Multi-stage coupling heating heat supply network circulating water system and working method thereof
Through the multi-stage coupled heating heating network circulating water system, the use of multi-stage pipelines and valve controls has solved the problem that the existing technology is difficult to meet the heating heat load needs of northern cities such as Northeast China, and achieved flexible multi-stage heating and peak heating , reduces power consumption, improves heating efficiency and meets standards.
Patent Information
- Application Number
- CN202411525880.4
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2024-10-30
- Publication Date
- 2025-01-10
AI Technical Summary
The existing single heating method is difficult to meet the increasing heating load demand in northern cities such as the Northeast, making it difficult for some areas to meet the heating temperature.
The multi-stage coupled heating heating network circulating water system is adopted, including the first station of the thermal network, the first steam turbine generator set and the second steam turbine generator set. Through multi-stage pipelines and valve control, the first, second and third-stage heating is achieved. and peak heating, flexible to meet the heat load needs of different weather temperatures.
Step-by-step heating is realized, the factory power consumption rate is reduced, the urban heating area is expanded, the heating meets the standard, and the economical heat load needs are met.
Smart Images
Figure CN119289415A_ABST
Abstract
Description
Technical Field
[0001] The invention belongs to the technical field of heat network heating, and specifically relates to a multi-stage coupled heating heat network circulating water system and a working method thereof. Background Art
[0002] The existing technical solution is to use steam turbine intermediate pressure cylinder to punch holes to extract steam, and then transport it to the heat exchanger at the first station of the heat network through pipelines to heat the heat network circulating water and realize external heat supply. However, with the continuous increase of heating load in northern cities, especially in northeastern cities, the heating capacity of the existing single heating method is increasingly unable to meet the heat load demand in the heating area, resulting in the difficulty of heating temperature in some areas to meet the standard. Summary of the invention
[0003] The present invention is aimed at the above-mentioned problems, makes up for the deficiencies of the prior art, and provides a multi-stage coupled heating heat network circulating water system and a working method thereof; the present invention can realize multi-stage coupled heating, can flexibly adopt different levels of heating methods according to different heating needs, and meet the heat load requirements under various weather temperatures while meeting the economic requirements.
[0004] To achieve the above purpose, the present invention adopts the following technical solution.
[0005] The present invention provides a multi-stage coupled heating heat network circulating water system, comprising a heat network head station, a first steam turbine generator set and a second steam turbine generator set, wherein the first steam turbine generator set and the second steam turbine generator set both comprise a high-pressure cylinder, a medium-pressure cylinder and a low-pressure cylinder, the main pipe inlet of the heat network head station is connected to the medium-pressure cylinders of the first steam turbine generator set and the second steam turbine generator set through a pipeline, the main pipe outlet of the heat network head station is connected to the return water port of a heat user through a return water main pipeline, the low-pressure cylinders of the first steam turbine generator set and the second steam turbine generator set are both connected to a steam exhaust device, and each of the steam exhaust devices is respectively connected to an air cooling island; The heat user water outlet is connected to the high back pressure condenser inlet through the water outlet main pipeline, the high back pressure condenser outlet is connected to the main pipe inlet of the first station of the heat network through the first-level water outlet pipeline, the first-level water outlet pipeline is also connected to the second-level water inlet pipeline connected to the inlet of the electric heat accumulator, the outlet of the electric heat accumulator is respectively connected to the second-level water outlet pipeline and the third-level water inlet pipeline, the second-level water outlet pipeline is connected to the first-level water outlet pipeline, the third-level water inlet pipeline is connected to the inlet of the back pressure unit, and the outlet of the back pressure unit is connected to the first-level water outlet pipeline through the third-level water outlet pipeline.
[0006] Furthermore, a first valve is provided on the secondary water inlet pipeline, a second valve is provided on the tertiary water inlet pipeline, and a third valve is provided on the secondary water outlet pipeline.
[0007] Furthermore, a fourth valve is provided on the first-level water outlet pipeline between the connection points with the second-level water inlet pipeline and the second-level water outlet pipeline, and a fifth valve is provided on the first-level water outlet pipeline between the connection points with the second-level water outlet pipeline and the third-level water outlet pipeline.
[0008] Furthermore, a sixth valve is provided on the third-level water outlet pipeline.
