帶式輸送機技術(shù)的最新發(fā)展@中英文翻譯@外文翻譯

附錄 A 帶式輸送機技術(shù)的最新發(fā)展 M. A. AlspaughOverland Conveyor Co., Inc. MINExpo 2004 拉斯維加斯 , 內(nèi)華達(dá)州，美國 ， 9， 27, 2004 摘要 粒狀材料運輸要求帶式輸送機具有更遠(yuǎn)的輸送距離、更復(fù)雜的輸送路線和更大的輸送量。為了適應(yīng)社會的發(fā)展，輸送機需要在系統(tǒng)設(shè)計、系統(tǒng)分析、數(shù)值仿真領(lǐng)域向更高層次發(fā)展。 傳統(tǒng)水平曲線和現(xiàn)代中間驅(qū)動的應(yīng)用改變和擴大了帶式輸送機發(fā)展的可能性。本文回顧了為保證輸送機的可靠性和可用性而運用數(shù)字工具的一些復(fù)雜帶式輸送機。 前言 雖然 這篇文章的 標(biāo)題表明在皮帶輸送機技術(shù) 中 將提出 “ 新 ” 發(fā)展， 但是提到的 大多 思想和方法都已存在很長時間了 。 我們 不 懷疑被提出 一些部件 或想法將是 “ 新 ” 的對 你們 大部分人來說 。 所謂的“新”就是利用成熟的技術(shù)和部件組成特別的、復(fù)雜的系統(tǒng)； “新”就 是 利用 系統(tǒng)設(shè)計工具和方法 ， 匯集 一些部件組成 獨特的 輸送機系統(tǒng)，并 解決 大量粒狀原料的裝卸問題；“新”就是 在第一次系統(tǒng)試驗 (委任 )之前 利用日益成熟的計算機技術(shù)進(jìn)行 準(zhǔn)確節(jié)能計算機模擬。 同樣，本文的重點是特定復(fù)雜系統(tǒng)設(shè)計及滿足長距離輸送的要求。 這四個具體課題將覆蓋： 托輥阻力 節(jié)能 動力分散 分析與仿真 節(jié)能 減小設(shè)備 整體電力消費是所有項目的一個重要方面，皮帶輸送機是 也不例外 。 雖然與其他運輸方法比較皮帶輸送機總是運輸大噸位高效率的手段，但是減少帶式輸送機的功率消耗的方法還是很多的 。 皮帶輸送機的主要 阻力 組成 部分有： 托輥阻力 托輥與皮帶的摩擦力 材料或輸送帶彎曲下垂引起的阻力 重力 這些阻力加上一些混雜阻力組成輸送材料所需的力。 1 在一臺輸送長度 400 米的典型短距離輸送機中 ,力可以分為如圖 1 所示的幾個部分，圖中可以看出提升力所占比例最大，而阻力還是占絕大部分。 圖 1 在高傾斜輸送帶中如礦用露天傾斜輸送帶，所受力可分解為圖 2 所示的幾個部分，其中提升力仍占巨大比例。由于重力是無法避免的，因此沒有好的方法減少傾斜式輸送機所受力。 圖 2 但是在長距離陸上輸送機中，所受力更趨向圖 3 所示的幾個部分，不難看出摩擦力幾乎是所受力的全部。這種情況下考慮主要受力才是最重要的。 圖 3 力量演算具體是超出本文的范圍之外，但是 值得一提的是 ，在過去幾年對所有四個區(qū)域橡膠凹進(jìn)、對準(zhǔn)線和材料或者傳送帶彎曲 等方面的重要研究都在進(jìn)行 。 并且，雖然 在 處理每特定區(qū)域 時大家有不同意 見 ，通常對整體項目經(jīng)濟 是必要和重要的 是 被大家 被接受 的。 在 2004 個 SME 年會上， MAN Takraf 的 Walter Kung 介紹了題為“ Henderson 粗糙礦石輸送系統(tǒng) 回顧組裝、起動和操作” 2。 這個項目在1999 年 12 月被實施并且包括一個 24 公里 (3 飛行 )陸上轉(zhuǎn)達(dá)的系統(tǒng)替換地下礦碾碎路軌貨車使用系統(tǒng)。 圖 4 - Henderson PC2 到 PC3 調(diào)動站 最長的傳動機在這個系統(tǒng) (PC2)是 16.28 公里長與 475m升距。最重要的系統(tǒng)事實是提供的功率 (4000 千瓦在 1783 mtph 和 4.6 m/s)的 50% 被要求用來轉(zhuǎn)動一條空載的帶子，因此輸送系統(tǒng)的效率是很重要的。需密切注意托輥、傳送帶蓋子橡膠和對準(zhǔn)線。用文件說明有關(guān)的效率的差別是的一種方法， 使用 相等的摩擦系數(shù) f的 22101 標(biāo)準(zhǔn)定義作為比較主要抵抗的總數(shù)的另一種方法。過去，象這樣典型輸送裝置的綜合設(shè)計噪音系數(shù)大約是 0.016f。 MAN Takraf 正估計他們對力的敏感達(dá)到到 0.011 的 f，超過 30%的削減。這在減少設(shè)備建造成本上做出了重大貢獻(xiàn)。通過六次的實際動態(tài)測量顯示價值是0.0075， 甚至比期望值低 30%。 Kung 先生強調(diào)這將在僅僅用電費用一項上每年減少費用 10 萬美元。 線路優(yōu)化 圖 5 中國天津 水平適應(yīng)性 當(dāng)然最高效率的材料運輸方式是從一點到下一點的直線輸送。 但是，由于自然和認(rèn)為障礙的存在，我們在長距離輸送過程中直接直線輸送的可能性越來越小。第一臺水平彎曲輸送機已在很多年前安裝使用，但它今天似乎關(guān)于安裝的每臺陸上傳動機在方向至少有一個水平變化。并且今天的技術(shù)允許設(shè)計師相對地容易地調(diào)整這些曲線。 圖 5 和圖 6 顯示的是把煤從蘊藏地運輸?shù)街袊旖蚋劭诠芾硖幍年懮陷斔脱b置。這 套運輸機由 E.J. ODonovan & Associates 設(shè)計，由 Continental Conveyor Ltd of Australia 公司承建，長達(dá) 9 千米的輸送距離 4 臺 1500 千萬電機驅(qū)動運輸能力達(dá) 6000 mtph 。 圖 6 天津輸送線平面圖 Wyodak 礦位于美國懷俄明州粉河流域，是記錄中最古老的連續(xù)經(jīng)營的煤礦，自 1923年運營至今。它一般運用坡面 (圖 7)從新的礦坑到裝置 756m (2,482 ft)與 700m (2,300 ft)水平的半徑。 這表明由于水平輪的應(yīng)用輸送機不需 要設(shè)計太長 3。 圖 7- Wyodak 煤礦 隧道式 如通過沒有水平曲線線路，另一項產(chǎn)業(yè)，隧道挖掘，就不能使用帶式輸送機了。 隧道就想象廢水和運輸那樣的基礎(chǔ)設(shè)施在全世界有。 移動隧道糞肥的最有效率的方法通過把推進(jìn)的輸送裝置和隧道機器的后部連結(jié)起來。但是這些隧道極少是直的。 這里有一個例子，西班牙 10.9m直徑隧道的在巴塞羅那之下作為地鐵 (火車 )引伸項目一部分。大陸輸送機機有限公司安裝了前 4.7km 傳動機如圖 8和 9 所顯示和最近接受合同安裝第二臺 8.39 公里輸送機。 圖 8- 巴塞羅那隧道平面圖 圖 9- 隧道內(nèi)部 另一個例子， 肯珀建設(shè)邊境時，建設(shè)一個直徑 3.6 米長 6.18 公里的隧道作為大都市圣路易斯的下水道區(qū)。鮑姆加特納隧道 (圖 10)將裝有 600 毫米寬的用 4 個中間運動用帶子系住的 6.1 公里輸送裝置。 圖 10- 鮑姆加特納隧道平面圖 管狀輸送裝置 如果常規(guī)輸送機不能滿足必須的輸送要求，帶式輸送機的一種管狀輸送機會是不錯的選擇。 圖 11- 管狀輸送裝置 它最簡單的描述，管狀輸送機就是由管狀橡膠管和空轉(zhuǎn)輥組成。這種設(shè)計具有其他傳送方式的優(yōu)點，更有自己的特點。 托輥可以在各個方向傳 力允許更復(fù)雜的曲線輸送。這些曲線可以是水平或垂直或混合形式。這樣的輸送機輸送帶與托輥之間的重力和摩擦力保證原料在輸送管道內(nèi)。 Figure 12 管狀輸送機的另一個好處可以輸送粉狀原料并且可以減少溢出浪費，因為材料是在管道內(nèi)部。一個典型的例子是環(huán)境效益和適應(yīng)性特好的美國猶他州地平線礦（圖 12）。這個長 3.38 公里的管狀輸送機由 ThyssenKrupp Robins 安裝通過一個國家森林并且橫斷了 22 個水平段和 45 個垂直段。 Metso 繩索輸送機 另一種由常規(guī)衍變來的是 Mesto 繩索輸送機（ MRC），通常以纜繩傳送帶著名。這個產(chǎn)品以長途輸送著名，在距澳大利亞 30.4 公里的沃斯利鋁土礦上應(yīng)用的輸送帶是最長的單個飛行輸送機。在鋼繩輸送機上，驅(qū)動裝置和運載媒介是分離的。 圖 13 - MRC-平直的部分 這種驅(qū)動與輸送裝置的分離允許輸送有小半徑的水平彎曲，這種設(shè)計優(yōu)于根 距張緊力和地勢的傳統(tǒng)設(shè)計。 圖 14 MRC 與常規(guī)輸送機水平曲線的不同 圖 15- 位于加拿大 Line Creek 的 MRC 圖 15 顯示的是位于加拿大 Line Creek 河畔的一條長 10.4 公里水平半徑 430米的纜繩輸送帶 立式輸送裝置 有時材料需要被提升或下降而常規(guī)輸送機被限制在 16 18 度附近的傾斜角度內(nèi)。但是帶式輸送機的非傳統(tǒng)衍變不管是在增加角度還是平直方面都是相當(dāng)成功的。 大角度輸送機 第一臺大角度輸送機由 Continental Conveyor & Equipment Co.