Khetri Tank House Modern Is At Ion

KHETRI TANK HOUSE MODERNIZATION

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SOME TECHNICAL AND ECONOMIC ASPECTS P, Balachandran, M, J. Alam, G. L. Bhotoa Hindustan Copper Limited Khetri Copper Complex Khetri Nager-333504, (India)

m&mt Abstract The paper o u t l i n e s the exi s t i n g f a c i l i t i e s and worki ng p r a c t i c e s at the K h e t r i e l e c t r o - r e f i n e r y of Hindustan Copper L i m i t e d . Plans have boon drawn up to mechanize sonic key ope cations to improve tho q u a l i t y . o f cathodes and the working environment as v;e 11 as economize the refinery operations. The economic analysis for determining v a r i o u s optimum o p e r a t i o n a l parameters under c o n d i t i o n s e x i s t i n g i n I n d i a have also been o u t l i n e d . The impact of c a p a c i t y u t i l i s a t i o n and mechanization under d i f f e r e n t sets of c o n d i t i o n s on o p e r a t i o n a l costs have been h i g h l i g h t e d .

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KHETRI TANK HOUSE MODERNIZATION h

SOME TECHNICAL AND ECONOMIC ASPECTS

BY P. BALACHANDRAN M. J. ALAM G. L. BHOTOA

PAPER PRESENTED AT SYMPOSIUM SPONSORED BY THE TMS COPPER, NICKEL, PRECIOUS METALS AND ELECTROLYTIC PROCESSES COMMITTEES HELD AT THE TMS 116TH ANNUAL MEETING IN DENVER, COLORADO, FEBRUARY 24-26, 1987..

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Introduction H i n d u s t a n Copper L t d . , a Government o f I n d i a E n t e r p r i s e , i s t h e s o l o producer of copper in India. The company has two underground mining / m e t a l l u r g i c a l u n i t s s i t u a t e d in ttie eastern and western pa,rts of the country and an open-cast mine s i t u a t e d in the c e n t r a l p a r t . The u n i t si tuated in the western Complex (KCC), has faci l i t i e s to electrolytic grade copper. The c o n c e n t r a t o r , smelter refinery and

s e c t o r , c a l l e d the K h e t r i Copper produce 31,000 m e t r i c tqns of facil i ties consist of [nines, acid / f e r t i l i z e r plants, The

smelter utilizes the flash furnace, converter and anode furnace route for producing anode copper. The electrolytic refinery, operating at a conventional current density produces copper at 80-855! of the rated capacity. The metallurgical complexes wore were commissioned during ttic year 1974. In order to increase the production of copper in the country, the concentrates which are available from the new mine located at Malanjkhand i ti the state of Kadhya Pradesh, are also proposed to be smelted at KCC. Bo LI) smelter and refinery units arc going through major' modi fications to improve opera tions to accommodate the increased production. As a part of this modernization scheme the facilities at the? electrolytic plant are expected to be mechanized. It is also proposed to set up an electrolyte regeneration and purification plant. In this, paper an attempt has been made to analyze.the technical and economic aspects of the Tank House operation, especially as it relates to mechanizing the eel 1 operation. Cost curves have been developed to obtain a better understanding of the impact of various technical parameters on the operating expenses. Description of the exi sting instailation

1.

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The existing installation consists of 440 cells of which 44 cells are stripper cells. Three independent electrolyte circuits are used to supply hot, condi tioned, fi11 nred electrolyte, one circuit is used for the stri pper eel 1 s and two i or the commercial cells. Ten coiiunercial cells, distributed equally over the electrolytic plant have been converted t o c o n t r o l c e l l s •".ing insoluble anodes. They are utilized to c o n t r o l the b u i l d - u p of COJ1: •r in the electrolyte. The cells themselves are assembled i n groups of il cells to facilitate electrical isolation for cell operations. The cells are constructed using 100 m.m thick concrete and 43! antimonial lead liners. Their dimensions are 3.6m ( length ) x 0.93m ( width ) xx 1.60m ( height ). The cells have a draining c i r c u i t f o r e l e c t r o l y t e r moval and slime collection. The slime Is sent to the fi H e r press locati i in the separate building for filtration. The e l e c t r o l y t e and slime pip; ; a\-c made of PVC lines with Fill', The Tank House is d i v i d e d i n t o three a d j o i n i n g bays, two bays of at the end are 24,25 m wide and a c e n t r a l one i s 1.1.5 m wide. The two end bays accommodate the e l e c t r o l y t e c e l l s and the c e n t r a l bay accommodates the equipment f o r heat, i n g , pumping and condi t ion ing of the e l e c t r o l y t e , as given in Figure 1. The production bays are s e r v i c e d by three 12 tonne EOT Cranes, The c e n t r a l boy is p r o v M ' d wi th one 5 ton no EOT Crane f o r maintenance of