[0009] Furthermore, a maintenance pipeline is connected between the water outlet main pipeline and the first-level water outlet pipeline, a seventh valve is arranged on the water outlet main pipeline between the connection point with the maintenance pipeline and the high back-pressure condenser, an eighth valve is arranged on the first-level water outlet pipeline between the connection point with the maintenance pipeline and the high back-pressure condenser, and a ninth valve is arranged on the maintenance pipeline.
[0010] Furthermore, the high back-pressure condenser is connected with a steam supply pipeline, and the steam supply pipeline is connected with a pipeline between one group of the exhaust devices and the air-cooling island, so that the high back-pressure condenser is supplied with steam.
[0011] The present invention also provides a working method of a multi-stage coupled heating network circulating water system, using the multi-stage coupled heating network circulating water system, the working method comprises the following steps: 1) Primary heating: the fourth valve and the fifth valve are opened, and the first valve, the second valve and the third valve are closed. The heated water from the heat user enters the high back pressure condenser through the outlet water main pipeline for primary heating to obtain primary hot water. The primary hot water enters the first station of the heat network through the primary outlet water pipeline, and then returns to the heat user through the main return water pipeline for primary heating; 2) Secondary heating: open the first valve, the third valve and the fifth valve, close the second valve and the fourth valve, the heated water from the heat user enters the high back pressure condenser through the outlet main pipeline for primary heating, then enters the electric heat storage through the primary outlet pipeline and the secondary inlet pipeline for secondary heating to obtain secondary hot water, the secondary hot water enters the heating network head station through the secondary outlet pipeline and the primary outlet pipeline, and then returns to the heat user through the main return pipeline for secondary heating; 3) Three-stage heating: open the first valve and the second valve, close the third valve, the fourth valve and the fifth valve, the heated water from the heat user enters the high back pressure condenser through the outlet water main pipeline for primary heating, enters the electric heat storage through the primary outlet water pipeline and the secondary inlet water pipeline for secondary heating to obtain secondary hot water, the secondary hot water then enters the back pressure unit through the tertiary inlet water pipeline for tertiary heating to obtain tertiary hot water, the tertiary hot water enters the heating network head station through the tertiary outlet water pipeline and the primary outlet water pipeline, and then returns to the heat user through the main return water pipeline for tertiary heating; 4) Peak heating: open the first valve and the second valve, close the third valve, the fourth valve and the fifth valve, the heated water from the heat user enters the high back pressure condenser through the outlet water main pipeline for primary heating, enters the electric heat storage through the primary outlet water pipeline and the secondary inlet water pipeline for secondary heating to obtain secondary hot water, the secondary hot water then enters the back pressure unit through the tertiary inlet water pipeline for tertiary heating to obtain tertiary hot water, the tertiary hot water enters the heating network head station after passing through the tertiary outlet water pipeline and the primary outlet water pipeline, and then passes through the heat exchanger of the heating network head station for peak heating to obtain peak hot water, and the peak hot water then returns to the heat user through the main return water pipeline for peak heating.
[0012] Furthermore, the first-level hot water can reach 60°C, the second-level hot water can reach 70°C, the third-level hot water can reach 90°C, and the peak hot water can reach 100°C.
[0013] Beneficial effects of the present invention.
[0014] The present invention can flexibly adopt different levels of heating methods according to different weather temperatures. By multi-stage coupling to heat the circulating water of the heating network, it realizes the step-by-step heating of the circulating water of the municipal heating network, which can reduce the power consumption rate of the plant to expand the urban heating area, meet the heat load requirements under various weather temperatures while meeting the economy, improve the efficiency of the unit, and improve the degree of heating compliance. BRIEF DESCRIPTION OF THE DRAWINGS
[0015] In order to make the technical problems, technical solutions and beneficial effects solved by the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and specific implementation methods. It should be understood that the specific implementation methods described herein are only used to explain the present invention and are not used to limit the present invention.
[0016] Figure 1 It is the overall connection principle diagram of the present invention.
