7 replies to this topic

[ssengr62]

Dear all,
I hope you are fine.

I have been given some assignment. We have water in deaerator and we want to evaporate this by spargin steam through the sparger.

Deaerator size 5830mm ID x 21800T/T.

Steam available at 144 deg C and 5.5 bar.g through 4inch line.

Is it possible to evaporate water through deaerator by using this steam.

How can I calculate?

Urgent help needed.

Thank you

Best Regards

Sajid

[breizh]

http://www.spiraxsar...-deaerators.asp

Consider this resource , it might helps you.

Note : Consider this link to support additional needs:
http:// www.spiraxsarco.com


Breizh

[kushal.raval]

one thing...why require to evaporate water? I think absorbed gases are required to be removed.

[Bobby Strain]

The deareator's function is to strip oxygen and/or CO2 from the feedwater. Steam requirement depends on the internals design. So, best to consult the equipment supplier.

Bobby

[T.S.MURALI]

Deaerator is meant to dislodge oxygen and non condensables (inerts, Co2/N2) from Feed water -not to evaporate water.
First , you must know the principles of Deaeration.

Pressurised Deaerator pressure is o.2 bar g which corresponds to Tsat =105 Deg C.

Deaerator removes O2 , to ensure that O2 concentration is 7 parts per billion minimum. Deaerator is an equipment designed to combat corrosion contributor Oxygen.

Steam is required just to ensure the said temp. is maintained.

O2 and other non condensable gases are vented out from D.A through properly sized vent nozzle

Steam required may be around 3% of Boiler capacity. Of course , you can always arrive at this by H& M balance. So Deaerator is not an evaporator.

[S.AHMAD]

ssengr62
Do a heat balance and find out whether it can e done! I have a strong feeling that it cannot be done. Water in the de-aerator accumulates instead. In your heat balance, please include sensible heat of water and heat loss to surrounding.

[T.S.MURALI]

Equation Cited is the mass / heat balance equation used for this purpose.

Equation

Where: = Maximum boiler output at the initial feedwater temperature (kg / h) - This is the boiler 'From and At' figure x the boiler evaporation factor. _s = Mass of steam to be injected (kg / h) h₁ = Enthalpy of water at the initial temperature (kJ / kg) h₂ = Enthalpy of water at the required temperature (kJ / kg) h_g = Enthalpy of steam supplying the control valve (kJ / kg) - Note: if the supply steam is superheated, this value is the total heat in the superheated steam (h).
To calculate the required steam flowrate, Equation is transposed to solve for _s,and becomes Equation

Equation

Example- Determine the amount of steam needed to heat a deaerator

Typical pressurised deaerator installation

An existing boiler plant is fed with feedwater at a temperature of 85°C. Due to the rising cost of chemical treatment, it is proposed that a pressurised deaerator be installed, operating at 0.2 bar g to raise the feedwater temperature to 105°C, reducing the solubility of oxygen to quantities typically measured in parts per billion. Steam, produced in the boiler at 10 bar g, is to be used as the heating agent. If the 'From and At' rating of the boiler plant is 10 tonne / h, determine the flowrate of steam required to heat the deaerator.
Where:

Boiler 'From and At' rating = 10 000 kg / h

Initial feedwater temperature = 85°C

Initial feedwater enthalpy at 85°C (h₁) = 356 kJ / kg (from steam tables)

Boiler pressure = 10 bar g

Enthalpy of saturated steam at 10 bar g (h_g) = 2 781 kJ / kg
Before any calculations can be made to estimate the size of the deaerator, it is important to know the maximum likely feedwater requirement. This is determined by calculating the boiler(s') maximum useful steaming rate, which in turn, depends on the initial feedwater temperature. The maximum steaming rate is found by determining the Boiler Evaporation Factor

Where:

A = Specific enthalpy of evaporation at atmospheric pressure is 2 258 kJ / kg

B = Specific enthalpy of saturated steam at boiler pressure (h_g) in (kJ / kg)

C = Specific enthalpy of the feedwater (h₁) in (kJ / kg)

Equation shown is used to find the required amount of steam to heat the deaerator.

From steam tables;
Enthalpy of feedwater at the required temperature of 105°C (h₂) = 440 kJ / kg
Enthalpy of steam supplying the control valve @ 10 bar g (h_g) = 2 781 kJ / kg

From above;
Enthalpy of the feedwater at say 85°C (h₁) = 356 kJ / kg
Mass flowrate of water make-up to deaerator () = 9 311 kg / h

Therefore, the control valve has to be able to supply 334 kg / h of steam with a supply pressure of 10 bar g, and with a downstream pressure of 0.2 bar g.


ACK:
Thanks to Spirax sarco for their site info

[ssengr62]

Deaerator is filled with water

35

%
Capacity of Drum

990

tons
Quantity of water in tank at 28 C

347

tons
Quantity of steam required at 155 C

4000

tons
Steam flow rate from 4" line

8.25

tons/hr
Total time required to evaporate water

485

hr

20

days











I answered my boss like as above. Actually the idea of my my boss was to evaporate and blow the 18" line at the top of evaporator that was impossible becuase even though we evaporate we cannot have so high velocity to blow the line.

Thank you so much for all you.