WHB in Steam Reformer and T/A interval

[1906]

Re the refomer unit, there is waste heat boiler at the reformer outlet to recover energy from process gas for a steam generation. But, one or 2 years later this waste heat boiler should be opened in order to inspect and clean because of its' loss of performance. This unwanted WHB cleaning, forced us go to shut-down every one or two years. If any body experienced and solved this kind of trouble, please let me know the reason and countermeasure.
And, if you guys inform me turn-around interval(for example 3 or 4 years) of your own experience, it would be very helpful.
For your reference, mentioned unit is steam reformer and followed by PSA unit to supply H2 to the hydrotreating unit with the capacity of 100,000 Nm3/Hr production(H2 99.99%). And, our feed stock was "treated C5/C6 naph" from Naph. HDS.

 

[rtcamejo]

I have a particular experience with a waste heat boiler at the exit of natural gas reformer.

The exit temperature of the boiler was increased slowly since the start up and high pressure steam production fell down in the same way. The phenomenon also occurred in the BFW preheater located downstream of the boiler.

This situation forced us to increase the exit temperature of the reformer to attempt maintain the steam production until certain limit.

After every plant trip the boiler suffered a self-cleaning process due to thermal cycling, with no need of intervention for mechanical cleaning. Then the boiler recovered its full capacity and the fouling process started again.

Since BFW had no problem, there were two possibilities causing this fouling.

1. Potash released by reforming catalyst.

2. Silica coming from internal lining of transfer lines.

We open the BFW preheater (gas side) and took a sample and we found a soft deposit composed mainly by silica. There was practically nothing of potash.

Transfer lines had others problems (lots of hot points) that together with this finding lead us to replace them.

We finally totally replaced transfer lines and changed the specification of the refractory material to low silica and the problem disappeared.

Even though the cause of the problem in our case was silica, let me tell you that a potash release from the reforming catalyst have similar effects, so the way for you is to consult your catalyst supplier to find out the potash composition in your catalyst itself. The catalyst for natural gas reforming has lower amounts of potash than those that are used for naphtha reforming.

For this reason you should consider the possibility of having either or both problems.

I hope this can help.