Biomass Gasification Technologies for Biochar Production and Energy Generation

13th Global Summit and Expo on Biomass and Bioenergy Sept. 04-05, 2018 – Hilton, Zurich Airport, Switzerland Biomass Gasification Technologiesfor Biochar Production and Energy Generation prof. Ferruccio Pittaluga, University of Genoa and also: TecnoforestLtd., president www.tecnoforest.wordpress.com

Starting from 2012, the innovative SME Tecnoforest Ltd. (formerly an academic spin-off of the University of Genoa) has addressed its activity towards the testing of existing, and the development of new, small-scale biomass gasification technologies aimed at assuring electric and thermal self sufficiency to rural enterprises of the agricultural and wood-based sectors (www.tecnoforest.wordpress.com). Tecnoforestresearchers took great advantage from the parallel activities being carried out at DIME/SCL, the Combustion Laboratory of the DIME Department, University of Genoa (www.en2.unige.it/savona-combustion-lab/). TecnoforestLtd. 13th Global Summit and Expo on Biomass and Bioenergy Sept. 04-05, 2018 – Hilton, Zurich Airport, Switzerland

Biomass gasification genset BioSyn-3: 20 kWel, 45 kWth. Electric efficiency: 26.5%. Wood consumption: 21 kg/h. • Cost: ̴ 5000 € /kWel (manufacturers: Rayo Eng. Co. and Tecnoforest Ltd.) TecnoforestLtd. On the other hand the intrinsic limitation of these power plants’ typologies, common to both downdraft and updraft gasifiers, has become apparent as the main obstacle preventing, in absence of costly abatement provisions, their continuity of operation: namely, the unavoidable need of progressively heavier maintenance provisions, especially related to the removal of sticky carbon-rich deposits and soot on the internal surfaces of the various plant components. 13th Global Summit and Expo on Biomass and Bioenergy Sept. 04-05, 2018 – Hilton, Zurich Airport, Switzerland

Currently there is no market-available small wood-gasification genset which would guarantee reliable continuity of operation (in unattended modality) if not at the price of a rather high technological sophistication, especially for tars’ control and pollutant abatement provisions. But this increases the cost per installed-kWel up to about 7000 €/kW, thus substantially precluding the penetration of such plants in a territorial reality with low investment capacity. In addition, these plant technologies link the reliability and continuity of operation to a whole series of operational constraints that, if not satisfied, lead to the cancellation of the guarantee. Among them, the utilization of wood chips of high quality, bark-free and very well dried, which implies higher operating costs adding up to investment’s. TecnoforestLtd. 13th Global Summit and Expo on Biomass and Bioenergy Sept. 04-05, 2018 – Hilton, Zurich Airport, Switzerland

The ‘smart’ gasification technology which has been conceived, in order to overcome the critical issues inherent in standard downdraft (or, even more so, in updraft) gasifiers, features extreme simplicity (and therefore very low costs), is highly robust and shows great operational reliability. So to say, its design philosophy is based upon a trivial principle: ‘no issue can arise from a component which is not there’. TecnoforestLtd. 13th Global Summit and Expo on Biomass and Bioenergy Sept. 04-05, 2018 – Hilton, Zurich Airport, Switzerland

One of the innovative aspects of the new gas generator (its name is 'Bio-SynChar') is represented by the absence of any physical 'hearth’, with its related air injectors, which usually are metal or ceramic components, where air is sucked-in and hot embers are produced. High localized temperatures, combined with the mechanical friction of embers scraping hearth’s surface, impact these components with serious erosion/ corrosion issues, making thus necessary frequent maintenance. TecnoforestLtd. 13th Global Summit and Expo on Biomass and Bioenergy Sept. 04-05, 2018 – Hilton, Zurich Airport, Switzerland

