Steam turbine seal

Application of "Wang Changchun" energy-saving steam sealing technology on 300MW and 600MW steam turbines

Wang Shengwu, Harbin Tongneng Electric Co., Ltd.

Abstract: " Since the advent of "Wang Changchun" energy-saving steam seal, it has brought a revolution to the steam seal industry. Through the current demonstration of the design and operation of the 300MW and 600MW main power generating units in my country, some reasons for the low cylinder efficiency of the units were found, and the practicality and benefits of using "Wang Changchun" energy-saving steam sealing technology were explained. The future economic benefits are discussed, and the safety, economy and other aspects during installation and use are discussed.

Keywords: 300MW, 600MW steam turbine "Wang Changchun" energy-saving steam seal "contact steam seal" patent safety and energy saving

Foreword

With the development of global energy As the situation becomes increasingly severe, energy conservation has become a major theme of energy policies in various countries. my country's National Development and Reform Commission clearly stated in the "Medium and Long-term Special Plan for Energy Conservation" that the macro-energy conservation target is an average annual energy conservation rate of 3% from 2003 to 2020, with an energy-saving capacity of 1.4 billion tons of standard coal. Steam turbines have now become one of the high-energy-consuming equipment. How to reduce energy loss, improve unit availability, unit thermal performance and increase output, that is, reduce energy consumption, has become an increasingly prominent issue.

1 Analysis of the reasons for the low cylinder efficiency of the current unit

Steam turbine losses can generally be divided into: internal losses and external losses of the steam turbine. Internal losses are various losses that directly affect the thermal state of steam, and external losses are losses that do not affect the state of steam (mainly mechanical losses and shaft end losses). The 300MW and 600MW steam turbines that have been put into production in recent years have introduced world-leading technologies in the design of throughflow, such as the design and processing of nozzles, the three-dimensional and four-dimensional design of moving and static blades, etc. Therefore, internal and external losses of the steam turbine will cause the unit to The main problem of low cylinder efficiency focuses on the structural type of the steam seal. At present, in order to improve the operating efficiency of the unit, the power plant uses various advanced and mature technologies to carry out technical transformation of the steam seal to improve the safety and reliability of the unit, as well as the availability rate of the unit, thermal performance and output of the unit, which has become a way to save energy and improve efficiency. an important measure. At present, the 300MW and 600MW steam turbine units, which are the main units, all have phenomena such as large steam seal leakage, especially the high and medium pressure combined cylinder units. Due to the wear of the steam seal between the high and medium pressure, the steam in the middle and high cylinders leaks partially into the interlayer, and the interlayer steam flow affects Problems such as the upper and lower temperatures of the cylinder, low efficiency of the high-pressure cylinder, and serious wear of the through-flow radial steam seal are the main reasons that affect the economical operation of the unit.

As the phenomenon of steam seal leakage has attracted more and more attention from the steam turbine industry, major power generation companies and steam turbine design and manufacturing manufacturers have demonstrated the use of new steam seals. As one of the important technical measures to solve the above problems, the promotion and use of "Wang Changchun" energy-saving steam seals in power plants and manufacturers across the country has brought huge economic benefits and has attracted widespread attention in the industry.

2 "Wang Changchun" energy-saving steam seal usage

Harbin Tongneng Electric Co., Ltd. has been committed to the research and development of sealing problems for more than 20 years since its establishment. To solve the problem of steam seal leakage (gas), we developed a patent for "contact steam seal" (invention patent number: ZL 02 1 28382.6), and developed a series of "Wang Changchun" energy-saving steam seal products. Since 2001, it has been installed on more than 300 steam turbines with a capacity of 3~600MW (covering almost all domestic models), including more than 50 300MW and 600MW steam turbines. After years of operation practice and thermal performance and The data obtained from the vacuum tightness test prove that "contact steam seal" is an energy-saving, consumption-reducing, safe, reliable, advanced and mature new technology. It was listed as a national key new product in 2005 and became a national key new product in 2008. The first batch of key energy-saving technology promotion products. Due to the obvious energy-saving effect, some of the larger domestic steam turbine manufacturers (such as Harbin Steam Turbine, Beizhong, Dongqi, SAIC, etc.) are using this patented technology product in the manufacture of new units and the renovation of existing units.

