CN115822988A - Centrifugal compressor and inlet temperature control method of centrifugal compressor - Google Patents
Centrifugal compressor and inlet temperature control method of centrifugal compressor Download PDFInfo
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Abstract
The invention discloses a centrifugal compressor and an inlet temperature control method of the centrifugal compressor. The centrifugal compressor comprises a centrifugal compression main machine and an inlet superheater connected with a low-grade working medium inlet of the centrifugal compression main machine, wherein the inlet superheater is used for heating working medium steam to be compressed into superheated steam and sending the superheated steam into the centrifugal compression main machine through the low-grade working medium inlet. The temperature compensation type centrifugal compressor can be used for compressing special working media with saturated gas phase lines inclining to the right and keeping stable and reliable work for a long time.
Description
Technical Field
The invention belongs to the technical field of compressors, and particularly relates to a centrifugal compressor and an inlet temperature control method of the centrifugal compressor.
Background
In chemical industry and other industries, a compressor is often needed to pressurize working medium steam with lower pressure and temperature and improve the corresponding saturation temperature, so that the heat energy grade of the working medium steam is improved and then the working medium steam is reused.
However, some working fluids have special physical properties (such as n-hexane and freon), as shown in fig. 3, a saturation gas phase line in a physical property T-s diagram inclines to the right (that is, entropy of corresponding saturated steam increases gradually when saturation temperature increases), which results in that when these working fluids are compressed, if the working fluid steam before compression is in a saturated state, the compression process may enter a two-phase region, so that the working fluids in the compressor and at the outlet thereof are in a liquid-carrying state. If a centrifugal compressor and a constant-speed compressor are adopted for compression, liquid drops in working medium steam can impact the impeller, so that the compressor cannot work stably, and the impeller can be damaged. Therefore, in the past, such a working medium is often compressed mainly by a screw-type or piston-type constant volume compressor.
However, the volumetric compressor has disadvantages in that: the volume flow of a single volume type compressor is small and has an upper limit, when the required flow is large, a plurality of compressors are required to be connected in parallel, so that the equipment complexity is greatly improved, and the compression cost is greatly increased.
Disclosure of Invention
The invention aims to provide a centrifugal compressor and an inlet temperature control method of the centrifugal compressor, wherein the centrifugal compressor can compensate the temperature of working medium steam entering the compressor so as to ensure that the compressed working medium does not contain liquid drops.
In order to achieve the purpose, the technical scheme of the invention is as follows:
a centrifugal compressor comprises a centrifugal compression main machine and an inlet superheater connected with a low-grade working medium inlet of the centrifugal compression main machine, wherein the inlet superheater is used for heating working medium steam to be compressed into superheated steam and sending the superheated steam into the centrifugal compression main machine through the low-grade working medium inlet.
The invention arranges an inlet superheater at the upstream of the centrifugal compression main machine, when in compression, a working medium to be compressed firstly enters the inlet superheater for temperature compensation, and the temperature of the working medium steam rises after absorbing heat in the inlet superheater and is converted into superheated steam with a certain inlet superheat degree; and then the superheated steam enters a centrifugal compression main machine, the pressure is increased through a centrifugal compressor, the corresponding saturation temperature is increased, and the pressurized working medium steam enters the subsequent process flow for use. Because the working medium steam entering the centrifugal compression main machine has proper inlet superheat degree, the whole compression process of the centrifugal compression main machine on the working medium steam is in a superheat area and cannot enter a two-phase area, so that the problem of impact on an impeller caused by liquid carried in the compressor is solved, and the service life of the impeller in the centrifugal compression main machine is greatly prolonged.
The temperature compensation type centrifugal compressor can be used for compressing special working media with saturated gas phase lines inclining to the right and keeping stable and reliable work for a long time.
In the invention, the modes of temperature compensation of the inlet superheater for the working medium steam are various, and the skilled person can select the modes according to the actual conditions.
For example, electrical heating may also be used, namely: the inlet superheater is an electric heater, the electric heater comprises a shell, a steam pipeline penetrates through the shell, and the steam pipeline is provided with a working medium steam inlet and a superheated steam outlet which extend out of the shell; an electric heating element is arranged in the shell and positioned on the periphery of the steam pipeline.
Alternatively, a working medium heat exchange mode can be adopted, namely: the inlet superheater is a heat exchanger, the heat exchanger is provided with a tube side and a shell side, the tube side or the shell side is provided with a working medium steam inlet and a superheated steam outlet, the shell side or the tube side is provided with a heat exchange medium inlet and a heat exchange medium outlet, a circulating pipeline is communicated between the heat exchange medium inlet and the heat exchange medium outlet, and a heat exchange medium heating element is arranged on the circulating pipeline.
