Evaluation of pumping systems in a power company in Cuba

Summary

An Energy Management method was developed at the Las Tunas Fuel Trading Company with the aim of identifying potential for improving energy and economic efficiency, reducing emissions to the environment. To achieve this, an energy diagnosis was carried out using the Pareto diagram as a fundamental tool in the identification of the carriers, areas and equipment that most affect the entity's energy consumption until the fuel pumping systems are identified as elements with potential for saving electricity. The obtained result allowed to propose solutions to increase efficiency in the operation of these systems, based mainly on the replacement of some pumps that are currently inefficient;evaluating various alternatives from a technical and economic point of view, currently being feasible the replacement of two of the diesel handling pumps, allowing to reduce the annual electricity consumption by approximately 23.7 MWh, which also means to stop emitting to the atmosphere 25.6 tons of CO2 annually.

Introduction

Worldwide, the industry works to achieve greater efficiency in all production processes; and Cuba, an underdeveloped country, doubles its efforts by implementing different technological tools that allow the entrepreneur to make decisions to invest in Energy Efficiency Projects and thus achieve savings and economic benefits, reducing operating costs in equipment and industrial processes.

Energy management is defined by some authors as analysis, planning and decision-making in order to obtain the highest possible performance from the energy required; that is, to achieve a more rational use of energy, which allows reducing its consumption without reducing the quality of services and production. The fundamental objective of Energy Management is to obtain optimum performance, minimizing costs without affecting the quality and / or quantity of production in each of the processes or services where the use of energy is essential. It is also proposed that it can be conceived as an organized and structured effort, to achieve maximum efficiency in the supply, conversion and use of energy, that is, to achieve a more rational use of energy,that allows reducing consumption without prejudice to comfort, productivity, quality of services and in general, without lowering the standard of living; It is considered one of the best ways to achieve energy conservation objectives, both from the point of view of the company itself and at the national level.

According to some authors, Energy Efficiency implies achieving the requirements established by the client with the least possible energy expenditure and the least environmental contamination for this concept. Efficient energy management also contributes to achieving greater environmental responsibility, by allowing the negative effects that can be associated with the production and use of energy to decrease per unit of the resulting product or service. In summary, all those activities to be carried out to achieve substantial energy savings and an improvement in the energy efficiency of a factory can be considered within the energy management systems.

In Cuba, the issue of energy efficiency acquires transcendental importance if you take into account the conditions in the area where the country develops, where the insufficient development of the oil industry, the lack of financing to undertake energy projects and the environment of hostility to which the country has been subjected since the very triumph of the Revolution in 1959.

The project focuses its research activity on the following objectives:

Overall objective:

Perform a method of Energy Management in the Company.

Specific objectives:

Carry out an energy diagnosis of the company. Identify the carriers, areas and equipment that most affect the entity's energy consumption. Identify potential for improving energy and economic efficiency.

Materials and methods

The energy audit or diagnosis constitutes a basic stage, of utmost importance within all the activities included in the organization, monitoring and evaluation of a program for saving and efficient use of energy, which in turn constitutes the fundamental piece in a system energy management. The energy diagnostics or audits allow analyzing the energy situation of the different equipment of an installation, to know how it is purchased, where, how and with what efficiency it is used; In addition, they allow establishing the relative costs of the different forms of energy used, their use and points of inefficiency. The information they provide is essential for establishing energy conservation projects.

Different techniques are used to diagnose energy, evaluating the degree of efficiency with which energy is produced, transformed and used. In one of the stages of the energy diagnosis, the operating conditions in areas, equipment and systems are analyzed to determine their energy efficiency; emphasizing the identification of sources for possible improvement in the use of energy.

Within the auxiliary systems of a technological process, it is said that the electric motors that activate equipment, such as pumps, compressors, fans, blowers, consume approximately 40% of the electrical energy of said industrial facilities. It is for this reason that knowledge, control, and improvement of energy efficiency in this type of equipment are key steps to reduce energy consumption and greenhouse gas emissions (ARPEL Guide No. 32, 2000).

The handling of petroleum products is carried out in the Production, Refining and Distribution facilities, and is complemented by the Transportation process. In the movement of oil and its derivatives from the production or manufacturing points, that is, from the oil fields or refineries to reaching the consumers, it passes through several stages and throughout this process, the pumping systems play a fundamental role; and if their proper functioning is not achieved, the development of the economic activities of the other branches of the economy is put at risk.

Experimental part

By means of a visual inspection, as part of the preliminary diagnosis, the possible energy savings that can be obtained immediately are defined, only with the application of technical-organizational measures or small investments. Applying some mathematical and statistical techniques, the carriers, areas, and equipment with the highest consumption are graphically determined. Subsequently, the technical and energetic functioning of certain equipment is studied in depth; evaluating their behavior. Taking this analysis as a reference, opportunities for improvement are identified and alternative solutions are proposed, evaluating them from a technical-economic point of view, also considering the possible reduction of emissions to the environment;and finally the most feasible variant is selected according to the result of the values obtained for each evaluation indicator.

