Electric Power Generation Using Coal

Coal Fired Power Plant

Electricity is generated at most electric power plants by using mechanical energy to rotate the shaft of electromechanical generators. The mechanical energy needed to rotate the generator shaft can be produced from the conversion of chemical energy by burning fuels or from nuclear fission; from the conversion of kinetic energy from flowing water, wind, or tides; or from the conversion of thermal energy from geothermal wells or concentrated solar energy. Electricity also can be produced directly from sunlight using photovoltaic cells or by using a fuel cell to electrochemically convert chemical energy into an electric current.

The combustion of a fossil fuel to generate electricity can be either: 1) in a steam generating unit (also referred to simply as a “boiler”) to feed a steam turbine that, in turn, spins an electric generator: or 2) in a combustion turbine or a reciprocating internal combustion engine that directly drives the generator. Some modern power plants use a “combined cycle” electric power generation process, in which a gaseous or liquid fuel is burned in a combustion turbine that both drives electrical generators and provides heat to produce steam in a heat recovery steam generator (HRSG). The steam produced by the HRSG is then fed to a steam turbine that drives a second electric generator. The combination of using the energy released by burning a fuel to drive both a combustion turbine generator set and a stream turbine generator significantly increases the overall efficiency of the electric power generation process.

Coal is the most abundant fossil fuel in the United States and is predominately used for electric power generation. Historically, electric utilities have burned solid coal in steam generating units. However, coal can also be first gasified and then burned as a gaseous fuel. The integration of coal gasification technologies with the combined cycle electric generation process is called an integrated gasification combined cycle (IGCC) system or a “coal gasification facility”. For the remainder of this document, the term “electric generating unit” or “EGU” is used to mean a solid fuel-fired steam generating unit that serves a generator that produces electricity for sale to the electric grid.

7 Important Considerations When Applying Inline, Spring-loaded Check Valves

Inline Spring-loaded Check Valve
(courtesy of CheckAll Valve)

1) Installation and Mounting

Inline, spring loaded check valves can be used in horizontal or vertical applications with proper spring selection. This is most evident in vertical flow down installations. The spring selected must be heavy enough to support the weight of the trim in addition to any column of liquid desired to be retained.

2) Elbow's, Tee's or other Flow Distorting Device's

Inline, spring loaded check valves are best suited for use with fully developed flow. Although there are many factors affecting the achievement of fully developed flow (such as media, pipe roughness, and velocity) usually 10 pipe diameters of straight pipe immediately upstream of the valve is sufficient. This is particularly important after flow distorting devices such as elbows, tees, centrifugal pumps, etc.

3) Valve Material Selection

There are many factors that influence the resistance of materials to corrosion, such as temperature, concentration, aeration, contaminants, and media interaction/reaction. Special attention must be paid to the process media and the atmosphere where inline check valves are applied. It is always recommended that an experienced application tech be consulted before installation.

4) Seat Material Selection
Several seat material options are available for inline, spring loaded check valves. An allowable leakage rate associated with the “metal-to-metal” as well as the PTFE o-ring seat, is 190 cc/min per inch of line size, when tested with air at 80 PSI. Resilient o-ring seats can provide a “bubble tight” shut-off (no visible leakage allowed at 80 PSI air).

5) Sizing and Spring Selection

It is very important to size check valves properly for optimum valve operation and service life. Sizing accuracy requires the valve be fully open, which occurs when the pressure drop across the valve reaches or exceeds three times the spring cracking pressure. Again, it is recommended that an experienced application tech be consulted for help with sizing.

6) Shock-Load Applications

Inline, spring loaded check valves are not designed for use in a shock-load environment, such as the discharge of a reciprocating air compressor. These types of applications produce excessive impact stresses which can adversely affect valve performance.

7) Fluid Quality

Inline, spring loaded check valves are best suited for clean liquids or gasses. Debris such as sand or fibers can prevent the valve from sealing properly or it can erode internal components or otherwise adversely affect valve travel. Any particles need to be filtered out before entering the valve.

