Evaluation of Energy Efficiency in a Grain Unloading Platform

This paper aims to conduct an energy efficiency study in the tipping system of the unloading platform of a grain storage unit, based on the use of electrical devices to control the operation of the engine. For this purpose, two scenarios were established. The first scenario considers the platform in its current state, with engine start-up performed using a wye-delta switch. In the second scenario, wye-delta start is switched off, and a frequency inverter and a programmable logic controller (PLC) are coupled to control the electric motor. For both scenarios, the consumption of active and reactive energy in the discharge platform was measured, and the costs of the energy consumed were calculated over a period of one year. Finally, the discounted payback was calculated to evaluate the economic feasibility of installing the proposed equipment. The results obtained were as follows: For the current scenario, the energy consumed to tipping one metric ton of grain was 35.44.10 kWh; for the proposed scenario with the frequency inverter, the energy was 32.78.10 kWh. With an annual projection, the current scenario would consume the equivalent of 10 921.35 kWh, and the proposed scenario, 10 100.81 kWh, generating an annual savings, with the installation of the equipment, of R$721.49; the discounted payback found was approximately 31 years. It can thus be concluded that there is a reduction in electricity consumption from the use of the frequency inverter; however, the time of return of the invested capital is very long, making the proposal economically unfeasible.


Introduction
Mankind learned to master fire in the Paleolithic period, over 10 000 years ago.Since then, man has benefited from a reliable source of heat and light, altering its history.Unfortunately, almost nothing has changed for one out of three people in the world today.It is estimated that there are still more than 1.5 billion people in the world without access to electricity, and this is one of the most important issues for quality of life and human development (UN, 2010).
Access to clean, efficient and renewable energy is indispensable for global growth.Developed countries must expand access to more modern types of energy in order to reduce poverty, improve and provide more health for citizens while accelerating production and promoting global growth.
In this line of reasoning, mankind must pursue two paths; first: the development of new forms of generating and supplying electricity; second: rationalization in the use of this energy, so that this resource is available to people who do not yet have it.
The processing of agricultural products requires high electricity consumption, due to the need to store such products.Moreover, the lack of investment in more efficient equipment makes consumption inefficient.
Grain production is performed on a seasonal basis, the volume harvested in these periods being greater than consumption.Based on that, it becomes necessary to store and preserve them, so that they can be traded in the future, according to the convenience of the market.This use becomes effective thanks to the scarcity of such a product on the market or through the business strategy of storage companies.The agri-industrial grain market revolves around this infrastructure of grain storage and processing, which is responsible for the largest economy in Brazil (Portal Brasil, 2017).
Brazil is currently the second largest producer of soybeans and one of the largest grain producers in the world.According to the latest survey of the 2016/2017 harvest, Brazil is expected to beat all previous records of productivity (EMBRAPA, 2017).
The official estimate issued is 237.22 million metric tons, accounting for a growth of 27.1% in relation to the 2015/2016 harvest.The planted area is estimated at 60.49 million hectares, with an estimated growth of 3.7%, which shows that the increase in production was much more influenced by the efficiency of new technologies than the area of planting itself.Thus, the country has been gaining prominence, crop after crop, and claiming the title of the "world's granary" (CONAB, 2017).
Because it is a tropical country, Brazil relies heavily on quality storage to preserve grain and offer flexibility to companies to meet the demands of the market.In terms of storage, Brazil's static capacity as of 2016 is 157.62 million metric tons.It is observed that the storage capacity is below production, which implies an even greater need for speed in receiving and shipping this grain (CONAB, 2017).
Grain storage units are equipped with a platform called truck lift, which is responsible for removing the product from inside the trucks and referring it for processing and storage.This equipment operates by tipping the truck with the aid of gravity, and all material is drained into hoppers.At harvest times, the equipment operates 24 hours a day, 7 days a week, for the duration of the harvest, so that its use can extend for several weeks.The energy propellant, responsible for elevating this platform, is a three-phase induction motor, which operates uninterruptedly throughout the mentioned period.Nevertheless, when analyzing a truck unloading cycle, the amount of time during which the use of this energy is required represents about 50% of the cycle time, since there is a need for power only during the elevation of the assembly, as gravity is responsible for the descent, and the time of ascent and descent is virtually the same.That is, during the entire period in which the equipment descends to its initial position, it can be said that there is a waste of energy.
This problem is addressed in this study.The proposed solution to minimize such loss of power would be to control the power of the electric motor with the use of a Frequency Inverter and a Programmable Logic Controller (PLC), making some initial investments necessary.Nevertheless, there is an expectation of savings in the costs of the energy consumed, and to quantify this economy, the discounted payback model, which indicates the time of return of the capital invested, was used.
Therefore, this paper aims to make a technical and economical evaluation of energy efficiency in a hydraulic pump unit, driven by a three-phase induction motor, applied to a grain unloading platform, called a truck lift.The study proposes the installation of a frequency inverter and a PLC to control and reduce the energy consumed by the induction motor.

