| LTH Ammonia Plant with the capacity of 150, 000 t/a is the first ammonia plant in China using natural gas.as raw material. The plant was imported from H&G CoMPany in Britain, which was put into operation early in 1966. The original design capacity of ammonia production was 100, 000 t/a. After technical revamping and capacity expansion in 1988, the capacity of ammonia production reached 15t/a. But a problem of unsteady steam quality had existed in the waste boiler system for over 10 years during the period of 1989-2002. The output steam from drum V116, which is shared by two waste heat boilers of H111 and H115 for reforming gas and shifting gas respectively, often had high humidity and very heavy salt contamination. The steam quality problems of V116 caused salt deposition on the surface of rotor of natural gas compressor turbine KT124 for many tunes during the period. Meanwhile the backpressure of the first stage of the turbine would be risen exceeding critical value. Thus the whole plant had to be shut down completely for over 10 times. This had caused economical loss to LTH coMPany over 5000, 000RMB.In order to settle the problem of steam quality of V116, the specialties at LTH had been making various efforts to explore and improve over ten years. However the ultimate reasons remained unrevealed so the problem could not be eliminated fundamentally. From 2001 to early 2002, the author conducted a complete thermodynamic analysis and boiler hydrodynamic calculation to reveal the fundamentals and look for the effective measures to solve the existing problem. It was found by this work that the original reason is owing to boiler HI 15 out of normal operation condition. Therefore the volume flow rate in the 4 ascending pipes leading to VI16 from boilers Hill and HI 15 lost their balance. In turn the unbalanced flow rate and linear speed of two phase mixture of steam and water at the inlet of ascending pipes causes bias flow in the drum VI16. This breaks the design required two phase flow distribution in the separation space in the drum for separation of droplets contained in steam. That is to say the separation space was not effectively utilized so that the high contamination of droplets could not be avoid for steam, output from drum V116.Based on this analytic results for the steam quality problem existing in VI16, further work was made to determine the specific solution for solving the problem. The major measurements suggested by this work are: 1) a special drainage pipe added on bottom of drum level; 2) a 105?inclined baffle installed on each mouth of the ascending pipe to reduce the kinetic energy of steam and water two phase mixture and guide the stream jetting beneath normal level; 3) a corrugated plate as a shutter and a perforated plate as an auxiliary separator equipped at front of the steam header. These technical improvements were implemented during the annual maintenance overhead in July, 2002.It has been demonstrated by the over one year's operation practice that the improvement measurements based on the fundamentals revealed by this work are very successful in solving the steam quality problem for V116. Sincethe measurements were executed, there has been no sign of deposited salt found in turbine KT124. Emergent shut-down caused by the steam quality problem never happen again. It can be concluded that the steam quality problem which had been obsessing the 150, 000 y/a ammonia plant for many years has been eliminated fundamentally. It can be expected that this technical improvement must have very prospective foreground of application in helping to solve the problems for other similar waste heat boiler systems.
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