Why is acidic water injected in front of the oil-gas heat exchanger at the top of the catalytic fractionation tower?

It is generally used in conjunction with corrosion inhibitors, mainly for anti-corrosion. Injecting acidic water is mainly to prevent pipe bundles from scaling and causing corrosion under the scale.

Since the raw materials contain elements such as sulfur and nitrogen, sulfur and nitrogen compounds are generated during the reaction, which are easily soluble in water. The purpose of water injection is to separate most of them from the gasoline and send them to the acid water stripping device in the form of sulfur-containing sewage. This has two purposes. One is to reduce the difficulty of gasoline treatment and ensure that the product quality is qualified.； The second is to reduce corrosion on subsequent equipment.

Acidic water is generally stabilized by absorption, one is washing, and the other is stripping sewage from V201.

Acidic water injection is usually combined with ammonia injection and corrosion inhibitor injection to ensure that the acidic water will no longer corrode the pipe bundle. . . If acidic water is injected alone without neutralizing corrosion inhibitor and ammonia, the control will definitely be over in a few days. . . :lol

It seems that ammonia or water is injected to prevent dew point corrosion, but why is acidic water injected? Oil and gas already contain acidic water. Doesn't this actually increase the acidic water content in oil and gas?

Generally, water injection and ammonia injection are used in combination to improve the anti-corrosion effect. Acidic water is not necessarily acidic, but can also be neutral or alkaline.

The moderator is absolutely right. Acidic water is a way of saying that it is either neutral or alkaline, or weakly alkaline.

Injecting acidic water is just a common term. In fact, this water can come from purified water after sewage stripping. The sulfur content has been reduced. It absorbs the acidic hydrogen sulfide gas in the tower top gas before injecting it into the tower top heat exchanger and removes it at the crude gasoline filling dehydration package. This can reduce the acid corrosion of subsequent equipment.

Washing contains sulfides, phenols and other substances that are prone to corrosion, which play a role in protecting equipment.

In my unit, the acidic water injected in front of the oil-gas heat exchanger at the top of the catalytic fractionation tower is pumped back from the acidic water buffer tank of the oil-gas separator at the top of the fractionation tower. I wonder what the purpose of pumping back the acidic water is?

Some raw materials will contain a small amount of chlorine. Although the content is small, the crude oil processing is large, and the amount of chlorine will eventually accumulate. After ammonia is injected, ammonia ions will combine with chloride ions to form salts. Ammonium chloride will crystallize easily. The instant water temperature is 80~90°C. The purpose of injecting acidic water is to wash away the salt and prevent salt crystallization from clogging the pipes. in addition: Acidic water is not necessarily acidic, but can also be neutral or alkaline.

The raw materials in the catalytic cracking unit contain elements such as sulfur and nitrogen, and the content in the catalytic cracking of residual oil is even greater. During the reaction process, sulfur and nitrogen compounds will be generated, which are easily soluble in water and enter the fractionation tower along with the reacted oil and gas. In order for sulfur and nitrogen compounds to enter the top of the fractionation tower and enter the top vapor-liquid separator, ammonia water (concentration of 2% to 5%) and water are injected at the top of the fractionation tower. The purpose of injecting acidic water is to neutralize excess ammonia and dissolved salts of sulfur and nitrogen compounds, reduce the alkalinity of crude gasoline, reduce corrosion of equipment such as fractionation towers and absorption stabilization towers, and stabilize gasoline refining to reduce the discharge of alkali residue.

I have seen devices that do not use any acid water injection process in front of the oil-gas heat exchanger at the top of the fractionation tower. I don't think there is any problem. There is still a gap between some processes in theory and practice. If it cannot be verified that it is good, it doesn't matter if it is not used.

When processing coked wax oil, the alkali nitrogen is high. Usually the water at the top of the fractionation tower is alkaline. The acidic water can neutralize some alkaline substances and also avoid dew point corrosion.

The sulfur and nitrogen compounds in the raw materials will produce some acidic substances in the oil and gas during the catalytic reaction, such as H2S, RSH, HCL, HCN, etc., so ammonia water with a concentration of 0.5% to 3.0% can be injected into the oil and gas line at the top of the tower to neutralize it. The reaction product ammonium salt will be dissolved in water and discharged as sulfur-containing sewage.

Acidic water is used to remove oil and sulfur, and neutralize corrosion inhibitors.

It can reduce the difficulty of gasoline processing, ensure product quality, and reduce corrosion to subsequent equipment.

Acidic water should be used with ammonia so it does not corrode equipment.

Preventing salt formation is also an important reason.

The pH value of acidic water is between 8-9. It can be used in conjunction with ammonia injection to reduce equipment corrosion.