Pyrolysis Of Oil Shale By Solid Heat Carrier In Moving Bed With Internals

Oil shale is an unconventional solid fossil fuel with a vast resource,and the potential shale oil production is predicted to be far more than the proved petroleum reserves in China.Pyrolysis can extract the inherent oil and gas resources containing in oil shale,which is the core technology for high-value utilization of oil shale resource.However,there is still no commercial technology for pyrolyzing small-size oil shale in China,causing about 20?40%of mined oil shale to be abandoned.Aims at solving the problems for pyrolyzing small-size oil shale via solid heat carrier including low oil yield,high contents of dust and heavy components,this study proposes a new technology for pyrolyzing small-size oil shale using solid heat carrier in moving bed reactor enhanced with internals.This work of thesis focused on understanding of pyrolysis mechanism,clarification of technological fundamentals and demonstration of the proposed technology.The characteristics of oil shale pyrolysis was investigated to clarify the oil generation process and further propose a mechanism model for kerogen pyrolysis.Then,oil shale pyrolysis in fixed-bed with internals and dual-stage fixed-bed reactor was carried out to demonstrate the working mechanism of internals and the secondary reactions occurring to oil vapor when it crossed a layer of high-temperature shale ash.Furthermore,a 10 kg/h moving bed reactor with internals using solid heat carrier was designed and built to verify a new pyrolysis technology for small-size oil shale with the aim of producing shale oil at both high yield and high quality.The result well presented a good prospective of the newly proposed pyrolysis reactor and process.1.Carbon chemical structure transformation in oil shale pyrolysis.The effect of pyrolysis temperature on the distribution and property of products and the accompanying carbon chemical structure transformation were investigated.Thermal decomposition of organic matters was in 350?550 ?,and that of minerals mainly was in 630?760 ?.Oil was mostly generated in 350?460?,while gas and water were the main product at pyrolysis temperatures above 460?.The generated oil in the initial pyrolysis stage was primarily gasoline and diesel,while VGO and heavy oil fractions were largely produced subsequently.At temperature over 460?,the light oil content in shale oil increased due to the conversion of heavy components.Most of the aliphatic portion in kerogen decomposed into shale oil and gas,while the aromatic carbons were considerably inert to thermal process.On this basis,an updated mechanism model was proposed to show that the aliphatic carbon moieties largely produce oil and gas,while aromatic carbon portion is apt to be converted directly into carbon residue(char)in conventional pyrolysis like Fischer Assay.The aromatic carbon in oil product was primarily from converting aliphatic carbon through aromatization,and the proportion of this aromatization as a kind of secondary reactions was determined by the structure nature of aliphatics.Overall,we clarified that primary pyrolysis determines the potentially maximal oil yield and composition according to the decomposition degree of original kerogen,while the subsequent secondary reactions to volatiles determine the yield and quality of final oil product.This mechanism offers the idea that an optimal reactor design has to ensure both yield and quality of pyrolysis oil,which requires essentially a quick decomposition of organic matters in feedstock and in turn the product-orienting secondary reactions towards the desired pyrolysis products.2.Working mechanism of internals and effect of shale ash on pyrolysis.Oil shale pyrolysis was conducted in a fixed-bed reactor with internals and a laboratory dual-stage fixed-bed reactor to investigate the effect of internals and shale ash on final product distribution and quality.The examined factors included the temperature of shale ash(i.e.,cracking temperature),residence time of pyrolysis volatile and oxides species in shale ash.The internals worked to direct pyrolysis volatiles to flow laterally across particle bed from high-temperature zone to low-temperatture zone in the reactor,which much improved the oil yield by reducing secondary decomposition of volatiles.The increase in blending ratio of ash to oil shale caused the loss in oil yield but increased the gas yield,due to the increased secondary reactions and cracking of oil vapor.The reduced shale oil was mainly cracked into C1?C3 hydrocarbon gases with little coke produced.Shale ash exhibited obvious catalytic effect on secondary cracking and upgrading of oil vapor by reducing the boiling point of