No matter which temperature compensation mode is adopted, preferably, a first temperature sensor for detecting the temperature of the working medium to be compressed is arranged at the saturated steam inlet, a second temperature sensor for detecting the temperature of the superheated steam of the working medium to be compressed is arranged at the superheated steam outlet, and a pressure sensor for detecting the steam pressure of the working medium to be compressed is arranged at the saturated steam inlet or the superheated steam outlet;
the centrifugal compressor further comprises a main control module, the first temperature sensor, the second temperature sensor, the pressure sensor and the inlet superheater are all connected with the main control module, and the main control module is used for controlling the inlet superheater to work according to detection results of the first temperature sensor, the second temperature sensor and the pressure sensor.
The first temperature sensor is used for detecting whether the actual temperature of a working medium to be compressed reaches the saturation temperature, because generally, the working medium steam entering the inlet superheater is saturated steam, the main control module calculates the inlet superheat degree of the superheated steam (namely the temperature difference between the superheated steam and the saturated steam) on the basis of the saturation temperature of the working medium steam, the first temperature sensor is used for detecting the actual temperature, a correction basis can be provided for the calculation of the main control module, and if the actual temperature is lower than the saturation temperature, the main control module can also calculate the temperature difference between the actual temperature and the saturation temperature into the inlet superheat degree.
The second temperature sensor is used for detecting the temperature of the superheated steam of the working medium to be compressed so as to ensure that the temperature of the superheated steam reaches a preset value; if the preset value is not reached, the main control module controls the inlet superheater to increase the heating power.
The pressure sensor is used for detecting the pressure of working medium steam to be compressed (namely the pressure of superheated steam) so as to obtain the saturation temperature of the steam under the pressure, and a basis is provided for determining the degree of superheat of the inlet.
The invention also provides an inlet temperature control method of the centrifugal compressor, which sequentially comprises the following steps:
(1) Performing physical property analysis on the working medium to be compressed, and entering the next step if the isentropic compression end point of the working medium is in a two-phase region;
(2) Calculating the minimum inlet superheat degree of the superheated steam of the working medium to be compressed;
(3) And calculating the heating power required to be provided by the inlet superheater according to the minimum inlet superheat degree.
In the above method for controlling an inlet temperature of a centrifugal compressor, the step (1) comprises:
(1) drawing a saturated steam isobar a, a superheated steam isobar b and a saturated gas phase line c of a working medium to be compressed in a T-S diagram, wherein the pressure on the saturated steam isobar a is P a The pressure on the superheated steam isobar b is P b The saturated steam isobaric line a and the saturated gas phase line c intersect at a saturation temperature point 1, and the superheated steam isobaric line b and the saturated gas phase line c intersect at a saturation temperature point m;
(2) respectively obtaining the temperature T of the working medium to be compressed at the saturation temperature point 1 in the working medium physical property database 1 Entropy value S 1 And enthalpy value H 1 And the temperature T of the working medium to be compressed at the saturation temperature point m m Entropy value S m And enthalpy value H m ；
(3) According to the entropy value S 1 Obtaining the temperature T when the working medium to be compressed is compressed from Pa isentropic to Pb in the working medium physical property database 2s And enthalpy value H 2s ；
(4) H is to be 2s With enthalpy value H m Making a comparison if H 2s Is less than H m And the isentropic compression end point of the working medium to be compressed is shown to be in the two-phase region.
Wherein, P a Less than P b The compression process of the working medium to be compressed is performed by the pressure P of the working medium to be compressed a Is pressurized to P b To represent; when the working medium to be compressed is saturated steam, the saturated steam isobar a intersects with the saturated gas phase line c at a saturation temperature point 1, and the working medium to be compressed is started from the point 1 by a pressure P a Isentropically compressed to pressure P b The temperature of the steam reaches the intersection point 2s of the isentropic line and the superheated steam isobaric line b, and 1-2s are the isentropic line; at the intersection point m of the superheated steam isobar b and the saturated gas phase line c, the working medium to be compressed is in a complete gas phase; since the right half of the saturation gas phase line c is tilted to the right, if H is present 2s Is less than H m (i.e. temperature T) 2s Less than T m ) If the point 1 is taken as the temperature of the compression starting point, the problem that the steam carries liquid occurs in the compression process, and the temperature of the steam of the working medium to be compressed needs to be increased.
