Influence of briquetting and coking parameters on the lump coke production using non-caking coals

Fuel xxx (2017) xxx–xxx

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Influence of briquetting and coking parameters on the lump coke production using non-caking coals Franz Fehse a,⇑, Katharina Rosin b, Hans-Werner Schröder a, Ronald Kim c, Matthias Spöttle c, Jens-Uwe Repke a,d a

TU Bergakademie Freiberg, Institute of Thermal, Environmental and Natural Products Process Engineering, 09596 Freiberg, Germany TU Bergakademie Freiberg, Chair for Environmental & Resource Management, 09596 Freiberg, Germany Thyssen Krupp Industrial Solutions AG, Friedrich-Uhde-Straße 15, 44141 Dortmund, Germany d TU Berlin, Chair of Process Dynamics and Operations, Straße des 17. Juni 135, Sekr. KWT-9, 10623 Berlin, Germany b c

a r t i c l e

i n f o

Article history: Received 6 October 2016 Received in revised form 21 April 2017 Accepted 2 May 2017 Available online xxxx Keywords: Lump coke Brown coal Coal processing Agglomeration Briquetting Coking of brown coal

a b s t r a c t In terms of transforming the energetic usage to the material usage of low-rank coals, the production of lump coke is a promising perspective. Therefore, two essential steps are necessary: Firstly, the processing and agglomeration of the non-caking coal is highly important, since they do not offer any baking capacity and thus the reachable quality of the coke is mainly set by the briquette quality. Secondly, to obtain high quality cokes the briquettes need to be coked using a well-adapted heating regime to ensure the gentle degassing of volatile matter with a minimum weakening of the briquette structure. The brown coal high temperature technology (BHT technology) developed in 1952 by Rammler and Bilkenroth was a milestone in coal conversion for brown coal but the coke strength was limited at that time. In current systematic studies, the lump coke quality of Lusatian brown coal and Indonesian brown coal was investigated varying the processing, briquetting and heating regime in laboratory scale. Those investigations should lead to a new processing and agglomeration technology to create lump coke from non-caking coals. The experiments varying the processing parameters of the coal showed that the briquetting of pregranulated coal or pellets from a modified flat die press achieve the highest increase in briquette and coke quality. In the second step, the heating regime during pyrolysis was investigated. The results show, that the highest coke quality may be achieved using the Vollmaier regime. However, a single-stage heating regime with a heating rate of 2.85 K min
1 shows promising results as well. Ó 2017 Published by Elsevier Ltd.

1. Introduction Lower ranked coals, as brown coals, lignite or sub-bituminous coals, are mainly used for power and heat production. Regarding the transformation of the energetic utilisation of coal to a material utilisation of even lower ranked coals the coking of the coal enables the production of new materials for various applications [1]. The four main products of coal pyrolysis are coke, tar and oil as well as gas. Since low-rank coals exhibit higher volatile matter they offer comparatively high amounts of tar/oil and gas. That is why besides gasification the pyrolysis of those coals could be very promising. The accruing gases, tars and oils may be processed to chemical raw materials. The quality of the produced coke is highly dominated by the operation parameters of the pyrolysis as well as the previous steps of refinement and in particular by the raw ⇑ Corresponding author. E-mail address: [email protected] (F. Fehse).

material properties. Therefore, every coal needs specially matched processing and coking parameters. In contrast to so-called coking coals, low-rank coals do not exhibit any caking capacity. Thus, if lump coke shall be produced from low-rank coals, e.g. brown coal, this is only possible by a gentle pyrolysis procedure up to 1000 °C of high quality briquettes. The processing of lump coke from Lusatian brown coal was developed by Erich Rammler and Georg Bilkenroth in 1952 [2]. Using this approach the raw brown coal was pre-comminuted to a grain size of Dd = 6/0 mm and dried to a moisture content of 11 %. Afterwards the coal was fine comminuted to Dd = 1/0 mm and sized if necessary. Briquetting was done at briquetting pressure p  120 MPa and briquetting temperature in the range of 0P = 65 – 75 °C (Fig. 1, approach 1). Coking the briquettes, a special heating regime was developed by Vollmaier [3] using a heating rate of 0.83 K min
1 from 20 °C up to 320 °C and a heating rate of 2.85 K min
1 from 320 °C to 1000 °C with a following dwell time of 1 hour at 1000 °C. The produced coke offered a compressive

http://dx.doi.org/10.1016/j.fuel.2017.05.002 0016-2361/Ó 2017 Published by Elsevier Ltd.

