How is the oxygen-coal ratio determined during coal gasification?
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During coal gasification, how is the oxygen-to-coal ratio determined, and what impact does the level of this ratio have on the effective gas produced and on the operation process?
The oxygen-coal ratio is determined based on the reaction ratio between dry coal and pure oxygen in the gasification chemical reactions. The Texaco process specification sets specific requirements, and the design agency provides the design values; the production unit adjusts the temperature according to its own coal slurry preparation conditions and furnace temperature. However, this ratio does not become too high, with an upper temperature limit of 1400 degrees. A high oxygen-coal ratio results in a decrease in the concentration of the useful components in the syngas
The oxygen-to-coal ratio is around 500.
For the Texaco process, the oxygen-to-coal ratio generally refers to the volume ratio of oxygen to coal slurry, and it is around 480, depending on the type of coal!
The oxygen-coal ratio refers to the volume ratio of oxygen to coal slurry; in actual production, this ratio needs to be adjusted appropriately depending on the quality of the coal and the concentration of the coal slurry.
In the SHELL process, the oxygen-coal ratio is determined by a preset curve; it is related to the load and has a certain range of adjustment, which is fine-tuned according to the steam output.
Oxygen-coal ratio: It is the ratio of the amount of coal (i.e., carbon) to the amount of oxygen in the reaction. The reactions that occur are: C+O2->CO+Q, C+H2O->CO+H2-Q, CO+H2O->CO2+H2+Q. 1. When the oxygen-coal ratio is very low, CO produced by the combustion of carbon will predominate, while CO2 produced as a side reaction will be in smaller quantities； 2. When the oxygen-to-coal ratio is high, complete combustion occurs, and the CO content is definitely low ； 3. The oxygen-coal ratio is reduced and the temperature of the gasifier is low, which is unfavorable for steam decomposition and leads to an increase in CO content ； 4. A lower oxygen-to-coal ratio and a lower temperature in the gasifier contribute to balancing the CO and steam reforming reactions, resulting in a reduced CO content ； 5. An increased oxygen-to-coal ratio and higher temperature in the gasifier facilitate steam decomposition, resulting in a decrease in CO content ； 6. An increase in the oxygen-to-coal ratio and a lower temperature in the gasifier are not conducive to maintaining equilibrium in the CO and steam reforming reactions, resulting in an increased CO content ； 7. Since the CO2 content in syngas is usually very low, the effect of the shift reaction factor is minimal ； Except in special cases. 8. The actual result is the accumulation of the interactions among carbon combustion, steam decomposition, shift reaction kinetics, and thermodynamics. 9. While maintaining production in the gasifier, as the oxygen-to-coal ratio increases, the overall trend is a decrease in CO content.
The oxygen-to-coal ratio in slurry coal gasification is generally set at around a ratio of 1 oxygen atom to carbon atoms. Therefore, the oxygen-coal ratio is affected by coal quality and slurry concentration, and it is generally 450–500 under normal conditions. Its specific determination depends on parameters such as the operating temperature of the gasifier and the melting point of coal ash.
The C content is calculated based on the elemental analysis of coal; then, the number of oxygen atoms is roughly set to be 1:1 with the number of carbon atoms. During the growth process, the ratio of the volumetric flow rate of oxygen to that of the water-coal slurry is commonly used as a basis for regulation and control. It is mainly to facilitate accurate measurement; of course, adjustments are needed when the type of coal changes.
In the water-coal slurry gasification process, the oxygen-to-coal ratio should more accurately be referred to as the oxygen-to-slurry volume ratio – that is, the ratio of the volumetric flow rate of the water-coal slurry fed into the gasifier to the volumetric flow rate of the oxygen fed in. Under normal conditions, this ratio lies within the range of 460–500; it may vary slightly depending on factors such as the carbon content of the raw coal, the concentration of the resulting water-coal slurry, and the purity of the oxygen. Most manufacturers operate at a ratio of around 485 under normal conditions. It is generally best to calculate this value before starting the operation; the calculation is based on an oxygen-to-carbon atom ratio of 0.95~1.0, and finally the result is converted into a volume ratio of oxygen to coal slurry.
The amount of oxygen atoms = (standard flow rate of oxygen / 22.4 * 2), in units of Kmol. The amount of carbon atoms = (volume flow rate of coal slurry * density of coal slurry * percentage of carbon atoms in coal * concentration of coal slurry / 12), in units of Kmol. The ratio of oxygen atoms to carbon atoms should be around 1.0； Then, oxygen flow rate/coal slurry flow rate = oxygen-to-coal ratio
Our company’s oxygen-coal ratio is 0.95 (set value), and the process used is the SHELL vaporization process! ~~
The oxygen-coal ratio is the oxygen flow rate divided by the slurry flow rate. The lower the ratio, the lower the consumption. What we are asking for is around 470.
