A question about a bakery oven

[Gholam Baghery]

Hello everyone
I have a bakery oven with a conveyor that carries the dough through the oven to cook it. It does not function properly, and the resulting bread is of poor quality. I checked it and discovered that the conveyor parts are only one mm thick plate. I believe it should be at least 4 mm in order to store the heat and provide a good result. What are your thoughts? Also, what is your take on the fact that there are no refractory breaks or clay? It does not have any heavy parts to store heat and only has 20 mm of Rockwool insulation. Can I consider this factor to be a cause of the problem? The oven runs on natural gas, with eight flames and a gas consumption of 20 kg per hour. I will appreciate it if someone can share his or her experience with me.
Thank you in advance.

 

[LittleInch]

So what is the actual issue?

What does the manufacturer / manual say?

Is this a new issue or have you bought an old oven?

Is there too much dough?
Too fast a speed of the conveyor?

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[Gholam Baghery]

Many thanks, Littleinch
1. The actual issue is the oven will turn to cool after a while of cooking. Some of the first bread is acceptable (not perfect) and after a while, the others are not cooked. Although the flames are turned on.
2. The oven is a chain oven. Its manual says it has the capacity to provide us with 16000 bread per day. (1200 per hour) . I don't trust the manual and the company.
3. It is not an old oven. We have just launched it.
4. There is not too much dough we feed the machine with the least dough.
5. We reduce the speed down to the minimum
I am guessing that the problem is with the thermal storage and that the conveyor belt does not have the ability to store energy to compensate for the heat loss when the dough falls on the conveyor belt. Is my opinion correct?
Thanks again for your help.

 

[MintJulep]

Is my opinion correct?

Probably not.

My guess, as someone who once set up industrial ovens as my job, is that you don't have enough gas pressure.

 

[LittleInch]

I don't think in this instance that it really matters what heat storage there is in the oven as this is a continuous process no?

So it's really about the heating power of the gas burners and the amount of energy that is being "absorbed" by the bread dough. Any heat storage capacity at the start will rapidly be extinguished after a few minutes.

So look a the gas supply and regulators to make sure they are at full capacity or temperature control is working properly.

Some pictures or technical data would help here to see where the issue might lie, but from what you've told us, it looks like there isn't enough heat going into the oven.

Not trusting the manual or the company isn't a good place to start though....

Insulation thickness looks a little low, but 20mm rockwool is not too bad.
The refectory lining would help even out the heat source for sure, but it looks like there just isn't enough heat going on for the amount of bread you're cooking.
SO I would try reducing your dough mass rate to start with and see if things improve?

So how much dough is being baked per hour?
What temperature is the oven supposed to be?
How do you keep the oven temperature high and not let it all escape?

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[Latexman]

3. It is not an old oven. We have just launched it.

If it was purchased new or used/pre-owned, call the supplier/company. Request technical assistance for start-up. Their expert or technician should be better than SGOTI.

Good Luck,
Latexman

 

[pierreick]

Hi,
As suggested by Latexman, check with vendor. You need to adjust the speed of the chain conveyor to the temperature profile in the oven. My comment is based on my experience with this type of oven used in the chemical industry to convert rare earth oxalate to rare earth oxide.
Note: you may have an issue with the temperature controller(s).
Good luck
Pierre

 

[MJCronin]

Buy your own accurate pressure gauge for the gas supply ...

Have the gauge professionally installed just upstream of the oven...

Now, is your fuel pressure within oven mfr's specification ? ... according to your own gauge ?

Is the operation of the burners stable ?.. Is some bread burnt while others undercooked ?

MJCronin
Sr. Process Engineer

 

[IRstuff]

Your supposed gas consumption works out to 52 kBTU/hr per burner, which is the capacity of a small burner on a stove. The large burners on a stove are typically around 120 kBTU/hr, so that's a possible issue.

However, you've not indicated whether the bread is underbaked or what. Also, have you proven your bread recipe in a regular oven; I would assume so, but assumptions are not always correct

TTFN (ta ta for now)
I can do absolutely anything. I'm an expert!

https://www.youtube.com/watch?v=BKorP55Aqvg

faq731-376 forum1529 Entire Forum list

http://www.eng-tips.com/forumlist.cfm

 

[LittleInch]

Are you sure?

I get about 310 kW of heat burning 20 kg of gas per hour.

That sounds a lot, but maybe not for an oven expecting to bake 20 loaves a minute.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[Snickster]

I do not have experience in baking ovens but it seems like it may be due to poor air flow. I believe a indirect oven will have a blower that blows the air across the burner heating coils then through the oven. If direct fired then I am not sure if the arragngement is for burners to be completely under then entire conveyor to evenly distrubute the heat.

If you are using 20 kg/hr gas that seems about right per other posts insofar as heat input is concerned so possibly something is wrong with your air system blower - check air filters on inlet of fans etc., and if air flow is sufficient - make sure all inlets and outlets are open with no flow obstructions.

I don't think it is a heat storage issue since I believe most commercial baking ovens are made without brick. ect. and are of insulated sheet metal design so any heat storage capabilities would have been built in the design if required. I think the instantaneous heat input itself was designed to heat the bread.

 

[IRstuff]

Are you sure?

Not 100%. I used the value in

https://www.engineeringtoolbox.com/heating-values-fuel-gases-d_823.html

and divided by 8 for the number of burners

TTFN (ta ta for now)
I can do absolutely anything. I'm an expert!

https://www.youtube.com/watch?v=BKorP55Aqvg

faq731-376 forum1529 Entire Forum list

http://www.eng-tips.com/forumlist.cfm

 

[LittleInch]

In engineering toolbox you need to click on the little blue symbol to get the second set of units which then gives you 45,000 KJ/kg. Still a bit low in my opinion ( I was effectively using 57,000 HHV). The methane figure is 55,000 in eng toolbox

So your calc even using the lower version is then 112,000 BTU / burner or 32 kW per burner.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[IRstuff]

@LI, thanks, I should have checked more carefully. At the higher value, it seems more plausible and consistent with conveyor pizza oven on steroids, but I couldn't find anything specific for conveyor bread ovens

TTFN (ta ta for now)
I can do absolutely anything. I'm an expert!

https://www.youtube.com/watch?v=BKorP55Aqvg

faq731-376 forum1529 Entire Forum list

http://www.eng-tips.com/forumlist.cfm

 

[chicopee]

From my past experience with a French bakery, the entire inside of that oven was covered with refractory which during firing the factory would appear to turn a red-whitish glowing color. Same with ovens used by Moroccans baking their round bread but those oven were of smaller size and not designed for commercial sales. Visit some of your local bakeries to get more knowledge from their owners. I would not visit pizzerias as their products is not line with baking bread.