Determining Boiler Capacity from Heating Surface Area 1

[EnergyRat]

Hi There:


I was once told that there is an equivalence between boiler capacity (steaming rate) and the heat exchange surface area. Does anyone know the relationship? I am talking about an older (1972 vintage) D-style watertube steam boiler with a design pressure of 250 psig. The nameplate states that the surface area is 3089 sq ft. The burners I know are oversized, but I am trying to determine by how much they are oversized. I think the surface area is the answer, but I need to convert this area into boiler horsepower, or kW or MMBTU/hr.

Any input much appreciated.

Thanks.

 

[GenB]

hp is calculated by the blr mfr but probably have
400 to 600 hp if you calc 5 sfhs to 8 sfhs per bhp.
newer boilers are squeezed to 5 or 6 sfhs/bhp but older mfrs were calulating 8 to 10 sfhs/bhp
ER

 

[chicopee]

Steam generating capacity can be determined from heating surfaces on a FT boilers but w/WT boilers the steaming capacity determination is a little more complicated because of their constructions.
W/ FT boiler, rule if thumb is 5-7.5 lbm/hr of steam per square ft of heating surface for continuous firing. W/ WT boilers I found it best to use the size of the combustion chambers to determine continous steam production. I dont remember the numbers that I used in the past and I'll dig thru my archive to get you that information in a few days.
I do remember the reference from which I got those numbers and that was Kent"Power" -edition probably dating around the 1940's.
On the other hand ASME power code VI uses the heating surfaces to determine the safety valve relieving capacities of both FT and WT boiler drums and superheaters and that could be a starting point for your information but those values are normally greater than the actual steam production of both boilers.

 

[cymro]

Spirax Sarco has a module on boiler ratings and boiler horsepower in their website learning centre. Block 3, module 3.5 I think. Not too sophisticated but it might be worth a look

 

[chicopee]

Since Your D-type WT boiler has water-cooled metallic walls,the average heat release in the furnace is 30,000 btu/hr per cu.ft. of furnace volume for continuous operation and 60,000 for peak operation per Kent"Power" 12 th Ed. pg 7-75 table 3. At 100% rating, for WT. boilers, steaming rate is 3 1/2 lbs saturated steam per sq.ft of heating surface, however dont us this value since WT boiler will produce steam well over 100% rating.For example,a horizontal WT boiler can generate 15.1 to 22.5 lbs of saturated steam per sq ft of H.S..
Since the only rule of thumb that I know for WT boilers is table 3 mentioned above, I would use that as my starting point to determine steaming rate. Also contact the manufacturer and if he is no longer in business read literature on boilers. You will eventually develop the info that you seek.

 

[MJCronin]

Rat,

How about something really approximate such as comparing outside dimensions to modern D-type boilers ?

In my opinion, if I have a "box" with the same overall dimensions as a newer design, I would call the capacities approximately equal. (this assumes that all D-types have approximately the same efficiency)

http://www.babcock.com/pgg/tt/pdf/E1013155.pdf

(Look at page #4)

MJC