Selection of alcohol-to-amine ratio in diol (found on a Baidu webpage)
Thread Content
A process flow for co-producing dimethyl methanol with controllable alcohol-to-ammonia ratio; the purpose of this dimethyl methanol production process is primarily to purify and refine the feed gas, with methanol being produced as a by-product. However, as the market and product demand change, the product structure must be adjusted at any time; in other words, the alcohol-to-ammonia ratio needs to be adjusted significantly. When the methanol market is strong, this ratio is required to reach 1:3 or even higher. At this stage, both alcohol production and the purification of raw gas are important tasks in the dimethyl process. Under these conditions, our process arrangement principleally involves installing two methanol towers: the first methanol tower is used for methanol production (it is preferably placed at a low pressure level), while the second tower serves the purpose of purification. After passing the second tower, CO+CO2 ≤ 0.3% (this parameter results in low consumption of fresh gas, high heat utilization efficiency, and simple operation; it will be discussed in more detail later). The dimethyl process with adjustable alcohol-to-ammonia ratio (higher alcohol yield). This arrangement is very flexible; when methanol production is the main objective and the alcohol-to-ammonia ratio is high, the feed gas passes through two towers, where in the first tower 80% of the CO and CO2 components are converted into alcohol, with alcohol production being the primary goal ； The second tower converts only the remaining 20% of CO and CO2, reducing it to less than or equal to 0.3%. If the demand for methanol in the market is weak, the dimethylation process focuses on purification and refinement, with methanol serving as a by-product that is produced in as small quantities as possible; for example, when the alcohol-to-ammonia ratio is between 1:10 and 1:20, only one alcoholization tower is needed, and a recycler can be omitted during operation ； Second tower standby ； When the catalyst activity in the first tower degrades, the second tower can be brought into use, and throughout this entire process it is possible to easily maintain a CO+CO2 level of ≤0.3% in the methanation reactor. The first stage of methanation is carried out at 3.0 MPa or 8.0 MPa, while the second stage of methanation and the methanation step used in ammonia synthesis take place at 12 MPa–32 MPa. In the first stage, alcohol production is the main objective; that is, 90% of CO and CO2 are converted into crude methanol at these pressures. The remaining 10% of CO and CO2 is converted into methanol at pressures ranging from 12 to 32 MPa (or 30 MPa), ensuring that the concentration of CO+CO2 entering the methanation step remains at ≤0.3%. After methanation, the concentration of CO+CO2 in the gas is ≤10 PPm, and this gas is then sent to the ammonia synthesis process. One of the advantages of this process is that methanol is synthesized at low pressure; that is, using gases accounting for 6% to 10% of the total feed gas (CO, CO2, and H2 required for methanol production), eliminating the need for higher pressures and thus saving electricity consumption. The second advantage is that methanation takes place at pressures of 3 MPa to 8 MPa, allowing the heat generated by the methanation reaction to be used to produce medium-pressure steam for power purposes; the steam remaining after backpressure can still be utilized as process steam. The third advantage is that, since reactions such as methanation and ammonia synthesis occur at constant pressure, there is no need to compress the process gases again to increase their pressure, thereby avoiding gas contamination. It is also possible to make use of the heat generated by the ammonia synthesis reaction to maintain the temperature required for the methanation reaction at low carbon levels (CO+CO2≤0.3%), without having to use electric heaters to sustain the reaction. For old plants that use the alcohol-to-hydrocarbon process, the high-pressure compressors do not have a pressure range of 3MPa–5MPa; instead, they have pressure levels of 7.8MPa, 12.5MPa, and 30MPa. Methanolization can be carried out at 7.8MPa and 12.5MPa, after which the pressure is increased to 15MPa or 32MPa for methanation and ammonia synthesis. The energy-saving effect of this process is also significant. This multi-stage, non-isobaric dimethyl process is a universal design method developed by our company in line with local conditions, which is beneficial for production as well as for purification and energy savings.
