Cause analysis of deformation and damage of anion bed Johnson screen header lateral

One of our American customers reported that their anion bed regeneration effect was poor, resin leakage, and other abnormal phenomena. After the equipment stopped running, through the internal inspection of the anion bed, it was found that the main pipe and branch pipe of the Johnson screen header lateral were seriously deformed, even the upper part of the main pipe was cracked, and the support bracket of the intermediate discharge device was bent and deformed, which affected the normal operation of the whole desalination and water making system. This paper will analyze the causes of the damage of the Johnson screen header lateral, and put forward the treatment methods for the faults.

Causes of damage to the Johnson screen header lateral of anion bed

Summary of the structure form of the Johnson screen header lateral
The anion bed used in the desalination process is a fixed bed with countercurrent regeneration, and the traditional fishbone drainage system with large resistance is used in the middle drainage device.

The Johnson screen header lateral main pipe is made of 316L material with a diameter of 133mm. One end of the main pipe is connected with the Johnson screen header lateral drainage pipe of the bed body by a blue plate, and the other end is sealed and fixed on the bed body by a U-shaped clamp. The two sides of the main pipe are connected with the Johnson screen header lateral branch pipe, and the upper part of the main pipe is welded with a reinforcing rib plate to increase the support strength. The Johnson screen header lateral branch pipe is made of 316L pipe with a diameter of 57mm and fixed by 120mm rubber-lined channel steel as the Johnson screen header lateral support bracket. The filtering mode is a V wire screen type frame.

Analysis of the causes of the failure of the Johnson screen header lateral

Based on the analysis of the damage phenomenon of the middle drainage device, the failure of the middle drainage device is mainly manifested by the upward huge supporting force, and the middle drainage device itself does not have enough strength to resist the supporting force, which leads to the damage of the whole middle drainage device. Therefore, it can be judged that the failure of the intermediate exhaust device is mainly caused by the following factors:

• Diaphragm pneumatic diaphragm valve is used in anion bed, cation bed and other equipment. The opening speed of the diaphragm pneumatic diaphragm valve is faster than that of the piston pneumatic valve. During the regeneration operation of an anion bed or cation bed, due to the rapid start and stop, the pressure inside the bed increases and decreases rapidly. Due to the resistance of resin in the bed, there is a large pressure difference between the lower part and the upper part of the equipment, Under the action of pressure difference and inertial impact force, the main pipe and branch pipe of the Johnson screen header lateral will bear a load of about 782t, resulting in serious bending deformation of the Johnson screen header lateral device inside the equipment and even cracking of the top of the main pipe.
• The support bracket of the wedge wire screen header lateral device is small. The support bracket size of the Johnson screen header lateral device is too small. At present, the width of the support bracket of the intermediate discharge device is only 120mm, which is lined with rubber channel steel. Its frame strength is far lower than that of the anion bed used in the old desalination workshop. The support bracket of the intermediate discharge device used in the old desalination anion bed is 150 mm × 300 mm square steel lined with rubber. According to the analysis of 20 years’ operation, this kind of failure has never occurred. However, the current support can not play the role of supporting protection and fixation when the water inlet pressure difference increases. Therefore, the low strength of the support bracket is one of the main reasons for this kind of failure.
• The stiffened plate of the Johnson screen header lateral main pipe has defects in design and manufacture. The existing Johnson screen header lateral main pipe is welded with a reinforcing rib plate on the upper part of the main pipe, but there is welding joint in the middle part of the reinforcing rib plate, and the welding joint is not beveled, and the weld does not go deep into the welding joint, so its strength is not enough, and the strength of the welding joint is less than that of the whole steel plate. During the operation of the equipment, the upward pressure on the center of the intermediate discharge device is the concentrated part There are welding joints in the concentrated parts, resulting in insufficient strength so that the welded joint is broken, the stiffener plate can not play its due supporting role, causing the upward bending deformation or fracture of the main pipe of the Johnson screen header lateral, causing the damage and deformation of the whole Johnson screen header lateral system. The crack of the main pipe and the crack of the branch pipe is the main reason for the resin leakage of the Johnson screen header lateral device.
• In the normal operation of the Wedge Wire Resin Trap Screenchemical desalting water treatment system, although the water source entering the cation bed equipment has been filtered in advance, more suspended substances are still produced in the process of ion exchange. When these suspended solids pass through the resin layers of the anion and cation beds, they are easily intercepted by the upper resin due to the adsorption of the resin pores and the resistance of the resin itself. With the continuous increase of filtration water, the suspended solids intercepted by the resin layer are also increasing, so the flow area of the resin layer is correspondingly reduced, which naturally causes the increase of the filtration head. When the equipment is regenerated, with the rapid increase of pressure, the upward moving resin exerts severe pressure on the middle drainage device, and the pressure difference of the middle drainage device increases abnormally, resulting in serious deformation and damage of the middle drainage main pipe and branch pipe.
• The material used inside the equipment is unqualified. In the process of anion bed operation, the intermediate water has strong acid corrosion, and the water contains a large number of Cl – ions which destroy the metal. The water containing H + and Cl – ions has strong corrosion to the metal. The ordinary stainless steel material does not meet the use requirements, so the parts made of stainless steel material containing a certain proportion of Cr, Ni, Ti and other elements must be used. For example 1Cr18Ni9Ti, 316L, and other hydrochloric acid-resistant materials to make parts. In the process of our inspection and repair, we found that many connecting screws did not meet the requirements of material, serious corrosion and even fracture, so that the stress distribution of the middle drainage system was uneven, and the whole middle drainage device was damaged.
• The vibration caused by equipment operation is one of the factors causing the damage of the middle exhaust device. During the operation of the equipment, due to the pressure change, the presence of gas in the water and other reasons, the internal equipment will produce violent vibration, which causes the internal connection of the equipment to loose, fall off and break. Due to the failure of the function of the connecting parts, some parts of the middle drainage device are stressed, resulting in the damage of the whole middle drainage device.

