Furnace redesign 1

[scoutb59]

My company builds a variety of equipment for a niche market, mostly process machinery and handling equipment but also furnaces and ovens. The company was founded in the 40s and was acquired in the 50s by a couple of guys with a combustion background. Our current furnace design was developed by those two over the next 30 years and has remained relatively unchanged since the 80s. I've been with the company for the last 23 years, initially in a machine design position and more recently in more of a new product development and R&D role. In all my years there has been little incentive to mess with the furnace design because it wasn't broke, so why fix it? The current design is fairly straightforward, just a direct flame impingement tunnel furnace with sealed premix nozzles, a preheat section that reuses the exhaust gasses, and temperature and pressure control to keep the process in check.
In recent years our competitors have made some headway by offering furnaces with higher efficiencies and less required maintenance, leading me to believe that our old tried and true design needs some modernization. Time marches on, after all. I have been doing as much research as possible on the internet but the information is farly limited. In particular I'm looking for information on burner nozzle design, burner velocity calculations, burner density requirements, effect of burner velocity on heat transfer, methods and calculations for preheating combustion air, etc. Many of my google searches have led me to textbooks and handbooks that sound promising. I don't mind spending big money for a good book or two but I'm having trouble determining which books will help me the most. That's where you guys come in (hopefully). Those of you that do this for a living must have some of these books and I would appreciate it if you could recommend something. And yes, I know there are consultants that I could hire to help with this. I may very well end up doing so but I need to educate myself enough to keep up my end of the conversation.

 

[davefitz]

scoutb59;
I think the focus on burner design mostly impacts combustion efficiency and Nox; some of the latest lo-nox burners designed for the strict california market also provide much better turndown and use less excess air ( which also means better boiler thermal efficiency)at low loads. So I would suggest you investigate the california market burners by Coen , Forney, etc. To avoid patent issues and technical issues, it would be better to simply buy the burners from such an outfit as opposed to building your own.

As far as improving the other furnace design characteristics, you will need a qualified engineer to compare the details of your design versus your competitors, and learn from the competition. Eventually, you'll find a design change that is competitive without violating patents. But the modern design tools now available to newly trained engineers (finite element models for stress , heat transfer ,and fluid mechnics) are required to be competitive- you will be able to find most errors in design via those simulations as opposed to trial and error in the field. If you cannot modify the company policy by modernizing the design process, then there is little chance you can succeed against competitors that have those modern tools available.

 

[scoutb59]

davefitz,
I understand your concerns and appreciate your advice. Nox is absolutely a concern. Perhaps I should clarify a few things though. We already make our own burner nozzles. There are upwards of 100 of them in our smallest furnace so it would be best if we keep making them ourselves. They are fairly simple "blast tip" type nozzles so I'm not really worried about patent issues, but I do want to explore modifying our existing design to achieve better heat transfer, whether that be by decreasing the nozzle output and increasing the nozzle density, increasing the nozzle velocity, preheating the combustion air, or a combination of these design factors. Also, I am the qualified engineer and I have evaluated the competitors designs as best I can. Preheated combustion air and mass air flow sensors for mixture control seem to be where they have achieved better efficiencies. I expect there are no patent issues with applying those concepts either. And your last point about design tools is well understood. We have those tools and use them regularly. That is where my frustrations lie at this point. I have the tools but not the knowledge to apply them properly when it comes to combustion, hence the search for textbooks/handbooks on the topic. I've learned what I can from the North American Combustion Handbook but it's not enough to get me where I want to be.