[0017] Markings in the figure: 1 is the first station of the heat network, 2 is the first steam turbine generator set, 3 is the second steam turbine generator set, 4 is the high-pressure cylinder, 5 is the medium-pressure cylinder, 6 is the low-pressure cylinder, 7 is the heat user, 8 is the return water main pipeline, 9 is the exhaust device, 10 is the air-cooling island, 11 is the outlet water main pipeline, 12 is the high back pressure condenser, 13 is the first-level outlet water pipeline, 14 is the electric heat storage device, 15 is the second-level inlet water pipeline, 16 is the second-level outlet water pipeline, 17 is the third-level inlet water pipeline, 18 is the back pressure unit, 19 is the third-level outlet water pipeline, 20 is the first valve, 21 is the second valve, 22 is the third valve, 23 is the fourth valve, 24 is the fifth valve, 25 is the sixth valve, 26 is the maintenance pipeline, 27 is the seventh valve, 28 is the eighth valve, 29 is the ninth valve, and 30 is the steam supply pipeline. DETAILED DESCRIPTION
[0018] As shown in the accompanying drawings, this embodiment provides a multi-stage coupled heating heat network circulating water system, including a heat network head station 1, a first steam turbine generator set 2 and a second steam turbine generator set 3, the first steam turbine generator set 2 and the second steam turbine generator set 3 both include a high-pressure cylinder 4, a medium-pressure cylinder 5 and a low-pressure cylinder 6, the high-pressure cylinder 4 is supplied with steam through a boiler at the front end, and the first steam turbine generator set 2 and the second steam turbine generator set 3 are powered by generators.
[0019] The main pipe inlet of the heating network first station 1 is connected to the medium-pressure cylinder 5 of the first steam turbine generator set 2 and the second steam turbine generator set 3 through a pipeline, and the main pipe outlet of the heating network first station 1 is connected to the return water outlet of the heat user 7 through the return water main pipeline 8. The low-pressure cylinder 6 of the first steam turbine generator set 2 and the second steam turbine generator set 3 are both connected to the exhaust device 9, and each exhaust device 9 is respectively connected to an air cooling island 10.
[0020] The water outlet of the heat user 7 is connected to the inlet of the high back-pressure condenser 12 through the main water outlet pipeline 11. The high back-pressure condenser 12 is used for primary heating. The high back-pressure condenser 12 is connected to a steam supply pipeline 30. The steam supply pipeline 30 is connected to a pipeline between one group of exhaust devices 9 and the air-cooling island 10, so that the high back-pressure condenser 12 is supplied with steam.
[0021] The outlet of the high back pressure condenser 12 is connected to the main pipe inlet of the heating network first station 1 through the primary water outlet pipeline 13. The primary water outlet pipeline 13 is also connected to the secondary water inlet pipeline 15 connected to the inlet of the electric heat accumulator 14. The electric heat accumulator 14 is used for secondary heating.
[0022] The outlet of the electric heat accumulator 14 is respectively connected to the secondary water outlet pipeline 16 and the tertiary water inlet pipeline 17, the secondary water outlet pipeline 16 is connected to the primary water outlet pipeline 13, the tertiary water inlet pipeline 17 is connected to the inlet of the back pressure unit 18, the back pressure unit 18 is used for tertiary heating, and the outlet of the back pressure unit 18 is connected to the primary water outlet pipeline 13 through the tertiary water outlet pipeline 19.
[0023] A first valve 20 is provided on the secondary water inlet pipeline 15 , a second valve 21 is provided on the tertiary water inlet pipeline 17 , and a third valve 22 is provided on the secondary water outlet pipeline 16 .
[0024] A fourth valve 23 is provided on the primary water outlet pipeline 13 between the connection points with the secondary water inlet pipeline 15 and the secondary water outlet pipeline 16 , and a fifth valve 24 is provided on the primary water outlet pipeline 13 between the connection points with the secondary water outlet pipeline 16 and the tertiary water outlet pipeline 19 .
[0025] In order to inspect or repair the back pressure unit 18 during the three-level heating, a sixth valve 25 is provided on the three-level water outlet pipeline 19. The sixth valve 25 is opened during the three-level heating. When the three-level heating is required to inspect or repair the back pressure unit 18, the sixth valve 25 and the second valve 21 are closed, and the third valve 22 and the fifth valve 24 are opened to temporarily perform the secondary heating.
