Pilot scale autothermal gasification of coconut shell with CO₂-O₂ mixture

Abstract

This paper explored the feasibility and benefit of CO₂ utilization as gasifying agent in the autothermal gasification process. The effects of CO₂ injection on reaction temperature and producer gas composition were examined in a pilot scale downdraft gasifier by varying the CO₂/C ratio from 0.6 to 1.6. O₂ was injected at an equivalence ratio of approximately 0.33–0.38 for supplying heat through partial combustion. The results were also compared with those of air gasification. In general, the increase in CO₂ injection resulted in the shift of combustion zone to the downstream of the gasifier. However, compared with that of air gasification, the long and distributed high temperature zones were obtained in CO₂-O₂ gasification with a CO₂/C ratio of 0.6–1.2. The progress of the expected CO₂ to CO conversion can be implied from the relatively insignificant decrease in CO fraction as the CO₂/C ratio increased. The producer gas heating value of CO₂-O₂ gasification was consistently higher than that of air gasification. These results show the potential of CO₂-O₂ gasification for producing high quality producer gas in an efficient manner, and the necessity for more work to deeply imply the observation.

Keywords

biomass gasification / CO₂ / downdraft gasifier / autothermal

Introduction

The increasing concern in global warming and depletion of fossil fuel has attracted a lot of interest in biomass utilization as a renewable energy source. Biomass gasification is one of the favorable pathways since its product gas has wide applications. The produced syngas (H₂ and CO mixture) can be the feedstock for synthesis of liquid fuels and chemicals [ 1, 2]. However due to its complexity, the system can be economically feasible only when it is larger than a certain scale. Alternatively, biomass gasification is also applicable for small and distributed power generation network since it can keep relatively high thermal efficiency even at a reduced capacity (below 500 kW).

Due to the simplicity and low cost, air is often used as gasification medium [ 3, 4] for distributed power generation. The process usually produces producer gas with 3-6 MJ/Nm³of the lower heating value (LHV) at 60%-85% of the cold gas efficiency [ 5- 8]. Low producer gas LHV due to the nitrogen dilution makes it difficult to use producer gas in some high efficiency combustion applications such as gas turbine, or fuel cell [ 1, 6]. Higher process efficiency might also be desirable since it can optimize the feedstock utilization. An improvement for the producer gas quality has been developed by altering the oxidizer from air to O₂, injecting steam to the gasifier, or the combination of both. However these methods are merely suitable for syngas utilization in liquid fuel synthesis since they tend to lower the thermal efficiency of the overall gasification system if it is compared with air gasification [ 9, 10].

Similar to steam, CO₂ has a function as gasifying agent through Bouduard’s reaction [ 11] and dry reforming [ 12]. It is also discovered that CO₂ introduction promoted pyrolysis by promoting the cracking of benzene ring and fracture of hydroxyl, methyl and methylene groups [ 13]. Moreover, CO₂ is in gas-phase at ambient condition, and is often separated in syngas conditioning or from final product during the product refining (SNG, DME, FT-diesel, etc.) [ 14- 16]. Many studies have been conducted to examine the potential usage of CO₂ as gasifying agent. Some studies have shown the effect of CO₂ on the gasification characteristics of biomass using chemically controlled laboratory-scale reactors [ 17- 20]. Some studies have compared the gasification reactivity of char with CO₂ with the gasification reactivity of char with steam [ 21, 22]. Furthermore, some performance studies have shown that CO₂ gasification is promising for obtaining high efficiency process [ 23] better than gasification with air [ 24] or steam [ 24, 25], as well as for decreasing the tendencies of ash slagging and fouling [ 26].

