In order for your boiler to operate at peak efficiency, it is important that the correct balance of fuel and combustion air is achieved. Air and fuel ratios are controlled through linkages, fans, dampers and the increase or decrease of gas pressure. Gas pressure is controlled through a pressure regulator and a fan controls the volume of combustion air.
If there are any problems with the fan, more energy may be introduced into the system, causing decreased efficiency. To help ensure that your equipment is running at its peak performance, please review the common fan problems below.
Fan Capacity/Pressure is Below Rating:
1. Dampers or variable inlet vanes are not adjusted properly
2. Fan inlet or outlet conditions are impaired
3. Multiple air leaks within the system
4. Damage sustained to the blower wheel
5. Direction of rotation is incorrect
Fan Vibration:
1. Worn bearings
2. Unstable foundation
3. Foreign material in the fan causing an imbalance
4. Misalignment of bearings, couplings, wheel or v-belt drive
5. Damaged wheel or motor
6. Bent shaft
7. Worn coupling
8. Loose dampers or variable inlet vanes
9. Speed too high or incorrect fan rotation
10. Vibration to fan transmitted from another source
11. Uneven blade wear
12. Loose or broken bolts or set screws
Overheated Bearings:
1. Improper lubrication
2. Poor alignment
3. Damaged wheel or driver
4. Bent shaft
5. Abnormal end thrust
6. Dirt in bearings
7. Improper belt tension
Overload on Driver:
1. Speed too high
2. Direction of rotation is incorrect
3. Bent shaft
4. Poor alignment
5. Improper lubrication
6. Wheel wedging or binding on fan housing
Taken from Nationwide Boiler Blog
Wednesday, March 7, 2012
What is Shaft Alignment?
For machinery installation, only the rotating shaft centerlines of different machines are aligned. Not the feet, not the coupling, not the shaft surfaces, not the machine housings, not the bearings; only the rotating shaft centerlines. It is important to understand that alignment refers to the positions of two centerlines of rotation or two rotational axes. Note that the shaft’s rotational centerline may be different than its machined centerline.
Shaft alignment means: Positioning two or more machines so that their rotational centerlines are colinear at the coupling point under operating conditions. Colinear means two lines that are positioned as if they were one line. Colinear as used in alignment means two or more centerlines of rotation with no offset or angularity between them.
The phrase “coupling point” in the definition of shaft alignment is an acknowledgement that vibration due to misalignment originates at the point of power transmission, the coupling. It does not mean that the couplings are being aligned. The shafts are being aligned, and the coupling center is just the measuring point.”At operating conditions” is an acknowledgement that machines often move after start-up due to wear, thermal growth, dynamic load shifts, or support structure shifts.Besides the above considerations, the term shaft alignment also implies that the bearings and shafts are free from preloads. In properly installed equipment, there are no forces or strains on the bearings and shafts, except those the designers intended. If the machine is installed with the frame distorted because of uneven or imperfect base plates, bent feet, pipe stresses, or whatever, then machine life will be shortened, often significantly.The only way to determine rotational centerlines is to rotate the equipment. There is no series of measurements that do not involve turning the shafts between readings that can be used to find the rotational centerline.
If you don’t turn the shafts…Any system that takes so-called alignment measurements without turning BOTH shafts is aligning surfaces, not centerlines of rotation. The results of any alignment efforts where one or both shafts are not turned are highly dependent upon surface quality, rotor eccentricity, shaft straightness, and other surface defects. In short: “If you do not turn the shafts, you are not doing shaft alignment.”
Taken from Ludeca Blog
Shaft alignment means: Positioning two or more machines so that their rotational centerlines are colinear at the coupling point under operating conditions. Colinear means two lines that are positioned as if they were one line. Colinear as used in alignment means two or more centerlines of rotation with no offset or angularity between them.