Please cite this article in press as: Fehse F et al. Influence of briquetting and coking parameters on the lump coke production using non-caking coals. Fuel (2017), http://dx.doi.org/10.1016/j.fuel.2017.05.002

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F. Fehse et al. / Fuel xxx (2017) xxx–xxx

Nomenclature Abbreviations BHT Brown coal high temperature coke d dry daf dry and ash free IBC Indonesian brown coal IfB (formerly) Department of Briquetting LBC Lusatian brown coal Symbols aSt C d d1 d2 Dd GHV H LHV

steam ratio % carbon grain size mm upper diameter of press channels in the die lower diameter of the press channels in the die mm grain size fraction mm gross heating value kJ kg
1 hydrogen lower heating value kJ kg
1

mCoal mass of dry coal for briquetting g mtot total mass of briquettes in the IfB drum g mass of briquettes on the 30 mm sieve g m30 N nitrogen O oxygen p briquetting pressure MPa Q3(d) grain size distribution % R30(100) abrasion resistance, residue on the 30 mm sieve % qRaw gross density g cm
3 St sulphur rPB, rPC briquette/coke compressive strength MPa tH dwell time h 0D drying temperature °C 0P briquetting temperature °C pyrolysis temperature °C 0Pyr vHR heating rate K min
1 vpiston velocity of the piston for the determination of the compression resistance mm min
1

Fig. 1. Approaches for the coal processing for lump coke production from brown coal, according to [25].

strength of 17 MPa and an abrasion resistance of 80 % (residue on the 30 mm sieve after 100 revolutions in an IfB drum [4]). This was a milestone in brown coal conversion and could substitute the coke of bituminous coals in several applications [5]. Due to the limited strength, the coke was especially used for pig iron production in low-shaft furnaces and the production of carbide and ferrosilicon. However, to enlarge the field of application of those cokes and extend the raw material base to coals of other deposits or ranks, further developments on the processing and refinement as well as the coking process are needed. To ensure a wide range of coke applications firstly the briquettes should offer a high compressive strength (rPB  30 MPa), abrasion resistance (R30 (100)  90 %) as well as a high thermal stability to guarantee the shape retention during the coking process. Secondly, the lump cokes need a high mechanical strength as well. In the best case the compressive strength reaches rPC = 50 MPa in minimum and an abrasion resistance R30(100) = 95 %. Besides the mechanical strength, a matching reactivity for the following application

(e.g. blast furnace process or smelting reduction process) is necessary too. To improve the coke quality produced from non-caking coals, four groups of influencing parameters may be identified: the raw material properties, the processing parameters, the briquetting parameters and the coking parameters. The quality of the raw material, varying in the coal rank as well as in the micro-petrographic properties, is very important since the choice of the following parameters is highly dependent on the raw material base. Comparing the results of various authors [6–17] the coal rank and provenience of the coal has a high effect in the briquetting behaviour as well as the coking behaviour of the coal. In the group of the processing parameters, especially the influence of comminution and the drying technology on the physical and chemical coal properties need to be determined. Numerous works studied the processing of coal: It is comminuted to more or less fine powder before or after drying. Clarke et al., Mollah et al., Nomura and Plancher et al. used the coal with a grain size

Please cite this article in press as: Fehse F et al. Influence of briquetting and coking parameters on the lump coke production using non-caking coals. Fuel (2017), http://dx.doi.org/10.1016/j.fuel.2017.05.002

