Wednesday, September 20, 2017

Components for Industrial Tank Venting and Flame Arresting

flammable gas line flame arrester
Flammable gas line flame arrester
Image courtesy Groth Corp.
Pressure and Vacuum Relief Valves are protection devices often mounted on a nozzle opening on the top of a fixed roof atmospheric storage tank. Their primary purpose is to protect a tank against rupture or implosion by allowing the tank to breathe, or vent, when pressure changes in the tank due to normal operations.

Pilot Operated Relief Valves serve the same primary purpose as pressure/vacuum relief valves, but with better performance characteristics than weight or spring loaded valves. Lower leakage and better flow performance make a pilot operated valve the solution when the focus is product conservation, expanded tank working band, and reduced fugitive emissions. A pilot operated relief valve provides the maximum available leakage control technology as specified in the Clean Air Act of 1990.

Emergency Relief Valves protect tanks against excessive pressure caused by external fire exposure or flashes within the tank. Emergency relief valves provide higher flow capacity than standard pressure/vacuum relief valves.

Deflagration Flame Arresters are fire safety devices used to protect stored or process media from deflagrations. A deflagration flame arrester can be used on the top of a tank or as an in-line safety device where combustible gases are transported through low pressure pipe lines.

Detonation Flame Arresters provide flame protection in cases where the ignition source pipe lengths are greater than what can be protected with a deflagration arrester.

Blanket Gas Regulators can provide both pressure and fire protection for storage tanks by supplying a blanketing gas which maintains a constant positive pressure in the vapor space of a storage tank. In addition to preventing outside air and moisture from entering the storage vessel, a blanket gas regulator reduces the evaporation of the stored product to a negligible amount, resulting in product conservation and greatly reduced emissions.

Matching the function and capacity of each of these safety valves requires engineering expertise to assure proper operation. Share your requirements with product application specialists, combining your own process knowledge and experience with their product application expertise to develop an effective solution.

Thursday, September 14, 2017

Reliable Level Switch Technology

Level switches in steam and other fluid systems deliver value by providing reliable service over long periods of time, and under sometimes challenging conditions. The Mercury-Free Level Switch, from Jerguson®, utilizes an external float chamber and a magnetic coupling of the float to the switch mechanism. The three magnet system produces a smooth and reliable snap action that is illustrated in the short video,

Share your fluid control and steam system challenges with combustion and steam system experts, combining your own knowledge and experience with their product application expertise to develop effective solutions.

Electric Actuator for Linear and Quarter Turn Control Valves

Many process control valve installations present the option of selecting either electric or pneumatic actuators as part of the control component train. Pneumatic actuators have been in use for many years, but advances in electric motor design that delivered greater torque and more precise operation have brought electric valve actuators into a prominent market position.

Electric actuators are compact and comparatively self contained, requiring only cable connections and none of the additional devices sometimes needed for a pneumatic installation. There are some points of advantage to consider with electric actuators. Rotork introduced their CVA line of electric actuators almost ten years ago, making it something of a mature product now. Here are some advantageous points about the CVA actuators that likely apply generically as well.

  • Setup is accomplished with a Bluetooth enabled device which provides quick calibration of open and closed positions, as well as establishment of valve setup parameters.
  • A separately sealed electrical connection compartment keeps motor and mechanical compartment isolated from the environment while electrical connection section cover is removed.
  • An on board datalogger records thrust and position data over time for use in asset management and service functions. Data can be downloaded by Bluetooth or transmitted by common protocol to another station.
  • Change in setpoint produces a rapid and precise change in valve position with high resolution accuracy and repeatability.
  • Actuator can be programmed to move to a preset condition in the event of a loss of electric power. The energy to achieve the failsafe position is stored in the actuator.
  • Force balance positioning used in pneumatic valves, with spring force vs. air pressure, has resilience that can result in a change in position of the valve trim in response to a bump in system pressure. Resistance from the gear train on electric drives prevents this movement.
  • Static friction of the valve packing and other parts increases the amount of force to intially get the valve moving toward a new position. The additional time required to build air pressure and force to overcome static friction results in delayed valve response, then overshoot of the new setpoint. A combination of a sensor system and the mechanical drive section of an electric actuator eliminates overshoot and delayed response.

