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Peat surface mining methods and equipment selection
Mikhailov Aleksandr
National Mineral Resources University, Saint Petersburg, Russia
Abstract
Peat plays an important role in the energy systems of the Nordic countries. The largest reserves of peat are in Canada and Russia. It has been a domestic fuel with a long tradition of use especially as a fuel in times of crisis. According to research conducted in Russia, peat is a very suitable raw material for local fuel production. The ash content of the peat local fuel is smaller than in cool, and the quality of the fuel is high.
The purpose of this paper is to develop performance criteria for fleet selection in surface mining of natural peat as a raw material for factory-made local fuel.
Proper fleet selection, in a way that it secures the production needs of a mine as well as minimizes costs of production, is one of the real challenges of mine planners. Classifying the equipment selection process into three phase’s: type of fleet, size of equipment and calculation of required numbers, the present article focuses on different application methods in each of these phases, their advantages and shortcomings.
Equipment selection involves choosing the optimum hydraulic excavator – truck combination to operate the peat raw material handling process. There are for primary considerations: maximum productivity; minimum power intensity of the process; purchasing and operating costs as low as possible; compatibility. Not all trucks and hydraulic excavators can work properly on the wet peat deposit surface.
Keywords
surface mining, open pit mining, peat excavation, loading, hydraulic excavators, tractors and semitrailers
1 Introduction
Surface peat mining is the most common method of peat production in the world. Current interest in peat as a fuel source can be linked directly to increases in the prices of conventional fuels, such as oil and natural gas. The purpose of this paper is to develop performance criteria for fleet selection in new surface mining of natural peat as a raw material for factory-made local fuel.
In recent years, a hydraulic excavator and tractor-semitrailer combination has been used in surface mining due to technological developments. Choosing appropriate equipment is one of the most important factors for production system efficiency.
Equipment selection involves choosing the optimum hydraulic excavator – truck combination to operate the peat raw material handling process. There are for primary considerations: maximum productivity; minimum power intensity of the process; purchasing and operating costs as low as possible; compatibility. Not all trucks and hydraulic excavators can work properly on the wet peat deposit surface.
2 Peat Surface Mining Method
The peat mining method selection problem focuses on choosing the correct excavation method for the
given peat deposit conditions. Renewal of peat fuel production at new technical and technological levels, will allow to provide necessary reliability of fuel maintenance.
Extraction of peat raw materials is based on excavation from peat deposit, drying and stockpiling. The focus was on following aspects [1]:
- Minimizing the environmental impacts;
- Maximizing the utilization of solar and wind energy and minimizing the weather sensitivity;
- Current cost level;
- Improving the final product quality.
For the majority of all technological processes involved with peat production the process of peat drying is the primary and most important process. Renewable energy sources for the peat drying process based on physical phenomena in nature include wind and solar energy.
Analysis of the potential of natural renewable energy sources, which can be utilized during peat production, was based on examination of climatic history (conditions) of the Northwest region of Russia [2]. The interactions of three primary climatic effects are considered: solar radiation, precipitation and wind (fig.1).
Fig.1: Monthly average energy balance on a peat field in Northwest of Russia:
1 - solar energy; 2 - wind energy; 3 - total of solar and wind energy; 4 - monthly precipitation; 5 - beginning of peat excavation season; 6 - ending of peat excavation season
In summary, solar radiation is at its maximum during the months of March through September. Precipitation (rain) is at a maximum in summer and autumn, with precipitation in the winter months predominantly as snow. Wind energy (speed) is usually moderate (medial monthly wind speed of 4-5 m/s), with maximum speeds occurring usually months with low solar radiation (September - May).
Normally the production season in Russia is from May 18 through August 31. The extraction of peat can be applied from April until September.
The quantity of energy above the surface of the peat fields can be estimated as the total of solar and wind energy (fig. 1). The analysis of the energy balance for the region demonstrates that energy balance of solar and wind energy are ‘measured’ values, lines 1 and 2 (total energy – line 3).
