精细优化回路设计以最大限度地抑制黄铁矿和加强煤炭市场化 毕业论文外文翻译.doc

精细优化回路设计以最大限度地抑制黄铁矿和加强煤炭市场化p. bethell (1)* , b. watters (1) , e. wolfe (1)(1) taggart global, llc, canonsburg, pa, usa, pb (* corresponding author)摘 要煤炭含硫量是焦煤和动力煤市场流通的重要属性。在这两个市场中，含硫量的降低大大增强了煤炭的价值。美国阿巴拉契亚北部地区某些潜在的炼焦煤硫含量通常在边际(1.1 - 1.5%)。在许多情况下大部分硫以黄铁矿的形式富集在细粒级中（1毫米x0.045毫米）。传统的粉煤加工流程(螺旋,浮选)往往会产生高硫产品。黄铁矿在浮选系统中通常可浮性良好，生产出高硫精矿泡沫。能够以较低的密度在1mm0.25 mm的粒级大幅降低硫含量。通过分级和螺旋分选相结合除去高密度黄铁矿，使低硫泡沫精矿得以产生。北阿巴拉契亚最近受委任的使用这种技术的工厂对回路设计和工厂业绩进行了讨论。同样，在美国伊利诺斯州盆地许多工厂，黄铁矿在粉煤中的含量已经排除了浮选的使用会引起显著产量损失。通过整合类似于先分选出黄铁矿再采用浮选处理去硫粉煤的方法，可生产出能为低硫市场所接受的精矿。再者，浮选产率是通过取出会流到工厂的精煤流中的富集黄铁矿，再进行精细旋流并浮选减少的含硫旋流物以除去这些黄铁矿来保证的。关键词：降硫，洗精煤，溢流，浮选1.北阿巴拉契亚山脉工厂1.1. 背景2011年，在北阿巴拉契亚的一处房产，一个新工厂在建设的早期阶段开发了一个工艺流程。该工艺是针对基坦宁下部煤层未来长壁开采煤矿的精煤设计的。基坦宁下部煤层,有大约32%的干燥挥发性物质,被认为是一个“高挥发性“炼焦煤，在市场价值上具有超过动力煤的相当大的溢价。原流程将此基坦宁煤炭设想把所有-1毫米精煤与从+1毫米重介质系统中产生的中煤一起配至较低变现的动力市场。原来的工厂设计利用主要的和次要的大块煤重介质容器，以及一级和二级重介质旋流器选洗+1mm的粒级。主要低密度d.m.产品用于炼焦煤市场。- 1毫米原始可选性数据表明,通过对1 x 0.25毫米粒级进行低密度分离（比重在1.55以下),通过最小化黄铁矿浮选槽入料,-1毫米中很大一部分可以作为焦化产品装运(40美元/吨的高收入)。新流程旨在取得这一低灰和低硫的好产品。1400吨小时的工厂投产2012年10月，,现在被称为莱尔矿业。1.2. 原始粉煤工艺流程 - 1毫米物料先过脱泥筛，再通过15”分级旋流器，理论上分成+ / - 150微米。+150微米用于混合旋流和-150微米用于传统浮选。旋流产品是在两段细金属丝筛进行脱泥，筛子的污水通过污水旋流器回路。旋流器溢流将在进入上述提及的传统浮选机而底流是循环回到螺旋精煤筛。脱泥螺旋产品和浮选精煤用转鼓离心机进行脱水。离心机精煤综合了旋流器/泡沫产品质量为灰分10%和硫分1.60%。这些品质阻止这种物料与粗焦化产品混合(重介质流程)。重介质回路必须在密度接近1.45的条件下操作以获得合意的炼焦质量，灰分近7%，硫分1.1 - 1.2%。1.3. 原工艺流程上升空间1.3.1. 1毫米x 150微米回路综合矿物可选性数据,特别是1毫米x150微米粒级,显示在1.45-1.55密度级使用逆流分级机(加尔文,2010),产品的硫分与模拟螺旋产品相比可减少约0.1%。除了低硫含量,回路中灰分也会降低到预期的大约2%。二次回路可能合并以回收高灰、高硫的中煤产品。1.3.2. 50微米x 0回路取-150微米的井底煤样进行释放分析，显示产品含硫在2.5%以上(表1)。原煤可选性数据显示,浮选精煤硫分高是由于黄铁矿硫。该煤有机硫通常为0.75%。原煤可选性显示黄铁矿极佳的释放到原料的细粒级中。表1.浮选释放分析(基坦宁下部)选煤厂中分级旋流器的仿真建模显示在密度为5.0解离黄铁矿，将成为比煤和岩石更细的粒度d50和d95分别为35和45微米。如果旋流器溢流单独进行浮选,入料和硫含量将会减少。厂内的测试也证实这个仿真。用一堆分级旋流器进行实验，入料类似于莱尔可选性，显示旋流器溢流中硫含量减少。硫从入料的2.28%减少到溢流的1.11%,底流中-150微米粒级含硫5.60%。因此，此时的理念是使超细黄铁矿的远离炼焦煤浮选回路而在动力煤泡沫回路中。1.3.3. 蒸汽泡沫回路入料分级旋流器底流中-150微米物料将经过清洗设备和脱泥设备,然后将进入浮选。回顾上述工厂的细微硫含量显示螺旋回路起到一些除硫作用(-150微米物料中硫含量由入料的5.65%降低到产品的2.63%)。然而,这2.63%硫在这个特定的工厂,与莱尔工厂的情况相符,经过脱泥筛和浮选回路会最终导致硫水平升高,或者被丢弃造成煤炭损失。1.3.4. 蒸汽泡沫回路脱硫对混合分级中-150微米物料进行实验显示降低黄铁矿硫含量大有希望(阿诺德,2011)(奥纳克,2007),(沃特斯,2011)。图1表示一个基坦宁煤样采用单独泡沫浮选或先混合分级再浮选。通过预处理浮选入料直接减少泡沫产品硫含量是明显的。图1表明,通过预先分级泡沫入料浮选硫降低0.2%。通过浮选前除去黄铁矿来减少细粒产品中的硫已纳入新工艺流程以减少产品硫分并尽可能回收炼焦煤。图1 基坦宁下部煤层浮选性能基于上述的实验工作以及将原料从动力煤时常转移到炼焦煤市场的财务影响,原工艺流程被抛弃,创立了精细回路如(图2)所示。 图2. 新工厂工艺流程图粗选是通过结合3x1毫米物料再使用一段1150毫米二段900毫米(高/低)重介质旋流器回路进行选洗，一段分选密度高,除去回路中粗粒碎石，二段分选密度较低,使得粗细分离。- 1毫米物料汇入一堆380毫米的原煤。1毫米x 150微米物料连同大部分-150微米黄铁矿用两级回流分级器处理。一级分选生产炼焦煤,密度1.50左右。一级分选产物进入二级进行中煤回收。一段和二段的产物分别进行独立脱泥，筛下物再经过细金属丝筛,在2段脱泥筛子之前预先脱泥(德哈特,2004)。