The phrase “coupling point” in the definition of shaft alignment is an acknowledgement that vibration due to misalignment originates at the point of power transmission, the coupling. It does not mean that the couplings are being aligned. The shafts are being aligned, and the coupling center is just the measuring point.”At operating conditions” is an acknowledgement that machines often move after start-up due to wear, thermal growth, dynamic load shifts, or support structure shifts.Besides the above considerations, the term shaft alignment also implies that the bearings and shafts are free from preloads. In properly installed equipment, there are no forces or strains on the bearings and shafts, except those the designers intended. If the machine is installed with the frame distorted because of uneven or imperfect base plates, bent feet, pipe stresses, or whatever, then machine life will be shortened, often significantly.The only way to determine rotational centerlines is to rotate the equipment. There is no series of measurements that do not involve turning the shafts between readings that can be used to find the rotational centerline.
If you don’t turn the shafts…Any system that takes so-called alignment measurements without turning BOTH shafts is aligning surfaces, not centerlines of rotation. The results of any alignment efforts where one or both shafts are not turned are highly dependent upon surface quality, rotor eccentricity, shaft straightness, and other surface defects. In short: “If you do not turn the shafts, you are not doing shaft alignment.”
Taken from Ludeca Blog
Tuesday, March 6, 2012
Sir Frank Whittle, Father of the Gas Turbine
Discussions about gas turbines and their application to land-based power generation, gas pipeline and process plants should rightfully begin with British engineer Sir Frank Whittle. The key word here is application. His predecessors were many, but Whittle should be credited for bringing ideas regarding the jet engine to fruition in industrial applications.
In 1941, Sir Frank Whittle designed the first successful turbojet engine for air defense during World War II. Dubbed the Gloster Meteor, it flew in defense over Great Britain. Whittle improved his jet engine as the war progressed. He shipped a prototype engine to General Electric in the United States in 1942. GE built America’s first jet engine for military aviation applications the following year.
Whittle came to the USA for the first time on a secret mission in the summer of 1942. He met with officials from General Electric in Lynn, MA and Bell Aircraft Company in Buffalo, NY. Later in 1942, he visited GE in Schenectady, NY, where a rudimentary propeller jet engine was under development. Whittle’s comments and suggestions to American engineers proved invaluable in modifications and improvements that soon followed.
One can argue that the development of jet engine might have been accelerated had World War II lasted longer. However, the other side of that argument is that the application of turbo-technology to other industries became a post-war quest of American industry. In the eyes of many engineers on both sides of “the pond,” this method of power production and propulsion could be used to drive land-based generators, compressors and other load devices, as well as to propel ships and aircraft in commercial applications. All that was needed was funding and the imagination of the engineers involved, eager as they were to apply this innovative prime mover.
Fig. 1-1: Sir Frank Whittle and his multi-combustor jet turbine (circa 1941)
The multi-combustor, turbo-jet engine (hereafter called the gas turbine) has Frank Whittle proudly standing beside it in Fig. 1-1. Notice that there are 10 combustion chambers (tube shaped) encircling the engine, with stainless steel nozzles to inject fuel into them at the front ends. The chambers are interconnected by cross-fire tubes, as is common on most modern gas turbines. The exhaust diffuser is in the center. The reverse-flow concept of the hot gases is obvious from the photograph. So are the transition pieces curling from the discharge of each combustor.
“If necessity is the mother of invention,” as preached to engineering students by college professors, then the end of WW-II brought many needs to the front burner ready to be invented. Jet engine technology needed to be harnessed and applied to other commercial endeavors. As a prime mover, the gas turbine needed to find applications that could deliver power to other modes of transportation, electrical power delivery and natural gas pipelines prime movers. However, as inventors soon found, not every idea has a viable application to industry, or a willingness of the public to accept them. Engineers like Whittle would encounter doubters, the enemies of progressive thinkers. Progress often depended upon inventors who could convince entrepreneurs and angel investors to take a chance on their ideas and innovations. This presumes that negative forces are not overwhelmingly against such visionaries. As explained in later chapters of this blog, GE engineers struggled to get funding in a fledgling gas turbine department in Schenectady, NY in the 1950s.
It is uncertain if Frank Whittle could have envisioned a modern gas turbine like the one shown in Fig. 1-2 below. A single-fuel (natural gas) General Electric MS7001EA gas turbine (approximately 80 megawatt rating) is shown, with fuel line “pigtails” coming from the manifold on the left leading to each combustor. The chambers themselves are inside the combustion wrapper, which encircles the turbine, so only the covers are showing.
