(1) Test purpose
In recent years, people have gradually realized that the experimental work is very important for the design of slurry tubes and troughs. At present, there are many calculation formulas for slurry pipe and trough hydraulic transmission at home and abroad, but they are all derived from experiments under certain conditions. There are great limitations in use, and some formulas calculate results. Partially safe, individual formulas may even result in a large gap with the actual situation. Therefore, for slurry pipeline transportation, especially long-distance slurry pipeline transportation, the necessary design parameters and recommended feasible are obtained through experiments. Calculate the formula.
(1) There are three main problems to be solved in the pipeline hydraulic transmission test:
1) Study the physicochemical properties of the slurry and find the ideal delivery conditions;
2) Study the law and characteristics of solid particle sedimentation in pulp;
3) Look for measures to reduce the abrasion of solid particles on equipment and pipelines.
The purpose of testing high-concentration pulp (homogeneous slurry) and low-concentration slurry (non-homogeneous slurry) is not exactly the same. Low-concentration pulp needs to be solved by selecting the slurry flow rate that can ensure safe production; while high-concentration pulp needs to explore the ideal conveying conditions. For the study of the sedimentation law of solid particles, high-concentration pulp is only to understand whether it is difficult for the system to restart when the conveyor system is shut down for some reason; and the sinking speed (hydraulic thickness) is The important factors affecting the ease of transport of low-concentration pulp, the empirical formulas of many low-concentration slurry streams in the world are almost always a function of the critical flow rate and hydraulic gradient as a function of solid particle sinking speed.
(2) The purpose of the slurry pipeline hydraulic transport test can be summarized as follows:
1) For concentrate:
Determine the optimal particle size composition, optimum transport concentration, and other conditions that are conducive to transport; propose design parameters such as critical flow rate, head loss, or recommended formulas for calculating these parameters; explore possible discontinuities in the overall delivery system shutdown Problems and preventive measures.
2) For tailings:
Find the range of the drag reduction zone of the slurry and the conditions for forming the drag reduction zone; propose design parameters such as critical flow velocity and head loss, or recommend the formula for calculating the values ​​of these parameters; when the tailings are transported at high concentration, it is necessary to propose a shutdown and restart. Possible problems and preventive measures. [next]
(2) Test content
A Basic data (1) Density of pellets (δ g ): refers to the weight per unit volume of the pellets in the slurry in a compact state (excluding pores). The unit is gram/cm 3 or ton/m 3 .
(2) Granularity grading of pellets: The more common methods of particle size analysis are standard sieve sieving and sedimentation analysis. The results of the analysis are plotted as a particle grading curve (Figure 1) or a particle size composition table. The weighted average particle diameter (d p ), the median diameter, and the content of the particles smaller than (or greater than) a predetermined particle size are determined. Its calculation unit is "mm".
(3) Chemical composition analysis of materials: The purpose of the analysis is mainly to understand whether there are any unfavorable components (such as CaO) in the slurry and the possibility of changes in the properties of the slurry during the transportation process. The results of the analysis are the basis for determining the reasonable transport concentration and the basis for the study of which harmful components should be removed. Chemical composition analysis is divided into two parts: qualitative and quantitative. [next]
B. Properties of slurry material properties (1) Rheological properties of slurry: It is mainly to explore the conditions under which the slurry can meet the shear stress and shear velocity relationship of Newtonian or Bingham fluid. The specific method is to select several kinds of solid particle size grading (the tailings only have one gradation), and respectively use the slurry with different particle size grading to carry out the rheological property test. The main tool for the test is a viscometer calibrated with water. The rheological rheological test results of the same temperature, the same particle size gradation and different concentrations are plotted as the T w -8υ/D curve, ie the slurry imaginary rheological curve (Fig. 2). One pass through the origin (ie T B ) is selected in the graph. =0) The curve with the highest concentration is the boundary between the Newtonian and Bingham type fluids. The slurry larger than this concentration is the Bingham type fluid flow type, and the smaller one is the Newtonian flow type. At the same time, it is necessary to determine the μ' (viscosity coefficient), T B (Binhan type fluid ultimate shearing force), η (stiffness coefficient) and other parameters of different concentrations of slurry (Fig. 3). The particle size composition and concentration range.
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