Who is Startech?
Startech Environmental Corporation is a Wilton, Connecticut based public company that
is a world leader in plasma processing technology utilizing its proprietary plasma
processing equipment known as the Plasma Converter System TM. Plasma technology has
been used for many years in the metals industry and involves using electricity to produce
an intense energy field called plasma. The plasma energy is so intense that it literally
breaks the molecular bonds of solid, liquid, and gaseous materials into elemental
components like hydrogen, oxygen and nitrogen.
The Plasma Converter System (PCS) achieves closed-loop elemental recycling to safely
and irreversibly dissociate materials such as MSW, organics and inorganics, solids,
liquids and gases, hazardous and non-hazardous materials, industrial by-products and also
items such as electronics, medical materials, pharmaceuticals, chemical industry products
and other specialty materials while converting many of them into useful commodity
products that can include metals and a synthesis-gas called Plasma Converter Gas
(PCG)TM . Among the many uses for PCG, it can, for example, be used to produce “green
power” alcohol and also hydrogen for sale.
What is Plasma?
In essence plasma is a gas that can conduct electricity. The electrical conductivity is
provided through the ionization of the gas (i.e. a state where atoms can gain or lose
electrons). In this ionized or plasma state, gases can be confined by electromagnetic
fields and assume an almost liquid like viscosity. Lightning provides a useful analogy to
the concept. Lightning occurs as a result of a large potential difference between a cloud
and the ground. In order to discharge that electricity a passage is ionized between the
cloud and the ground to create a ‘conductor’ for the electricity to be discharged. The
lightening bolt is an example of plasma.
Plasma Technology
Plasma technology has several advantages over competing technologies in that it is
flexible in the waste streams that can be processed, the waste streams do not have to be
sorted (though they may be to maximize the economic return of the overall recycling
process), and it can accommodate waste streams in solid, liquid, and gaseous form. High
temperatures and the aggressive reaction atmosphere associated with plasma dissociates
and gasifies organic components of the waste to create Plasma Converted Gas (PCG)
which can be reused or recycled as a fuel or as a synthesis gas to make industrial
products. The silicate and metallic portions of the waste stream are predominantly
captured as a layered molten material that is poured from the plasma vessel for recovery
and potential use in the construction and abrasives industries. The process offers
potential savings and drastic simplification in processing integrated mixed wastes such as
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electronics because little or no sorting is required for processing. Plasma conversion also
inherently separates metals and silicates from plastic and organics without prior
disassembly of the waste feedstock.
How plasma is used in the PCS
The basis of Plasma Converter System (PCS) is the generation of a continuous arc
(discharge of electricity) using a plasma torch. Due to the high resistance of the
atmosphere through which the arc passes, significant heat is generated. Whereas an upper
temperature limit of 1500oC is possible with fossil fuel-generated incineration,
electrically generated plasmas can produce temperatures an order of magnitude higher,
approximately 16000oC . By containing this plasma in a confined space, waste materials
can be broken down into atoms, ions and electrons, with only a few molecules remaining.
At the same time the plasma is a highly reactive medium, which facilitates the
dissociation of especially organic molecules. In other words plasma can be used to create
and control very high temperatures, which, together with the highly reactive condition of
plasma, can be used to destroy waste material by breaking down the component
molecules. The resultant output of the PCS is a vitrified slag and a gas stream consisting
of primarily CO and H2.
Plasma versus Incineration
Plasma waste destruction is not the same as incineration. The principal difference lies in
the fact that incineration is an exothermic reaction (i.e. heat is created) whereas plasma
waste conversion is an endothermic reaction (i.e. heat is absorbed). For incineration a fuel
gas is required and the reaction is self-sustaining as opposed to plasma waste conversion
where no fuel gas is required and the reaction is not self-sustaining making it a much
easier reaction to control. Also, and importantly, oxygen is required for incineration
which leads to a highly oxidizing state within an incinerator, whereas oxygen is not
directly required for plasma waste conversion but can be introduced in a controlled
fashion to enable the generation of usable products.
