5 replies to this topic

[KOSTAS]

Feedback is required on the preliminary sizing of an atmosperic vessel.
The preliminary sizing of the atmospheric vessel has been attached (RES_DRAIN.XLS). The process which takes place is adiabatic flash of steam. Finally, the flash calculations have been done according to IAPWSIF97_V13.

Thank you in advance.

Konstantinos Tsakonas.

Attached Files

•  RES_DRAIN.XLS   190.5KB   90 downloads

[Art Montemayor]

Konstantinos:

I'd like to offer some feedback and comments to your calculations, but I'm having difficulty in understanding with certainty what it is that you are flashing.

• Are you flashing saturated steam to a lower pressure? What are the pressures involved?
• I believe you indicate you are flashing three (3) streams, a HP at 6 bara, a LP at 3 bara, and an auxilliary at 14 bara. To what pressure are you flashing the 3 streams down to?
• I presume all 3 steam flows are in the saturated state prior to expansion. Is that true?

Your macro seems to be very detailed, but you furnish little or no documentation to explain your algorithm. Therefore, it is difficult to review or to follow the calculations. Can you give us more details on the algorithm and the concept of your calculations setup?

Await your reply.

[KOSTAS]

Dear Art Montemayor,

I would like to thank you for your willingness to provide feedback.

I would also like to inform you that I am working for an EPC company and currently we are currently working in the design and the construction of a power plant. The power plant is a combined cycle, with two gas turbines and one steam turbine.

I am currently working in the design of the hot drains system. My inquiry for feedback is for the atmospheric drain vessel, which receives the hot drains from the steam cycle.
The streams coming into this vessel are three, the High Pressure Steam (HP) stream, the Low Pressure Steam (LP) stream and the Auxiliary Steam stream. Each of these streams collects the relevant drain streams from each stage. As the exact conditions and the exact quantities of these three streams are not known, some assumptions have been done.

Two different cases have been considered. One is that the steam coming into the vessel from all three stages is saturated liquid (SL) and the other one is that the steam coming into the vessel is saturated vapour (SV). Hence adiabatic flashes have been performed for each case. From the adiabatic flash for the SL case the quantity of liquid coming out of the vessel has been estimated and from the adiabatic flash for the SV case the quantity of vapour coming out of the vessel has been estimated.

For the SV case where the saturated vapour going into the vessel is going to come out of the vessel superheated, as it will expand to atmosphere. The energy balances performed individually for each stage of pressure as the vessel will receive either the HP and the LP or the AUX. Hence the vessel has been sized for the maximum of the HP and the LP flow or the flow of the AUX.

The HP is at 6 bara and its flow is 1.287 kg s-1.
The LP is at 3 bara and its flow is 0.95 kg s-1.
The AUX is at 14 bara and its flow is 2.2 kg s-1.

All of them will be flashed at 1.03325 bara, which is 0.02 bar higher than the atmospheric in order to be able to flow through the vent line.

The equations for these flashes can be found in the attached file.
The macro that has been used is the one obtained from the following link:

http://www.cheresour...iapwsif97.shtml

Thank you once more.

Konstantinos.

Attached Files

•  ATM_DRAIN_VESSEL.DOC   31KB   62 downloads

[KOSTAS]

Dear Art Montemayor,

I forgot to upload the latest revision of the calculations.

The latest comments should be checked with the file RES_DRAIN_01.XLS

Konstantinos

Attached Files

•  RES_DRAIN_01.XLS   204KB   88 downloads

[mvancleave]

This sounds like a blowoff tank.

The National Board of Boiler and Pressure Vessel Inspectors (NBBI) provides a detailed guideline for the sizing and construction of such vessels: A Guide for Blowoff Vessels (NB-27). Get a hold of a copy of this document and your life should get much easier.

Just out of curiosity, can you say any more about your plant and who you are working with? I only ask because I work in the EPC power plant industry as well (for SNC Lavalin Constructors). I am currently working on combined-cycle projects in Toronto and Dubai.

Mike

[KOSTAS]

I am working for J&P-AVAX, a construction company in Athens, Hellas. I am working for the EPC department of J.&P.-AVAX. The power plant I am involved with is in Cyprus. Thank you for the reference.

Konstantinos.