Alternative fuel for gasser

[Mushroom Man]

Last year I burned between 10 and 12 cords of hardwood to heat 5800 sq.ft and DHW. That is a lot of cutting, hauling, bucking, splitting, stacking and loading. Good exercise but very time-consuming. I have enabled or am enabling changes to reduce that load by 30-40%

I've been researching alternative biofuels for gassers too. What I have discovered is that wheat straw (for example has 19% more btus than hardwood of the same MC. A gasser with big storage can take advantage of the more irregular burning cycle (fast hot).

I have a steady supply of spent mushroom substrate, which is mostly wheat straw, to use as a fuel. It needs to be processed (re-chopped and dried, then compressed) into a biolog. The plan is to create 14 lb. logs. By my calculations and estimated design heat load, I'll use 9-10 logs per evening and that should carry me through the night and next day.

One concern that I have is corrosion of the boiler. Many biofuels like switchgrass, miscanthus, and waste straws are high in chemicals that can react in a low oxygen environment to create corrosive elements. Chlorine is one of the chemicals. I think the resulting compounds are salts. Apparently, smaller amounts of these elements are present in the gasification of wood too, but the amounts in wood are sufficiently small to be of little concern.

Senescence of the biofuel materials (leaving it standing in the field through winter) reduces the chemicals to the levels present in hardwood. The rains and snows leach out the chemicals that cause the problem. Somewhere, don't ask me where, I read that soaking the biomass in 50-60 degree Centigrade water has the same effect as senescing the biofuel. Our straw is pasteurized in 60C degree water to kill pathogens prior to innoculating with spore laden grain. Problem solved maybe?

Were it not for my concern for the boiler corrosion, this fuel would be a good answer to my fuel needs. It is a waste product and by my calculations is (likely) available in sufficient quantity for heating of house, barn and domestic hot water.

If anyone knows much about the chemistry or what in the biofuel might cause corrosion problems, I would appreciate your input.

 

[jebatty]

What I have discovered is that wheat straw (for example has 19% more btus than hardwood of the same MC.

I would appreciate a reference on this. My understanding has been that all cellulose-based, natural biofuels of the same MC have about the same BTU content per pound. Data that shows differences would be useful to know.

 

[Mushroom Man]

http://www1.agric.gov.ab.ca/$department/deptdocs.nsf/all/eng3127

Flax straw is even better according to the attached article. I cannot vouch for the accuracy of the information.

 

[Piker]

With most of the gassers on the market these days, you will find that alot of the grassy biomass doesn't work so well, corrosive issues aside. Two reasons... one is that it has such a high ash content compared to wood, maybe 7 or 8 times the ash content, and two, it doesn't produce coals very well. In a downdraft gasifier, coaling is very important... it's natures renewable refractory, and it's very effective. A high ash producing fuel will work for a while, but the ash will quickly build up and insulate the fire and any coals that might exist from the refractory... and gasification will ultimately come to a screaching halt. Even a mix of grassy biomass with cordwood presents problems in this area of ash production. You might get by with say a 10% mix, but you will also have significant increase in cleaning.

Biomass btu/lb numbers do vary. Resinious woods from conifers is actually around 9000 btu's per lb - dry.

We have started using Bio-Brick made from compressed sawdust and wood chips. They are more expensive than firewood, but still cheaper than fossil fuels... at least while demand is down. There are some significany benefits from this product like ease of use, space requirements, and lack of bugs, critters, etc, that make the product marketable. Not to mention 5% moisture content. They do not coal like firewood, but you can burn them successfully by themselves in a downdraft, though I always recommend placing a few pieces of wood on top of the fuel load in the upper chamber to leave some coals behind for relighting.


cheers

 

[DaveBP]

Perhaps the key is to design a boiler with a burning chamber specifically for straw. These guys think they have done it.


http://www.herlt-holzheizung.de/engl/HSVE.html

Now, whether a boiler made for straw can efficiently burn cordwood also is another question.

 

[Dune]

What about using the waste staw in a methane digester, then running a water cooled generator on methane for combined heat and power? Make use of existing technology.

 

[Mushroom Man]

Biomass (straw, miscanthus and switchgrass ) interest is increasing. I am not alone. And yes, it has a higher ash content but you cannot burn and not expect some work to be associated with it.

In a phone conversation with the proprietor of New Horizon Corp. a major gasification boiler vendor in Vermont, I learned that many biomass processing units were being showcased at a Polish tradeshow that he recently attended.

Zenon indicated that I was not alone in wanting to use my gasification unit for biofuels rather than cord wood. He thought straw would be a good fuel in the EKO60, especially with storage.

When I mentioned the corrosives produced by gasification in the presence of chlorine, he indicated that the corrosive element created was hydrochloric acid.

I learned via google that the corrosive qualities of hydrochloric acid on steel in the presence of high heat is truly frightening (for a boiler owner).

But I also read a paper that discusses a remedy. Here is the conclusion:

Results obtained from both electrochemical methods showed that the Prunus cerasus juice acts as
an inhibitor for corrosion of steel in hydrochloric acid media. Corrosion inhibition action of Prunus
cerasus juice increased as its concentration increases. Inhibition of steel in HCl solution by Prunus
cerasus juice is attributed to adsorption of the phytochemical compounds in this juice. The reduction
of corrosion inhibition efficiencies by increasing the temperature, may be due to thermal degradation
of its organic content especially degradation of anthocyanine pigments.

Here is the article link:
http://www.electrochemsci.org/papers/1020092.pdf

By the way, Prunus cerasus is sour cherry.

A 4% solution if temperatures are below 85*C should suffice. Now I need 2 gallons of sour cherry juice. There are two trees in the yard but I don't know if there is enough fruit to produce 2 gallons.