Since CO₂ gasification is mostly controlled by a highly endothermic reaction, i.e. CO₂-char (Bouduard’s) reaction, heat supply becomes an important parameter that determines the overall process performance. The previous study [ 25] has shown that the autothermal (direct) gasification is potentially more effective for gaining high efficiency CO₂ gasification process than the allothermal (indirect) gasification. However, most of the CO₂ gasification performance studies have been conducted with the externally heated laboratory-scale apparatus (by electrical heater) where the heat supply is relatively stable and well distributed [ 8, 23- 25, 27]. Only few studies have reported the performance of CO₂ gasification in the pure autothermal gasification system [ 28] and no study has been performed in the pilot-scale gasifier to the best of our knowledge. A preliminary pilot-scale experiment of gasification with CO₂-O₂ mixture has been performed by Pettinau et al. [ 29], but no parametric study has been carried out due to the difficulty of the process control. Thus, the examination of the operability and performance evaluation of the autothermal CO₂ gasification using a pilot-scale plant still remains an important issue.

This paper presented the gasification performance of coconut shell using a pilot-scale fixed bed downdraft gasifier under various CO₂ flow rates with the presence of fixed amount of O₂. The reactor temperature, the producer gas composition and the producer gas heating value were examined to investigate the effect of CO₂/C ratio. The results were also compared with the performance of air-blown gasification.

Experimental

Material

Coconut shell obtained from the local area of Bandung, West Java, Indonesia, was used as the feedstock. The sample was naturally dried for more than 24 h and roughly ground to the size below 50 mm in diameter. The moisture content of the feedstock was (11.0±1.1)%. The proximate and ultimate analyses of the sample are listed in Table 1.

Apparatus

A pilot scale downdraft gasification system was utilized in this experiment. The gasification system is shown in Fig. 1, and the gasifier is depicted in detail in Fig. 2. The gasification system consists of a downdraft gasifier, a gas supply system, a cyclone, a gas-cooling system, a tar-capturing system, and a suction blower. 30-40 kg of feedstock bunker with a stirrer is attached to the gasifier. The gasifier has a throat of 160 mm internal diameter, covered by the castable refractory cement for the inner layer and steel plate for the outer layer. Three K-type thermocouples were attached to monitor the temperature inside the reactor (hereafter called T₁-T₃ points) and an S-type thermocouple was attached to measure the producer gas temperature (hereafter called T_gas point) at the position of flow measurement. Three orifice-type gas flow meters were used to measure the flow rate of O₂, CO₂ or air and the producer gas. O₂ and CO₂ (both are 99.5% (vol) purity) were supplied directly from gas cylinders and the flow rate was adjusted by the cylinder valve. The air supply was adjusted by the suction force of the blower. A GC-TCD (Shimadzu GC 14B) equipped with two columns (Molecular sieve and PoraPlotQ) was used for gas composition analysis.

Experimental procedure

The objective of this experiment is to examine the effect of CO₂ injection on the behavior of gasifer under stable condition. Therefore, the gasification tests were conducted in semi-continuous/semi-batch operations for 140 min. Each experimental run consisted of the preheating period and the measurement period. First, the gasifier was preheated by partial combustion of the sample at an air flow rate of 6.8 g/s for 60 min. Then, 12-17 kg of the feedstock was supplied to the gasifier and the measurement period continued for approximately 70 min with the preset CO₂-O₂ flow rate. The CO₂ flow rate was varied from 3.6 g/s to 9.2 g/s, corresponding to the CO₂/C ratio of 0.6-1.6. The O₂ flow rate was kept constant at 1.9 g/s, corresponding to the equivalence ratio (E/R) of approximately 0.35. CO₂/C and E/R were calculated based on Eqs. (1) and (2), respectively. The CO₂ supply rate and the biomass consumption during the measurement period are presented in Table 2.The carbon content of biomass was derived from Table 1.

(1) {\mathrm{CO}}_{\mathrm{2}}/C\mathrm{ratio}={\displaystyle \frac{{\mathrm{CO}}_{\mathrm{2}}\mathrm{supply}\mathrm{rate}(\mathrm{mol}/s)}{C\mathrm{in}\mathrm{biomass}(\mathrm{mol}/s)\times \mathrm{consumed}\mathrm{biomass}(g/s)}}

(2) \mathrm{Equivalence}\mathrm{ratio}(E/R)={\displaystyle \frac{O_2\mathrm{supply}(\mathrm{mol}/s)}{O_2\mathrm{for}\mathrm{stochiometric}\mathrm{combustion}(\mathrm{mol}/s)}}

