**4. Results**

#### *4.1. Sunflower Oil Mill Energy Consumption*

Top 10 of Ukrainian sunflower oil mills has capacity from 500 to 970 thousand tons of seed per year [43]. Annually they process 7 million tons or 50% of sunflower seed harvest. They use electricity from the grid and thermal energy produced by burning fuel in a boiler (Figure 2). Their specific energy consumption depends on the capacity (Figure 3). Average specific energy consumption is, kWt per ton of oil: Electricity—132.5; heat—779.1.

To reduce energy consumption costs, native mills use husk as a fuel. The output of sunflower seed husk ranges from 15.94% to 18.88% or from 159.4 to 188.8 kg per ton of seeds [44]. To meet their own requirements in heat, powerful Ukrainian vegetable oil mills consume around 46–48% of husk produced (direct burning in boilers). A few mills have their own combined heat and power (CHP) plants. For example, Kirovogradoliya LLC has a husk-based CHP. The CHP was developed to meet all own energy (electricity and heat) requirements. Its electric capacity is 1.7 MWe (electric efficiency—around 5%), thermal capacity is 26.7 MWt. This plant annually consumes up to 42.8 thousand tons of husk (around 57.8% of husk produced). It allows the mill to cover its own energy demands in heat and partially in electricity.

**Figure 2.** Basic scheme of a Sunflower Seed Oil Mill.

**Figure 3.** Specific energy consumption (kWh per ton of sunflower oil) vs. annual sunflower oil capacity (thousand tons of seed) [23].

Specific heat to electric consumption ratio of Ukrainian edible oil mills is decreasing with the increase in a plant capacity (Figure 4). The average ratio is 5.97. This means that the thermal efficiency of a CHP unit must be greater than the electrical efficiency by the same value. Surplus electricity can be sold into the grid. It contributes to its stability and to lower carbon dioxide emissions.

**Figure 4.** Heat/electricity consumption ratio vs. sunflower oil refinery capacity.

To generate electricity steam turbines and internal combustion engines running on syngas are used. Several oil mills (Galati Sunflower oil factory, Pology oil extraction plant PJSC, Centre Soya Ltd.) have experienced the gasification technology. Last mill has a gasification-based husk CHP plant (rated electric power—700 kW; heat—800 kW) (Flex Technologies Limited, London, UK) [40,45,46].

## *4.2. Biomass as Fuel*

The main results, which are planned to achieve by biomass utilization, can be divided into two groups: Economic and environmental. All products (oil and cake [47]) and by-product (husk) may be used as fuels. Their utilization has distinctive energy and economic efficiency. They can be used in their original form or improved before utilization (gasification, liquefaction, or methanation). Husk can be burnt directly or converted into syngas, biogas, or ethanol [48]. Sunflower meat (cake) can be used as solid fuel or converted into biogas [49]. Table 1 compares parameters of selected fuels.


**Table 1.** Properties of selected fuels.

Their improvement can ge<sup>t</sup> better both environmental and economic indicators of oil production. They can be used in steam boilers to substitute conventional fuel (in Ukraine it is natural gas). If products and by-product substitute natural gas (for steam generation), husk utilization has the best economic result (difference between cost of natural gas substituted and market price of any products and by-product) (Figure 5). The above calculations have been made for one kg. The above differences per one kg of biofuels are, UAH/kg: Husk—4.88; meal—3.32; oil—(−8.22). The sunflower oil is more expensive than natural gas. Therefore, husk as a fuel has an advantage. Husk energy potential is enough to cover energy demand in electricity and heat (Figure 6). It is estimated that the potential electricity production is four-fold higher than the electricity demand. In addition, the heat requirement is a third of the husk potential thermal power production. Excess power and heat can be delivered to external consumers.

**Figure 5.** Market prices and cost of natural gas substituted.

**Figure 6.** Installed and potential electric power vs. sunflower oil refinery capacity.

## *4.3. Carbon Dioxide Emission*

Ecological indicators may be divided into two groups: Hazardous emissions and carbon dioxide emission. In the study, carbon dioxide emissions were discussed further. This emission consists of two components: Fossil fuel combustion and in due to electricity consumption. For Ukrainian sunflower seed oil mills the first component ranges from 48 to 96 kg per ton of seed processed. The second component ranges from 37 to 77 kg per ton of seed processed.

According to our calculation, one ton of husk (used for steam production) reduces carbon dioxide emission and this range is from 790.10 to 1162.53 kg (Table 2). It corresponds to 51.3–75.5 kg of carbon dioxide per one GJ of thermal energy.


**Table 2.** Ecological impact of husk utilization.

Electricity consumption for a technological process is the largest sources of emissions for sunflower seed oil mills. Emissions from electricity consumption by any mill are calculated by applying an "emission factor" to the quantity of electricity consumed. Emission factor for grid electricity is taken from an official source. For Ukraine, carbon dioxide emission factor per kWh of electricity consumed is equal to 0.709 [49] or 0.896 kgCO2/kWh [50].

According to our calculations, power generation from husk (condensate steam turbine, electric efficiency of 31%) reduces carbon dioxide emission by 0.707 kg per kWhe (or 938 kg per ton of husk). Additionally, cogeneration has the potential of 1305 kg per ton of husk. Its carbon dioxide emission reduction potential depends on electrical efficiency (Figure 7). The last factor is prevailing. Gasification-based husk CHP plants allow higher value of carbon dioxide emission reduction compared to combustion-based husk CHP plants.