公司生產(chǎn)，非常利用常規(guī)輸送機零部件（圖 16）構(gòu)成。當(dāng)原料在兩條帶子之間輸送時，被稱為三明治輸送裝置。 圖 16 Continental 公司的第 100 套大傾角輸送裝置采用獨特的可平移式設(shè)計，作為Mexican de Canenea 的堆 過濾墊（圖 17）。 Figure 17 垂直式輸送裝置 第二種立式輸送裝置展現(xiàn)的是一種非常規(guī)的帶式裝置，它可以實現(xiàn)垂直輸送（圖 18）。 這種 Mesto 垂直輸送機， 2001 年由 Frontier Kemper 安裝在白縣煤礦Pattiki 2 礦（圖 19），將煤由 273 米深的礦井輸出并達(dá)到 1,818 mtph 的輸送能力。 圖 18 圖 19- Pattiki 2 礦 動力分散 在最近過去的一段時間里，一種最有趣的發(fā)展是電力沿輸送道路的分配?？吹捷斔蜋C驅(qū)動裝置安裝在收尾末端，讓尾端驅(qū)動完成 輸送帶的拉緊輸送工作。但是現(xiàn)在的發(fā)展觀念是把驅(qū)動安裝在任何需要的位置。 在帶式輸送機上多個位置安裝動力源的想法已經(jīng)存在很長一段時間了。第一次應(yīng)用是 1974 年安裝在美國 Kaiser 煤礦。緊接著是在地下煤礦中得到應(yīng)用，而且長臂開采法也越來越體現(xiàn)它的優(yōu)越性。采礦設(shè)備的效率和能力也得到巨大改善。礦工們也開始尋找大的礦區(qū)從而減少移動大型采礦設(shè)備的次數(shù)及時間。礦井寬度和礦井分格長度都得到增加。 當(dāng)?shù)V井分格長度增加后，輸送問題開始出現(xiàn)。接近 4-5 千米的輸送長度所需要的電力和輸送帶的強度比以前地下煤礦需要的大很多。問 題是大號的高電力驅(qū)動裝置安裝及移動困難。雖然膠帶技術(shù)能夠滿足膠帶所需強度要求，它意味著需要比鋼鐵更重要的強度及加硫處理。由于長臂開采法的盤區(qū)傳動機經(jīng)常推進(jìn)和后退，礦工需要經(jīng)常增加或取消滾筒的正傳與逆轉(zhuǎn)。而且硫化結(jié)合需要長期維護(hù)以保證強度，因而失去的產(chǎn)品生產(chǎn)時間在一個完全盤區(qū)中是很嚴(yán)重的?，F(xiàn)在需要超過風(fēng)險，并且中間驅(qū)動的應(yīng)用限制了輸送帶的伸長及張緊這樣就允許纖維膠帶在長距離輸送機中應(yīng)用。 現(xiàn)今，中間驅(qū)動技術(shù)被很好的接受并越來越廣泛的應(yīng)用于地下煤礦中。世界范圍內(nèi)的許多礦把這項技術(shù)整合到現(xiàn)在和未來礦業(yè)計劃當(dāng)中來 增加他們的整體采礦效率和效益 6。 表 20 所示的張緊圖顯示了中間驅(qū)動的重大好處。這種平面前驅(qū)的輸送機有簡單的皮帶張力分布如黑色線條所示。雖然平均皮帶張力在每個周期期間只約為最大值的 40%，但必須圍繞最大估量值附近。黑色線條的急劇回落表示頂頭滑輪要求的總扭矩和力量來啟動輸送機。 將受力分解到兩個地點（紅線），當(dāng)總功率基本相同的情況下，皮帶張力差不多減少 40%。因此更小的輸送帶和更小的電源組可以得到運用。為了進(jìn)一步擴展這種方式，增加第二中間驅(qū)動（綠線），皮帶峰頂張力進(jìn)一步下降。 隧道產(chǎn)業(yè)也迅速采用這種技術(shù)并且 把這項技術(shù)提高到更好的水平，更復(fù)雜更先進(jìn)。但挖隧道最需要的是水平曲線的進(jìn)步。 通過中間驅(qū)動（圖 21）的一種應(yīng)用例如 Baumgartner 隧道如前圖 10 所描述，皮帶張緊力可以通過在重要的地點安裝戰(zhàn)略驅(qū)動來控制，從而實現(xiàn)輸送帶的小曲線換向。 圖 20 圖 21 在圖 22 中，綠色投影區(qū)域代表彎曲結(jié)構(gòu)的地點。藍(lán)色線條代表輸送帶運載面，粉紅色線條代表輸送帶返回面。可以發(fā)現(xiàn)在彎曲半徑最小 750 米時輸送帶運載面和返回面所受張緊力均達(dá)到最小。 圖 22 盡管到目前為止，這項技術(shù)陸上輸送機中沒有 廣泛的應(yīng)用，一些傾向于水平曲線的技術(shù)卻得到發(fā)展。圖 23 顯示了南美洲的一條長 8.5 千米硬巖層輸送帶，它需要 4 個中間驅(qū)動來實現(xiàn) 4 段 2000 米半徑的曲線轉(zhuǎn)向。 Figure 23- 平面圖 圖 24 顯示在彎曲段有與沒有驅(qū)動時輸送帶的張緊力比較。 分散驅(qū)動的優(yōu)點在 MRC 纜繩輸送帶中也得到應(yīng)用。然而張緊運載的繩索有別于負(fù)載傳送帶，安裝中間驅(qū)動更加容易，輸送的原料不用離開運載輸送帶的表面。張緊運載的繩索與輸送帶分開足夠的距離，便利在安裝中間驅(qū)動后繼續(xù)工作。 (圖 25). 圖 24- 張緊曲線 圖 25 分析與 仿真 許多人在爭論我們建造以上描述的復(fù)雜輸送機的能力時，歸因于許多分析和仿真工具的發(fā)展。組件制造商可以通過測試他的產(chǎn)品以保證符合規(guī)格；然而系統(tǒng)工程師很少能測試完成的系統(tǒng)，知道它在站點完成。所以計算方法和工具在模仿各種各樣不同學(xué)科和組分上的作用是絕對重要的。 動態(tài)開始和停止 當(dāng)進(jìn)行開始和停止試驗時，假設(shè)所有的質(zhì)量單元同時加速；也就是把輸送帶看做一個剛體（非彈性體）。實際上，推進(jìn)扭矩通過滑輪產(chǎn)生的壓力波傳遞給輸送帶，并通過壓力波的傳播帶動輸送帶運行。壓力在輸送帶上傳播時發(fā)生由阻礙輸送帶運行的阻抗產(chǎn)生的縱波 引起的變化。 7 從 1959 開始許多出版物都指出彈性輸送帶的大輸送量、長距離輸送機在停止和啟動時會導(dǎo)致傳動裝置、驅(qū)動裝置、張緊裝置的選擇等錯誤。對彈性瞬變響應(yīng)的疏忽可能導(dǎo)致不精確的后果： 輸送帶最大壓力 滑輪上的最大壓力 輸送帶的最小壓力及原料泄漏 提升壓力要求 提升行程和速度要求 驅(qū)動輪 啟動轉(zhuǎn)矩 制動轉(zhuǎn)矩 各驅(qū)動間的負(fù)載分擔(dān) 原料在斜面上的穩(wěn)定性 為了長期應(yīng)用，通過數(shù)學(xué)模型對彈性輸送帶在開始和停止時的狀態(tài)進(jìn)行模擬是非常重要的。 一部完整輸送機系統(tǒng)的模型可通過劃分輸送機為一系列的有限元素來實現(xiàn) 。每個元素由一個質(zhì)量和一個流變彈簧組成，如圖 26 所示。 圖 26 許多分析輸送帶無力性能的方法都在研究，如把它看做一個流變彈簧，而且大量的技術(shù)也被用來這方面的研究。一個合適的模型需要包含以下幾個方面： 1. 傳送帶縱向拉伸量的彈性模數(shù) 2. 對從屬運動的阻抗 3. 凹陷處的粘彈性損失 4. 由于輸送帶的下垂引起的輸送帶模數(shù)變動 因為純數(shù)學(xué)解決這些動態(tài)問題是非常復(fù)雜的，它的目標(biāo)不是詳述基礎(chǔ)的動態(tài)理論分析。相反，它的目的是讓長距離輸送、水平彎曲、分散驅(qū)動在輸送機上更普遍，對傳送帶停止和開始進(jìn)行彈性動態(tài) 分析的重要性是開發(fā)適當(dāng)?shù)目刂扑惴ā?以圖 23 8.5 千米輸送機為例，兩個虛擬開始被模擬來比較它們的控制算法。一種是兩個 1000 千瓦的驅(qū)動安裝在頭部尾端，二個 1000 千瓦驅(qū)動安裝在輸送面的中點，另一個 1000 千瓦驅(qū)動安裝在尾部，要極端小心保證所有驅(qū)動的協(xié)調(diào)與維護(hù)。 圖 27 顯示一個不協(xié)調(diào)并嚴(yán)重擺動輸送機 120 秒啟動的扭矩圖及其相應(yīng)的速度輸送帶擺動圖。 T1/T2 滑動比率表明推進(jìn)滑動可能發(fā)生。圖 28 顯示對應(yīng)的一個 180 秒啟動圖，并能夠安全和順利的加速輸送機。 圖 27-120 秒惡劣啟動 圖 28- 180 良好啟動 轉(zhuǎn)運站的質(zhì)流 運用中間驅(qū)動和鏈板輸送能長期使用的一個原因就是消除轉(zhuǎn)運站。許多最困難的問題在帶式輸送機裝貨和卸載附近集中。傳送溜槽通常選在輸送機高效維護(hù)區(qū)域，同時重大生產(chǎn)風(fēng)險在這里集中。 堵塞 輸送帶和滑道損傷和磨蝕物質(zhì)退化 粉塵 裝貨 /溢出偏心 過去，沒有分析工具，反復(fù)試驗和經(jīng)驗是設(shè)計工程師唯一可用的設(shè)計方法；現(xiàn)在，數(shù)值仿真方法的存在允許設(shè)計師在制造之前測試他們的設(shè)計。 數(shù)字仿真是根據(jù)一個實際的物理系統(tǒng)設(shè)計的模型，并在計算機上模擬和分析結(jié)果。仿真體現(xiàn)在實踐中學(xué)習(xí)的 精神。為了了解現(xiàn)實及其復(fù)雜性，我們在計算機上建立虛擬物體并動態(tài)的觀察它們間的相互作用。 