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| Technical Review |
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| Plasma Gasification Basics |
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| Technical Review - back to top |
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| As with most other plasma gasification facilities, SPH will be developed as series of separate core processes focused on waste handling, gasification/vitrification and power production. Integrating the best practices and technologies within each core process ensures optimization for both economic and environmental considerations. For example, a Europlasma gasification/vitrification system can be a complement to a pre-existing recycling program, replacing the landfill as the final stop for non-recyclables. SPH is in direct competition only as the better alternative to incinerators and landfills. With a comprehensive system, the basic process flow would resemble the following: |
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The following diagram provides a process flow for the Europlasma gasification and vitrification system: |
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| The following diagram depicts in greater detail the core equipment in the Europlasma gasification and vitrification system: |
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Autothermal Gasification - back to top
The biomass and waste material is charged into the two-staged gasifier. The material is first dried at 200°C and then converted into a partly oxidized syn-gas at around 900°C.
This does not require any additional energy as the heat is recovered from the overall process itself. The addition of air is strictly controlled so that the maximum of original carbon converts into raw syn-gas that is refined in the second stage.
Almost every material on earth contains both some organic and inorganic components. For instance, wood and plants contains 1% inorganic components. MSW contains around 15% inorganics (metals, minerals). These elements do not turn into syn-gas and form ashes in the bottom of the gasifier that are conveyed to the melting unit. This is a closed loop system that does not require external disposal of the ash.
This first stage relies on a robust grid furnace that has been field-proven at this commercialized scale for more than 50 years. Syn-gas Plasma Cleaning
The raw syn-gas consists mainly of carbon monoxide and nitrogen. It is associated with a rather high content of tar-forming components (complex HC), and usually chlorinated hydrocarbons, hydrogen and water vapour.
The plasma torch jet provides a temperature of more than 5,000°C. Turboplasma powered with a plasma torch offers a homogeneous temperature of more than 1,200°C to all fractions of the syn-gas. This results in a complete dissociation of all hydrocarbons, even halogenated, with no indication of recombination. There are no toxic nor carcinogenic organic compounds present in the produced fuel gas because no such compounds can survive at this temperature. This means no formation of Volatile Organic Compounds (VOCs) such as dioxins and furans as are found with other technologies.
This second stage relies on more than 20 years experience of heating gas with plasma, a prime example being Peugeot factories in France.
Ash melting unit - back to top
The bottom ashes are introduced in the melting furnace and heated at 1300°C with a second plasma torch. This temperature is higher than the material fusion point and the slag is then turned into a glass-like product.
This product is inert and retains in its glass matrix the pollutants that the original waste may have contained. The results of the study of long-term behaviour are of the same order of magnitude as those obtained on natural basalts; they showed its long-term nature as non-hazardous and its vitrified stability for over 200,000 years. The product can be used for civil works, such as road construction, as well as several other applications.
Europlasma is a world leader of this technology, and this part of the process relies on fifteen years experience with six plants running with this exact process.
Heat Recovery - back to top
The syn-gas is quenched from 1200°C down to around 70°C. The recovered heat is used to feed the Auto-thermal Gasifier and a steam turbine for co-generation. Gas Scrubbing
Depending on the kind of input fuel, a gas scrubbing system is used in order to abate acid elements and to filter heavy metals.
Since there is no combustion, the volume of fuel gas to be cleaned amounts to only 25% to 30% of the corresponding volume of flue gas from an incineration process. Already well-proven scrubbing techniques are then even more efficient since there is less gas to treat for the same quantity of pollutants. Emission levels are far below the most stringent emissions level regulation, well-within prescribed limits in North America and the European Union.
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Power Production - back to top
The third island is the Power Production Island. Depending on the energy delivery option, the syn-gas can be delivered in different formats. The syn-gas has a calorific power (energy content) equivalent to one-third that of natural gas.
The most common output is to feed the syn-gas to gas engines or gas turbines in order to produce electricity. The end-to-end electrical efficiency is 30%. Several engine manufacturers have adapted their robust, reliable and field proven engines to this kind of gas, including: MAN, Caterpillar and General Electric.
Furthermore, the heat of the gas engines combined with heat from the heat exchanger can be used to feed a steam turbine for co-generation. In this scenario, the end-to-end process electrical efficiency can exceed 40% (ie: 40% of the waste calorific potential is transformed into electrical energy). As noted, four-hundred (400) tons per day of MSW and tires will generate around 20 MW of net electricity export.
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| Plasma Gasification Basics - back to top |
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Plasma is the fourth state of matter, an ionized gas that is created from an electrical discharge and which can meet extreme heats, as hot as the surface of the Sun.
