steam thermal efficiency in the transportation sector

[harlock]

I read that the most (however I'm not sure) efficient steam coal-fired train was 27% efficient in the past century 🙂

link: steam train thermal efficiency. (browse pages up to the Third Generation Steam(TGS)). 

 

So...I wonder if it's possible today to build biomass-fueled steam engines for bulky vehicles(agricultural etc...).

Energy content of 1 liter of diesel is equivalent to 2.5 kg of wheat straw pellet(An example). 

BUT 1 liter of diesel costs around 1.5 u.s. dollars while 2.5 kg of wheat straw pellet is around 0.25 u.s. dollars. 

Problems can be: 

1-wheat straw availability   2-power  3-volume

I'll try to give some answers to these three questions

1-Wheat straw yield is about 3-6 tonnes per hectare. It's energetically equivalent to more than 1 tonne of diesel...

Is there availability for agricultural vehicles and (maybe) trucks in general? We'he to consider efficiency also... 

2-Vapour pressure can produce a great power. We know that Force=Pressure*Surface so if vapour pressure is 100 bar(In the water state diagram T is around 300°C) and surface is only 1 cmq we have F= 100 * (1e5 Pa) * (1e-4 mq) = 1e3 Newton! It's the force applied to low-middle power cars... I think it's no comments... What about efficiency? It would've to be around 27%... Comments? 

3-Wheat straw pellet density is about 0.5 kg/dm3. So 5 'liters'(2.5 kg /(0.5 kg/dm3) ) of wheat straw pellet is energetically equivalent to 1 liter of diesel(So five to one about volume energy comparison). Would it be ok for bulky vehicles? 

  

 

 

 

Edited March 21, 2022 by harlock

[exchemist]

8 hours ago, harlock said:

I read that the most (however I'm not sure) efficient steam coal-fired train was 27% efficient in the past century 🙂

link: steam train thermal efficiency. (browse pages up to the Third Generation Steam(TGS)). 

 

So...I wonder if it's possible today to build biomass-fueled steam engines for bulky vehicles(agricultural etc...).

Energy content of 1 liter of diesel is equivalent to 2.5 kg of wheat straw pellet(An example). 

BUT 1 liter of diesel costs around 1.5 u.s. dollars while 2.5 kg of wheat straw pellet is around 0.25 u.s. dollars. 

Problems can be: 

1-wheat straw availability   2-power  3-volume

I'll try to give some answers to these three questions

1-Wheat straw yield is about 3-6 tonnes per hectare. It's energetically equivalent to more than 1 tonne of diesel...

Is there availability for agricultural vehicles and (maybe) trucks in general? We'he to consider efficiency also... 

2-Vapour pressure can produce a great power. We know that Force=Pressure*Surface so if vapour pressure is 100 bar(In the water state diagram T is around 300°C) and surface is only 1 cmq we have F= 100 * (1e5 Pa) * (1e-4 mq) = 1e3 Newton! It's the force applied to low-middle power cars... I think it's no comments... What about efficiency? It would've to be around 27%... Comments? 

3-Wheat straw pellet density is about 0.5 kg/dm3. So 5 'liters'(2.5 kg /(0.5 kg/dm3) ) of wheat straw pellet is energetically equivalent to 1 liter of diesel(So five to one about volume energy comparison). Would it be ok for bulky vehicles? 

  

 

 

 

In principle any kind of external combustion (EC) engine could do what you propose. There is no magic about steam as a working fluid in this respect. In fact something like the Stirling engine would probably be more compact and just as efficient.

The big snag, it seems to me, about an EC engine burning biomass for transport, is that the combustion can't be turned on and off in accordance with the variations of power demand. So you will intrinsically waste a huge amount of energy by keeping the heat source burning all the time, even though you only use the full heat output sporadically. When you add in the exhaust control measures needed to prevent pollution from straw burning, not to mention the inconvenience of needing to store five times the volume of fuel, and the need for getting rid of considerable amounts of solid ash at intervals, it becomes fairly plain why this idea is not going to fly.

EC heat engines make a lot more sense in fixed installations such as power plants, where these issues can be managed without the overriding need to keep everything compact and lightweight, and where energy demand from the system is fairly constant rather than intermittent. 