Application Example 1: 1. In June 2005, the shaft seal of Dongqi 300MW N300-16.7/537/537-6 #8 machine was carried out at Xuanwei Power Plant in Yunnan, and the high-pressure shaft seal 10 circle, 8 turns of the medium pressure shaft seal, 9 turns of the steam seal between high and medium pressure, and 10 turns of the low pressure front and rear seals. The unit was successfully started and connected to the grid after an overhaul.

In order to test the effect of use, Shanxi Electric Power Academy conducted a thermal performance test of #8 machine in February 2006.

The experimental results are as follows:

The influence of shaft seal steam leakage on heat rate

Amount of shaft seal steam leakage before and after overhaul

Name Unit design value before overhaul and after overhaul

High pressure rear shaft seal steam leakage flow kg/h 4417 10540.1 6577.1

Medium pressure rear shaft seal steam leakage flow kg/h 812 1648 1156.6

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High-pressure cylinder mezzanine leakage flow kg/h 1601 12560 5100

Medium and medium-pressure cylinder bridge leakage kg/h 6825 35498.1 15666

Pair of shaft seal systems before and after overhaul Economic impact

Name affects heat consumption (kJ/kW.h) Overhaul benefit

kJ/kW.h Overhaul benefit

g/kW.h

Before and after overhaul

The amount of steam leakage from the high-pressure rear shaft seal 27.163 8.935 18.228 0.691

The amount of steam leakage from the medium-pressure rear shaft seal

High-pressure cylinder interlayer steam leakage 8.969 2.862 6.107 0.232

Medium and medium-pressure cylinder bridge leakage 50.133 14.593 35.540 1.348

Total 86.265 26.390 59.875 2.271

After overhaul Significantly improved the bad steam leakage such as shaft seal steam leakage, bridge and interlayer steam leakage, the economic impact is 59.875kJ/kw.h, and the coal saving is about 2.27g/kw.h.

Application Example 2: In September 2005, the shaft seal of the 200MW CC140/N200-12.75/535/535 #11 machine produced by Harbin Automobile was carried out at the Hebei Handan Thermal Power Plant, and 11 high-pressure front-end steam seals were installed. There are 7 turns of high-pressure rear-end steam seals, 8 turns of medium-pressure front-end steam seals, 6 turns of medium-pressure rear-end steam seals, and 10 turns of low-pressure front and rear steam seals. The unit was successfully connected to the grid after being overhauled. In November 2005 and May 2006, Xi'an Thermal Engineering Research Institute Co., Ltd. conducted strict thermal performance tests on #11 steam turbine in accordance with the American Society of Mechanical Engineers "Steam Turbine Performance Test Procedures" (ASME PTC6-1996). The test results are as follows:

1. The steam seal leakage amount of the first and second shaft seal leaks reaches the design value. The design value of the shaft seal steam leakage of this unit is: first leakage 6.87t/h, second leakage 2.86t/h. The on-site measurement value is 5.1t/h for the first leakage and 3.0t/h for the second leakage. The steam leakage amounts of the first leakage and the second leakage before modification were 8.6t/h and 4.8t/h respectively. The amount of steam leakage from the steam seal is greatly reduced, and the economical efficiency of unit operation is significantly improved.

2. By installing a contact steam seal on the high-pressure inner gear steam seal, the extraction steam temperature in the first section of the unit is significantly reduced. After the transformation, the extraction steam temperature of the first section of the unit is 363°C. Before the transformation, the extraction steam temperature of the first section was 388°C. The design value of this temperature is 370°C. The decrease in temperature indicates that the amount of steam leaking into the interlayer of the inner and outer cylinders through the high-pressure inner gear steam seal is significantly lower than the design value, and the economical operation of the unit is improved.

3. By transforming the shaft end steam seals on both sides of the low-pressure cylinder into contact steam seals, the vacuum tightness of the unit operation is improved. The vacuum leakage rate of the unit before the transformation was 700-800Pa/min, and after the transformation it was 105Pa/min, which was better than the qualified value of 300Pa/min and reached an excellent level. The improvement of vacuum greatly improves the economical efficiency of unit operation.

4. Through the transformation, the amount of steam leakage from the outer gear of the shaft end of the unit is extremely small, and the problem of water in the oil is solved, ensuring the safe operation of the unit.

5. After the transformation, the axial displacement of the unit, the expansion difference between high and medium pressure cylinders, and the expansion of high, medium and low pressure cylinders are all within the qualified range, and the unit operates stably.