Fig 1-2; Multi-combustor GE MS7001EA Gas Turbine inside Combustion Wrapper (circa 2000)
Since the combustors are interconnected via cross-fire tubes, only one combustor needs to have a sparkplug (igniter) and another, a flame detector. However, for redundancy and reliability, modern gas turbines typically have at least two of each, as shown in Fig. 1-3.
Fig 1-3: Typical configuration of Multi-combustor Gas Turbine with Spark Plugs & Flame Detectors
Design of combustion systems, like those depicted herein, seems to be a “settled” issue. Most manufacturers have decided that this is the design that makes the most sense. It allows for temperature equalization and flow distribution to the first-stage turbine nozzle and rotating wheels with buckets (blades) that develop the output power. Refer to Fig. 1-4 below.
Fig 1-4: Cross-fire tubes between adjacent combustion chambers
Fig. 1-5 below should be studied for its completeness regarding the design of a typical modern combustion system for a GE MS7001EA gas turbine. Notice that the combustors are “canted” in design to straighten the hot gas flow through the transition pieces toward the first-stage nozzle (not shown). Also, this design shortens the length of the turbine and thus bearing spans. The reverse flow of the air from the compressor discharge casing is also shown entering the combustor.
Fig 1-5: Typical Modern Combustion Chamber and Transition Piece Configuration
Other areas of development have also occurred over the past 70 years with gas turbine technology. Advances in metallurgy, ceramic coatings and internal cooling designs have evolved over the past seven decades, to a point where efficiencies and higher internal firing temperatures have made the gas turbine a viable competitor to other forms of power generation.
In conclusion, over sixty years ago an engineer from Britain named Frank Whittle envisioned, designed and built a multi-combustor, aero-derivative gas turbine engine for land-based applications. His innovative design in gas turbine technology has prevailed for the following six decades well into the 21st century.
Taken from Lucier Blog
In 1941, Sir Frank Whittle designed the first successful turbojet engine for air defense during World War II. Dubbed the Gloster Meteor, it flew in defense over Great Britain. Whittle improved his jet engine as the war progressed. He shipped a prototype engine to General Electric in the United States in 1942. GE built America’s first jet engine for military aviation applications the following year.
Whittle came to the USA for the first time on a secret mission in the summer of 1942. He met with officials from General Electric in Lynn, MA and Bell Aircraft Company in Buffalo, NY. Later in 1942, he visited GE in Schenectady, NY, where a rudimentary propeller jet engine was under development. Whittle’s comments and suggestions to American engineers proved invaluable in modifications and improvements that soon followed.
One can argue that the development of jet engine might have been accelerated had World War II lasted longer. However, the other side of that argument is that the application of turbo-technology to other industries became a post-war quest of American industry. In the eyes of many engineers on both sides of “the pond,” this method of power production and propulsion could be used to drive land-based generators, compressors and other load devices, as well as to propel ships and aircraft in commercial applications. All that was needed was funding and the imagination of the engineers involved, eager as they were to apply this innovative prime mover.
Fig. 1-1: Sir Frank Whittle and his multi-combustor jet turbine (circa 1941)
The multi-combustor, turbo-jet engine (hereafter called the gas turbine) has Frank Whittle proudly standing beside it in Fig. 1-1. Notice that there are 10 combustion chambers (tube shaped) encircling the engine, with stainless steel nozzles to inject fuel into them at the front ends. The chambers are interconnected by cross-fire tubes, as is common on most modern gas turbines. The exhaust diffuser is in the center. The reverse-flow concept of the hot gases is obvious from the photograph. So are the transition pieces curling from the discharge of each combustor.
“If necessity is the mother of invention,” as preached to engineering students by college professors, then the end of WW-II brought many needs to the front burner ready to be invented. Jet engine technology needed to be harnessed and applied to other commercial endeavors. As a prime mover, the gas turbine needed to find applications that could deliver power to other modes of transportation, electrical power delivery and natural gas pipelines prime movers. However, as inventors soon found, not every idea has a viable application to industry, or a willingness of the public to accept them. Engineers like Whittle would encounter doubters, the enemies of progressive thinkers. Progress often depended upon inventors who could convince entrepreneurs and angel investors to take a chance on their ideas and innovations. This presumes that negative forces are not overwhelmingly against such visionaries. As explained in later chapters of this blog, GE engineers struggled to get funding in a fledgling gas turbine department in Schenectady, NY in the 1950s.
