The physico-chemical parameters of loquat seed were analysed and compared with those of other sources of residual biomass in order to evaluate its usefulness as a solid biofuel. Afterwards, an energy, economic and environmental analysis of the installation was carried out.
4.1. Loquat Seed Values
To evaluate the quality parameters of loquat seed, 2000 g of samples from the loquat industry were analysed.
Table 4 shows the mean value, the standard deviation, the maximum value, and the minimum value which determine the parametric distribution.
As can be seen from
Table 4, one of the main disadvantages of loquat seed is its high moisture content, above 30%. This decreases the efficiency of combustion, since water needs to evaporate before heat is available, resulting in a lower heating value. Furthermore, from a technical point of view, the presence of a high moisture content produces corrosion in the equipment and generates the emission of tars that accumulate in the outlet pipes and can cause them to block. As a result, pre-drying processes must be implemented in order to obtain a moisture content below 10%.
Ash is the inorganic fraction of the biomass that remains once the fuel has been burned, mainly in the form of SiO2 and CaO. The formation of ashes is linked to problems such as the formation of agglomerates on the walls of the grids and the formation of slag deposits which accelerate the corrosion of the installation and increase its maintenance costs. With respect to the ash content of the loquat seed, it is in the range of 2.31%–2.43%. If this value is compared with that of other standardized fuels, such as almond shell pellets (3.35%) or oak pellets (3.32%), it can be seen that in spite of its high value, it is below the ash content of other conventional fuels.
Table 5 compares the physicochemical parameters of several commercial biofuels and industrial wastes with those of loquat seed in order to evaluate the use of this by-product in the generation of thermal energy.
As shown in
Table 5, the ash content of loquat seed is higher than that of other industrial waste but lower than the ash content of the mango stone. This suggests that the formation of ash deposits will be greater and therefore will need additional maintenance.
As for the higher calorific value of loquat seed (17.205 MJ/kg), it is observed that it is lower than that of other standardized solid biofuels such as almond shells or olive stones. However, if we compare it with other industrial wastes such as wheat straw (17.344 MJ/kg) or pistachio shell (17.348 MJ/kg) [
31], it is shown to have similar values, showing the energy viability of this agro-industrial waste.
Another quality parameter to be considered in a biofuel is its chlorine and sulphur content. Sulphur, in addition to having a corrosive effect on the installation, is associated with the emission of greenhouse gases in the form of SOx. Loquat seed has a 0.03% sulphur content that is lower than that of other commercially available biofuels such as almond shells (0.050%) or olive stones (0.110%), which means that SOx emissions would be minimised if this biofuel were used.
Regarding the chlorine content, this has a significant effect on the corrosiveness of the plant due to the formation of chlorides, which have a dissociative catalytic effect on the steel pipes. Loquat seed has a low chlorine content (0.07%), like that of other standardized biofuels such as olive stone (0.06%) and lower than that of almond shells pellets (0.2%). In view of these results, corrosion problems would be minimized by using this solid biofuel.
However, in addition to its high calorific value, the main advantage of using loquat seed as biofuel is its carbon-neutral character. In fact, when the plant grows it fixes carbon from the atmosphere which is then released when it is burned, making the life cycle carbon neutral.
This residual biomass can be obtained from loquat processing industries in the surroundings, helping on the one hand to a better environmental management of these wastes and on the other hand to a reduction of greenhouse gas emissions.
4.2. Environmental Benefits
Biomass as an energy source has several advantages over other alternatives in the fight against climate change and local pollution. Biomass is a source of non-polluting energy. Plants emit CO
2 but also absorb CO
2 during their growth, so their total balance is zero (
Figure 10).
Once the energy characteristics of the loquat seed are known, it is possible to calculate the CO2 savings in the installations of the UAL indoor swimming pool, as well as the worldwide CO2 savings in loquat producing countries.
