ISSN 1068364X, Coke and Chemistry, 2012, Vol. 55, No. 6, pp. 197–203. © Allerton Press, Inc., 2012. Original Russian Text © M.V. Davydov, 2012, published in Koks i Khimiya, 2012, No. 6, pp. 2–8.

COAL

Stable Operation of the Water–Slurry System at Enrichment Facilities M. V. Davydov Moscow State Mining University, Institute of Coal Enrichment, Lyubertsy, Russia email: [email protected] Received May 10, 2012

Abstract—Practical data are presented regarding coal extraction and enrichment. Water flow rates for jigging are recommended. The additional secondary slurry formed is expressed as a function of the depth of coal enrichment. The quantity of additional slurry in the ≤0.5 mm class that is formed in the basic operations is determined. The major manufacturers of effective flocculants are listed. Russian and nonRussian approaches to improving the operation of water–slurry systems are analyzed and compared. DOI: 10.3103/S1068364X12060026

The strategic goal between now and 2030 is to pro vide the coal and coke industry with progressive Rus sian technology and equipment, including innovative designs. In this context, effective coal enrichment requires stable operation of the plant’s water–slurry system. In the past decade, global demand for coal has grown by almost 50% (as compared to 30% for natural gas and <10% for atomic power). Hence, nationally and globally, coal is a primary resource capable of meeting the needs of the metallurgical and power industry and also municipal and domestic needs. The extraction of Russian coal increased by a quar ter in the past decade; it was 336.7 million t in 2011. Exports almost tripled, to 117.1 million t. Note that all the exported coal is first enriched [1]. Within Russia, all the coking coal (67.0 million t in 2011) is enriched. The enrichment of energy coal has increased consid erably, to 132.9 million t. At present, 51 enrichment facilities and 12 smaller enrichment plants operate in Russia. They all employ wet enrichment methods: jigging (30%), heavy fluids (55%), flotation (9%), or counterflow (3%) and screw (3%) separation. Note that, taking account of auxiliary operations, the mean water consumption is 3–4 m3/t of processed coal (Table 1). In enrichment, the water is contaminated by slurry that is saturated with salts, flotation agents, floccu lants, and magnetite, with consequent change in its properties. Several forms of water are available at enrichment facilities: fresh water, recycled water, slurried water, regenerated water, and clarified water. Experience shows that regenerated water is the most effective. Such water is primarily employed in preliminary clas

sification of coal, slurry removal from the initial coal and enrichment products, repeated enrichment of the intermediate product in hydraulic cyclones, washing of magnetite with separation products, and wet dust trapping in dryers. The total consumption of recycled, regenerated, and clarified water depends on the depth of enrichment: with less enrichment, the water con sumption per 1 t of enriched coal increases. The structure of the water–slurry system largely depends on the purpose of the concentrate—for cok ing or for energy generation—since the coal quality depends on the filtration properties of the slurry. Table 1. Recommended water flow rates in jigging

197

Coal characteristics ease of enrichment

High and moderate

particle size, mm

oxide content, %

Total water consump tion, m3/t

Up to 13

≤15

2.0

15–25

2.4

>25

3.0

≤15

2.4

15–25

2.8

>25

3.5

≤15

2.2

15–25

2.6

>25

3.3

≤15

2.6

15–25

3.0

>25

3.6

Above 13

Up to 13

Low Above 13

0.0075 mm class, %

85

Yield of

VI

85 750 700 650 600 550 500

80 75 70 65 60 55

Ease of flotation

50

80 75 70 65

60 VI

450 400

55

350 300

45 40

250

35

0.075 mm class, %

DAVYDOV

50 45 40 35

% Ash content of

198

Fig. 1. Dahlstrom nomogram for determining the filtration properties of the slurry.

