*3.5. Electricity Consumption in the Hydromixture Transport*

As a result of the deflocculant addition, an economic effect was achieved by the reduction of electricity consumption when pumping the hydromixture in a pipeline. In order to determine the obtained economic effect, the power at the pump shaft (*Pw*) required to pump the hydromixture was calculated using the equation:

$$P\_w = \frac{Q\_v \cdot \Delta p}{\eta} \tag{14}$$

where *Qv* is the volumetric flow rate and *η* is the pump efficiency.

According to data acquired from the manufacturer of the equipment used in the production plant, the pump efficiency is 62%.

Knowing the pump motor efficiency of *η<sup>S</sup>* = 93.6%, the power consumption of the motor driving the pump (*PS*) can be expressed as:

$$P\_s = \frac{P\_w}{\eta\_s} \tag{15}$$

Assuming the constancy of the transported solid particles equal 27 t in the transport of hydromixtures with higher than 21.30% mass concentrations, the volumetric flow rates decrease and equal 80 m3/h for a hydromixture with a mass concentration of 28.14%, 61 m3/h for a hydromixture with a mass concentration of 35.00%, 48 m3/h for a hydromixture with a mass concentration of 42.75%, and 38 m3/h for a hydromixture with a mass concentration of 50.00%, respectively.

A decrease in the viscosity of hydromixture was achieved as the result of deflocculant addition, which can be observed in the flow curves of hydromixtures shown in Figure 3. Transport of hydromixture with a smaller volumetric flow rate but the same amount of solids is possible. This results in a significant decrease of energy consumption during the transportation of such hydromixtures compared to transportation of base hydromixture, with the mass concentration of 21.30%, which is presented in Table 4.

**Table 4.** Power consumption of the electric motor driving the centrifugal pump.


Figure 5 presents the electricity consumption during pumping of the hydromixture with the addition of deflocculant as a function of the mass concentration of the hydromixture. The maximum energy savings is 58% over the transport of basic hydromixture with the concentration of 21.30% by mass.

**Figure 5.** The electricity consumption during pumping of the hydromixture.

#### **4. Discussion**

The basis for the calculation of the pressure drop during the transportation of hydromixture in a pipeline is a determination of the rheological properties of tested hydromixtures.

The results of rheological behaviour measurements of hydromixture with different mass concentrations were described by the Bingham plastics model in the shear rate range from about 8–10 s−<sup>1</sup> to 100 s−<sup>1</sup> with high accuracy (98–99%), which confirms that the studied hydromixtures were shear-thinning non-Newtonian fluids with a yield stress. For all the tested hydromixtures, decreases in viscosity with increasing shear rate were observed.

Calculations of the friction factors of the analyzed hydromixtures in a 200 mm diameter pipeline was performed using Equations (5), (7) and (9). The friction factor values in the range of laminar flow calculated from Equations (5) and (9) were almost identical. Similarly, the friction factor values for the turbulent flow of non-Newtonian liquid calculated from Equations (7) and (9) were also very similar. In the paper, the possibility of friction factor calculating for non-Newtonian fluids in large diameter pipelines in turbulent flow using both Equations (7) and (9) is confirmed. The calculated friction factors of the hydromixtures in a pipeline of 200 mm diameter and 632 m length confirmed that the addition of deflocculant affects the reduction of friction factors for all the analyzed hydromixtures. Therefore, it was possible to pump hydromixtures with higher solids concentrations, resulting in significant energy savings in their hydrotransport and reduced water consumption in the limestone hydromixture transport process.

The positive effect of using a deflocculant in the transport of the hydromixture occurring in the analyzed pipeline has an influence on the increase in the efficiency of the whole production process. The additional effect that increases the efficiency of the hydromixture transport process is the reduction of the amount of water used in the pumping process, which improves environmental protection by reducing the amount of burdensome slurry. As a result, the estimated operating cost of the industrial installation of hydromixture transportation in a pipeline is significantly reduced.
