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Re: [WoodGas] Re: Downdraft gasifiers

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  • Ken Boak
    Alexis, The FEMA design has more or less been dismissed by the gasification community as a non-starter, or perhaps a branch of the evolutionary tree that s
    Message 1 of 16 , Oct 1, 2010
      Alexis,

      The FEMA design has more or less been dismissed by the gasification
      community as a non-starter, or perhaps a branch of the evolutionary tree
      that's going nowhere.

      If you read the first page of the report, they claim that it hasn't been
      tested, and are very vague about some of the dimensions, which are critical
      to produce good quality gas.

      At the very least, it needs insulation around the fire tube, plus a cyclone
      and good filtering.

      However, there is a company in California who are marketing such a product,
      and apart for a cast ceramic firetube which offers high temperature
      operation plus insulation , seem to have copied the FEMA design plus all its
      inherent faults.

      http://www.evingerinc.com/


      However, there are elements of the design which could be improved upon, and
      used as the starting point for further experimentation.

      For example, by placing a conical restriction at the bottom of the firetube,
      with say a 3" throat, and the introduction of secondary air into this cone -
      by way of a single airpipe with a valve to control airflow, would make the
      design more like the Mukunda design of open top gasifiers - but with a
      substantial fuel hopper above.

      This hybrid design might we worth exploring for someone who wants a gasifier
      that's easy to make from scrap, yet offers the possibility of reasonable gas
      quality. Indeed this could be implemented from a 4' length of twin wall 6"
      stainless fluepipe, using the heat of the exiting gas to transfer heat to
      the fire tube and the fuel contained in it. Better insulation and secondary
      air pre-heating would also be beneficial.

      It is imperative that the design of the gasifier operates in a way that
      burns the bulk of the tar within the gasifier, and is not wholly reliant on
      the gas clean-up chain for good gas quality.

      H.S. Mukunda's designs are featured in a book - most of which can be found
      on Google Books. Search "Mukunda open top gasifiers"



      Ken


      [Non-text portions of this message have been removed]
    • jim
      ... hopefully at some point one of us will experiment with the hybrid open top designs. so far all we have really is the original papers by the inventors,
      Message 2 of 16 , Oct 1, 2010
        --- In WoodGas@yahoogroups.com, Ken Boak <ken.boak@...> wrote:
        >
        >
        > This hybrid design might we worth exploring for someone who wants a gasifier
        > that's easy to make from scrap, yet offers the possibility of reasonable gas
        > quality.
        >
        > It is imperative that the design of the gasifier operates in a way that
        > burns the bulk of the tar within the gasifier, and is not wholly reliant on
        > the gas clean-up chain for good gas quality.
        >
        > H.S. Mukunda's designs are featured in a book - most of which can be found
        > on Google Books. Search "Mukunda open top gasifiers"
        >
        >
        > Ken
        >


        hopefully at some point one of us will experiment with the hybrid open top designs. so far all we have really is the original papers by the inventors, then the reality of how they are used in current indian production units (ankur, etc).

        we've made soem on our end, but never really tested them. here's a method to make multipoint air injection versions for any who want to try. http://www.gekgasifier.com/reactor-options/open-core-updraft-and-downdraft-variations/ scroll to bottom of page.


        while the authors calimed these designs to have good tar conversion, we need to remember that early stratified downdraft literature introduced it as an improvement to the long standing problems of tar. the reality was of course otherwise. tom reed told me a few months ago about a paper he is writing about why the imbert still hasn't been improved upon by the other downdraft contenders. not sure of the specifics he wants to cite, but that was the summary, from one of the gents who led the open top crusade.


        as for actual performance in the world, do note that all these "tar reburnging" units in india, where they are deployed in numbers well beyond any of our units, are all using extensive water filtering systems. the tar probem is not being solved in the reactor and significant band aids are required downstream to get to clean gas. both the drawings and pictures will usually show multiple stages of cyclones, water scrubbers, and packed filter, with the resulting very large, complicated and expensive installation. and of course, the tarry water pond next to the installation to deal with the scrubber water. in fact, the larger ankur installations ahve a whole separate sysetm to process the scrubber water to something tolerable.

        it is a fairly regular occurance that we (apl) get notes from people in india looking for a gasifier solution without the water filtering and of something other than giant spread out installation. the liabilities of this solution route seem rather clear and well experienced locally. the potential for doing this differently is a regular response we get when interacting with folks currently using or looking at these open top systems. of course this is biased reporting, so adjust accordingly . . .

        in north america, the cpc units are the ones most famously to use the open top, multipoint air injection solution. they also do not solve the tar problems in the reactor, but instead rely on a rather elaborate catalytic cracking system to do so. this is complicated and expensive to make, thus their mostly selling to the government customers these days. cpc uses 6 layers of air nozzles. the auburn university does about the same. not sure of their filtering solutions.

        the main problem with any nozzle addition to open top designs is you cannot generate any blast as you cannot pull a vacuum. air is going to just burbled out the nozzles and not penetrate the bed. this will get you some hot spots in front of the nozzles, but no real hot lobe across the bed.



        there are of course many ways to skin this cat, and many can be very successful, but the kitchen sink approach has again and again proved not terribly meaningful in actual deployment. it seems improtant to solve the tar problem in the reactor, and rely on as little as possible pre processing of fuel and post processing of gas to fix the limitations fo the reactors. if you don't, you tend to end up with a level of cost and complexity that prevents much meaningful deployment beyond demo units and govt subsidized benders.


        of course none of us yet have this tight, compact, cheap and easy to operate solution in any way fully solved. but the options for meaningful work towards it with open top designs seems very limited.

        all this is not to say the imbert type is in any way ideal. it has a bunch of fundamental problems that will continue to plague us as long as we beat on this limping horse. but in the realm of fixed bed downdraft reactors, it can made to do much more than the open tops. or at least that is my admitedly biased reading of the options here.


        jim
      • Ken Boak
        Jim, Thanks for your views on the open top / open core gasifiers. I hadn t realised that APL had made a test reactor. Mukunda s papers seemed so convincing
        Message 3 of 16 , Oct 1, 2010
          Jim,

          Thanks for your views on the open top / open core gasifiers. I hadn't
          realised that APL had made a test reactor.

          Mukunda's papers seemed so convincing that the tall geometry and the
          secondary air inlet had come up with something that gave superior tar
          handling performance - but you are right - just look at the gas clean up
          chain and you see that the same old problems persist.