The filtration properties may be characterized on the basis of the Dahlstrom formula c

D sl = A 0.075 γ 0.075 ,

(1)

c

where A 0.075 is the ash content of the <0.075 mm class, %; γ0.075 is the yield of the 0.075 mm class in <0.5 mm slurry, %. In design calculations, we may use data from the Dahlstrom nomogram (Fig. 1). The recommended upper limit on the slurry’s particle size is 0.5 (0.2) mm, which is optimal for flotation. Table 2. Total quantity of slurry Rank of coal B D D G G G G Erunakovsk and similar coal T T A A K(K10), 1K, 2K Zh, KZh, 1K, 2K, OS and corre sponding batch

Enrichment depth, mm

Additional slurry from initial coal, %

13 0 13 0 13(6) 25 0

20 10 8 Up to 10 Up to 5 Up to 3 Up to 22

13

Up to 16

0 13 13(6) 0 13

Up to 14 Up to 12 Up to 3 Up to 5 Up to 14

0

9–17

Largegrain slurry corresponds to the range 0.5– 2.0 mm, smallgrain slurry to 0.05–0.50 mm, and finegrain slurry to <0.05 mm. The weightedmean yield of ≤0.5mm particles, according to screening of the raw materials at enrichment facilities, should be around 2, 15, and 25% for enrichment depths of 25, 13, and 0 mm. The picture is much more complex for secondary slurries formed in the enrichment of differ ent ranks of coal, to different degrees (Table 2) [2]. Table 3 summarizes the data on slurry formation (class 0–0.5 mm) in different enrichment processes. Existing equipment for the removal of water and slurry from the separation products and for the purifi cation of slurrycontaminated water do not meet the prevailing standards. The solidphase concentration in recycled water should not exceed 50 g/L. For min eral impurities and finely disperse slurries that are dif ficult to separate, a concentration of no more than 5 g/L is required in the runoff from radial thickeners (with a moderate flocculant flow rate of 30–40 g/t of slurry) and in the filtrate from vacuum disk filters and filtering centrifuges [3]. Experience shows that in plants built before 1990, profound purification of slurrytainted water is extremely difficult, for three main reasons, in our view. 1. Unstable quality of the material sent for processing. 2. Nonuniform (and mainly excessive) load on the primary and auxiliary equipment. 3. Unbalanced consumption of flocculants and flo tation agents in the thickening and dehydration of granular and finegrain slurries and the regeneration of slurrytainted water. These factors are especially significant in the enrichment of coking coal. The production of stan dardized coke depends on the use of highquality con centrate: water content no more than 7%, ash content 8%, sulfur content 0.3%. However, to obtain such concentrate, we need not only a stable supply of raw materials but also profound regeneration of the water COKE AND CHEMISTRY

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recycled within the plant. In the last decade, numer ous highmolecular polymer reagents for use in coag ulation and flocculation have been developed and introduced, mainly in Germany, Russia, the United States, France, and Japan. Superfloc C500 organic coagulant is most widely used in the Kuznets Basin, where there are around 40 enrichment facilities, at which all the locally extracted coal is processed. The main benefits of this coagulant are its direct dosing in the system in commercial form, without any special preparation; and its effectiveness at low doses and over a wide pH range. The adoption of such reagents signif icantly reduces the need for inorganic flocculants. The broad variation in their molecular mass permits the selection of the optimal reagent for any specific pro cess. They dissolve instantaneously in water at any concentration. Table 4 lists the flocculants most com monly in use at present. Coal enrichment in Russia increased by 45% between 2000 and 2011: the increase was 13% for cok ing coal and more than 100% for energy coal. Regret tably, the Russian power industry hardly uses enriched coal, since it lacks the appropriate equipment. The picture is different for coking coal. Demand for coking coal is steadily rising in the steel industry. This is asso ciated with the expansion of steel production from scrap and has prompted improvements in the effi ciency of coke utilization. The plans for Russia’s steel industry up to 2020 call for additional coking coal (up to 47 million t) from new production capacity at deposits in the Kuznets Basin, the Far East, and the Yakutsk region. This is feasible, since it is a priority enshrined within the long term development program for the Russian coal industry (up to 2030). Improvement in the water–slurry system is also a concern for coalproducing countries such as Austra lia, Germany, India, China, and the United States. For example, in Germany, with an annual output of 120 million t of lignite and 12 million t of coal, coal is enriched separately at five enrichment facilities, despite its low ash content (1.5–8.0%) and sulfur con tent (0.15–0.50%). Large classes (>10 mm) are pro cessed in Dryuboi heavyfluid separators and small fractions, after preliminary dry slurry removal (limiting size 0.5 mm), in Batak sedimentation machines [4]. A distinguishing feature of German water–slurry systems is preliminary dry separation of the primary coal slurry (0.5 mm) from regular coal (size class ≤12 mm), with a moisture content below 6% in pneu matic centrifugal separators (diameter 4.7 m, produc tivity 180 t/h). With a moisture content above 6%, wet slurry removal, with the same limiting size, is under taken on vibratory screens. The particulate content at the screens is 350–400 g/L. Primary and secondary slurry is averaged out and thickened in radial systems with a peripheral drive (diameter 26–30 m), using Sidipur polymer floccu COKE AND CHEMISTRY

