Oxygen-to-coal ratio issue?
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The operating value of the oxygen-to-coal ratio in the Texaco process is over 400, while that for dry powder is around 0.8. Since both represent the ratio of oxygen to coal fed into the furnace, why is there such a difference? And what method is used to calculate these values?
One is the volume ratio, and the other is the molar ratio. The slurry concentration of water-coal slurry is generally required to be around 60 to 62. The oxygen-to-coal ratio is normally around 500. There is a calculation formula for dry powder furnaces; this formula is confidential and can be discussed with the design agency. This calculation formula is also specific to a certain type of coal; during normal operation, there are two control methods for the oxygen-to-carbon ratio: manual and automatic. However, due to reasons such as changes in coal type, control is performed manually, and the k value is adjusted on the logical control circuit diagram; moreover, there is a limit for the oxygen-to-carbon ratio, roughly between 0.6 and 1.2.
In my opinion, the oxygen-to-carbon ratio in coal-fired boilers is more precise, while the coal slurry in water-coal slurry systems is greatly affected by the concentration of the slurry.
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 value 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.
Regarding the setting of the oxygen-to-coal ratio: 1. The purpose of gasification is to produce as much CO as possible rather than CO2; therefore, theoretically, the optimal ratio of oxygen to carbon should be O2/C (molar ratio) = 0.5. 2. The heat generated by the reactions that produce CO is not sufficient to sustain the overall combustion process, so some oxygen is needed to “produce” CO2, thereby generating more heat to maintain this chain reaction and to meet the requirements for melting the ash. 3. CO2 is a \"by-product\" with little use in the results of the gasification reaction; therefore, while maintaining thermal balance, as much oxygen and coal as possible should be consumed by the burner to produce CO2. This requires preliminary measurement of parameters such as coal type (fixed carbon, ash melting point), as well as thermal balance calculations to determine the required oxygen-to-coal ratio. Improve economic efficiency while ensuring safety.