At present, some small and medium-sized steel plants and other metallurgical processing plants are still using liquid fuels without gaseous fuels (such as coal gas). The most widely used liquid fuel is heavy oil. For example, during the transportation and combustion process of heavy oil in the heating furnace combustion system, choosing a suitable pump unit is very important for the normal operation of the furnace.
Because the normal operating viscosity of heavy oil is generally relatively high (above 50×102-6m2/s at 80°C), its viscosity changes greatly with changes in temperature. This requires that we should choose the appropriate pump type to adapt to the transportation of these media so that it can operate stably and without failure. Especially for the injection of heavy oil, it is very important to keep the delivery pressure of the pump unit constant. According to the survey, most users still use external gear pumps (called gear pumps). In fact, there are more advantages if G-type screw pump is used in these systems.
1. G-type screw pump can work without pulsation
When the G-type screw pump is working, it is smoothly transported from the low-pressure area to the high-pressure area through the sealed chambers formed between the screw rotor and the hole wall of the pump sleeve. During the entire transportation process, the medium moves purely axially and can be completely to transport media without pulsation. This is different from gear pumps. When the gear pump is working, under the rotation of the gear, the medium moves in the axial, radial and composite directions, resulting in obvious stirring phenomena. The expression of its output pressure: the output pressure of the G-type screw pump is relatively stable, while the outlet pressure of the gear pump will fluctuate. This is more prominent when transporting high-viscosity media (such as heavy oil, etc.).
Now we will use the G-type single screw pump and gear pump of the same specifications on site to make a simple comparison under the same working conditions and when the delivery outlet pressure is 1 MPa, and measure these two sets of data.
When transporting heavy oil with a viscosity of about 75×102-6m2/s, the pointer jump range of the gear pump outlet pressure gauge is ±0.16, the pointer jump range of the three-screw pump outlet pressure gauge is ±0.05, and the pointer jump range of the twin-screw pump outlet pressure gauge is ±0.05. The amplitude of the beat is ±0.04.
When transporting heavy oil with a viscosity of about 150×102-6m2/s, the pointer jump amplitude of the gear pump outlet pressure gauge is ±0.22, the pointer jump amplitude of the three-screw pump outlet pressure gauge is ±0.06, and the double-G single-screw pump The pointer jump amplitude of the outlet pressure gauge is ±0.04. This shows that the medium delivery pressure of the G-type screw pump is very stable during the delivery and combustion process of heavy oil. And as the viscosity of the medium increases, the pulsation-free characteristics of the G-type screw pump (especially the twin-screw pump) become more obvious in comparison.
2. Service life of G-type screw pump
Whether it is a screw pump or a gear pump, the wear of the teeth is the most important factor that determines its life. Because tooth wear will lead to a significant decrease in flow rate and reduced efficiency. During the long-term investigation, it was found that the service life of the gear pump in continuous operation in the heavy oil transportation and combustion system is about 3 to 6 months, while the service life of the G-type screw pump is basically more than 1 year.
After investigation and consultation with relevant pump manufacturers about the processing and production processes, and multiple comparisons, it can be basically ruled out that the above differences are caused by the material of the rotor and its heat treatment. It is believed that the main reason is that, in addition to the above-mentioned G-type screw pump working smoothly without pulsation, the G-type screw pump is not sensitive to changes in the viscosity of the medium during operation, and the internal mechanical loss of the pump caused by small mechanical vibration during operation Small and other factors are directly related.
At the same time, statistics were made on the usage of gear pumps and G-type screw pumps in the heavy oil transportation and combustion system of a steel pipe factory. The usage conditions are continuous working systems. For gear pumps, the average service life was 4 months in 1999 and 4.5 months in 2000. After switching to the G-type screw pump in 2001, except for one seal damage and replacement of the seal in two years, there has been no problem of obvious tooth wear and scrapping.
3. G-type screw pump is used in the main rolling mill lubrication system
In a steel rolling mill, whether the lubrication system of the gearbox of the main rolling mill unit works stably and reliably affects the entire rolling production process. In the past, many factories used gear pumps. In the past two years, more and more factories have adopted G-type screw pumps. Because the use of G-type screw pumps for lubrication systems has the following advantages:
(1) A correctly used G-type screw pump unit has the characteristics of small vibration and low noise level.
There are many factors that cause vibration and noise in the pump unit. Under the same operating conditions, the vibration and noise levels of the G-type screw pump unit are lower than those of the gear pump unit.
For example, a vibration speed sensor is used to test the vibration of the unit. The test conditions are exactly the same. The test medium is hydraulic oil at 9×102-6m2/s. The displacement of the pump is 67mL/r. The rotation speed of the screw and gear rotor is changed. Vibration conditions of G-type single screw pump and gear pump. Similarly, use a noise meter to measure the noise level.
(2) The G-type screw pump can achieve a long working time without aggravating the emulsification of the conveyed medium.
The hydraulic system has strict requirements on the anti-emulsification performance of the working medium. When using a gear pump, because the gear pump will stir the working medium, the water in the oil can easily form an emulsion with the oil, making the oil-prone to sediment and reducing the lubrication of the oil. performance. The G-type screw pump performs pure axial movement when transporting the medium, which is smooth and pulsation-free. It does not stir the medium, so it will not aggravate the emulsification of the working medium for a long time.
