How does an excessive ammonia level in low-temperature methanol washing lead to an excessive sulfur level in the system?

Ammonium sulfide crystals are formed and decomposed at the top of the scrubber, producing H2S

An increase in ammonia content leads to the hydrosulfidation of ammonia in the thermal regeneration tower; when it encounters hydrogen in the absorption tower, hydrogen sulfide is formed.

Can it decompose in high-pressure and low-temperature conditions? Could you write down the equation? What chemical theory is it based on? I really can’t figure it out,?

Excessive ammonia levels can cause excessive system pressure; when a bypass is used, methanol is wasted, and the regeneration of methanol in the thermal regeneration tower is inadequate, which affects the absorption of hydrogen sulfide

Thiamine crystals are formed and cannot be absorbed by methanol; they decompose into H2S and ammonia at the top of the CO2 absorption tower, resulting in excess levels

Thiamine crystals are formed and cannot be absorbed by methanol; they decompose into H2S and ammonia at the top of the CO2 absorption tower, resulting in excess levels

Firstly, the ammonia level in the system exceeds the allowable limit, which results in inadequate regeneration of the methanol-poor stream. As the ammonia level in the system rises, the ammonia content in the methanol-poor stream also increases; subsequently, sulfurous acid is formed, and hydrogen sulfide is released at the top of the scrubber tower, causing the hydrogen sulfide level in the purified gas to exceed the permissible limits. I hope this can help you.

Raw coal contains amino organic compounds, which decompose in the gasifier to produce ammonia. Most of this ammonia is decomposed, with only a small portion remaining unreacted and being further removed in the ammonia washing tower. Trace amounts of ammonia enter the low-temperature methanol washing system and dissolve in the methanol solution; it is difficult to separate them. Over time, as an excessive amount accumulates, ammonium carbonate crystals form in the water cooler at the top of the regeneration tower. The general chlorine content requirement is that the ammonia level in the methanol returning to the top of the thermal regeneration tower should be kept below 5–10 mg/l; accordingly, the ammonia content in the methanol after thermal regeneration must be less than 20 mg/l, while the ammonia content in the methanol-rich stream within the system should be between 100–200 ppm. Excess pressure in the carbon ammonium crystal regeneration tower is generated; the pipeline valve to prevent carbon ammonium crystal formation is opened promptly to eliminate it. Furthermore, excessive ammonia levels can lead to the formation of thiourea, which decomposes at the top of the scrubber tower, resulting in elevated hydrogen sulfide levels in the purified gas. When the ammonia content in the transformed gas is high or the washing efficiency of the ammonia scrubber is poor, NH3 is not completely absorbed by water. Upon entering the methanol washing system, as NH3 accumulates, it may react with CO2 or H2S to form ammonium bicarbonate or (NH4)2S crystals, thereby causing blockages in components such as filters and pressure guide tubes. During methanol regeneration, (NH4)2S is formed, and this compound is carried along with the methanol to the scrubber. There, it decomposes into NH3 and H2S at the upper part of the scrubber, evaporating into the purified gas and thus causing an increase in sulfur compounds. A lower ammonia content in the reformate gas is not necessarily better; ammonia plays a positive role in regulating the pH value of the methanol circulating in the methanol washing system. According to the operational experience of some manufacturers and data provided by Linde, maintaining an ammonia content in the circulating methanol between 30–60 mmol/l can effectively prevent corrosion in the system. It also enhances the absorption capacity of the methanol solution, reduces the flow rate of methanol in the system, and lowers energy consumption. However, too high an ammonia content can disrupt the normal operation of the methanol thermal regeneration tower, resulting in excessive H2S levels in both the purified gas and the CO2 product gas. Generally, an ammonia content in the circulating methanol of no more than 100 ppm does not cause any adverse effects on the system. The ammonia content in the circulating methanol can be controlled by adjusting the amount of wash water for the shift gas and the bypass vent of the hydrogen sulfide heat exchanger in the low-temperature methanol washing system.