Friday, June 26, 2015

Selecting the Right Valve Type - Gate Valves

When it comes to controlling flow in an industrial fluid handling system, there are more choices than you can count. The journey of focusing in on the best option for your application can be shortened by employing some coarse filters to the vast array of available products and technologies, discarding choices that do not meet the basic criteria deemed essential to a successful project.

A common type of industrial valve is the gate valve. It regulates fluid flow by sliding a round or rectangular wedge, known as the gate or disc, in the flow path of the fluid. When the gate is fully retracted from the fluid path, flow is enabled to its fullest. Gate valves close by sliding the gate, which is commonly attached to a threaded shaft of other similar mechanism, into the path of the flow until it is fully obstructed. It is the movement of the gate, combined with the way in which a gate valve is constructed, that attributes this valve class with its positive and negative values.

Positives for gate valves:

  • When fully open, there is low resistance to fluid flow. The opening in the valve tends to mimic the cross sectional characteristics of connected piping and fluid can flow through the valve without a directional change.
  • Changing the gate position (opening or closing the valve) does not require as much force or power as some other valve types, due to the gate movement being perpendicular to the flow direction.
  • Gate valves work in both directions. The flow in the connected line can be reversed and the valve function is unimpaired.
  • The gate valve assembly tends to be shorter in length along the path of flow than some other designs.
  • Gate Valves in Pipeline
    Gate Valves in Process Pipeline
  • The rate of closure is generally slow, providing a graduated reduction in fluid movement and reduced physical shock to the piping system.
Operating or construction characteristics that may be an advantage to gate valve employment on one application may prove a disadvantage in another.

“Not so positives” for gate valves:

  • When the valve is open, the seals are exposed to the fluid flow. Foreign material, even elements of the process fluid, can deteriorate or contaminate the seals and impact the sealing of the valve when closed.
  • The gate valve opens at a comparatively slow rate, making it unsuitable for applications that may require rapid or immediate shutoff.
  • The service and maintenance space requirements, often extending overhead of the valve, can be substantial and may impact the ability to locate the assembly where desired.
  • Gate valves are not well suited for throttling fluid flow. Fluid flow through a partially open valve of this type may cause the gate to vibrate.

There are certainly more elements involved in proper valve selection than are shown here, but this quick check may help you focus on gate valves or another technology for further consideration. It is always beneficial to bring in experts and those with experience to participate in the selection process.

Friday, June 12, 2015

Guided Wave Radar to Lower Power Plant Costs

power plant
Reducing costs at power plants.
For most power plant operators, fuel expenditures account for seventy to eighty percent of production costs and millions of dollars per year. In fact improving heat rate one percent could generate five hundred thousand dollars an annual savings for five hundred megawatt power point.

To contain fuel costs, power plants must maximize the efficiency of their feed water heaters. That's why many companies today are focusing on improving heat rate as a way to use their feed water heaters more effectively, and significantly reduce their fuel costs.

guided wave radar
Guided wave radar
principle of operation
.
Heat rate is a measure of how efficiently a power plant uses heat energy. You can measure heat rate by the number of BTU’s your plant requires to generate a kilowatt hour of energy. As you're heat rate goes up so do you're fuel costs.

The condenser is the beginning of the feed water heaters process, where condensed steam from the feed water heater drains, and HP, IP and LP turbines is routed through successive feed water heaters. At the same time,  extractions steam from your turbines reaches the appropriate feed water heaters and the transfer of energy takes place.

Maintaining accurate and reliable level control throughout this cycle is critical to achieving the final feed water heater temperature that your process requires.

Let's take a closer look at how this works.  Feed water heaters use the heat of condensation to preheat water to the correct temperature for the boiler. During this process, shell and tube heat exchangers allow feed water to pass through the tube side and extract steam from the turbine to the shell side.

The primary benefit of this process is that the feed water heater decreases the fuel costs by using recovered energy, rather than costly hot gas, to heat the water.

Achieving optimum water level in a feed water heater is a critical component of maximizing energy transfer and minimizing controllable losses.

There are normally six to seven stages of feed water heating. Making an investment in level control can help you achieve optimum heat transfer and improved terminal temperature difference to provide a significant return on investment.

guided wave radar
Guided wave radar
transmitter
(courtesy of
Magnetrol)
With a guided wave radar level control, you can optimize the condensing zone of your feed water heater to deliver accurate level control, maximize energy transfer, and minimize undue wear and tear. This can help you generate the savings needed to recover your investment.

Older level technologies, such as differential pressure, magnetostrictive, or RF capacitance and torque tubes are vulnerable to process conditions and induced instrument errors, such as shifts in specific gravity and mechanical or electronic drift.

