Heat transfer superheated steam pipeline 1

[GabrielCorelich]

Good day to everyone,

Im doing the analysis of transporting superheated steam vs saturated steam. THe reason of this is because we are going to have steam from a steam turbine and the question is either if its worst to desuperheat the steam inside the steam generation building or outside the consumption point.

The question is how to calculate the heat and temperature loss every 100m of a isolated pipe for superheated steam.

Thansk!

 

[IRstuff]

Isn't the usual purpose of transporting steam to do actual work of some sort at the consumption end? If so, why would you want to reduce the amount of potential work available?

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[chicopee]

Tell us more about the turbine inlet and outlet conditions of the steam; for conditions I am asking for pressure, temperature and quality.

 

[davefitz]

The overwhelming "resistance to heat transfer" is in the pipe's insulation, so the loss of heat can be easily computed based solely on the insulation. The steam's heat transfer coef ( inverse of resistance) is not so important. The other issues relate to draining the condensed water so as to avoid liquid buildup in the pipe.

"...when logic, and proportion, have fallen, sloppy dead..." Grace Slick

 

[chicopee]

To calculate heat and temperature losses, you'll need to determined the convective heat transfer coefficient (hc) of superheated and saturated steam. Libraries of major cities and institutions of higher learning have an abundant number of books on boilers and heat transfer text books in which "hc" values are indicated. So do some research. I'll check out my sources for hc values to help you out.

 

[georgeverghese]

Superheated steam would be the better choice, from a flow assurance point of view, to pipe over long distances in comparison to saturated steam,since you wouldnt have condensate dropping out all over the place with superheated steam. Suggest desuperheating close to the point of use for each user.

 

[racookpe1978]

Concur with georgeverghese about the higher efficiency of superheated steam in transport, but with a few caveats.
Higher superheat = higher temperature (in general) down the pipe and thus probably a higher alloy steel pipe and higher welding costs. Higher flange and valve costs too. Need actual steam temperature and pressure at the turbine outlet port(s)!

Some steam will still condense after Tsat is reached at the P_Turbine_Outlet pressure. During warmup and cooldown, condensate will definitely have to be managed anyway.

Energy loss is proportional to temperature difference to atmosphere. Run the numbers, a lower T_Steam "might" reduce energy loss overall if you actually need to use saturated steam (or less) at the final point, but I doubt it. If the vented steam off of ther turbine is "free" (no effect on other systems or by-products like cogenerated power), then you've GOT to run the numbers specific to your source steam expense, cogen loss, turbine tap loss, turbine reheat loss to condenser water or IP turbine, and pipeline energy loss at destination.

 

[chicopee]

Reading the comments about superheated steam be a better choice, this is a correct statement because its convective heat transfer coefficient(Hc) ranges between 5 and 50 btu/hr sq.ft.F whereas wet steam(saturated) will range 1000 to 20,000 btu/hr sq.ft.F.. In essence the greater the value of Hc the greater heat loss and drop in temperature of the medium travelling thru the piping system. Another benefit of superheated steam is the speed thru its piping system that can range fromm 14,000 to 20,000 ft/min whereas saturated steam is around 10,000 ft/min..
Searching thru my archive, the periodical Plant Engineering-directory and specification D-7 has an article titled "Calculating heat thru buried pipe" offers an inkling on solving heat loss and temperature drop thru piping suspended in air. Its premise is the first law of Thermo. which can be summarized as follows : Energy in- Energy out-heat loss= change in internal energy of steam within a segmental section of piping. A time step analysis on a spread sheet is an appropriate tool to find approximate results. I would not be surprised if similar articles could be found in past Chemical Engineering articles, so a little research would be of benefit.
Desuperheat at point of consumption, if needed.

 

[crshears]

Looks like another case of "Post & Ghost"...

OP writes of superheated steam exiting a turbine, which suggests to me quite to very highly superheated steam would have to be supplied to the turbine such that the exiting steam would still be superheated after doing work [how much work?] in the turbine...and it is difficult to provide meaningful response in the almost complete absence of numbers to go along with the query.

CR

"As iron sharpens iron, so one person sharpens another." [Proverbs 27:17, NIV]

 

[davefitz]

As a general rule, the need for considering the working fluid's heat transfer coefficient is important when it represents a significant reistance to overall heat transfer to the system of fluid+ pipe wall + insulation, but if it represents less than 1% of the reistance to heat transfer then it can be safely ignored for heat balance and overall heat loss calculations. It becomes very important when the tube is deliberately being used to traasnsfer heat, as in absorbing heat in a furnace or discharging heat in a condenser. For a long transfer pipe that is insulated then the fluid's heat transfer coeficient is not of primary importance. However, for undergroudn piping it often occurs that the insulation becomes compromised over time and its thermal resistance can be much lower than during initial installation.

"...when logic, and proportion, have fallen, sloppy dead..." Grace Slick