Incinerator Project

Post Reply New Topic

So I'm hoping to use this as a way to get rid of household trash. The idea is that I blend all my garbage into a slurry, and feed it into an incinerator.

I'll raise the temperature enough to ensure a through incineration, during the process, I'd spray water to hopefully catch some smoke particles before they escape through the exhaust pipe.

The exhaust pipe will feed into a submerged heat exchanger, and eventually through an electrostatic precipitator, which will trap more smoke particles.

The diagram above explains the process too. I'm working on the greenhouse right now, it'll be well over a year before I can say whether this will work or not.

Am not a chemist, or an engineer but...

Wouldnt the pipes leading out from the incinerator get clogged up really fast?

Especially in the heat exchange segment of pipes?

Even if the whole thing worked it would only work for a matter of minutes or hours before the whole thing would jam up I would think.

You would be either perpetually cleaning pipe. Or perpetually replacing pipe. Wouldnt you?

Normally the whole point of incinerating refuse is to combust it so it combines with the oxygen in the atmosphere to transform it in to hot gas, and fly ash, so it all floats away in the outside air. But here you're trying to recapture your garbage just after combusting it before it goes into the atmosphere. So you would be taking say a hundred pounds of garbage- burning it- which increases its weight because you're combing the garbage with atmospheric oxygen, and you're also injecting water into it. So the hundred pounds of garbage becomes (I dunno) 150, or 200, pounds of soggy ash that you're trying to force through pipes. Good luck!

The point of spraying water into the exhaust pipe is to capture some of the smoke particles and drag them back down into the incinerator before they continue through the exhaust pipe.

Ideally, I want only air to escape, but there are going to be parts of the pipe that capture the particles, I might have another inlet port to spray into those areas (or see if there are chemicals that I could use to break up the ash) and another outlet port carry it back to the incinerator.

A design feature I didn't mention was a door, I want to manually remove the ash from the incinerator for disposal, not force all the soggy ash through the pipes.

I'm no chemist either, but I know some elements tend to double up and escape as gas such as H2, N2, O2, F2, and Cl2. I can't anticipate how they'll react with each other, or what proportions of each I'll even start with. I'm assuming this will be stuff I don't want to put in the atmosphere, so I'll send it to an enclosed greenhouse in hopes that the plants will metabolize it first.

Well as an engineer who deals with fairly similar systems frequently, I can throw in my input. First off, what exactly is your goal with this? Is it to "live green" by converting your solid waste to vapor? If so, then I wouldn't put my money on it. For one, many of the household wastes that we throw away can be quite hazardous when combusted, and will create far more of an environmental issue than if they had just been thrown away. Plastics are a major one, as are things like batteries, household chemicals, etc. Even burning certain seemingly-innocuous organic items such as certain foods can create issues.

Secondly, I wouldn't expect the water above the incinerator to do much other than significantly increase your electricity costs to operate the incinerator and generally make a mess. If your goal is to remove solid particulates, it would be better to do so in something like a cyclone or a filter downstream from the incinerator - the water will mostly just provide direct-contact cooling/condensation, and will be re-vaporized in the incinerator (and vaporizing water takes a LOT of energy input).

Your heat exchanger doesn't make any sense to me. It's not going to do a thing with respect to removing solids (other than the ones that will inevitably clog up the tubes over time). It will simply cool the vapor and, depending on the outlet temperature, condense some liquid. Your heat transfer in this setup will be terrible also, since it has vapor on one side and natural convection on the other, so you'd probably have to have a fairly large coil length to cool the vapor depending on how hot your incinerator gets. This liquid has no outlet in your drawing, so you will probably accumulate a liquid level in the tubes that will block vapor flow, causing the vapor to instead exit through your blender, unless you install appropriate valves. Even if you do that, the liquid level will create issues with high pressure and unsteady slug flow that you don't want to have. You also have the coils sitting in a water bath - unless you replenish this water with a fresh feed, the temperature of the bath will simply rise to the vapor temperature over time (which would likely mean it would vaporize and run dry) and become ineffective.

