Preparation and Performance Study on Lignite Briquette Coke
In order to promote the energy utilization efficiency and reduce the environmental pollution in the process of lignite direct utilization, lignite briquette and its coke were prepared. The effects of pyrolysis temperature and holding time on the briquette coke were investigated through the pyrolysis experiments of lignite briquette. The results showed that the changes of yield, volatile, ash, fixed carbon, elemental composition and oxygen functional groups content of briquette coke were dependent on increasing pyrolysis temperature and holding time. The mechanical properties of the briquette coke were assessed by means of their cold strength, compressive strength, thermal strength, immersion strength, falling strength, and so on. The fine quality briquette coke prepared from lignite briquette with high strength, heat stability more than 96%, low calorific value on dry basis higher than 6600Cal/g, and its volatile content could reach no more than 3%.
Study on the comparison of the pyrolysis gas release of lignite and its briquette
In this experiment, lignite was refined and processed through binderless briquette preparation process from low-rank coal and became briquette. Then, lignite and its briquette were pyrolysed as materials to compare the nature of their pyrolysis. In this study, the experiment was carried out through a lab tube furnace, at a heating rate of 10 °C/min, and the gas was analyzed and compared, which was collected at different temperatures. The results show that: in the pyrolysis temperature of 550∼850 °C, the semi-coke yield of briquette is 2%∼6% higher than lignite, the tar yield of briquette is 2%∼3% higher than lignite and the gas yield of briquette is 4%∼9% less than lignite. The time required for complete release of the briquette is about 20 min less than lignite. The components in the pyrolysis gas of lignite and its briquette are the same, and their variation with the pyrolysis temperature is similar.
ASSESSING AGE AND GENDER DIFFERENCES IN PERCEIVED RISK AND FEAR OF CRIME
Much of the research on fear of crime indicates that women and older persons are highly afraid of crime. These findings, especially older persons' fear of crime, are widely communicated in the scientific and popular media. This study examines age and gender differences in perceived risk and fear of crime. The data are from telephone interviews of 320 randomly selected residents in a southeastern metropolitan area of the United States. The relationships of age and gender to fear of crime are compared using a National Crime Survey (NCS) measure of fear of crime and 11 alternative indicators of fear of specific offenses. Women reported signifcantly greater perceived risk and fear of crime than men regardless of how fear of crime was measured and older adults reported the greatest fear of crime when the NCS measure was used. but not when the alternative individual measures of fear of crime were used. A LISREL model with latent constructs for fear of personal crime and fear of property crime also indicates that older adults do not have higher levels of fear of crime. In short, the extent of fear in the everyday lives of most older persons has been overestimated in many previous studies because of measurement problems.