Steam injection calculation

[bogu]

Can somebody help me? I need to calculate the amount of steam required to heat a tank of water via direct injection. This is the type of thing I should know but have forgotten. Can some body please provide a formula.

Thanks

Bogu

 

[TD2K]

If you know the inlet pressure and temperature of the steam, you know its enthalphy. Then, you know the temperature of the water when you start the heating cycle and thus its enthalphy. At the end of the heating cycle, you know the temperature and thus its enthalpy. For the enthalphy, use the steam tables.

Estimate the mass of water in the tank when you start and do an enthalphy balance. I'm sure you can handle the math.

 

[25362]

If the heating of water is at atmospheric pressure and below boiling conditions a simplified result would be:

S=w(t₂-t₁)/(H-t₂)

from an enthalpy balance,

S.H+w.Cp.t₁=(w+S)Cp.t₂

where
S: mass of steam; w: original mass of water; t_1,2: water temperatures, initial and final; H: enthalpy of steam from tables.
The above assumes the heat capacity, Cp, of water is constantly equal to 1.0.
Use consistent units.

 

[isofuncurves]

I do not know what your application is but you may not want to forget about the energy required to heat up the mass of the vessel. This is often very significant.

Carl

 

[chicopee]

td2k has not said much about mass baly

 

[SAK9]

25362,

I am doing a similar project.Steam is injected into a tank containing water to heat up water from 30C to 135C. Steam at 3~4 bar is being used.But heating is done with vessel sealed so the pressure inside the tank is same as the steam pressure.I have done the steam flow calculation based on a simple heat balance ie same as the formula you indicated above.But you mentioned this equation holds for heating at atmosphereic pressure only.What other factors should I take into account for heating above atmospheric presure?Could you please indicate the formula for steam rate calculation for such a process?

Many thanks

 

[quark]

SAK9!

I don't see any problem in using the equation(simple enthalpy balance) stated by 25362. Moreover, this seems to be more appropriate for a pressurized application, for there won't be energy escape.

But how are you maintaining same pressure in the tank? By steam in the free space? If you require to heat up large quantity of water, try for hot water generators.

Regards,


Believe it or not : Though human body is made up of intricate and subtle mechanism, it is very poor in energy conversion. The maximum efficiency is 20% during cycling. During under water swimming it is just 4%.

 

[SAK9]

Quark,
Thanks for your reply.This is biowaste tank.The contents need to be steam sterilised before discharging the waste.The tank is pulled to vacuum and steam at 3~4 bar is injected in.Once the water reaches 100C,the the tank vent valve is closed.There is no pressure control inside the tank.The tank pressure would rise from vacuum level to an ultimate pressure level equal to the steam pressure ie 3~4 bar.

 

[25362]

The enthalpy of water at @ 30^oC is 30.02 kcal/kg, and @ 135^oC, it is 135.6 kcal/kg.
That of steam at 144^oC is 654.2 kcal/kg.

An enthalpy balance would show:

m_w*30.2 + m_s*654.2 = (m_w+ m_s)*135.6,
thus
m_w*(135.6-30.2)=m_s*(654.2-135.6)
or
105.4*m_w=518.6* m_s
and
m_s/m_w=105.4/518.6=0.203.

The mass of steam m_s= 0.203* m_w

Plus any additional steam to heat up the container walls and to replace heat lost to the surroundings.

 

[quark]

SAK9!

I think you are talking about Kill Tanks. Why do you require to vacuumise the tank? If your vent is on till you get 100⁰C, there won't be any air left in, which will significantly disturb your temperature distribution. This is what we do generally. Anyhow it is your own process.

BTW, sometime back I downloaded an excel spreadsheet about kill tank design which I can send to you if you want. Just see whether it will be of any help to you. Give me your id.

Regards,


Believe it or not : Though human body is made up of intricate and subtle mechanism, it is very poor in energy conversion. The maximum efficiency is 20% during cycling. During under water swimming it is just 4%.

 

[SAK9]

Quark,

Many thanks for your help.

anil5@singnet.com.sg

 

[SAK9]

25362,
Many thanks indeed for the derivation of the equation.