what code to use? control philosophy?

[eddie2314]

Folks, your help is greatly appreciated on this one. I am involved in the design of an item for use on the international market and am struggling to define what code the basic design should adhere to.

The item is an indirect fired rotary kiln. It can be used in many industries. It consists of a combustion chamber fired by burners. The chamber is vented to atmosphere so no pressure code requirements here. Inside the chamber sits a rotating tube filled with solids. The solids are heated in the tube, and the resultant vapor goes out a vent at the end of the tube. However, the vapor is under back-pressure (approx 7psig, or near 0.5 barg).

I've been looking at ASME code and can see that because the MAWP is < 15psig i don't need to adhere to section VIII. I then looked at section IV for low pressure and it doesn't seem to fall under that either. In my interpretation the unit is not strictly a steam boiler (although the majority of vapour will be steam and minor quantities of hazardous compounds). So my question is, what code, if any, do i need to apply??

Also, i was considering two potential pressure control philosophies.

1. a manual butterfly valve locked in position to create a back-pressure (a restriction orifice basically). Set and forget during commissioning, with a high pressure alarm to interlock the system into shutdown should high pressure arise (the feed moisture is variable so the resulting gas pressure will also be variable but it's intended to set the restriction to be open sufficiently for worst case conditions).

2. a PCV adjusting to a set pressure (looks expensive given the temperatures and vent diameter - 700degC and 6inch). Again, a high pressure alarm would shut the system down.

I'm not fully sure if a pressure relief device is required (given the low pressures, the uncertainty over code requirements, the inclusion of a high pressure interlock already etc).What do you think? Thoughts welcome!

Thanks

 

[metengr]

You can still use ASME B&PV Code, Section VIII, Div 1 for guidance in design/fabrication/ materials selection and PRV's. For burner design, which I suspect would be the main concern, you can investigate NFPA codes.

Over the years, we have had pressure vessels designed and built to ASME B&PV Code that were exempt from stamping requirements. Your vessel will not require stamping because it is not under the scope of Section VIII, Div 1 as a pressure vessel.

 

[davefitz]

I am not sure an alarm is adequate- perhaps 3 indpeendent pressure wsitchs hardwired to a trip would be more reliable.

What does the competition use?

 

[eddie2314]

Thanks metengr / davefitz. Other manufacturers maintain an open vent to atmosphere, so no pressure code requirements. It sounds like the vessel will not require stamping / registration because it is operating at <15psig. I'm wondering if a pressure interlock is sufficient to trip the system (software not hardwired), or if a relief valve should also be included as a back-up (not sure if there's a regulatory/code obligation for this, or if it's just down to opinion as to whether a credible risk exists?)