ОПТИМИЗАЦИЯ РЕЖИМОВ РАБОТЫ НАСОСНЫХ СТАНЦИЙ, ОСНАЩЁННЫХ ПАРАЛЛЕЛЬНО РАБОТАЮЩИМИ ЦЕНТРОБЕЖНЫМИ НАСОСАМИ

УДК 532.54 

Abstract

This article examines the reduction of hydraulic head losses and optimization of electricity consumption in pumping stations equipped with pumps operating in parallel. The study focuses on improving energy efficiency by minimizing hydraulic resistance and selecting the economically optimal pipeline diameter. A combined hydraulic and economic approach is proposed to assess system performance under different pipeline configurations. The operation of three D1600–90 centrifugal pumps connected in parallel is analyzed, considering the effects of pipeline diameter on flow velocity, friction losses, energy consumption, and overall efficiency. Both capital investment costs and long-term operating expenses are evaluated. The results show that larger pipeline diameters reduce hydraulic losses, improve pump operating conditions, and increase system efficiency. Although initial construction costs rise, lower electricity consumption provides significant long-term savings. Comparative calculations identify the most cost-effective pipeline diameter, balancing investment and operating costs. The proposed approach can be applied to the design and modernization of pumping stations to improve reliability, energy efficiency, and sustainability.

Аннотация

В статье рассматриваются вопросы снижения гидравлических потерь напора и оптимизации потребления электроэнергии на насосных станциях с параллельно работающими насосами. Основное внимание уделено повышению энергоэффективности за счёт уменьшения гидравлического сопротивления и выбора экономически оптимального диаметра трубопровода. Предложен комплексный гидравлический и экономический подход к оценке работы системы при различных диаметрах трубопроводов. Исследована работа трёх центробежных насосов Д1600–90, соединённых параллельно, с учётом влияния диаметра трубопровода на скорость потока, потери на трение, энергопотребление и общую эффективность системы. Проанализированы капитальные затраты и эксплуатационные расходы. Результаты показывают, что увеличение диаметра трубопровода снижает гидравлические потери, улучшает условия работы насосов и повышает эффективность системы. Определён наиболее экономически выгодный диаметр трубопровода, обеспечивающий баланс между инвестиционными и эксплуатационными затратами.

Keywords: pumping station, parallel-operated pumps, head loss, hydraulic resistance, pipe diameter, energy efficiency, optimal operating mode, electricity consumption.

Ключевые слова: насосная станция, параллельно работающие насосы, потери напора, гидравлическое сопротивление, диаметр трубопровода, энергоэффективность, оптимальный режим работы, потребление электроэнергии.

Introduction

Currently, in the Republic of Uzbekistan, 48% of the 1,687 operating pumping stations are equipped to allow parallel operation of pumps (i.e., multiple pumps simultaneously supplying water to a single pressure pipeline) [1]. Although operating multiple pumps on a single pressure pipeline can reduce costs associated with large-diameter pipelines, this mode of operation results in increased electricity consumption due to head losses. To prevent this, the operation of pumping stations must be optimized by selecting pumps appropriately, adjusting their operating modes, and choosing the optimal diameters of internal pressure pipelines, including pipes and check valves.

The optimization of operating modes for parallel-operated pumps (i.e., multiple pumps operating simultaneously on a single pressure pipeline) is carried out using two approaches: improving the hydraulic characteristics of the pipeline system and adjusting the operating modes of the pumps [2, 3].

Minimizing head losses in parallel pump operation is an important issue, as the parallel operation of pumps serves to increase the supplied water volume, while head losses can significantly reduce the efficiency of water delivery. Therefore, this issue must be addressed together with the determination of the pumps’ optimal operating modes.

Main Body. The energy expended to overcome the hydraulic resistances in the pipeline system can be determined using the following equation [2, 3].

       (1)

where, – local resistance coefficients in the pipeline, L_pipe, D_pipe.i – the length and diameter of the pipe, Т – the operating time of the pump on the pipeline, in hours, and λ – the hydraulic coefficient of the pip.

This equation can be simplified and written in the following form.

                                            (2)

where

The negative effect of head losses in the pipeline system of parallel-operated pumps on operating efficiency can be observed from the pump operating schedule shown in Figure 1.