Much like an arc-welding machine, a plasma arc is formed when an electrical arc between two electrodes creates a high temperature, highly-ionized gas. A thermal plasma field then forms in an enclosed chamber. Finally, an electric current enters an atmospheric pressure gas sream that can heat to as high as 15,000°C (see Diagram). |
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Non-Transferred Arc Technology - back to top
The Europlasma non-transferred arc plasma torch technology was first developed in the 1980's by EADS-LV (ex-AEROSPATIALE, French national aerospace company) to simulate the intense heat encountered by intercontinental ballistic missiles (ICBMs) and spacecraft during atmospheric re-entry.
Europlasma's plasma technology consists of two tubular metal electrodes connected to a swirling gas injection chamber. Test sessions have shown that the torch can be fed with almost any gas mixture (air, Ar, CO, helium, CO2, H2, N2, CH4, O2).
Arc ignition is obtained through short-circuit. The resulting plasma plume temperature is typically around 4000 °K, while its mean enthalpy is in the range of 5 MJ/kg air to 8 MJ/kg air. To increase electrode lifetime, a time-varying magnetic field controls the upstream arc root motion, while gas injection naturally controls the downstream one. Electrodes and injection chamber are cooled by pressurized, de-ionized water.
From the process standpoint, non-transferred plasma technology offers significant advantages:
- high thermal efficiency;
- flexibility regarding the choice of gas to ionize;
- rapidity and flexibility to start and stop the system automatically when necessary;
- total independence for plasma generation between torch and furnace, which makes for very easy operating conditions;
- less vaporization due to absence of a "hot spot", the arc root attached to the slag;
- operating flexibility: 25 to 100% of the power range;
- built-in safety devices.
Gasification - back to top
Gasification is a thermal reaction where waste is heated in low oxygen atmosphere, in rather small furnaces. Organic waste does not burn, as there is not oxygen enough but downgrades into simple elements CO and H2, called "syn-gas". The syn-gas contains virtually all of the energy in the original fuel through its chemical composition.
This syn-gas can then be burned in a gas engine to produce electricity or be transformed into synthetic diesel through a Fischer Tropsch catalyser. Heat of the syn-gas is usually used to dry the input waste and to maintain the gasification reaction. Remaining steam/heat can be sold as such or can be recovered through a steam turbine.
Gasification is a well-proven technology that has been mainly used to produce gas from coal for homes and industry. It has a long history tracing back many years even before natural gas was introduced for heating and energy.
Plasma as the key technology - back to top
Temperatures used for gasification are in the range 600 to 1200°C with an energy conversion efficiency that can be as high as 87%. The higher the temperature is, the best efficiency is reached, ie almost all organics of the input waste are transformed into syn-gas, without tars and other components. The plasma technology allows it to reach this high temperature, making it a key technology in the field of gasification.
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| Europlasma: Industrial Plasma Specialist - back to top |
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Europlasma, established in 1992, based in Bordeaux (France), is specialized in plasma based high temperature industrial process applied to waste treatment. Europlasma plasma torches are based on know-how from the European Aeronautic Defence and Space Company (EADS) that used them to test materials that protects space machines from heating when re-entering the atmosphere.
The plasma torch is an efficient thermal tool, able to produce very high temperatures - more than 5000°C, sun surface temperature. This allows to heat large volume fast, triggering new applications for industrial thermal treatment.
Europlasma has mastered the use of these high technology torches in an industrial context, very demanding when it comes to reliability and and performance. Thirty-two torches using Europlasma technology have been delivered for various applications in metal industry and hazardous waste destruction.
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Europlasma developed a process to melt ash coming from MSW incineration. This ash concentrates extremely hazardous pollutants - heavy metals, dioxins, etc. - which today are dumped in landfills, and contribute in the long-run to lixiviation and water pollution. The Europlasma process offers an alternative by melting ashes and retaining pollutants in the glass matrix, preventing their release in nature. Five ash melting unit relying on this process have been installed in France and Japan.
In 2001, Europlasma took control of the industrial site of INERTAM near Bordeaux, that is specialized in plasma vitrifcation of asbestos contaminated waste. INERTAM treats 7000 tons per year. In 2006, Europlasma took control of Europe Environnement, company specialized in air and odours treatment, based in Mulhouse (France). Europlasma is listed at Marché Libre - Euronext.
In 2007, Credit Suisse injected 33M in the company in order to accelerate its development in the gasification market. That year also marked the impressive achievement of surpassing 1 million operating hours on Europlasma torches. |
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