筛上物与中小柱浮选精矿结合并使用转鼓离心机脱水生产焦煤和动力煤产品。低硫380毫米分级旋流器溢流给入150毫米分级旋流器入料箱。这些旋流器用来脱泥，理论粒度为45微米,并对高灰粘土进行浓缩。选择在柱浮选前先对45微米进行脱泥有很多原因。莱尔煤具有很高哈德格罗夫可磨度指数，达到80，导致高百分比的细粒，没有脱泥回路消除高水分微细粒很难使水分达标。同样,-45微米物料具有高灰和低煤回收率。150毫米脱泥旋流器底流进入直径4米的浮选柱。选择这些机器是因为他们在其他燃煤电厂的得到成功运用(卡迪纳尔、洛内和洛内帕迪)(贝瑟尔,2010)。150毫米旋流器底流被视为厂里最低硫流，因此作为炼焦煤浮选回路的唯一原料流。一段浮选精矿与回旋分级筛筛上物混合，并在干燥筛分机中进行脱水。150毫米脱泥旋流器的溢流进入浓缩机。初级和二次细金属丝筛下废水用泵注入150毫米浓缩旋流器，在此之前先进行脱硫。在这种技术下物流中硫含量预计将至少减少0.2%。旋流器底流中富含黄铁矿，经过高频筛出去。螺旋脱硫后的精煤和中煤以及150毫米浓缩旋流器溢流和主浮选柱尾矿进入直径在4米浮选柱进行二次浮选。为了达到预期的硫分，二次浮选精矿被用来与细金属丝筛筛下产品混合。这些物料进沉降过滤式离心机脱水。二次浮选尾矿进入浓缩机。沉降过滤式离心机筛下水(富含黄铁矿)再循环回原煤筛进一步脱硫。1.5. 实际工厂性能结果 工厂2012年10月开始生产。1.5.1.逆流分级机回路现在逆流回路实现一致的生产，接近6%的灰,在1.5比重下分选一段产品硫分为1.05%。每月对三个密度进行回路检测，表明存在快速分离。第一个逆流回路测试结果如表2所示。费解的是二次回流单元的最初遭遇。在一段相当长的时间里从这些单位释放的微粒是微不足道的，伴随这些大量增加的微粒使得动筛超载。这是通过稀释二次回流入料(粗选尾矿)来调整的。回流性能最近的一个“快照”由表3组成。表2.第一次回流测试表3.逆流分级机快照主要产品质量符合密度1.50附近的分离和二级1.70附近。从工厂原煤入料可洗性数据估计对同一煤采取混合分级回路会产生2%高灰和0.1%高硫，在1.80比重下典型分选情况下。对于1毫米x 0.25毫米物料和0.25 x 0.15毫米物料密度减少会引起相当大的差异。可控制的粒度分布给入和流出逆流回路，确保这可能对效率的负面影响是最小的(表4)。产品从2段筛子接收回流主要产品包含最小错配物。表4.主要rc筛分产品(57.6%固体)1.5.2. 浮选柱回路初级和二级浮选性能(0.250 x 0.045毫米)最大化是通过调整起泡剂和捕收剂剂量、泡沫含量、洗水量来实现的。从样本数据很明显看出一段和二段浮选回路是等价的。两个回路都可生产出合格的冶金质量。综合原煤分级旋流器之间数据显示入料和溢流之间主要的硫分减少是旋流器底流中细粒黄铁矿分级的结果。典型的380毫米旋流器,结果显示溢流硫分在1%或以下在-0.15毫米的粒度范围内，占150毫米入料的2%。这就解释了为什么主要产品的硫分低。回顾脱硫螺旋抽样数据显示极好的降低了硫。最新的采样显示旋流器入料中含硫2.2%，产品含硫1.2%,一段尾矿含硫4.8%,二段尾矿含硫3.5%,中煤产品含硫1.8%。基于浮选和脱硫分级的结果,它决定了把旋流精煤用于一段入料代替二级单元从而增加结焦率。效果可以从一段旋流器入料中固体百分比的增加和二段入料灰分的增加看到。旋流精煤流进入浮选的日常抽样结果变动如表5所示。表5.分级精煤浮选1.6. 结论1)新工厂优化回路已被成功证明可以最小化产品硫分。这已经通过从浮选回路中分类和螺旋移除黄铁矿,以及降低回路密度得以实现。2) 逆流回路已被证明有效运行密度接近1.50,这使得生产低灰、低硫的产品能够插入到焦化市场。3) 改变流程设计的影响从-0.15毫米浮选到脱硫、脱泥、粗选、清洁浮选回流已经将大约200吨小时高灰、高硫动力煤转入为低灰、低硫炼焦煤市场。2. 伊利诺斯州工厂(奈特霍克设备）2.1. 引言骑士鹰煤炭有限责任公司在2005年开发了草原鹰煤矿生产煤炭由表面和地下采矿方法。500吨小时草原鹰选矿厂建于2005年来洗煤用于热能市场。洗煤规范(收到基):灰分10%，水分11，热量200，但硫分在2.8-3.2%。最初的cpp回路包括一个单一的大直径重介质旋流器用于处理+1毫米粒级。粉煤选洗回路(1 x 0.15毫米)利用水力旋流器和螺旋分级机作为粗选配置。由于市场需求,骑士鹰煤开始研究提高工厂生产能力和效率的方法。为了满足煤炭销售预测,骑士鹰决定了煤炭处理和加工厂必须维持750吨/小时。泰戈特全球化承包给工程师并设计升级。2.2. 原始煤炭加工工艺流程原粉煤选洗回路利用水力旋流器和螺旋分级机在粗选配置中进行中煤回收。旋流精煤被回收到水力旋流器入料以提要提高回路效率。研究表明,回收螺旋中煤大大增强了此回路的效率。水力旋流器旋用于生产一个低密度分选(1.45)，而螺旋分离密度接近1.80。380毫米直径水力旋流器溢流,包含1毫米x0.15毫米精煤和0.15毫米x0原煤,螺旋精煤进入380毫米直径精煤分级旋流器。分级旋流器产生0.15毫米达到95%。水力旋流器底流进入细金属丝弧形筛(0.35毫米孔径，0.030金属丝)来剔除夹带在1 x 0.15毫米精煤种的错配物。弧形筛筛下物用ebw-40离心机脱水,离心机的很大一部分的0.15毫米x0粒级的尾矿。该回路产生的低灰产品,允许在重介系统中获得更高的离心力;这不仅最大化产品产量,而且通过降低产品总水分提高发热量。适当的分级是这一回路成功的关键。弧形筛废水,含有煤、粘土、黄铁矿硫粒子的混合物，进入到废水浓缩池。末煤离心机废水回收到精煤分级旋流器入料。原始粉煤洗选回路简化的流程描绘如图3所示。图3.原始粉煤选洗流程2.3. cpp升级测试工作骑士鹰煤炭委托塔格特全球开发一个工厂集中于升级产能和效率。评估超细物料回收的可能性,塔格特聘请美国弗吉尼亚理工大学完成成套测试来充分确定0.15毫米x 0组分的浮选特征。