The relevance of using the renewable fuels for power grids

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Introduction Nowadays the shortage of energy carriers in Europe indicates that studies in this regard are relevant. On the one hand, the energy resources are saved, on the other, various types of fuels instead of hydrocarbons extracted from the bowels of the earth, are used. The problem of the fuel economy can be solved on the basis of applying the cogeneration system used at various facilities requiring the energy resources, such as electricity and heat. The document,1 which states that “the potential of using cogeneration as an energy saving measure is not fully used in the Commonwealth today, is devoted to the issues of cogeneration and its effective application. The promotion of high-efficiency cogeneration based on the demand for useful heat is a priority for the Commonwealth, given the savings of the primary energy sources, the prevention of distribution losses and the reduction of harmful emissions (greenhouse gases) into the atmosphere.” Moreover, the efficient use of the energy produced by cogeneration can also contribute to the continuity of energy supply and has a positive impact on the development of competition in the European Union and member states. Therefore, it is necessary 1 Directive 2004/8/EC of the European Parliament and of the Council of 11 February 2004 on the promotion of cogeneration based on a useful heat demand in the internal energy market and amending Directive 92/42/EEC. Available from: https://base.garant.ru to take measures to ensure the best use of the potential within the domestic energy market. Besides, it seems interesting, relevant, and appropriate to use the relevant provisions contained in Directive 2003/54/EC and Directive 2001/77/EC of the European Parliament and of the Council of 27 September 2001 on the promotion of electricity generated from the renewable energy sources. In this case, the issue of using the energy generated from the renewable energy sources is noteworthy. This contributes to the development of the general-purpose heat and power plants based on the reciprocating steam engines [1]. The given plant is powered by steam generated by using the renewable fuels which include firewood from various types of trees, pellets, manure and some other fuels, including gas generator gas. Gas generator gas production technology is also relevant since various types of fuels and materials can be used to produce gas. 1. The relevance of using the renewable fuels Russian Energy Strategy paper2 states that “the growth rate of the global primary energy consumption contained in ES-2035 is expected to be 1.2% per year” and further the paper states that “the emergence of new producers, the growing importance of unconventional hydrocarbon resources 2 Energy Strategy of Russia for the period till 2035, main provisions (as amended on 07.02.2014). and the accelerated development of the renewable energy sources lead to the tougher competition in the global energy markets. When studying the prospects for external demand for Russian energy resources formulated in ES-2035, the analysis results of energy strategies of the largest consumers and producers of energy resources aimed at the energy self-sufficiency are also taken into account.” This confirms the relevance of considering and applying unconventional energy resources and accelerated development of renewable energy sources. Such fuels include firewood of different types, pellets, and a number of others. It is worth considering the parameters of such fuels which include not only energy parameters, e.g., the fuel calorific value, but also the weight and size values. These data should facilitate their application at the specific facilities of power plants. Such power plants have been previously considered in paper, where the concept [2; 3] of their development has been proposed. Paper describes the energy complex calculated depending on its purpose. Simultaneously, it is necessary to analyse its parameters as the entire energy technology complex, thereby defining its performance specifications. Furthermore, the parameters of the reciprocating steam engine, such as the pressure and temperature of steam, its flow rate and rotor speed are defined. The horizontal arrangement of the machine, namely double expansion compound steam engine is the most appropriate. The estimating calculations of the main values have been presented. The diameter of the high-pressure cylinder is 310 mm, the diameter of the low-pressure cylinder is 460 mm, while the steam pressure required for the operation is 1.2 MPa (12 kg/cm2) with a temperature of 573 K (300 °C), its consumption is 1887 kg/hour, the number of revolutions is 2.66 s-1 (160 rpm) [3]. A steam engine rotates a generator through a manual transmission to generate the electric current. The generator BG-160M-4 by the Baranchinsky Electromechanical Plant was selected from a catalogue. The specifications of the generator are as follows: the rated power is 160 kW, the rated rotor speed is 25 s-1 (1500 rpm), the stator current is 289 A, the efficiency is 91.6%, the transmission ratio is 9.4. According to the preliminary design study of the reciprocating steam engine, its dimensions are 4500×4200×1000 mm, and necessary auxiliary power equipment and components are selected from the commercially available ones. A typical scheme of the power plant is shown in Figure 1. Besides, the economic efficiency of its application has been analysed and shown. When calculating the economic efficiency of the power plant aimed at increasing the validity of the results obtained, the most common option was adopted as a fuel - maple firewood with a calorific value of 1600 kcal/dm3 and a specific gravity of 0.65 kg/dm3. When determining the cost of the power plant, we used the publicly available data, while the cost of the reciprocating steam engine was defined based on the expert knowledge by comparing it with the cost of producing the equipment similar in design. Moreover, we took into consideration the cost of the equipment installation and commissioning. The total