Electric actuators can be had in quarter turn and linear versions, with torque ranges suitable for a broad range of process control applications. The datasheet below, from Rotork, provides useful illustrations of the actuator interior, along with additional detail about electric actuators. Share your process control valve requirements and challenges with product application specialists, combining your own process knowledge and experience with their product application expertise to develop the best solutions.

Wednesday, September 6, 2017

Differential Pressure Transmitter Inferential Applications

industrial process measurement instrument for differential pressure
Differential pressure transmitter for industrial
process control applications.
Image Courtesy Azbil North America
Differential pressure transmitters are utilized in the process control industry to represent the difference between two pressure measurements. One of the ways in which differential pressure (DP) transmitters accomplish this goal of evaluating and communicating differential pressure is by a process called inferential measurement. Inferential measurement calculates the value of a particular process variable through measurement of other variables which may be easier to evaluate. Pressure itself is technically measured inferentially. Thanks to the fact numerous variables can be related to pressure measurements, there are multiple ways for DP transmitters to be useful in processes not solely related to pressure and vacuum.

An example of inferential measurement via DP transmitter is the way in which the height of a vertical liquid column will be proportional to the pressure generated by gravitational force on the vertical column. The differential pressure transmitter measures the pressure exerted by the contained liquid. That pressure is related to the height of the liquid in the vessel and can be used to calculate the liquid depth, mass, and volume. The gravitational constant allows the pressure transmitter to serve as a liquid level sensor for liquids with a known density. A true differential pressure transmitter also enables liquid level calculations in vessels that may be pressurized.

Gas and liquid flow are two common elements maintained and measured in process control. Fluid flow rate through a pipe can be measured with a differential pressure transmitter and the inclusion of a restricting device that creates a change in fluid static pressure. In this case, the pressure in the pipe is directly related to the flow rate when fluid density is constant. A carefully machined metal plate called an orifice plate serves as the restricting device in the pipe. The fluid in the pipe flows through the opening in the orifice plate and experiences an increase in velocity and decrease in pressure. The two input ports of the DP transmitter measure static pressure upstream and downstream of the orifice plate. The change in pressure across the orifice plate, combined with other fluid characteristics, can be used to calculate the flow rate.

Process environments use pressure measurement to inferentially determine level, volume, mass, and flow rate. Using one measurable element as a surrogate for another is a useful application, so long as the relationship between the measured property (differential pressure) and the inferred measurement (flow rate, liquid level) is not disrupted by changes in process conditions or by unmeasured disturbances. Industries with suitably stable processes – food and beverage, chemical, water treatment – are able to apply inferential measurement related to pressure and a variable such as flow rate with no detectable impact on the ability to measure important process variables.

Share your process measurement challenges with instrumentation specialists, leveraging your own process knowledge and experience with their product application expertise to develop an effective solution.

Wednesday, August 16, 2017

Compact Electric Control Valve Actuators

electric linear control valve actuator
CML linear valve actuator
Image courtesy of Rotork
Rotork's CMA line of electric valve actuators are intended for use in industrial process control applications where precise response and positioning are key requirements. The variants of linear, rotary and quarter-turn actuators span a wide range of application requirements and support on-board programming and connection via any of several recognized communication protocols.

The compact actuators are available with enclosures rated for several environments, ranging from non-hazardous to hazardous. Low temperature operation to -40 degrees Celsius is provided with the inclusion of a low temperature option.

These are but a small recounting of the useful features incorporated into the product line. More detail is provided in the document included below. For best results, share your valve automation requirements and challenges with process valve automation specialists, combining your own process knowledge and experience with their valve automation expertise to develop effective solutions.

Tuesday, August 8, 2017

Rotary and Linear Drives for Damper Control on Combustion Air and Flue Gas Applications

pneumatic vane type damper drive
Pneumatic vane damper drive, one of several
variants available.
Image courtesy Rotork
Combustion air and flue gas damper drives fill a critical role requiring safety, accuracy and reliability above all else. It is critical to deploy the best drive technology to maximize combustion efficiency, minimize emissions and reduce installation costs.

