Charcoal Gasification

Marcos Buenijo wrote:

r john wrote:Marcos

If your talking thermal efficiency thats a total different ball game. Most CHP plants run at 80 to 90 per cent efficiency its just how you split between electric and heat that is the difference.

http://www.bios-bioenergy.at/en/electricity-from-biomass/screw-type-engine.html

OK, so we've cleared things up - these engines do not (indeed, cannot) have the extremely high thermal efficiency suggested in your previous posts. Thermal efficiency is what fundamentally distinguishes/differentiates one heat engine from another. When people consider the "efficiency" of a heat engine, then it is thermal efficiency that is generally considered. Hence, you can understand my consternation at your claim of "50% electrical efficiency" (BTW, the only way I know to interpret this claim is that 50% of the heat provided to the system is converted to electricity, and this implies a thermal efficiency so high as to be unbelievable).

The engine in the link you provided lists "Electric efficiency at nominal load operation of 12,6 %" using steam at 500F and about 360 psig. This is very good efficiency for a once through expander at these parameters, especially with the fairly high exhaust pressure. In particular, the high condenser pressure/temperature makes for excellent use of the heat in cogeneration applications. I agree that these seem to be great for combined heat and power purposes. However, they really should be made much smaller for real impact.

Marcos

I think you need to understand how steam efficiencies are calculated. The efficiency is a function of the temperatures used with the limiting factor being the strength of stainless steel at high temperatures. If you use power station temperatures in a screw expander you will get power station efficiencies in fact a screw expander can be used at higher temperatures as the stainless steel deteriorates more in a blade than a screw.

Coal slurry technology which can also be used for charcoal

http://www.egcfe.ewg.apec.org/publications/proceedings/CFE/Austrailia_2012/4D-3_Wibberley.pdf

Note the power generation efficiency curves are cradle to grave so includes energy used in digging coal out the ground through to final distribution. This is obviously lower than what is normally quoted for just power station efficiency.

r john wrote:Marcos

I think you need to understand how steam efficiencies are calculated. The efficiency is a function of the temperatures used with the limiting factor being the strength of stainless steel at high temperatures. If you use power station temperatures in a screw expander you will get power station efficiencies in fact a screw expander can be used at higher temperatures as the stainless steel deteriorates more in a blade than a screw.

R John, if you can provide resources that demonstrate an engine using screw expanders and achieving a net thermal efficiency higher than conventional modern steam power plants, then please do so. Personally, I have strong doubts that this has been done, but I would love to learn otherwise.

...actually, I'm interested to know about any such system over 20% as well.

Marcos Buenijo wrote:

r john wrote:Marcos

I think you need to understand how steam efficiencies are calculated. The efficiency is a function of the temperatures used with the limiting factor being the strength of stainless steel at high temperatures. If you use power station temperatures in a screw expander you will get power station efficiencies in fact a screw expander can be used at higher temperatures as the stainless steel deteriorates more in a blade than a screw.

R John, if you can provide resources that demonstrate an engine using screw expanders and achieving a net thermal efficiency higher than conventional modern steam power plants, then please do so. Personally, I have strong doubts that this has been done, but I would love to learn otherwise.

...actually, I'm interested to know about any such system over 20% as well.

Marcos

As I said its very important to understand steam cycles when it comes to power station efficiencies. At present conventional steam power stations have an upper temperature limit imposed due to the type of metal used in the turbine blade and a lower limit set at approx 350C due to water droplets eroding the turbine blades. To overcome this MHD technology is used for the higher temperature phase the output of which produces a conventional steam phase with a lower temperature ORC phase recovering the heat below 350C. Its this lower phase where twin screw technology is being used very effectively.

As for discrimination between technologies of twin screw expanders and turbines both have similar usage maps its just twin screws will tolerate wet steam whereas turbines certainly wont.

http://www.engineering.zhaw.ch/fileadmin/user_upload/engineering/_Institute_und_Zentren/IEFE/Kompetenzen/ORC_Final_Paper_WEC2011_2011-07-30.pdf

The other high thermal efficiency option is the DICE using coal or charcoal slurry but with ORC capture of waste heat from the exhaust and cooling systems.

r john wrote:
Marcos

As I said its very important to understand steam cycles when it comes to power station efficiencies. At present conventional steam power stations have an upper temperature limit imposed due to the type of metal used in the turbine blade and a lower limit set at approx 350C due to water droplets eroding the turbine blades. To overcome this MHD technology is used for the higher temperature phase the output of which produces a conventional steam phase with a lower temperature ORC phase recovering the heat below 350C. Its this lower phase where twin screw technology is being used very effectively.