          Ken


          [Non-text portions of this message have been removed]
        • bigotes_bigotes
          Ken and Jim, Yesterday professor Chandra (yes, he is from India) from LSU came by to see our unit and our conversation drifted over to the open top vs. closed
          Message 4 of 16 , Oct 1, 2010
            Ken and Jim,
            Yesterday professor Chandra (yes, he is from India) from LSU came by to see our unit and our conversation drifted over to the open top vs. closed top designs. There are trade-offs on each.
            Chandra is of the opinion that all gasifiers will produce tars, some more than others obviously, and that to be 100% sure, if such a thing is possible, one should go to catalysts. There is nothing wrong with that conclusion, and with the progess being made on that issue catalysts could become the easy fix for all tar problems. From what I heard yesterday catalysts are rapidly becoming more accessible for general use. One issue of the catalysts seems to be that they require 600 C gas temps which most of us little guys would find hard to provide once the gas leaves the unit, but there has recently been developed one that works with 400 C temps, something that most of us would have no problem with. The actual size of these new cats is surprisingly small, no larger than our typical condensers or filters. I couldn't get much more info from him on this due to a certain amount of secretiveness, not from him but from the developer of the catalyst.
            But he did emphatically state that tar problems should first be attacked in the gasifier, not in the downstream. I think we all can agree on that point.
            The open top has advantages and drawbacks as does the closed tops.
            One thing I noticed in Jim's comment was the lack of blast and lobes in the stratified. That really doesn't apply and is like comparing oranges to apples. The dimensions of the stratified tube take into consideration the elimination of "dead zones" and seem to deal with it quite well.
            Like I said, there are trade-offs. Spray scrubbers are used because they work well. The water ponds can be complicated if they use the water to remove ashes. There might be issues with EPA here in the states if the water is not cleaned. Water cleaners add moisture to the gases and if not compensated for can rob the final gases of calorific value. Plusses and minuses.
            It would seem to me to be a question of which devil of gasification one wants to bed down with. Both systems have their pros and cons. I would suggest that this would be determined by each individual's unique situation and that the final choice would be determined by, as I said, which devil you prefer. At this point to categorically state that one system is superior to another leaves many questions begging at the door.
            As far as the complexity of downstream goes, I have seen some very complicated systems and some as simple as spray tower, water pond, and sand filter. The gases leaving that simple system seem to fall well within acceptable bounds for ICE.
            But I have not built one, yet, and am relying on the veracity of what I've been able to read.

            Sincerely,
            Bigotes

            --- In WoodGas@yahoogroups.com, Ken Boak <ken.boak@...> wrote:
            >
            > Jim,
            >
            > Thanks for your views on the open top / open core gasifiers. I hadn't
            > realised that APL had made a test reactor.
            >
            > Mukunda's papers seemed so convincing that the tall geometry and the
            > secondary air inlet had come up with something that gave superior tar
            > handling performance - but you are right - just look at the gas clean up
            > chain and you see that the same old problems persist.
            >
            >
            > Ken
            >
            >
            > [Non-text portions of this message have been removed]
            >
          • Al Shinn
            Jim, re the lack of blast at the nozzles; just for idea exploration and disregarding the added complexeties and unpleasantness regarding air preheat and etc,
            Message 5 of 16 , Oct 1, 2010
              Jim,
              re the lack of blast at the nozzles; just for idea exploration and disregarding the added complexeties and unpleasantness regarding air preheat and etc, would positive pressure blown nozzles perhaps be a possible cure?

              -----Original Message-----

              From: jim

              Sent: Oct 1, 2010 1:10 AM

              To: WoodGas@yahoogroups.com

              Subject: [WoodGas] Re: Downdraft gasifiers

              --- In WoodGas@yahoogroups.com, Ken Boak <ken.boak@...> wrote:

              >

              >

              > This hybrid design might we worth exploring for someone who wants a gasifier

              > that's easy to make from scrap, yet offers the possibility of reasonable gas

              > quality.

              >

              > It is imperative that the design of the gasifier operates in a way that

              > burns the bulk of the tar within the gasifier, and is not wholly reliant on

              > the gas clean-up chain for good gas quality.

              >

              > H.S. Mukunda's designs are featured in a book - most of which can be found

              > on Google Books. Search "Mukunda open top gasifiers"

              >

              >

              > Ken

              >



              hopefully at some point one of us will experiment with the hybrid open top designs. so far all we have really is the original papers by the inventors, then the reality of how they are used in current indian production units (ankur, etc).



              we've made soem on our end, but never really tested them. here's a method to make multipoint air injection versions for any who want to try. http://www.gekgasifier.com/reactor-options/open-core-updraft-and-downdraft-variations/ scroll to bottom of page.



              while the authors calimed these designs to have good tar conversion, we need to remember that early stratified downdraft literature introduced it as an improvement to the long standing problems of tar. the reality was of course otherwise. tom reed told me a few months ago about a paper he is writing about why the imbert still hasn't been improved upon by the other downdraft contenders. not sure of the specifics he wants to cite, but that was the summary, from one of the gents who led the open top crusade.



              as for actual performance in the world, do note that all these "tar reburnging" units in india, where they are deployed in numbers well beyond any of our units, are all using extensive water filtering systems. the tar probem is not being solved in the reactor and significant band aids are required downstream to get to clean gas. both the drawings and pictures will usually show multiple stages of cyclones, water scrubbers, and packed filter, with the resulting very large, complicated and expensive installation. and of course, the tarry water pond next to the installation to deal with the scrubber water. in fact, the larger ankur installations ahve a whole separate sysetm to process the scrubber water to something tolerable.



              it is a fairly regular occurance that we (apl) get notes from people in india looking for a gasifier solution without the water filtering and of something other than giant spread out installation. the liabilities of this solution route seem rather clear and well experienced locally. the potential for doing this differently is a regular response we get when interacting with folks currently using or looking at these open top systems. of course this is biased reporting, so adjust accordingly . . .



              in north america, the cpc units are the ones most famously to use the open top, multipoint air injection solution. they also do not solve the tar problems in the reactor, but instead rely on a rather elaborate catalytic cracking system to do so. this is complicated and expensive to make, thus their mostly selling to the government customers these days. cpc uses 6 layers of air nozzles. the auburn university does about the same. not sure of their filtering solutions.



              the main problem with any nozzle addition to open top designs is you cannot generate any blast as you cannot pull a vacuum. air is going to just burbled out the nozzles and not penetrate the bed. this will get you some hot spots in front of the nozzles, but no real hot lobe across the bed.



              there are of course many ways to skin this cat, and many can be very successful, but the kitchen sink approach has again and again proved not terribly meaningful in actual deployment. it seems improtant to solve the tar problem in the reactor, and rely on as little as possible pre processing of fuel and post processing of gas to fix the limitations fo the reactors. if you don't, you tend to end up with a level of cost and complexity that prevents much meaningful deployment beyond demo units and govt subsidized benders.



              of course none of us yet have this tight, compact, cheap and easy to operate solution in any way fully solved. but the options for meaningful work towards it with open top designs seems very limited.



              all this is not to say the imbert type is in any way ideal. it has a bunch of fundamental problems that will continue to plague us as long as we beat on this limping horse. but in the realm of fixed bed downdraft reactors, it can made to do much more than the open tops. or at least that is my admitedly biased reading of the options here.



              jim











              Looking forward,
              Al Shinn
            • sabbadess@aol.com
              Al; One interesting thing I ve seen is that blown gasifiers tend to run hotter because they can push steam out of the unit rather than using steam to satisfy
              Message 6 of 16 , Oct 1, 2010
                Al;

                One interesting thing I've seen is that blown gasifiers tend to run hotter because they can push steam out of the unit rather than using steam to satisfy the pressure/flow balance. I am playing with a sucked and blown system(fan pressure to the nozzles and ejector drive) right now.

