Award as “Low Carbon Model Company of the Year”
Gasification as a technology for energy recovery from waste has been researched intensively worldwide, especially in Japan. The technology was developed in the 1970s, the oil crisis of those years increased interest in Japan in converting household waste into energy and recycling resources. The Direct Melting System (DMS), a gasification and melting technology developed by Nippon Steel Engineering Co. Ltd., was introduced for the first time in 1979, in the city of Kamaishi. To this day it has prevailed against all other gasification technologies of the time. Steinmüller Babcock Environment offers the coveted DMS method in Europe under license from the parent company Nippon Steel Engineering. Thus we are bringing this unique technique and decades of expertise to Europe.
The Direct Melting System (DMS) is a shaft furnace gasification and melting technology. In contrast to pyrolysis, oxygen is added to this process. Waste flexibility is one of the greatest advantages of this system. The high temperatures, up to 1,800 degrees, enable the treatment of all types of waste, from household waste to slag, special waste to clinical waste and the co-combustion of sewage sludge. In contrast to a fluidised bed gasifier, it is not necessary to pre-treat the waste. The technique has been used commercially for more than 35 years at more than 40 sites.
The capacities range from 10,000 to 230,000 tonnes per year. The DMS system produces very few pollutants. The use of limestone in the combustion process minimises the emission of hydrogen chloride and sulphur dioxide, and a reduction in dioxins and furans is enabled by syngas combustion in a secondary combustion chamber. Therefore considerably fewer pollutants are emitted at the flue than are allowed by strict European regulations. The slag and metal products from the process contain only low quantities of toxic heavy metals and can be completely recycled. The slag can be used, for example, as a sand substitute or for the production of composite stones. In Japan, the slag is certified as fertilizer. Thanks to the almost complete reusability of the end products, the DMS system actually facilitates a zero-waste policy. The system provides consistently high efficiency with very high energy generation and the largest capacity of all gasification technologies, at 14 t/h/line. In all: an absolutely reliable and durable technology.
An alternative to the disposal of hazardous waste is combustion in a rotary kiln plant. Talk to us, we will be happy to advise you on which system is the best solution for you.
All types of waste - from slag to household and clinical waste, sewage sludge and bulky refuse - are fed directly into the gasification and melting furnace without any pre-treatment. Coke and limestone are also added here as reducing agents and to regulate viscosity.
1. Drying and preheating zone
In the upper drying and preheating zone of the gasifier, the waste is dried and preheated gradually. The temperatures are 300 - 400° C.
2. Thermal decomposition zone
Combustible waste is decomposed thermally in the second zone at 400 – 1,700°C. Non-combustible waste continues to the combustion and melting zone. Syngas is produced during the process, with the main components CO, CO2, H2, CH4, and N2. The syngas is fed to a secondary combustion chamber downstream from the gasifier and completely incinerated there.
3. High temperature zone (combustion and melting zone)
The high temperature zone at the bottom of the gasifier allows stable gasification and the melting of all waste at 1,700 – 1,800° C. Here, inert materials such as glass, wires or cans are melted by the heat of the burning coke and converted into valuable materials. A reduced atmosphere forms on the floor of the gasifier, in which toxic heavy metals vaporise. The melted material is discharged discontinuously through a tap hole, cooled and separated into metal and slag by a magnetic separator. The limestone added with the waste regulates the viscosity of the melted materials and prevents any clogging of the process. Thanks to the very small quantities of heavy metals, the slag and metal are fully recyclable.
A cyclone system is installed behind the gasifier. With the help of a cyclone separator, the combustible dust is removed from the syngas and fed back into the furnace. This returned dust reacts as a coke substitute with the oxygen-rich blower air, thus reducing coke consumption. The process improves the conditions in the secondary combustion chamber and significantly reduces the amount of fly ash for the downstream areas.
The syngas generated in the gasifier, from which the dust has been by and large removed, is now fed to the combustion chamber. The low proportion of dust allows a homogenous gas-gas combustion with improved combustion conditions at 950 – 1,100° C. The homogenous combustion lowers thermal NOx generation and dioxin formation, and allows stable and complete syngas combustion. The necessary conditions for the reduction of pollutants are also met: 2 seconds dwell time, temperature above 850° C, and turbulence.
The flue gas is fed from the combustion chamber into a steam generator, where energy is recovered from the heat of the flue gas. Conventional power generation takes place here, using a steam turbine system. Typical values for the steam pressure and temperature are 40 bar and 400° C.
After heat recovery, the flue gas is fed through a flue gas cleaning system. Hydrogen chloride HCl, sulphur dioxide SO2, nitrogen oxides NOx and polychlorinated dibenzo-p-dioxins and dibenzofurans are removed here.