Damper Operator (Drives) Types :

Damper drives can be one of three types: pneumatic, electric, or electro-hydraulic, as described below.
  • Pneumatic. These damper operators are used whenever controls rely primarily on compressed air (pneumatic) for moving operators.
  • Electric. These damper operators are used whenever controls rely primarily electricity as the power source.
  • Electro-hydraulic. These damper operators are the same as the electric type described above, but also have a hydraulic system to position the damper.
A very important part of damper design is determination of damper torque, and sizing and selection of the damper actuator for the maximum torque. Actuator torque should be selected to provide the maximum torque required to operate the damper as well as to provide margin and allow for degradation over the life of the damper. Actuators should be evaluated for damper blade movement in both directions, at the beginning of blade movement, and while stroking blades through the full cycle of movement.

The Goal for Selecting the Best Drive Technology:

Reduced emissions, lower fuel consumption and improved boiler draft control.

Ways to achieve this goal:
  • High speed continuous modulation of ID/FD fan and inlet guide vanes 
  • Improved modulation and control of secondary air dampers 
  • Improved automation and burner management 
  • Quick response to plant demand 
  • Improved reliability in high temperature environments 
  • Precise damper and burner positioning 
  • Simple commissioning and diagnostics 
  • Low running costs, virtually maintenance free 
  • Pneumatic, analog and bus network communications 
For more information, share your requirements and challenges with combustion experts. The combination of your facilities and process experience and knowledge with their application expertise will yield an effective solution.

Thursday, August 3, 2017

The Application of Heat in Industrial Settings

industrial shell and tube heat exchanger
Heat exchangers are found throughout industrial and
commercial settings in many sizes and types.
The measurement and control of heat related to fluid processing is a vital industrial function, and relies on regulating the heat content of a fluid to achieve a desired temperature and outcome.

The manipulation of a substance's heat content is based on the central principle of specific heat, which is a measure of heat energy content per unit of mass. Heat is a quantified expression of a systems internal energy. Though heat is not considered a fluid, it behaves, and can be manipulated, in some similar respects. Heat flows from points of higher temperature to those of lower temperature, just as a fluid will flow from a point of higher pressure to one of lower pressure.

A heat exchanger provides an example of how the temperature of two fluids can be manipulated to regulate the flow or transfer of heat. Despite the design differences in heat exchanger types, the basic rules and objectives are the same. Heat energy from one fluid is passed to another across a barrier that prevents contact and mixing of the two fluids. By regulating temperature and flow of one stream, an operator can exert control over the heat content, or temperature, of another. These flows can either be gases or liquids. Heat exchangers raise or lower the temperature of these streams by transferring heat between them.

Recognizing the heat content of a fluid as a representation of energy helps with understanding how the moderation of energy content can be vital to process control. Controlling temperature in a process can also provide control of reactions among process components, or physical properties of fluids that can lead to desired or improved outcomes.

Heat can be added to a system in a number of familiar ways. Heat exchangers enable the use of steam, gas, hot water, oil, and other fluids to deliver heat energy. Other methods may employ direct contact between a heated object (such as an electric heating element) or medium and the process fluid. While these means sound different, they all achieve heat transfer by applying at least one of three core transfer mechanisms: conduction, convection, and radiation. Conduction involves the transfer of heat energy through physical contact among materials. Shell and tube heat exchangers rely on the conduction of heat by the tube walls to transfer energy between the fluid inside the tube and the fluid contained within the shell. Convection relates to heat transfer due to the movement of fluids, the mixing of fluids with differing temperature. Radiant heat transfer relies on electromagnetic waves and does not require a transfer medium, such as air or liquid. These central explanations are the foundation for the various processes used to regulate systems in industrial control environments.

The manner in which heat is to be applied or removed is an important consideration in the design of a process system. The ability to control temperature and rate at which heat is transferred in a process depends in large part on the methods, materials, and media used to accomplish the task. Share your process control challenges with application specialists, combining your own knowledge and experience with their product application expertise to develop effective solutions.