Small steam turbine

[kwired]

at one point the one Farmer was growing about 15-20% of the mint in the USA. About 7,000 acres were in Oregon. His still was at Boardman, OR. They used “waste” steam from a coal fired power plant there. Seems like the steam was still at 200-300 psi when they they got it. I know the stills here run at more than 15 psi, have annual inspections and licensed operators.

What is "waste steam"? Only thing I can think of is if they had a sudden drop in output demand or similar situation where they would have to relieve pressure to protect the main vessel from rupture. Seems that would be somewhat less predictable as to when it would be available, and even then when they need to dump, it they need to dump it.

 

[gadfly56]

Steam is badass. Definitely would be a cool factor over more boring solar panels!

On the other hand, your solar panels are very unlikely to explode and scald you to death. That's probably unlikely with any steam plant you could purchase too, but not zero probability.

 

[gadfly56]

What is "waste steam"? Only thing I can think of is if they had a sudden drop in output demand or similar situation where they would have to relieve pressure to protect the main vessel from rupture. Seems that would be somewhat less predictable as to when it would be available, and even then when they need to dump, it they need to dump it.

For power production, "waste" steam is steam at a pressure too low to produce electricity economically. On the other hand, if you've got a nearby metropolitan area in the frosty zone of the US, you could sell that waste steam for district heating. Or cooling, using ammonia absorption.

 

[zbang]

IIRC, the district heating system in Seattle used to generate electricity as a byproduct of making heating steam- it's almost as easy enough to generate superheated 1000 psi steam as 200 psi, and you can use some turbines as pressure-dropping/expansion devices. (This might have changed in the last 20-30 years.)

 

[drcampbell]

Medium-pressure steam can also power summertime district cooling, using absorption-cycle air conditioning.

 

[gadfly56]

Medium-pressure steam can also power summertime district cooling, using absorption-cycle air conditioning.

Yep, just like that fella said in post #43.

 

[winnie]

For small scale operation you might consider a different working fluid. There are turbines or screw expanders designed for use with refrigerants rather than steam as the working fluid.

Jon

 

[kwired]

For power production, "waste" steam is steam at a pressure too low to produce electricity economically. On the other hand, if you've got a nearby metropolitan area in the frosty zone of the US, you could sell that waste steam for district heating. Or cooling, using ammonia absorption.

Must be much more complicate boiler(which wouldn't surprise me) then I am used to, where the entire vessel is under same pressure. Must also cost less to route that to the neighborhood than to recycle it somehow back into the main boiler? Or at least more profitable to sell it than to recycle it?

 

[winnie]

Must be much more complicate boiler(which wouldn't surprise me) then I am used to, where the entire vessel is under same pressure. Must also cost less to route that to the neighborhood than to recycle it somehow back into the main boiler? Or at least more profitable to sell it than to recycle it?

Or it might be steam after it has gone through a turbine and is now cooler and at lower temperature.

-Jon

 

[kwired]

Or it might be steam after it has gone through a turbine and is now cooler and at lower temperature.

-Jon

Again don't know a lot about details of such facilities, but many other applications that would be returned to the boiler to be reheated again.

 

[hillbilly1]

On the other hand, your solar panels are very unlikely to explode and scald you to death. That's probably unlikely with any steam plant you could purchase too, but not zero probability.

They can catch on fire though!

 

[zbang]

Or it might be steam after it has gone through a turbine and is now cooler and at lower temperature.

That's it- the steam has been used already and given up some energy. Goes into the turbine at 1200 PSI and 800 degF*, comes out at 40 PSI and 300 degF, not really useful for more than heating now so send it out to heat places (or run is through a heat exchanger and send the resultant steam out, keeps treated boiler water in the facility).

*representative, but made-up numbers; modern multi-MW power plants are more much higher pressure

Professionally-operated steam plants are pretty good at squeezing the last possible joule out of the water before if goes back in the boiler. Even so, I read somewhere that even the best combustion plants still operate under 50% thermal efficiency.

BTW, district and campus heating systems are often quite lossy for the water, some don't/didn't even collect condensate because there isn't enough on one place to bother piping it back.

Covering another point- AFAIK no systems force exhausted steam back into the boiler to reheat; I'm not sure it's even possibly (compress the gas to force it in). They all condense the steam to liquid water and pump that in, which is easier at boiler pressure since liquids are no compressible.