On the contrary, inside SynChar, the woodchip column is ignited from above, so that its upper ‘free surface’ becomes a kind of virtual hearth, where the ‘embers front’, a red-hot layer typically of about 5 cm thickness, performs, while proceeding toward the bottom of the column, a rather efficient, clean, smoke-less wood-to-char conversion. The gaseous product of this process is, in its turn, a hot, tar-free syngas which, due to the local lack of oxygen, does not light up near the embers (in which case we would get a standard ‘wood combustion’), but, instead, rises toward the gasifier top where it finds prompt ignition thanks to the locally provided ‘crown’ of air openings. TecnoforestLtd. 13th Global Summit and Expo on Biomass and Bioenergy Sept. 04-05, 2018 – Hilton, Zurich Airport, Switzerland

The upper part of the gasifier is contoured so to form a ‘dome’ followed by a nozzle: the syngas flame which there takes place is a so-called ‘lifted flame’ that protrudes outward, ready to be utilised for direct air heating purposes or as thermal source for water boilers. TecnoforestLtd. 13th Global Summit and Expo on Biomass and Bioenergy Sept. 04-05, 2018 – Hilton, Zurich Airport, Switzerland

SynChar operates in ‘batch’ modality: at the start of a ‘cycle’, a new charge of wood-chips is fed through the top nozzle, making up a column reaching about 3/4 of the overall reactor height. Ignition takes place at the upper surface of the column producing a layer (‘front’) of hot embers ready to progress downward through the whole pile of woodchips. When the embers reach the bottom of the piled-up woodchips, these latter have been converted into a column of high-quality biochar, to be promptly discharged by turning the reactor upside down. SynChar is provided with two crowns of adjustable openings, one at bottom, to control the primary air (for gasification purposes) and one near reactor’s top, to control the secondary air (for syngas-air premixing aims). Indeed, the primary air flow-rate should be kept quite limited so that the embers front, proceeding downward through the woodchips, and leaving the hot biochar behind, would locally find low oxygen levels, suitable just for gasification but not for combustion. TecnoforestLtd. 13th Global Summit and Expo on Biomass and Bioenergy Sept. 04-05, 2018 – Hilton, Zurich Airport, Switzerland

TecnoforestLtd. Sequence of the processes taking place inside reactor SynChar 13th Global Summit and Expo on Biomass and Bioenergy Sept. 04-05, 2018 – Hilton, Zurich Airport, Switzerland

The hot syngas, evolving from the embers, rises upward due to thermal convection, ‘creeping’ through the biochar and thus undergoing a chemical reduction process which increases its heat value. An extremely simple design allows to realize reactors of SynChar typology (i.e. biochar-producing syngas-generators) of a wide range of sizes and power capacities. Whilst the prototypes shown in the pictures, with diameters of about 300 mm and heights of 1200 mm, yield a flame of about 100 kWth, thermal power sizes up to 500 kWth can be easily attained, by properly scaling-up the dimensions, without major changes in the overall design. TecnoforestLtd. Bio-SynChar in operation: the top flame is nearly undiscernible. 13th Global Summit and Expo on Biomass and Bioenergy Sept. 04-05, 2018 – Hilton, Zurich Airport, Switzerland

As a rough estimate, a charge of about 50 kg of woodchips (average bulk density: 350 kg/m3) is converted, in a process time of about 20 min, into 13 kg of the cleanest biochar (average bulk density: 250 kg/m3). If the input feedstock is virgin wood, the residue of the process is a biochar of nearly edible quality (its certification in next slides). Due to the biochar high porosity, the mass conversion efficiency is thus about 26%, whereas the volume conversion efficiency, which is much more important from an agronomic point of view, turns out 71%. TecnoforestLtd. Top quality biochar as produced by Syn- Char reactor fed with hardwood chips. 13th Global Summit and Expo on Biomass and Bioenergy Sept. 04-05, 2018 – Hilton, Zurich Airport, Switzerland

13th Global Summit and Expo on Biomass and Bioenergy Sept. 04-05, 2018 – Hilton, Zurich Airport, Switzerland

At left, the analysis of the residues from a 400 kWel downdraft gasifier in Northern Italy shows high levels of PAH’s (ref.: J. of En. & Power Eng., David Publ., n.7, 2013). Aside from PAH’s levels, for woodchip gasifiers aimed at power generation, the presence of carbon-rich residues (often, but improperly, called ‘biochar’) is sign of thermochemical inefficiency. In Italy, max level of PAH allowed in biochar for soil amendment is <6 mg/kg. In Europe (EBC) is <12 mg/kg. The Intnl. Biochar Initiative prescribes <20 mg/kg. A general, agreed-upon, official legislation is still lacking. TecnoforestLtd. 13th Global Summit and Expo on Biomass and Bioenergy Sept. 04-05, 2018 – Hilton, Zurich Airport, Switzerland

