3 replies to this topic

[mohammed yussuf]

hi there
am new at this...
but when i do some research i do find very valuable stuff here...

am a chemical engineer student and this is my last course..

we were asked to design a waste heat boiler..
i need some hints and leads on how to design
there are some obstcals that stopped me.

properties of the water that will take the heat.
all i know is:

Edited by mohammed yussuf, 12 July 2011 - 07:11 AM.

[kkala]

I have "edited" your post to make it more legible, since all formatting (B B code) was apparent (so confusing to reader). Please check for omissions, if any.
Comments (underlined or bold) are written at the relevant place of your text, hopefully they can help a bit.
Try for your own design, making assumptions and collecting data. If a point seems unsolved, ask for help in the forum.
May you be successful.

hi there, am new at this...but when i do some research i do find very valuable stuff here...
am a chemical engineer student and this is my last course..we were asked to design a waste heat boiler..
i need some hints and leads on how to design, there are some obstacles that stopped me (properties of the water that will take the heat)... all i know is:

hi irfan, i have a waste heat boiler and the inlet of the hot stream is T= 899.6 oC, P= 1000 unit?, m= 9851 kmol/h, CO : 1082.6 kmol/h, CO2 : 504.15 kmol/h, H2O= 2993.3 kmol/h, H2= 5003 kmol/h, CH3OH= 0 kmol/h, N= 229.56 kmol/h, CH4= 38.31 kmol/h. There is still combustible material in these gases, that has to be burnt, giving more heat to water. However at temperature as high as 899.6 oC, I think there will be uncontrolled burning of it as the gases enter the combustion chamber of the new WHB. There has to be combustion chamber, plus burners of at least intermittent operation in my opinion. But advice on this matter is welcomed, since I do not know the matter, or clarify the point with your teacher. Do not let this combustible material escape through the stack.

T = 48 oC, P= 1000 KPa, the cold (water). So a boiler feed water pump is needed to introduce this water into the steam drum of the boiler (pressure as below).

the outlet is HPS that ranges (2.41-10.34) MPa, so I choose 2.5 MPa that has a 223.95 at saturation point.
It is understood that required steam pressure varies from 2.41 to 10.34 MPa. Boiler should be designed for max steam pressure, i.e. 10.34 Mpa (103.4 Bar). Saturation steam pressure is about 313 oC.
Those are the only information that i got.
Well, this may mean you can chose all rest parameters and justify.

the prof. is very stubborn made me write this
1- objective of designing (identify stream , what type of pressure steam ). Produced steam usually has some superheat (say, at least 30 oC in this case). This also depends on uses of steam generated.
2- types of boilers (when they are used . adv. disadv. -concentrate on horizontal and vertical tubes )- there is a face change. Type can be your choice, start investigation from water tube vertical boiler with steam and mud drum. You can ask advice from Waste heat boiler manufacturers or literature. If you have combustibles to burn, conceptual design may have similarities to a common boiler (but special combustion chamber, bigger convection section of WHB). Make a heat balance to estimate capacity, after settling the issue of unburnt material (see above).
- HTC (?) should be in liq and vap.- boiler drum , we separate vapor from liquid - should be treated - how do we treat it. Boiler drum usually receives oxygen scavenger solution and anti scale solution through metering pumps.
However boiler feed water treatment by ion exchange resins (a unit upstream BFW pumps) is quite significant. Required specification depends on boiler pressure, see http://www.engineeri...its-d_1064.html, http://www.cip.ukcentre.com/steam.htm, or other WEB sources. Boiler water is understood to be the water in steam drum, having same quality as continuous blow down. "Handbook of Industrial Water Conditioning" by BETZ is another source.
my questions : how to get the properties of the water? my main concern is the type and the quality of the water. see above

Note: I have made a few corrections on the text, one day after the original publication.

Edited by kkala, 10 July 2011 - 05:02 AM.

[mohammed yussuf]

ThnQ dear very much
everything is going well right now ...

but my feedwater temperature is around 420 oF
how it is heated uptill this point ?
and why do we heat it ?

[kkala]

The concept of my post of 9th Jul 2011 was: hot stream gases were actually flue gases, eventually going to atmosphere through a stack after burning of their combustible content. Waste Heat Boilers (WHBs) exploiting the heat of flue gases (which do not contain combustibles) are used in combined cycle power plants, and I have met such WHBs in feasibility studies. These are similar to steam boilers, having steam & mud drum and usually economizer; economizer heats boiler feed water by the flue gases (just before they enter stack) to a temperature at least, say, 20 oC lower than that of boiler water (i.e.temperature at steam drum) to avoid boiling in economizer tubes. "At least" indicates that said temperature difference of (say) 20 oC can be much higher (and actually is in met cases). Probably you have considered 420 oF as boiler water temperature. Boiler feed water temperature (upstream economizer and downstream deaerator) is 220 - 290 oF, according to my information.
However mentioned concept may not include all sorts of WHBs. Look at http://www.cheresour...h__1#entry46240. I would consider it as exchanger, but characterization as WHB is also valid. Your teacher most probably means this sort of WHB, just cooling the gases to produce heat. No steam or mud drum, no burning of combustibles, design is simplified. Quality of feed water is expected to be same as before, or stricter seeing that there is no continuous blow down in this case. You have to chose the exchanger type, but I do not have experience on this. Concerning boiler feed water temperature, I would expect 220 - 290 oF (as before), unless process has already available desalinated water of 420 oF (not likely, no mention in the information).
A discussion with your teacher would clarify matters. Sorry for initially having considered a "boiler-type" WHB, neglecting other sorts of WHB.

Edited by kkala, 13 July 2011 - 01:24 AM.