Marcos Buenijo

Small Steam System

I am adding this link and discussion to the thread as it's relevant to the topic. Those who have read through the thread will understand the relevance.

The link describes a small steam system used to power a small boat. The system uses a small monotube steam generator. The steam generator is made from 40 feet of roughly 1/4" diameter stainless steel tubing. While the system is crude and inefficient (the builder stated elsewhere that he was all about K.I.S.S. and didn't give a damn about efficiency or cosmetics), it shows clearly that a simple length of small diameter tubing can generate quality steam at a surprising rate.

The control system is interesting to me as it's similar in some respects to a configuration I considered independently. The system in the link uses a bimetallic strip exposed to the peak steam temperature supplied to the engine (it's in thermal contact with the steam supply line by mounting the strip to a small copper block clamped onto the steam line). The strip bends in response to the steam temperature changes, and this bending actuates the potentiometer of a Pulse Width Modulating (PWM) controller for a small DC motor. The motor drives the water feed pump for the steam generator. As the steam temperature approaches 600F, then the water is pumped into the coil at the max rate and this cools the coil. Since the the system uses a more or less uncontrolled wood furnace, then this would also increase steam pressure and increase engine output. A simple means to control engine output was devised: an adjustable steam relief valve is placed to manually vent excess steam and drop the steam pressure as required to lower engine output. While wasteful, it does make some sense in this case (uncontrolled wood furnace). The builder states that the steam temperature stays between 550F and 600F during operation, and the pressure is 150-200 psig during normal operation (pressure would be determined primarily by the load on the engine).

More than anything else I just wanted to show that a simple and surprisingly small coil of 1/4" steel tubing can in fact generate steam to run a useful steam engine. In fact, since this system has high thermal losses from the flue (due to the less than ideal shape and placement of the tubing coil), and since the engine design shows low efficiency (simple small counterflow slide valve unit), then it's clear that an efficient system could produce a lot more power with the same steam consumption rate. The engine in the link is described as having an output that corresponds to about 2/3 hp. A good single acting bump valve uniflow engine exhausting to a vacuum (fully condensing) could show twice the efficiency. Add to this a highly efficient steam generator coil and excellent insulation, and the output could approach 2 hp with the same size tubing coil. In any case, the steam generator required for a 1-2 hp steam engine system can be a great deal more compact than most people understand.

Now, the control system I considered also called for using a bimetallic strip to govern steam temperature. However, I considered using it to (1) control a PWM for the small blower fan of a gasification furnace, or (2) control a damper for the air supplied to a rocket furnace. The water feed pump in these cases would be driven mechanically by the engine, and there would be a relief valve on the pump discharge to limit the pressure in the system (this relief should also be able to handle steam just in case). The system would be operating at a constant output that might be adjusted up or down as desired by adjusting the relief valve. An alternative approach would be to set the relief valve at a constant setting, then throttle the steam supply to the engine to vary its output. Other features might include a high flue temperature thermostat to stop the blower fan of a gasification furnace, and a thermostatic damper shut off for high flue temperature in a rocket furnace (both these high flue temp conditions would occur if the engine were to stall while the furnace is putting out).

Hopefully this shows how small scale steam does not require dangerous pressure vessels - and it's not quite rocket science when kept simple.

John Polk wrote:The construction/operation of steam engines is not for the inexperienced.
Without proper training, steam engines can be quite dangerous.

I agree. Old school steam systems with their large boilers can be dangerous (and expensive!). Joe Blow shouldn't mess with it. Of course, Joe probably shouldn't be doing anything remotely DIY. Until a commercial system becomes available, or unless an individual is willing to build and test a suitable small furnace and safe monotube steam generator for a low power system, then a wood gas engine system is the only thing going for wood => electricity. Hopefully, there will be a commercial small scale steam option in the near future as it is better suited for micro scale CHP with biomass. Something like this would be ideal: http://uniflowpower.com/.

John Polk wrote:
I worked on a ship that had electric forklifts for each hold... Those buggers were heavy !

