Pilot Development of Polygeneration Process of Circulating Fluidized Bed Combustion combined with Coal Pyrolysis

A pilot polygeneration process of a 75 t h^–1 circulating fluidized bed (CFB) boiler combined with a moving bed coal pyrolyzer was developed based on laboratory‐scale experimental results. The process operation showed good consistency and integration between boiler and pyrolyzer. Some critical operating parameters such as hot ash split flow from the CFB boiler to the pyrolyzer, mixing of hot ash and coal particles, control of pyrolysis temperature and solid inventory in the pyrolyzer, and pyrolysis gas clean‐up were investigated. Yields of 6.0 wt‐% tar and 8.0 wt‐% gas with a heating value of about 26 MJ m^–3 at 600 °C were obtained. Particulate content in tar was restrained less than 4.0 wt‐% by using a granular filter of the moving bed. Operation results showed that this pilot polygeneration process was successfully scaled up.     

褐煤固体热载体热解提质工艺进展

介绍了国内外几种典型的褐煤固体热载体热解提质工艺,并从原理、操作条件、原料、热解产品、能量利用率、局限性等方面对各种工艺进行了分析对比;分析了工业上常用的固体热载体的优缺点,提出了褐煤固体热载体热解技术的发展方向。     

Optimal design and operation of a steel plant integrated with a polygeneration system

A process integration approach has been applied to integrate a traditional steelmaking plant with a polygeneration system to increase energy efficiency and suppress carbon dioxide emissions from the system. Using short‐cut models and empirical equations for different units and available technologies for gas separation, methane gasification, and methanol synthesis, a mixed integer nonlinear model is applied to find the optimal design of the polygeneration plant and operational conditions of the system. Due to the complexity of the blast furnace (BF) operation, a surrogate model technique is chosen based on an existing BF model. The results show that from an economic perspective, the pressure swing adsorption process with gas‐phase methanol unit is preferred. The results demonstrate that integration of conventional steelmaking with a polygeneration system could decrease the specific emissions by more than 20 percent. © 2013 American Institute of Chemical Engineers AIChE J, 59: 3659–3670, 2013     

Fundamentals of coal topping gasification: Characterization of pyrolysis topping in a fluidized bed reactor

Coal topping gasification refers to a process that extracts the volatiles contained in coal into gas and tar rich in chemical structures in advance of gasification. The technology can be implemented in a reactor system coupling a fluidized bed pyrolyzer and a transport bed gasifier in which coal is first pyrolyzed in the fluidized bed before being forwarded into the transport bed for gasification. The present article is devoted to investigating the pyrolysis of lignite and bituminite in a fluidized bed reactor. The results showed that the highest tar yield appeared at 823 to 923 K for both coals. When coal ash from CFB boiler was used as the bed material, obvious decreases in the yields of tar and pyrolysis gas were observed. Pyrolysis in a reaction atmosphere simulating the pyrolysis gas composition of coal resulted in a higher production of tar. Under the conditions of using CFB boiler ash as the bed material and the simulated pyrolysis gas as the reaction atmosphere, the tar yields for pyrolytic topping in a fluidized bed reactor was about 11.4 wt.% for bituminite and 6.5 wt.% for lignite in dry ash-free coal base.     

Decomposition and gasification of pyrolysis volatiles from pine wood through a bed of hot char

Pine wood was pyrolyzed in a fixed bed reactor at a heating rate of 10 °C and a final temperature of 700 °C, and the resultant volatiles were allowed to be secondarily cracked through a tubular reactor in a temperature range of 500-700 °C with and without packing a bed of char. The thermal effect and the catalytic effect of char on the cracking of tar were investigated. An attempt was made to deconvolute the intermingled contributions of the char-catalyzed tar cracking and the char gasification to the yields of gaseous and liquid products. It was found that the wood char (charcoal) was catalytically active for the tar cracking at 500-600 °C, while at 650-700 °C, the thermal effect became a dominant mode of the tar cracking. Above 600 °C, the autogenerated steam gasified the charcoal, resulting in a marked increase in the yield of gaseous product and a significant change in the gas composition. An anthracite char (A-char), a bituminous coal char (B-char), a lignite char (L-char) and graphite also behaved with catalytic activities towards the tar cracking at lower temperature, but only L-char showed reactivity for gasification at higher temperature.     