shale oil product.It facilitated the conversion of heavy components into light oil and gas to improve the light oil content and yield.The shale ash bed temperature was the key factor affecting the product distribution,and the optimal temperature for secondary cracking and upgrading was found to be 550?.At 550?,prolonging the pyrolysis volatile residence time in shale ash bed from 0 to 10 s decreased the oil yield by 31.0%but increased the fraction of gasoline and diesel in shale oil product by 46.4%.The heavy components with high boiling point was easier to be absorbed and further cracked over shale ash,and heavy oil was completely converted at volatile residence time above 8 s.The catalytic activity of shale ash for cracking shale oil was shown to be closely dependent on the oxides in ash.CaO and Na2O were conducive to promote the conversion of pyrolysis volatiles towards oil product and tended to inhibit coking of heavy components and formation of coke,showing actually the action of catalytic cracking and reforming of shale oil.SiO2 and Al2O3 in ash didn't show obvious effect on cracking and upgrading of oil vapor,but they certainly increased the light oil content and yield.While Fe2O3 showed good activity in cracking shale oil and reducing oil yield by significantly promoting polymerization or condensation of heavy components to form coke on the surface of shale ash,which had H/C molar ratio of only 0.3.3.Oil shale pyrolysis by solid heat carrier in moving bed with internals.An innovative moving bed with internals(MBI)for pyrolyzing small-size(0-13 mm)oil shale by solid heat carrier was designed.The pyrolysis was tested by varying the temperature of solid heat carrier,thickness of particle bed,blending ratio of ash to oil shale,moisture content of oil shale,etc..The internals in moving bed reactor regulates pyrolysis volatile to flow laterally across the particle bed in the reactor,endowing the particle bed to realize in-bed dust removal via filtering and in-situ oil upgrading through ash-involved secondary reactions.The obtained shale oil yield was close to 90%of Fischer Assay yield in the new reactor.Of the produced oil,over 70 wt.%was gasoline and diesel and its dust content was only about 0.1 wt.%,with the simultaneous production of pyrolysis gas having higher heating value above 20 MJ/Nm3.At pyrolysis temperature of 460?530?,the shale oil yield was over 80%of Fischer Assay yield.The shale oil yield decreased but light oil content increased with increasing the particle bed thickness,as a result from the increased shale oil cracking over shale ash in the prolonged residence time of volatile product inside the particle bed.Pyrolysis of oil shale with the moisture content of 10 wt.%caused obvious increase in shale oil yield,clarifying a kind of protective effect of steam atmosphere on pyrolysis product by its reducing secondary reactions and passivating shale ash for catalyzing cracking and coking of oil vapor.Comparing with ceramic balls,shale ash as the heat carrier presented the favorable catalytic effect on cracking and upgrading of shale oil,and enabled better dust removal.Generally,the dust carried with gaseous product in the reactor without internals was in sizes below 30 ?m,further demonstrating that oil shale pyrolysis using shale ash heat carrier in MBI process has the obvious advantages of in-situ shale oil upgrading and in-bed dust removal to allow the better pyrolysis performance.The increases in yield of hydrocarbon gases and related molar ratios(as alkenes to alkanes)clarified that the oil vapor cracking,rather than coking,was the main secondary reactions at the pyrolysis temperature over 495 ?.Cracking increased the carbon and nitrogen contents of oil but decreased its hydrogen and oxygen contents to obviously decrease the atomic H/C and O/C ratios of shale oil with raising temperature.Aromaticity of shale oil and the absolute yield of aromatic carbons in oil considerably increased due to selective concentration of aromatics and aromatization of aliphatics.Via oil vapor cracking,a part of long-chain aliphatics was transformed into short-chain alkanes,alkenes and gas species to increase the low-carbon hydrocarbons.The formation of alkene gas species was much higher than of alkane gases during cracking of oil vapor.Consequently,the study in this thesis demonstrates that the newly devised pyrolysis technology by solid heat carrier in moving bed reactor with internals is highly suitable for processing fine oil shale in sizes of 0?13 mm.It makes possible to produce shale oil both in high yield and high quality,and to generate pyrolysis gas with high heating value.These show the good prospective of the new technology for industrial application.