                Stephen
                -----Original Message-----
                From: Al Shinn <alshinn@...>
                To: WoodGas@yahoogroups.com
                Sent: Fri, Oct 1, 2010 12:57 pm
                Subject: Re: [WoodGas] Re: Downdraft gasifiers





                Jim,
                re the lack of blast at the nozzles; just for idea exploration and disregarding the added complexeties and unpleasantness regarding air preheat and etc, would positive pressure blown nozzles perhaps be a possible cure?

                -----Original Message-----

                From: jim

                Sent: Oct 1, 2010 1:10 AM

                To: WoodGas@yahoogroups.com

                Subject: [WoodGas] Re: Downdraft gasifiers

                --- In WoodGas@yahoogroups.com, Ken Boak <ken.boak@...> wrote:

                >

                >

                > This hybrid design might we worth exploring for someone who wants a gasifier

                > that's easy to make from scrap, yet offers the possibility of reasonable gas

                > quality.

                >

                > It is imperative that the design of the gasifier operates in a way that

                > burns the bulk of the tar within the gasifier, and is not wholly reliant on

                > the gas clean-up chain for good gas quality.

                >

                > H.S. Mukunda's designs are featured in a book - most of which can be found

                > on Google Books. Search "Mukunda open top gasifiers"

                >

                >

                > Ken

                >

                hopefully at some point one of us will experiment with the hybrid open top designs. so far all we have really is the original papers by the inventors, then the reality of how they are used in current indian production units (ankur, etc).

                we've made soem on our end, but never really tested them. here's a method to make multipoint air injection versions for any who want to try. http://www.gekgasifier.com/reactor-options/open-core-updraft-and-downdraft-variations/ scroll to bottom of page.

                while the authors calimed these designs to have good tar conversion, we need to remember that early stratified downdraft literature introduced it as an improvement to the long standing problems of tar. the reality was of course otherwise. tom reed told me a few months ago about a paper he is writing about why the imbert still hasn't been improved upon by the other downdraft contenders. not sure of the specifics he wants to cite, but that was the summary, from one of the gents who led the open top crusade.

                as for actual performance in the world, do note that all these "tar reburnging" units in india, where they are deployed in numbers well beyond any of our units, are all using extensive water filtering systems. the tar probem is not being solved in the reactor and significant band aids are required downstream to get to clean gas. both the drawings and pictures will usually show multiple stages of cyclones, water scrubbers, and packed filter, with the resulting very large, complicated and expensive installation. and of course, the tarry water pond next to the installation to deal with the scrubber water. in fact, the larger ankur installations ahve a whole separate sysetm to process the scrubber water to something tolerable.

                it is a fairly regular occurance that we (apl) get notes from people in india looking for a gasifier solution without the water filtering and of something other than giant spread out installation. the liabilities of this solution route seem rather clear and well experienced locally. the potential for doing this differently is a regular response we get when interacting with folks currently using or looking at these open top systems. of course this is biased reporting, so adjust accordingly . . .

                in north america, the cpc units are the ones most famously to use the open top, multipoint air injection solution. they also do not solve the tar problems in the reactor, but instead rely on a rather elaborate catalytic cracking system to do so. this is complicated and expensive to make, thus their mostly selling to the government customers these days. cpc uses 6 layers of air nozzles. the auburn university does about the same. not sure of their filtering solutions.

                the main problem with any nozzle addition to open top designs is you cannot generate any blast as you cannot pull a vacuum. air is going to just burbled out the nozzles and not penetrate the bed. this will get you some hot spots in front of the nozzles, but no real hot lobe across the bed.

                there are of course many ways to skin this cat, and many can be very successful, but the kitchen sink approach has again and again proved not terribly meaningful in actual deployment. it seems improtant to solve the tar problem in the reactor, and rely on as little as possible pre processing of fuel and post processing of gas to fix the limitations fo the reactors. if you don't, you tend to end up with a level of cost and complexity that prevents much meaningful deployment beyond demo units and govt subsidized benders.

                of course none of us yet have this tight, compact, cheap and easy to operate solution in any way fully solved. but the options for meaningful work towards it with open top designs seems very limited.

                all this is not to say the imbert type is in any way ideal. it has a bunch of fundamental problems that will continue to plague us as long as we beat on this limping horse. but in the realm of fixed bed downdraft reactors, it can made to do much more than the open tops. or at least that is my admitedly biased reading of the options here.

                jim

                Looking forward,
                Al Shinn




                =


                [Non-text portions of this message have been removed]
              • Mike LaRosa
                Hi John, We ve been to freezing twice here now and if things go as predicted, most sensitive stuff will get killed off on Saturday night. Basically what this
                Message 7 of 16 , Oct 1, 2010
                  Hi John, We've been to freezing twice here now and if things go as predicted, most sensitive stuff will get killed off on Saturday night. Basically what this means to me is that water is not an option for anything the next 6 or 7 months. Best not to make tar in the first place so there is no reason to remove it or protect against it. Garbage in, garbage out. Hope all's well your way. Will you be headed to the southern hemisphere again this (our) winter ? Mike L


