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(China Electric Power News) The Upgrading of Our Country’s Coal and Electricity Unit Stepping into “Deep Waters”--VVVF Type Fluid Coupling Electrically Driven Feed Pump “Operates” on the “Heart” of Power Plant2012-05-31

(China Electric Power News) The Upgrading of Our Country’s Coal and Electricity Unit Stepping into “Deep Waters”
--VVVF Type Fluid Coupling Electrically Driven Feed Pump “Operates” on the “Heart” of Power Plant
                                
Release Source: China Electric Power News, the 5th edition the Electric Weekly
Release Date: May 31, 2012

In the mid-February this year, the National Energy Administration and the Ministry of Finance jointly issued the Notice on the Launching of Integrated Upgrading Work on Coal Plants, which was called No. 25 document of State Power by insiders. It explicitly indicates that "the implementation of upgrading of in-service coal and electricity unit is an important task proposed in ‘the 12th five-year plan’ of energy and the ‘12th five-year plan’ of electric power which has significance to improving the utilization efficiency of energy resources, promoting the power industry to accelerate the transformation and development mode, and building a resource-saving and environment-friendly society"; the upgrading of our country’s coal and electricity unit steps into “deep eaters” and it means that coal and electricity unit will further get “slimming”.

“Electrically driven feed pump is an important auxiliary engine with the maximum power consumption in coal unit; its power consumption accounts for the largest proportion of power plant electricity production, which directly affects the net coal consumption rate and energy consumption", said Zhang Wenhai, president of Changchun Times Machine & Electricity Technique Co., Ltd. (Changchun Times for short), professor senior engineer, and patent inventor of VVVF Type Fluid Coupling Electrically Driven Feed Pump.”
  

“Feed pump is been called the ‘heart’ of the thermal power unit; its motor power grade is large and it is demanding on the reliability of variable-frequency drive. The reconstruction project of feed pump variable-frequency drive is the technology commanding height of the power plant frequency conversion and energy saving application, and is also the important auxiliary engine with great potential in energy saving and consumption reducing, so it has a positive effect for promoting the integrated upgrading project of large coal and electricity units.” added by Liang Zhilong, president of Dongfang Hitachi (CD) Electrical Control Equipment Co., Ltd. (DHC for short).
 

On May 23, two "masters” in reconstruction technology program of the country's first coal unit VVVF Type Fluid Coupling Electrically Driven Feed Pump accepted exclusive interview from Electric Weekly.

A "Good Recipe" for Energy-Saving of Pump

In September 2011, Changchun Times and DHC jointly hands once again to implement project reconstruction of VVVF Type Fluid Coupling Electrically Driven Feed Pump of No. 1, 2 eclectically feed pump, No. 1, 200,000KW turbo generator unit of Datang Shuangyashan Thermal Power Co., Ltd. The project was started on September 18, and officially put into operation on October 7; the project cycle was shortened to be a month less than that of the traditional reconstruction programs. The project program did not change the original connection type of the system, and retained the original fluid coupling functions; it used a small "project amount" to "operate" the "heart" of coal and electricity unit.
 

Zhang Wenhai said, “reconstructing fluid coupling into multi-functional fluid coupling with switch of pump impeller speed control and volume speed control solves the operation problem of switch of frequency conversion and power frequency of electrically driven feed pump, realizes the reconstruction of VVVF Type Fluid Coupling Electrically Driven Feed Pump, and ends the history that the fluid coupling can not be with VVVF”.
 

According to the analysis of user monitoring statistical data, after reconstruction under the same load, the load current of the feed pump motor drops 107A on average; under the operating conditions of annual average load rate 76%, feed pump operates with frequency control of motor speed, the annual electricity can be saved for 5,304,063KWH with the saving rate 21%, reducing the power consumption rate of power plants by 0.5 percentage points. That equals to increasing the same KWH on-grid energy, annually increasing output value 2.02 million which amounts to 1664 tons of standard coal.
 

On January 12 this year, Datang Corporation implemented technology identification on the application achievement of the project, and gave the evaluation that “this project as a whole reaches the leading domestic level, has good promotional value, and applies for the 200,000KW grade unit installed with a fluid coupling electrically driven feed pump set; by continuing in-depth study, it can be gradually pilot for 300,000KW, 600,000KW grade units”.
 

