Delayed Coker - Coking Safety & Communications

Problem

We have an issue with silicon anti-foam addition - what is the most effective way people have found to inject the anti-foam to ensure maximum distribution over the reaction surface, minimum addition and minimum carry-over? What types and vendors have people found to minimize cost and minimize carry-over into the naphtha stream?

Solution

Discussion Thread Summary on Anti-Foam

This is a compilation of 4 discussion threads.

1/5/99 Check out this research article I found at http://www.aem.umn.edu/research/foam/ "...Applications of foams and foaming are found in many industries like...Delay-Coker reactors. However, foaming and defoaming are not yet understood. Foams trap gas and are not wanted in many applications. Guitian and Joseph (1997) proposed fundamental studies of their observations on foam suppresion experiments they carried out in a cold slit bubble reactor. They present their most recent findings.

1/5/99 You should have the anti-foam nozzle as far away from the overhead nozzle as possible. The carrier should be as heavy an oil as you can get to the top of the drums and you should use as much carrier oil as your process will allow without actually quenching the drum or causing excess vapor/liquid traffic in the fractionator. One idea is to actually inject the anti-foam in large batches instead of a continuous small stream. A larger batch quickly dumped into the top of the coke drum would avoid vaporizing the carrier and thus reduce the carrying of the antifoam out of the drum.

1/24/99 We are finding that by using flow meters on the silicone and carrier medium we can reduce usage of both significantly. In addition we inject antifoam continuously in the fresh coking drum from the time the previously coking drum goes to blowdown in the cooling cycle. Also, it seems to only take about 2 gpm of carrier to get the silicone to the drum in a timely fashion. This reduces the velocity of the mixture going into the drum and reduces carryover for our configuration. It also improves reducing the foam head. We are using 0.4 to 0.8 gph of silicone (based on throughput) and 1 to 2 gpm of carrier. Our larger coke drums are 24 foot in diameter and 100 foot tall.

4/18/99 There are many ways to inject silicon. Nalco/Exxon has an efficient way of Anti-foam injection. They have an inline blending system that works well. This system can be easily adapted to any system.

4/28/99 What type of silicone antifoam do cokers use? It is my understanding that some use a mixture of kerosene and high viscosity silicone antifoam or is just the silicone antifoam OK. I think that they refer to the kerosene / antifoam as "coker oil"

5/10/99 The antifoam used in many cokers is a 50/50 mixture of high viscosity (60-100 cS) silicone and kerosene.

6/3/99 Is there any real success in mid level detection or even prediction to allow a reduction of anti-foam use?

6/3/99 We have had a good history with K-ray probes. These are set up to switch on the anti-foam pumps.

8/9/99 How to cope with foam over?

8/9/99 Depends on how bad the foamover was. Did you have a foamover? A major foamover will shut you down a lot of the time. If you are not down, you probably have a sick furnace, meaning the furnace tubes are coked. If this is the case, you can try on-line spalling. This can be risky due to the foamover and the amount of coke that got layed down in the furnace tubes you may or may not be able to spall. The risk of spalling a lot of coke at one time and plugging a return been or the outlet header goes up when you foam a drum over. If you spall and you cycle temperatures during

9/23/99 You're talking powder coke coming to your farc.btm. ..well there are coke stelling drums that you should operate at max ... when foaming takes place. Also you can do this. Try to minimize chances of foaming by setting your system to alarm you about things that might cause foaming ... i.e low inlet temperture sudden pressure surge ... etc

8/30/99 Besides Nalco/Exxon, there is Baker Petrolite, Chemlink, Betz and independants. What exactly are you looking for besides suppliers?

9/1/99 BetzDearborn has excellent antifoam agent for delayed coker as well as any other prupose. In Korea, one company is using Prochem 6A2, BetzDearborn product,for several years. If you want to know more,please send mail to me.

9/30/99 I think Dow Chemical is a producer of the anti-foam and the others are just resellers who package it so that you can use it as anti-foam.

9/9/99 Does any one have experience using only LCGO as antifoam during filling cycle? How can we manage this problem?

9/13/99 What do you mean by using only LCGO as antifoam? you mean LCGO could be used alone during coke filling without chemical defoamer?

9/13/99 I mean LCGO could be used alone without chemical defoamer during coke filling.

9/13/99 Some people have use LCGO or HCGO (with out antifoam) when the first alarm comes on. As soon as the first alarm activate for the second time the mixture antifoam/LCGO is added. This will help to reduce the silicon carry over.

In coker that work with very low Furnace out let temperature (900 - 915 ºF) this may not work due to the fact that at low furnace out let temperatures the foaming tendency in the drum increase. For coker operation higher than 920 ºF this could be a good practice.

9/30/99 Why put in HGO without anti-foam. Without the anti-foam, I think, you are wasting your time. HGO is the best carrier because it will not flash off as fast as it falls down the drum.

10/11/99 I have seen foam being knocked down by just adding carrier however the silicone is the best way to consistently knock it down. There are other ways to minimize foam with limiting down stream poisoning.

10/14/99 In Cardon Refinery (PDVSA) the Furnace out let temperature is 915 ºF and we use LCGO (without antifoam) when the first alarm comes on. As soon as the first alarm activate for the second time the mixture antifoam/LCGO is added.

10/17/99 I assume from some of the discussions that you are injecting only carrier at the level detection of activity in the coke drum and then carrier and silcon. Question,how effective is carrier alone and how long before the level detector detects a level again? I won't think that carrier alone would be that effective, otherwise why would you be injecting silcone at the next level detection? I mean no disrespect, but in my experience and opinion, using only carrier is like spitting into the wind and eventually you will be shooting yourself in the foot, without silcone.

I have tried HGO, LGO and nap, as carrier. The heavier the carrier is the more effective it is. However, I did not see a really big difference in either HGO or LGO. So which you use is just purely economics.

As Mr. Kolek has indicated there are methods of controlling silcone carryover and effectively controlling the injection rate. As I understand it Mr. Kolek's company has mastered various method's and ways to effectively control silcone carryover and also have a proprietary patented method of antifoam injection into the coke, for effective silicon carrier distribution, minimizing injection rate and carryover to downstream hydrotreating units. These methods also I understand have been proven by them, but you would have to get the details from Mr. Kolek. Don't treat the sympton, but the problem and good luck.