[Gasification] Gasification Digest, Vol 11, Issue 35

Thu May 10 08:11:02 CDT 2007

Interesting reply. I happen to be Swedish and am working in Sweden with questions related to supply and use of energy and related environmental matters, but I have not before seen such concise and as I understand correct information in such a short text. The matter of circulating ash is not simple and the same is also valid for certain other materials that people want to recycle. We have taxes on commercial fertiliser depending on the ratio between Cd/P and if the ratio is too high for a certain batch of commecial fertiliser it is forbidden to use. However it may happen that cattle manure is above that limit but still it can be spread on the fields. The reason for this is of course that there is not really any other good alternativ and it is sometimes said that the cadmium came from the field to start with. This argument is of course disputable. The manure is of course also beneficial for the soil structure and for N and K.

It is said that the cadmium content in commercial feriliser can be decreased by heat treatmen in the manufacturing process  but I have not heard about anyone doing it yet. However from this I guess that P and Cd will behave in different ways in a combustion or thermal gasification process so that they will be distributed differently between bottom slag, rough fly ash and filter ash. For cadmium this has actually been tested in a waste incineration plant many years ago. Most of the Cd was collected in the electrostatic filter. The distribution of metals is related to their boiling temperature. However I have not seen any such tests for phosphorus compunds. I suspect that posphates will be more evenly distributed on varius kinds of slag and ash but this is only a suspicion.

If the Cd/P ration in straw is low enough for it to be acceptabvle to leave on the fields and plowed under for keeping enough organic carbon in the soil but the ash from the straw is not, then the reason might be that P and Cd are partly separated in the combustion process, with an even dirtibution for P and an enrichment of Cd in the fly ash.Have you seen anything written about that.

Regards
Bjorn Dahlroth
The Stockholm County Association of Local Authorities

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Ämne: Gasification Digest, Vol 11, Issue 35

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Today's Topics:

   1. Re: OT Welding (David G. LeVine)
   2. Re: Ash to land? Each case different (Pels, J.R. (Jan))

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Message: 1
Date: Tue, 08 May 2007 21:01:15 -0400
From: "David G. LeVine" <dlevine at speakeasy.net>
Subject: Re: [Gasification] OT Welding
To: Discussion of biomass pyrolysis and gasification
	<gasification at listserv.repp.org>
Message-ID:
	<mailman.6.1178730002.25031.gasification_listserv.repp.org at listserv.repp.org>

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At 03:53 PM 5/8/2007, you wrote:
>Household/project items is the scale I'm looking at.  Steel tanks for 
>gasifiers, bike tubing for a recumbent etc.  Nothing terribly large or 
>esoteric such as titanium.  Good, starter to learn on advice for common 
>materials.  Anything specialty I will learn later.  I plan on taking a 
>course but in the meantime want to know what to look for if a good 
>piece of equipment comes up for sale and what not to get as too 
>ambitious right now.

Warning:  Expensive free advise.  AVOID THE REALLY CHEAP UNITS!  Get a small MIG and use flux core unless you need gas.

Harbor Freight (and others) sell some $100 MIG/FC units which require more skill to get set up than many of us have.  Miller, Hobart, Lincoln, et al have both cheap junk and good units.  They will help you and their units can be repaired.

David G. LeVine
Nashua, NH  03060

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Message: 2
Date: Wed, 9 May 2007 10:08:48 +0200
From: "Pels, J.R. \(Jan\)" <pels at ecn.nl>
Subject: Re: [Gasification] Ash to land? Each case different
To: "Discussion of biomass pyrolysis and gasification"
	<gasification at listserv.repp.org>
Message-ID:
	<FEE823E55C8FFB4699D28936A0E8F716EEAE06 at ecntex1.energy.ad.intra>
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There is indeed a lot of information out there. Here is another long contribution with comments on several issues raised today.

Indeed, each case is different. There is as least as much variation in ashes as there is in fuels. And ashes from the same fuel may be different in different installation types. 

On cadmium:
There are two main sources of Cd en Europe. Firstly in rural areas, Cd is present because it is a contaminant in mineral fertilizers. When used for over 100 years on fields, it accumulates even when annual dosage are below the limits. The US may not be suffering from Cd because the time that fields are used is shorter. Perhaps fertilizers with low Cd content are use. The main source in industrialized areas, is pollution: metal works and coal plants, including 'city gas' plants. Both from waste water and from air emissions. For most of the times water and smoke stacks were not filtered at all.
Cd when deposited on the land is in the top layer and is transported with dust to places downwind. In the Netherlands we have Cd emitted long ago by our English friends, the first to industrialize. On top of that, Cd is mobile. It gets into the water and deposits. Rivers are dredged and the sludge is used as fertilizer. 
Even Austria, which is not so industrialized has high Cd levels as a result of industry in Germany, France, etc.
I grew up in region that was industrialized by wind mills in the 1700s.
The locations of the mills where paint pigments were produces are still known for their contaminated soil. 

