COAL TRANSPORTABLE MOISTURE LIMIT PROJECT. Technical Submission to the Australian Maritime Safety Authority

Transcription

1 COAL TRANSPORTABLE MOISTURE LIMIT PROJECT Technical Submission to the Australian Maritime Safety Authority 25 th November 2014 Page 1 of 24

2 TABLE OF CONTENTS 1. Executive Summary Recommendations for Implementation Background - Ship casualty study Review of current TML tests described in IMSBC code Flow table test Penetration test Proctor/Fagerberg Test Scope of scientific study Suite of coals Sample preparation Cargo bulk density investigation Development and evaluation of modified Proctor/Fagerberg test conditions Apparatus Selection of compaction hammer Sample reconstitution Maintenance of particle size Interpretation of results Summary of results for coals used in the study Repeatability and reproducibility - Interpretation of results Blends Recommendations Conclusion References Page 2 of 24

3 1. Executive Summary This report provides a summary of the technical background to the modified Proctor/Fagerberg method for determination of Transportable Moisture Limit (TML) for coal. This method has been developed through extensive research undertaken by the Australian coal industry under the auspices of the Australian Coal Association Research Program (ACARP). The scope of this research was reported to the CCC1 session of the IMO in September 2014 (1). The IMSBC Code (2) describes three methods for determination of bulk cargo transportable moisture limit (TML). In each case maximum particle size for application of the test method is less than the typical maximum particle size of Australian export coals, which are typically sized from zero to 50 mm. Key aspects of the original Proctor/Fagerberg procedure which have been modified are: Selection of a larger, 150 mm diameter test cell; Preparation of 25 mm top size sample by a specified reconstitution procedure; and Compaction using a D energy hammer in place of the IMSBC code specified hammer to ensure that material bulk density is consistent with that measured in the cargo hold of a bulk carrier. The report describes the scientific basis for these modifications and test procedure is described in the document titled Modified Proctor/Fagerberg method for coal. The modified TML method returns one of two results for each coal tested: A non Group A designation for where leakage is observed from the cell prior to reaching 70% saturation. By reference to the IMSBC Code s7.2.2, such coals are cargoes where liquefaction does not occur and hence are Group B only. A Transportable Moisture Limit for coal that is liable to liquefaction. For coal that is able to achieve 70% saturation without water leaking from the test cell, a PFD70 value is reported, which is representative of the Transportable Moisture Limit for the coal. As noted in CCC 1/5/8 (1), further research work has been carried out and this work still continues. The results of the full study will be documented for submission to the IMO CCC2 meeting in September 2015 for which papers will be submitted in June Recommendations for Implementation It is recommended that: 1. The Modified Proctor/Fagerberg method for Coal be adopted for application to materials transported in accordance with the Coal schedule in Appendix 1 of the IMSBC code (2). 2. Where cargoes are assembled by blending multiple coal products, the transportable moisture limit of the overall cargo shall be established by either: Directly measuring the transportable moisture limit of the blended product, or Through adopting the minimum transportable moisture limit value of the individual cargo constituents. Page 3 of 24

