20 CFB boiler operation FAQs

CFB boiler operation FAQ

In the production, CFB boiler operation often has some tricky problems. Without further ado, I have compiled 30 common problems and solutions for boiler operation, don't forget to share them with your friends after learning them.

1

What is the circulation rate of circulating fluidized bed boiler? What are the operating factors that affect the circulating multiplier.

There are many operating factors that affect the circulation multiplier, mainly in the following areas.

Separator efficiency, fuel particle size, fuel ash content, fuel composition, ash characteristics, and the abrasion characteristics of ash particles have a decisive effect on the circulation multiplier.

Effect of boiler load. As the unit load decreases, i.e., the boiler evaporation volume decreases, the overall boiler air volume and flue gas flow rate must decrease, prompting the CFB boiler cycle multiplier to decrease accordingly.

2

When the steam package boiler is in normal operation, why should the coal conservator recirculation door be closed?

Because the feed water through the coal saver recirculation tube directly into the steam ladle, reducing the temperature of the furnace water in the local area, affecting the separation of steam and steam quality, and make the recirculation tube and the metal at the interface of the steam ladle subject to temperature stress, which may produce cracks over time. In addition, it also affects the normal operation of the coal conservator, making the exit temperature of the coal conservator too high, so in normal operation, the coal conservator recirculation door must be closed.

3

Why should the newly installed and overhauled boiler be chemically cleaned?

Boiler in the manufacturing, transportation and installation, maintenance process, in the steam system of each pressure-bearing parts of the internal inevitably produce and sticky some oil scale, iron filings, welding slag, iron oxides and other impurities. These impurities will cause great harm to the boiler and turbine once they enter the operating steam system, so the boiler must be chemically cleaned to remove these impurities before it is officially put into operation after new installation and overhaul.

4

Why is it necessary to carry out boiler blowing?

Some equipment in the boiler steam system, such as desuperheated water, start bypass, superheater, reheater piping system, etc., are not suitable for chemical cleaning due to the structure, material, layout, etc. Therefore, the newly installed boiler needs to be physically cleared of internal residual debris before it is officially put into operation, so the steam generated by this furnace is used to blow the steam system and equipment for pipe treatment.

5

What are the time and temperature regulations for the boiler water before start-up? Why?

Boiler start-up before the water speed should not be too fast, generally not less than 4h in winter, 2 ~ 3h in other seasons, the water should be especially slow at the beginning. Cold boiler water temperature is generally 50-90 ℃, so that the temperature of the feed water into the ladle and the temperature difference between the ladle wall is not more than 40 ℃. Not completely cooled boiler, the water temperature can be compared to the wall temperature of the steam package, the general difference should be controlled within 40 ℃, otherwise the water should be slowed down. The reasons are.

(1) due to the thicker wall of the steam ladle, slow expansion, and the thin wall of the tube connected to the wall of the steam ladle, faster expansion. If the water inlet temperature is too high or the water inlet speed is too fast, it will cause uneven expansion and cracking of the welds, resulting in equipment damage.

(2) When the water enters the ladle, it is always in contact with the lower half of the ladle wall. If the temperature difference between the water and the ladle wall is too large, and the speed of the water is too fast, the upper and lower walls of the ladle will have a large expansion difference between the inner and outer walls, causing a large additional stress to the ladle, causing deformation of the ladle and cracking in severe cases.

6

What are the common maintenance methods for boilers?

(1) wet protection: hydrazine method, ammonia method, keep the feedwater pressure method, steam heating method, alkaline method, trisodium phosphate and nitrite mixed solution protection method.

(2) dry protection: there are drying method (with pressure release) and desiccant method.

7

What are the causes of steam quality deterioration (steam pollution)?

(1) steam with water. The make-up water of the boiler contains impurities. Feed water into the boiler is heated into steam, impurities are also mostly transferred to the furnace water, so many cycles, the concentration of impurities in the furnace water is increasingly high. Containing a high concentration of impurities in the furnace water carried by saturated steam is called steam with water, steam with water is called mechanical carry, is the first cause of steam pollution.

(2) steam dissolved salt. Boilers in the higher working pressure, steam can dissolve certain salts, steam dissolved salt is called selective carry, which is the second reason for steam pollution.

8

How is low-temperature corrosion of the tail heating surface generated?

Combustion of sulfur in the fuel to generate SO2, SO2 and oxygen in the flue gas combined to generate SO3, when the temperature of the heated surface is lower than the dew point of the flue gas, water vapor in the flue gas and SO3 combination to generate sulfuric acid steam, condensing on the heated surface, resulting in low-temperature corrosion of the heated surface. The cold end of the air preheater is prone to low-temperature corrosion.

9

What is the case of emergency furnace shutdown?

(1) When the water level of the steam package exceeds the limit value.

(2) when all boiler water level meter damage.

(3) When the superheated steam piping, reheated steam piping, and the main feed pipe burst.

(4) When re-burning occurs at the end of the boiler.

(5) When all suction and delivery fans and air preheaters stop running.

(6) When reheat steam is interrupted.

(7) when the boiler pressure rises to the safety door action pressure, and all safety doors refuse to move.

(8) an explosion in the furnace or flue, so that the equipment was seriously damaged.

(9) When the boiler fire.

(10) When a fire occurs in the boiler room, directly affecting the safe operation of the boiler.

(11) When the furnace tube burst can not maintain the normal water level of the steam package.

