Економічні переваги сухий Triboelectric поділу мінералів

Економічні переваги сухий Triboelectric поділу мінералів

Льюїс Бейкер, Кайл P. Флінн, Frank J. Грач, and Stephen Gasiorowski

ST обладнання & Технології ТОВ, Массачусетс місті Needham 02494 США

Абстрактні

ST обладнання & Технології ТОВ (ЗАЛИШИТИ ЯК БУЛО) triboelectrostatic belt separator provides the mineral processing industry a means to beneficiate fine materials with an entirely dry technology. The high efficiency multi-stage separation through internal charging/recharging and recycle results in far superior separations than can be achieved with other conventional single-stage electrostatic systems. Технологія сепаратора трибоелектричного ременя була використана для розділення широкого спектру матеріалів, включаючи суміші скляних алюмосилікатів / вуглецю., Кальцит/кварц, Тальк/магнезит, та барит/кварц. Можливості розширення поділу STET системи може бути дуже ефективною альтернативою флотаційних процесів. An economic comparison conducted by an independent mineral processing consulting firm of the triboelectrostatic belt separator versus conventional flotation for barite / quartz separation illustrates the advantages of dry processing for minerals. Utilizing this dry process results in a simpler process flow sheet with less equipment than flotation with both capital and operating expenses reduced by ≥30%.

Ключові слова: Мінерали, сухий розлуки, бариту, трибоелектростатичні зарядки, пояс сепаратор, золи

ВВЕДЕННЯ

Відсутність доступу до прісної води стає основним фактором, що впливає на доцільність гірничих проектів по всьому світу. За словами Юбер Флемінг, колишній світовий директор з Люк води, "З усіх гірничих проектів у світі, які або були зупинені або сповільнилися протягом останнього року, Він був, практично в 100% з випадків, результаті води, either directly or indirectly‿ (Блин 2013)1. Dry mineral processing methods offer a solution to this looming problem.

Wet separation methods such as froth flotation require the addition of chemical reagents that must be handled safely and disposed of in an environmentally responsible manner. Inevitably it is not possible to operate with 100% water recycle, requiring disposal of at least of portion of the process water, likely containing trace amounts of chemical reagents.

Сухі методи, такі як Електростатичний поділ, усунуть необхідність прісної води, і пропонувати потенціал для зниження витрат. One of the most promising new developments in dry mineral separations is the triboelectrostatic belt separator. Ця технологія розширила діапазон розмірів частинок на тонкі частинки, ніж звичайні електростатичні технології поділу, в діапазоні, де тільки флотація була успішною в минулому.

TRIBOELECTROSTATIC BELT SEPARATION

The triboelectrostatic belt separator utilizes electrical charge differences between materials produced by surface contact or triboelectric charging. Коли два матеріалів знаходяться в контакті, material with a higher affinity for electrons gains electrons and thus charges negative, в той час як матеріал з меншою спорідненістю електронів заряду позитивний. Цей контакт обмін безкоштовно спостерігається повсюдно на всі матеріали, Іноді викликаючи Електростатичний шкідливого впливу, що проблема в деяких галузях. Electron affinity is dependent on the chemical composition of the particle surface and will result in substantial differential charging of materials in a mixture of discrete particles of different composition.

In the triboelectrostatic belt separator (Цифри 1 і 2), матеріал подається в тонку щілину 0.9 - 1.5 см (0.35 -0.6 in.) between two parallel planar electrodes. Частинки трибоелектрично заряджені міжчастинкових контактів.

