Industrial Control Valves

Cutaway view of industrial control valve
Courtesy Cashco

Control valves are at the heart of almost every fluid based industrial control process. Understanding their basic operation and function is essential for the process engineer, operator, or other stakeholder. A previous blog provided a good information source for those wishing to learn about control valves or review and hone their technical knowledge. The applications for which control valves are used seem uncountable in their variety, but common operating traits of control valves enable their use in every one.

Cashco, globally recognized manufacturer of industrial control products including control valves, regulators, controllers, pressure/vacuum relief vents, and flame and detonation arrestors, will be exhibiting at Interphex in Booth 3464 on March 21 through March 23 at the Jacob Javits Center in New York City. Knowledgeable personnel will be on hand to discuss your industrial control applications and challenges. If your plans include attendance at Interphex this year, take advantage of the opportunity to speak face to face with representatives of an industry leader.

E-Book on Fired Heaters and Combustion Efficiency

Modern high power boiler room

Yokogawa, globally recognized leader in a number of process control fields, has authored an e-book which provides useful insight into how operators of combustion based equipment and systems can improve efficiency and enhance safety by employing modern technology.

[All quoted passages in this article are from the Yokogawa e-book]

The Yokogawa e-book Combustion & Fired Heater Optimization offers “an analytical approach to improving safe & efficient operations” related to the use of combustion & fired heaters in the process industries. Through presenting an overview of combustion sources, such as furnaces and fired heaters, the book states that while “fired heaters pose a series of problems from safety risks to poor energy efficiency,” those problems “represent an opportunity for improved safety, control, energy efficiency and environmental compliance.” Fired heaters “account for 37% of the U.S. manufacturing energy end use.” Tunable Diode Laser Spectrometer (TDLS) technology helps mitigate safety concerns by “measuring average gas concentrations across the high temperature radiant sections.”

The book states that the four main concerns applicable to fired heaters are asset sustainability, inefficient operations, the operator skillset, and safety and compliance. Outdated diagnostics and controls have placed unnecessary stress on operator response, making sustainability of fired heaters difficult. The emissions of fired heaters are generally higher than designed, and can be coupled with control schemes for firing rates little changed over the past 40 years. Operators, generally, lack a clear understanding of design, and even engineering principles of heat transfer are not typically included in education related to fired heaters. Confounding the situation further, “many natural draft heaters do not meet this [safety regulation] guideline with existing instrumentation and control systems.” These complications combine to form a noticeable problem Yokogawa’s technology hopes to address. The company notes how the fired heater relies on natural draft instead of forced air, meaning the heaters “typically lack the degree of automation applied to other process units in the plant.” Offering a full detail of both the control state of most fired heaters and their systems defines the process situation currently considered common in the field, while emphasizing high excess air as providing a “false sense of safety.”

The proposed TDLS system allows for the measurement of “both the upper and lower conditions in a fired heater” by “simultaneously controlling the fuel and air supply based on fast sample intervals.” Safer burner monitoring and heater efficiency results from the TDLS measurements of CO, CH₄, and O₂. The optimization of air flow control reduces “O2 concentration … from 6% to 2%” and increases the furnace’s thermal efficiency. Combustion control is achieved by managing fuel flow and the arch draft. The TDLS integrated system works in tandem with already established logic solver systems in the plant. The TDLS technology works as a non-contacting measurement with “full diagnostic capability” and offers “distinct advantages over single point in situ analyzers” via reduction of false readings. Specific gas measurements, fast response time, optical measurement technology, and “high and variable light obstruction” are featured components of the TDLS system highlighted to show the technology’s durability and flexibility. The longevity and reliability of the system is showcased by how the TDLS combustion management system has been operational in a major refinery since 2010. The percentage of excess O₂ in sample fired heaters has decreased by 1% to 1.5%. Measurements by the TDLS system have been verified by other gas analyzers. The furnace conditions in the plant are more efficiently monitored and controlled. As a result, the furnace in the functional environment is “now near its optimum operating point, using minimum excess air.”

