Contact US

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Dilution air question

Dilution air question

Dilution air question

I have been working with the commissioning of burners on asphalt plants for many years in Australia on both gas and oil fuels. I am due to commission one on propane in the very near future and have put in all submission documentation for the burner (eg fuel rates, start gas, purge rates and time etc) to the gas authority for approval of commissioning gas. This has up to now sufficed.

This particular inspector was surprised to hear we intended introducing bitumen into the rotary drum as this is a drum mixer. Obviously he has only seen batch plants which only dry the aggregate and mix bitumen externally. He is worried about volatiles in the heated bitumen or asphalt mix exceeding the limit on LEL values. and requires a dilution air calc submitted. This is of the type found in NFPA 86A and copied into our Australian codes. I personally have never done this before but started working through it. I feel however that it isn't applicable to bitumen for the following reason. Bitumen has a flash point of >250degC. Our normal product temp will be 180deg to 200degC max and an overtemp cutout set at 220degC. Hence there should be no combustable vapours given off of any significance. So a dilution air requirement to keep this from reaching say 50% or even 25% of the LEL is unnecessary. Sometimes asphalt plants use RAP a recycled pavement which could contain contaminants of higher volatile compounds but this will not be the case at our plant where only virgin bitumen is used.

Does any knowledgeable person on explosive atmospheres agree or have any comments?

As an aside to this. Other asphalt plants make a product called cold mix. This is made at a low temperature of about 80degC and definitely adds diesel to the aggregate. If it was required to do a calc on minimum dilution air what values would you put in for the equation for dilution air flow in NFPA 86A.Years ago when involved with emission tests on a specific stack they had to calibrate their instrument to check for hydrocarbons from a diesel fired burner. Hexane was used as the calibrating fluid. So would you use values for hexane shown in the tables we have(ie for vapour generated by 1 litre of liquid etc) to insert in the equation. If so there is one equation quantity designated Q which is the max instantaneous evaporation rate in litres/sec at our operating temp. Where would you find that for diesel.
Hope this isn't too long to respond but the first issue on straight bitumen is the most inportant.
Thanks in advance

Rod Nissen.
Combustion & Engineering Diagnostics

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members! Already a Member? Login


Low-Volume Rapid Injection Molding With 3D Printed Molds
Learn methods and guidelines for using stereolithography (SLA) 3D printed molds in the injection molding process to lower costs and lead time. Discover how this hybrid manufacturing process enables on-demand mold fabrication to quickly produce small batches of thermoplastic parts. Download Now
Design for Additive Manufacturing (DfAM)
Examine how the principles of DfAM upend many of the long-standing rules around manufacturability - allowing engineers and designers to place a part’s function at the center of their design considerations. Download Now
Taking Control of Engineering Documents
This ebook covers tips for creating and managing workflows, security best practices and protection of intellectual property, Cloud vs. on-premise software solutions, CAD file management, compliance, and more. Download Now

Close Box

Join Eng-Tips® Today!

Join your peers on the Internet's largest technical engineering professional community.
It's easy to join and it's free.

Here's Why Members Love Eng-Tips Forums:

Register now while it's still free!

Already a member? Close this window and log in.

Join Us             Close