4 3. Background - Ship casualty study A systematic study was undertaken of all reported ship casualties from January 1978 to June 2014, which covered over 1900 events relating to vessels of greater than 10,000 dwt. The investigation found no cases where liquefaction of a coal cargo led to a vessel casualty. However: Bulk carriers transporting coal accounted for 18% of total casualties. All casualties reported as having a type of foundered were investigated to determine any link to cargo destabilisation as the cause. The review identified seven nickel-ore cargoes where the vessel was reported to have foundered. Of these, four were identified as having capsized or sunk. One vessel with a cargo of iron ore was identified as having sunk on a voyage from India to China in In respect of coal cargoes, there were eight events where the vessel was reported as having foundered. In all cases the cause was reported as either taking in water or mechanical failure. 4. Review of current TML tests described in IMSBC code A systematic review was undertaken to establish the potential for each of the three published transportable moisture limit tests to be extended to be suitable for 50mm coal cargoes, and a summary of the finding for each method is presented below. 4.1 Flow table test The scale of this test is designed for bulk cargoes where the maximum particle size is 7 mm. There is no scope to upscale the test to suit a material with the size distribution of coal and Appendix 2 of the IMSBC code states It (flow table test) may also be applicable to materials with a maximum grain size up to 7 mm. It will not be suitable for materials coarser than this The flow table test has not been further investigated for application to 50 mm top size coal. 4.2 Penetration test Appendix 2 of the IMSBC Code describes this test as being suitable for mineral concentrates, similar materials and coals up to a top size of 25 mm using the larger diameter test cell. This Appendix does not make reference to treatment of coals of greater than 25 mm top size although almost all seaborne traded coals are sold to a specified top size of 50 mm. In the limited time available the penetration test has not been developed for application to 50 mm top size coal due to the potential need to optimise test parameters beyond particle size reconstitution. 4.3 Proctor/Fagerberg Test The Proctor/Fagerberg test is described as applicable to fine and relatively coarse-grained ore concentrates or similar materials with a top size of 5 mm. Extensive investigation for adoption and improvement (such as that undertaken for application to coal) is recommended before application to coarser materials (IMSBC Code Appendix 2 Section (2) ). Recognising the effective application of a modified Proctor/Fagerberg test to iron ore fines, this test has been modified for determination of TML for 50 mm top size coal. Areas requiring development were: Page 4 of 24

5 Sample preparation to yield valid results for 50 mm coal whilst allowing TML determination in a simple small scale test; Selecting the size of the apparatus to match the sample preparation; Ensuring that the test conditions closely represent the in-hold cargo status particularly in respect of bulk density; and Confirmation of the repeatability and reproducibility of the method. Appendix 2 of the Code in Section (2) states the Proctor/Fagerberg method should not be used for coal or other porous materials. Whilst the code offers no rationale for this comment, the present research examined two aspects to ensure validity of the method: 1. That coal particles are not significantly degraded through the compaction process as this would influence compaction in the Proctor/Fagerberg cell; and 2. Allowing sufficient time between adding moisture to a test sample and subsequently testing the coal for moisture equilibration between internal pores and fissures throughout the sample. 5. Scope of scientific study 5.1 Suite of coals A suite of 14 coals provided the basis for experimental work. These coals are representative of Australian export coal sourced from an arc of coalfields stretching over 1700 km from North Queensland to the Illawarra region of New South Wales. In the 2011/12 financial year Queensland exported around 165 Mt of coal from some 43 open cut and 13 underground mines. New South Wales, over the 2010/11 financial year exported around 120 Mt of coal from 30 underground and 31 open cut mines. The majority (72%) of Queensland coal was classified as metallurgical coal (used for coke making or pulverised coal injected to blast furnaces) with the remainder being thermal coal used in power generation and other industrial processes. The majority of the coal (~80%) exported from NSW was thermal coal with the remainder being metallurgical coals. To achieve the best spread of coal properties practicable within the suite of 14 coals the study has selected coals: From New South Wales (5 coals) and Queensland (9 coals); Mined from 8 different coal basins and 10 coal measures within those basins; Covering 13 washed coals and 1 unwashed coal; Spanning volatile matter content from low to high levels; Sold for metallurgical and thermal application; and Where particle size distribution covers the normal range of most Australian export coals. Page 5 of 24

6 Figure 1 - Coal size distribution for 30 Australian coals (in grey) and the 14 testt coals (in red) (note the log-log scale) Figure 1 overlays the particle size distributions of coals selected for the t study with 30 Australian coals. One of the coals included has a significantly coarser particle size s than thee remainderr of the reference coals. It was not possible to includee this coal in the study, as it is no longer shipped. 5.2 Sample preparation In principle the TML test can be specified on the basis of test samples which: a) Contain the full particle size distribution; b) Are reconstituted to createe a representative sample by removing large particles (e.g. above 25 mm) and replacing them with particles close in size to thee maximum test particle size; or c) Have had larger particles scalped from the original sample prior to testing. Each of these methods offers advantages and limitations as noted inn sections to below Full particle size distribution In the case of testing the full size distribution, impacts are: This test is most representative of thee material being characterised. For coals with 50 mm top size, representative testing requires a test celll diameter of 300 mmm with a similar height based on thee cell diameter being sixx times the largest particle diameter in order to ensure large particles do not interact in the t test. Thee test sample size would hence be approximately 20 kg. By contrast, the sample size for the Proctor/Fagerberg test described in the Code is approximate ely 1 kg. Larger test samples introduce manual handling hazards for laboratory operators as well as greater complexity. One particular consequence is that high-level diligence is required to avoid size segregation in the test cell, which would create errors in the results obtained. It is concluded that a test carried out with the full coal size distribution is not practical. Page 6 of 24

