Wednesday, May 24, 2017

Desuperheating and Attemperation of Steam

electric power plant
Electric power generation plant
Steam heats or powers a respectable swath of industrial operations, plus there is electric power generation. Steam is an important sort of "back office" component of the lives of many dwellers in modern economies.
What is steam?
Sorry, but we need to get everybody on the same page here. Steam is water vapor, produced by the application of heat to water. In order for steam to do work and serve as a useful energy source, it must be under pressure. There can be applications that employ steam at atmospheric pressure, but most are pressurized.

The heat goes on, the water boils, steam is produced and flows through the piping system to where it is used. Sounds simple, sounds easy. It is not. There are intricacies of designing and operating a steam system that determine its raw performance, as well as how efficiently it uses the fuel or other heat source employed to boil water. Steam utilization equipment is also carefully designed to provide its rated performance when supplied with steam of a given condition.

Steam at any given pressure has a saturation temperature, the temperature at which the vaporized water content of the steam is at its maximum level. Heat steam above its saturation temperature and you have superheated steam. Cool it below the saturation temperature and vapor will start to condense. The way in which the steam is to be used determines whether, and how much, superheat is desirable or necessary.

  • Turbine operations benefit from properly superheated steam because it avoids exposure of the turbine to liquid water droplets, generally a source of surface erosion and other accelerated wear.
  • Heat exchanger performance is based upon certain inlet conditions, one of which is the degree of superheat.
  • Maintaining sufficient superheat throughout a continuously operating steam system minimizes the need for, and size of, a condensate return system
Processes are designed to deliver a predictable output when provided with known inputs. In the case of steam, the temperature of the steam may be an input requiring control. This brings us to attemperation, which in the case of steam most often refers to lowering the temperature of a steam supply. Attemperation and desuperheating (reducing the degree of superheat) are accomplished in a similar fashion, but with differing objectives. Attemperation involves simply controlling the temperature of the steam, without any direct regard for the level of superheat. Desuperheating, as a control operation, is not directly related to the temperature of the steam, just the degree by which it exceeds the saturation temperature at the current condition. For attemperation, steam temperature measurement is all that is needed. For desuperheating, pressure and temperature measurements are needed. Decreasing the temperature of superheated steam will naturally reduce the amount of superheat.

Some process requirements may focus on temperature of the delivered steam, without regard to superheat level. Others will rely on a specified level of superheat. The application scenarios are vast, with equipment available to accomplish whatever is needed. 

Either operation can be accomplished with some sort of heat exchanger that extracts heat from the steam. A more flexible option relies on the addition of atomized water to the flowing steam to manage temperature or superheat level. Share your steam system challenges with experts, combining your own facilities and process knowledge with their product application expertise to develop effective solutions.

Tuesday, May 16, 2017

Shell and Tube Heat Exchangers

diagram of shell and tube heat exchanger
Shell and tube heat exchanger diagram
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 equipment 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.

Wednesday, May 10, 2017

High Pressure Valves for Industrial Processes and Operations

engineer working on pump and piping system oil refinery
Industrial operations present substantial
challenges to engineers and equipment
I am convinced that there is a valve out there for every conceivable application. Of course, that is not literally true, but there is an enormous array of manufacturers producing countless valve variants to meet specific requirements of the many industrial fluid processing applications.

A valve installed in a fluid process needs not only to perform its intended control function, but to stand up to the impact of several physical challenges.
cutaway view of high pressure angle valve for industrial process control
Cutaway view of high pressure angle valve
Courtesy Flowserve - Kammer
  • Temperature
  • Pressure
  • Corrosion
Any combination of these factors in the extreme can call for the use of a severe service valve. A good match between the valve ratings or capabilities and the demands imposed by the process conditions is essential for achieving safe operation and a reasonable useful valve lifespan.

Valves designed to handle very high pressure will exhibit specific attributes designed to accommodate the imposed physical stress. Body construction, assembly hardware, seats, and trim will all be noticeably heavier, stronger.

Rely on a valve specialist to contribute product expertise to the valve selection process. Combine your own process knowledge and experience with their product application expertise to develop an effective solution.

Tuesday, May 2, 2017

Operating Principles and Application of Vortex Flowmeters

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

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

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

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

The advantages of the vortex flowmeter, in addition to the aforementioned rangeability and steam-specific implementation, include available accuracy of 1%, a linear output, and a lack of moving parts. It is necessary for the pipe containing the measured fluid to be completely filled in order to obtain useful measurements.
Applications where the technology may face hurdles include flows of slurry or high viscosity liquids. These can prove unsuitable for measurement by the vortex flowmeter because they may not exhibit a suitable degree of the von Kármán effect to facilitate accurate measurement. Measurements can be adversely impacted by pulsating flow, where differences in pressure from the relationship between two or more compressors or pumps in a system results in irregular fluid flow.

