The oil and gas storage and transportation company’s main business is pipeline transportation of crude oil and natural gas, and it undertakes the oil and gas transportation task produced by Xinjiang Oilfield Company. In recent years, the proportion of heavy oil produced by Xinjiang Oilfield Company has increased year by year. The proportion of thick and thin oil has risen to about 55%, and with the continuous development of oilfields, the proportion of heavy oil will continue to increase. The existing oil transportation equipment (DKS centrifugal pump, 200D centrifugal pump) has been unable to meet the delivery task of high-viscosity oil, mainly reflected in the low efficiency of the pump and high energy consumption. For this reason, the oil and gas storage and transportation company began to test the three-screw pump at the 703 pumping station in 1999. After reliability evaluation and pump efficiency test, the three-screw pump was selected as the pumping station for the Ke-Wu line and other high-viscosity crude oil pumping stations. The export pump has achieved a remarkable energy-saving effect. At present, the company has promoted and applied it in stations 701, 702, 703, 704, 705, 706, Hongqian, 91# and 92#.
1. The principle and characteristics of the screw pump
At present, the company mainly adopts SNHG-type three-screw pump and HPW-type twin-screw pump, and its working principle is as follows:
1) Three-screw pump
Its interior is mainly composed of a driving screw, two driven screws and a bush containing three screws to form a sealed cavity. The liquid in the cavity moves axially with the rotation of the screw to achieve the purpose of transporting the liquid. The special structure of the pump ensures that the main and slave rods are not affected by the axial force. The axial force is hydraulically balanced. The bearing only bears the self-weight of the screw and a small residual axial force. balance the axial force, and used as a lubricating bearing), the geometry of the screw ensures that no torque is transmitted from the main rod to the slave rod, and the driven rod is rotated by the pressure of the conveying liquid, thus ensuring that the three-screw has a long service life and high mechanical efficiency, perfect linear design and processing technology, make each sealing chamber completely separated, thus having high volumetric efficiency.
2) Twin screw pump
It mainly consists of a driving screw, a driven screw and a bush containing the two screws to form a sealed cavity. The liquid in the cavity moves axially with the rotation of the screw to achieve the purpose of transporting the liquid. The distance between the two screws is very small. Small, not in contact with each other, the driving screw transmits torque to the driven screw through an external synchronous gear.
The screw pump has the stable operation of a centrifugal pump and has no noise (only the sound of the motor is heard), no auxiliary equipment such as water cooling, no oil leakage, and no waste oil recovery device; in addition, the screw pump has the efficiency of a positive displacement pump It has the characteristics of high pressure, pressure change and constant displacement (constant speed), and also has many advantages such as fewer leakage points, less maintenance, low maintenance cost, and short maintenance time.
2. Energy saving effect and monitoring unit
The oil and gas storage and transportation company asked the China National Petroleum Corporation Northwest Energy Conservation Monitoring Center to test the screw pump installed in the 703 pumping station. When transporting oil with a thick-to-thin ratio of 50%, the pump efficiency of the screw pump can reach up to 85.7%, which is 33.8 percentage points higher than the pump efficiency of the 200D centrifugal pump in use at the time for transporting the same medium. (At that time, the oil delivery temperature was 35C. If it was tested in winter or spring, the difference in efficiency between the two pumps was 47 percentage points).
3. Economic benefit analysis
1) Calculation of Energy Saving Benefits of Ke-Ukraine Oil Pipeline In order to seek oil transportation equipment suitable for thick and thin mixed crude oil, the oil and gas storage and transportation company installed a SNHG5300R46E15 three-screw pump at the 703 pumping station in 1999. On May 15, 2000, The Northwest Energy Conservation Monitoring Center of China National Petroleum Corporation tested the operating efficiency of the oil delivery unit of the 703 pumping station. According to the test report, the pipe pressure is under the working condition of 2.45Mpa, and the data are as follows:
The efficiency of the screw pump unit is 81.2%, and the unit oil consumption is 0.95kw.h/t.