Very heavy! Good news is there is a nation wide (U.S.) company (GB Industrial Battery) that manufactures and sells forklift batteries with pricing that includes delivery in the 48 states. They will also pick up a discarded battery free of charge (for the scrap). Even if one must transport the battery, then I still consider it worthwhile due to how long these units seem to last in the stationary RE setting. I've seen many accounts showing 15-20 years, and even 10+ years on some accounts that started with a used battery. More important, they seem to be the most cost effective alternative.

In my opinion, if one desires to generate electricity in a remote setting and using only wood fuel, then using a wood gas engine system to periodically bulk charge a fairly large battery system seems the most practical alternative. I think it could be a reliable and even practical set up when electrical demands are low. Justin, I suggest you take another look at Ken Boak's system. Now, he has a much higher electrical demand than you expect to require. However, his basic configuration is what I suggest. Incidentally, Ken also has a small wood furnace for supplemental heat. He uses a central hot water storage tank and provides most of the heating in the home with a hydronic heating system. I like this idea for use with a low power fan coil unit using a DC mag drive pump and DC fan. Sure, it's an additional load, but if you're running a wood gas engine system to charge a 24 volt forklift battery, then you'll have a little more capacity. The engine system should be used to heat the thermal mass whenever battery charging is done. When additional heat is desired, then a more traditional furnace can be used. One might go with a different thermal mass such as those used in rocket "mass" heaters, and there has been some discussion of using the heat from an engine to charge this kind of mass as well. A benefit of this approach is that the intensive fuel processing required for the gasifier is limited by the electrical demand. A low demand means less fuel processing. So, much or most of the wood fuel consumed can be used for a traditional furnace, and this means wood splits.

I'll provide an estimate on fuel consumption for a good wood gas engine system, assuming it operates at an optimal rate for good efficiency. Expect roughly 15% efficiency in the engine system (fuel to shaft work). Battery efficiency is a conservative 80% (assuming bulk charging at a modest rate from a low state of charge). Alternator efficiency can be 80% with a good permanent magnet unit. Throw in a 0.8 factor as some systems would require a dc converter or small inverter, and there is some battery self discharge. This corresponds to roughly 7.7% conversion of wood fuel to end use electricity. This is a realistic estimate assuming a good system, and it's fairly conservative for a good system running at optimal output while battery charging. Green wood provides roughly 4400 btu per pound, so one needs to prep about 10 pounds of green wood for every KWh of electricity consumed. This is an estimate, of course, but it's based on data that I've gleaned from real world units.

Justin Jones wrote:What is the best way to generate electricity, at the home scale, from woody biomass?

Wood gas engine system used to bulk charge a large battery system.

While steam has the potential to be better in many respects, there is not suitable hardware available.

I suggest a wood gasifier that can handle fairly large wood pieces to lessen fuel processing requirements (imagine 1-2" diameter branches cut in 1-2" lengths). The larger the chunks, then the less fuel processing required - and the larger the gasifier/engine/battery system required. If your electricity demands are modest, then you could set up a system to charge the battery on a weekly basis. By all accounts I have seen, the forklift battery is the most cost effective battery alternative.

Justin, I lifted this just as one example (see link below). It's a dc voltage booster for using laptops and other electronics from a 12 vdc source. It's designed for automotive use. This should lessen losses. I expect efficiency is on the order of 85% like inverters, but this should be verified. Note that electronics run on dc. So, using an inverter goes from battery dc voltage, to inverter ac voltage, then back to laptop dc voltage. There are unnecessary losses there.

http://www.powerstream.com/Produz10.htm

NOTE: I don't know much about these devices, I am only listing it to make you aware they exist.

Justin, the math is fine - but I am wondering about the underlying assumptions. Note that a small inverter is probably more like 85% efficient, but the effective efficiency is often much less when used with low loads. An inverter often has a certain minimum draw that can be a significant proportion of a low load, and this can take the effective efficiency (eff) to much lower levels. Also, it's necessary to consider the inverter loss in addition to the load - so, 720 Wh/eff would be the actual load on the battery since the inverter loss is taken from the battery. More important, I'm wondering about additional loads? Fan(s)? Water pump(s)? These can be DC, so that helps.

