6 replies to this topic

Hi,

I am trying to determine the continuous blowdown rate of a gas boiler.

the information that i have is the properities of the feed water (i.e. the hardness, silica content etc....), the steam load which is 275000 lb/hr and and the recommended silica carry-over in the steam.

Vendor data supplied had the total solids in the boiler water, recommended silica content is the boiler water and maximum phosphates required to precipitate the calciuma and magnisum ions.

can you assist as to how do you determine the blow down rate of a boiler?

thanks

[S.Chittibabu]

Hi,I am trying to determine the continuous blowdown rate of a gas boiler.the information that i have is the properities of the feed water (i.e. the hardness, silica content etc....), the steam load which is 275000 lb/hr and and the recommended silica carry-over in the steam.Vendor data supplied had the total solids in the boiler water, recommended silica content is the boiler water and maximum phosphates required to precipitate the calciuma and magnisum ions.can you assist as to how do you determine the blow down rate of a boiler?thanks

Mr Spreppy,You have not mentioned what is the operating pressure and what is the feed water quality. The quality varies as per the pressure rating and treatment also differs. Visit Spirax Sarco boiler site and read module 3.12, Boiler house, to have more about the basic of controlling the blowdown rate.GoodluckS.Chittibabu

Hi,

I am trying to determine the continuous blowdown rate of a gas boiler.

the information that i have is the properities of the feed water (i.e. the hardness, silica content etc....), the steam load which is 275000 lb/hr and and the recommended silica carry-over in the steam.

Vendor data supplied had the total solids in the boiler water, recommended silica content is the boiler water and maximum phosphates required to precipitate the calciuma and magnisum ions.

can you assist as to how do you determine the blow down rate of a boiler?

thanks

Mr Spreppy,

You have not mentioned what is the operating pressure and what is the feed water quality. The quality varies as per the pressure rating and treatment also differs. Visit Spirax Sarco boiler site and read module 3.12 Boiler house to have more about the basic of controlling the blowdown rate.

Goodluck
S.Chittibabu

Thanks will research this site immediately. The feed water quality is as follow,
<0.05 hardness
<0.01 iron
<1.00 silica
0 chlorine
8.5-9.0 ph

The boilers are required to produce 650 deg F and 450 psig superheated stem

[mishra.anand72@gmail.com]

May be 0.05 to 0.1 % of total flow. Consequently sodium sulhite dosing needs to be adjusted.

May be 0.05 to 0.1 % of total flow. Consequently sodium sulhite dosing needs to be adjusted.

Okay, 0.05% to 0.1%,
Is there is a calculation to determine the blowdown rate, if so can you assist step wise as to how you determine the blowdown rate.

With regard to the cycles as well, to optimize the blowdown rate

please assist and thanks very much for you timely response

[ahmedsoorma]

May be 0.05 to 0.1 % of total flow. Consequently sodium sulhite dosing needs to be adjusted.

Okay, 0.05% to 0.1%,
Is there is a calculation to determine the blowdown rate, if so can you assist step wise as to how you determine the blowdown rate.

With regard to the cycles as well, to optimize the blowdown rate

please assist and thanks very much for you timely response

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1. Cycle is usually caculated by dividing the blowdown water TDS by the feed water TDS. For the 450 psig boiler, the blowdown TDS is available in table form at the ABMA site. This number is your blowdown limit and the boiler needs to have automatic blowdown with actuating controller run by a TDS meter monitor.

For Feed water, you need to ensure that recovered steam as condensate is counter currently passed into the feed tank so that the feed water temprature is as near as possible to 90 deg C. This will cut your catalyzed sodium sulphite dosage as well as the cost. For each ppm Oxygen, the theoretical limit is 8 ppm on a stoichiometric basis but practicaLLY YOU SHOULD FEED IT IN AT BETWEEN 10 TO 12 PPM TO TAKE INTO ACCOUNT THE AIR LEAKAGE VIA THE FEED PUMP.

Ensure that the gland packing of the feed pump meets the temperature critreia for the feed water temperature.

Ahmed Soorma

[Satyajit]

Spreppy,
Normal Continuous Blow down ( CBD) rate should be @5500 Lbs/Hr which is @2% of your Boiler feed Water flowrate.
But you have to adjust it based on conductivity of the boiler blow down water. Normally Conductivity in all such boilers are kept < 50 ms/cm.

For Silica: you should go for Intermittent Blow down ( IBD) to keep silica in blow down water < 0,2 ppm. THis has to be done carefully for 30 sec may be 2-3 times a day or a week depending on silica content. Watch Boiler drum level while doing this job or it may end up in tripping the boiler on low low level.
Hope this meets your requirement.
Kind regards,
Satyajit