10 replies to this topic

[abbaschemical]

Dear Experts,
I am thinking of utilizing the CBD water from a steam drum (115 kg/cm2 g) of approximate flow of 4 ton/hr which has high heat content.
I found in many plants that this CBD water is always flashed and recoverd as LP(3 kg/cm2 or 12 kg/cm2)steam. Is there any practice of utilizing the CBD water in any process heat recovery requirement? The silica content in this CBD water is just 0.04ppm). I am planning to utilise this CBD water to heat a fraction of GV solution(Gimmarco Vetrocoke solution used in CO2 absorption unit - solution temperature is 130 C).
Please for all your comments , ideas and suggestions

Regards,
Abbas ali

Edited by abbaschemical, 11 December 2012 - 03:36 PM.

[S.AHMAD]

abbas
1. Recovering of CBD is quite common nowadays. The most common I have seen is to flash the CBD and the overhead steam is sent to de-aerator as supplement of dearating steam.
2. Or if you have any other cold streams that required heating, why not?

[abbaschemical]

Dear Ahamed,
Thanks for ur reply. Will this 4 T/hr of CBD water is feasible to design an exchanger and recover the heat. I mean to get to know about the design possibility.

[S.AHMAD]

You need to conduct an economic analysis - whether the additional investment is worth the capital. I believe, for recovery flashed-steam would be justifiable with 4t/h CBD. Alternatively consider to heat-up portion of BFW using double-pipe heat exchanger.

[kkala]

I remember a proposal in 2008 of 60 t/h steam boiler (40 kgf/cm2 g, 410 oC, max CBD=3 t/h - actually much lower) rejecting the continuous blow down (CBD), on the ground that flashing and sending steam to deaerator was not economically justified. Our client, having a different view on long term fuel prices, dictated the extra flash drum and piping to deaerator. Using CBD as hot water is usually more (economically) attractive than taking flash steam from it, since water can end up with a temperature lower than 100 oC.
Consequently I agree with S.AHMAD on that 4 t/h of CBD (115 kgf/cm2 g, 322 oC) is anticipated to be worthy of exploitation, to be verified by a brief feasibility study. Long term price of fuel saved through this extra investment has to be considered.

[abbaschemical]

Dear S.Ahamed and Kkala Sir,
Thanks for ur valuable suggestions and i will carryout my further studies regarding this. The only concern for me is that when this CBD water comes in contact with GV solution in an exchanger i feel about disintegration of GV(140 C) at that point in the first pass.

[kkala]

I would look into letting the CBD down to 2.6 Barg, to have about 4x0.4=1.6 t/h of 140 oC saturated steam (attached condflash.xls); in theory GV solution would not be overheated, even if this steam is blocked. And resulting low pressure liquid could be also used for heating.
Nevertheless I have no expertise on heating such sensitive liquids, e.g. margins indicated to avoid desintegration and suitable instrumentation (GV solution was briefly searched in WWW to no avail). Opinion from others is welcomed on the subject, as well as on other alternatives / feasible ways out.

Attached Files

•  condflash.xls   22.5KB   35 downloads

[ankur2061]

Abbaschemical,

Refer the links below in boiler blowdown heat recovery including calculated heat content of hot blowdown water.

http://www.spiraxsar...er-blowdown.asp

http://www1.eere.ene...er_blowdown.pdf

Regards,
Ankur.

[abbaschemical]

Dear Ankur,
Thanks for your link. Had highly enriched me on this topic

[abbaschemical]

Dear Kkala,
Thanks for your reply. And in the excel file you attached i couldnot understand the result " Value " and i m not clear with the file. Can you please elaborate on it.

[kkala]

Value in "condflash.xls" is the calculated figure described in the second column; e.g. Enthalpy of HP CBD (in kJ/kg) is 1466.
The spreadsheet indicates that 41% of the original CBD mass shall be vaporized into flash steam, if let down to 2.6 Barg. An enthalpy balance per kg of original CBD is applied to arrive at such a result.
If values in first rows of spreadsheet are not legible, water97_v13.xla add-in does not work, or has not been installed, http://www.cheresources.com/invision/topic/14130-calculating-time-required-to-cool-steam-with-cold-water-and-ambient-air; so enthalpies are not calculated. In this case lower rows (green) of the spreadsheet present same arithmetic values, but functions/ arithmetic operations are not apparent.

Edited by kkala, 16 December 2012 - 11:26 AM.