Boiler Output & Efficiency

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fredrosse
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Re: Boiler Output & Efficiency

Post by fredrosse » Sun Oct 19, 2014 3:53 pm

The FAQ subject "Launch Engines - Steam Consumption" will clear up your questions. Yes, steam consumption per horsepower varies very much, depending on the engine, its design, and its operating conditions. The FAQ subjects are close to truth here, although, as stated in these subjects, there will often be machines that perform somewhat better, as well as machines that perform very poorly.

Sometimes people want to publish numbers that are very optimistic, rather than realistic. A steam launch that has an efficiency above 10% would be as rare as hen's teeth. I have been employed conducting performance tests on all kinds of steam machinery for many years, and have learned that many performance claims are just wishful thinking.
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Re: Boiler Output & Efficiency

Post by fredrosse » Fri May 06, 2016 12:56 am

A bit more information relevant to boiler output and its relationship to engine power:

The term "Boiler Horsepower" was originally developed at the Philadelphia Centennial Exhibition in 1876, where the best steam engines of that period were tested. The average steam consumption of those engines (per output horsepower) was determined to be the evaporation of 30 pounds of water per hour, based on feed water at 100 °F, and saturated steam generated at 70 PSIG. This original definition is equivalent to a boiler heat output of 33,485 Btu/hr. Years later in 1884, the ASME (American Society of Mechanical Engineers) re-defined the boiler horsepower as the thermal output equal to the evaporation of 34.5 pounds per hour of water "from and at" 212 °F. This considerably simplified boiler testing, and provided more accurate comparisons of the boilers at that time. This revised definition is equivalent to a boiler heat output of 33,469 Btu/hr. Present industrial practice is to define "Boiler Horsepower" as a boiler thermal output equal to 33,475 Btu/hr, which is very close to the original and revised definitions. Boiler horsepower is still used to measure boiler output for industrial boiler engineering in Australia, New Zealand and the USA.

For the Beckman boiler Mike mentions, with 100,000 BTU per hour steam output, the 1876 ASME standard would be calling this a "3 horsepower boiler". As mentioned previously, better engines, working as compound expansion with higher initial steam pressure, and vacuum exhaust can do considerably better. A simple lawn mower engine converted to steam by an armature would probably do much worse.
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Re: Boiler Output & Efficiency

Post by cyberbadger » Wed Sep 27, 2017 1:10 pm

How does PPH relate to the PPH Maximum Designed Steam Capacity (field 20 on my ASME P-2 FORM) that is stamped on ASME code*stamped boilers?

-CB
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fredrosse
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Re: Boiler Output & Efficiency

Post by fredrosse » Thu Sep 28, 2017 1:56 am

The old "rule of thumb" values for boiler output, 3 PPH per square foot heating surface for firetube boilers, or 6 PPH for watertube boilers is a somewhat crude, yet useful approximation.

The ASME Code for Power Boilers has a somewhat different approach, determining the steam flow in PPH (pounds per hour) with distinction as to the heating surfaces which receive direct radiant heat transfer from the fire, vs. heat transfer surface which does not receive direct radiant heat from the fire. Surfaces which receive direct radiant heat produce more steam (for example, the wet furnace sheet of your firetube boiler) vs the firetube internal heat surface, which "sees" very little radiant heat.

The ASME Code also makes distinction as to the firing method, with less steam production associated with hand firing vs automatic firing. The purpose of the basic PPH stamping on your ASME Code boiler is to determine the size / relief capacity required for the safety valve.
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Re: Boiler Output & Efficiency

Post by cyberbadger » Fri Sep 29, 2017 4:12 pm

fredrosse wrote:The purpose of the basic PPH stamping on your ASME Code boiler is to determine the size / relief capacity required for the safety valve.
Which ends up just being the smallest available valve for most steam launches. Mine is roughly double in capacity. This meets the safety aspect, but it's too big. It's a category not really catered to by the manufacturers. - not enough market to make smaller ones. There maybe an ASME shop that could change the settings, but that costs more then the valve from any shop I've seen.

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