coal pulverizer maintenance improves boiler combustion

coal pulverizer maintenance improves boiler combustion

Coal pulverizers are the heart of a pulverized coal-fueled boiler. Often, the root causes of nonoptimized combustion lie with the pulverizers. Capacity; reliability; and environmental issues such as slagging, fouling, and higher-than-desired CO or NOx emissions; overheated superheater and reheater tube metals; and cinder fouling of selective catalytic reduction catalyst and air heaters have all, at times, been linked to poor pulverizer performance.

It is common in our experience to find pulverizers that are performing poorly, yet the degree to which unit reliability, efficiency, capacity, and environmental emissions are affected by them is often underappreciated. However, there are steps that can be taken to measure, quantify, and monitor pulverizer operation so that changes can be made to improve performance.

Obtaining representative samples of coal fineness and fuel distribution is the first step. The best method we have found to do this is by using an isokinetic coal sampler. All fuel lines must be sampled and the fineness sieved from each coal pipe separately. The fuel mass flow to each burner must also be measured.

An isokinetic sampler similar to the one shown in Figure 1 can be used with a dirty-air velocity probe to establish the proper sample extraction rate. The fuel line velocities that are measured are used to compute the primary airflow and air/fuel (A/F) ratios of each coal pipe. The velocities and A/F ratios are valuable for diagnosing combustion issues.

Tuning improvements can only be implemented after the true current performance is measured. Sampling single pipes, or sampling at a single location, is totally unacceptable in our experience. All fuel pipes must be sampled and sieved individually for best accuracy.

The fuel lines must be tested/sampled under normal operating conditions. Often during testing, we have observed that operating conditions are changed. For example, we have seen primary airflow reduced, classifiers reset for best fineness, and fuel flow brought back to mill design fuel flow rates. In other words, the assessment is not representative of normal operation. Testing under special conditions proves nothing. Only testing under normal operational conditions enables a useful diagnosis.

Acceptable standards for best low-NOx burner performance are coal fineness of 75% passing a 200-mesh sieve and less than 0.1% remaining on a 50-mesh sieve. Fuel balance should be within the range of plus or minus 10%. However, in our experience, it is common to find fuel fineness that is well below 65% passing through a 200-mesh sieve and more than 1% remaining on a 50-mesh sieve. Furthermore, it is common to see fuel imbalances that exceed plus or minus 30% to the burners.

2. Lopsided fuel distribution. This test data shows pulverizer fuel flow rates measured during an actual test. The fuel distribution is poor in this case. It should be balanced within plus or minus 10%. Source: Storm Technologies

Once the data are compiled, out-of-specification readings must be investigated. An internal inspection should be completed to check the wear of grinding elements and classifier housings, vanes, and other internal components. Also, check for foreign matter that might be blocking fuel flow paths. Any problems identified should be corrected.

Achieving best fuel balance is done by first balancing the system resistance in all of the fuel lines using orifices and then increasing fuel fineness. Figure 3 shows the typical results of this approach to fuel balancing. Of course, internal pulverizer blue printing to best mechanical tolerances and optimizing an accurate and repeatable air/fuel ration is also important.

There are various adjustments and mechanical tuning measures that can be completed to improve the performance of a modern coal pulverizer. Locations identified on Figure 4 are keyed to the following improvements (journal pressures listed are for a #943-size pulverizer):

Install synchronized straight vane coarse particle guide blades (A). The retrofit lengthens the classifier blades, improves material to 3/8-inch-thick AR400 or better, and implements critical synchronization of the classifier blades for fuel/air two-phase mixture homogenization.

Install orifice housings (E) to support future balancing efforts. The change offers two advantages: It is easier for maintenance personnel to change out orifice plates, and it speeds testing and balancing efforts.

Verify that roll-to-ring clearances (I) are absolutely no greater than 1/4-inch over the full grinding length of the rolls and that the clearance is parallel to the bowl for the full width of the rolls.

Additionally, ensure that venturi sensing lines, connections, and transmitters are all in good condition. Tempering air dampers should be stroked and corrections made to ensure that they close at least 99%. This should also be done for hot air dampers.

All internal mill surfaces must be smooth so that the swirl of the coal/air mixture may enter and leave the classifier without spoiling or turbulence caused by double layer tiles, welded pad eyes, or other internal surface discontinuities. This, combined with precise primary airflow measurement and control, is important for uniform fuel distribution at the classifier outlet. All internal dimensions should be verified and technically directed by a qualified service engineer during installation of performance parts and before closing the mill.

Overhauling Stock gravimetric feeders can also be worthwhile. The refurbishment should include calibrating load cells properly, installing modern microprocessors, adjusting belt tension appropriately, and completing accurate speed calibration.

Another pulverizer performance monitoring technique is to observe the drive motor power input in correlation with the coal feed rate. The relationship of ton/hour to kWh power input is a very helpful leading indicator (Figure 5). A reduction in the power used by a coal pulverizer does not usually result in an improved heat rate. Instead, more grinding power nearly always correlates with better coal fineness. The only exception is with a ball tube mill.

Pulverizer capacity is not simply a measure of coal throughput; capacity refers to a certain coal throughput at a given fineness, raw coal sizing, HGI (Hardgrove Grindability Index), and moisture. Often, if the desired coal throughput or load response is not achieved, the primary airflow will be elevated to higher flow rates than are best for capacity. However, increased throughput achieved in this way sacrifices fuel fineness (Figure 6).

6. A negative correlation. The three main factors that constitute pulverized capacity are Hardgrove Grindability Index (HGI), fineness, and coal throughput. Increasing throughput will adversely affect fineness. Source: Storm Technologies

This is very common. When the primary airflow is higher than optimum, it creates entrainment of larger-than-desired coal particles leaving the mills, promotes poor fuel distribution, lengthens flames, and impairs low-NOx burner performance. We have found that targeting an A/F ratio around 1.8 lb of air per lb of fuel is best. For some pulverizer types, such as ball tube mills and high-speed attrition mills, often a 1.6 A/F ratio is optimum. Never have we observed good combustion conditions or good mill performance with A/F ratios of 2.5 or greater. However, it is common to find A/F ratios of 2.2 to 2.5 during baseline testing.