[0026] In order to inspect or repair the high back pressure condenser 12, a maintenance pipeline 26 is connected between the outlet water main pipeline 11 and the first-level outlet water pipeline 13, a seventh valve 27 is arranged on the outlet water main pipeline 11 between the connection point with the maintenance pipeline 26 and the high back pressure condenser 12, an eighth valve 28 is arranged on the first-level outlet water pipeline 13 between the connection point with the maintenance pipeline 26 and the high back pressure condenser 12, and a ninth valve 29 is arranged on the maintenance pipeline 26.
[0027] Under normal heating conditions, the seventh valve 27 and the eighth valve 28 are opened, and the ninth valve 29 is closed. When the high back pressure condenser 12 needs to be inspected or repaired, the seventh valve 27 and the eighth valve 28 are closed, and the ninth valve 29 is opened. The heated water from the heat user 7 directly enters the primary water outlet pipeline 13 through the inspection pipeline 26, and is temporarily heated by the heat exchanger of the heating network first station 1, or temporarily heated by the electric heat storage device 14, the back pressure unit 18 and the heat exchanger of the heating network first station 1 cooperate with each other.
[0028] The embodiment adopts the above-mentioned multi-stage coupled heating heat network circulating water system to provide a working method of the multi-stage coupled heating heat network circulating water system, including the following steps: 1) Primary heating: open the fourth valve 23 and the fifth valve 24, close the first valve 20, the second valve 21 and the third valve 22, and the heated water from the heat user 7 enters the high back pressure condenser 12 through the outlet water main pipeline 11 for primary heating to obtain primary hot water, and the primary hot water enters the heat network head station 1 through the primary outlet water pipeline 13, and then returns to the heat user 7 through the main return water pipeline for primary heating; The first-level heating is enabled at the beginning and end of heating. At the beginning and end of heating in winter, the hot water temperature required by the heat user 7 is relatively low, and the circulating water in the heating network only needs to be heated at the first level by the high back pressure condenser 12. The first-level hot water can reach 60°C, that is, the circulating water in the heating network at 35°C is heated to about 60°C to provide heat to the heat user 7. At this time, the economy of external heating is very considerable, because the heat source for heating the circulating water in the heating network comes from the exhaust steam after the steam turbine unit does work, and the pipeline between the exhaust device 9 and the air-cooling island 10 is connected to the high back pressure condenser 12 through the steam supply pipeline 30.
[0029] 2) Secondary heating: open the first valve 20, the third valve 22 and the fifth valve 24, close the second valve 21 and the fourth valve 23, the heated water from the heat user 7 enters the high back pressure condenser 12 through the outlet main pipeline 11 for primary heating, then enters the electric heat storage 14 through the primary outlet pipeline 13 and the secondary inlet pipeline 15 for secondary heating to obtain secondary hot water, the secondary hot water enters the heat network first station 1 through the secondary outlet pipeline 16 and the primary outlet pipeline 13, and then returns to the heat user 7 through the main return pipeline for secondary heating; Secondary heating is enabled in the early and late stages of heating. In the early and late stages of winter heating, as the outdoor ambient temperature gradually becomes colder, the heating network circulating water at around 60°C cannot meet the needs of heat user 7. In the late and early stages of winter heating, the outdoor temperature gradually warms up, and heating network circulating water at around 90°C is no longer necessary. At this time, secondary heating is performed through the electric heat accumulator 14, so that the secondary hot water can reach 70°C to meet the heating demand. Of course, the secondary heating can also be flexibly turned on according to changes in temperature.
[0030] 3) Three-stage heating: open the first valve 20 and the second valve 21, close the third valve 22, the fourth valve 23 and the fifth valve 24, the heated water from the heat user 7 enters the high back pressure condenser 12 through the outlet water main pipeline 11 for primary heating, enters the electric heat storage 14 through the primary outlet water pipeline 13 and the secondary inlet water pipeline 15 for secondary heating to obtain secondary hot water, the secondary hot water then enters the back pressure unit 18 through the tertiary inlet water pipeline 17 for tertiary heating to obtain tertiary hot water, the tertiary hot water enters the heat network first station 1 through the tertiary outlet water pipeline 19 and the primary outlet water pipeline 13, and then returns to the heat user 7 through the main return water pipeline for tertiary heating; The three-stage heating is activated in the early and middle stages of heating. In the early and middle stages of winter heating, as the outdoor ambient temperature becomes colder, the heating network circulating water at around 70°C cannot meet the needs of heat user 7. In the middle and late stages of winter heating, as the outdoor ambient temperature begins to rise, the heating network circulating water at 100°C is no longer necessary. At this time, the back pressure unit 18 is used for three-stage heating, so that the three-stage hot water can reach 90°C to meet the heating demand. Of course, the three-stage heating can also be flexibly turned on according to changes in temperature.