Quite interestingly, even when the target of the gasification process is not biochar (batch) production, but rather continuous energy generation, the technology presented in relation to reactor Bio-SynChar appears well suited also to this aim, provided a few accessories are added to the gasifier. Remarkably, the equipment design philosophy remains the same, in particular its ‘virtual hearth’ feature as well as the overall context of an extremely simple, rugged, ‘appropriately rural’, technology. The name of the continuous syngas generator is SynBurner. TecnoforestLtd. First phases of conversion (in the shop) from SynChar to SynBurner 13th Global Summit and Expo on Biomass and Bioenergy Sept. 04-05, 2018 – Hilton, Zurich Airport, Switzerland

The three main add-up components necessary to achieve a continuous gasification process are: • a bottom blower, for forced air injection through the reactor’s lower crown of holes • a woodchip feeder, made up of a hopper-auger assembly, to be positioned directly below the chips’ silo and connected to an inlet opening at mid reactor height • a gate-valve (actually a tilting disc-plate) to be periodically operated for discharging the ashes through the reactor base-plate. TecnoforestLtd. A first prototype of SynBurner in continuous operation. The clean flame from the top is hardly visible, whilst some water vapour is released from the hopper. 13th Global Summit and Expo on Biomass and Bioenergy Sept. 04-05, 2018 – Hilton, Zurich Airport, Switzerland

SynBurner’s continuous-operation capability allows the syngas, issuing from the top nozzle, to be conveyed at distance and directly utilised as thermal source in air-heaters, boilers or furnaces. In this way, the equipment attains the characteristics typical of gas burners, with several advantages in comparison to solid fuel burners, especially fixed or moving grids, well known sources of high atmospheric impacts. TecnoforestLtd. SynBurner in operation 13th Global Summit and Expo on Biomass and Bioenergy Sept. 04-05, 2018 – Hilton, Zurich Airport, Switzerland

With SynBurner, not only is by far easier and prompter its power control, but it readily allows to achieve a fully premixed syngas-air flame to the advantage of very low emissions. Thanks to its compact, vertical set up, SynBurner design is suitable to be arranged in multiple-burner arrays so to achieve the overall power levels required by the combustion chambers of large water boilers or steam generators. Also the revamping of existing furnaces or combustion chambers, equipped with moving grids, can be obtained by means of their replacement with a proper number of SynBurner units in parallel: overall efficiency, power control and emissions would all turn out greatly optimised. TecnoforestLtd. SynBurner in operation. The blower can be seen at bottom right. 13th Global Summit and Expo on Biomass and Bioenergy Sept. 04-05, 2018 – Hilton, Zurich Airport, Switzerland

The gasification mechanism which takes place within SynBurner is peculiar. Although similar to that already discussed in connection with BioSynchar, non the less it shows different modalities particularly in connection with the behaviour of the embers making up the ‘virtual hearth’. This latter, within BioSynChar, would move downward through the woodchips charge (while converting it into a column of biochar) in a slow manner, owing to the limited availability of air as supplied, by convection, through the reactor bottom holes. On the contrary, within SynBurner, the air blower supplies the embers, from below, with a much higher amount of oxygen, inducing the ‘hearth’ to quickly proceed toward the reactor bottom, producing syngas (more than before, but probably of lower calorific value than in Synchar, due to the now higher O2 level) while converting woodchips into biochar. But in this case the gasification process does not stop once the embers reach the reactor bottom, rather, the virtual hearth now reverses its direction, proceeding upward while gasifying the column of the impending hot biochar and converting it into ashes. TecnoforestLtd. 13th Global Summit and Expo on Biomass and Bioenergy Sept. 04-05, 2018 – Hilton, Zurich Airport, Switzerland