Results of as-found airflow to fuel flow testing from a sample plant are shown in Figure 7. In this particular case, the A/F ratios tested were well above the desired A/F ramp. When operators bias the primary airflow up, above the optimum, it may improve wet-coal drying, load response, and reduce coal spillage from the grinding zone, but it is not good for the furnace burner belt performance.

7. Missing the mark. The air-to-fuel (A/F) flows shown in this graph are much higher than optimum. Installing properly sized rotating throats is often required to achieve targeted A/F ratios. Source: Storm Technologies

All combustion airflow inputs should be measured and controlled, if possible. We prefer to use the tried and proven venturi or flow nozzles for this purpose because they are rugged, reliable, offer repeatable results, and are less prone to impulse line plugging.

Several components can be retrofitted to improve the performance of MPS mills. The changes may cost a significant amount of money, but the work will usually pay for itself through improved heat rate. One 450-MW coal-fired unit in the Midwest spent $750,000 on testing, changes, and tuning, but calculated that it saved millions by improving heat rate and by allowing higher-slagging fuel to be used at a reduced cost, which greatly increased its market competitivness.

8. Extending component lives. Getting 8,000 hours per year performance requires condition-based maintenance utilizing periodic isokinetic coal sampling and venturi hot K testing and calibration. Source: Storm Technologies

Cold air has a different density than hot air, which can result in a variance in measured velocity at similar mass flow rates. Because the K-factor will vary, we prefer to conduct Hot-K airflow calibrations that use typical operational air or gas density when developing an average K-factor. That information is important when developing a pulverizer primary airflow curve and when measuring all combustion airflows.

Most instrumentation technicians can calibrate and check using the Hot-K method to verify calibration accuracy. As previously mentioned, high primary airflows are one of the most common root causes of poor pulverizer performance, in our experience, so obtaining accurate and representative measurements is very important.

The goal is to obtain the best possible burner belt combustion because it improves heat rate, reduces slagging/fouling, lowers emissions, and reduces cost. All of the following actions can help improve burner belt combustion:

coal pulverizer_zk ball mill_rotary kiln_grinding equipment

coal pulverizer_zk ball mill_rotary kiln_grinding equipment

1. The shovel is made of high manganese steel which is more durable and the blade can replace easily. 2. Cone gear whole transmission-compact conformation, convenient installation, reducing dissipation of energy. 3. Isolation type cyclone powder collector. Effectively improve the efficiency and precision of choosing powder. 4. The observe door and air inlet volute is in the same surface, voiding the eddy current effect and reducing energy consumption. 5. Optimization design for grinding roller grinding ring of main-spring pressurization, high-wearing feature. 6. Internal thin oil lubrication system. Advanced and reliable, prolong service life. 7. Curved duct. Loss of the air volume is small, the liquidity of material is good and not easy plugging material.

Coal pulverizer is a mechanical device used to pulverize coal for combustion in the steam-generating furnaces of fossil fuel power plants. Coal pulverized machine is the ideal powder making equipment in electric power industry, metallurgy industry, chemical industry, building construction, coal industry, fireproofing materials making industry and some others. The final products fineness of coal pulverized machine can reach 38micron (400mesh).

Coal pulverizes are designed to achieve the maximum rated capacity grinding a design coal with a grindability of 55 HGI and 8-12 percent moisture and achieving a discharge fineness of 70 per cent passing a 200 mesh screen (74 micron) and 99.5 per cent passing a 50 mesh screen. Variation of the coal hardness and/or moisture content will effect, up or down, the discharge capacity or the discharge fineness.

To achieve these design considerations it is essential that the grinding elements are in good condition and they maintain a consistent profile. The loss of the grinding profile results in a loss of grinding efficiency, meaning the pulveriser must work harder to achieve an equal result.

Ultimately a point will be reached in which either a loss of capacity or a loss of fineness will result under uniform conditions. Longer lasting, more consistent grinding elements are crucial to pulveriser operation yielding longer operating campaigns, reduced maintenance and a lower overall invested cost.

According to collected the feedback from customer's long-term experiences, we designed the coal pulverized machine. It is an upgrade grinding mill that adopts bevel gear overall drive, trapeziums working surface, inner automatic thin-oil lubricating system, arc air channel and several latest patent technology, which is designed to substitute for ball mill, Raymond mill, vertical mill etc.

Raw material feed into discharege pipe through rotary discharger. Discharge pipe enter into the mill through the side or the center of separator. Material will fall into the center of mill disc with the help of gravity and air flow. Mill disc connect with the reducer constantly. Constant speed rotation of mill disc will distribute materiao evenly in the lining plate of mill disc. There inclined mill roller will be bite material and pulverize. Grind material with the function of pressure and friction. Centrifugal force will make pulverized material at the edge of mill disc from the middle of mill disc. Material off mill disc will enter into hot gas in the mill through air ring. Via the middle of the mill shell and enter into the separator. During the process, material will exchange hot gas. The moisture will be evaporated. The rest moisture can reach 1%. Unpulverized material as request will be selected by the separator and send back mill disc.

ball tube mill coal feed chute

ball tube mill coal feed chute

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a low-speed ball tube mill and a high-speed attrition pulverizer. Specific topics include throughput capability, fuel type, availability, reliability, power consumption, product fineness, coal drying capability, feed size re- quirements and application data.

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a low-speed ball tube mill and a high-speed attrition pulverizer. Specific topics include throughput capability, fuel type, availability, reliability, power consumption, product fineness, coal drying capability, feed size re- quirements and application data.

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1/5/2014 Tube mills use steel balls as grinding media. Due to wear in the abrasive environment it is necessary to charge new balls periodically to maintain a steady balanced ball charge in the mill. The amount and ball size distribution in this charge, as well as the frequency ...

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dynamic classifiers improve pulverizer performance and more

dynamic classifiers improve pulverizer performance and more

No one in this industry underestimates the difficulty of transforming an unwieldy and distinctly nonuniform substance like coal into a fuel whose physical and chemical characteristics are consistent enough to supply a workhorse power plant boiler. Designers of fuel-handling and pulverizer systems have wrestled with this problem since the first traveling-grate furnace was invented. The more predictable a fuel is, the easier it is for engineers to tune a boiler burning it for maximum performance and minimum emissions.

From the grizzly to the burner tip, the pulverizer plays an essential role in maximizing the consistency of fuel delivered to the steam generator. Most existing pulverizersboth the vertical-shaft and ball-mill typescome with a static classifier. Its blades reject coarse particles to produce a stream of coal particles that are mostly about 0.0029 inches (74 microns) across.