In the above method for controlling an inlet temperature of a centrifugal compressor, the step (2) comprises:
(5) determining the intersection point n of an isentropic line passing through a saturation temperature point m and a saturated steam isobar line a in a T-S diagram, and acquiring the temperature T of the working medium to be compressed at the point n in a working medium physical property database n ；
(6) Calculating T n And T 1 The difference value of (1) to obtain the minimum inlet superheat degree delta T min 。
I.e. when the compression start temperature is T n Then, after isentropic compression, the temperature of the working medium steam is Tm, and the working medium steam is a complete gas phase; after the compression efficiency and the loss generated in the compression process are considered, the actual entropy value can be increased, and the compression end point can be more inclined to the right, so that the whole compression process is ensured to be in a superheat area, and liquid drops can not exist in the working medium steam.
Preferably, step (2) further comprises: obtaining the actual temperature T of the working medium to be compressed 0 And will T 0 And T 1 Making a comparison if T 0 Less than T 1 Then calculate T n And T 0 The difference value of (1) to obtain the minimum inlet superheat degree delta T min 。
Obtaining T from a first temperature sensor 0 If the actual temperature T appears 0 Less than saturation temperature T 1 In the case of (1), the minimum inlet superheat degree Δ T min Should be given by T n And T 0 The difference of (c) is standard.
In the above method for controlling an inlet temperature of a centrifugal compressor, the step (3) comprises:
(7) according to the required degree of superheat of an inlet, a point 3 positioned on the right side of a point n is taken on a saturated steam isobar a, and an enthalpy value H corresponding to the point 3 is obtained in a working medium physical property database 3 ；
(8) Calculating the heating power P required to be provided by the inlet superheater according to the following formula:
P=（H 3 -H 1 ) X M; wherein M represents the mass flow of the saturated steam of the working medium to be compressed.
To ensure that no liquid droplets will be present in the centrifugal compressor main unit, the actual inlet superheat is preferably set slightly above Δ T, taking into account the uncertainty of the actual compression process and the complexity of the flow inside the centrifugal compressor min Then the corresponding compression start point temperature T 3 The corresponding point 3 is to the right of point n.
Preferably, in step (7), the temperature T at point 3 is 3 Temperature T of specific point n n The height is 1-3 ℃.
Liquid drops in the steam cannot be completely eliminated if the inlet superheat degree is insufficient, and the heat of the inlet superheater is wasted if the inlet superheat degree is too large, so that the economy is reduced.
When the inlet superheater adopts a heat exchanger, the inlet temperature control method further comprises the following step (9): the mass flow rate M' of the heat exchange medium to be supplied to the inlet superheater is calculated according to the following formula:
M’= P/（H’-H’’）；
wherein, P is the heating power needed to be provided by the inlet superheater, H ' is the enthalpy value of the provided heat exchange medium under the given temperature and pressure, and H ' ' is the enthalpy value of the saturated liquid of the heat exchange medium under the same pressure (namely, the pressure is the same as the saturated vapor pressure of the heat exchange medium).
The main control module obtains the corresponding enthalpy value H 'from the physical property database and the enthalpy value H' 'of the saturated liquid of the heat exchange medium under the same pressure after obtaining the temperature and the pressure of the heat exchange medium steam, and the mass flow M' of the heat exchange medium needed to be provided for the inlet superheater can be obtained by combining the calculated P.
Compared with the prior art, the invention has the beneficial effects that:
(1) The invention arranges an inlet superheater at the upstream of the centrifugal compression main machine, when in compression, a working medium to be compressed firstly enters the inlet superheater for temperature compensation, the temperature of the working medium steam is increased after the working medium steam absorbs heat in the inlet superheater, and the working medium steam is converted into superheated steam with a certain inlet superheat degree from saturated steam; and then the superheated steam enters a centrifugal compression main machine, the pressure is increased through a centrifugal compressor, the corresponding saturation temperature is increased, and the pressurized working medium steam enters the subsequent process flow for use. Because the working medium steam entering the centrifugal compression main machine has proper inlet superheat degree, the whole compression process of the centrifugal compression main machine on the working medium steam is in a superheat area and cannot enter a two-phase area, so that the problem of impact on an impeller caused by liquid carried in the compressor is solved, and the service life of the impeller in the centrifugal compression main machine is greatly prolonged.
(2) The temperature compensation type centrifugal compressor can be used for compressing special working media with saturated gas phase lines inclining to the right and keeping stable and reliable work for a long time.