Energy Characterization of the company:

The first step of this work was the determination of the carriers, the areas and reaching the identification of the equipment that most affects the energy expenditure of the company, to then evaluate some proposals that may lead to the decrease in consumption of each one of these teams.

Based on the data on the annual consumption of energy carriers, it was possible to determine that Diesel and Electricity are the most representative, representing around 84% of the entity's total consumption, within which electricity represents about 20% of the total consumption.

Despite the fact that diesel represents the highest percentage in terms of total consumption, it was decided by the authors, after coordinating with the entity, that in this work, the study of electricity consumption should be studied in depth by considering the existence of energy saving reserves in this regard.

By stratifying electricity consumption by areas, it was found that the area that most affects electricity consumption is the Fuel Tank with about 20% of total consumption, which is why it was decided to study the equipment in depth, seeking savings potentials from technological modifications or changes in operating strategies.

Graphing the electrical consumption of each equipment of the Fuel Tank in a Pareto diagram, it is possible to determine which are the ones that have the greatest impact on the consumption of electrical energy in this area. As a result, it was determined that the consumption of the equipment that makes up the fuel pumping systems represents 89% of the electrical energy consumption in this area, the others are means that operate less frequently or consume low energy levels.

Equipment Electricity Consumption - Fuel Tank

As can be seen in the previous figure, there are four pumps where about 81% of the electricity consumption in this area is concentrated, which are the four pumps in charge of handling diesel, which is at the same time the fuel that is operated the most in the deposit right now.

Taking into account the analysis set out above, this work will focus on evaluating the operation of these seven pumping equipment, all consisting of horizontal centrifugal pumps, with many years of operation, which have never been evaluated from the point of view energy, to determine potential electricity saving potentials and thus contribute to reducing the consumption of energy carriers for the country and improving the environment.

The pumps that will be studied in this research are:

Diesel Discharge Pump No. 1, Diesel Discharge Pump No. 2, Kerosene Discharge Pump, Alcohol Discharge and Charge Pump, Diesel Charge Pump No. 1, Diesel Charge Pump No. 2. Kerosene Loading Pump.

Evaluation of the operation of the pumping equipment:

The pumps currently installed do not have their characteristic curves or other sheet data, so the methodology described by Igor Karassik in his book "Centrifugal Pumps. Operation, Selection and Maintenance ”(1968) based on the physical measurements of the impellers.

Necessary data to be obtained from the installed pump:

D1: Diameter of the Suction Eye (cm).

D2: Impeller Outer Diameter (cm).

W2: Width of the Impeller Discharge Slot (cm).

S2: Blade thickness (cm).

Z2: Number of Blades (units).

n: Number of Revolutions per Minute of the Electric Motor (rpm).

As several pumps were evaluated by this method in the work, Table Curve Windows Version 1.0 software was used as a tool to adjust the correlation of the values that appear in each of the graphs that must be used according to the methodology, thus facilitating the work. and the necessary calculations. After obtaining the equations to which these relationships respond, it is then possible to use Microsoft Excel as a calculation tool. Polynomial equations of up to third order were selected because they were less complex for the calculations and had correlation coefficients greater than 99%.

A total of 92 equations were obtained as a result of the adjustment of the different correlations, distributed as follows:

23 in the adjustment of the figures of the literature used, 48 for the correction of the nominal parameters of the pumps for the working fluids by the variation of the viscosity, and 21 for the obtaining of the characteristic curves of each of the seven pumps evaluated on the job (load, efficiency and power).

Additionally, the graphics that allow the correction of the operating parameters of each of the three existing pump models in the company were obtained, which can be used as a reference for when any liquid with a viscosity other than water is handled with any of them.

The curve of each of the evaluated pumping systems was obtained from the equations used in conventional hydraulic calculations (Bernoulli equations, the Darcy-Weisbach Formula and the Complete Balance of Mechanical Energy). These are defined by the total static load and the pressure losses in the system (dynamic load).

In order to obtain the characteristic curves of the systems associated with each of the pumps, a visual inspection was first made of them to take the necessary data to carry out the corresponding calculations.

Data to be obtained from the pumping system:

∆Z: Total static load, that is, height difference between the product level in Suction and Discharge (m).

L: Length of each pipe section (m).

D: Nominal Diameter of each pipe section (mm).

Accessories: Quantity and type of accessories along each section of pipe (units).

Density (ρ): Density of the product that circulates through the system (kg / m3).

Viscosity (µ): Dynamic Viscosity of the product that circulates through the system (Pa * s).

Flow (Q): Flow of the products through each of the systems (l / min).

A Microsoft Excel Spreadsheet was used to perform the calculations, in which the adjustment of the equations of the graphs used in the calculation of piping systems was also introduced, such as the one used in the correction of the coefficient of friction in turbulent regime (fturb.) as a function of relative roughness (İ). It was developed taking into account up to four sections of pipe in the suction and discharge, and all possible accessories in each section. Data on the physical properties of the manipulated products were obtained from laboratory analyzes and the existing literature.The local resistance values of each of the accessories come from the specialized bibliography and in some cases from those provided by the manufacturers documentation for the specific cases of filters and meter meters.

