Gasification and Co-gasification Low-rank Coal with Biomass

Transcription

1 The Proceedings of 2 nd Annua Internationa Conference Syiah Kuaa University 12 Gasification and Co-gasification Low-rank Coa with Biomass 1 Asri Gani, 2 Ichiro Naruse 1 Department of Chemica Engineering, Syiah Kuaa University, Banda Aceh 23111, Indonesia; 2 Department of Mechanica Science And Engineering Nagoya, Japan. Corresponding Author: asri.gani@che.unsyiah.ac.id Abstract. Recenty, there has been significant research interest in cogasification of coa and various types of biomass bends to improve biomass gasification and syngas production. In addition, ash present in biomass catayses the gasification of coa. This experiment was conducted on the cogasification of various types of coa and biomass using drop tube gasifier under two sets temperatures 1173 and 1273K respectivey. Most of the reactions are considered as endothermic, the heat input is needed to conduct the reactions. The additions of biomass to NL coa during co-gasification give no effect on gasification, since the reaction is endothermic. The increasing temperature from 1173 to 1273K ony give sma increase in the yied gas and efficiency due to the short of residence time. Keywords: Gasification, Co-gasification, Low-rank Coa, Biomass Introduction Gasification has been considered for many years as an aternative to combustion of soid or iquid fues. The gasification process can produce cean gaseous mixtures by gasification technique. The cean gas can be used in interna combustion-based power pants. Eectricity generation from renewabe sources such as biomass becomes interesting due to higher conversion efficiency and ow-cost. The gasification technoogies are aso avaiabe for the biomass to produce the gaseous fue. For the requirement to reduce the CO 2 content of the goba atmosphere, on the other hand biomass is recognized as one of the suitabe fue. There are severa experimenta gasification systems avaiabe, which are mainy deveoped for either coa or biomass wastes gasification, but there is not much information avaiabe about co-gasification of coa mixed with biomass or wastes. The resuts obtained by Reinoso et a. in two fuidized bed pants of 1.7 and 2 MW (Reinoso et a., 1995) showed that the gasification was improved by addition of wood wastes to the coas. Other authors aso reported that co-gasification of biomass with coa did not ead to any serious operationa probems (Mc Lendon et a., 4). In this experiment, pure CO 2 is used as the gasification agent to eucidate fundamentas on the co-gasification characteristics. The objective of this study is to eucidate co-gasification characteristics of biomass with coa, comparing the resuts for ony biomass or coa gasification. Materias and Methods The experiments of gasification and co-gasification of severa types of biomass and coas are aso conducted, using an eectricay heated drop tube furnace (DTF) as shown in Figure 3.1 in chapter 3. Principay, the procedure for the gasification experiments by using the drop tube furnace is amost simiar to the combustion tests. Coa and biomass sampes are injected from the fue feeder in the upper parts of the furnace system. Pure CO 2 gas used as the gasification agent is suppied from a CO 2 cyinder. The CO 2 fow rate is maintained constant at 1.8 /min. In order to maintain the simiar condition, the fue feed rate is adjusted regarding to the ratio of carbon in CO 2 to in the sampe of 1.2. The experiments are conducted for around 6 minutes for each set of experiment. The temperature is maintained constant for two set of 1173 and 1273K. Residue, tars, soot and condensabe iquids carried by the gas are removed by using a thimbe fiter and two 26

2 The Proceedings of 2 nd Annua Internationa Conference Syiah Kuaa University 12 impingers before introducing a gas anayser. The weight of residue for each experiment is determined by weighing the fiter before and after the experiments. The samping probe is water-cooed and is quenched and diuted by argon gas at the probe tip to prevent additiona chemica reactions and water-vapour condensation through the samping ine. The reaction gas is diuted at three times. The produced gas such N 2, CO 2, CO, O 2, H 2, CH 4 and severa ight hydrocarbons gases are measured continuousy by a micro GC. Rigaku (TAS ) thermo gravimetric anayser (TGA) and Yanaco CHN coder are aso used to determine the carbon conversion of each fue. Two coas and one sawdust are gasified as a sampe. Their proximate and utimate anayses and other reevant properties are shown in Tabe 1. This tabe shows that the biomass contains a high VM content and a sma amount of ash. The NL coa has the greatest FC content and highest fue ratio, comparing to TH coa. The experimenta conditions of the co-gasification test are shown in Tabe 2. The furnace temperature and the ratio of carbon in CO 2 to sampes are maintained at 73 K and 1.2, respectivey by adjusting the feed rate, respectivey. Pure CO 2 is used as the gasification agent. The fow rate is kept at 1.8 /min in a experiments. Pyroysis experiments in nitrogen atmosphere are aso conducted to discuss the effect of gasification. Proximate and utimate anaysis of sampe Sampe Proximate anaysis Moisture Tabe 1. Coas and biomass properties H. Sawdust NL coa+h. Sawdust NL coa TH coa VM wt% air dry FC Ash Fue ratio Utimate anaysis C H N wt% air dry S O H/C mo ratio Combustibe Carbon in residue Sampe Tabe 2 Experimenta conditions during Gasification and Co-gasification Hinoki sawdust H. sawdust + NL coa NL coa TH coa Temperature [K] 1173, 1273 Atmosphere CO 2 C(CO 2)/C(sampe) ratio 1.2 Sampe feed rate [g/min] CO 2 fow rate (tota) 1.8 -Primary.23 -Secondary.85 Diution with Ar (Samping) 3 times Fow in samping probe Samping distance [mm] 1 Sampe gas CO 2, CO, H 2, CH 4, CxHy 261