7 5.2.2 Scalping top size Scalping of the sample involves screening at the maximum particle size for the test and removing the oversize material. Impacts are: This method is simple to apply, however: Removal of oversize concentrates the fines fraction in the test sample; and As a consequence the test may be unrepresentative of the cargo Reconstituted sample The method of sample preparation selected for the modified Proctor/Fagerberg test is to reconstitute the sample by: 1. Designing test apparatus to use the most representative sub-sample whilst maintaining a practical top size, which is 25 mm; 2. Removing all particles above the maximum size for the test equipment; and 3. Replacing these with near size particles (16 x 25 mm). Impacts of this method are: Through appropriate selection of the maximum particle size, the proportion of the bulk sample material used in the test is; By replacing oversize particles with near size particles, concentration of fines in the test sample is avoided; and Balance is achieved in ensuring a representative sample whilst avoiding manual handling concerns and minimising particle size segregation. 5.3 Cargo bulk density investigation Eight cargoes of coal were nominated for in vessel bulk density determination, with the bulk density measured again at the discharge port on two of these cargoes to assess degree of compaction of the cargo during the voyage. Data were generated using 3 dimensional laser survey equipment and computer software to calculate material volume from the survey. The mass of coal was determined from belt weighers and confirmed against ship draft survey. Actual moisture content was measured on routine incremental samples taken during loading. Figure 2 below shows the 3 dimensional survey unit in place on a vessel. This unit was moved to each corner of the hold to allow the full cargo surface to be scanned. Figure 3 shows a representation of the cargo volume generated from the processing software and from which the cargo volume was calculated. Page 7 of 24

8 In each case, the hold was surveyed empty and again of completion of filling Figure 2 - Laser survey equipment in place on board a vessel Figure 3 - Representation of cargo from three-dimensional survey Page 8 of 24

9 6. Development and evaluation of modified Proctor/Fagerberg test conditions 6.1 Apparatus The standard Proctor/Fagerberg cell specified in the IMSBC Code has a diameter of 100 mm with total volume of 1 litre. Allowing cell diameter of 5 times the maximum particle size, this cell is suitable for maximum particle size of up to 20 mm. In order to deliver the test under the balanced conditions of 25 mm top size sample and avoidance of particle size segregation, the modified Proctor/Fagerberg test for coal specifies use of a 150 mm test cell with 2121 ml volumetric capacity. This configuration allows a maximum test particle size of 25mm with the cell diameter six times the maximum particle diameter. The D energy hammer dimensions have been scaled to allow the number of hammer drops to be maintained in moving to the larger diameter test cell. Cell and hammer details are given in Figure 4 and Table 1 below. Page 9 of 24

10 Removal extension piece Hammer 337.5g Mould Base Base Recess Drop Height 150mm Air relief hole Hammer Diameter 75mm Compaction Cylinder Compaction Hammer Figure 4 - Proctor/Fagerberg Cell and Hammer Page 10 of 24

11 Table 1 - Key dimensions of Proctor/Fagerberg Cell Parameter Units Dimension Tolerance Hammer mass g ± 2 Hammer diameter mm 75 ± 0.2 Drop height mm 150 ± 2 Mould inner diameter mm 150 ± 0.5 Mould inner height mm 120 ± 1 Mould inner volume cm ± 18 Removal extension piece height mm 75 ± Selection of compaction hammer Based on TML test development for iron ore, the compaction hammer energy was also reviewed resulting in selection of and the Proctor/Fagerberg D energy hammer. Figure 5 compares the in vessel bulk density calculated from surveys of selected holds containing the designated coals with the Proctor/Fagerberg wet bulk density at equivalent moisture. In all cases the D energy hammer results in bulk density marginally higher than that observed in a vessel. Comparison of Vessel and PF Test Bulk Density Bulk density (kg/cubic meter) D E F H O O Coal Designation 12% 11% 10% 9% 8% 7% 6% 5% 4% 3% 2% 1% Moisture (&%) Vessel wet bulk density PF test wet bulk density Total moisture % Figure 5 - Comparison of bulk density between Proctor/Fagerberg cell and vessel Page 11 of 24