It is uncertain if Frank Whittle could have envisioned a modern gas turbine like the one shown in Fig. 1-2 below. A single-fuel (natural gas) General Electric MS7001EA gas turbine (approximately 80 megawatt rating) is shown, with fuel line “pigtails” coming from the manifold on the left leading to each combustor. The chambers themselves are inside the combustion wrapper, which encircles the turbine, so only the covers are showing.
Since the combustors are interconnected via cross-fire tubes, only one combustor needs to have a sparkplug (igniter) and another, a flame detector. However, for redundancy and reliability, modern gas turbines typically have at least two of each, as shown in Fig. 1-3.
Design of combustion systems, like those depicted herein, seems to be a “settled” issue. Most manufacturers have decided that this is the design that makes the most sense. It allows for temperature equalization and flow distribution to the first-stage turbine nozzle and rotating wheels with buckets (blades) that develop the output power. Refer to Fig. 1-4 below.
Fig. 1-5 below should be studied for its completeness regarding the design of a typical modern combustion system for a GE MS7001EA gas turbine. Notice that the combustors are “canted” in design to straighten the hot gas flow through the transition pieces toward the first-stage nozzle (not shown). Also, this design shortens the length of the turbine and thus bearing spans. The reverse flow of the air from the compressor discharge casing is also shown entering the combustor.
Other areas of development have also occurred over the past 70 years with gas turbine technology. Advances in metallurgy, ceramic coatings and internal cooling designs have evolved over the past seven decades, to a point where efficiencies and higher internal firing temperatures have made the gas turbine a viable competitor to other forms of power generation.
In conclusion, over sixty years ago an engineer from Britain named Frank Whittle envisioned, designed and built a multi-combustor, aero-derivative gas turbine engine for land-based applications. His innovative design in gas turbine technology has prevailed for the following six decades well into the 21st century.
Taken from Lucier Blog
Air-Operated Double-Diaphragm (AODD) Pump
The ancient Greek philosopher Plato is credited with coining the phrase, “Necessity is the mother of invention,” meaning that a need or problem encourages creative efforts to meet the need or solve the problem. It is unknown whether that phrase was going through Jim Wilden’s head as he watched water from a ruptured pipe gush into a shop at a steel factory in San Bernardino County, Calif., 50 years ago. Knowing that it needed to be removed, Wilden went to work, and in 1955, he had the solution—the air-operated double-diaphragm (AODD) pump.
The same ingenuity still occurs today, but now for a multitude of biopharmaceutical processes. The AODD pump has evolved to uniquely solve complex fluid transfer needs in this industry. Because of the critical nature of some processes, inefficient product transfer methods such as manual rolling carts with containers, purging tanks to evacuate product or manual gravity feeding transfers have been common. However, specifically designed AODD pumps for this industry now allow further use of pumped transfer processes (and associated production and energy efficiency) approaching the degree already found in the general chemical/industrial sector.
First, Do No Harm
The diaphragm pump already has a cousin in the industry…the diaphragm valve. The diaphragm valve has long been the valve of choice in these types of applications because of its high product containment and clean ability traits. These are also available with AODD pump technology, along with a sealless stem and shaft-free product-side environment.
This is important as both the diaphragm valve and diaphragm pump have less risk of producing product damaging shear, and neither technology has dynamic seals that would risk leaks that could contaminate the product or the production environment.
This is important as both the diaphragm valve and diaphragm pump have less risk of producing product damaging shear, and neither technology has dynamic seals that would risk leaks that could contaminate the product or the production environment.
So with innovations and enhancements for the ultra-sanitary conditions needed by the pharmaceutical industry, the diaphragm pump is now an attractive option for many fluid transfer needs. These processes—and the products they produce—must meet a wide array of regulations and certifications to ensure that they are being performed in a high-purity environment. Among the regulations that AODD pumps can satisfy are those from EHEDG, 3A, CE, ATEX, USP Class VI and FDA CFR 21.177. This includes a validation package with mill, 3.1b, polish, passivation and classified area use certifications.