The feedstock was refilled prior to the measurement period to minimize the effect of the sample on the reaction of the system. The stirrer attached in the feedstock bunker was used every ten minutes to ensure a proper feedstock distribution and down-flow. The temperatures in the attached thermocouples were recorded every 2 min. Figure 3 demonstrates the temperature changes over time at T₁, T₂, T₃ (see Fig. 2 for the locations) and T_gas (No.12 in Fig. 1) during run No. 4. The temperature increased during the pretreatment period (first 60 min) at every measurement point. The stable condition in this paper was defined when the temperature change was less than 5°C/min. T₁, which is highly affected by partial combustion, became stable after 90 min. T₂ and T₃ (located at the lower position of the gasifier) and T_gas became stable earlier during the preheating period.

The flow rate of producer gas was measured by an orifice flow meter simultaneously with the temperature measurement. The gas composition was analyzed by a GC-TCD every 7 min during measurement. Figure 4 shows the changes of producer gas composition and flow rate over time during runs No. 3 and 6. The average values and standard deviations of the temperature and the gas data were utilized for further analysis. The data shown in Fig. 4 were also used to calculate the gas evolution rate (Eq. (3)) and the gas yield (Eq. (4)). x is the volume percentage of the gas, F is the instantaneous gas flow rate at the correlated timing (mL/s), ∆t is the time interval of the GC measurement (s), and m is the total mass consumed during the examination period (g). The subscript i refers to the gas specyi, subscript p refers to producer gas, and subscript b refers to biomass. The total biomass consumption during the measurement period was quantified by weighing up the required amount of feedstock for refilling the bunker to the initial feedstock amount (the amount before the measurement period was started) soon after the experiment ended.

(3) y_{\mathrm{i}}=x_{\mathrm{i}}{F}_{\mathrm{p}},

(4) Y_{\mathrm{i}}=\Sigma (y_{\mathrm{i}}\Delta t)/m_{\mathrm{b}} .

Results and discussion

Despite some fluctuations, relatively stable operation under CO₂-O₂ flow can be observed from the profiles of temperature and gas composition in Figs. 3 and 4. These show that CO₂-O₂ gasification is able to be operated in the pilot scale downdraft autothermal gasifier. On the other hand, gas flow rate fluctuated in most of the experimental runs as shown in Fig. 4. The fluctuation in gas flow rate is likely to be caused by the tar condensation on the orifice flow meter rather than the instability in the gasification process. The constriction of the orifice hole by tar condensation was observed at the end of every run in the experiment and it might reduce the accuracy of flow measurement. In addition, gas leak was observable at the lower end of the gasifier in some period during the CO₂ injected experiments. Therefore, the calculated data involving the gas flow rate, i.e. the producer gas yield and the cold gas efficiency, can be used merely for qualitative/indicative analysis and not for investigating the absolute value. The main objectives in this paper were consequently focused on the producer gas flow rate independent data i.e. reactor temperature, producer gas composition and producer gas heating value.

Table 2 summarizes experimental conditions and the measurement results. Although no air was supplied during the measurement period of CO₂-O₂ gasification experiment, the molar fraction of N₂ in producer gas remained 33%-39%. It indicated the unexpected N₂ entrainment to the system. Because no O₂ was detected in producer gas, as shown in Table 2, the source of entrained N₂ is thought to be the air intake from the feedstock hopper due to the applied negative pressure (suction force). Since the entrained air can act as an additional gasifying agent, the actual equivalence ratio (E/R) in the gasifier can be approximately 1.4-1.8 times higher than the values shown in Table2. Therefore, the listed E/R conditions are merely indicative values and cannot be the absolute guidance for operating CO₂-O₂ gasification. The clarification of the effect of E/R on CO₂-O₂gasifier behavior, which would be preceded with an improvement on the sealing of gasification system, will be the focus of the research in the near future.

