| STI Engineering |
| Steam Injected Biomass Reactor |
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| Copyright © 2010 STI Engineering/ Regis Renaud ALL RIGHTS RESERVED |
Introduction
Based on the data obtained from the Steam Injection Pilot Study performed at the Miramar Landfill in San
Diego, California, STI has designed the following patent pending Steam Biomass Reactor (Application #
61/073,709). It was demonstrated during the study that for every cubic foot of steam injected into the waste
prism, 1 cubic foot of landfill gas was produced with 66% methane and 34% CO2.
Anaerobic digestion processes produced this gas, which can be reproduced inside an airtight steel
vessel. In the landfill process the rule of thumb is that for every ton of organic waste converted, 12,000
cubic feet of biogas will be produced. (Landfill Challenges, Neal Bolton, MSW 09-2007) This should be
the same for an in-vessel process once the waste is purged of oxygen and inoculated with anaerobic
bacteria. Most of the inoculating bacteria will come from the bottom portion of the reactor however by
discharging some of the waste from the bottom of the reactor to the hopper unit which is mixed with the
fresh waste the inoculation process will be accelerated. The STI patent for steam injection in landfills
allows for the injection of ammonia gas and steam into the waste prism to balance the pH of fresh waste
and to jump-start the anaerobic digestion in fresh waste.
Currently, wet biomass reactors use large amounts of water to enhance the anaerobic biodegradation of
the organic waste. In most cases this water is heated to a preferred temperature requiring a lot of energy.
It can take weeks for the anaerobic conditions begin to produce methane. When less water is used such
as; in compost piles, the interior of the piles will go anaerobic in just a couple of days so the piles have to
be turned often or they can spontaneously combust. The steam can simulate this condition in just a few
hours.
Steam expands 1,600 times its original volume, therefore much less water will be required to biodegrade
the organic waste and produce the maximum amount of gas. The steam also increases the temperature of
the reactor to 105o to 120oF, which is the preferred temperature for maximum biodegradation.
To produce the maximum amount of biogas the waste needs to be of a small grain size, such as manure.
The manure will have to be de-watered to about 30% moisture content.
The smaller the material the more refuse will be able to be placed into the reactor and the more biogas will
be produced faster. If the feedstock is too fluffy a shaker on the reactor wall, is used to pack the material
tighter inside the vessel to slow down the migration of the steam through the matrix and to allow time for
the conversion to take place. Highly ground green waste can be mixed with the manure or other feedstock
to increase the amount organic material for conversion.
The reactors can be manufactured in various sizes to meet daily input levels of waste or to produce the
amount of methane required to meet the daily fuel requirements. Ultimately it is the amount of steam
injected into the reactor that will control how much biogas is produced.
As stated above for every ton of organic waste 12,000 cubic feet of biogas will be produced. (Landfill
Challenges, Neal Bolton, MSW 09-2007) Therefore, if 500 tons are converted to biogas (500 x 12,000) an
estimated 6,000,000 cubic feet of biogas will be produced per day. With 60% methane this comes to
3,600,000 cubic feet of methane. This gas should contain about 1,000 Btu’s per cubic foot, which equates
to 3,600,000,000 Btu or 3,600 mmBtu’s per day. With a heat value of 9,700/Kwhr this can produce 15 Mwhr.
The loading of the reactor can be continuous to match the rate of decomposition of the waste, however air
must be kept from entering the reactor chamber. To achieve this, another tank used as a hopper would be
used to pre-load the refuse where it would be sealed, purged with steam and then conveyed to the reactor,
this should maintain an anaerobic condition (Figure 1). The reactor would be loaded twice per day once in
the morning and again 12 hours later, so the hopper should hold at least 400 tons.
Steam Production
In the reactor the goal is to inject steam at a rate not too fast that it passes through the waste before it has
a chance to convert into biogas. Approximately 28,000 gallons of water at 19gpm, converted to steam could
convert 500 tons of organic waste per day.
The water should be preheated by solar or waste heat to about 120oF and then heated to 250oF which is
an increase of 130 degrees. So 130o x (28,000 gals. x 8.3 lbs. = 232,400 lbs.) = 30,212,000 Btu’s or
30,212 cubic feet of methane. If 500 tons produces 6,000,000 cubic feet of methane then .05% of the
methane would be used to create the steam for the reactor leaving 99% for power production, pipeline or
CNG/LNG after scrubbing.
The Reactor
The Miramar Landfill Pilot Study indicated that the steam had to travel at least 20 to 25 feet through the
waste before it was converted to biogas. The same should be true for in vessel reactors. Therefore the
tank should be at least 30 to 35 feet high to allow for some headspace for reloading.