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

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

Saturday, April 29, 2017

Scotch Yoke Valve Actuators

Scotch Yoke Pneumatic Valve Actuator
Courtesy Flowserve - Automax
A Scotch yoke is a mechanical linkage arrangement that converts linear motion into rotational motion. A common usage of the mechanism found in modern industry is valve actuators for quarter turn valves with high torque requirements. These applications would emerge most frequently in chemical and oil and gas industrial installations.

Quarter turn valves, such and ball, plug, or butterfly valves, only require a 90 degree rotation from their fully closed to fully open positions. In this case, the Scotch yoke is not used to produce continuous rotating motion, as it may in some engine applications. For the valve actuation case, the Scotch yoke functions much like a hand on a lever. The pneumatic variants use air pressure to drive the slider in one direction until a preset stop position is reached. Usually, a spring provides a counterforce that will drive the valve to a desired fail-safe stop position in the absence of air pressure. Other combinations of driving force and fail-safe operation are available to suit differing application needs.
Diagrammatic representation of Scotch yoke valve actuator
Illustration excerpted from Automax RG Standard Pneumatic Valve Actuator IOM 
with text added
The drive assembly consists essentially of a slider, a pin, and the yoke. The slider is moved laterally by whatever power sources are appropriate for the unit (pneumatic, hydraulic, spring, hand wheel, etc.). The pin is affixed to the slider and extends through a slot in the yoke. One end of the yoke is mounted to the valve shaft. As the slider is driven through is range of motion, the pin moves with the slider and forces movement of the yoke. This movement of the yoke translates into rotational force on the valve shaft and the repositioning of the valve trim.

Selecting and configuring the right actuator and valve for any application benefits from consultation and cooperation among the process engineers and valve automation specialists. Share your process valve and automation challenges with experienced professionals, combining your own process knowledge and experience with their product application expertise to produce an effective solution.

Wednesday, April 19, 2017

Introduction to Flowmeters

Electromagnetic Flow Meter
Courtesy Azbil N.A.
Flowmeters measure the rate or quantity of moving fluids, in most cases liquid or gas, in an open channel or closed conduit. There are two basic flow measuring systems: those which produce volumetric flow measurements and those delivering a weight or mass based measurement. These two systems, required in many industries such as power, chemical, and water, can be integrated into existing or new installations. For successful integration, the flow measurement systems can be installed in one of several methods, depending upon the technology employed by the instrument. For inline installation, fittings that create upstream and downstream connections that allow for flowmeter installation as an integral part of the piping system. Another configuration, direct insertion, will have a probe or assembly that extends into the piping cross section. There are also non-contact instruments that clamp on the exterior surface of the piping and gather measurements through the pipe wall without any contact with the flowing media.

Because they are needed for a variety of uses and industries, there are multiple types of flowmeters classified generally into four main groups: mechanical, inferential, electrical, and other.

Quantity meters, more commonly known as positive displacement meters, mass flowmeters, and fixed restriction variable head type flowmeters all fall beneath the mechanical category. Fixed restriction variable head type flowmeters use different sensors and tubes, such as orifice plates, flow nozzles, and venturi and pitot tubes.

Inferential flowmeters include turbine and target flowmeters, as well as variable area flowmeters also known as rotameters.

Laser doppler anemometers, ultrasonic flowmeters, and electromagnetic flowmeters are all electrical-type flowmeters.

The many application classes throughout the processing industries have led to the development of a wide range of flow measurement technologies and products. Each has its own advantages under certain operating conditions. Sorting through the choices and selecting the best technology for an application can be accomplished by consulting with a process instrumentation specialist. The combination of your own process knowledge and experience with their product application expertise will develop an effective solution.

Tuesday, April 11, 2017

CTi Controltech In-House Capabilities and Solutions for Combustion, Automation, and Instrumentation

CTi Controltech has operated in northern California and Nevada for many years, satisfying customers and building their capabilities into today's top flight provider of equipment and services to industrial and commercial markets. The short piece included below is a synopsis of the company's range of products and services.

Share your combustion, emission, steam, process control, and automation challenges with experts in the field. The combination of your own process knowledge with the expertise at CTi Controltech will produce effective solutions.