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
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