测试工作表明,如果设计得当,浮选回路升级会提高整体产品产量和质量。2.3.1. 分级测试工作是在实验室由抽取现有精煤旋流器溢流(0.15毫米x 0)再使物料通过一个150毫米脱泥旋流器开始的。脱泥旋流器入料、底流和溢流都要进行取样。结果表明,脱泥尾矿占入料的62.4%，而溢流灰分含量为71.8%。脱泥旋流器中存在可回收率小的+0.045毫米物料。脱泥物料给入浮选的效益已经通过试剂用量、回路规模和能力得到很好的证明。对脱泥旋流器溢流和底流都要进行进一步的测试。2.3.2.浮选试验结果0.15毫米x 0对每个物流进行浮选释放分析，结果绘制在图4。因为高灰分的0.15毫米x0物料,产品产量很低。可获得27.2%的产率，产品灰分为7.6%，硫分为7.6%。图4.基准实验室浮选性能脱泥旋流器底流,是66.9%的0.045毫米x0物料,产生48.2%泡沫产品产率、7.5%灰灰和7.5%硫分。尽管这煤流具有高灰分含量,实验结果表明浮选对灰分具有选择性。正如所料,脱泥煤流产生的泡沫产品含硫量最高。虽然脱泥旋流器溢流占产品的17.8%,灰分含量为6.24%和硫分6.24%,但浮选物料90%为0.045毫米x0,这造成离心机分离和产品水分脱除困难。2.3.3.浮选试验结果筛下水下一阶段的测试工作包括弧形筛污水流的特性。厂内的抽样显示,精煤弧形筛废水灰分从30.6%变成42.9%,而硫分从3.84%变成5.96%。尽管质量太差而不能直接作为产品,但这物流仍然含有低灰可回收物料。如果发送到未经处理产品,弧形筛底流中高硫含量可能迫使大块煤回路的离心力降低来抵消细粒产物中额外的灰和硫。+1毫米组分包含大量中煤，所以产率会显著减少。如果硫含量在浮选前可以减少，这污水将很适合浮选。通过实验室测试工作，对比三个流程:弧形筛废水直接浮选、弧形筛废水用精密旋流器选洗、精细化旋流再将产品进行浮选，总结结果如图5。图5.弧形筛污水浮选结果 实验表明,单独的精细螺旋系统本身不能有效降低原料的灰分含量。可获得36%灰的细螺旋产品，硫分4.5%，90%左右产率。这表示分别减少9.5%灰分和18.7%硫分。把弧形筛污水直接注入浮选可提供61.1%的收益，产品灰分17.5%和硫分5.78%。灰分减少了59.3%，但是硫分只减少了3.0%。细粒螺旋和泡沫浮选结合得到最好的结果,54.5%的精矿产量，3.99%硫分和3.99%的灰。精矿可获得低于10%的灰分和4%的硫分。正如所料,精煤中含硫(%)高于浮选入料,必须着重硫铁矿的可浮性和浮选前的移除。这个选项被选为流程开发来评估整个项目的优缺点。2.4. 工艺选择塔格特设计和模式化了一个流程。模拟显示额外的10吨/小时精煤可经过脱泥浮选回收，灰分为10%灰、硫分3.0%。浮选柱因为泡沫清洗功能(高灰柱形入料)和简单实用的布局而被选择。旋转筛能最小化表面水分。精煤弧形筛污水用泵送入三重旋流器组在进入脱泥旋流器之前。脱泥旋流器底流进入浮选柱，溢流被丢弃。升级后的工厂粉煤选洗流程如图6。图6.升级的粉煤选洗工艺2.5.cpp升级测试工作工厂抽样表明浮选池性能符合预期。浮选样本经过不久后的调试说明产率从25上升到43.6%取决于入料灰分。获得精煤灰分和硫分分别为10.8%和3.1% 。根据厂内评论,当前回收的额外的9吨/小时浮选产品硫或灰分含量无显著变化。这些需要额外的工作来加强。计算浮选单元增加的回收期为30个月。3. 结论本文展示了使用螺旋分选机去除浮选入料硫分是怎样引起美国两个不同煤田的工厂主要经济效益的不同的。参考文献galvin, k. et al., gravity separation of coal in the reflux classifier: new mechanisms for suppressing the effects of particle size, icpc 2010, pp 345-352dehart, g., fine circuit upgrade at hobet mining, coal prep 2004, pp 35-42arnold, b., personal communication 2011watters, l., personal communication 2011honaker, r., status of current coal preparation research, designing the coal preparation plant of the future, s.m.e. 2007bethell, p., arch coal processing philosophy east and west, 2010icpc 2010, pp 1-9honaker, r.q.; and forrest, w.r., advances in gravity concentration, operating characteristics of water-only cyclone/spiral circuits cleaning fine coal, bethell, p.; and, moorhead, r., pp 93-106bethell, p., froth flotation: to deslime or not to deslime, cpsa journal 2004, vol. 13, no. 1, pp 12-15.optimizing fine circuit design to maximize pyrite rejection and enhance coal marketabilityp. bethell (1)* , b. watters (1) , e. wolfe (1)(1) taggart global, llc, canonsburg, pa, usa, pb (* corresponding author)abstractcoal sulfur content is a critical