Tuesday, June 20, 2017

Shell and Tube Heat Exchangers

large shell and tube heat exchangers at oil refinery
These shell and tube heat exchangers are at an oil refinery, but
their application crosses all industry boundaries.
Cars are something which exist as part of the backbone of modern society, for both personal and professional use. Automobiles, while being everyday objects, also contain systems which need to be constantly maintained and in-sequence to ensure the safety of both the machine and the driver. One of the most essential elements of car ownership is the understanding of how heat and temperature can impact a car’s operation. Likewise, regulating temperature in industrial operations, which is akin to controlling heat, is a key process control variable relating to both product excellence and operator safety. Since temperature is a fundamental aspect of both industrial and consumer life, heat management must be accurate, consistent, and predictable.

A common design of heat exchangers used in the oil refining and chemical processing industries is the shell and tube heat exchanger. A pressure vessel, the shell, contains a bundle of tubes. One fluid flows within the tubes while another floods the shell and contacts the outer tube surface. Heat energy conducts through the tube wall from the warmer to the cooler substance, completing the transfer of heat between the two distinct substances. These fluids can either be liquids or gases. If a large heat transfer area is utilized, consisting of greater tube surface area, many tubes or circuits of tubes can be used concurrently in order to maximize the transfer of heat. There are many considerations to take into account in regards to the design of shell and tube heat exchangers, such as tube diameter, circuiting of the tubes, tube wall thickness, shell and tube operating pressure requirements, and more. In parallel fashion to a process control system, every decision made in reference to designing and practically applying the correct heat exchanger depends on the factors present in both the materials being regulated and the industrial purpose for which the exchanger is going to be used.

The industrial and commercial applications of shell and tube heat exchangers are vast, ranging from small to very large capacities. They can serve as condensers, evaporators, heaters, or coolers. You will find them throughout almost every industry, and as a part of many large HVAC systems. Shell and tube heat exchangers, specifically, find applicability in many sub-industries related to food and beverage: brewery processes, juice, sauce, soup, syrup, oils, sugar, and others. Pure steam for WFI production is an application where special materials, like stainless steel, are employed for shell and tube units that transfer heat while maintaining isolation and purity of a highly controlled process fluid.

Shell and tube heat exchangers are rugged, efficient, and require little attention other than periodic inspection. Proper unit specification, selection, and installation contribute to longevity and solid performance. Share your project challenges with application experts, combining your own process and facilities knowledge with their product application expertise to develop effective solutions.

Thursday, June 15, 2017

Natural Gas Fueling Station Process Filter and Dryer

natural gas vehicle fueling station dryer with stationary regenerator
Single tower natural gas dryer with stationary regeneration system
used for removing water vapor and particulate contaminants from
vehicle fuel.
Courtesy SPX Flow - Pneumatic Products
Natural gas fueled vehicles now occupy a formidable niche in the transportation market. With low cost, low emission operation, natural gas vehicles continue to expand their presence in fleets around the world.

Commercially available engines of almost all types operate best and longest when powered with clean fuel that is free of particulates and other contaminants that increase wear on internal and moving parts. Water vapor also has some deleterious effects on many components and should be kept at very low levels.

Fuel can change custody and container numerous times during transport from production to consumption point. Opportunities for contamination exist along the supply chain, making a final processing of the fuel immediately prior to its dispensing to a vehicle a positive and beneficial operation.

SPX Flow, under the Pneumatic Products brand, manufactures single and twin tower desiccant dryers designed to remove water vapor from natural gas. The skid mounted units also include particulate and coalescing filters that capture solid contaminants to a submicron level.

Specifically engineered for large flow heavy-duty natural gas vehicle fleet refueling applications, units are available for intermittent, low, moderate, and heavy demand operations. Single tower units are economical for low to moderate levels of use. Twin tower systems, with self-contained regeneration, provide continuous operation and delivery of dried compressed natural gas (CNG) for fueling operations.

Single tower dryers can be provided with a stationary desiccant regeneration system on board. This enhances convenience by eliminating the need for a third party regeneration service. The desiccant is processed in place, without replacement. Single tower dryers are suitable for low to moderate volume application.

Single tower units, without a stationary regeneration system, are suitable for intermittent or low volume use. A mobile regeneration unit can provide self directed processing of the desiccant media in place, eliminating the need for disposal and replacement. Alternatively, third party service providers can come to the site and replace or regenerate the desiccant.

