Monday, May 22, 2017

CSB Animation and Analysis of Torrance Refinery Explosion

The United States Chemical Safety Board investigates industrial accidents related to chemical processing. It is an advisory agency that provides recommendations for improving safety in chemical related operations.

Some accident events are illustrated with animated reenactment, along with the events determined to be contributory to the cause. In the case of the Torrance, CA refinery explosion, the animation shows how a worn valve that did not provide adequate shutoff was part of the string of events that ultimately led to disaster. Also of concern was the procedure followed in responding to the discovery of an unexpected condition indicating substantial process malfunction.

Fortunately, the flammable gases were detected by personal safety gear, enabling workers to clear the area before ignition occurred.

The video describes how the process operated and what failed. The key takeaway is that a single failure condition can reveal another that may have gone undetected. Also, operating under adverse conditions, trying to formulate strategy, is difficult and may not produce the most effective plan.

Industrial processing can be complicated and dangerous. Diligence in design, installation, and continuing maintenance of process equipment is part of the overall safety plan for every facility.

Consider your own process and where weaknesses may be lurking. Reach out to equipment and instrumentation vendors for advice and expertise regarding specific items of concern.

Thursday, May 18, 2017

New Thermal Mass Flow Meter

industrial process measurement instrument thermal mass flowmeter transmitter
The new model FT4A thermal mass flowmeter, shown
inserted in process pipe.
Courtesy Fox Thermal Instruments
Fox Thermal Instruments, manufacturer of thermal technology based mass flow instruments for industrial process measurement, has introduced a new more advanced product providing the accuracy and reliability users expect from Fox, along with some new features extending the ease of use and applicability of the instrument.

The basic operation involves measuring flow in relation to its heat dissipating effect on a temperature sensor. Higher mass flow produces a higher rate of heat transfer.

The mass flow measurement instruments are very popular for several reasons. They have no moving parts, have a fairly unobstructed flow path, are accurate over a wide range of flow rates, calculate mass flow rather than volume, measure flow in large or small piping systems, and do not need temperature or pressure compensation. While most thermal flow meters are used to measure flowing gas, some also measure flowing liquids.

The new model FT4A incorporates the latest feature updates and technology advancements. More information can be found in the datasheet provided below. Share your gas flow measurement challenges with instrumentation specialists. Combine your own process experience and knowledge with their product application expertise to develop effective solutions.

Tuesday, May 9, 2017

In-Line Process Refractometer

Refractometry, a combination of physics, materials, and chemistry, is a measurement technique which determines the composition of known substances by means of calculating their respective refractive indexes (RI). RIs are evaluated via a refractometer, a device which measures the curve, or refraction, resulting when the wavelength of light moves from the air into and through a tested substance. The unitless number given by the refractometer, usually between 1.3000 and 1.7000, is the refractive index. The composition of the substance is then determined with a comparison of the measured RI to standard curves developed for the substance. There are four general types of refractometers: digital, analog, lab, and inline process. Although refractometry can measure a variety of substances, the most common group of known substances to calculate is liquids. Liquid based continuous processes benefit from the use of an inline process refractometer to provide real time data about process output or intermediate steps.

The ultimate focus of industrial refractometry is to describe what is in a final product or output of a process step. A field which relies directly on the results of refractometry is gemology. Gemological refractometry is crucial for accurately identifying the gemstones being classified, whether the gemstones are opaque, transparent, or translucent.

Other common examples of industrial refractometry uses include measuring the salinity of water to determine drinkability; figuring beverage ratios of sugar content versus other sweeteners or water; setting eye-glass prescriptions; understanding the hydrocarbon content of motor fuels; totaling plasma protein in blood samples; and quantifying the concentration of maple syrup. Regarding fuels, refractometry scrutinizes the possible output of energy and conductivity, and for drug-testing purposes, refractometry measures the specific gravity, or the density, of human urine. Regarding food, refractometry has the ability to measure the glucose in fruit during the fermentation process. Because of this, those in food processing can know when fruit is at peak ripeness and, in turn, also understand the most advantageous point in the fruit’s lifetime to put it on the market.

The determination of the substance composition of the product examples listed above all speak to the purpose of quality control and the upholding of standardized guidelines. Consumers rely on manufacturers not only to produce these products safely and in vast quantity, but to deliver the customer a consistent taste experience when the product is consumed. Brand marketing success relies on maintaining the standards for the composition of substances that comprise the product. One could argue that an in-line process refractometer is actually a marketing tool of some sort, at least to the extent that it is employed to maintain consistent product quality.

Equipment manufacturers have developed numerous refractometer configurations tailored to specific use and application. Each has a set of features making it the advantageous choice for its intended application. Product specialists can be invaluable sources of information and assistance to potential refractometer users seeking to match the best equipment to their application or process.