The test results show that the thermal performance of the unit has reached the international leading level.

Application example three: In February 2009, Harbin Automobile 73B steam turbine N300-16.7/537/537-2 was modified at the #1 machine of Guizhou Qianxi Power Plant. The scope of steam seal modification: high-pressure rear axle Sealing---4 channels are contact ferrite steam seals, medium pressure rear shaft seal---4 channels are contact ferrite steam seals, balance ring steam seals---10 channels are floating gear ferrite Steam seals, low-pressure front and rear shaft seals - 6 contact ferrite steam seals.

Name of the design before and after the change, the design value of the deviation after the change and the deviation after the change

Main steam flow (t/h) 902.5 932.1 900 ↓-32.1 ↓-2.5< /p>

Main steam pressure on machine side (MPa) 16.67 16.74 16.88 ↑0.14 ↑0.21

Main steam temperature on machine side (℃) 537 541 539 ↓-2 ↑2

Regulating stage pressure (MPa) 11.831 11.9 11.47 ↓-0.43 ↑0.36

High discharge pressure (MPa) 3.534 3.29 3.2 ↓-0.09 ↓-0.334

High discharge temperature (℃) 311.1 319.8 310.1 ↓-9.7 ↓-1

Machine side reheat steam pressure (MPa) 3.171 3.05 2.96 ↓-0.09 ↓-0.21

Machine side reheat temperature (℃) 537 540 540 0 3

Unit side feed water temperature (℃) 274.1 270.18 268.6 ↓-1.5 ↓-5.5

First-stage extraction steam pressure (MPa) 5.792 5.55 5.44 ↓-0.11 ↓-0.35

First-stage extraction temperature (℃) 381.4 398.7 388.3 ↓-9.6 ↑6.9

Second-stage extraction pressure (MPa) 3.534 3.17 3.15 ↓-0.02 ↓-0.384

< p>Second-stage extraction temperature (℃) 316.8 327.3 317.7 ↓-9.6 ↑0.9

Third-stage extraction pressure (MPa) 1.575 1.51 1.51 0 ↓-0.065

Third-stage extraction temperature (℃) 435 465 462 ↓-3 ↑27

Four-stage extraction steam pressure (MPa) 0.7442 0.75 0.74 ↓-0.01 0

Four-stage extraction temperature (℃) 338.9 366 362 ↓-4 ↑23.3

Five-stage extraction steam pressure (MPa) 0.2509 0.26 0.26 0 ↑0.01

Five-stage extraction temperature (℃) 235.5 290.8 275 ↓-15.8 ↑39.5

Six-stage extraction steam pressure (MPa) 0.03 0.05 0.05 0 ↑0.02

Six-stage extraction temperature (℃) 136.9 222 196 ↓-26 ↑59.1

Seven-stage extraction Extraction steam pressure (MPa) -0.027 -0.0063 -0.0045 ↑0.0018 ↓-0.0225

Seven-stage extraction temperature (℃) 86.6 89.5 86.3 ↓-3.2 0

Eight-stage extraction pressure (MPa) -0.066 -0.0615 -0.05 ↑0.015 ↑0.016

Eight-stage pumping temperature (℃) 62.7 64.5 62.7 ↓-1.8 0

Low pressure cylinder [exhaust steam temperature 37.5 38.3 38.3 0 0

Thrust tile temperature (℃) 48℃ 48℃ 0

Remarks: The above data are instantaneous data. When recording, the main steam pressure, main steam temperature, post-reheat temperature, and exhaust steam temperature on the machine side before and after the unit overhaul are all the same and recorded at the same time. The parameter recording time before the overhaul is: April 30, 2008; the parameter recording time after the overhaul is the data from 10:30 to 10:50 on April 13, 2009. The speed regulating valve control method is: valve forward.

It can be seen from the operating data that the steam consumption rate under THA operating conditions decreased from 3.107kg/kw.h before transformation to 3.00kg/kw.h under the same operating conditions. High-pressure exhaust steam The temperature dropped from 311.1℃ before modification to 310.1℃, which is close to the design value. The operating data of each tile is good, the thrust has not changed, and the self-sealing operation requirements are met.