I don't know enough about electrostatic precipitation to comment.

Slurries are very difficult to deal with, and would likely clog the line frequently between the "blender" and the incinerator". I wouldn't have much faith at all in a typical household blender to deal with much household trash...I know that I have a fairly good one and it has trouble even making a smoothie sometimes. The incinerator and associated piping will likely build up quite a bit of scale over time that will necessitate cleaning.

Materials of construction may be important - depending on your waste you may see corrosion or issues with the high temperature (particularly with the PVC if your heat exchanger isn't up to par).

Several compounds that will be generated via combustion will not be removed by your system (and cannot easily be with any household setup as far as I know). These potentially include some environmentally hazardous ones such as NOx and SOx, in addition to the ones I already mentioned. I wouldn't bet on plants metabolizing this stuff - the only thing they will take care of is some of the CO2. Also, some of your trash may not combust, and will just collect in the incinerator.

In short, I don't think that this is a good idea, unless your goals are substantially different from what I imagine they are. These are just a few quick thoughts so don't take my word as gospel, but I definitely see a few potential pitfalls and wouldn't want to operate something like this myself.

I appreciate your insight, although I doubt you'd talk me out of it. This is mostly a hobby, but having a way to incinerate garbage off-grid is where I'd want to take this.

I use a pretty effective blender, I'm certian it'll pulverize most household trash. I wouldn't throw anything as solid or metallic as a battery into this thing. But it seems like adding more water to the slurry would help move it along.

The heat exchanger was there under the assumption that the air escaping the incinerator would be very hot, and since I want to use the precipitator with PVC piping, I'd have to cool the pipe temperature. Of course this project just might force me to look for an earlier point to place the precipitator to make it really count.

I want as few particles to escape through the exhaust as possible, I just assumed there would be some spray thickness / rate I could use to bring the particles back down. Yea, kinda figured it would lower the temperature too.

Of course I don't know what to do about Nitrous or Sulfuric compounds, how to minimize them, or how to divert them. But I'm not throwing in the towel yet. Thanks again for the comment.

If you want to get rid of waste and do it cleanly, build a plasma gasifier.

I read your post a few days ago and let my mind sit on it for a while. Here is what I came up with so far:

The water jet in the exhaust flume is a bad idea, as the heated water vapor can react with NOx and SOx formed in the combustion process to make some strong acids: nitric (H2NO3) and sulfuric (H2SO4) being two of them. If you keep the water spray, you need to put in a basic trap (something like calcium carbonate would work) to help neutralize the acids before they corrode the system. The exhaust pipe near the water spray to the trap would likely have to be made out of high-Cr stainless to survive the acidic conditions.

A catalyst system can be used on some of the NOx products to reduce them back to N2 and O2, much like is done in a automobile's catalytic converter. (SOx is a bit more complicated to reduce, but can be done.) However, that will raise the cost of your apparatus as you would have to use Pt, Pd, Rh, Ir or a combination of the four metals to get the reduction reaction to work properly. Electrocatalysts may also be used, but again that may add considerably to the overall cost for the system.

The biggest thing is the fuel source. Your idea would work best if burning mostly light hydrocarbon-based fuels like strait chained hydrocarbons (ie. propane/butane, hexanes/octanes) or wood products (cellulose). Coal is a tricky one to use as it can contain lots of sulfur and even Hg depending upon where it was mined. Plastics would be a big no-no, as previously mentioned by Stargazer43, as the combustion products can be very toxic and/or difficult to completely combust properly. (Yes, it would work if you went to plasma, but doing so increases the overall cost.) Polystyrene cups produce many carcinogens when burned and those would be transferred into your greenhouse. Since so many things that people use contain plastics, this would seriously cut back on what could go into the unit. (Even metal food cans contain thin plastic coatings.) The oxygen content of the flame would also have to be monitored to prevent the production of carbon monoxide, a very toxic byproduct of incomplete combustion of carbon materials.