F. Fehse et al. / Fuel xxx (2017) xxx–xxx

under 3 mm or even finer [6–9,14,15,17]. Liu et al. and Bayraktar comminuted the coal to a powder of d < 0,2 mm before briquetting [11,16]. The influence of the grainsize and the grinding conditions of the charging material is well known, even for other materials than coal [18–22]. Besides grinding, the coal can also be treated with chemicals such as acids or alkalis or by hydrothermal dewatering causing a significant improvement in coke reactivity [6,8,9]. In addition to grain size (distribution), important briquetting parameters are the moisture content of the coal, briquetting pressure, briquetting temperature and briquetting time [23,24]. Using hydraulic stamp presses or universal testing machines in laboratory scale the briquetting parameters might be varied independently from each other. In their investigations, Papin et al. discussed the variation of the pressing regime between a stage-wise and single stage compression. The influence of the briquetting pressure variation was discussed in a previous work as well as the influence of moisture content [25]. The briquetting temperature is important as it may lead to a plastification of the coal and an increasing binding potential. If the temperature is raised over 200 °C hot briquetting can lead to a partial degassing of the coal and a better coke strength and reactivity [7]. An adapted briquetting temperature is also important if binding agents are used. Especially hard coals need binders for agglomeration (e.g. tar pitch, starch, PVA etc.) since they do not offer enough binding potential for binderless briquetting [14,15,22,26,27]. An increasing briquetting time generally leads to a quality improvement of the briquettes and cokes since the adhesive forces may be increased [7,24]. If low-rank coals are briquetted without any binder, curing of the briquettes under defined atmosphere is less important. But if binders are used (especially for hard coals) the curing could significantly increase the briquette quality [7,8,15]. For the coking process, the selection of a suitable heating regime is most important. Coals with high volatile matter need very gentle heating rates for degassing to support deformation of the briquette/coke substance. For higher ranked coals, higher heating rates are suitable since the volatile matter decreases. For German brown coal, Vollmaier investigated the influence of the heating rate for different temperature ranges and end temperatures during pyrolysis. The result was the previously mentioned gentle heating regime which was also transferred to industrial scale using a vertical chamber oven [2]. Other studies on the coking behaviour of low-ranked coal used higher heating rates. Mollah et al. used a regime of 4 K min
1 under 500 °C and 4 K min
1 above 500 °C. The end temperature varied between 900 °C and 1300 °C with a dwell time of 2 to 5 hours [6–9]: In general a higher coking temperature and dwell time leads to higher coke quality (e.g. higher bulk density and compressive strength, lower surface area and reactivity). Bayraktar and Lawson used heating rates of 2.5 K min
1 up to 200 °C, 5 K min
1 up to 350 °C, 2.5 K min
1 up to 500 °C, 5 K min
1 up to 610 °C and 10 K min
1 up to 885 °C for the coking of Turkish lignite. For another type of briquettes, the pyrolysis was extended to 900 °C with a heating rate of 14 K min
1 above 770 °C. The different coals and heating regimes led to coke compressive strengths of 22.7 MPa and 48.2 MPa. As literature shows, mostly the influence of coal blend, type and amount of binder, chemical coal treatment as well as the variation of briquetting parameters, curing and heating rate during pyrolysis (with minimum heating rate of 2.5 K min
1) on the coke quality was investigated. Whereas the chemical coal treatment is a pricey process step due to the need of chemicals, hot briquetting of the coal is costly since the safety requirements need to be high as partial degassing of the volatile matter occurs during briquetting. Even the utilisation of binders as tar pitch or PVA demand essential environmental and safety requirements. A promising alternative could be a new mechanical processing of the coal before briquetting. As mentioned before the traditional

