Woodchip Handling
Nick,
I would do some feeding / pneumatic conveying tests with the woodchip material. If these prove successful you could consider receiving the woodchip material in a tipping tanker. That would make the unloading / silo filling process very easy indeed.
Regards,
Dennis Hauch ■
Woodchip Handling
Nick,
Bulk woodchips are typically handled by open tipper truck, 40 to 50 cu.m (or more) capacity, and delivered to a "walking floor" which feeds the material to a screw conveyor. This does not seem practical in your case. If you are able to arrange for the material to be delivered by pneumatic tanker, that is probably the best solution (unloading by pneumatic conveyor into a silo). Your ideal solution depends on how you are able to arrange transport. Some discussion with transport companies who handle waste products would be a good place to start.
Don't forget, storing the material in a silo is going to raise other problems for you. The manufacturers who use wood chips for particle board and MDF have to go to a lot of trouble to get the stuff out of silos. There are no simple, inexpensive solutions for this issue.
I have lots of experience here. Please let me know if you need more info.
Good luck,
Michael Reid. ■
Re: Wood Chip Handling
Dear Nick,
It would be better if you could inform the height and diameter of the storage silo. Also, the unloading capacity in tonnes/hr or time interval for unloading of the truck of specific capacity. What would be the weight of one piece of chip or its thickness and width, so as to judge its suitability for type of conveying.
Regards,
Ishwar G Mulani.
Author of Book : Engineering Science and Application Design for Belt Conveyor
Email : parimul@pn2.vsnl.net.in ■
Re: Wood Chip Handling
Dear Nick,
I gather from your description that you have not, as yet, installed silos behind the schools -- and that your primary objective is minimize the unload time from the delivering carrier to storage. If so, a simpler answer may be to use a block (in your case English stone) building that the delivery vehicles can drive up to and dump directly into the top. The wood chips can then be moved to a chute to feed the boiler by a front end loader. Alternatively, a belt system to move the chips from storage to the boiler can be used, if you install a gate system under the storage pile.
Naturally, there are other alternatives.
Regards, ■
Wood Chips
Don't forget the potential of heat generation in storage, especially near a school. ■
Re: Wood Chip Handling
Listen closely to what Mike R. has to say. As plant engineer I have been dealing with wood waste/chips from plywood, sawmill, OSB for over 30 yrs and will 2cd the fact that storing in a cylcone with a tapered cone at bottom is asking for grief. Is it a homogenious mix or random with sawdust/flakes/chips. Any bark thrown in for good measure? How uniform are the chips? Best bet is no cone, altho manufacturers sell them, there are better ways to go with straight side wall storage. If storage is small enough, even a screw feed out would be much better than tapered cone. Have fun!
Must be old age, wanted to say silo not cyclone! ■
Hopper For Wood Chips
Re - Feeding Wood chips
As many of the contributors have said, the awkward flow properties of wood chips can give rise to flow difficulties, with serious arching, piping and rathole formation problems. Cones are just about the worst shape for flow, although convenient for strength and fabrication. The basic design impediment in this application is that the shear strength of this type of material grows very rapidly with compacting stress. There is an associated difficulty in that the description ‘wood chips’ is totally inadequate to define the product and its shear strength is subject to wide variations according to its composition and condition. Both these obstacles to determining a suitable hopper design are compounded by the elastic nature of the material in bulk form.
The problem is not insuperable, but is not to be taken lightly. The most effective route is to employ a container that exploits Vee section flow channels with Sigma-two relaxation of the end walls and insert technology. This construction allows the flow channel to diverge slightly in one plane whilst converging in the other. The effect is to reduce the confining stresses and facilitate minimum converging wall inclinations to be used and flow to take place through the minimum possible width of opening. Although this technique is not as effective on materials that have a very high value of internal friction, it still counters the end-wall effect of a plane flow channel and offers a weaker region for failure than the normal wedge shape. Measurement of wall friction values with different contact materials and surface finish also permits an optimum selection to be made of the contact material for the construction of the walls.