The liquids can run the gamut from extremely shear-sensitive to extremely viscous, and semi-solids can range from liquid glucose to polymer slurries. Pharmaceutical and biochemical fluids currently pumped with diaphragm pumps include: blood and by-products, live cell cultures and vaccine producing solutions, egg emulsions for vaccine production, pill coatings, eye care solutions, fluids for oncology, specialized disinfectants, nutraceuticals, vitamins, topicals (creams/lotions) and filter media. The use of AODD technology can guarantee safe transfer during the production process.
According to Hoover’s, Inc., which analyzes companies and industries that drive the economy, as many as 1,500 companies in the U.S. manufacture and market pharmaceuticals (defined as a compound manufactured for use as a medicinal drug), with combined annual revenue of more than $200 billion. These numbers indicate that the manufacture of pharmaceuticals is one of the lynchpins of the American economy. The actual creation of pharmaceuticals involves one of three major methods:
Synthesis—using chemical reactions to build a drug from simpler components
Extraction—using solvents to remove and purify a drug from a natural source
Biotechnology—using methods such as gene-splicing or the production of antibodies using mammalian (animal-based) cells
Extraction—using solvents to remove and purify a drug from a natural source
Biotechnology—using methods such as gene-splicing or the production of antibodies using mammalian (animal-based) cells
No matter the method used to produce biopharmaceuticals, the actual manufacturing process is a precise one that must be performed under demanding, exacting conditions, often in a cleanroom environment that prohibits instances of product leakage, fouling or cross-contamination.
AODD Benefits
Specifically, AODD technology is a boon to pharmaceutical manufacture in a number of crucial areas:
Sterile product transfer —AODD pumps remove the need for gas-purge systems in continuous processes because the technology allows both the filling and emptying process to occur at the same time while keeping the product contained and pure.
Process flexibility —AODD pumps can handle highly variable process conditions found in many hygienic applications.
Sampling—complex pharmaceutical processes under strict conditions require frequent and multipoint sampling. AODD pumps provide the ability to extract these samples while maintaining a high degree of containment and avoiding cross-contamination.
Clean in place (CIP) —the AODD pump’s self-priming, dry-running and sealless design is ideal for CIP operations.
Chemical feed —this is a traditional role for AODD pumps as their sealless design and reliable product containment ensure safety when handling volatile or potent chemicals.
Ingredient unloading —because they self-prime, run dry and have negative suction lift, AODD pumps meet pharmaceutical-validation requirements and can be applied where needed.
Product recovery and semi-solids removal —again, the AODD pump’s dry-run, self-priming and full product containment makes it ideal for use in most filtering or separation processes.
Chromatography, separation, purification and filter feed —these processes often require shear-sensitive transfer and constant pressure feed, traits found in AODD pumps. Extracting delicate cell structures from centrifuge discharge is a good example (see Figure 1)
Process flexibility —AODD pumps can handle highly variable process conditions found in many hygienic applications.
Sampling—complex pharmaceutical processes under strict conditions require frequent and multipoint sampling. AODD pumps provide the ability to extract these samples while maintaining a high degree of containment and avoiding cross-contamination.
Clean in place (CIP) —the AODD pump’s self-priming, dry-running and sealless design is ideal for CIP operations.
Chemical feed —this is a traditional role for AODD pumps as their sealless design and reliable product containment ensure safety when handling volatile or potent chemicals.
Ingredient unloading —because they self-prime, run dry and have negative suction lift, AODD pumps meet pharmaceutical-validation requirements and can be applied where needed.
Product recovery and semi-solids removal —again, the AODD pump’s dry-run, self-priming and full product containment makes it ideal for use in most filtering or separation processes.
Chromatography, separation, purification and filter feed —these processes often require shear-sensitive transfer and constant pressure feed, traits found in AODD pumps. Extracting delicate cell structures from centrifuge discharge is a good example (see Figure 1)
Maintenance
Simplicity defines the cleaning and maintaining of these pumps. In the highest hygienic configurations, these pumps are designed for CIP so that manual labor and contamination risks do not occur. However, at the same time, these pumps have been purposely designed to be simple to disassemble for either manual cleaning procedures or routine maintenance.
