5 Results and discussion
5.6 General discussion
Results from this work indicate that several possibilities to reduce energy consumption in grain preservation exist as well in technological, methodological and managerial levels. Figure 35 pre-sents the energy saving methods examined in this work and the energy saving potential compared to the conventional hot air drying system. The figures presented in Figure 35 are estimations based on the results from the included research combined with the figures received from the literature.
For example, the effect of heat insulation detected in the publication III was very high compared to the results presented in literature, and therefore an approximate range based on these figures was chosen to Figure 35.
The utmost energy savings in grain preservation can be achieved by utilizing the moist grain preser-vation methods instead of drying. Energy savings up to 90% are possible with the grain crimping method with certain prerequisites, when hot-air drying is the reference. However, the moist grain preservation methods limit the end use possibilities of the grain and they are therefore best suited for the home-grown feed grain, as discussed before. Table 5 sums up the energy saving potential of the examined methods compared to the total energy used for grain preservation in Finland in current situation (ca. 660 GWh in average, calculated from the results in publication III). Moist grain preservation was assumed to be utilized for all of the home-grown feed grain which is currently preserved by hot-air drying (see publication V for detailed information). Hot-air drying was applied for the market quality grain, which thereby presented the total grain yield of ca. 3.7 billion kg sub-tracted by the 1.3 billion kg of the home-grown feed grain (Tike 2013b). Total energy savings were calculated by summing the energy saving potential of moist grain preservation methods with the examined energy saving methods in drying. Finally, the economic significance of the energy savings was calculated, since this is the ultimate decision making factor for the farmers.
Figure 35. Energy saving methods, according to the end-use purpose of the grain, and the energy saving potential of each method compared to conventional hot-air drying.
Table 5. National energy saving potential of the examined methods with respect to the total energy consumption in grain preservation in current situation.
Method Energy saving potential Moist grain
preservation
% 16 GWh 106
Drying Process control Heat insulation Heat recovery
% 3 – 10 3 – 10 10 – 27
GWh 22 – 67 22 – 67 89 – 178
Moist grain preservation
and drying combined Process control Heat insulation Heat recovery
% 20 – 26 20 – 26 30 – 43
GWh 128 – 173 151 – 173 195 – 284
Economic savings* Process control Heat insulation Heat recovery
M€ (total)** 10 – 14 10 – 14 16 – 23
€/ha*** 9 – 12 9 – 12 13 – 19
*Savings due to the energy costs only
**Price of fuel oil 0.8 €/l
***Grain cultivation area in 2014 1.2 million ha (Luke 2015b) Grain
According to table 5, the total energy saving potential with the examined methods is 128 – 284 GWh, which corresponds to the average economic savings of 9 – 19 € per hectare of grain cultiva-tion area. This indicates that the economic significance of the energy saving measures in grain preservation is not very high with the current energy prices, even with energy savings of more than 40 %. In fact, also in the moist grain preservation, which offers the largest energy saving potential when examined as an individual method (Figure 33), the major part of the economical savings comes from the decreased fixed costs, as indicated by the Figure 28. However, while the total direct energy use of arable farming in Finland is ca. 2500 GWh (Luke 2012), the total energy savings in table 5 corresponds to 5–11% of the total energy use. This implies that the energy saving potential in grain preservation is significant with respect to the total energy consumption in the arable farm-ing sector.
Table 5 considers the examined energy saving measures in grain drying individually. Further bene-fits could be achieved by combining these methods. The combinations of the methods were not discussed here as they were not examined during the research work. However, it may be assumed that additional benefit can be achieved by combining the heat insulation method with the process control or heat recovery methods, since their effects are based on different phenomena. Using the process control method together with heat recovery would probably not provide significant addi-tional benefit since the sensible heat of the exhaust air will be at least partly utilized in the heat recovery process. Further research could focus on finding the optimal combinations, considering both energy efficiency end economy, from the methods examined in this work.
Considering only drying, the highest energy saving potential is found from heat recovery. Even sim-ple and low cost passive heat exchanger may provide significant energy savings. Additionally, even though the problems related to the heat pump systems discussed in the chapter 4.1.3 exist, some new heat pump installations for grain dryers have recently been introduced in Finnish markets (Ca-lefa 2015). Another method for significant energy savings in grain drying could be found from en-hanced use of ambient air or low temperature drying, but these too have some problems in the Finnish climate, as discussed in chapters 3.1.3 and 5.5.1. Converting ambient air drying to low tem-perature drying introduces additional energy requirements to the process, but when conducted in thick layers it benefits from the high exhaust air humidity and thus effective energy utilization. For large capacity drying systems it could hence be feasible to invest in low temperature drying bins in addition to a hot air dryer, which would enable combination drying as discussed in chapters 3.1.6 and 5.5.1.
The energy saving potential via management measures in grain preservation is difficult to estimate numerically since there is no available information about the current average situation. It is how-ever important to recognize the factors discussed in chapter 5.5, since both the initial moisture content of the crops and the final moisture content after the drying process may have a significant effect on the energy consumption in grain preservation, and drying in particular, as indicated by Figures 30 and 33. One fundamental problem considering management of drying is the lack of a robust and reliable on-line grain moisture sensor, which would help to reduce over drying and pro-vide aid for the process control.
