Tools for Mining: Techniques and Processes for Small Scale Mining (GTZ, 1993, 538 p.) E. Mechanization and energy supply E.1. Introduction E.2. Energy source E.3. Drive unit E.4. Energy conversion E.5. Distribution of energy E.6. Energy systems E.7. Aspects of mechanization in mining E.8. Environmental and health aspects

Tools for Mining: Techniques and Processes for Small Scale Mining (GTZ, 1993, 538 p.)

E. Mechanization and energy supply

E.1. Introduction

Small-scale mining in developing countries operates at varying technical levels. The simplest level is the artisan or manual small-scale mining in which all tasks are performed by hand and no external energy is employed to ease the workload.

Examples are the gold diggers who win gold or mine tin with shovels, double-pointed picks, sluices and gold pans, in which drilling and blasting is performed by hand, transportation is performed with wheelbarrows and beneficiation with see-saw (rocker-type) crushers, hand jigs and settling basins.

In mining at an intermediary technical level, single work stages in the extraction, hauling and beneficiation processes are mechanized through the application of machines, whereby the control and regulation of the machines are usually performed manually. At this level, the proportion of work performed manually or with physical labor is still very high.

Examples are numerous small mining operations which drill using pneumatic drills on jacklegs, load the ore manually or with simple loading machines, sometimes employ crushers in the comminution process, and employ non-mechanized wet mechanical gravity beneficiation techniques. An additional example is sand-pumping operations in the mining of alluvial tin deposits.

In fully-mechanized mining at the progressive stage, most or all work phases are mechanized through the use, in part, of automated machinery.

Examples are the modern mining operations in industrial countries which are developed using tunnel boring machines.

The majority of the machines described in the previous sections find application in mining at the artisan and intermediary levels. If an external source of energy is necessary, a drive unit (e.g. engine or motor) must be added to the machine:

Energy Source	Drive- unit	Conversion	Energy distribution	Machine
diesel	internal comb. engine	compressor	compressed air line	pneumatic drill mill
water	water wheel	transmission gear	stamp mill

The machines and their intended applications determine the amount and form of energy required. In small-scale mining, the various operational steps should be considered separately.

For underground mining, machines are available for operation by three different basic drive-systems:

- electric
- pneumatic
- internal-combustion devices.

For reasons of mine safety, sturdiness, low maintenance, etc., compressed air tools and equipment have proven to be superior despite the low efficiency of the total system.

The energy requirement for mechanization of underground operations is determined by the size of the operation, surface facilities, geological conditions and particularly the degree of mechanization. There is practically no upper limit. The minimal energy demand is determined by the compressed-air consumption of drills on jacklegs, since drilling is usually the most energy-intensive activity in underground mining, and is accordingly the first area to be mechanized with the help of machines.

Depending upon the characteristics of the deposit, i.e. the hardness of the ore and host rock, drilling of blast holes requires approx. 0,5 kWh drilling work per drilled meter. Hence, mechanization of the drilling can lead to enormous increases in work productivity. A comparison of data from drifting activities in mechanized versus manual operations in solid-rock underground mining clearly demonstrates the differences:

purely manual:	0.02 to 0.243m³ loosened mass/MS
mechanized drilling, manual loading:	0.6 to 1.5 m³ Ioosened mass/MS
mechanized drilling and loading:	2.7 up to 4.6 m³ loosened mass/MS

Compressed-air demand for drilling lies at a minimum of approx. 2 m³/min at 7 bar air pressure and therefore approx. 10-15kW compressor power consumption.

In beneficiation, the comminution of the raw ore is the most energy-intensive processing step. Depending upon the geology of the deposit, the comminution of a ton of raw ore to a flotable fineness (100 % <100 µm) can require up to around 50kWh of crushing and grinding. The minimal power requirement for beneficiation is established by the consumption of a small crusher which lies between 3 - 5 kW.

Branches of mining which have to move bulk materials (for example, sand-pumping operations) need to orient their operations around their planned transport capacities; sulfur mines require, in part, high thermal energy for the operation of autoclaves for smelting.