Twin tower purification systems are completely self-contained, fully automatic, heat-reactivated, closed-loop blower purge units capable of continuous operation for facilities with high flow requirements or uninterrupted 24 hour operation.

More detail is provided in the datasheet below. Share your natural gas vehicle fueling station challenges with a product application specialist for help in determining the most suitable equipment for your application.

Wednesday, June 7, 2017

Metal Diaphragm Valves - Best Applications

pneumatically operated diaphragm valve industrial valve
Diaphragm valve, pneumatically actuated
Courtesy GEMU
There are more valve selection options available than one can count. Differing types, sizes, materials, and other special characteristics distinguish each and every product as unique in its own way. Matching the design and performance strengths of a particular valve to the requirements of an application may require some investment in time and research, but the payback can be years of trouble free performance.

Diaphragm valves are beneficial for applications requiring hermetic isolation of the valve bonnet and stem from the media. The diaphragm serves as the isolating barrier. The valves are generally tolerant of particulate matter entrained in the media, and provide good shutoff and throttling capability. Body and diaphragm materials should be selected that are compatible with the media.

Body styles are either weir or straight through design. Straight through body styles offer a less restricted flow path than the weir type, but diaphragm movement in the weir style is reduced. Diaphragms do wear and will need to be replaced at some point. Valves should be installed with good service access.

There are many variants of diaphragm valves, broadening their suitability for a wide range of industrial applications. Share your fluid process control challenges with application specialists, combining your process knowledge with their product expertise to develop effective solutions.

internal diagram of weir type diaphragm valve
Weir body style diaphragm valve
Coutesy GEMU

Friday, June 2, 2017

Self Contained Temperature Regulators

pilot operated temperature regulator valve
Pilot operated temperature regulator
Courtesy Spirax Sarco
Not everything in process control is complicated. Some requirements can be fulfilled by proper application of the right product.

Temperature control, the regulation of heat content, transfer of heat, or whatever else it may be called, is an ubiquitous operation in industrial, commercial, and institutional settings. The range of complexity or challenge in temperature control applications extends from very simple to almost blindingly complex. The key to finding the right solution for any of these applications lies in understanding how the process works, setting an appropriate measurement method for the process condition, establishing a control method or algorithm that adequately responds to the process, and integrating an output device capable of delivering heat or cooling in accordance with the controller commands.

Somewhere along the continuum of project complexity is a zone that is well served by simple and rugged devices that incorporate temperature measurement and control into a single device. Self contained temperature regulators are pilot or direct operated units comprised of a filled bulb temperature sensor that operates a modulating valve that controls the flow of liquid or steam used to regulate the process temperature. The regulators offer a host of advantages.

  • No external power source required for operation
  • One device to specify, purchase, and install
  • Installed by a single trade
  • Low, almost no, maintenance
  • Intrinsically safe operation
The document provided below illustrates several variants, along with application examples and principal of operation. Not every application needs a microprocessor controller. Share your temperature control applications and challenges with process control specialists, combining your own process knowledge and experience with their product application expertise to develop an effective solution.

Monday, May 22, 2017

Introduction to Valve Parts or Components

cutaway view forged steel gate valve
Cutaway view of a forged steel gate valve
Courtesy Crane-ChemPharmaEnergy
Although there are many different classifications of valves specific to their respective functions, there are standard parts or components of valves you may find regardless of the classification. They are the valve body, bonnet, trim, seat, stem, actuator, and packing.

The Valve Body is the primary boundary of a pressure valve which serves as the framework for the entire valve’s assembly. The body resists fluid pressure loads from connected inlet and outlet piping; the piping is connected through threaded, bolted, or welded joints.

The Valve Bonnet is the opening of the Valve Body’s cover. Bonnets can vary in design and model, is built using the same material as the Valve Body, and is also connected to the entire assembly through threaded, bolted, or welded joints.

The Valve Trim collectively refers to all the replaceable parts in a valve, e.g. the disk, seat, stem, and sleeves––all which guide the stem as well.

The Valve Disk allows the passage or stoppage of flow. Disks provide reliable wear properties and differ in what they look like per valve type. For example, in the case of a ball valve, the disk is called a ball, whereas for a plug valve it is a plug.

The Valve Seat(s) or it’s seal rings provide surface seating for the disk. For example, a globe valve requires only one seat and this seat forms a seal with the disk to stop flow.

The Valve Stem provides the proper position which will allow the opening and closing movement of the Valve Disk. Therefore, it is connected to the Valve Disk on one end and the Valve Hand Wheel or the Valve Actuator on the other.

