Mass balances for Direct Thermochemical Liquefaction (DTL) processes – Considerations and best practice
The most basic approach to characterize DTL processes is by establishing mass balances to gain insight into product distribution. One important figure that is derived from these mass balances is the yield of the main product, the DTL bio-oil. Apart from being of fundamental importance to develop business cases based on DTL processes, this yield is also one important parameter to compare different process conditions and varying DTL process setups.
There are some specific considerations to be made when processing biomass in general as feedstock. Moreover, there are even DTL process specific issues that require attention due to their impact on the results of mass balances. This technical note – developed in the frame of IEA Bioenergy Task 34 (Direct Thermochemical Liquefaction) – aims at summarizing potential sources for inconsistencies and providing guidelines so that the reported values can be evaluated efficiently. Most of the recommended practices are already widely used in the scientific DTL community.
Main recommendations resulting from this report:
- The three mass balances derived from the different biomass reference states* hold important information to characterize DTL process. The availability of data for the different mass balances is mandatory to enable comparison of different technologies and studies.
- In addition to the three reference states of biomass, carbon balances prove to be a reliable result to evaluate DTL processes, especially for the case of Hydrothermal Liquefaction (HTL).
- It is recommended to sample DTL products (and the feedstock) many times during the course of an experiment in order to increase accuracy of mass balances.
- The choice of solvent and how it is used to recover biocrude is a crucial consideration for HTL batch experiment balances.
* Three reference states to report weight: (1) dry, ash free, (2) dry (including ash), (3) as received
Technical note available here:
Technical note: Mass balances for DTL processes – Considerations and best practice
Figure: Results from different mass balances for the example of fast pyrolysis with fractionated condensation