ABC of graphite electrodes: how are graphite electrodes produced? (3b) – formulation

this article focuses on the third production step for making graphite electrodes >>formulation<<. Small particles are combined with larger ones to form what we call the “bonestructure and binding material” of graphite electrodes. Our goal is to create a dense grain structure keeping the formation of pores to a minimum.

For each graphite electrode manufacturer this stage is a well kept trade secret. As explained in the raw material section, the most ideal raw material to produce graphite electrodes is needle coke. Therefore, electrodes of the highest quality contain as much of needle coke as possible – 100 %. However, as we will see later, there are also inferior qualities sold and so the formulation may contain petroleum coke as a substitute for needle coke.

There are three components to the structure (please also compare diagram below)

Screenshot (1)
particle structure of graphite electrodes. Source: GES Europe
  • aggregate material (= bone structure)
  • filling material
  • binding material (=pitch)

We call a grain size big with grain diameters is bigger than 1 mm. Medium in the range of 0,8 mm to 0,5 mm. Small grains have diameters of between 0,5 mm and 0,042 mm the last being the technical minimum at the moment.

Aggregate and filling material might be either petroleum or needle coke depending on the targeted quality. The three parameters to compose a recipe are thus: choice of raw material(s), grain sizes of aggregate and filling materials, ratio of aggreate, filling and binding materials.

As the name suggests, pitch is used to bind the different grains together and further increase density of the structure. It is also important for the later forming process. For the production fo graphite electrodes, this will be extrusion. Therefore, a higher content of pitch is desirable. Reason: for extrusion, bigger grain sizes are use for aggregate and filler; therefore more pitch is needed to fill up the pores.

Since the most important aspect about the composition is the different grain sizes to generate a high density, there is almost no limitation to the recipe. One formulation using four different grain sizes (petroleum coke alone, needle coke alone, or a mixture of both) might read as follows:

-> 0,8 mm – 40 %; 0,4 mm  – 20 %; 0,2 mm – 20 %; 0,1 mm – 20 %.

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The ABC of graphite electrodes: How are graphite electrodes produced? (3a)

this is part 3 of our mini series into graphite electrodes. It covers the basics of graphite electrode manufacture. Since we want to delve deeper into each phase, it will be necessary to talk about the production in several articles. This one gives you an overview of the production stages.

Introduction into graphite electrode production

Here is a concise overview of the production stages

a) Calcination of petroleum coker & recrystallization

b) form ulation

c) kneading

d) forming

e) baking

f) (impregnation)

g) graphitization

h) machining

You may have noticed that I put the phase f) into brackets. The reasons is that some graphite electrode qualities do not undergo this step. More on this in later postings. Also, technically we can only speak of >>graphitized<< electrodes after phase g) is complete. This is when a change in molecular structure has happened from carbon to graphite.

a) Calcination of petroleum coke & recrystallization

The purpose of this phase is decomposition/purification of petroleum coke. To know more about petroleum coke, please have a look back on our article on the raw materials of graphite electrodes.

Essentially, we try to remove organic materials and moisture (=volatiles or volatile matter) inside the petroleum coke. Before the calcination process, we typically refer to the coke as >>green coke<< or sometimes >>raw coke<<. For this process, electrode producers use a rotary kiln (diagram below).

rotary kiln as a means to calcination

Source: Yongchang Cai, Mathematical problems in engineering, 2017.

In the kiln there are several zones inside. The petroleum coke enters the kiln in a pot (inner pot) that subsequently moves from the right to the left end on the trajectory of entry to exit in the rotary tunnel/corridor. In the first zone, called the drying or preheating zone, the pot is heated temperature is about 800°C to 900°C. The volatile matter starts evaporating at around 300°C.

The calcination zone, which makes up about half of the furnaces length, is 1,200°C to 1,350°C. There is also a cooling zone (or a second kiln). It is not shown in the drawing above but just imagine a third zone with a temperature range of 800°C to 900°C. The whole process takes about 30 to 50 minutes to completion. The released volatile gases in the kiln go to a waste heat recovery boiler to produce steam and ultimately refire the kiln.

Recrystallization

The thermal treatment of petroleum coke has yet another benefit besides a mere purification: we somewhat alter the directionality and density of the petroleum coke which is important later for a superior electrical and mechanical properties.

 

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Sources: 

Yongchang, Cai, Modeling for the Calcination Process of Industry
Rotary Kiln Using ANFIS Coupled with a Novel Hybrid Clustering Algorithm, (2017)in: Mathematical problems in engineering 2017: Mathematical Problems in Engineering Volume 2017, Article ID 1067351, 8 pages https://doi.org/10.1155/2017/1067351,

Graphite electrode prices on a roller-coaster ride (2)

Four main factors cause graphite electrode price chaos

Of the global graphite production, approximately 70% are being accumulated by China. For meeting its own steel industry’s huge demand, China is already trying to keep graphite inside of its own borders by imposing export duties.

Not least these measures caused the increase of graphite electrode prices, which oscillated between 500 and 600 US-Dollars around the turn of the millenium. Reaching their peak in 2012 at roughly 3.000 US-Dollars per ton, electrode prices quickly plummeted under the level of 2.000 US-Dollars.

graphite electrode prices, JAN 17 - APR 18

However, after graphite electrode prices had hit an all-time low, vast turbulences erupted in spring 2017 culminating in record high graphite electrode prices. Panic purchases by steelworks managers, unreliability of many partners and general upheaval were the consequence. But what caused those turbulences? We found a total of four main factors.