Definitely it seems a larger battery is desirable. I suggest sizing the battery for 3+ days capacity. I wouldn't suggest this for a high electrical demand. Otherwise, a very large battery would be necessary. Consider that during an extended period of inclement weather it will be necessary to bulk charge the battery with a small generator when it reaches a low state of charge. This will not be efficient and it will be hard on the battery if it's a particularly small battery, and you would have to do it daily. Also, you want to conserve fuel and labor by avoiding the generator until it's absolutely necessary. A larger battery buys time for solar/wind to start producing. There is also the matter of battery charging being very inefficient while the battery is at a high state of charge. Bulk charging a larger battery is a lot more efficient. A common strategy is to not use the generator until the battery is at a fairly low state of charge, then bulk charge up to absorption - let solar/wind take it to float to avoid fuel consumption. Again, propane would solve a lot of problems, but I am assuming you want to stick with wood fuel. If I were in your position (at least as I understand it), then I would go with a "small" 12v forklift battery or pallet jack battery. One model of which I'm aware stores 8 KWh at the 20 hour rate and is rated for 1500 full cycles. This should buy you several days of zero charging if necessary, and it can go a few weeks without a full charge without significant damage. If you were to only bulk charge such a battery when required to protect against a low state of charge, then get it to float and perhaps a short equalization once a month, then I think this would work out very well. I expect such a battery to last many times longer than alternatives you might have considered.

Back to the original thread - if you are looking to make use of wood for electricity and you desire a commercial product to meet your needs, then I see only a small wood gasifier as a possibility. These products might interest you: http://northernselfreliance.com/get-the-nsr-hardware/isabella-gasifier/ , http://vulcangasifier.wix.com/vulcangasifier#!product/prd15/1585769955/m-series-ii-gasifier-refinery-system . Of course, you would need a small generator, and a Honda is best in my opinion. There is also wood processing equipment required. You could process fairly thin branches by cutting into small chunks. However, I suspect this would get old really fast if you were to rely on wood as a primary source of electricity. For backup power only, and with very low electrical loads, then maybe it would be doable. You would need on the order of 10 pounds of green wood (that must be dried before use) to generate one KWh electricity for end use - assuming a reasonably efficient and very small system, and considering all the losses involved. Most of the heat from the system could be captured for use, so that's a plus. There are no micro scale systems that are turn key, so you would have to develop something (not terribly difficult with the gasifier and engine already had). If you're willing to do this, and if you're dedicated, then you will get something impressive with time.

Now, if you are considering long term prospects, then I suggest a small piston steam engine system as a superior possibility for your particular application. However, that's a more difficult prospect since there's nothing suitable on the market. You would have to do some development work. The reason I consider this prospect to be a good match for your setting is the combination of plentiful wood fuel, low electricity requirements, and high heat requirements. Also, the fuel processing required for a small steam system would be a great deal less than a wood gas engine system. It could be made to use small seasoned wood splits. If you're going to be burning firewood for heat anyway, then a micro steam engine system could give you the heat and the electricity you need.

Justin Jones wrote:For my purposes, heat and char production are of primary importance. My electricity needs are relatively small and can be met by a stationary bicycle generator, though I understand there's a lot of sweat involved for even small yields, so a cogeneration system is definitely more desirable.

Why char?

How much heat do you need (i.e. northern climate with harsh winters)? Is space cooling necessary during summer months? What about food storage - a freezer is probably the best thing for long term food storage, and that's a substantial electrical load. It seems you'll be using a laptop computer at the very least - well, what about internet connection? This will require additional electricity. Try to get a realistic estimate on the electrical loads you expect to need, and do not low ball there - if anything, be conservative in the estimates. I don't expect even the most modest off grid homes to get by on less than 3 KWh daily.

In my opinion, solar panels are the most practical means to generate electricity in a remote setting, at least in most settings. If a solar array and battery system can meet your electrical needs most of the time, then it makes practical sense to keep a tank of propane to run a small backup generator (assuming infrequent use - that is, only when required to bulk charge the battery and protect from a dangerously low state of charge). I suggest propane because it stores indefinitely vs gasoline or diesel fuel, and I see your electrical demands as very modest. A small Honda generator is a good choice for a very small system (like an EU1000).

