Pyrolysis Of Low-rank Coal Research Articles

Performance study of pyrolysis of Indonesian low rank coal using a thermogravimetric analyzer and bubble fluidized‐bed reactor

AbstractPyrolysis is a process of thermal decomposition in the absence of oxygen. Gasification occurs first and is accompanied by complete or partial oxidation. Pyrolysis can generate syngas at low temperatures. In this study, thermogravimetric analysis and a fluidized‐bed reactor were used to conduct pyrolysis reaction experiments. The objective was to determine the characteristics of syngas produced by this process. The influence of K2CO3 catalyst on the syngas composition and reaction rate of pyrolysis was studied, and experimental values of the activation energy and pre‐exponential were obtained and evaluated. © 2016 Curtin University of Technology and John Wiley & Sons, Ltd.

Pyrolysis of low rank coal by nickel based zeolite catalysts in the two-staged bed reactor

Pyrolysis is an important process in the coal conversion and has a significant effect on the distribution of volatile products. In this work, ZSM-5 zeolite with different Ni loading was studied to upgrade volatile matter using low rank coal (Shengli, Inner Mongolia) in the two-staged bed reactor. All prepared catalysts were characterized using X-ray diffraction (XRD), Brunauer⿿Emmett⿿Teller (BET) analysis and ammonia temperature-programmed desorption (NH3-TPD). The role of Ni metal loading toward the pyrolysis gas yield and upgraded pyrolysis oil was investigated. The yield of non-condensable gases decreases as Ni loading increased in the catalysts, especially the yield of CO2 decreased significantly. Moreover, the catalysts reduced the pitch contents in the pyrolysis oil and promoted the fraction of light pyrolysis oils (BP<360°C).

Methane-rich syngas production in an integrated fluidized bed by coupling pyrolysis and gasification of low-rank coal

An integrated fluidized bed which combines a fluidized bed gasifier and a transport bed pyrolyzer was proposed to produce CH4-rich syngas from coupling pyrolysis and gasification of low-rank powder coal below 10mm. This study investigated the effects of major operating parameters on CH4 content in the syngas produced from processing a kind of subbituminous coal in a laboratory facility. It was found that the formation of CH4 was facilitated under the conditions of lower overall excessive oxygen ratio (ER), lower temperature of gasification (830–970°C), higher temperature of pyrolysis (500–700°C) and higher holdup of coal in transport bed. The CH4 content in the produced syngas increased with elevating the operating pressure but decreased with increasing the steam to carbon ratio (S/C) for gasification. Coupling transport bed pyrolysis with fluidized bed gasification at atmospheric pressure caused the CH4 content in the syngas to be 7.1vol.% under the conditions of ER=0.1, S/C=0.1, gasification temperature of 900°C and pyrolysis temperature of 700°C, which was higher than 5.1vol.% for the case without coupling coal pyrolysis. At the operating pressure of 1.4MPa the CH4 content reached about 11.2vol.%, about six times higher than 2.0vol.% for the usual fluidized bed gasification and close to 12.0vol.% for the Lurgi gasifier.

Application and research on Regenerative High Temperature Air Combustion technology on low-rank coal pyrolysis

Abstract Regenerative High Temperature Air Combustion (RHTAC) technology is composed of circular-ceramic regenerator, burners, small four-way reversing valve and control system. RHTAC technology works by using the regenerator in burners to complete heat exchange between the high-temperature fume exhausted and the combustion air. Based on RHTAC technology, Regenerative Radiant Tube Combustor (RRTC) has been developed, and was adopted by Shenwu Pyrolysis Process (SPP), which is a new pyrolysis technology with the heat-carrier-free rotating bed. SPP was researched and developed to upgrade low-rank coal into the upgraded coal, tar and pyrolyzing gas. Presently, various coals from China and other countries have been conducted, including Lignite and Long flame coal. To understand the function of the RRTCs in SPP, a pilot plant has been constructed and used to investigate the effects of the RRTCs on the fume and pyrolyzer temperature distributions and pyrolyzing products. The results show that low calorific value gas fuel (>700 kcal/Nm3) can be used, the heat loss in fume exhausted is low (temp. about 150 °C), so thermal efficiency of the RRTC is greatly improved; the RRTCs can realize accurate temperature control and the separation of volatile materials and fume in the pyrolyzer, so as to increase tar yield and improve gas quality. The tar yield is more than 90% of the Gray-King tar yield; the pyrolyzing gas contains high contents of CH4, H2 and CO. Moreover, SPP could solve some technical problems, such as high dust content in coal tar, likely blockage of pipeline and greatly increasing the subsequent tar processing cost.