(3) The control method can accurately calculate the heating power required by the inlet superheater, thereby ensuring that the working medium saturated steam is converted into the superheated steam with a certain inlet superheat degree, completely eliminating liquid drops in the steam, keeping the heating power of the inlet superheater within a proper range, and ensuring the economy.
Drawings
FIG. 1 is a schematic view of the structure of the centrifugal compressor of the present invention;
FIG. 2 is a block diagram of a centrifugal compressor according to the present invention;
FIG. 3 is a diagram of working medium T-S for the centrifugal compressor of the present invention.
Detailed Description
The technical solution of the present invention will be further described in detail with reference to the accompanying drawings and the detailed description.
Example 1
As shown in fig. 1, the centrifugal compressor of the present embodiment includes a centrifugal compression main unit 20, where the centrifugal compression main unit 20 has a low-grade working medium inlet 21 and a high-grade working medium outlet 22; the inlet superheater 10 is communicated with a low-grade working medium inlet 21 of the centrifugal compression main machine 20 through a pipeline, and is used for heating the working medium steam to be compressed into superheated steam and sending the superheated steam into the centrifugal compression main machine 20 through the low-grade working medium inlet 21.
Because the working medium steam entering the centrifugal compression main machine 20 has a proper inlet superheat degree, the whole compression process of the centrifugal compression main machine 20 on the working medium steam is in a superheat zone and cannot enter a two-phase zone, so that the problem of impact on an impeller caused by liquid in the compressor is solved, and the service life of the impeller in the centrifugal compression main machine 20 is greatly prolonged.
In the present invention, the inlet superheater 10 has various temperature compensation modes for the working medium steam, and those skilled in the art can select the temperature compensation mode according to actual conditions. For example, the electric heating mode shown in fig. 1 can be adopted, namely: the inlet superheater 10 is an electric heater, the electric heater comprises a shell, a steam pipeline penetrates through the shell, and the steam pipeline is provided with a working medium steam inlet 11 and a superheated steam outlet 12 which extend out of the shell; an electric heating element is arranged in the shell and positioned on the periphery of the steam pipeline.
The mode of working medium heat exchange can also be adopted, namely, the inlet superheater 10 is a heat exchanger which is provided with a tube side and a shell side, the tube side or the shell side is provided with a working medium steam inlet 11 and a superheated steam outlet 12, the shell side or the tube side is provided with a heat exchange medium inlet and a heat exchange medium outlet, a circulating pipeline is communicated between the heat exchange medium inlet and the heat exchange medium outlet, and a heat exchange medium heating element is arranged on the circulating pipeline.
The steam can pass through a tube pass or a shell pass; the heat exchange medium can be in a tube pass or a shell pass, and steam and the heat exchange medium can be selected from one.
No matter which temperature compensation mode is adopted, a first temperature sensor 30 for detecting the temperature of the working medium steam to be compressed and a pressure sensor 40 for detecting the steam pressure of the working medium to be compressed are arranged at the working medium steam inlet 11; a second temperature sensor 50 for detecting the temperature of the superheated steam of the working medium to be compressed is arranged at the superheated steam outlet 12;
the first temperature sensor 30, the second temperature sensor 50, the pressure sensor 40 and the inlet superheater 10 are all connected to the main control module 60, and the main control module 60 is configured to control the operation of the inlet superheater 10 according to the detection results of the pressure sensor 40, the first temperature sensor 30 and the second temperature sensor 50.
The first temperature sensor 30 is used for detecting whether the actual temperature of the working medium to be compressed reaches the saturation temperature, because generally, the working medium steam entering the inlet superheater 10 is saturated steam, the main control module 60 calculates the inlet superheat degree of the superheated steam, namely the temperature difference between the superheated steam and the saturated steam, on the basis of the saturation temperature of the working medium steam, the first temperature sensor 30 is used for detecting the actual temperature, a correction basis can be provided for the calculation of the main control module 60, and if the actual temperature is lower than the saturation temperature, the main control module 60 can also calculate the temperature difference between the actual temperature and the saturation temperature into the inlet superheat degree.
The second temperature sensor 50 is used for detecting the temperature of the superheated steam of the working medium to be compressed so as to ensure that the temperature of the superheated steam reaches a preset value; if the preset value is not reached, the main control module 60 controls the inlet superheater 10 to increase the heating power, for example, feedback control of the inlet superheat degree is realized by means of adjusting the flow rate of a heat exchange medium or the electric power of an electric heating element, and meanwhile, the steam pressure at the low-grade working medium inlet 21 is monitored in real time to adapt to the change of working medium inlet parameters, such as the fluctuation of parameters such as flow rate and pressure, so that the working medium steam entering the compressor always has the proper inlet superheat degree.
