NEWSLETTER
ISSUE
Jan to Apr, 2018 Volume 5
TUBE-TO-TUBE SHEET EXPANSION JOINT
The welding joints where the tubes are connected to the tube sheets in the WFI and pure steam generation plant are more prone to corrosion and leakages than any other components within the system. Analysis indicates that the welding joints lead to a microstructure change of the tube in the metal region as the joint is created by fusing the tubes to the tube sheets. This change in microstructure, when subjected to extreme conditions of temperature, pressure, and a high flow of water comprising of several oxidized gasses results in corrosion followed by leakage. Secondly, the tubes and its joints are subjected to temperature variation due to the continuous heating and cooling in the operation cycle; this variation also induces stress at the joint, leading to the development of cracks, resulting in leakage, contamination, and ultimately to the production breakdown
The latest features include a higher grade of SS 316L (DIN 1.4435), expanded pipes in the tube sheet plates, a non-condensable gas removal system for the feed water, a unique purification system due to the purging of endotoxin rich condensate from each column, reduced cooling water requirement, and energy saving capabilities due to the reduced boiler steam consumption.
This hurdle is adequately addressed by developing expansion joint design. Here, the tubes are connected to the tube sheet by expanding them in the tube-sheet’s double grove through a unique expansion process. This is done by applying uniform torque, thereby maintaining equal strength, resulting in leak-proof joints, unlike the welded joints. This tube-to-tube sheet joint eliminates stresses that arise due to the welding process, and thus overcomes corrosion, cracks, leakage through the welded joints, and the contamination of the product, leading to an uninterrupted and trouble-free operation of the āWFI Generation Plantā.
UTILITY SAVINGS FEATURE
Our continuous drive for the development of energy efficient equipment has resulted in a newly evolved WFI plant which incorporates an increased number of columns. This enables the optimum use of the previously unutilized energy. The fundamental principle remains that in the Multi-Effect Distillation Still, the first column is heated by an external energy source (boiler steam), and the pressure/temperature gradient is maintained across individual columns, enabling it to perform without any additional energy consumption. By optimizing the steam pressure in the first column and increasing the number of columns and pre-heaters, we have absorbed the available energy efficiently, resulting in the reduced consumption of plant steam (boiler steam) and cooling water.
With an increased number of columns, the pure steam temperature gradually decreases while progressing through each column so the temperature of the steam in the last column is lower than in the systems which utilize the regular 5 or 6 column design. This lower steam temperatures, reducing the ĪT at the cooler, resulting in the cooling water requirement reduced dramatically.
Similarly the heat energy is optimally extracted by passing feed water through each of the additional pre-heaters installed within every column. As a result the feed water in the machine with additional columns attains higher temperatures before entering the first column. This increased temperature reduces the ĪT required within the first column, resulting in lower plant steam consumption.
