Biomass to generate sustainable energy and steam

Energy producer Twence in Hengelo aims to provide at least half of the targeted sustainable energy in shareholding municipalities, meaning at least 7 per cent of the total sustainable energy production. Their green electricity and steam can be widely used, including in cooling processes, heating grids and industrial drying processes. Additionally, Twence structurally re-uses, recovers and adds value to both natural resources and dairy manure. 

Since 2011 Twence supplies AkzoNobel in Hengelo with electricity that is generated in their conventional waste incineration plant. Since 2007 Twence’s biomass energy plant converts biomass to green energy, sufficient to power a city like Hengelo. Their new biomass energy plant now also produces green steam, generated by burning waste wood. The new plant triples efficiency: the same amount of biomass now generates three times the amount of sustainable energy. The current capacity is 450 gigawatt per hour.  

Heat usage on the scale present at Twence us unique in The Netherlands. A pipeline from Twence to the Marsstreden industrial area is used to transport warm water to the heating plant that is located there. Some remaining heat is sold to existing customers, including the district heating in Enschede and salt producer AkzoNobel in Hengelo. Green steam is supplied to the Grolsch beer brewery and tyre factory Apollo Vredestein, both in Enschede. This enables them to reduce their natural gas usage, making their processes more sustainable. The hot steam is used by Grolsch in their brewing process, cleaning installations and the heating of the buildings, while Apollo Vredestein uses the steam in their tyre production process. The new energy plant can save up to 11 million cubic meters of natural gas yearly, comparable to the usage of 7.500 households. This saves 20.000 tons of CO2 per year. Another heat remainder is used by Twence in their processes, for example for capturing and trading CO2.

For years Twence has efficiently converted process heat of the conventional waste incineration plant into energy carriers to deliver heat, steam and electricity. Around 54% of the produced energy in the conventional plant is seen as sustainable because of the biogenic substance level that is still present in the ‘grey’ waste, even though it should not be present. Technologically speaking, the Dutch power plants are among the most progressive in Europe. Combined, they produce 15 per cent of the total produced sustainable energy in The Netherlands. The new biomass power plant functions like the conventional one, as in both plants the boiler walls contain water-filled tubes, converting heat into steam. The difference is that the biomass power plant uses waste wood as fuel, and since this is not produced using fossil fuel, the resulting energy can be labelled as ‘green’. This may be a bit misleading since some CO2 is still released, depending on the age of the wood. Young wood (e.g. prunings) contains less CO2 compared to older wood.

Tightened manure legislation requires alternative solutions. Manure contains phosphate, nitrogen and potassium, scarce and essential resources in the worldwide food production. Due to the Dutch manure surplus, there is too much phosphate in the soil. It leaches to the groundwater, causing unwanted growth of algae and plant species. Since mid-2017, a large-scale installation at Twence in Hengelo can add value to up to 250,000 tonnes of manure per year by fermenting and separating the fertilisers. Because the system is closed and stable, no greenhouse gases are emitted and constant quality of raw materials and biogas is provided. With this installation, Twence contributes to a more sustainable and profitable agricultural sector. If desired, farmers can have more manure processed than is required by law. This allows agricultural entrepreneurs to create tradeable Processing Agreements (Vervangende Verwerkings Overeenkomsten / VVOs).

Twence deliberately chooses to use organic materials in the production process of bioenergy. This means no biomass is used that is grown specifically for this purpose at the expense of agricultural land for the food chain. The organic waste that is used consists, among other things, of peels, remains of vegetables, fruit and potatoes, remains of cooked food, meat and fish, nutshells, eggshells, vegetable oil, solidified fat, weeds, pruning waste, mowed grass and leaves. In the Netherlands, this waste is collected separately in the so-called ‘green bin’. By fermenting this organic material, bioenergy is generated, after which the natural remains are composted. By using these two processes, the waste is optimally reused.