3 Safety and economical situation of using "Wang Changchun" energy-saving steam seal

When the power plant decides to adopt the feasibility analysis of this technology, the first concern is the safety issue. Whether there will be shaft system vibration during the starting and stopping process is the issue that users are most concerned about, followed by the economic benefits generated.

"Wang Changchun" energy-saving steam seal, during the transformation, the steam seal structure and installation plan were reasonably designed and used based on the original unit design concept and actual operation conditions. For example, pressure section: ⅰ. Outer shaft seal, contact shaft seal is mainly used: non-metal contact teeth can adjust the radial gap to 0-0.05mm gap that cannot be achieved by the original steam seal teeth, and the average dynamic and static clearance is reduced by 0.30-0.40 mm. ⅱ. In balance ring steam seals (or bridge steam seals) and middle and high school partition steam seals, due to the relatively large steam flow and pressure difference, gap floating tooth type steam seals are used: floating teeth can ensure that a small part of the steam flow passes through , without changing the performance design of the original unit, it can effectively reduce the dynamic and static gaps while ensuring safety, and adjust it to a 0.25-0.30mm gap that cannot be achieved by the original steam seal teeth.

This can not only greatly reduce the amount of steam leakage at each leakage point in the cylinder, but also ensure that all the steam entering the steam turbine proceeds along the cascade passage of the steam turbine to do work, and effectively prevents the cylinder from leaking. The internal steam leaks out of the cylinder, causing the bearing temperature to rise or the lubricating oil to contain water, thereby reducing energy loss and significantly improving the efficiency of the unit. Through the use of patented technology - the combination of gap floating tooth steam seal and non-metallic sealing tooth steam seal, the problem of steam seal leakage is solved, thereby achieving the purpose of energy saving and efficiency improvement;

In the vacuum section, the shaft The seal adopts a contact shaft seal, and the non-metallic contact teeth adopt a radial gap of 0-0.05mm that cannot be achieved by metal teeth. This effectively prevents the air outside the steam turbine from leaking into the steam turbine and ensures a good vacuum in the steam turbine vacuum system. This ensures that the steam turbine has the lowest possible back pressure parameters, which ensures the efficiency of the steam turbine.

It is the working principle of "Wang Changchun" energy-saving steam seal with the above-mentioned working characteristics, which increases the user's determination to use this technology, which can ensure safe operation and obtain great economic benefits. Taking 300 MW as an example, through the transformation of all shaft seals and high and medium balance ring steam seals (or bridge steam seals), the average heat consumption is reduced by about 60kJ/kw.h.

4 Issues concerning the use of "Wang Changchun" energy-saving steam seal

4.1 Whether self-sealing operation can be guaranteed

According to the working principle of the steam seal, the so-called self-sealing That is to say, the steam used for the shaft seal mainly depends on the leakage steam of high and medium pressure shaft seals. The steam seal leakage of current 300MW and 600MW steam turbines is far greater than the design value. The "Wang Changchun" energy-saving steam seal transformation is to transform 1/3---1/5 of the original steam seal's steam seal teeth into small gap steam seal teeth , to ensure that the steam leakage in each section of the unit is close to the design value and improve the operating quality of the unit. Therefore, through the transformation of the shaft seal and balance ring steam seal of Unit #1 of Qianxi Power Plant and the practical application of Unit #8 of Xuanwei Power Plant, it can be proved that this steam sealing technology does not change the self-sealing performance.

4.2 Whether the values ??of steam extraction in each section are changed and whether the axial thrust changes?

Tongneng Company conducted the "Wang Changchun" test for the 300MW steam turbine produced by Qianxi Power Plant #1 Jihaqi "Energy-saving steam seal transformation is an example: this model is composed of 34 stages. The high-pressure cylinder has 1 single-row adjustment stage and 12 pressure stages, the medium-pressure cylinder has 9 pressure stages, and the low-pressure cylinder has 2×6 pressure stages; return There are 7 sections of steam extraction from the thermal heater, which are extracted from the 9th, 13th, 18th, 22nd, 24th, 31st, and 26/32nd stages respectively to supply steam for three high-pressure heaters, one deaerator and three low-pressure heaters. , there is a shaft seal heater between the condensate pump and the No. 7 low-pressure heater. This transformation only involves the shaft seal and balance ring steam seal, and does not involve the baffle and blade top steam seal, that is, the changes in steam extraction in each section will not be affected. The experimental data of the #1 machine can illustrate this problem.

