8 replies to this topic

[atul_chem]

How much amount of 60 psig saturated steam should be mixed with 140 psig saturated steam to get 120 psig saturated steam using PRDS.

I will be grateful if you can show the calculations also.

[sheiko]

How much amount of 60 psig saturated steam should be mixed with 140 psig saturated steam to get 120 psig saturated steam using PRDS.

I will be grateful if you can show the calculations also.

Hello,

Heat will be transferred from 140 to 60 psig saturated steam.

So if we call:

ta = (equilibrium) temperature of 120 psig (8.3 barg) saturated steam = 178°C
t1 = temperature of 60 psig (4.1 barg) saturated steam = 153°C
t2 = temperature of 140 psig (9.7 barg) saturated steam = 182°C
m1 = amount of 60 psig saturated steam
m2 = amount of 140 psig saturated steam
m = total amount of saturated steam

And:

ta = (m1*t1 + m2*t2) / (m1+m2), given that the bodies in contact are of the same nature (steam) and there is no phase change.
m = m1+m2

Then, assuming a value for m, you can solve for m1 and m2 (as there are 2 unknowns (m1 and m2) and 2 equations).

This is the way i would solve it. To be confirmed.

Please let us know the result!

[Qalander (Chem)]

Dear sheiko,

Excellent Response! I must say.
Regards
Qalander

[katmar]

I am not sure that the method proposed by Sheiko is meaningful. If there were a way of simply mixing them, like mixing hot water with cold milk in a bowl in your kitchen, then the temperature change will be a simple ratio to the masses (assuming constant specific heat) the way Sheiko has done it.

But you can't just bleed the 60 psig steam into the 140 psig steam pipe because it will not flow into the zone of higher pressure. Similarly, you cannot bleed 140 psig steam into a 60 psig steam line to get 120 psig because the 60 psig steam will stop flowing.

You will need to use a venturi vacuum ejector and the mixing rules are a lot more complex. Perry has some simple charts for estimating ejector flows. You may well find that when you mix 60 psig steam with 140 psig steam to give 120 psig as the outlet pressure you do not get saturated steam as a result.

[ankur2061]

Hi,

I agree with Harvey. The scenario does not look to be a practical scenario. The only mixing scenario I know in steam is when you do a mass and enthalpy balance for a desuperheater in which water is sprayed in steam to remove the degree of superheat from the steam specially after a pressure reduction station, which causes a further increase in the degree of superheat.

The desuperheater calculations are done to calculate the quantity of water sprayed for desuperheating and generally the mass flow at the desuperheater outlet is specified. The other inputs required are the temperature and pressure (read enthalpy) of the water sprayed and the temperature and pressure (read enthalpy) of the inlet superheated steam.

Regards,
Ankur.

[atul_chem]

Thanks to all for your reply.

I agree with Katmar. Mixing of two sreams at different pressures is only possible with thermocompressors.

but i need examples of calculations of the topic described earlier.

[Qalander (Chem)]

Probably I had some 'Between the lines' feelings conveyed through my previous post.

My implied meanings were

1) Whenever someone wants his/ her own work done unduly through others, then he/ she should only be guided 'at the most ' in a way the help was provided by sheiko in the aforementioned response.

2) This must have presumably made the OP to ponder about and work little bit more than just posting queries in such forums.

Dear Harvey/ankur; there was no other intention whatsoever.

Specifically and Technically speaking in all fairness Harvey, you had been accurate in pointing out about correct approach to the OP's query resolution.

I Hope no Hard feelings, still I apologize if any inconvenience caused to anyone in any way.

Best regards
Qalander

[katmar]

Hi Qalander,

I don't understand what you mean by "Hope there are no hard feelings". If I have offended you in any way I offer my unreserved apologies. Certainly, there are no hard feelings from my side.

I have not done the venturi calculations for this exercise myself. Too much like hard work for me!! All I was suggesting is that there may be wider issues to consider.

Regards
Harvey

[Qalander (Chem)]

Hi Qalander,

I don't understand what you mean by "Hope there are no hard feelings". If I have offended you in any way I offer my unreserved apologies. Certainly, there are no hard feelings from my side.

I have not done the venturi calculations for this exercise myself. Too much like hard work for me!! All I was suggesting is that there may be wider issues to consider.

Regards
Harvey

Actually my apology was directed to all Including the OP and as such 'General'
Best Regards
Qalander