Characterization of Recycled Wood Chips, Syngas Yield, and Tar Formation in an Industrial Updraft Gasiﬁer

environments

Article Characterization of Recycled Wood Chips, Syngas Yield, and Tar Formation in an Industrial Updraft Gasiﬁer

Ehsan Oveisi 1, Shahab Sokhansanj 1,2, Anthony Lau 1,*, Jim Lim 1, Xiaotao Bi 1, Fernando Preto 3 and Cliff Mui 4 1 Department of Chemical and Biological Engineering, The University of British Columbia, 2360 East Mall, Vancouver, BC V6T 1Z, Canada; [email protected] (E.O.); [email protected] (S.S.); [email protected] (J.L.); [email protected] (X.B.) 2 College of Engineering, University of Saskatchewan, Saskatoon, SK S7N 5B1, Canada 3 CanmetENERGY-Ottawa, NRCan, Ottawa, ON K1A 0E4, Canada; [email protected] 4 Nexterra Systems Corporation, Vancouver, BC V6B 4N8, Canada; [email protected] * Correspondence: [email protected]; Tel.: +1-604-822-3476

Received: 15 June 2018; Accepted: 20 July 2018; Published: 22 July 2018

Abstract: In this study, the moisture content, calorific value, and particle size of recycled wood chips were measured. The wood chips were used to fuel an 8.5 MWth updraft gasifier to produce syngas for combustion in a steam-producing boiler. In-situ syngas composition and tar concentrations were measured and analyzed against biomass fuel properties. No efforts were made to adjust the properties of biomass or the routine operating conditions for the gasifier. A sampling device developed by CanmetENERGY-Ottawa (Ottawa, ON, Canada) was used to obtain syngas and tar samples. Wood chip samples fed to the gasifier were taken at the same time the gas was sampled. Results indicate that as the fuel moisture content increases from 20% to 35%, the production of CO drops along with a slight decrease in concentrations of H2 and CH4. Tar concentration increased slightly with increased moisture content and proportion of small fuel particles (3.15–6.3 mm). Based on the findings of this study, biomass fuel moisture content of 20% and particles larger than 6.3 mm (1/400) are recommended for the industrial updraft gasifier in order to achieve a higher syngas quality and a lower tar concentration.

Keywords: biomass gasiﬁcation; industrial updraft gasiﬁer; urban wood wastes; fuel moisture content; syngas composition; tar concentration; sampling device

1. Introduction Combustion and gasification are key thermal/thermochemical conversion technologies. In terms of climate change mitigation, gasification processes have the advantage of lesser greenhouse gas emissions compared to full oxidative combustion processes. The syngas produced can be further processed into biofuels and chemical products [1]. In this work, two commercial gasification systems are studied. The University of British Columbia (UBC) installed a fixed-bed updraft biomass gasification system (Figure1) at the Vancouver Campus in 2012. The 8.5 MWth gasifier was designed to provide up to 5% of 40 MW campus power and 15% of 40 MW thermal-based heat. In addition to the gasifier at UBC, a tissue plant that produces household paper products in Metro Vancouver has also been operating two gasifiers identical to UBC’s system since 2010. The wood wastes consist of two types of materials: scraps from construction and demolition (C&D), and municipal tree trimmings collected from Metro Vancouver’s curbsides and landfill.

Environments 2018, 5, 84; doi:10.3390/environments5070084 www.mdpi.com/journal/environments Environments 2018, 5, 84 2 of 13

Environments 2018, 5, x FOR PEER REVIEW 2 of 13 A recycling yard located 50 km from the gasification plant collects the wood scraps and trimmings. The materialsmaterials are are sorted sorted so so as as notnot toto containcontain any non-woody materials. materials. The The woody woody portion portion is ground, is ground, screened, and stored under a covered flat storage. About 12,500 dry tonnes of ground and chipped screened, and stored under a covered flat storage. About 12,500 dry tonnes of ground and chipped wood waste per year (2–3 truckloads per day) are trucked to the gasification plant. Once at the plant, wood wastethe wood per chips year are (2–3 sampled truckloads for moisture per day) and are size trucked measurements. to the gasification Occasionally, plant. the ash Once content at the and plant, the woodcalorific chips value are sampledof chipped for fuels moisture is measured. and size measurements. Occasionally, the ash content and calorific valueFollowing of chipped the fuel fuels specifications, is measured. particles should not be greater than 76 mm. The proportion of Followingparticles with the fuela size specifications, below 6.3 mm particlesshall have shoulda mass fraction not be greaterless than than 25%. 76 Our mm. recent The work proportion on the of particlesgasifier with [2] a sizeshowed below that 6.3 12% mm more shall steam have could a mass be generated fraction if less the fuel than moisture 25%. Our content recent was work reduced on the gasifierfrom [2] showed35% to 20% that wet 12% basis more (wb). steam could be generated if the fuel moisture content was reduced from 35% to 20% wet basis (wb).

FigureFigure 1. The 1. updraftThe updraft gasiﬁer gasifier at theat the University University of of British British Columbia,Columbia, Vancouver Vancouver campus. campus.