分離元素法是解決工程學(xué)和應(yīng)用科學(xué)如粒狀材料流等不連續(xù)的機械行為問題的一種數(shù)字模擬技術(shù)。值得注意的是，由非連續(xù)行為引起的行為不能依靠傳統(tǒng)基基于計算機的連續(xù)流塑造方法例如有限元素分析、有限差規(guī)程和甚而計算流體動力學(xué) (CFD)的來進(jìn)行模擬。 DEM 系統(tǒng)模仿每個部件或微粒的動態(tài)行為和機械互作用，并提供分析期間每個部件和微粒的位置、速度、和力量的詳細(xì)描述。 8 在分析過程中，微粒被塑造成有形狀的物體，這些物體之間及于界限表面、 運載表面互相作用，這些物體接觸和碰撞形成他們之間法向、切向力 . 正常接觸分力在碰撞過程中引起一個線性有彈性恢復(fù)的組分和一個粘阻力來模擬能量損失。線性有彈性組分系數(shù)根據(jù)自身屬性確定，正常粘滯系數(shù)可以根據(jù)一個等效恢復(fù)系數(shù)的彈簧來塑造（圖 29）。 圖 29 圖 30 顯示顆粒下落通過傳送帶溜槽。圖示中顆粒的顏色代表他們的速度。紅色代表零速度，而綠色代表最高速度。也許這些工具的最大好處就是一位老練的工程師能通過形象化表示設(shè)計施工前有個行像的表現(xiàn)。有了這個形象的感覺在施工過程中可以盡量減少不必要的工作。 其他定 量數(shù)據(jù)也可能被隱藏包括在輸送帶或滑道墻壁的沖擊和剪切力。 圖 30 前景 更大的帶式輸送機 本文提到了一臺最長的唯一飛行常規(guī)輸送機，長 16.26 公里的 Henderson PC2。但一臺 19.1 公里的輸送機在美國正在建設(shè)中，并且一臺 23.5 公里的飛行式輸送機在澳洲被設(shè)計。其他長 30-40 公里的輸送機在世界其他地區(qū)討論研究。 當(dāng)定量凹進(jìn)的方式為人所知，輸送帶制造商開發(fā)了低輾壓抗壓儲力10-15%的橡膠輸送帶。與改進(jìn)的設(shè)施方法和對準(zhǔn)線一起作用，節(jié)能是可以實現(xiàn)的。 地下煤礦和隧道承包商將繼續(xù)使用已經(jīng)證明對他們 有好處的分散驅(qū)動方式；至少有兩種在表面輸送機中安裝中間驅(qū)動的輸送機在 2005 年運行。 在德國， RWE Rheinbraun 使煤礦用輸送機輸送量達(dá)到 30,000 tph ，并且其他表面煤礦也在有計劃的接近這個輸送量。隨著輸送兩的增加，輸送帶的速度也在增加，這樣就要求更好的設(shè)備、工藝公差、阻力和動力分析。 我們希望輸送機能夠更遠(yuǎn)、更寬、更高、更快，采用所有分析工具來分析系統(tǒng)性能。因為每臺輸送機都是獨特的，我們唯一的預(yù)見方式就是外面的數(shù)據(jù)分析和模仿工具。因此由于外面的目標(biāo)越來越大，我們有必要改進(jìn)設(shè)計工具。 附錄 B Latest Developments in Belt Conveyor Technology M. A. Alspaugh Overland Conveyor Co., Inc. Presented at MINExpo 2004Las Vegas, NV, USA September 27, 2004 Abstract Bulk material transportation requirements have continued to press the belt conveyor industry to carry higher tonnages over longer distances and more diverse routes. In order keep up, significant technology advances have been required in the field of system design, analysis and numerical simulation. The application of traditional components in non-traditional applications requiring horizontal curves and intermediate drives have changed and expanded belt conveyor possibilities. Examples of complex conveying applications along with the numerical tools required to insure reliability and availability will be reviewed. Introduction Although the title of this presentation indicates “new” developments in belt conveyor technology will be presented, most of the ideas and methods offered here have been around for some time. We doubt any single piece of equipment or idea presented will be “new” to many of you. What is “new” are the significant and complex systems being built with mostly mature components. What is also “new” are the system design tools and methods used to put these components together into unique conveyance systems designed to solve ever expanding bulk material handling needs. And what is also “new” is the increasing ability to produce accurate Energy Efficiency computer simulations of system performance prior to the first system test (commissioning). As such, the main focus of this presentation will be the latest developments in complex system design essential to properly engineer and optimize todays long distance conveyance requirements. The four specific topics covered will be: Idler Resistance Energy Efficiency Distributed Power Analysis and Simulation Energy Efficiency Minimizing overall power consumption is a critical aspect of any project and belt conveyors are no different. Although belt conveyors have always been an efficient means of transporting large tonnages as compared to other transport methods, there are still various methods to reduce power requirements on overland conveyors. The main resistances of a belt conveyor are made up of: Idler Resistance Rubber indentation due to idler support Material/Belt flexure due to sag being idlers Alignment These resistances plus miscellaneous secondary resistances and forces to over come gravity (lift) make up the required power to move the material.1 In a typical in-plant conveyor of 400m length, power might be broken into its components as per Figure 1 with lift making up the largest single component but all friction