The total energy requirement can be categorized into individual forms of energy, namely:

- mechanical
- electrical
- thermal

General opinion ascertains - especially from the viewpoint of industrialized countries with their extensive supply of electric power - that mechanization through electrical energy is particularly advantageous. Under closer scrutiny, however, it becomes evident that in the majority of cases, electrical energy is again transformed back into mechanical energy (with corresponding losses in efficiency). This is especially true in small-scale mining in developing countries.

Mechanical Drives for:

- Ventilators	- Jigs
- Pumps	- Vibrating screens
- compressors	- Tables etc.
- Crushers

In small-scale mining, electrical or thermal energy is only necessary in special cases.

Electrical energy for:	- charging lamps
	- magnetic separation
	- electrostatic beneficiation
Thermal energy for:	- drying
	- distillation
	- autoclaves

In order to meet the energy demand in terms of the energy form and amount, an energy supply system with the above-mentioned individual components is required. These are:

- energy source
- drive unit (engine or motor)
- energy conversion
- energy distribution

Relevant aspects for planning the energy system and its individual components are briefly systematized and outlined below.

E.2. Energy source

The essential criteria for planning the energy source are the costs and availability.

As energy sources for small-scale mining purposes, the following come into consideration:

- fossil fuels, especially diesel and gasoline
- electrical power originating from a central power supply
- water

The regenerative energy forms - wind, biomass and solar energy - cannot be used for the basic mechanization of mining, but are suitable in some cases for isolated tasks (such as solar charging stations for mining lamps).

When possible, the data collected should not only pertain to the present conditions, but should also, when possible, take into consideration any possible (foreseeable) future changes over the longterm. An important example which indicates the variability of absolute and relative costs for the energy source is the price data for diesel fuel in Bolivian tin mining relative to the price of the raw material produced (in this case tin):

The following table shows a comparison of the price development of tin and diesel in Bolivia:

1984	1 lb mined Sn ca. 6 US$
	while 1 lifer diesel 0.03 US$
1987	1 lb mined Sn ca. 3 US$
	while 1 lifer diesel 0.30 US$

While a miner could still buy 200 lifers of diesel/lb Sn sold in 1984, in 1987 he could only buy 10 lifers/lb Sn produced. Similarly, the price relation for electric energy from the central power supply (public utility network) reflects a parallel development.

The potential price-fluctuations and supply-shortages (poor infrastructure, strikes, market changes) associated with conventional energy sources suggest that the planning of an energy system which uses regenerative energy should be given priority. A prerequisite for this is the availability of a regenerative energy source on a daily and yearly basis, and comparatively favorable investment costs for the drive system (i.e. engine -possibly through local manufacture).

E.3. Drive unit

The drive systems for supplying energy are discussed in detail in Chapter 19. Decisive planning criteria are obtained by comparing the various systems with regard to the following parameters:

- costs, i.e. operating and investment costs
- repair and maintenance requirements
- adaptability
- suitability for local manufacture

A comparison of investment costs for drive-systems employed in mining is presented in the following table, whereby effort was given to consider machines which can be manufactured locally; these units are not only characterized by lower costs, but also by their comparatively simpler and quicker maintenance and repair requirements.

Table: Investment costs for drive units and energy. supply systems

Internal combustion engine	150 - 300 DM/kW (cif Bolivia)
Diesel generator	500 - 1000 DM/kW (fob)
Water wheels, hydromechanical (local production)	200 - 500 DM/kW (without hydro engineering measures)
Turbine, hydromechanical (local production)	100 - 200 DM/kW (local engineering measures)
Hydroelectric	3000 - 10.000 DM/kW (fob without hydro engineering measures)
Wind, mechanical (local production)	3000 - 5000 DM/kW
Wind, electrical	5000 - 15.000 DM/kW (fob)
Photovoltaic	15.000 - 20.000 DM/kW (fob)

At increasing efficiency or output, prices per installed kW react degressively; an exception is the linear trend in costs for solar electricity. The investment-cost ranges listed above pertain approximately to the maximum and minimum power requirements of small-scale mining.