Syngas composition depends on the fuel composition and amount of oxygen in the air, and Syngas composition depends on the fuel composition and amount of oxygen in the air, and variation in syngas composition can disrupt the usage of syngas [3,4]. Rajvanshi [5] suggested that variationfuel in moisture, syngascomposition ash content and can its disrupt elements, the particle usage of size, syngas heating [3,4 value,]. Rajvanshi and bulk [5 ]density suggested are major that fuel moisture,fuel ash properties content that and affect its elements, biomass gasification. particle size, Molino heating et al.value, [6] summarized and bulk density the effect are of major these fuel propertiesbiomass that feedstock affect biomass characteristics gasification. on syngas Molino composition; et al. [6 ]they summarized also discussed the the effect effect of of these operating biomass feedstockconditions, characteristics including on gasifying syngas composition; agent and equivalence they also discussedratio (ER, the ratio effect of of actual operating A/F value conditions, to includingstoichiometric gasifying agentA/F value). and equivalence Van der Drift ratio et (ER,al. [7] the suggested ratio of actualthat the A/F ER valueneeded to to stoichiometric be raised with A/F value).increasing Van derDrift fuel moisture et al. [7] content suggested in order that to the keep ER the needed gasifier to temperature be raised with constant. increasing An increase fuel moisturein ER contentresults in order in an to increase keep the in gasifier temperature, temperature as more constant. feedstock Anis combusted increase in to ER produce results more in an heat increase and in temperature,promote as carbon more feedstockconversion is [8]. combusted It is important to produce to have morean appropriate heat and ER promote level to carbon ensure conversionthe balance [8]. between reactor temperature and syngas production. In contrast, without adjusting the ER, high It is important to have an appropriate ER level to ensure the balance between reactor temperature moisture biomass would have a negative impact on the internal heating rate of a particle since latent and syngasheat is production. needed for evaporating In contrast, water. without The resulting adjusting slow-down the ER, highof biomass moisture devolatilization biomass would leads to have a a negativelower impact gasification on the temperature internal heating and less rate carbon of a particleconversion since and latent syngas heat yield is [9–12]. needed Couto for evaporatinget al. [13] water.assessed The resulting the gasification slow-down of of municipal biomass solids’ devolatilization wastes in a leads semi-industrial to a lower gasifier. gasification They temperature noted an and lessincrease carbon in H conversion2 and CO contents and syngas due to a yield higher [9 –gasifier12]. Couto temperature, et al. [which13] assessed in turn led the to gasification an increase of municipalin the solids’ lower wastesheating value in a semi-industrial (LHV) of syngas. gasifier. They noted an increase in H2 and CO contents due to a higherTar may gasifier be defined temperature, as the hydrocarbon which in turn and led oxygenated to an increase compounds in the lower in the heating combustible value gas (LHV) of syngas.stream with a molecular weight greater than benzene [14]. Lignin is a main precursor of tar due to its Tararomatic may be nature defined [15]. as The the tar hydrocarbon in the gas stream and oxygenated is an undesired compounds by-product in of the biomass combustible gasification. gas stream It may cause fouling of heat transfer surfaces and engine parts when the gas is used as a combustion with a molecular weight greater than benzene [14]. Lignin is a main precursor of tar due to its aromatic fuel, resulting in the malfunctioning of engines, mechanical, and handling equipment. Besides, naturecatalysts [15]. The cannot tar in survive the gas for stream long in is the an presence undesired of tar by-product [16]. The concentration of biomass gasification. and composition It may of tar cause fouling of heat transfer surfaces and engine parts when the gas is used as a combustion fuel, resulting in the malfunctioning of engines, mechanical, and handling equipment. Besides, catalysts cannot survive for long in the presence of tar [16]. The concentration and composition of tar depend on the gasifier Environments 2018, 5, 84 3 of 13 type, operating conditions, and fuel properties/quality [17]. Although it is the updraft gasifier which is known to produce syngas with the most tar, it has advantages over other types of gasifiers. Fixed bed gasifiers (updraft or downdraft) are simpler than the fluidized bed; besides, the thermal output of fluidized bed gasifiers is limited to 10 MWth or less. Updraft gasifiers can operate with wetter biomass with up to 60% MC (moisture content) (wb) whereas the downdraft gasifiers must operate with biomass with less than 25% MC (wb) [18]. With air as the gasifying agent, Li et al. [19] studied the gasification of western hemlock sawdust in a pilot-scale circulating fluidized bed at two temperatures (700 and 850 ◦C) and with moisture content ranging from 6.6% to 22% wb. For the reducing species, they observed a decrease in (CO, H2, CH4) concentrations from (16.6%, 5.5%, 3.4%) to (9.6%, 3.0%, 1.9%) as ER increased from 0.20 to 0.54. According to Huang et al. [8], CO2 content in the gas increases while H2 and CO contents decrease. Van Paasen and Kiel [20] conducted a lab-scale experiment with constant ER (0.25), gasifier bed temperature (around 815 ◦C), and three levels of moisture content (10%, 26% and 43% wb). The effect of moisture content on temperature and ER was eliminated by using a supplemental heater. They reported a modest increase in H2 and a similar decrease in CO, along with a decrease in tar concentration from 14.2 g/m3 to 11.4 g/m3 and 8.5 g/m3 as fuel moisture content increased from 10% to 43% wb. Atnaw et al. [21] investigated the effect of gasifier temperature and moisture content of biomass fuel (oil palm fronds) on syngas composition and calorific value. Lower CO concentration was observed at higher fuel moisture content, but the changes in H2 and CH4 concentrations were only marginal; syngas calorific value almost doubled within the range of 2.5–6.0 MJ/Nm3 as biomass moisture content was reduced from 29% to 22% wb. James et al. [22] assessed the effect of biomass physical properties on updraft gasification of woodchips. The H2 content was found to have no significant changes while the CO content was somewhat reduced as the moisture content increased from 10% to 22% wb, resulting in a decrease in the higher heating value of the syngas from 3.67 to 2.84 MJ/m3. In a related study, James et al. [23] found that as ER increased from 0.21 to 0.29, tar formation was raised from 1.6 to 3.1 g/m3 for all types of biomass in their experiment, but there was no influence on syngas composition. Chianese et al. [24] investigated H2 production from catalytic conversion of syngas generated in a fixed-bed biomass gasification pilot plant, using steam as gasifying agent. They showed that tar concentration decreased as operating temperature increased. Bronson et al. [25] evaluated the effect of moisture content and particle size of forest residues (hog fuel) on tar formation at three gasifier temperatures (725, 800 and 875 ◦C) in a small (0.16 m diameter) pilot-scale bubbling fluidized bed gasifier. At each temperature, ER was adjusted to compensate for the effect of moisture content in order to maintain a constant temperature. They found that moisture content ranging from 25–31% (wb) had a negligible effect on tar concentration—rather, the smallest particles (with sizes less than 3.15 mm) resulted in the highest tar concentration, as compared to the larger particles with sizes ranging from (3.18–6.35 mm) and (6.35–19 mm). Published data from highly-controlled laboratory experiments on gasification of biomass indicates that there exists a direct relation between biomass fuel properties (such as moisture, ash, and particle size) and syngas yield and tar formation [5,26–28]. However, similar data on industrial gasifiers is lacking in published literature. The main objective of this research is to investigate the effects of fuel quality on syngas quality and tar formation in an industrial gasifier that is operating routinely under commercial obligations. No attempt is made to influence the fuel properties or operating conditions of the gasifier for the sake of this research.

