Foreword

Impurities in sulfur can be divided into soluble and insoluble impurities two categories. Soluble impurities include organic hydrocarbons, arsenic, selenium, tellurium, etc. Insoluble impurities include soil, ash, pyrite, phosphate ore, and woven bag debris mixed in the transportation process.

1. Harm of impurities

If the organic hydrocarbon enters the sulfur burner, it will consume oxygen in the air, resulting in a lower O/S ratio, thereby reducing the conversion rate. At the same time, some hydrocarbon combustion will produce water, water vapor into the subsequent section, easy to form condensing acid, corrosion equipment. In addition, the hydrocarbon content increased in direct proportion to the formation of nitrogen oxides in the flue gas, which had a significant effect on the quality of sulfuric acid. Arsenic entering the converter can lead to catalyst poisoning, triggering the deV phenomenon, making the catalyst permanently inactive.

When liquid sulfur enters the sulfur burner through the mechanical spray gun, the insoluble impurities of large particles will block the nozzle of the sulfur-gun, resulting in a reduction in the amount of sulfur-spraying and affecting the load of the device. After the insoluble impurities of small particles enter the converter, they will adhere to the catalyst surface, increase the resistance of the catalyst bed, increase the kinetic energy consumption of the system, and affect the conversion rate of the system. Sulfur becomes acidic after melting, and if the acidity is too high, it will corrode equipment. In addition, acid liquid sulfur or sulfur vapor can react with the nozzle at high temperature, resulting in corrosion of the nozzle.

2, sulfur refining methods

1, sedimentation method: liquid sulfur in the sedimentation tank natural settlement of 1-3 days, less dense impurities will float on the surface of the liquid, while the density of larger impurities will settle at the bottom of the pool. Initial purification treatment can be achieved by removing surface float and periodically removing bottom fallout. The method is simple in equipment, but occupies a large area, and is difficult to remove small particles of impurities. It is only suitable for the preliminary purification of general sulfur insoluble matter.

2, filtration method: the liquid sulfur and an appropriate amount of filter aid (such as diatomaceous earth) after mixing, through the filter for treatment. On the filter plate of the filter, the liquid sulfur and the filter aid jointly form a filter cake, the liquid sulfur passes through the filter cake into the next system, and the impurities are intercepted on the filter cake, so as to achieve the separation of liquid sulfur and impurities. When the impurities on the cake accumulate to a certain thickness, it is necessary to clean it regularly. This method can effectively remove small particle size impurities and some insoluble hydrocarbons.

3, active clay adsorption method: active clay has the characteristics of preferentially adsorbing hydrocarbon compounds in sulfur, and removes hydrocarbon organic compounds dissolved in sulfur through adsorption, so as to achieve the refining of crude sulfur. If the crude sulfur contains undissolved hydrocarbons, it should be removed by other filtration methods before this method is used to remove the hydrocarbons from the crude sulfur.

4, sulfuric acid method: 93-99% sulfuric acid and liquid sulfur (black sulfur) under the temperature of 125-135℃ sulfonation reaction, and then through hot water extraction, the sulfonated hydrocarbons are removed.

5, high temperature oxidation method: when the liquid sulfur is heated to 315℃, the hydrocarbons in the liquid sulfur will undergo a chemical reaction: hydrogen reacts with sulfur to produce hydrogen sulfide and escape, while carbon and sulfur generate sulfur carbon complex and dissolve in the liquid sulfur. The liquid sulfur containing the sulfur carbon complex obtained from this is the refined sulfur. However, the purity of the product produced by this method is not high.

Analysis of reasons for poor liquid sulfur refining effect

In sulfur acid production equipment, liquid sulfur is usually refined by filtration. If the number of liquid sulfur storage tanks is sufficient, the secondary sedimentation method can also be used to alternately use large tanks, so that the filtered fine sulfur can be used after 1-3 days of static settlement in the large tank. In this way, part of the unfiltered impurities will be deposited at the bottom of the large tank, thus further improving the purity of the liquid sulfur. This method is especially necessary for the filtration of poor liquid sulfur.

In the production process of sulfur acid, due to poor filtration effect, impurities often enter the sulfur conversion section, which has a serious impact on production. The following is the analysis of the main reasons for the poor filtering effect:

1, screen plate reason: if the screen is improperly installed, the edge is not pressed, there is a gap, or between the screen plate and the pipeline “ O” The ring seal is not strict, will lead to liquid sulfur leakage. In addition, if the filter screen is damaged, it will also cause liquid sulfur leakage. Therefore, when installing the screen plate, it is necessary to carefully check each link to ensure that it is installed in place. At the same time, when cleaning the filter, it is strictly prohibited to use sharp tools to directly contact the filter, so as not to cause damage.

2, filter cake reason: filter cake is a filter layer formed by diatomite on the filter plate. Most devices use two different types of diatomaceous earth: First, the pores of the filter screen are filled with crude diatomaceous earth to form a dark gray base filter layer; The Spaces between the coarse diatomaceous earth are then filled with fine diatomaceous earth to form a fine filter layer of light gray. In this way, the pores of the filter layer become small enough to effectively block most insoluble impurities. As filtration proceeds, impurities gradually accumulate on the surface of the cake, forming a black layer of impurities, so the cleaned cake can usually clearly see the three-layer structure.

The filter plate is installed vertically. After the filter cake is formed on the filter plate, it is maintained by the force perpendicular to the direction of the filter screen. The force is achieved by the pressure difference between the inlet and outlet of the filter. If there is no pressure difference, the diatomaceous earth will fall to the bottom of the filter due to the action of gravity, resulting in the destruction of the filter cake, and the filtration effect will be reduced. During the pre-coating process, it is necessary to ensure that the inside of the filter is completely filled so that the entire filter plate can be evenly pre-coated with diatomaceous earth to form a complete filter cake.

During operation, the pressure difference between the inlet and outlet of the filter must always be maintained, and the valve should be changed slowly to avoid zero pressure. Especially for filters in series of one and two levels, extra care should be taken when switching valves. If the filter pump suddenly stops and the filter loses pressure, it indicates that the filter cake has begun to fall off and needs to be re-pre-coated. If the liquid sulfur storage tank level is high, the filter needs to be switched to the reflux state to maintain the stability of the filter cake. It should be noted that the operation mode of stopping the pump and maintaining pressure must not be used, because after closing the filter inlet and outlet valve, although there is still pressure inside the filter, the pressure difference between the filter inlet and outlet is zero, and the diatomite will fall to the bottom of the filter due to the action of gravity, resulting in the filter cake being destroyed and the filtration effect being reduced.