The first part, three screw pump
I. Overview
Three screw pump belongs to the rotary positive displacement pump, which is mainly used for conveying all kinds of lubricating fluids containing no solid particles and corrosive oils or similar oils. There are only three rotating elements in three screw pump & a master rod and two slave rods, which is the most basic and key factor to determine the performance characteristics of three screw pump. The master rod and the slave rod contained in the bushing are closely engaged with each other, forming two closed chambers in space, which look better than they look. When the main rod rotates, these closed chambers move continuously and uniformly from the pump suction chamber to the discharge chamber along the axis of the main rod, completing the suction and discharge of liquid. This uniform axial movement determines that three screw pump has good suction performance, small pulsation and stable operation.
Schematic diagram of three screw pump structure
Due to the specially designed screw profile, there is no force transmission between the master rod and the slave rod during normal rotation. The driven rod generates hydraulic torque by accumulating pressure liquid without manual rotation. At the same time, through the structural design, the axial force of the master rod and the slave rod is out of balance, so that the three screw pump can work in a very good balanced state, and the mechanical efficiency is very high, that is, the friction power of the pump is very small. On the premise of advanced technology and equipment, the machining accuracy of the master rod and the slave rod is ensured, and the meshing gap is very small, so that the pump also has high capacity efficiency under high pressure. In this way, the overall efficiency of three screw pump is very high.
Because there is no force transmission between the master rod and the slave rod, their respective axial forces are completely out of balance, and the oil film formed between the master rod and the slave rod and the bushing will not be destroyed, so there is actually no direct contact between the metal between the master rod and the slave rod and the bushing, thus ensuring that the three screw pump has a good service life.
Second, the main features
, high efficiency
For γ= 1500mm2/s, △P=5.5Mpa, and Q= 1 15/h, the total efficiency of the pump can reach over 85%.
Second, the scale of performance
△P=5.5Mpa For the medium pressure in three screw pump, as long as the screw lead number is increased, the pressure can be higher, and it is easy to reach△ p = 6.4mpa or higher.
Q= 1 15/h flow rate belongs to medium and high.
3, good inhalation performance
In view of the above performance requirements, the necessary cavitation allowance NPSH of the pump is 4.5, and the pump is equipped with a 6-stage motor.
The lead of the screw is very small.
4. Simple structure
There is only one set of mechanical seal and one set of bearing, so there are few leakage points, and the bearing only plays a positioning role, which ensures the reliability of the mechanical seal, bears little load, is convenient for lubricating oil and has long service life.
5, convenient use and maintenance, and low cost.
Because the structure is simple, and the composition of the pump only depends on the accuracy of each part, there is no matching or adjustment, the disassembly and inspection are convenient and quick, and the maintenance is simple. After the parts are repaired and replaced, the performance of the pump can be restored to 100% without manual positioning, and any part in the pump can be replaced independently, so that the maintenance cost is minimized.
6. Good wear resistance
For the fine sand or surface sand in crude oil, it will not affect the normal operation of the pump. Because of the small diameter and low rotation speed of the screw, the wear of the screw itself is very small, and the wear of three screw pump mainly exists between the driven rod and the bushing hole. Because the driven rod needs to bear a certain radial force, metal contact will lead to wear when the oil film is damaged, so the structural design of the pump is very important. The higher the pressure, the more leads the pump should have. In this way, the pressure per unit area between the rod and the bushing hole will be less, and the possibility of wear will be less. This time, four lead wires were designed, two more than ordinary pumps. For sand content of 0. 1%, we guarantee that the service life of casing is more than 2 years. The service life of the master-slave rod is more than 5 years.
The clearance between the master-slave rod and the bushing is 0.05~0.07mm, and the diameter of fine sand is less than this value (note: there is a filter in front of the pump).
7. Good corrosion resistance
Crude oil contains sulfur, which makes it weakly corrosive, so the materials of the main parts of the pump are determined as follows:
The bushing is made of tin bronze: ZQSn 10- 1.
