Shendong Coal Pyrolysis And Co-pyrolysis With Its Direct Liquefaction Residue Through Solid Heat Carrier

Low-rank coal contains high volatiles, for which pyrolysis is an effectiveway to get oil under mild conditions. Conventional technology of coal pyrolysishas a low efficiency of upgrading. The yield of tar is low and the amount ofheavy component in tar is high. Pyrolysis through solid heat carrier canaccelerate the heating rate and realize fast pyrolysis, which can increase theyield of tar and improve the efficiency of upgrading and heat utilization. Exceptfor the material of heat storage and transfer, the solid heat carrier can also havesome catalytic activity to regulate the quality of oil and gas. Besides, coalpyrolysis for oil is limited by the lack of hydrogen, so it can improve the taryield by introducing hydrogen donor to interact with coal pyrolysis reactions. Inthis paper, Shendong coal pyrolysis with solid heat carrier was conducted in afixed bed reactor to investigate the effect of heat carrier on pyrolysis products,including three kinds of minerals, two kinds of industrial wastes and four kindsof chars. And, the recycling experiments of olivine and SDC were conducted tostudy their performance during recycling. Besides, two kinds of catalytic heatcarrier were prepared to activate pyrolysis atmosphere. In addition, theliquefaction residue and rice straw were chosen to conduct co-pyrolysis with Shendong coal, and the effect of heat carrier on co-pyrolysis products was alsoinvestigated. The main conclusions of this paper are obtained as follows:1. Pyrolysis temperature has a significant effect on the pyrolysis products.When the pyrolysis temperature changed from550to700°C, the tar yieldincreased and reached the maximum at650°C, then decreased. Besides, thepyrolysis gas yield increased gradually and the pyrolysis water yield changedlittle. In addition, the tar yield changed little with changing of coal particle size.Above all, the most appropriate reaction conditions were650°C and1.18-2.00mm.2. Compared with quartz sand, solid heat carriers, including olivine,ceramicite, FCC, red mud and char, have catalytic cracking for conversion heavyfractions to light ones, leading to tar yield decreased, pyrolysis gas and wateryield, and the n-hexane soluble content in tar increased. Besides, the catalyticcracking activity of exotic heat carriers followed the order: red mud> FCC>olivine> ceramicite. Moreover, the catalytic cracking activity of four charsfollowed the order: SMC1> SMC2> SDC> JCC.3. The catalytic cracking effects of solid heat carrier was closely relative totheir physical and chemical properties, including the specific surface area, porestructure, mineral species and content and acidity. The larger specific surfacearea and more developed pore structure is, the stronger the cracking effect is.Besides, the more active metal component is, the stronger the cracking effect is.For the char heat carrier, the minerals are the main active component for tar decomposition.4. Calcination may change the properties of heat carrier. The activity ofolivine and FCC changed little after calcination, while the activity of red mudand ceramicite changed much. The properties of olivine were very stable duringthe recycling, so the pyrolysis products distribution and composition changedlittle. Although SD char heat carrier and char product would become the mixtureof fresh and used char, the pyrolysis products distribution and composition wererelatively stable. The internal heating way through solid heat carrier has a fasterheating rate and can accelerate the speed of volatiles formation and evolution, soit reduced the secondary reactions of volatile, improving the tar yield anddecreasing the pyrolysis gas and water yield. It shortened the time of volatilescontacting with heat carrier at the same time, resulting in the cracking effect ofheat carrier weakened.5. The solid heat carrier impregnated with active metal component hassome activation effect on the pyrolysis atmosphere. Compared with olivine,Co-olivine and Co/Mo-olivine in synthesis gas atmosphere increased the taryield and decreased pyrolysis gas yield, but the effect was not ideal. Thecatalytic activity of heat carrier might be not good enough to provide hydrogeneffectively and the rate of pyrolysis reaction and hydrogen dissociation did notmatch with each other. Besides, pyrolysis volatiles might poison the active metal.Compared with olivine, Ni-olivine did not increase the tar yield in CH4/CO2atmosphere as expected. Although Ni-olivine had good methane reforming activity, it had some catalytic effect on tar reforming, so that it did not realizeexpected effect.6. Co-pyrolysis of SD and DLR showed synergistic effect. The tar yieldincreased, but the quality of tar and gasification reactivity of char decreased. Thesynergistic effect mainly came from the interactions of volatiles. Co-pyrolysis ofSD and RS showed no synergistic effect, which mainly resulted from thedifference of pyrolysis characteristics between them. The overlap region of RSand SD pyrolysis was very narrow.7. Solid heat carrier could help to improve the quality of co-pyrolysis tarthrough cracking effect. But due to the adhesive effect of DLR, the crackingeffect of co-pyrolysis char and the gasification reactivity of char productdeclined during the recycling of co-char as heat carrier. The internal heating waythrough solid heat carrier would decrease the synergistic effect between SD andDLR.