Search results

Home Model Engine Machinist Forum

Help Support Home Model Engine Machinist Forum:

This site may earn a commission from merchant affiliate links, including eBay, Amazon, and others.
  1. T

    Monotube Flash Boiler Design

    Apples & oranges - In both hot water and wet steam pressure washers the hot water vessel and related piping upstream of the pump on the low pressure side - the only things downstream of the pump are the flexible high pressure hose and the washing gun. In boilers, the pressure vessel and piping...
  2. T

    Monotube Flash Boiler Design

    Sort of - engine exhaust is a compressible fluid, while water is not, so the characteristics are different.
  3. T

    Monotube Flash Boiler Design

    Actually high pressure boiler systems (defined as operating at > 80 bar) almost universally use multi-stage barrel or ring pumps, either in a single pump or main+booster configuration. The pumps also don't dead head into the boiler, but operate in conjunction with a bypass feedwater regulator...
  4. T

    Monotube Flash Boiler Design

    Assuming equal displacement, the individual pulses will be smaller, but the overall energy will be about the same or even slightly greater due to combined efficiency losses. What will change is the pulse frequency - if you use a 9 piston pump, the pulse frequency for any given speed will be 4.5X...
  5. T

    Monotube Flash Boiler Design

    This is still a positive displacement design and like the pressure washer pump, it will generate output pressure pulses. The frequency will be higher (CPM= # of cylinders multiplied by the motor RPM; frequency in HZ=CPM/60) because there are more cylinders, but they will still be there. It...
  6. T

    Monotube Flash Boiler Design

    Pressure washer pumps are positive displacement pumps and the pressure pulses you are seeing are a normal characteristic of their operation. The frequency of the vibration in CPM will be the number of pistons multiplied by the run speed of the pump motor, so it will vary with motor speed. Those...
  7. T

    Monotube Flash Boiler Design

    These are design issues. Sometimes you can compensate via operational control changes, other times you just have to bite the bullet and make the necessary mechanical modifications. Case in point: I had a client that used the bow thruster on a large vessel for operational steerage control. They...
  8. T

    Monotube Flash Boiler Design

    Steamchick, Your suggestion of an O2 sensor in the boiler exhaust is a good one. It looks to me like Toymaker is setting up his burner control as an exclusively feed-forward algorithm. While you can do this in theory, in the real world there are just too many variables to compensate for. I...
  9. T

    Monotube Flash Boiler Design

    Troll, Hot spot tube failures in a water tube boiler are rarely caused by fire side issues - rather they are overwhelmingly the result of water side issue - either scaling that inhibits heat transfer from the metal to the water, allowing the metal under the scale to overheat, or corrosion due...
  10. T

    Boiler for putting around in small dinghy.

    I agree. In water tube boilers, the feed water is typically injected about 1/3 from the bottom of the steam drum. In fire tube boilers, the injection point is typically near the mid-drum level. To minimize thermal shock, fabricate a simple economizer tubing coil that is located in the boiler...
  11. T

    Monotube Flash Boiler Design

    This information is incorrect. 1. DI water in and of itself is by definition neutral - it is neither an acid nor a base. That said, because of it's lack of ions (low ionic strength), it can be corrosive to some materials by leaching ions. It can also become very slightly acidic in some...
  12. T

    Monotube Flash Boiler Design

    Did a quick look - the minimum recommended sulfite concentration in the boiler water is 20ppm. Minimum pH should never be less than 8.5, 9.0-9.5 is better.
  13. T

    Monotube Flash Boiler Design

    Even in a sealed system you're probably going to have some leakage losses. The majority of potential contaminants come from the makeup water. If you're using DI water, that shouldn't be an issue, and you won't have to worry about blowdown. Na2SO3 as an oxygen scavenger is usually injected into...
  14. T

    Monotube Flash Boiler Design

    Actually, pure water is neither an acid nor a base - it has a neutral pH. It also has a very low conductivity/high resistivity due to it's extremely low ionic strength. That said, it is a very good solvent. Corrosion in steam systems is mostly due to the presence of oxygen, which will react...
  15. T

    Monotube Flash Boiler Design

    There are a number of things that can cause what you are experiencing. Check to make sure that both the combustion air inlet and the exhaust are clear and unobstructed. Also check the condensate drain system to make sure it is functioning correctly, as issues with condensate removal can cause...
  16. T

    Monotube Flash Boiler Design

    Since he is using DDC, I'd suggest adding some type of an external watchdog timer circuit that has to be reset by the control board or it will cut the mains power. It's relay should be N.O. and can be initially energized when the system is started. I would never let the system auto-ignite - it...
  17. T

    Monotube Flash Boiler Design

    In the industry we call that DDC - direct digital control.
  18. T

    Monotube Flash Boiler Design

    I never believed in letting the DCS, or analog control systems for that matter, handle flame safeguard functions. We would typically use a dedicated Fireye system that interfaced with the boiler combustion control system. Once all the basic safety interlocks, pre-purge timers, main fuel valve...
  19. T

    Monotube Flash Boiler Design

    It's actually not that tough - it's been done for many years in industrial boiler systems. How complex the controls have to be depends on the characteristics of the system. For base loaded systems it is relatively straightforward for both the basic control strategy, and to add feedback trim...
  20. T

    Monotube Flash Boiler Design

    If you find yourself needing to restrict combustion air, the most energy efficient method (depending on blower design) is usually to damper the combustion air blower inlet, not the outlet. Water entrainment (wet stream) can be minimized a couple of ways. Most boilers are designed with a steam...
Back
Top