Yokogawa presents a process-related problem, then details the key points of the problem while unpacking the causes. The e-book introduces Yokogawa’s technology, explains the mechanics, and demonstrates how TDLS acts as a solution to the problem, supported by a tangible example. The book offers great insight for both the operational principles of fired heaters and a new technology designed to maximize efficiency in the control process.

The e-book is included below. More detail is available from product applicationspecialists, with whom you should share your combustion and fired heater related challenges. Combining your own facilities and process knowledge and experience with their product application expertise will lead to effective solutions.

Fired Heater and Combustion Optimization From Yokogawa from Miller Energy, Inc.

Consolidated Tool Kit for Sensor Maintenance

Configured repair kit contains everything needed
Courtesy United Electric Cotnrols

Keeping things going, working, no matter your industry, is a continuous challenge. In process measurement and control operations, sensors and transmitters perform an essential function that often calls for immediate repair upon failure. Being properly prepared by having any needed parts on hand empowers technicians to quickly and effectively return sensor assemblies or transmitters to operation.

United Electric offers their "Sensor Box™" a kit that is preloaded with everything needed to effect temperature sensor and transmitter repairs in the field. The kit keeps everything needed in one spot, ready to go.

The video shows the convenience with which a technician can use the kit to make field repairs. Share your temperature measurement and process control challenges with product application experts, combining your own process knowledge with their product expertise to develop effective solutions.

Level Measurement Using Isolating Air Flow

Bubbler method of liquid level
measurement is simple and reliable
Courtesy Yokogawa

Remotely utilized measurements of tank liquid level are common throughout the fluid processing industries. Various means of inferential or direct measurement are available, each with its own set of performance, maintenance, and cost attributes that may make it the preferred choice for a particular application.

Inferring liquid level using a hydrostatic pressure measurement is a simple, easy to implement strategy for delivering a continuous level signal to the process operating and control system. There can be situations where mounting the measuring gear near the bottom of a tank or other vessel may be impractical or undesirable. A pressure transmitter mounted low on a tank may expose it to damage from plant traffic or other physical hazards. It is also possible that the tank may not have a suitable fitting located low enough to provide the needed measuring range. Having a potential leakage point at a fitting low on the tank may also be undesirable. Another, and certainly not final, scenario would be an application involving a corrosive liquid which must not come in contact with the pressure sensor.

The bubbler method of liquid level measurement employs an arrangement that overcomes all of the previously mentioned impediments. It can utilize connections at the top of the tank, above the liquid level. The way in which the method works will keep the pressure sensor out of contact with the process liquid, providing isolation from potential corrosive effects.

The apparatus for level measurement using the bubbler method employs a simple dip tube that extends from the pressure sensor or transmitter to nearly the bottom of the tank or vessel. A small amount of purge air or gas continually flows through the dip tube and will bubble out the bottom of the tube. This dip tube arrangement essentially transfers the hydrostatic pressure at the bottom opening of the tube to the pressure transmitter, while the purge gas keeps the liquid from advancing up into the pipe. The bubbler can be used on atmospheric or pressurized tanks with a properly configured pressure or differential pressure transmitter.

Probably the most significant application point of the bubbler method that will distinguish its use from many other level measurement methods is the importance of maintaining air or gas flow in the dip tube. The flow provides isolation of the sensor, but the flow must also be set to a level that will not impact the pressure measurement in the tube itself. If the flow is excessive, backpressure in the tube can be offset from the level imparted by the tank contents, with the result being an incorrect measurement.

Below is an application note from Yokogawa, showing how their pressure transmitters and rotameters can be used to create the setup. Share your process measurement challenges and requirements with instrumentation experts, combining your own process knowledge with their product application expertise to produce effective solutions.

Liquid Level Measurement Using the Bubbler Method from Miller Energy, Inc.

Yokogawa Differential Pressure Transmitter from Miller Energy, Inc.

Yokogawa Rotameter Flowmeters for Industrial Applications from Miller Energy, Inc.

