Calculating Steam Production in Fire Tube Boiler | 180ºC Dry Saturated Steam

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Discussion Overview

The discussion revolves around calculating the amount of steam produced in a fire tube boiler using dry saturated steam at 180ºC, based on the cooling of flue gases. Participants explore the necessary equations and concepts related to heat transfer, enthalpy, and energy balance in the context of a heat transfer and combustion task.

Discussion Character

  • Homework-related
  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • One participant expresses confusion about how to start solving the problem, indicating a lack of understanding of the concepts involved.
  • Another participant suggests rearranging the problem statement to identify the source of heat and the heat transfer involved in producing steam.
  • A participant questions the validity of the temperature at which the flue gases leave the boiler, suggesting it may be a typo.
  • There is a discussion about the change in enthalpy of flue gases when cooled from 1500ºC to 200ºC, with a focus on calculating the rate of heat transferred.
  • Some participants inquire about the familiarity of others with heat and heat capacity concepts, indicating varying levels of understanding among participants.
  • One participant mentions that the problem is part of a heat transfer and combustion task, which adds context to the discussion.
  • There are requests for equations related to heat transfer, with some participants expressing frustration over the lack of coverage in their course materials.
  • Suggestions are made to look up relevant information online, including heat capacity and latent heat of vaporization, to aid in understanding the problem.

Areas of Agreement / Disagreement

Participants generally express uncertainty and confusion about the problem, with no consensus on how to proceed. There are multiple competing views regarding the necessary equations and concepts to apply.

Contextual Notes

Some participants mention the energy balance equation, but there is no clear definition or example provided in the discussion. The lack of a textbook and reliance on course notes may limit the understanding of key concepts.

Big Jock
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Homework Statement


Dry saturated steam at a temperature of 180ºC is to be produced in a fire tube boiler from cooling of 50000 kg/h of flue gases from a pressurised combustion process. The gases enter the tubes of the boiler at 1500ºC and leave at 100ºC. The feed water is externally preheated to 180ºC before entering the boiler.
The mean specific heat capacity of the flue gases is 1.15 kJ/kgK. The latent heat of vaporisation of the water at 180ºC is 2015 kJ/kg. Feed water temperature = 180ºC.
Determine the amount of steam produced per hour, if the total heat loss is 10% of the heat available for steam raising.

Don't even know where to begin with this so any advise to get me started would be extremely grateful as I am completely lost at the moment.

Many thanks in advance...
 
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Try rearranging the problem statement...

It describes a source of heat...

"50000 kg/h of flue gases"
"enter the tubes of the boiler at 1500ºC and leave at 100ºC"
"The mean specific heat capacity of the flue gases is 1.15 kJ/kgK."

That's enough information (using a suitably relevant equation) to calculate the amount of heat (per hour) "available for steam raising".

It describes where that heat is going...

"The feed water is externally preheated to 180ºC"
"Dry saturated steam at a temperature of 180ºC is to be produced."
"The latent heat of vaporisation of the water at 180ºC is 2015 kJ/kg"

You can apply that data to [strike]the same[/strike] a similar relevant equation to find the mass (per hour) of steam produced.
 
Last edited:
The flue gasses cannot leave at a lower temperature than the feed water, is that 100 Deg C a typo?
 
Yes Jobrag it was a typo should have been 200 deg C
 
I assume you are familiar with the concept of enthalpy. What is the change in enthalpy of 1 kg of flue gas if you cool it from 1500 C to 200 C? What is the change in enthalpy of 50000 kg of flue gas if you cool it from 1500 C to 200 C? What is the rate of heat transferred (per hour) from the flue gas?

Chet
 
afraid not Chet this is how I'am finding this question extremely difficult. I would imagine once you have a handle on what you stated the question is relatively simple?
 
Have you learned about heat Q and heat capacity Cp? What kind of course is this? Physics 101 or Thermo?

Chet
 
yeah Chet I know about those. Its actually from a heat transfer and combustion task I have been set...
 
Big Jock said:
yeah Chet I know about those. Its actually from a heat transfer and combustion task I have been set...
OK. In that case, how much heat do you have to remove to cool 1 kg of flue gas from 1500 C to 200 C?

Chet
 
  • #10
Have you an equation for that so I can look through the course work...
 
  • #11
Big Jock said:
Have you an equation for that so I can look through the course work...
The idea is for you to look through the course work and find the equation you need. What text are you using? Look up heat capacity in the appendix. Do you realize that you are spending more of your valuable time asking questions than it would take to just look it up in your notes and textbook?

Chet
 
  • #12
Chet trust me this was a last resort. I have spent 3 days 12 hour days reading my course work and this isn't covered at all hence why I need the help.

The tutor is asking if I have ever used the energy balance equation but I have no idea what this even looks like
 
  • #13
Big Jock said:
Chet trust me this was a last resort. I have spent 3 days 12 hour days reading my course work and this isn't covered at all hence why I need the help.

The tutor is asking if I have ever used the energy balance equation but I have no idea what this even looks like
What's the title of your textbook? Have you tried Googling "heat capacity?"
 
  • #14
Don't have a textbook Chet only course notes they have provided. If you could recommend a good book or relevant PDF files I can find online feel free...
 
  • #15
Big Jock said:
Don't have a textbook Chet only course notes they have provided. If you could recommend a good book or relevant PDF files I can find online feel free...
I already suggested that you Google heat capacity. Also, check Amazon for any book on freshman physics.

Chet
 
  • #16
Wikipedia has a lot of info. Make sure you understand the difference between "Heat Capacity" and "Specific Heat Capacity". You will also need to look up and understand "latent heat of vaporisation" for the second part.
 

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