Now, let's assume you want to get away from commercial fuels entirely and use wood for electricity generation. In that case, there are three options (well, only two really). A wood gas engine system, a charcoal engine system, or a small piston steam engine.

1. Wood Gas Engine System - The best example of which I know is the system developed by Ken Boak of the UK. See description here: http://www.powercubes.com/listers.html . Mr. Boak has the system set up to run the engine for part of each day on wood chips. Heat exchangers on the system pick up the heat from the cylinder cooling water and the engine exhaust to heat a large store of water in an insulated vessel. The heat is transmitted to the home using a hydronic heating system (pumping hot water into the home for heating applications). The down side of this is primarily the fuel processing required. A second down side is the necessity to operate the system at a fairly high rate to keep temperatures in the gasifier high enough to generate a clean fuel gas. On this last point, Mr. Boak uses most of the electricity generated in electric space heaters just to load down the engine and help keep the gasifier temps up. It's possible to run a smaller system, but the smaller the system the more fuel processing is required - sort of a catch 22.

This system seems overkill for your application. Also, the fuel processing required to run a system like this for primary heat would be daunting. A better configuration for making use of a wood gas engine system would be to use traditional firewood for heating applications, then process only enough wood fuel as required for use in a small backup generator system - sort of like making small wood chips or chunks for a small engine wood gasifier in lieu of storing propane. However, you would need solar/wind/hydro for primary electricity.

2. Charcoal Engine System - This process entails processing wood to charcoal, but capturing the heat from the process and storing in a thermal mass such as water. The heat can then be used for heating applications, and the charcoal can be stored for use in small engines as required. I don't know of a viable system in operation, at least not on a residential scale, but it's clear that it's possible. Note that charcoal can run very small engines more easily and more cleanly than wood.

3. Piston Steam Engine - Personally, I believe this has the most promise. However, it's not practical due to the lack of hardware. There are decent small engine expanders available that are very durable, but one would have to engineer a steam generator with control system and an efficient small wood gasifying furnace to operate unattended - possible, but not for the faint of heart. The benefit of this system is primarily the ability to use wood with very little processing, and the ease in heat recovery (most of the heat is available at the steam condenser). It can also be very quiet and operate at a low output for long periods. Steam engines have also earned a reputation for longevity.

In my opinion, I say stick with PV/wind/hydro with battery system, and use a small propane fueled backup generator as required. Use wood only for heating applications.

austin lerwick wrote:Hi,
"WVO Blending with Gasoline to Make Diesel Fuel" I don't understand can you please elaborate and the link is not going on particular topic too.

http://beyondbiodiesel.org/forum/index.php/topic,12.0.html

Just peruse the forum and you might find what you need. Note that I have no experience or real interest in it, I was merely sharing the info for those who might have interest.

http://www.ebay.com/itm/NEW-12V-DC-Micro-Brushless-Magnetic-Pump-High-Solar-Hot-Submersible-Water-Pump-/360881662635?pt=BI_Pumps&hash=item5406392aab

Solar water heating is popular in China. Small dc (12 volt and 24 volt) magnetic drive pumps are manufactured by the millions to meet the demand. They are highly reliable by all accounts I've seen with some models claiming a 30,000 hour life. They are highly efficient, and some models I've seen show impressive performance with fairly high head loads. Of course, any significant pressure differential should use a positive displacement pump - or two mag drive pumps in series could work. However, for transfer of water under modest heads, a dc mag drive pump is unbeatable.

The link provides one example of many.

ronald bush wrote:is there a chart on here, or the web, that gives the amount of usage of electricity by average appliances? seems i would be more apt to conserve if i knew how much it was saving. lol

I've looked and found little that's actually useful. A problem is that usage varies with households, so charts have little value. Those looking to conserve should simply note that using electricity for heating applications or air conditioning will almost certainly be the primary loads. Another big one is air moving equipment like whole house fans, but these are normally associated with space heating and air conditioning usage. I'd say focus on the big ones, then just make sure you're not leaving lights and electronics on unnecessarily, and tackle the "phantom" loads, and you'll be doing well.