Calculation of Desuperheater 1

[scdaiwei]

Hi,
I am a new engineer in a chemical industry plant.
When I calculate on the desuperheater with auxiliary steam in our steam reduction station,I run into difficulties. How to make certain the relationship of auxiliary steam and cooling water.So I can calculate the flux of auxiliary steam and cooling water.
Can you help me?
Thank you.

 

[toothless]

Perform and enthalpy balance. m = mass, h = enthalpy

m1h1 + m2h2 = m3h3

 

[scdaiwei]

Ordinally?the desuperheater can be solved with two equations. But the desuperheater with auxiliary steam stil have another equation to be solved. So I want to find the third equational.
Thank you for reply.

 

[rmw]

In the end it is still just a balance. You have to write your input and output equations to account for all streams, inlet steam, aux steam, water and outlet steam.

 

[scdaiwei]

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.

 

[hacksaw]

you need to better explain your piping config, there is some confusuion about your aux. steam as a separate stream.

it is not a problem to solve.

 

[rmw]

Most steam atomized desuperheaters that use steam for atomization use a fixed amount of steam that is given by the desuperheater manufacturer for the specific desuperheater model based on the inlet and outlet pressure of the steam atomizer. In that case, the auxiliary steam flow is a known value that plugs into the input side of the balance. This steam is not normally controlled except with an on/off type valve. Some systems have the on/off function triggered by the opening/closing of the water control valve.

The water, however, is controlled and varies with the main steam flow and temperature fluctuations.

If it is the auxiliary steam that you are trying to solve for, no wonder you are stumped. That is not a calculable variable.

rmw

 

[scdaiwei]

Thank rmw reply.
I understand.
Could you give me a example of selection of the auxiliary steam flow in a desuperheater.
Thanks.

 

[scdaiwei]

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.

 

[toothless]

We used both types of desuperheater nozzles - those which require atomizing steam and those that do not. I much prefer the type that does not (such as a Fisher DMA/AF).

 

[rmw]

Here is a site;

http://www.spxprocessequipment.com/sites/copes/products/desuperheaters/sa.asp

and here is another.

http://www.graham-mfg.com/desuperheaters.html

Those ought to do for a start. By the way, steam assist DSH's are usually picked for a reason and as toothless says above, if the job can be done without using a steam assist, things are much simplier.

rmw

 

[scdaiwei]

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.

 

[whylie]

Check SPIRAX SARCO website and Armstrong University ,both give design information on steam systems

 

[scdaiwei]

Could you give some detail web links.
Thanks.