Talking about chlorine dehumidification and pressure conveying unit

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At present, the production capacity of ionic membrane caustic soda of Jiangsu Northern Chlorine and Alkali Group Co., Ltd. (hereinafter referred to as the North Chlor-Alkali Company) is 100,000 t/a, and there are 2 sets of supporting hydrogen chloride treatment equipment. The old equipment can handle the production of 40,000 t/a caustic soda plant. Cl 2 and H 2, the new device is capable of handling Cl 2 and H 2 produced by a 60,000 t/a caustic soda unit. The two sets of chlorohydrogen treatment units were completed and put into operation in February 1997 and August 2005, respectively. In the construction of the new plant, the North Chlor-Alkali Company carefully summarized the gains and losses of the company in actual production, fully borrowed the production experience of the same industry, digested and absorbed new processes, new equipment and new materials, and considered energy conservation, environmental protection and safety factors. . The following two sets of chlorohydrogen treatment devices are compared from the aspects of process flow, selection of main equipment, and energy saving.

1 The process of the chlorine gas cooling and dewatering unit is: the wet chlorine gas from the electrolysis first enters two parallel titanium coolers, exchanges heat with the cooling water between the tubes, and then enters the second stage titanium cooler (1 And the water mist trap, the condensed chlorine water is sent for dechlorination. The three titanium coolers use a tube-and-tube cooler with a heat exchange area of ​​110 m 2 . Due to the large temperature difference between the wet chlorine gas and the cooling water, the heat exchanger is in the form of a packing. The disadvantage is that the cooling water is easily leaked from the packing seal. Site environment. The water mist trap is a filled mist eliminator made of hard PVC material with poor strength and easy to leak.

The new device adds a chlorine water washing tower. The wet chlorine gas that is electrolyzed first enters the tower, and is sprayed with normal temperature chlorine water to remove impurities such as salt mist entrained in the chlorine gas. The temperature of the chlorine gas drops to 45, and then enters a titanium tube-type cooler (which is a fixed tube plate type) with a heat exchange area of ​​150 m 2 , and finally removes water droplets in the water mist trap. The water mist trap housing in the new device is a PVC / FRP composite structure, the inner layer PVC has excellent corrosion resistance in the chlorine system, and the outer layer FRP is used to increase the strength of the equipment and ensure the safe use of the equipment. The filter cartridge is selected from the domestic professional manufacturer of fiber mist eliminator. The demisting efficiency is high, and the skeleton is processed with Hetlon resin, which has good strength and resistance to wet chlorine gas.

2 chlorine gas drying and pressurized conveying unit old device process: the chlorine gas from the water mist trap enters a foam drying tower, and the concentrated sulfuric acid is in contact with the surface of the tray to form a foam absorption layer, and the water in the chlorine gas is The sulfuric acid is absorbed to achieve the drying of the chlorine gas; the dried chlorine gas is discharged from the top of the column, and the sulfuric acid mist entrained in the chlorine gas is removed by the acid mist trap, and then compressed by the Nessler pump (liquid ring compressor) to 150 200 kPa, and sent Enter each department. The foam tower is an overflowed sieve tray tower made of a hard PVC material. The inner diameter of the tower body is 700 mm and the wall thickness is 16 mm. There are 4 layers of trays. The top of the tower is provided with a swirling demister. The diameter of the trays is 3 mm, the hole spacing is 8 mm, and the triangles are arranged. The advantage of the foam drying tower is that the mass transfer rate is high, the production intensity is large, the volume is small, the land occupation is small, and the manufacturing and maintenance are convenient, but the resistance loss of the foam drying tower is large. The Nessler pump is a liquid ring compressor that uses concentrated sulfuric acid as a circulating medium when delivering chlorine gas under pressure. Although Nessler has been widely used in chlor-alkali enterprises, it has low capacity, high power consumption, short life, large maintenance and poor maintenance work environment. During the compression process, concentrated sulfuric acid will absorb the residual water in the chlorine gas, its concentration will decrease, the corrosiveness to the metal will be enhanced, and the impeller will be corroded, which will affect the normal operation of the Nessler pump. Due to the use of concentrated sulfuric acid, some impurities will enter the Nessler pump with concentrated sulfuric acid, and the solid particles will reduce the precision of the friction surface of the mechanical sealing surface and cause leakage.

The process of the new device is as follows: the chlorine gas from the water mist trap enters the section packing drying tower, the section packing drying tower and the blister packing drying tower, and is dried in countercurrent contact with concentrated sulfuric acid in the tower. The dried chlorine gas is transported by a turbo compressor through an acid mist trap. The above three towers have a tower diameter of 1 400 mm, the shell is a PVC / FRP composite structure, and the filler is 57 CPVC multi-faceted hollow spheres. The section and section packing drying tower has two layers of packing, each of which is 3 000 mm high, and a sulfuric acid redistributor is arranged in the middle. The blister packing drying tower has 5 layers of blister-mounted trays with a tray spacing of 700 mm and a total of 110 blister packs. The lower part of the tower is provided with a packing layer with a height of 2 800 mm.

The characteristics of the packed tower are stable operation, convenient control, large operation flexibility, low resistance of equipment, and different concentrations of sulfuric acid can be added to each tower and circulated and cooled to achieve better drying effect and meet the requirements of the turbo compressor; Big, more investment. In new installations, the use of turbo compressors is the greatest success. Since the use of turbo compressors, production management has been greatly facilitated and economic benefits have been significantly improved. The turbo compressor uses two LY J - 2200 /0. 30 centrifugal chlorine compressors produced by Hangzhou Zhenxing Industrial Pump Manufacturing Co., Ltd., one open and one standby.