To prevent the steam from bypassing the waste before it is converted into biogas the steam injector pipes
are placed at the bottom of the reactor and the extraction ports are placed at the top of the reactor but under
the waste. This forces the steam to make contact with the organic waste before it leaves the reactor.
Therefore, the surface of the waste must be kept above this port at all times.
A ceiling mounted feedstock spreader is used to reload and distribute the feedstock evenly over the waste
pile in the reactor. A light and camera is mounted on the top hatch cover to monitor the level of waste in the
reactor and to ensure the reloaded waste is evenly placed across the top of the reactor pile.
Temperature sensors are installed at various locations around the reactor to monitor the migration of the
steam through the waste matrix. If the temperature of the waste at the top of the reactor is too high, the
shakers should be used to densify the waste bed. At the same time additional cooler waste should be
conveyed into the reactor to slow down the migration of the steam and/or the steam injection can be
throttled back.
Over time, dirt will accumulate at the bottom of the reactor. The bottom of the tank should have sloping-
floors toward the centerline to an auger trough. Periodically the auger discharge unit would clear this
material without affecting the reactor’s process.
The Hopper
The tank hopper will be used to pre-condition the waste prior to conveying it to the reactor. The hopper
should be able to contain at least half a day’s volume of waste that is to be digested so that it can be
reloaded twice a day. A hatch at the top of the tank/hopper allows the hopper to be loaded with waste either
by loader or a conveyor. The hopper will be connected to the steam system to purge the air from the
hopper and to heat and moisture condition the feedstock. Once the hopper is loaded, the hatch is sealed.
Steam is then injected into the waste. A check valve will allow the air to be purged from the hopper. A
sealed auger conveyor is connected between the hopper and the reactor. Shakers are also used to move
the waste into the auger feed unit.
Algae Injection
Then main challenge for biomass reactors is insuring a constant supply of organic feedstock. Another
challenge is dealing with the emissions from the generators that use the biogas to generate power. By
injecting the exhaust from generators or scrubbers into algae tanks it will assist in getting an air permit and
produce another source of feedstock.
There are over 65,000 known species of algae in the world. Alga is basically seaweed that is found in
saltwater as well as freshwater, the type we are interested in, is fresh water.
Also the two main freshwater types we are interested in are the “heavier than water” type and the
microalgae, which contain oil, therefore they float in the water column. This type of algae can contain
between 20 to 60% oil, which is used to make biodiesel. This same oil will be converted into biogas very
rapidly by methanogens. The methanogens will also convert the cellulose of the cell walls or lipids
although not as fast.
The heavier than water type is of interest only for the Biomass Reactor as feedstock because it would be
easier to harvest and de-water than microalgae, although it has very little oil. It grows as a carpet on the
bottom of the tank and can be raked up and shook to remove water, ground and then loaded into the
reactor the same as green waste.
It has been reported that algae will grow 20 to 30 times faster than food crops. The optimal temperature for
alga growth ranges from 70o to 80o F. This should be able to be maintained by injecting the exhaust from
generators. Most microalga will double its population every 48 to 72 hours while some can split 16 times
within 24 to 48 hours. Therefore, if 100 tons per day is required for feedstock then at least 400 tons should
be maintained to allow for a 100-ton off-take per day.
Another challenge is to inject the exhaust from generators or biogas scrubbers (10,000+ scfm) into the
algae beds and not evaporate the water or increase the temperature of the water to the point where it will
cook the alga. A heat exchanger on the generator exhaust system would make steam for the reactor and
cool the exhaust. On average it requires 2.5 pounds of CO and CO2 to make 1 pound of alga.
If 100 tons of algae are injected into a Steam Biomass Reactor per day then an additional 3 Mw/hr of power
can be generated or without adding more power, reduce the amount of imported feedstock.
Alternative Fuels & Products
The steam injection process at Miramar produced 66% methane and 34% CO2 the minimum ratio would
be a 50/50 the 60/40 with an 80% efficiency for the scrubber was used in the table below. Although the
process can generate 15 Mw some of this power will be used as parasitic power.
The table below will indicate the amount of revenue that can be generated by alternative fuels and note the
amount of revenue from selling the algae if it is not used as feedstock.
* Gasoline Gallon Equivalent
Table 1
All wet digesters produce H2S occasionally due to the water becoming foul or from sulfur compounds that
are introduced. If H2S is detected in the Steam Biomass Reactor then a small amount of Ferric Chloride
can be added to the steam water and it will precipitate the H2S out of the biogas before it leaves the reactor
tank.
The cost of a 500 ton reload reactor and the algae tank with associated equipment, (Grinder, Loader, etc.)
will cost an estimated $3,300,000. This does not include the cost of generators or scrubbers.
By incorporating the algae tank with the Steam Injected Biomass Reactor makes this whole process
carbon negative, which can also add revenue to the project. This process uses 100% of the organic waste
and 100% of the water used, only a little dirt is disposed of.
