Use of Process Analyzers in Fossil Fuel Plants

Steam Power Plant

In spite of all efforts concerning energy savings and efficiency, the growing world population and the aspired higher 'standard of living' will lead to a further in- crease of world energy demand. In this context, almost half of the primary energy demand will continue to be covered by solid fuels, particularly by coal, until 2020 and many years beyond.

This results in the challenge to power plant engineering to implement this increasing energy demand by using new technologies and applying the highest possible conservation of the limited resources of raw materials and the environment.

This includes new materials for higher operating temperatures and, therefore, higher efficien- cies of the power plants, as well as combined power plants that drastically reduce the share of unused waste heat or improved methods for reducing emissions.

Optimizing processes without delay, designing flexible operating conditions, improved use of the load factor of new materials and safely controlling emissions of toxic substances are all tasks that require the use of powerful measurement techniques. For this purpose, devices and systems of process analytics per- form indispensable services at many locations in a power plant.

In spite of all the alternatives, the undiminished increasing world energy demand also makes the expansion of energy recovery from fossil fuels necessary. However, the use of new materials and technologies further increases the efficiency of power plants and further reduces environmental pollution from the emission of toxic substances.

In this context, process analytics plays an important role: It determines reliable and exact data from the processes and thereby allows for their optimization.

Take a moment to review the document below, or if you prefer,  download the "Use of Process Analyzers in Fossil Fuel Plants" PDF file here.

Use of Process Analyzers in Fossil Fuel Plants from Ives Equipment

Differential Pressure Transmitters and Inferential Measurement

Differential Pressure Transmitter
(Siemens)

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 are relatable 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.

Process Instrumentation White Paper: Seven Switch Myths Busted

One Series Pressure and Temperature
Transmitter-Switches (United Electric)

Reprinted from United Electric Controls ViewPoint.
More UE ViewPoints can be found here.

Summary

With more than 80 years of evolution since its introduction, switch technology as changed significantly enough that some of the common beliefs about switches are no longer true. Seven common myths surrounding switches are analyzed. Recent technology advancements in switch design and how these advancements solve problems in industrial and OEM applications are discussed. Readers will acquire a better understanding of the new technology available to improve control, process efficiency and safety.

1. Blind & Dumb

Prior generations of switches were incapable of displaying process measurements locally, forcing the installation of gauges that created more leak paths and added additional costs. Operators were unaware when installed switches stopped functioning due to welded contacts in the microswitch. Switches required removal from service and manual testing to conform functionality. Often, the control or safety function would go unprotected for days while the switch was in queue to be bench tested, creating an immediate safety concern.

These industry-wide problems inspired manufactures to innovate the next generation of switches that incorporate liquid crystal displays (LCD), presenting local process variable measurements, and integrated internal diagnostics, monitoring the health of the device. The addition of LCDs and device diagnostics increases up me and improves overall plant safety. Original equipment manufacturers (OEM) benefit from a reduction in installed components and a more dependable turnkey product for their customers.

2. Difficult Adjustments

Set point and deadband adjustments were a nuisance for operators and technicians. The instruments were required to be removed from service and calibrated on a bench in the maintenance shop. Installation instructions were not always available for installed devices, leading to wasted me searching for documentation or requesting additional information from the manufacturer. Delicate adjustments were required to achieve desired set points and deadbands, the dead time where no action happens, varied based on the microswitch inside the control. More often than not, instruments were mis- handled leading to premature failure due to inexperienced technicians.

Today’s generation of switches offer electronic platforms that reduce setup and programming to a ma er of seconds. A user interface on the local LCD provides simple prompts that allow users to program switch set points instantly without the need to remove the instrument from the process. Deadband and set point are now 100 percent adjustable, allowing operators to choose the desired range based on the application requirements. No longer are operators required to order and stock redundant devices in the event one failed in the eld. Users now have the flexibility of programming one switch to match many different process requirements.

3. Unsafe in Critical Applications - Not Appropriate for SIS

Industrial process plants are pushing pressure and temperature limits to new boundaries in an effort to stay competitive in a global market. Many of the systems designed 20 years ago were not intended to run at the current process extremes. It is only a ma er of me before these systems fail. Safety instrumented systems (SIS) are being installed to protect the process, people and the environment. These systems require devices that have been rigorously tested by third party agencies to verify the level of safety performance. Mechanical switches, referred to as sensors in SIS, are one of the most common components to fail in these systems. Users and designers require a switch that matches their required system performance level while also being fault tolerant.

Based on the strict performance requirements of SIS, newly introduced hybrid switches integrate the functionality of a switch and a transmitter. The switch portion of the device provides a direct digital output (relay output) to a final element that will instantly bring a process to a safe state in the event of a critically abnormal situation. The analog transmitter signal can be used for trending to determine the health of the device and the process. These new transmitter-switches and recently SIL 2 and 3 exida-certified devices (One Series Safety Transmitter) offer operators a simple and safe product that matches the demanding performance requirements of safety instrumented systems.