At this point it should be recognised that in certain regions it is advantageous to employ contact surfaces that have a high frictional value and flow obstacles, whilst in other locations the lowest friction value possible is needed. This is because high resistance to slip and flow where flow is not a problem will reduce the flow over-pressures lower down in the stored contents, where the span of the flow route is less. The profile of the flow surfaces is established from measured wall friction values, to determine the wall inclination needed for mass flow and that for self-clearance, for where these modes of flow are appropriate.
The next stage is to find the critical arching span for the material at differing conditions of relatively low consolidation pressures and time storage, if time effect are found to be relevant. It should be noted that a Vee hopper is not able to sustain a stable ‘rathole’ if live flow is generated over the full length of the outlet slot. A key feature of the installation is that inserts are used to control the maximum over-pressure that can develop in the flow channel, and therefore limit the span over which a stable arch can form. The design and placement of inserts can then be evaluated from the determination of arching potential at different heads of storage. The overall design can then be firmed up from this data, to accommodate any cross sectional area required. All that remains it to fix the length of the outlet, in an interactive exercise with the setting of the cross section of the container, to secure the total volume of storage that is required for the installation.
Well, almost all that remains. It is still necessary to install an extraction device that will guarantee to generate live flow over the total cross section of the outlet slot. A well-designed screw feeder can develop this pattern over an axial length of up to about ten diameters of the flights, but an aspect ratio of eight to one is a more conservative working figure. Two or more screws can be used to give a wider opening than obtained by a single screw, but the use of multiple screws can lead to very high over pressures and large torques on the screw drives.
The reason for referring earlier to the slope of the wall inclination needed to affect self-clearing is that a mass flow channel is not necessarily the best form of flow channel in these circumstances, in fact in some regions is best avoided. The gain of width of the container within a given height is achieved far better, and reliable flow more effectively achieved, by inserts that form twin unconfined flow channels to an orifice slot, than with a mass flow channel that induces high passive converging stresses on the flowing bulk.
The design sophistication of this approach should not suggest that the constructional cost is more expensive than a conventional ‘brute force’ approach in fact it should be less. The development of an effective design does involve more thorough and experienced ‘up-front’ attention and costs, but offers considerable more interest and satisfaction, with eventual cost savings, over crude designs such as using vertical or diverging hopper walls with a full ‘live-bottom’ design that employs multiple screws. The nature of the material demands that special attention is inherent in securing a solution and this must cost more than a storage device for a free flowing material. There is nothing more expensive than plant that does not work and the overall viability of the plant must be verified by the total economics of the undertaking. If the installation is to be repeated for many locations, I would suggest that it is well worthwhile undertaking a professional approach of this kind, with start-of-art technology. All you really need to do is find your expert with whom you can work closely. ■
Wood Chip Handling
Two companies in Europe design and install silos for handling wood chip, and other difficult materials, SHW and Saxlund. Their equipment is used extensively in particle board and MDF plants world-wide.
If you need to know how to store and retrieve wood fibre, don't try to re-invent the wheel, contact them.
Michael Reid. ■
Re: Wood Chip Handling
I think the problem here is one of scale. As Michael Reid has said companies like SHW, Saxlund, Redler and many others have established equipment for handling wood chips, sawdust, wood waste and similar products. However such equipment is normally used in particle board plant and now in biomass power stations, operations which are much larger than that which would be required for a school in the UK.
Because of the well known poor handling and storage properties of these materials the necessary equipment is not cheap. Just because the handling rates and storage capacities for a school would be low it is not easy to shrink down the size of equipment necessary. The capital cost for school installations must be a major consideration in the current UK economic climate.