property in both coking and thermal coal marketability. sulfur level reduction in both markets greatly enhances coal value. in the northern appalachian region of the u.s. sulfur levels in some potential coking coals are often marginal (1.1 - 1.5 percent). on many occasions much of the sulfur is concentrated in the form of pyrite in the finer sized fractions (1 mm x 0.045 mm). traditional fine coal processing circuitry (spirals, flotation) tends to produce high levels of product sulfur. pyrite reaching the flotation circuit typically floats well, producing high sulfur froth concentrate.being able to run at lower densities in the 1 mm x 0.25 mm size fraction reduces sulfur level considerably. removal of high density pyrite by a combination of classification and spiraling allows low sulfur froth concentrates to be produced. circuit design and plant results for a recently commissioned plant in northern appalachia using this technology are discussed.similarly in the illinois basin of the u.s. the pyrite concentration in the fines has precluded the use of froth flotation in many plants giving rise to significant yield losses. by incorporating a similar approach of classifying out the pyrite and then treating the de-sulfured fines in flotation, acceptable concentrates can be generated for the lower sulfur market. once again the flotation yield is supplemented by taking the concentrated pyrite, which flows to the plants clean coal effluent streams, and removing this by fine spiraling and floating the reduced sulfur spiral concentrate.key words:sulfur reduction, fine coal cleaning, fine spirals, flotation1. northern appalachian plant 1.1. backgroundin a northern appalachian property in 2011 a flowsheet had been developed for a new plant which was in the very early stages of construction. the flowsheet was designed to clean coal from a future longwall mine in the lower kittanning seam. the lower kittanning seam, having a dry volatile matter of approximately 32%, is considered a “high volatile a” coking coal which has a considerable premium in market value over steam coals.the original flowsheet to treat this kittanning coal envisaged placing all minus 1 mm clean coal to a low realization steam market along with middlings generated from the plus 1 mm dense media circuits. the original plant design utilized primary and secondary coarse coal dense medium vessels, and primary and secondary dense medium cyclones to wash plus 1 mm size fractions. primary low density d.m. product was to serve