Firstly, the potential energy obtained from the use of loquat seed as a biofuel is calculated using Equation (2). This potential energy is calculated considering the worldwide production of loquat for each country.
where:
Up denotes energy obtained from the loquat seed as biofuel (MWh);
RH is relative humidity (10%);
Ploquat seed: loquat seed production (kg);
HHV: higher heating value (17.205 MJ/kg);
fs is the percentage of seed in a whole loquat (15%);
Fc factor conversion for units (0.000277778 Wh/J).
Figure 11 shows worldwide bioenergy potential using loquat seed as biofuel (MWh).
The next step in the study will be to calculate the CO2 reductions that would occur if loquat seeds were used as a biofuel instead of fuel oil.
As mentioned above, Biomass is a source of non-polluting energy, with zero CO
2 emissions. The CO
2 emission of fuel oil would be calculated as:
where:
M: mass of carbon dioxide emitted (kg/year).
: consumption of fuel oil per year (kWh/year).
carbon dioxide emission factor of fuel oil (kg/kWh).
Table 6 shows the CO
2 emission factor for biomass and fuel and the total CO
2 emission reduced annually using loquat seed as biofuel.
The change of the boiler to biomass in UAL indoor swimming pool means a reduction of 147,973.8 kg CO2 in emissions into the atmosphere.
Figure 12 shows the worldwide CO
2 saving using loquat seed as biofuel (Tn).
The five main countries that would reduce their annual CO2 emissions by using loquat seeds as biofuel are: China (51,184.92 Tn), Spain (10,617.54 Tn), Turkey (3454.98 Tn), Pakistan (3275.83 Tn), and Japan (2621.95 Tn). Further, the annual worldwide reduction of CO2 emissions if loquat seed is used as biofuel would be 76,363.80 tn.
In a society committed to sustainable development, the use of biomass for heat and electricity production is an important source of renewable energy. Its increasing use as a substitute for fossil fuels can significantly reduce CO2 emissions. However, in recent years discussion has focused on the sustainability of biomass, and the environmental implications of its use must be taken into account.
Particularly important is the particle size of the emissions that are produced, which have been identified as a relevant factor of the deterioration of air quality. Not so long ago, the existing legislation for emission control in combustion plants only took into account total particles with a diameter of less than 10 micrometers (PM
10). However, particles with a diameter of less than 5 micrometers (PM
5) and especially those with a diameter of less than 2.5 micrometers (PM
2.5) have the most harmful effect on health. Fine particles (PM
2.5) emitted during biomass combustion can be divided into three groups, based on their chemical composition and morphology: particles spherical organic carbon particles, sooty aggregate particles and inorganic ash particles. Because of their small size, these particles are able to reach the pulmonary alveoli and pass into the bloodstream. This is associated with an increased risk of respiratory and cardiovascular disease, especially when the environmental concentration of these particles exceeds 35.4 µg/m
3 [
40,
41,
42,
43].
This has led to a boost in research activity, both in the characterisation of emissions and in the development of control equipment, and in enacting legislation at national and European level.
For our case study, the R.D. 1073/2002 transposing the Directive 1999/30/EC on air quality, establishes in relation to PM10, that the limit value of 50 µg/m3 must not be exceeded in 24 h for more than 35 days, on the date of entry into force of 1 January 2005.
In the year 2015, new European legislation has been published (Directive (EU) 2015/2193 of the European Parliament) that involves air emissions from the combustion of solids, such as biomass, in equipment and installations with a rated thermal input of more than 1 MW and less than 5 MW, and that makes a big impact on particle emissions.
Conversely, the European Directive 2009/125/EC establishes a framework for setting ecodesign requirements for energy-related products. The national transposition of this regulation is the Royal Decree 187/2011 of 18 February.
The result of this directive is Regulation 2015/1189 of 28 April on solid fuel and wood biomass boilers of nominal output not exceeding 500 kW, which is mandatory from 1 January 2020. The environmental aspects considered important in this regulation are energy consumption and emissions generated by particulate matter (PM), organic gaseous compounds (OGC), carbon monoxide (CO), and nitrogen oxides (NOx) in the use phase of this equipment. This regulation stipulates that seasonal particle emissions from heating may not exceed 40 mg/m3 for automatically fed boilers and 60 mg/m3 for manually fed ones.