Oil production from mild pyrolysis of low-rank coal in molten salts media

Abstract The present study focused on the utilization of molten carbonate salts as a media for the pyrolysis process to produce oil from low-rank coal. A ternary eutectic mix of alkali carbonate salts (Li 2 CO 3 , Na 2 CO 3 , and K 2 CO 3 ) was used to pyrolyze two kinds of low-rank coals. The effect of molten salt to the reactivity of coal was investigated by comparing the thermal decomposition profile of coal before and after it was mixed with the molten salt. The oil yield and its composition were also investigated. The results showed that the reactivity of the coal increased when the pyrolysis was performed in the molten salt. The molten salt increased the pyrolysis conversion about 16.5% and 16.4% for Loy yang and Xinghe coals, respectively, when they were pyrolyzed at 600 °C. The use of molten salt increased the oil yield since it can rapidly heat the coal to make the pyrolysis occur effectively. The total hydrocarbon content in the oil also increased about 13.6% and 11.0% for Loy yang and Xinghe coals, respectively. However, the molten carbonate salts failed to retain the sulfuric compound during the pyrolysis period due to the short residence time of oil in the molten salt phase.

Structural transformation of nascent char during the fast pyrolysis of mallee wood and low-rank coals

The changes in char structure during the fast pyrolysis of three different feedstocks from 600°C to 1200°C were investigated. Western Australian Collie sub-bituminous coal, Victorian Loy Yang brown coal and Australian mallee wood were pyrolysed in a wire-mesh reactor at a heating rate of 1000Ks−1 with holding time ranging from 0s to 50s. FT-Raman/IR spectroscopy was used to characterise the structural features of the chars obtained at different temperatures. The combined use of a wire-mesh reactor and an FT-Raman/IR spectrometer has provided significant insights into the rapid changes in the chemical structure of nascent char during fast pyrolysis. Our results indicate that the three fuels began significant ring condensation at different temperatures. Mallee wood showed significant growth of large rings within 1s holding at 600°C; however Loy Yang and Collie coals showed significant ring condensation at 800°C and 900°C respectively. With increase in temperature to 1000°C and higher, most ring condensation occurred at <1s holding time. The decrease in the intensity of FT-IR spectrum at ~1600cm−1 confirmed the rapid growth in ring systems at relatively high temperatures.

Application of House of Quality in evaluation of low rank coal pyrolysis polygeneration technologies

Increasing interest in low rank coal pyrolysis (LRCP) polygeneration has resulted in the development of a number of different technologies and approaches. Evaluation of LRCP processes should include not only conventional efficiency, economic and environmental assessments, but also take into consideration sustainability aspects. As a result of the many complex variables involved, selection of the most suitable LRCP technology becomes a challenging task. This paper applies a House of Quality method in comprehensive evaluation of LRCP. A multi-level evaluation model addressing 19 customer needs and analyzing 10 technical characteristics is developed. Using the evaluation model, the paper evaluates three LRCP technologies, which are based on solid heat carrier, moving bed and fluidized bed concepts, respectively. The results show that the three most important customer needs are level of technical maturity, wastewater emissions, and internal rate of return. The three most important technical characteristics are production costs, investment costs and waste emissions. On the basis of the conducted analysis, it is concluded that the LRCP process utilizing a fluidized bed approach is the optimal alternative studied.

Formation of nascent char structure during the fast pyrolysis of mallee wood and low-rank coals

The structural evolution of nascent chars during the fast pyrolysis of a wood and two low-rank coals was investigated in this study. Western Australian Collie sub-bituminous coal, Victorian Loy Yang brown coal and Western Australian mallee wood were pyrolysed in a wire-mesh reactor that is capable of providing rapid heating rates (up to 5000Ks−1) and accurate holding time (in increments of 10ms) at peak temperature. FT-Raman spectroscopy was used to characterise the key structural features of raw fuels and nascent chars. The combined use of a wire-mesh reactor and a FT-Raman spectroscopy has given insights into the structural transformation from coal/biomass to nascent chars. There were insignificant changes in the aromatic ring systems of two coals during the initial fast heating from room temperature to 600°C. During holding at 600°C, the changes that occurred in ring systems for the three fuels were different. Mallee wood and Loy Yang coal underwent more changes than Collie coal. In addition, mallee wood had ring condensation during holding at 600°C up to 30s. However, little growth in large aromatic rings of two coals was observed during holding at 600°C up to 50s.