Obviously, not all of the particles leaving the pulverizer are that size. The fineness of coal is measured using a U.S. standard sieve with a sleeve opening of 0.0030 inches. Particles smaller than 74 microns will pass through a 200-mesh screen, and those larger will not. Passing coal through several screens in series yields a profile of the particle size distribution (PSD) of a pulverizer/classifier. The industry standard for PSD has been 70% passing through a 200-mesh sieve. Other common U.S. standard sieves are 325 and 50 mesh, which stop particles larger than 0.0017 inches (45 microns) and 0.0117 inches (300 microns), respectively.

Coarse particles of coal dont burn as quickly, easily, or cleanly as finer particles. Because they take longer to burn, coarse coal particles raise a boilers average NOx emissions. They also foster agglomeration and deposition of slag, making boilers and heat-recovery boilers more vulnerable to fouling. Coarse coal can even poison the catalyst of a selective catalytic reduction (SCR) system. If enough coarse coal passes through a boiler without being burned completely, its flyash may have too much unburned carbon (UBC) for commercial use.

Upgrading a pulverizers classifier from static to dynamic can improve two key pulverizer performance measures: its throughput and its coal fineness. As their name implies, dynamic classifiers (see box) use static as well as rotating vanes to sort coal particles more precisely by size. Retrofitting a pulverizer in this way:

A classifier separates coarse from fine coal by allowing the fine coal to pass and rejecting the coarse particles for regrinding. A dynamic classifier has an inner rotating cage and outer stationary vanes. Acting in concert, they provide what is called centrifugal or impinging classification.

A Loesche LSKS dynamic classifier (Figure 1) was retrofitted to each of four Babcock Wilcox (BW) Model 10E10 ring and ball pulverizers at E.ONs Ratcliffe-on-Soar Power Station in the UK. Ratcliffe has four 500-MW natural-circulation, single-furnace, dry-bottom BW boilers. Each pulverizer has two coal outlet pipes, which then split into three smaller pipes that each feeds a BW Mark 3 low-NOx burner (LNB). Each boilers 48 burners are arranged as four rows of 12.

1. Top of the heap. An LSKS dynamic classifier like this one was installed atop an existing Babcock Wilcox ball mill at E.ONs Ratcliffe-on-Soar Power Station in the UK. Source: Loesche Energy Systems

E.ON installed the dynamic classifiers as part of its plan to comply with the new European Large Combustion Plant Directive, which calls for reductions in emissions of NOx, SO2, and particulates by 2008 and beyond. Making the typical 35% reduction in a plants NOx levels (to 0.42 lb/mmBtu) that the directive requires would normally necessitate adding an SCR system and/or upgrading to LNBsat considerable cost.

E.ON, however, chose to reduce the NOx output of the Ratcliffe plant by adding an overfire air (OFA) system and dynamic classifiers. The utility took this approach mainly to ensure an acceptable level of UBC in the plants flyash, which is sold as filler to cement makers. But another reason was to reap the classifiers biggest benefit: more consistent coal particle sizing.

The first dynamic classifier was installed at Ratcliffe in July 2003, and six more followed in the summer of 2004. All of them had already passed their tests when the overfire air system was installed.

Pre-retrofit data indicated that with static classification, 75% of the pulverizers output could pass through a 74-micron screen, and 97.5% of particles through a 300-micron screen (Figure 2). After the dynamic classifier was installed, about the same percentage (78%) passed through the 74-micron screen, but far more (virtually all) particles could pass through the 300-micron mesh. In other words, all coarse (>300 micron) coal particles were removed from the stream of coal fed to the boiler. The slopes of the pre- and post-retrofit lines on the Rosin-Rammler graph are 31.7 degrees and 52.7 degrees, respectively.

As dynamic classifiers were added in turn to the other pulverizers at Ratcliffe, it became possible to compare their effect on the individual performance of each of the plants four identical 500-MW boilers. All had been upgraded with BW UKs LNBs in the mid-1990s. A 62% average reduction in UBC levels at normal excess-air levels (Figure 3) was noted during post-retrofit testing.

3. Reduced LOI. Plotted here are flyash loss-on-ignition levels (a measure of unburned carbon content) vs. stack O2 levels at three different dynamic classifier speeds. The data were taken following the retrofit at Ratcliffe-on-Soar Power Station. Source: Loesche Energy Systems

The retrofits bigger payoff, however, was a 13% average reduction in the plants NOx emissions (Figure 4). Testing also produced a plant CO emissions profile (Figure 5) that engineers could correlate with the NOx and UBC profiles to fine-tune operations. For example, knowing that the plant could tolerate a slight increase in CO and UBC levels, the engineers could feel safe lowering the stack O2 level by 1% or more, in order to further reduce NOx emissions.

4. Par for the coarse. Eliminating large coal particles from the fuel mix also reduced NOx emissions of the Ratcliffe plant. Shown are post-retrofit measured NOx levels vs. stack O2 levels at three different dynamic classifier speeds. Source: Loesche Energy Systems

These results were from tests conducted after adding the dynamic classifiers but before installing the overfire air system. Now that the OFA system is in place, the Ratcliffe plant can meet its 2008 NOx emissions standard using only it and the LNBs. At press time, dynamic classifiers had been retrofitted to three of the plants four 500-MW boilers; the fourth is slated to be upgraded later this year.

Tilbury Power Station in the UK. In 2006, dynamic classifiers were retrofitted to the five MPS Model 180 pulverizers feeding the 300-MW front-wall-fired Foster Wheeler boiler of this RWE plant. Two similar units are scheduled to be similarly retrofitted this year. Results for the projects first phase are just in: a 50% reduction in UBC (enabling the units flyash to be sold, rather than landfilled) and a distinct improvement in particle fineness. Now, >99.8% of particles can pass through a 300-micron screen (vs. 99% before), while 85% can pass through a 75-micron screen (vs. 70% before).

J.B. Sims Power Plant in Grand Haven, Mich. Dynamic classifiers were retrofitted to three BW Model EL56 ball mill pulverizers feeding an 83-MW BW front-wall-fired boiler. As at Tilbury Power Station, the upgrade improved particle fineness. Now, 98.8% of particles can pass through a 150-micron screen (vs. 95% before), while 92.1% can pass through a 75-micron screen (vs. just 72% before).

