Dear colleagues,

i have a question and honestly i am feeling a little ashamed for that, but i really do not get it:

I am wondering if it makes more sense to run a 7barg or a 3,5barg steam system (both saturated).

Of course i already looked in a lot of websites and found out about the advantages and disadvantages of using higher and lower pressures for the steam system:

Advantage high pressure steams: smaller diameters, higher temperatures

Advantage low pressure steam: higher specific heat content, less production costs, less flash losses

I also read that the steam traps would become cheaper using low pressure steam, which i acually do not really understand.

How ever the most important question for me is if the pressure level has an influence on my batch times (heating up liquids in vessels via jacket pipes):

I have a formula to calculate the heat up time based on the steam temperature and and the process liquid:

time = C1*LN(t0-t1/(t2-t1)) with C1 = (cpp * mp + cpv * mv) / (k*A);

with

cpp the heat capacity of process fluid,

mp the mass of process fluid inside the vessel;

cpv the heat capacity of the vessel and mv the mass of the vessel;

k = heat transfer coeficient;

A = heat transfer area between jacket/coil and vessel;

to = batch start temperature of process fluid

t1 = steam temperature:

t2 = batch end temperature

all with SI Units.

In this formula the batch time depends clearly on the steam temperature (t1)

How ever looking in the internet around for formulas describing the heat up time of a fluid in a vessel (via jacket or half coils) i only find the formula

time = (t2 - t0) * (cpp * mp + cpv * mv) / (Dh * ms).

With Dh = vaporization enthalpie of steam at given pressure (= latent heat during condensation) and

ms = the mass flow of steam.

In the latter formula, the batch time decreases with low temperature steam due to the higher latent heat (assuming the same amount of steam for both pressures; maybe this assumption is wrong?). In the latter formula the temperature of the steam does not play any role.

Can anybody help me here? Does higher steam pressure lead to shorter heat up times?

BR

Thomas

**Edited by ThomasH1985, 14 January 2021 - 11:47 AM.**