Importance of Test Block for Boiler PA, FD, Secondary Air Fans, ID fans

When undertaking 3T boiler tuning projects, it has been observed that some boilers do not get tuned properly after several attempts.

The main reason that can be attributed to this, is the fan performance does not match the design specifications.

Fans have issues with impellers or tongue clearance or bearings or leakages in ducts where in the fan delivery pressure does not suffice to furnace operations.

Why the fan design pressure is important ?
The fan pressures are a function derived by furnace dimensions, bed height & bed weight. For PF the flame length, curvature, flame spread etc..

For the same furnace dimension if there is a drop in fan design pressure, it gets compensated to volume & increases load on ID fans & the user ends up in losing Boiler Efficiency in the Direct Method.


In the test block these fans do not conform to the pressure volume curve, as provided by OEM.

There are two primary problems with the fans

1) Pressure compensating to volume means the air delivery pressure reduces, increases volume delivery
2) Volume compensates to pressure means the air delivery volume reduces

Both the above problematic fans give distinct combustion problems & many times the client will never know that there is an issue with the fans, they keep suspecting the fuel or any other mechanical part in the boiler.

These boilers have functionally lower efficiency in the Direct Method & 3T conditions cannot be implemented.

The FD fan had an issue of low delivery pressure from commissioning & went undetected for 2 decades at one client. There are several examples where this type of problem go undetected.

For the fan testing there are many codes like BS 848 / AMCA 210 / ISO 5801 / ASME PTC 11 etc.

Whether the boiler is Stoker / FBC / AFBC / CFBC / PF, the test block has to be conducted on all fans to conform all parameters of design, which should be checked every time during annual shutdown.

What should be done if the pressure, volume curve by design & actual installation does not match ?

Check the original drawing & verify what is not matching, repair & reconduct the test block.

Even after all the repairs do not produce matching curves, replace the fan after thorough verification at the time of installation.

Check the following regularly during shutdowns for a consistent & smooth operation, long life of boilers, with excellent combustion characteristics :
1) Test block of fans & take necessary action
2) Test block all air & flue gas ducts, to check pressure drop across all points to conform to design parameters

Advantages of Fans correction ::

Improves fan performance, air delivery by pressure & volume, sets off many combustion issues, faced in operations.

The boiler becomes fully tunable to 3T exercise, where in highest efficiency by Direct Method can be realized.

This issue of fans conforming to design pressure & volume is of very high importance & criticality, as these very parameters define inter relationships with others.

PA pressure is critical to coal density & volume of flow, furnace dimensions.
FD pressure is critical for combustion, C + O2 reaction stability, controls turbulence & time functions in 3T, flame height or length, curvature, bed resistance, flue gas velocity, furnace dimensions etc.

A correct fan profile will relieve the user of many tensions in the combustion front,

If you have any questions, please mail me at sap@chargewave.in

Big Boiler vs. Small Boiler -- Combustion & heat dynamics

What are the differences between PF Boiler, Super Critical Boiler, CFBC Boiler, AFBC, FBC, Stoker & Manual fired Boilers ?

Design & Engineering Point of View :
There is higher steaming capacity in PF, Super Critical, CFB & the others are of lower capacity & manual fired boilers have lowest capacity.

The Engineering side for large boilers up to Stokers is to
1) deliver the fuel in the required crushed size & all fuel handling systems, coal crushers, coal mills etc. are performing this task
2) deliver the air required for combustion + excess air, through the air fans
3) deliver water, cooling towers, tubes etc., to handle the steaming capacity
4) operate through DCS or PLC systems to automate handling processes

From PF to Stokers, the difference is the fuel size input into the system, rest others being common.

For a manual fired boiler, the fuel size is 4 inches or 100 mm, to stoker which is 12mm to 25 mm, FBC & AFBC < 8mm, CFBC < 4 to 6 mm & PF it is around 300 microns.

Do the Combustion reactions change due to Boiler design ?
Not at all. Interesting thing is there is no difference what so ever in the combustion reactions, from manual fired to PF boilers. They are the same.

Why there is an Efficiency difference in Boilers ?
Air to Fuel ratio, factor of time & distance play a major role in Boiler Design.

For example, in a Manual fired boiler, the first pass to second or third pass, the flue gases pass through, generating the steam.

The distance between the flame & the heating surface area, dictates the Efficiency of the system.

The Engineering feats of design & capacity however cannot over rule the basics of Boiler design.

Simply put, the more the time taken for heat to reach the surface areas, the lower is the Efficiency. The quicker the heat travels, higher is the Efficiency.

What has been accomplished in different Boiler Designs, as a factor of time & distance ?
1) In a manual fired Boiler, the time & distance is more, therefore lower Efficiency
2) In a stoker, the fire is surrounded by water tubes, reducing the time, therefore higher efficiency of the Boiler than manual fired one
3) In a FBC, AFBC & CFBC where the fire is, the heat absorbers are present, reducing the time lag therefore higher efficiency than Stokers
4) In PF, the environment is similar to that of Stokers, however the volume of flame generated is higher, therefore higher Efficiency

Heat travels & flows like water, lesser the time, more intensity it has.

What is the role of flame temperature ?
It reduces progressively with distance travelled. Flame temperature role is in conjunction with heat intensity only & not individually.

What is the most important factor, heat intensity or flame temperature ?
It is the intensity which is more important than the temperature. Intensity can be explained like concentrated temperature. In many boilers, the temperatures are operated very high, even then the Efficiency in the Direct Method & steaming capacity is low. The reason is the intensity is low.

Thermal Zones in a Boiler
The Boiler has primarily 9 thermal zones, 6 within the boiler & rest outside the Boiler.

The first 3 thermal zones are
1) Pre combustion zone
2) Combustion zone
3) Tail zone or finishing zone

The fuel which is input, has to complete its preliminary heating in the pre-combustion area of the zone & starts combustion in the Combustion zone & should finish in the tail zone.

Where the fuel characteristics change, the zones shift, & Boilers where such occurrences are present, have lower steaming capacity, with higher steam temperatures.

The Heat absorption systems are exactly placed in the Combustion zone & tail zone.

The above zones are responsible for steam generation. There will be no steam tonnage generated in any other part of the boiler other than the first three zones, where the flame is present.

The next 3 thermal zones
1) the first starts soon after the flame is invisible & extends upto 500 deg C flue gas temperature
2) the second zone & third zones are together up to 300 / 330 deg C

These zones are responsible for building up the pressure & temperature & span the Boiler drum, tube verticals, super heaters.

The last 3 thermal zones
The APH, Economizer & the radiation

The Boilers other than once through design, do not have capacity to absorb heat below 300 deg C, as the heat intensity is not sufficient to cause absorption in the Boiler internals. Such boilers come with APH & Economizers to absorb the heat.

If you examine the design of APH & Economizer, the heating surface area is very low but handles very high volume of flue gas, heat gets concentrated in the lower surface area, developing intensity & therefore exchange of heat.

The first 3 zones are critical for Steaming capacity
The middle 3 zones are critical for steam temperature & pressure
The last 3 zones are important for waste heat recovery

Does the heat exchange by Radiant heat in a Boiler ?
My studies indicate otherwise. If the radiant heat was the answer, the boiler should have performed well with high flame or bed temperatures, the ground reality is, it is not. It is the heat intensity & heat concentration, which transfers the heat.

Heat travels most efficiently in a medium & least in vacuum & the transfer medium in the Boiler is flue gases. The flue gases are freely moving in the furnace. When heat is exchanged, there is drop in its temperature. Every where in the Boiler, the flue gas temperature only is transferring the heat.

When heat transfer medium becomes important, then density also becomes important. Heat travels more efficiently in denser mediums & less in low density. The flue gas density is a very important parameter for heat transfer.

The Boiler is not a super conductor of heat that whatever is put in, it absorbs some & leaves some other, challenging laws of thermal coefficient of absorption of the metals. The metallurgy employed for boiler banks, super heaters, does not have super conducting or super absorbing capacity. There are physical limits.

When there is more heat concentration than what the tubes can absorb, thermal stresses, DNB get created.

Nowadays super conduction is achieved in below minus 150 deg C temperatures & not in higher temperatures like what exist in a boiler. If this is the case, how come that the GCV input vs. exchange is matching by Efficiency methods ?. See the explanation below

Missing explanation about Heat
There are several missing things about heat.

Heat is the only parameter in physics which is represented quantitatively i.e. Kcal / Kg & has no qualitative factor to talk about, other than temperature. All other parameters, steam, power, metals, anything & everything, have a qualitative factor & quantitative factors. Temperature is only measuring degree of hotness or coldness. Temperature alone cannot indicate quality.

Surprising ? Yes it is.

