水煤浆燃烧技术用于造纸黑液处理的研究

第8卷(2002)第1期燃烧科学与技术JOURNAL OF COMBUSTION SCIENCE AND TECHNOLOGYVol.8(2002)No.1Research on Application of Coal-Water Slurry Techniquesto Disposal of Wheat Straw Pulping black liquorYUAN Kun, Chen Li-fang. WU Cheng-kang(Institute of Mechanics, Chinese Academy of Sciences, Beijing 100080, China)Abstract: A pilot test on disposal of wheat straw pulping black liquor by Coal-Water Slurry (CWS) combustiontechnology as an alternative of traditional alkali recovery technique has been performed. Experimental study orcombustion feature of several kinds of Coal-Blackliquor Slurry(CBS was carried out in a 6. 5 t/h chain-grate boiler In the test flue gas, slag and dust were analyzed and the boiler's thermal efficiency was measured. The resultsdemonstrate that the co-combustion of CBS with granular coal increases the boiler's thermal efficiency and decreas-es poisonous emission. The successful combustion of CBS demonstrates its promise as a key technique in a novelmeasure of comprehensive disposal of wheat straw black liquor.Keywords coal-water slurry coal-blackliquor slurry wheat straw black liquor水煤浆燃烧技术用于造纸黑液处理的研究原鲲,陈丽芳,吴承康(中国科学院力学研究所,北京100080)摘要:对水煤浆燃烧技术用于造纸黑液处理进行了中试研究。多种不同组成的黑液煤浆在改造过的6.5t/的链条炉上进行了燃烧试验。对黑液燃烧产物如烟气、烟尘及灰渣进行了成分测试,对锅炉混烧水煤浆前后的效率进行了分析比较。结果表明,黑液煤浆与层燃煤混烧提高了锅炉效率并降低了污染。水煤浆燃烧技术在该领域的成功应用为造纸黑液的处理提供了新的思路。关键词:水煤浆;黑液煤浆;黑液中图分类号:X793文献标识码:A文章编号:1006-8740(2002)01-0013-04The impact of continuous development of the pa- of wheat straw black liquor utilizing CWS technologyper industry on the environment is getting serious in as well as the effects of secondary pollution are invesChina. The conventional alkali recovery system, how- tigated in this study CWS arose as an alternative ofever, works far less than satisfactorily in handling fuel oil in the crucial oil crisis in 1970s. During thewheat straw black liquor due to its inherent draw- past two decades, CWs technology has matured inbacks that lead to failure in the aspects of black terms of preparation, trans portation, atomization andliquor extraction, evaporation, combustion and causti- combustion. As a substituent of the corcization. But pollution caused by the paper industry posal of wheat straw black liquor, the Cws technolomust be solved urgentlgy possesses apparent advantages. DiroTo overcome the difficulties, viability of disposal of black liquor assisted by coal may naturally avoid燃烧科学与技术第8卷第1期some difficulties met in the conventional alkali recovery process1 Experimental多多The system diagram for CBs preparationage, transportation and combustion is shown insed to obtain多多black liquor with a concentration up to around 21%Subsequently the black liquor was diluted to certainFig 3 Diagram of CBS nozzleconcentrations demanded by the test. Coal was pulerized and mixed with black liquor as well as addiContrary to the conventional CWS which, typi-cally made up of about 70% coal 30 water and 1%0tive in a vibrating ball mill.additive, was prepared aiming at a maximum coal con5tent, CBS was prepared with a minimum coal contentin order to increase the disposal output of blackliblack liquor, much higher than that of water, increasing significantly with a higher solid concentrationadds to difficulties in preparation of cBs. The rheologic characteristics of typical CBS is shown in Fig. 4.1. extruder 2. ball mill 3. precombustorI boiler 5. air compressor 6. air blower 7. CBS tank8. pulp 9. fiber 10. coal Il additive 12. black liquor 13. CBSFig. 1 Diagram of systemThe self-stabilizing type CBS precombustor witheccentric jet is based on the method of flame sta biliza406080tion by use of nonsymmetrical jets. The structure ofthe Eccentric Jet Burner and the inner recirculationzone l, 2, induced by interaction between the primaryFig. 4 CBS rheologic characteristicsair & CBS jet and ash-blowing jet, is shown schematically in Fig. 2. Atomized CBS droplets get ignited in 2 Results and Discussionthe precombustor, forming a stable flame at the exit 2. 