Regarding investment costs, internal combustion engines are comparatively inexpensive, especially when compared to other drive units manufactured in industrialized countries; the high cost of fuels, however, leads to comparably high operating costs.

E.4. Energy conversion

A number of devices are available for converting one form of energy into another. The most important of these are presented in the Table. It is generally known that every conversion of energy is coupled with a loss in efficiency, which in some cases is very strongly dependent upon location; this is particularly true for conversion of electrical and pneumatic energy, whereby temperature and elevation are the primary influencing parameters.

In converting mechanical into pneumatic energy in two-staged compressors at 8-bar operating pressure, the following elevation-dependent efficiency losses are measured:

Copresor Type	Decrease in % for every 1000 m Elevation increase
	Delivery Quantity	Power Consumption
Medium-size, air-cooled compressor	2.1	7.0
Screw compressor with oil injection	0.6	5.0
Larger, water-cooled piston compressor	1.5	6.2
Larger, water-cooled screw compressor	0.3	7.0

The conversion of mechanical into electrical energy in generators is calculated through the use of the following elevation and temperature dependent correction factors:

Elevation of the machine	1000 m	1500 m	2000 m	2500 m	3000 m
factor f1	1	0.96	0.91	0.87	0.83
ambient temperature °C	25	45	50	55	60
factor f2	1.07	0.96	0.93	0.91	0.88

Mechanical energy conversions for the purpose of altering transmission torque and rpm are listed in the following tables (including values for maximum limit and degree of efficiency).

Transmission type	For one transmission step			Capacity N1(PS) up to	RPM n1 (RPM) up to	Periheral speed v (m/sec) up to	Periheral force (wheel) U0(kg) up to	Torque of wheel M0(mkg) up to
	Transmission		Total efficiency of efficiency %
	usual up to	extreme up to
Spur gear		8	(20)	95...99	25000	100000	200	-
Planetary gear	8	(13)	98...99	10000	40000	-	-	-
Worm gear	60	(100)	97...45	1000	30000	70	50000	25000
Chain drive	6	(10)	97...98	5000	5000	17	28000	-
Flat-belt drive	5	(10)	96...98	2200	18000	90	5000	17500
V-belt drive	8	(15)	94...97	1500	-	26	-	2150
Friction wheel drive	6	(10)	95...98	200	-	20	-	-

E.5. Distribution of energy

Finally, the equipment for bringing the energy from the generator to the machine (drive unit) must be planned. These distribution systems are characterized by different distance ranges and efficiency-losses:

- mechanical drives are limited in range to a few meters but operate a high degrees of efficiency,

- electric drives require power lines and, depending upon the range, high-tension transformers to reduce resistance losses,

- pneumatic drives require expensive compressed-air lines which are characterized by high losses in air pressure (pressure drop) and in the delivered quantity (see Technical Outline 19.1 3).

E.6. Energy systems

In planning a complete energy-supply system for small-scale mining in developing countries, in addition to efficiency, the following parameters are also relevant:

economic factors:	investment costs,
	operating costs,
technical factors:	overall efficiency,
	worker safety,
	environmental aspects
	(see below)

A comparison of complete energy-supply systems is presented in the following tables. Generally, installations with a high degree of complexity present greater problems concerning operation, maintenance and repair. The conversion of mechanical into electrical energy and the reconversion for machinery drive-units is not only associated with high efficiency losses and high investment costs, but is also too complex for application in developing countries. Mechanical drives with direct use of torque, for example in internal combustion engines and small turbines, contribute greatly to simplifying mechanized equipment (see also Technical Outline 19.12).

E.7. Aspects of mechanization in mining

The most important aim of mechanization and partial mechanization is to increase efficiency. This goes hand in hand with a reduction in production personnel.

