Understanding gasification – UNTHA UK digs deeper
At UNTHA UK, we are keen to maintain our position as knowledgeable leaders within the waste and recycling industry. This is why we try to comment on varied topics, trends and issues within our exciting and ever-changing sector – it allows us to pass on our advice and ideas, and hopefully encourages debate and positive change.
We noticed recently that one thing we are yet to discuss at any great length is gasification. This technique is becoming more and more sophisticated, and indeed in many countries there is huge hype surrounding the technologies within this arena. However uptake in the UK has been generally low.
So what exactly is gasification?
Of course gasification is incredibly complex, and numerous types of gasifiers exist. However, explained simply, gasification is a flexible and relatively clean technology that transfers low-value feedstocks into high-value products. Specifically of interest to UNTHA UK of course is the use of gasification to convert waste into energy.
How does gasification work?
Gasification is not to be confused with incineration – the combustion of waste material in an oxygen-rich environment. In contrast, gasification relies on the conversion of the simplest feedstock molecules – carbon monoxide, methane and hydrogen – which can be used to generate power. It is therefore a ‘clean burn’ technology which lends itself to smaller volumes of waste.
Both Municipal Solid Waste (MSW) and Commercial and Industrial (C&I) waste is suitable for gasification. However the chosen waste stream must first be thoroughly sorted and all metals, glass and inorganic material removed, before the resulting waste is shredded to a homogenous particle size. The UNTHA shredder model used within this phase, would depend on the type of waste material being processed.
The shredded fraction is then packed into a vessel before a controlled amount of pure oxygen is added to facilitate a natural reaction at high temperatures. This produces a raw synthesis gas (syngas) which can be cleaned of any impurities prior to it being used in an engine or turbine to generate electricity. Alternatively the clean syngas can be used to manufacture products such as fertilizers, transportation fuels or substitute natural gases and fed into the gas network.
Whatever the output, waste materials can be transformed into valuable and clean resources utilising the gasification concept.
So how valuable is gasification?
Like most technologies and waste processing systems, gasification is not perfect. For instance gasification produces a highly efficient fuel (syngas) that can be converted into electricity. However the waste must be thoroughly pre-processed before it can be treated in a gasification plant, which negates some of the gross value of this technique.
Some are unimpressed by the reported statistic that modern gasification plants only achieve approximately 30% efficiency. It is important to remember though that coal fired plants operate at a similar level.
However gasification is a flexible process which can create a number of valuable products that we continue to consume in the UK and overseas, and it also allows us to make good use of waste that unfortunately, as yet, is still being generated.
Take plastics for instance. Some plastics are particularly hard to recycle so would historically have been sent to landfill; however plastics are an excellent, high energy feedstock for gasification. This means that landfill diversion is achieved, energy and economic value can be harnessed from what would otherwise be considered a waste, and alternative natural resources which cannot be replaced are saved.
The gas produced by this process could technically be added to the UK’s gas network although the technology required to do this is still in relative infancy. Elsewhere in Europe though, the value of gasification is being harnessed. In Finland for instance, municipal gasifiers are used to produce electricity from waste and the heat is utilised in district heating systems.
Of course the uptake of a technology such as gasification should never override the priority to reduce the amount of waste that consumers and businesses create in the first place. Yet it is another process that is becoming ever more sophisticated and should therefore perhaps be on our radar.