Material and Methods
This work was carried out in October and November of 2017, at AB Agrobrasil, located in the city of Cascavel, PR.The geographical coordinates of the unit are: 24°59′24.5″S and 53°19′19.0″W.
For a better understanding, the measurements were divided into three topics: Electrical Devices; Hydraulic Devices; and Mechanical Devices.

Electrical Devices
In order to measure the electricity values, an RE7080 Energy Analyzer, by the Embrasul brand, was used to read the Voltage (V), Current (A), Power (kVA, kW, and kVAr), and Power Factor.The device is capable of measuring and storing this data for a detailed analysis of the results.The readings were stored every 200 milliseconds and were performed during the grain unloading period.

Hydraulic Devices
The hydraulic devices, which make up the unloading platform, are the hydraulic unit, composed of a Parker gearbox hydraulic pump, 20300C 5N3 model; a valve block, used for driving the cylinders; and the hydraulic fluid reservoir.These are two parallel cylinders with four stages, and in each stage having a stroke of 1,731 mm, to a total stroke is 6,924 mm.
For the measurement of the pressure (kgf/cm²) of the hydraulic assembly, the analog gauge of the equipment was used, located in the unloading platform in question.The values obtained were compared with the data provided by the manufacturer, as shown in Table 2. Source: SAUR (2017).

Mechanical Devices
The mechanical devices are composed of the discharge platform and the AB Agrobrasil truck scale.
The data for the unloading platform are shown in Table 2.
The truck scale, installed at the unit, is of the Balanças Capital brand, BC CONTROLLER 3.0 model, certified by INMETRO.With it, the total weight of the truck was obtained, before and after unloading the product, making it possible to determine the weight of the product unloaded.

Methodology
The Mechanical Power, used to tip the platform, is given by Equation 1.

Source: Si
The calcu acceleratio Where, F =

To calcula
Where, CC The Hydra Where, Ph The mecha 5: Where, Pm The Electr Where, V The yields Where, n p of the platf

Scenario 1 control equ initial cond
To measur motor con connected The weights used in the calculations followed the following legend: On October 27, 2017, at 8:28 am, measurements were started for the conventional wye-delta starting system.Five (5) trucks were unloaded in a row, all with wheat, with the last truck leaving the platform at 9:36 am, completing the recording of the energy analyzer.The analyzer data was uploaded to the computer for analysis, and the weights of the trucks, whose plates were recorded, were reported by AB Agrobrasil, according to Table 3.For comparative purposes, a measurement unit was established by dividing the energy consumed during the measurement interval in kWh by the total weight of the analysis period, according to equation 10.This total weight includes the PBT (weight of the loaded truck) plus the weight of the platform, which, according to the manufacturer, has 20 metric tons.Therefore: Where, E/T = Energy per Metric Ton (kWh/ton); kWh = Energy spent in the measurement range; PT = Total Weight of the cycle, considering PBT plus platform weight.
This index shows the amount of energy consumed, in kWh, per ton of product that the platform needs to lift.
Based on this, it is possible to compare the two scenarios, regardless of the number of cycles, truck weight and time interval.
Scenario 2: It is characterized by the tipping system operating with the frequency inverter and the PLC, to control the induction electric motor.Similarly, in this scenario, electric, hydraulic and mechanical quantities were also collected to evaluate the operating conditions of the system.
To measure the electrical quantities, the Energy Analyzer was installed in the three phases (R, S, and T) of the motor control panel.The installed equipment follows the correct order of the TPs and CTs, which will be connected in their respective phases, before the frequency inverter, as shown in Figure 4.As the energy data collected in the two scenarios were in off-peak hours, the total value of the energy bill was divided, considering all the tariff and tax variables, by the amount of active energy.In this way, a single tariff was created contemplating tariff and tax divisions, facilitating the estimated cost reduction according to equation 11.
To carry out the consumption reduction study, AB Agrobrasil informed the net weight of the products received for a period of one year, counting from October 2016 to September 2017 (month in which an energy invoice is submitted).These values are presented in Table 5.Source: AB Agrobrasil (2017).
For the projection of the values obtained, the mean net weight of the measured values was calculated.The number of cycles in a month was estimated by dividing this Net Weight by the monthly receipt amount.This data was important because, for each cycle, 20 metric tons (Platform Weight) were added.In addition, the mean Truck Weight was calculated and added to the value of each cycle, enabling the determination of the Total Weight was tilted each month Equation 12).After the definition of the Total Weight tipped monthly, the value was multiplied by the energy index by metric ton to obtain the total electricity consumed in each month by the unloading platform, in the current scenario and in the scenario with the frequency inverter (Equation 13).
This amount of energy was then multiplied by the Single Tariff (TU), in order to verify the amount spent on electricity consumed with the platform, for the two scenarios under study.The difference between these values and the monthly cost electricity avoided (Equation 14) was calculated.Subsequently, the annual cost avoided was also calculated.
Another b productivi this experi the platfor time and, receipt com

