CN105864093A - Multistage centrifugal high pressure liquefied hydrocarbon pump - Google Patents

Abstract

A multi-stage centrifugal high-pressure liquefied hydrocarbon pump, including an axial force balance mechanism, a mechanical seal self-flushing mechanism, and a rotating shaft. There is a second-stage middle section sealing rubber ring, and a suction box body sealing rubber ring is installed between the suction box body, the outer cylinder body, and the first-level middle section; one end of the balance return pipe assembly is connected to the balance chamber through the pump cover, and the other end is connected to the balance chamber. It is connected to the suction chamber of the second-stage impeller through the outer cylinder; one end of the forward flushing pipe assembly is connected to the outlet of the first-stage impeller, the other end is connected to the mechanical seal assembly on the driving side, and one end of the reverse flushing pipe assembly is connected to the suction chamber The other end is connected to the non-drive side mechanical seal assembly. It also includes a self-controlled reflux thermal control mechanism. The invention can prevent the vaporization of the pumping medium, improve the cooling and lubrication of the end face of the mechanical seal, reduce the quantity of the minimum continuous heat-limited flow rate, reduce energy consumption, and ensure the safe and reliable operation of the pump.

Description

Multistage Centrifugal High Pressure Liquefied Hydrocarbon Pump

technical field

The invention relates to the field of pump valves, in particular to a multistage centrifugal high-pressure liquefied hydrocarbon pump, including an axial force balance mechanism, a mechanical seal self-flushing mechanism and the like.

Background technique

The liquefied hydrocarbon pump belongs to the light hydrocarbon pump, and it transports dangerous media that are flammable, explosive, easy to vaporize and volatile, low density, low ignition point, and high saturated vapor pressure, and the change of temperature is extremely sensitive to its vaporization pressure. For example, low-carbon liquid ethylene, butane and propylene. Liquefied hydrocarbon pumps, especially high-pressure liquefied hydrocarbon pumps, are the most critical dynamic equipment in the processes of petrochemical industry and petroleum refining plants.

At present, vertical high-speed pumps (tangential pumps) or reciprocating plunger pumps are generally used for low-flow and high-lift liquefied hydrocarbon pumps, some of which are imported or domestic. Piston pumps are unstable in operation and require a lot of maintenance; due to performance limitations, vertical high-speed pumps cannot meet the requirements of large displacement and high power, unless multiple units are used in parallel, which is troublesome to operate; ordinary multi-stage centrifugal pumps, when running It is easy to vaporize and evacuate, and the vibration is large. Therefore, for liquefied hydrocarbon pumps with large flow, high head and high power, there are almost no suitable products available in China at present, and we can only rely on imports. Although the double-casing multi-stage centrifugal pump widely used in modern times has the advantages of high pressure resistance, reliable static sealing, convenient maintenance, advanced shaft sealing and auxiliary system technology, it is still prone to vaporization and pumping when transporting high-pressure liquefied hydrocarbon media. There are disadvantages of unsafe operation.

The main reason for the vaporization and pumping of multistage centrifugal pumps is that people in the industry did not pay enough attention to the hazards of temperature rise and lacked effective temperature rise control measures. For example, there is no emphasis on the value of the minimum continuous thermal limit flow, the lack of a reasonable configuration of the axial force balance protection pipeline, and the lack of a reasonable configuration of the minimum continuous heat limit flow protection mechanism. The so-called minimum continuous thermally limited flow is the minimum flow value at which the centrifugal pump can maintain its operation without being damaged by the temperature rise of the pumped medium (liquid). The purpose of specifying this value is to avoid the operation of the pump in the area below this value. It is even more necessary to specify the minimum continuous thermal limit flow rate for high-pressure liquefied hydrocarbon pumps. The minimum continuous thermally limited flow rate of the pump is not only related to the structure of the pump and the characteristics of the pumped medium, but also related to the characteristics of the device where the pump is installed. Therefore, the minimum continuous thermally limited flow rate of the same pump is not fixed, and must be determined by corresponding calculations based on specific operating conditions. If this value is set too large, energy will be wasted, and if this value is set small, it will cause vaporization and evacuation. Therefore, it should be carefully discussed in the engineering design stage, and it should be controlled (preferably automatic control) and guaranteed during operation. Most of the pump vaporization is caused by the temperature rise of the inlet medium of the first-stage impeller, and most of the lost power in the pump is converted into heat energy and absorbed by the pumped medium. But for segmental multistage pumps, the highest temperature rise in the pump is at the rear of the balance mechanism. Generally speaking, the smaller the flow rate, the lower the pump efficiency, the greater the temperature rise of the pumped medium, and the greater the possibility of vaporization. The above viewpoints were not paid enough attention in the past, and the measures were not effective.