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Lin.1 cast In the smelter on an anode casting wheel, u thickness is manually control led resulting in wide variations in anode weight. Use of such anodes adversely affects the steady operations in the oloctrolyt fc plant. It also liar, an impact on materials hand] Jny operations. Hence it lias been decided to introduce automatic weight control for anodes during casting and to supply anodes of uniform weight to the electrolytic plant. Si nee no lead or other heavy metals are present in the KCC anodes, slimes produced in the electrolyte has a tendency to float. Settling and filtration systems originally envisaged by the consultants proved inadequate to deal with the situation at a high level of capacity utilization. Consequently the slime filtration system, the electrolyte filtration system and electrolyte make-up system were modified to supply clear electrolyte to the electrolyte Circuits by using a S c h o o l e r filter.

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The material handling in the electrolytic plant is manual in nature. Anodes received from Smelter are dressed and spaced manually on racks, A 12 tonne EOT crane lifts the anodes in hooking devices and charges them into the eel 1. Copper shims are used under the anode lug to ensure proper vertical alignment. The starting sheets are manually stripped from copper mother blanks and are conveyed to the main riveting press by means of e hand driven troiicy. The riveted sheets are then straightened through a pair of rolls which also ridgedizes the sheets. The round current carrying bar is placed in the loop manually and tfie sheets are manually transferred on storage rac' ;. Starting sheets are transferred by EOT Crane and then charged again n ...ally between the anodes in the cell. Cells are filled with electrolyte and the electrical circuit is switched on by removing the isolating shunt. Proposed Mechaniza tion/Kodernization These operations are \-?ry labor intensive and need highly skilled operators. Operators and supervisors were leaving, causing occasional high labor turn over and posing a problem in maintaining a hi gh standard of operations. Moreover, the cost of labor has more than doubled for the past five years and this trend is likely to continue into the future. The cost of fuel and electricity has increased three times over the past few yoars, Hence, it has become very necessary to introduce mechanization In i.ho electrolytic plant in order to i;educe costs and improve the operating efficiency and productivity. It was felt at the outset that some of the operations of the existing plant ore necessary to be strengthened 'modified to improve the materia1 handl Ing and the plant operation. The proposed system deals with the a relatively, low current efficiency, the high rate of anode scrap generation, the high level of floating slimes in the electrolyte and the highly labor intensive handling equips it. In order to improve the operating efficiency and p r o d u c t i v e of the unit the fol lowing faci 1 i ties are proposed to be added and lodifi cation in some areas of operation are planned. 1. 2. 3. 4.

Anode milling and spacing machine Automatic starting sheet preparation machine Cathode washing machine Mist separators Lo improve the ventilation system

Milli-volt

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each

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to

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short

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M o d i f i c a t i o n s i n e l e c t r o l y t e and s l i m e c i r c u i t s t o r e d u c e t h e l e v e l o f f l o a t i n g slimes i n tiie e l e c t r o l y t e S e t t i n g u p o f a n e l e c t r o l y t e p u r i f i Cd'. i o n p l a n t f o r p u r i f i c a t i o n o f e l e c t r o l y t e and r e - c i r c u l a t i o n o f black a c i d t o t h e e l e c t r o l y t e c i r c u i t with a d d i t i o n a l f a c i l i t y for recovery o f c r u d e n i c k e l sut f a t e . Mechanized system f o r a d d i t i o n of reagents.

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These measures have been planned for implementation after a detailed analysis of the problems faced i n the day-1 o-da.y operations on the shop floor. The following table gives the expected benefits of the modernization compared with the existing plant operation. PftestNT LEVEL

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LEVEL OF OPERATION AFTER

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of OPERATIONS

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Average current efficiency Percentage of Anode

ii)

\ Cathode production Total power consump tion Floating slime Percentage downtime of eel 1s Cathode Quality Copper Nickel Selenium Telluri um Sulphur Iron Antimony Bismuth Lead Silver Gold Recovery of acid