The pressure sensor 40 is used for detecting the pressure of the working medium steam to be compressed (namely the pressure of the superheated steam) so as to obtain the saturation temperature of the steam under the pressure, and a basis is provided for determining the degree of superheat of the inlet.
Example 2
The method for controlling the inlet temperature of the centrifugal compressor comprises the following steps:
(1) Performing physical property analysis on the working medium to be compressed, and entering the next step if the isentropic compression end point of the working medium is in a two-phase region;
specifically, the method comprises the following steps:
(1) as shown in FIG. 3, a saturated steam isobar a, an overheated steam isobar b and a saturated gas phase line c of a working medium to be compressed are drawn in a T-S diagram, and the pressure on the saturated steam isobar a is P a The pressure on the superheated steam isobar b is P b The saturated steam isobaric line a and the saturated gas phase line c intersect at a saturation temperature point 1, and the superheated steam isobaric line b and the saturated gas phase line c intersect at a saturation temperature point m;
wherein, P a Less than P b The compression process of the working medium to be compressed is performed by the pressure P of the working medium to be compressed a Is pressurized to P b To represent; when the working medium to be compressed is saturated steam, the saturated steam isobar a intersects with a saturated gas phase line c at a saturation temperature point 1; at the intersection point m of the superheated steam isobar b and the saturated gas phase line c, the working medium to be compressed is in a complete gas phase;
(2) respectively obtaining the temperature T of the working medium to be compressed at the saturation temperature point 1 in the working medium physical property database 1 Entropy value S 1 And enthalpy value H 1 And the temperature T of the working medium to be compressed at the saturation temperature point m m Entropy value S m And enthalpy value H m ；
(3) According to the entropy value S 1 Obtaining the temperature T when the working medium to be compressed is compressed from Pa isentropic to Pb in the working medium physical property database 2s And enthalpy value H 2s ；
The working medium to be compressed is started from the point 1 by the pressure P a Isentropically compressed to pressure P b The temperature of the steam reaches the intersection point 2s of the isentropic line and the superheated steam isobaric line b, and 1-2s are the isentropic line (vertical straight line);
(4) h is to be 2s With enthalpy value H m Making a comparison if H 2s Is less than H m Indicating that the isentropic compression end point of the working medium to be compressed is in a two-phase region;
because the right half of the saturation gas phase line c inclines rightwards, if the H2s is smaller than Hm at the moment, the point 2s is positioned in the two-phase region on the left side of the saturation gas phase line c; the saturation temperature and the pressure in the two-phase region correspond to each other, so the isobars are corresponding isotherms, and the steam isobars b are in a horizontal linear state in the two-phase region; if the point 1 is taken as the compression starting point temperature, even if the efficiency of the compression process is considered, the actual compression end point may be a point 2 on the right side of the point 2s, but the point 2 may still be in a two-phase region, so that the actual compression process line 1-2 is located in the two-phase region, which means that the problem of vapor carrying liquid in the interior and the outlet of the centrifugal compression main machine occurs, and the impact is easily caused on the impeller; at the moment, the temperature of the working medium steam to be compressed needs to be increased, so that the steam is superheated;
(2) Calculating the minimum inlet superheat degree of the superheated steam of the working medium to be compressed;
specifically, the method comprises the following steps:
(5) determining the intersection point n of an isentropic line passing through a saturation temperature point m and a saturated steam isobar line a in a T-S diagram, and acquiring the temperature T of the working medium to be compressed at the point n in a working medium physical property database n ；
(6) Calculating T n And T 1 The difference value of (1) to obtain the minimum inlet superheat degree delta T min 。
I.e. when the compression start temperature is T n Then, after being compressed by isentropic, the temperature of the working medium steam is T m At the moment, the working medium steam is in a complete gas phase; after the compression efficiency and the loss generated in the compression process are considered, the actual entropy value can be increased, and the compression end point can be more inclined to the right, so that the whole compression process is ensured to be in a superheat area, and liquid drops can not exist in the working medium steam.