At present, in the well-known multi-stage centrifugal (segmental) balance system in China, the medium with high temperature rise in the balance chamber P of the axial force balance mechanism returns to the suction chamber X of the pump, so that the first-stage impeller inlet The temperature rise of the medium increases, and it is easy to vaporize; in addition, the medium of the mechanical seal self-flushing mechanism comes from the outlet K of the first-stage impeller, and then divides into two branch pipelines through the tee joint, and decompresses through the throttle orifice , respectively corresponding to the flushing fluid ports d, e connected to the end caps of the drive side and non-drive side mechanical seal components. Such a flushing scheme, if the pump vaporizes, will affect the stability of the self-flushing pressure of the mechanical seal, which may lead to a series of operational failures such as mechanical seal damage and leakage. With the large scale of liquid ethylene and other projects, in order to realize localization, it is very necessary to specially develop large displacement, high power, multistage centrifugal liquefied hydrocarbon pumps.

Contents of the invention

The object of the present invention is to overcome the above disadvantages and provide a multi-stage centrifugal high-pressure liquefied hydrocarbon pump with an axial force balance mechanism for preventing vaporization of the pumped medium and a matching mechanical seal self-flushing mechanism. It is also optional to use the temperature rise as the design criterion of the self-controlled reflux thermal control mechanism to limit the minimum thermal control operating flow rate, so as to automatically control the minimum continuous limit flow rate.

The purpose of the present invention is achieved through the following technical solutions: a multistage centrifugal high-pressure liquefied hydrocarbon pump, including an axial force balance mechanism, a mechanical seal self-flushing mechanism, a bearing component, and a rotating shaft, and the axial force balance mechanism includes a balanced liquid return pipe assembly , the middle section of the pump, the impeller, the balance drum, the suction body, the pump cover, and the outer cylinder. The mechanical seal self-flushing mechanism includes a forward flushing pipe assembly, a reverse flushing pipe assembly, and mechanical seal components. Stage impeller suction chamber, suction chamber, discharge chamber, pump suction port, pump discharge port, a liquid return hole is arranged on the first-stage middle section of the middle section of the pump, and a liquid return hole is arranged on the second-stage middle section of the middle section of the pump and the outer cylinder There is a second-level middle-section sealing rubber ring between the suction body and the outer cylinder body, and a suction-body sealing rubber ring between the first-level middle section; one end of the balance return pipe assembly passes through the pump cover and the first-level middle section. The balance chamber is connected, and the other end is connected to the suction chamber of the second-stage impeller through the outer cylinder; one end of the forward flushing pipe assembly is connected to the outlet of the first-stage impeller of the impeller, and the other end is connected to the driving side of the mechanical seal component The mechanical seal assembly is connected, one end of the reverse flushing pipe assembly is connected with the suction chamber, and the other end is connected with the non-driving side mechanical seal assembly of the mechanical seal component.

The pump suction port and the pump discharge port are respectively connected to a self-controlled backflow thermal control mechanism, the self-controlled backflow thermal control mechanism includes a self-controlled backflow valve connected to the pump outlet, and the self-controlled backflow valve is connected to the outflow gate valve and the backflow gate valve respectively , the return gate valve is connected to the suction port of the pump through the liquid storage tank.