I’ve thought a lot about this topic. As mentioned earlier, the previous process used was reciprocating compression, but these days, most new facilities employ centrifugal compression. The pressure at the outlet of the low-pressure cylinder is around 8.0 MP; in other words, both the methanol tower and the methane tower operate at this pressure level. What is the maximum possible ratio of alcohol to ammonia that can be achieved? However, the final emission must definitely meet the methane precursor limit of (CO+CO2≤0.3%). Are there any experts in this field in the country currently?
In the methanol synthesis reaction, carbon dioxide serves to inhibit the formation of dimethyl ether; it also protects the copper-based catalyst. The question is, how does it protect the catalyst? Which expert can give some hints? Thank you so much!
The issue of protection should be clear by now, and as for the appropriate ratio in our process, it needs to be explained in detail at this point. In our process, there are two methanol towers and one methane tower, all arranged in series. Among them, one tower is a tubular reactor, and the other two are adiabatic reactors; secondary lines are included in the process design leading to these two towers as well as the methane tower. If the heat of reaction is insufficient, steam heating is used exclusively during the startup phase. Currently, due to considerations regarding energy consumption and catalyst activity, one column together with the methane column is sufficient to meet the purification requirements of the process; therefore, a second column is used for normal-temperature gas flow at present, but it is not in operation, as doing so would increase the heating steam required by the methane column and thus raise energy consumption.
The issue of protection should be clear by now, and as for the appropriate ratio in our process, it needs to be explained in detail at this point. In our process, there are two methanol towers and one methane tower, all arranged in series. Among them, one tower is a tubular reactor, and the other two are adiabatic reactors; secondary lines are included in the process design leading to these two towers as well as the methane tower. If the heat of reaction is insufficient, steam heating is used exclusively during the startup phase. Currently, due to considerations regarding energy consumption and catalyst activity, one column together with the methane column is sufficient to meet the purification requirements of the process; therefore, a second column is used for normal-temperature gas flow at present, but it is not in operation, as doing so would increase the heating steam required by the methane column and thus raise energy consumption.
The day before yesterday, a colleague from Erhua called and said that the new plant in Zhoucun uses the Anchun process. The production capacity is set at 200,000 tons of methanol and 240,000 tons of ammonia; accordingly, the urea production capacity is 400,000 tons. I found such an alcohol-to-ammonia ratio to be quite incredible when I heard about it. Moreover, their budget for construction was 900 million yuan, which is really low. Yet their efficiency is indeed excellent, and one can’t help but admire that.
Below is the analysis report for our plant’s crude alcohol products. The relatively low purity is mainly due to the presence of a water washing tower after the second distillation column; in order to ensure that the methanol content at the outlet does not exceed 100PPM, a large amount of water is used, which increases the energy consumption required for distillation. Methanol: 65.67% Water: 32.99% Dimethyl ether: 0.1341% Methyl formate: 0.12%
In fact, when considering this issue, our main concern is to ensure that the level of trace CO+CO2 at the inlet of the synthesis tower remains below 10 PPM. At the same time, we also need to take into account the temperature in the methane purification tower, as well as the safety of the catalysts in both towers. Therefore, for our process, if this level is too high, the system cannot handle it; whereas if it is too low, it will increase energy consumption and raise the cost of the product. We still have a long way to go in terms of cost accounting. If a cycle machine is introduced, this problem remains the main issue; factors such as the compression ratio also need to be taken into account. But I’m not sure if any expert has worked out how to evaluate them – could you teach me?
These days, the management has finally decided to increase the production of crude alcohol. Hehe, after all, it’s a market economy; there must be some pressure involved. However, after calculating it, our costs are still relatively high. The specific approach is actually quite simple: by adjusting the level of CO, the second methanol tower can be put into use, which allows an increase of about 70% in the amount of crude alcohol produced, roughly 15 cubic meters per day. Of course, the overall steam consumption increases slightly, but this still proves beneficial for the conversion process as well as the overall efficiency. During the actual process of charging the two towers, the system did not reduce the pressure; in other words, the temperature was increased at a pressure of 7.0 MP. Could this pose a significant risk to the synthesis of copper-based catalysts? Please, experts, point it out! Let’s discuss more!
Let me take a look too; I haven’t been here in a long time