12 In addition, Proctor/Fagerberg tests were carried out on 4 coals at the as received moisture using the C, D and E energy hammers. Note the C energy hammer is specified for use in the IMSBC code. As shown in Figure 6, dry bulk density decreased as the hammer energy decreased. In vessel dry bulk density consistent with Figure 5 varied from 830 to 930 kg/cubic metre with a mean of 897 kg/cubic metre. It is concluded that use of the C energy hammer results in over compaction of the sample, the E hammer results in under compaction. The D energy hammer provides maximum consistency with the bulk density measured in the vessel hold whilst continuing use of a standard proctor/fagerberg test hammer Bulk Density (tonnes /m 3 ) C Energy D Energy (1) D Energy (2) D Energy (3) E Energy 0.5 Coal A Coal B Coal D Coal G Coal type Figure 6 - Comparison of C, D and E energy hammers impact on bulk density at as received moisture 6.3 Sample reconstitution The reconstitution process removes particles larger than 25 mm and replaces them with mm particles. Figure 7 compares the resulting particle size distributions for coal D and shows the impact of reducing top size buy this method. Reconstitution serves to provide a test sub-sample, which is consistent with the bulk material in the finer size fractions which most impact potential for liquefaction. Page 12 of 24

13 100 Coal D - Particle Size Distribution Percent Finer (%) Reconstituted sample Full sample as received Sieve Opening (mm) Figure 7 - Coal D - Impact of reconstitution on particle size distribution Page 13 of 24

14 6.4 Maintenance of particle size Figure 8 - Coal A - Comparison of particle size distribution before and after testing Analysis was undertaken to review whether coal particles were degraded in sizee during compaction in the Proctor/Fagerberg cell by comparing the particle size distribution for coalss A and D between as received or reconstituted coal with that determined following testing. Figure 8 shows particle size distribution (PSD) for coal A prior to sample reconstitution and subsequently for six samples taken after testing and drying. In all cases the post-test particle size distributions were comparable with those prior to testing, indicating no n evidencee of particle attrition or degradation for this coal during compactionn in the new coal PF test. Figure 9 below shows similar dataa for coal D, again indicating no attrition of this coal under compaction in the Proctor/Fagerberg test cell. In this case, there are 2 particle size distributions shown prior to testing. One is for the t full as received material and thee second for the reconstituted sample prior to testing. Page 14 of 24

15 Figure 9 - Coal D - Comparison of particle size distribution before and after testing Figure 10 below showss scanning electron microscope images of +1-3 mm particles of coal B, with the left hand image showing particles prior to testing. The right hand image shows similarly sized particles following testing. Similar images aree shown in Figure 11 forr coal A. These images indicate no visible change in particle morphology. This observation coupled with no reduction in particle size following testing, indicates that the Proctor/ Fagerberg methodology does not cause particle size degradation, providingg confidencee the test is not in itself changing the properties of the product during the test. Figure 10 - Comparison of Coal B particles before (left) and after (right) testing Page 15 of 24

16 Figure 11 - Comparison of Coal A particles before (left) and after (right) testing In order to further characterise any potential size degradation, particle morphology has been compared before and after testing using the images in Figure 11. Comparison has been based on particle aspect ratio, polygonality and circularity, with results shown in Figure 12 for coal A. In the event of significant particle attrition, changes to particle morphology are expected. Figure 12 shows no discernible change in these measures consistent with there being no significant particle size degradation in the test. Tested Sample Untested Sample Nominal 3mm ~ 1mm samples Criterion 1 Aspect ratio Criterion 2 Polygonality Criterion 3 Circularity Figure 12 - Coal A - comparison of particle morphology before and after testing Page 16 of 24

