Other thermal conversion technologies

Besides these almost classic technologies as mentioned here above, new technologies are being investigated and partly already developed, among which will be hydro thermal processes (HTP), which would open up some attractive application for SR2.0’s clients. HTP can efficiently convert biomass - and in particular highly-wet, biogenic residues and waste materials - under increased pressure and temperature into high-quality refined solid, liquid or gaseous carbonaceous products. A large variety of starting materials can be used to make a wide range of products available. Thus, HTP sustainably contribute to resource protection and are an essential component of a future bioeconomy.

Hydrothermal processes can be divided into hydrothermal carbonisation (HTC) and hydrothermal liquefaction (HTL) since different products are created with increasing temperatures and pressures.

Hydrothermal carbonisation (HTC)

Hydrothermal carbonisation (HTC) converts wet biogenic residues into so-called hydrochar. The process uses the unusual properties of liquid water at high temperature (180-280 °C) and high pressure (10-65 bar). In addition to its properties as a solvent, water also functions as a reaction partner and heat carrier.

The hydrochar can be used for different applications: energetic use (combustion or gasification), but also possible to be used e.g. as activated carbon or soil additive. Besides, the HTC process shows potential for the recovery of valuable nutrients such as nitrogen and phosphorus when using nutrient-rich, biogenic residues such as sewage sludge or liquid manure. The yield of biochar obtained from this process is at around 35%–65% of dry charge with a calorific value of about 13–30 MJ/kg.

Hydrothermal carbonization is one of the most promising and future-oriented methods of thermal conversion of biomass waste, because, due to relatively low temperatures and the possibility of processing moist raw materials that do not require pre-drying, it is the least energy-consuming. This technology however is still under development with our partner in Switzerland, GRegio Energie AG in Chur (https://gregio.ch/produkt/htc-und-vtc/).

Hydrothermal liquefaction (HTL)

Hydrothermal liquefaction (HTL) takes place at higher temperatures (250-400 °C) and pressures (30-250 bar) then with HTC, as well as shorter reaction times (5-60 min). Due to the much more severe reaction conditions, biomass is almost completely liquefied. The resulting liquid consists of two phases: an aqueous and an oily phase, also called bio-crude. While the aqueous phase contains mainly organic acids, the oily phase contains non-polar and aromatic hydrocarbons. The bio-crude oil can thus reach a calorific value between 30 and 36 MJ kg-1 depending on feedstock. However, the oil still contains an oxygen content between 10 and 20 %. By removing the oxygen with hydrogen (hydrogenation) and subsequent fractionation (rectification), the bio-oil can be processed into various fuels (kerosene, petrol, diesel etc.)

Hydrothermal gasification (HTG)

Hydrothermal gasification (HTG) a technology converting wet biomass and treating organic wastes and residues at very high pressure) and gasification temperatures between 300 and 700°C. It uses the water contained into the biomass as the reaction environment in its supercritical phase to produce a synthesis gas. The cost for this type of gasification is still simply so high - compared to other normal gasification technologies like draft type or fluid bed type reactors - that there seems little chance this technology will be soon brought to market.