Наприклад, у разі спалювання вугілля Fly Ash, суміш частинок вуглецю і мінеральних частинок, позитивно заряджено вуглець і негативно заряджені мінерал притягуються до протилежних електродів. Частинки потім змішані шляхом безперервного переміщення відкритих сітчастих ременів і передав у протилежних напрямках. Ремінь рухається частинок примикає до кожного електрода на протилежних кінцях розділювач. Електричне поле потрібно тільки перемістити частинок крихітної фракції сантиметра, щоб перемістити частинку від лівого переїзду до правого рухомого потоку. The counter current flow of the separating particles and continual triboelectric charging by carbon-mineral collisions provides for a multistage separation and results in excellent purity and recovery in a single-pass unit. Швидкість Паса висока також дає дуже висока throughputs, до 40 тонн на годину на одному сепараторі. Контролюючи різних параметрів процесу, Наприклад, швидкість Паса, годувати точки, розрив електрода і швидкість подачі, пристрій забезпечує низький вуглець літати золи на вміст вуглецю 2 % ± 0.5% від корму літати попіл, починаючи з вуглецю з 4% до більше ніж 30%.

Фігура 1. Схема сепаратора трибоелектричного ременя

Конструкція сепаратора відносно проста. До пояса пов'язано ролики можна тільки рухомі частини. Електроди мають стаціонарні і складається з відповідним чином міцного матеріалу. Ремінь виготовлений з пластикового матеріалу. Довжина сепаратора електрода приблизно 6 м. (20 метрів.) і ширина 1.25 м. (4 метрів.) для повнорозмірних комерційних підрозділів. Споживана потужність становить близько 1 кіловат-годин на тонну матеріалу, обробленого більшою частиною потужності, споживаної двома двигунами, що приводили ремінь.

Фігура 2. Деталі зони розділення

Процес є повністю сухий, не вимагає додаткових матеріалів і не виробляє жодних стічних вод або викидів повітря. У випадку з карбону з льоту зола кольороподілу, відновлені матеріали складаються з Fly Ash знижується вміст вуглецю до рівнів, придатних для використання в якості pozzolanic домішки в бетон, і висока вуглецева фракція, яка може бути спалена на заводі з виробництва електроенергії. Використання обох потоки продукт забезпечує за 100% вирішення проблем утилізації золи.

The triboelectrostatic belt separator is relatively compact. Машина призначена для обробки 40 тонн на годину - це приблизно 9.1 м. (30 метрів) довгий, 1.7 м. (5.5 метрів.) широкий і 3.2 м. (10.5 метрів.) висока. Необхідний баланс заводу складається з систем для передачі сухого матеріалу до і з сепаратора. Компактність системи дозволяє гнучко встановлювати конструкції.

Фігура 3. Commercial triboelectrostatic belt separator

Comparison to other electrostatic separation processes

The triboelectrostatic belt separation technology greatly expands the range of materials that can be beneficiated by electrostatic processes. The most commonly used electrostatic processes rely on differences in the electrical conductivity of the materials to be separated. In these processes, the material must contact a grounded drum or plate typically after the material particles are negatively charged by an ionizing corona discharge. Conductive materials will lose their charge quickly and be thrown from the drum. The non-conductive material continues to be attracted to the drum since the charge will dissipate more slowly and will fall or be brushed from the drum after separation from the conducting material. These processes are limited in capacity due to the required contact of every particle to the drum or plate. The effectiveness of these contact charging processes are also limited to particles of about 100 µm or greater in size due to both the need to contact the grounded plate and the required particle flow dynamics. Particles of different sizes will also have different flow dynamics due to inertial effects and will result in degraded separation. The following diagram (Фігура 4) illustrates the fundamental features of this type of separator.

Фігура 4. Drum electrostatic separator (Elder 2003)2

Triboelectrostatic separations are not limited to separation of conductive / non-conductive materials but depend on the well known phenomenon of charge transfer by frictional contact of materials with dissimilar surface chemistry. This phenomenon has been used in “free fall‿ separation processes for decades. Such a process is

illustrated in Figure 5. Components of a mixture of particles first develop different charges by contact either with a metal surface, or by particle to particle contact in a fluidized bed feeding device. As the particles fall through the electric field in the electrode zone, each particle’s trajectory is deflected toward the electrode of opposite charge. After a certain distance, collection bins are employed to separate the streams. Typical installations require multiple separator stages with recycle of a middling fraction. Some devices use a steady stream of gas to assist the conveying of the particles through the electrode zone.

