**2. Literature Review**

Ukraine has a highly developed agricultural industry, especially edible oil production. From 2013 its share of the world in sunflower seed production ranges from 24.8% to 30.16% [22]. Sunflower seed production is stimulated by high demand for vegetable oil and its high price. Over the last five years, Ukrainian farmers have produced more than 10 million tons of sunflower seed (Figure 1). Despite the increase in production, it has been slowing down since 2012, its value is rather high, and Ukraine is ranked first among the world producers.

Both feedstock and energy costs are important factors that a ffect the production cost of sunflower oil. The sunflower oil industry in Ukraine is energy intensive. Electricity consumption ranges from 96.6 to 198 kWh per ton of oil and heat consumption (steam) ranges from 348 to 1184 kWh per ton of oil [23]. It is higher compared to other edible oil production [24–26]. It impacts on production cost. To raise the competitiveness of the industry, reducing energy costs is paramount.

It can be reached by means of biomass utilisation. Sunflower oil mills produce a by-product (husk). Husk and products (oil and cake) can be used to generate electricity and/or heat. This substitutes the energy resources sold (fossil fuels and electricity) and reduces greenhouse gas emission. Moreover, biomass CHPs could improve the stability and reliability of the electrical grid. In Ukraine there are about 70 husk boilers in operation. However, only three sunflower oil mills use husk-based combined heat and power plants (CHP) [27,28].

Renewable energy is of grea<sup>t</sup> importance in terms of preventing climate change and reducing harmful emissions [29]. The European Union (EU) supports the increase of renewable energy production [30–32]. A lot of scientists have analyzed the influence of renewable energy usage on economic indicators and economic growth [33–37].

**Figure 1.** Sunflower seed production history [28].

Previous research has studied the energy supply systems of edible oil plants based on biomass [25,38–40]. They considered a general concept of husk application for energy supply [41,42] and the energy balance of oil mill [40]. However, this problem for sunflower oil mills has been studied insufficiently. Therefore, optimal energy supply schemes are currently being sought. The purpose of the paper is to assess the optimal mode of biomass-based energy supply systems. More specifically, the article aims to reveal specific energy consumption for edible oil production, assess the husk utilization impact on carbon dioxide emission, to analyze different options for biomass utilization.

## **3. Materials and Methods**

The methodology used is as follows. Information and data are collected from the public domain and interactions are made with industrial's officials. Prices of energy, fuels, and products are widespread indicators. Information resources (publications, statistics, and websites) were used. The information was used for further calculations.

All kind of fuels (renewable and fossil) can be compared within the following domains: Energy, environmental, engine efficiency, economics including efficiency of technological equipment.

The energy indicators are as follows: Lower heating value and energy density. The lower heating values were taken from handbooks. The energy density is the amount of energy per unit volume (liter, cubic meter, etc.)

$$DE = LHV \cdot \rho\_\prime \text{ MJ/m}^3,\tag{1}$$

where *LHV* is the lower heating value of the fuel, MJ/kg; ρ is the density of fuel, kg/m3.

The higher the energy density of fuel, the better the fuel is for consumers.

The ecological indicators may be divided into two groups: Hazardous emissions and carbon dioxide emission. Carbon dioxide emissions are discussed further. This kind of emission has two components: From fuel combustion and in due to electrical consumption. The combustion of hydrocarbon fuels results in the production of carbon dioxide, which is known as a greenhouse gas. This specific value from fossil fuel substitution can be calculated as

$$ERh = HH \cdot \eta\_b^{-1} \cdot EF \text{ } t\_{\text{CO2}} \tag{2}$$

where *HH* is the heat energy of fossil fuel substituted, GJ; *EF* is the carbon dioxide emission factor for conventional fuel, tCO2 /GJ; η*b* is the thermal efficiency of the conventional fuel boiler.

The husk is a carbon dioxide neutral fuel. Its utilization reduces carbon dioxide emission compared to a certain fossil fuel. This specific value on one ton of husk can be calculated as

$$\text{LSRs} = LHV\_h \cdot \eta\_h \cdot \eta\_b^{-1} \cdot EFm\_\prime \,\text{kg}\_{\text{CO2}}/\text{t},\tag{3}$$

where *LHVh* is the lower heating value of one ton of husk, GJ/t; *EFm* is the carbon dioxide emission factor for conventional fuel, kgCO2/GJ; η*h* is the thermal efficiency of the husk boiler (gasifier).

Emission reduction from onsite electricity production

$$ER\_{\mathfrak{c}} = EC \cdot EF\mathfrak{c}, \ t\_{CO\_{2'}} \tag{4}$$

where *EC* is the electricity onsite consumption from grid substituted, MWh; *EFc* is the emission factor for grid electricity, tCO2/MWh.

Engine performance indicators can be divided into three groups: Break thermal efficiency or engine efficiency, brake specific fuel consumption, and brake specific energy consumption.
