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Pulp and Paper Industry Wastes to Fuel

Periodic Reporting for period 1 - Pulp and Fuel (Pulp and Paper Industry Wastes to Fuel)

Reporting period: 2018-10-01 to 2020-03-31

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 the project 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 first period of the project was dedicated to the identification of the resources, exploratory experiments, the identification of the base case and setting up of the simulation models. The resources considered in the project are black liquor, bark and rejects of the paper recycling industry, these include plastics and deinking sludge.
A significant effort was put in the analysis and preparation of the resources. Entrained flow gasifiers need a free flowing powder. The first injection experiments at CEA showed that injection of ground bark is very difficult due to a strong cohesion in the powder. Bark is a low density, fibrous and ash rich material. It is difficult to obtain a free flowing powder required for an entrained flow reactor and this could only be obtained after sieving with a significant loss.
A first entrained flow gasification experiment at CEA showed however that ash management is efficient in this kind of reactor and a good quality syngas can be produced from bark. The design of a new innovative injection system (planned for period 2) is underway to allow the injection of bark with a much higher overall gasification yield.
Experiments in the fixed bed gasifier at ETC have started. A new ash extraction facility (planned for period 2) will be needed to perform longer experiments to collect more relevant data. Due to the large amount of ash produced, a new ash extraction unit needs to be designed for this reactor.
Initial supercritical water gasification experiments of black liquor showed that it is possible to produce a hydrogen rich syngas from black liquor. It also revealed some technical issues that need to be addressed. These issues are mainly concerned with the management of inorganics species and carbon conversion. An important work is underway concerning the underlying chemistry of the conversion of black liquor in sub- and supercritical water and the management of the inorganic species during the process.
The gas conditioning has been defined to be adapted to the constraints of the pulp process. Experimental work on syngas conditioning by water-gas-shift has started. Preliminary testing of reactor units on using a Cobalt-based reference catalyst has been completed while awaiting the completion of milestone MS2 that defined the syngas compositions to be worked on. Preparations have started for scaling up a 2-stage reactor unit for synthesis of fuel volumes required for mild hydrocracking.
As for the process design and evaluation, the project identified the base case scenario. The first process flow diagrams have been issued. The first simulation results and process evaluations have yielded two publications. The project was presented to the Advisory Board as well as on different scientific conferences.
The Pulp&Fuel project will show 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.
To achieve this goal, some advances need to be made in the available process technologies, as well as their performances.
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. Both technologies need adaptations to allow them to process bark. The entrained flow gasifier, working with pulverized feedstocks, needs an adapted injection device. This patented injection device can also process feeds with limited amounts of plastics.
The fixed bed gasifier, on the other hand, is operated with pelletized fuels. Fuel injection is less of a problem. 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. The technology has been developed on a pilot scale and so far only allows operation until the bed is filled with ash. To make the concept commercially viable, the entire process needs to be made continuous with a continuous ash discharge.
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 studies the conversion of black liquor in sub- and supercritical conditions to propose a pathway that allows maximum conversion while allowing better salt management. A two-step process should allow us to improve conversion, while opening the possibility to valorise specific side-products.
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.
Both pulping and fuel synthesis process are energy intensive, but also produce heat. Process and energy integration tools are used to ensure optimal use of resources to minimise losses. A standard gasification-fuel synthesis unit produces energy and material streams that can be employed elsewhere on the pulping plant, important synergies can be found between the two units. The pulp plant can reduce the amount of biomass needed in its combustion units while the efficiency of the biomass gasification can be boosted.
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