Фігура 5. “Free fall‿ triboelectrostatic separator

This type of free fall separator also has limitations in the particle size of the material that can be processed. The flow within the electrode zone must be controlled to minimize turbulence to avoid “smearing‿ of the separation. The trajectory of fine particles are more effected by turbulence since the aerodynamic drag forces on fine particles are much larger than the gravitational and electrostatic forces. The very fine particles will also tend to collect on the electrode surfaces and must be removed by some method. Particles of less than 75 µm cannot be effectively separated.

Another limitation is that the particle loading within the electrode zone must be low to prevent space charge effects, which limit the processing rate. Passing material through the electrode zone inherently results in a single-stage separation, since there is no possibility for re-charging of particles. Тому, multi-stage systems are required for improving the degree of separation including re-charging of the material by subsequent contact with a charging device. The resulting equipment volume and complexity increases accordingly.

На відміну від інших процеси доступні Електростатичний розлуки, the triboelectrostatic belt separator is ideally suited for separation of very fine (<1 µ м) для помірно грубої (300µ м) матеріали з дуже високою throughputs. The triboelectric particle charging is effective for a wide range of materials and only requires particle – particle contact. З вузьким проміжком, висока електричного поля, поточний потік лічильник, vigorous particle-particle agitation and self-cleaning action of the belt on the electrodes are the critical features of the separator. The high efficiency multi-stage separation through charging / recharging and internal recycle results in far superior separations and is effective on fine materials that cannot be separated at all by the conventional techniques.

APPLICATIONS OF TRIBOELECTROSTATIC BELT SEPARATION

Золи

The triboelectrostatic belt separation technology was first applied industrially to the processing of coal combustion fly ash in 1995. For the fly ash application, the technology has been effective in separating carbon particles from the incomplete combustion of coal, з глиновалюмосилікатних частинок мінеральних речовин у льоту золи. Технологія сприяє утилізації мінерально-багатих Fly Ash як заміна цементу в бетонному виробництві. З 1995, 19 triboelectrostatic belt separators have been operating in the USA, Канада, ВЕЛИКОБРИТАНІЯ, and Poland, processing over 1,000,000 tons of fly ash annually. The technology is now also in Asia with the first separator installed in South Korea this year. Промислова історія поділу літаючої золи вказана в таблиці 1.

Таблиця 1. Industrial Application of Triboelectrostatic belt separation for fly ash

Mineral Applications

Electrostatic separations have been extensively used for beneficiation for a large range of minerals “Manouchehri-Part 1 (2000)‿. While most application utilize differences in electrical conductivity of materials with the corona-drum type separators, triboelectric charging behavior with free-fall separators is also used at industrial scales “Manouchehri-Part 2 (2000)‿. A sample of applications of triboelectrostatic processing reported in the literature is listed in Table 2. While this is not an exhaustive listing of applications, this table illustrates the potential range of applications for electrostatic processing of minerals.

Таблиця 2. Reported triboelectrostatic separation of minerals

Extensive pilot plant and field testing of many challenging material separations in the minerals industry have been conducted using the triboelectrostatic belt separator. Examples of separation results are shown in Table 3.

Таблиця 3. Examples, mineral separations using triboelectrostatic belt separation

Use of the triboelectrostatic belt separator has been demonstrated to effectively beneficiate many mineral mixtures. Since the separator can process materials with particle sizes from about 300 мкм до менше ніж 1 µ м, and the triboelectrostatic separation is effective for both insulating and conductive materials, the technology greatly extends the range of applicable material over conventional electrostatic separators. Since the tribo- electrostatic process is entirely dry, use of it eliminates the need for material drying and liquid waste handling from flotation processes.