For coal mining at constant production rates, Noetstaller has quantified the number of personnel required as follows:

Finally, the costs accrued due to mechanization must be considered, i.e., the investment costs as well as the operating costs. Mechanization or partial mechanization exerts influence on the following factors, amongst others:

- the extent of investment costs not only for drive units but also for the machines and the associated related investments,

- the energy costs,

- cost of wages, since every mechanization step leads either to increased production or lower personnel requirements as a result of increased efficiency. (A consequence which poses problems in developing countries with their already high rate of unemployment.)

- investment costs for imported equipment are higher than in industrialized countries

- service costs on capital are higher than in industrialized countries,

- costs of wages are significantly lower than in industrialized countries.

The investment capital requirements for a coal mining operation are described by Noetstaller for the following ranges of mechanization:

A further major consequence of mechanization or partial mechanization is a change in the cost-structure of the operation; this is exemplified by ore beneficiation plants in Bolivia with varying degrees of mechanization:

A problem in the mechanization or semimechanization of plants or processes is the estimation of coupling (indirect) effects. Mechanization usually leads to increased efficiency in the mechanized processing step. However, in order to accommodate the newly-installed machine's operating mode (for example, a continuous mode of operation requiring continuous, homogeneous feed quantities), or the changed economic conditions (for example, higher production capacity), increases in efficiency/production must also be achieved in the preceding and succeeding processing steps. This may be difficult to realize, depending upon the characteristics of the deposit and on the operation's physical and personnel infrastructure. Increased production in th shaft-hoisting system, for instance, can only be attained through major investments or change of the haulage system. In the event that the steps preceding and succeeding a mechanization upgrade cannot be altered, the newly mechanized step cannot be operated economically at full production capacity. Inorder to achieve an improvement in production through mechanization, a prior calculation of the effect on the entire processing procedure is critical.

Fig.:Relative distribution of beneficiation costs in plants with varying degree of mechanization. Source: Priester.

A mechanization or partial mechanization of a plant can then be justified on an economic basis only when the production costs for the final product do not increase as a result of the investment. Aside from the economic aspects, the social, humanitarian, safety, environmental and regional-development aspects in conjuction with mechanization are also important. These are difficult to quantify and hence no concrete suggestions can be offered here in this regard (see Noetstaller).

In providing energy for direct use in mining operations, the welfare of the miners and their families should also be considered. The difficult living conditions in the mining regions located at elevations as high as 5000 m or more above sea level could be alleviated through the provision of warm water, energy for heating, lighting or electricity in general, or energy for cooking. Energy requirements in this area should not be negleted during planning.

E.8. Environmental and health aspects

For economic and especially ecological reasons, it cannot be regarded as reasonable to meet increasing primary-energy demands through the use of fossil fuels, either in the Andean region or worldwide. Unfortunately, ecological considerations in planning in developing countries remain an exception (for instance, mining in the watershed area of drinking-water reservoirs in Potosi, Bolivia). For the long-range and middle. range conservation of the ecological life-support systems, the protection of the atmosphere, water, soil and flora and fauna is imperative. Even small-scale mining in developing countries can and must contribute to protecting the future, without having to suffer economic disadvantages because of it.

In developing countries, the use of renewable energy sources could make a valuable contribution to environmental protection and increase the environmental awareness. This also applies to small-scale mining, where consideration of environmental aspects has so far been lacking.

The diesel-run generators used in conventional decentralized electrical-energy supply, as well as the internal combustion engines used in the operation of machines, burn fossil fuels and, in so doing, emit toxic residues in the form of exhaust fumes. The regenerative energy sources, to the contrary, use water, wind or sunshine as an energy-producing medium, but does so without consuming it and without creating residues. The operation of internal combusion engines not only produces environmental impact through exhaust fumes and noise, but also creates a serious problem concerning waste-oil contamination and disposal. In the remote regions of small-scale mining, environmentally-sound waste-oil disposal is either not possible, or due to inadequate environmental awareness is not available. Usually, waste-oil ends up directly in the soil or in the drainage system, which can have catastrophic effects on the unstable ecosystems of the high-altitude Andes region. Even the rural population in the larger vicinity can be adversely affected since flowing bodies of water (e.g. rivers) are often used for drinking water and for irrigation (possible solution is in Technical Outline 11.3).