17 6.5 Interpretation of results Void Ratio e Water Content W1 (%) Figure 13 - Typicall compaction curve for coal H Details of calculation of the compaction curvee generated by the modified Proctor/Fagerbergg test are included in Modified Proctor/Fagerberg Method for Coal (3) and are not repeated here. Figure 13 shows the compaction curve for a single determination on coal H. Features are: The compaction curve crosses the 70% saturation curve at total moisture (gross water) content of 15.4%; The optimum moisture content (OMC) at which level void ratio is minimised occurs at approximately 16.6% total moisture. The OMC is the moisture content at which bulk material strength is maximised m and for safety should lie above the moisture level nominated as thee TML. Consistent with the Proctor/Fagerberg method in the IMSBC Code Appendix A 2 Section (2), intersectionn of the compaction curve with the 70% saturation curve iss proposed as the TML for coal using the present method. Page 17 of 24

18 Figure 14 - Tests on coals returning TML at partially saturated and near fully saturated moisture content Typical coal and test cell appearance at 2 moisture contents are shown in Figure 14 for a coal which has returned a compaction curve whichh crosses the 70% saturation line. The left hand photographh shows partially saturated coal above the testt cell following removal of the collar. In the right hand photograph the coal appearance indicates a high degree of saturation. In the case of coals where moisture freely drains from the sample such that the test sample compaction curve does not extend to or beyond 70% saturation. In this case, moisture drains to the base of the cell and leaks from the joint where the cell is seated into the base. Further, coal above the top of the cell following removal of the collar appears unsaturated. An example is shown s in Figure 15. Following from this observation, for coals where there is visual evidence that water passes through the spacess between particles and the compaction curve does not extend to or beyond the 70% saturation line, the coal is deemedd to be free draining and a TML value is not applicable. By reference to the IMSBC Code s7.2.2, such coals are cargoes where liquefactionn does not occur. Page 18 of 24

19 Non-saturated top Moisture leaking at the base Moisture leaking at the base Figure 15 - Test showing water leakage from the base of the cell indicating moisture migration within the test sample 6.6 Summary of results for coals used in the study Figure 16 - Summary of results forr 14 Australian coals and 2 international coals Page 19 of 24

20 Table 2 - Summary of duplicate Proctor/Fagerberg test results for 14 Australian and 2 International coals Coal Sample A B C D E F G H J K L N O P X Y PFD70 - Test 1 (%) NA 15.6 NA NA NA NA NA NA 13.0 NA 15.4 NA PFD70 - Test 2 (%) NA 15.6 NA NA NA NA NA NA 13.3 NA 15.6 NA Figure 16 and Table 2 summarise results of testing the 14 Australian coals in the study, together with 2 international coals tested at the initiative of the respective producers with results provided by them for this study. For coals where PFD70 moisture content could not be determined, in Figure 16 the bar height represents the free draining saturated moisture content for that coal. Within the bar, the saturation degree at this moisture content is shown. In summary: 14 Australian coals were tested For 8 Australian coals, moisture was found to freely drain from the test sample at saturation levels below 70% and hence no PFD70 could be determined. The remaining 6 Australian coals returned PFD70 moisture content ranging from approximately 13% to approximately 15.5%. International coal X returned a PFD70 value of 15.5%, which is consistent with results obtained for Australian coals. International coal Y was found to freely drain from the test sample at saturation levels below 70% and hence no PFD70 could be determined. Page 20 of 24

21 6.7 Repeatability and reproducibility - Interpretation of results PFD70 repeatability tests Moisture Content (% wet base ) 20% 19% 18% 17% 16% 15% 14% 13% 12% 11% 10% 9% 8% 7% 6% 5% 4% 3% 2% 1% 0% PFD70 original duplicate, test 1 PFD70 original duplicate, test 2 PFD70 repeatability, test 1 PFD70 repeatability, test 2 E 1 E 2 F H 1 H 2 H Ship Figure 17 - Repeatability of PFD70 Moisture Content Development of the modified Proctor/Fagerberg test was undertaken using duplicate determinations. Figure 17 compares repeat determinations on coals E, F and H. In the case of coal E, duplicate determinations were completed on each of 2 samples of the bulk coal taken on different dates. Coal H also had 2 samples supplied at different times on which duplicate determinations were performed together with a single determination on a third sample taken in association with the vessel survey for bulk density determination. Evident from Figure 17 is: a) Repeat determinations on the same bulk sample yield PFD70 results with a range of < 0.5 percentage points; and b) The test is sensitive to changes between different bulk samples. Further, in the case of each coal tested where water was observed to leak from the apparatus prior to reaching the 70% saturation line, the same result was obtained in the duplicate test. The reproducibility of determinations for the modified test was then assessed, by testing the same coal bulk sample at a second laboratory. Results are summarised in Figure 18, which illustrates: Average results PFD70 on each coal are within 0.6 percentage points; Both laboratories showed similar repeatability between determinations on the same bulk sample; and Page 21 of 24