For more information on Algae Injection please click the Algae Injection above.
Based on the data obtained from the Steam Injection Pilot Study performed at the Miramar Landfill in San
Diego, California, STI has designed the following patent pending Steam Biomass Reactor (Application #
61/073,709). It was demonstrated during the study that for every cubic foot of steam injected into the waste
prism, 1 cubic foot of landfill gas was produced with 66% methane and 34% CO2.
Anaerobic digestion processes produced this gas, which can be reproduced inside an airtight steel
vessel. In the landfill process the rule of thumb is that for every ton of organic waste converted, 12,000
cubic feet of biogas will be produced. (Landfill Challenges, Neal Bolton, MSW 09-2007) This should be
the same for an in-vessel process once the waste is purged of oxygen and inoculated with anaerobic
bacteria. Most of the inoculating bacteria will come from the bottom portion of the reactor however by
discharging some of the waste from the bottom of the reactor to the hopper unit which is mixed with the
fresh waste the inoculation process will be accelerated. The STI patent for steam injection in landfills
allows for the injection of ammonia gas and steam into the waste prism to balance the pH of fresh waste
and to jump-start the anaerobic digestion in fresh waste.
Currently, wet biomass reactors use large amounts of water to enhance the anaerobic biodegradation of
the organic waste. In most cases this water is heated to a preferred temperature requiring a lot of energy.
It can take weeks for the anaerobic conditions begin to produce methane. When less water is used such
as; in compost piles, the interior of the piles will go anaerobic in just a couple of days so the piles have to
be turned often or they can spontaneously combust. The steam can simulate this condition in just a few
hours.
Steam expands 1,600 times its original volume, therefore much less water will be required to biodegrade
the organic waste and produce the maximum amount of gas. The steam also increases the temperature of
the reactor to 105o to 120oF, which is the preferred temperature for maximum biodegradation.
To produce the maximum amount of biogas the waste needs to be of a small grain size, such as manure.
The manure will have to be de-watered to about 30% moisture content.
The smaller the material the more refuse will be able to be placed into the reactor and the more biogas will
be produced faster. If the feedstock is too fluffy a shaker on the reactor wall, is used to pack the material
tighter inside the vessel to slow down the migration of the steam through the matrix and to allow time for
the conversion to take place. Highly ground green waste can be mixed with the manure or other feedstock
to increase the amount organic material for conversion.
The reactors can be manufactured in various sizes to meet daily input levels of waste or to produce the
amount of methane required to meet the daily fuel requirements. Ultimately it is the amount of steam
injected into the reactor that will control how much biogas is produced.
As stated above for every ton of organic waste 12,000 cubic feet of biogas will be produced. (Landfill
Challenges, Neal Bolton, MSW 09-2007) Therefore, if 500 tons are converted to biogas (500 x 12,000) an
estimated 6,000,000 cubic feet of biogas will be produced per day. With 60% methane this comes to
3,600,000 cubic feet of methane. This gas should contain about 1,000 Btu’s per cubic foot, which equates
to 3,600,000,000 Btu or 3,600 mmBtu’s per day. With a heat value of 9,700/Kwhr this can produce 15 Mwhr.
The loading of the reactor can be continuous to match the rate of decomposition of the waste, however air
must be kept from entering the reactor chamber. To achieve this, another tank used as a hopper would be
used to pre-load the refuse where it would be sealed, purged with steam and then conveyed to the reactor,
this should maintain an anaerobic condition (Figure 1). The reactor would be loaded twice per day once in
the morning and again 12 hours later, so the hopper should hold at least 400 tons.
Steam Production
In the reactor the goal is to inject steam at a rate not too fast that it passes through the waste before it has
a chance to convert into biogas. Approximately 28,000 gallons of water at 19gpm, converted to steam could
convert 500 tons of organic waste per day.
The water should be preheated by solar or waste heat to about 120oF and then heated to 250oF which is
an increase of 130 degrees. So 130o x (28,000 gals. x 8.3 lbs. = 232,400 lbs.) = 30,212,000 Btu’s or
30,212 cubic feet of methane. If 500 tons produces 6,000,000 cubic feet of methane then .05% of the
methane would be used to create the steam for the reactor leaving 99% for power production, pipeline or
CNG/LNG after scrubbing.
The Reactor
The Miramar Landfill Pilot Study indicated that the steam had to travel at least 20 to 25 feet through the
waste before it was converted to biogas. The same should be true for in vessel reactors. Therefore the
tank should be at least 30 to 35 feet high to allow for some headspace for reloading.
To prevent the steam from bypassing the waste before it is converted into biogas the steam injector pipes
are placed at the bottom of the reactor and the extraction ports are placed at the top of the reactor but under
the waste. This forces the steam to make contact with the organic waste before it leaves the reactor.
