A Precise Combustion Airflow Measurement Station Designed for the Power Industry

The objectives in the power industry today are twofold;

• To lower emissions 
• Increase plant performance

Precise measurement of combustion airflow and fuel rates positively contributes to achieving those objectives, by providing the information needed to optimize stoichiometric ratios and facilitate more complete, stable combustion. Usable measurements cannot be obtained from existing devices such as Venturis, foils, jamb tubes, etc., or instrumentation such as thermal anemometers due to limited available straight duct runs, low flow rates, proximity to modulating control dampers, broad turndown range, and high concentrations of airborne particulate (flyash). 

There is a product, however, by Air Monitor Corporation that reliably and consistently provides precise combustion airflow measurement. The CA Station has both an integral airflow processing cell and Fechheimer-Pitot measurement technology and is engineered to meet the challenging operating conditions of the typical power plant. It's capable of providing mass flow measurement of PA, SA, and OFA within an accuracy of ±2-3% of actual airflow.

The Air Monitor CA Station

While the main functions of primary air are to first dry and then pneumatically convey the pulverized coal from the mill to the individual burners, it also determines coal particle velocity at the burner exit, influencing the flame position relative to the burner tip and impacting flame stability, both key factors in achieving optimized burner performance. Accurate PA measurement obtained with a CA Station can contribute to reducing NOx and CO, improving flame stability, avoidance of coal pipe layout, minimizing LOI/UBC, reducing waterwall corrosion, and increasing combustion efficiency.

The CA Station is also ideally suited to measure SA entering each burner level of a partitioned windbox, SA being taken out of a windbox to supply multiple OFA ports, at the ducted inlet of FD fans, and bulk SA entering each windbox of a corner fired unit.

For more information about the CA Staton, contact Power Specialties by visiting http://www.powerspecialties.com or calling (816) 353-6550.

DAQ - Data Acquisition's Role in Process Control

DAQ incorporating data acquisition, process

control, recording, display and networking

in a single compact unit

Courtesy Yokogawa Corp.

Data acquisition, like an equipment acquisition, is the procurement of an asset. Data is an asset. It helps an operator evaluate process or business conditions and make decisions that impact the success of the organization.

Let’s define data acquisition as the sampling of signals that represent a measurement of physical conditions and the conversion of those signals into a numeric form that can be processed by a computer. A data acquisition system will generally consist of sensors, transmitters, converters, processors, and other devices which perform specialized functions in gathering measurements and transforming them into a usable form.

Industrial process operators and stakeholders benefit from the collection and analysis of data by enhancing performance of valuable facets of the process or activity. Data acquisition, commonly known as DAQ, is widely employed in high stakes and sophisticated processes where there is a true need to know current conditions. A desire for increased profit drives the need for increased process output and efficiency. A desire to reduce risk of loss drives the need for reduced downtime and improved safety. Today, there are likely many useful applications for data acquisition that are not being tapped to their fullest potential. The modest cost and simplicity of putting a data acquisition system in place, compared to the benefits that can be derived from a useful analysis of the data for your operation or process, makes the installation of a data acquisition system a positive move for even small and unsophisticated operators in today’s market.

What we call DAQ today started in the 1960’s when computers became available to businesses of large scale and deep pockets. By the 1980’s, personal computers employed in the business environment could be outfitted with input cards that enabled the PC to read sensor data. Today, there is an immense array of measurement and data collection devices available, spanning the extremes of price points and technical capability. For a reasonable cost, you can measure and collect performance data on just about anything.

Data acquisition has an application anywhere an operator or stakeholder can benefit from knowing what is occurring within the bounds of their process or operation. Here is a partial list of the many physical conditions that can be measured in industrial settings:

• Temperature
• Pressure
• Flow
• Force
• Switch Open or Closed
• Rotational or Linear Position
• Light Intensity
• Voltage
• Current
• Images
• Rotational Speed

Consider your industrial process or operation. Are there things you would like to know about it that you do not? Would you like to increase your insight into the workings of the process, how changes in one condition may impact another? Do you know what operating condition of each component of your process will produce the best outcomes? Is reducing maintenance, or heading off a failure condition before it occurs something you would like to have in your operation? Applying your creativity, ingenuity and technical knowledge, along with the help of a product expert, will help you get the information you need to improve the outcomes from your industrial process or operation. 

Wireless Instrumentation In Process Measurement and Control

Wireless Instrumentation (Yokogawa)

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^TM, 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^TM.

