11 replies to this topic

[ToddT]

I read about tars containing napthalene and other aromatic solvents. In my world, that isn't necessarily a bad thing. I design industrial cleaning chemicals, specializing in non-haz blends. My current push is to have all my formulations readily biodegradable and made from renewable/sustainable ingredients. I'm about 95% of the way toward biodegradability but having trouble on the renewable side. Getting solvents from wood is very interesting.

Could we take the tars from gasification, mix them with a co-solvent like biodiesel (a methyl ester), and then do some fractional distillation to selectively pull off certain solvents? "Green solvents" would be great. But, would these renewable solvents have any different biodegradability than their fossil fuel counterparts?

By the way, certain co-solvents could impact biodegradability. Straight biodiesel (methyl soyate) added to a crude oil spill will render the spill readily biodegradble. The biodiesel breaks down the oil into bite size snacks and then once the oil is gone, the biodiesel is readily biodegradable. Works better than the standard application of Dawn detergent. Just an interesting aside.

[JayAlchemAPL]

With gasification, we are trying to crack all of these tars through partial oxidation because there is so much energy contained in the tars.
I could see reclaiming the wood tars from the making of biochar through capturing the pyrolysis gases. Something I have been meaning to do is to subject the distillates to an acid wash or a basic wash to separate components. This is done to isolate napthalene I believe. There should be methanol in the distillate as it is the wood alcohol. Its boiling point is around 64.7C I would assume to be the first to come off the top. I would encourage you to do this, it would be interesting.

We are going to be using biodiesel as one of our gas scrubbing agents and tar solvents in the filter media and cyclone to test it out. Should be interesting. Biodiesel, however more biodegradable than oil, is still considered a hazardous material. Any oil floating on the water's surface blocking oxygen from aquatic life is considered a serious and hazardous situation. Though returning the biodiesel into the gasifier might be an interesting way to dispose of the solvent as a reclaimed energy, as opposed to ending up with a large amount of contaminated water.

[Dutch John]

ToddT said:

Could we take the tars from gasification, mix them with a co-solvent like biodiesel (a methyl ester), and then do some fractional distillation to selectively pull off certain solvents? "Green solvents" would be great. But, would these renewable solvents have any different biodegradability than their fossil fuel counterparts?

What do you want to do with the heavy, un-distilled part?

I consider tar not to be present, except for monorator tar, so called Stockholm tar. Excellent for wood preservation in our mouldy climate. After use, this wood can be gasified. No pollution.

A bigger problem is the toxic condensate from both monorator and cooler. It has water soluable tars.

Regards,
DJ
http://woodgas.nl/

[JayAlchemAPL]

The first is a picture of a 50/50 mixture of a watery, or less viscous distillate of tars from the bottom of the cyclone and biodiesel. There is still the clear distinction between the water and oil layer. A thin layer of soot floats on top of the water layer. It may not be that it is less dense than water, but that its active groups still have a greater affinity for the oily environment or they are not able to break the surface tension. There is a thicker layer of heavier particulates that have settled to the bottom of the jar.

The second picture came from recycling the biodiesel through the filter and cyclone (without filter media) as a test for the scrubber. There isnt any water in the second sample. Expected the soot particulates at the bottom and tar suspended in the biodiesel.  
The biodiesel could be reintroduced to the gasifier, or possibly be added to a diesel engine? I believe there might be enough energy in the biodiesel to be able to crack the tars because they are suspended and separated.

Intentionally collecting the tars for the use as chemicals though is interesting. You might want to check out this site: http://www.thersites.nl/ They have done some work on tar due points and might lead to some insight on what could be valuable in wood tars.

[HarryN]

Sasol (S Africa) does extensive gasification of coal.  Their process collect virtually every possible condensate group for each temperature range, and tries to value / sell it.

Of course, they have quite an advantage, in that they are a large, highly integrated gasification / refinery / chemical plant / FT fuels maker.  At that scale, a lot of things are possible.

I also have wondered about the value of the liquid wood tars though.  It seems like in some cases, they are quite valuable (stockholm tar) and in other cases, they seem to be considered dangerous.

Lots of reading to do.

ps - Hi - first post.

[jimmason]

harry, yes, sasol does very interesting work on the liquids front.  most of this, however, is building up to liquids after clean co and h2 gas.  i am not aware of their working with the tar condensate of the primary gasifier to do much of anything, other than avoid it. maybe you have more specific info on this?  more generally, sasol is of course the longstanding "best art" example of FT at plant scale.

they're also now doing some work on smaller FT systems.  they recently got a GEK system to provide the gas for these small scale experiments.  hopefully we'll get a report here soon about their work.

i'm trying to find an excuse to visit.  we have a power pallet about to ship over to south africa.  we also get lots of inquiry notes from there.  hopefully all this will lead to a plane going south soon (with me on it).

jim

[HarryN]

Hi, well I seem to have been mistaken.  I went back and looked through their site again, and realized that I had mis read one of their documents.  The condensates were in fact after the FT process, not before.  Sorry about that.

It's interesting that they bought one of your units for the lab work - you should be quite proud,  given their own internal knowledge base on gasifier work.  It is sort of a long plane ride for a customer courtesy visit, but that is the nature of building customer relationships.

[HarryN]

Hi, I was curious about the nature of some of these tars.

From reading this forum, and other sources, the pyrolysis reaction of the various wood components takes place over various temperature ranges.  This sort of makes sense, as the more tightly bound, larger molecules will naturally require higher temperatures.

If we were to capture all of the tars and try to use them as a mix, then of course it would be a mess.  This is probably a rehash question of the centuries of knowledge, but would it make any sense to try to separate the tars emitted over various temperature ranges and see if they have redeeming value.  (example - from 150 - 250 C, then 250 - 350 C, maybe a zone from 350- 450C ), then run the rest through the system for fuel / CO generation ?

There doesn't seem to be a shortage of tar to work with in the process.  Obviously, some serious zoning and process separation would be required.

[HarryN]

Hi, I guess the old hands around here already know all of this stuff, but for me and other new people, after the wood is "dry", the next step in low temperature processing (200 - 300 C or so) is referred to as torrification.  From a wikipedia link, here is a presentation from the Netherlands on the subject, complete with some analysis of the output.

http://www.ieabcc.nl...ves/03_Kiel.pdf

The experimental process time was 30 minutes, although it is not clear how well that is optimized.

It appears that there is considerable water both from the more complete drying, and possibly from the chemical reaction, although there was not enough data to do this calcuation accurately.

I have not examined the value of the condensable organics from this process, although certainly some of them have value to the right end user, in the right purity and volume.

One complication is that the solid material becomes extremely friable, which would be a bit of a pain for a down draft gasifier.

[ToddT]

I have a friend experimenting with torrefied wood. He seems to think it will flow better down the gasifier, requiring less agitation.

[HarryN]

An interesting article related to the resin, rosin, and terpine content of woods.  Maybe their is value after all.

http://www.fao.org/d...00.htm#Contents

[Cloggie52]

Hi there,

There is a Dutch article on tar here: http://www.ecn.nl/do...1999/c99102.pdf . There is a english summary, but the most instresting for this discussion is a graph on page 23, where the tar production (on a logaritmic scale) is shown. It indicates that fixed bed (Vast bed) is a low tar producing construction. It also underpins Jim's statement that the operational conditions are an important parameter, which can change the tar production by e factor of 100 (especially in fixed bed downdraft gasifiers).

Hugo