Combining Rupture Discs With Pressure Relief Valves

Applying a rupture disc in concert with a safety relief
valve can deliver real benefits.
Image courtesy Continental Disc Corporation

Common elements of any pressurized system include safety and pressure relief valves. Their general purpose is to stop system pressure from exceeding a preset value, preventing uncontrolled events that could result in damage to personnel, environment, or assets. Their operating principle and construction are comparatively simple and well understood.

Long term exposure of a relief valve to process media can result in corrosion, material buildup, or other conditions which may shorten the useful life of the valve, or worse, impair its proper operation. This excessive wear will increase the ongoing cost of maintaining or replacing a prematurely worn valve. One other aspect of relief valves can be the reduction in their seal integrity or force as the system pressure approaches the setpoint. This could possibly lead to fugitive emissions, an undesirable condition.

An effective approach to mitigating some of the effects of exposure to the process media is to install a rupture disc upstream of the safety valve inlet. Isolating a relief or safety valve from the process media through the installation of a rupture disc upstream of the valve inlet will eliminate exposure of the costly valve to effects of the media. It is necessary to establish proper rating and selection for the rupture disc to avoid any impairment of the overall operation of the relief valve, but the selection criteria are not complex. A number of benefits can accrue with this concept.

• Rupture disc isolates the valve from the media, allowing application of less costly valves fabricated of non-exotic materials.
• Rupture discs are leak free and bubble tight, eliminating possibility of fugitive emissions from the safety relief valve, especially when system pressure may approach valve setpoint.
• Relief valve inventory can be evaluated for reduction.
• Longer valve life.
• Less downtime.

The additional cost for the rupture disc enhancement can have a reasonable payback period, with all factors considered. In any case, the rupture disc protection makes for a cleaner relief valve installation. The document provided below provides some additional application recommendations and details.

Rupture discs and holders are available in sizes and materials for most applications. Share your ideas with a product specialist, combining your process knowledge with their product application expertise to develop an effective solution.

Combining Rupture Discs and Safety Relief Valves from CTi Controltech

Quarter Turn vs Linear Valves

This lined ball valve is an example of a
quarter turn valve.
Image courtesy Flowserve - Atomac

Different types of valves are designed and applied for different roles in the process control. Linear valves and quarter-turn valves are two different types of valves utilized throughout industry to regulate and control fluid flow. Their design and construction reflect the intent of the valves’ application, with each being suited for a different class of use.

All valves operate by providing control of the position of an internal structure that impedes fluid passage to some degree. Generally, fluid flow at the valve can be characterized as one of three conditions, unrestricted (valve fully open), stopped (valve fully closed), and throttled (valve partially open). Process operational requirements will dictate whether just two (fully open and fully closed) or all three of those conditions will be needed. Many aspects of the fluid, the process, and the surrounding environment come into play when making an appropriate valve selection. Not always an easy task.

Linear valves are generally characterized by their straight line motion that is used to position the valve plug, disc, diaphragm or other flow controlling element. The shape, size, and arrangement of the linear valve trim is generally intended to empower the operator with a range of flow through the valve. Through its positioning, the linear valve is able to regulate fluid flow at a slower, but more accurate rate. The valves can move a disk or a plug into an orifice, or push a flexible material, such as a diaphragm, into the flow passage. Gate valves and fixed cone valves are common examples of linear motion valves. Linear valves are best applied as flow controllers, and are often suited for frequent operation and repositioning.

Quarter turn valves traverse from fully open to fully closed by a 90 degree rotation of a shaft connected to the controlling element. Their comparatively simple operation allows for a design that is rugged and compact. One distinction of the quarter turn valves is their ability to quickly reposition from open to closed positions. Torque requirements to operate the valves are generally low to moderate. Ball and butterfly valves are examples of quarter turn valves.

Depending on the specific scenario, linear valves and quarter-turn valves are optimal choices for particular process environments. The accuracy of the linear valve and its ability to move in a linear fashion as opposed to a quarter-turn comes coupled with easy maintenance and decreased likelihood of cavitation. Both valve types enjoy widespread use and should generally not be viewed as competing designs for the same application. Each has a range of applications where it excels.

Share your fluid flow control challenges of all types with valve specialists, leveraging your own knowledge and experience with their product application expertise to develop effective solutions.

