Conversion from #6 to #2 1

[Sam654]

We are in the initial stages of converting from #6 oil to #2 as a backup to NG in a 165 MMBTU process heater. To answer those of you that wonder why we are giving up our "#6 grandfather". Suffice it to say we tired of fighting the fouling from junk that's in today's #6 oil to the point where we can't get 100% capacity from our heater on NG after an interruption (long story). A few questions for anyone who may have gone through this process.

Obviously, we will eventually need to change gun tips but, initially we will use our existing tips until we run through a few loads of #2. Our intent is to burn the tank to about 10% (~3,000 gal) and top off with #2 (~14,000 gal) and recirculate. The tank itself should be fairly clean as it has only been in service ~18 months and used regularly (~15,000 GPD). I'm doing this to save time and cost. How well does 2 and 6 mix? I have heard both good and bad.

What problems can I expect if the current gun tips are used until we get to the point where we are essentially at 100% #2. I will probably heat the oil to ~140 deg while I have the initial mixture to minimize potential problems with the residual #6 yet stay below the flash point of #2, then cut it off.

Should my atomizing steam increase or decrease? I currently run about 13 psid (Coen burners).

More air, less air? Recharacterizing isn't a problem, I just prefer to understand the beast before taming.

 

[rmw]

You better worry first about your pumps. Are they capable of pumping the (eventual) #2 oil at a pressure that any tips (2 oil or 6 oil) can atomize it?

I have seen a couple of boilers in my life where #2 oil was delivered into #6 oil tanks by mistake, and the units were only able to run at ~ 20% of their rated capacity until they got the tanks emptied enough to refill with a significant amount of 6 oil.

I don't think (in fact I know) that #6 oil tips won't do well on #2 oil. Two oil isn't normally steam atomized, rather pressure or air atomization is common. Not that steam won't work, however.

Six oil is heated so that it can be pumped and will flow to the gun tips. Two oil doesn't require this heating.

I think you should contact Coen and ask them for a set of guns for your BTU requirement for #2 oil. They can tell you whether or not steam atomization is advisable as well.

And, by the way, I understand well what you are faced with with today's #6 oil. It is Six oil in name only. Otherwise it is just refinery junk sold to you as six oil.

rmw

 

[Sam654]

Thanks rmw, I do appreciate your response. All very good and valid points.

I have not checked out the pumps. They were initially sized to handle two heaters, one of which is now out of commission. I probably recirculate more than I feed to the heater. Good point though! I'll get in touch with the pump manufacturer.

It's my intent to switch to tips more suited to #2 oil and our heat input requirements but my concern is during the transition period when I have a mixture of 2 and 6 that I may plug the tips. Also, there may be some environmental permit issues doing this. Our environmental dept still needs to review our scope and design.

I have had some experience with using steam to atomize #2 that seemed to work OK. I'll be sure to question Coen on this point. I'm also considering mechanical atomization... any experience out there with this? I have none.

I won't be heating the 2 oil after the initial tank fill. This will be another question I have for Coen. Again, I have had different opinions of the ability of 2 and 6 to mix well. One would think they would since they were both from crude but, my ignorance is why I'm here asking these questions.

I expect to use more #2 since it has a lower heating value and flame temperature. That's one of the problems I have with running NG. This heater was designed to run #6 only in the late 60's. As such, we don't get as much heat gain in the radiant section with NG and the convection section is undersized as a result of the initial design, with NG as a fuel. Luckily, I had our project engineers to design in the ability to co-fire oil and NG when we did the conversion. This has saved us more times than not.

 

[MisterDonut]

Are the guns insulated? Sometimes for #6 oil the guns are not insulated. #2 oil guns sometimes require this, otherwise the fuel can get too hot in the gun before it reaches the tip, causing "coking" which can clog the gun.

Mixing #2 and #6 during the switch has been done before, it can help clean the #6 out of the system. You have strainers in the system, I hope. Keep it circulating.

 

[whammett]

I agree with rmw in that I have never seen #2 atomized with steam, although I'm sure it is possible. However, I can garuntee you that you will need to change guns after your oil mixture gets below 50% wt #6 to be safe.


As all units vary, I'm not sure what kind of permissives and LLL you have on your unit, but keep in mind if you have an LLL set up on a pressure device that is set to run on #6, you will have to change the settings for it to run #2. It should allow you to start up, but you could be feeding #2 at a very low flow rate, and the devices will see the flow as negligible. This is rare, but still something to be wary of.



"Scientists dream about doing great things. Engineers do them." -James Michener

 

[USAeng]

Hi Sam,

I was just reading through your thread here. We most likely sell aftermarket parts to fit your equipment, as well as our own designs. We would be able to help your commpany put together a good working setup. Please feel free to call us. We are a small company that specializes in ignition equipment, so we can give you the personal/quick service that companies like Coen and others have a hard time providing.

Thanks.

Eric Fox
Project Engineer
Control Systems Co.

If you want to talk to someone: 330-656-3557 and ask to speak to someone in sales. You can mention my name if you want.

We will also be at the Power Generation Conf. in Orlando if you will be there.

Have a good one.