Tuesday, September 14, 2010

P-o-o-o-f-f Goes the Chemical Reactor

Norcross M10 Viscosity  Sensor
Norcross has been measuring the viscosity of fluids in chemical reactors for many years. This can be done under a full vacuum or under pressure and at a wide range of temperatures and viscosities.

We recently had a very curious issue, with a customer in China. The M10 would be up and running and working fine. After a few batches there would be a build up of vaporized fluid in the head assembly of the M10. This would eventually cause the unit to malfunction. Why is that we thought?

After visiting the customer we found that when one batch was completed they would pressurize the main reactor to 'push' the product out of the reactor.

Then they would pressurize another feed reactor to 'push' the fluid into the main reactor.

These reactors were being pressurized to only about 15psi but their volume was approx 300 cubic feet. This means the total pressure force in the reactor is tremendous. Thus as the fluid reached the bottom of the feed reactor the pressure blew through the fluid into the 4 inch feed pipe connecting to the main reactor. This action vaporized all the remaining adhesive.

This blow through is like a burst of high energy steam but it is high energy vaporized adhesive at high temperature. There are release ports on the main reactor to vent this pressure burst. The "P-o-o-o-f-f" as we named it lasted approximately 1/2 second.

Even with purge gas flowing in through the M10 the pressure spike was so great that it blows back through the purge lines, in addition to blowing out through the release ports. Thus depositing a vapor of adhesive all through the M10.

Conclusion: When a reactor is emptied by pressure, things will work but it must be filled via a pump to avoid the "P-o-o-o-f-f".

Best to you all,

Bob Norcross

Wednesday, September 8, 2010

24vdc circuits are inherently intrinsically safe - NOT SO

An intrinsically safe circuit can be of many voltage levels but of only limited power levels with certain limits on resistivity, inductance and capacitance.

Thus just because a circuit is 24vdc does not mean it is Intrinsically Safe.

After all, if you took a 12volt car battery into a factory using acetone based liquids, then attached jumper cables and then touched them together over the tank (i.e. making nice large sparks) it would probably be the last spark you saw.

The energy of that 12volt batter is too large!!!  It is low voltage but can generate high current flow (otherwise your engine starter motor would not turn over your engine). Thus there is a lot of power (watts).

Thus there is the very high probability of an experiment such as this turning you over into the hands of a local emergency room doctor.

When Intriniscally Safe IS NOT Intrinsically Safe


In the world of process control of flammable fluids there are many sensors that can be used with intrinsically safe barriers.

However, many individuals do not understand one, of many, technical points.

You cannot run the wires of intrinsically safe circuits in cables or conduits or raceways without special isolation.

We have one version of a viscosity sensor that has integrally mounted valves and a switch. They are all piped to NEC XP standards and the components are all UL Listed.

On occasion a customer will want to use an intrinsically safe barrier for the switch ( which itself is already UL Listed Explosion Proof ). We then point out that the six wires (two from each component) are carried away from the explosion proof junction box in a single cable. Thus making the intrinsically safe effort futile.

If you want to use an intrinsically safe connection to a switch, typically done so that you can avoid hard XP conduit connections. Then wire the switch separate from any other devices, such as valves.  Then you have a great Intrinsically Safe Installation.

Norcross Standard in Chinese Text Book on Printing

Greetings, after many years of testing and working in China Norcross has now been placed in a nationally known text book used by most of the printing colleges in China.

More details to follow.

Water Based Ink - Don't Add Water Until ...

Caution, many water based inks are not pH stabilized. Thus you can have color and viscosity shifts due to changing pH.

Therefore, do not begin to add water until after you have checked the pH. A small change in pH can cause a large change in viscosity, as well as hinder drying and tack.