Ammonia purification operation
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Dear experts, the ammonia purification system in my plant is experiencing frequent blockages in the pipelines due to salt deposition while it is in operation. Do any of you have similar experience? How should it be prevented and controlled? Waiting for the experts to provide answers
Which part is blocked? Consider the following aspects: 1. Stripping tower operation: Is the side draw due to too high a hydrogen sulfide level? What is the sulfur content in the crude ammonia gas entering and leaving the ammonia purification tower? 2. How are the temperature and circulation rate controlled in the ammonia purification tower? 3. How is the operation of the hydrogen sulfide adsorption tank, and are there any issues with the adsorbent?
The main areas of blockage are the pipeline leading from the ammonia feed to the ammonia crystallizer in the ammonia purification tower, as well as the gas-phase pipelines of the second and third degasers. Regarding the operation of the stripping tower, it is likely that the hydrogen sulfide content in the material drawn off via the side stream is high, based on current operational conditions; the temperature at which this material is drawn off is 141–142 degrees, and it is not possible to increase this temperature any further. There are no analysis data available regarding the hydrogen sulfide content in the ammonia gas entering and leaving the ammonia purification tower. The operating temperature of the ammonia purification tower is higher than the designed value, with the circulation rate being around 7 tons per hour
The side-line withdrawal temperature is generally around 151°C; increasing the pressure of the tower appropriately will raise this temperature.
If the path ahead of the rectification tower is blocked, the possible reasons are: 1. Improper operation of the stripping tower, resulting in a low emission rate of acidic gases from the top of the stripping tower. 2. The temperature at the side line extraction point is low, resulting in a high sulfur content in the gaseous stream extracted from the side line. 3. The operating conditions of the tertiary side-line condenser are not properly set, resulting in poor performance in terms of \"separating water at high temperatures and sulfur at low temperatures\"; in particular, the temperature of the third-stage condenser is too high. If there is a blockage in the downstream section of the purification tower, the possible reasons are: 1. The influence of the three factors mentioned above, resulting in a high desulfurization load on the purification tower. 2. The temperature control of the refining tower is too high. 3. The ammonia liquid circulation volume in the refining tower is low. 4. The desulfurizer has become ineffective.