Coal Superintending

Coal Origin

Coal is a sedimentary rock composed predominately of organic material, with a greater or lesser amount of mineral matter

Coal is derived from plant remains in a sedimentary basin and is altered to solid rock by heat and pressure applied during the basin’s formation

Different coals are produced depending on formation and tectonic histories

Coalification

• Peat
• Lignite
• Sub-Bituminous
• Bituminous
• Semi-Anthracite
• Anthracite

• Increase in Coal Rank
• Increase in Calorific Value
• Increase in Carbon Content
• Decrease in Moisture
• Decrease in Reactivity

Constituents of Coal

Moisture, Inherent and Free

Mineral Matter, Inorganic

Organic

Matter

C, H, N, S, O

Coal Utilisation

Coal Quality and Price

The Coal Quality determines the suitability for end use and the Sale Price

An accurate knowledge of Coal Quality is essential at all stages of production and delivery to buyer/end user

Supply Contract 100,000 tons @ 40.00 USD per ton

COAL QUALITY and QUANTITY GOVERNS PRICE

VALUE 4 m$

BUYER

SELLER

Sales Contract

• Defines the commercial agreement between buyer and seller
• Technical clauses must be unambiguous and not open to different interpretations
• Quality and Availability
• Security of Supply
• Relationships / Brand Name
• Quality meets end use specification
• Price

All drive the Sales Contract

Sales Contract Technical Clauses

Where is the point of custody transfer?

• Quality and Quantity parameters
• Guaranteed or Typical values
• Penalty / Bonus limits
• Rejection limits
• Price Adjustment formulas
• Sampling, sample preparation and testing methods
• Location of sampling
• Alternative methods - contingency
• Basis and units for reporting results
• Precision objectives for sampling and testing
• Nominate the IIA

• Type, format and content of certificates
• Timeframe and destination of certificates
• Sample custody, retention and distribution
• Umpire laboratory
• Third party witnessing
• Draught survey method
• Load or discharge port results final?
• Tolerance limits for comparison of results
• Mechanism for initiation of umpire sample analysis
• Arbitration
• Contamination and source of coal

Superintending

• Independent inspection and certification of coal cargo at the point of custody transfer e.g.
• Loaded/discharged to/from vessel or barge
• Coal hauled to ROM
• Quality – sampling and testing
• Quantity – draught survey
• Vessel condition inspection
• Timely issue of certificates

Superintending results should confirm what is predicted

They should not be a surprise

Independent Inspection Authority

• Clear and unambiguous letter of appointment to IIA
• Who is the customer of IIA?
• Who does IIA release results/certificates to?
• Signed acceptance of work and terms by IIA
• Determine work plan and contact persons at customer and IIA
• Minimum
• Point of custody transfer
• ETA and location of shipment
• Sampling and testing standards
• Certificate format and headings
• Handling of samples
• Retained samples
• Buyer and Umpire sample delivery

Sampling

Why take samples?

• To determine the quality of the bulk material e.g
• In-situ seam
• Exposed seam
• Product coal
• Plant product/reject
• Shipment
• Collection of a representative sample

The sample properties must reflect the bulk coal properties both physical and chemical

THE SAMPLING LOOP

What is a sample ?

Factors influencing Sampling

• Quality variability
• Coal is a heterogeneous bulk commodity
• Each particle has different qualities
• Quality varies within the coal tonnage, depending on coal source/s, processing, blending and handling
• Precision
• Higher precision achieved by taking more increments
• Typical aim is 0.2% ash
• Top size
• Greater top size means greater increment mass
• Quantity
• Maximum sampling sub-lot size 10,000 tons
• Method
• Manual or Mechanical
• Location
• Logistics of sampling and delivery to laboratory

Representative Sample

Homogenous Products

A smaller number of increments are required to collect a sample which is representative of the whole.

Heterogeneous Products

A larger number of increments of sufficient size and frequency are required to collect a representative sample.

Number of increments

Example – Sampling product coal, 12,000 tons production per 12 hour shift. The sampling lot is the shift production, the required precision is 0.2 % ash and samples will be taken every hour meaning 12 sub-lots. The quality variation is known and following values have been determined, primary increment variance VI = 1 and preparation and testing variance VPT = 0.02

n = (4 x 1) / [(12 x 0.22) – (4 x 0.02)] = 10

So 10 increments are taken for each sub-lot, increment collected every 6 minutes.