2. Materials and Methods

2.1. Gasifiers Two commercial fixed-bed updraft gasifiers were used in the study. As previously mentioned, these gasifiers were identical models made by the same manufacturer, and the only difference between Environments 2018, 5, 84 4 of 13 them was the utilization of their output energy. The gasifier installed at UBC used the energy for steam generation while the other gasification system provided energy for a tissue plant. Each of the gasifier reactors was made of a cylindrical chamber 5 m in diameter and 5 m in height (Figure1). The chips were vertically fed to the reactor by a feeder screw located at the center of and underneath the reactor. The fuel then passed through several stages before it was converted to syngas. The major stages were drying, partial oxidation (combustion), pyrolysis, gasification, and reduction to ash. Air was introduced to the fuel pile at the combustion stage. The gasifier temperature was kept constant by controlling the fuel feed rate, equivalent ratio, and fuel pile height. The bed temperature generally ranges from 815–980 ◦C when combustion occurs. The fuel gets converted into three major components: syngas, tar, and non-combustible ash. The tar-rich syngas is directed to the thermal oxidizer where it is burned to generate heat. Ash is removed by an automated system. An electrostatic precipitator is in place to treat the particulate matter to ensure the emission standard specified in the air quality permit is met.

2.2. Gas and Tar Sampling Various tar sampling methods have been developed over recent decades, each with their own advantages and disadvantages [29]. The most common method for tar sampling is condensing the tar in a cooled liquid solvent, such as isopropanol [30]. The contents of the solution are analyzed to determine the tar concentration via gravimetric evaporation or gas chromatography (GC). The tar measurement and CEN/TS 15439 standard is an impinger-based sampling protocol developed by the European Union [31,32] following the work done by Kiel et al. [30]. CanmetENERGY-Ottawa (CE-O) has designed, tested and fabricated an alternative syngas and tar sampling device [30] for in-situ industrial applications. The unit comprises of a sampling probe, chiller, vacuum pump, and gas flow meter. Robinson [33] conducted a series of experiments using a lab-scale bubbling fluidized bed gasifier and hardwood pellets as fuel, and showed that the CE-O was able to sample syngas with tar concentrations less than 10 g/m3. Robinson found the samples taken by the CE-O and the CEN/TS 15439 standards provided a similar syngas profile and tar production. In this paper, the CE-O and the CEN/TS 15439 standards were used side-by-side to sample syngas and collect tar from the gasification reactor. The gas chromatography-thermal conductivity detector (GC-TCD) technique was used to identify and quantify syngas composition. The amount of solvent, or isopropanol, for each sampling event was about 600 g. Approximately 170 L of syngas was pulled through the sampling device over a period of 90 min. The concentration of the tar samples was quantified using GC-FID equipped with a column packed with DPDM-siloxane (5% diphenyl + 95% dimethyl). The heating program applied to the sample in GC was as follows: initial temperature 50 ◦C for 5 min, ramp at 8 ◦C/min to 300 ◦C and hold at 300 ◦C time for 5 min. GC-FID identified the major compounds in the sample. Other unknown peaks in the GC-FID results were added to the major compounds to calculate the total tar concentration in the solvent Cs. Tar concentration in syngas, Cg was calculated according to the following equation:

M Cs × Vs Cg = = Vg Vg where M is the mass of tar, Vs is the volume of solvent, Vg is the volume of syngas, and Cs is the concentration of tar in the solvent as measured by GC.

2.3. Biomass Fuel Sampling Biomass fuel samples were taken from the port near the gasifier feeding auger. Approximately 5 kg of fuel was collected during each syngas sampling event for subsequent measurements of moisture content, ash content, and caloriﬁc value. Fuel samples were taken before, during, and after tar Environments 2018, 5, 84 5 of 13 collection following the CEN/TS 14778-1 standard [34], and fuel MC (moisture content) was measured in accordance with the CEN/TS 14774 standard [35].