Dynamic classifiers can increase the throughput of a pulverizer while maintaining the fineness of its output. Such retrofits make the most sense for units burning Powder River Basin coals, whose lower heat content and higher ash and moisture content require an increase in fuel flow to maintain unit rating. They also are applicable to units that blend high-heating-value and PRB coals to maintain their output. Experience with vertical-shaft pulverizers used in the coal mining industry suggests that replacing a units static classifier with a dynamic classifier would increase its throughput by more than 30% and simultaneously increase coal fineness by 10%.

Dynamic classifiers can increase both fineness and capacity, but to a lesser extent than a system optimized to increase one or the other. Again, experience with vertical-shaft pulverizers at coal mines suggests that capacity increases of 10% to 35% and increases in fineness of 25% to 50% are achievable.

A dynamic classifier is retrofitted to a vertical-shaft pulverizer by installing a duplicate upper pulverizer casing that houses the classifiers fixed and rotating vanes, motor, and drive connections. A typical dynamic classifier assembly has a center coal feed pipe and several coal outlet pipes (Figure 6). The rotor drive is mounted on the side of the casing and driven by a belt. If the coal feed is off-center, the drive can be directly coupled, as was the case at the J.B. Sims Power Plant in Michigan (Figure 7).

7. Nice installation. At the J.B. Sims Power Plant in Grand Haven, Mich., retrofitting each of three LSKS dynamic classifiers required mounting a direct drive for it in the center of the existing Model EL 56 pulverizer. Courtesy: Loesche Energy Systems

In most cases, dynamic classifiers can be installed as "slide-in" retrofits with little need to move existing equipment. Figure 8 shows another type of dynamic classifier, with one inlet and outlet, favored by the cement industry.

It should go without saying that gains in fineness, capacity, or both, depend on many factors, such as the type of coal, the brand of existing pulverizers, and the design of the overall fuel-handling system. Likewise, the costs of a retrofit are site- and unit-specific, not so much for "as found" equipment but as a result of fuel system or other unit modifications.

For this job, the break-even point for fuel savings alone is estimated at 2.4 years. The break-even on fuel savings plus NOx credits is 1.6 years (which falls to 1.3 years if revenues from sales of flyash with less UBC are factored in).

Robert E. Sommerlad is strategic accounts manager for Loesche Energy Systems; he can be reached at [email protected] Kevin L. Dugdale is managing director of Loesche Energy Systems Ltd; he can be reached at [email protected]

coil pulverizers for boilers - bright hub engineering

coil pulverizers for boilers - bright hub engineering

Boilers for steam generation in power plants and process industries use coal as fuel. The percentage of boilers operating with coal as fuel outnumbers the boilers using all other fuels combined. Coal is pulverized before firing for achieving a stable and efficient combustion. Many types of pulverizers are used in boilers by different designers.

History of pulverizationThe history of pulverization dates back as early as 1824 and was envisioned by Carnot in a coal fired engine. In 1890 Diesel made use of pulverized coal in his diesel engine. Pulverized coal firing was first developed in the cement industry and then migrated to the power and process industries. Actually Thomas Alva Edison and the Niepce brothers of France were pioneers in pulverized coal firing. This technology gained momentum after World War I in the power generating industry. It was John Anderson, chief engineer of power plants at the Wisconsin Electric Power Company who introduced pulverized coal firing in power stations.Pulverized coal is the most efficient way of using coal in a steam generator. The coal is ground so that about 70 % will pass through 200 mesh (0.075 mm) and 99 % will pass through 50 mesh (0.300 mm). A pulverized coal boiler can be easily adapted for other fuels like gas if required later without much difficulty. However, during the design stage it is possible to make boilers firing multiple fuels. With pulverization technology, large size boilers could be designed, manufactured, erected, and run much more efficiently.Types of pulverizersMainly there are three types of pulverizer used in industry: the slow speed mills like ball tube mills, the medium speed mills like bowl, ball and race, roller mills fall in this category, and the third type is the high speed impact mill. The slow speed and medium speed mills are selected for coals ranging from sub-bituminous to anthracite. The high speed mills are used mainly for lignite.The purpose of a pulverizer in a coal fired boilerTo supply pulverized coal to the boiler as per requirement of steam generationTransport the pulverized coal from pulverizer to the burners in the boilerTo remove moisture in coal to an acceptable level for firing in boilerTo remove high density inorganics from coal during pulverizationTo classify coal particles to the required level of fineness, normally 70 % through 200 mesh and less than 2% on 50 meshCoal parameters affecting pulverizer outputWhile selecting a pulverizer, the coal characteristics play an important role. The Hardgrove index, total moisture, input coal size, output fineness, and mill wear have direct impact on the mill output.The Hardgrove index of coal tells us about the ease with which it can be pulverized. A higher Hardgrove index indicates the coal is easier to grind. 50 HGI normally is taken for calculating the base capacity of the mill. When coal with HGI higher than 50 is fed to the pulverizer, the output will be higher than base capacity, and below 50 HGI, the output will be lower.The total moisture in coal has a high effect on mill output. The higher the moisture, the lower the output.Higher pulverized coal fineness increases the recirculation in the mill and the output reduces.The inlet size of the coal also affects the mill output directly.Mill air flow variations result in changes in mill outlet temperature and fineness as well as capacity.Ball tube millBall tube mills are either pressurized or suction type. In the pressurized type, the hot primary air is used for drying the coal and to transport the milled coal to the furnace. In this type, leakage in the mill area is high.In the suction type, the exhauster is used for lifting the milled coal from the pulverizer to the furnace through a cyclone. The tube mills have a large circular drum, with adequate ball charge, which is rotated at about 70% of the speed at which the ball charge would be held against the inner surface by centrifugal force. In this mill the grinding balls can be replenished on the line.Normally the ball mill designers use three types of balls with three different diameters. These balls reduce in size as the mills operate and so the highest size ball is normally used for recharging. In earlier days, most of the ball mills had a single inlet and outlet, but now designers use both ends to feed coal and also for taking out pulverized coal. The control systems are well made to understand the requirement of ball charge and the output from the mill. Ball mills are always preferred to be operated at full capacity because the power consumption of this type of mill is very high at lower loads when compared with other types. Ball mills can be designed for a very high capacity like 75 tons per hour output for a specific coal.Vertical spindle millThere are many different varieties of vertical mills. Designers use large steel balls ranging from 2 to 6 or more between two grinding rings for pulverizing. There are also other types like conical rollers with shallow bowl; deep bowl, etc. where load is applied on the rollers and the bowl rotates while pulverizing. These types of mill are designed normally up to 60 tons per hour for a specific coal; however there are vertical mills with 90 tons per hour output. A vertical spindle mill is also designed for pressurized and suction type requirements. Boiler designers use this type of mill for poor quality coal as this type of mill rejects foreign materials like stones and other high density materials. The power consumed by the mill per ton of coal ground is only two-thirds of the ball mills. However if the primary air fan power is also taken into account, in the case of a pressurized mill the power consumption is lower only by about 15%.High speed impact millThis type of mill uses a central horizontal shaft which has a number of arms, and a beater of different design is attached to these arms to beat the coal to be pulverized. High speed impact mills are mainly used in pulverizing lignite. Today all boiler designers opt to use ball or vertical spindle mill for coal other than lignite.While selecting the type of mill boiler designers must clearly understand the coal characteristics, the overall system being used, and the maintenance requirement. It is always seen that if the advantage of the mill alone is considered, then the overall boiler economics can prove to be different.