So how do you achieve heat quality ?, by intensity and managing time & distance. The angle at which the heat wave hits the absorbing surface also is important.

The intensity can be explained as total volume of identical temperature heat, and higher heat volume per m3 generates higher intensity.

The boiler tubes are designed to absorb a particular concentration of heat say for example 150,000 Kcal / m3 (depends upon design). If the heat available is above this value, the heat absorption cannot happen, as capacity of the absorber has been breached.

Similar way there is a minimum concentration or intensity which is required, below which the heat absorption will be poor. This information is said as Min. 60% operating capacity is required for Boiler to be Efficient.

Combustion Reactions in different types of Boiler Design -- Reaction point of View
There is no difference whatsoever in the combustion reactions for any boiler, be it PF, CFB or Manual fired. The reactions & heating properties are exactly identical.

Does High Thermal Efficiency mean, that the Boiler Design is Efficient ?
In recent times, Thermal Efficiency which indicates heat absorption capacity of the boiler and assumes that 100% energy is generated in the reactions, has taken center stage in Boiler Operations & its performance assessment.

Even more, new boilers come with Thermal Efficiency of 87 to 89% reported on NCV basis. Higher thermal efficiency only means, the boiler is designed to capture more heat energy leaving the generation part to the operator.

The engineering feat for heat absorption can be appreciated, however the critical part is to conduct the reactions efficiently.

Good heat generation is not achieved by Design, it is achieved by 3T operations alone.

Steam Attemperation & connection to Thermal Zones
Boiler Steam not requiring any attemperation, is a good design from drum capacity & indicates the thermal zones have not shifted. Frequent or excess attemperation means that the thermal zones are shifting & raising the steam temperature. Check the first 3 thermal zones first, & analyse what caused the shift in the first place.

I have corrected many operations in the Boiler from lower generation capacity issue to higher steam temperature & pressure issues, all were caused due to shifting of thermal zones & upon correction delivered the results.

Have questions ?

write to sap@chargewave.in

SAP

Efficiencies terminology & Questions for Boilers

Important Efficiencies & what they represent.

Thermal Efficiency : Thermal Capture or heat capture efficiency of the Boiler. It determines the heat exchanging efficiency in the Boiler.
Verified by the Loss method & 100 minus Losses = Thermal Efficiency

Fuel to Fluid Efficiency or Boiler Efficiency : It is energy input by heat vs. what is converted to steam.

Output / Input %, verified by the Direct Method

Here
Output is Steam MT * Steam Net Enthalpy
Input is fuel CV * fuel quantity

Reaction Efficiency : Efficiency of C, O2 reaction or Efficiency of the reaction conditions (turbulence) created by operations

Combustion Efficiency : Efficiency of how much fuel is consumed in the furnace & what is left over.
100 minus LOI = Combustion Efficiency

Design Efficiency : Efficiency of the Boiler by Design, for design fuel, design air, design air & flue gas velocities, design conditions of all aspects in operation

Most important of the above are represented in ascending order below

1. Design Efficiency
2. Reaction Efficiency
3. Boiler Efficiency
4. Combustion Efficiency
5. Thermal Efficiency

There are others, however for Boiler Operations, the above are good enough.

Thermal Efficiency & Boiler Efficiency are similar & equal ?

No. Thermal Efficiency assumes 100% energy is generated & measures losses, it is more representative of heat exchange or heat absorption capacity of the boiler. 

Boiler Efficiency, measures the actual heat generated vs. heat absorption. It measures the reaction condition side of the Boiler.

Thermal Efficiency is more or less constant in any operation load of the Boiler & seldom changes.

There are 27 distinct turbulence conditions that can be created in Boiler Operations.

Thermal Efficiency is constant in all the 27 conditions, irrespective of the operation load.

Boiler Efficiency varies in 26 conditions, as reaction conditions created change. Boiler Efficiency is load dependent, lower the load, lower the Efficiency & only > 75% loads, only all thermal zones get loaded & Boiler starts to operate in higher efficiency.

Only in 1 operational (3T) condition, the Boiler Efficiency is close to Thermal Efficiency & also Design Efficiency, however the operation load has to be > 75%.

This also means that in 26 conditions, energy generated is far less than the potential of the fuel.

If every calorie offered by the fuel is your target, Boiler Efficiency method is the Key to identify which of the 27 conditions, the Boiler operates & correction is possible.

We offer consultancy for Boilers to identify & bring the operation to the 27th condition.

For any comments, write to sap@chargewave.in

SAP

Critical factors in Boiler Design & Operation

When anyone thinks about a boiler, the first thing which flashes is the steam, steam quality, turbine etc.

However when the Boiler Design aspects are looked into, the most critical factors are presented in ascending order

1) Density of the fuel
    a) Fuel density is the most critical factor, as increase in density reduces flame throw for PF boilers, reduces fluidization in FBC, AFBC & CFBC boilers, reduces fuel flows
   b) The PA Fans are designed for the fuel density & volume delivery
   c) The furnace dimensions (more width or height) are determined again by fuel density & volume delivery
   d) The FD fans are designed for handling the fuel density & its reactivity patterns
   e) reactivity and reaction efficiency of the fuel is also a function of its density, as higher density slows the combustion reactions & lower density speeds it up
   f) The air & flue gas velocities are also determined as a function of fuel density
  g) The air duct dimensions are also function of fuel density
  h) Direct Method Efficiency of the boiler also is a dependent parameter of fuel density
  i) Time, turbulence & temperature or the 3T equilibrium is a dependent parameter of fuel density
  j) LOI in the fly ash, clinker, etc., density of the fuel plays a major role
 k) Flue gas density which is the heat carrier in the furnace also is dependent upon fuel density

The density of the fuel commands the entire combustion process, hence it is the most critical parameter. Most of the combustion related problems arise from change in density of the fuel.

In fact 70% to 80% design work is attributed to combustion related issues, fuel handling etc..

In almost every Boiler installation, the density goes unchecked & is not reported. Many times, when I ask what is the fuel density, it is checked almost the first time ever.


Ask the OEM, what is the fuel density consideration for design.

2) The rest of the boiler, viz., bank, bed tubes, etc. fall in the reminder work

3) Critical parameter is also the steam drum size, ensure the steam drum size is big enough to hold at least 20% to 30% of the steaming capacity as water holding capacity.
   
    When the boiler drum is small, the thermal stresses get created, as there will always be conditions where heat produced > heat absorption. If this condition occurs, if clinker is formed, it is good, as the heat has been removed through clinker.

If the clinker has not formed, then there is a good chance of the tube surfaces getting heated up, becoming red hot & become stressed, readying them for failure.

As the water is the only coolant removing the heat in the whole boiler system, water supply or its velocity >> steam velocity. This measure will keep thermal stresses at bay.

In big steam drum boilers, the boiler tube failure is a slow or remote possibility, due to more than sufficient cooling arrangement.

In small steam drum boilers, the tube failures are high, as the tubes display highest characteristics for easy erosion only when they are red hot.

Steam drum size is a determinant factor in natural circulation rates, which is never measured in Boiler operation.

4) Fuel density in usage : This is also a very critical parameter. Often it happens, that the fuel for which the boiler stands designed, is no longer available. The decisions for purchasing a fuel should include its density as a parameter, which removes much of the anxiety in operations

5) 3T condition : The Boiler should operate in 3T condition, this is most critical parameter in operation

If you have any comments or queries, please send to sap@chargewave.in

SAP

Fuel Additives -- Are they necessary ?

What are Fuel Additives
Fuel Additives are organic or inorganic chemical formulations mostly employed for the LOI reduction, clinker problems, reducing O2 in combustion, in Boilers.The formulations come in as liquids & powders or even as sticks.

What is the role & function of Fuel Additives in combustion ? Actually speaking none.

Boiler Operation Types
There are 27 distinct Boiler operation types, methods or conditions.
Out of these 13 cause higher flue gas or air velocity, another 13 cause deficient flue gas or air velocity. The 27th condition is where the flue gas velocity is neither higher or lower, it is exact.

Air or Flue gas velocity impact
Increased air velocity ejects the fuel out of the system & deficient air velocity produces un-burnt carbon. However both get classified as LOI.

How to check air velocity ?
When the LOI is segregated & checked for Volatile matter presence, the air velocity behaviour can be verified.

If the LOI shows VM presence, the boiler is working with higher air velocity & is ejecting the fuel out.

If the LOI shows no VM presence, the boiler is working with deficient air velocity.

For boilers where switching between high load & low load is frequent, the VM presence will be 50-50, means present in some samples & absent in some samples.

Fuel Additives -- Limitations
Fuel Additives can perform some what in the 13 conditions where there is deficient flue gas velocity. Deficient air velocity produces Fixed Carbon, no volatile matter ash which require higher combustion temperature.