3 The Proceedings of 2 nd Annua Internationa Conference Syiah Kuaa University 12 Resuts and Discussion Gasification and co-gasification characteristics In gasification where the gasifying agent is CO 2 and the products of gasification are combustibe gases ike Carbon monoxide (CO), Hydrogen (H 2 ) and traces of Methane and non-usefu products ike tar and dust, the production of these gases is by reaction of water vapour from fue itsef and carbon dioxide through a gowing ayer of charcoa. Thus the key to gasifier design is to create conditions such that fues (biomass and coa) are reduced to charcoa and then charcoa is converted at suitabe temperature to produce CO, H 2, CH 4 and other ight hydrocarbons. Three distinct processes take pace in gasification by using CO 2 as gasifying agent. They are drying of fue, pyroysis which a process in which tar and other voaties are driven off, and reduction. It is desirabe to use fue with ow moisture content because heat oss due to its evaporation before gasification is considerabe and the heat budget of the gasification reaction is impaired (Davidson, 1997). Thus in order to reduce the moisture content of fue some pretreatment of fue is required. Gasification begins with pyroysis giving a soid residue; char, consisting mainy of carbon and ash, a gas phase and condensabe phase consisting of tar and water. The products of gasification and gasifying agent (water, uncombusted partiay cracked pyroysis products and carbon dioxide) react with charcoa where the foowing reduction reactions take pace (Mizutani, 2). Boudouard C + CO 2 = 2CO ( MJ/kg moe) (1) Water - gas C + H 2 O = CO + H 2 ( MJ/kg moe) (2) Water gas shift CO + H 2 O = CO + H 2 ( MJ/kg moe) (3) Methanation C + 2H 2 = CH 4 (+ 75 MJ/kg moe) (4) Steam reforming CH 4 + H 2 O = CO + 3H 2 ( MJ/kg moe) (5) Dry reforming CH 4 + CO 2 = 2CO + 2H 2 (6) Reactions (1) and (2) are main reduction reactions (main gasification reaction) and being endothermic has the capabiity of reducing gas temperature. Reaction 4 ony occurs for high hydrogen concentration. Consequenty the temperatures in the reduction zone are normay 8- o C. Temperature in the gasification was suppied by 3 (three) sets eectric heaters and maintain isotherma for 2 (two) sets temperature at 1173 and 1273K. The heat input was used for the reaction above to convert fue carbon to combustibe gas. In order to eucidate the gasification process, gasification experiments for a cases were aso conducted at 1173 and 1273K as shown in Figure 1 (a) and (b). The figures show CO 2 and another combustibe gas is produced such as CO, H 2, CH 4 and C 2 H 4. If we compare Figure 1 (a) and 1 (b) we can observe the summary effect of increasing temperature on combustibe gas produced. Reaction temperature is one of the most important variabes in the gasification process, since the main gasification reactions are endothermic. When temperature rises it aso increases the rate of severa reactions as mention earier. Corté et a., (1987) studied the infuence of temperature on fast pyroysis of beech wood in an eectricay heated furnace. These authors found that the optimum temperature range for producing fue gas is about 8 to 9 C; above this temperature, both the hydrocarbon yied and the heating vaue decrease. The higher temperature range of 9 to C, however, is an optimum for the production of synthesis gas that is mainy composed of a mixture of H 2 and CO. Figure 5.9 and 5.11 represent the summary effect of temperature on gasification and co-gasification for a cases. From the figures it was aso detected a decrease in CO 2 concentration with the rise of temperature, which may be expained as a resut of CO 2 consumption by boudouard reaction (1) and dry reforming reaction of CH 4 (6). The water shift gas reaction (3) woud produce CO 2, but resuts obtained by Gi et a., 1999 aso seem to indicate that when temperature increase the CO 2 consuming reactions 262

