Discussion on improving boiler availability in pow

2022-08-11
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Discussion on improving the availability of boiler in power plant

Abstract: according to the situation after the boiler equipment in power plant is put into operation, the availability of boiler is analyzed and discussed in three stages, and suggestions are put forward to improve the availability of boiler in terms of boiler shutdown events that are easy to occur, corresponding measures that should be taken, reasonable arrangement of maintenance interval, reduction of minor maintenance times, etc

key words: boiler; Availability; Discussion; Unplanned outage

1 preface

boiler is one of the main equipment of power plant. Practice has proved that improving the availability factor of boiler is very important to the economic benefits of power plant. This paper summarizes the operation of #6 and #7 hg-220/boilers in Hebei Weishui power plant from 15 and 15 respectively, the specification parameters of battery acupuncture experimental machine: from 974 and 1975 to the end of 2002, focuses on the analysis of boiler availability, and discusses the measures taken during the maintenance of the boiler. Generally, the availability factor and forced outage rate of equipment are used as statistical evaluation indicators:

in the above two equations, available hours = operating hours + standby hours; Forced outage hours = the sum of unplanned outage hours of the first, second and third categories

2 boiler operation overview analysis

6 and 7 boilers have been in operation since they were put into operation to the end of 2002 22.016 . It can be seen from the for and AF curves 1 and 2 that their characteristics are as follows: they basically belong to the "L" type change form, but they bulge at the middle and rear part, then drop to the flat, and bulge at the rear part in recent years, and the forced outage events are relatively concentrated in time. For the convenience of analysis, the influence of main components such as economizer and Superheater of boiler on for is discussed in stages

2.1 early failure stage

6 furnace was the highest stage of for from 1974 to 1977 at the beginning of operation. In 1974, the high-temperature superheater was shut down for 5 times due to craters, sand holes, etc., for a total of 154 hours; In 1977, due to the leakage of low-temperature economizer and water-cooled wall, it was shut down for 4 times, with a total of 171 hours. For is 3.39%

From 1975 to 1978, 4 A was also the peak period of the failure of the

7 boiler. In 1976, due to the lack of water in the low-temperature economizer and the water-cooled wall, the boiler was shut down for 215 hours, and the for was 4.02%, which was the highest point

The early failures of p>6 and 7 furnaces mainly reflect the poor quality of the equipment, especially the sand holes in the welded junctions and pipelines. It can be seen that doing a good job of metal supervision before the installation of new power plant equipment and dealing with equipment defects in advance are essential means to reduce early boiler failures and improve availability

2.2 stable operation stage

the faults in the early stage of the boiler exposed the defects of the equipment, so some pipelines of the economizer were replaced during the overhaul of #6 boiler in 1977 and 1978. After maintenance and treatment, from 1980 to 1982, 6 furnaces had zero for 3 consecutive years. In 1984, acid pickling was carried out on #6 furnace, which reduced the amount of scaling and prevented tube explosion. Therefore, in 1984 and 1985 #6 furnaces achieved zero for two consecutive years

in 1978 and 1979, according to the wear condition of #7 boiler economizer (the operation has reached 34000 h), the high and low temperature economizers were partially replaced, and the welded junction was inspected and treated. Thereafter, from 1980 to 1984, for five consecutive years was zero, and there was a golden period of safe operation

in 1983, acid pickling was carried out according to the scaling condition of #7 furnace. After that, for was zero for two consecutive years in 1985 and 1986. From March, 1978 to June, 1987, the #7 boiler operated for more than 60000 hours

by pickling the boiler, the amount of scaling is reduced, the boiler is protected, and the number of boiler shutdown caused by boiler tube explosion is reduced. Since the defects of the boiler in the early stage have been treated, at this stage, the equipment wear is not serious, forming a stable stage. Therefore, the boiler should be operated for 30000 ~ 40000 hours for maintenance. In this way, we can change the regular scheduled maintenance in the past 3 years, reduce the number of overhauls, save costs, increase power generation, improve equipment availability, and improve economic benefits

2.3 in the later stage of operation

it can be seen from the for curve of #6 boiler in Figure 1 that the forced shutdown rate was 2.85% in 1988, and there was a peak point, which was mainly caused by 4 times of shutdown caused by the leakage of high and low temperature superheaters. It can be seen that at the later stage of boiler operation, the equipment has reached the loss period, and explosion and leakage have occurred in different parts for many times. Therefore, it was overhauled according to the operation state of #6 boiler in 1990, and some excess tubes of economizers were replaced. In 1993, high-temperature Economizers and superheaters were replaced. During the maintenance, metal inspection was carried out on all welded junctions of the replaced parts, and the unqualified welded junctions were treated in time. Therefore, from 1994 to 1996, the unsatisfactory forced shutdown event was basically controlled, the operation was stable, and the good operation stage occurred again. It can be explained that according to the health status of the equipment, taking condition based maintenance to completely eradicate the defects of the equipment can reduce for