The axial force balance mechanism returns the balance liquid at its outlet to the inlet of the second-stage impeller, which reduces the temperature rise at the inlet of the first-stage impeller and reduces the failure rate caused by the vaporization of the pumped medium; The adaptive mechanical seal self-flushing mechanism (only involves the self-flushing part), the mechanical seal assembly on the driving side (low pressure side) adopts the forward flushing scheme, and the mechanical seal assembly on the non-driving side (high pressure side) adopts the reverse flushing scheme; according to the centrifugal According to the structure type of the pump, the characteristics of the pumping medium and the characteristics of the relevant devices used in the centrifugal pump, calculate the temperature rise value of the pumping medium, determine the minimum continuous heat limit flow value, and select the automatic control according to the minimum continuous heat limit flow value and the corresponding lift. Backflow thermal control mechanism, so as to realize the control and protection of the minimum continuous thermal limit flow. Its beneficial effects are:

1. Since the axial force balance fluid of this centrifugal pump adopts the scheme of returning to the inlet of the second-stage impeller, although the medium with a large temperature rise after the balance mechanism is carried here, the working pressure here is higher than that of the first-stage impeller. The inlet pressure of the impeller is higher than the vaporization pressure of the medium at this temperature, so it is not easy to vaporize; because the medium with a higher temperature rise at the outlet of the balance mechanism is not carried to the inlet of the first-stage impeller, the temperature rise of the medium at the inlet of the first-stage impeller is relatively low. Low, the vaporization pressure is relatively low, and the working pressure here is low, so the pump is not easy to vaporize. In this way, the vibration caused by vaporization is avoided, and even the damage and failure shutdown of the pump are avoided, so as to ensure the safe and reliable operation of the centrifugal pump. 2. The mechanical seal component is the key component to ensure the safe operation of the high-pressure liquefied hydrocarbon pump. Since the centrifugal pump adopts the forward flushing (low pressure side) and reverse flushing (high pressure side) modes of the mechanical seal self-flushing mechanism matched with the axial force balance mechanism, it ensures sufficient and stable self-flushing pressure and improves The effect of cooling, lubricating and preventing vaporization of the end face of the mechanical seal is improved, and the reliability and service life of the mechanical seal are improved. 3. Due to the adoption of the above-mentioned structure, the centrifugal pump can reduce the quantity of the minimum continuous heat-limited flow (obtained by calculation), so that the flow discharged to the bypass can be reduced, and the energy consumption can be reduced. Since the centrifugal pump is equipped with a self-control backflow thermal control mechanism suitable for the minimum continuous thermal limit flow, it plays the role of control and protection to ensure the safe and reliable operation of the pump.

Description of drawings

The present invention will be further described in detail below in conjunction with the accompanying drawings and specific embodiments.

Fig. 1 is a schematic diagram of the application structure of the present invention.

Fig. 2 is a schematic diagram of the application process of the balanced liquid return pipe assembly, the forward flushing pipe assembly, the reverse flushing pipe assembly and the self-controlled backflow thermal control mechanism suitable for the minimum continuous heat-limited flow rate of the present invention.

detailed description

As shown in Figure 1, the multistage centrifugal high-pressure liquefied hydrocarbon pump of the present invention includes an axial force balance mechanism, a mechanical seal self-flushing mechanism, bearing components (including a left bearing assembly 191 and a right bearing assembly 192), a rotating shaft 20, and the shaft The force balance mechanism includes the balance return pipe assembly 3, the middle section of the pump (including the first-stage middle section 15 and the second-stage middle section 10), the impeller (including the first-stage impeller 13 and the second-stage impeller 11), the balance drum 7 (and the balance drum sleeve 8 ), suction box body 14, pump cover 9, outer cylinder body 16, the mechanical seal self-flushing mechanism includes forward flushing pipe assembly 1, reverse flushing pipe assembly 5, mechanical seal components (including driving side mechanical seal assembly 61 and non- Drive side mechanical seal assembly 62), which has a balance chamber P (formed by the inner cavity of the pump cover 9, the end surface of the balance drum 7 and the balance drum sleeve 8), the secondary impeller suction chamber R, the suction chamber X, the discharge chamber The chamber T, the pump suction port A, the pump discharge port B, the drive side sealed chamber M1, the non-drive side sealed chamber M2, etc. (are known technologies).

