Black Smoke in Solid Fuel Boiler

Is this a new boiler? Has it run clean before?

Has something happened to your air supply - that is, severely limited the amount of oxygen to the flame?

Did your fuel become contiminated with something, such as plastic?

Dear Sir,

this boiler is 20years old and it was running fine till 2008.

What type (make/model) of boiler is it?

How much excess oxygen do you have?

How is your airflow (forced/induced)?

Is the stack flow restricted?

Are there any major casing air leaks?

Have you noticed drastically reduced performance from the boiler?

Did you change fuels/suppliers around that time? Id you talk to your fuel supplier?

What changed in 2008?

Dear Sir,

we moved from coffee powder to coffee brcqutes as fuel with modification in travogate for air supply

What is preventing changing back again?

The reason for asking is that the surface area per unit of volume of a powdered fuel is greater than for a briquette fuel. Combustion takes longer for the briquette fuel, therefore it makes more smoke.

If so what will happen if we increase secondary air ? will this be benificial or reducing the bricqute size ?

Try it and find out!

It needs more air!

Wayne

Every boiler needs to be shut down, so that the heating tubes can be thoroughly cleaned "every once in a while."

A boiler burning natural gas in Chicago, for a factory building's heat supply was cleaned once a year. Even thought natural gas is a "clean" fuel, it was a big job. It took one man about a week to complete the work.

With briguette fuel, I would estimate that the carbon buildup is quite thick.

The carbon build-up will cut down the insided diameter of the heating tubes, thereby restricting the air-flow.

PL CHECK FOLLOWING.

COMBUSTION BED TEMP SHOULD BE ABOVE 800 DEG C.

COMBUSTION BED SHOULD BE FREE FROM CLINKERS.

BOILER TUBES ARE CLEANED.

ACTUAL LOAD ON BOILER SHOULD NOT BE MORE THAN RATED 5 T.

FLUE GAS TEMP SHOULD BE < 200 DEG C.

REGARDS

P.BHANDARI

<...FLUE GAS TEMP SHOULD BE < 200 DEG C...>

...and above the dewpoint of sulphuric acid, otherwise the flue will begin to rot.

Please turn off Caps Lock.

Guest,

This application is a biomass one and bed temperatures suggested by you are in the region of slag formation. You would need careful temperature monitoring and reduction techniques to avoid the whole thing gumming up pdq.

Massey.

Dear L.R

The answer to your problem (post 2008) seems to lie somewhere between the changes to the grate and the fuel with the overarching issue of incomplete combustion being caused by a lack of secondary air. Does the boiler rely on an ID fan to induce air into the combustion chamber or is that achieved through stack draught alone?

Did you carry out any other modifications to the combustion chamber during the changes to the grate mechanism? I.e changes to the refractory lining.

Depending on the moisture content of the fuel and the rate of travel of the grate you can profoundly alter the characteristics of the bed temperature and as this affects the overall quality of combustion it must be taken into account when looking at the smoke issue. If the boiler has a brick arch over the fire bed this plays a role in assisting with the promotion of good top surface pre-heating/carbonisation which form part of the combustion process.

More info would assist in forming a clearer picture of your set-up.

Regards,

Massey.

Ok, in my humble opinion when you changed fuels . . . the quality of the fuel changed . . . the Heating Value probably increased. Is this bricquet fuel a "compressed pellet fuel" or "charcoal" produced from biowaste (coffee-saw dust-nuthusk). If you were using a powdered biowaste . . . coffee waste . . . and go to a charcoal . . . the Heating value probably saw a significant order of increase. What was the orginal design fuel for the boiler? If the heating value of the new fuel is far outside the design you have a whole new set of conditions that must be determined. If I were in your situation, the first thing I would do is have a fuel analysis performed and determine if the fuel you are now using falls with in the capability of the steam generation system as a whole to efficiently use the fuel. Perhaps the biggest mistake made by many boiler operators to to take for granted that a better, high heating value fuel, will get me better efficiency . . . this is not true at all . . . if the entire system is not upgraded to burn the better fuel . . . you lose efficiency and the better fuel actually cost you a heck of a lot of money.

Dear Ramamurthy

Obviously black smoke is an indication of insufficient excess air required for complete combustion.

Gas fuel normally requires 15% excess air. Fuel oil requires about 20 t0 25% excess air, for solid powder probably around 30% excess air. So in your case probably you need an excess air of around 40 to 45 %.

