15 replies to this topic

[Brian Hughes]

A little bit of background- some blokes of a certain age play golf in their spare time, I make charcoal. And I run my Land Rover on it. To understand how I do it, watch this video:

 

https://www.youtube....h?v=yL79ci4TH7k

 

Using a scaled up version of this setup, I've had about 8 20-30 minute test runs on my Land Rover.

 

And one explosion.

 

This scared the living daylights out of me, the good luck was nobody getting hurt, the good judgement was stopping gasifier runs until I've redesigned the system to mitigate the possibility and consequences of an explosion. The thing is, I want to be able to induce a controlled explosion to reassure myself, and skeptical H&S inspectors that the risks are managed.

 

My questions are: would pyrotechnic squibs (solid fuel and oxidant) accurately simulate the effects of a gas and air explosion, or are the characteristics of the explosion (speed, temperature and other factors) too different for a good comparison?

 

Can low power squibs be purchased and stored legally? I'm obviously new to this.

 

And can anyone point to any "up to speed" reading on the nature and theory of explosions?

 

Thanks for any help.

[digger]

OK Interesting one

 

I guess the issue you have is that gas explosions can vary significantly in their power depending on the constituents and the stoiciometric ratio's. For instance hydrogen can detonate when mixed with air in the right quantities, making it extremely difficult to design for.

 

I am a chemical engineer and work with various reactor designs. The basis of design for all of these reactors is that we do not let explosive mixtures of gasses into them.

 

The best method is to design your system so that an explosive mixture can't build up, it is possible. 

 

However i guess the main constituent of your gas is carbon monoxide. http://www.sciencedi...062289649800274

 

I think you will struggle to convince the H&S that a design that has regular explosions within it is safe. Their argument will also look at fatigue life so you won't have to set off an explosion, it will be hundreds or thousands. Unless you can do the design calculations based upon the measured worst case explosion velocity. An FE/CFD design tool would give the most convincing results for calculating the fatigue life of the unit.

 

Good luck, it is an interesting project. Far better than hitting a small ball with a stick

[Arthur Brown]

Have you fully searched the terms Gasogene and Gazogene? These were functional units for powering tractors during the WW2 Nazi occupation of France when no significant petroleum fuel was available. These units were rechargeable with wood chips during a working day.

 

As a guess the gas mix from the reaction doesn't burn or bang til there is air entrained in it. You may well have an air leak or ten!

 

If you want to minimise the size of potential bangs then look at minimising the volume of gas available in the system. If you want to attempt to trigger a bang what about adding a suitable thread to the container and fitting a spark plug and an ignition coil.

 

I'd advise against adding an explosive device (even a small maroon or squib ) as this would have it's own destruction method which would change the potential method that you think is happening now.

[Brian Hughes]

Thanks for the replies. What happened- an educated guess- was that there *was* an air leak into the gasifier- 20 litres at slightly below atmospheric pressure- and the mixture ignited. The only path for the explosion was back through the air inlet, sending burning charcoal into the air. I'm aiming to mitigate the consequences as well as the likelihood of an explosion by giving it somewhere safe to go- a sprung lid, or something similar to a vehicle air bag- hopefully, making sure that any explosion is a "whumf", not a "KABOOOOOOOOOOOOM". I like the idea of a spark ignition source to ensure that an explosion happens sooner rather than later. My game plan for for checking out squibs was to have a method of testing and demonstrating explosion containment with the system cold. 

 

How are commercial squibs specified? Do the manufacturers quote a figure for the explosive energy in joules?

 

@Arthur Brown- there were several gasifier designs that kept countries moving when petroleum was scarce- the Imbert downdraft system seems to be the common theme, and a lot of interest today. Check out:

 

https://northernselfreliance.com/

 

and:

 

http://thedrizzlerga...blogspot.co.uk/

[Arthur Brown]

Theatrical maroons are available for a price. Try http://www.lemaitreltd.com/ ask them for a local supplier to wherever you are.

[Crazy Cat]

Charcoal production and safety.
http://www.fao.org/d...5E/x5555e06.htm
https://ir.library.o...88E2?sequence=1


Charcoal pyrolysis gases. https://scholar.goog...s=1&oi=scholart

http://www.mdpi.com/...3/5/12/4952/pdf
http://www.biochar-i...oal100508-3.pdf
http://www.bioforsk....

Edited by Crazy Cat, 11 June 2016 - 01:30 AM.

[cooperman435]

While not fluent with gasified uses (strange really as I'm notorious for my money saving!) my understanding is they heat solid fuel to release flammable gasses used to then run an internal combustion engine?

If that's close enough then surely the problem your facing is dealt with by any flammable vapour producing liquid run veichle already? And I can't see a petrol veichle passing any tests with an "explosive pressure release vent" needed on the tank!

Diggers comments are a far better worded version of my opinion in that recreating a gas-air explosion has too many variances to be possible as a demonstration of safety

An explosive device also doesn't show an appropriate safety test either as its so far from real use

The bit I spotted though is the gasifier runs as slightly negative pressure? I assume things is due to the fuel delivery system scavenging generated gasses by sucking them out of the unit? Surely eliminating this and allowing neutral or even slightly elevated internal pressures completely removes the chance of air/oxygen entering the chamber and therefore cannot create an explosive mix?

