# p. 1 of 3

From: Curt Wells [ mailto:cwells@aluminum.org ] Sent: Friday, May 30, 2014 11:29 AM To: Charles D. Johnson; Putney, David Cc: Michael A. Palazzolo Subject: RE: Anode coke questions

David –

We have researched the questions that you asked bel ow and have the following answers regarding them –

Anode coke specifications – Smelters set specificat ions for the upper amount of certain metals that may affect aluminum quality or the smelting process . Coke suppliers provide a metals analysis for those specific metals, which typically include As, Be, Cd, Cr, and Pb. V is also an important metal o f concern in anode performance so it’s presence is mo nitored as well.

Using coke produced from coal in anode production - Coke produced from coal, including metallurgical coke, has been evaluated in the past as an alternate for the petroleum-based coke used t o produce aluminum today. However, unprocessed coke produced from coal does not have properties suitable for the production of carbon anodes. Coal -based coke has a high ash content (high level of impurities) and this leads to unacceptable properti es, including poor electrical conductivity, high carbon consumption and unacceptable aluminum purity

. Coal or coal-based coke could be processed (for exa mple by solvent extraction) to remove the impurities at a considerable cost. However, anodes produced with 100% processed coal-based coke have similar drawbacks, such as brittleness and hig h carbon consumption. (See attached 2010 article). While it may be technically feasible to produce acceptable anodes by blending petroleumbased coke and processed coal-based coke, the need to blend with petroleum coke to produce usable or acceptable anodes defeats the initial benefits of r emoving the impurities. Suitable processed coal-bas ed coke is not commercially available today in any cas e.
Please let me know if you have any questions regard ing this information and/or would like to discuss i t further.

Thanks.

Curt Wells Manager, Regulatory Affairs The Aluminum Association (703) 358-2976 (w) (804) 385-6351 (c) cwells@aluminum.org

# p. 2 of 3

From: Charles D. Johnson Sent: Monday, May 19, 2014 10:13 AM To: Putney, David Cc: Charles D. Johnson; Michael A. Palazzolo; Curt Wel ls Subject: Re: Anode coke questions



# David,

We're looking in to this and we will get back to yo u as soon as possible.

Regards, Chuck

Sent from my iPhone

On May 17, 2014, at 4:24 AM, "Putney, David"

< putney.david@epa.gov > wrote:
Chuck/Mike,

Once again, I’m reaching out to The Aluminum Associ ation and the technical subcommittee for assistance/infor mation. Specifically, I’m wondering if the primary aluminum facilities generally get information on the metal H AP content of the petroleum coke that they purchase fo r use in manufacture of anodes. That is, do the facilities g et specifications from the petroleum coke providers on how much nickel, arsenic, cadmium, etc. is in the petro leum coke that you buy from them?

Also, is there any technical reason why metallurgic al coke (as opposed to petroleum coke) could not be used in anode production? That is, is there any reason other than cost that drives primary aluminum reduction facilities t o use petroleum coke instead of metallurgical coke in the ir anode production operations?

# p. 3 of 3

Thanks,

David Putney, Environmental Engineer U.S. Environmental Protection Agency Office of Air Quality Planning and Standards Sector Policies and Programs Division 109 T.W. Alexander Drive, RTP, NC 27711 Mail Drop D243-02 Ph: (919) 541-2016 Fax: (919) 541-3207 Email: putney.david@epa.gov

### PREBAKED ANODE FROM COAL - UTILIZATION OF COAL EXTRACT AS A COKEFEEDSTOCK1 Maki Hamaguchi, 1 Noriyuki Okuyama, 1 Nobuyuki Komatsu, 2 Jiro Koide, and 2 Keisuke Kano
1 Kobe Steel, Ltd. ; Takasago, Hyogo 676-8670, Japan.
2 Sumitomo Corporation, Harumi, Chuo-ku, Tokyo 104-8610, Japan

Keywords: Coal, Solvent Extraction, Coke, Anode.

Abstract

Preparation of prebaked anode utilizing coal solvent extraction technology has been reported for the first time. A steaming coal was extracted with methylnaphthalenes under nitrogen atmosphere at 653K, and ash-free coal extract (Hypercoal, HPC)was obtained at ca. 60wt% yield. The HPC was further heattreated at 1273K to convert HPC to HPC coke (HPCC). Prebaked anode test specimen were fabricated from HPCC according to the conventional procedures, and were evaluated in terms of the standard prebaked anode test methods. It was demonstrated that prebaked anodes prepared from HPCC have various advantages such as extremely low impurities such as Sulfur, Vanadium and Nickel, high apparent density, and low air- and CO 2 -reactivity compared to those from anode grade calcined petroleum coke.

