Steam Generation Question

[Lopez Mike]

Mine is certainly too big for my five hp engine and cold sea water. I can run the return water over my finger much of the time without serious pain. And the hot well is just mildly warm most of the time. About a two gallon hot well. The bypass flow through the flat valve is small too. My direct drive Hypro has perhaps a 20% reserve capacity.

My condenser now is a 3/4" o.d. copper pipe about six feet long. Not large by most rules of thumb. I have given occasional thought to some scheme of having two smaller pipes in parallel and cutting out one when in cold water. Or valving one down at any rate. I don't have a condensate pump. Just let the little single push the water out of the condenser to the hot well.

Has anyone here heard of regulating a condenser?

Mike

[fredrosse]

In large steam-electric power plant practice regulation of a condenser is often applied to improve plant efficiency. The condensers and their circulating water systems are designed to perform adequately in summertime conditions, when the cooling water is relatively warm. When cooler water temperatures occur during winter, the return condensate temperatures are often reduced to the point of hurting plant efficiency, and typically the cooling water flow rate is reduced by turning off one of the circulating pumps.

With a steamboat keel condenser, you cannot "turn off" one of the cooling pumps, as the cooling water just flows around the condenser tube by way of the boat's motion thru the water. Cutting out some of the heat transfer surface area could accomplish the same result, and reduce the excessive cooling of the condensate. Of course, if you have an inboard surface condenser, you could actually reduce the cooling water flow when the sea temperature is low.

[fredrosse]

Control of steam engine power output and steam consumption can generally be accomplished two ways. The most simple is "throttling control". This is to close down on the steam valve between boiler and engine, resulting in lower steam pressure to the engine, less power output, and less steam flow.

The other option is to "Link Up" the valve gear. With this process the steam pressure to the engine is kept up to boiler pressure, and the length of piston stroke during admission of high pressure steam is stopped, or "cutoff" earlier in the stroke, so less steam flows thru the engine. Reducing the length of stroke during steam admission both reduces steam flow and reduces engine output.

Either method works OK, however the "Link Up" method is more efficient than throttling control.

The valve gear of a steam engine, (typically Stephenson Type), when shifted a little toward the reverse rotation position, will shorten cutoff. Typically the valve gear can be set at a "Linked Up" position. If the valve gear is set to allow maximum piston stroke before cutoff, then we have "full gear", as opposed to "Linked Up". Maybe that is clear as mud??

[Lopez Mike]

To add to Fred's explanation, locomotives have a situation where they regularly need full torque at essentially zero rpm for getting a heavy train started. Therefor they are set up to use steam admission to almost full stroke. The normal drill with a train is to set the valve gear 'all the way in the corner' when starting a train and feed as much throttle as possible without spinning the wheels. As the speed picks up and the loses in the ports, piping and valve gear restrict the flow, the throttle may well be all the way open without wheel slippage. If restricting the power is needed, the first adjustment will be to shorten the percentage of the stroke during which steam is admitted. The exhaust note changes from a chuff to a much shorter bark. The fireman is grateful.

To my knowledge, marine power never needs to develop full torque at zero speed. Our valve gears in full forward or reverse tend to admit over a much shorter percentage of the stroke. Perhaps 60 percent? Someone else on here will have a better number. We do shorten the cutoff with increasing rpm but it there is little of the nearly infinite adjustment we find on locomotives. We seldom need to climb a hill or coast down a grade. We hope not!!

On my boat, I have only three notches on the valve gear. Full astern, full ahead, and a reduced cutoff in forward motion. I am boiler limited and I find that shortening up the cutoff gives me about another knot before the pressure drops. "Your mileage may differ."

End of lecture. Sorry. Time for the old hands to point out my omissions and errors.

Mike

[JonRiley56]

Howdy all,

I have not got my condensation loop set up yet. I am still running on salt so I am carrying 15 gallons of make up water as I do my testing etc in the harbor. I am heating the hotwell. I recirc through the heater to try and keep the water hot until i need it and then pump to the boiler. The heater is before my pump, all of my feedwater goes through it, either from the hotweel or my make up tank.

I was thinking if I could get my hotwell to 150 - 170 that it would make for a better maintainence of steam pressure when replenishing the steam drum. My boiler is very well built, welded, and insulated. There is not an easy way for me to put a copper economizer in, although I could "force it above the tubes if I had to.

As I read more of your posts I am thinking that part of my isse may just be that I stink at building and maintaining a fire.......... even though I have a fair amount of space between the grate and the crossover of the steam generation tubes. The flames are actually touching the tubes which according to the steamboating guide from the UK is a no no.

I think that my wood may be to large............(please hold your comments)............. Perhaps I need to split down to smaller sizes so that I can build a hotter more controlled fire. I am also not sure how I judge whether I have to much air.......... Is there a way that I can tell how effective my fire is ? What if I measure stack temperature ? I have an opening in the stack that I could possibly shoot with a handheld infra red thermometer.

On the link up procedure, I think I understand that I leave the setam setting alone, throtteled to the speed I am looking for and then move the stephenson gear towards center as far as possible without losing speed. Is that correct ?

thanks

jon

[fredrosse]

Usually the heater should be on the discharge side of the feed pump, as very hot water is often not good for a pump. My Hypro pump instructions indicated 140F maximum inlet temperature, I do not know if they come with other maximum allowable inlet temperatures.

As far a linking up, when you do this you will reduce both the steam consumption and the power output, however you will have a slightly higher efficiency of converting heat into power, thus you would need less fire.

[JonRiley56]

Howdy All,

I was able to run the boat yesterday in the dirveway and check a couple of things out. Here is what I learned.

1. I was not firing hard enough, a buddy of mine helped be get a storonger fire going and that made a difference.

2. I started off with the water in the lower portion of the glass like I have been running it and let the pressure run up to about 100 lbs. I then added water to the boiler. (the water was cold, around 45 degrees or so, becasue I am bypassing the heater right now). As the cold water entered the relatively small mass of hot water in the boiler, the pressure started to drop rather quickly. This is what Has been happening to me on the water, so I confirmed the issue.

3. I then took the water level in the boiler up to over half the glass, let the pressure come up to 100psi, and then tried the same thing. THe pressure did drop with the intorduction of cold water, but not nearly as quickly as before.

4. I then took the water up to about 3/4 of the glass and repeated the test. WIth the water this high, the pressure hardly moved at all when I introduced cold water to it.

I guess the larger quantity of heated water (at or above steam temperature) is storing a lot of heat relative to the cooling effect of water coming in at typical pumping rates, and makes the system more stable.

I was encouraged and look forward to trying it on the water. I will likely try and put it inthe harbor this weekend if it is not too cold. It gets a little raw with air temps in the 30s and a 15 to 20 mph wind..........

jon

[DetroiTug]

Hi Jon,

Definitely need a big fire. My brother was firing my boiler last week and he was having trouble keeping up steam and it was a case where the fire was just too small. On this firebox and the amount of steam needed, if there is room for a log, put it in. Otherwise it just will not keep up.

Another thing we did and it worked really well for taking on water. Even though I'm using an 50 foot economizer, the lake waters are so cold now, the coil eventually cools off. One of two things must be done. Either pump water in small increments or try to adjust the bypass on the pump to where it just maintains the boiler at a constant level. The latter is the best if you can get it set right.

Learning as I go here, but it is definitely harder to fire and make steam in the winter months. What works in July, may not work in November.

-Ron