“Changchun Times and DHC applied a number of patented technologies, and initiated the reconstruction technology program of the coal-fired unit VVVF Type Fluid Coupling Electrically Driven Feed Pump which broke the ‘bottleneck’ of using power plant ‘heart' part to apply frequency conversion technology so as to achieve energy saving; it provided the best plan and optimized and energy-saving technology for the integrated upgrading of the coal and electricity units, and achieved demonstration effect of integrating innovative technology, and popularizing application of high efficiency energy saving equipment,” said Liang Zhilong.

“Dilemma” of Coal and Electricity Unit

  In fact, due to electricity consumption growth slows down and thermal power suffers losses in successive years, the adjustment of electric power structure accelerates, electric power installed structure appears new features, the proportion of clean energy increases and thermal power installed proportion gradually decreases. At present, the national coal and electricity installed capacity is about 700 million KW, and the consumption of coal accounts counts the half of the total consumption of the whole society. With the gradual deepening of the national “energy-saving and emission reduction”, in recent years, through measures like “developing large units and suppressing small ones”, technical progress and strengthening management, etc., the national average coal consumption of electricity supply fell 10% than that at the initial stage of the "Eleventh Five-Year Plan". But on the other hand, there are still problems like extensive technology, mismanagement, high energy consumption and others in some coal and electricity units.
 

However, from the view of national conditions of our country's energy distribution, in a quite long period in the future, our country's electric power structure will be still based on thermal power, which puts forward higher requirements for the upgrading of the coal and electricity units.
 

Zhang Wenhai provided a set of data: “electrically driven feed pump is an important auxiliary engine with the largest power consumption in coal and electricity unit; its power consumption is the largest. The power consumption of 200,000KW coal and electricity feed pump accounts for 2.5% of the electric energy production and almost 33% of power plant power consumption rate; the rate of 300,000KW coal and electricity unit is 3.1%, almost 37%; that of 600,000KW coal and electricity unit is 3.27%, almost 42 percent; that of 1 million KW coal and electricity unit is 3.5%, almost 45%.”
 

It is easy to see that coal and electricity unit electrically driven feed pump urgently needs upgrading. To conservatively calculate according to average electricity saving rate 20%, the economic and social benefits brought by VVVF Type Fluid Coupling Electrically Driven Feed Pump after reconstruction are difficult to measure.
 

Electrically driven feed pump is droved by speed control type fluid coupling; though comparing to throttling adjustment mode, feed pump with speed control type fluid coupling is far more advanced, comparing to feed pump with VVVF, it is still of high energy consumption. For a long time, the conventional electrically driven feed pump with fluid coupling speed control can not directly realize VVVF. How to reconstruct speed control type fluid coupling to meet the need of VVVF energy saving reconstruction has become the technical “bottleneck” needed to break through.

Breaking the Technical “Bottleneck”

At present, there are mainly three types of the adjustment methods for speed control type fluid coupling at home and abroad: import adjustment type, export adjustment type and import-and-export adjustment type. They all belong to the volume speed control method---under the same condition of pump impeller speed control and load characteristics of the fluid coupling, changing its filling amount to achieve the goal of adjusting its output power and revolving speed. However, the frequency control is not applicable to the volume control type of fluid coupling; it has to be reconstructed by pump impeller (frequency conversion) speed control method into the fluid coupling with pump impeller speed control function. The so-called pump impeller speed control method works in this way: under the condition of constant fluid and load characteristics in the working oil chamber of the coupling, change the revolving speed of its pump impeller so as to change its input and output characteristics and to achieve the goal of adjusting its output power and revolving speed. This is the pump impeller speed control method.
 