A liquid return hole 18 is provided on the first-stage middle section 15 of the middle section of the pump, and a second-stage middle section sealing rubber ring 4 (O type) is installed between the second-level middle section 10 and the outer cylinder 16 of the middle section of the pump, and its The pressure-stabilizing chamber Y is isolated from the discharge chamber T (with pump outlet pressure); a suction casing sealing rubber ring 12 (O type, three pieces in total), which isolates the pressure-stabilizing chamber Y from the suction chamber X (with pump inlet pressure). The inner wall of the outer cylinder 16, the suction box body 14 and the outer circle of the first-level middle section 15, the outer circle of the second-level middle section 10, the second-level middle section sealing rubber ring 4, and the suction box body sealing rubber ring 12 form a stable pressure Chamber Y, the liquid return hole 18 communicates with the pressure stabilizing chamber Y and the suction chamber R of the second-stage impeller.

As shown in Figure 1 and Figure 2, one end of the balance return pipe assembly 3 is connected to the balance chamber P (outlet) through the pump cover 9, and the other end is connected to the secondary impeller suction chamber R through the outer cylinder 16 (that is, a liquid return hole 18 is provided on the first-stage middle section 15); a balanced pressure gauge 31, a pressure transmitter 32, a balanced thermometer 33 and a temperature transmitter 34 connected to each other are provided in the balanced liquid return pipe assembly 3, On-site display and remote detection and control of the pressure and temperature of the balanced return liquid system. When the balance pressure and temperature are higher than the specified value, the sound and light alarm will be implemented to avoid the temperature rise in the downstream of the balance mechanism caused by the abnormal operation _. Causes vaporization of the pumped medium.

One end of the forward flushing pipe assembly 1 is connected to the outlet K of the first-stage impeller 13 of the impeller, and the other end (ie, its outlet d) is connected to the driving side mechanical seal assembly 61 of the mechanical seal component; the forward flushing pipe The component 1 is provided with a connected forward flushing regulating valve 111 , a throttling orifice 112 and a forward flushing pressure gauge 113 . The forward flush regulating valve 111 is used in the debugging process for determining the size of the throttle orifice 112 . Through the adjustment of the throttling orifice 112, the working pressure PR of the suction chamber P of the second-stage impeller is reduced to P _{M1 +} 0.2MPa, and this value is indicated by the forward flushing pressure gauge 113.

One end of the reverse flushing pipe assembly 5 (i.e. its outlet f) is connected to the suction chamber X, and the other end (i.e. its inlet e) is connected to the non-driving side mechanical seal assembly 62 of the mechanical seal component; The flushing pipe assembly 5 is provided with a connected lower regulating valve 51, an upper regulating valve 52, a cooler 53, a reverse flushing pressure gauge 54, a lower thermometer 55 and an upper thermometer 56. The cooler 53 is located between the lower regulating valve 51 and the lower thermometer. 55, between the upper regulating valve 52 and the upper thermometer 56. After the small amount of medium with higher temperature rise from the balance mechanism is cooled by the cooler, its temperature is lowered and then returned to the suction chamber. The lower thermometer 55 is the temperature of the medium before cooling, and the upper thermometer 56 is the temperature of the medium after cooling. The cooler is provided with a flange cooling water inlet h and a flange cooling water return port g, and the reverse flushing pressure gauge displays the medium pressure P _p of the balance chamber P.

Among them, the balance liquid return pipe assembly 3 has the inlet a and outlet b (connecting flange) of the balance liquid medium; the forward flushing pipe assembly 1 has the inlet c and outlet d (connecting flange) of the self-flushing medium; the reverse flushing pipe The assembly 5 has an inlet e and an outlet f (connecting flange) for the self-flushing medium. The inlets and outlets a, b, c, d, e, and f represent the interface connecting flanges of the above-mentioned various pipe assemblies. The balance liquid return pipe assembly 3 connects the balance chamber P (high pressure end) and the secondary impeller suction chamber R (low pressure end), which allows the balance liquid to flow from the balance chamber P to the stabilizing chamber Y and the secondary impeller suction chamber Room R, to achieve the purpose of balancing the axial force. The pressure-stabilizing chamber Y is the pressure chamber generated by the first-stage lift of the pump, and communicates with the second-stage impeller suction chamber R. The pressure-stabilizing chamber Y is isolated from the discharge chamber T (with pump outlet pressure) through the second-stage middle-section sealing rubber ring 4 (O-type) installed between the second-level middle section 10 and the outer cylinder 16; The suction body sealing rubber ring 12 (O type, three pieces in total) on the suction body 14 isolates the pressure-stabilizing chamber Y from the suction chamber X (with pump inlet pressure).