8 Critical Control Valve Selection Criteria

Control Valve (Valtek)

Choosing an improperly applied sized or improperly sized control valve can have serious consequences on operation, productivity and most important, safety. Here is a quick checklist of basics that need to be considered:

1. Control valves are not intended to be a an isolation valve and should not be used for isolating a process. 
2. Always carefully select the correct materials of construction. Take into consideration the parts of the valve that comes in to contact with the process media such as the valve body, the seat and any other "wetted" parts. Consider the operating pressure and operating temperature the control valve will see. Finally, also consider the ambient atmosphere and any corrosives that can occur and effect the exterior of the valve. 
3. Put your flow sensor upstream of the control valve. Locating the flow sensor downstream of the control valve exposes it to an unstable flow stream which is caused by turbulent flow in the valve cavity.
4. Factor in the degree of control you need and make sure your valve is mechanically capable. Too much dead-band leads to hunting and poor control. Dead-band is roughly defined as the amount of control signal required to affect a change in valve position. It is caused by worn, or loosely fitted mechanical linkages, or as a function of the controller setting. It can also be effected by the tolerances from mechanical sensors, friction inherent in the the valve stems and seats, or from an undersized actuator. 
5. Consider stiction. The tendency for valves that have had very limited travel, or that haven't moved at all, to "stick" is referred to as stiction. It typically is caused by the valves packing glands, seats or the pressure exerted against the disk. To overcome stiction, additional force needs to be applied by the actuator, which can lead to overshoot and poor control.
6. Tune your loop controller properly. A poorly tuned controller causes overshoot, undershoot and hunting. Make sure your proportional, integral, and derivative values are set). This is quite easy today using controllers with advanced, precise auto-tuning features that replaced the old fashioned trial and error loop tuning method.
7. Don't over-size your control valve. Control valves are frequently sized larger than needed for

   

   Control Valve
   Specialized for Food/Bev
   Pharmaceutical (Kammer)

   the flow loop they control. If the control valve is too large, only a small percentage of travel is used (because a small change in valve position has a large effect on flow), which in turn makes the valve hunt. This causes excessive wear. Try to always size a control valve at about 70%-90% of travel.
8. Think about the type of control valve you are using and its inherent flow characteristic. Different types of valve, and their disks, have very different flow characteristics (or profiles). The flow characteristic can be generally thought of as the change in rate of flow in relationship to a change in valve position. Globe control valves have linear characteristics which are preferred, while butterfly and gate valves have very non-linear flow characteristics, which can cause control problems. In order to create a linear flow characteristic through a non-linear control valve, manufacturers add specially designed disks or flow orifices which create a desired flow profile.

These are just a few of the more significant criteria to consider when electing a control valve. You should always discuss your application with an experienced application expert before making your final selection.

Consider Flangeless Wafer Style Control Valves for Excellent Flow Control

Jordan Mark 75 Flangeless
Wafer Style Control Valve

Valves are essential to industries which constitute the backbone of the modern world. The prevalence of valves in engineering, mechanics, and science demands that each individual valve performs to a certain standard.

One category of valves are "control valves". These can be linearly operated, or rotary operated. There are many types of control valves, such as gate, globe, ball, butterfly, and plug. All of these valve types have some sort of ball, plug, gate, or disc that throttles the flow as the valve opens and closes. Some valve designs are better suited to uniformly control flow, such as gate valves or valves with specially machined disks. This post is about the Jordan Mark 75, a valve that uses a unique sliding gate design.

According to Wikipedia, "A control valve is a valve used to control fluid flow by varying the size of the flow passage as directed by a signal from a controller. This enables the direct control of flow rate and the consequential control of process quantities such as pressure, temperature, and liquid level."

The Mark 75 Series control valve is a industrial process control valve manufactured by Jordan Valve. It's design benefits include the sliding gate seat design, low weight, and compact wafer style body. The Mark 75 offers an incredible pricing advantage in the market place due to its wafer style body.

The stroke length of the Mark 75 is a slightly longer stroke than standard sliding gate valves. This longer stroke enables better turndown. Combined with the capacity of the Mark 75, the increased turndown makes for a great control valve.

Please watch the video below, and see the specification sheet at the bottom for further details. For more information about this valve, or any Jordan Valve product, contact Swanson Flo at 800-288-7926 or visit http://www.swansonflo.com.

Jordan Valve Mark 75 Flangeless Wafer Style Control Valves from Swanson Flo

Understanding Industrial Rack and Pinion Valve Actuators

Basic concept of
rack and pinion gear.