TecnoforestLtd. Overall sequence of the processes taking place inside reactor SynBurner (further assessment and verification needed). 13th Global Summit and Expo on Biomass and Bioenergy Sept. 04-05, 2018 – Hilton, Zurich Airport, Switzerland

However, after the first minutes of operation, the process reaches its steady-state regime: owing to the continuous supplies of air from the bottom blower and of fresh woodchips from the auger, the hearth attains, within the reactor, a more or less ‘equilibrium’ position, with, below of it, a mix of biochar and ashes (the concentration of these latter increasing toward the bottom) and, above of it, a mix of biochar and TC (‘torrefied & charring’) woodchips, the concentration of these latter increasing toward the top of the column. The thermo-chemical process is more complex in SynBurner than in SynChar reactors, mostly because now the syngas is produced by the gasification of a mixture of TC woodchips and biochar of variable composition as a function of the air and wood rates of supply, i.e. of the reactor power level. To be remarked here again, the overall process within SynBurner is quite different from those taking place either in downdraft or in updraft gasifiers: indeed, contrarily to the former, almost no biochar is here produced, whilst, at difference with the latter, no thick pyrolytic zone is crossed by syngas near the outlet. The net result, is a clean flame from top and clean ashes discharged from bottom. TecnoforestLtd. 13th Global Summit and Expo on Biomass and Bioenergy Sept. 04-05, 2018 – Hilton, Zurich Airport, Switzerland

SynBurner is directly derived from biochar maker Synchar: as such, its dimensions are about 300 mm diameter and 1200 mm height. Thanks to the forced-air injection feature, its flame thermal power can reach up to 150 kW, becoming a rather suitable heat source for air unit heaters or water heaters to be used for greenhouse applications. On the other hand, it appears also scalable toward higher power levels by way of increasing its dimensions: a reactor of 450 mm in diameter should easily reach about 500 kW in thermal power output. TecnoforestLtd. SynBurner in operation. The blower can be seen at bottom left. Auger feeder is hand operated (motorized version under way). Notice the quite clean scenario all around. 13th Global Summit and Expo on Biomass and Bioenergy Sept. 04-05, 2018 – Hilton, Zurich Airport, Switzerland

Inside SynBurner, the embers are located in a ‘virtual hearth’ position, some-where between the ash-rich lower portion of the reactor and the TC woodchips-rich upper part. By means of a proper ‘tuning’ between the forced-air supply from below and the height (dependent on woodchips feeding rate) of the solid material piled up within the reactor, it is possible to achieve and maintain the most proper ‘gasification’ temperature at the embers’ bed. Experimental evidence so far has shown a wide, safe operational envelope of the reactor for varying woodchips feeding rates and air flow injections. In relation to cold-gas efficiency, optimal conditions are yet to be determined. Too low air-to-fuel ratios would shift the syngas generator SynBurner into a biochar producer (SynChar). Too high above ratios, would give rise to syngas combustion inside the reactor. No operational conditions appear to induce production of condenses, tars or smokes, issuing from anywhere. TecnoforestLtd. 13th Global Summit and Expo on Biomass and Bioenergy Sept. 04-05, 2018 – Hilton, Zurich Airport, Switzerland

In order to perform analysis of syngas as produced by SynBurner, in addition to on-line measurements, gas samples were taken for different operating conditions and then analysed off-line. Continuous analyzers were utilised for N2 and O2 (in this latter case, equipped with electro-chem. cell), according to EPA 3A 1989 prot. For CH4 and CO2 a continuous FTIR analyzer was used (same EPA prot.), for H2 a GC-TCD (Gas Chromatography-Thermal Conductivity Detector) analyzer was employed whilst for CO a Horiba analyzer was used (following protocol UNI EN 15058:2006). TecnoforestLtd. 13th Global Summit and Expo on Biomass and Bioenergy Sept. 04-05, 2018 – Hilton, Zurich Airport, Switzerland

