Most of our waste is used as fuel in large waste incinerators which are used for generating electricity and sometimes heat. This is more efficient than simply dumping waste, which is what we did in the past. ECN's Rian Visser believes this can and should be improved in the future. “Plastics in our waste should be recycled, which would save a lot of energy. And you convert the residual waste from the sorting and recycling industry into a flexible product gas.”

Although generally referred to as waste, the term professionals use is Refuse Derived Fuel (RDF). This is the term they use for waste that mainly comprises plastics, once the metal and wet component have been removed. What remains is a flammable product with a calorific value which is too high for most waste incinerators. To avoid losing the high energy content, special plants can be constructed for the RDF stream, to enable incineration or preferably gasification.
Gasification at ECN is mainly linked to biomass. The Milena technology developed by ECN is mainly used for gasifying clean wood and, after intensive cleaning and reprocessing, the resulting gas is similar to natural gas. It's known as Green Gas. However, according to Visser, of ECN's Biomass, Coal & Environmental Research unit, there is no reason to limit operations to clean wood. “The waste sector has discovered that it's sitting on a raw material, RDF, also known as Fluff. It's a familiar fuel in the cement industry. We'd like to show that Fluff gasification is much more flexible. The gas can be used in many more places.”

Energy from waste
Producing raw material from waste sounds like a revolutionary concept. However, a closer look shows that it's already the norm for some production streams. Visser: “Cars are returned as scrap to steel plants and reused in the steel production process. That's been the case for decades and a whole infrastructure has grown up around scrap merchants and parts recycling.” The same process is only just getting off the ground in other material streams. Visser coordinates the Energy from Waste research programme at ECN and is currently focusing on Fluff.
Rian Visser cites the situation in the construction industry as an example. “Look closely. In major renovation or restoration work you always see a row of waste skips. Waste and demolition materials are separated at the building site into wood, brick, glass and so forth. We're interested in a skip for waste plastics. We're currently conducting a research project to determine how suitable waste like this is for gasification; it's only a residual stream from rubble crushers at the moment and it contains a very large volume of cement as an unwanted ash component. There are two advantages to better separation beforehand: it provides opportunities for recycling raw materials and the higher yield increases energy recovery.”

Chlorine and tar
Visser started using RDF with the fluid bed setup for biomass. As expected, the gas produced by the fluid bed setup was full of unwanted tar. However, oil-gas scrubber technology known as OLGA technology makes short work of the tars. Nevertheless, it wasn't always easy. Visser: “The tars were different from what we were used to with OLGA technology.”
She was able to make some improvements by modifying the gas scrubbing process. The release of chlorine gas proved to be an important factor in the reason for the problems with OLGA technology. Using sorbent technology between the gasifier and OLGA now ensures that chlorine gas is captured at high temperatures. Visser: “To understand the process properly, we made our own sorbent and tested it against commercially available sorbents. And by removing the chlorine beforehand we prevent corrosion in the rest of the plant, which is also better for OLGA.”
However, it turned out that capturing chlorine had not removed the problem completely and a particular type of clogging persistently reoccurred. Because RDF is always a mix of different plastics, it was unclear which tar, i.e. which type of plastic, resulted in clogging each time. Visser therefore gasified plastics separately. “We are examining which one is responsible and whether we can separate it beforehand, or whether the design of OLGA needs to be modified.” The most recent tests were extremely successful. We're on the right track.

The future
Until not so long ago (before the financial crisis) there was plenty of waste. There was a lack of incineration capacity and RDF was unwanted as a fuel. However, given the present or impending surplus in incineration capacity, processors will start to look at RDF again. Visser: “There's quite a lot of competition. The large waste incineration plants that were built in recent years have to operate at full capacity to pay for themselves. The existing surplus RDF, for which work is underway on a new combination of raw material recovery and optimal energy recovery, is in danger of disappearing because the waste incineration plants have to be full and operators are mixing RDF into the fuel. That's the effect of market forces. So there's less urgency. But in any case we've shown that RDF is a suitable source for producing a ‘product gas’. It can be reprocessed into natural gas but it can also be used immediately in the industry.”
Visser hopes that the government won't abandon her recycling targets, as the prospects for processing RDF seem promising. “Reusing raw materials saves a lot of energy in the case of plastics. And it fits in nicely with our current work on gasifying the residual stream. So there's a good basis. We can make good use of the period until the economy recovers, to further develop the best technological combination.”

Contact
Rian Visser
ECN Biomass, Coal & Environmental Research
Tel.: +31 (0)22 456 4557
E-mail: Rian Visser 

Info
Click here to find a document on the gassification of Fluff.

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