2.4. Test Procedure Initially,Environments we 2018 conducted, 5, x FOR PEER a test REVIEW using the CE-O and compared the results with those derived 5 of 13 from the impingers. This test occurred at the tissue plant. Samplings using the two pieces of equipment Initially, we conducted a test using the CE-O and compared the results with those derived from were donethe impingers. in parallel This and test from occurred the same at the port tissue over plant. two daysSamplings (Figure using2). Eachthe two syngas pieces and of equipment tar sampling event lastedwere done for aboutin parallel 20 min. and from the same port over two days (Figure 2). Each syngas and tar sampling Forevent the lasted impingers for about technique, 20 min. a sampling probe was connected to an in-line particulate matter filter, whichFor was the thenimpingers attached technique, to the a first sampling impinger probe bottle was connected in the ice to bath. an in-line The lastparticulate impinger matter bottle was infilter, thehot which bath was and then connected attached to to the a pump first impinger which sentbottle the in gasthe ice through bath. The a flow last impinger meter to bottle exhaust. Overallwas cleaning in the hot was bath carried and outconnected at the endto a pump of the which entire sent testing the day,gas through whereby a flow the probes meter to were exhaust. washed with isopropylOverall cleaning alcohol was in carried order to out collect at the end the of heavy the entire tar that testing had day, not whereby been absorbed the probes by were the washed impingers. with isopropyl alcohol in order to collect the heavy tar that had not been absorbed by the impingers. The cleaning procedure took an additional 10 min to complete. The cleaning procedure took an additional 10 min to complete. The testing procedure using the CE-O approach was in accordance with the specifications in the The testing procedure using the CE-O approach was in accordance with the specifications in the CanmetENERGYCanmetENERGY report, report, which whichincluded included instructions instructions regarding regarding device operation, device operation, assembly assembly guidelines, samplingguidelines, procedures, sampling and procedures, use of solvent. and Setupuse of ofsolvent. the CE-O Setup device of the consistedCE-O device of threeconsisted main of modules:three hot gasmain particulate modules: filtration hot gas particulate and heated filtration lines; and tar heated collection lines; flask, tar collection chiller, flask, and pump;chiller, and and pump; gas flow rate measurements.and gas flow rate measurements.

Figure 2. Side-by-side syngas and tar sampling arrangement using impingers and the CE-O Figure 2. Side-by-side syngas and tar sampling arrangement using impingers and the CE-O (CanmetENERGY-Ottawa) device. The sampling port is located about 2/3 distance from the bottom of (CanmetENERGY-Ottawa) device. The sampling port is located about 2/3 distance from the bottom the reactor. of the reactor.

A follow-upA follow-up test wastest was performed performed at theat the UBC UBC gasiﬁer gasifier overover aa period of of two two months. months. The The tests tests involvedinvolved 40 sampling 40 sampling events events using using the the CE-O CE-O device. device. TheThe devicedevice was was checked checked for for oxygen oxygen leakage. leakage. After theAfter test, the thetest, concentration the concentration of oxygenof oxygen in in the the syngas syngas was was evaluated.evaluated. Those Those samples samples with with high high oxygen levels (greater than 0.5%) were deleted from the dataset to ensure that there was no gas oxygen levels (greater than 0.5%) were deleted from the dataset to ensure that there was no gas dilution dilution due to outside air. due to outside air. 3. Results

3.1. Fuel Properties The biomass fuel samples obtained from the gasifier at the tissue plant were fractionated into five sizes (Figure 3) using round-hole screens with diameters of 25, 12.5, 6.3, and 3.15 mm, and a pan.

Environments 2018, 5, 84 6 of 13

3. Results

3.1. Fuel Properties Environments 2018, 5, x FOR PEER REVIEW 6 of 13 The biomass fuel samples obtained from the gasiﬁer at the tissue plant were fractionated into Figure 4 shows the size distribution of the biomass samples. Almost half of the material were large ﬁve sizes (FigureEnvironments3) 2018 using, 5, x FOR round-hole PEER REVIEW screens with diameters of 25, 12.5, 6.3, and 3.15 mm, 6 of 13 and a pan. pieces (greater than 25 mm) on day 2, whereas 40% of the mass was between 12.5 and 25 mm on day Figure4 shows the size distribution of the biomass samples. Almost half of the material were large 1. TheFigure mass 4fraction shows theof smallsize distribution pieces (below of the 3.15 biomass mm) samples. was less Almost than 2% half on of boththe material sampling were days. large pieces (greaterpieces than (greater 25 than mm) 25 on mm) day on 2,day whereas 2, whereas 40% 40% of of thethe mass was was between between 12.5 and 12.5 25 and mm 25on mmday on day 1. The mass fraction1. The mass of fraction small piecesof small (belowpieces (below 3.15 3.15 mm) mm) was was less less thanthan 2% 2% on on both both sampling sampling days. days.

