4 replies to this topic

[Felix Fernando]

Good Day,

 

In one of our contract document, we have mentioned that "Flue gas exhaust stack to suit the arrangement of the heater, including steelwork support, if required, rain hood, stack damper and actuator, spart arrestor, silencer and strakes/vortex breaker."

 

The contractor has replyed back to us saying that the rain hood, spark arrestor and silencer are not applicable to the stack of natural draft direct heater type and those facilities are applied to the air intake stack located in a forced draft fan section.

 

For this reason, the stack will not include a rain hood, spark arrestor and silencer.

 

My question is: IS THE CONTRACTOR VIEW CORRECT?

[ankur2061]

Felix,

 

If you refer to API STD 560 - Fired Heater for General Refinery Service, Annex A of this standard has a typical datasheet for Fired Heaters. If your refer to the section related to "Stack" of the datasheet "rain-hood", spark-arrester" and "Silencer" are not part of this section.

 

Apparently, your contractor knows fired heaters and has given you the right advice.

 

Regards,

Ankur.

[Felix Fernando]

1. Then on our Project Specification we have specified that inlet stack shall be minimum of 4500mm high and shall be suitably self supported and fitted with a flexible joint at the fan suction.

 

Contractor replyed back that the requirement of minimum 4500mm high for inletstack is not applicable considering the purpose of air purge fan, and the air intake duct / stack will be designed by vendors standard. 

 

what is your view on this.

 

2. In our contract we said contractor shall comply with the specification and provide the required air flow venturi for purge air.

 

contractor replyed backj saying that venturi is not required since the main purpose of the fan is for purging during start -up only and will not be used during operation. The application for venturi is used to measure the actual air flow coming from the combustion air for maintaining the air/fuel ratio and is generally done for Forced Draft system. It means that the purge air does not need to be measured and controlled.

 

what is your view on this

 

3. We said that the vendor shall demonstrate that their design will not result in the maximum metal temperature exceeding the process fluid temperature by more than 56 deg C in the convection section and by more than 44 deg C in the radiant section

 

contractor replyed back that the process feed of the heater are designed with lower temperature. In this condition the above  requirement is not applicable and contractor will follow the data sheet with maximum tube metail temperature of 710 DegF in order to avoid corrosion on tube materials

 

What is your view on this

[Felix Fernando]

In fired heater data sheet we mentioned as

 

- Radiant section

 

Shield and Exposed  wall ----- ceramic fiber

Arch Section           ------------- Castable

 

- Convection section

Side & end  wall      ---- castable

Breeching          --------  Ceramic fiber

 

Contractor replyed back that refractory system for readiant and convection section are applied same refreactory material in accordance with above mentioned  project spec

 

Radiant section including arch section to be applied ceramic fiber lining

Convection section including breeching to be applied castable lining

 

please confirm that the applicaton of same refractory material for radiant and convection section is acceptable.

 

[ankur2061]

Felix,

 

Please go through API STD 560 to understand more about fired heaters. Also refer the standard datasheet template in Annex A for what requirements are there for fired heaters if they are to be designed as per API STD 560. You will need to do the study, I cannot study on your behalf and find contradictions on what your contractor has offered and what requirements are provided as per API STD 560.

 

Sufficient to say that API STD 560 provides a bench mark for fired heaters for critical and refinery services. There are other standards also which provide design guidelines for fired heaters. One standard that applies for thermic fluid fired heaters is DIN 4754.

 

Regards,

Ankur.