22 Although not shown on Figure 18, both laboratories consistently identified coals where water was observed to pass through the spaces between particles and the compaction curve does not extend to or beyond the 70% saturation line. PFD70 reproducability tests PFD70 Moisture Content (%) 20% 19% 18% 17% 16% 15% 14% 13% 12% 11% 10% 9% 8% 7% 6% 5% 4% 3% 2% 1% 0% PFD70 repeatability, test 1 PFD70 repeatability, test 2 PFD70 repeatability, test 3 PFD70 (ATC Williams), test 1 PFD70 (ATC Williams), test 2 PFD70 (ATC Williams), test 3 E 2 F H 2 Figure 18 - Results of reproducibility assessment across 2 laboratories 6.8 Blends Coal producers regularly ship blends of coal brands for which it is considered impractical to periodically determine a representative TML. Blend components and ratios regularly vary over wide range. In order to identify a potential protocol for reporting a TML for a blend of coals where TML analysis has been undertaken for the individual brand coals but not for a blend representative of that being shipped, two blends of test coals have been tested at different blend ratios in order to estimate the impact of blending on the resulting cargo TML. Figure 19 shows the impact on PFD70 from blending coals B and O. This graph suggests the variation of TML with blending ratio is approximately linear. Figure 20 shows a similar plot for coals H and N, noting that coal N freely drains in the test cell at saturation below 70%. In this case, blends of up to 50% coal N with coal H maintain the PFD70 value record for coal H, with the value increasing at a blend with 75% coal N. Based on the findings of this initial work, and in order to ensure a safe interim protocol, it is recommended that in the case of blended cargoes, where a TML has not previously been established, that shippers should adopt the minimum TML value of individual cargo constituents as the TML value for the cargo. Page 22 of 24

23 Figure 19 - PFD70 results for blends of coal B with coal O Figure 20 - PFD70 results for blends of coal H with coal N (note coal N does not return a PFD70 moisture conten as water freely drains at moisture content below 70% saturation) Page 23 of 24

24 7. Recommendations It is recommended that: 3. The Modified Proctor/Fagerberg method for Coal be adopted for application to materials transported in accordance with the Coal schedule in Appendix 1 of the IMSBC code (2). 4. Where cargoes are assembled by blending multiple coal products, the transportable moisture limit of the overall cargo shall be established by either: Directly measuring the transportable moisture limit of the blended product, or Through adopting the minimum transportable moisture limit value of the individual cargo constituents. 8. Conclusion The Proctor/Fagerberg test described in the IMSBC Code for the purpose of reporting transportable moisture limit for bulk materials, which may liquefy, has been modified to the extent necessary to allow its application to coal with a top size of 50 mm. The modified test returns one of two results for each coal tested: 1) A critical moisture content which is determined from the intersection of the compaction curve and the line S = 70% degree of saturation, with the gross (total) water content corresponding to this intersection being defined as the PFD70 value. The PFD70 value is reported as the Transportable Moisture Limit. 2) In coals where visual evidence as noted above indicates water passes through the spaces between particles and the compaction curve does not extend to or beyond the 70% saturation line, the coal is deemed to be free draining and a TML value is not applicable. By reference to the IMSBC Code s7.2.2, such coals are cargoes where liquefaction does not occur and hence are Group B only. As noted in CCC 1/5/8 (1), further research work has been carried out and continues. The results of the full study will be documented for submission to the IMO CCC2 meeting in September 2015 for which papers must be submitted in June References 1. CCC 1/5/8 Australian Coal Industry Liquefaction Research Project, Sub-committee on Carriage of Cargoes and Containers, 1 st Session, 4 July IMSBC Code (2013), International maritime solid bulk cargoes code, International Maritime Organization. 3. Modified Proctor/Fagerberg method for coal, November Page 24 of 24