Steam Calculation

[remp]

How do you calculate approximatly the energy (kWatts)required to generate 300kg/hr of steam. I have medium temp hot water at 138/115 deg C serving a humidifiers heat exchanger, and I need to know the kW and L/s of the hot water.???

 

[sailoday28]

What is the condition of the steam, Pressure and Temperature (or saturated)?

 

[remp]

Dont know. Its for an air handling unit humidifier

 

[quark]

Latent heat of steam is approximately 550 kcal/kg or 2310 kJ/kg. As you may not require any sensible heat(the pressures corresponding to the temperatures you specified are well enough for humidification application) to bring water temperature near to saturation, just calculate energy required for latent portion of heat.

For 300 kg/hr you require 300x2310 kJ/hr or 693000 kJ/hr or 192.5 kW. As there are no water losses, your hot water flow rate should be 0.083L/s (add 1 to 2% for blowdown).

Not a good idea to go with electric boilers.

Regards,

 

[friartuck]

Why not try an air spray washer. It will cost much less to run.

Try JS Humidifiers.

Friar Tuck of Sherwood

 

[remp]

quark,

Should the water flow rate in L/s be 2.0l/s since the delta T of the hot water serving the humidifier Heat exchanger is 23deg C.???, It's the Hot water flow rate im trying to calculate.

 

[quark]

Ok, now I have a better idea. You want to produce steam by utilizing hot water. The theoretical calculation will be,

693000 kJ/hr = m(kg/hr)x4.2 kJ/kg⁰Cx23⁰C

So the mass flow rate of hot water will be 7173.91 kg/hr or 1.99 kg/hr (~1.99 Lit/sec). This calculation considers supply of 100⁰C feed water.

If your water temperature is 30⁰C and you want to use a dT of 23⁰C, then the hot water flowrate should be 8086 kg/hr or 2.25 L/s for steam at 1 atmosphere.

You have some important things to check.

1. Is overall heat transfer coefficient of the heat exchanger is sufficient to produce the steam quantity required?

2. Is it primarily designed for similar application? (steam formation near the pipe wall will reduce the overall heat transfer coefficient)

3. Dryness fraction of steam produced in the above manner will be low and subsequently the humidified air temperature will drop down. You have to provide reheating.

Regards,

 

[25362]

To produce 300 kg/h of humidity, by vaporizing water in your exchanger/humidifier (isothermally) at 25^oC, with hot water cooled in a range of 23 ^oC, you'll need 300 kg/h*2442.5 kJ/kg=732750 kJ/h or 203.5 kJ/s.

A hot water drop from 138 to 115^oC would mean a drop of about 98 kJ/kg which would result in 2.08 kg/s = 2.24 L/s of hot water.