However in the rest 14 conditions, there is no effect of Fuel Additives whatsoever.

If the Boiler employs a fuel additive and there is some result attributed, then the possibility is that the operation is of deficient air velocity types.

Clinker Problems -- the Truth & the Story
The ash fusion temperature, chemistry of fuel, ash, iron etc, causes clinkers is a good story. The truth is that deficient air velocity can only produce clinkers.

Deficient air velocity operations, produce Fixed carbon in Ash & also have clinker problems.

Deficient air velocity is produced by increased bed height or bed thickness, improper settings of PA, FD.

Clinker formation is caused primarily due to low FD or PA pressure & increased bed height.

The heat energy is like water, it flows. When the flue gases cannot pick up the heat due to low velocity, the heat flows to the ash & forms clinker.

The only heat carrier in the boiler is the flue gas only & it has to flow quite clear.

In some cases, the bed volume itself is very low, however the operating load of the boiler will be higher, meaning lower bed volume handles more heat energy, when load drops & heat has no flowing opportunity to water side, it flows to fuel and causes clinker.

I have solved many clinker formation problems in CFBC, AFBC, FBC, Manual fired boilers, by correction of bed thickness & air pressure.

Lowering O2% while using a Fuel Additive
Some Fuel Additive formulations have O2 releasing compounds, which release O2 or nascent Oxygen. The density of the flue gas is a very important parameter in heat carriage. If the density is higher, it carries more heat & vice versa.

When O2 is reduced due to Fuel Additive usage, the results may be good for Indirect Method assessment, which shows increase in Efficiency, however the reaction conditions will take a good beating, along with flue gas density.

Many times, reducing O2%, only will cause increase in fuel consumption & lower Direct Method Efficiency.

Where there is measurement of fuel, the activity of lowering O2% can be discarded, as the effect of increased consumption can be noticed.

However where is no measurement of fuel or the installation follows Indirect Method, the real effect cannot be known till very long time, as there is no counter check or verification.

Do Fuel Additives reduce fuel consumption ?
If there is LOI, due to deficient air velocity operations, Yes to an extent of 0.2 to 1%, as per the scale of LOI occurrence.
In all other cases, they have no effect

Fuel Additives are Combustion Catalysts ?
The Combustion reaction itself, happens very quickly. Catalyzing already an over speeding reaction only worsens the case. 
When already the combustion is suffering, employing a catalyst, only increases the suffering.

Will increased reactivity improve the combustion ?
Yes. Only in 3T condition. A Fuel Additive cannot produce a 3T condition.
3T condition is a physical reaction environment condition produced by fans, WBP & fuel

IS CATALYSIS OF COMBUSTION REACTION REQUIRED ?
Not at all. Only correction of reaction conditions is required, which takes care of every thing.

How to eliminate Fuel Additives usage

Fuel Additives are only needed when there are incorrect Boiler operation which cause deficient air or flue gas velocity. 

Deficient air velocity correction or boiler switching to 3T operations, eliminate usage of Fuel Additives, once & for all.

In 3T condition,
1. the air velocity is exact, therefore raising the reaction efficiency of Carbon & oxygen
2. high reaction efficiency conditions or environment exists, the LOI is automatically near zero
3. the air pressure is right, the clinker formation also gets eliminated

Fuel Additives are not needed, however become compulsive due to improper operational issues.

The above information is for solid fuel fired boilers.

For Oil fired & Gas fired Boilers
Turbulence correction or 3T operation, eliminates all the combustion issues


Any comments write to sap@chargewave.in

SAP

Power Plants CO2 emissions -- Challenges & Opportunities

In the present moment, the CO2 emissions are taking center stage in every discussion. What are the challenges & opportunities ?

Challenges : As the power demand is ever increasing, so are the CO2 emissions as most of the plants are either coal or biomass based ones

What are the opportunities for CO2 reduction ?
Is the CO2 capture alone the solution ?
Are there any other options ?

While CO2 capture is expensive to invest, the cheapest alternative is to employ the 3T (time, turbulence, temperature) equilibrium condition in Boiler Operations.

What 3T can achieve is much bigger as an immediate alternative, as it brings down the Boudouard Reaction to within the theoretical limits and the fuel consumption itself is reduced.

While the CO2 emission is directly proportional to the fuel employed per ton of Steam, when the fuel consumption itself lowers, the CO2 gets lowered too.

We also manufacture chemicals, which can block Boudouard Reaction & lower the fuel consumption.

Together 3T + chemicals the is maximum reduction option at hand.

The biggest challenge is not measuring the fuel or its GCV and the employment of Indirect Method.

Unless the Indirect Method is debated, unshackled, understood & restructured, the possibility of CO2 emissions reduction is remote.

Any queries ?

You can contact me at sap@chargewave.in

SAP

Thermal Efficiency & Indirect Method -- Limitations & Opportunities

Thermal Efficiency -- Limitations & Opportunities

Thermal Efficiency, is a term which has to be clearly understood in relationship with Boiler Operations.

What does it indicate ?
1. Boiler is first a carbon & oxygen reactor, where the energy generation is taking place
2. After the energy is generated, it is exchanged throughout the boiler in different thermal zones

So, we can measure two efficiencies based upon 2 different phenomenon

1. Efficiency of the reaction (carbon & oxygen reactor)
2. Efficiency of the heat capture or heat exchange

The Indirect method focusses on Efficiency of heat exchange part and assumes 100% energy is generated from the combustion of fuel.

What is considered in the Indirect Method
Losses from stack, LOI, radiation, blowdown, moisture, Hydrogen etc., so these are the energy losses what the boiler cannot capture.

Where is the energy generation here ??? 
Energy generation has no mention. 100% energy generation is an assumption. 

What is ignored in the Indirect Method

 Reaction conditions created in the furnace by the fans
 Reaction Efficiency of Carbon & oxygen
 Boudouard Reaction (CO2 + C --> 2CO -- 6000 Kcal / Kg) condition assessment
 Actual measurement of energy generated in the reaction

My question is why assume that Energy generated is 100% ?. What is the guarantee that it has been generated & is available ?

If the Boudouard Reaction is higher than the theoretical limit, more heat is consumed in the Endothermic reaction & less is available for heat transfer.
 
If only 85% energy has been generated in the furnace, then 85% minus losses will be the Thermal Efficiency.

Can the formula be modified to Heat generated minus Losses = Thermal Efficiency ? to include what they have forgotten ?

CO2 is measured & assumed that it is formed by C + O2 reaction only, where as there are two routes for CO2 formation, one directly by C + O2 reaction & another by 2CO + O2 reaction.

The question is how heat capture efficiency can explain heat generation as an assumption, when there are two distinct processes happening.

Is heat absorption more critical than its generation ?
Is the reaction condition not at all important ?
Is the heat generation so simple and easy that it could be assumed to be 100% always ?


Questions ?
I was asked at one of the presentations, that the Indirect Method is the only reliable method to assess the Thermal Efficiency ?

I replied, how the boiler designer would assess the efficiency on the drawing board or at the designing stage ?
Is the Indirect Method assessment the only way after commissioning of the Boiler, for derivation ?
How the designer would know, the efficiency at the design stage ?
Is there another possibility or processes of derivation ?

In fact, the Boiler has to have the necessary combustion air + excess air. How do we assess this ? In the boiler if you reduce excess air, combustion air is also reduced, & when it happens it promotes Boudouard Reaction.

Higher Thermal Efficiency by design is a factor of excess air, lower the excess air, higher is the heat capture, this is an offshoot of heat exchanger.

Does higher Thermal Efficiency mean the reaction efficiency is high enough ? Not at all.

There are 27 different or distinct ways or methods, a boiler can be operated, in which only 1 method aligns the 3T's & the rest do not.