Power and Fluid End Separation
As biopharmaceutical processes evolve, more attention is paid to optimizing the process. The separation of mechanical and utility functions is an example of area/floor space optimization. AODD pumps can be split so that the “power side” is mostly located remotely in an unclassified area and the fluid end can be placed in a classified area, with only an instrument air-supply line connecting the two. This means that electric motors, oil-filled gear cases and greased bearings no longer need to be located in the clean area, raising the level of hygiene and reducing the risk of product contamination.
Figure 1. Integral piston diaphragms (IPD) are featured in certain AODD pumps.
Integral Piston Diaphragm
For high purity industries, one primary innovation that has made this pump among the most viable selections in the industry has been the integral piston diaphragm (IPD) (see Figure 1). Unlike traditional pump diaphragms that have an outer plate that supports the diaphragm that is subject to more difficult cleaning or can be a potential leak point, the IPD is completely laminated with USP Class VI PTFE on the product contact side. This offers the highest degree of containment and clean ability among pumps.
Inside an AODD Pump
The uncomplicated design of AODD pumps features few moving parts, and those that do move have simple, specific tasks: • Air chamber—houses the air that powers the diaphragms
• Air distribution system—the heart of the pump, it is the mechanism that shifts the pump to create suction and discharge strokes
• Outer diaphragm piston—connects the diaphragms to the reciprocating common shaft and seals the liquid side from the air side of the diaphragm
• Inner diaphragm piston—located on the air side of the pump, it does not come in contact with the process fluid
• Valve ball—seals and releases on the check-valve seats, allowing for discharge and suction of process fluids to occur
• Valve seat—provides the ball valves a place to check
• Discharge manifold—allows fluid to exit the pump through the discharge port, which is typically located at the top of the pump
• Liquid chamber—separated from the compressed air by the diaphragms, it fills with process fluid during the suction stroke and is emptied during the discharge stroke
• Diaphragm—acts as a separation membrane between the process fluid and the compressed air that is the driving force of the pump; to perform adequately, diaphragms should be of sufficient thickness and of appropriate material to prevent degradation or permeation in specific process-fluid applications
• Inlet manifold—allows fluid to enter the pump through the intake port located at the bottom of the pump
(Above): Inside an AODD Pump
Taken from Pump-Zone website
Monday, March 5, 2012
Myth and Truth about Shaft Alignment and Shimming
MYTH: “You should always do your shimming first and then make your horizontal moves.”
TRUTH: This is generally true for the final alignment after soft foot has been corrected, but is not universally true for all alignments. In fact, for the initial rough alignment you should correct the plane with the largest misalignment first, even if this means making a horizontal move first.
Reason: If you have gross misalignment, you could be binding the coupling, deflecting the shafts and imposing undue load on the bearings. By relieving strain from excess misalignment, a truer picture of the alignment condition emerges, and you eliminate one important outside force that affects your soft foot distortion. Therefore, the correct sequence of events in any alignment job is:
1) Safety: Lock out & tag out
2) Clean up and Rough Align
3) Find, diagnose and eliminate Soft Foot
4) Final Alignment: shimming first, then moves.
Tips from Ludeca Blog
TRUTH: This is generally true for the final alignment after soft foot has been corrected, but is not universally true for all alignments. In fact, for the initial rough alignment you should correct the plane with the largest misalignment first, even if this means making a horizontal move first.
Reason: If you have gross misalignment, you could be binding the coupling, deflecting the shafts and imposing undue load on the bearings. By relieving strain from excess misalignment, a truer picture of the alignment condition emerges, and you eliminate one important outside force that affects your soft foot distortion. Therefore, the correct sequence of events in any alignment job is:
1) Safety: Lock out & tag out
2) Clean up and Rough Align
3) Find, diagnose and eliminate Soft Foot
4) Final Alignment: shimming first, then moves.
Tips from Ludeca Blog
10 Tips to Improve Boiler Efficiency
The need to operate a boiler efficiently in today’s environment and competitive landscape is at the top of many plant owners and operators list. Unfortunately operating a boiler efficiently while meeting local emission regulations do not always go hand in hand. However, advances in boiler system design and low NOx technology solutions have made this a much more achievable task.
The list below includes 10 tips which can instantly improve overall boiler performance and sustainability, helping to achieve more cost-effective maintenance and operations of your steam system.