                  --- In WoodGas@yahoogroups.com, "bigotes_bigotes" <johnbigotes@...> wrote:
                  >
                  > Ken and Jim,
                  > Yesterday professor Chandra (yes, he is from India) from LSU came by to see our unit and our conversation drifted over to the open top vs. closed top designs. There are trade-offs on each.
                  > Chandra is of the opinion that all gasifiers will produce tars, some more than others obviously, and that to be 100% sure, if such a thing is possible, one should go to catalysts. There is nothing wrong with that conclusion, and with the progess being made on that issue catalysts could become the easy fix for all tar problems. From what I heard yesterday catalysts are rapidly becoming more accessible for general use. One issue of the catalysts seems to be that they require 600 C gas temps which most of us little guys would find hard to provide once the gas leaves the unit, but there has recently been developed one that works with 400 C temps, something that most of us would have no problem with. The actual size of these new cats is surprisingly small, no larger than our typical condensers or filters. I couldn't get much more info from him on this due to a certain amount of secretiveness, not from him but from the developer of the catalyst.
                  > But he did emphatically state that tar problems should first be attacked in the gasifier, not in the downstream. I think we all can agree on that point.
                  > The open top has advantages and drawbacks as does the closed tops.
                  > One thing I noticed in Jim's comment was the lack of blast and lobes in the stratified. That really doesn't apply and is like comparing oranges to apples. The dimensions of the stratified tube take into consideration the elimination of "dead zones" and seem to deal with it quite well.
                  > Like I said, there are trade-offs. Spray scrubbers are used because they work well. The water ponds can be complicated if they use the water to remove ashes. There might be issues with EPA here in the states if the water is not cleaned. Water cleaners add moisture to the gases and if not compensated for can rob the final gases of calorific value. Plusses and minuses.
                  > It would seem to me to be a question of which devil of gasification one wants to bed down with. Both systems have their pros and cons. I would suggest that this would be determined by each individual's unique situation and that the final choice would be determined by, as I said, which devil you prefer. At this point to categorically state that one system is superior to another leaves many questions begging at the door.
                  > As far as the complexity of downstream goes, I have seen some very complicated systems and some as simple as spray tower, water pond, and sand filter. The gases leaving that simple system seem to fall well within acceptable bounds for ICE.
                  > But I have not built one, yet, and am relying on the veracity of what I've been able to read.
                  >
                  > Sincerely,
                  > Bigotes
                  >
                  > --- In WoodGas@yahoogroups.com, Ken Boak <ken.boak@> wrote:
                  > >
                  > > Jim,
                  > >
                  > > Thanks for your views on the open top / open core gasifiers. I hadn't
                  > > realised that APL had made a test reactor.
                  > >
                  > > Mukunda's papers seemed so convincing that the tall geometry and the
                  > > secondary air inlet had come up with something that gave superior tar
                  > > handling performance - but you are right - just look at the gas clean up
                  > > chain and you see that the same old problems persist.
                  > >
                  > >
                  > > Ken
                  > >
                  > >
                  > > [Non-text portions of this message have been removed]
                  > >
                  >
                • bigotes_bigotes
                  Mike, I ll be back in Peru at the end of the year. Hopefully I can stay this time. Water scrubbers are certainly not for everyone. Difficult in vehicular
                  Message 8 of 16 , Oct 1, 2010
                    Mike,
                    I'll be back in Peru at the end of the year. Hopefully I can stay this time.
                    Water scrubbers are certainly not for everyone. Difficult in vehicular use, also in cold climates. Many people like them because they clean the gas and lower the temps at the same time.
                    Everyone agrees that tar should be dealt with in the unit, not in the downstream, but professor Chandra says that ALL woodgas will have some amounts of tar (even those of us producing crystal clear flares), and that there should definitely be filtration to protect against the occassional burn that goes south. Who amongst us has not had the occassional "dirty burn"?

                    As for my unit, I saw it coming as soon as the decision was made to purchase the 5 liter genset.....................I built this beast to run a 2000 cc engine. Now I'm having to make a larger reduction tube, haha. At least it will be an easy fix. The whole tube and bottom hearth plate unbolt.
                    I will probably upsize the cyclones also, but keep the dual set-up.
                    You can see the beast running at this link:
                    http://www.wood-gasification.com/profiles/blogs/john-amp-the-southern-boys
                    The motor really sings, but at the same time I watch my manometer go past 25 inches and get slurped up into the tank, haha. Like I said, I saw this coming.

                    Anybody out there cruising the southern roads in a wood-burner is more than welcome to drop by and get a stock of 2" heartpine cubes to continue their trip. High resin rocket fuel!
                    Take care, and hope you have a mild winter.
                    Bigotes


                    --- In WoodGas@yahoogroups.com, "Mike LaRosa" <ook187@...> wrote:
                    >
                    > Hi John, We've been to freezing twice here now and if things go as predicted, most sensitive stuff will get killed off on Saturday night. Basically what this means to me is that water is not an option for anything the next 6 or 7 months. Best not to make tar in the first place so there is no reason to remove it or protect against it. Garbage in, garbage out. Hope all's well your way. Will you be headed to the southern hemisphere again this (our) winter ? Mike L
                    >
                    >
                    > --- In WoodGas@yahoogroups.com, "bigotes_bigotes" <johnbigotes@> wrote:
                    > >
                    > > Ken and Jim,
                    > > Yesterday professor Chandra (yes, he is from India) from LSU came by to see our unit and our conversation drifted over to the open top vs. closed top designs. There are trade-offs on each.
                    > > Chandra is of the opinion that all gasifiers will produce tars, some more than others obviously, and that to be 100% sure, if such a thing is possible, one should go to catalysts. There is nothing wrong with that conclusion, and with the progess being made on that issue catalysts could become the easy fix for all tar problems. From what I heard yesterday catalysts are rapidly becoming more accessible for general use. One issue of the catalysts seems to be that they require 600 C gas temps which most of us little guys would find hard to provide once the gas leaves the unit, but there has recently been developed one that works with 400 C temps, something that most of us would have no problem with. The actual size of these new cats is surprisingly small, no larger than our typical condensers or filters. I couldn't get much more info from him on this due to a certain amount of secretiveness, not from him but from the developer of the catalyst.
                    > > But he did emphatically state that tar problems should first be attacked in the gasifier, not in the downstream. I think we all can agree on that point.
                    > > The open top has advantages and drawbacks as does the closed tops.
                    > > One thing I noticed in Jim's comment was the lack of blast and lobes in the stratified. That really doesn't apply and is like comparing oranges to apples. The dimensions of the stratified tube take into consideration the elimination of "dead zones" and seem to deal with it quite well.
                    > > Like I said, there are trade-offs. Spray scrubbers are used because they work well. The water ponds can be complicated if they use the water to remove ashes. There might be issues with EPA here in the states if the water is not cleaned. Water cleaners add moisture to the gases and if not compensated for can rob the final gases of calorific value. Plusses and minuses.
                    > > It would seem to me to be a question of which devil of gasification one wants to bed down with. Both systems have their pros and cons. I would suggest that this would be determined by each individual's unique situation and that the final choice would be determined by, as I said, which devil you prefer. At this point to categorically state that one system is superior to another leaves many questions begging at the door.
                    > > As far as the complexity of downstream goes, I have seen some very complicated systems and some as simple as spray tower, water pond, and sand filter. The gases leaving that simple system seem to fall well within acceptable bounds for ICE.
                    > > But I have not built one, yet, and am relying on the veracity of what I've been able to read.
                    > >
                    > > Sincerely,
                    > > Bigotes
                    > >
                    > > --- In WoodGas@yahoogroups.com, Ken Boak <ken.boak@> wrote:
                    > > >
                    > > > Jim,
                    > > >
                    > > > Thanks for your views on the open top / open core gasifiers. I hadn't
                    > > > realised that APL had made a test reactor.
                    > > >
                    > > > Mukunda's papers seemed so convincing that the tall geometry and the
                    > > > secondary air inlet had come up with something that gave superior tar
                    > > > handling performance - but you are right - just look at the gas clean up
                    > > > chain and you see that the same old problems persist.
                    > > >
                    > > >
                    > > > Ken
                    > > >
                    > > >
                    > > > [Non-text portions of this message have been removed]
                    > > >
                    > >
                    >
                  • Mike LaRosa
                    JB, I just loaded the hopper up with a blend of 1.5 cherry and 2 pine chunks. Off to Mineral Point to play some violin ?? SWEM, Mike
                    Message 9 of 16 , Oct 1, 2010
                      JB, I just loaded the hopper up with a blend of 1.5" cherry and 2" pine chunks. Off to Mineral Point to play some violin ?? SWEM, Mike