It is generally accepted that the degree of utilization of solar energy for milling peat production is 15-20 % [2]. The consensus is that wind essentially does not influence peat drying, and is not typically used in general peat production methods for drying. Its role is reduced to venting of the processed peat, i.e. ablation and replacing the moisture saturated air with dry air. The average wind speed along the ground stratum of a peat field is 0.2-0.5 m/s. Thus, the peat drying process uses no more than 1 % of wind energy.
At the modern level of technical development of civilization, currently the following can potentially be realized. Up to 1/5 the potential solar energy and up to 1/3 the potential of wind energy can be utilized. Consequently, in our case the energy use limit for peat production is 1/4 of the total annual energy potential.
Analyzing the technological level of peat production manufacturing processes, we selected two key directions to enhance the degree of energy potential use:
- magnification of peat production season duration;
- intensifying the processes of peat excavation and drying.
Due to the climatic conditions in Northwestern Russia, the optimum moisture content for peat processing is peat with a moisture content range of 60 – 65 %. Using the “wet harvesting” method, peat deposit maintain their wetland function and can regenerate to become a carbon sink within 2-3 years. The main fleet for excavation of peat raw materials consists from excavator, tractors and semitrailers (fig.2).
Fig. 2: Peat mining process:
1 - excavation and loading of peat;2 - local transportation on field; 3 - leveling, disking, drying and harvesting; 4 - stockpiling; 5 - loading with crushing and separation; 6 - transportation on plant.
Advantages of a this peat production method:
- reduction of influences by environment;
- expansion of a production season;
- optimum use of weather conditions;
- economic efficiency of production in 20 times is higher, than the current methods;
- the quantity of peat resources suitable for use increases;
- fast restoration of the peat areas absorbing CO2.
3 Equipment Selection in Peat Surface Mining
The problem of equipment selection in a peat surface mine is complex. Many features, restrictions and criteria need to be considered. The equipment selection process begins with the initial conception of peat development. For selecting of hydraulic excavators and tractor-semitrailer combination, equipment selection criteria must be determined. These criteria are collected in 3 different categories, which are:
- Production criteria
- Peat deposit parameters
- Equipment criteria
Characteristic of hydraulic excavators are a low Nominal Ground pressure (NGP) on the peat deposit surface. Characteristic of tractors&semitrailers are a low Mean Maximum Pressure (MMP) on the peat deposit surface, and high maneuverability (tab. 1). Some kind of limiting value for soft soils is thus MMP=150 kPa (for multiple pass) [3].
Tab.1: Effective parameters in selection fleet types
|
Equipment |
Type |
Weight, kg |
Engine output, W |
Bucket capacity, m³ |
Volume, m³ |
Track width, mm |
Tyres |
NGP / MMP, kPa |
|
Hydraulic excavators |
JS-220LC |
22 490 |
128 |
1.19 |
900 |
NGP= 28.0 |
||
|
Hyundai R210LC-9 |
22 760 |
113 |
1.34 |
900 |
NGP=32.0 |
|||
|
Kraneks EK-270 LC |
31 000 |
132 |
1.75 |
1200 |
NGP=28.0 |
|||
|
Tractors (dual front & rear wheels) |
BELARUS 2022.5 |
7 220 |
156 |
420/70R24- 580/70R42 |
89.64 |
|||
|
John Deere 7730 |
7 300 |
155 |
480/70R30- 620/70 R42 |
71.23 |
||||
|
Valtra T193 |
7 300 |
155 |
480/70R30-620/70 R42 |
71.23 |
||||
|
Semitrailers (dual front & rear wheels) |
Jaroslavich PS-12B |
4 500 |
11.0 |
600/50R22.5 |
139.66 |
|||
|
JOSKIN Trans-CAP |
4 500 |
10.2 |
600/50R22.5 |
139.66 |
||||
|
Bobruisk-agromash PST-9 |
3 400 |
10.8 |
600/50R22.5 |
132.68 |
One of features of peat tractor operation is change of largely bearing and coupling properties of a basic surface of a peat deposit.
Thus, there are the operational factors, which are not allowing completely realizing high potential traction and power properties of wheel mover and engines, which should be considered at justification of rational operating modes and an objective choice of peat equipment.