As has been described earlier, the Startech Plasma Converter System (PCS) is a
technology that can convert both feedstock and waste materials to an energy rich gas,
ensuring in the process that no harmful products are released into the environment. The
principle of operation of the PCS is the generation of a high intensity energy (plasma)
field, which is then used to break down material entering the field into its elemental
components. Through controlled reforming, an energy rich gas can be generated.
Remaining solids are bound into an obsidian-like slag that is non-leachable and that can
be used as a commodity by varied industries. The reduction in volume of the material
entering the system is dramatic with a ratio of about 300:1 (i.e. 300 drums of solids in to
the system results in 1 drum of solids exiting the system) typically prevailing for
primarily organic waste materials.
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The Five (5) Step PCS Process
Feedstock
Material In
Plasma
Converted
Gas (PCG)
Step 1
Feed
Plasma
Vessel
Step 2
Dissociate
Molten
Silicate
and Metal
Step 3
Cool
For
Use
PCG
Filter
Step 4
Filter
Packed
Columns
Plasma
Converter
Feed System
Heat
Recovery
Boiler
Clean
PCG
Step 5
Neutralize
Schematic illustration of the major components of the Startech Plasma
Converter System (PCS).
What type of materials can be fed into the PCS?
The PCS can accommodate a wide range of waste types with the added characteristic of
being able to handle different types of waste simultaneously. Where hazardous waste will
be treated and disposed, care can be taken to ensure that the chemical characteristics of
the waste are well understood and carefully controlled and managed. The chemical
properties of the waste can be entered into a model, for example, that will show how the
materials will be dissociated within the PCS to assess the effectiveness of the PCS in
dealing with a particular hazardous waste type.
The PCS has been tested on medical waste but more importantly has been tested on
Municipal Solid Waste (MSW), which is recognized as being of the same highly variable
nature as medical waste in most countries. MSW may contain anything from lighter fluid
and a range of solvents and other hazardous materials, through to household appliances
and old car engines. Regardless of the composition of the waste stream, the materials in
that waste stream will either be gasified or melted in the PCS. Comparisons between the
gas flows and the gas compositions from MSW and medical waste that have been tested
in the PCS show little variation between various organic feedstocks
In addition, the following waste types have been tested successfully in the PCS:
•
•
•
•
•
•
•
•
•
•
PCBs
Asbestos
Sludge
Bio-Medical Waste
Blood and Body Parts
Municipal Solid Waste
Spent Pot Linings (from aluminum smelters)
Solvents
Solvent Contaminated Debris
Contaminated Soils
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•
•
•
•
•
•
•
•
•
Waste Oil
Filters
Insecticide and general pesticides
Chemical Weapons related waste materials
Explosives
Ammunition (small arms)
Munitions
Rocket propellant
Spent activated charcoal.
A variety of mechanisms can be used to feed waste into the PCS. Liquid wastes
(including sludge) can be pumped directly into the PCS through the wall of the vessel and
the refractory into the plasma field, through the in feed nozzle. The nature of the pump
system is a function of the composition, viscosity and corrosiveness of the material to be
fed. The liquid feed system is also designed to accommodate any entrained solids that
may be present. These considerations are all standard fluid transfer engineering matters.
Solids, liquids and gases, depending on the specific composition of the same, can be
continuously or batched into the vessel. Standard proven industrial feed systems are
adapted to the Plasma Converter System and consist of conveyors, screw augers, and
shedders and are configured based upon the process application requirements.
The Plasma Converter System (PCS)
The following information provides a general description of the major equipment and
concept of process operation of the Plasma Converter System. A detailed system
specification for a 25 TPD system is included in Attachment A
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The Plasma Vessel
Description
The plasma vessel is a cylindrical container made of steel with an opening in the
roof through which the plasma torch is inserted. The plasma vessel is lined with
insulation and refractory to allow both maximum retention of internal energy
(high thermal inertia) and to protect the steel container from the heat inside the
plasma vessel. The plasma vessel contains inspection ports and openings for the
waste feed and gas and melt exit. The plasma vessel is hinged so that it can be
tipped hydraulically to decant the melt.
