[Gasification] Safe Operation of Gasifiers. Was: Re: filtration options and their varying discontents

Mon Dec 10 15:31:06 CST 2012

Dear Jim

Gasification is basically safe, as evidenced by the fact that the vast number of gasifier start-ups go smoothly, without a backfire, hiccup, poof, burp, explosion, etc. However, as you say, there are the "outliers"that are the problem.

It seems there are two general Operating Procedures where there is a potential for an explosion:
1: Start-up
2: Re-fuelling.

It is difficult, and perhaps impossible, to specify Start-up and refuelling procedures that are absolutely 100% safe. Even with reasonable care, it may still be possible for a poof to happen. One of the difficulties in operating a gasifier is that with blow-backs and poofs happening so infrequently, it may be difficult to see the particular pattern that must be in place for the poof to happen. 

Nobody on the Wood Gas List wants harm to come to their Customers and Friends. I wonder if it would be possible for the Wood Gas List to write a FAQ Document to answer the question 
"What is a reasonably safe procedure to follow for start-up and refuelling of a gasifier?"

Probably most of the experienced Wood Gassers have had their incidents, with singed eyebrows, burned arm hairs, etc. Such a Proposed Document would go a long way toward reducing these these embarrassing incidents and would go a long way toward preventing possibly serious injuries.

I would like to suggest, as a starting point, a general outline as shown below. Many people on the List have real and valuable first hand experience in starting, re-fuelling, and operating gasifiers, and I would encourage them improve on the "starting point outline."

1: General Introduction and Disclaimer
2: How explosions and unsafe conditions result
3: Examples of Incidents resulting in poofs, flash-backs, and explosions
4: What likely went wrong, and how to prevent them
5: Suggested "Good Practise" for starting, refuelling, and on-going operation.

Once the outline is finalized, I would volunteer to do a write-up which pulled together all the operating experiences and suggestions into a document for review by the Wood Gas List.

Best wishes,

Kevin
  ----- Original Message ----- 
  From: jim mason 
  To: Discussion of biomass pyrolysis and gasification 
  Sent: Monday, December 10, 2012 3:44 PM
  Subject: Re: [Gasification] filtration options and their varying discontents

  On Mon, Dec 10, 2012 at 12:41 PM, David G. LeVine <dlevine at speakeasy.net> wrote:

    On 12/09/2012 10:34 PM, jim mason wrote:

      other than the explosive risk

    There is an interesting question here:

    Is there an explosion risk if the gasses have not been diluted by the atmosphere?

  well, in principle, the gas should not be diluted with air during typical operation, and thus no explosion problem.  you are correct.  

  the problem is typical operation is variable.  during start up you always go through a stoich point as you move air out of the system and progressively make gas.  even if you leave the system full of gas on shut down, start up in the reactor can pass lots of air until things get up to temp again.  this can easily result in a combustible mixture in the system.

  we've found this to be a fairly significant operational reality that needs to be addressed for regular users.  similar for the impact of backfires from the engine igniting the intake stream.  while things are "usually" ok, the marginal events can be quite, umm, compelling . . .   we've started adding more pressure relief points where typically not needed to cover these outliers.  we're also looking to add a flame arrestor right  at the manifold to prevent backfires propagating.

  again, you never use these during typical operation.  somewhat like an ESP shouldn't cause any problems during regular operation.  it is the outliers that are of concern.  when you start running these systems regularly, you tend to find all the outliers.  and the ones you don't find in house, those out in the fields certainly will.

  j

    Let's start with gasoline, if we evacuate a bell jar and inject enough gasoline so there is a layer of liquid gasoline on the floor or in a pan, and we generate a hot arc 1/2" above the gasoline, will there be an explosion?  The correct answer is "only if there is an air leak."  

    Without an air leak, there will be no oxidizer, fire (or explosions) require three things:  Fuel, Oxidizer and Ignition.  Fuel is gasoline (in this case), Ignition is the spark, but where is the oxidizer?  

    If woodgas has excess oxidizer as it exits the reaction zone, it simply burns off the extra gas.  So, unless there is an air leak, the reaction can not occur.  However, if there is an air leak in _any_ fuel system, there will be severe problems.

    Dave  8{)

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