Three-stage co-current gasifier separates the pyrolysis, combustion and gasification (reduction) steps. If all goes well, the result is low-tar gas (20-200 mg / Nm3).
Unlike the classical Imberts in the 1940's or FEMA (tar-makers), this type of reactor can output clean producer gas, but requires automatization with pressure sensors and high-temperature thermocouple sensors.
This laboratory gasifier has 4 modes of operation. 3 good, and 1 bad (which gives tarry gas, unavoidable during warmup).
- The air must be preheated. Optimally min 400C or rather 500C. (using the exhaust heat and/or the producer gas heat in production).
- this test-reactor is too small for straw, because straw bridges easily
- on the good side, slagging was not a problem even when operating on 100% straw.
At this occasion (not always!), the middle-burner burns even with 15C air input.
- 50-1000 kWe (200 - 3500 kWth) is a practical size for now (and multiple reactors can always run in parallel)
- 50 kWe appr 4-5 months (~ 2000 EUR / kWe inside Hungary)
- 250 kWe or bigger (~ 1800 EUR / kWe inside Hungary) on 6-8 months notice.
- the smaller 4-20 kWe seems more problematic, eg. more prone to fuel-flow "bridging" problems.
- We hope to deploy at least one 12 kWe test unit for evaluation on a friendly farm in 2011 summer, to collect fuel-bridging and fuel-tolerance experience.
- We do not expect as problem-free operation (or near as good return-of-investment) as with the 50kWe and bigger units.
- even smaller 2-4 kWe size is beyond aims for now, but not impossible in far-future
Q: what do you use for stoichiometric point with the gas mixture?
- lambda=1.05 at peak power
- lambda measured with Bosch LSU4 wideband oxygen sensor and [VEMS v3 controller] from exhaust gas O2 content
- 1.05 is used for for low CO. Lambda near 1.00 or 1.01 would raise CO ppm considerably.
- Unlike natural gas, wood-gas (with low tar content) likes high compression without knocking. We use max 15 (compression ratio, max volume/min volume) but [TS] uses up to 19 (yes, nineteen) with near-stoich lambda.
- we use lambdatarget=1.2 at low power. 1.2 to 1.25 definitely burns well, but with reduced peak power (we do not know the exact part-load efficiency numbers, efficiency difference between 1.05 and 1.2 lambda is small)
Nice project ( applaus :)
We are researching the use of maize/wheat straw gasification cogenerators in farms and small-medium sized businesses. We're very interested in your project. Could you please contact us to discuss the possibilities of buying your system? jean.hupperets(that[a]sign)gmail.com.
Thanks in advance!
- where are you located ?
- electric power rating needed ?
- fuel size
- fuel moisture content (dry base)
- if a naturally aspirated spark-ignition genset is available, all parameters are required
- compression ratio
- displacement, cyl arrangement
- make, model
- it is not guaranteed that it is feasible (and cuts project investment), but chances are good if naturally aspirated
- if genset is turbocharged, we don't recommend using it (it is not impossible though if a very experienced local turbo-engine expert takes the challange and responsibility to install the safety pressure-relief valve(s) and tune it)
As of 2011-09 the 4-stage gasifier base system totals 2940 EUR /kW in EU (230/400V 50Hz) for 45kWe (predrier + reactor + filtering system + genset with accessories and automation)
- it does not include the moving-floor fuel-container (or other suitable fuel-container, typically for 3-7 days max-load that is kWe rating * 1.2kg/kWhe * 72 hours) normally made in-place, but includes 2kW hydraulic supply for it.
- electricity is required (4kW) to start the plant. Diesel or LPG genset is OK (but not included in the price).
- minimum system is 30 kWe (slightly higher per kW cost than the 45 kW). Bigger plants costs less (per kW).
- we currently do not have any plants in planning stage above 500kWe but bigger plants are feasible
- wheat straw is planned for 2012 August
- wheat straw has low ash-melting point that causes problems with many types of devices. According to our tests - in complience with Viking tests in Denmark - (ours with manual feed, as our automatic straw plug-feeder is not ready yet and only feasible for ID > 630mm reactor) these multi-stage gasifiers are not prone to slagging. The char-content prevents ash-fusion at the top of the reactor bed and when the char burns out, temps is lower than 850C and no channeling.
- most of our experiments used woodchips as fuel, maize tests (4 cm pieces) are carried out 2011 October.
- For ID>630mm reactors (90kWe) it is safe to assume that maize will work. ID=450 mm ... we don't know yet. Bridging is more likely to be a problem than ash-fusion.
We are completing the system (including CE paperwork) with experienced technology partners (who can make even an Imbert type reactor operate reliably, at least with wood-chips) and will make advertisement soon.