The overall scenario of the syngas components and characteristics is still not complete. On average, the resulting concentrations for standard woodchips as feedstock, were the following: • N2 = 44.3 ÷ 48.4 % • CO = 16.5 ÷ 19.8 % • H2 = 14.3 ÷ 18.7 % • H2O = 9.0 ÷ 12.5 % • CO2 = 7.5 ÷ 11.5 % • O2 = 2.2 ÷ 3.1 % • CH4 = 0.8 ÷ 1.2 % • corresponding to a LHV = 4.3 ÷ 4.6 MJ/Nm3 . • The above outcome could be certainly improved by providing an adequate reactor insulation as well as by feeding the reactor with well-dried woodchips. • A further necessary provision would be the installation of a cyclone filter for particulates’ abatement. TecnoforestLtd. 13th Global Summit and Expo on Biomass and Bioenergy Sept. 04-05, 2018 – Hilton, Zurich Airport, Switzerland

Now at Tecnoforest we are pursuing the target of achieving a syngas quality suitable for fueling internal combustion gensets (‘engine grade’ fuel). In order to avoid the issues encountered with spark ignition engines for guaranteeing a stoichiometric mixture with air , and also in order to take advantage of the higher robustness and efficiencies of compression ignited engines, a solution has been envisaged in which the gasifier is going to be connected to a dual-fuel high compression-ratio diesel genset. The reactor which is undergoing above upgrading is essentially a version of SynBurner equipped with a valve-controlled switch, at the bottom, suitable to exclude the blower when the engine takes on its own suction capability. In the duct connecting the gasifier to the engine intake, after the cyclone filter, a peculiar ejector-venturi scrubber will be provided, where properly treated vegetable waste-oils are sprayed, finely atomised, into the syngas stream to be cleaned. TecnoforestLtd. 13th Global Summit and Expo on Biomass and Bioenergy Sept. 04-05, 2018 – Hilton, Zurich Airport, Switzerland

Thanks to the still high syngas temperature ( ̴130 °C) entering the oil scrubber, no water condensation occurs, whilst the vegetables oils’ viscosity markedly decreases making thus possible their efficient atomization. The first result of the process is the cleaning of the syngas. A second outcome is the following. Thanks to the turbulence-driven entrainment of the oil micro droplets, as well as to their partial evaporation, the peculiar mixture syngas+oil (‘dual-fuel’) exiting the scrubber should attain a cetane number compatible with its prompt self-ignition in high compression-ratio diesel engines. TecnoforestLtd. Oil-sprayed ejector-venturi scrubber 13th Global Summit and Expo on Biomass and Bioenergy Sept. 04-05, 2018 – Hilton, Zurich Airport, Switzerland

The syngas generator which, based upon SynBurner technology, is undergoing the upgrading above discussed has been called Syngen. The development is still under way. Some technological and process aspects are still confidential. TecnoforestLtd. The gasification-based genset with a dual-fuel diesel engine. Note: picture is just for demonstration purposes 13th Global Summit and Expo on Biomass and Bioenergy Sept. 04-05, 2018 – Hilton, Zurich Airport, Switzerland

CONCLUSIONS • A novel, self-complementary set of ‘rural technology’ biomass gasifiers has been presented, all featuring a simple, rugged design and construction • and therefore also an affordable cost for a wide territorial deployment. • Their main characteristic resides in a quite clean solid-to-syngas conversion process, achieved, at difference from downdraft and updraft technologies, by providing an open top to reactor and avoiding to ‘stifle’ the embers with an overwhelming amount of feedstock weighing upon them from above. • This concept has been implemented in three similar types of ‘gasifiers’: • a high-quality biochar maker (SynChar, already on the market) • a syngas generator for thermal applications (SynBurner, on the market) • an ‘engine grade’ syngas generator (SynGen, still in development) • More details, including the interesting outcome of the agronomic use of our biochar, can be found at www.tecnoforest.wordpress.com TecnoforestLtd. 13th Global Summit and Expo on Biomass and Bioenergy Sept. 04-05, 2018 – Hilton, Zurich Airport, Switzerland

TecnoforestLtd. Enhanced growth and fragrance of basel, thanks to the Ligurian sun and a biochar-enriched soil Thank you for your attention ! 13th Global Summit and Expo on Biomass and Bioenergy Sept. 04-05, 2018 – Hilton, Zurich Airport, Switzerland

Biomass Gasification Technologies for Biochar Production and Energy Generation