensing probe and the ground reference (usually the side metal sidewall) also rises and falls. This change in capacitance is converted into a proportional 4-20 mA output signal. Requires contact between the media and the sensor, as well as a good ground reference. No moving parts.

Ultrasonic Non-Contact – Ultrasonic emission from above the liquid is reflected off the surface. The transit time between emission and return are used to calculate the distance to the liquid surface. No contact with media and no moving parts.

Differential Pressure – Pressure sensor at the bottom of a vessel measures the pressure developed by the height of the liquid in the tank. No moving parts. A variation of this method is often called a bubbler, which essentially measures hydrostatic pressure exerted on  the gas in a tube extending into the contained liquid. It has the advantage of avoiding contact between the measuring instrument parts, with the exception of the dip tube, and the subject liquid.

Laser - Probably one of the latest arrivals on the liquid level measurement scene, laser emission and return detection is used with time interval measuring to accurately determine the distance from the sensor source to the liquid surface.

Load Cell - A load cell or strain gauge can be incorporated into the support structure of the liquid containing vessel. Changes in the liquid level in the vessel are detected as distortions to the structure and converted, using tank geometry and specific gravity of the liquid.

All of these technologies have their own set of attributes which may make them more suitable to a particular range of applications. Consulting with a product specialist will help determine which technologies are the best fit for your application.