forces making up the majority. Figure 1 In a high incline conveyor such as an underground mine slope belt, power might be broken down as per Figure 2, with lift contributing a huge majority. Since there is no way to reduce gravity forces, there are no means to significantly reduce power on high incline belts. Figure 2 But in a long overland conveyor, power components will look much more like Figure 3, with frictional components making up almost all the power. In this case, attention to the main resistances is essential. Figure 3 The specifics of power calculation is beyond the scope of this paper but it is important to note that significant research has been done on all four areas of idlers, rubber indentation, alignment and material/belt flexure over the last few years. And although not everyone is in agreement as to how to handle each specific area, it is generally well accepted that attention to these main resistances is necessary and important to overall project economics. At the 2004 SME annual meeting, Walter Kung of MAN Takraf presented a paper titled “The Henderson Coarse Ore Conveying System- A Review of Commissioning, Start-up and Operation”2. This project was commissioned in December 1999 and consisted of a 24 km (3 flight) overland conveying system to replace the underground mine to mill rail haulage system. Figure 4- Henderson PC2 to PC3 Transfer House The longest conveyor in this system (PC2) was 16.28 km in length with 475m of lift. The most important system fact was that 50% of the operating power (4000 kW at 1783 mtph and 4.6 m/s) was required to turn an empty belt therefore power efficiency was critical. Very close attention was focused on the idlers, belt cover rubber and alignment. One way to document relative differences in efficiency is to use the DIN 22101 standard definition of “equivalent friction factor- f” as a way to compare the total of the main resistances. In the past, a typical DIN fused for design of a conveyor like this might be around 0.016. MAN Takraf was estimating their attention to power would allow them to realize an f of 0.011, a reduction of over 30%. This reduction contributed a significant saving in capital cost of the equipment. The actual measured results over 6 operating shifts after commissioning showed the value to be 0.0075, or even 30% lower than expected. Mr. Kung stated this reduction from expected to result in an additional US$100, 000 savings per year in electricity costs alone. Route Optimization Figure 5- Tiangin China Horizontal Adaptability Of course the most efficient way to transport material from one point to the next is as directly as possible. But as we continue to transport longer distances by conveyor, the possibility of conveying in a straight line is less and less likely as many natural and man-made obstacles exist. The first horizontally curved conveyors were installed many years ago, but today it seems just about every overland conveyor being installed has at least one horizontal change in direction. And todays technology allows designers to accommodate these curves relatively easily. Figures 5 and 6 shows an overland conveyor transporting coal from the stockpile to the shiploader at the Tianjin China Port Authority installed this year. Designed by E.J. ODonovan & Associates and built by Continental Conveyor Ltd of Australia, this 9 km overland carries 6000 mtph with 4x1500 kW drives installed. Figure 6- Tiangin China Plan View The Wyodak Mine, located in the Powder River Basin of Wyoming, USA, is the oldest continuously operating coal mine in the US having recorded annual production since 1923. It currently utilizes an overland (Figure 7) from the new pit to the plant 756m long (2,482 ft) with a 700m (2,300 ft) horizontal radius. This proves a conveyor does not need to be extremely long to benefit from a horizontal turn. 3 Figure 7- Wyodak Coal Tunneling Another industry that would not be able to use belt