Continuos flow drying with biomass

There’s quite a bit of interest on the various forums on the subject of Biomass and the RHI scheme. There is already widespread use of biomass in chicken sheds and commercial greenhouses but my system is for drying grain. Biomass is an ideal bolt on for floor drying systems and a number of people have already adopted it. My system however is on a continuous flow drier which has posed a different kind of challenge.

I have recently installed 2 x 490kW batch boilers.The main use for the heat produced is a modified Graintek 30t/hr tower grain drier. All the air entering the drier passes through 7 cores of heat exchanger that raises the temperature of the air to around 70 degrees. The system allows for drying with purely biomass, purely diesel or a combination of both.

The Grain drier pulls between 700kW and 1000kW depending on the exhaust fan speed and whether or not the drier is in Batch or Continuous flow mode. With grain at 17% moisture it runs at 25t/hr …at 24% moisture it runs at 6t/hr running purely biomass on continuous flow.

This year I dried 3500t. Most of it was below 17%. I used in excess of 200MW of biomass heat which is the equivalent of 18,000l diesel which equates to £12,000 of diesel saving and £10,000 RHI. I only used 1500 litres of diesel. All the drying with the exception of beans was continuous flow. I batch dried the beans (24% mc) and used 220kW/tonne. If I’d used diesel it would have cost £13/tonne whereas it cost £1.10/tonne using biomass.

I have a number of modifications to make to the system that will boost boiler and drier output and raise the air temperature entering the drier.

Hope this is of interest.

As far as I was aware @Robert Ramsay has one up in Scotland

Thanks for tagging me. Yes I have 900 Kw of straw powered bioboiler to run my drier.
I would say that with RHI it is a no brainer if you have someone running your drier. If you have to get someone to be there just to load bales then maybe less so. We find that we like to run the boiler 24 hours a day to keep up with the combine. I have not got figures to hand but you can PM me with a phone number and we could talk through it. We have an open day on December 5th.
http://www.eventbrite.co.uk/e/greenworks-2-tickets-9198634363

This year I dried 3500t. Most of it was below 17%. I used in excess of 200MW of biomass heat which is the equivalent of 18,000l diesel which equates to £12,000 of diesel saving and £10,000 RHI. I only used 1500 litres of diesel. All the drying with the exception of beans was continuous flow. I batch dried the beans (24% mc) and used 220kW/tonne. If I’d used diesel it would have cost £13/tonne whereas it cost £1.10/tonne using biomass.

That sounds interesting. What are you burning, and did you have any problems getting RHI?

I am burning a mixture of things but primarily Oilseed rape straw which burns far better than Wheat straw because the fire penetrates into the bale quicker and releases its calories faster. I also burn shredded pallets, slabwood, clearfell timber and chaff. It’s essential that the fuel is dry for maximum efficiency and less smoke. Fuel price ranges from £20/MW to £5/MW depending on how well I source a supply. The different fuels all have differing burn characteristics. Per kg they yield virtually the same number of kW but the speed with which they do it varies greatly.

Getting RHI accreditation for the grain drier went smoothly. Ofgem have had several applications for floor driers but this was one of the early ones as far as continuous flow was concerned and at the time of applying there hadn't been any other accredited. I believe there are now several continuous flow systems that have qualified from a variety of different installers.

The problem at the moment is that getting an emission certificate (necessary for RHI , post 24th September) for a large batch boiler is difficult. All the boiler manufacturers are having to develop smoke filtration systems to control particulate emissions. No certificate...No RHI

We have been looking at an on floor system, but had heard of potential emissions issues with the new RHI regs. Sounds as if it should still be possible but maybe at higher cost. I didn't realize it was possible to get the heat for continuous flow until your post. Is acid condensation an issue with osr straw?

Acid condensation is a concern although as yet I haven't noticed any ill effects but we are monitoring the situation. Dry fuel is the key. Barn dry OSR straw will be less problematic than wheat straw that has been exposed to the elements. John Seed of Topling Biomass and Robert Ramsay who has an Earthfire energy system will probably have more experience on the subject of acid corrosion.

Here are some photos of our recently installed 2 x 490kW, RKT Renewable and Plumbing modified Dragon boilers. The boilers are the standard Dragon D50 with the new double pass (9 tubes at 120mm) heat exchanger fitted with turbulators. RKT have also altered the air flow that allows for more gasification and greater high temperature combustion. The water flow within the boilers has been RKT modified ensuring that there are no “hotspots”, that in the past, have led to a drop in performance. RKT Renewable have also fitted heat recovery units on the flues which preheat the water entering the boiler





Each boiler is capable of producing 490kW. At times they produce more than this but due to the nature of a batch burning system there is a period at start up and wind down where the kW output drops off.





The blue tanks are expansion vessels. Behind them in the wooden box is the 45,000 litre insulated accumulator which is the distribution point for the Grain drier, houses and workshops. We try to maintain a temperature of 90 degrees in the accumulator when drying grain. This is difficult to achieve as water absorbs less heat from the boiler the hotter it is so we dramatically increase the flow rates of the water circulating as the temperature rises to avoid “boiling” the boilers.