Effects of CO Atmosphere on the Pyrolysis of a Typical Lignite

To reveal the effect mechanism of CO atmosphere on coal pyrolysis, a study on raw and demineralized lignite was carried out in a horizontal tube furnace under N₂ and CO/N₂ atmosphere. CO had a negligible effect on the char yield at low temperatures, whereas it enhances the char yield at temperatures higher than 550 °C. The release of tar was higher in the presence of CO above 450 °C because of more free radicals, which reduced low‐temperature crosslinking, and higher selectivity of hydroxyl groups to phenols in the CO‐containing atmosphere. The yields of CO₂ and H₂ increased, water and CO yields decreased under CO/N₂ atmosphere. Light hydrocarbon gases were not affected by changing the reaction atmosphere. The difference between product yields from raw and demineralized coal confirmed that the catalysis of inherent minerals had a great catalytic effect on the water‐gas shift reaction and Boudouard reaction.     

低阶煤与玉米芯低温共热解的产物特性分析

采用低温干馏装置对不同玉米芯加入量的褐煤/玉米芯混合物进行低温共热解实验。结果表明：当玉米芯加入量为30%时,焦油产率最大为11.70%,比褐煤单独热解提高了53.75%。随着玉米芯的加入量增加,热解气中CO、CH₄和H₂含量逐渐增大。对热解焦油进行GC-MS检测,发现添加30%玉米芯后脂肪族质量分数从褐煤单独热解的24%提高到了30.67%,酚类质量分数从6.29%提高到了18.49%,杂原子质量分数从29.75%降低到了13.33%,一定程度上实现了焦油的轻质化和高品质化。对热解半焦进行SEM、比表面积分析和热值测定,发现共热解半焦表面变粗糙,孔隙结构得到改善,热值明显高于褐煤单独热解半焦热值。     

Optimization of energy usage for fleet‐wide power generating system under carbon mitigation options

This article presents a fleet‐wide model for energy planning that can be used to determine the optimal structure necessary to meet a given CO₂ reduction target while maintaining or enhancing power to the grid. The model incorporates power generation as well as CO₂ emissions from a fleet of generating stations (hydroelectric, fossil fuel, nuclear, and wind). The model is formulated as a mixed integer program and is used to optimize an existing fleet as well as recommend new additional generating stations, carbon capture and storage, and retrofit actions to meet a CO₂ reduction target and electricity demand at a minimum overall cost. The model was applied to the energy supply system operated by Ontario power generation (OPG) for the province of Ontario, Canada. In 2002, OPG operated 79 electricity generating stations; 5 are fueled with coal (with a total of 23 boilers), 1 by natural gas (4 boilers), 3 nuclear, 69 hydroelectric and 1 wind turbine generating a total of 115.8 TWh. No CO₂ capture process existed at any OPG power plant; about 36.7 million tonnes of CO₂ was emitted in 2002, mainly from fossil fuel power plants. Four electricity demand scenarios were considered over a span of 10 years and for each case the size of new power generation capacity with and without capture was obtained. Six supplemental electricity generating technologies have been allowed for: subcritical pulverized coal‐fired (PC), PC with carbon capture (PC+CCS), integrated gasification combined cycle (IGCC), IGCC with carbon capture (IGCC+CCS), natural gas combined cycle (NGCC), and NGCC with carbon capture (NGCC+CCS). The optimization results showed that fuel balancing alone can contribute to the reduction of CO₂ emissions by only 3% and a slight, 1.6%, reduction in the cost of electricity compared to a calculated base case. It was found that a 20% CO₂ reduction at current electricity demand could be achieved by implementing fuel balancing and switching 8 out of 23 coal‐fired boilers to natural gas. However, as demand increases, more coal‐fired boilers needed to be switched to natural gas as well as the building of new NGCC and NGCC+CCS for replacing the aging coal‐fired power plants. To achieve a 40% CO₂ reduction at 1.0% demand growth rate, four new plants (2 NGCC, 2 NGCC+CCS) as well as carbon capture processes needed to be built. If greater than 60% CO₂ reductions are required, NGCC, NGCC+CCS, and IGCC+CCS power plants needed to be put online in addition to carbon capture processes on coal‐fired power plants. The volatility of natural gas prices was found to have a significant impact on the optimal CO₂ mitigation strategy and on the cost of electricity generation. Increasing the natural gas prices resulted in early aggressive CO₂ mitigation strategies especially at higher growth rate demands. © 2009 American Institute of Chemical Engineers AIChE J, 2009     

Process characteristics investigation of simulated circulating fluidized bed combustion combined with coal pyrolysis

