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Pulp and Paper Industry Wastes to Fuel

Periodic Reporting for period 3 - Pulp and Fuel (Pulp and Paper Industry Wastes to Fuel)

Reporting period: 2021-04-01 to 2023-03-31

The production of paper is a two-step process, from wood to cellulosic fibres to paper. Cellulosic fibres are produced by the pulp industry via a chemical pulping process. Paper is produced from cellulosic fibres and inorganic additives. The pulp & paper industry mobilises large amounts of biomass (mainly wood) as well as recycled paper. As such, the pulp & paper bio-refineries play an important role for the circular economy, even before this subject became in vogue.
Wood is a complex resource containing cellulose, hemicellulose and lignin. Pulping is the process that extracts cellulosic fibres from wood by cooking with chemicals. The process generates two significant residue streams: bark and black liquor. The latter stream consists of the cooking chemicals and the lignin.
The objective of the project Pulp&Fuel is to show how biofuels can be produced from residues found on a standard pulp mill. The project studies different gasification technologies adapted to each resource, including fixed bed and entrained flow gasification applied to bark and paper recycling waste. Black liquor is gasified by supercritical water gasification. The project further studies gas cleaning and fuel synthesis with technologies adapted to the scale and the constraints of a pulp mill.
The objective of This last period is to propose a basic engineering design of a biofuels’ production unit integrated in a pulp mill. The project will show how biofuels can be produced cost effectively without negatively affecting the regular operations.
The project's initial phase was spent identifying resources, conducting preliminary experiments, defining the base case, and creating simulation models. The resources included black liquor, bark, and rejects like plastics and deinking sludge from the paper recycling industry.
Effort was devoted to resource analysis and preparation. Entrained flow gasifiers require a free flowing powder, but initial CEA injection experiments revealed difficulties with ground bark due to strong cohesion. Bark, being a low-density, fibrous, and ash-rich material, doesn't easily produce the necessary powder, which was only obtained after significant sieving loss.
Despite these challenges, the first entrained flow gasification experiment at CEA demonstrated efficient ash management in this reactor, yielding good quality syngas from bark. A new injection system is being designed to allow for better gasification yield from bark.
Work at the ETC's fixed bed gasifier started. To accommodate longer experiments and handle the high ash volume, a new ash extraction unit for the reactor is being planned.
Initial experiments revealed the possibility of producing hydrogen-rich syngas from black liquor using supercritical water gasification. However, it also exposed technical issues relating to the management of inorganic species and carbon conversion. Research is ongoing into the conversion chemistry of black liquor and inorganic species management.
Gas conditioning is defined, considering the constraints of the pulp process. Experimental work on syngas conditioning via water-gas-shift started. Preliminary tests have been done on reactor units using a Cobalt-based reference catalyst. The team is preparing to scale up a 2-stage reactor unit for synthesizing the necessary fuel volumes for mild hydrocracking.
Regarding process design and evaluation, the base case scenario was identified. The first process flow diagrams were created. Initial simulation results and process evaluations led to two publications. The project has been presented to the Advisory Board and at several scientific conferences.
The Pulp&Fuel project has shown how biofuels production can be integrated into a pulp mill. The involvement of the pulp & paper industry in the production of biofuels would imply a major advance for both the European pulp & paper industry as well as for the mitigation of CO2 emissions via the use of biofuels.
Bark is a high ash fuel and is difficult to inject as a powder into any gasifier. The project compares two different gasification technologies: fixed bed and entrained flow gasifiers. The project has shown that very high gasification efficiencies can be reached with a fixed bed gasifier. Fixed bed gasifiers are generally associated with a poor syngas quality and often require a separate reforming reactor downstream of the gasifier. The innovative design of the fixed bed gasifier used in this project allows gasification and reforming in one single reactor. This concept, therefore, means significantly reduced investment cost for the gasification plant compared to the conventional design.
Carbon conversion is generally relatively low in supercritical water gasification due to excessive char formation. Supercritical water gasification is also notoriously difficult due to precipitation issues of salts. The Pulp&Fuel project studied the conversion of black liquor in sub- and supercritical conditions to propose a pathway that allows maximum conversion while allowing better salt management. The results show that it is possible to achieve good results in a two-step process, first removing salts and valuable phenolic compounds and then secondly perform a catalysed gasification.
Fischer-Tropsch fuel synthesis is well known and adapted to large-scale plants. The specificity of the Pulp&Fuel concept is that a carbon monoxide rich stream is available from the dry gasifiers and a hydrogen rich stream comes from the supercritical water gasifier. This configuration can be exploited in a staged fuel synthesis unit increasing yields, while remaining suitable to small-scale units. The gas conditioning must also be adapted to the constraints of the pulp process. The project has shown, that it is possible to improve yields with a two-stage process.
The simulation and optimisation task was completed during this period. The objective was to increase the mass yield from a state of the art at 18 % for wood, to 28 % with the technology proposed in the project. The overall mass yield of 25 % is achieved, and 28 % on a dry ash free basis. This yield corresponds to the targeted 50 % carbon efficiency which is also achieved. The energy yield is 68 % which compares well with the 69 % target value. The full process will be difficult to implement as a demonstration plant for economic reasons. A simplified version of the process was defined by Sofsid and proposed as a demonstration plant.
The economic evaluation was completed and presented in D4.4. The foreseen production cost is around 50 €/MWh or 0.46 €/L. This is largely below the project target of 0.91 €/L. The carbon emission reduction is however slightly less than the project goal. The objective was 0.37 kg/L compared to the state of the art of 0.6 kg/L. The environmental analysis shows that 0.55 kg/L is achievable with the Swedish electricity mix (and somewhat lower in the case fully renewable electricity is assumed). The final environmental sustainability assessment indicates however that the performance of the industrial scale application can be improved also in other countries if full process optimization and process integrations is explored.