PetroStreet

Salam alekum,

How do you define design duty of process heater.Does heater performance affected due to fouling?ca we improve heat duty & how we can do that.

1. Design duty for any industrial equipment is defined by its design memorandum. In case you plan to design from grass root level, the things that are to be considered are Approach Temperature, LMTD, FLows, velocities but most importantly a) Max fouling factor, which is usually given in literature for different services. b) frequency of cleaning.
2. Heater performance does get affected by fouling which is entirely dependent upon type of heater service, so you need to state the service of the heater.
3. Design heat duty is fixed for an already designed heat exchanger, until unless you a) change heating fluid with higher heat transfer coefficient b) increase the velocity of fluids through heater if possible, this his will improve overall heat transfer coefficient.

It would be helpful if you explicitly describe your problem,

I'd agree to Idris that it very much is dependent upon the type of heater. Like there are many type of heaters are available.
1- Direct fired heaters
2- Process-Utility heaters
3- Process-process Heaters etc
Fouling can very severely affect the performance of all heat transfer equipments. In case of direct fired heaters carbon suit deposition on tubes can affect the performance of heater to a larger extent.
Heat duty of a heater can be improved by improving heat transfer coefficient and Mr. Idris has explained ways to to so.

Waalikum Salam,

Ahmed, if you can elaborate your problem then i may suggest you further, but in short yes you can increase /decrease heat duty of heater/exchanger by changing flows, temperatures, fluid types, orientation, fuel gas type (if it is fired heater) or changing mechanical parts (eg addition or deletion of tubes).

Wasalam Ahmed,

If i understand correctly, there are two separate parts of your question; a) Design duty of the Heaters [related with the designing of the exchanger] b) Fouling in heaters and its effects?

Heat duty of any heat exchanger, as imran said, is primarily based on its design or TEMA type. Secondly the type of fluid or the service u intend to use during the design of your exchanger. Service of heater has a major role in type and area of the exchanger. For better approach of your exchanger the service would be different, so does for better range. Similar the characteristics of your fluid as well e.g. pure saturated liquid, mixed phase, or gas liquid mixture. So that the maximum heat you want to recover [duty of your heater] from the heating media will be different for different media like steam, heating condensate or even direct fired heaters.

Fouling directly affects heat duty of any heater. Although steam and heating condensates are considered clean services, the design fouling factor still required for both and for the heated service as well. In that case heat duty can be improved by defined cleaning frequency based on the evaluated performance/ heat transfer coefficient of your heater.