The history of pulverization dates back as early as 1824 and was envisioned by Carnot in a coal fired engine. In 1890 Diesel made use of pulverized coal in his diesel engine. Pulverized coal firing was first developed in the cement industry and then migrated to the power and process industries. Actually Thomas Alva Edison and the Niepce brothers of France were pioneers in pulverized coal firing. This technology gained momentum after World War I in the power generating industry. It was John Anderson, chief engineer of power plants at the Wisconsin Electric Power Company who introduced pulverized coal firing in power stations.

Pulverized coal is the most efficient way of using coal in a steam generator. The coal is ground so that about 70 % will pass through 200 mesh (0.075 mm) and 99 % will pass through 50 mesh (0.300 mm). A pulverized coal boiler can be easily adapted for other fuels like gas if required later without much difficulty. However, during the design stage it is possible to make boilers firing multiple fuels. With pulverization technology, large size boilers could be designed, manufactured, erected, and run much more efficiently.Types of pulverizersMainly there are three types of pulverizer used in industry: the slow speed mills like ball tube mills, the medium speed mills like bowl, ball and race, roller mills fall in this category, and the third type is the high speed impact mill. The slow speed and medium speed mills are selected for coals ranging from sub-bituminous to anthracite. The high speed mills are used mainly for lignite.The purpose of a pulverizer in a coal fired boilerTo supply pulverized coal to the boiler as per requirement of steam generationTransport the pulverized coal from pulverizer to the burners in the boilerTo remove moisture in coal to an acceptable level for firing in boilerTo remove high density inorganics from coal during pulverizationTo classify coal particles to the required level of fineness, normally 70 % through 200 mesh and less than 2% on 50 meshCoal parameters affecting pulverizer outputWhile selecting a pulverizer, the coal characteristics play an important role. The Hardgrove index, total moisture, input coal size, output fineness, and mill wear have direct impact on the mill output.The Hardgrove index of coal tells us about the ease with which it can be pulverized. A higher Hardgrove index indicates the coal is easier to grind. 50 HGI normally is taken for calculating the base capacity of the mill. When coal with HGI higher than 50 is fed to the pulverizer, the output will be higher than base capacity, and below 50 HGI, the output will be lower.The total moisture in coal has a high effect on mill output. The higher the moisture, the lower the output.Higher pulverized coal fineness increases the recirculation in the mill and the output reduces.The inlet size of the coal also affects the mill output directly.Mill air flow variations result in changes in mill outlet temperature and fineness as well as capacity.Ball tube millBall tube mills are either pressurized or suction type. In the pressurized type, the hot primary air is used for drying the coal and to transport the milled coal to the furnace. In this type, leakage in the mill area is high.In the suction type, the exhauster is used for lifting the milled coal from the pulverizer to the furnace through a cyclone. The tube mills have a large circular drum, with adequate ball charge, which is rotated at about 70% of the speed at which the ball charge would be held against the inner surface by centrifugal force. In this mill the grinding balls can be replenished on the line.Normally the ball mill designers use three types of balls with three different diameters. These balls reduce in size as the mills operate and so the highest size ball is normally used for recharging. In earlier days, most of the ball mills had a single inlet and outlet, but now designers use both ends to feed coal and also for taking out pulverized coal. The control systems are well made to understand the requirement of ball charge and the output from the mill. Ball mills are always preferred to be operated at full capacity because the power consumption of this type of mill is very high at lower loads when compared with other types. Ball mills can be designed for a very high capacity like 75 tons per hour output for a specific coal.Vertical spindle millThere are many different varieties of vertical mills. Designers use large steel balls ranging from 2 to 6 or more between two grinding rings for pulverizing. There are also other types like conical rollers with shallow bowl; deep bowl, etc. where load is applied on the rollers and the bowl rotates while pulverizing. These types of mill are designed normally up to 60 tons per hour for a specific coal; however there are vertical mills with 90 tons per hour output. A vertical spindle mill is also designed for pressurized and suction type requirements. Boiler designers use this type of mill for poor quality coal as this type of mill rejects foreign materials like stones and other high density materials. The power consumed by the mill per ton of coal ground is only two-thirds of the ball mills. However if the primary air fan power is also taken into account, in the case of a pressurized mill the power consumption is lower only by about 15%.High speed impact millThis type of mill uses a central horizontal shaft which has a number of arms, and a beater of different design is attached to these arms to beat the coal to be pulverized. High speed impact mills are mainly used in pulverizing lignite. Today all boiler designers opt to use ball or vertical spindle mill for coal other than lignite.While selecting the type of mill boiler designers must clearly understand the coal characteristics, the overall system being used, and the maintenance requirement. It is always seen that if the advantage of the mill alone is considered, then the overall boiler economics can prove to be different.