  1. the decrease of available raw materials for graphite.
  2. an increase in demand for steel.
  3. the chinese government introduced bold restrictions.
  4. partners involved acted unpredictably.

As a consequence of all these factors, chaotic market situations emerged, which complicated the situation further. The common denominator? The biggest graphite producer – China!

Supply, demand and governmental intervention

The demand for graphite electrodes skyrocketed in 2017 due to the steel industry’s demand. Yet, the recovering global economy and thereby driven steel industry only faced empty graphite warehouses, because the producers sold most of their stocks after the lowest electrode prices in history. Everyone with stocks, had quickly sold them after the first few demand increases at relatively low electrode price levels.

Just as the West, China is increasingly interested in environmental protection. For solving this tremendous task, the government tightens environmental regulations to a strangeling degree. This caused many graphite electrode producers to halt their production in favor of government inspections, shrinking the total output in spring 2017 to almost zero.

Facing this supply bottleneck, end users paid double or triple of the regular electrode price, causing further electrode price increases. Some suppliers noticed that willingness, disregarded contracts and sold in favor of the highest bid. Consequences were not to be feared, since the contracting parties were to far abroad. By declaring “Force Majeure” some European contractors also ignored contracts hoping for better conditions but causing further insecurity.

And – what does the future bring?

So, what will the future be like? Well, even stricter environmental regulations are a heavy burden for the graphite industry. The latest example happened in northern China from 2017 to 2018, when governmental actions caused the production to stop between October and March.

Furthermore, the most populated nations in the world, China and India, are experiencing the rise of an increasingly wealthy middle class, which yearns to show off their wealth in western means – how about a trendy and sophisticated electric vehicle, which communicates perfectly with the owners smartwatch and smartphone? Due to these and similar shifts, the Swiss UBS predicts a rise of global graphite demand in the next decades by an immense 264% of todays world market volume.

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Sources
1) „Graphit hat Zukunftspotenzial“, In: miningscout.de, 19.01.2018,
https://www.miningscout.de/blog/2018/01/19/graphit-hat-zukunftspotenzial/, accessed: 22.05.2018.
2) UBS-Studie: Diese Rohstoffe profitieren vom Siegeszug der Elektroautos“, In: wallstreet-online.de, 23.10.2017, https://www.wallstreet-online.de/nachricht/9996039-ubs-studie-rohstoffe-profitieren-siegeszug-elektroautos, accessed: 22.05.2018.

ABC of graphite electrodes (2) – what are electrodes made of?

this is part 2 of our series. As promised, the first article covers the raw materials of graphite electrodes.

Raw materials of graphite electrodes

We only mention here the raw materials which become a part of the electrode end product. Apart from those we can mention auxiliary materials such as Quartz Sand for the baking process. The raw materials that make up an electrode recipe are as follows.

Petroleum coke & needle coke

Petroleum coke is produced using the route of crude oil vacuum distillation and delayed coking. Needle coke is a highly crystalline petroleum coke type with clear striped texture with directionality to allow for high thermal expansion coefficient and electrical conductivity. Therefore, needle coke is the most ideal material for the production of graphite electrodes.  Interesting for us is the ratio of petroleum coke and needle coke. In practice of electrode making, petroleum and needle coke contents have an inverse relationship: the lower the content of needle coke, the higher that of petroleum coke and vice versa. As we will see in the section about graphite electrode grading system, we can denote an electrode formula superior in quality, the higher. The leading manufacturers for needle coke by annual output are as follows: Seadrift coke LP (USA), Conoco Philips (Britain), Mizushima Ferroalloy Co., Ltd (Japan), Jinzhou CNPC (Jinzhou, China), Gaoqiao CNPC (Shanghai, China), Mitsubishi Chemical (Japan), Hongte (Shanxi, China), Sinosteel Anshan Research Institute of Thermo-energy Co., Ltd (Anshan, China)

Metallurgical coke

In the form of powder & particles, metallurgical coke is a coal with a low ash and sulfur content. It is beneficial to add this ingredient to increase hardness and decrease the release of burned ash during electrode use.

Coal tar pitch

Used during the kneading and the impregnation phases of the production process. When kneading, the liquid coal tar pitch is added to combine the otherwise loose particles to form a soft mass. Like metallurgical coke, it is produced from coal over the route coal -> coal tar -> coal tar pitch utilizing fractional distillation. For the impregnation stage (which is the production step between baking and graphitization; more on this process later), it is used to decrease the porosity by filling the many small holes inside the semi-finised electrode. Thereby, the product gains in density.

In the next article, we will be concerning ourselves with the question: how are graphite electrodes produced? We are going to focus on the production process overview.

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Graphite electrode prices on a roller-coaster ride (Intro)

With this series that bears the name “Graphite electrode prices on a roller-coaster ride”, I would like to address a most relevant topic of the electrode shortages and thereby caused price chaos beginning in spring 2017. Many steel mills were hit hard and the consequences are still perceptible now.

Recently, I came across an interesting article on a popular question-and-anwer site, Quora Digest as well as on LinkedINThe question about whom we can attribute the copyright to doesn’t matter for our purposes. Its name was “What is the reason and trend of graphite electrode price increase?” – I was really excited and its title grabbed my attention within a nanosecond. 

You must know that during my visits and discussions with purchasing managers of steel plants, one of the first questions I most often encountered was: >>Mr Sarkoezy, please tell us, what caused this price increase in graphite electrode prices in 2016/2017?<<

Before I present my point of view (which is essentially the position of GES Group’s), I would like to relate to above article. I am not giving the post in full; instead I am summarizing my thoughts on it. Continue reading Graphite electrode prices on a roller-coaster ride (Intro)