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.

For more information on wireless instrumentation, review the document below. Please feel free to call Power Specialties at (816) 353-6550 to speak with an applications specialist.

Yokogawa Field Wireless Solution from Power Specialties, Inc.

PID Control Tutorial

PID is an acronym for proportional band, integral and derivative. This control action allows a measurement (process variable) to be controlled at a desired set point by continuously adjusting a control output. These control parameters act on the error or deviation between set point and process variable.

P: Proportional Band in %
I: Integral Time in sec/repeat
D: Derivative Time in seconds

Proportional Control

With proportional band, the controller output changes in "proportion" to the error between process variable and set point. The amplitude of the change is adjustable from 1% to 999.9%.







Refer to Figure 1. This example of a temperature controller shows a proportional band setting of 5%.

• Set point = 500°
• Measurement range = 0-1000°
• 5% PB = 5% of 1000° = 50°
• 100% output at 475° (2.5% of 1000°)
• 0% output at 525° (2.5% of 1000°)

If the process variable equals the set point (500°), there is a 50% output. As the temperature decreases, the proportional band increases the output linearly toward 100% as the temperature falls toward 475°. The output decreases below 50% as the temperature rises toward 525°.

In this example, a small change in temperature provides a large change in output. If the setting is too small for the process dynamics, oscillations will occur and will not settle at set point. A large PB setting makes the controller act sluggish and will not respond adequately to upsets. Since proportional control does not incorporate the time that the error has existed, there will always be an offset from set point.

Typically, flow or pressure controllers have a much larger proportional setting due to a possible narrower measurement range and fast process reaction to a change in the control output. For example, a flow controller may have an input range of 0 to 60gpm and a set point of 30gpm.

• Measurement range = 60gpm
• Set point = 30gpm
• 100% PB = 100% of 60 = 60gpm
• 100% output at 0gpm
• 0% output at 60gpm

Proportional + Manual Reset

To eliminate the inherent offset observed with proportional control, a manual reset function can be used. Virtually no process requires precisely 50% output to maintain the process variable at the set point. An offset will be present. Manual reset allows the user to bias the output accordingly to compensate for the steady state offset using P only. Refer to Figure 2.

Proportional + Automatic Reset (Integral)

Automatic reset or integral action corrects for any offset between set point and process variable
automatically by shifting the proportional band over a pre-defined time. The integral time repeats the proportional action over the time set. Integral redefines the output requirements at the set point until the process variable and set point are equal. Integral engineering units vary by controller manufacturer. Some use repeats/minute (reset rate), minutes/repeat or seconds/repeat. In Figure 3, seconds/repeat is used. The integral term is added as follows:

The smaller the integral number, the proportional action will be repeated more often. If integral is too small, the process variable will oscillate through set point and create erratic control action. If the number is too large, the action will be sluggish and unable to compensate for process upsets.

The integral number should be approximately 5 times the dead/lag time of the process variable. If the output is manually changed, dead time is defined as the time required for the process variable to initially react after the change. The length of time that it takes for the process variable to stabilize at a steady state is lag time.

• Example: 40 sec (dead/lag) x 5 = 200 sec/repeat

Proportional + Integral + Derivative

Derivative action is used primarily in processes with long dead and lag times. This control function looks at the rate of change of the error and adjusts the control output based on that rate. The derivative term is added to the control algorithm as follows:

The amount of derivative added to the control output is based in time units. Figure 4 shows how derivative acts on the proportional band. The dashed line shows a proportional only control due to a process variable error from set point.

Using derivative (solid line), the control output jumps up, rises in a ramp and then falls back to proportional control action when the error becomes constant. In essence, it applies the "brakes" on the process error by quickly shifting the proportional band. Derivative has no effect on the output if the error is not changing. The derivative term should be approximately ¼ the integral time.

Derivative is typically not used in control loops with short dead/lag time, e. g., flow or pressure. This is an anticipatory action that will contribute to the inherent instability of these fast acting control loops.

Reprinted with permission from Yokogawa Corp.

Manual Tank Level Transmitter Adjustment on Yokogawa DPharp Transmitters

If you have ever replaced a level transmitter with remote seals on a tank, you know the problems you may face if the tank can't be empty to allow you to correct for an elevated or suppress zero. With today's smart transmitters, this is now an easy thing to do.

Watch the video below for a quick tutorial on spanning and zero'ing the level transmitter.