If the sampling, preparation and testing variances are not known then you can either determine the values or use the standard assumed values: VI = 20, VPT = 0.2 and PL = 1/10 of ash %. These are conservative values and usually much lower values are achieved in practice.

However it is stressed that the sampling, preparation and testing standard deviations (or variance) should be determined for each sampling situation. This provides data to support the sampling procedures and ensures you obtain the required degree of precision.

where

n = number of primary increments

VI = primary increment variance

m = number of units (sub-lots)

PL = estimated overall precision of sampling, preparation and testing

VPT = preparation and testing variance

Sampling Golden Rules

• Increment must be collected from entire cross section of coal
• Each particle must have an equal opportunity to be included in the increment
• Integrity of increment and gross sample must be maintained
• Sampling equipment aperture must be at least 3 times the top size of coal
• Safe working practices
• If you cannot take a representative sample, do not take a sample as incorrect results lead to wrong decisions

Manual Sampling

Advantages

• No capital investment
• Can take stationary samples
• Relatively flexible

Disadvantages

• Operator dependent
• Easily prone to bias
• Limited to max. 500 t/h and 2.4 m/s belt speeds
• Operator safety

Stationary Stockpile sampling

• Manual
• Performed when building or breaking down a stockpile
• If sample taken from formed stockpile cannot be considered representative

Stationary Barge or Vessel

• Sampling directly from barge or vessel hold is not recommended
• Not a safe work practice and not representative
• Alternative is to collect sample from vessel’s grab above deck

Mechanical sampling General requirements

• Sampler shall collect bias free increments
• Sampler can operate under all expected conditions
• Have sufficient capacity to retain or pass the entire increment
• Be self-clearing and non-clogging
• Does not allow coal to enter when in park position
• Minimize size degradation
• Minimize moisture loss

Cross belt sampler

Falling Steam Sampler

Mechanical sampling Comparison of primary samplers

Falling stream

• Higher capital cost
• Must have transfer tower
• Collects larger increment mass

Cross belt

• Lower capital cost
• Can be retrofitted to existing conveyor belt
• Collects smaller increment mass

Treatment of gross sample

• Falling stream sampler – 10 tons
• Cross belt sampler – 1 ton
• How to prepare the gross sample for testing? Retaining sample integrity and producing lab samples within time frame

On-line sample preparation

• Secondary/tertiary sampling system on line with primary sampler
• Crush and divide each primary increment to obtain manageable sample mass

Off-line sample preparation

• Gross sample delivered to laboratory for sample preparation
• Size of gross sample dictates capacity of preparation equipment – usually want at least 1 t/h crushers and 100 kg dividers

SAMPLE PREPARATION FLOW CHART

Bias Testing

• Mechanical sampling systems must be bias tested to prove they operate free of significant bias
• Bias testing performed by comparing a series of sample pairs
• Reference samples collected by stopped belt method
• System samples collected by sampling system

Analysis

• Steaming coal parameters – energy and combustion characteristics
• Coking coal parameters – coking characteristics
• Chemical – e.g. proximate, ultimate, ash analysis, trace elements
• Physical – e.g. HGI, ash fusion, abrasion index, fluidity, dilatometer, reflectance, CSN or FSI

Metallurgical Coals

• Coals with coking properties
• Over the temperature range 300 to 500 °C display “plastic” properties
• When heated in a coke oven produce a strong porous solid residue “Coke”
• ~ 25% of world coal production
• Moisture
• Ash
• CSN
• Fluidity
• Dilatation
• Maceral Analysis
• Mean Maximum Reflectance
• Phosphorus
• Size Distribution
• Coke Strength

Steaming Coals

• Coals used to raise steam for power generation
• Can also be used to provide direct heating in cement manufacture
• ~ 70% of world coal production
• Energy is what is sold – CV is most important parameter
• Moisture
• Ash
• Volatile Matter
• Total Sulphur
• Calorific Value
• Carbon and Hydrogen
• Nitrogen
• Ash Analysis
• Ash Fusibility
• Trace Elements
• Size Distribution
• HGI

Conversion Coals

• Coals used as feed to gasification or liquefaction processes
• Used for special purposes like active carbon electrodes
• ~ 5% of world coal production
• Fischer Assay
• Petrographic Analysis
• Steaming Coal Parameters

