Sustenable energy sources utilisation.

Kralikova, R. ; Wessely, E.

Abstract: Sufficient, reliable, safe and environmentally acceptable assurance of fuels and energy may be classified as one of most global tasks of mankind to which the countries world-wide pay extraordinary attention. Necessity of energy and exploitation of the energetic sources is increased permanently and it subjects to the population increase with which the economic and environmental problems are also advanced.

Key Words: Environment, energetic plants, energy sources

1. INTRODUCTION

Sufficient, reliable, safe and environmentally acceptable assurance of fuels and energy may be classified as one of most global tasks of mankind to which the countries world-wide pay extraordinary attention. Necessity of energy and exploitation of the energetic sources is increased permanently and it subjects to the population increase with which the economic and environmental problems are also advanced.

2. ENERGY SOURCES AND ENERGY SOURCE UTILISATION

From the total balance consumption of the primary energetic sources such as crude oil, natural gas, coal, lignite, etc. with respect to the limited resources, the necessity of utilisation of the secondary energetic sources which originate as a consequence of usage of fuels and energy used in the energetic and production processes and of energetically usable technological wastes is resulted.

At the present, special attention shall be paid to renewable energetic sources such as water, wind, solar, geothermal energy as well as energy recovered from the bio-mass.

Their importance consists in relative inexhaustibility of them and the energy to be recovered from the bio-mass may be classified as the most perspective of them. Energy may be recovered from the bio-mass using the wooden material wastes, agricultural wastes, excrements of agricultural animals, plant, household and other biologic wastes. Renewable energy sources are forward energetic sources of domestic origin, mainly the energy from water, bio-mass and geothermal energy with the minimum environmental impacts. Technically usable potential of the renewable energetic sources is illustrated in the Table 1.

As resulting from the above-mentioned data, no renewable energy source is sufficiently utilised at the present. The primary energetic sources in 1997, the renewable sources covered 3,33% of the total energy consumption. Usable potential of renewable energy sources is generally conditioned by sufficiency of investment capital and achievement of the environmental requisitions.

The long-term target in the area of renewable energy source utilisation in the Slovak Republic is the achievement of the level to be comparable with the utilisation level in the most countries of the European Union. To achieve this target it is necessary to make true the prices of fuels and energy, to create the suitable legislation, economic and financial background and support the business activities systematically.

Higher utilisation of renewable energy sources should be manifested in energetic industry impact reduction to the environment, employment rate increase when constructing and operating the renewable energy sources and approximately the same number of work position may be achieved in developing, projecting, consulting, trading, producing and sub-delivering the renewable energy sources.

3. ENERGY CONSUMPTION--SUSTAINABILITY PROBLEMS

The energy consumption is increased permanently. Energy used at the present is originated from prevailingly fossil fuels. Although the fossil fuels are created continuously, their present consumption exceeds their creation multiply and so they are considered to be non-renewable.

Limitation of these energy sources and damage of environment as a consequence of fossil fuel combustion require to solve these issues. The most important negative demonstration of the fossil fuel combustion may be seen on the global climatic changes which are the result of the glass-house gas emissions.

The production reduction of the glasshouse gas originated when combusting the fossil fuels may be reached by conversion to cleaner fuels and reduction by their consumption. These alternative is represented by renewable energy sources which are capable to assure the permanent society development because they are cleaner and more favourable for the environment that the fossil fuels. Production and consumption of the "green energy" may be the instrument to support the energy production from renewable energy sources even in the spite of increased costs to be incurred by the consumers to green energy products according to the principle "the contaminator shall pay".

4. ENERGY PRODUCTION FROM THE BIO-MASS

The bio-mass is one of the most universal and most prevalent energy sources world-wide. Its advantage is that it offers not only a wide variety of the input raw materials but also its universal usage in the energetic industry. It is possible to use it not only to produce the electric energy and heat in modern incinerators. Liquid and gaseous forms of the bio-mass (Ethanol, Methanol, wooden gas, bio-gas) may be used to drive the motor cars. From the point of view of its perspective, the bio-mass is considered to be the key renewable energy source on the level of both small and big technological units.

With respect to various bio-mass forms, the energy included in it is different. Energetic content of dry plants (moisture content: 15-20%) is approximately 14 MJ/kg. Chemical composition of the bio-mass, however, makes the bio-mass to be more ecological fuel than the coal significantly. It is connected with the lower Sulphur content of the bio-mass than that of the coal. The ash content after combusting also is lower than that of the coal and, moreover, the bio-mass ash may be used as dung because it does not consist of any toxic substances and other contaminants but it consists of nutritive only. From the point of view of energy production from the bio-mass, the following processes are enforced at the present in the practice:

* Direct incineration.

* Thermo chemical processing (such as pyrolyses or degassing).

* Biologic processes such as anaerobic decay or fermentation, which cause the production of gaseous and liquid bio-fuels.