Interesting facts about Indirect Method
1. Even if the load of the boiler is 10% or 20% or < 60% or 100% the Efficiency is always higher than 82% plus & does not change
2. Design Efficiency of the boiler can be exceeded in this method ?
    Several commissioning reports of boiler installations & also in Energy Audit reports, this is observed, is this true ?
3. Can the boiler function higher than its design efficiency ?
4. 100% energy generation is assumed in 100 minus losses formula
5. Fuel, GCV of fuel can be back calculated without consideration to reaction efficiency, actual fuel GCV or actual fuel quantity fired
6. Time, turbulence & temperature equilibrium present or absent, it has no effect on heat generation
7. In precise measurement of fuel, fuel GCV, the Thermal Efficiency is always greater than Direct Method Boiler Efficiency
8. In all the 27 types of Boiler operations, the Indirect Method shows similar values
9. Lesser Direct Method Efficiency does not raise the stack temperature or other losses (again indicating it is a measurement of heat exchange capacity)
10. Fuel density, furnace draft, operating loads etc. have no impact on the Efficiency

Is the Indirect Method so efficient ?
1) does it mean that there is no need to use Bomb Calorimeters, fuel measurement systems, Boiler instrumentation ? Is the design enough ?
2) does it mean that it has all solutions for combustion problems ?
3) does it mean following the Indirect Method has no validation system vis-a-vis measurement of fuel & its CV


Why is the Indirect Method followed ?
1) Heat exchange capacity of the Boiler does not change & very stable
2) It is easy to report & measure
3) Everyone says it is scientific so, it has to be
4) Everyone follows it
5) No one asks for validation, includes Managements, Auditors, Operators
6) Method is recommended by OEM's & Auditors
7) Fuel quantification & its CV have lot of variations, is cumbersome which justifies not validating it & hence forth skipped altogether
8) Reason no. 7 justified & supported by OEM's, Auditors & others irrespectively 

It is a fact that in 98% of the installations, the Indirect Method cannot be validated in the input fuel or its CV, as the boilers function at much lower efficiency than what is factually reported. Observations show that the fuel quantities & its CV's are tailored when Efficiencies are low.

If the Indirect Method cannot be validated in the input fuel or its CV, why do we follow it in the first place ?


Fuel can be measured precisely by weight by bunker weighing systems instead of belt weighing systems which have errors, stacking fuel in separate identifiable lots, will resolve fuel measurement. Frequent sampling from feeders & increasing no. of samples, will lower the error in the CV measurement.

A bold, factual assessment will reveal all the short comings of the Indirect Method, open opportunities for correction & cost savings.

The reverse ash reconciliation method also can be employed, to calculate the coal input. There are options for measurement, however they have to exercised.

Its time, there is a thorough review of this method, which does not allow actual heat generation assessment in the Boiler & change the operations which support the 3T condition.

What if the the formula is changed to

"Heat generated minus Losses = Thermal Efficiency %"

Heat generated = Fuel Quantity x Fuel CV
Losses = The same as in the Indirect Method

A MAGIC WILL UNFOLD WITH LOT OF OPPORTUNITY 

Opportunity to see a great magic in the above formula, as the heat generated can be increased by invoking the 3T equilibrium. I have already done this in many boilers. There is a great cost saving when you adopt the above change.

It is not all that difficult, it is the first step to Boiler Operation mastery.

Start the step for fuel measurement & the guarantee is that you can save a min. of 4 to 5% fuel in this method. The average saving I got is > 8% till date, only by tuning the boilers for 3T.

If you have questions, please write to sap@chargewave.in

Regards
SAP

TurCom Software -- Run Highest Boiler Efficiency in Direct Method

TurCom Software

Welcome to the world of Boiler Operations.

Introduction : There are 27 distinct Boiler Operation combinations that can be derived from

1) One PA or FD fan, One SA fan & Wind Box Pressure, for CFBC Boilers
2) One PA fan, One FD fan & Wind Box Pressure, for AFBC Boilers
3) One FD fan, One SA fan & Wind Box Pressure, for FBC Boilers
4) One FD fan, One SA fan & Wind Box Pressure, for Stoker Boilers

PA fan can be operated as PA Exact, PA High, PA Low
FD fan can be operated as FD Exact, FD High, FD Low
SA fan can be operated as SA Exact, SA High, SA Low
WBP can be operated as WB Exact, WB High, WB Low

Only one combination PA Exact, FD Exact, SA Exact & WB Exact is the right combination, in consideration to the input fuel density & this combination produces, the 3T (time, turbulence & temperature) alignment.

All other combinations do not align the 3T's. Most of the other combinations either produce excess air or flue gas velocity or deficient flue gas velocity.

Only in 3T condition the following results are possible
1) Highest Efficiency in the Direct Method
2) Lowest LOI
3) High reaction efficiency of Carbon & Oxygen
4) Real or true excess air in the stack
5) Lowest consumption of Coal or biomass
6) No adjustments needed for Coal or Biomass CV or their quantities to match the Indirect Method Efficiency
7) Very low erosion for FBC, AFBC & CFBC boilers
8) Perfect air & flue gas velocities
9) All thermal zones take their place (no zone shifts)

Do the DCS or any other software which is available today, measure the 3T's ?

No.They dont. The DCS's today are offer more functional control rather than give a picture of what's right or not in the system.

The 3T's has been a Boiler operation concept for very long time, many times heard in lectures & never ever in operational experience or assessments.

TurCom, gives you that strength of 3T alignment, what is missing out in the entire Boiler operation & knowledge spectrum.

TurCom Introduction : TurCom is a software which calculates the 3T's alignment or misalignment & then guides the operator for adjusting the fans & WBP to deliver the objectives.

Advantages of TurCom :
1) No learning curve or experienced operators required for operations
2) Boiler is very stable
3) Lowest LOI
4) Operation flexibility of fuels
5) High Efficiency in the Direct Method
6) Low erosion as excess or deficient air or flue gas velocities are corrected
7) Straight advisory
8) Lowest costs in energy as every calorie the fuel offers is extracted

TurCom is available as 3 options
a) Consultancy
b) Software Installation
c) Software Installation + proof of performance

If you have any questions, please write to sap@chargewave.in


PS Anand Prakash

O2 in Stack, True or False value ?

Oxygen Measured in Boiler Stacks -- Is the captured value true or false ?

Consider the Reaction C + O2 --> CO2, the following conditions are available in the furnace

Condition     Carbon         Oxygen          Carbondioxide      Reaction

       1             Reactive          Reactive           100% probability      Successful

       2             Reactive          Non-reactive     0% probability         Fail

       3             Non-reactive   Reactive            0% probability         Fail

       4             Non-reactive   Non-reactive     0% probability         Fail

In the boiler furnace only 25% probability exists for a successful carbon & oxygen reaction.

What if conditions 2, 3 & 4 are present in the furnace, then the following is probable

a) Carbon showing up as LOI
b) Reaction failure O2 shows up as a component of excess air

Hence the indication of O2% in stack, may not be true if the reaction conditions are not examined & also if LOI is present.If LOI is present, the fact is that there is reaction failure O2 showing up as excess air.

So, what is excess air now ?. True excess air is obtained only when the LOI is near zero, till then it is only a mixture of excess air + reaction failure O2.

How do we achieve true excess air ?
Can be achieved by synchronizing 3T's, time, turbulence & temperature.
In 3T alignment, the reaction condition 1, prevails.

There are 27 types of Boiler Operation combinations considering
1) PA or FD Fan, SA Fan & WBP for CFBC boilers
2) PA Fan, FD Fan & WBP for AFBC boilers
3) FD Fan, SA Fan & Bed thickness for Stoker boilers
4) PA Fan, FD Fan & WBP for PF boilers

In 26 Boiler operation combinations conditions, improper reaction conditions reign & reaction failure O2 shows up as excess air.

How to recognize, that the O2% indication is true excess air ?
If 
         1. LOI is near zero for CFB & PF boilers
         2. LOI is < 2% for AFBC & FBC boilers
         3. LOI is < 4% for Stoker Boilers
         4. Direct Method efficiency is 1.5% to 2% less than Indirect Method Efficiency
         5. No adjustments made for CV of coal, Coal quantity or Steam quantity & real data has been considered
         6. 3T's are in alignment

If you have any questions on the same, write to me at sap@chargewave.in

Thanks for reading

PS Anand Prakash

Boiler Automation Equipment to run the FBC, AFBC, CFBC Boilers Efficiently in Direct Method

After years of solving combustion related problems in FBC, AFBC & CFBC boilers, I have developed an algorithm to calculate required turbulence for given boiler design & operating fuel.

Turbulence in the boiler is the key vertice in the triangle of Turbulence -- Time & Temperature.

It is the turbulence which controls rate of reaction of C & O2, & responsible for Reaction Efficiency of C & O2.

If turbulence is high, it leads to unburnt fuel being shot out of the bed, incorrect reaction efficiency, higher fuel consumption, higher Boudouard reaction, incorrect draft.

If turbulence is low, it leads to unburnt carbon being generated in the bed, incorrect reaction efficiency, higher fuel consumption, higher Boudouard reaction, adjusted draft.

Detailed analysis of turbulence conditions show that the boiler can be operated in 27 turbulence combinations.

Out of the above combination 26 attribute to incorrect operation contributed by increased or reduced fuel density, bed height, bed density, incorrect fans settings, furnace draft  & only 1 combination corresponds to the right operation of the boiler.

This means the boiler can be operated incorrectly in 26 ways & it can never be realized unless the last option is exercised which is the correct one.

Trial & errors can be eliminated directly with an equipment which can provide guidance in setting right the turbulence in the system.

The system which is being run following the Indirect method of Boiler Efficiency often fall into the trap of these 26 incorrect ways, since the Indirect Method is incapable of detecting operational probabilities.