[0031] 4) Peak heating: open the first valve 20 and the second valve 21, close the third valve 22, the fourth valve 23 and the fifth valve 24, the heated water from the heat user 7 enters the high back pressure condenser 12 through the outlet water main pipeline 11 for primary heating, enters the electric heat storage 14 through the primary outlet water pipeline 13 and the secondary inlet water pipeline 15 for secondary heating to obtain secondary hot water, the secondary hot water then enters the back pressure unit 18 through the tertiary inlet water pipeline 17 for tertiary heating to obtain tertiary hot water, the tertiary hot water enters the heat network head station 1 after passing through the tertiary outlet water pipeline 19 and the primary outlet water pipeline 13, and then passes through the heat exchanger of the heat network head station 1 for peak heating to obtain peak hot water, and the peak hot water then returns to the heat user 7 through the main return water pipeline for peak heating.
[0032] Peak heating is enabled in the middle of heating. In the middle of winter heating, the outdoor ambient temperature reaches the coldest. At this time, the heat exchanger at the first station 1 of the heating network is turned on to perform peak heating on the tertiary hot water, so that the peak hot water can reach 100°C to meet the heating demand. Of course, peak heating can also be flexibly turned on according to changes in temperature.
[0033] It can be understood that the above specific description of the present invention is only used to illustrate the present invention and is not limited to the technical solutions described in the embodiments of the present invention. Those skilled in the art should understand that the present invention can still be modified or replaced by equivalents to achieve the same technical effects; as long as the use requirements are met, they are within the protection scope of the present invention.
Claims
1. A multi-stage coupled heating heat network circulating water system, comprising a heat network head station (1), a first steam turbine generator set (2) and a second steam turbine generator set (3), wherein the first steam turbine generator set (2) and the second steam turbine generator set (3) both comprise a high-pressure cylinder (4), a medium-pressure cylinder (5) and a low-pressure cylinder (6), the main pipe inlet of the heat network head station (1) is connected to the medium-pressure cylinder (5) of the first steam turbine generator set (2) and the second steam turbine generator set (3) through a pipeline, the main pipe outlet of the heat network head station (1) is connected to the return water inlet of a heat user (7) through a return water main pipeline (8), the low-pressure cylinder (6) of the first steam turbine generator set (2) and the second steam turbine generator set (3) are both connected to a steam exhaust device (9), and each of the steam exhaust devices (9) is respectively connected to an air cooling island (10); It is characterized in that The water outlet of the heat user (7) is connected to the inlet of the high back-pressure condenser (12) through a main water outlet pipeline (11); the outlet of the high back-pressure condenser (12) is connected to the main pipe inlet of the heat network head station (1) through a primary water outlet pipeline (13); the primary water outlet pipeline (13) is also connected to a secondary water inlet pipeline (15) connected to the inlet of an electric heat accumulator (14); the outlet of the electric heat accumulator (14) is respectively connected to a secondary water outlet pipeline (16) and a tertiary water inlet pipeline (17); the secondary water outlet pipeline (16) is connected to the primary water outlet pipeline (13); the tertiary water inlet pipeline (17) is connected to the inlet of a back-pressure unit (18); the outlet of the back-pressure unit (18) is connected to the primary water outlet pipeline (13) through a tertiary water outlet pipeline (19).
2. A multi-stage coupled heating network circulating water system according to claim 1, characterized in that: The secondary water inlet pipeline (15) is provided with a first valve (20), the tertiary water inlet pipeline (17) is provided with a second valve (21), and the secondary water outlet pipeline (16) is provided with a third valve (22).
3. A multi-stage coupled heating network circulating water system according to claim 2, characterized in that: A fourth valve (23) is provided on the primary water outlet pipeline (13) between the connection points with the secondary water inlet pipeline (15) and the secondary water outlet pipeline (16), and a fifth valve (24) is provided on the primary water outlet pipeline (13) between the connection points with the secondary water outlet pipeline (16) and the tertiary water outlet pipeline (19).
