When selecting pumping equipment, we should consider whether the suction, lift and water output can meet the design requirements, and whether the hole depth and aperture can meet the requirements of pumping equipment, as well as the handling and cost. For example, in the case of large amount of water, shallow groundwater and reduced depth, centrifugal pumps can be used. Buried depth or depth drop is large, requiring high accuracy. When the well diameter is large enough, use deep well pump or deep well submersible pump. If the accuracy requirement is not high and the well diameter is small, air compressor (or air compressor, air pump, gas-liquid elevator) can be selected. Small well diameter, deep burial and small water inflow, reciprocating pump or jet pump can be used.
(1) air compressor (air pump)
1. Water lifting principle
The pumping principle of the air compressor is: when the air compressor works, compressed air is pressed into the borehole, and the compressed air enters the water pipe evenly through the mixer (a tube with dense holes), and expands outside the mixer to mix with water to form a milky water-gas mixture. Because its specific gravity is lighter than water, driven by the pressure difference between inside and outside the water pipe and the expansion of air flow, it rises to the nozzle and flows out, and the water in the well flows upward to supplement it, thus achieving the purpose of pumping water (Figure 5-2). The amount of compressed air should be appropriate. If the amount of compressed air is insufficient, or the water cannot be pumped, or the water flow is uneven, it will pulsate. If the air volume is too large, the air will flow quickly in the water pipe, occupying a large cross section, which will reduce the water outlet efficiency, and even light air will not come out.
2. Device in the hole
Pumping wells are usually equipped with air pipes, water pipes and sometimes measuring pipes (specially used for measuring water level). Its basic installation method is concentric and parallel (Figure 5-3a, B). Concentric type is suitable for smaller aperture, but its water inflow is parallel or larger than the same aperture, because its water outlet area is larger. The parallel type is suitable for larger aperture, and the parallel installation has higher pumping efficiency and less gas demand. When the aquifer is buried deeply, and some confined aquifers or incomplete wells pump water, the pipeline above the well wall or filter can be used as a water pipe (Figure 5-3c) to supply gas between the water pipe and the well wall pipeline to increase the water outlet section (Figure 5-3d). Although these devices are different, they are still concentric or parallel in nature.
Figure 5-2 Schematic Diagram of Pumping Installation of Air Compressor
1-air duct; 2- outlet pipe; 3- mixer; 4— Shaft lining pipe; A- natural water level; B- dynamic water level; H—— the depth to which the mixer sinks below the dynamic water level (sinking depth); H refers to the height (lift) from the dynamic water level to the outlet; H0 —— the elevation from the natural water level to the outlet.
Figure 5-3 Schematic diagram of air compressor pump air supply duct installation
Concentric; (b) parallel type; (c) use perforated wall pipes as water pipes; (d) winding the pipeline by using the gap between the water pipe and the tunnel wall pipe.
1-air duct; 2- water pipe; 3— Bored pipe or filter pipe; 4- Water measuring tube; 5- mixer
If the water surface is buried too deep or the water level difference is too large, for example, when the dynamic water level is more than 100 m from the water surface, two air compressors can be used to pump water in relay.
The diameters of air duct and water pipe should also match. If the diameter of the water pipe is too small, the water output will be too small; The diameter of the water pipe is too large, and the water is uneven, or even can't be pumped (please refer to the relevant manual for the size matching between the two). In addition, the gap between the water pipe and the filter is too small, which is easy to increase well loss and affect the movement of water into the well. The water measuring tube should be thin so that it can be put into the water level gauge.
3. Calculation of relevant data
The efficiency of air compressor and the normal operation of pumping water largely depend on the sinking ratio. In order to choose a suitable air compressor, it is necessary to calculate the air supply and starting pressure.
