## Steam temp set point for Rebiolers

## Steam temp set point for Rebiolers

(OP)

Hi,

i'm working on figuring out how much flow of steam we need in our reboilers

currently the steam temp to our reboilers is much higher the design temp of the reboilers which is affecting the efficiency of the reboilers

but working on the flow to the reboilers is the key solution. i need to change the set point of flow to the reboilers?

the calculations will involve LMTD and Q=mU(DeltaT)

but if someone know the procedure for the calculation

thank you

i'm working on figuring out how much flow of steam we need in our reboilers

currently the steam temp to our reboilers is much higher the design temp of the reboilers which is affecting the efficiency of the reboilers

but working on the flow to the reboilers is the key solution. i need to change the set point of flow to the reboilers?

the calculations will involve LMTD and Q=mU(DeltaT)

but if someone know the procedure for the calculation

thank you

## RE: Steam temp set point for Rebiolers

Katmar Software - AioFlo Pipe Hydraulics

http://katmarsoftware.com

"An undefined problem has an infinite number of solutions"

## RE: Steam temp set point for Rebiolers

Depending on inlet and outlet temperatures of both fluids, you might run into trouble with the LMTD being undefined. I would try to see if you can get the results you want by equating the heat of vaporization rate on the boiling side with the enthalpy surrendered on the steam side.

Would NTU effectiveness work here?

## RE: Steam temp set point for Rebiolers

1. steam desuperheating

2. steam condensing

3. condensate subcooling

To calulate the steam flow rate you need, the heat supplied by the steam will be:

delta H steam = Fsteam x [Cp steam x (Tsteam-Tsat) + latent heat + Cp water x (Tsat-Tcond)]

where:

Tsteam = steam supply temperature

Tsat = saturation temperature of water on the steam side of the reboiler

Tcond = condensate temperature leaving reboiler

The highest heat transfer rate occurs for steam condensing. This regime also releases heat most efficiently, pound for pound. Therefore, a higher steam supply temperature is not beneficial because the steam needs more surface area to desuperheat, leaving less area for the condensing regime. This may be why you have an "efficiency" problem. You want to maximize the condensing regime to best utilize the available surface area.

The pressure on the steam side will depend on the regime heat transfer coefficients and surface area. As the pressure rises, Tsat increases which increases the heat transfer rate across the tubes in the condensing regime. The steam side pressure finds a value so that the heat balances.

So, the steam supply should ideally have just enough superheat to ensure there is no condensate formed in the supply lines. The flow of steam should be adjusted to give the desired heat duty based on the process side requirements. If your steam side pressure is very high, you may have condensate flooding the tubes and/or a lot of fouling.

## RE: Steam temp set point for Rebiolers

## RE: Steam temp set point for Rebiolers