 

[swansont]

In addition to exchemist's observations, you'd be in a situation like the old steam locomotives you mentioned - an engine but also a place to store the fuel, which you have to lug around with you. Along with the storage container and the fuel delivery system, which are likely to be more massive than a fuel tank and piping. That's an additional drain on your efficiency.

That worked for trains, but not so much for other applications.

[exchemist]

1 hour ago, swansont said:

In addition to exchemist's observations, you'd be in a situation like the old steam locomotives you mentioned - an engine but also a place to store the fuel, which you have to lug around with you. Along with the storage container and the fuel delivery system, which are likely to be more massive than a fuel tank and piping. That's an additional drain on your efficiency.

That worked for trains, but not so much for other applications.

And indeed, if, as in a steam locomotive, you use an open cycle steam engine to avoid the bulk of a condenser, you exhaust the working fluid and need to replenish that as well. So you need a water tank, as you had in the tender of a railway engine.  

[harlock]

2 hours ago, exchemist said:

The big snag, it seems to me, about an EC engine burning biomass for transport, is that the combustion can't be turned on and off in accordance with the variations of power demand. So you will intrinsically waste a huge amount of energy by keeping the heat source burning all the time, even though you only use the full heat output sporadically. 

I think some energy needs to be stored first of all. Energy can be stored by melting some salt...or by storing water under pressure in an insulated tank... For example I know that NaCl heat of fusion value is around 30 kj/mol ( 300 kwh/m3! ) so 1 m3 of NaCl can store 300 kwh of thermal energy. But it's a high fusion temp for straw combustion...  

[harlock]

3 hours ago, exchemist said:

When you add in the exhaust control measures needed to prevent pollution from straw burning, not to mention the inconvenience of needing to store five times the volume of fuel, and the need for getting rid of considerable amounts of solid ash at intervals, it becomes fairly plain why this idea is not going to fly.

It isn't a problem for agricultural vehicles... However solid ash represents only 3% as regards the combustion of wheat straw. Also corn stove pellets are  interesting(especially in the U.S.). Infact corn stover left in the field after grain harvest represents an estimated yield of 8-10 tonnes of dry matter per hectare! In addition it seems to have a solid ash content about 5%. It doesn't seem a high value.  

Edited March 21, 2022 by harlock

[exchemist]

1 hour ago, harlock said:

I think some energy needs to be stored first of all. Energy can be stored by melting some salt...or by storing water under pressure in an insulated tank... For example I know that NaCl heat of fusion value is around 30 kj/mol ( 300 kwh/m3! ) so 1 m3 of NaCl can store 300 kwh of thermal energy. But it's a high fusion temp for straw combustion...  

Think what you are now proposing: to add an energy storage system, as well all the other stuff I have itemised. If you are going to do all that you might as well run a static EC engine somewhere, convert the energy to a convenient form and put that in your on-board storage system.  In short, run a generator and store the energy electrically in a battery. 

[harlock]

6 hours ago, exchemist said:

In short, run a generator and store the energy electrically in a battery. 

Surely it's a good option.

[sethoflagos]

On 3/21/2022 at 2:27 AM, harlock said:

I read that the most (however I'm not sure) efficient steam coal-fired train was 27% efficient in the past century 🙂

link: steam train thermal efficiency. (browse pages up to the Third Generation Steam(TGS)). 

 

So...I wonder if it's possible today to build biomass-fueled steam engines for bulky vehicles(agricultural etc...).

Energy content of 1 liter of diesel is equivalent to 2.5 kg of wheat straw pellet(An example). 

BUT 1 liter of diesel costs around 1.5 u.s. dollars while 2.5 kg of wheat straw pellet is around 0.25 u.s. dollars. 

Problems can be: 

1-wheat straw availability   2-power  3-volume

I'll try to give some answers to these three questions

1-Wheat straw yield is about 3-6 tonnes per hectare. It's energetically equivalent to more than 1 tonne of diesel...

Is there availability for agricultural vehicles and (maybe) trucks in general? We'he to consider efficiency also... 

2-Vapour pressure can produce a great power. We know that Force=Pressure*Surface so if vapour pressure is 100 bar(In the water state diagram T is around 300°C) and surface is only 1 cmq we have F= 100 * (1e5 Pa) * (1e-4 mq) = 1e3 Newton! It's the force applied to low-middle power cars... I think it's no comments... What about efficiency? It would've to be around 27%... Comments? 