Application of Regenerative High Temperature Air Combustion Technology on Low-rank Coal Pyrolysis

Abstract Based on Regenerative High Temperature Air Combustion technology (RHTAC), a Regenerative Radiant Tube Combustor (RRTC) has been developed and adopted into Shenwu Pyrolysis Process (SPP). SPP is a new regenerative pyrolysis technology with heat-carrier-free rotating bed, which has been researched and developed to upgrade low-rank coal. To understand the RRTC function, a pilot plant has been constructed and used to investigate the effect of RRTC on the fume, reactor temperature distribution and pyrolysis products. The results show that low calorific value gas can be used as fuel, the heat loss in fume exhausted is low while thermal efficiency of the RRTC is greatly improved; the RRTC could realize accurate temperature control and the separation of volatile materials and fume in the reactor, so as to increase tar yield and improve gas quality. The tar yield is more improved; the gas contains high content of CH4 and H2. Moreover, heat-carrier-free rotating bed could solve some technical problems.

Research on the Microwave Pyrolysis of Coal under N&lt;sub&gt;2&lt;/sub&gt; Atmosphere

Microwave pyrolysis of low rank coal is a new technology of cleaner production. The effect of microwave power and flow rate of N2 on the yield of pyrolysis products under N2 atmosphere was explored. The results showed that the higher microwave power was, the higher all the terminal temperature, the yield of liquid products and the weight loss rate were. The flow rate of N2 had little influence on the yield of pyrolysis solid products, while it exerted a greater influence on the yield of pyrolysis liquid products. When the low rank coal was pyrolysised under the conditions of microwave power of 800W and flow rate of N2 of 4.0×10-4 m3/min, the yield of Bluecoke and liquid products respectively reached 65.8% and 18%.

Study on the Process Analysis and Kinetics during the Co-Pyrolysis of Low Rank Coal and Enteromorpha

The pyrolysis of low rank coal (LRC) , enteromorpha (EN) and their mixture were carried out in a special prolysis equipment. The experiments showed that the maximum tar yield of blends was 11.39% with a EN ration of 30%, which increased by 28.61% compared to LRC pyrolysis alone and 8.87% compared to calculated value. The thermogravimetric analysis (TGA) of LRC, EN and their mixture indicated that there was significant synergistic effect in the co-pyrolysis process of LRC and EN during 240~750°C. The relative maximum value of synergistic effect was 18.5%. Kinetics analysis showed there was compensation effect between activation energy and pre-exponential factor of co-pyrolysis. The mix of LRC and EN enhanced the reaction activity and lowers the reaction rate. Synergistic effect mainly was reflected in enhancing the reaction activity of co-pyrolysis.

Low-Temperature Co-Pyrolysis Products of Low Rank Coal and Enteromorpha

Co-pyrolysis characteristics of low rank coal (LRC) and enteromorpha (EN) in different proportins were studied in a dry distillation equipment. The results show that he maximum tar yiled of blends was 11.39% with a EN ration of 30%, which increased by 28.61% compared to LRC pyrolysis alone. In the co-pyrolysis tar ,the alkanes’ content was 48.66% and the phenolic was 9.12%, which was significantly higher than the content of the corresponding components of the original tar. The H/C ratio was increased by 9.87%. It indicated the pyrolysis tar became lighter on some degree. While the contents of CH4and H2in the pyrolysis gas were increased. SEM analysis showed the surface of co-pyrolysis semi-coke became rough and formed obvious center cracks. The heat value of co-pyrolysis semi-coke was higher than that of semi-coke from LRC.

Research Progress in Pyrolysis of Low-Rank Coals under Different Conditions

Coal is absolute dominance in reserves-to-production ratio terms. The development of fuels derived from pyrolysis of low-rank coals is beneficial to lower fossil fuels cost and greenhouse gas emissions. The research proposal briefly summarized energy situation and sustainable development strategy as they were by 2013 at first. Then some recent process in the understanding of the pyrolysis behaviors of coal was reviewed. The influencing factors of atmospheres, additives, and catalysts during coal pyrolysis will be followed to literature. The review paper on pyrolysis characteristics will achieve the development of advanced technologies for the clean and efficient utilization of low-rank coals

Multifluid Modeling of Mixing and Segregation of Binary Gas–Solid Flow in a Downer Reactor for Coal Pyrolysis

The mixing and segregation characteristics of different types of solid particles in a downer reactor are of fundamental importance in the pyrolysis of low-rank coals where sand particles are used as the heat carrier. However, relevant fundamental studies are seldom reported. This work presents a computational investigation of the hydrodynamic behavior of binary gas–solid flows in a downer using an Eulerian-Eulerian method with a modified gas–solid drag force model, taking the effect of mesoscale particle clustering structures into consideration. Three-dimensional CFD simulations were carried out and the results obtained were compared with the experimental data available in literature. It was shown that a reasonable agreement with experimental data can be obtained with the proposed drag modification. The segregation/mixing behavior in the downer was then analyzed with two popular methods, which results in the conclusion that the solid particles in the downer reactor can mix reasonably well, therefore offer...