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approach by Rammler and Bilkenroth could not reach the requirements for blast furnace utilisation. To improve the coke, quality new processing regimes for the coal were developed in which the coal was fine comminuted in wet state to break a high amount of the primary particles of the coal followed by briquetting and coking. Besides this, the influence of the heating regime was investigated for a German and Indonesian brown coal starting from the regime created by Vollmaier. As literature shows even higher heating rates were successfully tested even by using brown coal and lignite [6–9,16]. Hence, a higher heating rate was tested by switching to a single-step heating regime. To evaluate the trend of coke quality during pyrolysis different end temperatures were used. In this work in a first step, the influence of the coal processing on the briquette and coke quality was investigated using new processing approaches. In a second step, the coke quality was determined at 320 °C, 520 °C and 1000 °C using different heating rates. This offers the chance to evaluate coke quality during pyrolysis and the influence of different heating rates. 2. Material and methods 2.1. Material For the present investigations two typical brown coals of different provenience were taken: A Lusatian brown coal (LBC) with an ash content of 5.98 % (d) and a moisture content of 56,5 % and an Indonesian brown coal (IBC) with an ash content of 2.96 % (d) and a moisture content of 54.3 % were used. The ultimate analyses of both coals as well as the lower and gross calorific value are given in Table 1. For the comparison of coke properties, a commercial lump coke from Schwelgern coke oven plant in the grain size fraction of d > 40 mm and a moisture content of w  0 % was used. 2.2. Methods of the investigation Investigating the influence of the processing parameters three different approaches were used (Fig. 1). In the first approach the coal was processed according to BHT procedure using pre-comminuted coal after the jaw crusher and hammer mill (Dd = 6/0 mm), for comparison against the new technique approach (Fig. 1). For drying a laboratory drying cabinet at air temperature of 0D = 105 °C was used. Afterwards the coal was comminuted in an impact mill with beater disc rotor using a 4 mm sieve to a grain size of Dd = 1/0 mm. In laboratory scale, no sizing was needed since 90 % of the grains were smaller than 1 mm. The comminuted coal was briquetted at the hydraulic stamp press (RASTER Zeulenroda PYE with a maximum force of 2500 kN) using a mould with 50 mm diameter. The mass of briquetting coal was adjusted to mCoal  50 g, so that each briquette had a cylindrical shape with a diameter of 50 mm and a height of 20 mm. The briquetting pressure was set to 140 MPa (d = 50 mm: Fp  275 kN) for all investigation as previous results showed an optimum at this briquetting pressure [25]. The coal and briquetting mould were heated to briquetting temperature of 0P = 80 °C according to [23]. The produced briquettes are subsequently coked in charges of maximum 15 briquettes in a laboratory retort as shown in Fig. 2 using the Vollmaier heating regime. Using approach 2, the coal does not necessarily need to be precomminuted but for better comparability pre-comminuted coal like in approach 1 was used. The coal was fine comminuted in wet state in a modified flat die press (A. Kahl, type 14-175) and granulated in a high-shear mixer (Eirich, type R02) according to [28,29]. In the flat die press, the coal is highly comminuted between roller and die due to shear and compressive stress, and

Please cite this article in press as: Fehse F et al. Influence of briquetting and coking parameters on the lump coke production using non-caking coals. Fuel (2017), http://dx.doi.org/10.1016/j.fuel.2017.05.002

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F. Fehse et al. / Fuel xxx (2017) xxx–xxx

Table 1 Ultimate Analysis, lower and gross heating value of a Lusatian and an Indonesian brown coal. C

H

O

St

N

% (daf) LBC IBC

LHV kJ kg

67.94 69.03

4.92 4.44

26.16 25.26

0.73 0.72

heating element

refractory retort with cap heat isolation

0.25 0.55

GHV
1

25,028 25,691

(daf) 26,436 26,661

lower heating rate up to 520 °C, which should be tested in the trials No. 2 and 4. In trials No. 5 to 7 a one-step heating rate (2.5 K min
1) was investigated. For comparison, a heating rate of 10 K min
1 was chosen showing the effects of the heating rate for typical higher ranked coals. After the dwell time of one hour at the maximum temperature every trial finished.

thermocouple 2.3. Parameters of characterisation

condenser

gas

water

water

gas

box with briquettes/coke collecting vessel Fig. 2. Laboratory retort (schematic).

leaves the machine trough the die. The press channels of the flat die show an upper diameter of d1 = 2 mm and a lower diameter of d2 = 4 mm which causes a sudden re-expansion of the agglomerates, resulting in a slight agglomeration, a limited strength and high porous structure of the ‘‘semi-pellets”. Those semi-pellets were subsequently granulated in the high-shear mixer using granulation time of 180 s, mixing tool speed of 11,1 m s
1 and steam as agglomeration aid (LBC: aSt = 20 %, IBC: aSt = 25 %). The granules were dried in a laboratory drying cabinet, briquetted and coked using the same conditions as in approach 1. For the IBC the granules were secondary crushed to eliminate coarse particles over 4 mm with a double roller crusher. As our previous investigations showed, the amount of agglomeration aid has the highest impact on the granule quality (grain size distribution, strength; [28]) as well as on the briquette and coke quality under constant briquetting and coking conditions according to approach 1 [25]. Due to the high amount of steam, the coal temperature increases. In combination with the rising moisture content, the binding potential increases and stronger granules may be produced. The third approach directly uses the semi-pellets out of the modified flat die press for briquetting after drying in the laboratory drying cabinet analogue to approach 1. The coking of the briquettes took place in the laboratory retort using the Vollmaier regime. Using comprehensive tests, the influence of the press channel diameter in the flat die on the briquette and coke quality was investigated. The best results showed the press channel diameter of d1 = 2 mm [25]. This approach could only be investigated for LBC. For the first investigations of the influence of the heating regime, the coal was processed according to approach 1 and coked using varying heating rates. Table 2 shows the experimental design of those investigations. The Vollmaier heating regime should be the initial point of the investigation (No. 3). To get information about the quality of the coke during the coking process the coking was interrupted at 320 °C (No. 1). Vollmaier himself suggested an expansion of the

