Highlights from the VGB Workshop: Biomass Ash 2017 in Copenhagen, Denmark

This one-day workshop, attended by about 40 delegates, was a follow-up to a 2014 event, which had included technologies involved in biomass production and ash processing. The Copenhagen meeting included regulation, including the Circular Economy Initiative, but mostly activities on the use and processing of the ashes to provide nutrients for forests and farmland in EU countries.

Papers were presented from Denmark, Germany, Sweden, Finland and Poland.

In his welcome, Nicolai Bech, of Hofer A.S., Denmark, emphasised regarding biomass ash as a product. For example, triple superphosphate fertiliser generally has had a comparatively stable value of €300-400/t over the last five years.

The opening paper was a European overview from Hans-Joachim Feuerborn, of VGB. In a very detailed, comprehensive presentation, he referred to the shift from 60—70%/30% ratio of bottom ash to fly ash towards ratios more like that of pulverised coal ash, as the scale, and so technologies, for combustion had changed. He described the EU commitment to a low carbon economy (~90% reduction in CO2 by 2050) and the so-called Circular Economy Initiative, with its hierarchy of prevention, reuse, recycling, recovery and disposal of wastes.

It was followed by a report of a joint project examining fuel processing and its effect on ash properties from Sebastian Fendt, of the T.U. of Munich. The project will fill the main gap that they have identified as being the need for further analysis of the considerable amount of experimental data that exists in order to move towards practical outcomes. Most biomass ash is simply disposed of, but there is a need to increase use in future, as observed above.

The third paper was from Morten Igerslev (co-authored by Simon Skov), of the University of Copenhagen entitled: The real need for ash recycling – The Ashback project. The theme was that harvesting of the bark, needles, leaves and twigs takes nutrients out of the forest ecosystem. If roots are disturbed, leaching through roots may also be enhanced. Roundwood harvesting removes less of the nutrients. Modelling, e.g. with their ESBEN model, can help quantify the effects. Ash recycling by spreading can return much of the macro elements such as Ca, K and P, but only 3% of N. If deposition is allowed for, the balance can be positive for some elements. The presence or effects of any dioxins have not been examined by anyone yet, so any threat in that respect is unknown. The project includes biochemical/biological effects (a gap hitherto). There is evidence of some adverse effect on mosses initially, but they appear to recover, though the mix of species may change.

Lisbeth Sevel of HedeDanmark A/S, Denmark, presented on the technique they have for ash recycling in forests, in which the material is distributed as the vehicle moves slowly between the rows of trees. Around 3 t/ha might be typically used, best done in spring.

Mogens Lunde, of Fromsseier Plantation, Denmark, gave the experience of a forest owner in using such techniques on the poor soils of the forest plantations in southern Jutland, near Billund. They spread about 250-300 tpa on 90 ha. The poor soils came from the slash, burn and grazing practices in the past. Only Norway spruce or, in the worst locations, dwarf mountain pine, could be grown. The soils had been acidic (pH 4) and very low in P, K and Mg, and the levels of these elements had been doubled or tripled by the treatment. Adding water to give a moisture level of 50% in the ash is needed for easy spreading. Power plants pay a bit less than they would pay for landfill to send the ash for spreading.

A joint project: Ash utilisation in forests, was given by Daniel Glimtoft (Svenks Skogsgodsling, Sweden), a representative from Fortum Varme, Finland, and Brian Hermansen, of the utility Hofor, Denmark. In this joint project, CFB ash from biomass combustion will be granulated as small spheres, bound with water, at a scale of 3500 tpa. They see use of the granules as avoiding the need to store the ash first to harden, and the product has the advantage of looking like a familiar granular fertiliser. The ash granulation plant will initially be located at a power plant in Stockholm, then moved and reassembled in Copenhagen, at a new wood chip-fired CFB (BIO4). This unit will replace the current 600 MW CHP Amager coal unit (Copenhagen plans to be the first CO2-neutral capital).

Dorit Rasmussen (Agrotrade) and Slavomir Stankowski (T.U. Szczecin, Poland) presented on a study of use of wood ash and straw ash in fertilising fields in Poland. Various dosages and additives (lime or gypsum) were assessed. The effect on soil composition and on the winter wheat crop showed that applications of ash increased the P, K and Ca in the soil, while the micro-components were unaffected. There was no general effect on the chemical composition and baking quality of the grain.

Bjarne Sorensen, of HedeDanmark A/S, Denmark, presented on the economic and legal incentives. In Denmark, the Environmental Protection law is applicable and there is also legislation on biomass ash, which is almost identical to the Swedish regulations, allowing direct use as fertiliser without prior treatment.  There is a distinction between straw ash and wood ash (as the latter is expected to go back to forest application, though it can be used on farmland). Mixing of bottom ash and fly ash is permitted, though fly ash contains more heavy metals.

Recycling on farmland is cheaper than recycling to forestry, and recycling straw ash to forests is not economic. Straw ash costs up to 150 DKr/t (€20) and wood ash costs up to 400 DKr/t (€55/t) in handling costs. The landfill tax in Denmark is equivalent to €65/t.

The selection of utilisation processes was the subject of a five minute presentation without slides by Kim Lange, of NCC, Denmark. The basic economics and business case are key.

Another workshop is planned for May, 2019.