4 Concentration [Vo%] Concentration [Vo%] The Proceedings of 2 nd Annua Internationa Conference Syiah Kuaa University 12 woud be more important than the shift reaction. On the higher temperature the CO produced for co-gasification of NL coa and Hinoki sawdust biomass increases significanty. The highest conversion of combustibe gas produced is aso observed on TH coa gasification. The TH coa partice is smaer compared to the Hinoki sawdust and the voatie matter content is aso high. This resut suggests that TH coa surface area is arger than Hinoki sawdust make the conversion of TH coa is higher than Hinoki sawdust biomass. The reactivity of many types of coa and gasifying agent during gasification under atmospheric pressure has been examined by severa authors [8-9] Temperature = 1173K H. sawdust + NL coa Hinoki sawdust TH coa NL coa CO 2 CO H 2 CH 4 C 2 H 4 (a) Figure 1. Gasification and Co-gasification resuts at 1173K and 1273K Temperature = 1273K H. sawdust + NL coa H. sawdust TH coa NL coa CO 2 CO H 2 CH 4 C 2 H 4 (b) A Simiar tendency on increasing of CO production with decreasing of CO 2 is aso shows on TH coa profie for 1173 and 1273K. An increase in temperature, from 1173 to 1273K, ed to a decrease in methane and other hydrocarbons concentration, whie hydrogen concentration increased. The resuts obtained agree we to those of iterature and work conducted by Kim et a., 1 that aso detected an increase in H 2 and a decrease in CH 4 contents, when the temperature of coa gasification increased. Gi et a., 1999 studied pine wood chips gasification in a piot scae instaation aso observed an increase in H 2 and a decrease in hydrocarbons contents with the rise of temperature. Co-gasification of biomass and pastic mixtures (Pinto et a., 2) aso verified the favourabe infuence of temperature in promoting the formation of H 2. Cod gas efficiency A cod-gas efficiency is used to evauate the gasification performance. The cod-gas efficiency,, is defined as the percentage of the fue heating vaue converted into the cg heating vaue of the product gas. The cod gas efficiency (Li et a, 2) is defined as cg [ H [ H ] ] product sampe x% (7) The ower heating vaue of product [H ] product is determined by the concentration of CO, H 2, CH 4 and C 2 H 4 in the product gas mixture with the equation H H V.79[ H ] 12.63[ CO] 35.79[ CH ] 1.96[ H O] 59.3[ C ] (8) h s H4 Where high heating vaue of product gas mixture [H h ] is determined by the equation.75[ H ] 12.63[ CO] 39.72[ CH ] 62.95[ C ] (9) H h H 4 The ower heating vaue [H ] sampe of sampe is determine by equation H H 2.44(8.94h) () h Where high heating vaue of input sampe is determined by the equation H h 33.8c 144.3[( h o) / 7.94] s (11) 263

5 Cod gas efficiency [%] Cod gas efficiency [%] The Proceedings of 2 nd Annua Internationa Conference Syiah Kuaa University 12 Figure 2 (a) and (b) show cod gas efficiencies of gasification and co-gasification of NL and TH coas and Hinoki sawdust biomass at 1173 and 1273K respectivey. Figure 2(a) shows cod gas efficiency of Hinoki sawdust is the highest among others, whie NL coa is the owest. This resut because during gasification Hinoki sawdust produces high gas yieds since the voatie matter in the biomass is high and easiy evoves even in ow temperature. The increase of hydrocarbon aso increases high heating vaue. By adding biomass to coa in co-gasification case, it can be observed that the efficiency aso increases, but the increase is average of cumuative of NL coa and Hinoki sawdust. This mean the co-gasification is not affected by biomass addition. Gasification of TH coa higher than NL coa, since the voatie matter is high and more reactive C CO2 /C Sampe T = 1173K H. sawdust Co-fue NL coa TH coa (a) H. sawdust Co-fue NL coa TH coa (b) Figure 2. Cod gas efficiency during Gasification and Co-gasification at 1173K and 1273K. Where c, h, o and s are eementa anaysis of fues in weight percentage [wt%]. Higher or ower heating vaue of product gas and fues sampe was in (MJ/kg) The effect of temperature on the increase of cod gas efficiency can be seen by comparing Figure 2 (a) and (b). The significant increase of the efficiencies when temperature increase to 1273K was observed for NL and TH coa and co-fue cases. For Hinoki sawdust biomass gasification increasing of temperature from 1173 to 1273K give no effect on cod gas efficiency, since the voatie matter in the biomass is competey evove at 1173K. However, for coa case, the structure in which C, H and O are bound in the fues more aromatic moecuar structures (pyridinic, pyrroic) (Jukka et a., 1995), which is difficut to decompose. Biomass consists basicay of ceuose, hemi-ceuose and ignin (Vamvuka et a., 3). This eads to different behaviour during fash pyroysis, which is together with drying the initia step in the fuidized bed gasification process (Pinto et a, 3). This different behaviour resuts in a different yied of initia products. At higher temperature the conversion of carbon to gas yieds for NL and TH coa is increasing significanty. However, since the residence time is very short, the efficiencies are sti ow. The differences in fue type aso effects on gas heating vaue and as a resut it wi aso effect on cod gas efficiency (Van der Drift et a., 1). Concusions Gasification of different fues with CO 2 has been conducted by drop tube gasifier under two sets temperatures 1173 and 1273K respectivey. Most of the reactions are considered as endothermic, the heat input is needed to conduct the reactions. The use of CO 2 as gasifying agent in these experiments were subjected for the use of exhaust gas from coa-fired power pant which contains heat energy and has an advantages in reducing CO 2 emission in the atmosphere. Biomass gasification show higher gasification efficiency than NL coa, since the biomass contains high voatie matter and easiy evoves even in ow temperature. The additions of biomass to NL coa during co-gasification give no effect on gasification, since the reaction is endothermic. The resut of TH coa at higher temperature higher than hinoki sawdust biomass due to the partice of TH coa is smaer than Hinoki sawdust biomass. Since the residence time of gasification and co-gasification conducted by drop tube gasifier in these experiments is 2 seconds for each sampe. As a resuts, the cod C CO2 /C Sampe = 1.2 T = 1273K 264

