What are the effects of the particle size of the coal entering the furnace on the combustion of the

The particle size of the coal entering the furnace directly affects the particle size and distribution of the materials in the furnace, therefore, it has a great impact on the combustion of the fluidized bed boiler, and the specific effects are as follows: when the particle size distribution of raw coal is abnormal, it will cause abnormal air distribution in the combustion chamber. Because the critical fluidization wind speed of the material layer increases with the increase of particle size, it decreases with the decrease of particle size.

Therefore, when the particle size is too large, the secondary air rate decreases, resulting in.

The primary and secondary air distribution modes deviate from the reasonable operating conditions, resulting in poor air distribution, affecting combustion efficiency and environmental protection emissions; However, if the particle size is too small, it is not easy to form a stable material layer, and the sensitivity of air distribution increases. When the particle size distribution of raw coal is abnormal, it will cause a change in the degree of fluidization of the material layer. When the particle size is too large, the local fluidization will be poor under the condition of the same primary air volume, and the local bed temperature will rise, which is easy to cause coking in the bed. However, if the particle size is too small, the fluidization of the material layer will be enhanced, the bed temperature will be reduced, and fire extinguishing will easily occur.

When the particle size distribution of raw coal is abnormal, it will cause aggravated wear.

When the particle size is too large, the increase of primary air volume will increase the concentration of coarse particles, which will accelerate the wear of the water wall, bury pipe and refractory layer in the lower area of the furnace. If the particle size is too small, the particle concentration in the dense phase zone of the suspended section will rise, resulting in the aggravation of the wear of the heating surface inside the upper furnace. When the particle size distribution of raw coal is abnormal, fly ash will be generated.

and an increase in the carbon content of ash slag. When the fine particles are the majority, a large number of unburned fine particles escape, which increases the combustible content of fly ash. When the coarse particles are the majority, the burnout rate of combustible particles in the material layer decreases, and the carbon content of ash increases. When the particle size distribution of raw coal is abnormal, it will cause a serious imbalance in the heat transfer distribution relationship of the heating surface of each section in the furnace.

The influence of coal particle size on circulating fluidized bed boiler, the combustion characteristic of circulating fluidized bed boiler is that the coal particles of wide screening are rolled in the bed under the action of appropriate air flow, and burn on the other side, which is different from the combustion method of pulverized coal pot and layer combustion furnace, it is a kind of boiling combustion. It has been proved that the particle size of the incoming coal has a great influence on the ignition start, operation control, incineration efficiency, hood and water wall operation of the reincarnation fluidized bed boiler. Effect on ignition start-up:

The ignition process of circulating fluidized bed boiler is a dynamic process from heating the boiler bottom material to the ignition point of coal and normal combustion, and the success or failure of this process is related to many factors such as the height of the fluidized bed bottom material, air distribution, and coal feeding. The ignition operation is not only to heat the bottom material in the bed to the coal feeding temperature, but also to master the coal feeding process without deflagration and over-temperature coking, and then transition to normal combustion and receive heat radiation.

The influence of coal particle size on the operation of circulating fluidized bed boilers. Circulating fluidized bed combustion technology is a new type of combustion technology developed in the mid-70s in the world, and the successful application of this technology has made the circulating fluidized bed boiler develop rapidly. Compared with laminar boilers and chamber-fired boilers, it has the advantages of wide fuel applicability, high combustion efficiency, good environmental performance, flexible load regulation, and convenient comprehensive utilization of ash and slag.

Therefore, the development of circulating fluidized bed boiler is of far-reaching significance for making full use of inferior coal, saving energy and reducing environmental pollution. 1. The influence of coal particle size on circulating fluidized bed boiler The combustion characteristics of circulating fluidized bed boiler are that the coal particles with wide screening are in the bed under the action of appropriate air flow, and they are tumbling and burning on one side, which is not only different from the combustion mode of pulverized coal boiler, but also different from the combustion mode of layer combustion furnace, it is a kind of boiling combustion.

Answer]: The ignition temperature of the coal: anthracite, 700 800; bituminous coal, 400 500 ; lignite, 250 450 .

Ignition temperature of pulverized coal gas stream: anthracite, 1000; lean coal, 900 ; bituminous coal, 650 840 ; Lignite, 550.

The following conclusions can be drawn from the above data.

1) For the same kind of coal, the ignition temperature of the coal block is lower than the ignition temperature of the pulverized coal gas flow, so the ignition temperature of the layer beam serving furnace and the flow finger banquet bed boiler is lower than that of the pulverized coal furnace. Therefore, the pulverized coal furnace requires that the furnace temperature must be high enough, otherwise the pulverized coal gas flow will not be able to maintain a stable ignition process.