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91% 22$,

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2400 MT JOOKvJi/HT

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31,300 MT 210 Lo 250Kwh/MT

20 to 30 • pin 152

4 to 8 ppm 5 to 10%

99.99;i minimum 5.0 ppm 2 ppm 2 ppm 12-18 ppm 12-15 ppm 0,6 ppm 0.6 2 ppm 8-16 ppm

economic

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;,;•;:•• The e c o n o m i c a n a l y s i s has been b a s e d o n t h e h i s t o r i c a l c o s t d a t a o f the e x i s t i n g tank house. A n a n a l y s i s o f t h e o p e r a t i n g c o s t f o r the p a s t few y e a r s a t KCC R e f i n e r y i n d i c a t e s t h a t 40-50% o f t h e t o t a l c o s t o f p r o d u c t i o n amounts t o l o n g t e r m f i x e d c o s t s , They i n c l u d e d e p r e c i a t i o n , a l l o c a t e d f i n a n c i n g c h a r g e s and a l l o c a t e d c o s t o f s e r v i c e s . Out o f t h e b a l a n c e 4 0 - 6 0 S o f t h e c o s t s , power a l o n e a c c o u n t s f o r the 3'j.i. This is because power is a v e r y e x p a n s i v e commodity and at KCC the p r i c e i n c r e a s e p e r u n i t has buuti tour to] d over t h e l a s t b y u j r s . A;> (.lie p l a n t s i\\\; l o c a t e d i n a power clef i c i L area, c a p t i v e iji'iiut'i) L i o n of power i s b e i n g r e s o r t e d t o and t h e c o s t o f g e n e r a t i n g a n a d d i t i o n a l u n i t o f power

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amounts to Rs, 1.75 per KW/hr, The other major cost Hems arc manpower, spares and stores nnri operating supplies. However, these costs do not flic t u d e the c o s t s uf c a r r y lr«J t h e sm'La I l o c k e d up i n p r o c e s s ns w e i 1 3 s the cost of anode scrap remeltiny, but include allocated costs arid overheads which are beyond the control of the Project Planner gr Operating Manager. In analyzing the impact of operating parameters on cost, the concept of relevant cost has been adopted. Sunk costs which have already been incurred at the time of making the decision have not been considered. Future cash costs l i k e i n t e r e s t on metal locked up, cost of materials and energy which are p a r t i a l l y or f u l l y amendable for control by the Project or Operating Manager have been taken into account. The future impact of sunk costs l i k e interest on capital already employed have not been accounted f o r as they have no influence on tlie decision at hand, The results of these calculations on a few c r i t i c a l parameters are discussed in this section. Current density Current density is the most important parameter in any copper refinery. In conventional r e f i n e r i e s ( l i k e KCC), the current density is nta In tained between 180-240 amps/st) .01. Increased' current den si ty increases p o l a r i z a t i o n and f i n a l l y causes anode passivation. In the context of the KCC r e f i n e r y , however, it is possible to operate at f a i r l y high levels of current density cfue to lower value of impurities' in anodes, 1'ltG power consumption i ncrcases wi th the current densi ty as the production increases i n proportion to the current where as the power consumption increases by the square of the current even if a linear voltage current r e l a t i o n s h i p is assumed. Polarization and other resistances themselves increase with current d e n s i t y and this increase "in power consumption is even much larger. A higher current densi ty .also requires better operational . c o n t r o l , At a higher current density there is a tendency for excessive nodulation and formation of a spongy deposi t with the resulting cathode quality On tlie other hand a hi gher current density reduces .' the The investment and capi tal costs costs as as the output per cell increases. capital optimum current density depends not only on the capital cost, the cost of power and labor labor but but also also on the ski 11 and diligence of the operators. exi sting refinery refinery capital cost is a sunk cost and is not Tor an existing Increases in [.reduction arc relevant and have to be relevant. considered. If the current densi ty in an operating refinery like KCC is increased wi thout any improvements in the operation, 1 i ke better short circui t detection, or Letter electrolyte ci rculation, the current efficiency is 1 ikely to -'ateriorate wi th associated problems which may become counter-producti :•<.•. An economic analysis of the KCC Refinery indicates that the optinmi is reached at around 210 Amps/sq.m. i.el, at a production level of 3050 HT of cathodes per month. As the availability of anodes is below this level the tank house is presently being operated at a current density of 195 Amps/sq.m. Moreover, as the electrolyte regeneration cells in tank house are being serviced by the same rectifier it is not possible to iticrease the current density to the optimum. While calculating the relevant cost, the cost of power, manpower, operating materials, spares and the i nterest on the me to! locked has been' taken into account. The d-Ua is given in Figure 'I. This graph is comparative

358

in nature and the cost of exi sting operations is taken as 100. The y-axis is basically the ratio between the projected cost and the standard cost expressed as a percentage.

