Discussion on operation characteristics and Counte

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Through the analysis and discussion of several problems found in the commissioning and operation of a high rate circulating fluidized bed boiler in a thermal power company, this paper attempts to explore some internal laws in the operation of high rate circulating fluidized bed boiler, and puts forward corresponding treatment measures to guide the actual operation

1. overview of boiler operation:

1.1. the boiler is a xg-130/3.82-m13 type circulating fluidized bed boiler with medium temperature and medium pressure, single drum, single furnace chamber, natural circulation, full suspension and full steel frame "m" layout, which is produced by XX boiler factory. The material separation and return device adopts volute steam cooled cyclone separator and "U" type return feeder, and the boiler adopts DCS system for control and operation

1.2. the main design parameters are:

rated evaporation capacity change 130t/h,

main steam pressure 3.82MPa,

main steam temperature 450 ℃,

boiler thermal efficiency 90.37%,

material circulation ratio 25 ~ 30,

desulfurization efficiency (when ca/s is 2.0) ≥ 80%,

fuel consumption of design coal is 20.06t/h,

limestone consumption is 0.51t/h,

dense The combustion share in the dilute phase zone is 6:4

1.3. design coal combustion characteristics:

total water content on the basis of receipt (my): 8.22%

volatile matter on the basis of receipt (vy): 26.67%

carbon on the basis of receipt (CY): 47.56%

ash on the basis of receipt (Ay): 32.11%

hydrogen on the basis of receipt (HY) : in order to reduce the iron content in molten aluminum from the source, 2.5%

received basic oxygen (oy): 8.34%

received basic nitrogen (NY): 0.77%

received basic total sulfur (SY): 0.4%

the particle size range of coal into the furnace: 0 ~ 10mm, 50% cutting particle size d50=1.5mm

1.4。 Boiler commissioning and operation: the circulating fluidized bed boiler has shown good performance in the commissioning and operation process with a water injection port on the cover, which is mainly manifested in stable operation and strong load capacity. It can still maintain good operation performance at the maximum load of 143t/h and the minimum load of 30t/h. From the perspective of the whole operation, the separation efficiency of the material separator of the furnace is high, which ensures that the material circulation of the boiler meets the design requirements. From the perspective of the combustion effect, the combustion efficiency of the furnace is very high. The carbon content of fly ash and bottom slag are within 5% and 1.5% respectively, and the actual fuel consumption is about 16-18t/h. However, during the commissioning and operation of the boiler, abnormal conditions such as bed coking, material crushing the bed and the return feeder, bed or return feeder material disappearance, bed return feeder coking and so on have also occurred. These unstable factors have seriously affected the safety of boiler operation, and also caused large direct and indirect economic losses

2. Cause analysis of abnormal conditions:

2.1. According to the working condition statistics when abnormal operation occurs, most of them are in the process of changing working conditions of boiler raising, boiler stopping, or loading and unloading. Abnormal conditions also occur in the process of normal operation when the boiler load is high or low, but the number of times is less. That is to say, most abnormal conditions occur when the boiler is in an unstable working state

2.2. Operation characteristics of high rate circulating fluidized bed boiler: because the abnormal conditions mainly occur in the process of boiler startup and shutdown or load change, and occur when adjusting the primary and secondary air volume, return material volume and coal feeding volume, it is very important to grasp the operation characteristics of high rate circulating fluidized bed boiler. Because the circulating fluidized bed boiler is a high rate circulating boiler, the boiler plant selects the high rate circulating combustion mode according to the characteristics of high volatile matter, high calorific value and low ash content of the designed coal, which is completely correct and reasonable. The high combustion efficiency of the boiler also proves this point. However, the material circulation ratio of 25-30 means that when the coal is fed into the furnace at the rate of 16-18t/h, about t/h or higher circulating ash is circulated in the furnace and the main circulating circuit, in which the proportion of circulating ash in the furnace is absolutely dominant, that is, the particle concentration in the furnace is extremely high (2..0 times that of general circulating fluidized bed boilers), while the The particle concentration distribution (i.e. combustion share) in the lower part (i.e. dense and dilute phase area) is mainly determined by the proportion of primary and secondary air volume and the size of return material (the change of coal feed also has an impact, but it is weak). Therefore, in the process of variable load operation, if the adjustment of primary and secondary air volume and proportion, return ash volume and coal feeding volume fails to grasp the characteristics of the high rate circulating furnace, resulting in improper adjustment, it is bound to cause large fluctuations in the particle concentration at the upper and lower parts of the furnace. When the influence of this fluctuation reaches such a degree that the particle concentration ratio at the upper and lower parts of the furnace is seriously misadjusted, it will occur: or the material with too large particle concentration at the lower part will crush the bed; Or most or all of the materials are concentrated in the upper space, and the bed materials disappear

at the same time, the large fluctuation of particle concentration in the furnace also makes the particle concentration at the furnace outlet fluctuate greatly, and this concentration fluctuation also causes the temperature of dusty flue gas at the furnace outlet and the flue gas velocity (when the negative pressure value at the furnace outlet remains unchanged), which has a significant impact on the separation efficiency of the separator. Or because the particle concentration, temperature and speed at the outlet of the furnace (the change direction of these three is consistent, and the change values of the three are respectively in positive proportion to the change value of the separator efficiency), the separator efficiency is also greatly improved (the increase range is carried out at a nearly cubic speed), that is, the amount of returned material from the separator can be greatly increased, resulting in a significant increase in the pressure on the loose bed of the return feeder, Such pressure increase is instantaneous, and the loose bed will be unbearable and crushed to death; On the contrary, when the concentration, temperature and speed of particles at the outlet of the furnace decrease significantly, the efficiency of the separator also decreases significantly, and the amount of returned material also decreases. In case of extreme conditions such as bed crushing, the amount of returned material entering the riser is almost zero, and if the return air is not stopped in time, only a small amount of returned material left in the riser will still be sent to the furnace. When the gravity of the material level stored in the riser is not enough to offset the return air pressure, the material layer of the riser will be broken down, causing the empty bed of the returns. Due to the joint influence of the suction force of the induced draft fan and the resistance of the separator, the very fine particles in the furnace bed may backflow to the tail flue along the return channel

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