Zhenxing Industrial Pump Manufacturing Co., Ltd. supplies a set of units, including main engine, oil station, primary cooler, secondary cooler and corresponding electrical and instrumentation devices. The main engine consists of a compressor and an electric motor. It is mounted on the same base and is directly connected. The structure is compact. The coupling uses a diaphragm coupling for easy installation and alignment. The compressor is two-stage compression. After the secondary straight teeth increase speed, the impeller speed is up to 22 360 r/m in. The impeller form is semi-open and the strength is high. Due to the high speed, the whole transmission is equipped with a dedicated oil station to ensure the lubrication and cooling of the equipment; a high-position fuel tank is installed on the oil station. When the power grid is out of power, although the oil pump stops working, the high-level fuel tank can continue to supply oil in a short time. To avoid wear and wear of the transmission. Since the friction of chlorine gas in the compressor generates heat, in order to prevent the chlorine gas from being overheated, chlorine gas is generated. After the first stage compression, a primary cooler is set, and after the temperature of the chlorine gas is lowered, the secondary compression is performed, and then the secondary cooler is passed. Cool down to the next step.

Compared with the Nessler pump, the biggest advantage of the turbo compressor is that it has a large conveying capacity and requires less power. If you do not consider the various factors in the actual operation, the theoretical design of the LY J- 2200 /0. 30 turbo compressor is 2 200 m 3 /h, with a motor power of 160 kW, such as To use the Nessler pump to compress the same amount of chlorine, you need a YLJ-1200/0. 30 type Ness pump and a YLJ-1000 / 0. 30 type Nessler pump, each with 110 kW and 132 kW motors. The total power is 242 kW.

According to the turbo compressor in the North chlor-alkali company for more than one year of operation, the following aspects should be the focus of attention.

(1). The turbine compressor is more precise, and the requirements for the water and other impurities (mainly sulfuric acid mist) in the chlorine are also correspondingly increased. Generally, the water content is required to be less than 0.02%. The corrosion of the turbine compressor is mainly concentrated on the impeller. Although the impeller material is made of special alloy, it has high strength, wear resistance and corrosion resistance. However, if the water and impurities in the chlorine exceed the standard for a long time, the surface of the impeller will still have local corrosion. Will accumulate on the surface of the impeller. The impeller has a rotational speed of 22 360 r/m in and has undergone a rigorous dynamic balance test before use. Even if the impeller is slightly corroded, the unit will be shaken too much and the operation will be unstable.

(2) The gas seal used in the shaft seal of the turbo compressor is a labyrinth method, and the seal gas is a nitrogen gas or meter air that has been dried, and the sealing performance is reliable. In the actual operation, attention should be paid to the degree of dryness of the gas source and the stability of the pressure. The moisture content of the gas source is less than 0.01%, and the pressure is stable at 0. 25 0. 30 MPa. Seal the pressure regulator valve opening. To prevent chlorine leakage when the unit is parked, the air seal should not be closed.

(3) To prevent damage to the turbine compressor due to leakage of the chlorine gas cooler. Both the primary cooler and the secondary cooler use a tubular heat exchanger, the chlorine gas is taken away from the shell, the water is taken away, and the heat exchange area of ​​the cooler is 60 m 2 , and the material is carbon steel. The heat exchanger tubes of the cooler may leak due to various reasons, such as long use time, excessive water in the chlorine, problems with the quality of the cooling water, and problems in the quality of the cooler. Preventing corrosion of turbine compressors is a problem that must be considered. Since the heat exchange medium is chlorine gas and water, the dry chlorine gas is slightly corrosive to carbon steel, and once the chlorine gas comes into contact with water, a chemical reaction occurs: Cl 2 + H 2 O HCl + HClO, and the formed hydrochloric acid and hypochlorous acid to carbon steel It is highly corrosive.

The most common method is to reduce the pressure of the cooling water so that the pressure of the chlorine gas is greater than the pressure of the water. Once the heat exchange tube leaks, under the action of the pressure difference, the chlorine gas flows from the tube to the shell side, so that the corrosion concentrates on the heat exchanger itself. , to avoid corrosion of the turbo compressor in a short time. In actual operation, the cooler is operated without pressure backwater, and the trace chlorine in the cooling water is periodically detected to determine whether the cooler leaks.

(4) Chlorine fire is the biggest safety hazard of turbo compressors. The chlorine outlet temperature after compression at all levels must be much lower than 149! .

3 Hydrogen cooling and pressurized conveying unit The process of two sets of hydrogen processing units is basically the same. The hydrogen from the electrolysis tank is cooled and washed in the hydrogen cooling tower to remove the salt and alkali and other solid impurities entrained in the hydrogen, and reduce the temperature of the hydrogen. The majority of the water vapor is thus condensed and removed, and the cooled hydrogen is compressed by a hydrogen compressor to 0.08 M Pa and then sent to the next process. In this way, when hydrogen is compressed, the hydrogen generated by the new and old caustic soda plants is combined and compressed together, and the water ring compressor with larger processing capacity is selected, which reduces the number of equipment, spare parts and maintenance, and saves electricity.

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