Preferably, step (2) further comprises a correction step, namely: obtaining the actual temperature T of the working medium steam to be compressed 0 And will T 0 And T 1 Making a comparison if T 0 Less than T 1 Then calculate T n And T 0 The difference value of (1) to obtain the minimum inlet superheat degree delta T min 。
T 0 That is, the first temperature sensor detects and transmits the temperature to the main control module, if the actual temperature T occurs 0 Less than saturation temperature T 1 In the case of (1), the minimum inlet superheat degree Δ T min Should be given by T n And T 0 The difference of (A) is standard;
(3) Calculating the heating power required to be provided by the inlet superheater according to the minimum inlet superheat degree obtained by calculation;
specifically, the method comprises the following steps:
(7) according to the required degree of superheat of an inlet, a point 3 positioned on the right side of a point n is taken on a saturated steam isobar a, and an enthalpy value H corresponding to the point 3 is obtained in a working medium physical property database 3 ；
To ensure that no liquid droplets will be present in the centrifugal compressor main unit, the actual inlet superheat is preferably set slightly above Δ T, taking into account the uncertainty of the actual compression process and the complexity of the flow inside the centrifugal compressor min E.g. slightly higher than 1-3 deg.c, corresponding to a compression start temperature T 3 The corresponding point 3 is located on the right side of the point n, the isentropic compression line is 3-4s, and the actual compression end point is estimated to be located at a point 4 on the right side of 4 s;
as can be seen from FIG. 2, if the proper degree of superheat at the inlet is maintained, i.e., the distance between the point 3 and the point 1 is kept enough, the points 4s and 4 can be positioned at the right side of the gas phase saturation line c, i.e., the superheat zone, and at the moment, the whole compression process is in the superheat zone, so that the problem of liquid carrying inside the centrifugal compression main machine is avoided.
(8) Calculating the heating power P required to be provided by the inlet superheater according to the following formula:
P=（H 3 -H 1 ) X M; wherein M represents the mass flow of the saturated steam of the working medium to be compressed;
the degree of superheat of the inlet should be selected within a reasonable range to avoid H 3 Too high and excessive heating power lead to a decrease in economy.
Example 3
The saturated vapor pressure of normal hexane in a certain factory is 79 kPa (A), the temperature is 61 ℃, the pressure needs to be increased to 105.4kPa (A), and the saturated temperature is 70 ℃ correspondingly, and then the normal hexane is recycled; the temperature rise is 9 ℃, the flow rate is about 75 t/h, and the compression is carried out at the momentThe volume flow of the machine inlet is about 490 m 3 The flow rate is higher for a displacement compressor, and multiple compressors are generally required to be connected in parallel to meet the flow rate.
Therefore, the normal hexane saturated vapor was compressed by the centrifugal compressor of example 1 and the inlet temperature control method of example 2, and the control method was as follows:
(1) Performing physical property analysis on the working medium to be compressed, and entering the next step if the isentropic compression end point of the working medium is in a two-phase region;
n-hexane is a working medium in which the saturated gas line is inclined rightward in the present invention, but for the purpose of verification, the present embodiment also performs physical property analysis, specifically, includes the following steps:
(1) drawing a saturated steam isobar a, a superheated steam isobar b and a saturated gas phase line c of a working medium to be compressed in a T-S diagram, wherein the pressure on the saturated steam isobar a is 79 kPa, the pressure on the superheated steam isobar b is 105.4kPa, the saturated steam isobar a and the saturated gas phase line c intersect at a saturation temperature point 1, and the superheated steam isobar b and the saturated gas phase line c intersect at a saturation temperature point m;
(2) respectively obtaining the temperature T of the working medium to be compressed at the saturation temperature point 1 in the working medium physical property database 1 Entropy value S 1 And enthalpy value H 1 And the temperature T of the working medium to be compressed at the saturation temperature point m m Entropy value S m And enthalpy value H m ；
Wherein, T 1 At 61 ℃ and S 1 0.964 kJ/(kg. Multidot. DEG C), H 1 321.86 kJ/kg; t is m At 70 ℃ S m 0.982 kJ/(kg. Multidot. DEG C), H m 337.08 kJ/kg;
(3) according to the entropy value S 1 Obtaining the temperature T when the working medium to be compressed is compressed from Pa isentropic to Pb in the working medium physical property database 2s And enthalpy value H 2s ；
Wherein, T 2s At 70 ℃ and H 2s 330.76 kJ/kg;
(4) h is to be 2s With enthalpy value H m Making a comparison if H 2s Is less than H m Showing the isentropic compression end point of the working medium to be compressedIn the two-phase region:
in this example, H 2s Is indeed less than H m (ii) a Practice proves that when the pressure is 79 kPa (A) and n-hexane steam is in a saturated state (61 ℃), the n-hexane steam is compressed to 105.4kPa (A) in an isentropic manner, the dryness of the outlet is about 0.981, namely the outlet is in a liquid state, and the compression process and the compression end point are in two-phase regions; if the isentropic efficiency of compression is assumed to be 80%, calculating to obtain that the outlet dryness is 0.988 and still in a liquid state; indicating that the temperature of the saturated steam needs to be raised to obtain superheated steam with a certain degree of superheat.