Figure 3. TheFigure fuel 3. The samples fuel samples were were separated separated into into ﬁvefive sizes. sizes. Particle Particle size size(x) from (x) the from top theleft to top theleft to the Figurebottom: 3. The x fuel> 25 mm,samples 12.5 < were x < 25 separatedmm, 6.3 < x into< 12.5 five mm, sizes. 3.15 < Particlex < 6.3 mm, size and (x) x from< 3.15 mm.the top left to the bottom: x > 25 mm, 12.5 < x < 25 mm, 6.3 < x < 12.5 mm, 3.15 < x < 6.3 mm, and x < 3.15 mm. bottom: x > 25 mm, 12.5 < x < 25 mm, 6.3 < x < 12.5 mm, 3.15 < x < 6.3 mm, and x < 3.15 mm. 50 50 40 Day 1 Day 2 40 Day 1 30 Day 2 30 20

20 10 Particle mass Particle mass fraction, % 10 0 > 25 mm > 12.5 mm > 6.3 mm > 3.15 mm < 3.15 mm Particle mass Particle mass fraction, % Sieve size 0 Figure 4. Mass fraction> 25of themm biomass > 12.5 particles mm > and 6.3 theirmm size > 3.15 distribution mm < 3.15 for each mm day of the test conducted at the tissue plant. Sieve size

FigureFor 4. theMass UBC fraction gasifier, of particlethe biomass size distribution particles and analysis their sizeof the distribution fuel samples for shows each thatday aboutof the 70% test Figure 4. Mass fraction of the biomass particles and their size distribution for each day of the test conductedof particles at falls the intissue between plant. 3.15 and 25 mm. A somewhat smaller fraction of particles is greater than conducted25 mm. at The the samples tissue plant. “as received” at UBC were slightly wetter than the samples at the tissue plant. For theTable UBC 1 listsgasifier, the properties particle sizeof fuel. distribution Fuel MC ranged analysis from of the20.6 fuel to 33.3% samples wb with shows an thataverage about of 70% 26.8% and standard deviation of 4.3%. Bulk density and calorific value were 150.7 ± 17.3 kg/m3 and Forof particles the UBC falls gasiﬁer, in between particle 3.15 sizeand 25 distribution mm. A somewhat analysis smaller of the fraction fuel samples of particles shows is greater that about than 70% 19.2 ± 0.65 MJ/kg, respectively. The physical properties of the biomass between the two sites were not of particles25 mm.too fallsThe different, samples in between except “as thatreceived” 3.15 the and samples at 25 UBC mm. at thewere A tissue somewhat slightly plant wetterhad smaller a somewhat than fractionthe sampleshigher of ash particles at content the tissue is(1.8 greater plant.± than 25 mm. TheTable samples 1 lists the “as properties received” of at fuel. UBC Fuel were MC slightly ranged wetterfrom 20.6 than to the33.3% samples wb with at an the average tissue plant.of 3 Table26.8%1 and lists standard the properties deviation of of fuel. 4.3%. Fuel Bulk MCdensity ranged and calorific from 20.6 value to were 33.3% 150.7 wb ± with 17.3 ankg/m average and of 19.2 ± 0.65 MJ/kg, respectively. The physical properties of the biomass between the two sites were not 26.8% and standard deviation of 4.3%. Bulk density and caloriﬁc value were 150.7 ± 17.3 kg/m3 too different, except that the samples at the tissue plant had a somewhat higher ash content (1.8 ±

Environments 2018, 5, 84 7 of 13 and 19.2 ± 0.65 MJ/kg, respectively. The physical properties of the biomass between the two sites were not too different, except that the samples at the tissue plant had a somewhat higher ash content (1.8 ± 0.5% db vs. 1.06 ± 0.3% db at the UBC site). Table2 lists the ultimate analysis and proximate analysis results, indicating that the fuel’s speciﬁcations were within the expected values.

Table 1. Properties of fuel based on samples taken at University of British Columbia.

Moisture Bulk Density Ash Content Caloriﬁc Value Parameter Content (% wb) (kg/m3) (% db) (MJ/kg) Average 26.8 150.7 1.06 19.20 Standard deviation 4.3 17.3 0.28 0.65 Coefﬁcient of variation 0.15 0.11 0.27 0.03 wb: wet basis; db: dry basis.

Table 2. Ultimate and proximate analysis of fuel.

Parameter Measured Value (%) Expected Range from Gasiﬁer Specs (%) Volatiles 83.0 70–85 Fixed carbon 16.5 15–25 Carbon 54.6 48–52 Hydrogen 5.80 5–6 Oxygen 39.0 36–44 Nitrogen 0.09 <0.2 Sulphur 0.02 <0.025 Chlorine 0.04 <0.025

3.2. Syngas Composition Visual observations and lab results show that no char or unburnt biomass remained in the ash collected from the UBC gasifier. Thus, only results relevant to syngas and tar production are presented in this section and the following section. Table3 lists the average, minimum, and maximum concentrations of the syngas components (H 2, CH4, CO, CO2) for the two sampling techniques used at the tissue plant. During each sampling event, syngas was collected using sampling bags. Insignificant differences in the syngas composition were observed for the two methods. Moreover, the syngas calorific value of 3.7 MJ/m3 on day 1 was in the neighbourhood of 4.1 MJ/m3 measured on day 2.

Table 3. Comparison of gas composition using the impingers and CE-O sampling techniques.

CEN/TS 15439 Method CE-O Device Species Ave StdDev Min Max Ave StdDev Min Max

H2 9.1 0.5 8.4 9.9 8.0 1.2 6.0 9.8 O2 0.7 0.6 0.3 2.1 0.7 0.4 0.3 1.3 N2 57.3 1.9 54.6 61.3 57.2 2.3 53.7 61.7 CH4 1.3 0.3 0.8 1.9 2.0 0.5 1.1 2.7 CO 19.8 2.0 16.7 21.9 20.1 1.6 18.0 22.7 CO2 11.9 0.7 10.8 12.7 12.0 0.8 10.7 13.2

The UBC gasiﬁcation system was routinely managed to ensure the gasiﬁer bed temperature remained relatively constant between 875 and 1050 ◦C as fuel moisture content varied from 20% to 35% wb, and this was achieved by raising the ER from 0.11 to 0.22 in order to increase the O2 level and hence promote the combustion reaction.

