Design Pressure for Caustic Solution

I agree that redundant high-temperature shut-offs should be installed, preferably in series with the existing controls, so that any single one working is sufficient to prevent overheating. I would suggest that an overPRESSURE switch (or several!) also be installed; while this adds a degree of safety to the heating system, but it also functions to prevent accidents due to, say, loss of headspace, or a pump stuck "On." The overpressure switches could be used to control both the heater, and any powered valves, especially on the inlet side, to avoid pressure buildup. Purely mechanical pressure relief valves remain a good idea.

If it is in series when one fails the other is not anymore active they should be in parallel !

If a Normally Open switch "fails" it remains closed. Still, any other switch opening will break the circuit and stop the heating IF they are in series. If in parallel, ALL switches would have to open before the heating would stop, and any single failure would leave the heater active = unsafe.

This is like the safety switches that check whether the cover of an electrical enclosure is fully in place: each is Normally Open (N.O.), and only closed mechanically when the cover is fully seated. As long as any one of them works, the circuit is broken, making it safe to touch components inside. Even if several are stuck closed by dirt, welded contacts, etc., that single functioning switch saves the technician from shock [unless he/she touches exposed conductor on both sides of the open switch. Power should still be disconnected before opening an enclosure]. And, if any other failure occurs in the circuit, it is more likely to break the circuit than to make it at a point bypassing all switches. Any competent designer will ensure that it requires multiple failures to complete a bypassing circuit, by such means as separately insulating the wires into and out of the protected zone, or even running them at a significant distance from one another.

bhalchandra-

Can't give you a good answer unless you provide some more information. What are the measurements of the storage tank? is it horizontal or vertical? Are there any relief valves or vacuum breakers on the tank? Is there any over temperature safeguards, redundancies? Does the material circulate through this tank or is it stagnant? What is the unused head space in the tank? The tank is over 13,000 gal, more than 3 trailer trucks full, do you need that much in storage or is it shipped in rail tank cars?

It is better to give good information in a question in order to get a good answer. In my younger years this was termed as: Garbage In --> Garbage Out. Please help us give you a good answer.

Good Luck, Old Salt

Dear Sir,

Tank dimensions :- Diameter 4.0 m & Height 4.0 m.Vertical tank

Top dished end & bottom flat.

Head space - 8.0 m3 incl top dished head vol.

The vent line is connected to exhaust air system. No PV valve or vacuum breaker.

Temp. control for low temp. is given not for high temp, TICS available for low temp.

Caustic solution is required to process & unloading tanker at 15.0 m3/hr both are required intermittently.

Regards

Has a formal HazOp Study been completed?

Perhaps you would like to clarify your intent.

I am assuming that you are talking about Sodium hydroxide in solution.

FRP (or GRP) composite is good "material of construction" for this application. This material is good for all concentrations up to 180°F

I would suggest that you use ASME RTP-1 as your design code, if purchasing a new tank.

You could use self-regulating type tank heating pads or heating cable to maintain temperature.

Let me know if you need any additional information or would like to obtain a quote for a new vessel.

It is assumed that those comments are for the Original Poster.

Dear Sir,

Thanks for your valuable comments.

PID is incorrect as obtained from client. PV valve is installed in place.

As per Hazop point of view there should be High temp. switch for heater also for tank inbreathing PV valve or vacuum breaker is needed.

If we put up a high temp. switch then question of temp. rise violated.

So, only from pressure point of view only it is atm press.+ liquid fill as design pressure & vacuum is exhaust air sys. max. vacc.

Please correct my insight into the subject.

Please suggest For caustic solution, for the given capacity does the Conical head or dome head to be considered.

Thanks & regards

The P&IDs cannot be incorrect, as these are the documents that describe the design intent. They are the "lead document" from which everything else is hinged. As the design progresses, the statement of intent changes and the drawings are revised and re-issued.

Part of the design review is that of its passing through the HazOp Study. Please respond to the question on the HazOp Study.

Dear Sir,

About HAZOP study we have to check with client.

Thanks

Dear Sir,

If you need PID for your concern then I can upload its portion.

Regards

The P&IDs are not needed here. They are needed for the HazOp Study, though!