6 replies to this topic

[Rahul Jha]

Sizing spray nozzle for quenching flue gas from 310 degree C to 220 degree C

I fresh graduate from university, recently joined a project responsible for building flue gas desulphurization unit. I have been assigned to review a calculation done by a design company.

Objective: To determine amount of boiler feed water (900 psi, 140 degree C) will be required to cool flue gas from 310 to 220 degree C. Mass flow rate and mass fraction for flue gas component are know. Flue gas will be flowing in a duct where pressure is – 1’’ WC, and quench water will be sprayed co-currently.

My approach: Water will gain heat, (latent heat of vaporization and then the steam will be superheated to final 220 degree C) = Flue gas will loose heat and get to the temp of 220 degree C

Designer’s approach: Water will gain heat, (Only latent heat of vaporization was used, this means the water and gas mixture will have different temperatures i.e. water 100 degree C and flue gas 220 degree C) = Flue gas will loose heat and get to temp of 220 degree C.

Please help me to understand which approach is right. Also, if you have any sample calculations for quench water requirement, please send it to me.

Thanks,

Rahul Jha

Edited by Rahul Jha, 15 April 2010 - 08:22 PM.

[ankur2061]

Sizing spray nozzle for quenching flue gas from 310 degree C to 220 degree C

I fresh graduate from university, recently joined a project responsible for building flue gas desulphurization unit. I have been assigned to review a calculation done by a design company.

Objective: To determine amount of boiler feed water (900 psi, 140 degree C) will be required to cool flue gas from 310 to 220 degree C. Mass flow rate and mass fraction for flue gas component are know. Flue gas will be flowing in a duct where pressure is – 1’’ WC, and quench water will be sprayed co-currently.

My approach: Water will gain heat, (latent heat of vaporization and then the steam will be superheated to final 220 degree C) = Flue gas will loose heat and get to the temp of 220 degree C

Designer’s approach: Water will gain heat, (Only latent heat of vaporization was used, this means the water and gas mixture will have different temperatures i.e. water 100 degree C and flue gas 220 degree C) = Flue gas will loose heat and get to temp of 220 degree C.

Please help me to understand which approach is right. Also, if you have any sample calculations for quench water requirement, please send it to me.

Thanks,

Rahul Jha

Rahul,

The mixture (water + flue gas) temperature wiil definitely be at 220 deg C, but if you consider an enthalpy balance for water you will find that the water sees a saturation temperature corresponding to it's saturation pressure which in this case is 1" WC which makes the designers approach correct. You can check out the saturation temperature corresponding to a saturation pressure of 1" WC from steam tables.

Regards,
Ankur.

[Claudia K.]

The designer is right. Think about it: your gas and water are in co-current. So, how could water reach 220C (the same temperature as the gas)? At least 20-30 C difference between fluxes should be at the end of the quench process. Consider schematically that all the heat the gas delivers is used to evaporate the water at 140 C, 900 psi, so water enters liquid at 140C, 900 psi and goes out steam at 140 C, 900 psi.
Good luck,
Claudia K.

Sizing spray nozzle for quenching flue gas from 310 degree C to 220 degree C

I fresh graduate from university, recently joined a project responsible for building flue gas desulphurization unit. I have been assigned to review a calculation done by a design company.

Objective: To determine amount of boiler feed water (900 psi, 140 degree C) will be required to cool flue gas from 310 to 220 degree C. Mass flow rate and mass fraction for flue gas component are know. Flue gas will be flowing in a duct where pressure is – 1’’ WC, and quench water will be sprayed co-currently.

My approach: Water will gain heat, (latent heat of vaporization and then the steam will be superheated to final 220 degree C) = Flue gas will loose heat and get to the temp of 220 degree C

Designer’s approach: Water will gain heat, (Only latent heat of vaporization was used, this means the water and gas mixture will have different temperatures i.e. water 100 degree C and flue gas 220 degree C) = Flue gas will loose heat and get to temp of 220 degree C.

Please help me to understand which approach is right. Also, if you have any sample calculations for quench water requirement, please send it to me.

Thanks,

Rahul Jha

[Rahul Jha]

Sizing spray nozzle for quenching flue gas from 310 degree C to 220 degree C

I fresh graduate from university, recently joined a project responsible for building flue gas desulphurization unit. I have been assigned to review a calculation done by a design company.

Objective: To determine amount of boiler feed water (900 psi, 140 degree C) will be required to cool flue gas from 310 to 220 degree C. Mass flow rate and mass fraction for flue gas component are know. Flue gas will be flowing in a duct where pressure is – 1’’ WC, and quench water will be sprayed co-currently.