The Valve Yoke is the final piece in the valve’s assembly; the Yoke connects the Valve Bonnet with the actuating mechanism. The Valve Stem passes through the top of the Yoke which holds the Yoke or stem nut.

There are countless variants of valve designs, sizes, and configurations. These basic parts will be found on most, but the particular form and arrangement of the part may provide an advantage when employed for a particular application. Share your industrial process valve requirements and challenges with a valve specialist. Combine your own process knowledge and experience with their product application expertise to develop an effective solution.

Monday, May 15, 2017

Wireless Communications in Industrial Process Control

symbolic wireless communications or transmission tower antenna
Industrial wireless communications for process control
Electrical cables, for many years, were the only option for connecting measurement devices with their companion control and monitoring gear. While wired connections are still in widespread use, probably still the predominant connection method, wireless communication technology offers a range of advantages in connecting process measurement instruments and their controls.

Bandwidth, in wireless communication and modem data transmission terminology, is the analog range of the radio spectrum’s frequencies, or wavelengths, used to transmit a signal between transmitter and receiver. Jurisdictional agencies throughout the world regulate the use of bandwidth and assign ranges for use by public and private organizations.

Before there can be an appreciation of radio transmissions, there first must be an understanding on the transmission medium. Radio transmissions run on the UHF radio spectrum, or the Ultra high frequency spectrum, named by the International Telecommunication Union; the spectrum runs from 300 megahertz (MHz) to 3 gigahertz (GHz).

There are two prominent frequencies utilized for industrial wireless communications in the US: 900 MHz and 2.4 GHz. Within the allocated bandwidth, there are numerous individual channels that can be used for applications.

Each of the available bandwidths has its own transmission characteristics which may make it advantageous for a particular application. Amateur radio stations operate in the 900 MHz range because attenuation of the transmission signal is less than at higher frequencies. Higher frequencies have greater theoretical transmission range, but can be impaired by smaller sized objects in the transmission path because of their shorter wavelength.

Due to a number of practical application factors, 2.4 GHz technology is predominate in consumer and many industrial applications; one of the main reasons is the sheer amount of concurrent signals in the designated bandwidth. The 2.4 GHz band can accommodate more concurrent users or devices. Both frequency ranges have useful application in automation and process control, enabling effective connections between devices over distances from several feet to thousands of miles.

Thursday, May 11, 2017

Rack and Pinion Actuator - Double Acting vs. Single Acting

pneumatic valve actuator
Pneumatic rack and pinion valve actuator
Courtesy Emerson - Hytork
Automating industrial valve operation requires numerous considerations in selecting the correct power source, drive type, torque range, and much more. The widest range of possible operation conditions should be anticipated and accommodated by the actuator selection to assure safe and effective valve operation under normal and adverse conditions.

The use of compressed air or gas as the energy source for valve positioning has been in use for many years and remains popular to this day. Among the perceived advantages of this energy source are the ability to store it in pressurized vessels for emergency short term use and the absence of any potential ignition source, as may be the case with electric powered actuators.

A rack and pinion valve actuator delivers a linear torque output throughout its full range of travel. The movement of a piston causes movement of the rack. The rack is toothed, and drives the pinion, converting linear movement of the rack into rotational movement of the pinion. The pinion is connected to the valve shaft, providing re-positioning of the valve. Adjustable stops, part of the actuator, limit the travel of the valve trim.

spring return and double acting valve actuator diagrams
Double acting pneumatic rack and pinion actuator (left) on its inward stroke. Spring return actuator (right) on its
outward or air powered stroke  (Illustrations courtesy of Emerson - Hytork) 

There are two common configurations of rack and pneumatic pinion actuators. A double acting actuator has provisions for delivering or exhausting air from both sides of the piston. Small control valves coordinate the delivery and removal of pressurized air or gas to drive the pistons inward or outward, producing torque in a clockwise or counterclockwise direction. Its operation could also be described as "air to open, air to close".

The single acting version of the pneumatic rack and pinion actuator provides air driven movement in only one direction. In this case, reversing the direction of travel is accomplished with a spring installed within the chamber on one side of the pistons. The spring powered movement provides a fail safe positioning of the valve in the case of control air pressure loss. This actuator provides "air to open, spring to close" operation, although, in some cases the fail safe position can be changed.

This is the simple version. Share your process control challenges with a valve expert, combining your own process knowledge and experience with their product application expertise to develop effective solutions.