2) For pulverized coal gas streams, anthracite has the highest ignition temperature. Therefore, among the boilers that burn various types of thermal coal, the furnace temperature of the anthracite-burning rubber pulverized coal boiler should be the highest.

Answer] :(1) Pulverized coal boiler: the furnace temperature is about 1500, the particle size of pulverized coal particles is about 60 80um, the time for pulverized coal particles to burn out is about 10 80um, and the power of a single pulverized coal burner can be very large. NOX of pulverized coal boilers

High emissions, SOX

Emissions are also high. It is necessary to use special desulfurization and denitrification devices for flue gas purification, and the share of fly ash is more than 90%.

2) Circulating fluidized bed boiler: the temperature of the dense phase area is about 880 900, the particle size of the fuel particles into the furnace is about 1 10mm, the fuel particles can be repeatedly circulated and burned, and the area of a single air distribution plate is limited. As a result, circulating fluidized bed boilers are limited in terms of capacity expansion.

Due to the relatively low combustion temperature, NOx

The emission is low, and desulfurization and combustion can be carried out at the same time in the furnace, and the share of fly ash is generally between. The circulating fluidized bed boiler has a wide range of coal adaptability, but for a CFB boiler in operation, the circulating fluidized bed boiler cannot burn all solid fuels.

3) Laminar Combustion Boiler: The area of a single grate is limited, and it is only used for small industrial boilers. Combustion characteristics of laminar combustion boilers:

Coal type has wide adaptability. Combustion temperature 1000 1100 . Due to coal leakage in the grate and uneven combustion, the loss of incomplete solid combustion is large.

The emissions of nitrogen oxides and sulfur oxides are between the pulverized coal boiler and the circulating fluidized bed pot and the cluster furnace, and the share of fly ash is about about that.

The fluidized bed boiler is an efficient and environmentally friendly coal-fired boiler, and its main principle is to crush and burn fuel under the action of high-speed air flow. Although fluidized bed boilers have many advantages, there are also some disadvantages, among which the high thermal strength of the furnace is not its biggest disadvantage.

The furnace thermal intensity of fluidized bed boilers is indeed higher than that of general coal-fired boilers, because the combustion and heat transfer efficiency of its fuel in the fluidized bed are high, and the calorific value of the fuel can be fully utilized. However, the high thermal strength of the furnace is not the biggest disadvantage of fluidized bed boilers, and its main disadvantages include the following:

High investment cost: Compared with traditional boilers, fluidized bed boilers have higher investment costs, requiring the construction of more complex equipment and pipelines.

Difficult operation and maintenance: Due to the unique combustion mode of fluidized bed boiler, its operation and maintenance require professional technicians to operate and maintain.

Poor fuel adaptability: The fluidized bed boiler has poor adaptability to fuel, different types of fuel need to be adjusted and operated differently, and the content of pollutants will also affect its operation effect.

Poor cooling effect in the furnace: due to the large air flow in the furnace and the high temperature in the furnace, the cooling effect in the furnace is relatively poor, which will also affect the service life of the equipment.

To sum up, the high thermal strength of the furnace of fluidized bed boiler is only one of the aspects, and its disadvantages and advantages need to be considered comprehensively. When choosing to use fluidized bed boilers, it is necessary to judge and select according to the actual situation.

Circulating fluidized bed boilers are widely used because the concentration of NOx and SO2 in pollutant emissions is much lower than that of conventional coal-fired boilers. However, with the deepening of the research on CFB boiler combustion technology, it is found that the emission concentration of N20 in the tail flue gas of circulating fluidized bed boiler is much higher than that of ordinary coal-fired boilers, and N20 is a major greenhouse gas. Therefore, how to control the emission concentration of N20 in CFB boiler is of great significance.

When the particle size of the coal changes, the effect on the load is that the larger the particle size of the coal feed, the amount of particles escaping from the bed material decreases, so that the boiler can not maintain the normal return material, resulting in the decrease of the boiler load.

The effect of the water content of coal on the load is that when the moisture of the coal increases, the steam temperature will decrease due to the increase of the latent heat of vaporization absorbed by the steam, but the moisture can promote the volatilization analysis and coke combustion at the same time.

In order to weigh its fluidization state, the circulating fluidized bed boiler has strict requirements for the particles of the furnace coal, and the particle size of the powder entering the furnace is generally not more than 13mm. And the proportion of coal particles in each range of particle sizes should meet the requirements of boiler design.