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Table 3. Slurry formation in enrichment Slurry source Accumulation in pyramidal and silotype bunkers (including highcapacity bunkers): up to 10 m up to 20 m up to 30 m Accumulation in slopingwall bunkers Preparation: dry wet Heavyfluid separators and screens for suspension discharge and dehydration Slurry removal ahead of enrich ment in jigging machines Jigging machines Slurry removal ahead of enrich ment in heavyfluid hydrocy clones: in conveyer (elevator) supply in pumping Thickening hydrocyclones Feeder and flotation pumps and pumps supplying flotational concentrate and other pulp Heavyfluid hydrocyclones and screens for suspension discharge and dehydration Dehydrating centrifuges: vibration centrifuges screw centrifuges

Additional ≤0.5mm slurry from initial material, %

3–4 4.5–6.0 6–8 2–3

1–2 2–3 2–4

1–2 6–12

1–2 8–12 3–6 6–12

2–5

2–4 4–6

lants. The thickened product is enriched in sixcham ber Denver flotation machines. The spent thickener, with particulate content up to 10 g/L, is recycled. To reduce the fuel losses with the wastes, flotation is pre ceded by control screening (0.5 mm class). The partic ulate content is is 180–200 g/L in the supply to the screens and no more than 150 g/L in the supply to flo tation. In selecting optimal doses, we need to take account of the following factors: the density, specific surface, ξ potential, and hydration of the solid phase; and the salt content (pH), temperature, electrical conductivity, and fluidity of the liquid phase. Slurry water is purified by means of Superfloc A100 anionactive flocculant. The combined use of A100, A400, and A500 flocculant (produced by Kemira, United States) is satisfactory in the clarifica

200

DAVYDOV

Table 4. List of flocculant manufacturers Flocculant characteristics Manufacturer Kemira

Sanyo

BASF

BASF

Ashland Eurasia

Country United States

Japan

Germany–Switzerland

Germany–Switzerland

United States–Russia

Flocculant Superfloc: N1008; N100; N300; N300M; C420; C436; C 460; C461; C470; C484; C485; C486; C507; C521; C573; C577; A95; A100; A105; A110; A115; A120; A125; A130; A137; A150; A185 Separan: AP273; AP269; AP45; AP3O; X08494; X08492 Sanfloc: 520P AH210P; AH70P; AH33OP

ionic activity

molecular mass

n c

– –

c

–

a a a c

– – – – –

n a

– – –

Magnafloc: 351; 333 10 24 338 139 3105; 155; 342; 1011; 3127; 156; 336; 919; 25AP; 525; 611 455

n a↓ a↓ a↓ a↓ a

15000000–20000000 Up to 20000000 Up to 10000000 Up to 20000000 Up to 5000000 Up to 20000000

a↑ c↓

Up to 5000000 Up to 20000000

Zetag: 7645; 7623; 7634; 7650; 7692 7541; 7529; 7547 7565; 7648 7563 7566; 7664; 7562; 7580; 7535; 7653 7557; 7555; 7587; 7502; 7503 7689; 7651 7568

c↓ c↓ c c c↑ c↑ c↑ c↑

Up to 20000000 Up to 5000000 15000000–20000000 Up to 10000000 15000000–20000000 10000000–15000000 Up to 20000000 Up to 10000000