A poly-generation process of simulated circulating fluidized bed (CFB) combustion combined with coal pyrolysis was developed in a laboratory scale. Pyrolysis characteristics of three bituminous coals with high volatile contents were investigated in a fixed bed with capacity of 10 kg solid samples. The effects of initial temperature of solid heat carrier, pyrolysis holding time, blending (ash/coal) ratio and coal particle size on gas and tar yields were studied experimentally. The results indicate that the initial temperature of the heat carrier is the key factor that affects the gas and tar yield, and the gas composition. Most of the gas and the tar are released during the first few minutes of the pyrolysis holding time. For caking coal, the amount of char agglomerating on the pyrolyzer inner wall is reduced by enhancing the blending ratio. The experimental results may provide basic engineering data or information for the process design of CFB combustion combined with coal pyrolysis in a large scale.     

Product analysis of catalytic multi-stage hydropyrolysis of lignite

A lignite added with 0.2% MoS₂ as catalyst was pyrolyzed under H₂ using multi-stage heating method (MHyPy) which means holding a suitable time near the peak temperature. The product distribution and detailed analysis of products were performed. The results show that the tar yield increased to 63.9% during MHyPy compared with that of 51.8% in traditional hydropyrolysis (HyPy), while the gas yield decreased to a half. This suggests the effective utilization of hydrogen during MHyPy. The light aromatics in the tar from MHyPy increased remarkably 42, 37.8 and 115.4% for BTX, PCX and naphthalenes, respectively. Biphenyls were also observed in the tar from MHyPy, which indicated the effective hydrogenation occurs during catalytic MHyPy. The rich pore structure of the char from MHyPy hints its high reactivity in the subsequent conversion process such as gasification and combustion.     

Analysis of nitrogenous compounds in the effluent streams from a fluidized bed coal gasification reactor

A Texas lignite and a New Mexico subbituminous coal were gasified with steam and oxygen in a pilot-scale fluidized bed reactor at pressures from 770 kPa to 830 kPa, and temperatures form 795°C to 980°C. The make gas passed through a cyclone separator, and then a venturi scrubber in which condensable and water-soluble compounds were removed. The gasifier effluents (spent char, cyclone fines, tar, wastewater, and dry make gas) were analyzed for nitrogenous compounds.

For both coals, 6–12% of the nitrogen in the feed was retained in the spent char, with greater quantities being retained in the subbituminous coal char. Of the nitrogen volatilized from both coals, roughly 5% appeared in the tar, less than 0.2% appeared in the dry make gas as ammonia and NO_x, and the balance appeared in the wastewater as ammonia (60%), hydrolyzable nitrogenous compounds and possibly cyanate (10–15%), thiocyanate (1%), cyanide (0.5%), and other compounds (3–10%). The average concentration of NO_x in the dry gas was 7 ppm for lignite. No NO_x data for subbituminous coal were obtained. Reactor conditions (temperature, pressure, steam-to-carbon feed ratio) had no measurable effect on the production rates of nitrogenous compounds over the range of conditions investigated.     

褐煤与大豆荚共热解的产物特性分析

利用自制的低温热解装置研究褐煤与大豆荚共热解的产物特性,考察大豆荚掺混比和催化剂Fe₂O₃对热解产物特性的影响。通过FT-IR、GC-MS、SEM-EDX和UV-vis分析共热解产物的性质,并将半焦用于亚甲基蓝吸附实验。研究结果表明：掺混比30%时,共热解焦油的产率达到最大值11.98%,比煤焦油产率增加44.86%,与计算值的正偏差最大（0.8%）,同时,大豆荚的添加有促进焦油生成的协同作用。大豆荚的添加有利于共热解焦油中含氧杂环的断裂,使共热解焦油中直链烷烃增多,芳香族化合物减少,使重质组分转化为轻质组分,从而提高焦油品质;同时,大豆荚的添加使共热解半焦的含氧基团增加,微观形貌变粗糙。而Fe₂O₃的加入使共热解焦油中酚、醇类物质增加;加Fe₂O₃共热解半焦的褶皱更加明显。共热解半焦对亚甲基蓝的吸附率为33.62%,比煤半焦的吸附率提高8.84%,加Fe₂O₃共热解半焦的吸附率为55.57%,比共热解半焦提高65.29%。     

