High-temperature Waste Gasification by the Thermoselect process

Case Study Contents

• Thermoselect High Temperature Gasification (2)
  
  Thermoselect gasification process case study.
• Thermoselect High Temperature Gasification (3)
  
  Thermoselect High Temperature Gasification - RDF as Biomass Feedstock and Advantages and Opportunities for this green and renewable energy process with high environmental sustainability.

Introduction

Gasification conserves the chemical energy of waste in the syngas produced. One technology giving good results has been developed by Thermoselect of Switzerland. The process accepts a wide range of waste, and rather than an ash, it produces purified syngas as well as granulated metals and minerals that can be used in industry and construction.

Inspired by an Article by Wulf Kaiser and Masuto Shimizu, November-December 2004. (This article has been prepared for initial preliminary information only, is not up to date, and my contain inncauracies. Refer to Thermoselect direct or confirmation of all details.)

While a large number of different gasification systems have been developed over the past two decades, only a few have reached technical maturity. One of these is the Thermoselect process which transforms waste into usable end products without the need for pre-treatment. The system offers almost complete diversion of waste from landfill (sometimes also called zero waste), and offers the possibility of using hydrogen technology or fuel cells for sustainable energy production.

The process also neatly avoids the formation of dioxins, furans and other organic compounds as these are not significantly created. This is a big advantage over - say incineration where these toxins can be produced, but then need to be much more extensively removed before the gas leaves the chimney/stack.

Three large-scale Thermoselect plants were in operation in Germany and Japan back in 2004; another plant was in operation in Italy as long ago as 1992-1998. Vin those plants various kinds of wastes have been successfully treated, including mixed commercial streams, mixed plastic wastes, automotive shredder residues (ASR) and municipal solid waste (MSW).

Five more large-scale plants using this process, were under construction in Japan during 2004. By the end of 2005, the authors predicted that total capacity of plants using this process would reach 2700 tonnes per day.

We are sure that many more plants have been built since, At that time, it was in Japan that most of the global activity in gasification of waste was taking place, and where the technology was becoming main stream.

One motivation then, as now, has been to alleviate the shortage of available landfill space, and to comply with the EU Landfill Directive and Waste Framework Directive which has set all EU nations stringent targets for the large scale diversion of waste from landfill and in particular for the diversion of biological (organic) waste away from landfills.
The targets are backed up by a system of fines which will be imposed by the EU if any nation fails to meet their recycling or waste diversion (away from landfill) target; The levy falls on any nation which does not comply with the steadily increasing recycling rate targets and organic material reduction to landfills.
The success of the quest for more advanced technology has now also become important, as without new methods we will fail in the UK and fines will be imposed by 2013.

The Process

The Thermoselect gasification process recovers synthesis gas, usable vitreous mineral substances and iron-rich materials from various kinds of wastes such as MSW and commercial or industrial wastes. An uninterrupted process simultaneously gasifies organic waste fractions and melts down inert materials.

Synthesis gas is the main product of the process. Gasification transforms all organic materials in the waste into a synthesis gas, with a composition that reflects the thermodynamic equilibrium of the temperature at the top of the reactor - approximately 1200°C.

The high-temperature, oxygen-free environment, and the residence time of more than two seconds in the upper part of the reactor, ensures that the prime constituents of the exiting syngas only occur as the smallest possible molecular species in the form of H2, CO, CO2 and H2O.

At a gas outlet temperature of 1200°C, the synthesis gas is thus obtained from the organic fraction of MSW. This gas typically comprises (by volume) 25%-42% H2, 25%-42% CO, 10%-35% CO2, 2%-5% nitrogen, up to 1% methane, H2S at trace amounts, and other impurities.

Subsequent purification of this synthesis gas and the process water yields by-products in the form of salt, zinc concentrate and sulphur. Since this process does not deposit ash, slag, chars or filter dusts, no secondary treatment is required.

The synthesis gas can be converted into electrical energy with a high efficiency, or it can be used in its basic molecular form.

Melting of Inorganic Materials

All metallic and mineral components are melted down in the lower part of the reactor.
The mineral and metal melts are then collected in the lower homogenization reactor, which is heated with natural gas and oxygen. In this reactor, the minerals and metals automatically separate into a two-phase flow as a result of their differences in relative density.

Any residual carbon in the melt is further converted to syngas. The molten substances are subsequently granulated by water quenching, and are extracted from the quench basin using a bucket elevator.

Syngas Cleaning

The synthesis gas passes through several stages for cleaning: water quench, acidic scrubber, alkaline scrubber, dust removal, desulphurization and gas drying.

The crude synthesis gas first leaves the reactor at approximately 1200°C and flows into a water jet quench that almost instantaneously cools the syngas down to about 70°-90°C. According to computational fluid dynamics calculations, the quench takes about 30 milliseconds, and the total residence time in the quench apparatus is about 300 milliseconds.

This rapid cooling prevents syngas constituents from recombining into higher organic molecules, and separates the entrained dust or semi-liquid particles from the gas stream. According to measurements, dioxins and furans in the synthesis gas are virtually non-existent, as is also the case for existing coal-gasification processes.

Syngas Utilization

There are multiple applications for the utilization of the purified synthesis gas:
• hydrocarbon production - e.g. methanol
• hydrogen in fuel cells - as used in the Chiba facility in Japan - and carbon monoxide in solid-oxide fuel cells
• ammonia production - e.g. fertilizers
• electricity - e.g. gas engines, steam boiler and turbine for combined-cycle options, and gas turbines.

The choice of power-generating equipment depends on the price of power. Higher power-generating efficiency would need to be supported by higher electricity prices.

Environmental Benefits of Gasification

The Thermoselect resource recovery process was conceived for recovering the maximum possible benefit from various types of wastes that cannot be recycled by conventional methods. With Thermoselect, these wastes are continuously processed, with the primary goal of achieving the highest possible yield of high-quality recyclable products at the lowest possible level of pollution, as well as the simultaneous utilization of the chemical energy contained in the waste.

The by-products of the process can be used as:

• mineral granulate - reused as gravel substitute in concrete, as shot blast or as road-bed
• metal granulate - recycled into the metal industry
• sulphur - reused in sulphuric acid and in the fertilizer industry
• zinc concentrate - reused for zinc recovery
• salt - reused in the chlorine manufacturing industry
• water - reused in the process itself
• synthesis gas - converted either into further chemicals or power.

Now continue to read the rest of the Thermoselect Process case study:

• Thermoselect High Temperature Gasification (2)
  
  Thermoselect gasification process case study.
• Thermoselect High Temperature Gasification (3)
  
  Thermoselect High Temperature Gasification - RDF as Biomass Feedstock and Advantages and Opportunities for this green and renewable energy process with high environmental sustainability.

Return to Case Study Index page: Gasification Plant Technology Case Studies

Read another case study: Case Study: High-Temperature Gasification by the Thermoselect process

by Steve Evans based Kaiser and Shimizu (2004) See text - February 2009

Back to Top

page 1