Application Survey for Industrial Flame Arrester

Detonation flame arrester is one of several configurations
applicable to various installations.
Image courtesy Groth Corporation

A flame arrester operates by removing heat from the flame as it attempts to travel through narrow passages with heat-conductive walls. The arrester will stop a high velocity flame by absorbing heat away from the flame head, which lowers the burning gas/air mixture below its auto-ignition temperature, and creating an atmosphere where the flame cannot be sustained. The channels or passages in the flame arrester are designed to very efficiently conduct heat outward, but still allow the gasses to flow.

Many in-line flame arrester applications are used in systems that collect gases emitted by liquids and solids called vapor control systems. The gases are typically flammable. If an ignition occurs, a flame inside or outside of the system could occur with potentially catastrophic outcomes.

A vapor destruction system is a type of vapor control system that includes enclosed flare systems, elevated flare systems, burner and catalytic incineration systems, and waste gas boilers.

Vapor recovery systems are another type of vapor control system that uses in-line flame arresters. These systems include compression systems, vapor balancing, refrigeration, adsorption, and absorption.

Flame arresters are used in many industries including chemical, refining, petrochemical, pulp and paper, oil exploration and production, pharmaceutical, sewage treatment, landfills, power generation, and bulk liquids transportation.

The document below is a handy flame arrester application questionnaire. Please always consult with a properly qualified applications specialist prior to specifying, purchasing, or applying flame arresting devices.

Flame Arrester Application Questionnaire from CTi Controltech

Scotch Marine Boilers

Cutaway view of two-pass Scotch Marine Boiler
Image courtesy Williams & Davis Boilers

Boilers have a long history in the industrialization of the world. They were a primary source of motive power for many decades in the industrial revolution. Boilers continue to be an important source of both heat and motive power.

There is no shortage of lexicon in the boiler industry, with many legacy names for particular boiler designs. A Scotch Marine Boiler is a firetube boiler that was historically employed on ships. Firetube boilers channel the furnace combustion and resulting flue gases through an enclosure (for the furnace) and smaller diameter tubes. The shell of the boiler contains the water and steam, with the furnace and firetubes immersed within. Heat is transferred from the furnace and tubes into the water, producing hot water or pressurized steam as the unit design intends. Most of the heat from fuel combustion is passed to the water from the furnace chamber, with much of the remaining heat from the flue gases transferring from the firetubes. Once leaving the firetubes, the gases pass out of the boiler to a flue or chimney.

A dry-back boiler uses an enclosed chamber at the rear of the boiler to distribute the gases exiting the furnace section into the many firetubes. It is essentially just a box with the open entries to the firetubes and the open exit from the furnace penetrating its walls. The dry-back design facilitates access to the tubes for inspection and service.

There are other boiler configurations that serve to maximize various aspects of cost, service, and performance. Share your steam and hot water requirements with boiler and combustion specialists, leveraging your own knowledge and experience with their expertise to develop an effective solution.

Dry Back Scotch Marine Boiler from CTi Controltech

Eccentric Rotary Plug Control Valve

The MaxFlo 4 eccentric rotary plug control valve
Image courtesy of Flowserve Valtek

There is an extensive array of valves from which to select for a process control operation. Each candidate valve is targeted by its designers for a range of fluid applications, fortified with construction materials and design features specifically suited for meeting the challenges of that application range.

Flowserve, under their Valtek brand, developed a control valve that combines a number of useful design features. The MaxFlo 4 is an eccentric rotary plug valve intended for fluid control operations. The valve has some attractive design features.

• There is no shaft extending through the flow path, leaving flow unobstructed when the valve is fully open (see the illustration in the document included below).
• Valve trim provides tight bi-directional shutoff.
• Metal or soft seat construction is available to accommodate a wide range of applications.
• A variant provides flange to flange dimensions that allow the MaxFlo 4 to drop in as a replacement for standard size globe valves.
• High Cv rating may enable use of a smaller valve, when compared to other designs.
• Precise position control is delivered by the shaft form and plug mounting.
• Double offset eccentric plug eliminates sliding of plug across sealing surfaces, reducing wear and required seal maintenance.

More detailed information is provided in the document provided below. There is a revealing cutaway illustration showing the mounting and movement path of the plug. Share your industrial process control valve requirements and challenges with a valve selection and automation specialist to get the best match of control valve to application.