Introduction

In the prebaked anode industry, it is recognized that the quality of anode coke has continuously declined, namely, higher sulfur and impurities, higher volatile matter content, and lower density, mostly due to the deterioration of crude oil quality. Thus, technologies for alternative sources for anode coke are of great interest.We at Kobe Steel, Ltd., have been developing a new nonhydrogenative solvent extraction process for coal with the aim of applying the coal-extract as a binder for the metallurgical coke making. We named this process and the product (the ash-free coal-extract), a Hypercoal (HPC) [1-3]. Since the content of ash in HPC is usually extremely low, HPC is considered to be a promised candidate for alternative feedstock of anode cokes. In this paper, we will describe fabrication of prebaked anode test specimen using HPC as a feedstock of coke. It was demonstrated that prebaked anodes prepared from HPC coke have various advantages such as extremely low impurities such as Sulfur, Vanadium and Nickel, high apparent density, and low air- and CO 2 -reactivity compared to those from anode grade calcined petroleum cokes.

Experimental section

Materials

A steaming coal from Australia was used as the starting material. Proximate and ultimate analyses of the coal are shown in Table 1. Solvent extraction of the coal was carried out under the followingconditions: solvent, a mixture of 1-methyl and 2-methylnaphthalenes; solvent/ coal ratio (v/v), 4; temperature, 653K; initial nitrogen pressure, 2MPa; duration, 20min. A continuous bench scale extraction apparatus was employed. The coal extract (HPC) was recovered from the extraction slurry by filtering at high temperature and evaporating the solvent. In Figure 1 wasshown a schematic diagram of the HPC process. Since the asprepared HPC possesses extremely high dilatation during carbonization, the HPC was subjected to post heat treatment tosuppress dilatation rate. The reaction conditions of the heattreatment were as follows: temperature, 693K; initial nitrogen pressure, 2MPa; duration, 60 min. Proximate and ultimate analyses of the HPC and the post treated HPC are also listed in Table I. A commercially available coal tar pitch was used as the binder to fabricate the prebaked anodes. The properties of the pitch are listed in Table II.

Figure 1. Schematic for the HPC process diagram

TABLE I. Proximate and ultimate analyses for the coal and HPCs
Product Moisture Ash VM C H N S Odiff.

[wt%] [wt%]db [wt% daf]
Raw coal 2.9 12.2 41.3 82.5 5.5 2.0 0.6 9.5

HPC 0.3 0.12 41.2 86.6 5.4 1.9 0.6 5.5

HPC a) 0.1 0.10 26.2 88.6 4.4 1.9 0.7 4.4 a) After post heat-treatment

C oking of HPC and preparation of prebaked anodes

The post treated HPC was carbonized according to the conventional metallurgical coke making procedures. Namely, the HPC crushed under 3mm was poured into an iron-made container of 0.02m 3 , and was heated to 1273K at a rate of 3 K/min under inert atmosphere. Duration was 30 min.

Prebaked anode specimen of cylindrical shape of 50mm in diameter and 100mm length were fabricated according to the conventional methods. The crushed HPCC was mixed with the

C oal feeder P reheater E x t r a c tor

F ilter S pray dryer

Spray dryer Slurry m aker Settler

HPC Coal

Recycle solvent Residue coal C oal feeder P reheater E x t r a c tor

F ilter S pray dryer

Spray dryer Slurry m aker Settler

HPC Coal

Recycle solvent Residue coal



### 923 

## Attachment 1, 6 pagesbinder pitch of various amounts (13-17wt% in the paste), and was

hot-pressed at a pressure of 400 bar at 393K. The pressed green molds were carbonized at 1373K for 20 hours. Prebaked anodes utilizing blends of HPCC and a high-sulfur petroleum coke (HS coke) were also prepared. HPCC and prebaked anodes were evaluated in terms of the ISO standard test methods for anode cokes and prebaked anodes. The scheme of the prebaked anodes from HPCC and PC cokes is shown in Figure 2.

Table II. Properties of the binder pitch used

Figure 2. Schematic of prebaked anode preparation from coal.