Wednesday, May 3, 2017

Continuous Liquid Level Measurement Technologies Used in Industry

magnetic level indicator coupled with guide wave radar level transmitter
Magnetic level indicator coupled with
guide wave radar level transmitter
Courtesy Vega
Although continuous level measurement technologies have the ability to quantify applications for bulk solids, slurries, and granular materials, liquid level technologies stand out as being exceptionally crucial to the foundation of process control. Called “transmitters,” these continuous liquid level measurement devices employ technologies ranging from hydrostatics to magnetostriction, providing uninterrupted signals that indicate the level of liquid in a vessel, tank, or other container.

Hydrostatic devices focus on the equilibrium of dynamic and static liquids. There are three main types of hydrostatic transmitters: 1) displacer, 2) bubbler, and 3) differential pressure.

The displacer transmitters utilize a float placed within the liquid container. With its buoyancy characterized to the liquid and the application, the float, a connecting stem, and a range spring or similar counterbalance represents the liquid level in terms of the movement of the displacer (float). The displacement, or movement, of the assembly is converted into an electric signal for use by the monitoring and control system.

Bubbler transmitters are used for processing vessels that operate at atmospheric pressure. This method introduces a purge gas or an inert gas, e.g. air or dry nitrogen, into a tube extending into the liquid vessel. Precise measurement of the pressure exerted on the gas in the dip tube by the liquid in the tank is used to determine the height of the liquid.

Differential pressure (DP) transmitters rely directly on, in a basic explanation, the pressure difference between the bottom and top of the container. Precise pressure measurement is used to determine the height of the liquid in the tank. One of the most advantageous aspects of DP transmitters is that they can be used in pressurized containers, whereas displacer and bubbler transmitters cannot.

Other examples of level transmitter technologies––which are not hydrostatic devices––are magnetostrictive, capacitance, ultrasonic, laser, and radar.

In magnetostrictive level transmitters the measuring device, a float, has a series of magnets that create a magnetic field around a wire enclosed in a tube. Electrical pulses sent down the wire by the transmitter head product a torsional wave related to the position of the float, which moves with changes in liquid surface level. The transit time of the torsion wave back to the sensing head is measured and the depth of the liquid, as indicated by the float position, can be determined.

Capacitance transmitters are best applied to liquids that have high dielectric constants. Essentially, changes in the capacitance of the sensor / tank / liquid assembly will vary proportionately with the liquid level. The change in capacitance is measured and converted to an appropriate electrical signal.

Ultrasonic level transmitters emit ultrasonic energy from the top of the vessel toward the liquid. The emissions are reflected by the liquid surface and them time required for the signal to return to the source is used to determine the distance to the liquid surface.

Laser level transmitters operate similarly to an ultrasonic level transmitter. However, instead of using ultrasound signals, they use pulses of light.

Radar level transmitters involve microwaves emitting downward from the top of the container to the liquid’s surface and back again; the measurement is the entire time-frame. One variable radar level measurement echoes capacitance measurements: they both involve dielectric contact of liquid.

The precise measurement of transmit time for a wave or pulse of energy is employed in several of the technologies, the measurement of pressure in others. Each technology has a set of attributes making it an advantageous selection for a particular range of applications. Share your liquid level measurement challenges with an application expert, combining you process knowledge with their product application expertise to develop effective solutions.

Wednesday, April 26, 2017

Operating Principles and Application of Vortex Flowmeters

vortex flow meter flowmeter
Vortex Flowmeter
Courtesy Yokogawa
To an untrained ear, the term “vortex flowmeter” may conjure futuristic, potentially Star Wars inspired images of a hugely advanced machine meant for opening channels in warp-space. In reality, vortex flowmeters are application specific, industrial grade instruments designed to measure an important element of a fluid process control operation: flow rate.

Vortex flowmeters operate based on a scientific principle called the von Kármán effect, which generally states that a fluid flow will alternately shed vortices when passing by a solid body. “Vortices” is the plural form of vortex, which is best described as a whirling mass, notably one in which suction forces operate, such as a whirlpool. Detecting the presence of the vortices and determining the frequency of their occurrence is used to provide an indication of fluid velocity. The velocity value can be combined with temperature, pressure, or density information to develop a mass flow calculation. Vortex flowmeters exhibit high reliability, with no moving parts, serving as a useful tool in the measurement of liquid, gas, and steam flow.

