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General Science => General Science => Topic started by: vdblnkr34 on 15/11/2022 13:29:29

Title: Steam engine questions
Post by: vdblnkr34 on 15/11/2022 13:29:29

Hi. I was thinking about steam engines to run on electricity. It says to run 1HP need 40,000 btu. So, to run 200HP need like 8,000,000 btu. That is a huge numbers.

If to use inductive heater, how many btu in hour in Kw of electrical energy it will be needed?  Inductive heater have 80% efficiency, while gas has 40% efficiency.

Internet says 1Kw = 3,500 btu. In order to run 200HP engine on steam will need 1200Kw of steam power converted in Kw units???
Is this btu is a boilers HP or steam engine HP? Boilers HP is 13 times more than engine HP.
8,000,000 btu = 238 boiler HP. 238/13 = 18.
while 8,000,000 btu = 2,344Kw. 18 to Kw = 13Kw. I need 13Kw of induction heating to provide 8,000,000 btu??

Title: Re: Steam engine questions
Post by: Petrochemicals on 15/11/2022 13:42:53

Quote from: vdblnkr34 on 15/11/2022 13:29:29

Hi. I was thinking about steam engines to run on electricity. It says to run 1HP need 40,000 btu.

The economies of scale will be paramount, the smaller the engine the larger the ineficieny.

Title: Re: Steam engine questions
Post by: vdblnkr34 on 15/11/2022 13:51:27

Thanks. I didnt know that one. 

But for inductive heater what would be approximate btu in compare to gas. I just checked coal efficiency 33%.
So can induction heater efficiency be calculated same way?.

Title: Re: Steam engine questions
Post by: alancalverd on 15/11/2022 15:14:12

BTU is energy, HP and kW are power. Gas consumption is often rated as BTU per hour

1 horsepower = 2544.43 btu per hour or 0.746 kW.

Steam engine efficiency depends on the steam temperature and rarely exceeds 40% for a reciprocatiing engine, maybe 45% for a turbine.

Title: Re: Steam engine questions
Post by: vdblnkr34 on 15/11/2022 15:42:25

I found custom 200HP high pressure marine steam engine. High pressure piston driven marine steam engines have up to 70% efficiency.

If to run 200HP marine steam engine needs 8,000,000 btu per hour. So how much btu do I need to pass it to the boiler?

8,000,000 btu is about 2,000Kw of power. 200HP electric generator wont generate that much. Or calculations are wrong.

Title: Re: Steam engine questions
Post by: vdblnkr34 on 15/11/2022 16:01:13

Found a website says 200 hp = 508,886.7 btu/hour. Comes to 150Kw electrical. This is not so bad if it is true.  :-\

Title: Re: Steam engine questions
Post by: paul cotter on 15/11/2022 16:40:28

70% from a steam engine( reciprocating )? I think that is highly improbable. Even Alancalverd's 40% seems high to me, I would have said 20% tops.

Title: Re: Steam engine questions
Post by: alancalverd on 15/11/2022 17:19:02

You might get 70% of the theoretical Carnot efficiency from a real engine, but the Carnot value even with superheated dry steam (as in a nuclear power station or submarine)  is unlikely to exceed 60%. Railway locomotives rarely reached 20%. 

Title: Re: Steam engine questions
Post by: vdblnkr34 on 15/11/2022 19:35:51

Yeah, something like that. Higher the pressure more power and torque, square.

Title: Re: Steam engine questions
Post by: vdblnkr34 on 15/11/2022 19:37:19

And I was thinking, how much Kw of electrical power needs to run this by induction heater?.
Or to find this out I need to build one.

Title: Re: Steam engine questions
Post by: paul cotter on 15/11/2022 20:31:56

Why would you want to run a steam engine with induction heating? That would involve a massive waste of high grade electrical energy to run a 20% efficient heat engine. If you require rotation an electric motor would be the best option.

Title: Re: Steam engine questions
Post by: evan_au on 15/11/2022 20:47:56

As discussed above, a steam engine driven by electricity would be perhaps 20% efficient in turning electricity into mechanical energy.
An electric motor is something like 90% efficient at turning electricity into electrical energy.

