| Thermal upgrading process is the most effective technology that removes moisture and certain pollutants from lower-rank coals such as sub-bituminous and lignite (brown) coals and in order to raise their calorific values. The goals of lignite upgrading technologies are to increase efficiency and reduce emissions before coal utilization. Therefore, in this thesis, the changes of oxygen-containing functional group contents with thermal upgrading of lignite were studied in detail, the influence of upgrading temperature on the water quality including composition and distribution of organic matter in lignite-derived water was investigated and the effects of upgrading process on coal briquette were also studied.The main works and results of this research are as follows:1) Two Chinese coals, Huolinhe(HLH) lignite and Xiaolongtan(XLT) lignite, were used to investigate the lignite upgrading reaction within the ranges of100℃-400℃℃. The results showed that the reduction of its water proportion of upgraded coal was no more than50%when the temperature was100℃,and down to below5%when the temperature exceeded150℃. The volatile matter in the upgraded coals was decrease with an increase of upgrading temperature. The volatile matter in the upgraded HLH and XLT lignites was reduced by10.69% and15.60%respectively compared with the raw lignites. By calculating the average number of aromatic rings, we know that large aromatic molecules of lignites were changed considerably when upgrading temperature exceeded400℃for HLH lignites and350℃for XLT lignites.2) FI-IR and chemical analysis were used to investigate the changes of oxygen-containing groups with different upgrading temperatures. The results indicated that network systems like Coal-OH-O-Coal were found in raw XLT lignite which are analogous to peat. The Coal-OH-O-Coal network systems were destroyed easily while upgrading temperature went over250℃. Besides, the oxygen-functional groups contents of both upgraded HLH and XLT lignites decreased obviously, especially carboxyl groups, at400℃, the removal rate of carboxyl groups had reached90%. The removal rate of phenolic hydroxyl groups was commensurate with that of oxygen element. In addition, when the upgrading temperature was more than400℃,it had obvious effects on alkane chain, ether oxygen bond and CH2bridged bond.3) Lignite-derived water from lignite upgrading reaction was analyzed with COD, NH3-N, phenols etc. The experimental results showed that the water was colorless and transparent when the upgrading temperature was not more than200℃. 4) In order to better understand the composition and distribution of organic matter in lignite-derived water, GC-MS was used to analyze the organic matter in water. The results showed that the proportion of organic matter in water went up with the increase of the upgrading temperature. Furthermore the composition of organic matter was very complex, including aliphatic hydrocarbon, aromatic hydrocarbon, oxygen containing compounds and heterocyclic compounds. And phenols, alcohols, aldehydes, ketones, acids, esters and other complex compounds in oxygen containing compounds were detected as well. Phenols were found as the highest amount of organic matter. Phenols content in water was increased as the upgrading temperature increased, and noticeably increased after300℃. The content of simple phenols accounts for approximately80%of total phenols. The content of o-cresol, m-cresol, p-cresol was m-cresol>o-cresol>p-cresol, out of accord with cresol dealkylation activity. The yield of phenol in water went up with the increase of upgrading temperature, however, the content of phenol in phenols did not show the same tendency. By analyzing the phenols composition and distribution in lignite-derived water, it was concluded that it was due to inadequte dealkylation of cresol and decomposition of reactive intermediate.5) Aspen Plus software was applied in this study, NRTL equation taken as property, and extraction model established, in order to absorb phenol capability in extraction process. Model parameter of NRTL was corrected by detailed data from phase balance experiment to improve the accuracy of simulation. The sensitivity was analyzed in terms of phase ratio, temperature, number of plates and plate efficiency. The results indicated that at the temperature of20℃, with the phase ratio of3:1and number of plates of3, phenol concentration of final water dropped enough to meet the requirement of biochemical treatment.6) Lignite briquetting experiment was conducted in a hydraulic press. Compaction curves of the lignites show that the whole compaction process can be divided into stages of densification, the particle re-arrangement stage, the plastic deformation stage and the whole deformation stage. Rosin-Rammler-Bennet equation (RRB) was used to describe particle size distribution. Uniformity index n and characteristic feature size De were also calculated. In addition, characterization of particle group, briquetting pressure, water content and upgraded coal content were the major factors that affect briquette strength. |
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