4. Problematic in Tough Environments

Whether installed on plant rotating equipment, such as turbines, or on demanding OEM auxiliary equipment, such as pumps or compressors, switches are required to function in tough environments that include shock, vibration, heat and pressure. Vibration is one of the leading causes of electro- mechanical switch failure. Most switches are mechanical in design and utilize a plunger to activate a microswitch. In areas of high shock and vibration, the plunger position can fluctuate and lead to false trips.

New solid-state, electronic switches provide a solution to the common problems with mechanical switches installed in high vibration applications. Because they have no moving parts, these switches can be mounted directly to the equipment or process without connecting impulse lines to keep them isolated from vibration. Industry leading turbine manufacturers and end users operating large compressors in petrochemical plants are experiencing much more reliability and fewer false trips with these new electronic switches, compared to the old mechanical designs.

5. Deploy Electromechanical Designs When Line Power is Unavailable

Most pressure switches sold over the past 80 years were designed to operate without electric power by incorpora ng a sensor that measures pressure by placing force on a plunger that would actuate a microswitch.

The first genera on of digital switches required line power to operate and were not adopted due the unavailability of line power and the cost of wiring. The new genera on of switches operates from leakage current in the circuit when connected to a host device, such as a Programmable Logic Controller (PLC), allowing electronic switches to be drop-in replacements for the old mechanical switches. Today, we have the ability to replace a blind and dumb mechanical switch with a new solid-state, electronic switch that offers a digital gauge, switch and transmitter in one instrument without adding any wiring or hardware.

6. Antiquated Technology

Today’s process plants run their processes faster and ho er than they were originally designed. Ultimately, these plants will have to ini ate modernization projects to support the new demands of the process. Old switches provided users with digital, on-off signals that were either wired to control a piece of equipment directly or sent to a PLC for alarm functionality. As plants go through modernization projects, they restructure control system input/outputs (I/O) to support more analog signals than the digital signals used in the past. Transmitters are commonly chosen and recommended over switches in these new projects, but transmitters do not provide the internal control functionality found in switches.

These modernization projects are costly requiring new equipment, updated wiring, expanded I/O, extensive engineering resources, and costly down me. Users are diligently exploring new ways to reduce overall project costs. The average process transmitter can cost upwards of $2,000 compared to the average process switch costing around $500. Process plants often have 100 to 1,000 switches installed. To upgrade all switches to transmitters could cost a plant up to $1.5 million. Consequently, switch manufacturers researched and developed new electronic switches that are capable of producing both digital and analog signals required by these new modernization projects, while keeping a similar price point to the original mechanical switches installed.

This dramatic savings allows plants to reduce the overall modernization project costs by upgrading the 2nd most likely component (sensor) to fail in a tradional safety system, without upgrading the rest of the safety system and reducing the down me needed to complete the project during a short shut- down turn- around project.

7. The Speed of Response of Transmitters is Faster than Switches

Without question, electromechanical switches are faster than any pressure transmitter on the market. With transmitters, huge amounts of conversions, computations, compensation, and other work must be done to get an accurate signal. Even using today’s high-speed processors, they cannot match the speed of the instantaneous reaction of a mechanical device. The fastest of these devices can be be er than 5 milliseconds while process transmitters can range from 300-500 milliseconds or more. Purpose built transmitters for safety applications designed for speed of response in lieu of accuracy (not needed in safety applications) can be as fast as 250 milliseconds. New solid state transmitter-switches can react in 100 milliseconds or less in the switch mode. If your application requires fast response such as in positive displacement (PD) pumps and turbine trip for over-speed protection, consider new solid-state transmitter-switches over process transmitters.

Recommendations

United Electric Controls has recognized the challenges faced by users and developed new products to match their growing needs. In an effort to reduce plant project costs and help OEMs design and build affordable and reliable equipment for the industrial sector, we have developed a new line of electronic switches that provide drop-in replacement of old mechanical switches. These new switches reduce the costs of plant modernizations. Built-in digital and analog communication provides users the op on of control- ling a piece of equipment locally or sending information back to a central control system for process trending and health, or both.

About this white paper:

UE ViewPoint white papers provide Executive, Business and Technical Briefs written by product, application and industry subject matter experts employed by United Electric Controls.  For more UE ViewPoint papers, visit this link.

Introduction to a Closed Loop Control System

Closed Loop Control System

The video below explains the concept of a closed loop control system, using a steam heat exchanger and food processing application as an example.

A closed loop control system uses a sensor that feeds current system information back to a controller. That information is then compared to a reference point or desired state. Finally, a a corrective signal is sent to a control element that attempts to make the system achieve its desired state.

A very basic example of a temperature control loop includes a tank filled with product (the process variable), a thermocouple (the sensor), a thermostat (the controller), and a steam control valve feeding a tubing bundle (the final control element).

The video outlines all the major parts of the system, including the measured variable, the set point, the controlled variable, controller, error and disturbance.

Contact http://www.ivesequipment.com with any process control or instrumentation requirement. Call 877-768-1600 for immediate assistance.

Level Instrumentation for Your Entire Industrial Plant

Siemens level controls.