As designed it wont work

a) The ability of combustion particulates to absorb charge from a precip requires a low moisture content, precips i have worked with have an entry temp of 200-300 degC

b) An electrical heating element will not generate the required temp to combust rubbish properly, it has to have a freeboard temp of at least 850degC to ensure the destruction of dioxins

c) There is no mention of forced draught, incineration relies on excess o2 to do properly

d) The use of water as the medium will absorb too much energy

Well, strong acids complicate this, guess its back to the drawing board. I'm pretty set on being able to incinerate plastic, or really any waste I generate. I assumed that by raising something like plastic to a high enough temperature, I'd destroy the chemical bonds that made it plastic, release a few gases, and leave an ash mixture of mostly carbon.

If I want this to work, I'd have to make the burn area out of high-Cr stainless because I can expect acid to form in this process. Since NOx and SOx should be heavier than the surrounding O2 and CO2, I should be able to divert those gases as the exhaust cools.

Plasma gasification seemed like you had to carefully adjust the O2 level within the reaction in the anticipation that you could use the byproduct. I don't actually want to reclaim energy, I'd just as soon burn the gas than figure out how to store it and further process it. And controlling the O2 level is easier said than done. Although, if the outcome of gasification is a more benign byproduct, then it's worth looking into.

Thanks for the informed responses everyone.

My #1 concern is that you may be getting yourself involved with a process you don't fully understand, and it may end up creating a hazardous or dangerous situation as a result. Aside from the operational challenges in your proposed process, there are plenty of safety concerns that can have a significant impact on you. One I alluded to would be backflow of toxic vapors through your blender, which I presume is located in your house...if you installed the process as-is, I can almost guarantee that this would occur as liquid builds up in your condenser.

Also, another thing I forgot to mention that RTFM alluded to: sending a slurry of water to an incinerator isn't a good idea. The water will first cool everything off, and then you will have to spend a huge amount of energy heating and then boiling off the water, followed by re-heating the entire chamber once the water is boiled off, before you can even start combusting anything. Try filling a pot with water and see how long it takes to boil all of it on high heat on the stove - it's not trivial, and will probably account for 90+% of your energy costs.

And yes, if you generate SO3, dew point corrosion can be a serious concern...depending on your operating regime, there are very few materials that can withstand that.

Gotta ask a dumb question.

The whole point of this is to turn garbage into carbon dioxide for plants in the green house to breath. Is that correct?

If you are after converting plastic materials into other things, you really need to look at a device that was developed by an inventor in Japan a few years ago. Basically, the device is a combination of many microwave generators that "cook" the plastic materials back into the oil that it came from. By changing the frequency of the microwaves emitted from a normal microwave (set on the vibration mode of water), it can be absorbed by the target material and excite the carbon atoms in the plastic to break the carbon-carbon bonds. It is not really cost effective though due to the high amount of energy needed for this process to work. For one gallon of usable fuel out of the waste plastic materials, you spend almost $20 based upon the original device. The fuel is not absolutely pure either as it should be refined before use. Look at youtube and search for "plastic to oil microwave conversion machine", it should be in there (at least it was last year). I know that there are companies that are doing this now for profit, as they have a ready supply of cheap electrical energy nearby (ie. nuclear reactor likely the source). They probably have made a much more efficient device for the conversion process also.

I do not suggest taking microwaves apart and randomly sticking them together to make a similar device. The outcome might not be the one you want.

If that's the case the OP shouldn't be playing with that unless he really know what he's doing, which clearly he don't. In high concentration CO2 can be dangerous to breath and it's not a good idea to dump that in a closed system. There is also the problem of heat during summer, as CO2 retain heat.
https://en.wikipedia.org/wiki/Hypercapnia

just a little observation, this is very energy dependent,
you better start offgrid on the intake side first, imo

No, just getting rid of garbage off-grid without making another landfill.