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Syngas generation

The generated syngas (synthesis gas) is purified lean gas, comparable with town gas or coke oven gas. The combustible main components are CO, H2 and light hydrocarbons; inert components such as CO2 and N2 are mainly absorbed into the syngas through the use of air and water as gasifying agents. Its calorific value ranges between 2 and 2.4 kWh/Nm³, while its dust content is less than 1 mg/Nm3. When it is combusted temperatures up to 1,900 °C are achieved. Syngas is therefore also suitable for supporting high-temperature processes that require fossil fuels, such as in the cement industry, in glass foundries or in iron and steel production. It is also possible to use the gas as a chemical feedstock, depending on the recycled materials and the means of operation of the reactor. A plant that processes about 50,000 tonnes of waste a year generates up to 15,000 Nm3 of syngas per hour. That results in an average annual output of 250,000 MWh syngas, which corresponds to about 20,000 tonnes of natural gas.

First large-scale pilot plant

The first large-scale plant was designed to utilise up to 50,000 tonnes of waste plastic per year. This requires around 3,000 to 4,000 tonnes of coarse-ground lime per year. Air and water vapour are blown in as gasification and coolant agents. In the plant‘s vertical shaft kiln and supported by initial base load combustion, the material undergoes partial oxidation and a series of gasification and pyrolysis reactions at reaction temperatures between 450 and 1,200 °C. After the syngas has been cleaned with hot gas filters and cooled down it can be used, for example, as a fuel for industrial processes. This leaves about 8,000 to 12,000 tonnes of fines per year as residue; this mixture of fine-ground lime, ash and pollutants has to be landfilled.

The plant is designed for a rated thermal output of 32 MW. As a counter-flow gasifier it can achieve a thermal efficiency of over 80% with an external electricity requirement of about 1 MW. The system concept is flexible and can be used in industry and waste recycling. The Ecoloop technology can sensibly complement waste incinerators by materially converting in particular chlorine- and pollutant-containing waste streams into syngas instead of burning it as part of the overall waste mix. In order to utilise such materials thermally, until now these have been mixed with the total waste fed into waste incinerators. Although this prevents certain limit values from being exceeded, in particular the increased chlorine fractions create considerable technical disadvantages. To counteract the high-temperature corrosion that occurs as a result, combustion plants have to be operated at reduced temperatures and vapour pressures. This decreases the efficiency. Other consequences include increased operating and maintenance costs. In particular, high chlorine concentrations in combustion processes lead to the formation of highly toxic dioxins and furans, which have to be laboriously filtered out and deposited via flue gas cleaning plants.

The prevention of chlorine peaks in the overall waste increases the efficiency of the waste incineration, reduces the formation of pollutants and simultaneously enables the separate utilisation of problematic materials though their flue gas-free conversion via Ecoloop into purified syngas.

Current research and development work

In the first large-scale pilot plant, numerous gasification campaigns were carried out with plastic- and chlorinecontaining substitute fuels, whereby 2,000 tonnes of different types of material flows have already been used: mixed plastics and sorting residues from the yellow recycling bins and shredded heavy fractions from car recycling. The operating results and experience are being incorporated in research and development collaborations to optimise and further develop the technology.

Together with Clausthal Technical University, researchers are developing a comprehensive simulation model of the gasification process. Processing parameters and measurement data from the large-scale pilot reactor provide the input basis for much of the data.

The model is complemented by experimental results and data from laboratory and pilot plants.

Meanwhile, the programming of the simulation model is well advanced and the validation of different settings and model tests has already begun.

It is ultimately intended that the simulation model shall provide reliable process data from different input data. This will make it possible, for example, to simulate the use of different waste materials and to determine the expected syngas composition and the efficiency of the system without such tests having to be carried out on the large-scale plant.

Using the simulation model, it is intended to improve the method and the reactor design. The developers see the focus of their further work in optimally adapting the process for different reactor geometries and design sizes.

The medium-term goal is to develop an optimised, large-scale plant type that can efficiently utilise a large number of problematic waste streams on the spot, in different design sizes and without relying on expensive „waste tourism“.

Projektinfo 05/2016:
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Project management, system development
ecoloop GmbH

Development of the simulation model
TU Clausthal, IEVB

Project partner
Fels-Werke GmbH

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