[Gasification] RPS experience with linear hearth

[Peter & Kerry]

Hi Doug & list,

I have moved the discussion to a more appropriate message header that 
better reflects the content. Also the messages so far skip across a lot 
of ground and it is too easy to get confused trying to cover multiple 
threads of discussion within one reply, more so when there is no 
differentiation in the text style between  individual contributors.

In this message I will only focus on the gas out of the RPS linear 
hearth, it is already long winded but am attempting to provide as much 
detail as possible without compromising proprietary bits.

Doug has mentioned our gas analysis as being "very unusual" for an air 
drawn system so for the benefit of the list I provide it here so people 
can see for themselves:

Major Gasses,
Hydrogen: approx  36.00%
Carbon Monoxide : approx  28.00%
Nitrogen:    29.00%
Carbon Dioxide:      6.81%
Low level Gasses,
Oxygen:         Less than 0.02%
Methane:     0.96%
Argon:     0.37%
There were also a range of minor gases in the less than 50ppm range.

The flow rate measured at the time of the test  was 130m3/hr, though 
this was not recorded on the lab certificate.

This is not full flow and the same system has been measured up to 
400m3/hr without apparent over aspiration for a 20 minute run before 
overheating of the fan motor caused it to trip.  The sustained upper 
limit has not been determined and may well be lower or higher (it has 
taken a while to get a suitable high temperature fan of adequate 
capacity, but will have one within the next few weeks, like most 
components we have ended up building this ourselves), but the system is 
quite comfortable at 200m3/hr with similar gas quality observed in the 
flare and can be turned back to 40m3/hr without losing this.

Now at this point of our development we are not making any loud noises 
about this, other than simply reporting it in a couple of local industry 
presentations and now here. Up until recently it was only a single 
analysis result. Instead we have largely kept our heads down and tried 
within our own limited financial resources understand what is happening, 
identify the feed stock parameters involved and get it further validated 
when we could.

We have made numerous attempts to engage university researchers to 
formally measure system performance without any real success. We had 
enormous difficulties in early days trying to get  gas analysis done, 
with some amusing moments, like delivering a 4 litre gas sample bag of 
raw unfiltered gas taken hot from our development unit to the chemistry 
department of a local university because they indicated they could 
analyse it, then getting an excited phone call rattling off a long list 
of compounds they found, none of which included hydrogen or carbon 
monoxide gas... It turned out that they had released the gas and opened 
the bag to scrape a tiny amount of condensate from the inner 
sidewalls...and ran the analysis on this. The (uncertified) condensate 
analysis provided to us is nonetheless interesting and is copied below:

Condensate test results RPS first development unit

Percentage    Compound
40.625    Pyridine    C5H5N
2.298    Column Bleed
7.509    Phenol    C6H6O1
0.750    Methyl Phenol    C7H5O1
1.305    Methyl Phenol    C7H5O1

3.340    Naphthalene    C10H3
0.529    Dodlecene    C12H24
1.163    1 Methyl Naphthalene    C11H10
1.097    2 Methyl Naphthelene    C11H18
0.566    Tetradecine    C14H28
5.092    Biphenylene    C12H8
0.562    2, 3 Dimethyl 1 Naphthelene    C12H12
0.869    Dibenzofuran    C12H8O1
0.674    ?
1.125    Fluorene    C13H10
0.818    ?
0.552    ?
9.291    Anthracene    C14H10
2.077    Anthracene    C14H10
0.777    Anthracene    C14H10
1.626    4HCyclopentaphenathracene    C15H10
0.806    1methylAnthracene    C15H12
0.951    2Pheny1Naphthalene    C16H12
6.725    Fluroanthene    C16H10
1.762    Pyrene    C16H10
7.112    Fluroanthene    C16H10
100.001

  Doug also indicated that if we are only getting low overall condensate 
levels then the water is probably going out with the gas as steam, and 
ordinarily I would agree, except none of our observations of our linear 
system whilst operating on optimal fuels support this.

