Weekly Topic 10.11.29, Issue 5: What is the impact of varying specific gravities on the methanol distillation system?

The prognosis has a high weight; too much water may be added, resulting in high energy consumption； It is also possible that the pre-tower vent temperature control is set too high, resulting in severe methanol waste.

If the prognostic factor has little significance, it may be that the light components were not removed thoroughly

A high specific gravity simply means that more water is added; since methanol has a low specific gravity, a high specific gravity is beneficial for the extraction of pure methanol, though it results in steam waste. On the other hand, a low specific gravity reduces the boiling point difference between the azeotropes in distillation, which hinders the extraction of pure substances. It also has a significant impact on the temperature difference under pressure, reducing this difference and thereby complicating the distillation process. A reasonable yield ratio falls within the range specified during design, around 0.9. Nowadays, many manufacturers opt for a more straightforward method of measuring water content. When the distillation process is stable and product quality can be ensured, a slightly lower yield ratio reduces the energy consumption per unit of product, with no negative consequences; however, it does increase the operational difficulty. Of course, an excessively high yield ratio is also unfavorable for distillation operations, as it makes it difficult to adjust temperature conditions. The appropriate range has been determined through costly experience gained by many manufacturers; values that are too high or too low make operations increasingly difficult, which is not sustainable

Specific gravity is generally related to the water content and does not have a significant impact on the quality of pure methanol; the relationship between the two is minimal.

I’d like to share my views on the importance of prognosis: 1. Previous data indicate that the proportion allocated to prognosis should be kept between 0.83 and 0.86, with the amount of water added not exceeding 20% of the amount of material fed in. Now the quality of crude alcohols is much better than before, so everyone should abandon the previous approaches and think creatively; it’s possible to reduce the value to 0.82. 2. What are the advantages of having a low prognostic ratio? As we all know, this approach can reduce steam consumption, lower the load on the tower, as well as reduce the load on the conveying equipment (thereby saving electricity). It also reduces the amount of desalinated water that needs to be used; a system with a production capacity of 200,000 units can save 1 ton of desalinated water per hour. The cost of 1 ton of water is between 6 and 10 yuan, so you can calculate by yourself how much money can be saved. 3. It is very rare for the quality of the product to be affected by using less extraction water, so you can reduce the amount with confidence.

Generally, it is better to add more water; too little water may result in the product not meeting quality standards, although this leads to greater waste of steam and water resources. But too much has the opposite effect. If the product has poor water solubility, it is generally advisable to increase the amount of desalinated water slightly

Our predicted moisture content is only around 8%, so there are definitely no issues with the product quality. Those prognostic factors are all very old-fashioned concepts.

Another advantage is that it can reduce the discharge of residual liquids, thereby cutting down on wastewater treatment costs.

1. I would like to ask: if the prognostic specific gravity is reduced to 0.82, what will be the temperature in the atmospheric pressure tower bottom? Is the residue acceptable with a methanol content of less than 0.1%? What should be the temperature control in the pressurized tower? 2. I also want to know if there is a table showing the relationship between methanol content and water content for prognostic specific gravities ranging from 0.84 to 0.87, along with the calculation formulas for these values. Please share them. Thank you.

Has everyone’s prognosis improved now? Taking our factory as an example, if the distillation load is 60 cubic meters, the amount of water to be added is around 2.3 cubic meters. I’m not quite sure what the value for the forecasted figure is; I haven’t done the calculations, but it probably won’t exceed 0.82! The water content is around 0.1, and the products from the second and third towers are all fine! Personally, I think the amount of water removed through desalination can be reduced further, but the downstream manufacturers have requirements regarding the light components, so they don’t dare to reduce it any more