Research on the application of demulsifiers in the separation of ammonia water and tar

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Author: Jin Xuewen, Zhang Guanglian, etc. Date: 2009-1-19 10:13:09 Research on the Application of Demulsifiers in the Separation of Tar from Ammonia Water. Jin Xuewen, Zhang Guanglian (Shanghai Baosteel Chemical Co., Ltd., Shanghai 200942); Zhu Qinyong, Chen Tong (Nalco (Suzhou) Chemical Co., Ltd., Suzhou 215000). The ammonia water separator is primarily used for separating the mixture of tar and ammonia water resulting from the cooling of coke oven gas. Due to factors such as residence time, coal powder entrained in coke oven gas, and emulsions, fluctuations occur at the interface of the ammonia water separator. In severe cases, this leads to a significant increase in the moisture content of tar, while also causing a large amount of tar to be entrained in the recycled ammonia water. This affects the normal operation of the coke ovens and tar processing units, as well as the subsequent treatment of the remaining ammonia water. Currently, coking plants mainly rely on methods such as adjusting temperature, increasing residence time, and centrifugal separation to improve the quality of tar and enhance the separation efficiency of ammonia water from tar. The use of chemical agents in China to improve the separation of ammonia water from tar is not common, but this technology has begun to be adopted in Japan, North America, and Europe. Considering issues such as an increase in the amount of coal powder entrained and difficulties in separating tar from ammonia water that may arise from the deployment of Baosteel’s coal humidification system, this paper conducts an exploratory study on the use of chemical demulsifiers in the ammonia water tar separation system, in order to provide technical groundwork for coal humidification. 1 Static test: The chemical used in this test is designated as N9961, and its main physical and chemical properties are shown in Table 1. Table 1: Basic physical and chemical properties of N9961
Physical state: Liquid
Freezing temperature: ＜–45°C
Appearance: Amber-colored
pH (20%): 6.4
Density (25°C): 0.92–0.93 kg/L
Water solubility: Soluble

Its working principle is as follows: The demulsifier N9961 is a water-soluble demulsifying and viscosity-reducing agent. Once added to the system, it binds with the tar present in ammonia water. In the separator, it accelerates the separation process between tar and ammonia water and improves the efficiency of this separation. Through its demulsifying, dispersing, and viscosity-reducing effects, it thins the emulsion layer formed by tar and ammonia water, thereby enhancing the efficiency of separating them in the separator. This reduces the amount of suspended particles in the ammonia water, lowers the surface tension of the tar, and speeds up the separation of tar from tar residues, resulting in tar with lower moisture and residue content. At the same time, it minimizes the amount of suspended particles and oil that end up in the ammonia water, improving the quality of the recycled ammonia water and enhancing the effectiveness of treating residual ammonia water. The laboratory static simulation study primarily aims to simulate the conditions in the actual operation environment (internal temperature of the ammonia water separator: 75–80°C), to conduct laboratory tests on the N9961 chemical agent, determine the theoretically optimal dosage concentration, and assess the impact of using this agent on the quality of tar. Through static test studies under simulated operating conditions, the theoretical optimal dosage concentration of this agent was determined to be 100–400 ppm. Meanwhile, the tar quality under the condition of adding the agent was analyzed, with no significant changes, as shown in Table 2. Table 2 Analysis results of tar properties before and after addition of the agent. N9961 dosage, ppm: 0 (blank control sample); 400. Viscosity (80°C): 1.91, 1.85. Density (15°C), kg/L: 1.172, 1.173. Toluene-insoluble matter, %: 4.29, 4.71. Tar residue content, %: 1.0, 1.2. Initial boiling point, °C: 170, 172, 170–230°C fraction, %: 6.9, 7.9; 230–300°C fraction, %: 34.7, 36.5; 300–350°C fraction, %: 53.6, 55.1; Fraction >350°C, %: 4.8, 0.5. 2 Industrial testing. 2.1 Test procedure: This test was conducted in Baosteel’s first-phase ammonia water system. The chemical in the sump is continuously added to the ammonia water intermediate tank via a metering pump. Since N9961 is a water-soluble product, it returns to the coke oven along with the circulating ammonia water, and then enters the ammonia water separator after cooling the gas in the rising pipe. Inside the ammonia water separator, the demulsifier N9961 combines with tar; through its demulsifying, dispersing, and viscosity-reducing effects, it improves the separation between tar and ammonia water. The reacted N9961 agent then enters the tar system. Figure 1 Test procedure 1 – Ammonia water separator ； 2 – Tar separator ； 3 – Medication high-level tank ； 4 – Circulating ammonia water intermediate tank ； 5 – Medication pump ； 6 – Circulating ammonia water pump 2.2 Analysis of test results: In this industrial test, Nalco Specialty Chemicals N9961 was used, and it was added continuously to the ammonia water intermediate tank T-1103 using a metering pump; the concentration of the chemical added was maintained between 100 and 400 ppm. Considering the potential impact of the removal of the tar originally accumulated inside the pipes at the beginning of the experiment on the ammonia nozzles in the coke oven, a method of gradually increasing the concentration of the chemical was adopted, with the initial concentration set between 50 and 100 ppm. The industrial-scale testing lasted for about 3 months, during which the differences in the quality of ammonia water and tar before and after the addition of the chemical agents, as well as at different concentrations of these agents, were closely monitored. (1) Comparison before and after the addition of the chemical. After the chemical was added, there was no worsening of clogging in the ammonia nozzle on the coke oven, and as the experiment progressed, the clogging of the nozzle improved to some extent. The effects of reagent addition on the separation performance of ammonia water and tar are specifically manifested in changes in the moisture content, viscosity of tar, tar residues, and ammonia water suspensions. Table 3 Comparison of ammonia water and tar parameters before and after the test. Technical parameters: Before test / After test; Change. Tar moisture, %: 3.70 / 2.0 – 46%; Tar viscosity: 2.43 / 2.13 – 13%; Ammonia water suspended solids, mg/L: 113 / 78 – 31%. (2) Comparison at different reagent concentrations. During the experiment, changes in tar moisture and viscosity at different concentrations of the agent were monitored. Below 100 ppm, as the concentration of the agent increases, improvements in the moisture and viscosity of the tar are relatively significant; however, once the concentration exceeds 100 ppm, little change occurs in the moisture and viscosity of the tar. (3) Impact on the quality of circulating ammonia water in the coke oven. Changes in the quality of ammonia water are tracked as an auxiliary indicator to assess the impact of the chemical on the performance of the separator. Based on the test results, the content of suspended solids in the circulating ammonia water decreased by approximately 31% overall, and both the tar entrainment in the ammonia water and its viscosity were improved to a certain extent. More importantly, the quality fluctuations of tar and ammonia water were **reduced**; the standard deviation of moisture content in tar decreased by 44%, while the standard deviation of suspended solids in ammonia water dropped by 49%. By comparing the ammonia water from the first-stage cycle with additives and that from the second-stage cycle without additives, laboratory filtration tests using standard 0.45um filter paper showed that the filtration time for the first-stage sample was 2 minutes and 55 seconds, while it was 30 minutes and 47 seconds for the second-stage sample; this indicates that the fluidity of the ammonia water has been significantly improved. 3 Conclusions (1) The use of chemical demulsifiers to assist in the separation of tar from ammonia water is feasible in ammonia water-tar separation systems, and it has no significant effect on the composition of the tar. (2) Adding demulsifiers/reducing binders can significantly improve the separation performance between ammonia and tar, which is beneficial for maintaining the quality of both tar and ammonia; it can be used as a supplementary technique for the separation of ammonia from tar.