conveyors without the ability to negotiate horizontal curves is construction tunneling. Tunnels are being bore around the world for infrastructure such as waste water and transportation. The most efficient method of removing tunnel muck is by connecting an advancing conveyor to the tail of the tunnel boring machine. But these tunnels are seldom if ever straight. One example in Spain is the development of a 10.9m diameter tunnel under Barcelona as part of the Metro (Train) Extension Project. Continental Conveyor Ltd. installed the first 4.7km conveyor as shown in Figures 8 and 9 and has recently received the contract to install the second 8.39 km conveyor. Figure 8- Barcelona Tunnel Plan View Figure 9- Inside Tunnel In another example, Frontier Kemper Construction is currently starting to bore 6.18 km (20,275 ft) of 3.6m (12 foot) diameter tunnel for the Metropolitan St. Louis (Missouri) Sewer District. The Baumgartner tunnel (Figure 10) will be equipped with a 6.1 km conveyor of 600mm wide belting with 4 intermediate drives. Figure 10- Baumgartner Tunnel Plan View Pipe Conveyors And if conventional conveyors cannot negotiate the required radii, other variations of belt conveyor such as the Pipe Conveyor might be used. Figure 11- Pipe Conveyor In its simplest description, a pipe conveyor consists of a rubber conveyor belt rolled into a pipe shape with idler rolls. This fundamental design causes the transported material to be totaled enclosed by the belt which directly creates all the advantages. The idlers constrain the belt on all sides allowing much tighter curves to be negotiated in any direction. The curves can be horizontal, vertical or combinations of both. A conventional conveyor has only gravity and friction between the belt and idlers to keep it within the conveyance path. Figure 12 Another benefit of pipe conveyor is dust and/or spillage can be reduced because the material is completely enclosed. A classic example where both environment and adaptability to path were particularly applicable was at the Skyline Mine in UT, USA (Figure 12). This 3.38 km (11,088 ft) Pipe Conveyor was installed by ThyssenKrupp Robins through a national forest and traversed 22 horizontal and 45 vertical curves.4 Metso Rope Conveyor Another variation from conventional is the Metso Rope Conveyor (MRC) more commonly known as Cable Belt. This product is known for long distance conveying and it claims the longest single flight conveyor in the world at Worsley Alumina in Australia at 30.4 km. With Cable Belt, the driving tensions (ropes) and the carrying medium (belt) are separated (Figure 13). Figure 13- MRC- Straight Section This separation of the tension carrying member allows positive tracking of the ropes (Figure 14) which allow very small radius horizontal curves to be adopted that defeat the traditional design parameters based on tension and topography. Figure 14 MRC vs. Conventional Conveyor in Horizontal Curve Figure 15- MRC at Line Creek, Canada Figure 15 shows a 10.4 km Cable Belt with a 430m horizontal radius at Line Creek in Canada. Vertical Adaptability Sometimes material needs to be raised or lowered and the conventional conveyor is limited to incline angles around 16-18 degrees. But again non-traditional variations of belt conveyors have been quite successful at increased angles as well as straight up. High Angle Conveyor (HAC.) The first example manufactured by Continental Conveyor & Equipment Co. uses conventional conveyor components in a non-conventional way (Figure 16). The concept is known as a sandwich conveyor as the material is carried between two belts. Figure 16 Continentals 100th installation of the HAC was a unique shiftable installation at Mexican de Caneneas heap leach pad (Figure 17). Figure 17 Pocketlift. The second example shows a non-traditional belt construction which can be used to convey vertically (Figure 18). This Metso Pocketlift. belt was installed by Frontier Kemper Constructors at the Pattiki 2 Mine of White County Coal in 2001 (Figure 19). It currently lifts 1,818 mtph of run-of-mine coal up 273 m (895 ft). 