Effects of operation parameters on NO emission in an oxy-fired CFB combustor

Oxy-fuel Circulating Fluidized Bed (CFB) combustion technology, a very promising technology for CO₂ capture, combines many advantages of oxy-fuel and CFB technologies. Experiments were carried out in a 50 kW_th CFB facility to investigate how operation parameters influence the NO emission in O₂/CO₂ atmospheres. The simulated O₂/CO₂ atmospheres were used without recycling the flue gas. Results show that NO emission in 21% O₂/79% CO₂ atmosphere is lower than that in air atmosphere because of lower temperature and higher char and CO concentrations in the dense bed. Elevating O₂ concentration from 21% to 40% in O₂/CO₂ atmosphere enhances fuel-N conversion to NO. Increasing bed temperature or oxygen/fuel stoichiometric ratio brings higher NO emission in O₂/CO₂ atmosphere, which is consistent with the results in air-fired CFB combustion. As primary stream fraction increases, NO emission increases more rapidly in O₂/CO₂ atmosphere than that in air atmosphere. Stream staging is more efficient for controlling NO emission in oxy-CFB combustion than that in air combustion. Oxygen staging provides an efficient way to reduce NO emission in oxy-CFB combustion without influencing the hydrodynamic characteristic in the riser.     

Efficient drying and oxygen-containing functional groups characteristics of lignite during microwave irradiation process

To remove the high moisture of ZhaoTong lignite, the efficient drying characteristics and oxygen-containing functional groups changes in lignite during microwave irradiation process were highlighted in this study. As the microwave absorbers, lignite char and NaNO₃ were added to microwave drying of ZhaoTong lignite. The minimum chemical oxygen demand of waste water generated from microwave drying process of lignite was 99.89?mg?O₂?L^?1. The effects of microwave power, lignite mass, the weight ratio of lignite char to lignite and NaNO₃ content on the drying rate, and moisture diffusion coefficient of lignite were investigated during lignite microwave irradiation process. It was found that the drying rate and moisture diffusion coefficient of lignite increased with increasing microwave power, the weight ratio of lignite char to lignite and NaNO₃ content, but decreased with increasing lignite mass. Lignite char and NaNO₃ were mixed with lignite that can enhance the instantaneous surface temperature of lignite sample under microwave irradiation. Compared with addition of lignite char to lignite, the addition of NaNO₃ to lignite can decrease the unit electric power consumption of moisture evaporating. And the minimum unit electric power consumption of moisture evaporating was 9.44?Wh?g^?1. The FTIR technology was used to investigate the oxygen-containing functional groups changes in lignite during microwave drying process. The oxygen-containing functional groups of lignite were effectively removed with increasing microwave power.     

The effect of steam on pyrolysis and char reactions behavior during rice straw gasification

Steam gasification of biomass can generate hydrogen-rich, medium heating value gas. We investigated pyrolysis and char reaction behavior during biomass gasification in detail to clarify the effect of steam presence. Rice straw was gasified in a laboratory scale, batch-type gasification reactor. Time-series data for the yields and compositions of gas, tar and char were examined under inert and steam atmosphere at the temperature range of 873-1173 K. Obtained experimental results were categorized into those of pyrolysis stage and char reaction stage. At the pyrolysis stage, low H₂, CO and aromatic tar yields were observed under steam atmosphere while total tar yield increased by steam. This result can be interpreted as the dominant, but incomplete steam reforming reactions of primary tar under steam atmosphere. During the char reaction stage, only H₂ and CO₂ were detected, which were originated from carbonization of char and char gasification with steam (C + H₂O→CO + H₂). It implies the catalytic effect of char on the water-gas shift reaction. Acceleration of char carbonization by steam was implied by faster hydrogen loss from solid residue.     

Release of volatiles from the pyrolysis of a Victorian lignite at elevated pressures

A Loy Yang lignite sample was pyrolysed in a wire-mesh reactor at pressures from 1 to 61 bar. The char yield did not show considerable sensitivity to changes in pressure or heating rate and was mainly a function of temperature. However, the tar yield was sensitive to changes in pressure, holding time and heating rate. The tar yield at 1000 K s⁻¹ showed a minimum at around 6-11 bar. The tar yield at 1 K s⁻¹ increased slightly with increasing pressure from 1 to 20 bar. The UV-fluorescence spectroscopy of the tar samples indicated that the release of larger (three or more fused rings) aromatic ring systems was also greatly affected by increases in pressure. It is believed that increases in pressure have slowed down the bulk diffusion within meso- and macro-pores in the pyrolysing lignite/char particles. During the extended stay within the char particle, volatile precursors were thermally cracked to form mainly gaseous species as well as very small amounts of char. At very high pressures where the diffusion was very slow, the formation of light gases caused the pressure to build up within the particles, inducing the forced flow of volatile precursors out of the particles and leading to increased tar yield.     

