Tag Archives: MimboloveQingxin

Size matters, especially for cathode blocks

Written by Paul Adkins

Word filtering though to us in AZ China has it that the Chinese have made another breakthrough in cathode technology.

We understand that Qingxin Carbon, the cathode plant in Ningxia province right by the former Alcan smelter, has been able to develop a block which breaks new size records.   the new block, which is now being installed in Chalco’s 600KA plant in Liancheng, has dimensions of 720*560*3990.   This makes the blocks 20mm wider and 30mm higher than the blocks presently used at that smelter.

Going higher should in normal circumstances increase the life of the block.   There is more carbon between the liquid metal and the collector bar in the bottom of the block.   Whether that happens for Chalco Liancheng is a matter of conjecture, since the smelter is only 12 months old.

Going wider is something else.   We aren’t quite sure yet what the targeted gain is.   I consulted with a friend of mine who forgotten more about cathodes than I will ever know.   He tells me there are several possible gains to be had.

      • one less block in the lining,
      • just increasing the length of the pot with all other changes being increased proportionally (probably the most likely)
      • thinner joints (there is a technology where they basically butt the blocks together with a thin layer of glue in the joint)
      • reduce the width of the large joint along the headwall of the pot.

Either way, it’s an interesting move from a strategic viewpoint. Qingxin was already the only cathode plant in China that could make blocks to the old size. With Chalco accepting this new size into their 600KA line (and probably working closely with Qingxin on dimensions and specifications), the chances for other cathode plants to crack the 500KA and 600KA market just became a lot harder.

One basket, 288 eggs

Written by Paul Adkins

Chalco seems to be very confident in their new 500KA pots.   They have lined 100% of the pots with Qingxin cathode blocks.

According to our sources, Qingxin has now supplied something near 4000 pieces to Chalco’s flagship plant in Liancheng.   Since Liancheng has 288 pots, and assuming 10 – 12 blocks per pot, that aligns neatly with the information we heard, about the quantity delivered to Chalco so far.

So Chalco has a 100% supply agreement with Qingxin.   That’s a brave call, in my opinion, in a plant which is using new technology.   Of course, these blocks are massive, and long, and they have a unique shape, so probably Chalco had little choice when it came to finding someone who could extrude such sizes.   But if it were me, I would be out there working with back-up suppliers, paying for them to make the mould, and removing size limitations along the production line.   When you are the flagship plant, you don’t want to be brought undone by supplier problems.   Qingxin is a good supplier, and I don’t mean to malign them, but it’s a big risk by Chalco in such an important plant.   I will bet that Rio Tinto Alcan’s 600Ka plant is taking cathode blocks from multiple suppliers.

The next headache for the technical team at the Chalco 500KA plant will be to plan for the eventual failure of these cells.   How long will they last, running at 500KA, and using 50% graphite?    Of course, they will start a programmed phase-out of cells fairly soon, in order to avoid having all of them fail at the same time.   But how to plan the phase-out program when this is the first plant to run with these technology parameters?   If the cells only last 4 years, they will run into big problems if they under-plan the turnarounds.   If the blocks last 8 years, they will spend a lot of money that they didn’t need to.

Of course, this assumes that cell turn-around is roughly 4 days (you need to wait for the pot to cool, lift it out of place, put in the replacement shell, and start the heat-up routine).   That’s how long it took in Australia at my last plant, but who knows what corners are cut in the process in China.

This calculation is something that a lot of commentators miss when calculating a plant’s capacity.   If a plant has 400 cells and each cell produces 2 tonnes per day, doesn’t that mean that the plant capacity is 292,000t?   (400*2*365)   Theoretically yes, but if the pot life is say 1800 – 2000 days (5 – 5.5 years), then you need to allow for the fact that each year you will have about 70 pots shutdown for about 4 days each.    You have just lost 600 tonnes without even trying.   At US$2500 per tonne, that’s $1.5 million lost each year.   No wonder plant technical people push cathode life as a key parameter to the purchasing people.


Protected: Getting to the source – Qingxin Carbon

Written by Paul Adkins

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