Thread: Processor goes bang!

Perhaps you could tell us how you are going to be modifying the processors you build and the components you will be using so as your machines will be within the relevant laws?

I have a nasty feeling complying with these laws will be impractical through either cost or engineering but I am sure most people would be happy to make their processors as safe as practicaly possible if the componentry is available at a reasonable price.

When it comes right down to it, I very much doubt that processing bio at home would be able to satisfy all the requirements of local councils, fire standards, insurance issues and different laws anyway.

I guess the best thing is for us all to be very careful.

Hi there
Thanks for that it is a concern indeed
There are a number of threads here about safety this is one which should be added to the list
By your post I realise you are a manufacturer of reactors so I am not going to tell you how to suck eggs but here is a few bits of info which I have posted in the past for any one else reading this thread
If you are to strap the thermostat bulb to the element with a hose clamp or two the likelihood of the described event is reduced substantially
It is commonly done in hot water urns since they are also attended by "experienced" people
Another low cost safety is to weld a couple of 1 inch elbows on the reactor facing each other one right on the bottom but above the element the other as high as you recommend maximum fill
Place a piece of clear plastic tube so as to join them In the tube drop a cork from a wine bottle with a strong magnet glued on to it
Mount a reed switch with N/C which controls a small contactor to the element and pump power supply
If the cork is in line with the reed switch it will open it so the power circuit will be broken
If there is liquid in the tank the cork will rise up past the reed switch which will of course go closed completing the circuit
You need to drop a compression spring in the tube so as to adjust the height of minimum liquid level so the cork/magnet does not go below a certain height
The clear tube also helps as an oil level indicator as well as when phase separation has taken place
I am sure there are other ways but here are a couple of low cost safety features which can be used by home brewers to minimise risks

One remedy for the above mentioned problem.

A relay on the heater circuit that is required to be energized for the heater to work.
As soon as there is a "Glitch" in the electrical supply the relay drops out.
When electricity is restored, a warning is sounded and the relay must be re-set by hand to re-energise the heater.
You could go one step further and put the heater relay in the pump circuit so that the pump must be running for the heater relay to energize

Tilly

Originally Posted by Chris

Mount a reed switch with N/C which controls a small contactor to the element and pump power supply
If the cork is in line with the reed switch it will open it so the power circuit will be broken

Hi Chris, I see one main problem with this design. When you go to pump out the reactor the pump will stop before the reactor is drained. Also it will prevent the pump starting when you want to pump in your next batch of oil.
But having such a design only on the heating circuit seems logical to me.
In practise however, I don't see a need for this extra complication, because I find it only necessary to heat once. After that during the mixing time no further heating is required, so I then unplug the element. However, if you are to be constructing reactors for other people then it would be well worth using in the design.

Hi All
Good to see input on safety related issues All points are good value
In so far as the pump not being able to run so you can fill the reactor again there is a simple way around that
A two way switch marked Safe Manual will by pass the open circuit
It can be spring loaded so it can only function while you are holding it down Since you only have to get a very small qty of material out or in before the reed switch makes the circuit it would not take that much time
I am sure there is a heap of other ways as well
However this is a fairly low cost set up
A s/h contactor is about $10 if you where to get two it will make it even better as well as safer,
One contactor wired self latching to supply power to all of the system the other for the element
You wire one of the contactors as self latching with a push button labeled Start
It will come on when you press it suppling power to the whole system
If there is a power outage it will stay off until you press the start button again
The element contactor can then control temperature via the safety circuit mentioned before
A reed switch is about a $1.50 new
I am sure there are enough around from alarm systems that no one wants at the local demolition yard
The two way switch, since it only has to carry the current for the contactor which is in the milliamps may be about $5.00 from the local electronics store and about $10.00 of cable
So for about $30-$40 one can have a fair amount of "insurance"

Another idea would be to put a mechanical timer in the heating element circuit that requires the operator to rotate the dial to power the element for a specific period.

It will not stop a situation where there is a leak that drains the fluid below the element level but it will require the operator to be there to initialise any power to the element.
George

I offer some points of clarification;
The requirement in Australia comes from what is commonly known as "The Wiring Rules" (AS3000) and is for the occupier of premises to assess the area in accordance with an Australian Standard (AS2381) and determine if it is a "hazardous area". If it is, then the electrical equipment installed in that area must comply with IECEx requirements.

The IECEx scheme is the most stringent in the world, and so far only two compaines worldwide have equipment with Certificates of Conformity in accodance with the scheme. One of them is our company, Grimwood Heating in Villawood, NSW.

It is the responsibility of the user and the occupier of premises to determine if their operation is a "hazardous area", and if so to ensure any electrical equipment installed in that area complies with the standard.

It is also the responsibility of the purchaser to specify at the time of ordering equipment that the equipment is to used in a hazardous area and to specify the classification of that area.

Gentlemen,

Thank you for all the replies, and I'm happy to say that I agree with all of the suggestions offered and have already implemented my own version of most of them.

For the heating element safety interlock, I've used a slave switch that will only apply power to the element once the motor is up and running - motor stops, element stops.

It has a further refinement in that the element is run through a drop out relay. If the power is interrupted or the motor stops for any reason, the element is cut off and won't reconnect until a reset button is pushed.

David, you asked what sort of things can be done to comply with ATEX rules. The simple answer is to replace every component with Ex certified units. Heating elements for example are available in Ex 'd' which means that they hook up to their electrical supply via a junction box that will contain any flame/explosion.

Needless to say, such exotic components are expensive and have fairly stringent servicing requirements.

The other way is to think laterally and start replacing components with intrinsically safe versions. For example, industry makes extensive use of hot water for process heating and it wouldn't be very difficult for me to put in a water/oil heat exchanger in one of the recirculation pipes - added advantage being that I can then offer a solar collector and storage tank as part of the deal. Sounds a bit ridiculous, but I can still come in under the cost of a dread Fuelmeister.

In truth, I'm still thinking through the various permutations possible, and I'm sure the eventual bright side is that it will improve my designs.

BTW, I'm new to the whole ATEX thing myself so appreciate any advice. Grimwood mentioned the evaluation of hazardous areas, but I can't see how any biodiesel plant would not be rated at the very least as a Zone 2, with any vents into the processor tank as a Zone 0. The only variability seems to be in the area that the hazardous area occupies.

Originally Posted by gwalker

Another idea would be to put a mechanical timer in the heating element circuit that requires the operator to rotate the dial to power the element for a specific period.

Actually that's what I do. I just use a simple rotary timer switch on the heater plug and set it for 30 minutes or whatever. That way it will always switch itself off in case I forget. It won't exactly achieve ATEX rules, but it is a small thing that can help prevent an accident.

I also unplug my heating element when not in use. I don't consider just turning it off at the socket to be enough.