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the village idiot

An Idiot's guide to Ancient Woodland management

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RETORT KILNS.

 

Retort kilns differ from ring kilns in two fundamental respects. Firstly, in a retort kiln the fire used to fuel the process doesn't come into direct contact with the wood you are trying to convert. Secondly, a retort kiln 'recycles' the flammable wood gas released by the converting wood, feeding it back into the fire to produce a self sustaining loop.

 

This 'gas capture' system results in a retort kiln being not only significantly more efficient but also dramatically less polluting. Un-burned wood gas, which can billow for hours out of a ring kiln is not nice stuff.

 

There are a few different designs of retort kiln, though really only two or three serious manufacturers in the UK that I know of. The two types that I am most familiar with are the Exeter Retort which has a long firebox underneath the charge chamber but isolated from it, and the Pressvess Retort which often has two charge chambers side by side with a separate firebox between the two. They essentially work in a very similar way. I'll describe the process involved with the Exeter as this is the kiln that I have.

 

I purchased Puffing Billy in 2012. It was the second machine off the production line. Stubby's mate Alan Walters has the first. For those of you paying far too close attention you will have noted that this was before I had started in the Wood. My first forays into retort charcoal production took place at the farm where I was working on the ice cream. Ice cream and charcoal are not easy bedfellows and I was continually having to go for a scrub up.

 

These pictures of Billy were taken at the farm:

 

1565422551_retort2.thumb.jpg.c7a1fb088ebce3cbf0e14d9f5af2b53a.jpg

 

1344323059_retort3.thumb.jpg.cb03d68d48407d61a88f972b8214ef16.jpg

 

As you can see from the picture above, the Exeter Retort is composed of an inner 'charge chamber' where you put the wood you want to convert, and an outer chamber that surrounds all the gubbins. The outer chamber has a double skinned wall filled with insulation. The ash at the bottom shows the front end of the firebox, this is accessible when the kiln is closed up through a hatch in the outer doors.

 

The eagle eyed among you will be able to make out three structures on the top of the kiln in the top picture. All three are chimneys. The tall one in the middle is the flue for the firebox. The two either side are plumbed directly into the inner charge chamber and allow the water vapour from the charge wood to escape.

 

To operate the kiln you fill the inner chamber with as much wood as you can fit into it, preferably much more efficiently than I have managed in the photo example! The Exeter retort can be loaded from both ends. The charge chamber is then bolted shut. The doors are sealed with large diameter fire rope. The outer doors are then also bolted shut and the chimney caps removed from the two short chimneys.

 

You are now ready to start the burn. The process begins by lighting a fire at both ends of the firebox. There are hatches each end of the insulated outer doors to enable access. You keep feeding the fires with very dry wood (I used free pallet tops from a local office supplies firm). After a few minutes the fire extends the full length of the kiln.

 

The fire feeding continues for about 2 hours, at this stage in the burn the two small chimneys are belching out copious amounts of very white and cloud like water vapour, even with very seasoned charge wood.

 

1705491798_retort4.thumb.jpg.6b26f4f26d0e4ab2a000f394ca68a7ce.jpg

 

 

After about 2 hours the water vapour starts to take on a yellow tinge. This is a sign that the charge wood is running out of moisture and starting to emit wood gas. Wood gas is highly flammable stuff and not to be wasted, so when the emissions become predominantly yellow the two chimneys from the charge chamber are capped. This diverts the wood gas via two tubes directly to the firebox underneath. From this point on the conversion process is entirely self sustaining. The kiln runs off it's own juices.

 

The amount of energy stored in wood is phenomenal. The two gas pipes literally roar with intense flame sometimes for up to 8 hours. Left alone during this phase the internal temperature of the kiln would sky rocket and melt the retort. It is the charcoal maker's job to keep the internal temperature at around 550 degrees C. This is achieved very easily by tweaking a butterfly valve in the main chimney leading from the firebox, or opening and closing the firebox doors. There is a digital thermometer mounted on the side of the retort for monitoring the temperature of the flue gasses from the charge chamber. This gives a good approximation of the temperature of your converting wood.

 

When the gas peters out the conversion is complete. The kiln is shut down by closing the outer doors and the butterfly valve, and all you can do then is wait for it to cool down and eat your beautifully toasted savoury snack which has been warming on the thoughtfully included pasty shelf. (No extra charge)

 

To be continued...

 

 

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1 hour ago, The avantgardener said:

I sat through a FC meeting regarding woodlands in the South East shortly before the opening of the Black Hole at Sandwich.

The guy showed a map of the wooded area in total, it covered a vast area in green, he then superimposed a blue map showing all the woodlands without any form of management plan or rotation, it covered more than two thirds of the green.