(12) When all operator stations go black or die at the same time and the main parameters lose their monitoring means.

10

Why should the boiler be constantly monitored for changes in exhaust gas temperature during operation?

What is the general cause of boiler exhaust temperature increase?

(1) because the exhaust heat loss is the largest heat loss in the boiler, generally about 6% of the heat sent in; exhaust temperature increases by 12-15 ℃, the exhaust heat loss increased by 1%,; at the same time, the exhaust temperature can reflect the operation of the boiler, so the exhaust temperature should be one of the most important indicators of boiler operation, must focus on monitoring.

(2) so that the smoke exhaust temperature increases as follows.

1) heating surface scaling, ash accumulation, slagging.

2) Excess air coefficient is too large.

3)Excessive air leakage coefficient.

4)Increase of moisture in the fuel.

5)Increase of boiler load.

6)Fuel variety becomes worse.

7)Unreasonable operation of the powder making system.

8)Secondary combustion in the tail flue.

11

Water pressure test ramp-up, pressure relief speed, qualified standards?

A: The ramp-up speed of the water pressure test should be controlled at 0.2MPa/min, and the pressure relief speed should be no greater than 0.49Mpa/min. The qualified standard is: after closing the water inlet door, the pressure drop of the steam package should not exceed 0.29MPa after 5 minutes and the metal wall of the pressure-bearing parts and welds should be qualified without wetting, leakage marks and obvious deformation.

12

How to flush the water level meter of the steam package?

A: There are three processes to flush the water level meter: water side flushing: open the water release door, close the steam side door, open the water side door; steam side flushing: open the water release door, close the water side door, open the steam side door; steam and water flushing: open the water release door, open the steam side door, open the water side door. Close the water release door after flushing.

13

Why don't we use water jet to reduce the temperature of reheat steam?

The use of water injection desuperheating will reduce the thermal efficiency of the unit. This is because the use of water injection desuperheating will cause the low and medium pressure cylinders to increase the flow rate of the working mass. This steam will only do work in the low and medium pressure cylinders, limiting the work capacity of the high pressure cylinders as far as the whole heat recovery system is concerned. And in the case of the original thermal cycle efficiency is higher, such as increasing the amount of water injection, the cycle efficiency is reduced by more.

14

How to carry out the reheater water pressure test?

First of all, in the turbine high-pressure cylinder outlet steam pipeline to install pressure plugging plate, and then in the case of the turbine allowed to use the reheater cold section accidental spray water or temperature reduction water to the reheater on the water. Before the water should be closed in the turbine medium pressure cylinder inlet electric door and reheater hydrophobic door, open the reheater air door (see water after closing).

When the pressure rises to 1MPa, suspend pressure boosting, notify the relevant personnel to check. After no problems continue to boost pressure until rated. During this time should be strictly prevented from overpressure. When the inspection is completed, the pressure should be reduced to zero according to the specified pressure reduction rate. Open the air door and water evacuation door and drain the furnace water.

15

What are the main factors affecting the wear speed?

① Flue gas, material flow rate ② Concentration particle size and hardness of the material in the flue gas ③ The surface shape and hardness of the worn component ④ The direction of relative movement of the material and the worn component is most influenced by the speed of the airflow, and the wear is proportional to the third power of the speed.

16

Why should the bed temperature be controlled between 850-950?

①The ash will not melt at this temperature, thus reducing the risk of slagging ②Higher desulfurization efficiency at this temperature ③Less nitride gas in the combustion gas at this temperature ④The alkali metal in the coal will not sublimate at this temperature, which can reduce the slagging on the heated surface.

17

What are the manifestations of bed coking in circulating fluidized bed boiler

① bed temperature rises sharply ② oxygen indication drops or even to zero ③ primary fan current decreases, air chamber wind pressure is high and ④ negative pressure in the furnace chamber increases, the induced draft fan current decreases ⑤ slagging difficulties or can not drain slag ⑥ if the low temperature coking, the bed temperature, bed pressure distribution is uneven, deviation is too large, bed pressure, air chamber pressure, bed temperature is not normal, local bed temperature measurement point is not normal rise or decrease. (7) The bed pressure indication value fluctuates very little.

18

How to avoid coking accident when circulating fluidized bed boiler starts?

① Before starting, thoroughly check whether the wind cap opening is all smooth, whether the bed material is free of caking or slabbing ② When heating up, keep the heating up speed slowly ③ When heating up to ensure uniform bed temperature ④ Initial coal throwing, it is appropriate to throw coal in small amounts for several times ⑤ If the bed temperature rises too quickly, burning violently, it is appropriate to increase the primary air volume.

19

What are the factors affecting the load of fluidized bed boiler?

① coal quality ② bed temperature ③ bed pressure ④ oxygen and one or two air ratios ⑤ feed water temperature ⑥ cleanliness of the tail heating surface

20

How to ensure the safety of insulation, refractory and wear-resistant castables during the start-up process of circulating fluidized bed boiler?

In the process of circulating fluidized bed boiler startup, in order to ensure the safety of insulation, refractory and wear-resistant castables, it should be done as follows.

① Strictly control the temperature change of any point in the furnace less than 100℃/h to prevent uneven expansion of castables and metal

② Strictly control the substantial change of furnace chamber pressure during the process of starting fan and air volume adjustment.

③In the operation of coal feeding, must be a small amount slowly, never adjust the amount of coal feeding substantially.