(2) Calculating the minimum inlet superheat degree of the superheated steam of the working medium to be compressed;
specifically, the method comprises the following steps:
(5) determining the intersection point n of an isentropic line passing through a saturation temperature point m and a saturated steam isobar line a in a T-S diagram, and acquiring the temperature T of the working medium to be compressed at the point n in a working medium physical property database n ；
Wherein, T n Is 65 ℃;
(6) calculating T n And T 1 To obtain the minimum inlet superheat degree delta T min ；
T n - T 1 The temperature is 65-61 ℃ or 4 ℃, namely the minimum superheat degree;
through tests, saturated steam is subjected to temperature compensation, the temperature of the saturated steam is raised to 65 ℃, and then the saturated steam is subjected to isentropic compression to 105.4kPa (A), the outlet temperature of superheated steam is 70.7 ℃, and the superheated steam is already in a superheated state (the saturation temperature is 70 ℃); assuming an isentropic efficiency of compression of 80%, the outlet temperature of the superheated steam is 71.8 ℃ (specific T) m Superheat 1.8 ℃)); at the moment, the whole compression process is in an overheating area, the problem of liquid in the compressor is effectively avoided, the application of the centrifugal compressor under the parameters becomes possible, and the flow requirement can be met by adopting a single centrifugal compressor.
(3) Calculating the heating power required to be provided by the inlet superheater according to the minimum inlet superheat degree;
specifically, the method comprises the following steps:
(7) depending on the desired degree of inlet superheat, in saturationA point 3 which is positioned at the right side of the point n is taken from the steam isobar a, and an enthalpy value H corresponding to the point 3 is obtained from a working medium physical property database 3 ；
In this example, point 3 is not taken additionally, but the 4 ℃ obtained in step (2) is directly used as the inlet superheat, and the enthalpy value H obtained in the process n 329.32 kJ/kg;
(8) calculating the heating power P required to be provided by the inlet superheater according to the following formula:
P=（H 3 -H 1 ）×M=（329.32-321.86）kJ/kg *75 t/h =155.4291 kW；
wherein M represents the mass flow of n-hexane saturated steam;
(9) the mass flow rate M' of saturated steam to be supplied to the inlet superheater is calculated according to the following formula:
M’= P/（H’-H’’）=155.4291 kW/（2674.9-417.5）kJ/kg=0.25 t/h；
wherein H ' is the enthalpy of saturated water vapor at 100 ℃ and 0.1MPa (A), and H ' ' is the enthalpy of saturated water at 0.1MPa (A).
Namely, the normal hexane steam is required to be superheated from the saturation temperature of 61 ℃ to 65 ℃, for example, the normal hexane is heated by taking 0.1MPa (A) and 100 ℃ water steam as heat exchange media and utilizing condensation heat release of the water steam, and only about 0.25 t/h is required; it can be seen that the consumption of water vapor for inlet superheating is very small compared with the flow rate of normal hexane of 75 t/h, and the added cost is low.
Claims (10)
1. The centrifugal compressor comprises a centrifugal compression main machine (20) and is characterized by further comprising an inlet superheater (10) connected with a low-grade working medium inlet (21) of the centrifugal compression main machine (20), wherein the inlet superheater (10) is used for heating working medium steam to be compressed into superheated steam, and the superheated steam is sent to the centrifugal compression main machine (20) through the low-grade working medium inlet (21).
2. A centrifugal compressor according to claim 1, characterized in that the inlet superheater (10) is an electric heater comprising a housing, a steam line extending through the housing and having a working medium steam inlet (11) and a superheated steam outlet (12) extending to the outside of the housing; an electric heating element is arranged in the shell and positioned on the periphery of the steam pipeline.
3. The centrifugal compressor according to claim 1, wherein the inlet superheater (10) is a heat exchanger having a tube side and a shell side, the tube side or the shell side has a working medium steam inlet (11) and a superheated steam outlet (12), the shell side or the tube side has a heat exchange medium inlet and a heat exchange medium outlet, a circulation pipeline is communicated between the heat exchange medium inlet and the heat exchange medium outlet, and a heat exchange medium heating element is disposed on the circulation pipeline.
