Blockage in the acidic gas line

The acidic water stripping tower has no side streams; it’s difficult to imagine how hydrogen sulfide and ammonia can be separated, or what the temperature at the top of the tower should be. It would be abnormal if both gases exited from the top of the tower without causing crystallization and blockages.

Since acidic water mainly consists of hydrogen sulfide and ammonia, if the pressure and top temperature of the acidic gas stripping tower are not properly controlled, the ammonia content in the acidic gas will be high, and it will crystallize into ammonium salts upon cooling in the pipelines. Previously, in our facility, the pressure control and insulation at the top of the acidic gas stripping tower were inadequate; that’s why it would often get clogged when it got cold. Therefore, a strong heat tracing method must be employed, such as a jacket or multiple heat tracers. Generally, below 80 degrees Celsius, hydrogen sulfide and ammonia form crystals of ammonium hydrosulfide; therefore, the temperature at the top of the tower needs to be kept around 90 degrees Celsius or higher. The temperature drop in gas pipelines is significant; without proper heat tracing, acidic gas pipelines tend to crystallize, especially in winter. In typical pressurized wastewater stripping units, the ammonia content in the acidic gas at the top of the tower is very low, so crystallization generally does not occur. If the issue cannot be resolved through operational means (due to a design flaw – the absence of a side stream for extraction), it is recommended to periodically clean the pipelines and equipment prone to blockages using steam, as a preventive measure. Of course, the fundamental solution to this problem lies in proper operation of the acidic water stripping tower. Last edited by wdepei on 2009-3-26 20:39.]

Ammonium salt crystallization, with additional steam heating.

For ammonium salt crystallization, heat tracing can be installed at the level gauge outlet of the acidic gas tank. If the acidic gas pipeline is not functioning properly, it may be due to an excessively low temperature at the air-cooler outlet; generally, a temperature of around 90 degrees is sufficient. A condensate water flushing line can also be added to the acidic gas pipeline.

Crystallization has occurred; heat tracing should be added to the pipelines, and the temperature at the top of the tower needs to be controlled at a higher level. Controlling the temperature of the acidic gas at around 90 degrees will make things much better! In response to the comment in the second floor post: Nowadays, many stripping towers do not have side lines, and sulfur furnaces mostly use imported burners or burners fed with gas containing ammonia; for acidic gases containing ammonia, the furnace temperature generally needs to be maintained around 1300 degrees

The acidic water stripping unit fails to produce ammonia, which is in itself a process defect; even by injecting water at the top of the tower, it is difficult to prevent crystallization from blocking the pipes, and this also increases energy consumption. It is recommended to carry out the renovation next time.

The process mentioned is the atmospheric full-blowing process without ammonia extraction from the side line, which is also a relatively popular process at present. The aminoacid-containing gas coming out of the top of the tower is sent to a sulfur recovery unit for treatment (at this time, the sulfur recovery unit must be equipped with burners capable of burning ammonia as well). Due to the high ammonia content in acidic gases, it is easy for ammonium salts to form and block the pipelines. To prevent this phenomenon from occurring, the temperature of the aminoacid-containing gas must be maintained at at least 85°C. There are usually three heating methods: one is using multiple heating coils with 1.0 MPa steam, the second is jacket heating with 0.3 MPa steam, and the third is electric heating. Overall, the use of multiple heat tracing pipes with 1.0 MPa steam is the most suitable approach.

The pipeline should be insulated with heat tracing, and it is advisable to include a steam purge point for easy emergency use.

The acidic water stripping processes mainly include three process flows: single-tower pressurized side-stream extraction stripping, single-tower low-pressure full-blowout stripping, and two-tower pressurized stripping. Among them, the single-tower low-pressure full-blow stripping process is simple: the mixed gas containing hydrogen sulfide and ammonia is fed into a sulfur recovery unit equipped with ammonia combustion nozzles, where ammonia is converted into nitrogen at a high temperature of over 1250°C, while hydrogen sulfide is transformed into sulfur through partial combustion and catalytic reactions. The single-tower low-pressure full-blow-off stripping process is suitable for situations where the economic value of ammonia recovery is low or where there is poor demand for ammonia. Compared with other processes, its advantages lie in minimum investment, lowest energy consumption, and minimal land use. The temperature of the amine-containing gas at the top of the stripping tower must be above 90°C; otherwise, hydrogen sulfide and ammonia easily form ammonium salt crystals, which can block the pipelines. The acidic steam pipeline must be insulated throughout its length, with low-pressure steam used for heating. When I was working on sulfur production equipment, the pipeline got clogged once; it was completely blocked, and in the end we had to cut the pipeline open and use hot water on the ground to clear it.

Our wastewater stripping process is the same as yours; there is no side stream for extraction. The control parameters for our purified water are sulfur compounds at less than 8 ppm and ammonia nitrogen at less than 30 ppm. We usually maintain a bottom temperature of 110–116 degrees Celsius and an upper temperature of 101–105 degrees Celsius. The temperature of the acidic gas after passing through the overhead cooler must be at least 85 degrees Celsius. The system has been in operation for over half a year without any blockages, and the level gauge in the liquid separation tank can be equipped with backflow steam. Additionally, an deoxygenated water line can be added at an appropriate position in the acidic gas line, which can effectively clean the crystals and is more effective than steam.