Integrated Process Of Coal Pyrolysis With Methane Activation By Cold Plasma

The main purpose of this dissertation was to explore a new process which can effectively activate methane under relatively low temperature and match the optimal temperature range during coal pyrolysis for high tar yield. The main research works and results are summarized as follows:(1) Several kinds of dielectric barrier discharge (DBD) reactors were investigated for methane activation, and the optimum reactor with one dielectric layer located on the low-voltage electrode side was determined. The structural parameters of the reactor and reaction conditions were optimized to ensure that the discharge can be operated under high temperature. The results for CH4/CO2conversion in the designed DBD reactor show that increasing the gas flow rate, CO2content in the feed gas or adding Ar/H2to the feed gas can promote the stability of the discharge under high temperature; increasing the input power can remarkably increase the CH4and CO2conversion. However, increasing the temperature only has weak effect on increasing the CH4and CO2conversion and leads to the instability of the discharge. CH4molecule in DBD plasma are mainly dissociated to H-and-CH3.(2) The effects of reaction conditions on the product yields in the integrated process of Shenmu (SM) subbituminous coal and Huolinhe (HLH) lignite pyrolysis with CH4/CO2activation by DBD plasma were investigated. The results showed that when50%H2was added to CH4/CO2(1:1) to form a mixed gas (MG), the stability of the discharge could be promoted and a high tar yield could be achieved. The effect of different atmospheres on increasing the tar yield is in the following order:MG-P> CH4-P≈CH4/H2-P≈CO2/H2-P> H2-P> H2> N2, especially at low temperature range (400～500℃). Increasing the gas flow rate is favorable for the discharge stability and can improve the coal conversion, but the water yield increases, too, the tar yield of SM coal increases while that of HLH lignite decreases. Increasing the pyrolysis time and the input power can increase the tar yield on condition that the discharge is stable.(3) Ni/SiO2catalyst was prepared by exposing the precursor directly in H2plasma, and it shows better catalytic activity and stability compared with Ni/SiO2prepared by normal method in CO2reforming methane (CRM). The catalytic and plasma-catalytic performances of Ni/SiO2and Ni/Al2O3prepared by H2plasma were investigated and the results indicated that CH4and CO2conversion were improved in plasma-catalytic process compared with catalytic process on Ni/Al2O3, while only CO2conversion was improved in plasma-catalytic process on Ni/SiO2. The effect of reaction conditions on product yield in the integrated process of coal pyrolysis with CRM by catalyst (ICCC) or plasma-catalyst (ICCP) was investigated. The results showed that Ni/Al2O3catalyst and high reaction temperature, or long reaction time are beneficial to increase the tar yield in the ICCC, while Ni/SiO2catalyst, low reaction temperature, short reaction time, high H2content in the feed gas and high input power are good for the ICCP. The Ni loading amount has weak effect on product yield of both processes. The highest tar yield is25.5%and23.7%for the ICCC and ICCP, respectively, which is higher than the tar yield under MG plasma.(4) The FT-IR analyses of chars under different atmospheres indicate that the interaction between coal and plasma does exist and it is different under different atmospheres. The1H NMR analyses of tar show that the aromatic hydrogen content decreases while the aliphatic hydrogen content increases under plasma atmospheres except that under H2plasma which has the reversed change.13C NMR analyses show that the content of the saturated aliphatic C to three H bond increases under CH4/H2-P, CO2/H2-P and MG-P atmosphere, the content of the aromatic C which bond to-OH increases under CO2/H2-P and MG-P atmosphere, and the aromaticity decreases under plasma atmospheres. The main components identified by GC-MS and quantified by GC in the volatile fraction (280℃) of tar are phenol, naphthalene and their Ci-C3alkyl-substitute homologues, in which C1-C2substitutes are the main forms. All these analyses suggest that the abundant H·,·CHX,·OH radicals exist in plasma involved in tar formation during coal pyrolysis and have effect on upgrading the coal tar.(5) Analysis showed that the consumption of the effective discharge energy is about5.1Wh for1g of tar increment, which still need to be improved. Radicals like H, CH and C+are detected in plasma by Optical Emission Spectrum, and the rotational temperature and vibration temperature were analogue calculated according to the spectra. Isotope analysis of the tar formed in the integrated process show that more than one deuterium atom exists in the main component of tar, such as phenol, cresol and naphthalene, which indicates that the radicals decomposed from CD4(CH4) by plasma combined with those generated from coal in the integrated process.