Coke oven gas conversion: Can the ratio of methane produced to CO and CO2 be adjusted?
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The oxygen from the air separation unit has a temperature of 100°C and a pressure of 2.2 MPa(g); a certain amount of safety steam is added to it, and after being preheated to 300°C in a preheater, it enters the conversion furnace. There, it mixes with coke oven gas vapor at the top of the furnace, where it undergoes conversion reactions through the catalyst bed: 2H2 + O2 = 2H2O + 1.48 kcal (1); 2CH4 + O2 = 2CO + 4H2 + 17.0 kcal (2); CH4 + H2O = CO + 3H2 – 49.3 kcal (3); CH4 + CO2 = 2CO + 2H2 + 59.1 kcal (4); CO + H2O = CO2 + H2 + 9.8 kcal (5). The reactions ultimately reach equilibrium according to equation (5). The converted gas is drawn out from the bottom of the converter, at a temperature of about 960°C, with a methane content of less than 0.7%. The above text is taken from the feasibility study. My question is: once the methane content at the inlet and outlet of the conversion unit is controlled, are the levels of CO and CO2 exiting that unit fixed and unadjustable? In other words, is the ratio of CO to CO2 produced per unit of methane constant? For example, is it 0.8 units of CO and 0.2 units of CO2? (The figures of 0.8 units of CO and 0.2 units of CO2 are purely hypothetical; I would appreciate it if experts could tell me what this ratio is generally.) I believe that by adjusting the water-to-carbon ratio, it is possible to regulate not only the methane content at the outlet of the conversion furnace but also the ratio of CO to CO2 produced per unit of methane; in other words, by changing the equilibrium of equation (5), the final reaction products can be altered (although this ratio should change only slightly). If the above opinion is correct, then what is the maximum possible ratio of methane converted to CO and CO2? In this way, if CO2 is an inert gas (for example, when synthesizing methanol), it is possible to control the reaction so as to produce as much CO as possible. Hehe, these are just my personal ideas; they haven’t been verified at all, and there might be many errors. I appreciate any feedback you can provide. This post was last edited by wwqpinglu on 2009-3-17 at 18:55
The C02 content is lower after conversion. After normal conversion, the composition of the gas is as follows: H2 68.15%, CO2 3.22%, O2 7.33%, N2 0.47%, CH4 0.5%, H2O 0.33% on a molar percentage basis
Thank you, Floor 2, but could you please answer how to adjust the ratio of methane produced to CO and CO2?
There’s another question: if the ratio of CO to CO2 remains constant, and if the volume of gas and its components stay unchanged, then aren’t the amounts of oxygen and water vapor added fixed as well, with no need for adjustment?
The added oxygen provides heat for the lower-stage conversion in order to facilitate combustion; meanwhile, partial combustion also produces CO and H2. The amount of oxygen added is determined based on the gas volume and composition, as well as the bed temperature. With a water-to-vapor ratio of 2.8, steam is always in excess. I’m seeking expert advice; this is just my understanding. Bro, where are you from? Do you need to drive to make the transfer?
When performing conversion calculations, only the methane content at the outlet can be set as a variable; therefore, when the methane content at the outlet is fixed, the CO and CO2 contents at the outlet are also fixed accordingly. The methane steam conversion reaction and the CO conversion reaction reach equilibrium at the outlet of the converter. I hope we can communicate more.
I agree with the idea for the 1st floor; by adjusting the water vapor ratio and oxygen-to-carbon ratio, it is possible to modify the levels of CO and CO2 in the conversion gas. I haven’t done the calculations specifically, but it’s possible to estimate them based on the alcohol content in crude methanol. Give it a try.
When the methane content remains constant, the outlet CO and CO2 levels are also constant accordingly. CH4 + H2O = CO + 3H2 – 49.3 kcal; CH4 + CO2 = 2CO + 2H2 + 59.1 kcal. The ratio of H2 to CO can be fine-tuned by adjusting the CO2 content in the incoming gas. C0 + H2O = C02 + H2 + 9.8 kcal; this is an equilibrium issue with little impact, and the oxygen-to-coke ratio can be adjusted to control the amount of CH4 in the converted gas
Because it is uncertain what the general ratio of conversion into CO and CO2 is To what extent can it be adjusted (how is it adjusted? ), so it’s impossible to calculate, haha. I hope experts can offer some guidance
I’m not sure if the original poster has read any books on methanol synthesis. Generally speaking, there are two methods for adjusting the composition of syngas: one is two-stage conversion, which involves using pure oxygen in a second-stage furnace for conversion; the other is to recover CO2 from flue gas and use it to supplement carbon. As we know, an important aspect of producing methanol from natural gas is to minimize the amount of carbon used. Therefore, CO2 is recovered and added back in the first-stage furnace to increase the carbon-to-hydrogen ratio, while simultaneously reducing the formation of CO2. Many large methanol production facilities in China use this approach (starting from natural gas), which eliminates the need for air separation units and can increase production by around 10%. Of course, this depends on the scale of production; for smaller-scale operations, one-stage conversion is usually sufficient. If it’s necessary to increase the carbon content, raising the temperature is one method, but generally, there are limits on the operating temperatures for catalysts and furnace tubes. Some small factories try to raise the temperature, but this is very dangerous and not recommended. The original poster is dealing with methanol production from coke gas; the principle is similar, but due to the high hydrogen content, supplementing carbon is indeed another viable method. This post was last edited by dengzhai77 on 2009-3-18 at 16:28
This should be a practical issue that needs to be considered from the perspective of operational experience; conversion work here hasn’t even started yet! I’m sorry; the design institute provided the following composition for the raw gas: H2 61.41%, CO 20.95%, CO2 3.06%, CH4 12.21%. After conversion, the proportions are: H2 68.23%, CO 23.26%, CO2 7.31%, CH4 0.41% on a molar basis
For smaller scales, usually just one stage of conversion is sufficient; ours is a facility with a capacity of 200,000 tons of gas converted into methanol, which is quite large indeed.
Yes, it’s not small. In terms of its components, carbon can be added to it
Is equation 2 for methane conversion on the 1st floor incorrect? It should be； CH4+2O2=CO2+2H2O
Even the people at the design institute who prepared this feasibility study don’t know for sure; I guess it’s also a large figure, and the specific parameters will probably only become clear during the detailed design phase