COST OF TRIBOELECTROSTATIC BELT SEPARATION

Comparison to Conventional Flotation for Barite

A comparative cost study was commissioned by STET and conducted by Soutex Inc. Soutex is a Quebec Canada based engineering company with extensive experience in both wet flotation and electrostatic separation process evaluation and design. The study compared the capital and operating costs of triboelectrostatic belt separation process to conventional froth flotation for the beneficiation of a low-grade barite ore. Both technologies upgrade the barite by removal of low density solids, mainly quartz, to produce an American Petroleum Institute (API) drilling grade barite with SG greater than 4.2 g/ml. Flotation results were based on pilot plant studies conducted by the Indian National Metallurgical Laboratory (NML 2004)18. Triboelectrostatic belt separation results were based on pilot plant studies using similar feed ores. The comparative economic study included flowsheet development, material and energy balances, major equipment sizing and quotation for both flotation and tribo- electrostatic belt separation processes. The basis for both flowsheets is the same, Обробки 200,000 t/y of barite feed with SG 3.78 to produce 148,000 t/y of drilling grade barite product with SG 4.21 g/ml. The flotation process estimate did not include any costs for process water, or water treatment.

Flowsheets were generated by Soutex for the barite flotation process (Фігура 6), and triboelectrostatic belt separation process (Фігура 7).

Фігура 6 Barite flotation process flowsheet

Фігура 7 Barite triboelectrostatic belt separation process flowsheet

Theses flowsheets do not include a raw ore crushing system, which is common to both technologies. Feed grinding for the flotation case is accomplished using a wet pulp ball mill with cyclone classifier. Feed grinding for the triboelectrostatic belt separation case is accomplished using a dry, vertical roller mill with integral dynamic classifier.

The triboelectrostatic belt separation flowsheet is simpler than flotation. Tribo-electostatic belt separation is achieved in a single stage without the addition of any chemical reagents, compared to three-stage flotation with oleic acid used as a collector for barite and sodium silicate as a depressant for the silica gangue. A flocculant is also added as a reagent for thickening in the barite flotation case. No dewatering and drying equipment is required for triboelectrostatic belt separation, compared to thickeners, filter presses, and rotary dryers required for the barite flotation process.

Capital and Operating Costs

A detailed capital and operating cost estimate was performed by Soutex for both technologies using equipment quotations and the factored cost method. The operating costs were estimated to include operating labor, Обслуговування, energy (electrical and fuel), and consumables (наприклад,, chemical reagent costs for flotation). The input costs were based on typical values for a hypothetical plant located near Battle Mountain, Nevada USA.

The total cost of ownership over ten years was calculated from the capital and operating cost by assuming an 8% discount rate. The results of cost comparison are present as relative percentages in Table 4

Таблиця 4. Cost Comparison for Barite Processing

The total purchase cost of capital equipment for the triboelectrostatic belt separation process is slightly less than for flotation. However when the total capital expenditure is calculated to include equipment installation, piping and electrical costs, and process building costs, the difference is large. The total capital cost for the tribo- electrostatic belt separation process is 63.2% of the cost of the flotation process. The significantly lower cost for the dry process results from the simpler flowsheet. The operating costs for the triboelectrostatic belt separation process is 75.5% of the flotation process due to mainly lower operating staff requirements and lower energy consumption.

The total cost of ownership of the triboelectrostatic belt separation process is significantly less than for flotation. The study author, Soutex Inc., concluded that the triboelectrostatic belt separation process offers obvious advantages in CAPEX, OPEX (Івате), and operational simplicity.

CONCLUSION

The triboelectrostatic belt separator provides the mineral processing industry a means to beneficiate fine materials with an entirely dry technology. The environmentally friendly process can eliminate wet processing and required drying of the final material. The process requires little, if any, pre-treatment of the material other than grinding and operates at high capacity – up to 40 tons per hour by a compact machine. Energy consumption is low, less than 2 kWh/ton of material processed. Since the only potential emission of the process is dust, permitting is relatively easy.

A cost study comparing the triboelectrostatic belt separation process to conventional froth flotation for barite was completed by Soutex Inc. The study shows that the total capital cost for for the dry triboelectrostatic belt separation process is 63.2% of the flotation process. The total operating cost for triboelectrostatic belt separation is 75.8% of operating cost for flotation. The study’s author concludes that the dry, triboelectrostatic belt separation process offers obvious advantages in CAPEX, OPEX (Івате), and operational simplicity.

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