If the temperature of the pumped medium entering the suction chamber X of the pump is set to t ₁ ℃, the temperature rise due to power loss is set to Δt ₁ ℃, and the temperature rise due to the balance chamber P is set to Δt ₂ ℃, then the suction The temperature of the chamber X is (t ₁ +Δt ₁ )°C, and the temperature of the equilibrium chamber R is (t ₁ +Δt ₁ +Δt ₂ )°C. For a high-pressure pump, Δt ₂ >>Δt ₁ . Therefore, due to the increase in vapor pressure caused by temperature rise, the suction chamber R of the second-stage impeller is larger than the suction chamber X. Calculations and facts have proved: Since the working pressure of the suction chamber R of the second-stage impeller is higher than that of the suction chamber X, although the vaporization pressure increases due to temperature rise, it is still higher than (t ₁ +Δt ₁ +Δt ₂ ) The vaporization pressure of the medium at the temperature of ℃, so there will be no vaporization phenomenon.

The shaft sealing method of the high-pressure liquefied hydrocarbon pump adopts double-end (pressurized) mechanical seals. In order to cool and lubricate the end faces of the moving ring (rotating part) and the static ring (stationary part) in the mechanical seal components, it needs to be flushed. The flushing pressure is generally 0.2 MPa higher than the pressures of the driving-side sealed chamber M1 and the non-driven-side sealed chamber M2.

As shown in Figure 1, it is now assumed that the medium pressure in the drive side sealed chamber M1 of the pump is P _M1 , the medium pressure in the non-drive side sealed chamber M2 is P _M2 , and the medium pressure in the suction chamber X is Px , the medium pressure in the balance chamber P is P _p , and the medium pressure in the secondary impeller suction chamber R is P _R . Since P _M1 <P _R , the positive flushing of the driving side mechanical seal assembly 61 is realized (the flushing medium enters the driving side sealing chamber M1 through the positive flushing pipe assembly 1 from the outside to the inside); in addition, since Px<P _M2 < P _p realizes back flushing of the non-driving side mechanical seal assembly 62 (the flushing medium leaves the non-driving side sealing chamber M2 from inside to outside, and enters the suction chamber X through the back flushing pipe assembly 5). In addition, a heat exchanger 53 is installed in the back flushing pipe assembly 5 to cool a small amount of medium with relatively high temperature from the balance chamber P before entering the suction chamber X. In the forward flushing pipe assembly 1, since the temperature rise is relatively small, there is no need to install a heat exchanger.

As shown in Figure 2, the multi-stage centrifugal high-pressure liquefied hydrocarbon pump of the present invention is equipped with a self-controlled backflow thermal control mechanism 17 (also called a self-circulation protection mechanism) that prevents the pump from vaporizing and is suitable for the minimum continuous heat-limited flow rate. The pump suction port A and the pump discharge port B are respectively connected with the self-controlled backflow type thermal control mechanism 17. The self-controlled backflow type thermal control mechanism 17 includes a self-controlled backflow valve 171 connected with the pump outlet B. The self-controlled backflow valve 171 (through the pipeline ) are respectively connected with the outflow gate valve 172 and the return gate valve 173, and the return gate valve 173 is connected with the suction port A of the pump through the liquid storage tank 174. The self-control backflow valve 171 integrates check valve, flow sensor, bypass control valve, and multi-stage pressure-reducing functions; it adopts static sealing, no leakage, and is completely non-electrically connected and intrinsically safe. The pumped medium enters through the pump suction port A, passes through the rotation of the rotating shaft 20 and the delivery of the multi-stage impeller, and is discharged from the pump discharge port B. Open, flow out through the pipeline by opening the outflow gate valve 172, or open by the return gate valve 173 and re-enter the pump suction port A through the liquid storage tank 174 as required. It not only plays the main function of protecting the pump from vaporization, but also ensures safe use in dangerous situations.