Results and Discussion

Characteristics of HPC Cokes

Properties of HPCC were listed in Table III in comparison with the ranges of typical petroleum coke and a high sulfur PC coke (HS coke). Polarized light microphotographs of HPCC and PC are shown in Figure 3. It was noted that HPCC possessed lower real density in xylene, larger electrical resistance, and smaller crystalline size than pet cokes, which can be attributed partly to the lower calcination temperature employed for the HPCC (1273K) than that for petroleum cokes (1473K). The solid-state carbonization nature observed in this HPC may also be a cause for the slightly poor graphtizability of this HPC. The fact that the Hg apparent density of HPCC was larger than that of PC irrespective of its smaller real density suggests the existence of closed micropores in HPCC. From the detailed analyses of the coke and ash, it was revealed that the HPC gives highly purity coke in particular in sulfur, sodium, nickel and vanadium contents compared to petroleumderived coke.

Table III. Properties of HPC coke compared to the typical range

of petroleum calcined cokes

Properties Unit Range for PC HPCC HS Coke Sieving analysis +4mm % 30-45 45 31

-1mm % 25 27 33 Tapped bulk density 8-4mm kg/dm 3 0.64-0.70 0.735 0.68

2-1mm kg/dm 3 0.80-0.86 0.813 0.80 0.5-0.25mm kg/dm 3 0.88-0.93 0.87 0.87 Hg apparent density kg/dm 3 1.72-1.80 1.85 1.73 Grain stability % 75-90 93 82 Pulverizing factor - 0.80-1.20 0.43 1.12 Real density in xylene kg/dm 3 2.05-2.10 1.89 2.067 Crystalline size Å 25-32 16.9 27.0 Sp. el. resistance μΩm 460-540 933 489 Air reactivity (798K ) %/min 0.05-0.30 0.03 0.28 CO 2 reactivity % 3-15 4.1 6.8 S % 0.5-3.5 0.56 2.71 V ppm 60-350 5 243 Ni ppm 100-250 14 163 Si ppm 50-250 241 99 Fe ppm 50-400 125 112 Ti ppm 0-5 60 1 Na ppm 30-120 1 60 Ca ppm 20-100 77 51

100μm

Figure 3. Polarized light microphotographs of HPCC (upper)

and PC (bottom)

Characteristics of prebaked anode from HPCC

Figure 4 shows the properties of prebaked anodes pr epared from the HPCC and the binder pitch as functions of the p itch contents in the coking blends. Raw coal Solvent

Extraction HPC Post

treatment Coking
HPCC Prebaked anode Molding & Baking

Binder pitch PC coke (option) 

### Properties Method Value Unit 

### Softening Point Mettler ISO 5940 386 K Insoluble in Quinoline ISO 6731 8.4 % Insoluble in Toluene ISO 6376 27.7 % Viscosity 433K ISO 8003 1555 mPas Density in Water ISO 6999 1.312 kg/dm 3 

### Ash content ISO 8006 0.25 % S ISO 12980 0.47 % Na " 202 ppm Ca " 59 ppm Si " 106 ppm Fe " 277 ppm Zn " 311 ppm Pb " 232 ppm



### 924Whereas the green apparent density of HPCC anode was

comparable to the typical range of conventional PC coke anodes, the apparent density of the baked HPCC anodes was noticeably smaller than that of PC anodes. This is consistent with the existence of closed pores in HPCC as suggested by the relatively small real density of HPCC. The elasticity modulus and compressive strength of HPCC anode were superior to those of PC anode, which may by attributable to the hardness of the HPCC particle. The electrical resistance of HPCC anodes was slightly lower than PC anode. The HPCC anodes exhibited substantially larger CTE than those of PC anodes, which may be of concern for the formation of cracks or deformation during the course of industrial scale anode baking process. The CO 2 reactivities are poorer than usual even though the HPCC itself showed a good resistance to the CO 2 attack. This is related to the addition of pitch that are always contaminated with Na and Ca (200 and 60ppm resp. in the standard pitch used). Both catalysts are quite efficient on the HPCC as it contains low Sulfur level. Sulfur is known to be a strong inhibitor of the CO 2 burn and is normally present at a concentration 3 to 4 times higher in petroleum cokes than in the HPC coke.

The air reactivities are excellent as the HPCC does not have any Vanadium contamination. V is known to be a strong catalyst of the air burn.