In contrast, guided wave radar provides a truly reliable level measurement solution for feed water heaters. Guided wave radar performance is virtually unaffected by process variations and gives you a superior degree of accurate and reliable continuous level measurement without the need for calibration or gravity corrections.

With superior signal performance and advanced diagnostics, guided wave radar delivers premier level control for feed water heaters, as well as a broad range of challenging applications, such as condenser hot wells, deaerators, and cooling tower basins.

Combining a magnetic level indicator with guided wave radar merges the operating systems of a conventional flowed base magnetic level indicator with a leading edge solution. This allows you to effectively measure low dielectric media, high temperature, and high pressure process conditions and media, with shifting specific gravity and dielectric values accurately and repeatedly. The result is a diverse and redundant level measurement solution in a single chamber design.

For more information contact:

M.S. Jacobs and Associates
Phone: 800-348-0089
Fax: 412-279-4810
Email: msjacobs@msjacobs.com
www.msjacobs.com

Friday, May 29, 2015

Introduction to Rotameters

rotameter
Rotameter
(courtesy of
King Instrument)
A rotameter is one particular type of variable area flowmeter that measures flow by varying the cross-sectional area a fluid or gas travels through in a closed tube.

Advantages
  • Requires no external power.
  • Is a simple device that can be easily manufactured out of inexpensive materials.
  • Linear scale.
  • The clear glass tube is resistant to thermal shock and chemical reaction.
Disadvantages
  • Must be mounted vertically, with designated top and bottom, and with the fluid flowing from bottom to top.
  • Graduations on a given rotameter are only accurate for a given substance at a given temperature. Separate rotameters must be used for fluids with different densities and viscosities, or multiple scales on the same rotameter must be used.
  • Resolution is relatively poor and gets worse near the bottom of the scale.
  • Oscillations of the float and parallax lend to reduced accuracy.
  • Difficult to automate - primarily a manual / visual device



For more information on rotameters, contact:

M.S. Jacobs and Associates, Inc.
810 Noblestown Road
Pittsburgh, Pa 15205
Toll free: 800 348 0089
Fax: 412-279-4810
Email: msjacobs@msjacobs.com
www.msjacobs.com

Tuesday, May 19, 2015

Basics of Infrared Flame Detection

flame detector
Triple IR flame detector
(courtesy if Sierra Monitor)
A flame detector is a specialized sensor used to detect and respond to the presence of a flame, and accordingly notify an operator, sound an alarm, close a fuel supply valve, shut down a pump, and turn on a fire suppression system. 

Flame detectors are fast acting and accurate, much more so than smoke or heat detectors because of the technology they employ. Some flame detectors can detect fires up to 215 feet away and be accurate enough to detect a 1 sq. foot gasoline pan at 215 feet in less than 5 seconds. 

One popular type of flame detection technology used is measuring infrared (IR) light coming from a source. This type of sensor monitors the infrared light spectrum for very specific patterns given off by hot gases. These hot gases are sensed by a specialized fire-fighting thermal imaging (thermographic) camera. 

One method of determining if a fire exists is by looking for the infrared peak of hot carbon dioxide (approximately 4.4 micrometers). Response times of a typical IR detector is 3–5 seconds. 

There is the possibility, however, of false alarms caused by background thermal radiation and other hot surfaces in the area. Another potential concern is with the formation of condensate on the flame detector's lens, which can greatly reduce its accuracy. Direct exposure to sunlight for these types of detectors can also be problematic. 

An approach to overcome these issues is with dual or triple IR sensors, which compare the threshold signal in two or three infrared ranges. Often one sensor looks at the 4.4 micrometer carbon dioxide (CO2) emission, while the other sensors looks at additional reference frequencies. Modern flame detector design allow users to select different sensitivity levels to ensure no other detectors cross-over detection zones. 

Additional important features to be considered are heated windows to eliminate condensation and icing, HART and Modbus capabilities for digital communications, low excitation power, and compact design. 

When selecting a flame detector for any application, it is important to make sure it is approved and certified for that specific use. Check for third party agency approval including FM, ATEX, IECEx, TUV, and CSA. These approvals and certifications assure the highest quality of products and performance.

Finally, the proper application of flame detectors is critical in many applications for the safety and protection of property and personnel. Therefore, it is always suggested that your application be discussed with a qualified application engineer

Thursday, April 30, 2015

Steps to Installing a Rotameter

Rotameter
Rotameter


A rotameter, also known as a variable area flowmeter, is a device that measures the flow rate of liquid or gas in a closed tube. It measures flow rate by allowing the cross-sectional area the fluid travels through, to vary, causing a measurable effect. They are a cost-effective flow measuring device that provides excellent repeatability, requires no external power, can be made from a wide variety of materials, and may be designed for high pressure and high temperature applications.