Also, there is the question of operation and maintenance. Gas or oil fired boilers are relatively simple to run and maintain as handling and storage problems are minimal. This is not the case firing boilers with wood chips. Even ignoring the ash collection and disposal, the reception, storage and handling of wood chips etc will require significantly more attention. Remember just one piece of tramp material cam wreck havoc with the handling equipment, will the wood chips really be free of tramp? Is the necessary labour to look after the plant available at a school?
Overall I wonder if such schemes are actually viable in the long term for such small scale installations. ■
Wood Chip Handling
Nick,
I remember a small pneumatic conveying system I designed for a client who wanted to receive corn grits via bulk bags. It might be suitable for your scheme.
There was a small hopper, rotary valve, injector and blower all mounted on a skid for moving about by fork lift truck.
Bags (one cubic metre) were lifted off the transport truck by the fork truck using slings and suspended over the hopper. The bottom discharge sleeve was opened to allow the contents to flow at a controlled rate. The discharge from the injector was connected to a 30 m. vertical pipe riser (100 N.B) to the top of a silo and discharged via a cyclone. The horizontal to vertical connection was made by 100 N.B rubber hose with Camlock couplings.
The system was designed for 6.8 tonnes/h and operated at 0.225 bar.
The point made by Designer is a very good one. How feasible is it to build a system like this considering the low volume and low rate of utilisation? Is it a demonstration for use of renewable energy? It can hardly be an economic proposition.
Michael Reid. ■
Re: Wood Chip Handling
From my experience of big bags with bottom discharge sleeves I would have to regard them as a non-starter with wood chips. To sucessfully use such bags the material in the bag has to be reasonably free flowing and wood chips are anything but free flowing. I have seen wood chips produce an arch over a 12 ft diameter.
The use of 'one trip' big bags might be possible, but would require that the entire bag bottom is cut so the chips can discharge in one mass into a suitable reception unit. This then leaves 1-2 m3 of wood chips to be fed into the conveying system (which could be mechanical or pneumatic). This is not an impossible task, but overall the system would require a significant labour requirement and the use of 'one trip' bags will increase the costs.
Maybe one way to do this would be to use bespoke trailers fitted with self-discharging equipment, e.g. a walking floor. Two trailers could be left on site and used as storage then as the first emptied the second would start discharging and a third would brought in to replace the first. The discharged wood chips could then be fed directly to the boiler.
This thread has produced some interesting discussion points. ■
Re: Wood Chip Handling
Live Bottom Screw Bin.
It has been our experience that a screw feeder sized appropriately for the material has proven very efficient is feeding wood chips. We have manufactured a variety of sizes including one of the largest in the world with 48" diameter screws.
Attachments
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Wood Chip Handling
Thanks Peter Brown. I repeat my earlier suggestion about talking to waste transport companies. This is the way I have solved the problem in reverse, removing wood waste from small manufacturing plants via RORO bins with hydraulic spreaders. The waste went to landfill in this case, dumped through rear doors of the bin.
Michael Reid. ■
Wood Chips From Bulk Lorry
I would suggest to use a pneumatic suction/pressure system.
Any other mechanical system will give a lot of dust to the environment.
We can offer new and used diesel and electric driven units.
We also have a used woodchip furnace (1 MW) in stock.
Jur Lommerts
Jansen & Heuning Bulk Handling Systems
The Netherlands
www.jh.nl
jfl@jh.nl
tel: +31 50 3126 448 ■
Re: Wood Chip Handling
Will a pneumatic system for handling wood chips really produce less dust than a mechanical system? Screw conveyors and chain conveyors are totally enclosed as is their inteconnecting chutework and any storage bin. You just need a small bin filter/vent unit to clean the displaced air from the bin.
With a pneumatic handling system you are mixing the wood chips with a lot of air to start with, then you need a much bigger filter unit to clean not only the displaced air from the bin, but also all the air used for conveying.
You also need a lot more power for pneumatic conveying than mechanical conveying, but of course pipe runs are simple compared with screw and chain conveyors. ■
Wood Chips
Re: Wood Chip Handling
Emptying the truck, yes with wood chips that's the problem. But it's the same problem if you convey pneumatically or mechanically.
