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Combined Heat and Power use, Kohler 10RY62?this thread has 33 replies and has been viewed 1852 times


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#11




Re: Combined Heat and Power use, Kohler 10RY62?
I see, makes sense now, what you are trying to do.
If you can measure flow rate of exhaust somehow, and measure temperature of the same, could the heat contained be calculated that way? Then subtraction should give you the heat rejection figure of the radiator. 
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#12




Re: Combined Heat and Power use, Kohler 10RY62?
Birken,
As i initially stated in original post, I know just enough about those calculations "to be dangerous"! That's exactly why the invite to others who may actually know how to calculate those figures confidently and accurately. That's what i need. I AM confident in my ability to apply it properly and knowledgeably. If and when I get the remainder "figuredout" and implemented, I intend to expound on the system here for other's use. This may be a fairly long time out: I'm hoping for this coming summer. In the meantime, I really need the BTUsplit calculations to go forward the way I want/need to go. To recap: Input is 30 CFM (1,800 CFH) of air (@122 oF) + 68 CFH (1.13333 CFM) of propane ((1)C3H8) to yield total system BTU's work (ultimately the 10 KW electrical)+ "waste" BTU's out + (3)CO2 + (4)H2O [as exhaust at 800 oF & 75 CFM (4,500 CFH)]. The last parts of chemistry, temperature, and flow are what the calculations are based upon. I simply don't have enough knowledge or confidence to make those calculations reliably/believable  to my satisfaction for accurate use. Regards, JLB 
#13




Re: Combined Heat and Power use, Kohler 10RY62?
Understood.
Have you also sort of precalculated this from a dollars and cents perspective? Engine water heat recovery = easy and normal materials. Exhaust heat recovery = hard and exotic materials. My hunch is that exhaust heat recovery would not pay back, that it would be very expensive to implement. Thoughts? 
#14




Re: Combined Heat and Power use, Kohler 10RY62?
Birken,
Dollars and Cents makes sense for me as I am totally offgrid: So, no matter what I do to make practical use of the "waste" heat, I am money ahead using existing setup. You may very well be absolutely correct in your assessment of exhaust heat recovery vs materials. But, I need to know the possibilities/split in order to at least determine total BTU's available from the existing coolant system; and, I can't know that without subtracting the exhaust BTU losses in any case. So, I still need accurate calculations of same. As for the proposed exhaust gas heat exchanger, go back and look at what I proposed to use in my initial post. That was chosen for it's material and temperature properties as it MAY survive the proposed application better than plain steel or copper, for instance. Yes, I am aware of the corrosive nature of exhaust gasses; and, of the potential heat stresses involved. Regards, JLB 
#15




Re: Combined Heat and Power use, Kohler 10RY62?
JLB  OK here is a quick and dirty.
The wet manifold drops the exhaust about half way to STP (800 to 460), Dropping it to about 200 degrees will give you another ~18000 BTU/hr. This is your sensible heat recovery. There is about another 13500 BTU/hr latent heat in the water vapor of the exhaust gases but it will be tough getting it all out. This is based on propane being 18% hydrogen and ignoring the humidity of the combustion air. Your heat sink will have to be quite cold to condense it all. This gives you 31500 BTU/hr from the exhaust and by difference 50500 BTU/hr from the coolant. Checking....this gives 68000 BTU/hr total from the exhaust and ~50000 BTU/hr from the coolant. These numbers seem reasonable, although from my experience with stationary diesels they are reversed. My suspicion is that the diesels I am familiar with are all turbocharged units and turbos are very effective at extracting energy from exhaust gases. Remember, all calcs are approx. but should be good enough for your purposes. 
#16




Re: Combined Heat and Power use, Kohler 10RY62?
Larry,
Thanks very much! Adding the known 36,600 BTUH (from the wet exhaust) and the estimated 51,102 BTUH (into the coolant from the engine  82,602 total unknown split  31,500 total exhaust split = 51,102 split to radiator) gives me a workable total of 87,702 BTUH available from the coolant for use as a heat source at 10 KW electrical load. At 100% load (10 KW) the original fuel to electricity conversion efficiency was 19.5%; by using the "waste" heat for space heating, the total fuel efficiency goes up to 50.2% which equals a 257% increase in total fuel efficiency (I get ~21/2 X more value out of it at 100% electrical load)! I'll take that. I'd expect my total fuel efficiency to actually go UP with lower electrical generation (typical residential generation is virtually never at peak load) because at lower electrical loads, the electrical efficiency goes down (to 0 at 0 load at the extreme); but, due to internal engine losses, the fuel used continues to make (reduced) heat. That heat reduction should go down at a rate less than the reduced rate of electrical demand, so overall % of efficiency goes up when using the "waste" heat with reduced electrical load, and total fuel use goes down. Your figures of "leftover" ~18,000 BTUH of sensible exhaust heat do make adding an exhaust gas heat exchanger questionable as to it's valueadded worth. I may still try it for "kicks and giggles", as I already have one "inhand". And, the water vapor latent heat may be practicably unobtainable for my situation. I can now see that. Thanks again, JLB 
#17




Re: Combined Heat and Power use, Kohler 10RY62?
Actually, in rethinking this I believe I made a mistake. I assumed a final exhaust temp of ~200 degrees F. There is another ~18000 BTU/hr of sensible heat in the exhaust that is not recoverable because you are still above 60 degrees F (STP).So, instead of ~50000 BTU/hr going to the coolant it will be more like 32000 BTU/hr. The numbers aren't quite this because of my sloppy calcs, but you get the idea.
800 to 460 gives 36600 BTU/hr. 460 to 200 gives 28000 BTU/hr. 200 to 60 gives 15000 BTU/hr. latent heat gives 13500 BTU/hr. Soooo. 82600  28000  15000  13500 equals 26100 BTU/hr. in the coolant There, that's better. 
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#18




Re: Combined Heat and Power use, Kohler 10RY62?
Larry,
Thanks for the correction. It still gives me good reason to use it! Regards, JLB 
#19




Re: Combined Heat and Power use, Kohler 10RY62?
What effect does cooling the exhaust gas have on combustion byproducts clogging the heat exchanger over time? I could see something like this becoming clogged with soot easily and becoming a maintenance headache. Maybe the LP fueled engine will burn clean enough that this will not be a problem, but curious what real world experience says about this.
Tim 
#20




Re: Combined Heat and Power use, Kohler 10RY62?
Tim,
LP fuel is "the cleanest" of all the carbonbased common fuels out there. Crankcase oil looks almost new when changed at the required hours. From my research, LPG also shows the lowest wear rate on pistons/cyl walls/valves/valve stems/ etc. Almost 10,000 hrs on it now; and, still very minimal crankcase oil useage and no obvious signs of contaminants inside the exhaust system either; so, I expect minimal heatexchanger byproduct accumulation too. Though, if I get it to condense, that may change considerably. I wanted a sparkignited engine so that I could use woodgas as fuel if things went "way south": That'd be an entirely different story, I expect. Hope this answers your question. Regards, JLB 
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