My approach: Water will gain heat, (latent heat of vaporization and then the steam will be superheated to final 220 degree C) = Flue gas will loose heat and get to the temp of 220 degree C

Designer’s approach: Water will gain heat, (Only latent heat of vaporization was used, this means the water and gas mixture will have different temperatures i.e. water 100 degree C and flue gas 220 degree C) = Flue gas will loose heat and get to temp of 220 degree C.

Please help me to understand which approach is right. Also, if you have any sample calculations for quench water requirement, please send it to me.

Thanks,

Rahul Jha

Rahul,

The mixture (water + flue gas) temperature wiil definitely be at 220 deg C, but if you consider an enthalpy balance for water you will find that the water sees a saturation temperature corresponding to it's saturation pressure which in this case is 1" WC which makes the designers approach correct. You can check out the saturation temperature corresponding to a saturation pressure of 1" WC from steam tables.

Regards,
Ankur.

Thanks Ankur,
At the exit of vessel mixture ( water/Steam + flue gas) temperature is 220 degee C. So, water/steam @ 220 degee and flue gas is also at 220 degee C. How did water reach from T ( 100 c) saturation at 1'' WC reached 220 degre C. In order for water to reach that temperature, it requires heating steam from 100 degee C to 220 degree C, am I right or am missing something. Please help.

Regards,
Rahul Jha

[ankur2061]

Thanks Ankur,
At the exit of vessel mixture ( water/Steam + flue gas) temperature is 220 degee C. So, water/steam @ 220 degee and flue gas is also at 220 degee C. How did water reach from T ( 100 c) saturation at 1'' WC reached 220 degre C. In order for water to reach that temperature, it requires heating steam from 100 degee C to 220 degree C, am I right or am missing something. Please help.

Regards,
Rahul Jha

Rahul,

Can you provide your mass & heat balance calculations as an excel sheet attachment. Members could review it and suggest whether your methodology is correct or not.

Regards,
Ankur.

[Claudia K.]

Sorry for yesterday mistake: The steam going out from the system will have the quench system pressure. However, don't you think 900 psi is an enourmous pressure. Can you check it? It is more reasonable 90 psi.
Claudia K.

Sizing spray nozzle for quenching flue gas from 310 degree C to 220 degree C

I fresh graduate from university, recently joined a project responsible for building flue gas desulphurization unit. I have been assigned to review a calculation done by a design company.

Objective: To determine amount of boiler feed water (900 psi, 140 degree C) will be required to cool flue gas from 310 to 220 degree C. Mass flow rate and mass fraction for flue gas component are know. Flue gas will be flowing in a duct where pressure is – 1’’ WC, and quench water will be sprayed co-currently.

My approach: Water will gain heat, (latent heat of vaporization and then the steam will be superheated to final 220 degree C) = Flue gas will loose heat and get to the temp of 220 degree C

Designer’s approach: Water will gain heat, (Only latent heat of vaporization was used, this means the water and gas mixture will have different temperatures i.e. water 100 degree C and flue gas 220 degree C) = Flue gas will loose heat and get to temp of 220 degree C.

Please help me to understand which approach is right. Also, if you have any sample calculations for quench water requirement, please send it to me.

Thanks,

Rahul Jha

[Rahul Jha]

Sorry for yesterday mistake: The steam going out from the system will have the quench system pressure. However, don't you think 900 psi is an enourmous pressure. Can you check it? It is more reasonable 90 psi.
Claudia K.

Sizing spray nozzle for quenching flue gas from 310 degree C to 220 degree C

I fresh graduate from university, recently joined a project responsible for building flue gas desulphurization unit. I have been assigned to review a calculation done by a design company.

Objective: To determine amount of boiler feed water (900 psi, 140 degree C) will be required to cool flue gas from 310 to 220 degree C. Mass flow rate and mass fraction for flue gas component are know. Flue gas will be flowing in a duct where pressure is – 1’’ WC, and quench water will be sprayed co-currently.

My approach: Water will gain heat, (latent heat of vaporization and then the steam will be superheated to final 220 degree C) = Flue gas will loose heat and get to the temp of 220 degree C

Designer’s approach: Water will gain heat, (Only latent heat of vaporization was used, this means the water and gas mixture will have different temperatures i.e. water 100 degree C and flue gas 220 degree C) = Flue gas will loose heat and get to temp of 220 degree C.

Please help me to understand which approach is right. Also, if you have any sample calculations for quench water requirement, please send it to me.

Thanks,

Rahul Jha

we will be using boiler feed water for quenching. And the final pressure will be close to atmpospheric. Thanks