Eccentric Rotary Plug Control Valve from CTi Controltech

Lined Ball Valves

Lining of ball valves extends their application to a range
of corrosive fluids.
Image courtesy Flowserve - Atomac

Lined valves of all types have an isolating layer of material that keeps the media from contacting the valve body, maybe even the valve trim itself. The purpose of the lining is generally to extend the useful life of the valve by eliminating the corrosive effect that may be imparted by media on the valve construction. Lined valves, with no exception I can think of, will have metal bodies. The lining can be any of a number of materials that will be selected based upon resistance to degradation by the process media under consideration.

Lined ball valves deliver the performance of conventional ball valves, coupled with the corrosion protection afforded by an appropriate lining material.

• Low pressure loss
• Quarter turn operation
• Simple automation
• Positive shutoff
• Low to moderate operating torque
• Compact

Options for the ball configuration are available to meet throttling or other requirements. Automation can be accomplished via a range of means. For more information, share your valve and automation challenges with application specialists and leverage your own knowledge and experience with their product application expertise.

Atomac Lined Ball Valves from CTi Controltech

Expanded Product Offering at CTi Controltech

This weight loaded pressure relief valve is one of the many
products from Groth used for safe and efficient tank operations.
Image courtesy Groth Corporation

CTi Controltech has added Groth Corporation to its roster of valve and valve automation products. Groth is a well recognized manufacturer of an array of pressure relief and related products routinely used for tank operations and other processes.

• Pressure/Vacuum Relief Valves
• Pressure Relief Valves
• Vacuum Relief Valves
• Pilot Operated Valves
• Flame and Detonation Arresters
• Emergency Relief Valves
• Waste Gas Burners
• Pressure Regulators

Groth products have been protecting refineries, chemical processing plants and facilities with atmospheric fixed-roof storage tanks for more than 50 years. The new product line complements and expands CTi Controltech's ability to deliver full scale complete solutions to their customers.

A general product guide for the Groth products is included below. More detailed information, as well as product application expertise is available from CTi Controltech. Contact a product application specialist, leveraging your own knowledge and experience with their product application expertise to develop effective solutions to your industrial pressure relief challenges.

Groth Corporation Industrial Product Selection Guide from CTi Controltech

Rupture Discs - Designed to "Fail"

Rupture discs can be combined in series for additional functions.
Image courtesy Continental Disc Corp.

A rupture disc, sometimes known as a pressure safety disc, burst disc or bursting disc, is a one time pressure relief device most often used to protect a vessel, pipe, or container from over pressurization. As opposed to pressure relief valves, rupture discs are designed to function only one time by providing an instantaneous response to an over-pressure condition, providing sufficient venting flow to disallow any further pressure increase.

These sacrificial parts are designed to burst when pressure within production equipment exceeds a certain threshold by breaking down, stopping the process to prevent or mitigate hazardous events. Rupture discs are critical instruments utilized so that companies can ensure process safety as set forth by the International Safety Standards (IEC 61508/61511).

The safety devices prove most effective when they fail according to pre-established specifications. Inferior rupture discs may cause unnecessary and expensive production shutdowns by bursting at the wrong pressure. Adequate quality testing and manufacturing expertise assures performance in accordance with ratings.

Rupture discs are commonly used in chemical, petrochemical, nuclear, aerospace, medical, railroad, pharmaceutical, food processing and gas & oil applications. They provide primary or backup protection. Very often rupture discs are used in tandem with safety relief valves, protecting them from the process media and extending the life of the relief valve.

For more on rupture discs call CTi Controltech at 800-288-7926 or visit their website.

Rupture Disc Products For Industrial Process Safety from CTi Controltech

Considerations When Applying Inline Spring-loaded Check Valves

Cutaway view of connector style spring loaded
in-line check valve.
Image courtesy Check-All Valve

1) Installation and Mounting

Inline, spring loaded check valves can be used in horizontal or vertical applications with proper spring selection. This is most evident in vertical flow down installations. The spring selected must be heavy enough to support the weight of the trim in addition to any column of liquid desired to be retained.

2) Elbow's, Tee's or other Flow Distorting Device's
Inline, spring loaded check valves are best suited for use with fully developed flow. Although there are many factors affecting the achievement of fully developed flow (such as media, pipe roughness, and velocity) usually 10 pipe diameters of straight pipe immediately upstream of the valve is sufficient. This is particularly important after flow distorting devices such as elbows, tees, centrifugal pumps, etc.