As for discrimination between technologies of twin screw expanders and turbines both have similar usage maps its just twin screws will tolerate wet steam whereas turbines certainly wont.

http://www.engineering.zhaw.ch/fileadmin/user_upload/engineering/_Institute_und_Zentren/IEFE/Kompetenzen/ORC_Final_Paper_WEC2011_2011-07-30.pdf

The other high thermal efficiency option is the DICE using coal or charcoal slurry but with ORC capture of waste heat from the exhaust and cooling systems.

R John, I'm aware of how to go about estimating or measuring steam engine efficiencies as I used to be a steam plant operator at a power plant. I also have a physics degree. However, I'm not interested in speculation at the moment. Right now I'm only interested in what has actually been accomplished with these screw expanders. Note that I take no position as to what may or may not be possible. I'm interested only in what has actually been done. If you are aware of any case where these expanders have been used to design a steam engine system with a net thermal efficiency greater than 20%, then please share with the forum. Also, if you come across these expanders in the sub-10 hp range, then please share as I and others would be particularly interested.

I'm not interested in the charcoal slurry used to fuel Diesel engines, although I do think there is great promise in that technology. I tend to restrict my considerations to technologies suitable for the residential off-grid/remote setting, and it's hard for me to see this as superior to gasification in that setting.

Marcos

Given your background I am very surprised you have been arguing down the thermal efficiency road. Turbines are normally rated on isentropic efficiency hence the figures quoted by Kobelco for there steamstar.

As regards small steam power plants theres plenty on the market but the price makes them uneconomic. This article gives an insight at the low end of the market

http://peer.ccsd.cnrs.fr/docs/00/78/98/84/PDF/PEER_stage2_10.1016%252Fj.applthermaleng.2011.06.008.pdf

In addition on the larger scale are Ingersol Rand, Kobelco, Langson Energy and Turboden.

r john wrote:Marcos

Given your background I am very surprised you have been arguing down the thermal efficiency road. Turbines are normally rated on isentropic efficiency hence the figures quoted by Kobelco for there steamstar.

As regards small steam power plants theres plenty on the market but the price makes them uneconomic. This article gives an insight at the low end of the market

http://peer.ccsd.cnrs.fr/docs/00/78/98/84/PDF/PEER_stage2_10.1016%252Fj.applthermaleng.2011.06.008.pdf

My emphasis on thermal efficiency has a simple explanation. I consider the primary purpose of this forum as a resource for education. There is a lot of nonsense circulating on the net about steam engine systems, and I like to clear things up whenever I have an opportunity. The "thermal efficiency road" is exactly the one that most readers take when a discussion of "efficiency" in heat engines is made. Your previous claims on the "efficiency" of steam engine systems could easily lead many to believe that the thermal efficiency of steam engine systems are much higher than in reality. Therefore, my purpose in replying to your claims was to provide clarification for the casual reader.

The article you linked discusses possibilities for expanders in micro organic rankine cycle engines. I'm aware of all these possibilities. Unfortunately, it provides no information on actual products available for purchase. I am particularly interested in micro systems (under 10 hp) as I believe these would be best suited for the residential scale. Also, I am particularly interested in steam systems vs. ORC mainly because steam will more easily provide higher condenser temperatures that make additional heating applications possible. If you know of any such systems, then please let us know.

Marcos Buenijo wrote:

r john wrote:Marcos

Given your background I am very surprised you have been arguing down the thermal efficiency road. Turbines are normally rated on isentropic efficiency hence the figures quoted by Kobelco for there steamstar.

As regards small steam power plants theres plenty on the market but the price makes them uneconomic. This article gives an insight at the low end of the market

http://peer.ccsd.cnrs.fr/docs/00/78/98/84/PDF/PEER_stage2_10.1016%252Fj.applthermaleng.2011.06.008.pdf

My emphasis on thermal efficiency has a simple explanation. I consider the primary purpose of this forum as a resource for education. There is a lot of nonsense circulating on the net about steam engine systems, and I like to clear things up whenever I have an opportunity. The "thermal efficiency road" is exactly the one that most readers take when a discussion of "efficiency" in heat engines is made. Your previous claims on the "efficiency" of steam engine systems could easily lead many to believe that the thermal efficiency of steam engine systems are much higher than in reality. Therefore, my purpose in replying to your claims was to provide clarification for the casual reader.