Praestol: 2300 2500 2510 2415 2515 2520 2530 2440 2540

n n a↓ a↓ a↓ a a↑ a↑ a↑

6000000 14000000 14000000 9000000 14000000 14000000 14000000 9000000 14000000

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201

Table 4. (Contd.) Flocculant characteristics Manufacturer

SNF

Country

Flocculant

France–United States

ionic activity

molecular mass

2640

a↑

16000000

2350

a↑

6000000

185K

c↓

–

187K

c↓

–

189K

c↓

–

610BC

c↓

6000000

610BC, 611TR

c↓

6000000

851BC

c↓

9000000

630BC

c

6000000

622BC

c↑

4000000

650BC, 650TR

c↑

6000000

852BC

c↑

9000000

624BC

c↑

4000000

644BC

c↑

6000000

853BC

c↑

9000000

655BC

c↑

6000000

854BC

c↑

9000000

857BS

c↑

9000000

859BS

c↑

9000000

AN 905 VHM

a↓

25000000

AN 910 VHM

a↓

25000000

AN 923 VHM

a↓

25000000

AN 934 VHM

a

25000000

AN 945 VHM

a

25000000

AN 956 VHM

a↑

25000000

AN 970 VHM

a↑

25000000

AN 977 VHM

a↑

25000000

FO 4190

c↓

6000000

FO 4290

c↓

6000000

FO 4350

c↓

6000000

FO 4400

c

6000000

FO 4490

c

6000000

FO 4550

c↑

6000000

FO 4650

c↑

6000000

FO 4700

c↑

6000000

FO 4800

c↑

6000000

Note: The following notation is employed: n, nonionogenic; a, anionactive; a↑, strongly anionactive; a↓, weakly anionactive; c, cat ionactive; c↑, highly cationactive; c↓, weakly cationactive. COKE AND CHEMISTRY

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DAVYDOV

Concentrate Fugate slurry

CS

Flocculant

Compressed

–150 mm

air To store

To store

15–13 mm

To store

Recycled water

To store

Fugate slurry

CS

Supply

Fugate slurry

US

CS CS

Wastes

Wastes

To store

To bunker

0–13 mm

In circulation

To bunker To bunker

CS

Regular coal

To bunker 0–150 mm

Filtered recycled water

Regular coal 0–400 mm size class

Tailings

Fugate slurry

0–15 mm Supply tank for the hydrocyclones of the classification system

To vibrational screens (0–13 mm) Supply tank forthe heavy

CS

US

CS

US

Slurry tank

fluid hy dro cyc lones

CS Fugate slurry

Fig. 2. Optimal standard system for coking coal at enrichment facilities: CS, conditioned suspension; US, unconditioned suspension.

tion, thickening, filtration, and dehydration of coal slurry. OOO Mineral has some experience in using these reagents at Kuznets Basin plants. Effective utilization of the flocculants depends on correct preparation. They are usually employed in dilute solutions. In the first stage of dilution, the con centration must be 0.5–1.0%. In the second stage, a dilute solution with a working concentration of 0.01– 0.10 wt % is prepared in a special unit at 20°C, for 45 min. The basic flotation takes 5–7 min, while sec ondary flotation takes 4–6 min. The reagent employed is Montanol500. The particulate content in the mate rial supplied for flotation is 120–150 g/L. This process performs two basic functions: slurry enrichment; and regeneration of the water. The flotation wastes are treated with flocculant and then (with a particulate content of 350–400 g/L) sent for dehydration in a Dekanter sedimentation and fil tration centrifuge. On account of the high degree of separation (G = 500), the machine yields an external moisture content of the dehydrated product (together with the largeparticle concentrate) of 6.5%. The closed water cycle includes a final stage of dehydration by chambertype filter presses, since the moisture content of the sediment is 21–25%. No dryers are used for heat treatment of the flota tional concentrate. Thus, this is a stable water–slurry system with profound regeneration of the slurry tainted water. In the first stage, the recycled water is