[Brian Hughes]

@Cooperman435 Thanks for the reply- gasification covers two distinct processes, firstly, heating coal or biomass to pyrolyse and release tar vapours, and secondly, passing hot CO2 and water vapour through a bed of charcoal to form a reduction zone- get the temperature gradient right, and the gases reduce to carbon monoxide and hydrogen. The carbon monoxide is a great fuel gas in every way. Except one. It's poisonous and kills people, and producing it under positive pressure just isn't an option.

 

Vapour/air explosions do occur in the comparatively small volume of an engine inlet manifold, and there are sometimes provisions for this- in my case, there's a worst case scenario of 20 litres of explosive mixture, which I need to simulate to show that the explosion has somewhere harmless to go.

[Crazy Cat]

Gazogene http://en.academic.r.../enwiki/1204693

Look through the 'References' at https://en.wikipedia...d_gas_generator


2C + O2 <=> 2CO + 58 000 cal par mole (44 g)
C + O2 <=> CO2 + 97 000 cal par mole
2CO + O2 <=> 2CO2 + 136 000 cal par mole
CO2 + C <=> 2CO - 38 000 cal par mole

C + H2O <=> CO + H2 - 28 000 cal par mole
C + 2H2O <=> CO2 + 2H2 - 18 000 cal par mole
CO + H2O <=> CO2 + H2 + 9 400 cal par mole
https://fr.wikipedia...u_gazog.C3.A8ne



Woodgas powered trucks and cars in the United States, http://ps-survival.c...dation_2001.pdf


Can I suggest to use engine emission testing on the charcoal pyrolysis gases.

Testing Automotive Exhaust Emissions. Page 3: http://www.ni.com/pd...t-emissions.pdf

http://www.driveonwo...ry/auburn-test/
http://www.driveonwo...inal_report.pdf << Important data on gas analysis


More data at this site.
http://www.doc-devel...g/file/Energie/
http://www.doc-devel.../biomasse-bois/
http://www.doc-devel...-bois/gazogene/
http://www.doc-devel...yse test perso/

[pyrotrev]

The best way to handle this IMHO would be to make sure that the gasifier is always running well oxygen negative and then you only introduce sufficient oxygen for combustion in the carburettor as per usual: you might be able to use a lambda sensor from a car exhaust to monitor the situation and trigger a cutout or dump CO2 into the system. Using the "water gas" reaction (charcoal + water > carbon monoxide + hydrogen) as much as possible would help, but this is endothermic so you need to have some air getting in for the "producer gas" reaction (charcoal + oxygen > carbon monoxide) to generate heat. Look at how they managed such things in coking plants/steelworks for inspiration!

[Brian Hughes]

Thanks to all who took the trouble to reply, but I think the replies are drifting away from my original question: Can I use a pyrotechnic device to simulate an explosion within the gasifier to prove, for my own peace of mind, and for sceptical safety inspectors, that an explosion has somewhere safe to dissipate?

[digger]

OK, the answer is not easily, as you want to replicate the conditions of a gas explosion. You could probably get close if you work out the energy that would be generated and hence final gas volume and pressure under adiabatic conditions by a stoichiometric gas explosion. You could then use well documented information in the literature to calculate a black powder charge to produce the same final conditions.

 

I would steer well clear of thunder flashes etc as they are not net gas producers and can create large overpressures at short range.

 

Why don't you actually charge the vessel with a stoichiometric mix of the gasses produced with air and ignite it? Surely that would be the best test as it would simulate the actual conditions if it all went wrong.

 

Carbon monoxide and hydrogen bottles are available from BOC and other gas suppliers. with a couple of rotameter type flow meters it should be possible to recreate the ideal explosive gas mixtures in your tank. Maybe it would be worth thinking about how to ensure the vessel is at normal operating temperature as the material properties will change significantly at higher temperatures.

 

Just my 2p

[Brian Hughes]

@digger... Thanks for the reply- I'm leaning towards a spark plug in the can, a teaspoonful of petrol or a squirt of gas from a blowlamp, and stand well back.

 

 

 

 

I would steer well clear of thunder flashes etc as they are not net gas producers and can create large overpressures at short range.

3 new concepts- I was sort of under the impression that a bang is a bang- a fast release of gases. Are there any quick pointers to where I can get up to speed with the technicalities and distinctions of squibs, maroons, and thunderflashes?

 

Any idea what they use in vehicle airbags?

[Crazy Cat]

3 new concepts- I was sort of under the impression that a bang is a bang- a fast release of gases. (1) Are there any quick pointers to where I can get up to speed with the technicalities and distinctions of squibs, maroons, and thunderflashes?
 
(2) Any idea what they use in vehicle airbags?

(1) http://www.pyrosocie...ge-2#entry84814

(2) Older airbag systems contained a mixture of sodium azide (NaN3), KNO3, and SiO2. A typical driver-side airbag contains approximately 50-80 g of NaN3, with the larger passenger-side airbag containing about 250 g. Within about 40 milliseconds of impact, all these components react in three separate reactions that produce nitrogen gas. https://en.wikipedia...irbag#Operation

Blast wave overpressure. http://www.gastechno...n_M_Bonilla.pdf

As Digger has already stated, "replicate the conditions of a gas explosion" you need carbon monoxide and hydrogen in stoichiometric ratio's with oxygen.

[cooperman435]

The think you seem to have missed digger has tried to say is that to proof test something for a particular occourance you need to test that thing happening precisely.

Using petrol and a spark plug doesn't show what could happen actually happening neither will any form of pyrotechnic device.