Green apparent density (kg/dm3)

1.54 1.56 1.58 1.60 1.62 1.64 1.66 1.68 1.70

13 14 15 16 17

% Pitch Baked apparent density (kg/dm3)

1.46 1.48 1.50 1.52 1.54 1.56 1.58 1.60 1.62

13 14 15 16 17

% Pitch

Compr. Strength (MPa)

20 30 40 50 60 70 80 90 100

13 14 15 16 17

% Pitch Spec. El. Resistance (μΩm)

40 45 50 55 60 65 70 75 80

13 14 15 16 17

% Pitch Elasticity modulus (GPa)

3.50 4.00 4.50 5.00 5.50 6.00 6.50 7.00 7.50

13 14 15 16 17

% Pitch Thermal expansion (10-6/K)

2.50 3.00 3.50 4.00 4.50 5.00 5.50 6.00 6.50

13 14 15 16 17

% Pitch

CO2 reactivity residue (%)

82 84 86 88 90 92 94 96 98

13 14 15 16 17

% Pitch Air reactivity residue (%)

80 85 90 95 100

13 14 15 16 17

% Pitch

Figure 4. Properties of prebaked anodes prepared f rom HPCC and binder pitch as functions of the binder pitch Blue h atched area shows the range of PC anodes

.



### 925Characteristics of prebaked anodes from HPCC and PC blends

As described in the previous section, it was demonstrated that the HPC coke can be used as an alternative feedstock for prebaked anodes. At the same time, it is also clear that the HPCC prebaked anode has both several advantages and drawbacks compared to conventional petroleum coke based anodes. Thus, we have investigated the possibility of blending technology for HPCC and PC coke. In particular, we focused the utilization of a high-sulfur and low density PC by blending with HPCC. Table IV and Figure 5 summarize the results of evaluation for prebaked anodes prepared from the HPCC, the HS-coke, and the blends of the HPCC and HS-coke. In this experiment, we have examined the blending effects of HPCC grains and HPCC fines, separately on the properties of the prebaked anodes. The prebaked anodes from HS coke are characterized by their relatively low apparent density, large air reactivity, and high sulfur level. When the HPCC grains were substituted to half of the HS coke grains (35wt% in total), and the binder pitch was adjusted at 15wt%, the most appropriate properties has been achieved. That is, the anode from the blend of the HPCC and the HS coke exhibited a apparent density almost the same as those of PC coke anodes, and superior reactivities to air and CO 2 , and lower impurities such as sulfur, vanadium, and nickel, etc.

On the contrary, when the HPCC fines were used in place of HS coke fines, the properties of the anodes were not satisfactory. This suggests that some inhomogeneity may exist in the HPCC.

Table IV. Properties of prebaked anodes prepared from the HPCC, the HS-coke, and

the blends of the HPCC and HS-coke.