Co-pyrolysis of low rank coals and biomass: Product distributions

Pyrolysis and gasification of combined low rank coal and biomass feeds are the subject of much study in an effort to mitigate the production of green house gases from integrated gasification combined cycle (IGCC) systems. While co-feeding has the potential to reduce the net carbon footprint of commercial gasification operations, success of this strategy requires investigation of the effects of coal/biomass co-feeding on reaction kinetics and product distributions. Southern yellow pine was pyrolyzed in a semi-batch type drop tube reactor with either Powder River Basin sub-bituminous coal or Mississippi lignite at several temperatures and feed ratios. Product gas composition of expected primary constituents (CO, CO2, CH4, H2, H2O, and C2H4) was determined by in situ mass spectrometry while minor gaseous constituents were determined using a GC–MS. Product distributions are fit to linear functions of temperature, and quadratic functions of biomass fraction, for use in computational co-pyrolysis simulations.The results are shown to yield significant nonlinearities, particularly at higher temperatures and for lower ranked coals. The co-pyrolysis product distributions evolve more tar, and less char, CH4, and C2H4, than an additive pyrolysis process would suggest. For lignite co-pyrolysis, CO and H2 production are also reduced. The data suggests that rapid pyrolysis of biomass produces hydrogen that stabilizes large radical structures generated during the early stages of coal pyrolysis. Stabilization causes these structures to be released as tar, rather than crosslinking with one another to produce secondary char and light gases. Finally, it is shown that, for the two coal types tested, co-pyrolysis synergies are more significant as coal rank decreases, likely because the initial structure in these coals contains larger pores and smaller clusters of aromatic structures which are more readily retained as tar in rapid co-pyrolysis.

Catalytic effects of Na and Ca from inexpensive materials on in-situ steam gasification of char from rapid pyrolysis of low rank coal in a drop-tube reactor

Cost of catalysts is a crucial factor in realizing coal catalytic gasification process. In this study, inexpensive raw materials, soda ash (Na2CO3) and slaked lime (Ca(OH)2), were selected as catalyst precursors, and Na-, Ca- and Ca/Na-loaded coals were prepared by an ion-exchange procedure using a sub-bituminous coal (Adaro coal, Indonesia). These coal samples were rapidly pyrolyzed and in-situ gasified in an atmospheric drop-tube reactor (DTR) at 850–1000°C under a steam partial pressure of 0.05MPa. The Na and Ca catalysts showed remarkable activity for gasification, and the Ca/Na-loaded coal exhibited the highest reactivity among the coal samples prepared. The char yield of the Ca/Na-loaded coal at 1000°C was as low as 17.6mol-C per 100mol-C of coal, and more than 70% (on carbon basis) of its primary char was gasified within 3s. At 900°C, the coal with Ca-loading of 3.2wt.% showed catalytic activity higher than the coal with Ca-loading of 0.52wt.%. At 950 and 1000°C, however, the coal with the lower Ca-loading showed higher activity. The XRD analysis suggested that the Ca catalyst with the lower loading was more resistant to coarsening along with the progress of char gasification.

Pyrolysis and Combustion Characteristics of an Indonesian Low-Rank Coal under O2/N2and O2/CO2Conditions†

Pyrolysis and combustion characteristics of an Indonesian low-rank coal are studied under oxy-fuel (O2/CO2) and air (O2/N2) conditions using a drop tube furnace (DTF) and a thermogravimetric analyzer (TGA). Raw coal, dried coal, and binderless briquette samples of the same coal were used in the experiments, and the effects of drying and binderless briquetting on the reactivity of the coal under different conditions were investigated. Chars were prepared in the DTF in both N2 and CO2 atmospheres in the temperature range of 800−1400 °C. The reactivity of chars under oxy-fuel and air conditions was analyzed in the TGA. The coal reactivity under oxy-fuel conditions differed from that under air combustion conditions. The temperature at which significant gasification of the coal and char took place in the concentrated CO2 gas stream was also identified. Characteristics of chars from different conditions were compared. Drying and briquetting had some noticeable influences on the reactivity of the coal under oxy-...