The main rod and the slave rod are made of nitrided steel: 16MnDrS5, which on the one hand increases the surface hardness and on the other hand makes the screw resistant to sulfur corrosion.
8. Support requirements
The inlet must be equipped with a filter, and its filtering accuracy and flow area must meet the requirements of the pump at the same time. For crude oil with γ= 1500mm/S, we recommend that the mesh number of filter element is 16 mesh, the filtration area is 25 times larger than the inlet cross section, and the filtrate resistance is less than 2.5 water column.
9. The realization is relatively low
10, things environment
Because there is only one set of mechanical seal in three screw pump, and the pressure and liquid flow can be manually adjusted to seal the chamber, so that the seal can work under suitable conditions. Thereby ensuring that the pump has no leakage and long sealing life, which can reach more than 8000- 10000 hours, and ensuring that the environment is clean and pollution-free.
Third, the main performance
1. Liaohe Oilfield Oil and Gas Gathering and Transportation Company
●SNHG5300R46EBM-W29 1 set
Rotation speed n= 1450rpm, compression force P=4.5Mpa, flow rate Q=300m3/h, and efficiency η=85%.
● 2 sets of snhg 7400r40ebm-w29.
Rotation speed n= 1450rpm, compression force P=4.0Mpa, flow rate Q=350m3/h, and efficiency η=85%.
●SNH9400R40EBM-W29 1 set.
Rotation speed n= 1450rpm, compression force P=3.0Mpa, flow rate Q=450m3/h, and efficiency η=78%.
2. Shengli Oilfield Oil and Gas Storage and Transportation Company
●SMH2200R40E6.7-W29 1 set.
Rotation speed n= 1450rpm, compression force P=4.0Mpa, flow rate Q=300m3/h, and efficiency η=85%.
3. Xinjiang Karamay Oilfield Oil and Gas Storage and Transportation Company
●SNHG5300R46EBM-W29 7 sets.
Rotation speed n= 1450rpm, compression force P=4.0Mpa, flow rate Q=300m3/h, and efficiency η=85%.
● 6 sets of SMH2900R40E6.7-W29.
Rotation speed n= 1450rpm, compression force P=3.0Mpa, flow rate Q= 150m3/h, and efficiency η=80%.
The second part, twin screw pump.
I. Overview
Twin-screw pump is a kind of external meshing screw pump, which uses two mutually meshing but non-contact screws to pump liquid. As shown in the figure below, it is a double-suction unsealed twin screw pump. The driving screw with one end extending out of the pump is driven by the prime mover. The threads of the driving screw and the driven screw are different (if the former is right-handed, the latter is left-handed). The screw is closely connected with the pump body. The driven screw is driven by the driving screw through the process synchronization gear. As a positive displacement pump, the suction chamber of twin screw pump should be closely separated from the discharge chamber. Therefore, the gaps between the pump body and the cylindrical surface of the screw and between the screws should be as small as possible. At the same time, a sealed cavity is formed between the screw and the pump body and between the screws to ensure sealing, otherwise there may be liquid flowing back from the gap.
Double screw pump can be divided into two cases: inner bearing and outer bearing. In the structural type of built-in bearing, the bearing is lubricated by conveying material. The working chamber of twin screw pump with external bearing structure is separated from the bearing. Due to the structure of this pump and the side clearance between the screws, it can transport non-lubricating media. In addition, the synchronous gear is adjusted so that the screw does not contact, and at the same time, half of the output torque is transmitted to the driven screw. Just like all screw pumps, double screw pumps with external bearings also have self-priming ability, and most pump conveying parts are symmetrically arranged with double suction, which can eliminate axial force and have high oil absorption height.
These characteristics of pumps make them widely used in oilfield chemical industry and shipbuilding industry. The external bearing twin screw pump can be made of common cast iron, stainless steel and other different materials according to different service conditions. The conveying temperature can reach 250? D the pump has different heating structures, and the fixed flow rate can reach 2000m3/hour.
