[Gasification] Candle filter experiences

[James Joyce]

Thanks for the advice Doug, Bjorn and Leland. Hopefully you can prevent others from exploring again some of the many dead ends that gasification presents to us "starry eyed" technologists !

I am certainly more nervous that I was before. The flue gas application might go ok, as long as we keep the start-up emissions out of it ... but the pyrolysis gas application looks like trouble. I will have to follow up on ESP for that, however the last time I looked that the cost of the electrical items was more than twice the cost of the rest of the plant combined. 

I had considered burn-off as the option for tar fouling in the flue gas application. We will be running at 350 deg C with 30-40% excess air, so it might not need much encouragement to burn off any tars once it gets to temperature.

We were going to use a flooded auger for dust removal, recognising that a smouldering hopper fire is all but inevitable, because we can get ember carryover from our thermal oxidiser. Will have to look at how to manage the hold-up of the soot/ash. I have considered a sonic horn for that. They are used for soot/ash release in large coal fired furnaces ... not cheap and may present some risk to the candles.

Sounds like cyclones ahead are a bad idea ... just as well as I had no intention of doing that figuring the cake needed the larger particles to give it some "body".

Great to get some actual numbers on pressure drop. Unifrax were suggesting to keep it below 10" to avoid stressing the candles. In the flue gas application, we can use compressed air for the back-pulse, so we don't have to be as conservative as you would be with inert gas. For the pyrolysis gas application I can see this being another reason to have a good look at the electrostatic precips again ...or perhaps batch filtering with deep bed sand filters that are water washed once the pressure drop is too high ?

regards,

James


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Message: 1
Date: Wed, 1 Nov 2017 07:22:36 +1300
From: Doug <doug.williams.nz at gmail.com>
To: gasification at lists.bioenergylists.org
Subject: Re: [Gasification] Candle filter experiences
Message-ID: <cc176581-b195-4c73-2171-e7a59aa6fa3a at gmail.com>
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Hi James and Bjorn,

Bjorn's comments to you reminded me of more issues that we experienced with candles, which in hind sight looked simple to resolve at the time (just throw in a few more $$$ at the black hole). Pre-coating involved obtaining talcum dust, and using that to reduce the pore size of the ceramic pore structure. We also had a preference for removing all larger dust particles using cyclones, so only the finest dust reached the candle surfaces. This in turn created very rapid pressure drop across the ceramic wall, requiring more frequent pulsing. In the end, we let all the solids in gas suspension go to the candles so that a more mixed filter cake formed on the surface. Yes I said filter cake, because the candle surface only provides a platform for the impacting mixed particles to collect, because if they enter the ceramic pores, then they will block rapidly. From memory, we worked with our flow rate at 7-9" 
inches W.G. with the pulse initiating at around 14" W.G.? If you are tempted to work at hight pressure differentials, the ceramic wall can collapse, because the gas temperatures through the ceramic pores in localized spots is squeezed releasing more heat, weakening the ceramic fibres which collapse.. If you plan to operate at higher temperatures to start with, then watch the rates of pulsing to keep the pressure drop low.

.....

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Message: 2
Date: Tue, 31 Oct 2017 20:06:25 +0100
From: Bj?rn Kuntze <kuntze at mastergas.de>
To: "'Discussion of biomass pyrolysis and gasification'"
	<gasification at lists.bioenergylists.org>
Subject: Re: [Gasification] Candle filter experiences
Message-ID: <009701d3527b$5a17ca80$0e475f80$@mastergas.de>
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Hi Doug and James,

 

yeah, I missed to report at least one thing that always happens when it comes to hot gas candles: the increase of pressure drop over the time of operation. 

 

Doug mentioned this point. 

 

As far as I know, the pressure drop increases always over the time. So the jet-pulse cleaning (or reverse flow cleaning) will have to be done more often at much shorter intervals, Since you will have to use inert gas for this procedure, this will really become an issue after a short time. So very quickly somebody will come up with the idea of burning the dust away in an atmosphere with oxygen. This procedure will work may be two or three times. It will not be a lasting solution. It will not remove the mineral dust and it might even result in melting of the ceramic structure or slagging of the ash?

 

So, frequent replacements of the quite expensive filter elements should be considered right from the start anyway.