averaged out and clarified in a radial thickener; in the second, flotational regeneration of the water is accom panied by mechanical treatment of the wastes in decanters and chambertype filter presses. This optimal system is used at reconstructed Rus sian enterprises—the Belovskaya, Kuzbasskaya, Pechorskaya, Neryungrinskaya, and Severnaya enrichment facilities—and also at plants constructed in the last decade, such as the Antonovskaya, Mezh durechenskaya, Shestaki, and Raspadskaya enrich ment facilities (Fig. 2). Note that Russian experience is incorporated in the design of such new enrichment facilities. Thus, slurry in the (0.15–2.00)mm size class, once regarded as hard to enrich by the existing gravita tional and flotation methods, is now enriched by means of screw separators produced in Australia, the United States, and South Africa. However, such equipment was devised by Russian scientists at the Institute of SolidFuel Enrichment, where research on screw separators for the enrichment of coal slurry was undertaken in the second half of the twentieth century under the leadership of N.N. Vinogradov. Today, thanks to the efforts of ZAO Giprougol’ and Setko specialists, such equipment is successfully in use at the OAO Vorkutaugol’ and Pechorskaya enrichment facility and also at many Kuznets Basin plants built since 2000. Thus, in the reconstruction of Pechorskaya COKE AND CHEMISTRY

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enrichment facility, which processes coking coal, the installation of such separators improved the operation of the heavyfluid cyclones and reduced the consump tion of flotation reagents. The magnetite consumption was reduced from 4 to 1 kg/t of processed coal. Imported Zemag and Derrick highspeed crushers also perform well, as well as vibratory screens (with G up to 4), radial thickening systems with a central drive, belttype filter presses, and Dekanter clarifying and filtering centrifuges. Wearresistant lining materials (ceramic or tungsten carbide) permit operation for 3– 4 years without rotor replacement. Imported slurry pumps, in which parts made of highchrome cast iron undergo rapid wear, are characterized by adequate durability. Mechanically regulated pulleys in Vbelt drives permit rapid and precise adjustment of the water–slurry system, which is particularly important. These measures improve the quality of cokingcoal concentrates and reduce the environmental impact of the enrichment facilities. The leading Russian research institutes in the coal industry—the Institute of Coal Enrichment and OAO SibNIIugleobogash chenie—are at work in this field. For example, the Institute of Coal Enrichment tested the water–slurry system at the Anzherskaya, Ziminka, Koksovaya, Krasnogorskaya, Pechorskaya, and Neryungrinskaya enrichment facilities between 2005 and 2010. On the basis of a technological audit, the Institute’s specialists developed and implemented recommendations for improving the water–slurry systems, so as to permit stable and effective operation of the enrichment facil ities. Automation of the enrichment facilities plays an important role in ensuring stable operation of the water–slurry systems. Existing dispatchercontrol sys tems do not adequately ensure stable operation of the water–slurry systems. Effective operation of a com plex automated enrichment facilities calls for the use

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of software for dynamic optimization of the enrich ment conditions, ongoing parameter correction, and multifunctional regulation of the water–slurry system. CONCLUSIONS Operational experience with new and recon structed enrichment facilities shows that the following measures ensure stable and reliable operation of the water–slurry system: (1) stable quality of the initial coal, in accordance with comprehensive analysis of the available coal; (2) optimal selection of the equipment for effective enrichment and dehydration of coal slurry; (3) sparing use of highly efficient and environmen tally safe flotation agents and flocculants, so as to intensify the filtration kinetics and improve the selec tivity of flotation; (4) improvement in the automatic control system, on the basis of software for multifunctional parameter regulation of the water–slurry system; (5) the formulation of a development program for enrichment facilities, including technological audits at least every 3–5 years. REFERENCES 1. Prospects for the Coal Industry beyond 2011, Ugol’, 2012, no. 3, pp. 40–51. 2. Gainullin, I.K., Particulate Removal from Water at Enrichment Facilities, Ugol’, 2011, no. 5, pp. 105–106. 3. Antipenko, L.A., Tekhnologicheskie reglamenty obogati tel’nykh fabric Kuzbassa (Regulations Regarding Kuz nets Basin Enrichment Facilities), Prokopevsk: OAO SibNIIugleobogashchenie, 2007, 2nd ed. 4. Kirnarskii, A.S., Water–Slurry Systems at German Enrichment Facilities, Ugol’, 2012, no. 1, pp. 56–58.