To evaluate the influence of the processing approach the grain size distribution of the comminuted coal as well as of the granules and semi-pellets was determined by the sieving analysis. To characterise the briquette and coke quality the following parameters were determined: Gross density was determined by weighting the briquette/coke and measuring the briquette/coke geometry. Compressive strength was investigated according to former TGL 9491 [30]. The briquette/coke was put between two pistons of 30 mm diameter installed at a universal testing machine (Shimadzu, type AG 50 kN, vpiston = 12.5 mm min
1) and was loaded until breakage. The maximum load in unit MPa is indicated as the compressive strength. For each test, the compressive strength of five briquettes was determined and averaged. The former standard requires a maximum standard deviation of ±3 % of the indicated value. For the briquette compressive strength the standard deviation exceeds this limit only for approach 2 using LBC (±4.5 %). Higher standard deviations of maximum ±15.3 % (approach 2, IBC) in the coke compressive strength is the consequence of higher temperature gradients in the laboratory retort. The abrasion resistance was determined in a drum developed by the former Department of Briquetting (IfB) at TU Bergakademie Freiberg with 500 mm diameter and length with four blades of 80 mm displaced by 90° (IfB drum). Five briquettes/cokes are put in a drum for 100 revolutions at 25 min
1. The briquette/coke abrasion resistance is indicated as the residue of the briquettes/cokes on the 30 mm sieve (Eq. (1)) after the test.

R30ð100Þ ¼

m30 100% mtot

ð1Þ

Coke reactivity index (CRI) and Coke strength after reaction (CSR) were determined according to ISO 18894 [31] using an ETO 20/60 device of Prüfer Industrieofenbau. Differing from the ISO standard, first tests were done using the coke in its shape after pyrolysis. In further tests, CRI and CSR were determined of manually crushed and classified coke with the requested grain size of Dd = 22.4/19 mm. CRI and CSR were calculated using the following Eqs. (2) and (3):

CRI ¼

m1
m2  100% m1

ð2Þ

CSR ¼

m3  100% m2

ð3Þ

where m1 is the mass of the test sample before reaction, m2 is the mass of the sample after reaction and m3 is the mass of the sample after tumbling with d > 10 mm.

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F. Fehse et al. / Fuel xxx (2017) xxx–xxx Table 2 Experimental design for the coking tests using different heating rates. No.

