Heat Tranfer Equation for Mud Drum Heating Coils

[mpeck1982]

I have a water tubed boiler and I am trying to find out what is the temperature of my boiler water in the mud drum when it is on a cold stand-by operation... I have a carbon steel mud drum heating coil tubing with medium pressure steam of 140-lb at 390 deg F going into the mud drum. The boiler feed water and the main high pressure steam outlet is valved closed. The boiler water eventually settles to a certain temp after the heat transfer of the mud drum heating coil. Is there any kind of equation I can use to find out the resulting temperature of the boiler feed water from the heat transfer of the heating coil? The boiler water is stagnant in cold stand-by operation. Any help would be appreciated!!!

 

[rmw]

What type of boiler is this; Type A, Type D, Sterling, two drum, 3 drum, more drums than that? The natural circulation caused by the heating of the water would be different in each of these types of boilers and any formula would be different. What happens to the condensate generated by the heating coils? Can you measure the condensate flow? Do you know if the heating coils are well drained or are they partially full of condensate?

All the above have a bearing on any potential for generating a formula for calculating heat transfer.

rmw

 

[mpeck1982]

It is a two drum boiler. 1 steam drum and 1 mud drum. The condensate flow doesn't have a flow meter. Once the steam goes into the mud drum heating coil it returns back as patrially full of condensate and returns to a condensate tank.

 

[Tunalover]

You'd probably get more replies from the Heat Transfer/Thermodynamics forum.


Tunalover

 

[chicopee]

You seem to forget the purpose of a mud drum which is to accumulate a whole bunch of scale, mud, contaminants,etc.. to be flushed away. Second,there is no steam flow into mud drums. As I am trying to make sense of your title of your OP, be aware that mud drum should not have heating coils (unless originally designed to have such component), otherwise, any retrofit into mud drums will disrupt the water circulation back into the steam drum.
I think that you have misconceptions about the water and steam circulation of your boiler, so you should get the manufacturer's literature to read more about the medium circulation within your boiler.

 

[rmw]

OK, so here is your problem. The steam side is pretty straight forward. Steam is going to enter teh coil and if the inner surface of the coil is colder than the steam temperture, the steam is going to condense and give up its latent heat, produce condensate and repeat the process until the inner surface of the coil rises to steam temperature. For that to happen, heat has to transfer first into the coil metal and then on into the water on the outside. Therein lies the problem. The water on the outside of the tube is basically stagnant, with the only flow being created by the convection currents created by the heating of the water on the outside of the tube. But since the water on the outside of the tube is either stagnant or moving very slowly, the Reynolds number on the outside of the tube is very low, maybe too low for proper heat transfer so that the only heat transfer that happens is conduction into the water, not convection.

Add to that the conditon that Chicopee notes, namely that a mud drum is a nasty place and any accumulated sludge or scale will further impede good heat transfer, and what you end up with is a heat exchanger with very poor efficiency.

If you could find some heat transfer coefficients for this type of service, then you could solve a Q=UAdT considering all the film and metal coefficients needed for the "U" term. You should know the "A" and should be able to make a reasonable approximation of the dT.

rmw