[Stoves] Green Steam Engine

[Kevin]

Dear Crispin

Sadly, many "Boiler and Steam Regulations" are an unfavourable collection of Bureaucracy, Conservatism, and Obsolescence." The cruel fact is that many boilers have exploded in the past killing many people, due to incompetence, poor design, lack of attention, poor controls, etc. 'the Laws of the Day" were made to "plug the holes." A good steam plant is a great way to head building complexes, and only low pressures are needed. Steam Power Cycles typically use the Rankine Cycle, and it demands high temperatures and high pressures for efficiency.Most steam Power Plants operating at below 500 PSIG are considered obsolete. A "Steam power Plant" running on 15 psig steam (2 bar) can generate shaft power, but will be dreadfully inefficient. A 4 bar plant (60 psig) is much better, but still well within the "Dreadful Efficiency Class"

One cruel reality of steam is that it is a great concept, but surprisingly complex in practise. Another cruel reality about steam is that there are a lot of encumbering laws and Regulations associated with it. One can find ways to evade the regulations, and this is OK, until there is an accident. That's when the Boiler Inspector has a Field Day. 

As a General Concept.... "There is no way that one can sensibly generate shaft power with small steam engines, because of dreadful system efficiency. However, there may indeed be sensible "small steam power" generating systems, providing there is a sensible use for low grade waste heat from engine exhaust. For example, a small steam engine system for driving air circulating fans in a Lumber Kiln, or a Greenhouse.

Hot air engines would have approximately the same engine efficiency as would a steam engine having steam entering the engine at a temperature similar to the temperature of the hot air entering the "Hot air engine system."

Best wishes,

Kevin
  ----- Original Message ----- 
  From: Crispin Pemberton-Pigott 
  To: 'Discussion of biomass cooking stoves' 
  Sent: Thursday, May 16, 2013 2:10 AM
  Subject: Re: [Stoves] Green Steam Engine


  Dear Kevin

   

  150 kW is pretty high but 1 bar working pressure to atmospheric is nothing. I felt 4 bars gauge was reasonable. Compressors have to be inspected and certified every year but hardly anyone does. They commonly work to 10 bars. But with steam, that is another kettle of..well, another kettle!

   

  Maybe the best use of low pressure steam is as a heat transport medium to run a heat hot air engine.

   

  Regards

  Crispin

   

   

   

  Dear Crispin

   

  Boiler Inspection regulations differ significantly from area to area. Here is the Standard for Nova Scotia.:

  http://www.gov.ns.ca/just/regulations/regs/tsboiler.htm#TOC2_4

  Anyone considering steam installations should read through it, or the one in effect in their Jurisdictional Area, to appreciate the complexities of steam systems. 

   

  A pressure of 4 bars is about 60 psia, or 45 psig. In Nova Scotia, steam vessels are exempt if their energy output is less than 150 kw, and the relief valve is set at 15 psig (2 bar). See Section 4 (1) (c).

   

  There is a lot of history embedded in such regulations. Our pressure limit may have been set as a result of an accident 100 years ago, when someone was killed when a 30 psig boiler blew up. That is one reason why regulations differ significantly from area to area.

   

  Best wishes,

   

  Kevin 



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