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Impact of Material Handling This is an important section of Tank House from the cost point of view since most of the manpower is used for materials handling. As indicated earlier, it is possible to insulate the efficiency of cell operations from the manual skill of workers 1W introducing mechanization. Consequently, considerable scope exi sts in improving operational efficiency and productivity. W1 tli mochanized material hand] i ng, operations are expected to p r i m a r i l y take

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Manpower requirement is reduced

2.

Current efficiencies improve by .

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5, 6, 7,

Cell n v a i l a b i l i t i e s increase by 5-10? As tinotius and CitUtodos are uniform and s t r a i g h t the between the anode and cathode can be reduced by [ >% with consequent saving in power As a r e s u l t of the above f a c t o r s the o u t p u t Increases more in r e l a t i o n to the c u r r e n l . rlcur, il.y n; compared to n not) median i zcti opera I ion The chemical q u a l i t y of catliode improves ( t h e impact of t h i s cost cannot be e v a l u a t e d ) The c u r r e n t flow in almost a l l the anodes and cathodes in tank house would be u n i f o r m with very l i t t l e v a r i a t i o n in catliode weights as compared to manual o p e r a t i o n

The e f f e c t of the above on the c o s t of o p e r a t i o n is a l s o given in F i g u r e 2. It can be seen from the f i g u r e t h a t the c o s t of o p e r a t i o n s are h i g h l y s e n s i t i v e to the l e v e l s of p r o d u c t i o n a ' f t e r mechanization as compared to the manual o p e r a t i o n . This is because the costs a s s o c i a t e d w i t h the c a p i t a l e x p e n d i t u r e i . e . , f u t u r e d e p r e c i a t i o n and i n t e r e s t o n investment ( r o u g h l y 6%) have to be i n c l u d e d in the c o s t . The net r e s u l t is that i r tho r e f i n e r y is operated below 90$ of the production capacIty the mechanization would not be economical. On the o t h e r hand expanding the tank house by adding a few more o p e r a t i n g c e l l s w i l l reduce the cost and make the mechanization more v i a b l e . Cathode Weight Once a c u r r e n t d e n s i t y has been determined the next major parameter which a f f e c t s the cost is the cathode w e i g h t , Changes in the cathode weight i n an o p e r a t i n g r e f i n e r y have p r i m a r i l y the f o l l o w i n g cost implications: 1,

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Increased cathode weight decreases the s t a r t i n g sheet requirement and reduces the m a t e r i a l handling i n v o l v e d with anodes Increased cathode weight in t u r n increases the anode weight thus l o c k i n g up more work-in-progress and hence h i g h e r working c a p i t a l costs Increased cathode weigh' results in a decreased scrap m e l t i n g , load as the cathode d e p ; i . ; i t is more in p r o p o r t i o n to the anode scrap generated

Due to the above three i sasons., i n o r d e r to compare the cost behavior of the v a r i o u s pa rain;!ers and i t s s e n s i t i v i t y on c o s t , cathode weight can be taken as the independent v a r i a b l e to study c o s t s . However, due to p r a c t i c a l problems the cathode weight cannot be Immediately increased in an e x i s t i n g tank iiouse. Parameters l i k e i n t e r f a c e c o r r o s i o n a t the loops and c o n t r o l of d e p o s i t i o n a t the loops are some of the v a r i a b l e s w h i c h ' a r e process l i m i t a t i o n s . S i m i l a r l y f o r a manual m a t e r i a l h a n d l i n g system (as e x i s t i n g at KCC) the c a p a c i t y of the o p e r a t i n g personnel to unload the heavier cathodes manually also becomes a constraint. However, progressive increases in cathode weight over a p e r i o d of time would help in reducing c o s t s .

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360

Crops of cathodes per anode cycle In copper e l e c t r o - r e f i ning normally two crops of cathodes are obtained for one s e t of anodes charged ( i . e . , two crop o p e r a t i o n ) . In some o t h e r conventional refi n e r i e s three crops of cathodes are obtained for one s e t of anodes charged ( i . e . , three crop o p e r a t i o n ) . A major departure from t h i s p r a c t i c e has been introduced s u c c e s s f u l l y a t Onahama No. 3 tank house where a one cathode crop/anode crop method has been practiced. The e v a l u a t i o n of the three a l t e r n a t i v e s i s qui'te r e l e v a n t for a r e f i n e r y planning for mechani zation and hence a c o s t a n a l y s i s i s necessary for t h i s purpose.

180 170 ©

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2 3

3a 150

jjj 130 o 5 120 n

6

100 90 80 60

7r>

Cathode

80 weight

Fig-3: Effect .f cathode weight on handling costs & s t a r t i n g shoot costs for 1,2 & 3 of cathodo/anode cycle.