1 2 3 4 5 6 7 8

I

II

III

vHR

0Pyr

vHR

0Pyr

tH

0Pyr

K min
1

°C

K min
1

°C

h

°C

0.83 0.83 0.83 0.83 2.85 2.85 2.85 10

320 520 320 520 320 520 1000 1000

– – 2.85 2.85 – – – –

– – 1000 1000 – – – –

1 1 1 1 1 1 1 1

320 520 1000 1000 320 520 1000 1000

3. Results and discussion

3.2. Influence of the processing approach on briquette and coke quality

3.1. Influence of the processing approach on the grain size distribution

Using the differently processed coal, briquetting was carried out at the hydraulic stamp press. One charge of the briquettes was coked in the laboratory retort the other charge was used for determination of the briquette quality. Fig. 4 shows the gross density of the briquettes and cokes for the different processing approaches and a commercial lump coke. For the LBC the briquette gross density is nearly in the same range for all processing approaches. Only the usage of coal granules causes a slight increase in briquette gross density. Due to the granulation in the mixer and the shrinkage during the drying process, a pre-compaction takes place before briquetting resulting in a higher briquette gross density. This effect is even more obvious for the IBC. If the coal granules are briquetted the briquette gross density increases from 1.207 g cm
3 to 1.305 g cm
3. Regarding the LBCcoke gross density it is generally lower than the briquette gross density. The highest difference between briquette and coke gross density was detected for the LBC using approach 1. The comparison with the IBC shows, that it is mostly an effect of the raw material. The IBC coal shows better shrinkage behaviour during pyrolysis than the LBC. That means: At a given mass loss due to coke the volume shrinkage of the IBC is higher than for LBC, causing a compacter coke with a higher gross density. Using approach 2 for IBC even causes a coke gross density higher than the briquette gross density. Because of the intense comminution of the coal in the modified flat die press and the granulation in the intensive mixer, the shrinkage behaviour of the briquettes may be improved. Comparing the gross densities of brown coal coke with the commercial lump coke (dried to w  0 %) the cokes from the low-ranked coals can compete with the commercial coke’s gross density and even exceeds it using the new processing approaches. The determined differences in gross density should also have an impact on the compressive strength of the briquettes and cokes. Fig. 5 shows the compressive strength of briquettes and cokes for varying processing approaches using LBC and IBC. The compressive strength of commercial lump coke could not be tested due to its irregular shape. Using approach 1 briquettes with a compressive strength of 30 MPa were produced with the LBC. If IBC from approach 1 is used for briquetting, the briquette compressive strength is slightly smaller and reaches 24 MPa. If the coal is processed using approach 2 and 3, the briquette strength of LBC may be increased to approximately 40 MPa. For the IBC the briquette compressive strength using approach 2 rises to 43 MPa. An even higher influence of the processing regime was determined for the coke compressive strength. The BHT technology offers a coke compressive strength of 18 MPa for the LBC. With the new proposed approach 2, the coke compressive strength is 2.7 times higher in comparison to approach 1 (LBC). If the dried semi-pellets are briquetted and coked, the coke compressive strength could be increased from

Before briquetting, the grain size distribution was analysed by sieving analysis. Fig. 3 shows the influence of the different processing approaches on the grain size distribution of the briquetting coal. The comminution in the fine impact mill (approach 1) causes a fine grain size distribution for both coals. For the LBC 90 % of the particles are finer than 1 mm. The amount of fines is comparatively high: 50 % of the particles are finer than 0.35 mm. The grain size distribution of the IBC is slightly finer with 95 % of the particles finer than 1 mm and shows a median of 0.28 mm. With those grain size distributions both coals comply with the BHT technology specifications [5]. If the coal is processed according to approach 2, the grain size distribution gets coarser. Due to the mixer granulation of the semi-pellets, the fines are reduced drastically. For the Lusatian coal, 10 % of the particles are finer than 0.5 mm. Over 50 % of the particles may be found in the grain fraction of Dd = 1.6/0.8 mm. For the grain size coarser than 1 mm the grain size distribution of IBC granules is equal to the LBC granules grain size distribution. Due to the secondary crushing in the double roller crusher the amount of fines is higher than for the LBC granules. 24 % of the particles are finer than 0.5 mm and 37 % of the particles belong to the grain fraction Dd = 1.6/0.8 mm. The semi-pellets out of the modified flat die press show the narrowest particle size distribution. The fines are reduced to 7 %. Over 83 % of the particles belong to the grain fraction Dd = 2/1.25 mm.

Fig. 3. Grain size distribution of coal and granules using different processing approaches for Lusatian and Indonesian brown coal.

Please cite this article in press as: Fehse F et al. Influence of briquetting and coking parameters on the lump coke production using non-caking coals. Fuel (2017), http://dx.doi.org/10.1016/j.fuel.2017.05.002

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F. Fehse et al. / Fuel xxx (2017) xxx–xxx

Fig. 4. Gross density of briquettes and cokes using different processing approaches for Lusatian and Indonesian brown coal and commercial lump coke.

Fig. 5. Compressive strength of briquettes and cokes using different processing approaches for Lusatian and Indonesian brown coal.

18 MPa to 68 MPa (LBC). For the IBC the coke compressive strength using approach 1 mounts up to 64 MPa. With the degassing during the pyrolysis the mass of the briquette/coke decreases and a volume shrinkage takes place. If the volume shrinkage is conformal to the mass loss, the coke offers a high strength, which could be even higher than the briquette strength – analogue to the behaviour of the gross density. Due to the better shrinkage behaviour during the coking process the IBC creates a much higher quality coke in comparison to the LBC even using approach 1. Further, when approach 2 is used for IBC still an increasing in coke quality may be determined. Thus, the coke compressive strength reaches 103 MPa. The compressive strength of the LBC coke is highly determined by the processing approach as well. The higher comminution in the modified flat die press leads to a better shrinkage behaviour of the coal. Hence, the coke compressive strength could exceed the compressive strength of the briquettes by using the new approaches 2 and 3. As a third quality parameter, the abrasion resistance is shown in Fig. 6 for the approaches 1 and 2. For a better classification, the abrasion resistance of commercial lump coke determined in the special IfB drum is given as well. The LBC and IBC briquettes processed according to approach 1 both offer an abrasion resistance of 95 %. If approach 2 is used the briquette abrasion resistance increases to 98 % (LBC) and 96 % (IBC). Hence, the same effect as it was detected for the briquette compressive strength may be determined. The coke abrasion resistance shows a similar trend: Using the first approach the LBC coke abrasion resistance is slightly lower in comparison to the briquette abrasion resistance. This disadvantage could be