On contaminants:
Contaminants (Cd, Pb, PAHs) may be easy degradable, normally occurring, immobilised or whatever. Fact is that legislation exists that puts maximum levels. Most ashes I have analysed and assessed for fertilizer/recycling so far exceed at least one and typically more than two limits. Denmark has regulations for straw ash. They found that 90% of ashes exceed the Cd levels and cannot be used as fertilizer.
Typically Cd was 10x the limit. Other notorious elements that spoil utilisation are Pd, Zn, Cu, Mo and Se. When the wood has been machined with steel tool, the levels of Ni, Cr and V are elevated.
Furthermore, the speciation is important. Cr(III) is immobile, but
Cr(VI) is mobile and extremely toxic. Not all PAKs are equally toxic.

On the question of PAH:
The question is right. Fact is that plant owners have to comply with PAKs regulations that are supposed to guarantee safe levels for the environment and human exposure. I am not going to question the correctness of the legislation in this forum. Another fact is that all gasification ashes I have analysed so far smelled of naphthalene. I know there are PAHs in there, but my nose cannot detect levels or determine whether they are at too high levels. I just know that they are in there and I also know that part of them has moved through the air into my body.

On tests for land fill or fertilizer use:
Most ashes we have tested so far have have been approved for land fill.
Some have not, but these are exceptions and they are from combustion of not-so-clean biomass. Only one fly ash that did not pass the test for land fill came from combustion of clean wood (park waste, thinnings, etc.). However, when testing for utilisation as fertilizer, most ashes do NOT pass these more stingent criteria. Bottom ashes may pass the test, but bottom ashes are less relevant because a) they have less available nutrients and b) they can be used in road contruction at lower cost. Fly ashes on the other hand did not pass, except maybe one or two.

On use of ash in forests:
Decompostion of dead trees is different in different places. BC may have a conservating climate or persistent trees. In other forest it takes 10-20 years. In the Tropics probably even faster.
In Scandinavia, the boreal forests are limited in Nitrogen. Ashes contain no nitrogen, so the growth is not significantly influenced.
Ashes contain immobilized P that is released in 20 years or so. Ashes contain Ca and Mg that are benificial against acidification (from air pollution). Only K is leached fast, in about 3 years. The effect is that there is a relatively fast (3 years) growth of organisms in the soil that store this K. 
Furthermore, forestry is not nature. Forestry or silviculture is a form of agriculture with trees and long cycles. The Swedish have a set of well worked out recommendations to handle ash recycling. It is only mandatory in case of whole tree harvesting. When tops, leaves and needles are removed from the site and cannot return their nutrients. In case of stem extraction, this forest residue PLUS natural weathering of rock AND atmospheric deposition are enough to return the nutrients to the original level. (This level may not be natural, but it is the level the foresters want to have their 'crops' grow.) The ash is used 6 years after clearcut and only immobilized ash is used with a slow release of nutrient. Experiments in Sweden run for 25 years and this approach appears to be safe and not negatively affect the forest stands. I am not sure about biodiversity, etc. The conclusion is drawn from the perspective of silviculture.

On lead in road sides:
Yes, I remember when the government issued warnings against picking berries, etc. along the roads because of lead. I know alsow that nowadays these warnings are slowly lifted.

On installation scale:
The ashes from Scandinavian CHP plants are produced in installations of 50-200 MW. When they use uncontaminated waste wood (bark and cut off
pieces) they tend to be okay for recycling. They are regularly analysed.
No problem with larger scale. When they shift fuel, the ashes are analysed more intensely to establish that they are safe (or not) for recycling.
Small scale units tend to fire a larger variety of fuels and tend to have less analyses of ash, also by the one who is utilising the ashes for whatever purpose. Therefore, my conclusion is that those small volumes of ash with unknown or varying composition should be land filled and for the larger ash volumes with controlled quality utilisation options should be developed.

Jan Pels

========================================
Dr. Jan R. Pels
ECN - Biomass, Coals and Environmental Research P.O. Box 1, 1755 ZG Petten
telephone: +31-224-564884; fax: +31-224-568487
mobile: +31-6-10923218
e-mail: pels at ecn.nl
========================================

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