Effect of CO₂/C ratio on reactor temperature

Figure 5 shows the gasifier temperature profile under various CO₂/C ratios at the measurement zone of 0, 150 and 300 mm from the inlet of gasifying agent that pointed to T₁, T₂ and T₃, respectively. The measurement of temperatures at such distributed zone is aimed at detecting the flame position under various CO₂ and air atmospheres, as well as for investigating its movement related with the change of CO₂ concentration in gasifying agent. The average temperature was calculated after 90 min to avoid the disturbance of the transient phase at the early period of CO₂-O₂ injection.

T₁ and T₂ of the gasification tests under the CO₂/C ratios of 0.6-1.2 were higher than those detected during air gasification. However, the gasification test with the CO₂/C ratio of 1.6 did not show any higher temperature than that were shown in the air gasification runs at each measurement points. The high gasifier temperatures under the CO₂/C ratios of 0.6-1.2 can be explained by the higher fraction of O₂ in gasifying agent (22%-28% (vol)) than that in the air (21 % (vol)). The high O₂ fraction resulted in high reaction rate of combustion under low CO₂ injection rate, and combustion zone shifted upward, i.e. closer to the gas inlet port. This condition might be beneficial for enhancing the endothermic reactions since they can be triggered at closer position to the gas inlet port and eventually have a longer effective residence time in the reactor.

Compared with those of during air gasification, the low recorded temperatures during the gasification test with the CO₂/C ratio of 1.6 were observed despite the comparable O₂ fraction, showing the progress of the endothermic CO₂-char reaction (Eq. (6)). The low combustion rate of O₂ under CO₂ dilution compared to those of air might have played an important role as well. The low aggressiveness of O₂ in the CO₂-O₂ mixture which is related to the low diffusivity of O₂ under CO₂ dilution compared to those of O₂ under N₂ dilution has also been intensively investigated [ 30, 31].

Compared with the temperature profile under the CO₂/C ratio of 0.6, the low T₁ were observed in consort with the high T₂ under the CO₂/C ratios of 0.8 and 0.9. These implied that the increase in the CO₂/C ratio in that range resulted in the shift of flame front from the T₁ zone to the T₂ zone. A further increase in the CO₂/C ratio of up to 1.6 resulted in a further shift of the flame front to the T₃ zone. It is indicated by the occurrence of the highest temperature at the T₃ zone under the CO₂/C ratios of 1.2 and 1.6. By observing the temperature monitoring position in Fig. 2, it is detected that the combustion zone was located between the inlet of gasifying agent and throat at the CO₂/C ratio of 0.6 - 0.9 while it was located below the throat at the CO₂/C ratio of 1.2-1.6 and air gasification. Therefore, the CO₂/C ratio could have a trade-off between the change in CO₂ fraction and the residence time at high temperature zone, which both affect the extent of CO₂ involved reactions. In addition, there was a decrease in the maximum temperature of the gasifier due to the drop in adiabatic temperature as CO₂ fraction increased. It is significantly observable by comparing the temperature profile of the experiment runs under the CO₂/C ratios of 0.9 and above. The maximum temperature of CO₂-O₂ gasification in this experiment is comparable to that reported in the previous work on laboratory-scale CO₂-O₂ gasification [ 28]. Nevertheless, the maximum temperature of air gasification in this experiment is lower than that in other previous works [ 5, 28]. This is possible because the position of flame occurrence in air gasification does not fit with the allocated temperature measurement points.

Effect of CO₂/C ratio on producer gas composition

Figure 6 shows the effect of CO₂/C ratio on the producer gas composition. The average values of gas composition were calculated after 90 minutes to avoid the transient phase disturbance. The producer gas was diluted more by the unreacted CO₂ as the CO₂/C ratio increased. However, the decrease in the CO fraction was relatively insignificant compared with the increase in CO₂ fraction, indicating the increase in CO amount as the CO₂ injection increased. The progress of CO₂ to CO conversion might occur mainly through Bouduardrecation (Eq. (5)), dry reforming (Eq. (6)) and the reverse of water gas shift reaction (Eq. (7)). The progress of the CO evolving reactions were further demonstrated from the CO yield of CO₂-O₂ gasification that were consistently higher than that of air gasification, as shown in Fig. 7.