4. A centrifugal compressor as claimed in claim 2 or 3, wherein a first temperature sensor (30) for detecting the temperature of the steam of the working medium to be compressed is arranged at the saturated steam inlet, a second temperature sensor (50) for detecting the temperature of the superheated steam of the working medium to be compressed is arranged at the superheated steam outlet (12), and a pressure sensor (40) for detecting the pressure of the steam of the working medium to be compressed is arranged at the saturated steam inlet or the superheated steam outlet (12);
the centrifugal compressor further comprises a main control module (60), the first temperature sensor (30), the second temperature sensor (50), the pressure sensor (40) and the inlet superheater (10) are all connected with the main control module (60), and the main control module (60) is used for controlling the inlet superheater (10) to work according to detection results of the first temperature sensor (30), the second temperature sensor (50) and the pressure sensor (40).
5. An inlet temperature control method of a centrifugal compressor according to any one of claims 1 to 4, comprising the steps of, in order:
(1) Performing physical property analysis on the working medium to be compressed, and entering the next step if the isentropic compression end point of the working medium is in a two-phase region;
(2) Calculating the minimum inlet superheat degree of the superheated steam of the working medium to be compressed;
(3) And calculating the heating power required to be provided by the inlet superheater (10) according to the minimum inlet superheat degree.
6. The inlet temperature control method of a centrifugal compressor according to claim 5, wherein the step (1) comprises:
(1) drawing a saturated steam isobar a, a superheated steam isobar b and a saturated gas phase line c of a working medium to be compressed in a T-S diagram, wherein the pressure on the saturated steam isobar a is P a The pressure on the superheated steam isobar b is P b The saturated steam isobaric line a and the saturated gas phase line c intersect at a saturation temperature point 1, and the superheated steam isobaric line b and the saturated gas phase line c intersect at a saturation temperature point m;
(2) respectively obtaining the temperature T of the working medium to be compressed at the saturation temperature point 1 in the working medium physical property database 1 Entropy value S 1 And enthalpy value H 1 And the temperature T of the working medium to be compressed at the saturation temperature point m m Entropy value S m And enthalpy value H m ；
(3) According to the entropy value S 1 Obtaining the temperature T when the working medium to be compressed is compressed from Pa isentropic to Pb in the working medium physical property database 2s And enthalpy value H 2s ；
(4) H is to be 2s With enthalpy value H m Making a comparison if H 2s Is less than H m And indicating that the isentropic compression end point of the working medium to be compressed is in the two-phase region.
7. The inlet temperature control method of a centrifugal compressor according to claim 5, wherein the step (2) comprises:
(5) determining the intersection point n of an isentropic line passing through a saturation temperature point m and a saturated steam isobar line a in a T-S diagram, and acquiring the temperature T of the working medium to be compressed at the point n in a working medium physical property database n ；
(6) Calculating T n And T 1 The difference value of (1) to obtain the minimum inlet superheat degree delta T min 。
8. The inlet temperature control method of a centrifugal compressor according to claim 5, wherein the step (2) further comprises: obtaining the actual temperature T of the working medium to be compressed 0 And will T 0 And T 1 Making a comparison if T 0 Less than T 1 Then calculate T n And T 0 The difference value of (1) to obtain the minimum inlet superheat degree delta T min 。
9. The inlet temperature control method of a centrifugal compressor according to claim 5, wherein the step (3) includes:
(7) according to the required degree of superheat of an inlet, a point 3 positioned on the right side of a point n is taken on a saturated steam isobar a, and an enthalpy value H corresponding to the point 3 is obtained in a working medium physical property database 3 ；
(8) Calculating the heating power P required to be provided by the inlet superheater (10) according to the following formula:
P=（H 3 -H 1 ) X M; wherein M represents the mass flow of the saturated steam of the working medium to be compressed.
10. The inlet temperature control method of a centrifugal compressor according to claim 9, wherein the temperature T of point 3 in step (7) 3 Temperature T of specific point n n The height is 1-3 ℃;
further comprising the step (9): the mass flow rate M' of the heat exchange medium to be supplied to the inlet superheater is calculated according to the following formula:
M’= P/（H’-H’’）；
wherein, P is the heating power needed to be provided by the inlet superheater (10), H ' is the enthalpy value of the provided heat exchange medium at a given temperature and pressure, and H ' ' is the enthalpy value of the saturated liquid of the heat exchange medium at the same pressure.
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| CN85109765A (en) * | 1984-11-22 | 1986-07-09 | 株式会社日立制作所 | The compression cooling machine of carrying vapour-liquid separator |
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