Ensuring destruction
Waste materials cannot bypass the plasma field and exit the PCS intact as a result
of several features of the plasma vessel. Firstly, the feed port for waste is located
opposite the gas exit port, so the materials must physically migrate through the
vessel to get to the exit. Secondly, the required temperature and residence times
are maintained under all circumstances regardless of the type of waste. Solids that
are fed into the PCS drop into the molten pool upon entering the vessel. The direct
contact between the molten material and the waste entering the system is an
important part of the destruction process.
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Pressure and pressure variations in the plasma vessel
The plasma vessel is kept at slight negative pressure to ensure that no gases can
escape to the atmosphere. Pressure is monitored on a continuous basis and
controlled in response to pressure variations brought about by the change in phase
of materials (i.e. solid or liquid to gas) in the plasma vessel. The pressure in the
vessel does not increase very rapidly as the materials change phase and it is
relatively easy to ensure that a negative pressure is maintained during operations
of the PCS.
Method for controlling melt level:
A non-contact level sensor has been incorporated into the PCS, which is a device
that operates in a similar manner to radar systems returning a continuous output to
the Central Control Station. When the melt level reaches the high set point, the
operator is alerted that discharge is necessary. If the level reaches the high-high
alarm level cut-off, the feed system into the vessel is disabled until the melt is
discharged from the vessel.
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In addition to the level sensor, continuous visual monitoring and recording of the
inside of the Plasma Converter Vessel is also incorporated into the PCS. The
video feed returns directly to a monitor located in the control panel. Thus, the
operator is able to see the melt level and ensure that the signal from the level
sensor is accurate.
Decanting the melt
For systems with intermittent melt discharge requirements, the Melt Extraction
System (MES) is a simple, robust design consisting of a melt discharge door on
the plasma vessel, refractory-lined charge cars sized for the specific PCS in use, a
vessel tilt cylinder, and a removable enclosure around the pour operation.
For systems that require continuous discharge of melt a continuous flow tap is
installed. Depending on the specific application, the discharge system is either
configured to allow for the overflow of the silicate and metallic material into a
positioned charge car or into a water-locked bath with an inclined conveyor in the
bottom of the bath, which continuously removes solids from the bath.
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The Plasma Torch
Transfer versus non-transfer torches
The basis of PCS is the generation of a continuous arc (discharge of electricity)
using a plasma torch. The torch can take two forms either a ‘transfer’ or ‘nontransfer’ torch. A non-transfer torch is one in which the anode and the cathode are
contained within the torch. This is the more versatile of the two torch types
because the waste can contain non-conducting material (a characteristic of most
waste types). As one example, the non-transfer torch allows the PCS to safely
disassociate steel and electrical insulation material (conductor and non-conductor)
simultaneously.
Twin Torch – Non-Transferred and
Transferred Operation
Single Torch – Non-Transferred
and Transferred Operation
While the non-transfer torch is more versatile, it is also more energy intensive
than the transfer torch. In a transfer torch the arc is maintained between an anode
in the plasma torch and a cathode conductor installed in the bottom of the vessel.
As indicated, a transfer torch is used selectively for materials that are conductive.
The Plasma Torch system is well proven industrial equipment that is used
extensively in the metallurgical industry. Since the torch is water cooled, there is
no need for exotic materials of construction. The body of the torch is made of
stainless steel with internal components that are made of standard polymers and
electrical insulating ceramics. The only consumables in the torch are the
electrodes, which are machined components made of a readily available copper
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alloy and which can readily be made in many countries. Electrodes are typically
replaced after every 100-500 hours of operation.