(1) Sinking ratio: the depth at which the mixer sinks below the dynamic water level is called the sinking depth (h), the height from the dynamic water level to the outlet is called the head (h), the distance from the center of the mixer to the outlet is called the lifting height (H+h) (Figure 5-2), and the ratio of the sinking depth to the lifting height is called the sinking ratio (α), namely:
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The larger the sinking ratio is, the higher the efficiency is, and the smaller the air volume (i.e. the specific consumption value of gas and water) required to increase the unit water volume is. However, the larger α is, the greater the starting pressure is, which is limited by the pressure of the air compressor. Therefore, α is usually required to be 50% ~ 60%. If multi-stage mixers are used (several mixers are connected in series), α can be as low as 30%. The optimum depth of the air duct can be found in the hydrogeology manual.
(2) Calculation of air volume: the compressed air volume V0(m3) required for each lifting of 1m3 water is:
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Where k is an empirical number, which can be calculated as K=2. 17+0.0 16h, and it is an empirical kernel positive number for the above formula based on ideal gas.
When the water output is Q(m3/h), the required air volume Vn(m3/min) is:
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(3) Calculation of starting pressure (P0) during pumping;
P0 = P+δP≈0. 1(H+H-h0+2)(5-4)
Where: p is the hydrostatic pressure (PA) from the middle of the mixer to the natural water level; Δ p is the resistance of air duct, which is generally1.96×104 pa; H0 is the height (m) from the natural water level to the outlet.
The calculation formula of working wind pressure during pumping is:
Pn=0. 1(H+LP) (5-5)
Where: Pn is the working wind pressure (PA); LP is the pressure loss (converted into meters) during water supply, which is not more than 5, generally 2 ~ 3.
(2) Water pump
Pumps commonly used in pumping test mainly include centrifugal pump, deep well pump, submersible pump and jet pump.
(1) Centrifugal pump: Centrifugal pump works by using the centrifugal force generated by water when the impeller rotates. The device of centrifugal pump is mainly composed of pump shell, pump shaft, impeller, suction pipe and discharge pipe. Centrifugal pumps can be divided into single-stage single-suction centrifugal pumps, single-stage double-suction centrifugal pumps and segmented multistage pumps. Centrifugal pump is the most widely used. The suction range of centrifugal pump is theoretically 10m, but it is actually 7 ~ 9m due to the head loss when water flows in the suction pipe. Before starting the centrifugal pump, the pump housing and suction pipe must be filled with water before driving the motor.
(2) Deep well pump: it is a vertical pump that pumps groundwater from deep wells. Generally, it consists of three parts: filter screen, suction pipe and pump body, lifting pipe and transmission shaft, pump seat and motor. The first two parts are located underground, and the latter part is located on the well. Deep well pumps are usually multi-stage impellers. The more stages, the greater the lift. The lift of some deep well pumps exceeds 100 meter. ..
(3) Submersible pump: It is a kind of pump that integrates a pump and a motor and is immersed in water for lifting and conveying water. Because the submersible pump runs underwater, the submersible motor should have a special structure. The working part of submersible pump is generally a vertical single-suction multi-stage shunt centrifugal pump, and its basic structure is similar to that of deep well pump. Submersible pumps can be divided into deep well submersible pump and working face submersible pumps according to their different applications. Compared with deep well pump, deep well submersible pump has the advantages of light weight, low noise and simple installation and maintenance, and has been widely used in recent years.
(4) Jet pump: using the energy of high-speed water flow to transport water. After the water flow of the reciprocating pump equipped with the drilling rig passes through the drill pipe (water inlet pipe), the light beam sprayed by the nozzle generates negative pressure around it, which attracts the surrounding well water and flows into the injector facing the nozzle together. Well water is replenished through the intake hole, which is the water absorption process of the jet pump. The water flowing through the BOP is forced to flow into the outlet pipe from the outlet hole due to the continuous high pressure impact of the flow velocity, and rises with the circulating water to be discharged from the surface to complete the pumping function. Because the energy of lifting groundwater is provided by the pressure potential energy of the feed pump, its pumping elevation is limited by the pressure of the feed pump, and the pumping quantity is also determined by the pumping quantity.