The H₂ fraction slightly increased along with the increase in CO₂/C ratio from 0.6 to 0.8, and then significantly suppressed at higher CO₂/C ratios. The increase in H₂ fraction at low CO₂/C ratio might be related to the delayed occurrence of the high temperature zone in the reactor (discussed in Sub-section 3.2) which therefore lessened the extent of the endothermic reverse water gas shift reaction (the reverse of Eq. (8)). The lessened extent of the reverse water gas shift reaction, on the other hand, decreased the CO evolution. Thus, the CO fraction decrease as the CO₂/C ratio increased at this range was more significant than those as CO₂/C ratio increased at the other range. In addition to the dilution effect, the low H₂ fraction at the CO₂/C ratio of 0.8 and above might be related to the drop in the maximum temperature in the gasifier. The temperature decrease might have subsequently suppressed the H₂ evolution through devolatilization. The CH₄ fraction was trivially affected by CO₂ injection since the contradictory effect of the temperature on the CH₄ evolution through devolatilization and the dry reforming (Eq. (7)) might occur simultaneously.

(5) \mathrm{C}+{\mathrm{C}\mathrm{O}}_2\to 2CO\hspace{1em}\mathit{\Delta }\mathit{H}=\mathrm{171.1}\mathrm{k}\mathrm{J}/\mathrm{m}\mathrm{o}\mathrm{l},

(6) {\mathrm{C}}_n{\mathrm{H}}_m+n{\mathrm{CO}}_{\mathrm{2}}\to m/\mathrm{2}{\mathrm{H}}_2+\mathrm{2}n\mathrm{CO}\hspace{1em}\mathit{\Delta }\mathit{H}>0\mathrm{kJ}/\mathrm{mol},

(7) \mathrm{CO}+{\mathrm{H}}_2\mathrm{O}\leftrightarrow {\mathrm{H}}_2+{\mathrm{C}\mathrm{O}}_2\hspace{1em}\mathit{\Delta }H=-41.1\mathrm{kJ}/\mathrm{mol}.

Effect of CO₂/C ratio on producer gas heating value and H₂/CO ratio

Figure 8 shows the effect of the CO₂/C ratio on the lower heating value (LHV) and the H₂/CO ratio of the producer gas. LHV and the H₂/CO ratio are important parameters for judging the quality of producer gas, which determines its suitable utilization. The increase in the CO₂/C ratio resulted in a low producer gas LHV because of the dilution of combustible gases by the unreacted CO₂. However, the producer gas obtained in CO₂-O₂ gasification had a higher LHV, 4.6-5.8 MJ/Nm³, than that obtained in air gasification, 3.5-3.8 MJ/Nm³. The reduced amount of N₂ from air is one of the reasons. Although CO₂ diluted the producer gas instead of N₂, CO₂ is not inert and promotes the reactions to produce CO. In fact, LHV of the producer gas from CO₂-O₂ gasification at CO₂/C= 1.6 was higher than that from air gasification at the comparable O₂ fraction in gasifying agent. This occurrence agreed with the finding of the previous research [ 28].

As previously discussed, the producer gas from CO₂-O₂ gasification contained N₂ from air leakage mainly because the experiments were conducted by the minor change in the existing gasifier. However, CO₂-O₂ gasification is expected to produce N₂-free gas if the gasifier was designed to avoid gas leakage specially for CO₂-O₂ gasification. Therefore, the effect of CO₂/C ratio on the expected N₂-free LHV is also shown in Fig. 7. The LHV of N₂-free producer gas was 6.9-9.3 MJ/Nm³, which was roughly 1.5 times higher than that with N₂ and 1.8 - 2.7 times higher than that of air gasification. The H₂/CO ratio of producer gas from CO₂-O₂ gasification was the same (the CO₂/C ratio<0.8) or lower (the CO₂/C ratio>1.2) than that from air gasification. Hence, the utilization of the producer gas seems more suitable for heat and power generation than for the fuel and chemical synthesis, which in most case requires a H₂/CO ratio of over 1.