                      --- In WoodGas@yahoogroups.com, "bigotes_bigotes" <johnbigotes@...> wrote:
                      >
                      > Mike,
                      > I'll be back in Peru at the end of the year. Hopefully I can stay this time.
                      > Water scrubbers are certainly not for everyone. Difficult in vehicular use, also in cold climates. Many people like them because they clean the gas and lower the temps at the same time.
                      > Everyone agrees that tar should be dealt with in the unit, not in the downstream, but professor Chandra says that ALL woodgas will have some amounts of tar (even those of us producing crystal clear flares), and that there should definitely be filtration to protect against the occassional burn that goes south. Who amongst us has not had the occassional "dirty burn"?
                      >
                      > As for my unit, I saw it coming as soon as the decision was made to purchase the 5 liter genset.....................I built this beast to run a 2000 cc engine. Now I'm having to make a larger reduction tube, haha. At least it will be an easy fix. The whole tube and bottom hearth plate unbolt.
                      > I will probably upsize the cyclones also, but keep the dual set-up.
                      > You can see the beast running at this link:
                      > http://www.wood-gasification.com/profiles/blogs/john-amp-the-southern-boys
                      > The motor really sings, but at the same time I watch my manometer go past 25 inches and get slurped up into the tank, haha. Like I said, I saw this coming.
                      >
                      > Anybody out there cruising the southern roads in a wood-burner is more than welcome to drop by and get a stock of 2" heartpine cubes to continue their trip. High resin rocket fuel!
                      > Take care, and hope you have a mild winter.
                      > Bigotes
                      >
                      >
                      > --- In WoodGas@yahoogroups.com, "Mike LaRosa" <ook187@> wrote:
                      > >
                      > > Hi John, We've been to freezing twice here now and if things go as predicted, most sensitive stuff will get killed off on Saturday night. Basically what this means to me is that water is not an option for anything the next 6 or 7 months. Best not to make tar in the first place so there is no reason to remove it or protect against it. Garbage in, garbage out. Hope all's well your way. Will you be headed to the southern hemisphere again this (our) winter ? Mike L
                      > >
                      > >
                      > > --- In WoodGas@yahoogroups.com, "bigotes_bigotes" <johnbigotes@> wrote:
                      > > >
                      > > > Ken and Jim,
                      > > > Yesterday professor Chandra (yes, he is from India) from LSU came by to see our unit and our conversation drifted over to the open top vs. closed top designs. There are trade-offs on each.
                      > > > Chandra is of the opinion that all gasifiers will produce tars, some more than others obviously, and that to be 100% sure, if such a thing is possible, one should go to catalysts. There is nothing wrong with that conclusion, and with the progess being made on that issue catalysts could become the easy fix for all tar problems. From what I heard yesterday catalysts are rapidly becoming more accessible for general use. One issue of the catalysts seems to be that they require 600 C gas temps which most of us little guys would find hard to provide once the gas leaves the unit, but there has recently been developed one that works with 400 C temps, something that most of us would have no problem with. The actual size of these new cats is surprisingly small, no larger than our typical condensers or filters. I couldn't get much more info from him on this due to a certain amount of secretiveness, not from him but from the developer of the catalyst.
                      > > > But he did emphatically state that tar problems should first be attacked in the gasifier, not in the downstream. I think we all can agree on that point.
                      > > > The open top has advantages and drawbacks as does the closed tops.
                      > > > One thing I noticed in Jim's comment was the lack of blast and lobes in the stratified. That really doesn't apply and is like comparing oranges to apples. The dimensions of the stratified tube take into consideration the elimination of "dead zones" and seem to deal with it quite well.
                      > > > Like I said, there are trade-offs. Spray scrubbers are used because they work well. The water ponds can be complicated if they use the water to remove ashes. There might be issues with EPA here in the states if the water is not cleaned. Water cleaners add moisture to the gases and if not compensated for can rob the final gases of calorific value. Plusses and minuses.
                      > > > It would seem to me to be a question of which devil of gasification one wants to bed down with. Both systems have their pros and cons. I would suggest that this would be determined by each individual's unique situation and that the final choice would be determined by, as I said, which devil you prefer. At this point to categorically state that one system is superior to another leaves many questions begging at the door.
                      > > > As far as the complexity of downstream goes, I have seen some very complicated systems and some as simple as spray tower, water pond, and sand filter. The gases leaving that simple system seem to fall well within acceptable bounds for ICE.
                      > > > But I have not built one, yet, and am relying on the veracity of what I've been able to read.
                      > > >
                      > > > Sincerely,
                      > > > Bigotes
                      > > >
                      > > > --- In WoodGas@yahoogroups.com, Ken Boak <ken.boak@> wrote:
                      > > > >
                      > > > > Jim,
                      > > > >
                      > > > > Thanks for your views on the open top / open core gasifiers. I hadn't
                      > > > > realised that APL had made a test reactor.
                      > > > >
                      > > > > Mukunda's papers seemed so convincing that the tall geometry and the
                      > > > > secondary air inlet had come up with something that gave superior tar
                      > > > > handling performance - but you are right - just look at the gas clean up
                      > > > > chain and you see that the same old problems persist.
                      > > > >
                      > > > >
                      > > > > Ken
                      > > > >
                      > > > >
                      > > > > [Non-text portions of this message have been removed]
                      > > > >
                      > > >
                      > >
                      >
                    • seilertechco
                      Jim, OK, so I suggest taking the approach that there is a second stage, where the heat and tar laden first gas is combined with air, then put into a catalyst.
                      Message 10 of 16 , Oct 2, 2010
                        Jim,

                        OK, so I suggest taking the approach that there is a second stage,
                        where the heat and tar laden first gas is combined with air, then put into a catalyst. Then more fuel is added, metered through a tapered augar on the exit side of the cat.

