Delayed coking large steam injection

Set up a high-pressure steam low-temperature heat exchange system

I heard that in some cases, the gas at the top of the tower is vented during high-pressure operation and then recovered at the compressor inlet. Could that experienced marine engineer share their insights? Thanks in advance!

Since it is not a continuous operation, both heat and gas recovery are difficult.

The coking low-pressure gas line can be connected to the catalytic flare line; during venting, a portion of the gas is directed into the catalytic flare line and then sent to the dry gas pipeline network via compressors for use. However, based on the usage in my facility, the efficiency of this method is not very high

To the non-condensable gas tank at the top of the vent tower; the gas then goes to the gas pipeline network where it is burned up

For the large-scale steam injection in delayed coking units, the steam can enter the steam vent tower to recover some oil and gas, which is then sent to the flare gas network.

Although all the gas is released into the system during large-scale blowing in coking, it is still recovered by the gas tanks downstream; it is not directly burned in a flare, so there is no waste! For a refinery, dealing with certain issues is a plant-wide task; it’s not necessarily the case that something related to a specific unit must be handled by that unit itself.

I am a tailpipe recovery designer; if the company is interested, we can discuss this in detail

Please introduce the processing technique and its effectiveness

Our company uses direct steam injection into the overhead reflux tank of the fractionation tower to recover gas

In my system, the high-pressure steam is directed to the contact cooling tower (vent tower), from where it flows back to the top of the reflux tank in the vent tower. There are two paths from the top of this reflux tank: one leads to the reflux tank at the top of the distillation tower (where the oil and gas from the upper part of that tank go to the compressor), while the other path leads to the vent line that connects to the gas holder. During normal operation, when high-pressure steam is supplied, the valve leading to the reflux tank at the top of the distillation tower – and thus to the compressor inlet – is opened; once water supply begins, the flow goes through the vent line to the gas holder

If you send the heavy gas to the fractional distillation tower, you need to consider whether there is a serious issue with water content and coke powder. The exhaust gas recovery system I designed ensures that, from the start of large-scale steam supply until the end of small-scale water supply, there is basically no open flame in the flare; more than 8,000 cubic meters can be recovered per 100 tons of coking capacity

The effect is very good: with a processing capacity of 1 million tons and an operating load of 60%, it is possible to recover more than 8,000 cubic meters of exhaust gas. The recovery process takes place from the start of steam supply until the end of water supply, and there is basically no open flame in the flare

During the cold coking process in the coke tower of the delayed coking unit (the old tower), large amounts of steam are used to drive the oil and gas present in the tower to the flare for combustion. For the entire plant’s system, fuel gas is supplied only by this coking unit; therefore, the use of large amounts of steam causes significant fluctuations in the fuel gas pipeline network. It also leads to a shortage of dry gas as a raw material for the hydrogen production unit. To meet the requirements for hydrogen production, liquefied gas has to be added, which increases energy consumption and results in unnecessary losses. (Wasting and burning the liquefied gas, which is already a product, and also venting the residual oil and gas from the coke tower not only fails to save resources but also causes environmental pollution.) ) Modification details: To recycle the residual oil and gas in the coke tower, reduce the use of liquefied gas in the fuel gas, modifications were carried out by adding compressors and related equipment and pipelines. Various safety devices were installed to prevent air from entering, thereby facilitating the recovery of exhaust gases from the flare. Additionally, a fuel gas line was added to the sulfur incinerator, so that the recycled fuel gas can be used in place of the conventional fuel, which also increases the steam output of the waste heat boiler. Savings explanation: The delayed coking unit delays the production of coke by 24 hours; steam is injected on a daily basis. A total of 8,000 m³ of exhaust gas (containing components from coking processes and also having a high sulfur content) is recovered each day (as indicated by the inlet flow meter). Over one year, this amounts to 8,000 m³ * 30 days * 12 months = 2,880,000 m³. Before the modification, the sulfur incinerator used liquefied gas as a heat source, consuming 1,440 m³ of liquefied gas per day. The savings in liquefied gas usage over one year were therefore 1,440 * 30 days * 12 months = 518,400 m³, which equates to 375 tons per year. Additionally, 8,760 tons of steam were produced more per year

We also added a pipeline for fractional air cooling, which allows for better recovery of light hydrocarbons

Going directly to the compressor inlet may introduce coke powder; it is better to first cool the separated oil and gas through air cooling before sending them to the compressor

If any company wants to make changes, they can contact me directly

Before air cooling or after air cooling, what are your results? Is the pressure at the top of the tower subject to large fluctuations during operation?

After air cooling, there is a certain impact on distillation before air cooling, and it can also easily cause blockages in the tube bundles. I’m the designer; if you’re interested, we can discuss this further

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