 

[kwired]

That's it- the steam has been used already and given up some energy. Goes into the turbine at 1200 PSI and 800 degF*, comes out at 40 PSI and 300 degF, not really useful for more than heating now so send it out to heat places (or run is through a heat exchanger and send the resultant steam out, keeps treated boiler water in the facility).

*representative, but made-up numbers; modern multi-MW power plants are more much higher pressure

Professionally-operated steam plants are pretty good at squeezing the last possible joule out of the water before if goes back in the boiler. Even so, I read somewhere that even the best combustion plants still operate under 50% thermal efficiency.

BTW, district and campus heating systems are often quite lossy for the water, some don't/didn't even collect condensate because there isn't enough on one place to bother piping it back.

Covering another point- AFAIK no systems force exhausted steam back into the boiler to reheat; I'm not sure it's even possibly (compress the gas to force it in). They all condense the steam to liquid water and pump that in, which is easier at boiler pressure since liquids are no compressible.

I kind of was thinking of that when I asked other questions and makes sense. You still have energy there and the water is still in steam form. So you either need to find a way to condense it without losing significant energy before returning it, or find another use for that energy even if it comes from condensing it in the process.

I do know you generally don't want to put cold water into an operatingt temp boiler as replacement water and that if any return isn't at desired temp it is heated by the steam produced by the boiler in a "feed tank" before being fed into the boiler. If not enough return is coming back then the cold fresh water is introduced into this "feed tank" and not directly into an operating temp boiler.

And it only makes sense to return as much condensate as possible, for one thing you recover some heat, plus you also have water that has already been treated to be acceptable in your boiler system, new water being introduced needs treated.

 

[hillbilly1]

I don’t know if the still do it, but I heard NYC uses leftover heat from their power plants to heat buildings throughout the city.

 

[zbang]

There are multiple heat recovery schemes that can be involved- using exhaust steam in a feed-water heater , the economizer which uses combustion gasses to heat the water, using waste heat from an unrelated process, etc. Since the feed water can be kept under pressure, it can be heated a good deal higher than 212F.

Those boiler engineers are pretty clever folks.

NYC- they still do, and lots of it.

(It's a wonder I didn't become a stationary/mechanical engineer.)

 

[retirede]

I don’t know if the still do it, but I heard NYC uses leftover heat from their power plants to heat buildings throughout the city.

I think they do. It was only a couple years ago I saw on the news where one of the steam lines ruptured below a street.

 

[acolella]

At 100% efficiency you can get 9000 BTU per each pound of wood. If you burn the lb in one second you get 9 kw for one second. If I got the numbers and conversions right.

9 kW for one second is equivalent to 8.53 BTU. 9.495 MW for one second is equivalent to 9000 BTU. How did you figure that 9000 BTU in one second is equivalent to 9 kW for one second?

 

[don_resqcapt19]

I did one project for an industrial plant where they installed a small steam turbine that used 400 psi steam with a 250 psi drop. The intent was to produce steam at 400 psi, and use the turbine to drop the pressure to their normal plant steam distribution pressure of 150 psi.

It was a simple system using an induction generator, so not big expense for paralleling gear. Just some 5kV switch gear and protective relaying.

The problem was the only time they really could use all of the steam required to operate the turbine was in the winter, but in the winter their purchase cost for electricity was too low to justify the extra input energy needed to product 400 psi steam. In the warmer weather they did not need as much steam, so again even though the utility power costs were higher, the economics did not work for them, so the system was abandoned after a couple of years.



The economics of this will differ based on your utility costs. Our area is one of the lower cost areas in the country. Electrical energy saving projects that had a very good return on investment at the companies other plants were not implemented at the local plant because they did not have a good ROI.

 

[GeorgeB]

Covering another point- AFAIK no systems force exhausted steam back into the boiler to reheat; I'm not sure it's even possibly (compress the gas to force it in). They all condense the steam to liquid water and pump that in, which is easier at boiler pressure since liquids are no compressible.

Utility steam generation with fossil fuel, certainly since the 1940s, have at least 1 stage of reheat. Duke plants where I had experience usually had 2 reheat sections. Steam from the HP turbine stage(s) was reheated before going into the IP stage(s) then again before to the LP stage(s). I think, but don't remember for certain, that a major reason is to keep it dry. Wet steam erodes.