Syngas Composition and Fuel Properties Figure5 highlights the variability in parameters from the UBC gasiﬁer. The plot of syngas component concentrations vs. MC shows that as MC increases from 20% to 35%, CO concentration Environments 2018, 5, 84 8 of 13

Environments 2018, 5, x FOR PEER REVIEW 8 of 13 drops from about 30% to 20% (v/v). CO2 concentration increases mildly. H2 and CH4 show a mild Environments 2018, 5, x FOR PEER REVIEW 8 of 13 decrease.drops The from H 2about/CO 30% ratio to ranging 20% (v/v from). CO20.26 concentration to 0.54 is increases consistently mildly. less H2 than and 1.0.CH4 Theshow correlation a mild coefficientsdecrease. pertinent The H2/CO to (CO, ratio CH ranging,H from) vs. 0.26 syngas to 0.54 calorific is consistently value are less 0.91, than 0.85, 1.0. The 0.76 correlation respectively, drops from about 30% to 20% (4v/v). 2CO2 concentration increases mildly. H2 and CH4 show a mild indicatingcoefficients that CO pertinent has the tostrongest (CO, CH correlation4, H2) vs. syngas with MC. calorific Figure value6 shows are 0.91, the effect 0.85, 0.76 of moisture respectively, content decrease.indicating The that H 2CO/CO has ratio the ranging strongest from correlation 0.26 to 0.54 with is MC. consistently Figure 6 less shows than the 1.0. effect The of correlation moisture on syngascoefficients calorific pertinent value. to Despite (CO, CH a4 wide, H2) variation vs. syngas in calorific the calorific value are values 0.91, vs. 0.85, MC, 0.76 the respectively, calorific value content on syngas calorific value. Despite a wide variation3 in the calorific values vs. MC, the calorific showsindicatingvalue a mild shows overall that a mildCO decrease has overall the fromdecreasestrongest about from correlation 5.5 about to 3.5 5.5 with MJ/m to 3.5MC. MJ/mas Figure MC3 as increases MC6 shows increases the from effectfrom 20% 20%of to moisture 35%.to 35%. content on syngas calorific value. Despite a wide variation in the calorific values vs. MC, the calorific value shows a mild overall decrease from about 5.5 to 3.5 MJ/m3 as MC increases from 20% to 35%.

32 10

3228 109

2824 98 content, % content,

20 2 87 24 H CO content, % content, CO content, % content,

2016 2 76 H CO content, % content, CO 20% 24% 28% 32% 36% 20% 24% 28% 32% 36% 16 Fuel moisture content 6 Fuel moisture content 20% 24% 28% 32% 36% 20% 24% 28% 32% 36% Fuel moisture(a) content Fuel moisture(b) content

(a) (b) 5 15

54 1512 3 4 129 content, % content,

content, % content, 2

3 2 4 96 CO

CH 1 content, % content,

content, % content, 2 2 4 0 63 CO

CH 1 20% 24% 28% 32% 36% 20% 24% 28% 32% 36% 0 Fuel moisture content 3 Fuel moisture content 20% 24% 28% 32% 36% 20% 24% 28% 32% 36% Fuel moisture(c) content Fuel moisture(d) content

Figure 5. Variation(c) of gas contents with fuel moisture content: (a) CO, (b()d H) 2, (c) CH4, (d) CO2. Figure 5. Variation of gas contents with fuel moisture content: (a) CO, (b)H2,(c) CH4,(d) CO2. TheFigure gas content5. Variation is on of agas volume contents (v /withv) basis. fuel moistureTests done content: at the (a UBC) CO, gasifier.(b) H2, (c ) CH4, (d) CO2. The gas content is on a volume (v/v) basis. Tests done at the UBC gasiﬁer. The gas content is on a volume (v/v) basis. Tests done at the UBC gasifier. 6 3 6

3 5

5 4

Calorific value, MJ/m value, Calorific 4 3 Calorific value, MJ/m value, Calorific 20% 24% 28% 32% 36% 3 Fuel moisture content 20% 24% 28% 32% 36% Fuel moisture content Figure 6. Syngas caloric value vs. fuel moisture content.

Figure 6. Syngas caloric value vs. fuel moisture content. Figure 6. Syngas caloric value vs. fuel moisture content.