The efficiency of the 200D-65X 8 centrifugal pump unit is 52.9%.
The unit oil consumption is 2.25 kW. h/t.
KDY250-90 X 8 centrifugal pump unit efficiency is 63.7%.
The unit oil consumption is 1.75 kW. h/t.
The Ke-Uzbekistan line transports 3 million tons of crude oil a year, and there are six pumping stations along the line, which can save electricity for a year:
(1) For 200D: Pren 3000000X(2.25-0.95)X 6 =23400000 kw.h
0.4 yuan per 1 kw.h of electricity, saving money:
A1=23400000X 0.4=9.63 million yuan
(2) For KDY250: P2=3000000X (1.75-0.95)X 6=14400000kw.h
0.4 yuan per 1 kw.h of electricity, saving money:
A2=14400000X 0.4=5.76 million yuan
The above is only the statistical data under the condition of a single pump transporting crude oil throughout the year, but the actual situation is: before the screw pump is installed, the 200D-65X 8 centrifugal pump unit and the KDY250-90 X 8 centrifugal pump unit run for a period of time according to production needs (The 200D pump runs about 30% of the year, and the KDY250 pump runs 70% of the year). After the screw pump is installed, all crude oil is transported by the screw pump. Therefore, the actual energy-saving data are as follows:
A=A1*30%+A2*70%
=963*30%+576*70%
=6.921 million yuan
ROI Calculation
There are six pumping stations on the Ukraine-Uzbekistan oil pipeline, and each pumping station is equipped with two screw pumps, a total of 12 sets. The total planned investment is 16.4 million yuan, and the total investment this year is 13.07 million yuan. The payback period is:
Y=16.4 million yuan/6.921 million yuan/year
=2.37 years
The above is only the energy-saving data of the oil and gas storage and transportation company’s Ke-Ukraine pipeline line. In addition, all oil delivery points are already in use and will be promoted in various heavy oil lines in Dongjiang in the future. By then, the annual energy saving will be even more substantial.
While the use of screw pumps has high economic benefits, it also has good social benefits, mainly in the following aspects:
1) High efficiency and remarkable power-saving effect;
2) Relieve the power supply pressure of the power grid;
3) Small size, low noise and easy maintenance;
4) Basically no leakage, avoiding environmental pollution.
4. Scope of application of technology
At present, most of the domestic high-viscosity crude oil lines use centrifugal pumps, which have low efficiency, high energy consumption, and high oil transportation costs. This is a major problem facing our oil transportation industry. Therefore, it is imperative to improve the efficiency of the pump unit (At present, the efficiency of centrifugal pumps for transporting heavy oil is very low, the highest is about 40%), the most advanced centrifugal pumps in the world are only about 80% (clear water efficiency), and the efficiency for transporting high-viscosity oils is only 40%. ~ 50%, only positive displacement screw pumps can increase the efficiency of conveying high-viscosity oil to more than 85%.
Therefore, the use of screw-type heavy oil pumps on pipelines transporting high-viscosity oil products is the most effective and direct way to reduce costs. In 1999, the oil and gas storage and transportation company successively installed The application of screw pumps has been started in 100, 100 heavy seven stations and six pumping stations on the Ke-Wu line, all of which have achieved or are about to achieve good economic and social benefits. The screw pump not only has a remarkable energy-saving effect when transporting mixed oil and high-viscosity oil but also has an efficiency of about 80% when transporting thin oil (test results at Cainan Station on March 4, 2001). But the condition at this time is that the pressure at the pump outlet should not be too high, otherwise, the internal leakage will increase rapidly, and its efficiency will drop rapidly. Therefore, the application of the screw pump in thin oil transportation requires a lot of tests and pump improvements. In addition, the pump can also transport gas and liquid mixtures. Therefore, the positive displacement screw pump can be used in long-distance transportation and oil transfer pipelines and has a wide promotion prospect in various oil production plants.
To sum up, compared with centrifugal pumps, screw pumps have greater advantages in delivery efficiency in our pipeline transportation industry, especially in the delivery of high-viscosity liquids!