6 The Proceedings of 2 nd Annua Internationa Conference Syiah Kuaa University 12 gas efficiency, CO conversion and carbon conversion is ow. The increasing temperature from 1173 to 1273K ony give sma increase in the yied gas and efficiency due to the short of residence time. References Corté P., Héraut V., Castio S., Traverse J.P High-temperature gasification of carbonaceous materias by fash pyroysis: therma aspects. Fue, 66(8): p Davison, R Co processing waste with coa, IEA Coa Research. Gi J., Migue A., Cabaero, Juan A., Martín, María-Piar A., Corea J Biomass Gasification with Air in a Fuidized Bed: Effect of the In-Bed Use of Doomite under Different Operation Conditions. Industria Engineering Chemica Resources, 38(11): p Kim Y.J., Lee S.H, Kim S.D. 1. Coa gasification characteristics in a downer reactor. Fue. 8(13): p Leppäahti J., Kojonen T Nitrogen evoution from coa, peat and wood during gasification: Literature review. Fue Processing Technoogy, 43(1): p Li X.T., Grace J.R., Lim C.J., Watkinson A.P., Chen H.P., Kim J.R. 4. Biomass gasification in a circuating fuidized bed. Biomass and Bioenergy, vo. 26(2): p Mc Lendon T.R., Lui A.P., Pineaut R.L., Beer S.K., and Richardson S.W. 4. High pressure co-gasification of coa and biomass in a fuidized bed. Biomass and Bioenergy, 26 (4): p Miura K., Hashimoto K., Siveston P.L Factors affecting the reactivity of coa chars during gasification and indices representing reactivity. Fue, 68(11): p Mizutani Y. 2. Combustion Engineering, 3rd ed. (In Japanese). Morikita Press, Tokyo, Japan. Pinto F., Franco C., Andre R.N., Miranda M., Guyurtu I., Cabrita I. 2. Co-gasification study of biomass mixed with pastic wastes. Fue, 81(3): p Pinto F., Franco C., Andre R.N., Tavares C., Dias M., Guyurtu I., Cabrita I. 3. Effect of experimenta conditions on co-gasification of coa, biomass and pastics wastes with air/steam mixtures in a fuidized bed system. Fue, 82(15-17): p Reinoso C., Cuevas A., Janssen K., Morris M., Lassing K., Nisson T., et a Cean coa technoogy programme. In: Bemtgen JM et a, editor. University of Atuttgarrt Paper C5, vo. 3, 1995, p Takarada T., Tamai Y., Tomita A Reactivities of 34 coas under steam gasification. Fue, 64(): p Vamvuka E., Karakas E., Kastanaki P., Grammeis. 3. Pyroysis characteristics and kinetics of biomass residuas mixtures with ignite. Fue, 82(15-17): p Van der Drift A., Van Doorn J., Vermeuen J.W. 1. Ten residua biomass fues for circuating fuidized-bed gasification. Biomass and Bioenergy, (1): p