**Figure 7.** Carbon dioxide emission reduction potential per one ton of husk.

#### *4.4. Energy Supply System Based on Biomass*

There are three possible husk utilization pathways: Heat production only, electricity generation only, and combined power and heat generation.

Sunflower husk contains ash (at average 2.1%) [51]. The composition of this by-product of combustion includes calcium, potassium, micro elements, etc. Therefore, the ash can be used as a component to produce

fertilizer [52]. Moreover, it is suitable as a filler for the production of ceramics [53]. Its price is more than EUR80/t. Therefore, ash sale can give additional income.

Sunflower husk can be used to generate electricity and heat production. The first pathway substitutes electricity bought, the second—fossil fuels (natural gas, fuel oil, coal, etc.) bought. Their ratio is

$$R\text{Cs} = \eta\_{\text{c}} \cdot \eta\_{\text{b}} \cdot Epr \cdot LHV\_{\text{n\S}} \cdot \text{3\s} \, \text{6}^{-1} \cdot \eta\_{\text{h}}^{-1} \cdot NGpr^{-1} \,,$$

where *LHVg* is the lower heating value of natural gas, MJ/m3; *Epr* is the price of electricity, UAH/kWh; *NGpv* is the price of natural gas, UAH/m3; η*e* is the electric e fficiency.

Internal combustion engines and gas turbine generators have the highest electric e fficiency as compared with steam generators (Figure 8). They can be run on liquid or gaseous fuels. Therefore, husk to be used in the above method must be converted into combustible gas: Syngas or biogas [54,55]. Gasification technology is currently being used and biogas technology is under development.

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**Figure 8.** Electric e fficiency of gas turbine engines, reciprocating engines, and steam turbine combined heat and power plant CHP (adapted from [56–65]).

Electricity generation can substitute electricity whose cost is lower than solely heat generation (substitution of natural gas). Cogeneration allows mills to reduce more costs of conventional energy bought (Figure 9). As can be seen (Figure 9), the increase in electric e fficiency of CHP (and, therefore, the increase of electricity generated) results in the increase of economic benefits.

**Figure 9.** Economic e fficiency of CHP (developed by authors).

Husk utilization's economic efficiency depends on the electric efficiency of a CHP plant and can be calculated as

$$RC = \eta\_b \cdot LHV\_{\eta\_{\overline{\mathcal{K}}}} \cdot \frac{\eta\_t \cdot \eta\_e \cdot \frac{Epr}{\overline{\mathcal{K}} \cdot \overline{\mathcal{C}}} + NGpr \cdot \frac{(\eta\_r - \eta\_e)}{\eta\_b \cdot LHV\_{\eta\_{\overline{\mathcal{K}}}}}}{\eta\_h \cdot NGpr}.$$

where η*t* is the total thermal efficiency of CHP; *LHVh* is the lower heating value of husk, MJ/kg.

The more conventional energy resources are substituted, the higher income is made. The possible energy supply technologies are as follows (Figure 10): 1—steam turbine combined heat and power generation plant (CHP) via husk combustion; 2—gas turbine (GT) CHP via syngas combustion; 3—internal combustion engine (ICE) CHP via syngas combustion; 4—gas turbine or internal combustion engine with organic Rankin cycle (ORC).

**Figure 10.** Energy supply technologies of Sunflower Seed Oil Mill (developed by author).

## *4.5. Principles of Energy Production*

Ukrainian sunflower oil refineries use husk for steam production. Only some plants have CHP, but they cover only part of the electricity required.

There are three pathways of energy production by CHP (Table 3). The first pathway is to meet its own electricity requirement. However, in this case CHP cannot cover its own demand in heat. To correct the situation an additional steam boiler must be used. The second pathway is to meet its own heat requirement. In this case a CHP plant generates surplus electricity. It may be sold by green tariffs to electricity grid. For both cases, the remaining husk can be converted into pellets. The third pathway is the following. The husk combustion-based CHP plant can cover requirements in both electricity and heat. This energy supply system could have adapted the heat to electricity production ratio. If there is actual heat to electricity ratio (*HERa*) of a certain sunflower seed oil mill and total efficiency of a CHP plant then necessary electric efficiency (η*t*) is

$$
\eta\_{\ell} = \eta\_{\ell} \cdot \left(1 + HERa\right)^{-1}.
$$

During operation of a certain mill, the heat to electricity ratio may vary. In this case, surplus electricity can be delivered to the national grid.


**Table 3.** Relative gross income and carbon dioxide emission reduction.

The gross income comprises three pillars: Cost of natural gas substituted, cost of electricity from grid substituted and sold to the grid by green tari ff, and cost of husk pellets produced. Carbon dioxide emission reduction includes two components: Substitution of natural gas (or another conventional fuel) and electricity generation. The relative values of gross income and carbon dioxide reduction (the base is husk utilization to meet heat requirements only) are presented in Table 3. The second pathway of energy production has the best economic and ecological results. In this option, the cogeneration unit uses all available husks. Prerequisites for success are the sale of excess electricity by the green tari ffs to the grid and the full use of thermal energy for oil production. Therefore, the prospect energy supply scheme is shown in Figure 11.

**Figure 11.** Energy supply scheme of Sunflower Seed Oil Mill (developed by author).

As can be seen, the best strategy for CHP development is to cover heat demand by CHP. As compared with husk utilization for heat production only, it allows mills to increase total income by 21–23% and reduce carbon dioxide emission by 70–73%. Gasification-based technologies may be profitable if their specific investment costs are not more than 40% that of combustion-based technology.