                        You will find, I believe, that a balance of fuel and moisture content in the second stage, where water is disassociated more readily, will make a high H content and high CO gas, in proportions that would work in any engine (about 2 times or more btu of producer gas) or perhaps simple FT process. Or if anyone wants to try, a speed record.

                        So move away from thinking one reaction can be made better and move on to adding the heats from two reactors, in series, with the exiting gas from stage two, heating the first downdraft reactor, reclaiming the heat. Think of the reduction in air possible, reducing N.

                        I have termed the second stage reactor a "Prosyn" reactor, since it is both producer gas and synthesis gas.

                        Regards,

                        Toby Seiler
                        Seiler Technical Company




                        --- In WoodGas@yahoogroups.com, "jim" <jim@...> wrote:
                        >
                        >
                        >
                        > --- In WoodGas@yahoogroups.com, Ken Boak <ken.boak@> wrote:
                        > >
                        > >
                        > > This hybrid design might we worth exploring for someone who wants a gasifier
                        > > that's easy to make from scrap, yet offers the possibility of reasonable gas
                        > > quality.
                        > >
                        > > It is imperative that the design of the gasifier operates in a way that
                        > > burns the bulk of the tar within the gasifier, and is not wholly reliant on
                        > > the gas clean-up chain for good gas quality.
                        > >
                        > > H.S. Mukunda's designs are featured in a book - most of which can be found
                        > > on Google Books. Search "Mukunda open top gasifiers"
                        > >
                        > >
                        > > Ken
                        > >
                        >
                        >
                        > hopefully at some point one of us will experiment with the hybrid open top designs. so far all we have really is the original papers by the inventors, then the reality of how they are used in current indian production units (ankur, etc).
                        >
                        > we've made soem on our end, but never really tested them. here's a method to make multipoint air injection versions for any who want to try. http://www.gekgasifier.com/reactor-options/open-core-updraft-and-downdraft-variations/ scroll to bottom of page.
                        >
                        >
                        > while the authors calimed these designs to have good tar conversion, we need to remember that early stratified downdraft literature introduced it as an improvement to the long standing problems of tar. the reality was of course otherwise. tom reed told me a few months ago about a paper he is writing about why the imbert still hasn't been improved upon by the other downdraft contenders. not sure of the specifics he wants to cite, but that was the summary, from one of the gents who led the open top crusade.
                        >
                        >
                        > as for actual performance in the world, do note that all these "tar reburnging" units in india, where they are deployed in numbers well beyond any of our units, are all using extensive water filtering systems. the tar probem is not being solved in the reactor and significant band aids are required downstream to get to clean gas. both the drawings and pictures will usually show multiple stages of cyclones, water scrubbers, and packed filter, with the resulting very large, complicated and expensive installation. and of course, the tarry water pond next to the installation to deal with the scrubber water. in fact, the larger ankur installations ahve a whole separate sysetm to process the scrubber water to something tolerable.
                        >
                        > it is a fairly regular occurance that we (apl) get notes from people in india looking for a gasifier solution without the water filtering and of something other than giant spread out installation. the liabilities of this solution route seem rather clear and well experienced locally. the potential for doing this differently is a regular response we get when interacting with folks currently using or looking at these open top systems. of course this is biased reporting, so adjust accordingly . . .
                        >
                        > in north america, the cpc units are the ones most famously to use the open top, multipoint air injection solution. they also do not solve the tar problems in the reactor, but instead rely on a rather elaborate catalytic cracking system to do so. this is complicated and expensive to make, thus their mostly selling to the government customers these days. cpc uses 6 layers of air nozzles. the auburn university does about the same. not sure of their filtering solutions.
                        >
                        > the main problem with any nozzle addition to open top designs is you cannot generate any blast as you cannot pull a vacuum. air is going to just burbled out the nozzles and not penetrate the bed. this will get you some hot spots in front of the nozzles, but no real hot lobe across the bed.
                        >
                        >
                        >
                        > there are of course many ways to skin this cat, and many can be very successful, but the kitchen sink approach has again and again proved not terribly meaningful in actual deployment. it seems improtant to solve the tar problem in the reactor, and rely on as little as possible pre processing of fuel and post processing of gas to fix the limitations fo the reactors. if you don't, you tend to end up with a level of cost and complexity that prevents much meaningful deployment beyond demo units and govt subsidized benders.
                        >
                        >
                        > of course none of us yet have this tight, compact, cheap and easy to operate solution in any way fully solved. but the options for meaningful work towards it with open top designs seems very limited.
                        >
                        > all this is not to say the imbert type is in any way ideal. it has a bunch of fundamental problems that will continue to plague us as long as we beat on this limping horse. but in the realm of fixed bed downdraft reactors, it can made to do much more than the open tops. or at least that is my admitedly biased reading of the options here.
                        >
                        >
                        > jim
                        >
                      • seilertechco
                        Bigotes you have danced around the solution but didn t get there. Stand back and accept the limits of a downdraft gasifier and look at it as a chain, a series
                        Message 11 of 16 , Oct 2, 2010
                          Bigotes you have danced around the solution but didn't get there. Stand back and accept the limits of a downdraft gasifier and look at it as a chain, a series of gasifiers that improves the gas, not conditions it with scrubbers. Turn the limitations into asset.

                          The cat is refractory, made to make gas and air change directions and wipe surfaces...it doesn't have to be complex. It's burning the low quality producer gas generated in stage one with a small amount of air to make the heat necessary to process high water content fuel in a reactor specific to the purpose. I call it a "prosyn" reactor.

                          The gas is 2 times more btu (proven by General Atomic and others), higher CO and when recycling the second stage heat into the first stage reaction...requires very little air w/(N). I have not made the prototype to prove my design yet but have collected and made certain parts.

                          Given the limitations of the downdraft, why not move on to higher level of power by second stages (anything after the first reaction) that can improve, rather than condition the gas? Essentially this is a series connection of heat, with the second processing more water content fuel and dry fuel in the first stage, evaporated not pyrolyzed.