1 Boiler efficiencyof the precombustor and then burn out in the boilerThe degree to which CBS combustion is viablesynchronously with granular coal on the chain. a was determined in the test. The solute concentrationkind of low-pressure, multistage CWS nozzle (Fig 3) in black liquor varied between 3%20%,and thewas applied in the test [4]coal concentration in CBS varied between 35%51%the coal is shown in Tab. 1. Though CBS had a lowerheat value than that of cws with the same solid content, the result turned out that CBS meeting such criterion that heat value>9 MJ/kg and apparent vis2002年2月原鲲等:水煤浆燃烧技术用于造纸黑液处理15·of the precombustor. The efficiency of a typical chain- rate and simultaneous decrease of the feeding rate ofgrate boiler burning granular coal is relatively low. granular coal to maintain the stable boiler steam outHowever, the setting of the precombustor enabled the put, the NO content in the gas decreased due primar-CBS flame jet to flow toward the head of the chain to ily to the low-emission characteristics of combustionincrease the temperature there and thus help the igni. in the eccentriburner. But with further increasetion of granular coal ahead, favorable for enhance- of CBS feeding rate after that of granular coal havingment of the granular coal burn-out rate. On the other been decreased to a lower limit to maintain stableland, the high-temperature environment caused by combustion on the chain. NO, content increased as achain combustion compensated for the deficit of the result of the increase of overall fuel nitrogen. The lowboiler inner space needed for burnout of CBs. The NO emssion characteristics of the eccentric jet burnsynergistic interaction between granular coal and CBS er originate from its particular designation of reactionworked effectively. With proper operation, 1 ton of zones responsible for both efficient combustion andCBS with a heat value of 10. 8 MJ/kg could supplant low NO, emission. Certain study shows that 3,in the0.8 t of coal with a heat value of 20. 2 MJ/kg to upper part of the upstream portion of the combustormaintain the stable boiler steam output. The boiler is a zone of high temperature and vigorous combusefficiency increased from 63. 3% to 66.4%tion,whereas in the upper part of the downstreamportion is a reducing zone where NO formed in comTab. I Proximate and ultimate analysis of coalbustion can be converted to NMad/%Aa/%vda /%.Sat/%(M·kCaat/%pdu/%Nda//%oas/%6.286.8931.790.4220.280.593.641.541.242. 2 SO, and H, S emission characteristics of CBSWith the increase of solid content of wheat strawblack liquor in CBS, emisson of SO, measured at therear port of the boiler decreased drastically, as shownin Fig. 5, due to its neutralization reaction with ionCHS mass feeding rele/(kg.h)ized alkali which originated from the solid content ofblack liquor. The same reason caused the H2S contentFig 6 NO emission characteristicsin the gas to become negligible.2. 4 Temperature distribution in the precombustorFig. 7 presents the positions where thermal couples were mounted. Thermal couples were placed inprotecting cannulas and then inserted into holes A, Brespectively. When cannulas move horizontally alongthe hole, the temperature distributions on the track of150.20025presented in Fig 8. The R axis denotes the distancebetween the measured point and the central axis ofFig. 5 SO, emission characteristicsthe precombustor. The temperature on the central ayis of the combustor is relatively low due to the evapo-2. 3 NO, emission characteristics of the eccentric jet ration of the CBS droplet in the central jet. The tem燃烧科学与技术第8卷第1期bustion has taken place. But even the highestmeasured value is about 150 C less than that of com-bustion of pulverized coal at the same point l2J withduction of thermal nitrogen3 Conclusi6.5 t/h chain-grate boiler can enhance the overallcombustion intensity and thus causes increase of boilCannula2) The emissions of both nitrogen oxides andThermalsulfur oxides conform to the environmental regula3)Successful combustion of CBS may introducea novel viable and economic measure to the disposalof wheat straw pulping black liquor.ReferencesFig. 7 Placement of thermal couplesl200LI Wu Chengkang, Chen Lifang, Li Jun et al. The use of nonsymmetrical jets for the stabilization of low grade coal flames[R. 22nd一Bosium (Int)on Combustion. USAtal study on CWS combustion in a industrial boiler designed spe-cially for burning CWS[R]. 3rd Asian-Pacific Symposium (Int)eration of ne400in nonsymmetrical coal precombustor [D]. Beijing Institute ofMechanics, Chinese academy of Science, 1991[4] Yuan Kun Chen Lifang, Wu Chengkang. A study on the charac-14th Annual Pittsburgh Coal Conference (Int ) on Clean CoalFig8 Temperature distribution in the precombustorTechnology and Coal Utilization, Taiyuan: 1997. 23-27