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    Datang International Xiahuayuan Power Plant (Energ

    Energy-conservation and Consumption Reduction Expert System of Steel Ball Coal Mill in the Power Station Boiler

    I. Brief introduction to the Power Plant

    Xiahuayuan Power Plant of Datang International Power Generation Co., Ltd. has one 200,000 unit boiler with design fuel coal being bitumastic coal and designed pulverized coal fineness being R90 23%. It provides 4 DTM-320/580 single-input single-output steel balls manufactured by NHI and its coal pulverizing system is intermediate warehouse-type system and includes 2 pulverized coal bunkers.

    II. Introduction of technical modification

    1) Analysis of causes for relatively high ball consumption and power consumption in the ball mill

    Currently, grinding ball used by power industry in China is mainly divided into three types, namely low chromium cast iron grinding ball (with chromium contents being 0.5%~5%), medium chromium cast iron grinding ball (with chromium contents being 5%~10%) and high chromium cast iron grinding ball (with chromium contents being over 10%). These grinding balls have the following common shortcomings that cause relatively high ball consumption.

    A. Difference between abrasive resistance of surface layer and the core of grinding ball is relatively large, leading to the fact that diameter of grinding ball is decreased unevenly during its abrasion process, grading of grinding ball is deviated significantly and fineness or production of pulverized coal is lowered; to ensure the fineness and yield of pulverized coal, more steel balls are needed in the ball mill to increase the load. Excessive grinding balls that were already ground into small balls or even disabled balls fail to be removed from the operating or hot spare ball mill, thus further increasing the load of ball mill. The larger the load of ball mill is, the larger the power consumption will be.

    B. Abrasive resistance of grinding ball is relatively poor which worsens the gradation stability of grinding ball. After operating for a certain period of time, the proportion of small diameter grinding balls that meet gradation requirements decreases while the proportion of invalid balls increases, giving rise to poor fineness or lower production of pulverized coal.

    C. With gradual rise in the price of metallic materials, quality of products provided by grinding ball supplier has been reduced and precious metal contents of its grinding ball, such as chromium contents, are much lower than design requirements, which results in poor abrasive resistance and impact toughness of grinding ball, stronger abrasion and breaking rate of grinding ball and increase in ball consumption and power consumption.

    D. In the gradation of grinding ball, the proportion of small diameter grinding ball is relatively small. Currently, large diameter grinding ball is generally used by the Power Plant and the percentage of grinding ball with diameter greater than 30mm is at least 70%, resulting in decrease of the action point or area of grinding balls with same weight and making grinding efficiency relatively low. Particle size of coal used for power generation is mostly less than 3mm and grinding balls with diameter between 25mm and 30mm are sufficient to grind such coal into pulverized coal. In other words, grinding balls used by ball mill for pulverizing coal should, in theory, be mainly those with diameter less than 30mm. Obviously, if the average diameter of grinding ball is reduced under the condition of same total ball weight for ball mill, the number or surface area of grinding ball will be increased, action point or area of coal pulverization will be increased accordingly and efficiency of grinding pulverized coal under certain conditions will be higher.

    III. Analysis about modification benefits

    Energy-saving modification is analyzed in the following three aspects: firstly, economic analysis of ball consumption for operation every year; secondly, economic analysis of energy-saving and power consumption; thirdly, investment return period.


    1. Project input (single coal mill) 


    Input before modification

    Input after modification

    Ball load

    1.    Preliminary ball load: 55t

    2.    Price of grinding ball used currently: 6000 Yuan/t,

    Totaling RMB 330000

    1.    Anticipated ball load: 40t

    2.    Price of ultra high chromium rare earth grinding ball: 18000 Yuan/t

    Totaling RMB 720000

    2. Portion that can be saved for project (singe coal mill) 

    Portion that can be saved for project

    Economic type

    1.    Single coal mill throws away grinding balls used originally. It is estimated that 70% of them can be used as adding balls to other modified coal mills.

    2.    Preliminary ball load: about 55t, multiply by 70% is approximately equal to 38t, totaling RMB 228,000

    3.    Investment of single coal mill after the saving 720000-330000-228000=162000

    3. Project input and recovery (single coal mill) 

    Input Method

    Input Portion


    Economical type

    1.     Preliminary ball load of ultra high chromium rare earth grinding ball: RMB 162,000

    1.    Electric charge saved by single coal mill annually: about RMB 180,000

    2.    Expenses of fire coal saved by single coal mill annually: not in quantitative calculation

    3.    Expenses saved annually after the grinding ball modification of single coal mill: about RMB 180,000

    Investment recovery period

    If coal-saving is not taken into consideration, investment costs can be recovered after 10-month operation


    1. Ball consumption: (analysis based on the unit of single coal mill according to data design scheme of coal mill provided by your plant ) 


    Before modification

    After modification

    Ball consumption analysis:

    1.     Ball consumption of grinding ball used originally is about 110-150g/t

    2.    Price of grinding ball: 6000 Yuan/t

    3.    Expenses of grinding ball annually: about RMB 130000

    1.    Ball consumption: equal to or less than 60g/t, generally between 50g/t and 55g/t

    2.     Price of grinding ball: 18000 Yuan/t

    3.    Expenses of grinding ball annually: about RMB 150000

    Summary of ball consumption:

    Expenses of ball consumption increased by about RMB 20000 annually.

    2. Power consumption: (analysis based on the unit of single coal mill according to design scheme of estimated value) 


    Before modification

    After modification

    Analysis about power consumption

    1.    Actual current: 74A

    2.    Operation period of coal mill is about 6000 hours/year

    1     Reduce by 13%

    2.    Operation period of coal mill is about 6000 hours/year


    Based on 0.35 Yuan/kilowatthour, electric charges can be saved annually for about RMB 180000

    Copying screen before modification
    Copying screen after modification

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