Types of pulverizersMainly there are three types of pulverizer used in industry: the slow speed mills like ball tube mills, the medium speed mills like bowl, ball and race, roller mills fall in this category, and the third type is the high speed impact mill. The slow speed and medium speed mills are selected for coals ranging from sub-bituminous to anthracite. The high speed mills are used mainly for lignite.The purpose of a pulverizer in a coal fired boilerTo supply pulverized coal to the boiler as per requirement of steam generationTransport the pulverized coal from pulverizer to the burners in the boilerTo remove moisture in coal to an acceptable level for firing in boilerTo remove high density inorganics from coal during pulverizationTo classify coal particles to the required level of fineness, normally 70 % through 200 mesh and less than 2% on 50 meshCoal parameters affecting pulverizer outputWhile selecting a pulverizer, the coal characteristics play an important role. The Hardgrove index, total moisture, input coal size, output fineness, and mill wear have direct impact on the mill output.The Hardgrove index of coal tells us about the ease with which it can be pulverized. A higher Hardgrove index indicates the coal is easier to grind. 50 HGI normally is taken for calculating the base capacity of the mill. When coal with HGI higher than 50 is fed to the pulverizer, the output will be higher than base capacity, and below 50 HGI, the output will be lower.The total moisture in coal has a high effect on mill output. The higher the moisture, the lower the output.Higher pulverized coal fineness increases the recirculation in the mill and the output reduces.The inlet size of the coal also affects the mill output directly.Mill air flow variations result in changes in mill outlet temperature and fineness as well as capacity.Ball tube millBall tube mills are either pressurized or suction type. In the pressurized type, the hot primary air is used for drying the coal and to transport the milled coal to the furnace. In this type, leakage in the mill area is high.In the suction type, the exhauster is used for lifting the milled coal from the pulverizer to the furnace through a cyclone. The tube mills have a large circular drum, with adequate ball charge, which is rotated at about 70% of the speed at which the ball charge would be held against the inner surface by centrifugal force. In this mill the grinding balls can be replenished on the line.Normally the ball mill designers use three types of balls with three different diameters. These balls reduce in size as the mills operate and so the highest size ball is normally used for recharging. In earlier days, most of the ball mills had a single inlet and outlet, but now designers use both ends to feed coal and also for taking out pulverized coal. The control systems are well made to understand the requirement of ball charge and the output from the mill. Ball mills are always preferred to be operated at full capacity because the power consumption of this type of mill is very high at lower loads when compared with other types. Ball mills can be designed for a very high capacity like 75 tons per hour output for a specific coal.Vertical spindle millThere are many different varieties of vertical mills. Designers use large steel balls ranging from 2 to 6 or more between two grinding rings for pulverizing. There are also other types like conical rollers with shallow bowl; deep bowl, etc. where load is applied on the rollers and the bowl rotates while pulverizing. These types of mill are designed normally up to 60 tons per hour for a specific coal; however there are vertical mills with 90 tons per hour output. A vertical spindle mill is also designed for pressurized and suction type requirements. Boiler designers use this type of mill for poor quality coal as this type of mill rejects foreign materials like stones and other high density materials. The power consumed by the mill per ton of coal ground is only two-thirds of the ball mills. However if the primary air fan power is also taken into account, in the case of a pressurized mill the power consumption is lower only by about 15%.High speed impact millThis type of mill uses a central horizontal shaft which has a number of arms, and a beater of different design is attached to these arms to beat the coal to be pulverized. High speed impact mills are mainly used in pulverizing lignite. Today all boiler designers opt to use ball or vertical spindle mill for coal other than lignite.While selecting the type of mill boiler designers must clearly understand the coal characteristics, the overall system being used, and the maintenance requirement. It is always seen that if the advantage of the mill alone is considered, then the overall boiler economics can prove to be different.

Mainly there are three types of pulverizer used in industry: the slow speed mills like ball tube mills, the medium speed mills like bowl, ball and race, roller mills fall in this category, and the third type is the high speed impact mill. The slow speed and medium speed mills are selected for coals ranging from sub-bituminous to anthracite. The high speed mills are used mainly for lignite.

The purpose of a pulverizer in a coal fired boilerTo supply pulverized coal to the boiler as per requirement of steam generationTransport the pulverized coal from pulverizer to the burners in the boilerTo remove moisture in coal to an acceptable level for firing in boilerTo remove high density inorganics from coal during pulverizationTo classify coal particles to the required level of fineness, normally 70 % through 200 mesh and less than 2% on 50 meshCoal parameters affecting pulverizer outputWhile selecting a pulverizer, the coal characteristics play an important role. The Hardgrove index, total moisture, input coal size, output fineness, and mill wear have direct impact on the mill output.The Hardgrove index of coal tells us about the ease with which it can be pulverized. A higher Hardgrove index indicates the coal is easier to grind. 50 HGI normally is taken for calculating the base capacity of the mill. When coal with HGI higher than 50 is fed to the pulverizer, the output will be higher than base capacity, and below 50 HGI, the output will be lower.The total moisture in coal has a high effect on mill output. The higher the moisture, the lower the output.Higher pulverized coal fineness increases the recirculation in the mill and the output reduces.The inlet size of the coal also affects the mill output directly.Mill air flow variations result in changes in mill outlet temperature and fineness as well as capacity.Ball tube millBall tube mills are either pressurized or suction type. In the pressurized type, the hot primary air is used for drying the coal and to transport the milled coal to the furnace. In this type, leakage in the mill area is high.In the suction type, the exhauster is used for lifting the milled coal from the pulverizer to the furnace through a cyclone. The tube mills have a large circular drum, with adequate ball charge, which is rotated at about 70% of the speed at which the ball charge would be held against the inner surface by centrifugal force. In this mill the grinding balls can be replenished on the line.Normally the ball mill designers use three types of balls with three different diameters. These balls reduce in size as the mills operate and so the highest size ball is normally used for recharging. In earlier days, most of the ball mills had a single inlet and outlet, but now designers use both ends to feed coal and also for taking out pulverized coal. The control systems are well made to understand the requirement of ball charge and the output from the mill. Ball mills are always preferred to be operated at full capacity because the power consumption of this type of mill is very high at lower loads when compared with other types. Ball mills can be designed for a very high capacity like 75 tons per hour output for a specific coal.Vertical spindle millThere are many different varieties of vertical mills. Designers use large steel balls ranging from 2 to 6 or more between two grinding rings for pulverizing. There are also other types like conical rollers with shallow bowl; deep bowl, etc. where load is applied on the rollers and the bowl rotates while pulverizing. These types of mill are designed normally up to 60 tons per hour for a specific coal; however there are vertical mills with 90 tons per hour output. A vertical spindle mill is also designed for pressurized and suction type requirements. Boiler designers use this type of mill for poor quality coal as this type of mill rejects foreign materials like stones and other high density materials. The power consumed by the mill per ton of coal ground is only two-thirds of the ball mills. However if the primary air fan power is also taken into account, in the case of a pressurized mill the power consumption is lower only by about 15%.High speed impact millThis type of mill uses a central horizontal shaft which has a number of arms, and a beater of different design is attached to these arms to beat the coal to be pulverized. High speed impact mills are mainly used in pulverizing lignite. Today all boiler designers opt to use ball or vertical spindle mill for coal other than lignite.While selecting the type of mill boiler designers must clearly understand the coal characteristics, the overall system being used, and the maintenance requirement. It is always seen that if the advantage of the mill alone is considered, then the overall boiler economics can prove to be different.

