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    Two Men and a Burner (A Midco saga) (9 Posts)

  • MarkS MarkS @ 9:46 PM
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    Two Men and a Burner (A Midco saga)

    Last month JStar came out to help diagnose a hard light-off issue I'd been occasionally experiencing with the Midco burner. Long story short, we ended up rotating the burner head so that the spark rod assembly was on top of the burner, rather than below as supplied from the factory. Once we could watch the spark thru the firebox viewport (couldn't see it when it was underneath the burner), we observed that the spark would jump between the ground rod and the burner mesh. After repositioning and re-gapping the spark rod, we saw good ignition every time. I sent a detailed report to Midco describing our observations and changes, and they agreed with what we'd done. In over 200 firings since, there have been no hard light-offs.

    In August, when Midco replaced the 500 MBH burner head with a 300 MBH version they made up custom for this boiler, stack temps were still running high at 780 degrees at high fire (260 MBH), efficiency was around 72% (78% at low fire 75 MBH), and excess air was 42%. It was pretty clear that a lot of heat was being lost up the stack, but there wasn't much else that could be done to the burner to fix it.

    Today, JStar brought some ideas to try to bring down the stack temperature and increase the efficiency. First he installed some angle iron T baffles between the boiler sections. On the very next firing we saw the stack temperature drop by 100 degrees and the high fire efficiency increase to 78%, with excess air at 34%.

    The Midco has a variable speed blower so there's no other adjustment for combustion air. Joe brought in a HUGE PVC ball valve and attached it to the blower inlet. We tried several valve positions to restrict the combustion air to the blower and took analyzer readings for each. With the valve 5/8ths closed, Joe got excess air down to 11.5% with 81.1% efficiency at low fire, but CO went through the roof. The "sweet spot" seems to be with the valve half closed, with the following readings at low and high fire: stack temp = 575 / 685, excess air = 19 / 26.5, efficiency = 80.6 / 78, CO = 25 / 8. If you're interested, here's a link to all of the combustion results: Combustion Results

    In addition to the combustion analyzer readings, I was also watching the stack temp and steam pressure readings on my control system. With 1 ounce of pressure at the boiler and a constant firing rate, we saw steam pressure increase almost 2/10ths of an ounce when we introduced the 50% combustion air restriction, and half an ounce when 5/8 restricted. At first I thought it was a fluke but the results were repeatable, a clear demonstration of the actual impact changes like this make to system performance. Pretty neat.

    Next Sunday I'll be posting a summary report of the Midco's performance data for October and November.

    And finally, a picture of the reconfigured Midco burner with the combustion air restrictor valve in place. Kids, don't try this at home.
    Homeowner, Royersford PA | 1890 one-pipe steam system | 3009 sf | 3 floors | 14 radiators | Utica SFE5200S boiler
    NEW Midco LNB-250 Modulating Gas Burner | EcoSteam modulating controls | 70 to 300 MBH |
    607 sf EDR connected load | Operating pressure: 0.5 oz/in2
    Four main runs (insulated) totaling 135 ft in length | All Gorton vents on mains & rads |
    A Steam Odyssey | Odyssey 2 | A Steam Enthusiast's Outdoor Reset Control
  • MDNLansing MDNLansing @ 11:26 PM
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    Midco or Not

    I've read all you have to offer on your project. Being that I am embarking on my own controller adventure, would you buy the Midco again, or look to something different? I know your system is far from stock, but I'm interested in knowing if tweaking the Midco is the best way to go, or is there something else you would lean to if you were doing this all over again from scratch?

    So far in small scale tests I am seeing a difference in fuel consumption in round vs flat burners. However, I certainly haven't decided on a style yet. It's a good thing I'm not a kid, casue this is exactly what I'm trying at home. Kudos to you for sharing so much of you're project. It's really helped me a lot so far.
  • MarkS MarkS @ 1:14 AM
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    If I had to do it all over again...

    ... I would ditch the Utica boiler, buy the Midco and put it on a MegaSteam (or the Crown FSZ equivalent). Because I firmly believe that most of the issues we've been working through have more to do with the boiler than the burner. On the Utica, it's a straight shot from the burner 26" up through the sections to the stack. I think the out-of-the-box stack temps and efficiency would be much better and require much less, if any, tweaking with a Midco on a 3-pass boiler like the MegaSteam.

    This all started in 2010 as trying to solve the problem of end-of-cycle short cycling on pressure. I do industrial process control software by day, and knew that the "right" solution was to adjust the burner to maintain an even pressure. Problem was, there weren't burners that could do that in my btu range, until the Midco came along. And so far as I know, there still isn't a commercially available pressure control that's plug-and-play for this. Ah, the joys of adapting 21st century automation to 19th century technology.

