Wastewater Treatment Technology for Esterification Process of Ethylene Glycol Plant

The working principle of the esterification process of the ethylene glycol plant is to use the original esterification tower to transform the wastewater to a certain extent, but in the solution of the esterification system, its by-product contains 3%-5% of dilute nitric acid.

Although the waste liquid that needs to be discharged can meet the discharge standard, the dilute nitric acid and nitrate it contains will cause certain corrosion to the discharge pipeline and related equipment. How to eliminate this corrosion and effectively reduce the waste liquid The content of nitrate in the process is reduced, and the processing cost during the use of the process is reduced.

The use of ethylene glycol units to create greater benefits and effectively promote the better progress and development of the ethylene glycol process is what we need to do at this stage.

Improvement of technical solutions

In the design process of this scheme, the main purpose is to transform the original technology to make it more convenient to use. In the original technology, the dilute nitric acid and the corrosion of the nitrate to the pipeline is the most troublesome thing in the original process.

In order to effectively change this problem, in the process of transforming the process scheme, nitric acid can participate in the reduction reaction to combine the nitric acid in the process with the methanol and process synthesis gas produced in the ethylene glycol process production system. The NO generated in the catalyst undergoes a catalytic reaction at a certain temperature and a certain pressure.

This makes it possible to generate a new reactant, methyl nitrite (MN), which is itself a material required for the production of the ethylene glycol process.

In this way, this problem can be effectively solved, but this process has become more environmentally friendly, which is in line with the current Chinese government’s requirements for environmental protection, and at the same time, the raw materials required for the original reaction appeared in the reaction process.

It directly reduces the material cost required for the reaction and effectively reduces the cost consumed by the reaction. No matter from which point of view, it is beneficial to the development of my country at this stage. The catalytic reaction principle of dilute nitric acid in the improvement process is: HNO3 +2NO+3CH3OH=3CH3ONO+2H2O.

1.1 Process flow

The waste water is pressurized by the compressor, and the waste water in the gaseous state after the pressurization treatment is sent to the lower part of the esterification tower to be uniformly mixed with the material in the boiler outlet in the process system to ensure mixing. After the end of the process, the liquid in the treatment and the liquid coming down from the upper part of the esterification tower are countercurrent, and the reaction of gas-liquid contact is further realized.

In the course of the reaction, nitric acid reacts with nitric oxide and methanol to gradually generate methyl nitrite. During the reaction process, the generated liquid phase will be sent to the pump again through the still liquid of the esterification tower, and the liquid will be sent to the methanol recovery system, and the generated gas phase will be together with the main gas flow in the esterification tower. The ascent is carried out, and the rest will go out from the top of the esterification tower.

1.2 Relevant parameters in the reaction process

The main change of this plan is to reduce the original dilute nitric acid that corrodes the pipeline, so that it can be used as methyl nitrite and water. The methanol and catalyst existing in the wastewater are used to help it to carry out an effective reaction under a certain pressure. During the experiment, it was found that the main temperature, pressure and other related parameters for the reaction to be carried out. In conclusion, it is convenient to generate methyl nitrite and water better in the process of using this process in the future.

The temperature conditions required for the reaction are: 65°C to 90°C; the pressure required for the reaction is: 0.4MPa to 0.45MPa; the flow rate of the liquid phase during the reaction is: 12t/h; the flow rate of the gas phase is: 6000m3 /h.

1.3 Modification of the reactor

In order to realize the current process, it is inevitable to carry out a certain transformation of the existing process.

In order to realize the current process, it is inevitable to carry out a certain transformation of the existing process.

And a distributor for placing the liquid is installed, so that the liquid used in the reaction can be directly introduced into the liquid distributor, which is convenient for the reaction to proceed.

1.4 The recovery rate of nitric acid and the effect of recovery

After the transformation of the original scheme of the esterification process of the ethylene glycol plant, the use of this process for the treatment of wastewater can reveal that the dilute nitric acid contained in the original process wastewater was reacted with the new method.