Do you use a truck with a tipping trailer, park your truck on a tipping platform, or use a truck with a self discharging trailer?
This a school in the UK. I doubt the've too much money to spend so I can't see them using a tipping platform, but they won't have much labour around to help with the truck unloading either. So they will want the operation reasonably automatic. But automatic costs money ......... I feel 'Catch 22' coming on! ■
Wood Chip Boilers
your best bet would be to investigate the use of wood pellets, rather than wood chips. Pellets are far superior, their supply is not difficult and there are a variety of manufacturers of suitable boiler and feed systems. ■
Re: Wood Chip Handling
Good bit of lateral thinking by Richard.
For something really radical maybe there's someone who would contract to supply the pellets, the storage and handling equipment, a specialised boiler if necessary and service and maintain it all.
This concept is gaining ground as it free's the end user from having to justify capital investment. You 'rent' the equipment and it's maintenance and the supplier guarantees it's availability. The whole thing becomes an annual expenditure that you know in advance, with no sudden costs for replacement parts or getting a guy in to repair breakdowns. If a number of schools in the same area joined the scheme it might even pay someone to invest in a plant to produce the pellets if there were none available. ■
Re: Wood Chip Handling
Dear Nick,
You have had many suggestions regarding the method of delivery of woodchips to your boiler firing application, however I would be pleased if you would take the time to consider an innovative solution. Mikalen is a manufacturer of special side tipping containers (ISO standard) designed specifically for the transportation of wood chips by road and rail. The concerns other writers have had about the handleability of woodchips does not exist with these units since the whole floor of the container opens to discharge the contents.
These Tiltainers will be transported to the point of delivery by side-lifter and left on site to become the storage hopper. The devices themselves can be 30-60m^3 capacity depending on the container size you may require, the transport vehicle hydraulics will open the floor to allow the chips to enter the boiler feed system. Once the contents of the container have been consumed, the transport vehicle will return with a full container and swap it for the empty.
We will need additional info regarding the method of fuel injection into the boiler so that a viable proposal can be worked out for you to consider. Please visit our website (www.mikalen.com) to review the principle of operation.
Regards
John Hanna ■
Re: Wood Chip Handling
Dear Nick,
With all the possibilities and problems listed I believe that your simpliest method of resolving the issue is to use gas or oil fired boilers. These have the advantage of greatly reduced delivery costs and little maintenance requirements.
Regards, ■
Re: Wood Chip Handling
Many thanks to everyone for your suggestions/concerns and general good advice, much appreciated.
I particularly like the irony of Dave Miller's latter comment of choosing oil or gas: this is part of a renewable energy Project! :-)
We have been in contact with several contributors, some of which were of particular interest for when the scale of demand increases in the future.
Once again thanks, a very useful forum, we will try to let you know how our system evolves.......
Regards, Nick. ■
Re: Wood Chip Handling
Nick,
Just one final point, as you're in the UK and we have just passed the 1st July 2003, the Dangerous Substances and Explosive Atmospheres Regulations are now in force so any system you consider will have to conform to these regulations.
This is because wood dust mixed with air has the potential for producing an explosive atmosphere.
Just one more thing for the melting pot!! ■
Atex
Thanks Peter, I think you're refering to the ATEX Directive?
Yeh, we'll have to check-out its implications! Thanks. ■
Re: Wood Chip Handling
The Dangerous Substances and Explosive Atmospheres Regulations 2002 are the UK regulations that implement the European ATEX directive. Guides to ATEX can be found at
http://europa.eu.int/comm/enterprise...uide/index.htm
and
http://www.dti.gov.uk/strd/strdpubs.htm#exat
The Statutory Instrument is at
http://www.hmso.gov.uk/si/si2002/20022776.htm#1 ■
Wood Chip Handling
We manufacture briquetting equipment and these equipment turn loose wood chips of different sizes into compact-easy-to handle- briquettes, which can be transported/stored like logs.