Analysis

• Analysis performed depends on:
• Superintending - Sales contract requirements
• Exploration – bore core size, ply or seam composite, drilling program, type of coal, complexity of resource, budget
• Production – critical control parameters – e.g. total moisture, ash, sulfur, energy, ash analysis
• End use – critical control parameters for process
• Analysis carried out according to standard methods
• Indonesian coal sales contracts commonly follows ASTM and or ISO methods
• Results are reported to a defined basis and units
• The laboratory sample is tested and reported at air dried moisture basis
• The results can be converted to other basis e.g. as received, dry and dry ash free

Where:

Mad = Moisture in the Analysis Sample, as determined basis

Madb = Moisture in the Analysis Sample, air dried basis

TM = Total Moisture, as received basis

Aad = Ash Content, as determined basis

Aadb = Ash Content, air dried basis

Adb = Ash Content, dry basis

Moisture basis

• Common problem is encountered with gross air dried calorific value (GAD)
• The moisture in the analysis sample is a factor of the coal rank, humidity and temperature conditions during sample preparation and testing as well as sample preparation drying times
• Different laboratories will obtain different air dried moisture results

Moisture in Coal

• Free moisture – present on the coal particle surfaces and large capillaries, moisture in excess of the natural (inherent) moisture
• Inherent moisture – natural moisture of coal in situ or bed moisture, moisture contained in the pore structure of the coal
• Inherent moisture is sometimes wrongly used to mean moisture in the analysis sample
• Residual moisture is the moisture remaining in the coal sample after air drying
• Chemically bound moisture e.g. water of hydration
• Moisture in the analysis sample, at time of testing
• Moisture holding capacity – test that estimates the inherent moisture
• Equilibrium moisture is the ASTM test term used to estimate inherent moisture
• Total moisture – the moisture in the coal as sampled

Lab Design and Management

• Lab suited to your needs
• Safety, efficiency and accuracy
• Common error is under capacity sample preparation area
• Laboratory Quality Management according to ISO 17025

Draught Survey

• Determines the quantity of coal loaded to vessel – barge or motor vessel
• Based on Principle of Archimedes
• “A vessel when freely floating in water, will displace a weight of water equal to it’s own weight”

PLIMSOLL MARK

DECK LINE AND LOAD LINE

TF : Tropical Fresh

F : Fresh Water.

T : Tropical.

S : Summer.

W : Winter.

WNA : Winter North Atlantic.

VESSEL DRAUGHT MARKS

1. METRIC SYSTEM

Weighbridge Monitoring

• Calibration of weighbridge at recommended six monthly intervals
• Proper maintenance
• Independent tallying and reporting of gross and net truck weights

Quality Assurance

• Aim is a consistent within specification product
• Average results within specification and standard deviation of sub-lot analysis within acceptable (maybe contractual) range
• Clear responsibilities and decision making authority
• Reliable accurate data to make proactive decisions
• Information must be effectively shared between all concerned parties
• Good QA increases efficiency and profit for both producer and end user

Coal Quality and Quantity Management System

Flow of Information

• Information flows forwards and backwards along the coal chain allowing proactive decisions with respect to coal quality and quantity.
• Brief outline only.

Lower Rank Quality Control

• Sub-bituminous and lignite coals
• Relatively more Reactive
• Relatively easier to Break
• Spontaneous Combustion
• Stockpile management
• Temperature monitoring

Dust Management

• Minimize breakage throughout Coal Chain
• Dust suppression

Summary Example

• You load a vessel with predicted quality and quantity:
• TM %ar 15.0
• M %ad 10.0
• Ash %ad 5.0
• GCV ar 6050 kcal/kg
• 60,000 tons

Superintending results are:

• TM %ar 15.5
• M %ad 10.0
• Ash %ad 6.5
• GCV ar 5910
• 59,000 tons

Penalties apply if:

• TM > 18.0%
• Ash > 5.5%
• GCV ar <6000
• You will pay penalties for ash and GCV ar
• Low GCV ar is caused by increased TM and ash
• TM caused by rainfall
• Ash is caused by sampling errors (and or blending errors)

Say the penalties are calculated:

• GCV ar
• FOB price x (6000 – actual GCV ar)/6000 x 2.2
• Equals 0.825 USD per ton
• Ash
• 5.5 – actual ash x 0.50 USD per ton
• Equals 0.50 USD per ton
• Total penalties are 1.325 USD per ton
• Which is a total of 78,175 USD for a 59,000 ton vessel
• Plus possible claim for 1,000 ton quantity shortage

The risk of financial losses from incorrect Quality Assurance and Superintending is significant

The cost of correct Quality Assurance and Superintending is insignificant compared to potential financial, resource and market penalties