2) Change the impeller diameter:
The performance change of the pump impeller after initial cutting is best determined according to the specific experimental data. It can also be calculated by referring to the following method, but the cutting amount must not exceed 20%.
Where D 1 and D 2 ——— are the diameter of the impeller before and after cutting.
Other symbols are the same as before.
(10) Determination of flow and lift of water seal pump:
Most slurry pumps require water to be supplied with water. When the water pressure of the external water supply pipe cannot meet the requirements, a water seal pressure pump is required. The flow rate of the pump is generally 1 to 2% of the slurry volume (a small pump takes a small value; a small pump takes a large value). The pump head can be Determine by the following formula:
H ƒ =H s δ K +H c +h g +h j (18)
Where H Æ’ --- the head of the water seal pump, m;
H s ——— the clear water head of the slurry pump on the sample, m;
δ K ———the density of the pulp, t/m 3 ;
H c ———Requires water seal water pressure value, generally 196kPa (2kg/cm 2 );
h g ———Water seal water supply pipe along the head loss, m;
h j ——— partial head loss of water seal water supply pipe, m.
(11) Series operation of centrifugal slurry pumps:
In order to effectively utilize water pressure and facilitate management, the slurry pumps are often operated in series. This arrangement has become more widely used as the allowable pressure of the pump has increased. At present, most of the series working pumps are 2 to 3, and the characteristic curves of the front and rear single pumps are basically the same or similar. It is relatively rare to have multiple slurry pumps or pumps with different performances in series. Because the number of pumps in series is too large or the performance difference of single-stage pumps is too large, there will be a lot of trouble in production management, especially in the starting mode and the speed regulation of the pump, a series of adaptation measures should be considered.
The selection of the series pump operating conditions is mainly obtained by superimposing the single-stage pump performance curve (Q--H curve) (Fig. 1). The intersection of the pipeline characteristic curve and the series pump performance curve is the operating point of the series pump.
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It should be noted that when the multi-stage pumps are connected in series, the pressure inside the pump must be gradually increased, the bearing life of the bracket will be affected to some extent, and the over-current components will also accelerate the wear. Therefore, when it is proposed to use a multi-stage pump in series, it needs to be carefully considered.
When the series working pump is started, since the pipeline starts to be empty, if the slurry is directly input into the pipe, the instantaneous flow rate will be too large due to the small resistance, and the cavitation of the pump and the motor overload (the long-distance transmission pipe are more obvious). ), so the water should be transported before being sent to the slurry, and the slurry should be transported after the whole system is running normally. At the same time, starting from the first stage pump should be started step by step to ensure smooth operation.
In the long-distance slurry transportation, considering the change of the actual working conditions and the error of the selection calculation, the hydraulic coupling, the thyristor speed regulation, the frequency conversion speed regulation and the like should generally be adopted. The speed control device is mostly installed in the first stage pump or the last stage pump. Installed in the first stage pump can avoid cavitation or motor overload caused by small pipe resistance and large flow at startup; installed in the final stage pump can balance the work of the piping system. As for which stage pump is most reasonable, it should be based on the specific characteristics or needs of the user.
B Reciprocating mud pump a Reciprocating mud pump in long-distance pipeline transportation The most commonly used reciprocating mud pumps in the world are oil-isolated mud pumps, single-acting three-cylinder piston pumps, double-acting piston pumps, diaphragm pumps, etc. Four types. These pumps belong to a positive displacement pump, easy to form a high pressure, the maximum pressure up to 9810 kPa (100 kg / cm 3). At the same time, it also has the advantage that it is not easy to block. Therefore, at present, the long-distance and high-concentration slurry pipelines in the world mostly use reciprocating mud pumps as the main pressing equipment. Such pumps are not very common drawback displacement, generally in the 3/200 meters, however, GEHO piston diaphragm pumps type emerged in recent years the international community has to break this situation, the displacement will increase to 700 m 3 / Around. To name a few long-distance pipeline using a reciprocating mud Examples of metal slurry.
The reciprocating mud pumps currently used for slurry pipeline transportation in China are mainly oil-isolated mud pumps. There are not many examples of domestic use of other types of reciprocating mud pumps. Therefore, only the requirements for oil isolation mud pump selection are introduced here.
b Oil isolation mud pump model and main performance Oil isolation mud pump is mainly used for conveying tailings, concentrates and coal with particle size ≤1 mm, concentration ≤60～65%, temperature ≤80～100°C, pH value 6～8 densities of various powder or slurry ash, bauxite ...... like. The main manufacturers of oil-isolated mud pumps in China include Guangzhou Heavy Machinery Plant, Dalian 523 Factory, Benxi Water Pump Factory and Sichuan Air Compressor Factory. However, various manufacturers have not formed a series of production.
c Selection method of oil isolation mud pump The working pressure of oil isolation mud pump is generally large, and the flow rate is small, so it is often necessary to work in parallel. Oil-isolated mud pumps are rare because of insufficient pressure, but sometimes they also occur. In this case, there should be a slurry bin between the pumps. The main calculation steps for selecting an oil isolation mud pump are as follows:
(1) Ascent:
Q b =KQ x (19)
Where Q b ———the flow rate of the pump, m 3 /h;
Q x ———the amount of pulp, m 3 /h;
K———flow fluctuation coefficient; generally used 1.05~1.1.[next]
(2) Working pressure of the pump:
Where p b ———the rated pressure of the pump, kPa;
H x ———the total lift of the transport slurry, m;
H———the geometric height difference of the slurry delivery, m;
δ K ——— pulp density, t/m 3 ;
L———transport tube length, m;
i k ———pipe unit head loss, mm;
h j ——— local head loss of the pipeline, generally 10% of Li k ;
h n ———The head loss in the pumping station is generally 2~3m;
h y ———The remaining head of the pipeline, generally takes 1~2m;
9.81—The value of each kg/cm 2 is converted to the value of kPa.
(3) Motor power:
Where N———motor power, KW;
K———Motor power reserve coefficient, generally 1.05~1.1, large motor takes small value, small motor takes large value;
Q b ——— pump constant flow, L/s;
H x ———the total lift of the slurry pump, m;
η V ———The volumetric efficiency of the pump is generally 0.88~0.95;
η j ———The total mechanical efficiency, generally 0.94.[next]
(4) Reserve amount of pump:
D air chamber selection and effective volume calculation
In order to stabilize the oil isolation mud pump, an air chamber is generally installed on the extrusion pipe, which can stabilize the discharge amount of the pump and the working pressure. At the same time, it can also eliminate the violent vibration of equipment and pipelines that occur during work. When the suction pipe is too long, in order to eliminate cavitation and reduce the inertia resistance of the pipeline, an air chamber should be added to the suction pipe. Commonly used air chambers are cylindrical (Fig. 2) and spherical (Fig. 3). The spherical air chamber is smaller than the cylindrical air chamber, but there are disadvantages such as large pressure fluctuation in the cylinder, strong noise, and easy aging of the skin. Therefore, a cylindrical air chamber is generally used. The effective volume of the air chamber is calculated as follows:
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