Incinerator Chimney Design

Some physical dimensions of your system and what you are burning would be very helpful information to start us off with.

i intend burning domestic municipal waste

At what rate?

20kg per 30minutes

That's a small bonfire!

it's my final year project and for costs reasons i made it so

dimension of lower chamber: diameter is 60cm and height is 53cm while the stove ( the fuel which will b used to burn the waste is dry sawdust ) is diameter 50.2cm and height 48.2cm. dimension of burning chamber: diameter is 49cm and height is 47cm.

pls explain a little further ... i didn't get that

The comment has been deleted as, having read other posts that were made during the 15 minute edit period for registered users' posts, the comment contained within it was no longer relevant.

THe volumes you are dealing with are rather low so that is not a problem! Infact your estimates are fairly close to my own home incinerator boiler I made to heat my house with.

My chimney stack is ~2 mm thick stainless steel and ~200 mm diameter by 5 meters high.

Now that said for burning sawdust and most municipal waste material a good draft from below the material and above the material are required. I highly recomend the bottom draft be fan forced and the upper a controllable natural draft or fan draft system the blows across of the burning material.

i really appreciate your effort in helping me through but now that u mentioned it, what is this "draft" all about because i have read several articles that mentioned little about it but didn't understand it well and also how is it concerned with d design of the chimney?

Draft is the flow of fresh air through and around the burning material.

As you know hot air is less dense than cool air so it raises. By having your chimney very tall and hot you can produce a lot of upward air movement but at the expense of wasting heat energy.

More hot air makes it move up the chimney faster pulling in more cool air to drive the fire but at the same time les of the heat energy from the burning fuel is transferred to where you want it. 500 C from a fast burning fire will make a very fast draft up the chimney.

However if you take more heat energy out of the combustion gases by absorbing or transferring it into something else before it gets to the chimney the air will not move as fast going up the chimney. 100 C from a slow burning fire makes a slow weak draft up the chimney.

By using a forced draft by means of a electrically powered fan you can move lots of air through the system even though draw more of the heat energy from the hot combustion gases before it goes up the chimney and is lost. You can absorb the heat energy from the combustion gas temperatures bringing down to 100C but still have the fast airflow and fast hot fire of the 500 C chimney making for a more efficient system.

thanks alot sir for d info ... pls sir, when calculating for d adiabatic flame temperature of sawdust i got 2100.25K pls i this value reasonable?

That volume of sawdust does not count as municipal waste should it be a continuous stream.

Just put a 4in/100mm diameter flue some 9ft/3m upwards and arrange for the exhaust gases to pass up it. This isn't Mechanical Engineering; this is Building work.

I would have doubts on getting the combustion gases from burning ~50 #'s of wood through a 4" stack in 30 minutes.

My original boiler design had a 6" stack about 10 feet high and I had to use forced intake and exhaust draft systems to get it to burn properly and even then burning 50 #'s of wood in 30 minutes was pushing it.

So far the OP has not mentioned anything about realistic heat loading values relating to what exactly he is burning the sawdust for.

With my boiler system I can burn 50 #'s of hardwood pallets in a 30 minutes time which yields around 300K - 400K BTU's per hour depending on the wood characteristics and boiler operating conditions.

How about something like this....? 55 gal drum mounted on a hand truck, forced ventilation fan mounted on back....adjustable stack flow....

http://www.erosionpollution.com/drugdisposal.html

I make my summer time garbage burning barrels out of 55 gall drums. I cut four 'L' shaped slits just above the first ring on the bottom about 5" x 5" and fold the tabs in to get a high flow swirling intake air system on them.

WOW can that make things burn hot and clean! It's fairly common for me to burn a weeks worth of garbage in one shot and if there is a lot of paper, cardboard and plastic in the trash I can get a barrel to glow orange red most of the time!

That also works very well for getting rid of sticks and old wood and reducing them down to fine clean ash too!

Shame it doesn't power the lawn mower, really.

After you're done with it, you can make it into a barbecue or smoker....

Well all of my barrels are old commercial paint and farm chemical barrels so I have suspicions that they may add a bit of extra favor of their own!

After burning them to a high enough temperature for them to glow red, I find it hard to believe any residue is left that couldn't be rinsed out with some concentrated acid...

Good point. They do get burned clean of paint and everything else and a quick wire brushing does sweep all residue and remaining ash off down to clean base metal.

I however presently have little interesting making smoked meats at this time.

sacrilege! Pork is life.

Why not do what any enterprising student who has no clue would do.

Look on the internet for images of a boiler and copy what is already for sale.

Then the amount of effort you put inot the project will be minimal.

i appreciate all your help guys ... thanks and God bless

kenoniuwe-

A very important factor in designing what you are looking for is the environmental and air pollution laws of your country. If you were in the United States and operating within the parameters of the Environmental Protection Agency, EPA, it might be questionable as to whether your device would be allowed to operate. If you state more information concerning these you might get more relevant answers to you needs.

Good Luck, Old Salt

my supervisor said i should just design d incinerator to burn the waste and not bother about converting the heat product into any useful energy. in other words, i am not considering any environmental law or policy for that matter other than designing an effective incinerator

kenoniuwe-

OUCH!

Once worked for a chemical company in the NYC area that had a supervisor such as you speak of. One day I drove from one plant to this plant. Guess who was there! Many FBI agents, EPA agents and EPA police, customs agents, customs agents dogs, state police and a whole lot of unidentified people. Most of them had one thing in common, handcuffs. The supervisor left the site with a pair of those interconnected bracelets on his wrists. That could happen to the supervisor, and if he lies you too!

His "just get it done" attitude and actions cost him $100,000 and the company $1,000,000. He got a reduced sentence so he didn't have to go to jail.

i get your point sir

He lives in Nigeria.

As long as they can see the burning trash and tire piles from the international space station while on the day side of the planet he's fine.

We have similar enforcement standards here in ND as well.

very funny tcmtech ...

Well that changes things a bit since heat retention and recovery are not important.

Given that wide open burn criteria just as long as the flame coming out the stack is less than twice the length of the chimney inside diameter any amount of air you can put to it is okay!

Heavy forced air bottom draft and a wide open upper draft is all you need!

Put the air and fuel to it and let it roar like a fighter jet taking off!

kenoniuwe-

During the 40'w---->early 60's Secaucus, NJ, had the reputation of being the smelliest location in the metropolitan area. Having traveled through, forbid I would have to stop there, I can attest that the reputation was well earned. The source of the smell(s) were the local numerous pig farms and abundance of garbage incinerators. The incinerators were cone shaped (pointed end up) with a big screen at the top, more of a convenience design that engineered. After considerable investigation the town determined that the incinerators were the much greater source of the putrid smell. Eventually the town shut down the incinerators and the pig farms. Ironically land fills replaced the incinerators! Just mentioned it as an example of what can happen with a poor design. Most of the owners and operators of these establishment were of a certain organization very powerful in the area till this day. Success to you and your endeavor.

Good Luck, Old Salt

thanks old salt

Hi,

For this question you can use google or this web site for help

...

Engineering Services

i got a reply saying page not found.

guys pls check this out to see if i'm right;

i calculated for the total mass of flue constituents and divided it by the density of the flue gas at the combustion temperature to determine the volume of the flue. then, i went ahead to calculate the volumetric flow rate by dividing the volume by burning rate and calculate for the chimney's diameter and got 24cm ... pls is this value reasonable?