While different fluids present unique challenges when applying flowmeters, steam is considered one of the more difficult to measure due to its pressure, temperature, and potential mixture of liquid and vapor in the same line. Multiple types of steam, including wet steam, saturated steam, and superheated steam, are utilized in process plants and commercial installations, and are often related to power or heat transfer. Several of the currently available flow measurement technologies are not well suited for steam flow applications, leaving vortex flowmeters as something of a keystone in steam flow measurement.

Rangeability, defined as a ratio of maximum to minimum flow, is an important consideration for any measurement instrument, indicating its ability to measure over a range of conditions. Vortex flowmeter instruments generally exhibit wide rangeability, one of the positive aspects of the technology and vortex based instruments.

The advantages of the vortex flowmeter, in addition to the aforementioned rangeability and steam-specific implementation, include available accuracy of 1%, a linear output, and a lack of moving parts. It is necessary for the pipe containing the measured fluid to be completely filled in order to obtain useful measurements.

Applications where the technology may face hurdles include flows of slurries or high viscosity liquids. These can prove unsuitable for measurement by the vortex flowmeter because they may not exhibit a suitable degree of the von Kármán effect to facilitate accurate measurement. Measurements can be adversely impacted by pulsating flow, where differences in pressure from the relationship between two or more compressors or pumps in a system results in irregular fluid flow.

When properly applied, the vortex flowmeter is a reliable and low maintenance tool for measuring fluid flow. Frequently, vortex flow velocity measurement will be incorporated with the measurement of temperature and pressure in an instrument referred to as a multivariable flowmeter, used to develop a complete measurement set for calculating mass flow.

Whatever your flow measurement challenges, share them with a flow instrument specialist, combining your process knowledge with their product and technology expertise to develop effective solutions.

Friday, April 21, 2017

Thermal Mass Flowmeters

Thermal dispersion mass flow meters provide an accurate means of mass flow measurement with no moving parts and little or no encroachment on the media flow path. There are a number of different configurations to be found among various manufacturers, but all function in basically the same manner.

Two sensors are exposed to the heat transferring effect of the flowing media. When the media composition is known, the mass flow can be calculated using the meter reading and the pipe cross sectional area. One of the flow meter sensors is heated, the other is allowed to follow the media temperature as a reference. The heat dispersion from the heated sensor is measured and used to calculate mass flow.

Some positive attributes of thermal dispersion flow meters:
  • In-line and insertion configurations available to accommodate very small to large pipe sizes
  • Rugged Construction
  • No moving parts
  • Measure liquid or gas in a wide range of applications
  • Measurement not adversely impacted by changes in pressure or temperature
  • Wide range of process connections 
  • In-line versions provide unobstructed flow path
  • Wide turndown suitable for extended flow range
  • Flow rate and totalized flow
  • 4-20 mA output interfaces easily with other instruments and equipment
Share all your process measurement challenges and requirements with product application specialists, combining your process knowledge with their product application expertise to develop effective solutions.

Thursday, April 13, 2017

Digital Bar Graph Process Displays Still Have a Place in Your Panel

bargraph digital analog indicators for industrial control
Analog process value indicators are available in a wide
variety of form factors
Courtesy Ametek - Dixson
Analog indicators provide a graphic display of a process value. The value can be a setpoint for a particular operation, or the value returned from a sensor or transmitter. In the current digitally focused environment, we sometimes devalue analog displays. They do, however, have some attributes that set them apart from digital displays. Let's look at bar graph displays.

The ability of an analog display, such as a bar graph, to display useful information depends heavily on its graphical scale. The scale length and resolution should allow significant change in the process value to be displayed in a manner that is readily discernible to an operator. Bar graph displays are composed of illuminated segments, so any significant change in the process value should be sufficient to change the illuminated state of one or more segments.

The scale length and range of the display should extend across the whole of the process, and slightly beyond. An indicating range that far exceeds any possible process value can compromise the display resolution and fail to maximize the use of the instrument. For example, an operation with a maximum process value of 100 should not be paired with an indicating scale that extends to 2500. In this case, the entire range of possible process values indicated will only use four percent of the available indicating scale. A scale range extending to 150 would be more appropriate and deliver better performance.

Analog indicators, especially bar graphs, can provide rapid assessment of the state of a process value. As an illustration, it may not be necessary for an operator to know process temperature with resolution to a tenth of a degree. The key requirement may be to answer the question, "Is it too hot?". Analog displays excel at providing rapid answers to those types of decision-making questions. An onboard digital display of real time process value provides additional information about current process state.

Analog bar graph displays have a proven track record of accuracy and reliability over decades of field use. Modern units include programmable auxiliary functions and take advantage of their microprocessor based design to enable adaptation and setup for almost any application. More information is included in a data sheet below, or your can share your process indication requirements and challenges with instrumentation specialists. The combination of your own process knowledge and experience with their product application expertise will yield an effective solution.