Valves are essential to industries which constitute the backbone of the modern world. The prevalence of valves in engineering, mechanics, and science demands that each individual valve performs to a certain standard. Just as the valve itself is a key component of a larger system, the valve actuator is as important to the valve as the valve is to the industry in which it functions. Actuators are powered mechanisms that position valves between open and closed states.

Pneumatic rack and pinion actuators utilize air pressure as the motive force which changes the position of a valve.  A rack and pinion actuator is comprised of two opposing pistons, each with its own gear (referred to as the "rack"). The two piston racks are set against a round pinion gear. As pressure increases against one side of each piston, each rack moves linearly against the opposite sides of the pinion gear causing rotational movement. This rotational movement is used to open and close a valve. See the animation above (provided by Wikipedia) below for a visual understanding.

This short video introduces the basic parts and operation of rack and pinion valve actuators to anyone unfamiliar with the device.

Visit http://www.swansonflo.com to learn more about industrial valves, valve actuators, and valve automation.

Pressure Instrument Calibration

Proper pressure instrument calibration is critically
important for safety and quality.

Calibration of pressure instruments in industrial environments requires the establishment of known pressure magnitudes. With a stable input pressure established, the pressure measurement instrument is provided with a referential benchmark that can be used to evaluate instrument output. There are several physical test standards or methods that can be applied to pressure instruments.

A deadweight tester, sometimes called a dead-test calibrator, creates accurately known pressure using precise masses and pistons of a known area. The gauge or pressure instrument is connected to the deadweight tester. The device is comprised of tubes that contain either oil or water, with a primary piston positioned above the liquid and a secondary piston across from the place where the gauge connects to the tester. A mass of a known quantity is placed atop the primary piston, which is perfectly vertical. The earth's gravitational field acts upon the mass atop the piston. The combination results in a known value being applied to the deadweight tester and subsequently allows for calibration of the gauge.

Deadweight tester (Ashcroft)

Once pressure builds inside the deadweight tester, surpassing the weight of the piston, the piston will rise and float atop the oil. By rotating the mass atop the piston, the piston will rotate inside its cylinder and negate any impact from friction. Developments in technology have led to testers being equipped with hand pumps and bleed valves. The same principles applied to a deadweight tester which uses oil are applied to a pneumatic deadweight tester, where gas pressure suspends the mass atop the cylinder instead of oil or water pressure.

The manometer is another device which establishes a pressure standard to calibrate gauges. Alone, the manometer is simply a U shaped tube connecting a source of fluid pressure to the gauge being calibrated. Pressure applied to the gauge will be indicated by the corresponding heights of the fluid in the columns. If the value of the density of the liquid is a precise, known value, the aforementioned constant of the earth's gravitational field will combine with the applied pressure to permit calibration of the gauge.

Digital Test Gauge (Ashcroft)

Test instruments which couple with the calibration of pressure transmitters are also instrumental in ensuring correct pressure calibration. Electronic and pneumatic test instruments, along with precise air pressure calibration pumps, enable calibrating a pressure transmitter in place, in the field, or on a lab bench. These portable devices, though, require their own calibration to physical standards with referenced properties. While different devices exist for establishing pressure standards in either high or low pressure environments, the shared standard allows for varying types of instrumentation to exhibit similar performance quality and accomplish the same task.

Contact Swanson Flo for any pressure instrument repair or calibration requirement. Visit http://www.swansonflo.com or call 800-288-7926.

A Proven Actuator Ideal for Valves Requiring Rotary or Linear Movement

Limitorque L120 electric actuator.

Whether used with gate valves, globe valves, penstocks or sluice gates, versatile Limitorque L120 Series actuators operate without modification in any rising or non-rising stem application for linear-action valves.

When combined with a Limitorque WG or HBC series quarter-turn gear operator, L120 actuators can also be used to control butterfly, ball and plug valves, as well as damper drives, flop gates or any other device which requires rotary movement.

L120 actuators are specified for use in petrochemical, power generation, and water and waste treatment applications where failure of a single actuator can be extremely costly … even catastrophic.

For more information on Limitorque actuators, visit Swanson Flo's website or call 800-288-7926.

For your convenience, below you will find the Limitorque L120-85 installation and operation manual.

Flowserve Limitorque L120-85 Electric Actuator IOM from Swanson Flo