The next challenge will be drying the spent substrate and then compression into 6"X20" logs (that hold together). Wish me luck!

 

[jebatty]

Are you considering alternative fuels just for the fun of it, do you have an economical supply and storage for the alternative fuel, or are you in an area where firewood is not available at reasonable cost but an alternative fuel is? I was in Sault Ste Marie, Ont, just a few weeks ago, for a forestry conference, and firewood scavenging in logged Crown lands was indicated to be available. Round wood is so easy to obtain, store and use where I live that it would make no sense to even consider anything else.

 

[Mushroom Man]

In answer to your question Jebatty, I have a continual supply of straw that is waste from our mushroom operation. If I don't burn it, I will have to dispose of it in another way. At first blush, composting seems like the best use of the material but the spore and competing organisms load creates a high contaminent potential for developing mushrooms. My preference to use it as fuel is driven by several factors:
1. wanting to rid myself of a waste product
2. wanting to save time
3. wanting to save money
4. reducing risk to life and limb

 

[leaddog]

Biomass (straw, miscanthus and switchgrass ) interest is increasing. I am not alone. And yes, it has a higher ash content but you cannot burn and not expect some work to be associated with it.

In a phone conversation with the proprietor of New Horizon Corp. a major gasification boiler vendor in Vermont, I learned that many biomass processing units were being showcased at a Polish tradeshow that he recently attended.

Zenon indicated that I was not alone in wanting to use my gasification unit for biofuels rather than cord wood. He thought straw would be a good fuel in the EKO60, especially with storage.

When I mentioned the corrosives produced by gasification in the presence of chlorine, he indicated that the corrosive element created was hydrochloric acid.

I learned via google that the corrosive qualities of hydrochloric acid on steel in the presence of high heat is truly frightening (for a boiler owner).

But I also read a paper that discusses a remedy. Here is the conclusion:

Results obtained from both electrochemical methods showed that the Prunus cerasus juice acts as
an inhibitor for corrosion of steel in hydrochloric acid media. Corrosion inhibition action of Prunus
cerasus juice increased as its concentration increases. Inhibition of steel in HCl solution by Prunus
cerasus juice is attributed to adsorption of the phytochemical compounds in this juice. The reduction
of corrosion inhibition efficiencies by increasing the temperature, may be due to thermal degradation
of its organic content especially degradation of anthocyanine pigments.

Here is the article link:
http://www.electrochemsci.org/papers/1020092.pdf

By the way, Prunus cerasus is sour cherry.

A 4% solution if temperatures are below 85*C should suffice. Now I need 2 gallons of sour cherry juice. There are two trees in the yard but I don't know if there is enough fruit to produce 2 gallons.

The next challenge will be drying the spent substrate and then compression into 6"X20" logs (that hold together). Wish me luck!

In reading the paper It sounds like you need to have the cherry juice in liquid form and I don't know how that would work as you burn it but cherry pits are available here in Michigan by the truck load and maybe they could be mixed in with the straw and help.
Some people burn them instead of pellets and they have high btu's. they cost almost as much as pellets by the time you have them dried and bagged but if you weve to haul your own and dried them your self they might work out for you. Dried ones in bulk here were $150 ton durring the heating season but at the canning co. in June they are free in bulk form.
leaddog

 

[jebatty]

Mushroom Man -- makes cents to me -- hope you can get it to work; will wait to hear the outcome.

 

[renewablejohn]

In answer to your question Jebatty, I have a continual supply of straw that is waste from our mushroom operation. If I don't burn it, I will have to dispose of it in another way. At first blush, composting seems like the best use of the material but the spore and competing organisms load creates a high contaminent potential for developing mushrooms. My preference to use it as fuel is driven by several factors:
1. wanting to rid myself of a waste product
2. wanting to save time
3. wanting to save money
4. reducing risk to life and limb

Your answer could be to sterilize your spent mushroom compost by torrefication and then the remaining charcoaled product can be turned into briquettes with a heat equivalent to coal. Your corrosive straw gas is also eliminated by the torrefication process

 

[woodsmaster]

If it works out maybe you can sell bio logs and mushrooms !

 

[Mushroom Man]

Torrefication, pyrolysis, gasification...Is there no end to the complexity of staying warm efficiently.


Torrefication doesn't seem like a farm scale process. It has a characteristic that is appealing; namely being able to compress torrefied material and not having to worry about re-absorption of moisture. A compressed biomass log if not hermetically sealed will absorb moisture from the air. To some degree this can be minimized by keeping the logs in a heated building but that is a complication.

If anyone can explain how torrefication could be accomplished on a small scale, I would welcome the input.

 

[renewablejohn]

Mushroom Man

Torrefication is a relatively simple process similar to roasting coffee beans. The temperature required is around 230C which is the normal process heat of thermal oil so plate dryers such as Wyssmont can be utilised. PM me if you want more info

 

[benjamin]

I don't have any suggestion on how to deal with the chlorine content. I was thinking that the chlorine caused fire side corrosion and water treatments only address water side corrosion.

For burning your biomass I would think about an auger feed system instead of drying and compressing logs out of it. Maybe find an old coal stoker that has the auger "transmission", blower and hopper all in one unit and hook it up with another auger to feed it.

 

[renewablejohn]

I know these reports are a bit out of date and gasification technology has moved on a lot since this work was done but the fundamentals are still the same. Only difference is the price of fossil fuels has gone up to make any sort of Biomass plant cost effective in the long term so long as you have a cheap source of fuel and you dont have to transport it very far.

Sorry it is so long but it is good bedtime reading and the straw section is quite in depth.

http://www.berr.gov.uk/files/file14939.pdf