Concept of Biohydrogen Production by Agricultural Enterprises


 Biohydrogen production in agricultural enterprises is an urgent matter. It is appropriate to utilize two methods of biohydrogen production: a thermochemical method – from crop-based biomass and anaerobic digestion (fermentation) method – from animal-based biomass.. It is appropriate to use gasifiers for the thermochemical method and biore-actors for fermentation method.
 The theoretical potential of biohydrogen was established with due regard to the amount of biomass which is necessary for utilization in livestock agriculture, for fields fertilization as well as with the consideration of the coefficients of concordance with hydrogen equivalent and loss factor under biohydrogen production. The theoretical potential of biohydrogen from crop-based biomass in Ukraine amounts to 77 billion m3, during the period of three years (on average 25.6 billion m3 per year).


Introduction
Agricultural production mainly focuses on providing the population with foodstuffs (Golub et al., 2017). However, agricultural production can also effectively arrange for production of biofuel from biomass, in particular biogas, diesel biofuel, bioethanol, baled straw, fuel pellets, briquettes and generator gas (Kukharets, 2016;Rzeznik and Mielcarek, 2018;Ovcharuk et al., 2020). Such a production has become traditional, though the production of renewable energy from biomass causes some fear in researchers as to reduction of the level of core product production -foodstuffs, as well as to reduction ofthe amount of plant food in soil caused by the use of some cultivated areas for growing bioenergy crops and by the use of straw as fuel (Verdade et al., 2015;Gomiero, 2018;Tryhuba et al., 2021a, Tryhuba et al., 2021b. For this reason, it is necessary to coordinate the main criterion of functioning of the agricultural production: ecological safety, power supply and economic effectiveness. Such research was conducted and it was concluded that agricultural production can provide itself with energy resources (Yarosh, 2020;Golub et al., 2020b). However, this research was based only on biomass utilization. Thus, the effects of using hydrogen technologies on biological safety and economic effectiveness was not determined.
Though, according to the research, (Gas Decarbonisation Methods, 2020) the EU is planning to produce more than 1700 TWh using hydrogen technologies by 2050. That is why it is appropriate to use hydrogen technologies for energy production in agricultural production.
Two methods of biofuel production are appropriate for hydrogen production in agricultural production -thermochemical ( Fig. 1) and biofermentation (Fig. 2).  (Baeyens et al., 2020) Should be "Hydrolysis" instead of "hidrolysis" in the figure above When using the thermochemical method, hydrogen is produced as a result of decay of crop-based biomass (Bhoopendra et al., 2019;Pandey et al., 2019). To produce hydrogen from biomass by the thermochemical method it is appropriate to use gasifiers of a new type (Fig. 3) designed by the authors of the paper.
The main obstacle for production of generator gas from crop-based biomass is the formation of solid agglomerates (particles, residues) in the process of generator gas production. To avoid the formation of agglomerates, the authors of the paper have designed the gasifier construction which does not have a fire grate, and gas withdrawal occurs through joints on the side surface of the recovery zone (Golub et al., 2020a). 2 -bunker for fuel; 3 -gasifier; 4 -prime filter; 5 -cooler; 6 -fine filter; 7 -gas upgrading (Golub et al., 2020a).
In the process of fermentation, hydrogen is obtained by biomass processing with special bacteria (Baeyens et al., 2020).
To provide efficient production of hydrogen by fermentation under conditions of agricultural enterprises we suggest using bioreactors designed by us (Fig. 4).
The authors of the paper (Golub et al., 2019) suggest new engineering solutions in the system of substrate motion in a bioreactor. They insist on using direction change of gravity forces, that influence the movement of organic and mineral fractions of biomass. The bioreactor case is cylinder-shaped which spins around a horizontal axis. The bioreactor rotates in liquid which is in an outside case. Such a construction induces the lift for a rotary bioreactor while discharging the supporting bearings. The friction force reduces and the energy which is used for bioreactor rotation and substrate motion, reduces as well. The bioreactor construction contributes to a steady motion of a substrate and prevents the formation of floating organic particles as well as of immersed sediments.  8, 9, 12 -sockets;10 -gas collector;11 -the discharge chamber;13, 14 -bearing joints;15 -external drive;16, 17 -interpolator (Golub et al., 2019).
The use ofthe suggested equipment for hydrogen production requires further economic and technological research.

Material and Methods
The management of crop-based biomass for hydrogen production requires bulk-yield monitoring of grain-crops by-products (straw) and consideration of coefficient of its utilization for energy requirements.
To determine the theoretical potential of hydrogen production from plant raw materials of the agrarian origin when using the thermochemical method, the data on the available gross output of crops in crop farming and the average coefficients of the available, technical and economic potentials of by-products (up to 0.7) were used.
While determining the theoretical potential of biohydrogen it should be taken into account that some amount of straw is required to use in cattle breeding and for fields fertilization. Thus, while determining the potential, it the necessary to use the factor for reducing to by-products. (Avcıoğlu et al., 2019). It is also necessary to use the factor for reducing to a hydrogen equivalent with the heat value of 119.83 MJ·kg -1 (Mortensen et al., 2020;Cao et al., 2020).
Biohydrogen yield from 1kg of raw materials (e.g., for the straw from grain crops it equalled up to 2.8 m 3 ·kg -1 (Golub et al., 2018)), the hydrogen content in the received gas (up to 40%) as well as the loss coefficients in the process of gas purification and using (up to 0.3) were taken into account.
To determine the theoretical potential of hydrogen production from the plant raw materials of the agrarian origin by using the fermentation technique, similar to the thermochemical transformation, the data on the available gross output of crops in crop farming and the average coefficients of the available, technical and economic potential of by-products (up to 0.7) were used.
The coefficients of gas yield from 1 kg of dry mass of plant origin (up to 0.13 m 3 ·kg -1 ) (Kukharets and Golub, 2015) depending on the biomass kind, as well as loss coefficients in the process of purification and using the received gas, were taken into account.

Results and Discussion
With due regard to feasibility of hydrogen production, an advanced method of biofuel production at the agricultural enterprises has been suggested (Fig. 5). Diesel biofuel, bioethanol (in the amount necessary to provide the mobile machinery operation), biogas, biohydrogen, generator gas, solid fuel (rolls, pellets (granules), straw briquettes) are produced according to this method.
A part of plant biomass (straw) is used for the production of pellets (granules). Generator gas is made from granules. Generator gas is used for biohydrogen production. Biohydrogen and biogas are made from animal residues by means of fermentation.
Gross yield of grain crops which are grown on all types of farms in Ukraine is given in The theoretical potential of biohydrogen was determined with due regards to indices mentioned above (the thermochemical method -Tab. 2, Fig. 6 and anaerobic digestion method -Tab. 3).   Volume, bilion. m

Figure 5. Scheme of biofuel production at agricultural enterprises
The potential of hydrogen production in the agricultural production by using the technique of thermochemical transformation is approximately 10 times higher than the potential of hydrogen production when using the fermentation method. However, the hydrogen production by using the fermentation method makes it possible to receive organic fertilizers and is appropriate for using in animal husbandry.
Thus, theoretical potential of biohydrogen from crop-based biomass in Ukraine is 77 bilion m 3 , during 3 years (25.6 bilionm 3 on the average).
The further theoretical and experimental analysis of both methods of hydrogen production under conditions of agricultural production are required for the practical realization of hydrogen potential.