Combustion and air emissions from co‐firing a wood biomass,a Canadian peat and a Canadian lignite coal in a bubbling fluidised bed combustor

The effects of particle size, fuel blending ratio, moisture content and excess air ratio on combustion efficiency and air emissions (CO₂, CO, SO₂ and NO_x) from the co‐combustion of white pine or peat with a Canadian lignite coal, were examined in a pilot‐scale bubbling fluidised bed combustor. Pelletising was important for the efficient combustion of wood due to its high volatile content. Co‐firing lignite and pine pellets gave a proportional reduction in SO₂ and NO_x emissions with blending ratio, while co‐firing of peat and lignite resulted in increased SO₂ emissions, but decreased NO_x emissions. Moisture promotes combustion but with increased CO emissions, and results in increased NO_x emissions, and decreased SO₂ emissions. High excess air decreased CO, but moderately increased SO₂ and NO_x emissions. © 2011 Canadian Society for Chemical Engineering     

胜利褐煤负载镍生物质气化催化剂实验研究

为获得较低温度下生物质焦油高效裂解气化的廉价型催化剂,基于褐煤富含含氧官能团特点,通过离子交换法将镍负载到胜利褐煤上制备褐煤负载镍催化剂(Ni/SLC)。研究了溶液p H值和炭化温度对催化剂物理化学性质的影响,得到Ni/SLC催化剂最佳制备条件,最后在两段式移动床石英反应器中将催化剂用于玉米芯挥发分的催化气化,研究了催化剂对生成气产量和碳平衡的影响。结果表明:p H值为11,炭化温度为650℃时制备的Ni/SLC比表面积最大达到266.3 m2/g,镍微晶尺寸较小为5.0 nm。催化气化实验表明:650℃下Ni/SLC催化剂具有高的焦油裂解活性,气体产量高达43.9 mmol/g,相当于无催化实验气体总产量的3.3倍;水蒸气气化可将热解焦油完全气化,气体产量为85.1 mmol/g,H2产量高达61.9 mmol/g,占气体总量的72.7%,说明Ni/SLC催化剂可作为生物质催化气化制氢的潜在催化剂。     

温度梯度与产物流动对先锋褐煤热解产物分布的影响

通过两段固定床反应器分离了煤热解和二次反应过程,模拟了传统外热式固定床反应器和外热式内构件固定床反应器内挥发性热解产物流动与固相反应颗粒间的相互作用,研究了不同温度的半焦对先锋褐煤热解产物分布和品质的影响。结果表明：当半焦的温度在500～900℃时,焦油发生剧烈的二次反应,热解气收率增加,焦油收率大幅下降,H/C同时大量降低且均低于空白样,油品质下降;在100～400℃半焦作用下,焦油发生轻微的二次反应,热解气收率略微增加,焦油收率缓慢下降,但H/C均高于空白样,油品质提升。该结果验证内构件外热式固定床反应器热解产生的焦油具有更高的收率及品质。     

Experimental trends of NO in circulating fluidized bed combustion

Experimental trends for the dependence of CO, NO and N₂O emissions on bed temperature and oxygen concentration in circulating fluidized bed combustion (CFB) are presented. The main focus is on the nitrogen emission formation in the lower furnace area. A test campaign including seven tests with a laboratory scale CFB test rig were carried out to produce appropriate data of the phenomena. These experiments show that NO emissions above the dense bed decrease with decreasing temperature or oxygen concentration. Instead, N₂O emissions increase when the bed temperature is decreased and decrease when the oxygen concentration is decreased. These trends can partly be explained by heterogeneous reactions between NO and char, since decrease in temperature or oxygen concentration increases the bed char inventory. However, oxygen and temperature also affect directly on NO emissions. Correlations for the CO, NO, N₂O, NH₃ and HCN concentrations at the exit of dense bed were developed. This type of correlations can, among other things, be applied as boundary conditions to the more sophisticated CFD models that are usually applied to modelling of diluted part of the furnace. CFD modelling of the dense bed area is complicated and accuracy is not sufficient, thus simplified experimental correlations can aid in the development of furnace design towards better emission performance.