API flush plan for Asphalt service

[rotaryguy]

hi guys,

I am selecting Mechanical seal plan(API 682) for Asphalt service for rotary pump(API 676). from rundown asphalt rated temperature can be 450. I have selected plan 53. i am exploring other options as in plan 53 need to have pressuried reservior to pump barrier fluid.

Can anyone suggest other plan than plan 53 for viscous pumped fluid like Asphalt(keeping in mind shutdown time when asphlat properties changes?

Regards
Rotaryguy.

 

[JJPellin]

We have a number of three-screw pumps in similar service. All of them use a combination of flush plans. We have steam jackets built into the seal gland. We have a steam quench (Plan 61) on the atmosphere side of the seal. And we have a flush from discharge (Plan 11). The pumps are steam jacketed and steam traced and well insulated. We use 250# steam for the jacketing and tracing to keep the pump and seal hot enough when they are down to keep the asphalt from setting up between the seal faces. The configuration has worked well for us. Asphalt is usually not very difficult to seal. It is a good lubricant as long as you keep it hot enough.

 

[rotaryguy]

txs JJP,
here also,have 3-screw pump but... our guys are not comfortable with utilities issue. they are not interested in Jacketed body. somehow they are hesitant in the use of steam tracing too. only option is now electrical tracing with insulation, in order keep asphalt changing properties during shutdown.

have you tackle any 3-screw with electr. tracing with API plan? your inputs are appreciated.

Rotaryguy.

 

[JJPellin]

I have no experience with electric tracing in heavy services. Steam is plentiful in our plant. We only use electric tracing for water, amine, caustic, etc. We usually only use it for freeze protection and set it to 60 °F or so.

 

[rotaryguy]

JJ,

One more issue is that vendor deviating from API 676's requirement of Balanced mech. Seal(API 682) he is suppling unbalanced one. basis of selction is that seal is subjected to only inlet pressure(suction). the pumped fluid enters seal chamber & recirculted back to suction line.

I just stared as novice(few month back)i am trying to digest concepts as much as possible. need some mentor....

Rotor...

 

[JJPellin]

I don't see any problem with deviating from API 682. There are several provisions in that standard that I don't care for. But I would be reluctant to accept an unbalanced seal. Your description makes it sound like an API plan 11 with recirculation from the seal chamber back to suction. If this line were to plug up (very likely in asphalt), the the seal would see discharge pressure. Depending on the PSV setting, the discharge pressure of a screw pump can be quite high. I would insist on a balanced seal. The additinal cost should be minimal.

 

[rotaryguy]

thank u very much. i appreciate and my target is to help out othersguys like you are doing.

Rotor

 

[longeron]

A single seal with a steam quench is one way to do it. The steam will help keep the asphalt from coking up on the atmospheric side of the seal and will help to warm things up during start-up.

If you can afford some product dilution a Plan 32, injecting a process compatible cool fluid into the seal chamber, could also improve reliability of the seal by reducing coking and improving conditions at start-up. Take into consideration the cost of recycling or loosing the injected fluid into the process stream. The rate of injection depends upon the application and how tight a bushing can be fitted into the seal chamber.


Dual pressurized seals are another way to go.
My preference for hot asphalt in a big seal chamber/stuffing box - dual stationary mounted metal bellows with a Plan 54 seal support system.

A Plan 54 is essentailly a lube oil skid for the mechanical seal. The skid generally consists of a set of pumps, a heat exchanger, filter, oil reservoir of a decent size ( from 25 to 100+ gallons), regulators, relief valves, level switches and alarms, pressure switches and alarms and so on.
Sophisticated systems can track the pressure of the pump so that the system pressure is always 25 or so psig above the process side of the seal, and have systems to maintain pressure in the event of a power outage or pump failure.

This a significant initial outlay. However, this system will ensure that nice clean fluid is always lubricating the seal faces from start-up to shut down. No coking will occur, so no hang-up problems or "secondary seal face" build up.