amount of capital expenditures was about 16 million rubles. Figure 1. A typical scheme of a power plant: 1 - a steam boiler; 2 - a steam flow meter; 3 - a steam pressure regulator; 4 - a piston steam engine; 5 - a high-pressure cylinder; 6 - a receiver; 7 - a low pressure cylinder; 8 - a generator; 9 - an oil separator; 10 - a consumer heating system; 11 - a condenser; 12 - a condensate pump The cost-effectiveness analysis was carried out for a period of one month. From the condition of the need to ensure the superheated steam consumption of 1600 kg/h at the boiler efficiency of 88%, the required amount of heat was defined as the sum of the heat for heating water to the boiling point, the heat required for vaporization and the heat for overheating the steam to the required temperature. The final value for ensuring the piston steam engine operation under the design parameters was 1.195 Gcal/hour or 860.4 Gcal/month, which corresponds to the current district heating tariff of 1.376.640 rubles per month. The current costs of obtaining the same amount of thermal energy during the power plant operation have been estimated by the object of expenditures: the cost of firewood, the cost of the water system condensate flow, the stuffing costs, the maintenance costs, the costs of electricity for own needs (for the water circulation pump operation, for the power supply of the control and lightning system). Besides, we took into account the costs of maintenance consumables and the costs of the required amount of fuel (firewood). The total cost of operating expenditures was about 656 thousand rubles per month, which gives an economic benefit of about 720 thousand rubles. The payback period of the plant is approximately 1.9 years. The proposed calculation is estimates, and the economic benefit of the presented plant in every par- However, the most common way of measuring the amount of firewood is volumetric, which is simple and fast. The results of measurements by such a parameter are easy to check and control. Besides, there are appropriate methods for various types of storage, size of logs, etc. We should first consider the characteristics and parameters of such type of alternative fuel as firewood. It is necessary to point out their difference in one of the main characteristics, namely the calorific value. In this case, the volumetric and mass calorific values of various firewood are distinguished. Table 1 shows the examples of these values. Table 1 The volumetric calorific value of firewood ticular case will depend on the performance specifications [4; 5] of the facility and its configuration. More Wood No species Volumetric specific calorific value of firewood, kcal/dm3 detailed information about this is given in [6-8], while in Russian scientific and technical literature [9]. 2. Some types of alternative fuels and their parameters Some types of alternative fuels include firewood and their wastes. These include twigs, bark, off-cuts (wood processing wastes), as well as pellets based on production wastes and sawdust. Pellet 1 Birch 1389-2240 2 Beech 1258-2133 3 Ash 1403-2194 4 Hornbeam 1654-2148 5 Elm (analogue is field elm) 6 Field elm 1282-2341 7 Maple 1503-2277 8 Oak 1538-2429 9 Larch 1084-2207 The first group includes birch, beech, ash, hornbeam, elm, field elm, maple, oak, larch fuels have quite good parameters, including trans- 10 Pine 1282-2130 The second group portation and different types of packaging. Firewood is one of the most traditional and ancient sources of thermal energy.3 According to their characteristics, firewood is one of the most unstable fuels, but it is a renewable source of thermal energy which is the main advantage. Firewood is recorded according to the following parameters: on the one hand by weight (kilograms and tons), and by volume (cubic meters) on the other [10]. A composition of wood fuel is almost the same 11 Alder 1122-1744 12 Spruce 1068-1974 13 Cedar 1312-2237 14 Fir (analogue is spruce) 15 Aspen 1002-1729 16 Linden 1046-1775 17 Poplar 839-1370 18 Willow 1128-1840 includes pine and alder The third group includes spruce, cedar, fir, aspen, linden, poplar, willow for any type and is as follows: up to 60% of cellulose, from 7 to 8% of accompanying hydrocarbons, up to 30% lignin and the rest is from 1 to 3% of minerals. The firewood quantity mass measuring is rarely used, if it is convenient, e.g., when transporting firewood by car. The weight of the car is calculated before and after the firewood delivery to the place of consumption. This measuring also simplifies the calculation of the calorific value of the supplied amount of firewood. The presented characteristics4 make it possible to calculate the required volume or weight of the firewood for a certain time of operation or for the processing period by the amount of heat received. Table 2 provides the firewood characteristics of different varieties of trees, which allow us to obtain the necessary heat data from a specific volume of firewood. The volumetric calorific value of firewood for the same type of firewood may differ depending on 3 Wood heating. Available from: http://tehnopost.kiev.ua/drova/13-teplotvornost-drevesiny.html (accessed: 22.02.2022). 4 Wood heating. Available from: http://tehnopost.kiev.ua/drova/13-teplotvornost-drevesiny.html (accessed: 22.02.2022). the region of growth. This is due to the soil water saturation in the area. This factor must be taken into account when harvesting the firewood, i.e., the drier the firewood, the higher the reward, or if the firewood harvesting is carried out in a more arid region, the profit is also bigger. Although this difference is not great, only 2-5%, but at larger volumes it can affect the economic indicators in general in terms of the harvest volume.5 On this basis and from Table 3, it is necessary to take into account the specific weight of firewood depending on moisture. The specific calorific value of wood fuel for different types of wood1 Table 2 No Wood species Absolute (higher) calorific value of Net (lower) mass calorific value of wood fuel, kcal/kg wood fuel, kcal/kg 1 Oak 4753 4000 3240 0 .810 0.690-1.03 2 Ash --||-- --||-- 3000 