It’s very simple – as long as the temperature is above the fusion temperature FT, slag can be discharged. However, different types of gasifiers have different operating oxygen-coal ratios; for example, that of cold-wall gasifiers is definitely higher than that of hot-wall gasifiers. First, conduct simulation calculations, and then figure things out through actual operation.
Theoretically, the ratio of oxygen to carbon atoms should be 1:1; in actual production, this ratio needs to be adjusted based on the furnace temperature and the melting point of the ash, with it generally being kept between 450 and 500.
In the Shell powder coal gasification process, the oxygen-coal ratio is determined by the ratio of the mass flow rate of oxygen to that of powder coal. The mass flow rate of powder coal is obtained by multiplying the velocity of the powder coal by its density, while the oxygen flow rate is measured directly using a mass flow meter! When the oxygen-to-coal ratio is high, the temperature of the gasifier increases, and the CO2 content in the crude syngas produced by the gasifier also rises. More complete oxidation reactions occur within the gasifier; as a result, the total amount of useful gas produced by the gasifier should decrease ； When the oxygen-to-coal ratio in the gasifier is reduced, the CO2 content in the crude syngas produced by the gasifier will decrease; the complete oxidation reactions that take place within the gasifier will be reduced as well, and the content of useful gases will depend on the specific circumstances
During the startup phase of the shell furnace, the oxygen-coal ratio is determined by Shell based on the curve calculated from the quality of coal provided by your company; as pressure and load increase, the oxygen-coal ratio decreases. Once normal operation is achieved, the ratio is controlled according to the CO2 or steam output you specify – an increase in the oxygen-coal ratio leads to a decrease in the concentration of useful gas components and a higher temperature in the gasifier, while a decrease in the ratio has the opposite effect. However, the ratio should not be too low, as this prevents the coal from being completely gasified and results in low gasification efficiency.
During the startup phase of the shell furnace, the oxygen-coal ratio is determined by Shell based on the curve calculated from the quality of coal provided by your company; as pressure and load increase, the oxygen-coal ratio decreases. Once normal operation is achieved, the ratio is controlled according to the CO2 or steam output you specify – an increase in the oxygen-coal ratio leads to a decrease in the concentration of useful gas components and a higher temperature in the gasifier, while a decrease in the ratio has the opposite effect. However, the ratio should not be too low, as this prevents the coal from being completely gasified and results in low gasification efficiency.
This post was last edited by tqg8888 on 2009-5-10 at 18:21. The plant I work at uses the Shell gasification process, and the oxygen-coal ratio is also defined as the mass flow rate of oxygen to that of pulverized coal. Among these, the mass flow rate of the pulverized coal is determined by using a nuclear radiation densitometer from the German company Bertho to measure the density of the coal powder, and a velocity meter to measure its speed. A software package from Honeywell is used to calculate the mass flow rate of the coal powder, which is then adjusted using control valves to maintain it at the set value. As for the oxygen flow rate: a series of ROTAMOUNT 8800 series vortex flow meters are primarily used to measure the flow rate; 3051 intelligent differential pressure transmitters and temperature sensors are employed to compensate for temperature and pressure effects. The oxygen flow rate is then calculated, and flow control is used to maintain it at the set value. Furthermore, an oxygen-to-coal ratio control system is installed in the DCS and ESD to maintain the flow rates of the two at a fixed ratio. High and low alarm values are set, so that in the event the above flow regulation fails and results in an oxygen-to-coal ratio that is too high or too low, an action will be taken, causing the coal burner to shut off. But because there are four coal nozzles and four oxygen-coal lines, as long as two of them are in operation, it will not cause the gasification process to stop.
A low oxygen-to-coal ratio does not necessarily mean low oxygen consumption; if the slurry concentration is only 57%, the oxygen-to-coal ratio can be around 470. However, due to the high moisture content in the coal slurry, a large amount of heat is carried away, which necessarily requires more oxygen to participate in the oxidation reaction. Oxygen consumption is relatively high at this time, and the effective gas components in the process gas also decrease. Therefore, in addition to coal quality, slurry concentration is also a factor that cannot be ignored when determining the oxygen-to-coal ratio.