As previously discussed, the exact analysis of CGE is not performed in this study due to the occurrence of several experimental imperfection, mainly producer gas leak and inaccuracy in producer gas flow rate measurement. However, a brief qualitative analysis of the producer yield and heating value (derived from Table 2) shows that CO₂-O₂ gasification might produce comparable CGE to air gasification, which is calculated to be around 73 %. This shows that the implementation of CO₂-O₂ gasification might be favorable for producing high quality producer gas in efficient manner. Nevertheless, further examination with more precise gas flow measurement in continuous operation is required to accurately examine the effect of CO₂ injection on the gasification efficiency.

Conclusions

The operability and the effect of CO₂/C ratio on CO₂-O₂ gasification were examined in this paper. CO₂-O₂ gasification was stably operated in a pilot scale downdraft gasifier at the CO₂/C ratios of 0.6-1.6 and with the equivalence ratio of around 0.33-0.38. The temperature profile of CO₂-O₂ gasification with the CO₂/C ratio of 1.2 and below was more uniformly distributed than that of air gasification. The decrease in the CO fraction as the CO₂/C ratio increased was less significant than the increase in the CO₂ fraction, showing the progress of gasification reactions involving CO₂.Owing to the increase in the dilution by unreacted portion of CO₂, LHV of the producer gas was decreased by the increase in the CO₂/C ratio. Nevertheless, the producer gas from CO₂-O₂ gasification had higher LHV than that from air gasification even at the comparable O₂ fraction in the gasifying agent. The producer gas LHV of CO₂-O₂ gasification was1.2-1.7 times higher than that of air gasification.

References

[1] Bridgwater A V.&nbsp;The technical and economic feasibility of biomass gasification for power generation.&nbsp;Fuel,&nbsp;1995,&nbsp;74(5):&nbsp;631&ndash;653

[2] Wang T,&nbsp;Li Y,&nbsp;Ma L,&nbsp;Wu C.&nbsp;Biomass to dimethyl ether by gasification/synthesis technology—an alternative biofuel production route.&nbsp;Frontiers in Energy,&nbsp;2011,&nbsp;5(3):&nbsp;330&ndash;339

[3] Keche A J R,&nbsp;Amba Prasad Rao G.&nbsp;Experimental evaluation of a 35 kVA downdraft gasifier.&nbsp;Frontiers in Energy,&nbsp;2013,&nbsp;7(3):&nbsp;300&ndash;306

[4] Ruiz J A,&nbsp;Juárez M C,&nbsp;Morales M P,&nbsp;Muñoz P,&nbsp;Mendívil M A.&nbsp;Biomass gasification for electricity generation: review of current technology barriers.&nbsp;Renewable & Sustainable Energy Reviews,&nbsp;2013,&nbsp;18:&nbsp;174&ndash;183

[5] Simone M,&nbsp;Barontini F,&nbsp;Nicolella C,&nbsp;Tognotti L.&nbsp;Gasification of pelletized biomass in a pilot scale downdraft gasifier.&nbsp;Bioresource Technology,&nbsp;2012(116):&nbsp;403&ndash;412

[6] Wang L,&nbsp;Weller C L,&nbsp;Jones D D,&nbsp;Hanna M A.&nbsp;Contemporary issues in thermal gasification of biomass and its application to electricity and fuel production.&nbsp;Biomass and Bioenergy,&nbsp;2008,&nbsp;32(7):&nbsp;573&ndash;581

[7] Huang Z,&nbsp;Zhang J,&nbsp;Yue G.&nbsp;Status of domestic gasification technology in China.&nbsp;Frontiers in Energy,&nbsp;2009,&nbsp;3(3):&nbsp;330&ndash;336

[8] Jarungthammachote S,&nbsp;Dutta A.&nbsp;Equilibrium modeling of gasification: Gibbs free energy minimization approach and its application to spouted bed and spout-fluid bed gasifiers.&nbsp;Energy Conversion and Management,&nbsp;2008,&nbsp;49(6):&nbsp;1345&ndash;1356

