How does a water-coal slurry gasifier ensure that the coal slurry burns within 5-7 seconds?
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This post was last edited by 10086 on 2017-8-31 00:07, as the title indicates. The water-coal slurry enters the gasifier through a burner, where it burns completely within a very short time to form slag, which then goes into the quench chamber. How is this time period ensured? What factors are related to it?
It takes this long just to burn; do we not need vaporization? and the atomization state, furnace size, flow field distribution and shape, slag outlet size
This is related to the activity of the coal type, the design pressure, and the effective volume of the combustion chamber; since a time period of 5–7 seconds is required, it is necessary to properly control the design values for these factors.
To be precise, the retention time should be controlled between 5.8 seconds and 8 seconds.
The oxygen percentage at the center is very important; if possible, you should give it a try – we keep it between 12-14%
Factors affecting combustion time: coal quality and the inherent properties of the coal slurry (such as coal activity, composition of various components)； Slurry concentration, viscosity, amount of limestone added, etc.), design and operating pressures, operating temperature, size of the combustion chamber, size of the slag outlet, and pressure drop.
The reaction time for coal is less than 1 second; the residence time is determined by the length of the gasifier and the calculated flow rate, with the average time being the relevant value
After the water-coal slurry is injected into the gasifier through nozzles, under the action of radiation and counterflow convection heat transfer, the water in the slurry rapidly vaporizes into steam, while the coal heats up quickly and undergoes pyrolysis. The pyrolysis gases and semi-coke produced as a result react violently with the oxygen injected through the nozzles, resulting in the formation of CO2 and H2O; due to a lack of oxygen, some semi-coke remains. The remaining semi-coke reacts primarily with the steam (H2O) generated by the vaporization of water in the coal water slurry, as well as with CO2 produced by combustion, through the following gasification reactions: C + CO2 = 2CO and C + H2O = CO + H2. These reactions produce CO and H2. Due to the high gasification temperature of 1300–1400°C, the gasification rate follows the Arrhenius equation; that is, the gasification rate is inversely proportional to the exponential function of the absolute temperature. The higher the temperature, the faster the gasification rate ； At the same time, water-coal slurry uses pulverized coal with an average particle size of less than 100 micrometers; the smaller the particle size, the greater the specific surface area, and the reaction rate is positively correlated with the specific surface area ； Water-coal slurry gasification also employs high pressures, and the reaction rate is proportional to P raised to the power n, where n>0 and is approximately 0.5–0.6; therefore, the higher the pressure P, the greater the reaction rate. Therefore, in water-coal slurry gasification, a carbon conversion rate of over 98% can be achieved within just a few seconds. Furthermore, due to the high gasification temperature of 1300–1400°C, the CO conversion reaction proceeds rapidly and reaches thermodynamic equilibrium: CO + H2O = CO2 + H2. Since the aforementioned transformation reaction is exothermic, from a thermodynamic equilibrium perspective, the higher the temperature, the further the chemical reaction equilibrium shifts to the left, that is, in the direction of producing more CO and less H2 and CO2; as a result, the percentage of CO in the gasification products is high.
The insights on the 8th floor are profound~ pfpf
For young people, it is mainly related to the height-to-diameter ratio.