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
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
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