I have discussed putting a management plan together with a few woodland owners/farmers near me over the years, most are happy to leave it as it is as they think it is good for wildlife, the others think that their wood is worth its weight in gold, with all the cutting costs, extraction costs, haulage etc sometimes wood isn’t worth its weight in wood!

 

 Quite a high percentage of unmanaged woodland is used by their owners for shooting. Management works like the ones I have been describing make fantastic habitat for game birds and vastly improve the lines of sight for gun stands.

 

One way to get an 'in' might be to pitch the benefits to their favourite sport. I would think that a marvellous day's shooting is as good as money in the bank for a lot of land owners.

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Just a quick flash forward to a couple of pictures from today. 

 

It was a lovely morning when we first got to the Wood:

 

morning.thumb.jpg.9307ed37769f2f134be8874bd2c83c12.jpg

 

 

We are coppicing Ash in a compartment at the moment. This picture will give you an idea of the sort of size a lapsed coppice Ash can get to.

 

Steve is not a small chap.

 

920608783_ashstool.thumb.jpg.6a3dd864aa739e04b93cf405fe5d503f.jpg

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8 hours ago, the village idiot said:

Just a quick flash forward to a couple of pictures from today. 

 

It was a lovely morning when we first got to the Wood:

 

morning.thumb.jpg.9307ed37769f2f134be8874bd2c83c12.jpg

 

 

We are coppicing Ash in a compartment at the moment. This picture will give you an idea of the sort of size a lapsed coppice Ash can get to.

 

Steve is not a small chap.

 

920608783_ashstool.thumb.jpg.6a3dd864aa739e04b93cf405fe5d503f.jpg

Are you coppicing the lapsed stand in the photo, and if so do you expect it to regrow? We have a few lapsed coppices the same size but are hesitant of coppicing as concerned they won't survive.

 

Enjoying the thread and the nice structure to your posts. A mix of first half educational then second about your own experiences. Would make a good book/memoir perhaps.

 

 

 

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3 minutes ago, Lucan said:

Are you coppicing the lapsed stand in the photo, and if so do you expect it to regrow? We have a few lapsed coppices the same size but are hesitant of coppicing as concerned they won't survive.

 

Enjoying the thread and the nice structure to your posts. A mix of first half educational then second about your own experiences. Would make a good book/memoir perhaps.

 

 

 

Thanks Lucan,

 

You raise a very valid point. Ash stools of this size sometimes don't regenerate after being cut. We will take the risk as if we don't coppice it will not be too many more years before these stems fall anyway under their own weight. This cleaves the stool open and often kills the tree.

 

We are also in the epicentre of the Ash dieback outbreak. I have not seen an Ash in this Wood in the last two years that isn't on it's way out, and we have a lot of Ash! We will leave a certain percentage of stools as standing dead wood for habitat but the vast majority will be coppiced assuming we can get to them in time.

 

We are not certain that we will lose pretty much all of our Ash but the omens are not good.

 

The firewood that the felling generates will help to fund our activities to keep the Woodland thriving in the wake of Chalara.

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It's the same where I cut my hazel. 80% of the woodland is ash and there's not a single one that isn't showing signs of die-back. At this time of year you can stand back and clearly see the proportion of ash and without them it won't be a wood any more, just scrub land.

Unfortunately the owners of the woodlands have no management plan, other than to fill the place with pheasants and keep enough rides open to ride their horses. They aren't felling or thinning and I doubt they'll even bother to make use of fallen ash. It'll just be left to rot. 

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Excellent thread and great pictures VI.. Thanks for taking the time to put it together, really interesting.
We’ve lost a few mature oaks at our place. This has inspired me to pull my finger out and do some replanting in the spring. Hoping to get a couple of packs from the Woodland trust. Cheers.

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15 hours ago, the village idiot said:

Just a quick flash forward to a couple of pictures from today. 

 

It was a lovely morning when we first got to the Wood:

 

morning.thumb.jpg.9307ed37769f2f134be8874bd2c83c12.jpg

 

 

We are coppicing Ash in a compartment at the moment. This picture will give you an idea of the sort of size a lapsed coppice Ash can get to.

 

Steve is not a small chap.

 

920608783_ashstool.thumb.jpg.6a3dd864aa739e04b93cf405fe5d503f.jpg

I'm very jealous of your "office"...

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5 hours ago, Gimlet said:

At this time of year you can stand back and clearly see the proportion of ash and without them it won't be a wood any more, just scrub land.

 

Don't write off scrub; it's not a halfway house, it's a habitat in its own right.

I'm teaching Granny to suck eggs by telling you of all people, I know; I'm just trying to make the point that 'scrub' isn't a dirty word!

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