General farm management activities, such as attending the condition of the soil or timing of the field operations, affect both the yield levels and the initial moisture content of the crops at the
dryer, and they have thus multiplier impacts on the economy and energy consumption of the farm-ing. With proper management the utilization of the inputs is effective, which leads to high total energy efficiency of the production system. Another thing to consider is the balance between drying costs and higher yields produced by the longer growing time varieties. However, according to table 5, the economic significance of even considerable large energy savings is not very high with the current energy prices, and the increased profit due to the larger yields provided by later varieties can easily dominate over the increased drying costs. With the current grain prices, the economic savings in table 5 are equal to a yield increase of only ca. 100 to 200 kg/ha.
6 Conclusions
Results from this work indicate that realizable potential from moderate to significant energy savings in grain preservation exist as well in technological, methodological and managerial levels. Drying alone offers energy saving potential of 5% to 40% by utilizing the technologies such as real time process control, heat insulation of the drying equipment and heat recovery from the dryer exhaust air. The highest energy saving potential in drying is found from the heat recovery applications, but further research is necessary to ensure their practical operability and profitability. The utmost high-est energy saving potential in grain preservation is provided by enhanced utilization of moist grain preservation methods for home-grown feed grain, which enable energy savings of 50% to 90%
when compared to drying. The combined energy saving potential with all the studied methods was 20% to 43%, compared to the current total energy consumption in grain preservation in Finland.
Even though significant energy saving possibilities in grain preservation were recognized, their ef-fect on the economy of farming is quite modest. This is caused by the large proportion of fixed costs in grain preservation, and particularly in drying. However, measures taken here can help to achieve the national and EU-level energy efficiency targets, and if energy saving measures of this magnitude could be found in other areas of the agricultural production, their combined effect would be highly significant. Furthermore, while the farms sizes are expected to grow also in the future, the energy saving measures in grain drying will become increasingly important, especially if the energy prices increase at the same time. This will then lead to a win-win situation considering the economic profit and energy savings, which is the ultimate incentive towards more energy efficient production.
In addition to the energy saving methods examined in publications I-V, the causations between energy consumption in grain preservation and farm management activities were pointed out and analysed in this work. Even though any specific figures about the effect of farm management on the energy consumption in grain preservation were not given, it is essential to recognize the exist-ence of these connections, since they may have a significant effect not only on the energy con-sumption in grain preservation, but on the energy efficiency of the whole production system. Thus, considering the conclusive remarks above, this work seems to have reached its goals with respect to the objectives 2 to 4, defined in chapter 2. The actualization of the first objective, “To create an insight into grain preservation from the aspect of energy use”, I leave for the reader to judge.
Acknowledgements
The research work for this thesis was made altogether in three projects: ENPOS (Energy positive farm), Energy efficient grain preservation (in Finnish: Energiatehokas viljan säilöntä) and Energy efficiency in grain production (in Finnnish: Viljantuotannon energiankulutuksen vähentäminen). EN-POS was funded by the EU Central Baltic INTERREG IV A -program and the other two projects were funded by the Foundation of Marjatta and Eino Kolli. I would like to present my gratitude to the financiers, who made this thesis and all the included research work possible.
Many people contributed this work and I would probably fail in attempting to thank them all in a correct manner. Above all, I want to thank my main supervisor, Professor emeritus Jukka Ahokas, who originally offered me the PhD position in the ENPOS project and ever since organised the fund-ing for the research work included in my thesis. I hope that, under his supervision, I gained even a shallow glimpse of his knowledge and his practical and logical approach to the field of scientific research. I express my thanks also to co-supervisors, Docent Mikko Hautala and D.Sc. Hannu Mik-kola. With his deep understanding of physics and the open-minded ability to apply this knowledge into practice, Mikko Hautala gave an indispensable contribution to my work. Hannu Mikkola, again, provided lot of valuable help and advice during my work with his strong experience on agricultural engineering and his practical approach on concerned issues. I present my gratitude also for my co-authors for their contribution in the publications, especially for Docent Timo Oksanen, who offered valuable support to my work with his engineering skills and his utmost knowledge of agricultural automation and control systems. I thank also my current superior, Professor Laura Alakukku, for her very professional contribution in finalising my thesis. Her comments and advices improved the quality of this work considerably. I want to thank Laura also for guiding, and sometimes even push-ing me towards the dissertation.
I want to thank the entire staff of agrotechnology at the department of agricultural sciences for providing help whenever needed. My special thanks go to D.Sc. Mikko Hakojärvi and M.Sc. Juuso Tuure. Mikko Hakojärvi kept his door always open when I was struggling with programming or what-ever issues. Juuso Tuure assisted me in swhat-everal occasions with implementation of measuring sys-tems, as well as conducting the drying trials in practice.
I express my thanks to the reviewers, Professor Terry Siebenmorgen from the University of Arkan-sas and Professor Pekka Ahtila from Aalto University, for their valuable comments, which were of great importance considering the final quality of the work. Terence Garcia has also earned my grat-itude by doing the language revision for this thesis, as well as several included publications.
Many things has happened in my life during the previous year, while I have been preparing and finalizing this thesis. Things have been hectic, sometimes almost crazy. I want to present my warm-est thanks to the people closwarm-est to me for all the help and support I have received from you – with-out you, I would not have been able to make it.
Viikki, September 2016 Tapani Jokiniemi
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