STI Engineering
Waste To Energy
Copyright  © 2010  
STI Engineering/
Regis Renaud   

Using the STI steam processes, projects that were considered unfeasible in the past are now very feasible.

Landfill WTE

Small landfills or closed landfills with low gas flow rates make them high risk candidates for
Waste-To-Energy (WTE) projects.  Most of these landfills would be able to produce enough LFG to power a
500kwhr to a 1.5 Mwhr generator.  With the steam process the gas production can be enhanced to where a
6 Mwhr to 15 Mwhr generator can be installed respectively.

Most WTE projects are designed with a 10 to 20 year life span, but rarely do they make the target date.  
Usually most projects start running out of LFG after 2/3 of the planned schedule.  Then the generator has to
be shut down to allow the gas field to recover.  This is an indication that the landfill is running out of
moisture not organic material.  If it was out of organic material the gas field would never recover.  However
moisture can migrate back into the waste prism.  Usually the power equipment are removed from the site 5
years premature and leave tens of thousands of tons of organic material left in the landfill.   The waste has
been vacuum dried not converted.

Some opponents feel that the steam process will shorten the life of the gas field by converting the waste
too soon.  If the project is design properly the rate of conversion can be set to maximize the amount of gas
produced over the desired time frame.   The steam process actually extends the life of the gas field by
converting all of the organic waste in the landfill.

For example: A closed landfill with 1,000,000 tons of waste in-place with 500,000 tons being organic
material.  The landfill may have a natural gas production rate of 300 scfm.  This indicates that at least 36
tons of organic material is being converted to LFG per day.  At this rate the organic material should last 38
years if there is enough moisture in it.  If a 1 Mwhr generator is installed the moisture will be sucked out of
the landfill along with the LFG and gas production will begin to drop.  This project would be amortized for
20 years but will only last about 15 years if they are lucky and the landfill is in a wet climate.  If the power
plant is removed in 15 years there would still be over 250,000 organic tons remaining.

If 1 acre is steam treated at a time and we convert 70 organic tons per day and generate 2 Mw/hrs the gas
field will last 19.5 years.  If we treat 2 acres and convert 200 organic tons per day and generate 6 Mw/hrs
the gas field will last 7 years but we will have made 6 times the revenue per year.

Over the life of the two scenarios the 7 year plan will have made 2.8 times more revenue.  The equipment
can be removed and installed at another closed landfill and the stabilized landfill can be used in a more
productive and safe way.  The life of the gas field can be extended another 5 years if algae is injected with
the steam.  (see Algae Injection below)

On large and open landfills STI usually would treat 5 acres at a time.  This will produce about 6,000,000
cubic feet of LFG at 60% methane and can generate up to 15 Mw/hr of power.  The biggest bonus is the
recovered airspace, which will extend the life of the landfill for decades.

To learn more please click on the Steam Injection button above.

Biomass Reactor WTE

It appears the political wind now days is to divert as much waste from landfills as possible.  One approach
is to compost green waste and food waste and sell the remaining compost for $2.00/ton.  The problems
with this approach are the massive amount of space required, it is labor intensive, the odor and if you start
with 100 tons of waste you end up with less than 50 tons of compost to sell.  Also that lost 50% of product
went up as CO2 and vapor.  This process must be heavily subsidized by tipping fees.

Another approach is to use a wet anaerobic digester but these cannot digest woody green waste and
require huge amounts of water.  Dairy farms with anaerobic digesters usually install small power plants
since only 1/3 of the manure is converted to biogas.  The remaining manure must be disposed of or sold
as bedding and thousands of gallons of wastewater must be dealt with.  If food waste is used the denser
material such as bones and shells will not digest and will not make good bedding material so it will have
to be landfilled.  The steam reactor can digest green waste, which is always plentiful.

The Steam Biomass Reactor will eventually digest all organic material and all of the water turned to steam
will be converted to biogas.  The soft tissue material will digest rapidly, the denser material will migrate
downward towards the steam injectors as the soft tissue converts below it.  When the dense material is
close to the injectors it will break up and make it easier for the methanogens to digest it.  The only waste
may be dirt or inorganic debris that may mixed in the feedstock.  This material is discharged from the
bottom of the reactor periodically without interfering with the operation.

The Biomass Reactor can process the same amount of organic waste as the Steam Injection process for
landfills.  Converting 500 tons of organic waste per day in a reactor is the same as treating 5 acres of a

To learn more please click on the Biomass Reactor button above.

STI is currently developing a 500 ton reactor in Bakersfield, California.

Algea Injection

The steam injection process produces so much gas which allows projects to produce a lot power or other
methane products.  When this gas is converted to energy it creates CO2 and other emissions.  To mitigate
these emissions STI is proposing to inject this exhaust into algae tanks and sequester the CO2.  The
algae will then be harvested and injected into the steam stream and then injected into a landfill or be used
as feedstock in a biomass reactor.  For every 100 tons of algae injected per day 3 Mw/hr of power can be
generated or extend the life of the gas field another five years.

The use of this closed loop process cannot only  make our projects carbon neutral, but carbon negative.

For more information on Algae Injection please click on the Algae Injection button above.

 News Release

      El Dorado County approves gas-to-electricity project

By Cathy Locke
Published: Wednesday, Nov. 4, 2009 - 4:48 pm
El Dorado County plans to boost production of electricity from methane gas at its Union Mine Landfill.

The Board of Supervisors this week approved a contract with STI Engineering of Silverado to install and
operate a gas-to-electricity project on the 35-acre landfill south of Placerville. The project, to be undertaken
at no cost to the county, is expected to supply electricity for a wastewater treatment plant at the site.
Electricity also will be sold to power companies, and the county will receive a 10 percent royalty on the

Greg Stanton, deputy director of environmental management, said less than 30 percent of the methane
gas generated at the landfill is converted to electricity now using a system of micro-turbines. As much as
80 percent is burned in a landfill flare.

Reg Renaud, president of STI Engineering, said the firm uses steam injection to accelerate decomposition
of organic materials in the landfill and increase methane gas production. The process has made it
feasible to carry out gas-to-electricity projects at smaller closed landfills like Union Mine, he said.

"I was excited about this," Supervisor Jack Sweeney said. "This is where we were headed 20 years ago at
Union Mine."

Technological advances make it possible to improve on the existing system, he said.
The contractor will pay to install and operate the project.

The county expects to benefit by using some of the electricity to operate the Union Mine wastewater
treatment plant. Current electricity use at the plant costs about $250,000 annually, according to a staff

The 10 percent royalty on electricity sales is expected to generate at least $122,000 for the county each
year. In addition, the contractor will assume maintenance of the landfill gas collection system and landfill
cover, saving the county between $20,000 and $100,000.
Renaud said the system should be operating within 10 months.