About HTL
Hydrothermal liquefaction (HTL) is a thermochemical process that takes advantage of the water in the feedstock, at process conditions where the heat of evaporation for water is avoided. This makes the process very interesting for high-moisture feedstock such as organic residues and sludges. The technology uses high pressures and temperatures where the water is in a sub- or supercritical state. At these conditions, the water alters its physical and chemical properties, which results in chemical reactions that dissolve the organic structure of biogenic materials and convert them to fuel intermediates.
HTL, although not yet commercial, is seen as a very promising technology also from a techno-economic point of view. HTL is currently under demonstration.
About the continuous HTL reactor
Through the Norwegian national infrastructure project NorBioLab2, SINTEF Energy Research has invested in a continuous lab-scale HTL mini-pilot system, installed at the end of 2019. The reactor is built with a research focus, for studying feedstock types and eligibility, and operational issues such as the fate of inorganics, corrosion and the effect of depressurization on those. The mini-pilot typically operates at 1 L/h slurry feed with 10 w/w % dry matter content, and is able to operate at state-of-the-art conditions, i.e. up to 500 °C and 350 bar. The reactor is equipped with on-line gas measurement, where information on gas volumes and types generated can be obtained. By separating and analyzing the products, mass and carbon balances can be achieved.
The system has the possibility to include stress-loaded corrosion samples for material and weld testing under a real HTL environment. To facilitate this objective, a relatively large compartment was needed to insert the samples, and a CSTR reactor was therefore selected. The mini-pilot is equipped with dual piston pumps and a two-stage depressurization system to study the depressurization effect on the product composition and distribution.
Technical specifications
- Reactor type: Continuous CSTR reactor
- Internal volume 1000 ml
- Internal diameter 80 mm
- Internal height 200 mm
- Feed capacity: 0.5-2 L/h
- Preheat to 500 °C
- State-of-the-art operating conditions
- 500 °C
- 350 bar
- Dual pump
- Option for two-stage depressurization
- On-line gas measurement
- Gas volume (gas meter)
- MicroGC for permanent gases: CH4, CO2, CO, C2Hx, H2
- Possibility to study corrosion (6 samples/run)
- According to PED 2014/68/EU – CE certification
- Feedstock requirement: particle size under 120 µm, close-to-round shapes and non-hazardous material
- Drying and milling is available as pretreatment
Feedstock screening
The continuous reactor can be used to test various feedstock types and blends at different HTL conditions. The obtainable biocrude yield depends on the feedstock slurry, most importantly its dry matter, inorganics and carbon contents. For woody biomass, typically between 50-100 g of biocrude is produced after one run.
Examples from various national and EU projects
Feedstock types, blends and HTL operating conditions were studied to reveal how the operating conditions affect biocrude yield and quality, as well as how different feedstock types behave during HTL. Experiments were performed at both sub- and supercritical HTL conditions. It must be noted that different feedstock types require different operating conditions for optimum processing.
Corrosion tests
The continuous reactor has the possibility to investigate corrosion on different alloys under real HTL conditions.
The corrosion tests are performed in cooperation with Materials and Nanotechnology at SINTEF AS.
Small C-ring test specimens were stressed to their respective yield strength at the test temperature, i.e. compensated for high-temperature de-rating for each alloy. The specimens were inserted into the HTL reactor void and placed separated with ceramic spacers.
An example from the BL2F EU project, where the aim of the work was to expose industrially relevant construction alloys to real HTL conditions and evaluate their suitability for application in a full-scale plant. Rods and nuts of the same material quality as the C-rings were machined to avoid galvanic corrosion. Thereafter, the C-rings were pre-loaded with strain gauges to achieve the desired inside yield strength at the HTL temperature, 390 °C. In this project, a model salt solution was developed to avoid biocrude protective layer formation on the alloys’ surface. After the test, the alloys were cleaned and analyzed with an optical microscope to reveal corrosion attacks and types on the materials.
Hydrothermal Gasification (HTG)
Catalytic and low-temperature HTG can already be performed in the reactor up to 500 °C. During 2026, the rig will be upgraded with a new high-temperature (HT) reactor that will be capable of operating at temperatures up to 600 °C, as well as a state-of-the-art salt separator to remove most of the salts from the feedstock.
Examples of the benefits from hydrothermal treatment of biorest materials can be found here.