If interested the equipment is available as a stand alone Automation System, or Add on to an existing operation system, which on command can take over the operation & set it perfectly.

For an Add On system, this equipment requires entire boiler design data & will capture the operational data from the DCS & then advise the operators to correct the operations.

Any inquiries can be sent to sap@chargewave.in or sashank@exaact.co

Excess air consideration in FBC / AFBC & CFBC boilers

Excess air consideration in combustion for FBC / AFBC & CFBC boilers

My View

In FBC, AFBC, CFBC boilers the excess air is measured in the stack & often considered as excess air which can take care of proper combustion.

However based on my experiences in working with these boilers, the excess air determination has to be based on other assessments also along with Stack O2% for arriving to true excess air.

Methods for determining excess air

I) By given free O2 % value of the Boiler manufacturer
II) By calculation
III) By measurement 

I Value by Boiler Manufacturer

The free O2 % value for the stack given by the Boiler manufacturer is actually the design value by considering many parameters of fuel, air, excess air, flue gas velocity, thermal capture efficiency of the system etc.

II How does one calculate excess air :

After several studies upon boiler design, I present you with a simple formula which can help in calculating the free O2 % as per design

Free O2 % in Stack = ((100 / DE) -- 1) * 21.53 %

Here
DE is Design Efficiency of the Boiler
21.53 is a constant for O2 volume with 5% error (20.5*1.05)

The error of 5% is standard considering the ducts, air leakages etc.

For example for a 82% efficiency boiler by design, the free O2 can be calculated as

Free O2 = (100/82 -- 1) * 21.53 % = 4.73 %

Excess Air Calculation = Free O2 by Design / 20.5 * 100

Excess air = 4.73 / 20.5 * 100 = 23.05%

Inference 

1) The Boiler design efficiency is always a factor of excess air. Lesser the excess air, higher will be efficiency gain by design as per the above formula
(However the opposite is not true, if the excess air is reduced than design value, it does not increase efficiency but decreases it due to CO2 + C, reaction)

2) This also means that if free O2 is exceeded than design value, the extra volume of air removes the heat from the system & should lead to loss in efficiency

3) Achieving Design free O2% in the stack, means achieving design draft, design flue gas velocity, design air injection velocity, design turbulence & designed reactivity of C & O2 in the combustion chamber

4) Not achieving Design free O2 %, means the opposite

5) This also means that if free O2 is less than Design free O2 %, then draft will be compromised, flue gas velocity, air injection velocity, turbulence, designed reactivity of C & O2 in the combustion chamber are compromised

6) Running the boiler in Lesser than design O2 % is not a correct operation as it leads to lesser efficiency when checked in the Direct Method

My Experience :

1 % excess O2 (5% excess air) is increasing heat flight from the system approximately lowering the efficiency by 3.5 to 4% by Direct Method

1 % deficient O2 (5% deficient air) is increasing CO2 + C endothermic reaction in the system approximately lowering the efficiency by 3.5 to 4% by Direct Method

Which fan is giving excess air, when there are two or more fans ?

This has been my persistent question to many boiler users

I could deduce the following from my experience in working with the boilers

1) Boiler with PA fan & FD Fan
     a) The PA fan is giving maximum excess air in the boiler
     b) The FD fan is giving combustion air in the boiler with bare minimum excess air
     c) The PA fan air volume is approx. 15 to 18% which is of higher velocity & the balance air is from FD fan which is of lower velocity

2) Boiler with PA fan,  FD Fan & SA Fan

     a) The PA fan is giving maximum excess air in the boiler
     b) The FD fan is giving combustion air in the boiler
     c) The SA fan is giving minimum excess air in the boiler
     d) The PA fan air volume is approx. 15 to 18% which is of higher velocity & in the balance 82% to 85% air, the FD fan gives 82 to 85% & balance goes to SA fan

3) Boiler with FD Fan & SA Fan

     a) The FD fan is giving maximum excess air in the boiler
     b) The SA fan air volume is approx. 18% & the balance air is from FD fan

4) Boiler with FD fan only
 
     Excess air + Combustion air is given by FD fan

The above are average values & may vary by 1% to 3% as per boiler manufacturer.

PA Fan role : PA fan role is to ensure fuel feed + bed expansion is fully achieved + excess air in combustion due to its high pressure & velocity

Critical parameters in design :

Criticality about fuel density :
1) The PA fan's design is basically to drive a particular weight of the fuel as per its density
2) If the density increases due to either higher moisture content or higher fuel ash content in the fuel, the PA fan fails to deliver the fuel quantity per hour
3) Like wise if the density decreases either due to lower moisture content or lower fuel ash content in the fuel, the PA fan starts pushing excess fuel into the system

Criticality about Air Injection velocity into the fluidizing bed :
As the operating fans inject fuel & combustion air into the fluidizing bed, the air injection velocity plays a major role in determining turbulence in the system

Higher air injection velocity increases fuel flight from the system & the fly ash will contain unburnt fuel & the ash test will respond to VM% presence

Lower air injection velocity will lower turbulence & affect the C, O2 reaction increasing CO2 + C reaction & also unburnt carbon in the fly ash, the fly ash test will not or negligibly respond to VM test

Criticality about WBP :
WBP should be decided as per fuel density, base value from design & not by standard operation

Criticality about furnace draft or air resistance by fluidizing bed :
The PA air & FD air entering into the bed loses its velocity due to bed resistance & also suffers expansion in volume due to heat pick up upon conversion to flue gas.
The draft is the value obtained after both the above processes.
If the bed air resistance decreases, the flue gas velocity increases & causes flight of fuel particle & vice versa.

Achieving design Furnace draft is automatic if the right PA, FD, WBP are under operation.

Lower draft operation becomes necessary if the air injection velocity becomes higher than required.

Design flexibility for fuel, air, fans, operational parameters
As per my observation the design flexibility (after trouble shooting several FBC / AFBC boilers & careful calculations) is around + 3 to 4% at maximum


Question : If the boiler has been designed for 82%, can it be run at 89% efficiency by lowering free O2 in the stack

No. For solid fuel boilers atleast, it is not possible to achieve as portrayed above. Lowering the Air will increase CO2 + C, Boudouard reaction & will lower the Efficiency by Direct Method & wholly defeat the purpose.

It is advisable to run only on recommended O2 as per design.

Question : Whether the boiler design can include operation with number of fuels whose density is highly variable ?

In my experience, the boiler may be designed either at minimum fuel density or at mean or extreme fuel density with slight flexibility in density. It cannot be designed for all densities, viz., the air injection velocity will vary according to the fuel density & cannot be constant for all types of fuels.

Means that the boiler cannot be designed for either Husk & Coal, it can be one fuel as the density variation is too extreme.

The reason is PA or FD pressure has to change with the fuel density & its input volume.

How does one determine the right quantity or volume of air is being fed ?

As the knowledge of CO2 + C, Boudouard Reaction happening in oxyrich conditions is now a reality, it is important to give sufficient turbulence & bring back the C in the CO2 + C reaction to combustion.

I have developed the software which can perform this feature, for all sorts of operational loads.

III  By Measurement :

Measurement of free O2 % by O2 detector in the stack. However the value represented may not be factual as per the combustion reactions.

For example : When air volume is lesser, the CO2 + C reaction increases which consumes lesser oxygen than required, hence the free O2 will start showing an increase. I have checked this in few cases & found it to be correct

Case 1:
In a 100 TPH AFBC boiler the free O2 was showing drifting value of 4.9 to 6% & by Direct Method was working at 73 to 75% efficiency. However the Indirect Method showed an efficiency of 82.5%

After necessary calculations, I asked for an increase of 23 to 25% air volume to lower the CO2 + C reaction. This volume increase is equivalent to 5% O2.

The Boiler Incharge said that the free O2 will increase to 9.5 to 10% as already enough free O2 was indicated, but I insisted that free O2 would decrease as CO2 + C reaction consumes lesser O2 than C + O2 reaction & once proper turbulence could be created, the C + O2 reaction would increase & free O2 would decrease.

Upon increasing the air volume by 23% which was visible in the DCS, the free O2 started dropping & came to 4.1 to 4.2% stable.

Case 2:
In a 10 TPH, AFBC boiler similar situation existed, due to lower air volume. The same mantra was followed & the free O2 decreased from 7% to 4.3 to 4.5% when the air was increased by 25%

Case 3:
A 35 TPH AFBC boiler was operated at 3.1% O2 by controlling air volume. When excessive air control is made there will be more CO2 + C reaction happening & free O2 will drop down.

As per design the Free O2 was to be run at 6.8%, for 76% efficiency boiler. Here the Direct Method efficiency showed that the boiler was operating around 63 to 65% & the indirect method showed an efficiency of 84%.