EnvironmentsEnvironments 20182018,,5 5,, 84x FOR PEER REVIEW 99 of 13 13

3.3. Tar Concentration 3.3. Tar Concentration For the gasifier at the tissue plant, the measured tar concentration varied from 23.5 to 100 g/m3. For the gasifier at the tissue plant, the measured tar concentration varied from 23.5 to 100 g/m3. Lower tar was observed on day 2 along with a higher gasifier temperature. On day 2, a lesser quantity Lower tar was observed on day 2 along with a higher gasifier temperature. On day 2, a lesser quantity of fuel was fed to the gasifier; hence the O2 content in the gasifier was higher, resulting in a greater of fuel was fed to the gasifier; hence the O content in the gasifier was higher, resulting in a greater combustion. The average tar concentration2 derived from the impingers was 90.6 and 11.5 g/m on combustion. The average tar concentration derived from the impingers was 90.6 and 11.5 g/m3 on day day 1 and day 2, respectively. By comparison, the corresponding average tar concentration for the 1 and day 2, respectively. By comparison, the corresponding average tar concentration for the CE-O CE-O device was 82.1 and 23.4 g/m , respectively. Tar concentration has been estimated to be of the device was 82.1 and 23.4 g/m3, respectively. Tar concentration has been estimated to be of the order order of 100 g tar/m3 of gas for updraft gasifiers, 10 g/m3 for fluidized beds, and 1 g/m3 for downdraft of 100 g tar/m3 of gas for updraft gasifiers, 10 g/m3 for fluidized beds, and 1 g/m3 for downdraft gasifiers [36]. Downdraft gasifiers generate the lowest tar concentration because the produced tar has gasifiers [36]. Downdraft gasifiers generate the lowest tar concentration because the produced tar has to pass through the combustion zone [37–39]. to pass through the combustion zone [37–39]. A wider range of tar concentration (24–170 g/m3) with an average value of 78 g/m3 was observed A wider range of tar concentration (24–170 g/m3) with an average value of 78 g/m3 was observed during the 40 sampling events at the UBC gasifier. The gasifier bed temperature remained within the duringrange of the 875–1050 40 sampling °C. Since events the system at the UBCattempts gasifier. to keep The the gasifier bed temperature bed temperature relatively remained constant, within there the range of 875–1050 ◦C. Since the system attempts to keep the bed temperature relatively constant, are more data points around 900 °C.◦ Overall, tar concentration increased slightly with fuel MC there(Figure are 7), more but data the pointscorrelation around coefficient 900 C. Overall,was low tar at concentration around 0.50. increasedMoisture slightlyevaporation with fuelled MCto a (Figuredecrease7), in but temperature the correlation and coefficient hence a slight was increase low at around in tar 0.50.yield. Moisture Our measurements evaporation also led torevealed a decrease that 3 3 inat temperaturesomewhat higher and hence fuel MC a slight (27–32% increase wb), in ag/m smallar increase yield. Our in the mea gasifierg/m urements temperature also from revealed 875–925 that at somewhat higher fuel MC (27–32% wb), a small increase in the gasifier temperature from 875–925 ◦C °C to 925–1050 °C led to a decrease in the tar concentration from 100–160 to 60–100 g/m3. ◦ 3 to 925–1050Particle Csize led distribution to a decrease analysis in the tarof the concentration fuel samples from indicated 100–160 that to 60–100 particle g/m percentages. in the four Particlesize ranges size (3.15–25 distribution mm) analysisvaried from of the 17.8 fuel ± 4.3%, samples to 28.5 indicated ± 5.6%.that Roughly particle 27% percentages of particles inhad the a ± ± foursize sizegreater ranges than (3.15–25 25 mm, mm) and variedroughly from 6% 17.8 of particles4.3%, towere 28.5 below5.6%. 3.15 Roughly mm. Figure 27% of8 particlesillustrates had that a sizeparticle greater percentages than 25 mm, in andthe roughlysmall size 6% range of particles (3.15–6.3 were mm) below had 3.15 a mm. weak Figure correlation8 illustrates with that tar particleconcentration percentages (correlation in the small coefficient size range = 0.48). (3.15–6.3 Overall, mm) as had the a weakparticle correlation percentages with in tar this concentration size range (correlationincreased from coefficient 10% to over = 0.48). 25%, Overall, the tar asconcentration the particle percentagesincreased also in from this size approximately range increased 40 g/m from3 to 3 3 10%above to 90 over g/m 25%,3. the tar concentration increased also from approximately 40 g/m to above 90 g/m .

180

3 150

120

Tar Tar concentration, g/m 30

0 15 20 25 30 35 Fuel moisture content, % wb

Figure 7. Tar concentration vs. fuel moisture content. Tests donedone atat thethe UBCUBC gasiﬁer.gasifier.

Environments 2018, 5, 84 10 of 13 Environments 2018, 5, x FOR PEER REVIEW 10 of 13

