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

[Big Jock]

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...

 

[CWatters]

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.

 

[Jobrag]

The flue gasses cannot leave at a lower temperature than the feed water, is that 100 Deg C a typo?

 

[Big Jock]

Yes Jobrag it was a typo should have been 200 deg C

 

[Chestermiller]

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

 

[Big Jock]

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?

 

[Chestermiller]

Have you learned about heat Q and heat capacity C_p? What kind of course is this? Physics 101 or Thermo?

Chet

 

[Big Jock]

yeah Chet I know about those. Its actually from a heat transfer and combustion task I have been set...

 

[Chestermiller]

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

 

[Big Jock]

Have you an equation for that so I can look through the course work...

 

[Chestermiller]

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

 

[Big Jock]

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

 

[Chestermiller]

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?"

 

[Big Jock]

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...

 

[Chestermiller]

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

 

[CWatters]

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.