The list below includes 10 tips which can instantly improve overall boiler performance and sustainability, helping to achieve more cost-effective maintenance and operations of your steam system.
- Reduce Excess Air
- Install an Economizer
- Install a Condensing Economizer
- Upgrade to VFD Fan Controls
- Install a Selective Catalytic Reduction System (SCR) with a Standard Low Excess Air/No FGR Burner
- Perform Proper Water Treatment
- Reduce Boiler Pressure
- Consider Boiler Blowdown Heat Recovery
- Upgrade to a High Turndown Burner & Controls
- Implement an Energy Efficiency Program
Gas Turbine Performance, Simplified
It is generally known by observation that gases have particular characteristics. Variables like pressure (P), temperature (T) and volume (V) have a special relationship in gases that is best understood when considering the model below. In words, Pressure (P) multiplied by Volume (V) and then divided by Temperature (T) is always constant. It is a different constant for each gas. Air, which includes many gases, would have still a different constant than the particular gases in the mixture. Finally, when fuel (natural gas, for instance) is mixed with air in a gas turbine combustion system, still another constant is realized. However, when considering the various stages of the Brayton Cycle, the specific constant does not matter in the analysis.
In equation form, that would be:
This relationship holds through all stages of the gas turbine. It is important, however, that the units of each of the three variables be correct. In English units, that would be:
For the four regions of the gas turbine on the pressure-volume (PV) diagram we have:
Region 1 – 2 Region 2 – 3 Region 3 – 4 Region 4 – 1
Compresion Combustion Expansion Exhaust
Thus, we have:
P1 x V1 = P2 x V2 = P3 x V3 = P4 x V4
T1 T2 T3 T4
We know that pressure, volume and temperature are variables. However, they only vary throughout the gas turbine cycle in the relationship described above. Also, notice that the pressure from points P2 to P3 is considered constant, horizontal line on the P-V diagram. Thus, in the combustion zone, they would then P2 and P3 cancel out on each side of in the following equation leaving:
V2 = V3
The formula only works for temperatures in degrees Rankin. Converting to Fahrenheit we have
___V2___ = ___V3___
(T2 + 460) (T3 +460)
Take a typical General Electric model series MS5001P, a very popular gas turbine in the world-wide market. Assume that the turbine firing temperature is Tf = 1800 degrees Fahrenheit. Assume that the air temperature at the discharge of the compressor is approximately 500 F. Thus, we would have:
___V2___ = ___V3___
(500 + 460) (1800 + 460)
___V2___ = ___V3___
(960) (2260)
Thus, in the gas turbine’s combustion system, the pressure remains essentially constant (P2 ≈ P3). However, the volume more than doubles, or in this case V3 = 2.35 (V2)
View of the gas turbine in Fig. 1-2 above showing the compressor and turbine rotor installed inside the casings. Notice how the compressor stage passageways diminish in size as the air flows through the turbine (getting smaller with every stage). In Fig. 1-3 below, the compressor rotor blades diminish in size from the R-0 stage to the R-16 stage; again, the air passage ways for the air to flow diminish through this 17-stage compressor.
Gas turbine performance can be affected by many variables. One of the most important factors is the change of ambient temperature at the compressor inlet. Figure 1-4 below shows how changes in ambient temperature impact such variables as Heat Rate, Exhaust Temperature, Exhaust Flow, Fuel Flow and Power Output. Notice how the Heat Rate (thus the Thermal Efficiency) improves on colder days. Fuel Flow does increase, as does Power Output. However, notice that the slope of the Power line is steeper than that of the Fuel Flow, which flattens the Heat Rate line. More power output for less fuel means higher efficiency.
