NEWAPP Publication on HTC Char

Publication in relation the NEWAPP research project:

Production of a solid fuel from garden prunings, food waste,
OFMSW, digestate and sewage sludge on pilot plant scale

Michael Renza, Avelino Cormaa and Martin Hitzlb

a  Instituto de Tecnología Química (ITQ), Universitat Politècnica de València – Consejo Superior de Investigaciones Científicas, Avda. de los Naranjos s/n, 46022 Valencia, Spain; Tel.: +34 963 877 800, email:

b  Ingelia, S.L., C/ Jaime Roig 19, E-46010 Valencia, Spain, Tel.: +34 963 814 447, email:

Introductive summary

In the European Project NEWAPP ( five European biomass waste resources have been selected for Hydrothermal Carbonization (HTC) in pilot plant trials in Náquera, Spain, on a ton-scale: Green waste and garden prunings, food waste, the organic fraction of municipal solid waste (OFMSW), digestate and sewage sludge. The corresponding HTC carbons were analyzed and evaluated as solid biofuel based on the European norm EN 14961-6 for biofuels for non-industrial use. It was seen that ash content needed to be reduced in many cases and different procedures were evaluated for this purpose. A short overview on the complete NEWAPP project is also provided in the presentation.

Purpose of the work

The use as solid biofuel is the most promising application for HTC carbon or hydrochar. This valorization should be evaluated under industrial conditions employing real biomass waste feedstocks. Problematic properties of the product should be revealed and procedures developed to overcome potential restrictions or limitations.


The five biomass waste streams were processed on ton-scale and the ash content identified as the most critical factor. A post treatment facility was installed at the pilot plant to establish ash-reduction by means of flotation techniques. Separation is based on different density of HTC carbon and inorganic matter. Supplementary chemical treatment was evaluated for further reduction of the inorganic content. Thereby, two HTC carbon samples with different ash composition were considered as starting material: one rich in SiO2 and Al2O3 and another one with predominantly CaO.

Scientific innovation and relevance

The data obtained in the trials and ash reduction treatments provide interesting information for the elaboration of standards for HTC-derived biofuel pellets. It is a general aim of the NEWAPP project to contribute in this task. Furthermore, the data from the pilot plant trials allow predictions on the suitability of the HTC products as solid fuel depending on the properties of the biomass raw material.


The five biomass waste streams were processed and results will be compared in detail. It was found that some biomass waste streams (e.g. food waste) are suitable as solid fuel whereas others (garden prunings) often need an ash-reduction post treatment. SiO2 content of the ashes can be reduced by a two-step chemical procedure: an alkaline treatment at 225 ºC followed by an acidic treatment (H2SO4). For the reduction of the CaO content the acid treatment at medium temperature (approx. 100 ºC) is sufficient to meet one of the specifications (10 wt%) for solid biofuel (EN 14961-6). Further optimization should also allow undermatching the 5 wt% limit. From the engineering point of view this procedure is compatible with the HTC process and implantation to the pilot plant is discussed.


The HTC process is suitable for the valorization of wet biomass waste streams as solid fuel. If required ash content of the product can be adjusted by physical and chemical post-process treatments to meet specifications (EN 14691-6).


This work has been funded by the European Commission with the Grant Agreement no 605178 (FP7-SME-2013).