Compressing steam and water together

[Mech_Engineer]

What I know is if the steam will remain saturated during the process, compression will take much less power.

Take much less power for achieving what??

 

[pranj5]

For steam compression. If steam can be compressed with much less power, that means opening of new horizon in power generation.

 

[Chestermiller]

It's pretty simple. As for example, if wet steam has been compressed to 10 bars and it will become 20% wet steam at 180C.

This is the final state of the compressed wet steam. What do you envision as a typical initial pressure, temperature, and wetness of the steam for this situation?

 

[pranj5]

This is the final state of the compressed wet steam. What do you envision as a typical initial pressure, temperature, and wetness of the steam for this situation?

This has been written in reply to Mech_Engineer's post that wet steam has low quality and I just want to show him that the quality of steam at higher pressure can be increased by applying heat to it. I don't have any vision about the initial stage from where the steam has started. Just somehow its pressure has been increased and still it has water inside and therefore it's wet, saturated steam and can be considered as low quality.

 

[Chestermiller]

This has been written in reply to Mech_Engineer's post that wet steam has low quality and I just want to show him that the quality of steam at higher pressure can be increased by applying heat to it. I don't have any vision about the initial stage from where the steam has started. Just somehow its pressure has been increased and still it has water inside and therefore it's wet, saturated steam and can be considered as low quality.

I thought all along you have been talking about compressing it adiabatically, without adding any heat.

 

[pranj5]

Kindly note that heat will be added here after the compression being completed. Not before or during the process.

 

[Mech_Engineer]

For steam compression. If steam can be compressed with much less power, that means opening of new horizon in power generation.

I'm sorry to say this is incorrect. Thermodynamic cycles for power generation do not depend on compressing steam, as I've already pointed out in the discussion of the Rankine cycle which is used in power stations worldwide. The efficiency of the Rankine cycle is driven by the amount of work the turbine can extract, which is defined as step 3-4 in the diagram:

Typical methods for increasing the efficiency of this cycle are superheating the steam for a higher temperature starting point (higher carnot efficiency), and regenerative cycles which take advantage of residual heat in the tubine's exhaust with multi-stage expansion systems (in conjunction with superheating).

 

[pranj5]

I'm sorry to say this is incorrect.

If steam can be compressed to higher pressure from lower pressure, that will have many many applications than just power generation. Steam is used in many kind of industries and a huge amount is wasted at present as steam compressors will consume more energy and they are costly and therefore making new steam by using conventional fuel is cheaper in comparison to compressing low pressure steam to higher pressure. But, if the power consumption can be reduced by any means, much less fuel will be burnt and that means lower GHG emission.
As for example, at present it will take around 800 kW (multiple stage compressor with intercooler) to compress steam from 2.536 kPa (saturated steam pressure at 20C) to 1 bar @ 1 kg/sec. While the amount of heat embedded in 1 kg/sec steam flow is around 2.6 MW. Now, if we consider that the electricity comes from a thermal power plant with around 33% efficiency, that means it will take 2.4 MW of heat to produce 800 kW of electricity and at the end we will just have left with 200 kW of heat, a mere return against huge investment in steam compressor. But, if the steam will remain in saturated state during the whole process, that amount can be reduced to just 200 kW and you yourself can calculate the increase in the amount of additional heat which can make the investment in steam compressors more attractive and can save huge amount of fuel.

 

[Mech_Engineer]

But, if the steam will remain in saturated state during the whole process, that amount can be reduced to just 200 kW and you yourself can calculate the increase in the amount of additional heat which can make the investment in steam compressors more attractive and can save huge amount of fuel.

I think its time you calculate the alleged savings before making any more claims. Use a steam chart of your choosing, maybe the h-s chart we were looking at before.

 

[Chestermiller]

If steam can be compressed to higher pressure from lower pressure, that will have many many applications than just power generation. Steam is used in many kind of industries and a huge amount is wasted at present as steam compressors will consume more energy and they are costly and therefore making new steam by using conventional fuel is cheaper in comparison to compressing low pressure steam to higher pressure. But, if the power consumption can be reduced by any means, much less fuel will be burnt and that means lower GHG emission.
As for example, at present it will take around 800 kW (multiple stage compressor with intercooler) to compress steam from 2.536 kPa (saturated steam pressure at 20C) to 1 bar @ 1 kg/sec. While the amount of heat embedded in 1 kg/sec steam flow is around 2.6 MW. Now, if we consider that the electricity comes from a thermal power plant with around 33% efficiency, that means it will take 2.4 MW of heat to produce 800 kW of electricity and at the end we will just have left with 200 kW of heat, a mere return against huge investment in steam compressor. But, if the steam will remain in saturated state during the whole process, that amount can be reduced to just 200 kW and you yourself can calculate the increase in the amount of additional heat which can make the investment in steam compressors more attractive and can save huge amount of fuel.

You seem so very confident about all this. And, since you are so confident, what was your reason for starting this thread in the first place?

 

[pranj5]

I think its time you calculate the alleged savings before making any more claims. Use a steam chart of your choosing, maybe the h-s chart we were looking at before.

As per this http://www.criticalprocesses.com/Use%20of%20enthalpies%20to%20calculate%20energy%20needed.htm, it will take around 135.1 kJ/kg to compress steam from 2.536 kPa to 1 bar (20C saturation level to 100C saturation). And if the machine is 70% efficient, then the gross power consumption would be 193 kW for producing 1 kg/sec steam flow. And, that means the gross enthalpy stored in steam at 100C is around 2674.95 kW. Now, if we consider that the electricity comes from a 33% efficient plant, that means 193 kW of electricity equals to 579 kW of heat. If we subtract that from 2674.95, that equals to 2095.95 kW of heat. Not a bad amount at all.
All the data i have from this site.

You seem so very confident about all this. And, since you are so confident, what was your reason for starting this thread in the first place?

Simple. I just want to be more confident and want to see how much correct I am. After all, we all are human and anybody can make mistakes.

 

[RonL]

I have a question at this point, I have two books by Babcock and Wilcock (?) titled "Steam", in one they mention that super heated steam that receives heat above the super heated point, will deliver 100% of that added heat at the point of use, but that line of thermodynamics is beyond the scope of this writing. Is this the realm that is the object of this thread pranj5 ?
These are old books and if this is an already known area, why is it not in practice already ? I dismissed it as requiring equipment that exceeds practical standards, when I was trying to make that special power for a Tesla Turbine.
I have been interested in this thread and the extraordinary patients of Chestermiller (Thanks) but it's certainly well over my head.

 

[Mech_Engineer]

...that equals to 2095.95 kW of heat. Not a bad amount at all.

What would that heat then be used for?