The peat industry on nature of productions has no analogs in other industries. The principal factor for hauling and loading machines is their capacity. Specifics of peat transport and tractor units and conditions of their operation define the following factors:
- nature of transport operations;
- high deformability and low bearing ability of a peat deposit (tab. 2);
- low indicators of traction and grip of drive tires properties and the increased slipping of tractors on a peat deposit surface;
- basic characteristics and design features of the transport equipment [4].
Tab.2: Peat deposit parameters
|
Peat type |
Degree of decomposition (von Post) |
Moisture content, % |
Density ρ, kg/m3 |
Shear strength τ, kPa |
|
Oligotrophic |
H4 |
79 |
750 |
68 |
|
H5 |
81 |
820 |
52 |
|
|
H6 |
85 |
880 |
40 |
|
|
Eutrophic |
H4 |
77 |
780 |
98 |
|
H5 |
79 |
860 |
80 |
|
|
H6 |
83 |
960 |
48 |
The choice of allowed specific ground pressure is defined not only strength properties of a peat deposit surface. With increase in specific ground pressure, the energy spent for overcoming of resistance a crushing of peat increases.
At tractor movement on rather constant trajectories there is a repeated and variable impact on a surface to deterioration of conditions of passability.
Trailer body loading МТ influences transport work. The increase in loading leads to growth of energy expenses on movement and wheels slipping; decrease in loading causes power consumption and decline of productivity.
There are two private criteria of transport efficiency.
1. Minimum of specific energy consumption on unit of transport work
(1)
where ET - specific energy consumption, J / (kg · m); Nn - rated-output power of a tractor, W; ξn - factor of engine utilization; tm - movement time with peat, s; Lh - hauling distance, m; Mp - mass of peat in a trailer body, kg; vt - speed of transportation, m/s.
The analysis of a hauling cycle shows, that the main time of a cycle occupies movement of the loaded and empty semitrailer. Actually time of a hauling cycle is defined by hauling distance (time of movement of the empty and loaded trailer makes from 55 % of a cycle time at hauling distance Lh = 0.5 km and to 85 % - at Lh = 2.5 km). The choice of the rational scheme of placement of stockpiles on a technological plate is an important factor of ensuring efficiency of process of peat raw materials transportation [5].
The mass of peat Mp in a trailer body depends on body volume and density of peat.
2. Criterion of a maximum productivity corresponding to a minimum of energy consumption at movement with peat
(2)
where PT - productivity, (kg · m)/s; Nd max - the maximum drawbar force of a tractor, W; kat - specific motion resistance.
As specific motion resistance kat has a weak dependence on speed, the criterion of PT corresponds to a maximum traction efficiency and traction capacity.
Application of efficiency criteria allow to formulate a problem of efficiency increase of peat transportation and improvement of the transport equipment.
Conclusion
These and other technological developments can be a basis for scientific discussions with the purpose of examination and development of new technologies for reaching maximal results for the production of peat raw material. This method of peat raw material excavation with modern equipment is testing now in Leningrad region. As a result of new technology, economy of scale will continue to be an extremely important factor in the competitiveness of the peat industry.
At the final stage, with respect to daily production rate and capacity of each equipment, the required number of each of machines will calculate. At the first, considering production rate, number of excavators is determined and similarly, tractors-semitrailers number will determine with respect to the excavator, production rate, hauling distance and transportation condition.
References
[1] Korpi, J., Mutka, K. and Nyrönen, T. A new peat production concept – results of the development work during 2004-2007, Proceedings of the 13th International Peat Congress Tullamore, Ireland 8 – 13 June 2008.Volume 1. p. 120-122
[2] Mikhailov A., Nagornov D. Peat excavation and drying for factory-made local fuel production – Peatlands in Balance, Book of Abstracts of the 14th International Peat Congress Stockholm, Sweden June 3-8, 2012.
[3] Larminie, J. C. 1992. Modifications to the mean maximum pressure system. Journal of Terramechanics 29(2):239-255.
[4] Mikhailov A. Peat production scale and equipment selection – Processes and equipment for mineral mining and handling, Proceedings of ISTC, Minsk, 2012. ISBN 978-985-525-893-4
[5] Mikhailov A., Telego A. Peat production transport module– Innovation systems of transport planning and management, Proceedings of I ISTC, National Mineral Resources University, Saint Petersburg, 2013.