Case Study From CSB: Industrial Plant Heat Exchanger Explosion

Shell and tube heat exchangers

Industrial accidents, whether minor or catastrophic, can serve as sources of learning when analyzed and studied. Operators, owners, and technicians involved with industrial chemical operations have a degree of moral, ethical, and legal responsibility to conduct work in a reasonably and predictably safe manner without endangering personnel, property, or the environment. Part of  a diligent safety culture should include reviewing industrial accidents at other facilities. There is much to learn from these unfortunate events, even when they happen in an industry that may seem somewhat removed from our own.

The U.S. Chemical Safety Board, or CSB, is an independent federal agency that investigates industrial chemical accidents. Below, find one of their video reenactments and analysis of an explosion that occurred at a Louisiana chemical processing plant in 2013. A portion of the reenactment shows how a few seemingly innocuous oversights can combine with other unrecognized conditions that result in a major conflagration.

Check out the video and sharpen your senses to evaluate potential trouble spots in your own operation.

Accurate Level Measurement Contributes to Heat Rate Reduction

Industrial steam turbine

Steam production is a costly operation in any facility, but is of paramount importance in power generation plants. The bottom line of a combustion based power generation facility is sensitive to the cost of input fuel. Measures that can be taken to reduce fuel input for a unit of power output (called heat rate) can translate directly into profitability. An additional benefit of reducing heat rate is a commensurate reduction in emissions.

A major contributor to heat rate reduction is the recovery of heat from the process and transference of that heat into the boiler feedwater. A sizable feedwater preheater of the shell and tube type is used to recover the heat. Shell and tube heat exchanger efficiency can be maximized with accurate control of liquid level.

Magnetrol, globally recognized leader in level measurement technology, makes the case for using guided wave radar level measurement technology as the most advantageous means for this application. The video below describes the process and how the guided wave radar level transmitter can provide the best performance.

Magnetrol has an information kit devoted to heat rate reduction. Share your steam system and level measurement challenges with a product specialist, and ask how you can get the Heat Rate Reduction Kit. Combining your facility and process knowledge with the product application expertise of a specialist will result in effective solutions.

Applying Coriolis Flowmeters

Coriolis Flowmeter
Courtesy Yokogawa

Coriolis mass flow meters are widely used throughout the process measurement and control field. Their basic operating principle, combined with modern sensor and signal processing technology, provide a list of potential application advantages.

• Directly measure mass flow based on the principle of measurement.
• No "moving" parts (except the slightly vibrating sensor tubes).
• Coriolis sensors have the ability to measure flow of non-conductive fluids.
• Measure the mass flow rate with high accuracy.
• Instruments can be applied across a wide usable measurement range.
• Deliver density measurement based on oscillating frequency.
• Not materially impacted by fluid viscosity or density.
• Coriolis flow meters also do not need lengthy straight pipe sections upstream or downstream of the sensing unit.

SELECTION AND INSTALLATION RECOMMENDATIONS

Some considerations for product selection and installation of Coriolis mass flow meters:

• Rapid temperature changes within the measured medium can impact measurement accuracy.
• Wide ranges of connection types are available, specify the best match for your system.
• Select sensor tube construction material to accommodate media characteristics.
• For liquid measurement, the sensor tube will extend downward from a horizontal pipe run. 
• As with most industrial products, there may be restrictions on where the device may be used. For example, not for use in aircraft. Assure that your application conforms with the intended usage of the instrument.
• Install at least one tight shutoff valve adjacent to the instrument for purposes of zeroing. Isolation valves for inlet and outlet are preferred.
• Follow manufacturer recommendations for pipe supports, if required, at inlet and outlet sides of the unit
• Avoid installation at locations with high levels of vibration or strong electrical fields.
• Locate the sensor unit at the lowest practical level in the piping system. This helps avoid collection of gas bubbles in the sensor tubes.
• Sensor tubes need to be completely filled with subject medium to obtain accurate measurement.
• Avoid the use of flexible connections and reducers at the unit connection points, unless in accordance with specific manufacturer guidelines.

The Coriolis flow meters of different manufacturers may have some particular recommendations, all of which should be followed to insure the best available performance, safety, and longevity of the unit.

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