While selecting a pulverizer, the coal characteristics play an important role. The Hardgrove index, total moisture, input coal size, output fineness, and mill wear have direct impact on the mill output.The Hardgrove index of coal tells us about the ease with which it can be pulverized. A higher Hardgrove index indicates the coal is easier to grind. 50 HGI normally is taken for calculating the base capacity of the mill. When coal with HGI higher than 50 is fed to the pulverizer, the output will be higher than base capacity, and below 50 HGI, the output will be lower.The total moisture in coal has a high effect on mill output. The higher the moisture, the lower the output.Higher pulverized coal fineness increases the recirculation in the mill and the output reduces.The inlet size of the coal also affects the mill output directly.Mill air flow variations result in changes in mill outlet temperature and fineness as well as capacity.Ball tube millBall tube mills are either pressurized or suction type. In the pressurized type, the hot primary air is used for drying the coal and to transport the milled coal to the furnace. In this type, leakage in the mill area is high.In the suction type, the exhauster is used for lifting the milled coal from the pulverizer to the furnace through a cyclone. The tube mills have a large circular drum, with adequate ball charge, which is rotated at about 70% of the speed at which the ball charge would be held against the inner surface by centrifugal force. In this mill the grinding balls can be replenished on the line.Normally the ball mill designers use three types of balls with three different diameters. These balls reduce in size as the mills operate and so the highest size ball is normally used for recharging. In earlier days, most of the ball mills had a single inlet and outlet, but now designers use both ends to feed coal and also for taking out pulverized coal. The control systems are well made to understand the requirement of ball charge and the output from the mill. Ball mills are always preferred to be operated at full capacity because the power consumption of this type of mill is very high at lower loads when compared with other types. Ball mills can be designed for a very high capacity like 75 tons per hour output for a specific coal.Vertical spindle millThere are many different varieties of vertical mills. Designers use large steel balls ranging from 2 to 6 or more between two grinding rings for pulverizing. There are also other types like conical rollers with shallow bowl; deep bowl, etc. where load is applied on the rollers and the bowl rotates while pulverizing. These types of mill are designed normally up to 60 tons per hour for a specific coal; however there are vertical mills with 90 tons per hour output. A vertical spindle mill is also designed for pressurized and suction type requirements. Boiler designers use this type of mill for poor quality coal as this type of mill rejects foreign materials like stones and other high density materials. The power consumed by the mill per ton of coal ground is only two-thirds of the ball mills. However if the primary air fan power is also taken into account, in the case of a pressurized mill the power consumption is lower only by about 15%.High speed impact millThis type of mill uses a central horizontal shaft which has a number of arms, and a beater of different design is attached to these arms to beat the coal to be pulverized. High speed impact mills are mainly used in pulverizing lignite. Today all boiler designers opt to use ball or vertical spindle mill for coal other than lignite.While selecting the type of mill boiler designers must clearly understand the coal characteristics, the overall system being used, and the maintenance requirement. It is always seen that if the advantage of the mill alone is considered, then the overall boiler economics can prove to be different.

Ball tube millBall tube mills are either pressurized or suction type. In the pressurized type, the hot primary air is used for drying the coal and to transport the milled coal to the furnace. In this type, leakage in the mill area is high.In the suction type, the exhauster is used for lifting the milled coal from the pulverizer to the furnace through a cyclone. The tube mills have a large circular drum, with adequate ball charge, which is rotated at about 70% of the speed at which the ball charge would be held against the inner surface by centrifugal force. In this mill the grinding balls can be replenished on the line.Normally the ball mill designers use three types of balls with three different diameters. These balls reduce in size as the mills operate and so the highest size ball is normally used for recharging. In earlier days, most of the ball mills had a single inlet and outlet, but now designers use both ends to feed coal and also for taking out pulverized coal. The control systems are well made to understand the requirement of ball charge and the output from the mill. Ball mills are always preferred to be operated at full capacity because the power consumption of this type of mill is very high at lower loads when compared with other types. Ball mills can be designed for a very high capacity like 75 tons per hour output for a specific coal.Vertical spindle millThere are many different varieties of vertical mills. Designers use large steel balls ranging from 2 to 6 or more between two grinding rings for pulverizing. There are also other types like conical rollers with shallow bowl; deep bowl, etc. where load is applied on the rollers and the bowl rotates while pulverizing. These types of mill are designed normally up to 60 tons per hour for a specific coal; however there are vertical mills with 90 tons per hour output. A vertical spindle mill is also designed for pressurized and suction type requirements. Boiler designers use this type of mill for poor quality coal as this type of mill rejects foreign materials like stones and other high density materials. The power consumed by the mill per ton of coal ground is only two-thirds of the ball mills. However if the primary air fan power is also taken into account, in the case of a pressurized mill the power consumption is lower only by about 15%.High speed impact millThis type of mill uses a central horizontal shaft which has a number of arms, and a beater of different design is attached to these arms to beat the coal to be pulverized. High speed impact mills are mainly used in pulverizing lignite. Today all boiler designers opt to use ball or vertical spindle mill for coal other than lignite.While selecting the type of mill boiler designers must clearly understand the coal characteristics, the overall system being used, and the maintenance requirement. It is always seen that if the advantage of the mill alone is considered, then the overall boiler economics can prove to be different.

Ball tube mills are either pressurized or suction type. In the pressurized type, the hot primary air is used for drying the coal and to transport the milled coal to the furnace. In this type, leakage in the mill area is high.