Correction was made & air volume was increased by 35 to 40% & the free O2 increased from 3.1% to 6.5% -- 7%.

The efficiency of the boiler gained & the fuel consumption dropped by more than 10% in the above case.

NOTE : The % air increase can be deduced upon detecting the Boiler Efficiency by Direct Method & cannot be detected in the Indirect Method. % Air increase may vary upon case to case basis.

There are many examples where this correction gave a clear indication that CO2 + C reaction is occurring for low air volume systems.

Excess Air Conclusion for FBC / AFBC / CFBC boilers :
1) Run the boiler at excess air as per boiler design & not by excess air control
2) Calculate the excess air & ensure proper PA, FD, SA settings, furnace draft
3) Calculate the WBP required as per fuel density
4) Check what is the design fuel density considered
5) Achieve proper turbulence to avoid fuel over flow or unburnt carbon overflow in the fly ash
6) Do not depend upon measurement values & use necessary logic to deduce the actual excess air conditions vs. reaction condition in the furnace
7) Air volume has to be in sync with the load & fuel characteristics factors of the boiler

For any views on the subject, email me at sap@chargewave.in & visit our website www.chargewave.in

Regards
PS Anand Prakash

Tricks for lowering tube failures in FBC, AFBC boilers

Tricks for lowering tube failures in FBC, AFBC boilers

My Experience & view

Boiler not yet delivered : 

Go in for bigger steam drum size, which should be 50 to 60% of boiler capacity

Boiler already running :

Now the case becomes complicated.

In many installations, the boiler drum size is small which has major implication on the tube life as follows

Low Boiler Drum size creates the following condition

1) Low natural water re-circulation rates

2) Increased exposure of tubes to thermal stress

3) Tube surfaces receive more heat & become red hot & soft

4) Increased erosion due to point no. 3

5) Increased erosion due to increased recirculation rate of the bed material

What is bed material recirculation rate :

Imagine a coin which is flipped in air for HEADS or TAILS. Similar way for FBC & AFBC the fuel particle & bed material particle is flipped.

The maximum average height the bed material has to reach is called Bed Expansion Height

When due to low PA or low FD or high WBP or due to high bed material density, the bed expansion height reduces, it is known as a condition which promotes increased bed material recirculation.

Consider this

When bed material reaches a particular height it takes time & then returns back to same starting position & then again returns to the expanded height earlier

One cycle where it starts & ends at the same point is called recirculation & time take is the recirculation time

Now recirculation is inversely proportional to the time i.e. more the time, lesser the recirculation & vice versa

When bed expansion is lesser the recirculation rate increases & bed expansion is more the recirculation rate decreases

Heat retention in the bed is also directly proportional to recirculation rate, i.e. heat retention increases which higher recirculation rates & reduces with lower recirculation rates due to heat trapping

Tube failures occurrence the causes :

1) KEY or 90% reason is tube surface gets more heated due to smaller drum sizes, low drum level or low water recirculation rate

2) balance is increased recirculation rate of the bed which increases erosion

How to know, whether the current settings are increasing the bed recirculation ?

If the bed material density is over & above the stipulated value of 1000 to 1100 grams per liter then bed recirculation rate has increased

Higher bed recirculation increases mutual bed particle friction leading to increase in density

How to avoid tube failures :

1) Change smaller drum size to bigger drum size if possible

2) Run drum level at 70 or 75%, there will be no water hammering (explained in Steam dryness blog)

3) Set the right conditions for bed expansion by proper setting of PA, FD, SA, WBP etc.

4) Check drained bed density values frequently, once in a day

5) Avoid bed over draining

6) Drain the bed when the level reaches 20 mm above the set point & stop the drain at the set point

For example : WBP is say 500 mmwc, then Start drain at 520 mmwc & Stop draining at 500 mmwc

7) Operate at design furnace draft to keep the exact heat retention time by design (lower furnace draft increases retention time & therefore the thermal stress on tubes)

Results :

I have changed several boiler operations & reset the PA, FD, WBP, draft & drum levels, viz., all the above 

The result is there are no tube failures in AFBC or FBC boilers for over 5 years now & tubes display excellent characteristics to last another 3 years

The tube life has increased even in tubes which are not studded

The trick is to ensure to take care that tubes do not get thermally stressed due to excess heat retention in the bed, low bed expansion & low water recirculation rates, low drum levels.

Wish you happy increase in tube life

for any questions please contact me at

sap@chargewave.in

PS Anand Prakash

Director Technical

Chargewave Energykem Pvt. Ltd.

The SECRET is OUT regarding Fuel GCV

The SECRET is OUT regarding Fuel GCV

The Institute of Combustion & Power Plant Technology research upon Carbon Combustion confirms Boudouard Reaction occurring in Oxyrich & CO2 enriched conditions

Link :http://www.ifk.uni-stuttgart.de/allgemeines/Veroeffentlichungen/Diss2009/DissAl-Makhadmeh.en.html

There are 3 reactions occurring during Combustion

1) C + O2 --> CO2 ( 72% to 78% )

2) CO2 + C --> 2 CO ( 11% to 14% ), The Boudouard Reaction

3) 2 CO + O2 --> 2 CO2 ( 22% to 28% )

Out of the above the 2nd reaction is endothermic & the 3rd reaction releases around 1/4th of the energy released by the 1st reaction

Implications of this research

Energy generation potential is much higher than what has been previously thought, if the 2nd reaction is blocked or stopped from occurring

This reaction is occurring in all conditions where O2 is excessive or CO2 is excessive

The excessive energy available for tapping is around 30%, which is not available due to occurrence of Boudouard Reaction & Less exothermic reactions

The Secret is Out that Fuel GCV is 30% greater if the Boudouard Reaction is blocked

This energy can be extracted by Activiser chemical application, which blocks the Boudouard Reaction.

Visit us at www.chargewave.in

or write to me at sap@chargewave.in

Improving Steam Dryness Factor

Improving Steam Dryness factor

In Boilers the steam dryness constitutes a major milestone which cannot be measured online as no measurement systems are present

We have to buy the argument from the Boiler manufacturers, that the steam is 100% dry due to moisture separator efficiency in the drum

My view

Prologue :

1) In many power plants on identical turbine load the Steam / MW varies between 1% to 7%
2) In process boilers the steam trap losses account to 8% to 14% based on the distance travelled by Steam

The Steam velocity properties are closely associated with its dryness.
Increased dryness makes steam density lower & contributes to higher velocity & vice versa.

Look at the following questions
 
q1) Whether Steam velocity is relative to its enthalpy ? 
q2) Can the Steam velocity be increased for the same enthalpy ?
q3) What are the factors effecting the Steam velocity in the Boiler ? 
q4) Whether Steam is really 100% dry as portrayed ?
q5) What is the proof ?

If the Steam Velocity is relative to its enthalpy then at what dryness factor & if the dryness is reduced what would be the effect on steam properties ?

If the dryness factor varies, then Steam Velocity also should relatively change ?

Does Water pump, drum level, super heaters etc. the entire water circuit has a role to play regarding Steam velocity or it is just an assumed or concurred output ?

How does one come to knowledge instead of assumptions that Steam is Dry & at what % dryness ?

The drum is basically a cylindrically shaped construction with water injecting into it from the water pump, with a steam separator mounted at 80% level or height.

Drum Condition 1
The Drum level say considering average of 50%, the condition would be 

50% space for Steam
50% space for water
The steam separator is placed at 80% height

Water vapour will separate from the steam at the separator & pass through at the outlet

This means there is water vapour up to 25% height of the drum at mean value (space between water & dry steam) which is getting separated by the separator

Consider this,
1) Steam residence time in the drum is more due to 50% occupation of space
2) Water residence time is less due to its occupation of 50% space of the drum, its weight reduced due to decrease in density due to high feed water temperature
3) Water vapour formation is higher since higher residence time of steam will lead to its condensation i.e. increase its wetness

Drum Condition 2
The Drum level say considering average of 40%, the condition would be 

60% space for Steam
40% space for water
The steam separator is placed at 80% height

Water vapour will separate from the steam at the separator & pass through at the outlet

This means there is water vapour up to 35% height of the drum (space between water & dry steam) at mean value which is getting separated by the separator

Consider this,
1) Steam residence time in the drum is more than condition 1 due to 60% occupation of space

2) Water residence time is less due to its occupation of 40% space of the drum, its weight reduced due to decrease in density due to high feed water temperature
3) Water vapour formation is higher since higher residence time of steam will lead to its condensation i.e. increase its wetness
4) If Steam condensation increases due to not drawing the steam or any other reason, boiler stoppage etc., the steam residence time will further increase increasing the water vapour & water temperature & the possibility exists that all water, steam will convert into water vapour leading to water hammering

Drum Condition 3
The Drum level say considering average of 75%, the condition would be 

25% space for Steam
75% space for water
The steam separator is placed at 80% height

Water vapour will separate from the steam at the separator & pass through at the outlet

This means there is water vapour up to 5% height of the drum at mean value which is getting separated by the separator

Consider this,
1) Steam residence time in the drum is less due to 25% occupation of space

2) Water residence time is more due to its occupation of 75% space of the drum, its weight reduced due to decrease in density due to high feed water temperature
3) Water vapour formation is lesser since lesser residence time of steam will lead to its negligible condensation i.e. increase its dryness


Let us look into the physical equilibrium condition that exists in the Steam or water drum

Steam, Water Vapor & Water are all H2O, the same chemical substance but in different physical forms, all existing under one roof the Drum.