4. A multi-stage coupled heating network circulating water system according to claim 3, characterized in that: The third-level water outlet pipeline (19) is provided with a sixth valve (25).
5. The multi-stage coupled heating network circulating water system according to claim 1, characterized in that: A maintenance pipeline (26) is connected between the outlet water main pipeline (11) and the primary outlet water pipeline (13); a seventh valve (27) is provided on the outlet water main pipeline (11) between a connection point with the maintenance pipeline (26) and the high back-pressure condenser (12); an eighth valve (28) is provided on the primary outlet water pipeline (13) between a connection point with the maintenance pipeline (26) and the high back-pressure condenser (12); and a ninth valve (29) is provided on the maintenance pipeline (26).
6. The multi-stage coupled heating network circulating water system according to claim 1, characterized in that: The high back-pressure condenser (12) is connected to a steam supply pipeline (30), and the steam supply pipeline (30) is connected to a pipeline between one group of the exhaust devices (9) and the air cooling island (10), so that the high back-pressure condenser (12) is supplied with steam.
7. A working method of a multi-stage coupled heating network circulating water system, using the multi-stage coupled heating network circulating water system according to any one of claims 3 to 6, characterized in that: The working method comprises the following steps: 1) Primary heating: the fourth valve (23) and the fifth valve (24) are opened, and the first valve (20), the second valve (21) and the third valve (22) are closed. The heated water from the heat user (7) enters the high back pressure condenser (12) through the outlet water main pipeline (11) for primary heating to obtain primary hot water. The primary hot water enters the heat network head station (1) through the primary outlet water pipeline (13), and then returns to the heat user (7) through the main return water pipeline for primary heating. 2) Secondary heating: the first valve (20), the third valve (22) and the fifth valve (24) are opened, and the second valve (21) and the fourth valve (23) are closed. The heated water from the heat user (7) enters the high back pressure condenser (12) through the outlet water main pipeline (11) for primary heating, and then enters the electric heat storage device (14) through the primary outlet water pipeline (13) and the secondary inlet water pipeline (15) for secondary heating to obtain secondary hot water. The secondary hot water enters the heat network head station (1) through the secondary outlet water pipeline (16) and the primary outlet water pipeline (13), and then returns to the heat user (7) through the main return water pipeline for secondary heating. 3) Three-stage heating: the first valve (20) and the second valve (21) are opened, and the third valve (22), the fourth valve (23) and the fifth valve (24) are closed. The heated water from the heat user (7) enters the high back pressure condenser (12) through the outlet water main pipeline (11) for primary heating, and then enters the electric heat storage device (14) through the primary outlet water pipeline (13) and the secondary inlet water pipeline (15) for secondary heating to obtain secondary hot water. The secondary hot water then enters the back pressure unit (18) through the tertiary inlet water pipeline (17) for tertiary heating to obtain tertiary hot water. The tertiary hot water enters the heat network head station (1) through the tertiary outlet water pipeline (19) and the primary outlet water pipeline (13), and then returns to the heat user (7) through the main return water pipeline for tertiary heating. 4) Peak heating: the first valve (20) and the second valve (21) are opened, and the third valve (22), the fourth valve (23) and the fifth valve (24) are closed. The heated water from the heat user (7) enters the high back pressure condenser (12) through the outlet water main pipeline (11) for primary heating, then enters the electric heat storage device (14) through the primary outlet water pipeline (13) and the secondary inlet water pipeline (15) for secondary heating to obtain secondary hot water. The secondary hot water then enters the back pressure unit (18) through the tertiary inlet water pipeline (17) for tertiary heating to obtain tertiary hot water. The tertiary hot water enters the heat network head station (1) through the tertiary outlet water pipeline (19) and the primary outlet water pipeline (13), and then passes through the heat exchanger of the heat network head station (1) for peak heating to obtain peak hot water. The peak hot water then returns to the heat user (7) through the main return water pipeline for peak heating.
8. The working method of a multi-stage coupled heating network circulating water system according to claim 7, characterized in that: The first-level hot water can reach 60°C, the second-level hot water can reach 70°C, the third-level hot water can reach 90°C, and the peak hot water can reach 100°C.