Ammonia water is injected at the top of the distillation tower
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Why is ammonia water injected at the top of the distillation tower? What considerations are there? Where does ammonia water usually come from? Are such systems still in use in various facilities?
Ammonia injection at the top of the distillation tower is no longer used in large-scale operations these days
Our ammonia is supplied as part of a combined acid-base system, and we are still using it.
Reply to 1# Zhang Junmeng: Ammonia water is added to neutralize acidity and keep the top of the tower at a slightly alkaline level; generally, the pH value is kept between 8 and 9.5； Ammonia is available in all fertilizer plants; acid water treatment units that extract ammonia from side streams that do not produce liquid ammonia also generate ammonia ； Ammonia injection is a good and effective anti-corrosion measure, applicable to installations of all sizes
Reply to 1# Zhang Junmeng: If there is really no ammonia solution available, liquid ammonia can be considered as an alternative, but the pressure reduction equipment must be reliable
It’s generally not used these days. What is used now are neutralizing agents (corrosion inhibitors) that are alkaline in nature and come pre-formulated; their purpose is anti-corrosion, working by forming a protective layer on the surface. Note that the point of injection should be before water injection, and the amount to be injected depends on factors such as backflow and water cut, as well as the pH value and Fe ion levels
Ammonia water is primarily used to neutralize the acidic gases generated at the top of the distillation tower, such as hydrogen sulfide; if ammonia water is not readily available, caustic soda, or sodium hydroxide, can be used as a substitute. It should be noted that the purpose of corrosion inhibitors is to prevent and reduce the corrosion of hydrogen sulfide on the top of the fractionation tower, and they cannot neutralize acidic gases.
I will mention only one drawback; there are many advantages. This drawback is an increase in the pressure drop across the overhead system of the distillation tower, as well as a decrease in the pressure at the inlet of the compressor. This is because the ammonia water is injected at the oil-gas line at the top of the tower, where the temperature is around 120 degrees. Once the ammonia water is injected, it vaporizes immediately, thereby increasing the pressure drop resulting from two-phase flow in the cooling equipment at the top of the tower. .
Our equipment has shown that a too high pH value facilitates under-scale corrosion
The neutralizer at the top of the tower (ammonia or amine) serves primarily to neutralize the corrosive acids present at the top of the tower, increase the pH value of the condensate, and slow down equipment corrosion. When ammonia water is added, the pH value at the top of the tower is generally controlled between 7 and 9. Neutralizing agents include: fully organic amine neutralizers, ammonia water plus neutralizing corrosion inhibitors (widely used in refineries), and ammonia water plus corrosion inhibitors (used by few refineries). Now, neutralizing corrosion inhibitors are more commonly used; they are reasonably priced and have a dual function.