Evolution Kinetics of Hydrogen Generation from Low Rank Coal Pyrolysis and Its Relation to the First Coalification Jump

用开放体系的热重-质谱联用仪(TG/MS)研究了7种低煤级煤的热解特征、H2的生成动力学特征以及它们与第一次煤化作用跃变的关系. 结果显示, 煤热解失重率在碳含量(Cdaf)为80%(质量分数)和镜质组最大反射率(R0max)为0.60%附近发生转折; 氢气生成的特征温度参数以及动力学参数均在Cdaf为80%(R0max为0.60%)左右表现为最低; 氢气的总产率在此处最大. 这些特征参数的极值点刚好与第一次煤化作用跃变点一致, 说明这些参数可以反映第一次煤化作用跃变的发生. 结合傅立叶变换红外(FTIR)光谱法获得的煤结构特征, 对影响机制进行了分析解释, 认为是由以下3个方面的原因导致的: (1)煤中脂肪类含氧官能团的演化特征; (2)可溶有机质的低温热缩聚作用; (3)有机质的“两极分化”作用.

Mathematical modelling of Collie coal pyrolysis considering the effect of steam produced in situ from coal inherent moisture and pyrolytic water

Low-rank coals have high inherent moisture content, and high yield of pyrolytic water formed from the functional groups in the coal during pyrolysis. Steam produced from coal moisture can lead to significant in-situ char gasification during pyrolysis under conditions where there are strong and prolonged interactions between the char and the in-situ steam. This phenomenon can be encountered in many practical processes yet is often overlooked in pyrolysis modelling. Using Collie coal as an example, this study presents a mathematical model on low-rank coal pyrolysis, considering primary and secondary coal pyrolysis reactions, heat transfer, mass transports, as well as char gasification and volatiles cracking/reforming by steam produced in situ during pyrolysis due to both coal inherent moisture and pyrolytic water. Under conditions where there are strong and prolonged interactions between the pyrolysis products (particularly char) and steam produced in situ from the coal inherent moisture and pyrolytic water, lower char yields from both raw and demineralised coal are predicted, in agreement with the experimental data, under the current experimental conditions. This effect increases with increasing coal inherent moisture content, but decreases with increasing particle size due to the slower heating rate incurred during pyrolysis and the pore diffusion effect during char gasification for the large particles. Volatile steam reforming competes with char gasification for available steam, especially at high temperatures and for large particles. Experiments as well as model prediction also clearly demonstrate that char steam gasification reactivity data should be obtained from experiments carried out on the in-situ basis as the in-situ reactivity is significantly higher than that on the ex-situ basis.

Nitrogen chemistry in coal pyrolysis: Catalytic roles of metal cations in secondary reactions of volatile nitrogen and char nitrogen

The present review focuses on elucidating the chemistry of nitrogen release during coal pyrolysis, in particular, on making clear catalytic roles of inherent Ca and Fe ions in not only the partitioning of volatile-N to tar-N, HCN, NH3 and N2 but also the conversion of char-N to N2.In slow heating rate pyrolysis of low-rank coals at 1000 °C with a fixed bed reactor, the demineralization with acid washing increases tar-N and HCN, but it decreases NH3. On the other hand, the ion-exchange of Ca2+ ions with the demineralized coals shows the nearly reverse effect on the distribution of these nitrogen species, though the physical mixing of Ca(OH)2 is almost ineffective. Since the sum of tar-N, HCN and NH3 is unchanged significantly in any cases, it is likely that Ca cations, which exist originally in the ion-exchanged forms, can control the partitioning of volatile-N to tar-N, HCN, and NH3. The Fe3+ ions precipitated on the demineralized coals catalyze the decomposition of tar-N, HCN and NH3 into N2.The evolution of N2 from coal-N occurs even in the absence of any metal cations added. The extent is generally larger with a lower rank coal, at a slower heating rate and a higher temperature, and at a longer solid residence time when coal is rapidly pyrolyzed. N2 yield at 1350 °C reaches about 70% at maximum. Since a strong reverse correlation exists between N2 and char-N, N2 originates predominantly from char-N (and/or precursors). Demineralization of low-rank coals decreases N2, whereas subsequently added Fe or Ca cations enhance N2 mainly at ≤1000 °C or ≥1000 °C, respectively. As the sum of naturally present Fe and Ca cations increases, N2 yield at 1350 °C tends to increase up to about 1 mass%. It can be proposed that fine particles of metallic Fe and CaO, which are formed from these inherent ion-exchanged cations, promote efficiently N2 formation from char-N through solid–solid interactions with heterocyclic nitrogen forms in char matrix.