When the pumps operate at the overall working point A1, their characteristics are determined at points 1, 2, and 3. It can be seen that the pumps, with the exception of pump 3, operate outside the optimal working range and have low efficiency values. If measures are taken to reduce the head loss  in the pipeline system, the overall working point of the pumps shifts to point A2, and their characteristics are then determined at points 4, 5, and 6. In this case, it can be observed from the graphs that all three pumps operate within their optimal working range, and their efficiency values are higher.

Figure 1. Effect of head loss on the operating mode of parallel-operated pumps

From the above equation (2), it can be seen that the value of  depends on the hydraulic resistances and the pipe diameter. That is, to reduce the energy wasted, it is necessary to increase the pipe diameter and decrease hydraulic resistances. However, selecting an excessively large pipe diameter increases its capital costs, making the use of such a pipe economically unjustified. Taking this into account, the economically optimal diameter of the pipe and the equipment and fittings installed in it can be determined based on the minimum of the total costs, calculated using the following equation.

PC_i = CE_i(d + c + r) + t_e· → min                             (3)

where, PC_i – annual costs per 1 meter of pipe, CE_i - costs for purchasing and installing 1 meter of pipe, d – discount rate used for financing the pipe construction, ccc – depreciation allowance, c – depreciation allowance,  r – current maintenance costs, and, t_e – electricity tariff.

The above equation (3) is used to determine the minimum of PC​. This involves calculating capital and operational costs for various pipe diameters at a constant water flow rate and selecting the diameter that corresponds to the minimum total costs.

Based on this methodology, calculations are presented for optimizing the parallel operation of three D1600–90 pumps (pipe diameter = 540 mm, n =1450 rpm) to ensure minimal energy losses and determine the economic efficiency of the system.

For the calculations, the pipe length is taken as L_pipe = 1.0 m, and the pipe roughness coefficient is 0.012. The total water delivery capacity of the three pumps is Q_{total ​} = 1.02…1.36 m³/s, with head varying in the range Н = 88.5…96.7 m.

The operating time of the pumps is Т = 1500 hours, and the electricity tariff is assumed to be t_e = 1000 UZS/kWh.

The calculations are carried out using equations (2) and (3).

The indicators for calculating PC_i are determined in the following order.

The capital costs for the pipes, СЕ_i, are taken based on the prices in effect in the Republic of Uzbekistan in 2024. These values are adopted according to information from the construction portal Stroyka.uz, which provides prices for pipes from Metall Asia LLC [4].

 Annual investment payments for capital funds may include bank interest, investor-required returns, discount rates, and other forms. Currently, these payments range widely from 8% to 25%, with most values between 10% and 15% [2, 5]. Therefore, the value of  d is taken as 0.12.

The normative amounts of depreciation allocations for depreciation expenses are accepted as  с = 8 %   based on the depreciation expenses implemented in the Republic of Uzbekistan in 2022 [2, 6].

The allocations for current maintenance costs are accepted as r = 7 %  according to another applicable regulatory document [2, 6].

The results of the calculations are presented in Table 1.

Among the four options considered in the calculations, the option with a pipe diameter of 900 mm shows the lowest costs. However, in the case of a 1000 mm diameter, although the capital costs are slightly higher, the amount of lost electrical energy is lower. Therefore, if this option meets the investment conditions, it is advisable to select it.

Table 1. Determination of Optimal Parameters in Parallel Pump Operation

ased on the calculations presented above, the operating graph of the parallel operation of three D1600–90 pumps (pipe diametr = 540 mm, n = 1450 rpm, ΣL_pipe=2800 m) and the head characteristics of the pipeline system for various options are constructed to determine the pump parameters (Figure 2).

Figure 2. Determination of the operating mode of parallel-operated D1600–90 pumps in pressure pipelines of different diameters

Based on these graphs, the amount of electrical energy consumed to deliver the same water volume V = 8,000,000 m³ over the season is calculated for two options, with pressure pipe diameters of D = 900 mm and D =1000 mm.

In this case, the values of Н and η are obtained at the coordinates of the operating points where the pump head characteristics intersect with the head characteristics of the pressure pipelines for D = 900 mm and D = 1000 mm. 

Conclusion

Thus, the difference amounts to 98,069 kWh, which, assuming the current electricity tariff of 1,000 UZS/kWh, corresponds to no less than 98 million UZS.

For all variations in water consumption, the volume of water supplied by the pumps should be Q_i = Q_req.i ​, and the efficiency values (η) must be at their maximum.

References:

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