eliminated using the processing according to approach 2. Due to the better comminution and pre-agglomeration, the shrinkage behaviour of the cokes is improved and thus the strength of the coke increases. For the IBC the coke abrasion resistance matches the results of the compressive strength as well: The better shrinkage behaviour of the coal offers a high abrasion resistance of 98 % even using approach 1. If approach 2 is used the coke abrasion resistance could be slightly increased. If the results are compared with the abrasion resistance of the commercial lump coke, it is obvious that if approach 2 is used for coal processing the cokes of both coals could match the abrasion resistance of a commercial lump coke. The coke reactivity and strength after reaction was determined for cokes produced with approach 1 and 3 using Lusatian brown coal. The coke samples were split as mentioned in section 3.2: One sample was crushed matching the grain size as it is required in ISO 18894. The other trial was done with coke in its original shape since the coke should be utilised without comminution in potential applications. Fig. 7 shows the results of CRI and CSR for LBC. In general, the coke reactivity is on a high level. If the original cokes are comminuted to the required grain size the CRI using processing approach 1 increases as the surface area rises due to the crushing. The same tendency can be determined on a very low level even for processing approach 3. However, comparing the CRI of the original cokes no influence of the processing approach could be determined. The original cokes of approach 3 offer a higher strength after reaction than those of approach 1, but a comminution to the grain size of 22.4/19 mm reduces the CSR of the original coke of approach 3 to the level of the CSR using approach

Please cite this article in press as: Fehse F et al. Influence of briquetting and coking parameters on the lump coke production using non-caking coals. Fuel (2017), http://dx.doi.org/10.1016/j.fuel.2017.05.002

F. Fehse et al. / Fuel xxx (2017) xxx–xxx

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Fig. 6. Abrasion resistance of briquettes and cokes using different processing approaches for Lusatian and Indonesian brown coal as well as for commercial lump coke.

Fig. 7. Reactivity of the Coke and coke strength after reaction for the cokes using processing approaches 1 and 3 (Lusatian brown coal) and a commercial lump coke.

1. One promising perspective on the reduction of coke reactivity might be the chemical treatment of the coal [8] or the utilisation of coking additives (e.g. spent sulphite liquor or black liquor). 3.3. Influence of the heating regime on the coke quality The new processing approaches 2 and 3 allow a strong increasing of the coke quality. In a second step, the influence of the pyrolysis heating rate was investigated. Fig. 8 illustrates the coke compressive strength and abrasion resistance using different heating rates, for briquettes produced using approach 1. In the first step, the coking was finished at 320 °C and 520 °C using heating rate of 0.83 K min
1 and one hour dwell time. Due to the degassing process in this temperature field, the strength of the low-temperature coke offers only a limited strength. The compressive strength of LBC coke reaches 11 MPa (320 °C) and 10 MPa (520 °C). The abrasion resistance of this coke is on a lower level as well. At a coking temperature of 320 °C, an abrasion resistance of 24 % was determined. At a higher temperature of 520 °C, the abrasion resistance increases to 48.5 %. Regarding the IBC the compressive strength of the coke is also at a comparatively low level and reaches 28 MPa (320 °C) and 29 MPa (520 °C). In contrast, the abrasion resistance even of those low-temperature cokes is on a high level and reaches 96 % (320 °C) and 97 % (520 °C). Following the Vollmaier regime with 0.83 K min
1 up to 320 °C and 2.85 K min
1 up to 1000 °C the cokes reach their final strength at 14 MPa (LBC) and 80 MPa (IBC). In his research Vollmaier suggested the

