5 replies to this topic

[fahctory]

Hi everyone,

I’m currently working on a process design where a liquid stream needs to be heated from 75°C to around 350°C, and I’d like to get some insight on the most appropriate heating strategy.

Specifically, I’d like to ask:

1. Regarding the heating medium,

   • Is it still practical to use steam at this temperature range?

   • If so, what steam conditions (pressure/temperature) are typically used?

   • Or would hot oil / thermal fluid be a better and safer option?

2. From a design and operability standpoint,

   • Is it better to use two heating stages (e.g., preheater + main heater),

   • Or a single heater designed to reach the target temperature directly?

Thank You in Advance!

[latexman]

IMO, it’s not practical to use steam to heat a liquid to 350 C. That’s close to the critical point of water (374 C). Another heat transfer fluid (hot oil) will probably be more optimum.

[breizh]

https://htf.krahn.eu...on guide_en.pdf

 

Consider the link above to select a thermal fluid.

Not a lot of companies offer bulk temperature of 350 C, consider the Therminol family from Eastman (ex Solutia).

66,68,72 

About the second question you need to evaluate the capex and room available.

For this type of question, you may want to use Google AI.

Note: Because of risk of degradation of thermal fluid, you will need to consider to inert the storage tank of hot oil using N2. You will also need to add an expansion pot on the hot oil loop.

Unfortunately, you cannot use Steam, your temperature requirement is too high which also means high pressure.

Edit:

14_6_Manuscript_aak.pdf

Good luck in your studies

Breizh

Attached Files

•  HTF-66.pdf   85.54KB   9 downloads
•  hot oil design guide.doc   687KB   10 downloads
•  heat transfer calculator.xls   26KB   10 downloads

[Pilesar]

Consider a fired heater for such high temperature. Molten salt would be another option to reduce the risk of overheating.

[fahctory]

thank you so much for the answer

[exerland-co]

In most industrial applications, heating a process liquid up to around 350°C is usually where thermal fluid systems start becoming more attractive than steam systems.

While it is technically possible to use high-pressure superheated steam, the required pressure and operating conditions become quite demanding as you approach this temperature range. From a practical process design perspective, many engineers prefer thermal oil (Therminol, Dowtherm, etc.) because it can provide high temperatures with significantly lower system pressure and often simpler operation.

For the second question, I would say the answer depends on the process fluid, allowable film temperature, fouling tendency, and heat duty.

A two-stage arrangement is often worth considering:

• First stage: steam or another utility for preheating

• Second stage: thermal oil heater for the final temperature rise

This approach can improve energy efficiency and reduce the required high-temperature heating duty.

If the fluid is temperature-sensitive or prone to coking/polymerization, a staged heating approach may also help reduce local overheating at the exchanger surface.

A few additional factors that would influence the selection:

• Process fluid composition

• Flow rate

• Required heat duty

• Maximum allowable film temperature

• Fouling tendency

• Continuous vs batch operation

For many chemical and process plants, a combination of steam preheating and thermal oil heating for the final approach to 350°C is often a practical solution, but the details depend heavily on the fluid properties and operating constraints.

Could you share the type of liquid and approximate flow rate? That would help narrow down the heating strategy considerably.