3) Valve Material Selection
There are many factors that influence the resistance of materials to corrosion, such as temperature, concentration, aeration, contaminants, and media interaction/reaction. Special attention must be paid to the process media and the atmosphere where inline check valves are applied. It is always recommended that an experienced application tech be consulted before installation.

4) Seat Material Selection
Several seat material options are available for inline, spring loaded check valves. An allowable leakage rate associated with the “metal-to-metal” as well as the PTFE o-ring seat, is 190 cc/min per inch of line size, when tested with air at 80 PSI. Resilient o-ring seats can provide a “bubble tight” shut-off (no visible leakage allowed at 80 PSI air).

5) Sizing and Spring Selection
It is very important to size check valves properly for optimum valve operation and service life. Sizing accuracy requires the valve be fully open, which occurs when the pressure drop across the valve reaches or exceeds three times the spring cracking pressure. Again, it is recommended that an experienced application tech be consulted for help with sizing.

6) Shock-Load Applications
Inline, spring loaded check valves are not designed for use in a shock-load environment, such as the discharge of a reciprocating air compressor. These types of applications produce excessive impact stresses which can adversely affect valve performance.

7) Fluid Quality
Inline, spring loaded check valves are best suited for clean liquids or gasses. Debris such as sand or fibers can prevent the valve from sealing properly or it can erode internal components or otherwise adversely affect valve travel. Any particles need to be filtered out before entering the valve.

Share your fluid control challenges with product application specialists, leveraging your own process knowledge and experience with their product application expertise to develop effective solutions.

CTi Controltech Adds New Line of Industrial Check Valves

Cutaway view of spring loaded check valve
with flange connections.
Image courtesy Check-All Valve

Effective September 1, 2017 CTi Controltech is proud to announce that it is the exclusive Check-All Valve representative in Northern California and Nevada (excluding Clarke County).

Check-All manufactures in-line spring-loaded, piston-type check valves. All valves are available with metal to metal or soft seats. Sizes range from 1/8” NPT to 20 inch, and are available with a broad assortment of connections. Pressure ratings are available from full vacuum to 10,000 psi. Special materials available are Titanium, Alloy C-276, alloy 20 and many others. Fluoropolymer (FEP) encapsulated springs are available for special corrosion applications. Check-All is an outstanding source for all check valve, vacuum breaker, and low pressure relief applications.

Share your fluid control requirements with the fluid process experts at CTi Controltech, leveraging your own process knowledge and experience with their product application expertise.

Smart Position Indicator for Multi-Turn Valves

Model SPI Smart Position Indicator
Image courtesy Rotork

Centralized control systems need information in order to function. Reliable indication of valve position rates as essential information in maintaining fluid process control operations.

The Rotork product lineup includes the SPI Smart Position Indicator. Installed on multi-turn manual valves, the unit provides a reliable open/close signal to a control system. The unit is housed and constructed to provide maintenance free operation in an industrial environment. Commercially available switches from recognized manufacturers are used in the indicator for signalling. More detail is provided in the datasheet included below.

Share your valve automation challenges with application experts, leveraging your own knowledge and experience with their product application expertise to develop effective solutions.

Smart Position Indicator for Industrial Valves from CTi Controltech

CEMS vs PEMS

CEMS, "Continuous Emission Monitoring Systems" monitor the flue gas exiting to the atmosphere from a boiler, a furnace, or oven. Certain installations are subject to compliance with jurisdictional requirements for emissions at the state or federal level. CEMS are designed to comply with specific regulatory requirements for measuring and collecting data about specifically targeted pollutants, and installed by commercial and industrial plants to ensure operating compliance with applicable EPA or other jurisdictional rules and requirements.

In general concept, a CEMS samples flue gas, measures concentration of targeted pollutants, captures the measurements as data records, stores data records and produces reports of the emissions. CEMS may also incorporate other measurements and functions, such as as measuring and reporting fuel flow, its opacity and the gas moisture content.

CEMS usually have the same primary components.

• Sampling probe 
• Filter 
• Sampling line 
• Sample conditioning 
• Calibration gas 
• Gas analyzers for specific monitoring tasks 

Common targeted measurements include:

• Carbon dioxide 
• Carbon monoxide 
• Airborne particulate 
• Sulfur dioxide 
• Volatile organics 
• Mercury 
• Nitrogen oxides 
• Hydrogen chloride 
• Oxygen
• Liquid or gaseous fuel flow

The US Environmental Protection Agency requires a data acquisition system and handling process to collect and report the data, which CEMS provides. CEMS must operate and provide data continuously in order to assure operational compliance and meet record keeping requirements.