Extraction steam pressure change table before and after overhaul

Deviation of name before and after design change

Extraction pressure of one section (MPa) 5.792 5.55 5.44 ↓-0.11

Second-stage extraction steam pressure (MPa) 3.534 3.17 3.15 ↓-0.02

Three-stage extraction steam pressure (MPa) 1.575 1.51 1.51 0

Four-stage extraction steam pressure (MPa) 0.7442 0.75 0.74 ↓-0.01

Fifth-stage extraction steam pressure (MPa) 0.2509 0.26 0.26 0

The main factors affecting thrust are: 1. Load When it rises, the main steam flow rate increases and the steam pressure difference at each stage increases, which increases the axial thrust of the unit. 2. The main steam parameters decrease and the reaction degrees at all levels increase, which increases the axial thrust. 3. The separator steam seal is worn and the amount of steam leakage increases, which increases the pressure difference at all levels. 4. The through-flow part of the unit is scaled due to poor steam quality, and the pressure difference between the front and rear blades and the impeller of the corresponding stage increases, which increases the axial thrust. From the high-pressure exhaust temperature and thrust tile temperature change table before and after the overhaul, it can be seen that the thrust tile temperature before and after the overhaul has always been 48°C, which shows that the axial thrust has not changed. At the same time, the high-pressure exhaust temperature has significantly improved after the overhaul and is close to the design value.

Name design changed before and after

High discharge temperature (℃) 311.1 319.8 310.1

Thrust tile temperature (℃) 48℃ 48℃

Change table of high-pressure exhaust temperature and thrust tile temperature before and after overhaul

5 Feasibility of using "Wang Changchun" energy-saving steam seal for domestic main unit 300MW and 600MW steam turbines

5.1 Unit Existing problems

Nowadays, problems such as steam seal leakage and low cylinder efficiency of the domestic main unit 300MW and 600MW steam turbines are common. Operation results show that the efficiency of high-pressure cylinders is generally 76 to 80%, and the efficiency of the cylinder after overhaul drops rapidly after several starts and stops. The exhaust steam temperature of the high-pressure cylinder is higher than the design value. As a result, the amount of desuperheated water in the boiler reheater increases, and the shaft seal overflow is large. Compared with imported units of the same capacity and type, the operating coal consumption rate of the unit is generally higher. After the unit was overhauled and disassembled, it was found that there were varying degrees of changes in the high- and medium-pressure inner cylinders. The radial clearance of the steam seals was seriously worn, with some reaching 1.5 to 2.5 mm. The elastic retreat steam seals were generally stuck and had basically no retreat effect. Some units also had Problems such as the fracture of the back arc plate spring of the steam seal block were found.

Due to the large diameter of the balance plate and the large pressure difference between the front and rear, the steam seal gap will be slightly larger and the amount of steam leakage will increase significantly, resulting in greater safety hazards and economic problems.

5.2 The feasibility of using "Wang Changchun" energy-saving steam seal

Harbin Tongneng Electric Co., Ltd. passed the research on the steam seal structure, working principle, design, and Understand the technical conditions of processing and installation, and investigate the operation status of the unit and the results of overhaul inspections. In view of the structural characteristics and existing problems of steam turbines, we applied the patented technological achievements of "contact steam seal" to develop the "Wang Changchun" series of energy-saving steam seal products, which adopt a patented structure: contact floating seal teeth, honeycomb steam seal, ferrite steam seal The back spring adopts new structures such as coil springs, and adopts different steam seal gaps according to different parts to significantly reduce the amount of steam leakage from the steam seal, improve the vacuum degree of the unit, and significantly improve the operating economy of the unit. .

6 Conclusion

At present, domestic 300MW and 600MW steam turbines are widely used in power plants across the country as main units. They can increase unit output, reduce power generation coal consumption, and improve unit thermal performance. They are the major power generation units in the country. The company's main goal is to carry out technical transformation of the unit. "Wang Changchun" energy-saving steam seal has been used in supporting main engine manufacturing plants across the country and transforming more than 50 300MW and 600MW steam turbines in power plants, achieving very satisfactory results to users. Harbin Tongneng Electric Co., Ltd. will continue to sum up experience and strictly control the quality of design, processing and installation to provide reliable guarantee for energy saving and efficiency improvement of steam turbines and make positive contributions to the development of my country's electric power industry.