Its own recovery rate exceeds 45%, and it can be detected during the discharge of wastewater. Now it is detected from the export process liquid, and its own nitric acid content is basically controlled below 2.5%, which fully meets the national standard. , and have great benefits for environmental protection and improving the water quality of our country.

Benefit analysis after transformation

The purpose of the transformation is to improve the benefits of this process technology while protecting the environment. What kind of benefits can be obtained when applying this scheme is the most concerned issue after the process transformation. The annual output is 100,000. t-scale synthesis gas to ethylene glycol was used as the basis for the experimental analysis.

2.1 The cost of nitric acid saved

According to the previous data investigation and analysis, it can be known that in the liquid phase of 12t/h, it contains 63% nitric acid, which is about 856kg/h.

From this data, it can be inferred that the 63% nitric acid lost in the whole year is actually about 6856t/year by applying the unimproved process for treatment, and one year is calculated as 8000h.

The improved process method is used for calculation. According to the calculation data, it can be known that the amount of nitric acid recovered after the reduction is 262.23kg/h. It can be found that after applying this scheme, the 63% nitric acid recovered annually is more The actual weight is about 3328.8t/year.

According to market research, it can be known that in the current market, the purchase price of nitric acid with a content of 63% per ton in the market is mostly 1,200 yuan / t. In this way, it can be known through calculation that the application of the new scheme will cost it every year in terms of capital. Can save about 3.9949 million yuan / year.

The saved funds can be put into the next use, or the funds can be used to study better solutions, helping our country to make greater progress in the treatment of sewage.

2.2 Save the cost of liquid caustic soda

Through calculation and analysis, it can be known that 3328.8t/year of nitric acid with a content of 63% is calculated and analyzed according to the theory of the reaction. The amount of alkali added.

Then we can calculate it to know: 3328.8×0.63×40÷63÷0.47=2833.02t/year, but in the actual response, there is usually an increase of 15%, so according to this situation, the current problem is carried out. The consideration is: 2833.02×1.15=3257.97t/year.

According to market surveys, the current purchase price of 48% lye per ton is about 900 yuan/t, saving a total of 2,921,300 yuan per year.

2.3 Reduced consumption of N2O4

It can be known from the chemical reaction equation: 3N2O4+2H2O=4HNO3+2NO. According to the calculation, it can be known that the annual recycled content of 63% nitric acid is about 3328.8t/year, then the number is inserted into the chemical equation to know that the annual consumption of N2O4 can be reduced by about 2287.08t/year.

2.4 Consumption of electricity and steam

When using the new scheme, a certain amount of steam and electricity consumption will be increased. From the data, it can be known that using the new process will increase the consumption of 0.3MPa(g) low-pressure steam by about 12,000t/year. It can be seen from the calculation that 12,000t/year × 94 Yuan/t=1.128 million yuan/year.

The annual increase in electricity consumption is 63,000 kWh, which is equivalent to RMB 32,000 per year through calculation.

2.5 Overall economic benefits

Through the above analysis and calculation, we can always know that after the transformation of the process equipment is completed, the annual cost saving is 6.9162 million yuan/year, the annual cost is 1.16 million yuan, and the total saving is 5.7562 million yuan/year.

Conclusion

According to this article, we can know that when designing the scheme, what we do is not to overthrow the original scheme, but to retain it and then make a better transformation.

The scheme described in this article refers to the use of the original esterification tower to carry out some modifications to the scheme. The purpose of the modification is to reduce the dilute nitric acid contained in the wastewater treated by the ethylene glycol esterification process. Environmental protection and energy saving technology that can improve glycol esterification process.

At the same time, since there will be no corrosion of the pipeline, the self-efficacy has also been greatly improved, and it also saves the consumption of raw materials for the ethylene glycol process in the production process.

And effectively reduce the consumption of N2O4 and liquid caustic soda, eliminate the corrosion of the pipeline equipment by the two chemicals of dilute nitric acid and nitrate in the original process, and the whole process flow has no waste products.

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