Around the world, air quality standards require various levels of emissions monitoring to assure that excessive levels of harmful chemicals are not spread throughout the environment. The monitoring of emissions involves the application of sensors and processing equipment to provide information regarding the amount of specific pollutants discharged by a plant or process.

A continuous emission monitoring system (CEMS) consists of equipment necessary for determining the emission rate of targeted pollutants, using analyzer measurements and subsequent data processing to provide results in units pertaining to an emission limitation or standard. This type of monitoring system is applicable where required by statute or regulation, but can also be used to provide valuable combustion or process efficiency data to plant operators.

A predictive emissions monitoring system (PEMS) employs an empirical computer model which will relate the inputs of a combustion system (air and fuel) to the emissions produced by the process. Once the model is established for a particular installation, the emissions can be predicted continuously with accuracy in the range of direct measurements used in CEMS. There are instances where this type of system will fulfill governmental compliance requirements, in place of CEMS. PEMS can also be deployed as a complement to a hardware based CEMS. Plant conditions and an engineering evaluation will determine the best implementation of emissions monitoring equipment and systems to meet regulatory requirements and provide the level of risk management needed.

Share your emissions compliance and monitoring requirements with combustion and instrumentation experts. Leverage your own process knowledge and experience with their product application expertise to develop effective solutions.

Components for Industrial Tank Venting and Flame Arresting

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.

Flame control products for industrial fluid operations from CTi Controltech

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.

Differential Pressure Transmitter Inferential Applications

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.

Industrial Transmitters for Pressure and Differential Pressure from CTi Controltech

Compact Electric Control Valve Actuators

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.

Rotork CMA Compact Electric Valve Actuators from CTi Controltech

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

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.

The Application of Heat in Industrial Settings

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.

Pneumatic Control Valve Positioners

Smart valve positioner
Courtesy Rotork

Valve positioners can provide process operators with a precise degree of valve position control across the valve movement range, as well as information about valve position. A relationship exists between applied pneumatic signal pressure and the position of the valve trim. The relationship between the two elements is dependent upon the valve actuator and the force of the return spring reacting to the signal pressure. In a perfect world, the spring and pneumatic forces would reach equilibrium and the valve would return to the same position in response to an applied signal pressure. There are other forces, however, which can act upon the mechanism, meaning the expected relationship between the original two elements of pressure and position may be offset. For example, the packing of the valve stem may result in friction, or the reactive force from a valve plug resulting from differential pressure across the area of the plug may be another.
While these elements may seem minor, and in some cases they are, process control is about reducing error and delivering a desired or planned output. Inclusion of a positioner in the valve assembly can ensure that the valve will be set in accordance with the controller commands.

Each positioner functions as a self-contained small scale control system. The first variable in the positioning process is the current valve position, read by a pickup device incorporated in the positioner. A signal which is sent to the positioner from the control system, indicating the desired degree of opening, is used as the setpoint. The controller section of the positioner compares the current valve position to the setpoint and generates a signal to the valve actuator as the output of the positioning process. The process controller delivers a signal to the valve, and then the positioner takes that signal and supplies air pressure required to accomplish the needed adjustment of the stem position. The job of the valve positioner is to provide compensatory force and to act as a counterbalance against any other variables which may impact valve stem position.

Magnetic sensors can be employed to determine the position of the valve stem. The magnetic sensor works by reading the position of a magnet attached to the stem of the valve. Other technologies can be employed, and all have differing ways of overcoming degrees of inaccuracy which may arise with wear, interference, and backlash. In addition to functioning as a positioner, control valve positioning devices can also function as volume boosters, meaning they can source and subsequently ventilate high air flow rates from sources other than their pneumatic input signal (setpoint). These devices can positively affect and correct positioning and velocity of the valve stem, resulting in faster performance than a valve actuator solely reliant on a transducer.

The inclusion of a positioner in a control valve assembly can provide extended performance and functionality that deliver predictable accurate valve and process operation. Share your valve automation requirements with a knowledgeable valve automation specialist and combine your process knowledge and experience with their product application expertise to develop an effective solution.

Condensate Return in a Steam System - Basic and Essential

Efficient production of steam and return of condensate
are essential to the operation of this and many other
industrial operations.

