[Stoves] Clinker Formation

Sun May 18 12:08:16 CDT 2014

Otto,

The TLUD should be the perfect device for high ash fuels. Jock Gill has burned a lot of grass pellets in TLUDS so that should be  good indication. Paul W had burned bundles of grass as you, Otto, probably have. Just as you have described the temperature in the carbon should be well below sintering temperatures low until you reach the char burning stage. At that point you will be oxidizing he carbon at well above 1000C which will melt most ash and you will get clinkers.

The fine carbon burnout will only be as efficient as the gas burning portion of the TLUD even so it should be very good. I agree with Dean that the carbon burnout in a forced draft stove might be an issue. On the other hand you can have low velocities at the grate and higher velocities above the grate burnout should be very good. The challenge is doing that in stoves that operate at low power, poor air control, and burns with very high excess air. It would be difficult to recirculate flue gas in as small stove. Even then you need lower oxygen in the recirculating gas than you can get in a stove. 

Tom    

From: Stoves [mailto:stoves-bounces at lists.bioenergylists.org] On Behalf Of Crispin Pemberton-Pigott
Sent: Sunday, May 18, 2014 2:48 AM
To: stoves at lists.bioenergylists.org
Subject: Re: [Stoves] Clinker Formation

Otto that straw pellet test will be important because it may have all its Cl and K in it so the melting temp will be lowered. 

If processed agri-wastes are to be an important fuel they will have to be accommodated by the designer. 

Regards 

Crispin 

BBM 2B567C3

From: Otto Formo

Sent: Sunday, May 18, 2014 16:39

To: Stoves Bioenergylist

Reply To: Discussion of biomass cooking stoves

Subject: Re: [Stoves] Clinker Formation

Dean Still,
According to Crispin and to our experience, the flames reaching the cooler pot, instantly create char or black carbon - insufficient combustion create more PM and black carbon........!?

The fan driven Oorja, was tested here with woodpellets, four years ago.
At full blast the "room" was soon covered in a thin layer of soot and ash.
The cast iron combustion "chamber" was glowing instantly- around 1000 - 1100 C.
What about ultra fine particles......?? 

Natural Draft gasifiers, are the way forward................

We will soon test the Peko Pe with staw pellets and see the effects of clinker formation.

Using Corn colbs  (agri-waste) as fuel, we noticed a temperature of 450 - 550 C at the top of the flame and around 350 -400 C at the pyrolysis front.
At the end of the burn, when most gases are utillized and the char starts glowing, we can raech the temperature arond 900 - 1000 C.

To avoid clinker formation, we just removed the char , before it starts glowing, namely biochar.......problem solved?

Otto

Date: Sat, 17 May 2014 17:25:27 -0700
From: deankstill at gmail.com
To: stoves at lists.bioenergylists.org
Subject: Re: [Stoves] Clinker Formation

Hi Tom, 

Does cooling the burn reduce black carbon? Are ultra fine particles more of a problem in forced air stoves?

Best,

Dean

On Sat, May 17, 2014 at 3:36 PM, Tom Miles Easystreet <tmiles at trmiles.com> wrote:

Think of flue gas recirculation as a way of trimming excess air at the same burn rate while cooling the flame. The Kob boiler is nicely rigged for it. 

Tom

T R Miles Technical Consultants Inc.  

tmiles at trmiles.com

Sent from mobile. 

On May 17, 2014, at 9:00 AM, Crispin Pemberton-Pigott <crispinpigott at outlook.com> wrote:

How is it used to lower the temperature? By interfering with the O2 supply thus reducing the burn rate? Or the efficiency of combustion? 

Thanks 

Crispin 

 On Fri, 16 May 2014 07:59:49 -0700,"Tom Miles" <tmiles at trmiles.com>
wrote:

>
>Stages combustion in a pellet burner can be a challenge. Most pellet burners are designed to burn the fuel and air mixture at the highest temperature which is usually in the range of 1000C- 1100C range which will melt most dirty fuels. 

Does anyone use exhaust gas re circulation to lower the bed
temperature burning pellets?

We had this on the Kob boilers which burned shredded furniture waste,
but generally did not need it with G30 woodchip on the adjacent
boiler.

AJH

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