12 replies to this topic

[daiweisc]

Hi,

I am a new engineer in a chemical industry plant.

When I calculate the desuperheater with auxiliary steam in our steam reduction station, I run into difficulties related to the relationship of auxiliary steam and cooling water. I want to calculate the flux of auxiliary steam and cooling water.

Can you help me?

Thank you.

[Padmakar Katre]

Dear,

Its quite difficult to understand your problem.Could you tell somewhat specific because your query

doesn't make any sense to me.Please tell me exactly what you want probably I can help you as I

have done some assignments regarding desuperheaters and PRDS.

Regards,

Padmakar Katre

[daiweisc]

Ordinally the desuperheater can be solved with two equations. But the desuperheater with auxiliary steam still have another equation to be solved. So I want to find the third equation.

Thank you for reply.

[djack77494]

daiweisc,
Like Mr. Katre I find your query makes no sense. I have to question your terminology and your knowledge of what a desuperheater does. A steam desuperheater should have two inlet streams - superheated steam at a known temperature and pressure, and water (often condensate). The desuperheater itsef may be as simple as a mixing nozzle designed to ensure good contact between the two phases. Assuming good contact, the sensible heat of the superheated steam will be absorbed by the water until either the steam becomes saturated or all the water is evaporated. Generally, you'd probably want to strive for the former. Because the process is not 100% efficient, you normally wind up with steam that is slightly superheater. Good enough.

So, what equations are you referring to. All you have is an energy balance: energy of the 2 entering streams = energy of the near-saturated steam leaving. It's not that hard.
Doug

[daiweisc]

I am sorry to tell you that it only can list two equations in your way. This is a traditionally desuperheater way to solve. The desuperheater with auxiliary steam should have another equation to solve the problem.

The desuperheater with auxiliary steam is introduce a high pressure steam to enhance the atomizing of cooling water in the nozzle.

I try to solve the auxiliary steam flux and cooling water.

[pleckner]

daiweisc,

Draw a box around your desuperheater and remove from your picture or our mind any details of what is happening inside this box. We call this a "black box".

Now, show all your streams entering and leaving this block box: entering: superheated low pressure utility steam, cold water, high pressure atomizing steam; leaving: slightly superheated (or saturated) lower pressure steam.

Do a mass balance and an energy balance. It's only two equations. Your high pressure atomizing steam is just another heat source of a vapor that needs to be condensed.

If you want to treat the atomizing steam separately, you can. It is done the exact same way as you would do it for the utility steam. The final steam exiting the desuperheater is one stream that is made up of both the low pressure superheated utility steam and the high pressure atomizing steam and the flashed "cold" water used to do the desuperheating.

But, if you don't have the atomizing steam flow rate then you have a problem. You must know this value.

[daiweisc]

Thank your reply.

I understand that the auxiliary steam flow is a known value.
The problem is clear to me now. So I want to know how the desuperheater manufacturer select the value of the auxiliary steam flow.

thanks.

[pleckner]

It's a function of the nozzle they will use and the pressure you are operating at.

Ask the manufacturer, they don't bite!

[daiweisc]

Thank you very much.

Could you give me some references or books about relationship of nozzle, pressure, and auxiliary steam flux. I have no idea of it.

[Padmakar Katre]

Dear,
Here is the link from you will get information about the desuperheater (so much of information is available regarding steam engineering). Now regarding your specific query you can try your luck here by contacting them regarding relation between the nozzle,pressure and aux steam flux.

http://www.spiraxsar...ting-theory.asp

Regards,
Padmakar Katre

[daiweisc]

Thank you.
I have already contact them. But no one reply to me.
Could you give me some references or theory about relationship of nozzle, pressure and auxiliary steam flux.

[Padmakar Katre]

Dear
Please check in the following link i.e. in the Control valve handbook I read some material regarding desuperheating I am not sure at what extent it will help you.

http://www.documenta.../book/cvh99.pdf

Check specifically related to your query i.e. Page No 155 onward Chapter 7 Steam Condtioning Valves they haven given some theory regarding steam desuperheating,nozzle design and atomizing fluid.

Regards,
Padmakar Katre

[T.S.MURALI]

Hi!

Please visit Spirax sarco website. Based on mass& energy balance temp,flow controls canbe programmed. Two element control (PID control) will take care of spray water flow control, mass flow and temp of steam at the outlet of DSH. This is nothing unusual!

T.S.Murali