Equilibrium condition is when all the 3 phases merge into single phase either steam or water vapour or water. 

Of these possibilities, only water vapour possibility exists as the others are not possible to be achieved.

There are 3 conditions for the water drum

Water Quantity + Water vapor  Quantity > Steam Quantity
Water Quantity + Water vapor  Quantity = Steam Quantity
Water Quantity + Water vapor  Quantity < Steam Quantity

The 1st Condition : Water Quantity + Water vapor  Quantity > Steam Quantity
Steam is dry or with higher dryness factor due to its low residence time for condensation

This will improve its velocity & hence forth its kinetic energy driving the turbine
Increased velocity will lead to fewer losses in the steam traps

Equilibrium condition of Steam, Water vapour & water not achievable

The 2nd Condition : Water Quantity + Water vapor  Quantity = Steam Quantity
Steam is less dry or with higher wetness factor due to its increased residence time for condensation

This will decrease its velocity & hence forth its kinetic energy driving the turbine, leading to increased consumption of steam


Decreased velocity will lead to higher losses in the steam traps


Equilibrium condition of Steam, Water vapour & water in critical condition, which means it can swing either way


The 3rd Condition : Water Quantity + Water vapor  Quantity < Steam Quantity
Steam is much less dry or with increased higher wetness factor due to its maximized residence time for condensation

This will lower its velocity & hence forth its kinetic energy driving the turbine, leading to maximized consumption of steam


Lower velocity will lead to maximum losses in the steam traps

If steam condensation is high, then water vapour content will increase due to heat transfer between steam & water & the entire drum content will convert to water vapour, leading to water hammering.


Equilibrium condition of Steam, Water vapour & water is achievable


Now the key question is how to improve Steam Dryness ?

Simple, keep the steam residence time in the drum as mean or as low as possible

Example 1 :

A 6 TPH manual fired boiler was operating at 10.5 kg pressure & drum level of 40 to 50% in water pump auto mode, having reported Steam trap losses ranging from 9% to 12%

Correction was taken in the water level in the drum to run at 73% Max. & 63%. The Steam trap losses lowered by 75%

Example 2 :

A 90 TPH Stoker boiler operating at 65 kg pressure & 450 deg C temperature & drum level 35% to 40%, was having a unique problem that if the Steam load increased to > 50% i.e. 45 TPH, the steam temperature started to increase upto 490 deg C & pressure would drop to 56 kg. The boiler was never loaded to > 50% capacity in over 30 years of its installation

Correction was taken by raising the drum level to 75% & Steam Load achieved up to 100% of the Load, without any raise in Steam temperature or lowering of its pressure


Example 3 :


A 33 TPH with 42 Kg pressure rating, Stoker boiler was delivering Steam max. up to 22 to 27 TPH with 33 Kg pressure operation. The drum level was 40%, when the Steam load would increase, the boiler would tipsy turvy & compromise on pressure leading to higher demand. This problem was present for over 22 years of installation


Correction was taken by raising the drum level to 65% & boiler never had a problem in delivering load or pressure


Example 4 :

A client was complaining that their 8 TPH boiler was always over loaded & was never able to deliver steam properly when steam was in demand. The drum level was operated continuously at 30%

Analysis showed that they had demand of only 3.5 TPH, but the pressure dropped from 10 kg to 4 to 5 kg max. 


Correction was taken by raising the drum level to 75%, the pressure improved to 10 kg & steam demand dropped by 1 TPH for the highest production. The trap losses almost dropped by over 80%


There are scores of such cases, where correction of drum level improved the Generation as well as steam dryness properties.


Example 5 : A 70 TPH AFBC boiler had frequent tube failures & complained excessive erosion of bed coils even though the bed coils were studded


Reason was informed that they maintained very low drum level of 35% to 40% which had to be increased to 70 or 75%


What is happening ?
 
Where the drum level is low the Steam demand as well as steam parameters are unable to be achieved well. Even if achievement was possible, steam was wet & condensation losses also had to be produced increasing steam demand.


Most recent Boiler installations have witnessed reduction in Boiler Drum Sizes which are aggravating the above situation.


Small drum boiler installations are the easiest target for high erosion of tubes.


What are the dangers of small drum sizes, operating in Drum Condition 1 & Drum Condition 2 ?


The small drum size brings alive the situation where the water recirculation rate in the Boiler is low.

In small drum boiler installations the steam consumption per MW is higher & keeps wavering than prescribed values & such installations are more prone to tube failures.


Low water recirculation rate increases the possibilities of heat reception by the tubes & tube surfaces getting overheated & further opening up the possibilities of increased Erosion, Departure from Nucleate Boiling (DNB), leading to early tube failures ? Why ?


When Steel is in hot condition or tube surface is very hot, it becomes very soft & hence very vulnerable to erosion.


Alternatively if the tube surface is cold, it is always strong & has negligible vulnerability to erosion.

In almost all the cases where early tube failures have registered, they all lead to one common observation, low drum level operation or smaller size of the drum.

I myself have suggested many FBC & AFBC boilers to increase the drum level to 75% & operate. The result is they have no tube failures over past 5 to 7 years. 


The trick is to keep the tube surface cold i.e. enable increased water recirculation i.e. water should evacuate the heat & the tube should not be the recipient of the heat.


Increased Steam dryness


Ensure the drum size is large enough to hold 50 to 60% of generating capacity then @ 50% drum level 25 to 30% water will hold weight in the drum.


Operate drum level at 70 or 75% to increase water recirculation rates


Steam consumption will also lower & tube life also will be saved.

Hope you got some answers.

Thank you, for the attention
 
If you have any questions please write to me at  sap@chargewave.in

 

PS Anand Prakash

Director Technical

 

Chargewave Energykem Pvt. Ltd.

Reliability of Direct Method

Boiler Efficiency vs Thermal Efficiency

Direct Method vs. Indirect Method

Which one is reliable ?

My View
I have been researching into Boilers Design & Studying Boiler Design parameters for various types of Boilers viz. Manual Fired Boilers, Stoker Fired Boilers, FBC Boilers, AFBC Boilers, CFBC Boilers & Pulverized Fuel Boilers.

The basic question always remains as which method is more accurate for measuring Thermal Efficiency in a Boiler.

Two methods are available

A) The Direct Method
- Measures Output Energy / Input Energy
- Considers Energy converted is real & the rest are losses
- No losses are measured
- No assumptions, this is a straight method
- Efficiency of the Boiler is Output / Input * 100

Salient Points
* Fuel consumption has to be measured
* Steam output has to be measured
* Steam Temperature, Pressure has to be monitored
* Fuel quality viz., GCV has to be closely monitored
* Bunker Level deviations may be present in the order of 1 to 1.5%
* GCV deviations may be present due change in fuel quality, which will impact the operations
* Boiler Input Excess Air, Furnace temperatures  have to be recorded & have impact on boiler operations
* Furnace draft has to be monitored
* Efficiency depends upon Boiler Design
* Boiler Efficiency practically never reaches the Design Efficiency
* Boiler Design Fuel parameters, Design Excess Air, Design Air Injection Velocity, Design Draft, Design flue gas velocity, Design Reactivity of C, O2 etc. have role to play in Boiler Efficiency
* Efficiency depends upon Operation Steam Load
* Thermal zones play a major role in realizing operating efficiency

Boudouard Reaction Tracking
* CO2 + C, Boudouard Reaction occurrence % can be tracked, whether it is higher or lower than stipulated values

B) The Indirect Method
- Measures the losses from Stack, Specific heat lost in Ash, Blowdown losses, Radiation Loss, Moisture Loss, H2 Loss, LOI losses
- Assumes energy lost is real & the rest has been converted to Steam

Salient Points
* No need to measure fuel consumption
* No need to measure Steam output
* Steam Temperature, Pressure need not be monitored
* Fuel quality viz., GCV need not be monitored
* Bunker Level deviations need not be monitored
* GCV deviations do not have any impact on the system
* Boiler Excess Air, Furnace temperature need not be monitored & have no measurable impact
* Furnace draft has no reference in the method
* Efficiency does not depend upon Boiler Design & only Indirect Method measured parameters depict the Efficiency
* Boiler Efficiency can over reach the Design Efficiency, by control of excess air & LOI
* Boiler Design Fuel parameters, Design Excess Air, Design Air Injection Velocity, Design Draft, Design flue gas velocity, Design Reactivity of C, O2 etc. have no role to play in Thermal Efficiency
* Efficiency is independent of Steam Operation Load
* Thermal zones do not play a major role

Boudouard Reaction Tracking 
* CO2 + C, Boudouard Reaction cannot be tracked

My Experience with Boilers
Having been associated with products which enhance energy generation & absorption above input GCV in Boilers through modification of Reaction Efficiency parameters of C & O2, I have been monitoring the above two methods for over 14 years.