Second, the main features:
1, low efficiency
Because the double screw pump artificially separates the driving rod, the driven rod and the bushing by mechanical means, the gap is very large, generally above 0mm, so the capacity efficiency is low at high pressure. At the same time, because of its large screw diameter, the diameter of the main rod in three screw pump is d =&d；; P hello; 160mm, diameter of twin screw pump d =&m；; P hello; Above 268 mm, with deep teeth and four sets of mechanical seals, its friction power is high, which leads to the overall efficiency of the pump is low. For anisotropic performance index, its efficiency is lower than 65%.
Second, the scale of performance
In twin-screw pump, the screw is subjected to radial force, and its value is large. Because the screw shaft is a slender shaft with bearings at both ends, the screw in the middle is easy to bend due to radial force. In order to avoid the contact wear between the screw and the bushing, the outlet pressure of the twin screw pump is limited, that is, the pump will be damaged if it exceeds this pressure.
△P=55Mpa For a high-pressure twin-screw pump, the bearing arrangement must be very compact, the span is reduced, the screw lead is very small, and it must match a high speed. In order to achieve higher pressure, its structural lead must be modified accordingly to meet the requirements. Q= 1 15/h belongs to medium and low flow.
3, the inhalation performance is very good
Because its spiral lead value is very small and the axial speed of liquid flow is very small, it has good suction performance. NPSH = 2 ~ 3, and the pump can be equipped with a 4-pole motor.
4, the structure is complex
There are four groups of bearings, four groups of mechanical seals and a pair of synchronous gears in a pump, that is, there are three pairs of gears meshing with each other on two shafts. It is necessary to measure and adjust the machining accuracy with multiple adjusting gaskets before assembling the pump. The machining accuracy of multiple parts on two shafts is very high, otherwise the parallelism of the two shafts cannot be guaranteed, and the pump will fail.
5. It is difficult to use and maintain, and the maintenance cost is high.
Because the pump has four shaft extensions, there are four leakage points, which is four times that of three screw pump. If there is any mechanical seal leakage, only when the pump is completely disassembled during maintenance can the seal be replaced. The labor intensity of maintenance personnel is relatively high, and the on-site recovery after disassembly and inspection requires high technical level, otherwise the performance of the pump will change greatly and the reliability will not be guaranteed.
If it is necessary to re-measure, process and adjust the components in the pump on site, it will take a long time to complete the assembly of a new pump under the new benchmark, which will be labor-intensive and require high personnel. It needs the guidance of the manufacturer's personnel to complete the maintenance of the pump, and the cost is high.
6. Good wear resistance.
The fine sand in crude oil has no influence on the normal operation of the pump. As long as the sand content is 0. 1%, the screw and bushing of the pump should be hardened, and the performance of the pump can be guaranteed for a long time. Because of the large excircle, high rotating speed and high peripheral speed of the screw, the wear of the screw is also the most serious. With the increase of sand content, the wear of screw is accelerated sharply. At the same time, the clearance between the screw and the bushing is large, the liquid reflux is large, and high speed will also cause certain wear. After wear, the performance of the pump is obviously reduced. After the pump is worn, it is very expensive to replace the screw and bushing at the same time.
Fine sand particles are relatively large, less than 0.3mm, so the requirements for the filter at the inlet of the pump are low.
7. Good corrosion resistance
The materials of the components in the twin-screw pump can be combined at will, and the corresponding materials can be combined if the working conditions require, so as to prevent the corrosion of sulfur in crude oil, and the twin-screw pump is easy to achieve.
8. Support requirements
The water inlet must be equipped with a filter, the mesh number of the filter element is about 10 mesh, the filtering area is 20 times of the cross section of the water inlet, and the liquid resistance of the filter is less than 3 water columns.
9. The reality is relatively high
10, things environment
Because there are many leakage points in the four sets of mechanical seals of twin-screw pump, and the sealing cavity environment can not be adjusted, it is generally in a negative pressure state, and the sealing life can only be guaranteed by the wear life of the mechanical seals themselves. For sandy crude oil, its service life is below 8000, so it will cost a lot to ensure the site clean and pollution-free.