HP Steam Superheater Performance in Sulfur unit

[PetroDDP]

HP steam is generated from waste heat boiler at two places in Sulfur unit of the Petroleum Refinery one at reaction furnace and another at incnerator downstream equipment.This saturated HP Steam(261 deg C-Design value) is routed to Superheater where it is superheated to 391 deg C(Design value).Design value of Saturated HP Steam pressure is from 47.5 kg/cm2g to Design value of Superheated HP Steam pressure is 43.6 kg/cm2g.Superheater is Shell and tube type where Incinerator flue gases are used to superheat steam. (Shell side :Flue gases)
The area of concern is that actual superheated HP Steam temperature remains lower than design at 365 deg C (43 kg/cm2g actual pressure) against 391 deg C design value.

There are total 03 trains parallel to each other in Sulfur units in addition to this, all the tail gases passes through common TGTU unit, TGTU offgases are equally distributed to incinerator in three trains. other two trains Superheated HP Steam temperature remains close to the design as compare to one train where above concern/problem is faced.

potential causes for performance and remedial measures are requested.

Thanks in advanced.

 

[EmmanuelTop]

A sketch attached to this query is required to help us understand the configuration and the parameters. It would have taken less time to produce a simple sketch that to type what you have typed above, yet so many people still prefer writing.


Dejan IVANOVIC
Process Engineer, MSChE

 

[georgeverghese]

With what information is provided here, would suggest that the HP steam take off piping from the common manifold to train 3 superheater may be from the bottom of pipe or some low point which encourges HP steam condensate liquid carryover to go to train 3 superheater?

 

[MortenA]

train 3 superheater is fouled?

 

[PetroDDP]

Simplified sketch is attached. Superheated HP steam is routed to common manifold.
Thanks.

 

[georgeverghese]

Sketch makes things clearer now :
Presume the total BFW flow to each train is the same.
Is the fuel gas demand to the burners for each incinerator more or less the same? Or is it less than the other 2 for the train which is producing steam at 361degC ?

 

[0707]

I think MortenA touch the problem, maybe there is a fouling situation up stream your reaction furnace and another at your incinerator, try to check that.

Good luck

luis

 

[PetroDDP]

BFW flow and Fuel gas demand for burners is mostly same for all three trains.Superheater of train 3 may be fouled. Is there any effective solution to get rid of this issue ?

 

[georgeverghese]

Okay, confirmation of fouling only at train 3 incinerator would then be that incinerator exhaust after superheater should be higher in temp than that for other 2 trains.

If indeed all TGTU offgas is manifolded before distribution to the 3 incinerators, cannot think of a reason why only train 3 superheater would be fouled on shellside.
Could it be insufficient combustion air to train 3 incinerator, resulting in formation of sulphur rather than full oxidation to SO2? - highly unlikely.

 

[PetroDDP]

Excess oxygen is maintained more than 2 % in all the incinerators. So,very remote chance of formation of sulphur species in the exhaust.Usually , which type of fouling mechanisom happens ? Any online or offline fouling mitigation measures.Fouling of Upstream of reaction furnace is unlikely.

 

[georgeverghese]

Any reduction of conversion efficiency of hydrogenation reactor furnaces upstream would have shown up in 3 incinerators. Either there is
a) some maldistribution of reactor product streams ( with fouled reactor 3 product going predominantly to incinerator 3) or
b)there is insufficient O2 for incinerator 3, leading to sulphur deposition on superheater tube OD.

If the former is not possible, then suggest checking the combustion air flowmeter for incinerator 3 for some readout error (presume this is a forced draught furnace).

 

[georgeverghese]

Another probability could be a tube leak of colder satuated steam at the superheater bundle tube sheet on train 3 - this would have chilled the incinerator gas, reducing LMTD and hence reduced superheater performance?

 

[PetroDDP]

Maldistribution of reactor product stream is not likely cause because ,flow is evenly distributed in all three incinerators and floated with the stack back pressure.Train 3 incinerator blower is running at full capacity of its design as compare to other two trains, however, we will cross verify the flowmeter calibration. There may be possibilities but difficult to validate sulfur deposition on superheater tube and tube leak of colder saturated steam in running unit.Any measures to overcome this problem?

Thanks !!

Regards,

 

[georgeverghese]

If a gas analysis of the exhaust gas ex the superheater shows a higher water vapor content, this may a sign of a cold sat steam leak.

Else it could only be sulphur deposition due to insufficent combustion air to the TGTU tail gas FD burners at the incinerator. Check if there is a bypass damper on the comb air blower discharge that may be leaking or a blocked feed air strainer to the blower etc.