                          Best regards,

                          Toby Seiler
                          Seiler Technical Company

                          --- In WoodGas@yahoogroups.com, "bigotes_bigotes" <johnbigotes@...> wrote:
                          >
                          > Ken and Jim,
                          > Yesterday professor Chandra (yes, he is from India) from LSU came by to see our unit and our conversation drifted over to the open top vs. closed top designs. There are trade-offs on each.
                          > Chandra is of the opinion that all gasifiers will produce tars, some more than others obviously, and that to be 100% sure, if such a thing is possible, one should go to catalysts. There is nothing wrong with that conclusion, and with the progess being made on that issue catalysts could become the easy fix for all tar problems. From what I heard yesterday catalysts are rapidly becoming more accessible for general use. One issue of the catalysts seems to be that they require 600 C gas temps which most of us little guys would find hard to provide once the gas leaves the unit, but there has recently been developed one that works with 400 C temps, something that most of us would have no problem with. The actual size of these new cats is surprisingly small, no larger than our typical condensers or filters. I couldn't get much more info from him on this due to a certain amount of secretiveness, not from him but from the developer of the catalyst.
                          > But he did emphatically state that tar problems should first be attacked in the gasifier, not in the downstream. I think we all can agree on that point.
                          > The open top has advantages and drawbacks as does the closed tops.
                          > One thing I noticed in Jim's comment was the lack of blast and lobes in the stratified. That really doesn't apply and is like comparing oranges to apples. The dimensions of the stratified tube take into consideration the elimination of "dead zones" and seem to deal with it quite well.
                          > Like I said, there are trade-offs. Spray scrubbers are used because they work well. The water ponds can be complicated if they use the water to remove ashes. There might be issues with EPA here in the states if the water is not cleaned. Water cleaners add moisture to the gases and if not compensated for can rob the final gases of calorific value. Plusses and minuses.
                          > It would seem to me to be a question of which devil of gasification one wants to bed down with. Both systems have their pros and cons. I would suggest that this would be determined by each individual's unique situation and that the final choice would be determined by, as I said, which devil you prefer. At this point to categorically state that one system is superior to another leaves many questions begging at the door.
                          > As far as the complexity of downstream goes, I have seen some very complicated systems and some as simple as spray tower, water pond, and sand filter. The gases leaving that simple system seem to fall well within acceptable bounds for ICE.
                          > But I have not built one, yet, and am relying on the veracity of what I've been able to read.
                          >
                          > Sincerely,
                          > Bigotes
                          >
                          > --- In WoodGas@yahoogroups.com, Ken Boak <ken.boak@> wrote:
                          > >
                          > > Jim,
                          > >
                          > > Thanks for your views on the open top / open core gasifiers. I hadn't
                          > > realised that APL had made a test reactor.
                          > >
                          > > Mukunda's papers seemed so convincing that the tall geometry and the
                          > > secondary air inlet had come up with something that gave superior tar
                          > > handling performance - but you are right - just look at the gas clean up
                          > > chain and you see that the same old problems persist.
                          > >
                          > >
                          > > Ken
                          > >
                          > >
                          > > [Non-text portions of this message have been removed]
                          > >
                          >
                        • bigotes_bigotes
                          Toby, I m taking this as a general direction to look, and to that end, I have seen diagrams of two two stage tar burner designs that claim to be tar free.
                          Message 12 of 16 , Oct 2, 2010
                            Toby,
                            I'm taking this as a general direction to look, and to that end, I have seen diagrams of two "two stage tar burner" designs that claim to be tar free. One takes the rising pyrolysis gases and burns them in a separate chamber which then feeds back into the process. The other, if I remember right, does all this internally by compartmentalizing the separate areas of function.
                            Your concept is somewhat different and I would be interested in it's complexities.
                            My situation at the moment, other than the continuing interest and research, is to optimize what I have here and get back down to Peru. Hopefully I will be able to continue with this down south.
                            At my present stage of understanding gasification I think I'm finally ready to build a unit, haha.
                            Bigotes

                            --- In WoodGas@yahoogroups.com, "seilertechco" <seilertechco@...> wrote:
                            >
                            > Bigotes you have danced around the solution but didn't get there. Stand back and accept the limits of a downdraft gasifier and look at it as a chain, a series of gasifiers that improves the gas, not conditions it with scrubbers. Turn the limitations into asset.
                            >
                            > The cat is refractory, made to make gas and air change directions and wipe surfaces...it doesn't have to be complex. It's burning the low quality producer gas generated in stage one with a small amount of air to make the heat necessary to process high water content fuel in a reactor specific to the purpose. I call it a "prosyn" reactor.
                            >
                            > The gas is 2 times more btu (proven by General Atomic and others), higher CO and when recycling the second stage heat into the first stage reaction...requires very little air w/(N). I have not made the prototype to prove my design yet but have collected and made certain parts.
                            >
                            > Given the limitations of the downdraft, why not move on to higher level of power by second stages (anything after the first reaction) that can improve, rather than condition the gas? Essentially this is a series connection of heat, with the second processing more water content fuel and dry fuel in the first stage, evaporated not pyrolyzed.
                            >
                            > Best regards,
                            >
                            > Toby Seiler
                            > Seiler Technical Company
                            >
                            > --- In WoodGas@yahoogroups.com, "bigotes_bigotes" <johnbigotes@> wrote:
                            > >
                            > > Ken and Jim,
                            > > Yesterday professor Chandra (yes, he is from India) from LSU came by to see our unit and our conversation drifted over to the open top vs. closed top designs. There are trade-offs on each.
                            > > Chandra is of the opinion that all gasifiers will produce tars, some more than others obviously, and that to be 100% sure, if such a thing is possible, one should go to catalysts. There is nothing wrong with that conclusion, and with the progess being made on that issue catalysts could become the easy fix for all tar problems. From what I heard yesterday catalysts are rapidly becoming more accessible for general use. One issue of the catalysts seems to be that they require 600 C gas temps which most of us little guys would find hard to provide once the gas leaves the unit, but there has recently been developed one that works with 400 C temps, something that most of us would have no problem with. The actual size of these new cats is surprisingly small, no larger than our typical condensers or filters. I couldn't get much more info from him on this due to a certain amount of secretiveness, not from him but from the developer of the catalyst.
                            > > But he did emphatically state that tar problems should first be attacked in the gasifier, not in the downstream. I think we all can agree on that point.
                            > > The open top has advantages and drawbacks as does the closed tops.
                            > > One thing I noticed in Jim's comment was the lack of blast and lobes in the stratified. That really doesn't apply and is like comparing oranges to apples. The dimensions of the stratified tube take into consideration the elimination of "dead zones" and seem to deal with it quite well.
                            > > Like I said, there are trade-offs. Spray scrubbers are used because they work well. The water ponds can be complicated if they use the water to remove ashes. There might be issues with EPA here in the states if the water is not cleaned. Water cleaners add moisture to the gases and if not compensated for can rob the final gases of calorific value. Plusses and minuses.
                            > > It would seem to me to be a question of which devil of gasification one wants to bed down with. Both systems have their pros and cons. I would suggest that this would be determined by each individual's unique situation and that the final choice would be determined by, as I said, which devil you prefer. At this point to categorically state that one system is superior to another leaves many questions begging at the door.
                            > > As far as the complexity of downstream goes, I have seen some very complicated systems and some as simple as spray tower, water pond, and sand filter. The gases leaving that simple system seem to fall well within acceptable bounds for ICE.
                            > > But I have not built one, yet, and am relying on the veracity of what I've been able to read.
                            > >
                            > > Sincerely,
                            > > Bigotes
                            > >
                            > > --- In WoodGas@yahoogroups.com, Ken Boak <ken.boak@> wrote:
                            > > >
                            > > > Jim,
                            > > >
                            > > > Thanks for your views on the open top / open core gasifiers. I hadn't
                            > > > realised that APL had made a test reactor.
                            > > >
                            > > > Mukunda's papers seemed so convincing that the tall geometry and the
                            > > > secondary air inlet had come up with something that gave superior tar
                            > > > handling performance - but you are right - just look at the gas clean up
                            > > > chain and you see that the same old problems persist.
                            > > >
                            > > >
                            > > > Ken
                            > > >
                            > > >
                            > > > [Non-text portions of this message have been removed]
                            > > >
                            > >
                            >
                          • jim
                            toby, what you are describing sounds like a pyrolysis unit with a secondary partial oxidization tar cracker, assisted with cats. this will very much work.
                            Message 13 of 16 , Oct 3, 2010
                              toby, what you are describing sounds like a pyrolysis unit with a secondary partial oxidization tar cracker, assisted with cats. this will very much work. you should build it.