3-Wheat straw pellet density is about 0.5 kg/dm3. So 5 'liters'(2.5 kg /(0.5 kg/dm3) ) of wheat straw pellet is energetically equivalent to 1 liter of diesel(So five to one about volume energy comparison). Would it be ok for bulky vehicles? 

  

 

 

 

In principle, it should be possible to incorporate a micro Combined Cycle Gas Turbine power plant into the design of a large tractor unit. Modern designs of CCGT are routinely specified at >50% thermal efficiency, so it should represent a major advance on your historic baseline.

Putting solid fuel through a GT is a bit problematic so you'd likely be looking at some version of liquid biofuel (biodiesel, ethanol etc) for base fuel as a practical proposition. 

Following combustion in the GT, the exhaust gas would pass to a HRSG (Heat Recovery Steam Generator) raising superheated mains steam to feed a condensing steam turbine, with condensate recovered from (perhaps) overhead air cooled condensers for return to the steam drum. The water circuit would therefore be closed cycle.

The split of power output between the cycles would be of order 2:1 (GT:ST) so I guess it wouldn't quite be pure steam punkery. 

[harlock]

On 4/11/2022 at 9:16 PM, sethoflagos said:

In principle, it should be possible to incorporate a micro Combined Cycle Gas Turbine power plant into the design of a large tractor unit. Modern designs of CCGT are routinely specified at >50% thermal efficiency, so it should represent a major advance on your historic baseline.

Putting solid fuel through a GT is a bit problematic so you'd likely be looking at some version of liquid biofuel (biodiesel, ethanol etc) for base fuel as a practical proposition. 

Following combustion in the GT, the exhaust gas would pass to a HRSG (Heat Recovery Steam Generator) raising superheated mains steam to feed a condensing steam turbine, with condensate recovered from (perhaps) overhead air cooled condensers for return to the steam drum. The water circuit would therefore be closed cycle.

The split of power output between the cycles would be of order 2:1 (GT:ST) so I guess it wouldn't quite be pure steam punkery. 

Surely pellet(solid fuel) from agricultural residues would replace a liquid carburant(diesel especially...) where it'd be possible to use it(in agricultural machines for example). 

 

Please note

I read that one hectare of sugar cane produces 10 tonnes of dry bagasse and 10 of dry leaves left in the field(They aren't used to obtain sugar). 

It's an incredible resource to have solid fuels...  It's energetically equivalent to around 8E3 litres of diesel without considering efficiency etc... 

[exchemist]

58 minutes ago, harlock said:

Surely pellet(solid fuel) from agricultural residues would replace a liquid carburant(diesel especially...) where it'd be possible to use it(in agricultural machines for example). 

 

Please note

I read that one hectare of sugar cane produces 10 tonnes of dry bagasse and 10 of dry leaves left in the field(They aren't used to obtain sugar). 

It's an incredible resource to have solid fuels...  It's energetically equivalent to around 8E3 litres of diesel without considering efficiency etc... 

Bagasse is already used to provide power to run the sugar mill, with excess sold to the electricity grid. https://en.wikipedia.org/wiki/Bagasse. 

[sethoflagos]

On 6/27/2022 at 4:09 PM, harlock said:

Surely pellet(solid fuel) from agricultural residues would replace a liquid carburant(diesel especially...) where it'd be possible to use it(in agricultural machines for example).  

The primary argument of your OP was that pelletised wheat straw was a cheaper energy source than diesel. 

Since the price of both diesel and biofuel are determined primarily by demand (ie not production costs) this is a good indication that in general the reverse is true. Otherwise wood burning locomotives would simply have converted to general biomass fuels and still be with us. 

@swansontand @exchemisthave aleady listed a number of associated costs that you have ignored in your analysis.

A few more might be:

* Solid biomass fuels need to be heat dried whereas liquid hydrocarbon fuels are dried by gravity settlement.

* Pelletised biomass burns far more slowly than hydrocarbon aerosols requiring a much bigger combustion zone - increased capital costs.

* Pelletised biomass requires ~40% higher excess air to approach the combustion efficiency of liquid HCs - lower useful energy output.

And if we start to consider the environmental impact:

* The combination of low efficiency and high fuel oxygen content sends the CO2 produced per kJ of shaft energy through the roof. Coal is environmentally less damaging than this proposal.