The article you linked discusses possibilities for expanders in micro organic rankine cycle engines. I'm aware of all these possibilities. Unfortunately, it provides no information on actual products available for purchase. I am particularly interested in micro systems (under 10 hp) as I believe these would be best suited for the residential scale. Also, I am particularly interested in steam systems vs. ORC mainly because steam will more easily provide higher condenser temperatures that make additional heating applications possible. If you know of any such systems, then please let us know.

What nonsense on steam engines am I accused of writing. I point out good steam systems can achieve over 50% electrical efficiency and 90% overall thermal efficiency which is conservative to what current generating plants are achieving with existing technology going beyond 60 percent (GE claim for there systems).

http://www.ge-energy.com/products_and_services/products/gas_turbines_heavy_duty/flexefficiency_50_combined_cycle_power_plant.js

I provide articles which show steam conversion efficiencies of 50 to 60 percent at various points on the steam cycle. What you then do is ridicule steam performance because you isolate such a small element of the steam cycle for a particular technology Ie screw expander when in reality compound engines are always far more efficient using a greater part of the steam cycle. Typical compound would be HP piston, LP Piston, Turbine, Screw Expander.

Obviously achieving even in excess of 40% electrical efficiency on sub 1MW systems is not easy but can be done with a Jenbacher gas engine with exhaust heat recovery steam turbine and cooling system recovery screw expander. Alternatively a Capstone Gas Turbine , HP & LP Piston Steam Engine, LP Turbine and Screw Expander.

If you want a residential system then look at the Otag Lion which uses a linear generator (Linator) and was well ahead of its time but I believe went into receivership over patent arguments.

As for products for purchase if you look up the individual company websites in the article they do have a range of products to purchase but you will need to email the companies to obtain prices. Normally in the £1-2k per KW generated for plant in the 10KW to 250KW range.

r john wrote:What nonsense on steam engines am I accused of writing. I point out good steam systems can achieve over 50% electrical efficiency and 90% overall thermal efficiency which is conservative to what current generating plants are achieving with existing technology going beyond 60 percent (GE claim for there systems).

http://www.ge-energy.com/products_and_services/products/gas_turbines_heavy_duty/flexefficiency_50_combined_cycle_power_plant.js

I provide articles which show steam conversion efficiencies of 50 to 60 percent at various points on the steam cycle. What you then do is ridicule steam performance because you isolate such a small element of the steam cycle for a particular technology Ie screw expander when in reality compound engines are always far more efficient using a greater part of the steam cycle. Typical compound would be HP piston, LP Piston, Turbine, Screw Expander.

Obviously achieving even in excess of 40% electrical efficiency on sub 1MW systems is not easy but can be done with a Jenbacher gas engine with exhaust heat recovery steam turbine and cooling system recovery screw expander. Alternatively a Capstone Gas Turbine , HP & LP Piston Steam Engine, LP Turbine and Screw Expander.

If you want a residential system then look at the Otag Lion which uses a linear generator (Linator) and was well ahead of its time but I believe went into receivership over patent arguments.

As for products for purchase if you look up the individual company websites in the article they do have a range of products to purchase but you will need to email the companies to obtain prices. Normally in the £1-2k per KW generated for plant in the 10KW to 250KW range.

Read my comment carefully. I did not state nor imply that you wrote any nonsense. I stated that there is a lot of nonsense on the internet with respect to steam engine systems. For example, I corresponded with a young person just last month who had a strong interest in steam engines, but believed just as strongly that old piston steam cars were significantly more efficient than modern cars (they were suppressed by the evil oil companies, of course). IT TURNS OUT that he had been referencing sources that did not make a clear distinction between the various "efficiencies" that are often discussed between engineers. He interpreted the Carnot efficiency of steam engine systems as thermal efficiency. I believe strongly that this individual and others would have likely interpreted your comments in a similar manner.

It's now clear that we are not operating under the same definitions, and this had led to misunderstandings. For example, I define the term "thermal efficiency" of a heat engine as describing the proportion of heat delivered to an engine cycle that is converted to work (note that if the heat source is the combustion of a fuel, then the thermal losses from the steam generator should be considered as well). I define the term "electrical efficiency" of a heat engine as the proportion of heat delivered to an engine cycle that is converted to usable electricity. Also, I do not consider a combined cycle heat engine as a steam engine. Only the latter part of the cycle qualifies (where heat dumped from the gas turbine is used as the heat input to the steam cycle). By my definitions, the best thermal efficiency achieved by a steam engine system of which I am aware is 48% and this was a supercritical plant at hundreds of megawatts. Additional losses would have put the electrical efficiency at around 45%. I would be very interested to learn about a steam engine system that achieves significantly higher thermal efficiency as I consider this performance to be fantastic.