I would like to tell you my experience on the above

THE INDIRECT METHOD IS LESS RELIABLE THAN THE DIRECT METHOD


Example 1 : 20 TPH, imported coal fired AFBC boiler, with Coal GCV as fired of 3100 Kcal / Kg, was taken as a case study

Operating Steam Load of 18 TPH (90% of design TPH) was audited by a reputed company & certified that the Boiler was operating at 81.4% efficiency by the Indirect Method

Direct Method showed the Boiler was working @ 70% Efficiency in no. of tests

Example 2 : A 175 TPH, CFBC boiler was operating at 87% efficiency as per Indirect Method. The Efficiency by Direct Method was 73%

Example 3 : A 100 TPH AFBC boiler was operating at 84% efficiency as per Indirect Method. The Efficiency by Direct Method was 76%

Example 4 : A stoker fired boiler was operating with 81% Efficiency as per Indirect Method. The Efficiency by Direct Method was 56%

Example 5 : A Pulverized Fuel Boiler was operating with 91% Efficiency as per Indirect Method. The Efficiency by Direct Method was 65%

Example 6 : A 25 TPH AFBC boiler was running at 50% load & operation was only in 2 out of 4 compartments. The Indirect Method showed an efficiency of 81.7% & Direct Method showed 52%

There are scores of examples. I had observed that only 1.5 to 2% boilers are under operation where Direct & Indirect Methods closely match with deviation of < 2 to 3%, in all other cases the deviation is average of 8 to 10% & maximum deviation is around 20%.

Question : Why do both the methods show different values ?

The main reason for low efficiency in boilers was traced to improper combustion air pressure, lower furnace draft operation, lower loading of thermal zones, coal ash% deviation from design to operation, coal GCV deviation from design to operation, leakages in air ducts, improper design fuel mix selection by the user leading to increase in Boudouard Reaction.

Till now it has been assumed that there is only one reaction type happening during C, O2 oxidation conditions. Now the new research says the following

There are 3 reactions, not 1
 
1) C + O2 ---> CO2 is 72 to 78% of the total reaction, Exothermic
2) 14 % C equivalent weight of CO2 will react with 14% C equivalent weight to form 28% CO, this is called the Boudouard Reaction, Endothermic
3) 28% CO + O2 ---> 28% CO2, far less Exothermic than the first reaction


Boudouard Reaction is reaction of CO2 + C --> 2 CO, which is endothermic in nature.

Conditions that support this reaction are
1) Operation Air pressure / Air Velocity / Air Quantity / Excess Air / Flue gas velocity / Furnace draft is lower than Design Values
2) Over feeding of fuel
3) Improper settings of PA, FD, SA, WBP
4) Higher bed or furnace temperature operation
5) Mismatch of Operating fuel vs. Design fuel
6) Combustion time variance between operating fuel & design fuel
7) Ignition temperature variation between operating fuel & design fuel

Corrections
Correction can be applied in any Boiler, once the Efficiency is first tracked in the Direct Method. Deviation between Design Efficiency & Efficiency by Direct Method can be narrowed to less than 3.5% by applying corrections in operations, air settings & fuel selection.
I have corrected scores of Boilers, having identified the Working Efficiency &

Design Efficiency, by correction of Air parameters.

Example 1 : A 3 TPH manual fired boiler working at 2.3 TPH & consuming 14 tons of Coal per day. Coal GCV 4200 Kcal / kg @ Efficiency of 53%. Indirect Method Efficiency was around 76%. Here the lower efficiency was due to induced condition where Boudouard Reaction would increase in the furnace due to low FD pressure.
Correction was applied by increasing FD air pressure, by correction of Ducts & Duct dampers
The coal consumption reduced to 11 TPD from 14 Tons with a saving of 30%, with the same GCV.

Example 2 : A 8 TPH FBC boiler working at 5.5 TPH boiler was consuming 41 tons of Coal per day. Coal GCV 3100 Kcal / kg @ Efficiency of 52%. Indirect Method Efficiency was around 76%. Here the lower efficiency was due to induced condition where Boudouard Reaction would increase in the furnace due to low ignition time of the fuel in use vs. ignition time of the fuel by design. (ignition time mismatch)
Correction was applied by keeping all settings constant & only by decreasing FD air pressure & volume by 18%.

The boiler started consuming 25 tons to 26 tons of the same coal by this correction, for the same steam output, saving of more than 25%

Example 3 : In one installation where the FD, PA were identified, to be running lower than Design values & Direct Method efficiency was indicating 75 to 76% & Indirect Method showing 84%, the case was taken up for correction.
Having identified that Boudouard Reaction has increased due to the settings, I had asked for increasing 20 to 25% air by FD & PA, by volume. The free O2 started to decrease from 6 to 7% to 4.2 to 4.3%.

The coal feeder RPM's started to decrease by 8 to 10% lowering the coal consumption.

I have scores of these examples, where fuel saving was achieved by studying Design vs. Operation parameter deviation & conducting efficiency tests by Direct Method.

Direct Method Advantages over Indirect Method
Boudouard Reaction over flow can be identified
Air corrections can be applied by pressure or volume or both
Actual deviating condition can be easily identifed
Correction is straight & simple
Fuel saving is achievable than current values & even in indications of Highest Thermal Efficiency

Software
With all the experience & solutions I could conclude that DIRECT METHOD GIVES ADDITIONAL SCOPE FOR OPERATIONAL PARAMETERS CORRECTION & TO LOWER FUEL CONSUMPTION FIRST.

I have now developed a software to estimate the deviations & directly deduce the operating efficiency of the Boiler by Direct Method.

The software works with an efficiency of 97 to 98%.

I have corrected many boilers using this software.

You can contact me at sap@chargewave.in

My Advice to Boiler Users

Direct method gives you power & understanding what is wrong with the operation especially the occurrence of Boudouard Reaction which cannot be tracked in the Indirect Method

Fuel Consumption can be saved by 5 to 10% minimum in any type of Boiler when Direct Method is followed & deviations are corrected


Changing the Efficiency method to Direct Method & taking proper corrections itself will save India an annual consumption of 1 to 5 million tons of coal


In many Boiler installations, the GCV or moisture or coal quantity is freely corrected to adjust this aberration of Low Efficiency by Direct Method & High Efficiency by Indirect Method


The facts are visible, so take the step today & seek advice to what to be corrected to save energy

Energy saved is Energy Generated, change the assessment method & see the potential of saving


for more information on Boudouard Reaction, visit this Link from
Institute of Combustion, Stuttgart, Germany


Boudouard Reaction in Oxidation conditions published by Institute of Combustion



Heat Balancing Direct Method vs Indirect Method


When heat balance is conducted between Direct Method Output Energy vs. Input Energy & the Indirect Method, the bet is that over 98% of the cases there will be mismatch & in almost every case Direct Method Efficiency will be less than Indirect Method Efficiency.


Conclusion

Tuning the boiler to really run at high efficiency in Direct Method is a challenge once it becomes known that improper operations can lead to increase in Boudouard Reaction & increased fuel consumption leading to increased Steam generation costs.


Advice through our combustion projection software is available with us, which can project the severity of Boudouard Reaction in a particular operation.


The conclusion is that fuel consumption can be lowered by proper tuning of the Boiler resulting in lower Boudouard Reaction once the Direct Method Efficiency is known.

Fuel saving potential by adopting Direct Method & Boiler tuning
 
Through proper tuning itself, Indian boiler users have an opportunity to save more than 5 to 7 million tons of coal, just by switching the efficiency method & correcting the parameters.
 

Our Scope
 
We manufacture chemicals which severely limit Boudouard Reaction occurrence during combustion returning C to the system & generating GCV over & above the established value
 
Thank you very much for your attention

PS Anand Prakash
Director Technical
Chargewave Energykem Pvt. Ltd.
sap@chargewave.in