    Let me add that I'm neither discouraged nor disappointed by the experiences thus far. No one knew exactly how the burner would perform on this particular boiler. At some point you need to get these units out of the lab and onto real-world systems. Early adopters of any new technology need to expect a few bumps along the way, to smooth the road for those that follow.

    The performance data is telling me it's all worth it.
    Homeowner, Royersford PA | 1890 one-pipe steam system | 3009 sf | 3 floors | 14 radiators | Utica SFE5200S boiler
    NEW Midco LNB-250 Modulating Gas Burner | EcoSteam modulating controls | 70 to 300 MBH |
    607 sf EDR connected load | Operating pressure: 0.5 oz/in2
    Four main runs (insulated) totaling 135 ft in length | All Gorton vents on mains & rads |
    A Steam Odyssey | Odyssey 2 | A Steam Enthusiast's Outdoor Reset Control
  • BobC BobC @ 8:25 AM
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    This is how you really learn

    The empirical engineering that you and Joe are doing is top notch. Changing a single parameter through a range and observing the results gives you firm grip on what is going on inside the beast.

    You can design things to death at a computer or on the drafting board but you never really know how it's going to work till you slap it on a piece of working equipment and put it through it's paces

    keep up the good work,

    Bob
    Smith G8-3 with EZ Gas @76,700 BTU, Single pipe steam


    Vaporstat with a 12oz cut-out and 4oz cut-in


    3PSI gauge
  • PMJ PMJ @ 9:00 AM
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    combustion air

    What are your feelings about outside combustion air and how that would figure into your overall efficiency calculations?
  • MarkS MarkS @ 10:25 AM
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    Outside combustion air

    I'm sure it would help. It'son the list of things to try, but it involves breaking through two 1-foot thick stone walls to bring in outside air.
    Homeowner, Royersford PA | 1890 one-pipe steam system | 3009 sf | 3 floors | 14 radiators | Utica SFE5200S boiler
    NEW Midco LNB-250 Modulating Gas Burner | EcoSteam modulating controls | 70 to 300 MBH |
    607 sf EDR connected load | Operating pressure: 0.5 oz/in2
    Four main runs (insulated) totaling 135 ft in length | All Gorton vents on mains & rads |
    A Steam Odyssey | Odyssey 2 | A Steam Enthusiast's Outdoor Reset Control
  • PMJ PMJ @ 10:44 AM
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    outside air

    I am doing it now. Whan I saw how enormous just the natural draft was in a chimney with a 10 inch dia flue was it beacme high on the list. I am not familiar with you burner but can I assume that there is no air flow thru the boiler when it is off? Do you know the cfm at full fire? You can then see the actual loss burning air you have already heated.
  • MarkS MarkS @ 11:13 AM
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    cfm

    The LNB-500 burner is rated at 229 cfm. Mine has an orifice plate to bring the max btus down to 300 MBH, so if it's a linear relationship the max cfm is 137. I never run at more than 80% of full speed since my btu input requirements are lower, so again if it's linear that's 110 cfm.

    How do you keep critters, leaves, bugs, water, etc. out of the intake pipe?
    Homeowner, Royersford PA | 1890 one-pipe steam system | 3009 sf | 3 floors | 14 radiators | Utica SFE5200S boiler
    NEW Midco LNB-250 Modulating Gas Burner | EcoSteam modulating controls | 70 to 300 MBH |
    607 sf EDR connected load | Operating pressure: 0.5 oz/in2
    Four main runs (insulated) totaling 135 ft in length | All Gorton vents on mains & rads |
    A Steam Odyssey | Odyssey 2 | A Steam Enthusiast's Outdoor Reset Control
  • MDNLansing MDNLansing @ 12:59 PM
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    Air Restriction

    That 65% intake restriction really looks odd. The stats appear to say it's the most efficient, yet it obviously falls short on true catalytic combustion, being that the CO levels are so high. It's leaving a lot of by product but sure seems to be firing at optimum performance. I doubt 50 ppm CO levels would meet code in any state, but I wonder what the code says about dilution of the exhaust gas? Furthermore, I wonder if the stats are maintained at those levels if the exhaust gas is diluted. If you could introduce another air draft post boiler exhaust and get those levels diluted you might be able to get one past an oblivious inspector. "Never mind the two dozen CO sensors I have around the boiler, just test my exhaust gas and get out of here please" :)
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