As far as the products go, I had hoped you may be aware of low power steam engine systems that flew under my radar. I suppose not, but that's ok... they probably don't exist. Again, definitions are important. When I write "steam engine", I do not include those that use an organic working fluid.

The Linator in the Otag Lion is the best steam generator I have seen at such a small scale.

If you want a pure turbine at that size try

http://www.greenturbine.eu/en/home.php

Marcos Buenijo, we should be more acquainted. Our interests are very similar.

Hallo Marcos
I stumbled across this forum while surfing my favourite subject area. I found your ideas regarding charcoal/wood gasification interesting because this is almost exactly the same road that I want to
go down. This link http://six6.region-stuttgart.de/sixcms/media.php/773/ABS-61-Jesper-Ahrenfeldt.pdf contains information regarding the thesis from Jesper Ahrenfeldt regarding a 2 stage gasifier with partial oxidation of the pyrolysis gases to reduce the tar content. This link is also on the GEK site. This gasifier was built around 2005 so these ideas are not new. There is also book from 1907 called "A Treatise on Producer-Gas and Gas-Producers" which gives a good insight into the technology available at the end of the 18th century. I personally found the Riche Double-Combustion Wood Gas-Producer very close to the kind of gasifier design I would like to make (but a little bit smaller!!). We have the advantage nowadays of much better materials technology with greatly reduced costs. Maybe these connections give you a little food for thought.

Kind regards

Marcos Buenijo wrote:Just sharing one of my wacky ideas. I like the idea of using a modernized piston steam engine with good thermal efficiency and fueled by biomass as an off grid power plant. One of the main benefits of a piston steam engine in this setting is the ability to operate at very low power for extended periods while providing heat in a convenient package. Steam is an excellent heat transfer medium. Unfortunately, these systems are not available. So, I considered, why not a biomass fueled steam generator for heating applications? Furthermore, since my recent research shows that charcoal gasifiers can power very small engines cleanly and with impressive energy density, then how about a system that chars wood chips at a controlled rate while generating steam on demand? The charcoal produced from the system can then be stored for use as required in fueling small engines.

I'll describe a basic configuration to get the reader thinking on the topic. Particulate biomass like wood chips is gravity fed through a vertical pipe section. A hopper is connected to the top. A lower section of the pipe is surrounded by a combustion chamber fueled by pyrolysis gases generated from the heated wood chips. A key point to consider is that pyrolysis occurs at a rate directly proportional to the rate at which the biomass feeds through the system (within limits). So, it's possible to govern the steam rate with a motorized auger tha removes charcoal from the base of the system. A steam generator tubing coil is placed above the combustion chamber in the annular space between the pipe and exterior shroud used to form the combustion chamber. The draft draws air into the base of the system to cool the lower pipe (and charcoal within) and combust the pyrolysis gases escaping from a ring of holes in the inner pipe at the base of the combustion chamber. These hot combustion gases pass over the steam generator coil before heating the hopper that contains the fuel (thereby drying and/or preheating the fuel before it enters the pipe).

The steam generated is sent through an insulated line to a high point in the system, then distributed to various heating applications. This is controlled in two ways. First, each load has a valve to control flow. Second, the final pass of the steam/condensate is through an insulated water storage tank. The temperature of the water in this tank is used as a control for the auger motor.

Hello Marcos.. convert the thermal energy from an gasifier/burner into heat is good.. use tube coil for steam creation is good ... but please do not use an piston steam engine.. FORGET THE PAST AND THINK ORIENTED TO THE FUTURE.. the kinetic energy of steam can be useful (directly) for produce electricity  with high efficency if you are able to make water on pressure (with steam) and use that force using an pelton turbine generator. Starting from the charcoal and add wood pellet can be an simple solution for obtain an stable and good gasifier/burner in the time but why sent the exaust gas in atmosphere? Using an right REACTOR design you can recycle the exaust gas in an LOOP MODE and consume the carbon atoms of charcoal with the reduction reaction producing CO and H2. Another little problem can be the nitrogen present on air .. you use the oxygen present on air (21%) for increase the temperature of charcoal but the nitrogen (78%) works negatively (inert gas) but .. if your REACTOR increase an little the temperature of exaust gas to >1000° the chemical of combustion change and you can obtain NO molecules into exaust gas.. these reacts very hard with carbon creating CO and N2O.. WOOD (CHARCOAL)  & ARTIFICIAL PICO-HYDROGENERATOR (<5kW) are surely the next way for make an system for the creation of an home with an independent Electricity & Heat .. Think about ...  Cheers  Alessandro