the coking coal market.minus 1 mm raw washability data indicated that by making a lower density separation (below 1.55 s.g.) on 1 x 0.25 mm and by minimizing pyrite in flotation cell feed, a large portion of minus 1 mm could be shipped as coking product (at $40/tonne higher revenue). a new flowsheet was designed to achieve this lower ash and sulfur fine product. the 1400 tph plant was commissioned in october 2012, now known as leer mining.1.2. original fine coal flowsheetminus 1 mm material passing the desliming screens was to be split into nominally +/- 150 micron material via 15” classifying cyclones. plus 150 micron was to be sent to compound spirals and minus 150 micron was to be sent to conventional flotation. spiral product was to be deslimed on two-stage fine wire sieves with the effluent passing to an effluent cyclone circuit. the overflow of the effluent cyclones would be treated in the above mentioned conventional flotation cells while the underflow was to be recirculated back to the spiral clean coal sieves.both deslimed spiral product and flotation concentrate were to be dewatered in screen bowl centrifuges. the projected clean coal quality for the screen bowl combined spiral / froth product was 10% ash and 1.60% sulfur. these qualities prevented this material from being blended with coarse coking product (dense media processes). the dense medium circuits must operate near 1.45 s.g. to achieve acceptable coking quality near 7% ash and 1.1-1.2% sulfur.1.3. upside potential for original flowsheet1.3.1. the 1 mm x 150 micron circuitsa review of the mine washability data, particularly the 1 mm x 150 micron fraction, showed that by operating in the 1.45-1.55 s.g. range using a reflux classifier (galvin, 2010), sulfur levels in the product could be reduced by approximately 0.1% in comparison to the simulated spiral product. in addition to the lower sulfur levels, lower ash levels would also be expected in the rc by approximately 2%. a secondary circuit could be incorporated to recover a higher ash, higher sulfur middlings product.1.3.2. the 150 micron x 0 circuitsrelease analysis testing on a pit bottom coal sample of minus 150 micron material showed product sulfur levels above 2.5% (table 1). raw coal washability data showed high sulfur levels in flotation concentrate were due to pyritic sulfur. the organic sulfur of this coal is typically 0.75%. raw coal washability showed excellent liberation of the pyrite into the finer fractions of the feed stock.table 1. flotation release