Many industrial processes and plants, as well as commercial buildings, utilize steam in their operations. The generation and use of steam is one of the oldest industrial processes and is so well understood that it may be considered more of a utility than part an industrial process. Whatever the case, if your process or installation uses steam, then steam is a necessary input for successful operation. Keeping your steam system performing at capacity frees up time and resources for the more complex aspects of your work.

If steam is not consumed directly by the process as a component input, it is steam's heat of vaporization that is utilized by the operation. Efficient use of steam as a heating medium results in the conversion of vapor to liquid (water). Returning the liquid condensate back to the boiler for conversion to vapor again is a necessary step in the efficient operation of a closed loop system.

Condensate return systems are certainly not high technology, but keep in mind that a steam system may be the lifeblood of not just one, but many operations throughout a plant. Avoiding downtime in the steam system, of which the condensate return system is an integral part, ranks highly on the list of "Important Things for Plant Operations". Condensate return is critical.

Three general methods are employed to move the condensate from a collection vessel, a trap, to the feedwater side of the boiler. Gravity can be used when conditions permit. A pressure motive return arrangement uses steam pressure and a coordinated valve sequence to drive the condensate through the piping system and back to the boiler. Condensate pumps can also be employed as a positive means of moving condensate through the return piping system.

What are some strong attributes of a good and reliable condensate return pump?

• Minimize or eliminate cavitation at high temperatures. Cavitation will impede pump performance and cause premature deterioration of pump and drive components.
• Ability to handle a high load during cold starts through motor and pump design.
• Design and configuration to handle high temperatures without deterioration of pump and motor.
• Develop higher pressure at lower motor speeds for extended service life.
• Avoidance of mechanical seals below water line.
• Consider a single unit with dual pumps for handling high loads and extending service life.

Specifying and installing a solidly designed and built condensate return pump may require an investment of your time and consideration. The return on that investment will be reduced maintenance, repair, and downtime. hare your steam system challenges, from end to end, with knowledgeable application specialists. Combining your intimate operational knowledge and experience with their deep product knowledge and experience with many installations will yield a good solution.

Filled Impulse Lines With Pressure Sensors

Pressure sensors or transmitters are installed directly to
process lines or vessels, or remotely using impulse lines.
Image courtesy Azbil NA, Inc.

Pressure sensors intended for use in industrial process measurement and control applications are designed to be robust, dependable, and precise. Sometimes, though, it is necessary or beneficial to incorporate accessories in an installation which augment the performance of pressure sensors in difficult or hazardous environments. There are some scenarios where the sensor must be isolated from the process fluid, such as when the substance is highly corrosive.

A way to aid pressure sensing instruments in situations where direct contact must be avoided is by using a filled impulse line. An impulse line extends from a process pipe of vessel to a pressure measurement instrument or sensor. The line can have a diaphragm barrier that isolates the process fluid from the line, or the line can be open to the process. There are best practices that should be followed in the design and installation of an impulse line to assure that the line provides a useful transmission of the process pressure to the sensor and whatever degree of isolation or protection is needed remains in effect.

The filled impulse line functions via the addition of a non-harmful, neutral fluid to the impulse line. The neutral fluid acts as a barrier and a bridge, allowing the pressure sensing instrument to measure the pressure of the potentially harmful process fluid without direct contact. An example of this technique being employed is adding glycerin as a neutral fluid to an impulse line below a water pipe.

Glycerin’s freeze point is lower than water’s, meaning glycerin can withstand lower temperatures before freezing. The impulse line connected to the water pipe may freeze in process environments where the weather is exceptionally cold, since the impulse line will not be flowing in the same way as the water pipe. Since glycerin has a greater density and a lower freezing point, the glycerin will remain static inside the impulse line and protect the line from hazardous conditions.

The use of an isolating diaphragm negates the need for certain considerations of fill fluid density, piping layout, and the need to create an arrangement that holds the fill fluid in place within the impulse line. System pressure will be transferred across the diaphragm from the process fluid to the fill fluid, then to the pressure sensor. It is important to utilize fluids and piping arrangements that do not affect the accurate transference of the process pressure. Any impact related to the impulse line assembly must be determined, and appropriate calibration offset applied to the pressure sensor reading.

An essential design element of a filled impulse line without an isolating diaphragm is that the fill fluid must be compatible with the process fluid, meaning there can be no chemical reactivity between the two. Additionally, the two fluids should be incapable of mixing no matter how much of each fluid is involved in the combination. Even with isolating diaphragms employed, fluid harmony should still be considered because a diaphragm could potentially loose its seal. If such a break were to occur, the fluids used in filled impulse lines may contact the process fluid, with an impact that should be clearly understood through a careful evaluation.

