The March 2012 technical report on EastCoal's Menzhinsky mine in Ukraine describes a 50 t/h pneumatic cleaning plant built in the 1960s, ash falling from about 40% to 8% to 10% in clean coal, and a planned natural media plant to rewash a waste tip.
Menzhinsky is an underground coking coal mine in Lugansk Oblast, Ukraine, reported by EastCoal Inc. in a technical report prepared by Wardell Armstrong International and dated March 9, 2012. The ash content of the run-of-mine (RoM) coal as it is discharged from the skip is of the order of 40%. After screening and primary hand sorting, the ash content of the feed to the processing plant falls to 25% to 29%. The coal has a Hardgrove Index of 101, which indicates a very friable coal. Just 3.11% of the RoM coal is above 50 mm, and that fraction has an ash content of 74.7%. The coal processing operation mainly consists of hand sorting of the coarse RoM coal, with pneumatic cleaning of small coal.
Critical Data
| Parameter | Value | Unit | Notes |
|---|---|---|---|
| RoM ash at the skip | About 40 | % | Before screening |
| Feed ash after hand sorting | 25 to 29 | % | To the processing plant |
| Hardgrove Index | 101 | Not applicable | Very friable |
| Planned RoM production, 2012 | 138,000 | t | Rising to 1,000,000 t in 2017 |
| Planned RoM production, 2014 | 570,000 | t | Needs more cleaning capacity |
| Cleaning plant rating | 50 | t/h maximum | 300,000 tpa at 6,000 h/y |
| Operating rate | 35 | t/h | After adding 25 mm screening |
| Clean coal ash | 8 to 10 | % | Down from a lowest 12% at 50 t/h |
| Discard ash | 87 | % | Up from about 76% |
| Coal loss in discard | 5.19 | % | Float and sink analysis |
| Clean coal moisture | About 4 | % | Pneumatic, no water used |
| Clean coal sulphur | 1.3 | % dry basis | Largely pyritic |
| Clean coal specification | 9.6 | % ash, dry basis | Maximum total moisture 9.5% |
| Dry ash free calorific value | 35,458 | kJ/kg | Coal specification |
| Realistic plant capacity | 230,000 to 240,000 | tonnes per annum | 6,500 to 6,800 h/y |
Overview
The raw coal is easy to wash, with very low levels of middlings. In the 2011 sample, 64.1% by weight floated below a relative density of 1.4 at 2.8% ash, and 33.1% sank above 1.8 at 90.8% ash. Only 2.34% of the coal floats between 1.4 and 1.8, so the coal is regarded as easy to process. The ash content improves in finer sizes, because the coal is soft and has no clays. The fines below 0.5 mm are low in ash, while the sizes above 13 mm are much dirtier, so cleaning the fractions below 0.5 mm, 10% to 13% of the feed, would be essential only if a very low ash product were required.
Key Process Stages
Screening and hand sorting
RoM coal from the mine discharges from skips to a plate feeder and goes by conveyor to a screen at 60 mm. The plus 60 mm coal goes to a picking belt where operatives remove stone by hand, and the remaining coal is loaded to a truck and deposited on the clean coal stockpile. The minus 60 mm coal goes to a small bunker that controls the feed to the pneumatic cleaning plant.
Pneumatic cleaning
Inside the plant, the raw coal is screened again at 25 mm, and the oversize passes to a picking belt where operatives remove stone. The 25 mm by zero material gravitates to the air cleaner, understood to be of Ukrainian design. The machine is a linear motion vibrating feeder on a 5 to 10 degree incline with a perforated deck, and a large blower provides a constant air stream through the deck to classify the coal. Clean coal joins the 60 mm by 25 mm coal from the screen and goes to truck, and fine dust that becomes airborne is removed in cyclones and added to the clean coal.
Performance
The design capacity is 50 t/h. At that rate, feeding minus 60 mm directly to the air cleaner, the lowest ash that could be made was 12%, with discard ash of about 76%, indicating a significant loss of coal. By cutting the feed to 35 t/h and screening at 25 mm so that the air cleaner treats only 25 mm by zero, clean coal ash fell to 8% to 10% and discard ash rose to 87%. Pneumatic plants have few drives and should run at least 6,500 hours a year, possibly 6,800, giving a capacity of 230,000 to 240,000 tonnes a year. The report adds that the quality of hand sorting observed, and the difficulty of hand sorting 60 mm by 25 mm coal, suggest total coal loss might be higher than indicated.
Planned expansion
Increasing production to 570,000 t in 2014 will require more beneficiation capacity to keep or improve product quality. The existing cleaning section is rated 50 t/h, equal to 300,000 tpa at 6,000 hours a year, and the report puts the dry plant right at its limit in 2013. Natural media processing is planned for production beyond 2014, and a proposed natural medium plant would reprocess Waste Tip No. 4. The report suggests a rotary breaker at 50 mm with natural media cyclones for higher capacity washing, which would remove hand picking and large stone, with winter freezing a constraint on fines recovery.
Condition of the plant
The raw coal handling section was built in the 1960s and is generally in very poor condition. The report describes poor layout, inadequate access and lighting on the inspection belt, poor guarding and inadequate covering of holes in floors, and it recommends that safety standards be raised urgently. One of two installed raw coal screens is obsolete, and the report says it may need replacement for increased production. Large coal from the picking belt is recombined with the minus 75 mm cleaned coal from the air jigging process to make the final coking coal product, which goes by rail wagons to Ukrainian coking plants and steelworks. Development dirt and cleaning plant rejects go by road to Waste Tip No. 4, about 3 miles from the mine.
Additional Interesting Data and Summary
The high quality coking coal seams to be mined are classed as types Ж, КЖ and ГЖО. Analyses in 2010 and 2011 were done by the UKHIN Coal Chemistry Institute in Kharkov and verified by a WAI coal preparation engineer. No additional power or water is needed for the processing operations, since neither the air plant nor the proposed natural medium plant uses additional media such as magnetite.
Key Processes
- Skip discharge and screening at 60 mm
- Hand picking of stone from coarse coal
- Secondary screening at 25 mm
- Pneumatic air cleaning of small coal
- Dust recovery in cyclones
- Planned natural media cyclone washing and waste tip reprocessing
Source: Technical Report of the Menzhinsky Coal Mine, Lugansk Oblast, Ukraine, March 9, 2012.