The following are helpful, general guidelines in the proper installation of rotameters:
  1. Inspect meter for damage that may have occurred during shipping. Report any damage to the container to the freight carrier immediately. 
  2. Make sure your pressure, temperature, fluid and other requirements are compatible with the meter and components (including o-rings). 
  3. Select a suitable location for installation to prevent excess stress on the meter which may result from: 
    • Misaligned pipe. 
    • The weight of related plumbing. 
    • “Water Hammer” which is most likely to occur when flow is suddenly stopped as with quick closing solenoid operated valves. (If necessary, a surge chamber should be installed. This will also be useful in pressure start-up situations.) 
    • Thermal expansion of liquid in a stagnated or valve isolated system. 
    • Instantaneous pressurization which will stress the meter and could result in tube failure. note: In closed thermal transfer or cooling systems, install the meter in the cool side of the line to minimize meter expansion and contraction and possible fluid leaks at the threaded connections. 
  4. Handle the meter carefully during installation. 
    • Use an appropriate amount of teflon tape on external pipe threads before making connections. Do not use paste or stick type thread sealing products. 
    • Over tightening of plastic connections may result in fitting damage. 
  5. Install the meter vertically with the inlet port at the bottom. 
  6. Meters with stainless steel fittings will support several feet of pipe as long as significant vibration or stress resulting from misaligned pipe are not factors. 
  7. Meters with plastic fittings must be installed so that fittings are not made to support any part of the associated plumbing. In addition, meter frame should be fastened to bulkhead, panel or column. 
  8. Meters used in gas service should have suitable valves plumbed in at the inlet and outlet of the meter. These valves should be no more than 1-1/2 pipe diameters from the meter ports. The valve at the outlet should be used to create back pressure as required to prevent float bounce. It should be set initially and then left alone. The inlet valve should be used for throttling purposes. Depending on the installation, valves may not be essential, but they are most useful in many installations. Remember: To get a correct reading of flow in gas service, it is necessary to know the pressure right at the outlet of the meter (before the valve). 
  9. Pressure and temperature maximums must never be exceeded

Thursday, March 26, 2015

Thermal Dispersion Flow and Level Technology

thermal dispersion instruments
Thermal dispersion level and flow
instruments (courtesy of Magnetrol)
Thermal dispersion instruments work on the basis of heat transfer. The sensing probe consists of two separate components, both RTDs (temperature detectors). One RTD is used as the reference point and measures the temperature of the fluid right where the probe is immersed. The second RTD is self-heated to a known temperature and maintained. A resulting a temperature differential is created between the two RTDs. By varying the power to the self-heated RTD, the set point can be changed which allows the user to set the instrument for a specific application.

Convective heat is the mechanism of heat transfer for thermal technology level switches based on the principle that a liquid has a thermal conductivity far greater than the thermal conductivity of its corresponding vapor. When the sensor is dry, there is a temperature difference between the two sensors. When fluid comes in contact with both RTDs, there is a cooling effect as the liquid absorbs the heat from the self-heater RTD. The resulting temperature differential drops, and creates a point for high level reference. When the level drops and the sensor goes dry, the temperature difference increases again. The instrument electronics senses the increase in temperature difference and provides a low level reference.

When used for flow applications, the temperature difference under a low flow or no flow condition is controlled by the set point. As the flow rate increases, the sensing RTD is cooled by the fluid moving past the heated sensor - the greater the flow, the greater the cooling. Conversely, the reduction in the temperature differential between the two RTDs indicates that the flow rate is exceeding the set point of the instrument.

Sunday, March 15, 2015

Float Operated Level Switch Fundementals

Float Level Switch
Float Level Switch
(courtesy of Magnetrol)

Float operated level switches are suitable for use on clean liquid applications alarm, pump control and safety shutdown applications.

These float type units are typically designed, fabricated and certified to compliance with ASME B31.3 specifications.

The design of float operated level switches is based upon the principle that a magnetic field will penetrate non-magnetic materials such as 316 stainless steel. In the case of a float type level switch, the float moves a magnetic attraction sleeve within a non-magnetic enclosing tube which in turn trips an electrical switch mechanism. The enclosing tube of housing provides a pressure seal for the chamber as well as the process.

As the liquid level rises in the chamber (refer to Figure 1), the float moves the magnetic attraction sleeve up within the enclosing tube, and into the field of the switch mechanism magnet. Resultingly, the magnet is drawn in tightly to the enclosing tube causing the switch to trip, “making” or “breaking” the electrical circuit.

As the liquid level falls, the float drops and moves the attraction sleeve out of the magnetic field, releasing the switch at a predetermined “low level” (refer to Figure 2). The tension spring ensures the return of the switch in a snap action.