Predicting Coking Pressures Through a Combination of Different Analytical Parameters

Transcription

1 and its Applications (ECCRIA) Predicting Coking Pressures Through a Combination of Different Analytical Parameters Sylvia Kokonya, Miguel Castro Díaz and Colin E. Snape Department of Chemical and Environmental Engineering, University of Nottingham, Nottingham, NG7 2RD, UK

2 Outline Introduction Aims Materials and tests Results and Discussion Conclusions Acknowledgements

3 Introduction Coke oven degradation by high swelling coals is one the major causes of battery ageing. Dangerous coking coals can damage coke ovens due to the high wall pressures exerted. Although coke swelling pressure is not a new problem and has been investigated in the past, there is no simple, reliable, cheap methodology to predict high wall pressures.

4 Aims The main aim of this study is to establish relationships between parameters from different analytical techniques including high-temperature rheometry to: Identify dangerous coking coals. Predict wall pressures using a combination of different parameters obtained from laboratory tests.

5 Materials Seventeen coals with different rank were studied. Coal VM (db) Vitr. (%) Lipt. (%) Fusi. (%) Semifusi. (%) Inertodetrinite (%) A B C D E F G H I J K L M N P Q R

6 Materials Inertodetrinite content seems to be related to EWP values. Coal Ash (db) VM (db) Inertodetrinite (%) Gieseler MF (ddpm) Eq. WP (kpa) A B C D E F G H I J K L M N P Q R D a n g e r o u s

7 Tests High-Temperature Rheometry A Rheometrics RDA-III rheometer was used to monitor the viscoelastic behaviour of coal at high temperatures. Transducer Serrated parallel plates Furnace Motor

8 Tests High-Temperature Rheometry Approx. 1.5 g of coal ( m) were used to prepare a disc of 25 mm diameter and 2.6 mm thickness. The disc was placed between the two serrated parallel plates of the rheometer. The samples were heated in N 2 from room temperature to 330 C at 180 C/min and from 330 C to 500 C at 3 C/min, keeping the normal force constant at 200 g throughout the test. The complex viscosity (η*) and plate gap ( L) were recorded as a function of temperature. Transducer Coal disc Motor

9 L ( ) [mm] Tests High-Temperature Rheometry During carbonisation, coal softens, shows a maximum in fluidity (min. viscosity) and resolidifies. η*: complex viscosity (Pa.s) : softening stage : resolidification stage ΔL: plate gap (mm) 1 : mass expansion 2 : mass collapse * ( ) [Pa-s] Temp [ C]

10 Tests Sapozhnikov Test The Sapozhnikov test is a penetrometric method where the plastic layer thickness is measured with a thin needle. A sample mass of 100 g and coal particles < 1.6 mm is diameter are used for the test. The coal is placed in a steel crucible with 59 mm diameter and heated at 3 C/min. Measurements are taken in the temperature range C. This test provides the contraction of the charge (X, mm) and the thickness of the plastic layer (Y, mm).

11 Results High-Temperature Rheometry The higher the minimum complex viscosity the higher the wall pressure. Coal QUC B 2 (212 kpa) Coal PD 137 H (15 (50 kpa) * ( ) [Pa-s] * ( ) [Pa-s] *10 5 Pa.s Temp [ C] *10 4 Pa.s Temp [ C]

12 Results High-Temperature Rheometry The higher the coal mass expansion during softening the higher the wall pressure. Coal QUC B 2 (212 kpa) Coal PD 137 H (15 (50 kpa) L ( ) [mm] L ( ) [mm] mm mm Temp [ C] Temp [ C]

13 Results Sapozhnikov Test Two parameters were determined with this test, namely the contraction of the charge (X) and the thickness of the plastic layer (Y). Higher contraction and higher thickness lower equivalent wall pressure. Coal X (mm) Y (mm) Eq. WP (kpa) A B C D E F G H I J K L M N P Q R

14 Discussion The volatile matter content correlates with the temperature of minimum complex viscosity (rheometry).

15 Discussion The volatile matter content also correlates well with the Sapozhnikov contraction.

16 Discussion Other parameters such as: the thickness of the plastic layer (Sapozhnikov) the maximum phase angle (rheometry) the maximum axial force on top plate (rheometry) coal mass collapse during resolidification (rheometry) vitrinite and liptinite contents (maceral analysis) ash content (proximate analysis) did not show any obvious correlation with equivalent wall pressure values (i.e. scattered data). The min. complex viscosity, inertodetrinite content, Sapozhnikov contraction and mass expansion during softening are independent parameters that affect eq. WPs.

17 The expansion of the coal mass is expressed as the percentage of expansion with respect to the initial coal pellet thickness (i.e. 2.6 mm). Discussion These parameters have been combined to construct 3-D plots:

18 Discussion It is possible to identify dangerous coals (> 15 kpa) using a simple diagram based on viscosity, contraction and inertodetrinite content. It is not possible to predict WP values with these three parameters.

19 Conclusions Parameters obtained from maceral analysis, proximate analysis, high-temperature rheometry and Sapozhnikov test have been combined to establish correlations. The temperature of maximum fluidity (T mf ) and the volatile matter content (VM) correlate with the Sapozhnikov contraction (X). Only the minimum complex viscosity, inertodetrinite content, Sapozhnikov contraction and mass expansion during softening were found to be independent. 3-D plots represent a simple visual method to identify dangerous coals (> 10 kpa), but cannot predict the magnitude of wall pressures.

20 Conclusions Indeed, determining the equivalent wall pressure seems to be impossible due to the different mechanisms of wall pressure generation and the different analysis conditions when using laboratory techniques and testing facilities. However, a diagram that considers threshold values for the minimum complex viscosity, the inertodetrinite content and the Sapozhnikov contraction has been proposed to discern coals that generate dangerous (> 15 kpa) and relatively safe ( 15 kpa) equivalent wall pressures.

21 Acknowledgements 10 th European Conference on Coal Research and its Applications, University of Hull, 5-17 September 2014 The research leading to these results has received funding from the European Union's Research Programme of the Research Fund for Coal and Steel (RFCS) research programme under grant agreement No. [RFCR-CT ]. The authors would also like to thank: Dr Tatiana Rozhkova from Centre de Pyrolyse de Marienau (CPM) in France for supplying the coals Dr Bartosz Mertas from IChPW in Poland for carrying out the Sapozhnikov tests.