“The greatest disadvantage of the former volume control method is that the transmission efficiency equals to the rotational speed ratio and changes according to its change. The peak efficiency is the rated condition point; when it departs from the rated condition point, the efficiency decreases as the rotational speed ratio decreases. On the contrary, the VVVF type fluid coupling solves the problem well.” said Zhang Wenhai, “the combination of the fluid coupling with pump impeller speed control and the motor with frequency control make up the VVVF type fluid coupling. Its biggest feature is that manually keeping the working oil chamber of the coupling at its optimal filling amount in order to keep constantly the maximum efficiency of the coupling during the speed-adjusting process. It efficiently solves the problem of high energy consumption when the volume control coupling runs at a low revolving speed ratio, and it saves electricity for 20% (the load rate under 75%).”
  

“We can say that frequency control fluid coupling has altered the present single speed adjustment function that the speed control type fluid coupling only operates volume speed control under power frequency so far at home and abroad. It has also added the function of fluid coupling operating pump impeller speed control, which solves the problem of keeping the fluid coupling at its maximum efficiency when controlling the frequency and speed. It also achieves the goal of saving energy and reducing consumption through the use of VVVF technology.”
 

More importantly, the fluid coupling can be switched between pump impeller speed control and volume speed control within itself. It is convenient, flexible, safe and reliable. It has cured the “chronic disease” of mutual repulsion between the volume speed control fluid coupling and the frequency converter.

“New Era” for VVVF

Comparing with the tremendous economic benefits brought by the VVVF type fluid coupling, its safety and reliable advantages are more in favor by Liang Zhilong: “it does not only greatly reduce the operating temperature of the oil system of the fluid coupling, but also solves the problem of unstable auxiliary power system due to the huge start-up shock of the high-power electrically driven feed pump; the operation mode of each pump can be switched from frequency conversion operation to power frequency operation, and the back-up pump will start in a chain reaction if the failure of frequency conversion pump trips the operation.”
 

“Different from the former methods of ‘replacing speed-up gear box’ or ‘reconstructed into speed-up gear box’, the VVVF Type Fluid Coupling Electrically Driven Feed Pump does not need to remove the original fluid coupling, which greatly saves the costs; it does not change the original connection type of the system and keeps its original function of the fluid coupling”, explained Liang Zhilong, “the VVVF Type Fluid Coupling Electrically Driven Feed Pump provides the best innovation-integrated solution for the integrated upgrading and reconstruction of the electrically driven feed pumps of coal and electricity units, which is world-leading and able to be applied to the integrated upgrading and reconstruction of active-duty and newly-built 300,000KW, 600,000KW and 1,000,000KW electrically driven feed pumps of coal and electricity units.”
 

He gave a typical case: “In March 2010, DHC carried out a frequency conversion reconstruction project for the 200,000KW, 300,000KW, 600,000KW and 1 million KW coal and electricity units draught fan. With the technology and project application experience accumulated in this project, DHC completed the nation’s first frequency conversion and energy saving project for the 300,000KW coal unit high-power feed pump in Meizhou Bay, Fujian Province. The feed pump has been running smoothly since being put into operation, and the electricity saving rate reaches 30%. In May this year, the high voltage frequency converter of DHC was selected again for the second stage of the feed pump reconstruction project in Meizhou Bay power plant. When the frequency conversion reconstruction of the four feed pumps is completed, the quantity of coal saved can amount to 19,414 tons per year.”
 

Just as what Zhang Wenhai has said: “this innovation has turned the mutually repulsive relationship between the frequency converter and the fluid coupling into a brand new combined application, which creates a new era for the project application of the VVVF Type Fluid Coupling Electrically Driven Feed Pump”.
 

“VVVF Type Fluid Coupling Electrically Driven Feed Pump is an independent intellectual property right in the field of integrated upgrading and reconstruction of coal and electricity units. We hope that the community will give concern to it, and offer more support and protection as well,” said Liang Zhilong.

VVVF technology is the most widely used and most advanced speed control technology; the speed control range can reach from 0 to 100%, speed control accuracy up to ± 0.5%, the largest energy-saving rate can go up to 30%~70%. With the further deepening of the "12th Five-Year Plan" national economic development planning and energy saving and emission reduction planning, frequency converter as the "energy-saving tool" role will become increasingly significant; from the point of view of electric power industry, VVVF Type Fluid Coupling Electrically Driven Feed Pump technology will play an irreplaceable role in the upgrading of 200,000KW, 300,000KW, 600,000KW, 1 million KW coal and electricity units.
 

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