analysis (lower kittanning)simulation modeling of the classifying cyclones in the plant showed that liberated pyrite with a density of 5.0 s.g. would be classified at a much finer size than coal and rock with a d50 and d95 of 35 and 45 micron respectively. if this cyclone overflow stream was fed alone to flotation, feed and concentrate sulfur would be less. in-plant testing had also been conducted to confirm this simulation. testing around a bank of classifying cyclones with a coal feed similar to that of leer washability showed a reduction in cyclone overflow sulfur levels. sulfur was reduced from 2.28% in the feed to 1.11% in the overflow, with 5.60% in the underflow for the minus 150 micron fractions.the concept at this point was therefore to keep the ultrafine pyrite out of the coking coal flotation circuit and treat it in a steam froth circuit.1.3.3. steam coal froth circuit feedminus 150 micron material in the classifying cyclone underflow would pass through a cleaning device, a desliming device, and then would report to froth flotation. a review of the ultrafine sulfur levels from the aforementioned plant show some sulfur removal in the spiral circuit (5.65% in the feed down to 2.63% in the product for the minus 150 micron material). however, this 2.63% sulfur material in this particular plant, as was the case for the original leer plant, passes through the desliming sieve and would ultimately end up in the flotation circuit resulting in elevated sulfur levels, or alternatively be discarded with great coal losses.1.3.4. steam froth circuit desulfurizationtesting performed on minus 150 micron material on compound spirals has shown great promise in reducing pyritic sulfur levels (arnold, 2011) (honaker, 2007), (watters, 2011). figure 1 represents a kittanning seam sample treated by froth flotation alone or on compound spirals and then subjected to flotation. the immediate reduction in froth product sulfur levels is apparent by pretreating flotation feed with spirals.figure 1 shows that flotation sulfur was reduced by 0.2% by pre-spiraling froth feed. fine product sulfur reduction achieved by removing pyrite ahead of flotation has been incorporated into the new flowsheet to minimize product sulfur and maximize coking coal recoveries.figure 1. lower kittanning flotation performance1.4. the new flowsheetbased on the aforementioned test work and the financial impact of moving material from the steam market into the coking coal market, the original flowsheet was abandoned and the