The condensate analysis above does not show any free water at all (we 
did query this at the time and asked whether this result was after water 
had been excluded, ie reporting only the percentages of the non water 
component, but were told no, if water had been present it would have 
been reported).

Before I go on I would add that yes we have seen wet gas out of the 
system, but only when running truly excessively high mc feed stocks in 
the range of 30-50%. At 40% mc H2 drops to as little as 5% and CO to 11% 
with a corresponding increase in CO2 & N2 (lab analysis result during 
testing of mixed wood chip/ sewerage sludge blends). Stretching a length 
of paper towel over the (un-ignited!) gas stream under these conditions 
results in it getting rather damp quite quickly, and a brown condensate 
dripping off the outer rim of the flare head can be observed (no funny 
comments about the possible relationship to sewerage sludge please...). 
Under other much less extreme gasification conditions though no moisture 
collecting in the paper or free liquids on nearby metal surfaces are 
readily apparent.

The following additional observations are for "chunky" wood fuels below 
25% mc (the fuel spec at the time of the formal gas analysis, piece 
sizes ranging from 25mm to 50mm on a side).

* Yes we do have gas cooling (of our own design like the rest of it), 
and gas exit temperature immediately prior to the flare head are between 
40oC and 70oC, depending on flow rate, and the current system also 
includes mesh mist filters on the exit from the coolers, which we 
thought might also be an efficient way of trapping the sub 10 micron 
particulates, assuming that these would be wetted by condensate. You 
would therefore expect to see a higher level of condensate than we are 
getting, and I would have thought at least some steam visible in the 
plume on contact with cold air (we have run it at 0oC air temperatures 
in the middle of Winter without seeing such a plume).

*The formal gas analysis is consistent with a gas where a high 
proportion of the available moisture in the feed stock is being cracked.

* The system "chuffs" when the mc is below 25%, a resonance coming from 
the intakes sounding a little like a fast revving steam engine and the 
upper hopper vibrating like a long, low drum roll.... Hand held digital 
anemometer also records this as a regular, fast pulsing of the air 
intake flows.

This seems consistent with a rapid cycling of water cracking and the 
free oxygen made available displacing that from the incoming air.  This 
cracking uses up thermal energy which then drops below the threshold 
required to support this water shift reaction, and the process pauses, 
reverting to pulling in outside air to satisfy the oxygen demand, 
temperature rises again and the process repeats. This has an immediate 
knock on affect as for each air derived oxygen molecule displaced then 4 
nitrogen molecules don't make it into the system, lowering dilution from 
this source and raising overall gas quality.

* The reported gas quality is roughly mid way between a conventional 
down draft and a indirect pyrolysis system, which tends to support the 
above hypothesis as internal conditions cycle between air supported 
combustion and thermal mass as the gasification heat source. The big 
difference being the methane content, again consistent with more oxygen 
being available in the air drawn system, the preferred reaction then 
being Carbon + Oxygen, rather than Carbon + 4H2.

* We have seen a similar result when adding high oxygen content fuels 
such as glycerine (a triple alcohol group) to the wood chip feed, the 
flare quality and volume was maintained even though intake air flow 
rates dropped to <25% of their normal range!

*Simple mass balances taking into account gas flow rate (intakes and 
exit pipe), reported gas quality and measured fuel inputs closely agree.

*Charcoal from the ash bin has a very high fixed carbon in the 85-93% 
range (reported by a NATA certified lab) consistent with high 
temperature. Soot taken from the particulate collection system below the 
cyclones has been examined with a microscope and we are told it had a 
crystalline structure normally also only found when forming under high 
(>1000oC) temperatures.

My wife Kerry, equal co developer, has asked that I also point out when 
we designed the original system we made allowance for running it in 
either downdraft, or updraft, mode and have used this facility to break 
up bridging on occasion when working with difficult fuels (though on the 
early units this does interrupt the gas flow to the flare). The current 
(Mark 3.2?) under construction allows for this without stalling the 
system. This was done as part of improving the overall material handling 
side on the path to a more easily automated commercial model.


Cheers,
Peter