Share your pressure measurement requirements and challenges with experienced application specialists, combining your own process knowledge and experience with their technical expertise to develop an effective solution.

Industrial Uses of Steam - Part 2

Steam is used throughout commercial, institutional, and industrial facilities in various ways. In addition to other direct pressure and propulsion/drive applications, steam can be utilized as ‘motive fluid’ to assist in the movement of liquid and gas streams in a piping system. Jet ejectors can pull vacuum in equipment like distillation towers, allowing for the separation and purification of vapor streams. Continuously removing air from surface condensers via steam results in the desired vacuum pressure on condensing turbines to stay uniform. The entrance and subsequent diffusion of the steam through an inlet nozzle results in a low pressure zone, where the air from the surface condenser gets transferred. Similarly, steam serves as the primary motive fluid for secondary drainers, which pump condensate out of vented receiver tanks, flash vessels, and other process control components susceptible to stall conditions.

Steam is applicable to a process called atomization, wherein steam mechanically separates a fluid. Burners use steam for atomization by having steam injected into the fuel, thus maximizing the efficiency of the unit’s combustion while concurrently minimizing soot production. These steam generators and boilers, powered by fuel oil, use steam atomization to partition viscous oil into smaller droplets. Flares, similarly, utilize steam atomization as an exhaust pollutant reducer. In said flares, typically, the waste gas mixes with the steam prior to combustion.

Along with motive fluid and atomization, steam is also a fantastic cleansing tool. The soot in soot blowers gets removed via a steam cleaning process. Oil or coal fuel sourced boilers need soot blowers to cyclically clean the furnace walls and eliminate combusted deposits. These regularly scheduled cleanings allow for the capacity, durability, and effectiveness of the boiler to remain consistent. The nozzle of the soot blower directs the steam, dislodging dry, sintered ash and slag. Hoppers then catch the dislodged substances and they are expelled with other combusted gases.

Steam can also add moisture to a process while simultaneously acting as a heat supply source. In paper production, paper moving over rollers at high speed is moisturized by the steam, ensuring that no miniscule breaks or tears are suffered during the production process. Pellet mills, which produce animal feed, directly inject steam to heat and, concurrently, add to the water content of the feed as the feed passes through the mill’s direct conditioner section. The water softens the feed and then partially gelatinizes the starch content, leading to firmer pellets overall.

Lastly, commercial and industrial facilities utilize low pressure steam as a primary source of seasonal heating and humidification. Finned or bare coils, coupled with steam humidifiers, condition the facility air, keeping the temperature regulated for both comfort and preservation of items like books and records. Steam coils heat the cool air, resulting in the relative humidity dropping. The controlled injection of dry, saturated steam allows for moisture addition to regulate the relative humidity in a smooth and precise manner via steam humidifiers installed in air ducts.

Share your steam generation and use challenges with steam system and combustion experts, combining your own knowledge and experience with their expertise to develop effective solutions.

Industrial Uses of Steam – Part 1

Boilers are the most common production equipment
for industrial steam applications

Steam is used throughout industrial process control operations in various ways. The ability of steam to serve as a means to deliver heat and provide motive power to a facility or process keeps it in wide use throughout many industries.

Heating with steam can by of a direct or indirect nature. Direct heating uses steam distributed into or onto a substance to directly affect its temperature. In order to ensure success in direct heating, mixing needs to occur so that the temperature of the substance is uniformly impacted. Indirect heating uses one of the many available forms of heat exchangers to transfer heat from steam to process fluid across a physical barrier that isolates the process fluid from the steam.

Industries employ steam for many valuable uses. Food processing factories, refineries, and chemical plants utilize positive pressure steam. In most instances, steam is delivered to equipment, typically, at pressures above atmospheric and at a temperature exceeding 100°C. Process fluid heat exchangers, reboilers, air preheaters for combustion, and a range of other heat transfer equipment uses steam as the heat source. A shell and tube heat exchanger raises product temperature on its passage through the unit. Ideally, the heat exchanger expels condensate after removing the latent heat from the steam. Condensate can be collected and returned to the steam generation portion of the system, conserving much of the energy used to originally heat the water.