The invention has been applied to the reaction feed pump of a methyl ethyl ketone device in a chemical company in Taizhou, and the hydrogenation feed pump of an olefin project dehydrogenation device in a chemical company in Shandong. The transport medium is light hydrocarbons such as butane, butene, and propane. Kind of medium. The invention is mainly used in the transportation of high-pressure light hydrocarbon medium in the petrochemical and coal chemical industry, and can also be used in the transportation of high-pressure boiler feed water in thermal power plants.

Claims (6)

1. multistage centrifugal high-pressure liquefaction hydrocarbon pump, including axial force balance mechanism, mechanical seal from washer Structure, parts of bearings, rotating shaft (20), this axial force balance mechanism include balance liquid back pipe assembly (3), Pump stage casing, impeller, balancing drum (7), suction letter body (14), pump cover (9), outer cylinder body (16), This mechanical seal from flushing machine include forward flush pipe assembly (1), back flush pipe assembly (5), Mechanical sealing parts, it has balance chamber (P), sencond stage impeller intake chamber (R), intake chamber (X), discharge chamber (T), Pump Suction Nozzle (A), pump discharge opening (B), it is characterised in that: The one-level stage casing (15) in described pump stage casing is provided with hole for back flow (18), in two grades of described pump stage casing Equipped with two grades of stage casing O-ring seals (4) between section (10) and outer cylinder body (16), at described suction letter body (14) equipped with sucking letter body O-ring seal (12) and between outer cylinder body (16), one-level stage casing (10)； One end of described balance liquid back pipe assembly (3) is connected with balance chamber (P) by pump cover (9), it is another One end is connected with sencond stage impeller intake chamber (R) by outer cylinder body (16)；Described forward flush pipe assembly (1) one end is connected with the outlet of the one stage impeller (13) of impeller, its other end and mechanical sealing parts Driving side mechanical sealing assembly (61) be connected, one end of described back flush pipe assembly (5) and suction Chamber is connected, its other end is connected with the non-drive side mechanical sealing assembly (62) of mechanical sealing parts.

Multistage centrifugal high-pressure liquefaction hydrocarbon pump the most according to claim 1, it is characterised in that: described The inwall of outer cylinder body (16), suction letter body (14) and the cylindrical of one-level stage casing (15), two grades of stage casings (10) shape between cylindrical and two grades of stage casing O-ring seals (4), suctions letter body O-ring seal (12) Become voltage stabilizing chamber (Y), described hole for back flow (18) and voltage stabilizing chamber (Y), sencond stage impeller intake chamber (R) communicate.

Multistage centrifugal high-pressure liquefaction hydrocarbon pump the most according to claim 1, it is characterised in that: described Balance liquid back pipe assembly (3) is provided with connected balance Pressure gauge (31), pressure transmitter (32), Balanced thermometer (33) and temperature transmitter (34).

Multistage centrifugal high-pressure liquefaction hydrocarbon pump the most according to claim 1, it is characterised in that: described Forward flush pipe assembly (1) is provided with connected forward and rinses regulation valve (111), restricting orifice (112) With forward flushing pressure table (113).

Multistage centrifugal high-pressure liquefaction hydrocarbon pump the most according to claim 1, it is characterised in that: described Back flush pipe assembly (5) is provided with connected lower regulation valve (51), upper regulation valve (52), cooling Device (53) and back flush Pressure gauge (54), lower thermometer (55) and upper thermometer (56), should Cooler (53) be in lower regulation valve (51), lower thermometer (55) and upper regulation valve (52), on Between thermometer (56).

6. according to the multistage centrifugal high-pressure liquefaction hydrocarbon pump described in claim 1,2,3,4 or 5, its Be characterised by: described Pump Suction Nozzle (A), pump discharge opening (B) respectively with automatic control reverse-flow type thermal control mechanism (17) being connected, this automatic control reverse-flow type thermal control mechanism (17) includes the automatic control being connected with pump discharge opening (B) Reflux inlet (171), this automatic control reflux inlet (171) respectively with go out stream gate valve (172), backflow gate valve (173) Being connected, this backflow gate valve (173) is connected with Pump Suction Nozzle (A) by fluid reservoir (174).