In the suction type, the exhauster is used for lifting the milled coal from the pulverizer to the furnace through a cyclone. The tube mills have a large circular drum, with adequate ball charge, which is rotated at about 70% of the speed at which the ball charge would be held against the inner surface by centrifugal force. In this mill the grinding balls can be replenished on the line.Normally the ball mill designers use three types of balls with three different diameters. These balls reduce in size as the mills operate and so the highest size ball is normally used for recharging. In earlier days, most of the ball mills had a single inlet and outlet, but now designers use both ends to feed coal and also for taking out pulverized coal. The control systems are well made to understand the requirement of ball charge and the output from the mill. Ball mills are always preferred to be operated at full capacity because the power consumption of this type of mill is very high at lower loads when compared with other types. Ball mills can be designed for a very high capacity like 75 tons per hour output for a specific coal.Vertical spindle millThere are many different varieties of vertical mills. Designers use large steel balls ranging from 2 to 6 or more between two grinding rings for pulverizing. There are also other types like conical rollers with shallow bowl; deep bowl, etc. where load is applied on the rollers and the bowl rotates while pulverizing. These types of mill are designed normally up to 60 tons per hour for a specific coal; however there are vertical mills with 90 tons per hour output. A vertical spindle mill is also designed for pressurized and suction type requirements. Boiler designers use this type of mill for poor quality coal as this type of mill rejects foreign materials like stones and other high density materials. The power consumed by the mill per ton of coal ground is only two-thirds of the ball mills. However if the primary air fan power is also taken into account, in the case of a pressurized mill the power consumption is lower only by about 15%.High speed impact millThis type of mill uses a central horizontal shaft which has a number of arms, and a beater of different design is attached to these arms to beat the coal to be pulverized. High speed impact mills are mainly used in pulverizing lignite. Today all boiler designers opt to use ball or vertical spindle mill for coal other than lignite.While selecting the type of mill boiler designers must clearly understand the coal characteristics, the overall system being used, and the maintenance requirement. It is always seen that if the advantage of the mill alone is considered, then the overall boiler economics can prove to be different.

Normally the ball mill designers use three types of balls with three different diameters. These balls reduce in size as the mills operate and so the highest size ball is normally used for recharging. In earlier days, most of the ball mills had a single inlet and outlet, but now designers use both ends to feed coal and also for taking out pulverized coal. The control systems are well made to understand the requirement of ball charge and the output from the mill. Ball mills are always preferred to be operated at full capacity because the power consumption of this type of mill is very high at lower loads when compared with other types. Ball mills can be designed for a very high capacity like 75 tons per hour output for a specific coal.

Vertical spindle millThere are many different varieties of vertical mills. Designers use large steel balls ranging from 2 to 6 or more between two grinding rings for pulverizing. There are also other types like conical rollers with shallow bowl; deep bowl, etc. where load is applied on the rollers and the bowl rotates while pulverizing. These types of mill are designed normally up to 60 tons per hour for a specific coal; however there are vertical mills with 90 tons per hour output. A vertical spindle mill is also designed for pressurized and suction type requirements. Boiler designers use this type of mill for poor quality coal as this type of mill rejects foreign materials like stones and other high density materials. The power consumed by the mill per ton of coal ground is only two-thirds of the ball mills. However if the primary air fan power is also taken into account, in the case of a pressurized mill the power consumption is lower only by about 15%.High speed impact millThis type of mill uses a central horizontal shaft which has a number of arms, and a beater of different design is attached to these arms to beat the coal to be pulverized. High speed impact mills are mainly used in pulverizing lignite. Today all boiler designers opt to use ball or vertical spindle mill for coal other than lignite.While selecting the type of mill boiler designers must clearly understand the coal characteristics, the overall system being used, and the maintenance requirement. It is always seen that if the advantage of the mill alone is considered, then the overall boiler economics can prove to be different.

There are many different varieties of vertical mills. Designers use large steel balls ranging from 2 to 6 or more between two grinding rings for pulverizing. There are also other types like conical rollers with shallow bowl; deep bowl, etc. where load is applied on the rollers and the bowl rotates while pulverizing. These types of mill are designed normally up to 60 tons per hour for a specific coal; however there are vertical mills with 90 tons per hour output. A vertical spindle mill is also designed for pressurized and suction type requirements. Boiler designers use this type of mill for poor quality coal as this type of mill rejects foreign materials like stones and other high density materials. The power consumed by the mill per ton of coal ground is only two-thirds of the ball mills. However if the primary air fan power is also taken into account, in the case of a pressurized mill the power consumption is lower only by about 15%.High speed impact millThis type of mill uses a central horizontal shaft which has a number of arms, and a beater of different design is attached to these arms to beat the coal to be pulverized. High speed impact mills are mainly used in pulverizing lignite. Today all boiler designers opt to use ball or vertical spindle mill for coal other than lignite.While selecting the type of mill boiler designers must clearly understand the coal characteristics, the overall system being used, and the maintenance requirement. It is always seen that if the advantage of the mill alone is considered, then the overall boiler economics can prove to be different.

This type of mill uses a central horizontal shaft which has a number of arms, and a beater of different design is attached to these arms to beat the coal to be pulverized. High speed impact mills are mainly used in pulverizing lignite. Today all boiler designers opt to use ball or vertical spindle mill for coal other than lignite.While selecting the type of mill boiler designers must clearly understand the coal characteristics, the overall system being used, and the maintenance requirement. It is always seen that if the advantage of the mill alone is considered, then the overall boiler economics can prove to be different.

While selecting the type of mill boiler designers must clearly understand the coal characteristics, the overall system being used, and the maintenance requirement. It is always seen that if the advantage of the mill alone is considered, then the overall boiler economics can prove to be different.

foster wheeler ball mill - pulverizer modernization components and services | coal mill pulverizer upgrade parts | sas global

foster wheeler ball mill - pulverizer modernization components and services | coal mill pulverizer upgrade parts | sas global

The SAS Mill Modernization program can include available patented SAS modernization technology, rebuild / installation and then fine tuning of the mill. The first phase of this program should include a complete Mill inspection and accurate coal pipe testing which will establish baseline data. The information gained will include coal pipe balance, coal fineness, air/coal ratios, as well as the condition of the grinding components, mill throat, classifier, springs, and other components.

This information is then provided to the Power Plant in a comprehensive report and is used as a tool to determine which modifications are required to meet their specific target or performance goals. Before any Mill modifications take place it is very important to have discussions with all the appropriate plant personnel to develop a systematic plan of how to achieve realistic and attainable goals.

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