*Article* **A Kraft Mill-Integrated Hydrothermal Liquefaction Process for Liquid Fuel Co-Production**

**Benjamin H. Y. Ong 1,2, Timothy G. Walmsley 1,\*, Martin J. Atkins <sup>1</sup> and Michael R. W. Walmsley <sup>1</sup>**


Received: 7 September 2020; Accepted: 25 September 2020; Published: 28 September 2020

**Abstract:** There is a growing awareness of the need to mitigate greenhouse gas emissions and the inevitable depletion of fossil fuel. With the market pull for the growth in sustainable and renewable alternative energy, the challenge is to develop cost-effective, large-scale renewable energy alternatives for all energy sectors, of which transport fuels are one significant area. This work presents a summary of novel methods for integrating kraft mills with a hydrothermal liquefaction process. The application of these methods has resulted in a proposed kraft mill-integrated design that produces a liquid fuel and could provide net mitigation of 64.6 kg CO2-e/GJ, compared to conventional petrol and diesel fuels, at a minimum fuel selling price of 1.12–1.38 NZD/LGE of fuel, based on the case study. This paper concludes that a hydrothermal liquefaction process with product upgrading has promising economic potential and environmental benefits that are significantly amplified by integrating with an existing kraft mill. At the current global kraft pulp production rate, if each kraft mill transforms into a biorefinery based on hydrothermal liquefaction, the biofuel production is an estimated 290 Mt (9.9 EJ).

**Keywords:** hydrothermal liquefaction; black liquor; process integration; techno-economic analysis; utility system; total site heat integration