0 .750 0.520-0.95 3 Rowan --||-- --||-- 2920 0 .730 0.690-0.89 4 Apple tree --||-- --||-- 2880 0 .720 0.660-0.84 5 Beech --||-- --||-- 2720 0 .680 0.620-0.82 6 Acacia --||-- --||-- 2680 0 .670 0.580-0.85 7 Field elm --||-- --||-- 2640 0 .660 0.560-0.82 8 Larch --||-- --||-- 2640 0 .660 0.470-0.56 9 Maple --||-- --||-- 2600 0 .650 0.470-0.56 10 Birch --||-- --||-- 2600 0 .650 0.510-0.77 11 Pear --||-- --||-- 2600 0 .650 0.610-0.73 12 Chestnut --||-- --||-- 2600 0 .650 0.600-0.72 13 Cedar --||-- --||-- 2280 0 .570 0.560-0.58 14 Pine --||-- --||-- 2080 0 .520 0.310-0.76 15 Linden --||-- --||-- 2040 0 .510 0.440-0.80 16 Alder --||-- --||-- 2000 0 .500 0.470-0.58 17 Aspen --||-- --||-- 1880 0 .470 0.460-0.55 18 Willow --||-- --||-- 1840 0 .460 0.490-0.59 19 Spruce --||-- --||-- 1800 0 .450 0.370-0.75 20 Pussy willow --||-- --||-- 1800 0 .450 0.420-0.50 21 Hazelnut tree --||-- --||-- 1720 0 .430 0.420-0.45 22 Fir --||-- --||-- 1640 0 .410 0.350-0.60 23 Bamboo --||-- --||-- 1600 0 .400 0.395-0.405 24 Poplar --||-- --||-- 1600 0 .400 0.390-0.59 Net (lower) volumetric calorific value of wood fuel, kcal/dm3 Wood density, kg/dm3 Maximum wood density, kg/dm3 Fresh 100 80 70 Moisture percen 60 50 tage, % 40 30 25 20 15 940 1100 990 930 880 820 770 710 700 690 670 700 760 690 650 610 570 540 500 480 470 460 960 1110 1000 950 890 830 780 720 710 690 680 940 1100 1100 930 880 820 770 710 690 680 660 990 1160 1160 990 930 870 820 760 740 720 700 1060 1330 1330 1130 1000 990 930 860 840 830 810 740 750 750 640 600 560 520 490 470 460 450 910 1000 1000 850 800 750 700 650 630 610 600 760 830 830 710 660 620 580 540 540 530 500 1030 1330 1330 1190 1060 990 930 860 840 830 810 810 880 880 750 700 660 620 570 560 540 530 870 1160 1160 990 930 870 820 760 740 720 700 960 1150 1150 930 920 860 800 740 730 710 690 680 630 630 540 510 470 440 410 400 390 380 820 850 850 720 680 640 590 550 540 520 510 720 730 730 620 580 550 510 480 460 450 440 760 730 730 620 580 550 510 480 460 450 440 870 1050 1050 890 840 790 730 680 670 650 640 760 830 830 710 660 620 580 540 530 510 500 The specific weight of firewood, kg/m3, depending on the tree species and moisture percentage No Wood species 1. Larch 2. Poplar 3. Beech 4. Field elm 5. Oak 6. Hornbeam 7. European spruce 8. Walnut tree 9. Linden 10. Bustard acacia 11. Alder 12. Maple 13. European ash 14. Siberian fir 15. Common pine 16. Caucasian fir 17. Siberian pine 18. Birch 19. Aspen Table 3 5 Wood heating. Available from: http://tehnopost.kiev.ua/drova/13-teplotvornost-drevesiny.html (accessed: 22.02.2022); In the field of biomass processing. Available from: http://www.bm-biomass.com Figure 2. Methods of stacking the firewood In addition to these data, the ways of storing the firewood for various places of consumption are interesting and presented in Figure 2. Sawdust as a waste product of woodworking operations is also a fuel, but with worse combustion and storage properties. Nevertheless, sawdust is a good material for pellet production. Sawdust characteristics are presented in Table 4. Table 4 Weight of the landed dry sawdust depending on the tree species Wood species Bulk density, kg/m3 Weight of 1 cube of sawdust, kg Acacia 215 182-225 Ash 210 146-266 Beech 190 174-230 Hornbeam 213 207-223 Oak 227 193-288 Larch 186 151-186 Birch 182 143-216 Pine 146 87-213 Chestnut 182 168-202 Pear 188 164-199 No 1 2 3 4 5 6 7 8 9 10 Pellets can be considered as a type of renewable fuel. They are made from compacted sawdust, wastes from wood products, as well as other types and varieties of energy material (production wastes - seed and nuts husk, buckwheat hulls, sunflower husk, tree bark, some types of manure, etc.). The advantages of this type of fuel include the fact that the basis for its production are various renewable combustible materials.61 The production itself is uncomplicated and therefore the cost is very competitive in this sector. 6 Warmth in the house. Pellet Production. Available from: https://vse-otoplenie.ru/proizvodstvo-pellet-svojstva-toplivnyhgranul-osobennosti-processa-izgotovlenia-primenaemye-ustanovki (accessed: 22.02.2022). The shape of the pellets is close to cylindrical with the height of 5-15 mm and the diameter of 6-8 mm. At the same time, the thermal energy during combustion is about 17.216 kJ/kg and depends on the feedstock used, the ash content is no more than 5%. The density of pellets is 1200-1400 kg/m3, and the bulk density of pellets for storage and transportation is 650 kg/m3. We should mention one more significant advantage, namely the transportation in pellet bags of small weight from 10 to 15 kg and of large weight from 500 to 1200 kg. Besides, an auger feeds pellets for boiler equipment, which makes it possible to automate the heat production in the boiler, maintaining the necessary parameters of water or steam. 3. Results and discussion The presented materials provide a justification for the effective and expedient application of the fuel in the form of firewood. Moreover, this type of fuel is renewable due to planting seedlings to compensate felled trees. The given parameters of different types of trees make it possible to carry out calculations on their application onsite and to evaluate the effectiveness in specific conditions taking into consideration their transportation and storage. In addition, the main parameters and characteristics of pellets deserving a special attention as a renewable and efficient fuel for the operation of cogeneration plants based on steam piston engines have been presented [11]. Conclusion It should be noted that it is necessary to develop and effectively use the general-purpose heat and power plants based on the reciprocating steam engines using the renewable fuels in the form of various types of firewood and pellets. It would save the limited reserves of hydrocarbon fuel and extend its use in the existing power plants, as well as establish the isolated power plants with low power systems and units. Finally, further investigation is required regarding the possibility of using other types of alternative and renewable fuels considering the efficiency in various power systems and plants.