The following measures are used to deal with such faults

1. Strengthen the communication with operators on duty and thermal control personnel, and discuss the start stop and air intake mode of diaphragm pneumatic valve.

• Slow down the intake speed of the valve and adjust the opening of the valve.
• Reduce the outlet pressure of regeneration pump and intermediate pump. Avoid starting multiple pumps at the same time, for one or few equipment, to prevent the impact of head pressure on the equipment.
• During the operation of equipment regeneration and backwashing, carefully check the current condition of the equipment to prevent large pressure difference between the inlet and outlet water in the equipment.

2. Replace the wedge wire screen header lateral support bracket inside the anion and cation beds. The operation results show that the channel width of the original equipment support frame is only 120mm, which can not meet the requirements of equipment operation. Replace 150mm×300mm square steel with anti-corrosion coating is used as the support frame of the Johnson screen header lateral.
3. The stiffener plate of the Johnson screen header lateral is reformed. The stiffener plate of the Johnson screen header lateral main pipe shall be attached to the main pipe with a whole piece of material. In order to reduce the workload of maintenance and save the cost of purchasing steel, steel plates made of acid-resistant steel can be welded on both sides of the welded joint of the stiffener plate in the middle of the Johnson screen header lateral main pipe for reinforcement, so as to improve the strength of the stiffener plate of the whole Johnson screen header lateral main pipe.
4. Operators on duty should strengthen operation monitoring. Improve the sense of responsibility of operators, regularly carry out small backwashing and large backwashing operation on the equipment, and prevent the problems of hardening and excessive accumulation of flocculent matter in the resin layer inside the equipment.
5. Strictly control the quality of screws and other parts used inside the equipment. Only qualified parts can be used to prevent unqualified parts from being used in the equipment.
6. Reduce the damage caused by equipment vibration. Reduce unnecessary start and stop of equipment, adjust the temperature and pressure of medium, and prevent excessive dissolved gas in water.