5 Figure 18 Figure 19- Pattiki 2 Mine Distributed Power One of the most interesting developments in technology in the recent past has been the distribution of power along the conveyor path. Is has not been uncommon to see drives positioned at the head and tail ends of long conveyors and let the tail drive do the work of pulling the belt back along the return run of the conveyor. But now that idea has expanded to allow designers to position drive power wherever it is most needed. The idea of distributing power in multiple locations on a belt conveyor has been around for a long time. The first application in the USA was installed at Kaiser Coal in 1974. It was shortly thereafter that underground coal mining began consolidating and longwall mines began to realize tremendous growth in output. Mining equipment efficiencies and capabilities were improving dramatically. Miners were looking for ways to increase the size of mining blocks in order to decrease the percentage of idle time needed to move the large mining equipment from block to block. Face widths and panel lengths were increasing. When panel lengths were increased, conveyance concerns began to appear. The power and belt strengths needed for these lengths approaching 4 -5 km were much larger than had ever been used underground before. Problems included the large size of high power drives not to mention being able to handle and move them around. And, although belting technology could handle the increased strength requirements, it meant moving to steel reinforced belting that was much heavier and harder to handle and more importantly, required vulcanized splicing. Since longwall panel conveyors are constantly advancing and retreating (getting longer and shorter), miners are always adding or removing rolls of belting from the system. Moreover, since vulcanized splicing takes several times longer to facilitate, lost production time due to belt moves over the course of a complete panel during development and mining would be extreme. Now the need surpassed the risk and the application of intermediate drives to limit belt tensions and allow the use of fabric belting on long center applications was actively pursued. Today, intermediate drive technology is very well accepted and widely used in underground coal mining. Many mines around the world have incorporated it into their current and future mine plans to increase the efficiency of their overall mining operations. 6 The tension diagram in Figure 20 shows the simple principal and most significant benefit of intermediate belt conveyor drives. This flat, head driven conveyor has a simple belt tension distribution as shown in black. Although the average belt tension during each cycle is only about 40% of the peak value, all the belting must be sized for the maximum. The large drop in the black line at the head pulley represents the total torque or power required to run the conveyor. By splitting the power into two locations (red line), the maximum belt tension is reduced by almost 40% while the total power requirement remains virtually the same. A much smaller belt can be used and smaller individual power units can be used. To extend the example further, a second intermediate drive is added (green line) and the peak belt tension drops further. The tunneling industry was also quick to adopt this technology and even take it to higher levels of complexity and sophistication. But the main need in tunneling was the necessity of using very tight horizontal curves. By applying intermediate drives (Figure 21) to an application such as the Baumgartner Tunnel as described in Figure 10 above, belt tensions can be controlled in the horizontal curves by strategically placing drives in critical locations thereby allowing the belt to turn small