In equation form, that would be:
(P) multiplied by (V) then divided by (T) = constant
or simply (P x V) ÷ T = constant
This relationship holds through all stages of the gas turbine. It is important, however, that the units of each of the three variables be correct. In English units, that would be:
- Pressure (P) in pounds per square inch absolute, (psia)
- Temperature (T) must be in degrees Rankin, (˚R). That is, to convert from Fahrenheit to Rankin, it would be: T (˚R) = T (˚F) + 460
- Volume (V) must be in cubic inches, (in³)
Or it can be said, simply:
P (psia) x V (cubic inches) ÷ T (degrees R) = constant
For the four regions of the gas turbine on the pressure-volume (PV) diagram we have:
Region 1 – 2 Region 2 – 3 Region 3 – 4 Region 4 – 1
Compresion Combustion Expansion Exhaust
Thus, we have:
P1 x V1 = P2 x V2 = P3 x V3 = P4 x V4
T1 T2 T3 T4
Imagine a cubic foot of air. Assume that the “box” of air has dimensions of 12 x 12 x 12 inches, as it enters the compressor. Try to envision this air cube passing through the gas turbine.
- From the compressor inlet (point 1) the air cube passes through the axial-flow compressor diminishing in size through each stage.
- The air cube, now smaller in size, leaves the compressor discharge (point 2) and enters the combustors at essentially the same pressure. That is, P2 = P3.
- Then the smaller air cube expands through the combustors to the first stage turbine nozzle, to a point just in front of the turbine buckets at essentially constant pressure (point 3).
- After expanding through the turbine stages, the air cube increases in size, continuing out the exhaust reaching approximately the same pressure as the compressor inlet (point 4), That is, P4 = P1.
Fig 1-1 - Brayton Cycle-Pressure Volume Diagram
We know that pressure, volume and temperature are variables. However, they only vary throughout the gas turbine cycle in the relationship described above. Also, notice that the pressure from points P2 to P3 is considered constant, horizontal line on the P-V diagram. Thus, in the combustion zone, they would then P2 and P3 cancel out on each side of in the following equation leaving:
T2 T3
___V2___ = ___V3___
(T2 + 460) (T3 +460)
___V2___ = ___V3___
(500 + 460) (1800 + 460)
___V2___ = ___V3___
(960) (2260)
Thus, in the gas turbine’s combustion system, the pressure remains essentially constant (P2 ≈ P3). However, the volume more than doubles, or in this case V3 = 2.35 (V2)
Fig 1-2 - Compressor End View of a Typical Gas Turbine
View of the gas turbine in Fig. 1-2 above showing the compressor and turbine rotor installed inside the casings. Notice how the compressor stage passageways diminish in size as the air flows through the turbine (getting smaller with every stage). In Fig. 1-3 below, the compressor rotor blades diminish in size from the R-0 stage to the R-16 stage; again, the air passage ways for the air to flow diminish through this 17-stage compressor.
Fig 1-3 - Compressor Rotor View
Gas turbine performance can be affected by many variables. One of the most important factors is the change of ambient temperature at the compressor inlet. Figure 1-4 below shows how changes in ambient temperature impact such variables as Heat Rate, Exhaust Temperature, Exhaust Flow, Fuel Flow and Power Output. Notice how the Heat Rate (thus the Thermal Efficiency) improves on colder days. Fuel Flow does increase, as does Power Output. However, notice that the slope of the Power line is steeper than that of the Fuel Flow, which flattens the Heat Rate line. More power output for less fuel means higher efficiency.
Fig 1-4 - The Effects of Changes in Compressor Inlet Temperature
So what can I do to improve gas turbine performance without spending tons of money?
- Check compressor discharge pressure (CPD). If it is low, you should clean the compressor by on-line washing or other techniques.
- Boroscope the turbine on a regular basis. If the trailing edge of the first-stage turbine nozzle is distorted or missing metal, performance will suffer. The forces acting on the buckets that develop power output is diminished by a reduction in back pressure on the compressor reduces CPD.
- Be sure that the inlet guide vane (IGV) angles are set properly. This can be determined during a boroscope inspection. Incorrect settings can reduce air flow and adversely affect power output.
- Record FSNL Data. Once the gas turbine reaches operating speed (called Full Speed, No Load or FSNL), record the following data:
2. Fuel Flow (gpm, if liquid fuel or SCFM, if gas fuel)
3. Average Turbine Exhaust Temperature (TTXM)
4. Megawatts (MW) – Zero at the moment.
Then begin loading the generator and record power output (MW) and observe the other data points (CPD, FF and TTXM) until base load is reached. These variables should increase in essentially equal proportions from the FSNL data. Once base load is reached, you should determine if the correct turbine firing temperature, Tf is reached.
Taken from Lucier Blog
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