Circulating water requirements

[PhilMart]

Adamant has a 4" + 8" by 5" engine working at 125 psi which exhausts to a condenser with 14 No 22m mm copper tubes giving an area of approx 6 1/2 sq ft. Can anyone suggest the amount of circulating water required in say gals per hour please. The reason for the question is that I am considering changing the circulating pump.

[barts]

One would need to make a fair number of assumptions to avoid making a very conservative guess. To help reduce the uncertainty:

What's the highest temperature water in which you operate Adamant?
How much fuel (oil/wood/coal in BTU/hr) do you use at full speed?

Steam engines have a low enough efficiency that we can simply assume that all the fuel goes to heating up the condenser water... which means that we can calculate the heating value of the fuel, subtract 20% for boiler losses (and whistle blowing ) and, using the difference between the temperature of the water outside the hull and say 150F discharge temperature, figure out how many gallons/hour we need to pass through the condenser to cool it.

For example, say Adamant burns 3 gallons light fuel oil/hour at full speed... and we're floating in 70F water in the summer time.

120000 BTU/gallon oil * 3 gallons oil/hour * .80 * 1 lb-degree F/1 BTU * 1 gallon/8 lbs * 1/(150-70) = 450 gals/hour, or about 7.5 gallons/minute.

You can reduce this somewhat by increasing the discharge temperature, but you're limited by the desired condenser vacuum since most traditional condensers don't have a good counterflow circulation pattern.

- Bart

[johngriffiths]

Beware of Barts's gallons, they are short. Allow 135,000 BtU for a UK full blooded version of a gallon. Always had this problem when buying gas in the States, got 16.6% short measure all the time:-)

JohnG

[barts]

Beware of Barts's gallons, they are short. Allow 135,000 BtU for a UK full blooded version of a gallon. Always had this problem when buying gas in the States, got 16.6% short measure all the time:-)

JohnG

Well, if you use the same "oversized (:))" gallons to measure the cooling water flow, those would be commensurately larger, so since we're just multiplying it should come out to the same answer.
- Bart

[johngriffiths]

if your fuel consumption is 3 UK gallons/hr and you calculate pump ram diameter, stroke and RPM using as a base 3 US gallons/hr the cooling water delivery will be too small, by 16%, so you make sure you start with the right unit. It would be a hot summer here before our rivers reach 70.

JohnG

[PhilMart]

Thanks guys thats great! I had not thought of coin it this way i.e. simply by using the heat input = water temp rise. In fact Adamant burns coal but I can work from there ok, At present my yep rise is barely detectable !

[Dhutch]

Its really interesting that this topic is at the top of the list, because I was literally coming on to ask the same question myself.

EmilyAnne is a very similar setup to Adamant, the hulls/boilers/engine are I would say similar enough to be considered almost the same for this exercise although we run a slightly higher pressure of 200psi, our engine measured 4.5+7.5*4.
- I have not calculated the surface area of the condenser as yet, although this is on the cards as something which needs doing.

We are also coal-fired which make it slightly harder to calculate the incoming energy, and obviously this is not the same as the energy which goes into the steam due to the significant amount which goes up the funnel and directly to atmosphere. That said, I like the approach of effectually ignoring the energy consumed by the engine.

One thing I have thought of doing, more to assess the boilers performance than anything else, is to run the plant as hard as practicable until a fairly 'steady state' is achieved and then measure the flow-rate of the condensate. I cant see a better way of getting the evaporative rate of the boiler and hence through-put of the system than this. Combined with temperature measurements and steam pressure (which for wet steam, gives the temperature) you have I guess nailed a lot down.

I working litres and kilowatts rather than gallons and btu's , but am also aware our overseas posters use their own gallons!



Daniel

[Dhutch]

The reason for my asking the question, is that I am not convinced that our otherwise very satisfactory circulating pump flows enough to allow the airpump/condenser to develop as much vacuum as it might otherwise.

Obviously if not pre-heating your feed water you can over cool the condensate. However my empirical feeling/understanding is that failing to develop a good vacuum on the exhaust does far more for reducing efficiency that having hot feed water.

Our current pump is engine driven, so produces a viable flow rate (which I see as a good thing) but at 200rpm flows 13l/min. Flat out is around 300-350 rpm, with 150-180 being a common cruising range.
- With this flowrate, and the rest of the system as it is, we make plausible vacuum (19-21 inHg or -0.7bar) at slower speeds but this drops off sharply around 160rpm if not before and at around 200rpm the exhaust becomes mildly positive. *

Some what jumping the gun I jury rigged an electric feed pump (large bilge pump dropped into the mudbox) which provide a flat 60l/min.
- With this and no other changes things improved and we where maintain plausible vacuum until around 200-220rpm when ir drops off slightly more gently two only a mild vacuum at say 280rpm, running basically flat out. *

*I do not have the table or records in front of me so vac figures are from my head. The tables also record condensate and cooling water temperatures.



Daniel

[barts]

The warmer the cooling water leaving the condenser, the more increasing the pump circulation will help. 60l/min w the bilge pump should be plenty of cooling water. If you can post the cooling water (in and out) temps as well as the condensate temp leaving the air pump, we can try to determine if the problem is a too small condenser or an airleak somewhere/airpump that's too small.

- Bart

[PhilMart]

Have just had the covers off my condenser. Its area is a shade over 12 sq feet which should be OK for 12 HP. It was pretty muddy inside but otherwise OK. I had suspected some blockage as the return water temp has got pretty darn high of late around 80-90 deg C. Obviously not the condenser so I shall have to search further, possibly a pipe block or a problem with my old Simplite site pump I use for circulating water. Hence my original question as to the amount of water required.
Good luck Daniel, see you in June at SLW?>