expansion of the low heating rate up to 520 °C to increase the coke quality [3]. However, regarding the results in Fig. 8 this effect may not be evidenced. For the LBC no improvement of the coke quality could be determined but the coke quality of the IBC even decreases by the enlargement of the low heating rate-zone. In further tests, it was investigated if a single-stage heating rate may be suitable for lump coke production using LBC and IBC. Similar to the previous tests the quality of the low temperature cokes was determined at 320 °C and 520 °C using a heating rate of 2.85 K min
1. Fig. 8 shows that the coke compressive strength for LBC at 320 °C (13.2 MPa) and 520 °C (10 MPa) is at the same level as at the low heating rate. The abrasion resistance at 320 °C is even higher (60 %) than at the lower heating rate. But at 520 °C, the abrasion resistance decreases to 40 %. However, a distinct negative effect of the higher heating rate on the coke strength e.g. due to higher degassing processes could not be determined. The IBC coke exhibits almost the same behaviour as the LBC cokes albeit on a higher level. If the briquettes are heated up to 1000 °C, the LBC offers a coke compressive strength of 15.5 MPa, which is comparable to the Vollmaier regime. But the abrasion resistance decreased to 89 %. The IBC cokes offer a compressive strength of 66 MPa, meaning a strength loss of almost 15 MPa and the abrasion resistance reaches 98.2 %. So even if a decrease of the coke stability may be detected using the singlestage heating rate of 2.85 K min
1 it shows that the heating rate especially in the first temperature range should be investigated more detailed between 0.83 K min
1 and 2.85 K min
1. For comparison, a heating rate of 10 K min
1 was chosen for the coking

Please cite this article in press as: Fehse F et al. Influence of briquetting and coking parameters on the lump coke production using non-caking coals. Fuel (2017), http://dx.doi.org/10.1016/j.fuel.2017.05.002

8

F. Fehse et al. / Fuel xxx (2017) xxx–xxx

Fig. 8. Compressive strength and abrasion resistance of coke from Lusatian and Indonesian brown coal at different heating rates for approach 1.

of the briquettes. This single-stage heating regime is suitable especially for low volatile coals. As Fig. 8 shows, the coke compressive strength for the LBC is even lower than the compressive strength of the low temperature coke at 320 °C or 520 °C for the lower heating rates. For the IBC the coke compressive strength is at the same level as for the low temperature cokes at lower heating rates. However, due to the high heating rate the abrasion resistance for both coals declines to zero. Which means due to the faster heating rate the degassing process happens in a very short time. During the degassing the structure of the agglomerate is much more weaken and could not be stabilised in the higher temperature range.

4. Conclusion To produce lump coke from low-rank coals, e.g. brown coals, the intensive processing of the coal as well as the creation of highquality briquettes are indispensable steps before coking of the coals. Due to the high loading by intense comminution and preagglomeration of the coal during processing, the coal might be structurally modified and offers better lump coke creation property. Using the dried ‘‘semi-pellets” (approach 3), the coke compressive strength of the LBC lump coke is 3.7 times higher in comparison to the cokes using the BHT technology. The application of granules offers a compressive strength 2.7 times higher for LBC and 1.6 times higher for IBC. The abrasion resistance of cokes using the new processing approaches is comparable to commercial lump coke. The reactivity of the produced coke from LBC is on a high level and an additional processing approach would be needed, which is under investigations at the moment. The chemical treatment of the coal could be a promising perspective to reduce the coke reactivity as well as the utilisation of coking additives. A second possibility to influence the coke quality may be the variation of the heating rate in the coking process. Once Vollmaier developed a special heating regime for the lump coke production using Lusatian brown coal, which guarantees a suitable coking for the two investigated coals as well. Hence, first investigations on the coking behaviour of the brown coal briquettes showed that a higher heating rate in the first stage of the heating regime should be investigated in depth. As previously shown the creation of high

strength lump cokes using brown coal is possible by using the new processing approaches in laboratory scale in the next step the reactivity of the coke needs to be adapted to the possible field of application. If other coals should be used for the creation of high strength, coke the new approaches are the basis for further investigations but the different processing, briquetting and coking parameters need to be adapted experimentally.

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Please cite this article in press as: Fehse F et al. Influence of briquetting and coking parameters on the lump coke production using non-caking coals. Fuel (2017), http://dx.doi.org/10.1016/j.fuel.2017.05.002