As the product levels in each system are variable, calculations were carried out for extreme conditions, that is, in case of suction for minimum levels in storage tanks or tank cars and discharge for maximum levels of operation in tanks. storage, and in the loading area the level is constant at the same point. Under these conditions, if the system operates correctly there will be no difficulties when they change and only regulating the flows will suffice. Taking these considerations into account, the calculation procedure previously described was applied to evaluate each of the systems consisting of seven fuel pumps and a total of 28 variants or piping systems.The equations obtained for each system respond to the following model that represents a parabola displaced from the origin:

H = ∆Z + A * Q²

Results obtained

After carrying out the pertinent calculations, it was possible to summarize the operation of the evaluated pumping systems that do not operate efficiently, allowing the following conclusions to be reached:

The two diesel discharge pumps are currently only delivering about 60% of the nominal flow. The kerosene discharge pump currently pumps around 75% of the nominal flow and when tanker trucks are received the flow is further decreased due to the losses introduced in the suction. The flow delivered by the No. 1 Diesel Loading Pump is insufficient for the level of speed required to load this product. The No. 2 Diesel Loading Pump and the Kerosene Loading Pump they are delivering around 70% of the nominal flow.

Identification of improvement opportunities in each of the pumps evaluated:

For the recommended solutions, the possibility of investing in new equipment was taken into account whenever possible, due to the deterioration from the technical point of view of each of these pumps and the importance of each of them for the technological process that they must guarantee..

In the approach of each of the proposed alternatives, the most important pumps for the entity and the operation of the company were taken into account. For this reason, different variants were evaluated that considered the replacement of diesel pumps, which represents more than 80% of the total product handled.

The assessment was made considering the comparison of the current situation against the situation when the pumps are replaced, evaluating the economic benefits obtained through the reduction of operational costs (reduction of operating time, maintenance costs and improvement of the efficiency of the pumping) and environmental equipment that would be generated with the proposed replacement.

Approach, technical-economic evaluation and analysis of the reduction of emissions to the environment of each of the proposed alternatives:

The evaluation of each variant was carried out considering the comparison of the current situation against the situation when the pumps are replaced, evaluating the economic benefits obtained by reducing operating costs (reduction of operating time, maintenance costs and improving the efficiency of the pumping and environmental equipment that would be generated with the proposed replacement. The economic analysis includes the calculation of the NPV, IRR and PRD, in addition to the decrease in CO2 emissions due to the saving of electrical energy.

The alternatives analyzed were the following:

Replacement of the four diesel handling pumps. Replacement of the two pumps used for diesel discharge. Replacement of No. 2 diesel discharge pump and No. 1 used for loading. Replacement of No. 2 diesel pump. diesel discharge.

The economic indicators for each alternative are shown below:

Alternative	Annual Savings (kWh / year)	Annual Savings (%)	PRS (Years)	VAN (CUC)	IRR (%)	PRD (Years)	Emission reduction (t CO ₂ / year)
I	23890.0	51.7	9.3	-7 274.29	8.8	-	25.8
II	18240.0	39.5	6.3	3 374.36	14.8	13	19.7
III	23,720.0	51.3	5.0	9 364.85	19.5	8	25.6
IV	18240.0	39.5	3.3	11 901.21	30.1	4.5	19.7

As observed, from the economic point of view option IV is the most recommended, since the Simple Recovery Period is the lowest, it is the one with which a higher NPV is obtained, has the best Internal Rate of Return and recovers investment in the shortest time. However, it is technically recommended to evaluate proposal III taking into account the technical status of the diesel pumps currently installed, since they require constant monitoring to guarantee the reliability of the distribution in the province and with the application of this alternative, the less new equipment for each operation (loading and unloading); without ruling out the possibility of restoring, when conditions allow, the four diesel handling pumps,Due to the importance they represent for the distribution of this product to customers.

Taking into account that the parameters used to perform the economic calculations may change in the future, in the following figure it is possible to observe the sensitivity analysis of the substitution of the four diesel pumps to the variation of these factors.

Sensitivity analysis of different parameters for the replacement of Diesel pumps

It is observed that for certain values of increased manipulated diesel, increases in fuel price, decrease in the cost of the pump and decrease in the discount rate to a lesser extent, it is possible to undertake the replacement of these four pumps from the economic point of view, with the additional benefit of reducing CO2 emissions to the environment and contribute to reducing the damage caused by greenhouse gases.

Conclusions

The electric consumption of the studied area is mainly determined by seven pumping equipment, which consumes around 87.7% of the electricity, and in turn the four pumps that handle diesel represent 80.8% of the installation's consumption. In the pumping systems evaluated There are six teams that do not operate efficiently. The replacement of the four pumps of greatest importance to the company is not economically feasible under the current conditions and the parameters used for the evaluation. Of the alternatives analyzed, the most technically feasible and economical is the replacement of Diesel Discharge Pump No. 2 and Diesel Charge No. 1, which also guarantee the existence of a new pumping equipment for each operation.

Bibliography

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