[9] Umeki K,&nbsp;Yamamoto K,&nbsp;Namioka T,&nbsp;Yoshikawa K.&nbsp;High temperature steam-only gasification of woody biomass.&nbsp;Applied Energy,&nbsp;2010,&nbsp;87(3):&nbsp;791&ndash;798

[10] Yoon H C,&nbsp;Cooper T,&nbsp;Steinfeld A.&nbsp;Non-catalytic autothermal gasification of woody biomass.&nbsp;International Journal of Hydrogen Energy,&nbsp;2011,&nbsp;36(13):&nbsp;7852&ndash;7860

[11] Di Blasi C.&nbsp;Combustion and gasification rates of lignocellulosic chars.&nbsp;Progress in Energy and Combustion Science,&nbsp;2009,&nbsp;35(2):&nbsp;121&ndash;140

[12] Zhang W,&nbsp;Zhang Y.&nbsp;The catalytic effect of both oxygen-bearing functional group and ash in carbonaceous catalyst on CH₄-CO₂ reforming.&nbsp;Frontiers of Chemical Science and Engineering,&nbsp;2010,&nbsp;4(2):&nbsp;147&ndash;152

[13] Gao S P,&nbsp;Zhao J T,&nbsp;Wang Z Q,&nbsp;Wang J F,&nbsp;Fang Y T,&nbsp;Huang J J.&nbsp;Effect of CO₂ on pyrolysis behaviors of lignite.&nbsp;Journal of Fuel Chemistry and Technology,&nbsp;2013,&nbsp;41(3):&nbsp;257&ndash;264

[14] Gassner M,&nbsp;Maréchal F.&nbsp;Thermo-economic process model for thermochemical production of synthetic natural gas (SNG) from lignocellulosic biomass.&nbsp;Biomass and Bioenergy,&nbsp;2009,&nbsp;33(11):&nbsp;1587&ndash;1604

[15] Clausen L R,&nbsp;Elmegaard B,&nbsp;Houbak N.&nbsp;Technoeconomic analysis of a low CO₂ emission dimethyl ether (DME) plant based on gasification of torrefied biomass.&nbsp;Energy,&nbsp;2010,&nbsp;35(12):&nbsp;4831&ndash;4842

[16] van Vliet O P R,&nbsp;Faaij A P C,&nbsp;Turkenburg W C.&nbsp;Fischer-Tropsch diesel production in a well-to-wheel perspective: a carbon, energy flow and cost analysis.&nbsp;Energy Conversion and Management,&nbsp;2009,&nbsp;50(4):&nbsp;855&ndash;876

[17] Hanaoka T,&nbsp;Hiasa S,&nbsp;Edashige Y.&nbsp;Syngas production by CO₂/O₂ gasification of aquatic biomass.&nbsp;Fuel Processing Technology,&nbsp;2013,&nbsp;116:&nbsp;9&ndash;15

[18] Ahmed I I,&nbsp;Gupta A K.&nbsp;Characteristics of cardboard and paper gasification with CO₂.&nbsp;Applied Energy,&nbsp;2009,&nbsp;86(12):&nbsp;2626&ndash;2634

[19] Jaffri G R,&nbsp;Zhang J Y.&nbsp;Catalytic gasification of Fujian anthracite in CO₂ with black liquor by thermo gravimetry.&nbsp;Journal of Fuel Chemistry and Technology,&nbsp;2007,&nbsp;35(2):&nbsp;128&ndash;135

[20] Kwon E E,&nbsp;Castaldi M J.&nbsp;Urban energy mining from municipal solid waste (MSW) via the enhanced thermo-chemical process by carbon dioxide CO₂ as a reaction medium.&nbsp;Bioresource Technology,&nbsp;2012,&nbsp;125:&nbsp;23&ndash;29

[21] Ahmed I I,&nbsp;Gupta A K.&nbsp;Kinetics of woodchips char gasification with steam and carbon dioxide.&nbsp;Applied Energy,&nbsp;2011,&nbsp;88(5):&nbsp;1613&ndash;1619