Therefore, opening the secondary air would certainly helps.

If the secondary air still insufficient, what I suggest is that you revert back to powder and introduce solid fuel bit by bit until you reach the maximum amount of solid fuel. This is for short term solution. Of course for long terms you need to increase air flow either by installing bigger fan or higher stack to provide more draft or both.

Incomplete combustion, moisture high, low bed /flame temp ,dusts flowing out without combustion. It appears that total calorific value per ton has gone down. so if you need to charge more fuel mass ,you need a larger grate area. Can you try a gas burner flame over the bed to burn out the dust and increase temp? other option may be to use a cyclone in flue gas line to reduce dust emission.

Please, let's not over-engineer the issue.

unfortunately for most engineers that want to sound so smart on here but have very limited experience actually operating steam systems, I am a state licensed stationary engineer. Your problem is due to a lack of combustion air. We have been tweaking our traveling grate coal boilers lately where I work and have made several adjustments to the combustion air. The type of fuel used in a boiler is somewhat important to your firing techniques, but what you need to focus on is your O2 levels at the exit of the breeching for your boiler,being careful to stay within an efficient level, and the amount of combustion air introduced to the fuel. What type of draft system does your boiler have? Forced? Induced? Balanced? I'm going to assume that you have an ID fan on this system. You will need to increase your ID as you increase your FD air to maintain a smoke free environment. What kind of environmental control systems do you have in place? Baghouse or electrostatic precipitator?

Not to burst your bubble or break your heart . . . but it does appear to me that just reading through the posts previous to yours, and clearly not knowing who in the groups is "trained" . . . "licensed" . . . "educated" . . . "experienced" or otherwise so esteemedly qualified as yourself I detected not a single new shred of insight into the challenges that are defined in the initial posting.

Clearly, the reason that you have an ID and FD fan is due to the design work of an engineering organization. What gives you the capability to adjust and satisfy the requirement of the needed oxygen to reduce or control CO2, and the multitude of other combustion waste is defined absolutely and totally by the fuel specified for your boiler. Deviate from that fuel and even though your exhaust gases may be well within the limits of design, you may find that your boiler works less efficiently or may not at all be able to meet the orgininal design specifications. Clearly as a stationary engineer . . . which does perhaps qualify to operate the plant . . . it does not provide you with the creditials to design boilers.

So here we see again . . . the engineer vrs technician . . . seen, lived with it and it is a mind set that will always prevade and influence the perspectives . . . which all ultimately do come down to "engineering".

Hi there,

From the stunning lack of recent response from the enquirer I think that the glut of good advice, may I even suggest a bit of a 'carpet bombing' technique, has sent him back to the boiler house with a resolve to take a vacation!

I have observed that there is a tendency by some contributors to re-iterate and embellish; but then that happens everywhere, so its up to the individual to try to disentangle the 'wheat from the chaff'.

Have a Guid New Year.

Massey.

Dear Valued Experts,

Wish you all Very Happy new Year

Thanks each one for your valid support. I was on leave for past two days and resumed duty today and hence not able to reply to your responses. iam going to start the boiler tomarrow after taking all your valid suggestions and keep you posted on learings.

With Best regards

L.Ramamurthy

Hi there,

Nice to hear from you. I thought you had been dismayed by the wealth of good advice.

As they say up here ; 'Lang may your lum reek'

Which loosely translated means long may you be properous.(A reeking lum, smoking chimney, being evidence of a fire in the fire place and therefore an indication of having sufficient money to buy fuel!)

Which is probably the last thing you want to see...... But hey-ho its the New Year.

Best Wishes.

Massey.

I never claimed to be a boiler maker...and I am currently in school for mech. engineering so keep your us vs. them comments to yourself. Having actual operating experience, I can tell you, the engineer, that what works on paper does NOT always work in the field. Regardless of the fuel introduced to the boiler, the amount of combustion air, as I'm sure you read in my original post, is vitally important to your burn and the method of removing said combustion air is also as important. All I tend to see on sights like this is engineers trying to flaunt their intellect when it is actually severly limited to hands-on experience and the reason I am going for my degree in engineering is to bring back some of that common sense that so many of you seem to have never had or lost along the way. Good day to you sir.

Welcome to CR4! I am sure that you will find that this to be a different experience than all the other forums out there . . . much more open, enjoyable and respectful of all the input and quicker to provide assistance where needed.