curves. Figure 20 Figure 21 In Figure 22, the hatched areas in green represent the location of curved structure. The blue line represents carry side belt tensions and the pink line represents return side belt tensions. Notice belt tensions in both the carry and return sides are minimized in the curves, particularly the tightest 750m radius. Figure 22 Although aboveground overland conveyors have not used this technology extensively to date, applications are now starting to be developed due to horizontal curve requirements. Figure 23 shows a South American, 8.5km hard rock application which requires an intermediate drive to accommodate the four relatively tight 2000m radii from the midpoint to discharge. Figure 23- Plan View Figure 24 shows a comparison of belt tensions in the curved areas with and without distributed power. The benefit of distributed power is also being used on the MRC Cable Belt. However, since the tension carrying ropes are separate from the load carrying belt, installing intermediate drives is even easier as the material never has to leave the carry belt surface. The tension carrying ropes are separated from the belt long enough to wrap around drive sheaves and the carry belt is set back on the ropes to continue on (Figure 25). Figure 24- Tension Diagram Figure 25 Analysis and Simulation Many will argue the major reason for our ability to build complex conveyo rs as described above is advancements in the analysis and simulation tools available to the designer. A component manufacturer can usually test his product to insure it meets the specification； however the system engineer can seldom test the finished system until it is completed on site. Therefore computational methods and tools are absolutely critical to simulate the interactions of various diverse disciplines and components. Dynamic Starting and Stopping When performing starting and stopping calculations per CEMA or DIN 22101 (static analysis), it is assumed all masses are accelerated at the same time and rate； in other words the belt is a rigid body (non-elastic). In reality, drive torque transmitted to the belt via the drive pulley creates a stress wave which starts the belt moving gradually as the wave propagates along the belt. Stress variations along the belt (and therefore elastic stretch of the belt) are caused by these longitudinal waves dampened by resistances to motion as described above. 7 Many publications since 1959 have documented that neglecting belt elasticity in high capacity and/or long length conveyors during stopping and starting can lead to incorrect selection of the belting, drives, take-up, etc. Failure to include transient response to elasticity can result in inaccurate prediction of: Maximum belt stresses Maximum forces on pulleys Minimum belt stresses and material spillage Take-up force requirements Take-up travel and speed requirements Drive slip Breakaway torque Holdback torque Load sharing between multiple drives Material stability on an incline It is, therefore, important a mathematical model of the belt conveyor that takes belt elasticity into account during stopping and starting be considered in these critical, long applications. A model of the complete conveyor system can be achieved by dividing the conveyor into a series of finite elements. Each element has a mass and rheological spring as illustrated in Figure 26. Figure 26 Many methods of analyzing a belts physical behavior as a rheological spring have been studied and various techniques have been used. An appropriate model needs to address: 1. Elastic modulus of the belt longitudinal tensile member 2. Resistances to motion which are velocity dependent (i.e. idlers) 3. Viscoelastic losses due to rubber-idler indentation 4. Apparent belt modulus changes due to belt sag between idlers Since the mathematics necessary to solve these dynamic problems are very complex, it is not the goal of this presentation to detail