Hot water was the main agent traditionally used for heating at temperatures below 100°C. Using steam to heat at temperatures below the 100°C benchmark is an increasingly popular technique. Vacuum saturated steam can be applied in the same way as positive pressure saturated steam, but the steam temperature is adjustable by altering the pressure. The ability to change the pressure (and the temperature) allows for more precise temperature control when compared to using hot water. Another advantage of using steam over hot water is that the steam heating system is fast and precise. The desired temperature can be reached quickly and uniformly.

Another popular use for steam in industrial settings is as a propulsion or drive force. Steam turbines generate electricity in thermal power plants. A recent trend, developed to minimize wasted energy, is applying steam at increasingly higher temperatures and pressures. Superheated steam, used in steam turbines, acts as a counter to potential damage to the equipment resulting from condensate in the turbine section. Less chance of condensate in the turbine translates into a reduced risk of equipment damage or failure. Nuclear power plants, though, cannot utilize the advantages of superheated steam because of complications arising involving the steam and the turbine material. To combat this problem, high pressure saturated steam is utilized instead, with upstream separators installed to remove condensate from the steam flow. In addition to power generation, steam acts as the force behind turbine driven compressors and pumps, including gas compressors and cooling tower pumps.

Depending on the process being controlled and the specific industry’s demands, the simplicity and various applications of steam make this reliable medium a first choice for industrial operations. Share your steam system and use challenges with combustion and steam experts, combining your own knowledge and experience with their specialized expertise to develop effective solutions.

Wireless Transmitters In Process Measurement and Control

Industrial process instrumentation connectivity can present
substantial challenges.

In process control, various devices produce signals which represent flow, temperature, pressure, and other measurable elements of the process. In delivering the process value from the measurement point to the point of decision, also known as the controller, systems have traditionally relied on wires. More recently, industrial wireless networks have evolved, though point-to-point wireless systems are still available and in use. A common operating protocol today is known as WirelessHART™ , which features the same hallmarks of control and diagnostics featured in wired systems without any accompanying cables.

Wireless devices and wired devices can co-exist on the same network. The installation costs of wireless networks are decidedly lower than wired networks due to the reduction in labor and materials for the wireless arrangement. Wireless networks are also more efficient than their wired peers in regards to auxiliary measurements, involving measurement of substances at several points. Adding robustness to wireless, self-organizing networks is easy, because when new wireless components are introduced to a network, they can link to the existing network without needing to be reconfigured manually. Gateways can accommodate a large number of devices, allowing a very elastic range for expansion.

In a coal fired plant, plant operators walk a tightrope in monitoring multiple elements of the process. They calibrate limestone feed rates in conjunction with desulfurization systems, using target values determined experientially. A difficult process environment results from elevated slurry temperature, and the associated pH sensors can only last for a limited time under such conditions. Thanks to the expandability of wireless transmitters, the incremental cost is reduced thanks to the flexibility of installing new measurement loops. In regards to maintenance, the status of wireless devices is consistently transmitted alongside the process variable. Fewer manual checks are needed, and preventative measures may be reduced compared to wired networks.

Time Synchronized Mesh Protocol (TSMP) ensures correct timing for individual transmissions, which lets every transmitter’s radio and processor ‘rest’ between either sending or receiving a transmission. To compensate for the lack of a physical wire, in terms of security, wireless networks are equipped with a combination of authentication, encryption, verification, and key management. The amalgamation of these security practices delivers wireless network security equal to that of a wired system. The multilayered approach, anchored by gateway key-management, presents a defense sequence. Thanks to the advancements in modern field networking technology, interference due to noise from other networks has been minimized to the point of being a rare concern. Even with the rarity, fail-safes are included in WirelessHART™.

All security functions are handled by the network autonomously, meaning manual configuration is unnecessary. In addition to process control environments, power plants will typically use two simultaneous wireless networks. Transmitters allow both safety showers and eyewash stations to trigger an alarm at the point of control when activated. Thanks to reduced cost, and their ease of applicability in environments challenging to wired systems, along with their developed performance and security, wireless industrial connectivity will continue to expand.

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

Common Industrial and Commercial Process Heating Methods

Gas fired boilers used the combustion of fuel to produce
steam which is utilized by other process equipment

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, soley 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.

ELECTRICITY

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. CTI Controltech specializes in combustion applications and the industrial production and use of steam. Share your process and project challenges with them and combine your facilities and process knowledge and experience with their engineering expertise to develop effective solutions.