The immediate product of these processes is heat used in the production site or in surroundings of it. Heat is used either directly to prepare the hot water or to produce the steam with the consecutive drive of the power generator and power production. Other products are e.g. charcoal or liquid bio-fuels to drive the motor-cars.

4.1 Combusting the wood, straw and rapid-growing wood plants

Using the wood for the energetic purposes may be considered to be a local source which rates the minimum requirements to transport only and so it is relative cheap when comparing it with classical fossil fuels. At the present the boilers for wood fuels were improved significantly and so the combustion efficiency is very high. The basic types of the wood fuels are wood briquets, wood splits and wood pellets belong. Wastes from the agricultural production are a very important energetic source when considering their energy contents. Straw or dung belong to this group particularly. These sources are used very intensively in several countries. At the present, automated machines provided with straw charging having the minimum pollution emissions caused by the combustion process are prevailingly used. Some plant kinds characterized by rapid growth or by quality of oil to be produced may be raised for the purposes of their future energetic utilisation. So-called energetic plants are similarly used as wood or straw to produce heat, power etc. From the point of view if the energy pro-duction the total energetic balance of these plants is very good, i.e. ration of output and input energy is approximately 5:1.

4.2 Liquid bio-fuels

Unlike the solid and gaseous bio-fuels the liquid bio-fuels are used to drive the motor-cars. There ate the following liquid bio-fuels:

* Alcohol fuels (Ethanol and Methanol) which are the most used liquid bio-fuels world-wide and they are produced mainly from grain, maize and sugar-cane.

* Bio-oil may be produced from more than 300 plant kinds such as colza, sunflowers, olives, soya etc..

The bio-oil importance consists in the fact that almost each oil motor may be, in principle, converted to be driven by the bio-oil. In the countries of the European Union, the portion of the bio-oil driven cars to the classically driven cars is 15-40%. The bio-oil, under which the pure vegetable oil or MERO shall be understood, has almost the similar quality in one litre as the classical oil with this values being higher than the energetic density of other alternative fuels which fact is documented by the following table 2.

Main advantages of the bio-oil may be summarized as follows:

* positive energetic balance,

* low pollution emissions and C[O.sub.2], emission reduction,

* agricultural and ecological usage of the soil extracted from the production of food commodities

* safe when loading,

* rapid degradation in soil without any contamination etc.

4.3 Gaseous bio-fuels

The bio-gas is acquired mainly from the deposits of municipal and agricultural wastes at the present. The reaction of the bio-gas origin may be expressed as follows:

BIO-MASS + BACTERIA [right arrow] BIO-GAS (CH4, CO2 ..) + NUTRITIVES (N, P, K, S, ...)

The bio-gas composition depends on the input raw materials and bio-gas production conditions. The bio-gas may be valued when producing electric energy and heat.

5. CONCLUSIONS

From the total balancing consumption of the primary energetic sources, the necessity to use alternative renewable energetic sources is resulted. Their importance consists in relative inexhaustibility of them and as the most perspective source of them, the energy recovered from the bio-mass using the wooden material wastes, agricultural wastes, excrements of agricultural animals, plant, household and other biologic wastes may be considered. Renewable energy sources are forward energetic sources of domestic origin with the minimum environmental impacts and they are one of the suitable alternatives to solve the energetic and environmental problems of the present time. This paper continues to the grant project "Complex assessment of mechanical products from disassembly aspects" VEGA-1/0417/03 (50%), solved at Department of Environmental Studies and Control Process of Technical University of Kosice.

6. REFERENCES

Kralikova, R.--Lumnitzer, E.: Perspektivy v oblasti vyroby a vyuzitia cistejsich energii, Strojarstvo, rocnik VIII, ISSN 1335-2938, Media ST s.r.o. Zilina, 2/2004, s.34

Kralikova, R.--Lumnitzer, E.: Perspektivy v oblasti vyroby a vyuzitia eistejsich energii, Strojarstvo, 3/2004, s. 56

Kralikova, R.--Lumnitzer, E.: Trends in the area of alternativeenergy sources utilization, 6th International Conference MteM 2003- Modern Technologies in Manufacturing, Cluj-Napoca Romania, 2003

Table 1. Potential of renewable energy sources

Source Total energy production From it:
 electric
 energy
 (GWh/y) (TJ/y) (%) (GWh/y)

Bio-mass 2727 9817 39,7 5
Water energy 3800 13680 55,3 3800
Small water Power 202 727 3 202
Plants
up to 10 Mwe
Geothermal energy 338 1217 4,9 0
Solar energy 7 25 0,1 0
Wind energy 0 0 0 0
Total 6872 24740 100 3805

Table.2: Energetic value of the alternative fuels

FUEL Energy [MJ/l]

CRUDE OIL 35,1
Vegetable oil 34,3
MERO (bio-oil) 33,1
Ethanol 21,1
Methanol 18,0
Hydrogen 8,5
Battery energy 0,36