Properties



### Pitch (%) 15% 16% 14% 16% 14% 15% 16% 15% Apparent density green kg/dm 3 

### 1.600 1.619 1.563 1.608 1.615 1.633 1.654 1.630 Apparent density baked kg/dm 3 

### 1.526 1.534 1.499 1.513 1.550 1.558 1.531 1.560 Baking loss % 

### 5.20 5.62 5.05 5.94 5.19 5.55 6.27 5.20 Shrinkage % 

### 0.58 0.37 1.06 0.04 1.28 1.06 -1.30 0.80 Sp. el. resistance μΩm 

### 64 60 71 62 68 64 64 60 Compr. Strength MPa 

### 35 40 32 45 37 42 43 42 Elasticity Modulus GPa 

### 3.5 4.1 2.8 4.7 3.4 3.7 3.8 4.2 Thermal expansion 10 -6 /K 

### 3.80 3.81 4.22 4.23 4.44 4.55 4.44 3.6-4.4 Themal conductivity W/mK 

### 3.40 3.53 3.210 3.44 3.42 3.55 3.55 3.50 Density in xylene kg/dm 3 

### 2.070 2.071 2.051 2.042 2.029 2.034 2.031 2.07 Air permeability nPm 

### 1.40 1.30 2.03 1.58 1.42 1.69 5.91 1.20
CO 2 reactivity residue % 

### 94.2 94.7 92.2 90.3 94.8 95.3 93.1 93.0

dust % 

### 0.4 0.2 0.6 1.5 0.3 0.2 0.9 2.0
loss % 

### 5.4 5.1 7.2 7.7 5.0 4.6 5.9 5.0 Air reactivity residue % 

### 79.2 80.1 87.1 90.4 86.5 89.3 89.6 80.0

dust % 

### 4.1 3.4 0.6 0.1 2.4 1.1 0.3 3.0
loss % 

### 16.7 16.5 12.3 9.5 11.1 9.6 9.5 17.0
S % 

### 2.38 2.37 2.17 2.16 1.85 1.73 1.79 2.00 V ppm 

### 216 214 183 173 146 149 140 200 Ni ppm 

### 156 154 132 132 116 113 114 160 Si ppm 

### 132 133 120 137 140 152 150 180 Fe ppm 

### 188 192 137 140 139 141 142 250 Al ppm 

### 79 76 78 83 90 101 97 80 Na ppm 

### 80 81 69 69 67 57 67 80 Ca ppm 

### 64 65 53 65 68 65 69 70 Typical Pet. Coke Unit 

### HS coke 15% in fines 35% in grains Blends of HPCC (%) in HS coke

926As to the reactivity of the prebaked anodes, the CO 2 reactivity

figures are not deteriorated by the addition of HPCC. This is probably due to firstly the fact that the binder matrix contains no HPCC, and secondly there is enough Sulfur content in these anodes to inhibit the catalytic effect of Ca and Na species on the low Sulfur HPC cokes. Interestingly there is a dramatic improvement of the air reactivity figures thanks the massive reduction of the V content, which is a powerful catalyst of the air oxidation.

Conclusions

Results of this study can be summarized as follows: 1. The Hypercoal coke (HPCC) derived from the ash-free coal extract (Hypercoal, HPC) showed significant advantages such as lower impurities like S, Ni, Fe, V, Na and Ca, and consequently the excellent Air and CO 2 reactivity resistances. The HPCC is regarded as a promising candidate for alternative of deteriorating current calcined petroleum anode grade cokes.

2. The prebaked anode specimen of pure HPCC (without blending) showed the excellent air reactivity resistance as expected, however some drawbacks were observed such as the higher CTE, the brittleness, and the poor CO 2 reactivity resistance contrary to the expectation from lower impurity of coke itself.

3. The blending of HPCC in grains to the current HS petroleum coke maintained the inherent excellent air reactivity resistance and improved significantly the drawbacks observed with the pure HPCC specimen such as the higher CTE, the brittleness and the poor CO 2 reactivity resistance.

4. It is concluded that the blending of the HPCC in grains to the current HS petroleum coke is the best practical way to apply the superiority of the HPCC in purity and to avoid some nonessential drawbacks of the HPCC. Figure 5. Properties prebaked anodes prepared from the HPCC, the HS-coke, and the HPCC-HS-coke blends Blue hatched area shows the range of PC anodes. Green apparent density (kg/dm3)

1.54 1.56 1.58 1.60 1.62 1.64 1.66 1.68 1.70

13 14 15 16 17

% Pitch Baked apparent density (kg/dm3)

1.46 1.48 1.50 1.52 1.54 1.56 1.58 1.60 1.62

13 14 15 16 17

% Pitch

Compr. Strength (MPa)

20 30 40 50 60 70 80 90 100

13 14 15 16 17

% Pitch Spec. El. Resistance (μΩm)

40 45 50 55 60 65 70 75 80

13 14 15 16 17

% Pitch Elasticity modulus (GPa)

2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0 6.5

13 14 15 16 17

% Pitch Thermal expansion (10-6/K)

2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0 6.5

13 14 15 16 17

% Pitch CO2 reactivity residue (%)

82 84 86 88 90 92 94 96 98

13 14 15 16 17

% Pitch Air reactivity residue (%)

75 80 85 90 95 100

13 14 15 16 17

% Pitch



### ○: 

### HS coke △: 

### 15% HPCC in fines ■: 

### 35% HPCC in grains

927Furthermore, these results indicate that the HPCC become the

beneficial sweetener to the high S and/or high metals offspecification petroleum cokes increasing in the future.

Acknowledgement

Preparation and evaluation of anode was carried out at R&D Carbon Ltd., Sierre, Switzerland.

References [1] Okuyama, N., Komatsu, N., Kaneko, T., Shigehisa, T. and Tsuruya, S. (2004) Fuel Processing Technology , 85 947. [2] Okuyama, N., Furuya, A., Komatsu, N. and Shigehisa, T. (2005) International Conference of Coal Science and Technology Proceedings

. [3] Komatsu, N., Okuyama, N., Furuya, A. and Shigehisa, T. (2006) International Pittsburgh Coal Conference

.



### 928