The PCS is also equipped with a Torch Positioner System. This device allows the
plasma torch to be aimed at different points within the vessel by providing precise
positioning in all three planes (X, Y and Z) and thus to address any build-up of
solidified melt that may occur within the vessel. The refractory in the PCS vessel
is formulated to withstand very high temperatures and aggressive operating
conditions. To prevent the plasma jet from impinging directly on the refractory
inside of the PCS, since this may cause long term wear, the torch positioner is
equipped with stops and interlocks at the maximum allowed movement in all
directions. Furthermore, the PCS is thoroughly instrumented with thermocouples
that indicate the temperature inside of the vessel. In the event that the temperature
in the vessel rises above the control limits, the system will automatically
compensate by reducing power input to the torch.
The Gas Polisher
As indicated earlier, halogens, vaporized metals and other inorganic species may
be entrained in the gas stream leaving the plasma vessel. A gas polisher is used to
remove these contaminants from the PCG. The gas polisher consists of a heat
recovery steam generator, a high temperature particulate filter unit and a packed
tower absorber in which water is used to scrub (and neutralize) acid gases from
the PCG. The final unit in the Gas Polisher is the variable blower, which draws
the PCG through the Gas Polisher and maintains a slight vacuum in the PCS.
The PCS produces a substantially lower volume of off-gas than a conventional
incinerator – about 10% of the volume of a typical incinerator with an equivalent
throughput. The implication of this smaller volume is that the gas stream can be
more intensively cleaned without compromising the affordability of the complete
facility and that the gas cleaning equipment is substantially smaller than that
needed for a conventional incinerator.
Wastewater Treatment Skid
The Wastewater Treatment Skid is a commercially available unit using standard
technology for the treatment of the Gas Polisher blow down prior to discharge.
There are two basic configurations of the system. The first uses neutralization,
precipitation, flocculation and filtration to clean up the wastewater for discharge
and produce a filter cake. In many cases, the filter cake can be reintroduced into
the Plasma Vessel for processing under modified operating conditions. This
configuration is appropriate for sites where wastewater discharge capability
exists.
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The second configuration utilizes vacuum distillation technology to produce clean
water that can be reintroduced to the process and concentrated a brine that would
likely be shipped off site. This configuration is appropriate for site where there is
no wastewater discharge capability.
Plasma Converted Gas (PCG) Recovery
Once the Plasma Converted Gas (PCG) has been through the gas polisher it can
be captured for later use as a fuel gas. PCG is a very clean burning gas
(approximately 10 000 to 11 500 kJ/Nm3 for medical waste and municipal solid
waste and PCB contaminated liquids respectively) consisting of hydrogen (H2)
and carbon monoxide (CO) with low levels of nitrogen (N2), carbon dioxide
(CO2), methane (CH4) and acetylene (C2H2). The typical composition of PCG is
shown in Table 1.
Gas
Carbon monoxide
Carbon dioxide
Hydrogen
Oxygen
Nitrogen
Total hydrocarbon
Table 1.
Percentage
25-40
3-5
40-60
0-1
2-6
1-5
Typical composition of PCG (dry basis).
The control system
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The control system for the Startech Plasma Converter System is a very reliable
industry-standard Programmable Logic Controller (PLC)/Personal Computer
(PC)-based system. The primary process control is interfaced and executed
through a Siemens PLC architecture. This device provides a very stable platform
for the monitoring and control of the process and is much more stable than stand
alone Windows-based PC systems. The human-machine interface (HMI) is
accomplished using any of various software packages, with Siemens again being
the standard. This provides an easy-to-use, intuitive graphical interface for the
operators of the process. Furthermore, the process is highly interlocked to prevent
the propagation of human errors. The control architecture and philosophy are very
common in the chemical process industries.
The PCS is also equipped with numerous instruments for detecting and reporting
various process conditions. The process is user friendly and simple to operate.
The operators control the process through a simple and self-explanatory graphical
representation of the process. Process commands are executed primarily using a
computer mouse and the software operates in the universal Windows
environment.
