Pyrolysis of Shenmu coal was performed in fixed-bed reactors indirectly heated by reducing operating pressure and mounting internals in the reactor to explore their synergetic effects on coal pyrolysis. Mounting internals particularly designed greatly improved the heat transfer inside coal bed and raised the yield of tar production.Reducing pressure further facilitated the production of tar through its suppression of secondary reactions occurring in the reactor. The absolute increase in tar yield reached 3.33 wt% in comparison with the pyrolysis in the reactor without internals under atmospheric pressure. The obtained tar yield in the reactor with internals under reduced pressure was even higher than the yield of Gray–King assay. Through experiments in a laboratory fixed bed reactor, it was also clarified that the effect of reducing pressure is related to volatile release rate in pyrolysis. It did not obviously vary tar yield at pyrolysis temperatures below 600 ℃, while the effect was evident at 650 and 700 ℃ but became limited again above 800 ℃. Under reduced pressure the produced tar contained more aliphatics and phenols but less aromatics.
Thermochemical conversion of fuels via pyrolysis/carbonization,cracking,gasification and combustion has to involve a number of individual reactions called attribution reactions to form an intercorrelated reaction network for any conversion process.By separating one or some attribution reactions from the others to decouple their interactions existing in the reaction network,the so-called reaction decoupling enables a better understanding of the complex thermal conversion process and further the optimization of the conditions for attribution reactions as well as the entire conversion process to realize advanced performances.The dual bed conversion and two-stage conversion are the two representative types of fuel conversion technologies developed in recent years based on reaction decoupling.Many technical advantages have been proven for such decoupling fuel conversion technologies,such as poly-generation of products,low-cost production of high-grade products,elimination of undesirable products or pollutants,easy operation and control,and so on.The treated fuels with decoupling conversion technologies mainly include solid biomass and coal,as well as liquid petroleum oil.This paper is devoted to reiteration of the reaction decoupling concept and further to reviewing the research,developments and successful applications of several decoupling fuel conversion technologies of two such types by using fluidized bed as their major reactors.
Rapid pyrolysis of oil shale coupled with in-situ upgrading of pyrolysis volatiles over oil shale char was studied in a laboratory two-stage fluidized bed(TSFB) to clarify the shale oil yield and quality and their variations with operating conditions. Rapid pyrolysis of oil shale in fluidized bed(FB) obtained shale oil yield higher than the Fischer Assay oil yield at temperatures of 500-600 ℃. The highest yield was 12.7 wt% at 500 ℃ and was about1.3 times of the Fischer Assay oil yield. The heavy fraction(boiling point > 350 ℃) in shale oil at all temperatures from rapid pyrolysis was above 50%. Adding an upper FB of secondary cracking over oil shale char caused the loss of shale oil but improved its quality. Heavy fraction yield decreased significantly and almost disappeared at temperatures above 550 ℃, while the corresponding light fraction(boiling point < 350 ℃) yield dramatically increased. In terms of achieving high light fraction yield, the optimal pyrolysis and also secondary cracking temperatures in TSFB were 600 ℃, at which the shale oil yield decreased by 17.74% but its light fraction yield of 7.07 wt% increased by 86.11% in comparison with FB pyrolysis. The light fraction yield was higher than that of Fischer Assay at all cases in TSFB. Thus, a rapid pyrolysis of oil shale combined with volatile upgrading was important for producing high-quality shale oil with high yield as well.
The present work investigated the synergetic effect of pyrolysis-derived char,tar and gas(py-gas)on NO reduction,which may occur in circulating fluidized-bed decoupling combustion(CFBDC)system treating N-rich fuel.Experiments were carried out in a lab-scale drop-tube reactor for NO reduction by some binary mixtures of reagents including char/py-gas,tar/py-gas and tar/char.At a specified total mass rate of0.15 g·min^-1 for NO-reduction reagent,the char/py-gas(binary reagent)enabled the best synergetic NO reduction in comparison with the others.There existed effective interactions between char and some species in py-gas(i.e.,H2,CxHy)during NO reduction by pyrolysis products,meanwhile the tar/py-gas or tar/char mixture only caused a positive effect when tar proportion was necessarily lowered to about 26%.On the other hand,the synergetic effects were not improved for all tested binary reagents by increasing the reaction temperature and residence time.
This study aims to compare the pyrolysis behavior of Huadian oil shale in two infrared heating fixed bed reactors with different directions of infrared beam.Our previous work has shown that fast pyrolysis of oil shale conducted in the shallow fixed bed infrared heating reactor(co-current)presented the massive secondary reactions,which lowered the shale oil production(Siramard et al.,2017).Conversely,the cross-current infrared achieved shale oil yields higher than the Fischer Assay oil yield(13.07 wt%of dry basis),such as 117.7%of the Fischer Assay yield at our realized highest heating rate of 7℃/s under a specified pyrolysis temperature of 550℃.The shale oil from the cross-current infrared heating reactor was obviously heavier than the oil obtained from the cocurrent heating reactor.Thus,the infrared cross heating evidently suppressed the secondary reactions toward volatile.Our realized shale oil yield could reach 13.67 wt%or 122.5%of the Fischer Assay yield under reducing pyrolysis pressure of 0.6 atm,indicating that lower pressure is also beneficial to the release of volatile and reduction of the secondary cracking reactions.This work shows essentially that the infrared cross heating provides an effective merge of the advantages from quick heating and minimization of secondary cracking reactions to enable the shale oil yields being higher than the Fischer Assay oil yield.
This study investigated the characteristics of pyrolysis for waste tire particles in the newly developed fixed-bed reactor with internals that are a central gas collection channel mounted inside reactor.And a few metallic plates vertically welded on the internal wall of the reactors and extending to the region closing their central gas collection pipe walls.Experiments were conducted in two laboratory fixed bed reactors with or without the internals.The results shown that employing internals produced more light oil at externally heating temperatures above 700℃due to the inhibited secondary reactions in the reactor.The oil from the reactor with internals contained more aliphatic hydrocarbons and fewer aromatic hydrocarbons,leading to its higher H/C atomic ratios as for crude petroleum oil.The char yield was relatively stable for two beds and showed the higher heating values(HHVs)of about 23 MJ/kg.The gaseous product of pyrolysis mainly consisted of H2 and CH4,but the use of internals led to less pyrolysis gas through its promotion of oil production.
