Regarding Fired Tube Boiler Design as per ASME Code. 1

[gotothesky]

AS per ASME Code Sec.I,
One of The Requirements for Fired Heater tubesheet is PFT-25.2 as follows.

Any part of the tubesheet that comes between the tube,
furnace, or water‐cooled turnaround chamber, and the
shell [highlight #CC0000]need not be stayed[/highlight] if the greatest distance measured
along a radial line from the inner surface of the shell to the
center point of tangent to any two tube holes or tube hole
and furnace or water‐cooled turnaround chamber on the
shell side of such holes does not exceed 1.5 times the value
of p[highlight #EF2929][/highlight]

See figure. In top section, Normally, Demister should be installed to make a good quality of steam, and Water level should be below the demister. Due to above reasons, it seems difficult to keep 1.5 times the P. In this case, I can install the stays in top section only or all of tubesheet area should be stayed?

Thank you in advance......

Regards,
Moon.

 

[chicopee]

Then remove the top row of tubes, install the demister and the diagonal stays.

 

[chicopee]

Another item I want to point out is that I have never seen a Demister on fire tube boilers only on water boilers primarily those owned by utility companies.

 

[chicopee]

"...only on water boilers..." s/b"... water tube boilers..."

 

[gotothesky]

Thank you for your reply, chicopee.
But, I wound to get the proof for acceptance of installation of Diagonal Stays at Top section only from ASME Code....... Can you provide it????

 

[gotothesky]

I am highly appreciating your kind reply regarding a Demister, chicopee. I note it. I mentioned application of a demister referring to another company practice in Korea. Can you explain why the demister is not applied for a Fired tube boiler? Thank you in advance......

 

[chicopee]

Now if the steam is to be dry, there are superheaters specifically designed for fire tube boilers. Don't forget that the waterline in fire tube boilers has to be, if I remember correctly (double check the power boiler code I) 2" above the top of of the fire tubes.

 

[chicopee]

If you do remove the top row of tubes, you will be required to reduce the maximum firing rate.

 

[gotothesky]

Chicopee, I can't imagine Superheaters for Fired tube boiler.... The arrangement & application of superheaters in Fired Tube Boilers is very difficult. I know Fired Tube boiler produces Saturated Steam only..... If we want to make supersteam with Fired Tube Boiler, I think we have to adopt another heating media from outside. I mean It's very difficult to make supersteam by Fired Heater, itself.
But, Water Tube Boiler can make supersteam.

 

[chicopee]

gotothesky, with fire tube boilers classed as HRT's, you will see superheaters fasthened to the girth of the shell within the furnace.
you will not see superheaters in firetube boilers classed as scotch marine. If you are able to find old boiler books published in the 40's and 50's you may find pictures of them.

 

[MJCronin]

I agree with "gotothesky" ... I cannot imagine a superheater on a fire tube boiler

On a water tube boiler, the superheater tubing is always located directly in the path of the HOTTEST exhaust gasses. This promotes the best supreheat and an economy of design.

On a fire tube boiler, hot combustion gasses are generated low in the boiler.... they then travel back and forth and exit at the top of the shell. Gasses have lost heat as they traverse back and forth across the boiler.

The only realistic place for a superheater would be low in the unit, directly downstream of the burners... with all of the fire tubes above the superheater.

Unlike any fire tube boiler I have ever seen ...


MJCronin
Sr. Process Engineer

 

[gotothesky]

MJCronin,
Yes, It's very difficult by a Fired Tube Boiler to have Superheater.

But, I found out some boiler's manufacturer that apply Super heater for a Fired Tube Boiler.
Super heater is inserted into a Reversing chamber that is refractoryed........
(I see this kind of construction for the first time. The name of Manufacturer is 'BOSCH'.
Intentionally, If they control Temperature with Tube Dia, or Length to make reasonable temperature for Super heater, It seems possible.)

Regards,
S.W.Moon

 

[gotothesky]

What is a Dry Fan? Some manufacturer of Boiler adopts Dry Fan instead of Demister!! Can anyone provide Figure of Dry Fan??