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In order to system, co (R$10,000 Another v annual net represent t

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Where, U decimal at This calcu study, the m

Power
For the ca follows:  The active energy consumption during this time was 12.332 kWh.
Table 7 shows the energy index per metric ton, which was 35.44.10-3 kWh/ton.

Reducing Power Consumption and Improving Productivity
Based on the data obtained, it can be observed that the amount of energy required to tip one metric ton is sensitively smaller in the system with the frequency inverter than in the system with the wye-delta switch.
Table 10 presents the TU (single tariff), created to calculate the value in reais for each kWh of energy, consumed by the unloading platform.Based on these data, the net annual return, with the installation of the frequency inverter, is seven hundred and twenty-one reais and forty-nine centavos (R$721.49).
Another factor observed was the increase in productivity, with the inverter adjusted to operate at 20% above the nominal rotation.In this case, the platform took 2 minutes and 14 seconds to be lifted, the time being 2 minutes and 44 seconds previously.There is an increase of almost 19% in the tipping speed, and this reduction in total time can be very attractive in periods when there are many trucks to be unloaded.

Discounted Payback
After obtaining all the necessary data, the calculation of the discounted payback was made based on Equation 32, presenting a result for the return of the investment equal to 31 years.Considering that this time of return is very long, even well above the service life of the equipment that would be installed, it is concluded that the investment is economically unfeasible, for the particular conditions presented in this paper.

Conclusion
The application of the frequency inverter to reduce power consumption in the unloading platform is real, as the inverter has a relatively better energy efficiency result than the conventional wye-delta start system.The efficiency calculations made it possible to understand that this efficiency can be improved by applying better performance components, such as high-performance motors, hydraulic pumps with lower losses, etc.
The electric power required to tilt the platform is smaller in the wye-delta starter system compared to the frequency inverter, but this system operates continuously even at unnecessary times, during which the frequency inverter has a small advantage, as its consumption is practically zero.When comparing these two situations, the frequency inverter shows significantly lower energy consumption per metric ton tipped than the conventional system.
In addition to lower power consumption, the frequency inverter makes it possible to increase the flow rate of the hydraulic pump, as it is possible to increase the nominal rotation of the three-phase induction motor.This can be a major advantage for the storage units and can become an important device against the extended lines and delays in receiving the product.The inverter, in turn, can expedite by up to 19% the unloading speed, when compared to the current system.
Nevertheless, when the discounted payback (approximately 31 years) was calculated, it was found that the installation of a frequency inverter and a PLC for the control of the hydraulic unit is not economically feasible, as its investment can be considered high, compared to the annual avoided value that the system provides.This value is much higher than the service life of the equipment used, which is usually 10 to 15 years, making its investment unfeasible.
As suggestions for future work, it is important to evaluate a hydraulic unit for unloading platforms, using a high-efficiency motor, as well as the study of the formation of lines in storage units, in order to evaluate the impact of the agility of the process. Figure

Figure
Figure 4.with po

Table 1
shows the technical specifications of the equipment.

Table 1 .
Technical specifications of the RE7080 model energy analyzer

Table 2 .
Technical specifications provided by the manufacturer

Table 3 .
Weights of the trucks under study for scenario 1

Table 5 .
Net monthly weight of products received, from October 2016 to September 2017

Table 6 .
Electric quantities read by the energy analyzer in scenario 1

Table 7 .
Calculation of the energy index per metric tonFigure10shows the active power, collected in the frequency inverter starter system. jas.ccsenet.

Table 9 .
Electric quantities read by the energy analyzer in scenario 2