                              cats however are a giant hassle. in principle and in demo they do great things. in practice they are very difficult to make work for small scale uses and non-expert users. they are usually difficult to source, often expensive, and easy to foul.

                              i personally think all our problems can be solved with improved housekeeping of the thermal and chemical particulars. heat needs to be reused and chemical processes need to be separated for better control.

                              there a many different ways to do this. and maybe methods with cats will make it even better.

                              j




                              --- In WoodGas@yahoogroups.com, "seilertechco" <seilertechco@...> wrote:
                              >
                              > Jim,
                              >
                              > OK, so I suggest taking the approach that there is a second stage,
                              > where the heat and tar laden first gas is combined with air, then put into a catalyst. Then more fuel is added, metered through a tapered augar on the exit side of the cat.
                              >
                              > You will find, I believe, that a balance of fuel and moisture content in the second stage, where water is disassociated more readily, will make a high H content and high CO gas, in proportions that would work in any engine (about 2 times or more btu of producer gas) or perhaps simple FT process. Or if anyone wants to try, a speed record.
                              >
                              > So move away from thinking one reaction can be made better and move on to adding the heats from two reactors, in series, with the exiting gas from stage two, heating the first downdraft reactor, reclaiming the heat. Think of the reduction in air possible, reducing N.
                              >
                              > I have termed the second stage reactor a "Prosyn" reactor, since it is both producer gas and synthesis gas.
                              >
                              > Regards,
                              >
                              > Toby Seiler
                              > Seiler Technical Company
                              >
                              >
                              >
                              >
                              > --- In WoodGas@yahoogroups.com, "jim" <jim@> wrote:
                              > >
                              > >
                              > >
                              > > --- In WoodGas@yahoogroups.com, Ken Boak <ken.boak@> wrote:
                              > > >
                              > > >
                              > > > This hybrid design might we worth exploring for someone who wants a gasifier
                              > > > that's easy to make from scrap, yet offers the possibility of reasonable gas
                              > > > quality.
                              > > >
                              > > > It is imperative that the design of the gasifier operates in a way that
                              > > > burns the bulk of the tar within the gasifier, and is not wholly reliant on
                              > > > the gas clean-up chain for good gas quality.
                              > > >
                              > > > H.S. Mukunda's designs are featured in a book - most of which can be found
                              > > > on Google Books. Search "Mukunda open top gasifiers"
                              > > >
                              > > >
                              > > > Ken
                              > > >
                              > >
                              > >
                              > > hopefully at some point one of us will experiment with the hybrid open top designs. so far all we have really is the original papers by the inventors, then the reality of how they are used in current indian production units (ankur, etc).
                              > >
                              > > we've made soem on our end, but never really tested them. here's a method to make multipoint air injection versions for any who want to try. http://www.gekgasifier.com/reactor-options/open-core-updraft-and-downdraft-variations/ scroll to bottom of page.
                              > >
                              > >
                              > > while the authors calimed these designs to have good tar conversion, we need to remember that early stratified downdraft literature introduced it as an improvement to the long standing problems of tar. the reality was of course otherwise. tom reed told me a few months ago about a paper he is writing about why the imbert still hasn't been improved upon by the other downdraft contenders. not sure of the specifics he wants to cite, but that was the summary, from one of the gents who led the open top crusade.
                              > >
                              > >
                              > > as for actual performance in the world, do note that all these "tar reburnging" units in india, where they are deployed in numbers well beyond any of our units, are all using extensive water filtering systems. the tar probem is not being solved in the reactor and significant band aids are required downstream to get to clean gas. both the drawings and pictures will usually show multiple stages of cyclones, water scrubbers, and packed filter, with the resulting very large, complicated and expensive installation. and of course, the tarry water pond next to the installation to deal with the scrubber water. in fact, the larger ankur installations ahve a whole separate sysetm to process the scrubber water to something tolerable.
                              > >
                              > > it is a fairly regular occurance that we (apl) get notes from people in india looking for a gasifier solution without the water filtering and of something other than giant spread out installation. the liabilities of this solution route seem rather clear and well experienced locally. the potential for doing this differently is a regular response we get when interacting with folks currently using or looking at these open top systems. of course this is biased reporting, so adjust accordingly . . .
                              > >
                              > > in north america, the cpc units are the ones most famously to use the open top, multipoint air injection solution. they also do not solve the tar problems in the reactor, but instead rely on a rather elaborate catalytic cracking system to do so. this is complicated and expensive to make, thus their mostly selling to the government customers these days. cpc uses 6 layers of air nozzles. the auburn university does about the same. not sure of their filtering solutions.
                              > >
                              > > the main problem with any nozzle addition to open top designs is you cannot generate any blast as you cannot pull a vacuum. air is going to just burbled out the nozzles and not penetrate the bed. this will get you some hot spots in front of the nozzles, but no real hot lobe across the bed.
                              > >
                              > >
                              > >
                              > > there are of course many ways to skin this cat, and many can be very successful, but the kitchen sink approach has again and again proved not terribly meaningful in actual deployment. it seems improtant to solve the tar problem in the reactor, and rely on as little as possible pre processing of fuel and post processing of gas to fix the limitations fo the reactors. if you don't, you tend to end up with a level of cost and complexity that prevents much meaningful deployment beyond demo units and govt subsidized benders.
                              > >
                              > >
                              > > of course none of us yet have this tight, compact, cheap and easy to operate solution in any way fully solved. but the options for meaningful work towards it with open top designs seems very limited.
                              > >
                              > > all this is not to say the imbert type is in any way ideal. it has a bunch of fundamental problems that will continue to plague us as long as we beat on this limping horse. but in the realm of fixed bed downdraft reactors, it can made to do much more than the open tops. or at least that is my admitedly biased reading of the options here.
                              > >
                              > >
                              > > jim
                              > >
                              >
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