fines circuit shown (figure 2) was constructed.figure 2. new plant flowsheetcoarse cleaning is achieved by combining 3” x 1 mm material and washing it through an 1150 mm primary and 900 mm secondary (high / low) d.m. cyclone circuit. the initial cut made by primary cyclones is high s.g., removing coarse rock from the circuit. secondary cyclones operate at a lower s.g., making the met / midds separation.minus 1 mm material reports to a bank of 380 mm raw coal classifying cyclones. nominal 1 mm x 150 micron material along with a large portion of the minus 150 micron pyrite is treated in primary / secondary reflux classifiers. the primary refluxes produce coking coal, near a 1.50 s.g. separation. reject from primary reflux is retreated by secondary reflux where middlings are recovered. primary and secondary reflux products are deslimed on independent, 2-stage met and single-stage midds fine wire sieves due to the success seen using 2-stage desliming sieves previously (dehart, 2004). material carrying over the sieves is combined with primary and secondary column flotation concentrate and dewatered in screen bowl centrifuges producing coking and steam coal products. the low sulfur 380 mm classifying cyclone overflow is gravity fed to a bank of 150 mm classifying cyclones. these cyclones serve to deslime at nominally 45 microns, discarding high ash clays to the thickener.desliming at 45 micron ahead of column flotation was selected for a number of reasons. the leer coal has a high hardgrove grindability index of 80 which leads to a high percentage of fines and difficulty making moisture specifications without a desliming circuit to eliminate high moisture ultra-fines. also, the expected minus 45 micron material was to be high in ash and have low coal recoveries. the underflow of the 150 mm desliming cyclones is treated in 4 m diameter primary column flotation cells. these slamjet columns were selected due to their success in other arch coal plants (cardinal, lone mtn., and pardee) (bethell, 2010).the 150 mm cyclone underflow feed stream was viewed as being the lowest sulfur stream in the plant and was therefore kept as the sole feed stream to the coking coal flotation circuit. primary flotation concentrate is combined with primary reflux classifier clean sieve product and is dewatered in the coking screen bowls. overflow of the 150 mm deslime cyclones is discarded to the thickener.effluent from primary and secondary fine wire sieves is pumped to a bank of 150 mm thickening cyclones, prior