Instrumentation
Basic instruments include mechanical gauges with local indication of parameters
such as temperature, pressure, flow, and level. These basic instruments are
intended to provide local readout of non-critical process parameters to operating
personnel. Electronic instruments include thermocouples and RTD’s for
measuring temperature, pressure switches and transducers, flow sensors, limit
switches, proximity sensors, motion sensors, level sensors, load sensors and
process analyzers. All electronic instruments report electronically to either local
sub-system control panels or to the Central Control Station. Critical operating
parameters are integrated into the control software for automated response,
maintenance and alarms. Key parameters of gas composition, temperature and
pressure are continuously monitored during operation. These parameters are used
to maintain automatic optimum operation of the process.
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Gas composition monitoring
Key chemical composition parameters in the PCG are continuously monitored online in real time. Carbon monoxide and carbon dioxide are analyzed by Nondispersive Infrared (NDIR) Spectrophotometers. Other gas analysis capability can
be provided for specific customer applications.
Temperature monitoring
The temperature in the PCS vessel changes relatively gradually during operation.
The thermal mass of the PCS vessel provides a significant thermal inertia that
buffers temperature changes. Furthermore, the plasma torch continuously adds
energy to the process. Temperature of the PCS is continuously monitored by
several redundant thermocouples. The temperature of the PCG exiting the vessel
is monitored to control waste feed rate. The feed rate of the waste can be varied to
maintain a constant exit gas temperature. Alternatively, torch power can be
increased or decreased to maintain proper temperature at constant feed rate.
Pressure monitoring
The pressure in the PCS vessel is maintained at a nearly constant slight vacuum
through the use of a variable frequency drive induced draft blower. The blower
draws the PCG from the vessel and through the entire Gas Polisher System. The
control of the blower speed is interlocked with the pressure in the PCS vessel. The
blower speeds up in response to increasing pressure and slows down in response
to decreasing pressure. There is also a feed-forward loop interlocked with the
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solid feed system that ramps up the blower speed just prior to the introduction of
feed material. In this manner, the vessel pressure is always maintained at vacuum.
Quality control on PCG
The PCS process is easily controlled through the many levels of sensors in the
system that detect changes in process due to variations in waste feed. In terms of
maintaining control of the gas composition and PCS vacuum, most waste streams
are very similar in their processing characteristics. For instance, the PCG volume
and rate of evolution for medical waste and municipal solid waste are routinely
very similar. Accordingly, it is only when waste feed changes from mostly
organic to mostly inorganic that there is a significant change in the PCG flow rate
or composition. The PCS System adjusts to the changes in flow rate and
composition in real time with no loss of efficiency or quality.
Infrastructure and site requirements
Plasma Converter plants are built in accordance with the tonnage of materials
required to be processed. This can vary from as little as five tons per day, up to
plants that can process thousands of tons per day. Ideally, these large plants would
consist of several smaller units in order to ensure minimal down-time due to
maintenance requirements.
Expected Plant Downtime
The PCS is made up of a collection of commercially available off-the-shelf
components that are simply configured in a specific manner for the PCS. Motors,
pumps and electrical devices are of the highest quality and are purchased from
respected manufacturers. Large Plasma Converter Plants of 100 tpd and higher
throughput incorporate redundant systems that can essentially eliminate
downtime. For instance, the principle of a 100 tpd facility incorporates 2 vessels
each with a capacity of 50 tpd or 4 systems with a capacity of 25 tpd. The plant
design also incorporates redundant Gas Polishers each of which can service from
1 to 4 Plasma Converters. For smaller systems, it is simply a question of
maintaining a critical spares inventory to provide for quick replacement of
components that may fail.
Regarding the electrodes in the plasma torch, at least 300 hours mean time
between replacements has been proven by the manufacturer. The manufacturer
states that, for torches of 500 kW and above, 1,000 hours or more is now readily
achievable. At the same time changing electrodes can be accomplished in
approximately 15 to 30 minutes. Given these factors, the availability of the PCS is
projected at >95% (350 days per year of operation).
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