Whether you are measuring liquids, slurries or bulk solids, Siemens provides the ideal level measuring instruments for every job. Siemens level measurement devices set the standard in their respective disciplines for water, cement, mining, chemical, petrochemicals, food, beverage, pharmaceutical and other industries.

Point Level

Siemens level switches for point level measurement are distinguished by their outstanding performance. Their robust design ensures reduced cost of maintenance, spare parts, and downtime. Siemens level measurement instruments offer easy commissioning, connection to alarm or control systems, long service life, and low operating costs. Technologies include capacitance, rotary paddle, ultrasonic and vibrating.

Continuous

The product portfolio for continuous level measurement covers both contacting and non-contacting measurement. Radar, ultrasonic and gravimetric technologies are available for the non-contacting applications. Capacitance, guided wave radar and hydrostatic technologies are available for the contacting applications. As well, don’t forget that the safest engineered level measurement solution includes switches for back-up, overfill, low level and dry run protection. Technologies include radar, guided wave radar, ultrasonic, gravimetric, capacitance, and hydrostatic.

Interface

Siemens broad portfolio includes a large number of devices for many interface measurement applications, and includes the following products. SITRANS LC500, Pointek CLS 100, CLS 200, CLS 300 and CLS 500 are capacitance instruments for a wide range of tasks. The SITRANS LG uses guided wave radar technology.

Watch the entertaining video below to get a better idea of what level solutions Siemens (and Ives) has to offer.

Consider Controlled Environment Room Air Flow

Air flow characteristics can determine how well a controlled
environment room or chamber performs for an application

Environmental chambers, whether of the reach-in or walk-in variety, all rely on the movement of air within their controlled space to attain performance specifications. Various manufacturers will employ differing strategies for chamber air movement, and the manner in which their designs disperse air flow throughout a chamber of any size can have an impact on the work or process held within the chamber.

This article is about controlled environment rooms, but much of what is included here is also applicable to smaller sized chambers.

The design of air flow in a controlled environment room can be impacted by a number of factors, some of which may be based on specific application requirements, and others that may be influenced by cost, production simplicity, or other factors unrelated to the performance goal of the equipment.

What aspects of controlled environment room air flow bear on performance?

• Velocity - In the common usage of the term when referring to air flow, the speed of the moving air. Depending upon the air moving equipment arrangement and any dispersion devices, such as perforated suspended ceilings or wall plenums, air velocity can vary throughout a chamber. Users should consider how their work may be impacted by air flow velocity. The storage of material in closed and sealed containers may be impervious to air velocity effects because the "product" within the container is not in contact with the moving air. Plants and insects, on the other hand, are an example of items that may be significantly or severely impacted by air velocity. Higher air velocity at a chamber location exposes that location to more air per unit of time. Desiccation is one possible concern that is exacerbated by increased air velocity. Higher velocity can also be beneficial, even necessary, for some applications. Rapid cooling or heating of materials placed within a chamber is enhanced by increased air movement across the material surface.
• Volume - The volumetric flow of air through a controlled space or chamber is needed to transfer heat to or from the space in order to maintain temperature control. Much of the air in a controlled environment room is recirculated, with cooling, heating, and in some cases moisture applied to condition the air in the room to the setpoint. The volume of air movement is loosely related to velocity, so increasing volume will result in an increase in velocity unless other design changes are made with respect to how the air is dispersed throughout the room. Higher volume, or turnover rate, contributes to better temperature uniformity in the room. As with velocity, there may be application specific requirements for low air movement. Keep in mind that low air movement creates challenges to the attainment of close temperature control and uniformity. 
• Pattern - The way in which air is distributed throughout the controlled environment room can impact system performance once materials are placed in the room or process work is commenced. Empty chambers generally perform well, regardless of the air flow pattern, because there is little in the way of a load on the system and no solid materials in place to block or redirect air flow. Consideration should be given to the way in which air is dispersed throughout the work area. Loading patterns for stored product or the placement of work in process should be accommodated by the air flow pattern.

Matching the right air flow characteristics to the work to be achieved in a controlled environment room will result in better overall performance, not just when empty chamber tests are conducted, but when real work is being accomplished.

Share your environmental chamber and controlled environment room requirements and challenges with application experts. The combination of your own experience and knowledge with their specialized technical expertise will yield an effective solution.

Monitoring Catalyst Presulfiding

Catalyst ‘presulfiding’ is a practice which reduces the extent of early catalyst deactivation on by preventing coking (carbon deposits). The procedure involves passing a gas stream containing H₂S over the catalyst or into the reaction feedstock.

In order to generate the H₂S which will interact with the catalyst, a sulfur carrying agent (e.g. dimethyl sulfide) is injected into the stream. Under high temperature and catalytic reaction, the agent decomposes and releases its sulfur component, forming H₂S. The H₂S reacts with the catalyst’s metallic surface to substitute sulfur atoms for oxygen atoms.

Read the document below to learn more about monitoring this process with the Applied Analytics OMA-300 H₂S Analyzer

Monitoring Catalyst Presulfiding Step from Ives Equipment