from 1997 to 2002, the boiler operation has reached the aging stage. By the end of 2002, #6 boiler had operated for 220160 hours, and #7 boiler had also operated for 206 thousand hours. Therefore, the for curve in recent 6 years has a zigzag change. In 1997, #6 furnace for was 2.13%, which was the highest point in the later stage. During this period, there were 4 unplanned outages for 178.75 hours, all caused by leakage due to aging of the pipeline. In other years, it is generally about 1%, with a small range of change, which has little impact on the availability of the boiler. Especially in the second year after the overhaul, the for is low. Therefore, on the whole, the operation of the boiler at this stage is relatively stable. According to the above analysis, although the boiler is running to the aging stage, because #6 boiler was pickled in 1993 and 2001 during the overhaul work in 1992 and 2001, and the pickling interval is about 9 A, the for is reduced and the equipment availability is improved

3 availability analysis

from the AF curves in Figure 1 and Figure 2, the AF of #6 furnace was 97.13% in 1992 and 97.98% in 1994, that of #7 furnace was 97.08% in 1993 and 98.15% in 1996, both of which were the highest points

the main reasons are:

a. there are few forced stops# From 1994 to 1996, there was no unplanned shutdown of #7 boiler in 1995 and 1996

b. 6 boiler was only slightly repaired once in 1994, and the power was generated 16 hours in advance

c. 7 furnace was repaired once in 1993 and 1997 respectively

from 1991 to 1996, three minor repairs were reduced for the two boilers. Generally, only one minor repair was arranged in the second year of overhaul. The average planned outage interval was 4374.56 hours, and the average failure free available hours was ∧ 19641.54 hours, which was the best level in history

from 1997 to 2002, although the boiler has reached the aging stage, the availability rate is still relatively high due to factors such as timely maintenance and shortened overhaul period

the main methods are: strengthen the maintenance and management of equipment, deal with it according to the severity of equipment defects or as the focus of the next major and minor repair, and reduce the number of boiler shutdown caused by boiler pipe explosion and leakage; Strengthen equipment management, formulate and implement the "equipment defect management system", and maintain a good health level of equipment through the registration, supervision and inspection of eliminating defects on time

it can be seen from the AF curve that there are 8 points where the two furnaces reach 95.08% or above, and the highest point reaches 97.91%, which is still at a high level; The other five points are still in the range of 88.11% - 90%. The main reason is to reduce the number of minor repairs by 7 times, and generally, each overhaul is completed ahead of schedule to varying degrees. In 1999, the #6 boiler was scheduled to be overhauled for 40 days, 4 days ahead of schedule. During the overhaul in 2001, the overhaul period of #6 and #7 boilers was completed 7 days in advance respectively, and the minor overhaul period was generally completed about 1 day in advance. During the maintenance period, strengthen the management of the maintenance period, make the maintenance work flow chart, and reasonably arrange the cross operation; At the same time, pay attention to the metal inspection and registration of the welded junction and weld of the equipment. These practices effectively ensure the running time of the equipment, increase the available hours of the equipment, and thus improve the availability of the equipment

4 conclusion

a. boiler equipment generally operates for about 25000 hours, which is an early failure period, and most of the failures are caused by the equipment itself. If the inspection, treatment, acceptance and other work are done well before and during installation, the occurrence of early failures can be reduced

b. acid cleaning of the boiler can prolong its operation time and reduce forced shutdown events. It is recommended to carry out acid cleaning at the boiler operation interval of about 9 years

c. boiler explosion and leakage generally occur at the weld junction. It is one of the necessary means to improve the availability of boilers to do a good job in the metal inspection and treatment of welded junctions during maintenance

d. it is necessary to strengthen the maintenance management, reasonably arrange the maintenance progress, shorten the maintenance period and improve the availability

e. it is recommended to carry out only one mobile minor repair in the second year after the overhaul of the unit, and it is appropriate to carry out condition based maintenance when the boiler operates to 30000 ~ 40000 hours. This is one of the effective methods to improve boiler availability. In the future technical transformation, adding automatic data testing equipment can more timely and accurately find the defects of boiler equipment, and take more timely condition based maintenance after amplification by high-speed amplifier

f. during the normal operation of the boiler, do a good job in the defect elimination management and daily patrol inspection of the equipment, and timely find and deal with the hidden dangers and defects of the equipment; At the same time, take preventive measures to prevent or reduce the occurrence of boiler shutdown events and other accidents, which is a necessary method to improve the availability of equipment

g. carefully carry out chemical supervision and management work such as accurate recording of water quality test data, timely find out the substandard data in the boiler, and then arrange treatment, which is one of the necessary means to extend the safe operation cycle of the boiler

reference

[1] dl/t, code for reliability evaluation of power generation equipment (end)

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