[22] Marquez-Montesinos F,&nbsp;Cordero T,&nbsp;Rodríguez-Mirasol J,&nbsp;Rodríguez J J.&nbsp;CO₂ and steam gasification of a grapefruit skin char.&nbsp;Fuel,&nbsp;2002,&nbsp;81(4):&nbsp;423&ndash;429

[23] Renganathan T,&nbsp;Yadav M V,&nbsp;Pushpavanam S,&nbsp;Voolapalli R K,&nbsp;Cho Y S.&nbsp;CO₂ utilization for gasification of carbonaceous feedstocks: a thermodynamic analysis.&nbsp;Chemical Engineering Science,&nbsp;2012,&nbsp;83:&nbsp;159&ndash;170

[24] Pohořelý M,&nbsp;Jeremiáš M,&nbsp;Svoboda K,&nbsp;Kameníková P,&nbsp;Skoblia S,&nbsp;Beňo Z.&nbsp;CO₂ as moderator for biomass gasification.&nbsp;Fuel,&nbsp;2014,&nbsp;117(Part A):&nbsp;198&ndash;205

[25] Prabowo B,&nbsp;Umeki K,&nbsp;Yan M,&nbsp;Nakamura M R,&nbsp;Castaldi M J,&nbsp;Yoshikawa K.&nbsp;CO₂-steam mixture for direct and indirect gasification of rice straw in a downdraft gasifier: laboratory-scale experiments and performance prediction.&nbsp;Applied Energy,&nbsp;2014,&nbsp;113:&nbsp;670&ndash;679

[26] Svoboda K,&nbsp;Pohořelý M,&nbsp;Jeremiáš M,&nbsp;Kameníková P,&nbsp;Hartman M,&nbsp;Skoblja S,&nbsp;Šyc M.&nbsp;Fluidized bed gasification of coal-oil and coal-water-oil slurries by oxygen-steam and oxygen-CO₂ mixtures.&nbsp;Fuel Processing Technology,&nbsp;2012,&nbsp;95:&nbsp;16&ndash;26

[27] Zhao Y C,&nbsp;Zhang J Y,&nbsp;Liu H T,&nbsp;Tian J L,&nbsp;Li Y,&nbsp;Zheng C G.&nbsp;Thermodynamic equilibrium study of mineral elements evaporation in O₂/CO₂ recycle combustion.&nbsp;Journal of Fuel Chemistry and Technology,&nbsp;2006,&nbsp;34(6):&nbsp;641&ndash;650

[28] Chen W,&nbsp;Thanapal S S,&nbsp;Annamalai K,&nbsp;Ansley R J,&nbsp;Mirik M.&nbsp;Updraft gasification of mesquite fuel using air/steam and CO₂/O₂ mixtures.&nbsp;Energy Fuels,&nbsp;2013,&nbsp;27 (12):&nbsp;7460&ndash;7469

[29] Pettinau A,&nbsp;Frau C,&nbsp;Ferrara F.&nbsp;Performance assessment of a fixed-bed gasification pilot plant for combined power generation and hydrogen production.&nbsp;Fuel Processing Technology,&nbsp;2011,&nbsp;92(10):&nbsp;1946&ndash;1953

[30] Riaza J,&nbsp;Gil M V,&nbsp;Álvarez L,&nbsp;Pevida C,&nbsp;Pis J J,&nbsp;Rubiera F.&nbsp;Oxy-fuel combustion of coal and biomass blends.&nbsp;Energy,&nbsp;2012,&nbsp;41(1):&nbsp;429&ndash;435

[31] Wall T,&nbsp;Liu Y,&nbsp;Spero C,&nbsp;Elliott L,&nbsp;Khare S,&nbsp;Rathnam R,&nbsp;Zeenathal F,&nbsp;Moghtaderi B,&nbsp;Buhre B,&nbsp;Sheng C,&nbsp;Gupta R,&nbsp;Yamada T,&nbsp;Makino K,&nbsp;Yu J.&nbsp;An overview on oxyfuel coal combustion—state of the art research and technology development.&nbsp;Chemical Engineering Research & Design,&nbsp;2009,&nbsp;87(8):&nbsp;1003&ndash;1016

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