180

3 150

120

Tar Tar concentration, g/m 30

0 5% 10% 15% 20% 25% 30% Percent particles in the size range 3.15 - 6.3 mm

FigureFigure 8. 8.Tar Tar concentration concentration vs. vs. percent percent particles particles with with a smaller a smaller sizerange size range Testsdone Tests at done the UBC at the gasifier. UBC gasifier. 4. Discussion 4. Discussion Results pertinent to syngas composition indicate that the variation of CO as a syngas component withResults fuel moisture pertinent content to syngas is incomposition line with indicate studies that performed the variation by other of CO researchers as a syngas [ 8component,19–21,23]. Specifically,with fuel moisture as fuel MC content increases is in from line 20%with to studies 35%, CO performed concentration by other has researchersa pronounced [8,19–21,23]. drop and thisSpecifically, leads to aas reduction fuel MC increases in the syngas from HHV.20% to While 35%, ourCO resultsconcentration indicate has a mild a pronounced decrease in drop H2 andand CHthis4 leadscontent to a with reduction an increase in the in syngas fuel MC, HHV. Atnaw While et our al. [results21] and indicate James et a al.mild [22 decrease] reported in marginalH2 and CH or4 negligiblecontent with changes an increase in H2 and in fuel CH4 ,MC, though Atnaw Li et et al. al. [19 [21]] observed and James a decrease, et al. [22] and reported Paasen and marginal Kiel [20 or] foundnegligible a modest changes increase in H2 and in H CH2. The4, though increase Li et in al. CO [19]2 concentration observed a decrease, with increasing and Paasen MC and is similar Kiel [20] to findingsfound a bymodest Huang increase et al. [ 8in]. H2. The increase in CO2 concentration with increasing MC is similar to findingsOur by tar Huang measurements et al. [8]. for the industrial updraft gasifier demonstrate a similar relationship betweenOur tar tar formation measurements and gasifier for the temperature, industrial updraft in that gasifier published demonstrate lab-scale and a similar pilot-scale relationship studies onbetween fluidized tar formation bed and downdraft and gasifier gasifiers temperature, [19–21 in,40 that] have published also indicated lab-scale that and apilot-scale higher gasifier studies bed on temperaturefluidized bed led and to a downdraft lower tar concentration. gasifiers [19–21,40] Moreover, have also our findings indicated are that aligned a higher with gasifier Bronson bed et al.temperature [25], in that led biomass to a lower fuel tar with concentration. higher portion Moreover, of small particlesour findings caused are higheraligned tar with concentration. Bronson et al. [25], Overall,in that biomass our findings fuel with suggested higher thatportion even of for small a gasifier particles operating caused underhigher commercial tar concentration conditions,. syngasOverall, quality our would findings be enhanced suggested if the that biomass even for fuel a gasifier moisture operating content couldunder be commercial maintained conditions, at around 20%.syngas The quality CO concentration would be enhanced (~30%) and if calorific the biomass value fuel(>4 MJ/m moisture3) will content be high could while be tar maintained concentration at isaround kept below20%. The 60–70 CO g/m concentration3 for the commercial (~30%) and gasifier. calorific However, value (>4 unlike MJ/m the3) will published be high data while from tar controlledconcentration laboratory is kept experiments,below 60–70 theg/m data3 for collected the commercial from a commercial gasifier. However, unit indicate unlike a wide the published variation. Thisdata mayfrom be controlled due to conditions laboratory under experiments, which the the use data of automationcollected from for a process commercial control unit are indicate difficult. a Furtherwide variation. research This is required may be todue develop to conditions robust relationsunder which among the varioususe of automation operating conditionsfor process and control the qualityare difficult. of syngas. Further research is required to develop robust relations among various operating conditions and the quality of syngas. 5. Conclusions 5. Conclusions Two industrial updraft gasifiers were used in this study. Field data on the variability of urban woodyTwo biomass industrial fuel updraft vs. syngas gasifiers composition were used and in tar this concentration study. Field weredata analyzed.on the variability No efforts of urban were madewoody to biomass adjust the fuel properties vs. syngas of composition biomass and and operational tar concentration conditions were of the analyzed. gasifier. No The efforts measured were datamade is to characterized adjust the properties by its wide of variations biomass fromand operational one test to theconditions next. This of showsthe gasifier. that actual The operatingmeasured conditionsdata is characterized produce data by its that wide have variations much more from variation one test thanto the the next. highly This controlled shows that laboratory actual operating tests. conditionsFor the produce industrial data gasifier that have at UBC much with more a longer variation period than of the gasifier highly run controlled and sampling laboratory events, tests. the gasifierFor temperature the industrial ranged gasifier between at UBC 875 with and a 1075 longer◦C duringperiod theof gasifier testing run period. and Results sampling indicated events, that the gasifier temperature ranged between 875 and 1075 °C during the testing period. Results indicated that as the fuel moisture content increases from 20% to 35%, CO concentration drops from about 30%

Environments 2018, 5, 84 11 of 13 as the fuel moisture content increases from 20% to 35%, CO concentration drops from about 30% to 20% and CO2 concentration has a mild increase, H2 and CH4 concentrations decrease slightly. The H2/CO ratio of 0.26–0.54 is consistently less than 1.0 since air was used as the gasifying agent for the industrial gasifier. Tar concentration varied from 24 to 170 g/m3 with an average value of 78 g/m3. The 20–35% range of fuel moisture content did not have a significant effect on the tar concentration, while particle percentages in the smaller size range of (3.15–6.3 mm) was found to have a mild correlation with tar concentration. As the particle percentages in this size range increased from 10% to more than 25%, tar concentration also increased from 40 g/m3 to more than 90 g/m3. Our results are in line with the trends reported in the literature for lab-scale and pilot-scale studies, despite the different operating conditions and types of gasifiers which were used. Based on the findings of this study, biomass fuel moisture content of ±20% is recommended for the industrial updraft gasifier in order to achieve higher syngas quality and lower tar concentration.

Author Contributions: Investigation, E.O., S.S. and A.L.; Methodology, J.L. and F.P.; Resources, F.P.; Supervision, S.S. and A.L.; Writing–original draft, E.O.; Writing–review & editing, S.S., A.L., X.B. and C.M. Funding: The research of this article was funded in part by BioFuelNet Canada grant number 65 and Natural Sciences and Engineering Research Council of Canada grant number RGPIN 42377-12, and CanmetENERGY of NRCan. Acknowledgments: The authors gratefully acknowledge the continuing support from Cloverdale Fuel Ltd. (Cloverdale, BC) and the personnel at the UBC Bioenergy Research and Demonstration Facility. Thanks is also extended to Serge Milaire, electronics technician and Bahman Ghiasi, doctoral candidate for their help with the syngas sampling system installation, and Indah Andriani for assistance with the sampling events. Conﬂicts of Interest: The authors declare no conﬂict of interest.

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