Contact us with more details for full assistance.
Aswath Mohan Prabhu, mizun@bol.net.in ■
A Creative Non Conventional Approach
THINK about using a STONE SLINGER truck.....it would deliver the chips very quickly and will actually deliver them to a specific point by hydraulically controlled deliver conveyor system at the back of the truck.
George ■
Stone Slinger
Thanks George, any particular manufacturers you could point us towards? ■
Manufacturers......
contact an outfit that makes these devices:
DAHMS MFG LTD
ST Jacobs, Ontario
CANADA
The make a STONE SLINGER TRUCK for many years.
You will have to go thru information to get phone numbers etc.
Regards, George Baker ■
Wood Chip Handling
You may wish to consider our DSI Snake Sandwich high-angle conveyors to continuously elevate your wood chips. Our system hugs the wood chips gently yet firmly between smooth surfaced rubber belts. The material quality is preserved and the material is elevated efficiently with very low power consumption. Please visit our web site for more on our DSI Snakes. At the home page also click on the "ftp site" where you will find various fliers (in pdf format). I direct your particular attantion to the flier "Wood Chips-No Cost Solution".
Joseph A. Dos Santos, PE ■
Pellet Equipment
Hi, you could also check PelletBase for equipment suppliers, it has literally hundreds of suppliers listed. You can visit here: http://www.PelletBase.com ■
Re: Wood Chip Handling
Dear Nick,
You have had 30 replies to the question you raised 4 years ago and they are still coming. My question is what di you build and did it work? ■
Woodchip
Nick, have you considered converting your woodchip in pellets. Woodchip can be difficult to conveying and also difficult to discharge from silo/storage vessel. One option would be to convert the chip mateial into pellets to improve its flow characteristics ■
Re: Wood Chip Handling
Nick,
We currently ensure the supply of wood chips to furnaces by means of self-cleaning containers. The container is serves to collect, transport, store and supply the product, without any in-between handling operation. This saves the need for costly storage and reclaiming equipment. Please look through your files, as we previously met at a biomasse show in Lons-le-Saunier (or Mulhouse) some years ago. I would be glad to show you some refence projects in Burgundy
Jean-Claude Poncet
Silexport International
jcp.silexport@wanadoo.fr ■
Re: Wood Chip Handling
Hey you guys... If you go to http://www.nottinghamshire.gov.uk/ho...y/woodheat.htm you will find that this project was built 3 years ago!!!!!
How's about closing discussion.. Moderator where are you? ■
Re: Wood Chip Handling
This link gives a better description of the plant at Garibaldi School.
http://www.greenspec.co.uk/html/prod...inder2RRK.pdf.
It would be nice if nick.monether gave us some direct feedback of experiences now that the plant has been operational for some years before anyone closes the discussion. ■
Re: Wood Chip Handling
Dave,
it appears that wood fuel is contemplated for a few thousand schools in England. Garibaldi was a first but the subject may be far from closed.
Jean-Claude ■
Re: Wood Chip Handling
Originally posted by Silexport
Dave,
it appears that wood fuel is contemplated for a few thousand schools in England. Garibaldi was a first but the subject may be far from closed.
Jean-Claude
That may be so, but it has been 3 years since Nick posted a comment (coincidence?) and he has been asked for feed back so what is the point of continuing discussion? I suggest that if you feel there is a possibility for business you contact him direct, he has left his Number on the posting. ■
Wood chip handling
We are retrofitting small sites (schools) with wood fired boilers and need a pragmatic solution for fuel delivery & storage.
One route is standard agricultural silos filled by 'big bags'. This will be time consuming and not ideal.
ro-ro bins appear expensive for this application.
Does anyone have experience of augur / elevator / other means for rapid delivery of woodchip from bulk lorry to silo?
woodchip c. 30mm, mc 20%
Appreciate any advice offered. ■