The Drier is a Graintek. When full it holds 40 - 45 tonnes. It’s rated at 30tph but that all depends on moisture. The whole of the air intake side of the drier is boxed in and insulated. The oil burners are boxed around which allows the drier to be used conventionally as well as with biomass.



This show 3 of the 4 heat exchangers contained within the insulated box in the left hand of the drier. They are 7 cores thick. As stated earlier they deliver between 700kW & 1000kW depending on drier configuration and fan speeds. 70 degree air temp is achievable but we've a few modifications to make which will result in consistently achieving this temperature or possibly even higher.

When drying grain there is very little wasted heat from distribution losses as the drier uses the heat virtually the instant it is produced. Heat losses are significantly higher when the system is ticking over with the less demanding role of heating houses.

During grain drying, feeding the boilers is a labour of love as every 2 hrs they require re stoking. Each boiler takes 2 x 5’ round bales of rape straw. Each bale contains 500kW of energy. The drier operator (me) is kept busy! In winter, when it’s only the houses drawing heat, 1-2 fires a day are sufficient. Each fire produces 1MW of heat.

This past year our OSR crop failed and was pulled out so we had a shortage of dry OSR straw. As a result most of the high intensity drying was done with dry slabwood which, because of its large surface area, delivers the highest kW output per hour of all the fuels we use. I'd prefer to use straw for the holistic ideal of being self sufficient but have to recognise that other biomass fuels may be better suited but they require much more forward planning.

Like the idea of a biomass boiler to help drying on our floor stores.
Think 30kw fans drying 500 tonne floors. Currently use a diesel burner to lower humidity in poor summers but very expensive to run.
Also got a very ancient continuous flow dryer and hoping if I could use heat constantly on the air floors I be able to dry 2 batches of wheat and take pressure off the continuous flow dryer. To make better use of current drying floor seems a better option than building another drying floor or buying a mobile dryer.
Solar panels are helping to run the fan so biomass for the heat seems an attractive add on.
Anyone done this and recommend a company or particular boiler that is suitable and if they qualify for RHI.
Always seem to have excess of logs and waste wood on farm especially after winds this year.

Nitrams said:

Does anyone have experience with using a straw fired biomass boiler to provide heat for continuos flow drying? I want to work out how much heat (how high a temperature i can acheive ) using a certain size boiler. I know this is relative to air flow through the dryer but i dont know how to work it out nor do i know what the air flow is through the dryer.
Was hoping somebody out there might know of a similar system and could give there approximate results. My dryer is 20t.ph so for example i want to work out what is the maximum temperature i can acheive is through a 200kw /400kw and 600kw boiler.

Tia

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Worked in a place using the Biomass to dry biomass was filled 6 times a day with around 800kg of coppice and one smaller unit using 800kg of the dust when seperated.

was ok, but was a lot of work

Try looking at the Lin Ka range of boilers, Fully Accredited for Straw.
Andrew at Manco Energy

whose that 555? you never mention them before?

Why this obsession with biomass when the RHI on Solar is better than Biomass and no crazy emission rules.

http://www.agriculturesolar.com/3b_drying_process_of_solar_grain_dryer.html#.VCsg6RxuC84

You will need thermal solar to get the RHI but a solar wall can be useful if building a new grain store.

http://solarwall.com/en/products/uses-and-applications/agriculture.php

Manco energy, based just outside Market Weighton.
We have been into Biomass since early 2000. The Lin Ka range of boilers were originally designed to burn straw in Denmark. They are a duty boiler that likes to be worked hard, can do 8000hrs a year if needed! obviously would need to be looked after to achieve that. We have several systems up and running around the country, the changes last September were over come with the introduction of a new filtration system which is working well. Have a look at our web site, www.mancoenergy.com. Get in touch if this is of interest to you

Atomic SL said:

This year I dried 3500t. Most of it was below 17%. I used in excess of 200MW of biomass heat which is the equivalent of 18,000l diesel which equates to £12,000 of diesel saving and £10,000 RHI. I only used 1500 litres of diesel. All the drying with the exception of beans was continuous flow. I batch dried the beans (24% mc) and used 220kW/tonne. If I’d used diesel it would have cost £13/tonne whereas it cost £1.10/tonne using biomass.
.

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£13.00 a tonne in diesel costs to dry grain down from 17% ?
sure you don't mean £1.30 ?

The final part of the post above was referring to beans. Beans at 24% would have cost £13 last year. We had an accurate wet weight of beans and an accurate heat meter reading at the start and finish of bean drying. The heat meter recorded 220kw/tonne per wet tonne. Energy density of Gas oil is around 11kw/litre which is equivalent to 20 litres of diesel costing £0.65 = £13.00
It's a long and slow process drying wet beans. At that moisture you are looking at around 15% weight loss. That's a lot of water to evaporate. The worst we had the previous year was 38% for 3rd parties which was around 30% weight loss.

I agree that £13 is too high a price for 17% wheat but that wasn't what was posted.