Help requested on implementing temperature control system (0 - 60 C, 6,000Litre vessel)

[southwalesboy]

Hi all,

I am a chemist (PhD Synthetic chemistry) with no prior knowledge of electrical or mechanical engineering, but I am desperatly in need of implementing a temperature control unit and thermocouple device to a 6,000 Litre (Water/solvent) tank.

My basic understanding is that I need a thermocouple with a control unit, which we need to operate some kind of imposer relay, to power cycle our 18 KW (6 x 3KW elements) heating device.

I have limited/no access to the bottom of the tank, and the thermocouple preferably should be inserted from the top, which will result in it (and its extension cable) being submerged in up to 3 M of water (or solvent). The suppliers I have spoken to say they can't provide me with anything to do this job, and instead point me towards "Mineral insulated thermocouples with pot seals" e.g.:

http://www.tcdirect.co.uk/Default.aspx?level=2&department_id=190/1

My second question is about the relay system operated by the controller unit, I have 6 x 3 KW heating elements, do I run them all on to one single heavy amp cable with a powerful imposer relay operated by the control unit, or can I have a series of smaller amp relays operating each of the 6 circuits?

Many thanks in advance if anyone can offer any advice at all! Cheers!

 

[davidbeach]

You really need to be hiring a local consultant who can do the necessary engineering, while meeting the requirements of local codes and regulations. Free advice from a "Tips" web site isn't the solution to complex problems.

 

[itsmoked]

You should be using a well long enough to avoid ANY cable in the water.
You should have two separate T/Cs. One running a physically different over-temperature alarm with power/cutoff authority. Use a contactor for the safety and a 3ph SSR for the control unless temp cycles are going to be minutes. If the tank is not well stirred or the stirrer can fail you may need more sensors so local hot spots don't go unnoticed. Use a twenty foot long well if needed.

I recommend human intervention be required to initiate heating. This puts some responsibility on the button pusher. This is a start button that allows the safety contactor to pull in when not in alarm. Include with this an emergency stop button that will drop the safety contactor.



Keith Cress
kcress -

http://www.flaminsystems.com