Therefore, the surface of the waste must be kept above this port at all times.
A ceiling mounted feedstock spreader is used to reload and distribute the feedstock evenly over the waste
pile in the reactor. A light and camera is mounted on the top hatch cover to monitor the level of waste in the
reactor and to ensure the reloaded waste is evenly placed across the top of the reactor pile.
Temperature sensors are installed at various locations around the reactor to monitor the migration of the
steam through the waste matrix. If the temperature of the waste at the top of the reactor is too high, the
shakers should be used to densify the waste bed. At the same time additional cooler waste should be
conveyed into the reactor to slow down the migration of the steam and/or the steam injection can be
throttled back.
Over time, dirt will accumulate at the bottom of the reactor. The bottom of the tank should have sloping-
floors toward the centerline to an auger trough. Periodically the auger discharge unit would clear this
material without affecting the reactor’s process.
The Hopper
The tank hopper will be used to pre-condition the waste prior to conveying it to the reactor. The hopper
should be able to contain at least half a day’s volume of waste that is to be digested so that it can be
reloaded twice a day. A hatch at the top of the tank/hopper allows the hopper to be loaded with waste either
by loader or a conveyor. The hopper will be connected to the steam system to purge the air from the
hopper and to heat and moisture condition the feedstock. Once the hopper is loaded, the hatch is sealed.
Steam is then injected into the waste. A check valve will allow the air to be purged from the hopper. A
sealed auger conveyor is connected between the hopper and the reactor. Shakers are also used to move
the waste into the auger feed unit.
Algae Injection
Then main challenge for biomass reactors is insuring a constant supply of organic feedstock. Another
challenge is dealing with the emissions from the generators that use the biogas to generate power. By
injecting the exhaust from generators or scrubbers into algae tanks it will assist in getting an air permit and
produce another source of feedstock.
There are over 65,000 known species of algae in the world. Alga is basically seaweed that is found in
saltwater as well as freshwater, the type we are interested in, is fresh water.
Also the two main freshwater types we are interested in are the “heavier than water” type and the
microalgae, which contain oil, therefore they float in the water column. This type of algae can contain
between 20 to 60% oil, which is used to make biodiesel. This same oil will be converted into biogas very
rapidly by methanogens. The methanogens will also convert the cellulose of the cell walls or lipids
although not as fast.
The heavier than water type is of interest only for the Biomass Reactor as feedstock because it would be
easier to harvest and de-water than microalgae, although it has very little oil. It grows as a carpet on the
bottom of the tank and can be raked up and shook to remove water, ground and then loaded into the
reactor the same as green waste.
It has been reported that algae will grow 20 to 30 times faster than food crops. The optimal temperature for
alga growth ranges from 70o to 80o F. This should be able to be maintained by injecting the exhaust from
generators. Most microalga will double its population every 48 to 72 hours while some can split 16 times
within 24 to 48 hours. Therefore, if 100 tons per day is required for feedstock then at least 400 tons should
be maintained to allow for a 100-ton off-take per day.
Another challenge is to inject the exhaust from generators or biogas scrubbers (10,000+ scfm) into the
algae beds and not evaporate the water or increase the temperature of the water to the point where it will
cook the alga. A heat exchanger on the generator exhaust system would make steam for the reactor and
cool the exhaust. On average it requires 2.5 pounds of CO and CO2 to make 1 pound of alga.
If 100 tons of algae are injected into a Steam Biomass Reactor per day then an additional 3 Mw/hr of power
can be generated or without adding more power, reduce the amount of imported feedstock.
Alternative Fuels & Products
The steam injection process at Miramar produced 66% methane and 34% CO2 the minimum ratio would
be a 50/50 the 60/40 with an 80% efficiency for the scrubber was used in the table below. Although the
process can generate 15 Mw some of this power will be used as parasitic power.
The table below will indicate the amount of revenue that can be generated by alternative fuels and note the
amount of revenue from selling the algae if it is not used as feedstock.
* Gasoline Gallon Equivalent
Table 1
All wet digesters produce H2S occasionally due to the water becoming foul or from sulfur compounds that
are introduced. If H2S is detected in the Steam Biomass Reactor then a small amount of Ferric Chloride
can be added to the steam water and it will precipitate the H2S out of the biogas before it leaves the reactor
tank.
The cost of a 500 ton reload reactor and the algae tank with associated equipment, (Grinder, Loader, etc.)
will cost an estimated $3,300,000. This does not include the cost of generators or scrubbers.
By incorporating the algae tank with the Steam Injected Biomass Reactor makes this whole process
carbon negative, which can also add revenue to the project. This process uses 100% of the organic waste
and 100% of the water used, only a little dirt is disposed of.
For more information on Algae Injection please click the Algae Injection above.
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