In order to reduce the amount of particles emitted into the atmosphere due to the incomplete combustion of the biomass, modifications have been made to combustion equipment in recent years. In this way, for example, special emphasis has been placed on the modulation of the equipment to adapt to thermal demand, lambda probes have been used to ensure control of the most appropriate fuel-air ratio according to operating conditions and secondary and tertiary air has been introduced in different parts of the equipment.
However, the permitted emission limits are becoming increasingly restrictive, making it necessary to use of equipment that can be coupled to the stoves and boilers of biomass in order to reduce the emission of particles. In this way, research is being carried out into different technologies that can be adapted to the residential sector, such as the introduction of additives with the biomass, the use of catalytic filters or the use of electrostatic precipitators.
In low power installations (up to 1 MW) the most effective and profitable solution is the use of an electrostatic filter [
44]. Its operation is based on electrically charging the particles in order to direct them out of the gas towards plates with an opposite charge, to which they adhere. Therefore, in our case study an electrostatic filter will be installed consisting of a metal rod that rotates inside the metal chimney tube, carrying a voltage of 24,000 volts, so that it ionizes the solid particles, which are attracted by the walls of the chimney tube, where they accumulate until they fall by gravity into the equipment. This technology has proven to achieve efficiencies of over 90% in PM
2.5 abatement [
45].
4.3. Economical Benefits
The economic feasibility of the study of changing the fuel boiler for loquat seed as a biofuel is based on the following:
Annual hours of operation.
Annual consumption of fuel oil and biomass.
LHV of fuel oil and biomass to be used.
Current prices of fuel oil and biomass to be used.
Starting with a 267 kW boiler that will work approximately 6 h a day with an average of 297 days, the energy required is 475,800 kWh.
The high price of fossil fuels, which is also heavily taxed in many countries, is boosting the market for biomass boilers for heating generation. In order to calculate the economic benefit to be gained from the new biomass installation compared to the original fuel oil installation, the necessary fuel expenditure in both scenarios has been calculated to cover the annual energy demand. As shown in
Table 7, the annual fuel oil consumption of the existing facility during 2018 was 52,239 litres, and considering a fuel price of 0.94 euros/litre, a total annual cost of 49,104.67 euros is obtained.
The annual thermal demand of the installation (kWh/year) can be calculated as the product of the amount of fuel consumed by the lower heating value (LHV) of the same, but considering the efficiency of the boiler, this is:
Taking into account the necessary thermal demand of 475,800 kwh per year, with the new biomass boiler 133,651.7 kg of loquat seeds will be consumed, and taking as a reference price of this residual biomass a value of 0.1 €/kg already treated and transported, there would be an annual saving of 35,739.5 € which means a saving of 72.78% with respect to the previous fuel oil installation.
A sensitivity analysis has been carried out with a threshold of seven years, a range of 25% and the analysis is performed on equity payback, see
Table 8.
Table 8 shows that fuel cost will increases in 0.4 in 7 years if costs do not increase, however, in the worst case the costs will increases in 0.7 times if fuel cost increase in 25%.
A risk analysis is performed on net present value (NPV) and 500 combinations. In
Table 9 are presented the parameters and in
Figure 13 is presented a tornado chart to identify the impact of NPV on these parameters.
Figure 13 shows the economic impact of NPV on fuel cost of proposed case and base case, as it can be seen, the highest sensitivity variable is fuel cost-base case (fuel oil); debt interest rate, debt ratio and debt term have very small effects and can be ignored their uncertainty.
Financial viability presents the results provide to the decision-maker with various financial indicators for the proposed case, see
Table 10.
The internal rate return (IRR) is 20.6%, which is higher than European central bank interest rate (0.25%), payback is 1.3 years, and B-C shows that investment has financial viability.