About the authors

Alexander V. Razuvaev

Balakovo Engineering and Technology Institute - branch of the National Research Nuclear University MEPHI

Email: vipdomik@mail.ru
ORCID iD: 0000-0002-4593-0653

Doctor of Technical Sciences, Professor of the Department of Technology and Automation of Mechanical Engineering

140 Chapaeva St, Balakovo, 413800, Russian Federation

Ivan Ya. Redko

South Ural State University

Author for correspondence.
Email: redko_iya@mail.ru
ORCID iD: 0000-0002-0259-1268

Doctor of Technical Sciences, Professor, Head of the Electric Power Industry Development Strategy

76 Prospekt Lenina, Chelyabinsk, 454080, Russian Federation

Nikolay V. Krasnoludskiy

Balakovo Engineering and Technology Institute - branch of the National Research Nuclear University MEPHI

Email: krasnoludsky@yandex.ru
SPIN-code: 9297-4701
Candidate of Technical Sciences, Associate Professor of the Department of Lifting, Construction and Road Machinery 140 Chapaeva St, Balakovo, 413800, Russian Federation

Dmitry A. Kostin

Balakovo Engineering and Technology Institute - branch of the National Research Nuclear University MEPHI

Email: kostin8842@yandex.ru
SPIN-code: 4733-6124
Candidate of Technical Sciences, Associate Professor of the Department of Atomic Energy 140 Chapaeva St, Balakovo, 413800, Russian Federation

References