...This ignores the 30% efficiency of turning high-quality coal into electricity, or perhaps 20% efficiency turning brown coal into electricity (effectively via a steam engine: a rotary turbine rather than a reciprocating version).

Title: Re: Steam engine questions
Post by: vdblnkr34 on 15/11/2022 20:49:53

There are places where no electricity. They could use this to generate some.

Title: Re: Steam engine questions
Post by: vdblnkr34 on 15/11/2022 20:54:39

I guess electrically steam boilers to heat is a bad idea. Perhaps coal would be better, make a sand bath surrounding a coal place to keep more heat in up to 1000C per sq. ft, but today many coal plants are closed, probably prohibited.

Title: Re: Steam engine questions
Post by: Petrochemicals on 15/11/2022 21:54:45

Quote from: vdblnkr34 on 15/11/2022 13:51:27

Thanks. I didnt know that one. 

Wind turbines also run on the principle bigger is better, small turbines are not worth bothering with.
 
Efficiencies are also affected by the temperature of feed materials, the air the coolant etc.

A Stirling engine ?

https://en.m.wikipedia.org/wiki/Stirling_engine#Efficiency

Title: Re: Steam engine questions
Post by: vdblnkr34 on 15/11/2022 23:01:00

Stirling engine is good for huge steam boilers. Will do.

Wind turbines are good choice, what if its very cold outside.

Title: Re: Steam engine questions
Post by: alancalverd on 15/11/2022 23:09:30

So you want to run a marine steam engine from a wind turbine? Why not just use a sail and save a lot of weight?

Title: Re: Steam engine questions
Post by: vdblnkr34 on 15/11/2022 23:13:17

No. I want to run it using induction heater. And I want to find out how much electricity need to induce to run 200HP marine steam engine.

Title: Re: Steam engine questions
Post by: alancalverd on 15/11/2022 23:21:04

I think we have covered that.

To get 200 HP out of a steam engine, you will need at least 500 HP of electrical power, and quite possibly over 1000 HP depending on the design of the steam engine and boiler.

To generate 1000 HP of electricity, you need about 2000 HP of steam.

To generate 2000 HP of steam, you will need 10,000 HP of electricity

et sic ad infinitum.

Multiply any of the figures by 746 to get the answer in watts.

Title: Re: Steam engine questions
Post by: vdblnkr34 on 15/11/2022 23:28:46

thanks  :o

Title: Re: Steam engine questions
Post by: Petrochemicals on 15/11/2022 23:49:41

Quote from: alancalverd on 15/11/2022 23:09:30

So you want to run a marine steam engine from a wind turbine? Why not just use a sail and save a lot of weight?

Way ahead of you

responsive_big_webp_ZwEIIHJCegQwFhQy2k5AtrBGjH5wtMcll7oX2mFa034.jpeg (26.79 kB - downloaded 121 times)

https://www.weforum.org/agenda/2020/12/swedish-firm-wind-powered-cargo-ships

Title: Re: Steam engine questions
Post by: vdblnkr34 on 16/11/2022 00:24:56

I guess I go build famous Nicola Tesla wheel with 500 magnets on it and 50km long wire coil.

Shoot, will need lot of wire.

Title: Re: Steam engine questions
Post by: alancalverd on 16/11/2022 10:31:52

Quote

swedish-firm-wind-powered-cargo-ships

Indeed

https://www.rmg.co.uk/cutty-sark

been there, done that. And at 17.5 kt she was faster than any steamship in the 19th century.

Title: Re: Steam engine questions
Post by: Petrochemicals on 20/11/2022 16:41:12

Quote from: alancalverd on 16/11/2022 10:31:52

Quote

swedish-firm-wind-powered-cargo-ships

Indeed

https://www.rmg.co.uk/cutty-sark

been there, done that. And at 17.5 kt she was faster than any steamship in the 19th century.

And very considerably smaller.

Quote from: vdblnkr34 on 16/11/2022 00:24:56

I guess I go build famous Nicola Tesla wheel with 500 magnets on it and 50km long wire coil.

Shoot, will need lot of wire.

133 quid per 7km

https://brocott.co.uk/0-315mm-enamelled-copper-winding-wire-10kg/