The r e l e v a n t costs under c o n s i d e r a t i o n for a n a l y s i s are the cost of manpower and s t a r t i n g s h e e t s , i n t e r e s t on work-in-progress employed and cost of remelting anode s c r a p . Figure 3-6 give the r e l e v a n t c o s t s for copper r e f i n i n g in a conventional tank house. The e x i s t i n g cost ( a t 80 Kg of.cathode weight with 2 cycle o p e r a t i o n ) is taken as standard the above f i g u r e s . . I t c a n b e s e e n from F i g u r e 3 t h a t t h e c o s t o f m a t e r i a l h a n d l i n g a n d s t a r t i n g s h e e t p r e p a r a t i o n (with manual h a n d l i n g ) is h i g h e s t f o r a one crop operation. The c o s t d e c r e a s e s w i t h c a t h o d e w e i g h t d u e t o r e a s o n s mentioned e a r l i e r . The t h r e e c r o p o p e r a t i o n h a s minimum c o s t s d u e t o t h e l o w e r anode h a n d l i n g c o s t per c r o p .

The Figure 4 gives the c o s t of in process copper locked-up in' cells. Increased cathode weights i n c r e a s e t h i s f i g u r e . However, the co UKKIC crofi/itumfo eye lo ojiotMtion has .i t;l<*sr adv^nt^u)' 1 on t,ho other modes of operation as the anodes have l e s s o r weight and do not remain longer period of time in c e l l s .

the one two for

The F1 (jure r> gives the cost of scrap rcmel t i n g . At KCC, the scrap lin
300

•a 2 5 0 o 200 ••

150

100

50--

60

70

80 90 100 HO Weight of cathodo in K%.

^ . 4 t Fl'feot or cathodo weight on inventory c a r r y i n g cost for 1,2 & 3 crops of t l / cycle,

352

Cost Ratie/MT of cathode

Cost Ratlo/MT of cathode

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The t o t a l r e l e v a n t costs of processing are given in Figure 6, f o r a ope c r o p , I.wo eni]> .mil Ihrei 1 crop itpptMt. i o n , ; l i d i n he SMMI I nnu lite fftjW|»r t h a t t h e c o s t o f a t h r e e c r o p o p e r a t i o n i s a l m o s t I n d i f f e r e n t t o caLhii
wo are opera t i n y . I t must be pointed out that these curves are f o r an e x i s t i n g r e f i n e r y with manual material h a n d l i n g , where tho o t h e r advantages of pne cathode crop/a node c y c l e system 1 i ke reduced handling c o s t s , reduced Given those manpower and very high l e v e l of rnechan• zation do not e x i s t . advantages, the si ngle crop system may prove to be economical f o r a'new refinery. Conclusion The abovo economic a n a l y s i s has been tho primary basis for determining the f u t u r e course of a c t i o n to be taken to modernize and mechanize the r e f i n e r y . As the p r o d u c t i o n of copper i s 1 i k e l y to i n c r e a s e , it is expected t h a t the p r o d u c t i o n at the KCC r e f i n e r y could be increased economically wi th mechani z a t i o n . The exi s t i n g m o d e r n i z a t i o n scheme can a l s o f a c i l i t a t e expansion by a d d i t i o n of new c e l l s to meet"the f u t u r e demands a l s o . I t is expected t h a t the above t e c h n i c a l ' and economic models would be used a f t e r m o d e r n i z a t i o n to maximize b e n e f i t s i n an ever changing scenario of p r i c e s and c o s t s . :

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Annexure Basic o p e r a t i n g data of e l e r

1.

2.

'..colytic refinery

Anode Composi t i o n :

Cu

99.3 -99.5'

N1

750 ppm

Fe As Sb iSi Pb

120

ppm •

•10 ppm 9 ppm 60 ppm

Se To Au Ag 02

300 150 VI 160 45

ppm |)pm

ppm ppm

ppm 1500 I'I'm

1

30 ppm

Number of eel 1s:

44 ( i n one electrolytic ci rcuit) 396 ( i n two electrolytic ci rcuit of 198 e a c h ) CoiTiiiercifll Size of Anode: 942 x 760 x 35 inm3 (weight 220 Kg) Size of Cathode: 960 x 830x (). 6 mm Current densi t y : 195 Amps/Sq m Anode to cathode spacing 115 mm Number of anodes/ce 1 29

Stripper

3. 4. 5, 6.

Number of cathodes/eel 1 Number of c e l l / s e c t i o n

30 11

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