For more information about Yokogawa products in Kansas, Missouri, Iowa, and Nebraska, contact Power Specialties by visiting www.powerspecialties.com or calling (816) 353-6550.

Measuring Exact Resultant Forces In Web Tension

Accuracy and consistency of web tension is critical.

Paper quality is determined by several factors including density and wrinkling. Problems in these areas are common in the paper industry. Uneven density and wrinkling of paper reels occurs if there is inadequate control over the positions and forces that control critical stages of the winding process, i.e. winding and spool transfer from the primary arm to the secondary arm. Because paper is sold by the ton not by the foot, the density is obviously extremely important. Wrinkling causes big problems in newspaper manufacture as paper breaks lead to stoppage of the printing presses.

One typical problem occurs when the nip force is controlled by measuring the pressures in the cylinders. Because the cylinders are mounted some distance away from the spool, where the nip force is actually generated, the friction that arises in the machine reduces the accuracy of the measurement results. As the mechanical components in cylinders become worn, this problem grows and the inaccuracy of measurements increases. If you do not have force control on both sides, and do not have control over the prevailing conditions for each reel, the nip forces will lack repeatability. This increases the risk of varying density and wrinkle formation, both when changing reels, and during winding where paper breaks may also occur. When lowering the spool from the primary arm to the secondary arm, changes may occur in the lowering speed, and misalignment between the reels may also result in varying density, wrinkles, and paper breaks.

 

One solution from BLH Nobel is based on mounting load cells directly at the point of force application, as well as on the position sensors in each cylinder. The load cells are therefore installed in the primary arm and secondary arm, and in the spool clamp. This allows us to measure values in real time, which means that we know the actual forces in the critical transfer from the primary to the secondary arm. Acceleration speed and force can then be adjusted by positioning cylinders that are controlled by means of software.

By adopting load cells, paper reels of the right density, with wrinkle free paper, and less paper breaks are the outcome. In a typical mill with 3 to 4 percent of the jumbo role being rejected due to wrinkling, using load cells reduced the waste to less than 0.5 percent.

For more information, visit Power Specialties at http://www.powerspecialties.com or call (816) 353-6550.

Introduction to Industrial Transmitters: Transmitters 101

Differential Pressure Transmitter
(Yokogawa)

Transmitters are process control field devices. They receive input from a connected process sensor, then convert the sensor signal to an output signal using a transmission protocol. The output signal is passed to a monitoring, control, or decision device for use in documenting, regulating, or monitoring a process or operation.

In general, transmitters accomplish three steps, including converting the initial signal twice.

The first step is the initial conversion which alters the input signal to make it linear. After an amplification of the converted signal, the second conversion changes the signal into either a standard electrical or pneumatic output signal that can be utilized by receiving instruments and devices. The third and final step is the actual output of the electrical or pneumatic signal to utilization equipment  controllers, PLC, recorder, etc.

Transmitters are available for almost every measured parameter in process control, and often referred to according to the process condition which they measure. Some examples.

• Pressure transmitters
• Temperature transmitters
• Flow transmitters
• Level transmitters
• Vibration transmitters
• Current, voltage & power transmitters



Level Transmitter (MTS)

• PH, conductivity, dissolved gas transmitters, etc. 

Output signals for transmitters, when electrical, often are either voltage (1-5 or 2-10 volts DC) or
current (4-20 mA). Power requirements can vary among products, but are often 110/220 VAC or 24 VDC.  Low power consumption by electrical transmitters can permit some units to be loop powered, operating from the voltage applied to the output current loop. These devices are also called two-wire transmitters because only two conductors are connected to the unit. Unlike the two wire system which only needs two wires to power the transmitter and analog signal output, the four-wire system requires four separate conductors, with one pair serving as the power supply to the unit and a separate pair providing the output signal path. Pneumatic transmitters, while still in use, are continuously being supplanted by electrical units that provide adequate levels of safety and functionality in environments previously only served by pneumatic units.

Temperature and Flow Transmitter
(Fox Thermal Instrument)

Many transmitters are provided with higher order functions in addition to merely converting an input signal to an output signal. On board displays, keypads, Bluetooth connectivity, and a host of industry standard communication protocols can also be had as an integral part of many process transmitters. Other functions that provide alarm or safety action are more frequently part of the transmitter package, as well.

Wireless transmitters are also available, with some operating from battery power and negating the need for any wired connection at all. Process transmitters have evolved from simple signal conversion devices to higher functioning, efficient, easy to apply and maintain instruments utilized for providing input to process control systems.