the theoretical basis of dynamic analysis. Rather, the purpose is to stress that as belt lengths increase and as horizontal curves and distributed power becomes more common, the importance of dynamic analysis taking belt elasticity into account is vital to properly develop control algorithms during both stopping and starting. Using the 8.5 km conveyor in Figure 23 as an example, two simulations of starting were performed to compare control algorithms. With a 2x1000 kW drive installed at the head end, a 2x1000 kW drive at a midpoint carry side location and a 1x1000kW drive at the tail, extreme care must be taken to insure proper coordination of all drives is maintained. Figure 27 illustrates a 90 second start with very poor coordination and severe oscillations in torque with corresponding oscillations in velocity and belt tensions. The T1/T2 slip ratio indicates drive slip could occur. Figure 28 shows the corresponding charts from a relatively good 180 second start coordinated to safely and smoothly accelerate the conveyor. Figure 27-120 Sec Poor Start Figure 28- 180 Sec Good Start Mass Flow at Transfer Points One of the reasons for using intermediate drives and running single flight conveyors longer and longer is to eliminate transfer points. Many of the most difficult problems associated with belt conveyors center around loading and unloading. The transfer chute is often sited as the highest maintenance area of the conveyor and many significant production risks are centered here. Plugging Belt and Chute Damage and Abrasion Material Degradation Dust Off Center Loading/Spillage In the past, no analytical tools have been available to the design engineer so trial-and-error and experience were the only design methods available. Today, numerical simulation methods exist which allow designers to “test” their design prior to fabrication. Numerical simulation is the discipline of designing a model of an actual physical system, executing the model on a computer, and analyzing the results. Simulation embodies the principle of “l(fā)earning by doing. To understand reality and all of its complexity, we build artificial objects in the computer and dynamically watch the interactions. The Discrete Element Method (DEM) is a family of numerical modeling techniques and equations specifically designed to solve problems in engineering and applied science that exhibit gross discontinuous mechanical behavior such as bulk material flow. It should be noted that problems dominated by discontinuum behavior cannot be simulated with conventional continuum based computer modeling methods such as finite element analysis, finite difference procedures and/or even computational fluid dynamics (CFD). The DEM explicitly models the dynamic motion and mechanical interactions of each body or particle in the physical problem throughout a simulation and provides a detailed description of the positions, velocities, and forces acting on each body and/or particle at discrete points in time during the analysis. 8 In the analysis, particles are modeled as shaped bodies. The bodies can interact with each other, with transfer boundary surfaces and with moving rubber conveyor belt surfaces. The contact/impact phenomena between the interacting bodies are modeled with a contact force law which has components defined in the normal and shear directions as well as rotation. The normal contact force component is generated with a linear elastic restoring component and a viscous damping term to simulate the energy loss in a normal collision. The linear elastic component is modeled with a spring whose coefficient is based upon the normal stiffness of the contact bodies and the normal viscous damper coefficient is defined in terms of an equivalent coefficient of restitution (Figure 29). Figure 29 Figure 30 shows particles falling through a transfer chute. The colors of the particles in the visualization represent their velocity. T